1. Cardiovascular Monitoring
Dr abdollahi
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2. Although a stethoscope should be present in every anesthetizing location, continuous stethoscopy is an insensitive method for early detection of untoward hemodynamic events.
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3. Who cannot complain of arm pain
Most automated noninvasive blood pressure measuring devices use an oscillometric measurement technique and rarely cause complications. Caution should be exercised in patients:
Who cannot complain of arm pain
Those with irregular rhythms that force repeated cuff inflation
Individuals receiving anticoagulant therapy
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4. Direct arterial pressure monitoring should be widely used in operative patients with severe cardiovascular diseases or those undergoing major surgical procedures that involve significant blood loss or fluid shifts.
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5. The Allen test for palmar arch collateral arterial flow is not a reliable method to predict complications from radial artery cannulation. Despite the absence of anatomic collateral flow at the elbow, brachial artery catheterization for perioperative blood pressure monitoring is a safe alternative to radial or femoral arterial catheterization.
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6. The accuracy of a directly recorded arterial pressure waveform is determined by the natural frequency and damping coefficient of the pressure monitoring system. Optimal dynamic response of the system will be achieved when the natural frequency is high, thereby allowing accurate pressure recording across a wide range of damping coefficients.
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7. Rather than the common placement at the midaxillary line, the preferred position for alignment (or “leveling”) of external pressure transducers is approximately 5 cm posterior to the sternomanubrial junction. When using external transducers and fluid-filled monitoring systems, this transducer location will eliminate confounding hydrostatic pressure measurement artifacts
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8. Selecting the best site, catheter, and method for safe and effective central venous cannulation requires that the physician consider the purpose of the catheterization, the patient's underlying medical condition, the intended operation, and the skill and experience of the physician performing the procedure. Right internal jugular vein cannulation is favored by most anesthesiologists because of its consistent, predictable anatomic location and its relative ease of access intraoperatively
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9. Methods to reduce mechanical complications from central venous catheters include the use of ultrasound vessel localization, venous pressure measurement before insertion of large catheters, and radiographic confirmation that the catheter tip rests outside the pericardium and parallel to the walls of the superior vena cava.
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10. When using CVP as a measure of intravascular volume, the influences of ventricular compliance and intrathoracic pressure must be taken into consideration. In general, a trend in CVP values or its change with therapeutic maneuvers is more reliable than a single measurement. Important pathophysiologic information can be obtained by careful assessment of the CVP waveform morphology.
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11. Of the many complications of central venous and pulmonary artery catheters, catheter misuse and data misinterpretation are among the most common.
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12. Pulmonary artery wedge pressure is a delayed and damped reflection of left atrial pressure. The wedge pressure provides a close estimate of pulmonary capillary pressure in many cases but may underestimate capillary pressure when postcapillary pulmonary vascular resistance is increased, as in patients with sepsis.
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13. Use of central venous, pulmonary artery diastolic, or pulmonary artery wedge pressure as an estimate of left ventricular preload is subject to many confounding factors, including changes in diastolic ventricular compliance and juxtacardiac pressure.
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14. Most randomized prospective clinical trials have failed to show that pulmonary artery catheter monitoring results in improved patient outcome. Reasons cited for these results include misinterpretation of catheter-derived data and failure of hemodynamic therapies that are guided by specific hemodynamic indices.
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15. Thermodilution cardiac output monitoring, the most widely used clinical technique, is subject to measurement errors introduced by rapid intravenous fluid administration, intracardiac shunts, and tricuspid valve regurgitation.
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16. Mixed venous hemoglobin oxygen saturation is a measure of the adequacy of cardiac output relative to body oxygen requirements. It is also dependent on arterial hemoglobin oxygen saturation and hemoglobin concentration.
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17. Introduction to Cardiovascular Monitoring: Focused Physical Examination
Although cardiovascular monitors receive prime emphasis, the fundamental basis for circulatory monitoring remains in the eyes, hands, and ears of the anesthesiologist.
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18. اعتماد بيش از حد به مانيتورينگ هاي الكترونيكي باعث كاهش در مهارت و تشخيص فيزيكي مي گردد
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19. The most obvious, perhaps trivial, example is a patient whose electrocardiogram (ECG) shows asystole. Detection of a normal pulse by direct palpation focuses the anesthesiologist on correcting the monitoring artifact rather than initiating cardiopulmonary resuscitation.
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20. During cardiac surgery the beating heart may be observed directly, and palpation of the ascending aorta by the surgeon provides a useful estimate of aortic blood pressure. In fact, the surgeon's evaluation of any arterial pulse within the surgical field should be considered whenever severe hemodynamic instability develops.
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21. Stethoscopy
Laennec is credited with introducing the stethoscope into general medical practice in 1818, nearly a century elapsed before Harvey Cushing proposed in 1908 that the stethoscope be used as a routine cardiopulmonary monitoring device during surgery. For many years thereafter, intraoperative monitoring with either a precordial or an esophageal stethoscope became the most common simple method for monitoring ventilation and circulation in anesthetized patients.
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22. Though minimally invasive and practical only for patients receiving general endotracheal anesthesia, the esophageal stethoscope provides monitoring benefits not available with its precordial cousin.
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23. Clear breath sounds and distinct heart sounds are audible in most patients when the tip of the stethoscope is positioned 28 to 30 cm from the incisors, and esophageal temperature can be measured with an incorporated thermistor
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24. complications
Hypoxemia from unintended tracheobronchial placement or compression of the membranous posterior portion of the trachea in small infants, loss down the esophagus, detachment of the acoustic cuff, and distortion of surgical anatomy in the neck. Placement of the esophageal stethoscope may also cause pharyngeal or esophageal trauma and interfere with NGT positioning or TEE.
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25. The current role of intraoperative stethoscopy as a continuous monitor has become limited to special applications (e.g., pediatric anesthesia) and to institutions with insufficient resources to purchase electronic monitors
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26. از استتوسكوپ ايزو فاژيال براي تنظيم حرارت (تشخيص حرارت بدن) وبه عنوان ليد ECG براي تشخيص اريتمي دهليزي ايسکمی بطن راست وايسكمی Posteaior L.V. و همچنين براي استفاده جهت Pace قلبي در موارد برادي كاردي سينوسي وريتم جانكشنال استفاده مي شود.
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27. Heart Rate Monitoring
The simplest and least invasive form of cardiac monitoring remains measurement of the heart rate. Under most circumstances in modern anesthesia practice, electronic devices are used to continuously monitor this vital sign and provide an important guide to the influence of anesthetics and surgical stimuli on the patient's condition. The ability to estimate the heart rate quickly with a “finger on the pulse” is a skill as important as this expression is common.
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28. Although any monitor that measures the period of the cardiac cycle can be used to determine the heart rate, the ECG is the most common method used in the operating room.
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30. Artifacts
Electrical interference in the ECG trace may arise from sources other than the electrosurgical unit.
Muscle twitching and fasciculations, as well as from various medical devices, including lithotripsy machines, cardiopulmonary bypass equipment, and fluid warmers.
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31. Pulse Rate Monitoring
The distinction between heart rate and pulse rate centers on whether a given electrical depolarization and systolic contraction of the heart (heart rate) generate a palpable, peripheral arterial pulsation (pulse rate).
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32. Pulse deficit
Pulse deficit describes the extent to which the pulse rate is less than the heart rate. Such deficit is typically seen in patients with:
Atrial fibrillation, in which short R-R intervals compromise cardiac filling during diastole and result in reduced stroke volume and an imperceptible arterial pulse
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33. 2- Electrical-mechanical dissociation,
3- Pulseless electrical activity, seen in patients with cardiac tamponade, extreme hypovolemia,
4- Other conditions in which cardiac contraction does not generate a palpable peripheral pulse.
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34. AI (Bisference pulse)- increase PR Pulsus alternans - decrease PR
IABP - increase PR
AI (Bisference pulse)- increase PR
Pulsus alternans - decrease PR
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35. Arterial Blood Pressure Monitoring
Like the heart rate, blood pressure is a fundamental cardiovascular vital sign and a critical part of monitoring anesthetized or seriously ill patients. The importance of monitoring this vital sign is underscored by the fact that standards for basic anesthetic monitoring mandate measurement of arterial blood pressure at least every 5 minutes in all anesthetized patients.
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36. Direct arterial cannulation and pressure transduction
Techniques for measuring blood pressure fall into two major categories:
Indirect cuff devices
Direct arterial cannulation and pressure transduction
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37. Although direct arterial blood pressure measurement is the reference standard against which other methods are compared, even this technique can yield spurious results. Consequently, blood pressure measured in clinical practice with different techniques often yields significantly different values.
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38. Indirect Measurement of Arterial Blood Pressure
Manual Intermittent Techniques:
Most indirect methods of measuring blood pressure rely on a sphygmomanometer similar to the one first described by Riva-Rocci in This apparatus included an arm-encircling inflatable elastic cuff, a rubber bulb to inflate the cuff, and a mercury manometer to measure cuff pressure.
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39. Riva-Rocci described the measurement of systolic arterial blood pressure by determining the pressure at which the palpated radial arterial pulse disappeared as the cuff was inflated.
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40. A commonly used variation of the Riva-Rocci method, termed the “return-to-flow technique,” records the pressure during cuff deflation at which the pulse reappears and is detected by palpation. When the patient has a finger pulse oximeter or an indwelling arterial catheter in the ipsilateral arm, return to flow can be detected by reappearance of the plethysmographic or arterial pressure waveforms
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41. Return-to-flow methods provide a simple, rapid estimation of systolic blood pressure during urgent situations but do not allow measurement of diastolic blood pressure.
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42. To measure both systolic and diastolic arterial pressure, the most widely used intermittent manual method is the auscultatory technique, originally described by Korotkoff in 1905
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43. Using a sphygmomanometer, cuff, and stethoscope, Korotkoff measured blood pressure by auscultating sounds generated by arterial blood flow. These sounds are a complex series of audible frequencies produced by turbulent flow beyond the partially occluding cuff.
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44. The pressure at which the first Korotkoff sound is heard is generally accepted as systolic pressure (phase I). The character of the sound progressively changes (phases II and III), becomes muffled (phase IV), and is finally absent (phase V). Diastolic pressure is recorded at phase IV or V.
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45. phase V may never occur in certain pathophysiologic states such as aortic regurgitation.
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46. Pathologic or iatrogenic causes of decreased peripheral blood flow, such as cardiogenic shock or high-dose vasopressor infusion, can attenuate or obliterate the generation of sound and result in significant underestimation of blood pressure.
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47. In contrast, low compliance of the tissues underlying the cuff, as encountered in a shivering patient, will require an excessively high cuff-occluding pressure and produce “pseudohypertension.” A similar situation exists in patients with severe calcific arteriosclerosis, whose noncompressible arteries may be palpated distal to a fully inflated cuff (positive Osler sign).
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48. Other common sources of error during intermittent manual blood pressure measurement include selection of an inappropriate cuff size and excessively rapid cuff deflation. The optimal cuff should have a bladder length that is 80% and a width at least 40% of arm circumference.
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49. The cuff should be applied snugly, with the bladder centered over the artery and any residual air squeezed out. Although too large a cuff will generally work well and produce little error, use of cuffs that are too small will result in overestimation of blood pressure. The cuff deflation rate is another important variable that influences manual blood pressure measurement.
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50. Automated Intermittent Techniques
Many limitations of manual intermittent blood pressure measurement have been overcome by automated NIBP devices, which are now used widely. In addition, automated NIBP devices provide audible alarms and can transfer data to a computerized information system.
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51. However, the greatest advantage of automated NIBP devices over manual methods of blood pressure measurement is that they provide frequent, regular blood pressure measurements and free the operator to perform other vital clinical duties.
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52. Most automated NIBP devices are based on oscillometry, a technique first described by Marey in In this method, variations in cuff pressure resulting from arterial pulsations during cuff deflation are sensed by the monitor and used to determine arterial blood pressure values.
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53. The pressure at which the peak amplitude of arterial pulsations occurs corresponds closely to directly measured mean arterial pressure (MAP), and values of systolic and diastolic pressure are derived from proprietary formulas that examine the rate of change of the pressure pulsations.
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54. Consequently, systolic and diastolic values are less reliable than MAP values. Systolic pressure is typically identified as the pressure at which pulsations are increasing and are at 25% to 50% of maximum. Diastolic pressure is the most unreliable oscillometric measurement and is commonly recorded when the pulse amplitude has declined to a small fraction of its peak value.
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56. Complications of Noninvasive Blood Pressure Measurement
Although automated blood pressure measurement techniques are considered noninvasive and relatively safe, complications have been reported, including rare severe events such as compartment syndrome.
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57. These morbid events occur more often after prolonged periods of excessively frequent cycles of cuff inflation/deflation and are due to trauma or impaired distal limb perfusion. Other factors that may contribute include cuff misplacement across a joint or repeated attempts to determine blood pressure in the presence of an artifact-producing condition such as involuntary muscle tremors.
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58. Caution should be exercised when using these monitors in patients with
depressed consciousness,
preexisting peripheral neuropathies,
arterial or venous insufficiency, or
irregular cardiac rhythms,
those receiving anticoagulant or thrombolytic therapy.
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59. Complications of Noninvasive Blood Pressure Measurement
Pain
Petechiae and ecchymoses
Limb edema
Venous stasis and thrombophlebitis
Peripheral neuropathy
Compartment syndrome
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60. Automated Continuous Techniques
Advances in microprocessor and servomechanical control technology have enabled noninvasive techniques to provide a reasonable representation of the arterial pressure waveform and nearly continuous assessment of blood pressure without resorting to direct arterial cannulation. One such device measures finger blood pressure with an arterial volume-clamp method designed and first reported by Penaz in 1973
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61. Although several clinical investigators have demonstrated reasonable accuracy of finger blood pressure as a surrogate for intra-arterial pressure measurements, a number of factors have precluded more widespread application of this technology.
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62. In many circumstances, finger blood pressure monitoring will not reflect brachial arterial pressure. In addition, finger arteries are prone to spasm with the potential for distal ischemia, hand position will influence pressure values, and blood sampling cannot be performed without indwelling catheters.
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63. Other automatic continuous noninvasive techniques have been used to measure blood pressure by applying technologies based on arterial wall displacement, pulse transit time, arterial tonometry, and other methods. All techniques have limitations, including the need for calibration, sensitivity to motion artifact, and limited applicability in critically ill patients.
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64. It remains unclear whether any noninvasive technique will reduce the need for direct arterial pressure monitoring or whether these methods will replace automated intermittent oscillometry as the standard NIBP monitoring method in anesthesia and critical care.
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65. Direct Measurement of Arterial Blood Pressure
Arterial cannulation with continuous pressure transduction and waveform display remains the accepted reference standard for blood pressure monitoring despite the fact that it is more costly, has the potential for more complications, and requires more technical expertise to initiate and maintain than noninvasive monitoring does.
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66. Indications for Arterial Cannulation
Continuous, real-time blood pressure monitoring
Planned pharmacologic or mechanical cardiovascular manipulation
Repeated blood sampling
Failure of indirect arterial blood pressure measurement
Supplementary diagnostic information from the arterial waveform
Determination of volume responsiveness from systolic pressure or pulse pressure variation
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67. First and foremost, direct arterial pressure monitoring should be used when moment-to-moment blood pressure changes are anticipated and rapid detection is vital.
These conditions typically apply to patients with preexisting severe cardiovascular disease or hemodynamic instability or when the planned operative procedure is likely to cause large, sudden cardiovascular changes, rapid blood loss, or large fluid shiftsthe early detection of intraoperative hypotension and .
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68. In addition to continuous blood pressure monitoring, arterial catheterization provides reliable vascular access for frequent blood sampling and allows monitoring of blood pressure when NIBP measurement is impossible (as during nonpulsatile cardiopulmonary bypass). Perhaps the most underemphasized value of direct arterial pressure monitoring is that analysis of the arterial pressure waveform may provide many important diagnostic clues to the patient's condition
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69. Some of these diagnostic insights are readily apparent and commonly sought, such as identification of the arterial dicrotic notch to guide proper timing for intra-aortic balloon counterpulsation, whereas others are more subtle, such as recognition of excessive variation in systolic blood pressure as a sign of hypovolemia.
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70. Percutaneous Radial Artery Cannulation
The radial artery is the most common site for invasive blood pressure monitoring in anesthesia and critical care because it is technically easy to cannulate and complications are uncommon, in part because of the good collateral circulation of the hand.
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71. Slogoff and coauthors described the results of radial artery cannulation in 1700 cardiovascular surgical patients who underwent the procedure without ischemic complications despite evidence of radial artery occlusion after decannulation in more than 25% of the patients
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72. Before attempting radial artery cannulation, many clinicians assess the adequacy of collateral flow to the hand by performing a modified Allen test. This bedside examination, originally described by E. V. Allen in 1929, provided a technique to assess arterial stenosis in the hands of patients with thromboangiitis obliterans. To perform the Allen test, the examiner compresses the radial and ulnar arteries and asks the patient to make a tight fist to exsanguinate the palm.
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73. The patient then opens the fist while avoiding hyperextension of the wrist or fingers, and as occlusion of the ulnar artery is released, the color of the open palm is observed. Normally, the palm will show a striking flush in several seconds; severely reduced ulnar collateral flow is present when the palm remains pale for more than 10 seconds.
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74. Although the Allen test is often used to identify patients at high risk for ischemic complications from radial artery catheterization, the predictive value of this test is uncertain. Numerous reports of permanent ischemic sequelae note that a normal Allen test result was present before catheterization.
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75. In contrast, there are many descriptions of uncomplicated radial artery catheterization despite the presence of an abnormal Allen test result before the procedure. In recent years, the radial artery has been used safely as an access site for coronary stenting or excised and used as a graft for coronary bypass surgery, even in individuals with abnormal Allen test results.
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76. Metod
Consistent, successful radial artery cannulation should be easily achievable with attention to a number of procedural details. The wrist and hand are immobilized in mild dorsiflexion and secured with the wrist resting across a soft pad. Excessive dorsiflexion of the wrist should be avoided because of the possibility of attenuating the pulse.
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77. The course of the radial artery proximal to the wrist is identified by gentle palpation, the skin is prepared with an antiseptic, and a local anesthetic is injected intradermally and subcutaneously alongside the artery. Arterial catheterization can then be performed with a standard intravenous catheter or an integrated guidewire-catheter assembly designed for this purpose.
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78. 9/22/2018

79. Some clinicians choose the “transfixion” technique for arterial cannulation, in which the front and back walls of the artery are punctured intentionally, the needle is removed from the catheter, and the catheter is withdrawn into the vessel lumen. Although it is unnecessary to place an additional hole in the back wall of the radial artery for successful cannulation, the technique per se does not appear to influence the success rate or incidence of postcannulation complications.
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80. Other aids to arterial cannulation include the use of ultrasound imaging to guide catheter insertion. This may be particularly helpful when standard placement attempts by palpation have failed.
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81. Alternative Arterial Pressure Monitoring Sites
If the radial arteries are unsuitable for monitoring pressure, several alternative cannulation sites are available. The ulnar artery is cannulated with a technique much like that described for the radial artery. Even in circumstances in which previous attempts to cannulate the ipsilateral radial artery have failed, the ulnar artery may be cannulated safely.
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82. Although in theory the brachial artery does not have the anatomic benefit of the collateral circulation present in the hand, clinical trials have confirmed the safety of this cannulation site. Bazaral and coauthors reported the use of more than 3000 brachial artery catheters in patients undergoing cardiac surgery over a 3-year period, with only one patient requiring postoperative thrombectomy and no untoward sequelae.
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83. A slightly longer catheter is preferred for the brachial site because of the need for the catheter to traverse the elbow joint. Other peripheral arteries occasionally chosen for monitoring pressure include the dorsalis pedis, posterior tibial, and superficial temporal arteries. The dorsalis pedis and posterior tibial arteries are generally reserved for pediatric applications
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84. Axillary artery
The axillary artery provides another site for long-term pressure monitoring. Advantages include patient comfort, mobility, and access to a central arterial pressure waveform. Complications appear to be infrequent and similar in incidence to radial and femoral artery catheterization.
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85. If the axillary approach is chosen, the left side is preferred over the right because the axillary catheter tip will lie distal to the aortic arch and great vessels. Clinicians should be aware, however, that the risk of cerebral embolization is increased whenever more centrally located arterial catheters are used
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86. Femoral artery
The femoral artery is the largest artery commonly selected for monitoring blood pressure, and it appears to have a safety record comparable to that of other sites. As with axillary artery pressure monitoring, the femoral artery waveform more closely resembles aortic pressure than do waveforms recorded from peripheral sites
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87. When compared with radial artery catheterization, the risk of distal ischemia after femoral artery cannulation may be reduced because of the large diameter of the artery, but atherosclerotic plaque embolization is more likely during initial guidewire and catheter placement.
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88. Catheterization of the femoral artery is best achieved with a guidewire technique. The operator must be careful to puncture the femoral artery below the inguinal ligament, thereby limiting the risk of arterial injury causing uncontained hemorrhage into the pelvis or peritoneum, a potentially catastrophic complication
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89. Complications of Direct Arterial Pressure Monitoring
Widespread application of invasive arterial pressure monitoring in anesthesia and intensive care is related, no doubt, to the extremely good safety record of this technique. Large clinical investigations confirm the low incidence of long-term complications after radial artery cannulation, in particular, the small risk of distal ischemia, which is probably less than 0.1%.
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90. Although vascular complications from radial artery cannulation are uncommon, factors that may increase risk include vasospastic arterial disease, previous arterial injury, thrombocytosis, protracted shock, high-dose vasopressor administration, prolonged cannulation, and infection.
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91. Complications of Direct Arterial Pressure Monitoring
Distal ischemia, pseudoaneurysm, arteriovenous fistula
Hemorrhage, hematoma
Arterial embolization
Local infection, sepsis
Peripheral neuropathy
Misinterpretation of data
Misuse of equipment
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92. Technical Aspects of Direct Blood Pressure Measurement
Direct measurement of arterial blood pressure requires that the pressure waveform from the cannulated artery be reproduced accurately on the bedside monitor. Not surprisingly, the displayed pressure signal is influenced significantly by the measuring system, including the arterial catheter, extension tubing, stopcocks, flush devices, transducer, amplifier, and recorder.
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93. Blood pressure monitoring systems used in the operating room and intensive care units are described as underdamped, second-order dynamic systems. These fluid-filled systems may be modeled after mass-spring systems that demonstrate simple harmonic motion and exhibit similar behavior that depends on the physical properties of elasticity, mass, and friction.
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94. The natural frequency of the monitoring system quantifies how rapidly the system oscillates, and the damping coefficient quantifies the frictional forces that act on the system and determine how rapidly it comes to rest.
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95. Natural Frequency, Damping Coefficient, and Dynamic Response of Pressure Monitoring Systems
The arterial blood pressure waveform is a periodic complex wave that can be reproduced by Fourier analysis, which recreates the original complex pressure wave by summing a series of simpler sine waves of different amplitudes and frequencies.
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96. Arterial blood pressure waveform produced by summation of sine waves
Arterial blood pressure waveform produced by summation of sine waves. The fundamental wave (top) added to 63% of the second harmonic wave (middle) results in a pressure wave (bottom) that resembles an arterial blood pressure waveform (box).
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97. As a general rule, 6 to 10 harmonics are required to provide distortion-free reproduction of most arterial pressure waveforms. Hence, accurate blood pressure measurement in a patient with a pulse rate of 120 beats/min (2 cycles/sec or 2 Hz) requires a monitoring system dynamic response of 12 to 20 Hz.
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98. If the monitoring system has a natural frequency that is too low, frequencies in the monitored pressure waveform will overlap the natural frequency of the measurement system. As a result, the system will resonate and pressure waveforms recorded on the monitor will be exaggerated or amplified versions of true intra-arterial pressure .
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100. This phenomenon is the familiar arterial pressure waveform that displays overshoot, ringing, or resonance. In these instances, the recorded systolic blood pressure overestimates true intra-arterial pressure.
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101. Overdamping
In addition to a sufficiently high natural frequency, the bedside monitoring system must also have an appropriate damping coefficient. An overdamped arterial pressure waveform is recognized by its:
slurred upstroke,
absent dicrotic notch,
loss of fine detail
Severely overdamped pressure waves display a falsely narrowed pulse pressure, although MAP may remain reasonably accurate .
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102. Overdamped arterial pressure waveform
Overdamped arterial pressure waveform. The overdamped pressure waveform (A) shows a diminished pulse pressure when compared with the normal waveform (B). The slow-speed recording below demonstrates a 3-minute period of damped arterial pressure. Despite the damped pressure waveform, mean arterial pressure remains unchanged during this period
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103. Underdamping
In contrast, underdamped pressure waveforms display systolic pressure overshoot and contain additional artifacts produced by the measurement system that are not part of the original intravascular pressure wave .
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104. Most catheter-transducer systems are underdamped but have an acceptable natural frequency that exceeds 12 Hz. If the system's natural frequency is lower than 7.5 Hz, the pressure waveform is often distorted, and no amount of damping adjustment can restore the monitored waveform to adequately resemble the original waveform.
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105. Interaction between damping coefficient (D) and natural frequency (fn) in pressure waveform recordings. A, An underdamped pressure waveform (fn = 10 Hz; D = 0.1) displays small artifactual waves and systolic pressure overshoot. B, A small increase in D (0.2) diminishes these artifacts. C, Critical damping (D = 0.4) provides an accurate pressure waveform even though fn remains low. D, Overdamping results in loss of fine detail and precludes determination of fn or D. E, Increased fn (20 Hz) allows a low D (0.1) to have minimal impact on waveform morphology. Notice the similarities between waveforms C and E. (From Mark JB: Atlas of Cardiovascular Monitoring.
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107. Interaction between damping coefficient and natural frequency
Interaction between damping coefficient and natural frequency. Depending on these two system parameters, catheter tubing-transducer systems fall into one of five different dynamic response ranges. Systems with an optimal dynamic response will faithfully record the most demanding pressure waveforms, whereas those with an adequate dynamic response will accurately record most pressure waveforms seen in clinical practice. Overdamped and underdamped systems introduce artifacts characteristic of these technical limitations. Systems with a natural frequency of less than 7 Hz are considered unacceptable. The rectangular crosshatched box indicates the ranges of damping coefficients and natural frequencies commonly encountered in clinical pressure measurement systems. The point within the box shows the mean values of 30 such systems recorded by Schwid.
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108. From these considerations it follows that a pressure monitoring system will have optimal dynamic response if its natural frequency is as high as possible. In theory, this is best achieved by using short lengths of stiff pressure tubing and limiting the number of stopcocks and other monitoring system appliances.
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109. Blood clots and air bubbles trapped and concealed in stopcocks and other connection points will have similar adverse influences on the system's dynamic response.
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110. As a general rule, adding air bubbles to monitoring systems will not improve their dynamic response because any increase in system damping is always accompanied by a decrease in natural frequency. Somewhat paradoxically, monitoring system resonance may increase and cause even greater systolic pressure overshoot .
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112. Effect of small air bubbles within arterial pressure monitoring systems. Arterial pressure waveforms are displayed, along with superimposed fast-flush square-wave artifacts. A, The original monitoring system has an adequate dynamic response (natural frequency, 17 Hz; damping coefficient, 0.2). B, A small 0.1-mL air bubble added to the monitoring system produces a paradoxical increase in arterial blood pressure. Note the decreased natural frequency of the system. C, A larger 0.5-mL air bubble further degrades the dynamic response and produces spurious arterial hypotension.
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113. Fast flash test
To assess the amount of distortion existing in a pressure monitoring system, the fast-flush test provides a convenient bedside method for determining the system's dynamic response. To perform this test, the fast-flush valve is opened briefly, and the resulting flush artifact is examined.
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114. 1 cycle/1.7 mm × 25 mm/sec = 14.7 cycles/sec (14.7 Hz)
Natural frequency is inversely proportional to the time between adjacent oscillation peaks. It can be calculated as:
1 cycle/1.7 mm × 25 mm/sec = 14.7 cycles/sec (14.7 Hz)
Monitoring systems with shorter oscillation cycles will have higher natural frequencies.
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116. The damping coefficient is related to the amplitudes of successive oscillation peaks. The amplitude ratio thus derived indicates how quickly the measuring system comes to rest. The damping coefficient can be calculated mathematically, but it is usually determined graphically from the amplitude ratio.
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117. For example, if the amplitudes of two successive oscillation cycles are 24 and 17 mm, the amplitude ratio is 17/24, or This corresponds to a damping coefficient of 0.11 based on the graphic solution .
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119. Note that the monitoring system illustrated has an adequate natural frequency (approximately 15 Hz) but is underdamped (damping coefficient of 0.11), and one would expect to find systolic pressure overshoot in such a system according NIBP.
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120. Components of Pressure Monitoring Systems
Arterial pressure monitoring systems have a number of components, beginning with the intra-arterial catheter and including extension tubing, stopcocks, in-line blood sampling set, pressure transducer, continuous-flush device, and electronic cable connecting the bedside monitor and waveform display screen. The stopcocks in the system provide sites for blood sampling and allow the transducer to be exposed to atmospheric pressure to establish a zero reference value.
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121. The flush device provides a continuous, slow (1 to 3 mL/hr) infusion of saline to purge the monitoring system and prevent thrombus formation within the arterial catheter. Dextrose solutions should not be used because flush contamination of sampled blood may cause serious errors in blood glucose measurement.
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122. A dilute concentration of heparin (1 to 2 units heparin/mL saline) has been added to the flush solution to further reduce the incidence of catheter thrombosis, but this practice increases the risk for heparin-induced thrombocytopenia and should be avoided
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123. Transducer Setup: Zeroing and Leveling
Before initiating patient monitoring, the pressure transducer must be zeroed, calibrated, and leveled to the appropriate position on the patient. The initial step in this process is to expose the transducer to atmospheric pressure by opening the adjacent stopcock to air, pressing the zero pressure button on the monitor, and thereby establishing the zero pressure reference value.
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124. When a significant change in pressure occurs, the zero reference value can be rechecked quickly by opening the stopcock and noting that the pressure value on the bedside monitor is still zero. Occasionally, a faulty transducer, cable, or monitor will cause the zero baseline to drift. Though uncommon with modern monitoring components, this zero drift artifact must be identified to avoid important diagnostic errors.
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125. Historically, calibration of the transducer was the next step after zeroing. Calibration is an adjustment in system gain to ensure accurate transducer measurement relative to a known reference pressure value. Though traditionally calibrated against a mercury manometer, current disposable pressure transducers meet accuracy standards established by the Association for the Advancement of Medical Instrumentation and the American National Standards Institute.
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126. LEVEL
The final step in transducer setup is to adjust the pressure monitoring zero point to the appropriate level relative to the patient. Note that transducer zeroing and leveling are two distinct procedures. Zeroing exposes the transducer to ambient atmospheric pressure through an open stopcock. Leveling assigns this zero reference point to a specific position on the patient's body
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127. Although precise location of the zero reference level is essential for accurate monitoring of blood pressure, it is also critically important for measurement of cardiac filling pressures, where a small absolute error in pressure measurement will cause a large relative error.
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128. Arterial pressure transducers should be placed at a level that will best estimate aortic root pressure. In a supine patient, pressure transducer levels are often adjusted to the midchest position in the midaxillary line
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129. In some circumstances, the clinician may choose to adjust the arterial transducer level to a different position on the body. It is critically important to recognize that when this is done, the pressure is being measured at the level of the transducer and not at the level of the aortic root.
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130. For example, during sitting neurosurgical operations, if the arterial pressure transducer is raised to a level even with the patient's ear to approximate the location of the circle of Willis, the clinician is measuring blood pressure at the level of the brain and must recognize that the aortic root pressure is higher (by an amount equal to the vertical difference in height between the pressure transducer and the aortic root).
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131. Whenever the level of the pressure transducer is adjusted, there is no need to rezero the transducer because atmospheric pressure changes little over the few inches of height adjustment.
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132. Common errors in blood pressure measurement occur when pressure transducers are fixed to an intravenous pole and the height of the patient's bed is adjusted. Raising the height of the bed relative to the transducer will cause overestimation of blood pressure, whereas lowering the patient below the transducer will cause underestimation of blood pressure
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133. Proper interpretation of blood pressure measurements from a patient in the lateral decubitus position requires an understanding of the distinction between zeroing and leveling pressure transducers and the differences between noninvasive and invasive blood pressure measurement
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134. 9/22/2018

135. When a patient is in the lateral decubitus position, one arm is higher than the heart (and aortic root) and the other arm is lower. Regardless of whether direct arterial pressure is measured from the right or the left arm, as long as the pressure transducer remains fixed at the level of the heart, the location of the arms has no influence on the measured arterial pressure.
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136. However, noninvasive cuff blood pressure measurements will be different in the two arms, higher in the dependent (down) arm and lower in the nondependent (up) arm.
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137. Note that if the arterial pressure transducers were attached to the arms rather than fixed at the level of the heart, pressures recorded from the right and left radial artery catheters would equal those recorded by the ipsilateral noninvasive cuffs and would be higher in the dependent arm than in the nondependent arm.
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138. Normal Arterial Pressure Waveforms
Direct arterial pressure monitoring in anesthetized patients began nearly 60 years ago. In that early era, arterial pulse waveform analysis was noted to provide useful diagnostic information, but somewhat surprisingly, modern physicians pay little attention to the morphology and detail of the arterial pressure waveform.
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139. The systemic arterial pressure waveform results from ejection of blood from the left ventricle into the aorta during systole, followed by peripheral arterial runoff of this stroke volume during diastole.
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140. Normal arterial blood pressure waveform and its relationship to the electrocardiographic R wave. 1, Systolic upstroke; 2, systolic peak pressure; 3, systolic decline; 4, dicrotic notch; 5, diastolic runoff; 6, end-diastolic pressure
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141. The incisura is sharply defined and is undoubtedly related to closure of the aortic valve.In contrast, the peripheral arterial waveform generally displays a later, smoother dicrotic notch that only approximates the timing of aortic valve closure and depends more on properties of the arterial wall. Note that the systolic upstroke of the radial artery pressure trace does not appear for 120 to 180 msec after inscription of the ECG R wave .
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142. This interval reflects the sum of times required for spread of electrical depolarization through the ventricular myocardium, isovolumic left ventricular contraction, opening of the aortic valve, left ventricular ejection, transmission of the aortic pressure wave to the radial artery, and finally, transmission of the pressure signal from the arterial catheter to the pressure transducer.
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143. The bedside monitor displays numeric values for the systolic peak and end-diastolic nadir pressures. Measurement of mean pressure is more complicated and depends on the algorithm used by the monitor. In simplest terms, MAP is equal to the area beneath the arterial pressure curve divided by the beat period and averaged over a series of consecutive heartbeats.
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144. Although MAP is often estimated as diastolic pressure plus one third times pulse pressure, this estimate is valid only at slower heart rates because the proportion of the cardiac cycle spent in diastole decreases during tachycardia
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145. One of the most important features of the arterial pressure waveform is the phenomenon of distal pulse amplification. Pressure waveforms recorded simultaneously from different arterial sites will have different morphologies because of the physical characteristics of the vascular tree, namely, impedance and harmonic resonance .
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146. As the arterial pressure wave travels from the central aorta to the periphery, the arterial upstroke becomes steeper, the systolic peak becomes higher, the dicrotic notch appears later, the diastolic wave becomes more prominent, and end-diastolic pressure becomes lower. Thus, when compared with central aortic pressure, peripheral arterial waveforms have higher systolic pressure, lower diastolic pressure, and wider pulse pressure.
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147. 9/22/2018

148. Furthermore, there is a delay in arrival of the pressure pulse at peripheral sites, so the systolic pressure upstroke begins approximately 60 msec later in the radial artery than in the aorta. Despite morphologic and temporal differences between peripheral and central arterial waveforms, MAP in the aorta is just slightly greater than MAP in the radial artery.
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149. Pressure wave reflection is the predominant factor that influences the shape of the arterial pressure waveform as it travels peripherally. As blood flows from the aorta to the radial artery, mean pressure decreases only slightly because of little resistance to flow in the major conducting arteries. At the arteriolar level, mean blood pressure falls markedly as a result of the dramatic increase in vascular resistance at this site.
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150. This high resistance to flow diminishes pressure pulsations in small downstream vessels but acts to augment upstream arterial pressure pulses because of pressure wave reflection.These intrinsic vascular phenomena determine the shape of the arterial pulse wave recorded from different sites in the body, in both health and disease. For example, elderly patients have reduced arterial distensibility, which results in early return of reflected pressure waves, increased pulse pressure, a late systolic pressure peak, and disappearance of the diastolic pressure wave .
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151. 9/22/2018

152. From these considerations it becomes evident that the morphology of the arterial waveform and the precise values of systolic and diastolic blood pressure vary throughout the body under normal conditions in otherwise healthy individuals. Perhaps of even greater importance, the relationship between central and peripheral arterial pressure varies with age and is altered by various physiologic changes, pathologic conditions, and pharmacologic interventions.
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153. Arterial Blood Pressure Gradients
In addition to the normal physiologic phenomena that exert subtle influences on the arterial pressure waveform, a number of pathophysiologic conditions cause exaggerated arterial pressure gradients in the body.
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154. Frank and coworkers demonstrated that 21% of patients undergoing peripheral vascular surgery had a blood pressure difference between the two arms that exceeded 20 mm Hg. In view of the prevalence of this problem, when blood pressure is lower in one arm than in the other or when the pulses are weaker on one side, one should never insert an arterial catheter on the side with the weaker pulse because determination of blood pressure from this site will probably underestimate true aortic pressure. In addition to atherosclerosis, other pathologic conditions such as arterial dissection or embolism preclude accurate monitoring of pressure from the affected sites.
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155. Unusual patient positions during surgery may produce regional arterial compression, and surgical retraction, particularly during cardiothoracic operations, can produce local vascular compression. The nature of the operative procedure is always an important determinant of the appropriate site for monitoring arterial pressure.
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156. Operations requiring placement of a descending thoracic aortic cross-clamp may interrupt arterial flow to the left subclavian artery and its tributaries in the left arm, as well as branches of the aorta beyond the clamp. In these cases, blood pressure monitored from the right arm best estimates aortic root pressure and carotid arterial pressure and is used to guide anesthetic management. In addition, pressure may be monitored simultaneously from a femoral artery in an attempt to estimate perfusion pressure to vital organs distal to the aortic cross-clamp.
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157. Various pathophysiologic disturbances may produce generalized arterial pressure gradients in the body and should be considered when choosing a site for monitoring arterial pressure. Large differences in peripheral and central arterial pressure may be seen in patients in shock. Femoral artery systolic pressure may exceed radial artery systolic pressure by more than 50 mm Hg in septic patients who require vasopressor infusions, an observation that has significant therapeutic implications for the management of critically ill patients
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158. Other vasoactive drugs, anesthetics (particularly neuraxial blockade), and changes in patient temperature produce pressure gradients that alter the relationship between central and peripheral arterial pressure measurements. During hypothermia, thermoregulatory vasoconstriction causes radial artery systolic pressure to exceed femoral artery systolic pressure, whereas during rewarming, vasodilation reverses this gradient and causes radial artery pressure to underestimate femoral artery pressure
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159. Large differences between central and peripheral arterial blood pressure have also been described in cardiac surgical patients undergoing cardiopulmonary bypass .
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160. 9/22/2018

161. Shortly after initiation of cardiopulmonary bypass, mean radial artery pressure is lower than mean femoral artery pressure, and this difference seems to persist during the bypass procedure. Furthermore, in the initial minutes after bypass, radial arterial pressure continues to be lower than central aortic pressure, often by more than 20 mm Hg. In most patients, these pressure differences persist after bypass for only several minutes and resolve within an hour, but occasionally these pressure gradients are still present during the postoperative period.
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162. Abnormal Arterial Pressure Waveforms
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163. Arterial Blood Pressure Waveform Abnormalities
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164. Aortic stenosis produces a fixed obstruction to left ventricular ejection that results in reduced stroke volume and an arterial pressure waveform that rises slowly (pulsus tardus), peaks late in systole, and is small in amplitude (pulsus parvus) ( Fig A and B ). A distinct shoulder, termed the anacrotic notch, often distorts the pressure upstroke, and the dicrotic notch may not be discernible. These features make the arterial pressure waveform appear overdamped.
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165. 9/22/2018

166. In aortic regurgitation, the arterial pressure wave displays a sharp rise, wide pulse pressure, and low diastolic pressure as a result of runoff of blood into the left ventricle and the periphery during diastole. Because of the large stroke volume ejected from the left ventricle in this condition, the arterial pressure pulse may have two systolic peaks (bisferiens pulse) (see Fig C ).
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167. 9/22/2018

168. In hypertrophic cardiomyopathy, the arterial pressure waveform assumes a peculiar bifid shape termed a “spike-and-dome” configuration. After an initial sharp pressure upstroke that results from rapid left ventricular ejection in early systole, arterial pressure falls rapidly as dynamic left ventricular outflow obstruction develops during midsystole and is followed by a late systolic reflected wave, thereby creating the characteristic double-peaked waveform (see Fig D ).
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169. 9/22/2018

170. Pulsus alternans is recognized by the alternating beats of larger and smaller pulse pressures ( Fig A ). In general, it is considered to be a sign of severe left ventricular systolic dysfunction, often noted in patients with advanced aortic stenosis. Pulsus alternans should be distinguished from the bigeminal pulse that arises from a bigeminal rhythm, usually ventricular bigeminy. Both abnormalities create an alternating pulse pressure in the arterial pressure waveform, but the rhythm is regular in pulsus alternans.
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171. 9/22/2018

172. Pulsus paradoxus is an exaggerated inspiratory fall in systolic arterial pressure that exceeds 10 to 12 mm Hg during quiet breathing .
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173. 9/22/2018

174. The term is confusing because a small inspiratory reduction in blood pressure is a normal phenomenon and pulsus paradoxus is not truly paradoxical, but rather an exaggeration of the normal inspiratory decline in blood pressure. Pulsus paradoxus is a characteristic, almost universal finding in cardiac tamponade that occurs in many patients with pericardial constriction.
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175. It is said to occur in patients with airway obstruction, bronchospasm, dyspnea, or any condition characterized by large swings in intrathoracic pressure. However, in cardiac tamponade, pulse pressure and left ventricular stroke volume decrease during inspiration, in contrast to the blood pressure changes observed in patients with forced breathing patterns and exaggerated changes in intrathoracic pressure, in whom pulse pressure is relatively unchanged.
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176. The arterial pressure waveform provides diagnostic clues in other unusual physiologic states, such as for proper timing of intra-aortic balloon counterpulsation .
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177. 9/22/2018

178. During nonpulsatile cardiopulmonary bypass, minor variations in blood pressure created by the arterial roller head allow calculation and confirmation of the adequacy of systemic blood flow[28] (see Fig B ).
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179. 9/22/2018

180. Arterial Pressure Monitoring for Prediction of Volume Responsiveness
The starting point for hemodynamic resuscitation begins with optimizing cardiac preload. The limitations of static indicators of preload, such as central venous pressure (CVP), have been increasingly recognized because of the many factors that confound their interpretation.
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181. Newer dynamic markers of volume responsiveness have been described that provide more useful information for determining appropriate end points for fluid resuscitation. Variations in arterial blood pressure observed during positive-pressure mechanical ventilation are the most widely studied of these dynamic indicators.
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182. These changes in blood pressure are readily observed on the bedside monitor in patients who are receiving direct arterial blood pressure monitoring, and they result from the changes in intrathoracic pressure and lung volume that occur during the respiratory cycle.
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183. During positive-pressure inspiration, increasing lung volume compresses and displaces the pulmonary venous reservoir and propels blood into the left heart chambers, thereby increasing left ventricular preload. Simultaneously, the increase in intrathoracic pressure reduces left ventricular afterload. The increase in left ventricular preload and decrease in afterload produce an increase in left ventricular stroke volume and an increase in systemic arterial pressure
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184. In most patients the preload effects are more important, but in patients with severe left ventricular systolic failure, the reduction in afterload plays an important role in increasing left ventricular ejection.
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185. At the same time that left heart filling is increasing during early inspiration, the rising intrathoracic pressure causes a decrease in systemic venous return and right ventricular preload. The increased lung volume may also increase pulmonary vascular resistance (PVR) slightly and thereby increase right ventricular afterload. These effects combine to reduce right ventricular ejection during inspiration.
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186. During early expiration, the reduced right ventricular stroke volume that occurred during inspiration crosses the pulmonary vascular bed and leads to reduced left ventricular filling. As a result, left ventricular stroke volume falls and systemic arterial blood pressure decreases. This cyclic variation in systemic arterial pressure may be measured and quantified as the systolic pressure variation (SPV).
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187. SPV is often subdivided into inspiratory and expiratory components by measuring the increase (Δ Up) and decrease (Δ Down) in systolic pressure in relation to the end-expiratory, apneic baseline pressure ( Fig ).
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189. In a mechanically ventilated patient, normal SPV is 7 to 10 mm Hg, with Δ Up being 2 to 4 mm Hg and Δ Down being 5 to 6 mm Hg.[75] The greatest clinical use of SPV has been for the early diagnosis of hypovolemia.[76] In both experimental animals and patients, hypovolemia causes a dramatic increase in SPV, particularly the Δ Down component. An increase in SPV, particularly in Δ Down, may herald hypovolemia, even in patients in whom arterial blood pressure is maintained near normal levels by compensatory arterial vasoconstriction.
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190. In a heterogeneous group of intensive care patients, Marik demonstrated that a large SPV (>15 mm Hg) was highly predictive of low pulmonary artery wedge pressure (PAWP) (<10 mm Hg).[77] Using echocardiography to measure the left ventricular cross-sectional area as a surrogate for preload, Coriat and colleagues found Δ Down to be better than wedge pressure as a predictor of preload.[78] Other uses of SPV focus on changes in the Δ Up portion of the arterial pressure trace. Just as Δ Down may reveal changes in cardiac preload, the Δ Up portion of the arterial pressure trace may provide clues to the afterload dependence of the left ventricle.
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191. As a dynamic indicator of cardiac preload, SPV and Δ Down provide valuable clinical information beyond that provided by static preload indicators such as CVP or PAWP. It appears that the magnitude of blood pressure variation accurately predicts patients who will subsequently respond to a volume challenge by increasing stroke volume and cardiac output. Using receiver-operator curve analysis, Tavernier and coworkers showed that when compared with PAWP or left ventricular end-diastolic area, Δ Down was a far better indicator of volume responsiveness.
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192. Another dynamic marker of volume responsiveness is pulse pressure variation (PPV), defined as the maximal difference in arterial pulse pressure measured over the course of the positive-pressure respiratory cycle divided by the average of the maximal and minimal pulse pressure [80] [81] ( Fig ).
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193. 9/22/2018

194. Normal PPV should not exceed 13%
Normal PPV should not exceed 13%.[82] In addition to SPV and PPV, new pulse contour methods for measurement of cardiac output (see later) allow online measurement of variations in left ventricular stroke volume, so-called stroke volume variation (SVV). Like the other related dynamic indicators of volume responsiveness, normal SVV is approximately 10%, and greater variability accurately predicts a positive response to a fluid challenge.[83] Another approach to assessing fluid responsiveness has focused on the respiratory cycle–induced variation in the pulse plethysmogram, but this physiologic signal is even more subject to confounding influences than the arterial blood pressure waveform is.
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195. Despite rapidly accumulating evidence of the value of SPV and PPV and their related measures as accurate predictors of cardiac preload, they have not found widespread clinical adoption for a number of reasons. The original description of this method required transient interruption of mechanical ventilation to identify an apneic baseline for measurement of Δ Down and Δ Up.[75] Newer monitors use computerized algorithms to measure and display SPV or PPV continuously, but these automated measures are not yet routinely available in standard bedside monitors
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196. A number of additional factors have precluded the wider application of SPV and PPV for monitoring volume responsiveness. The magnitude of blood pressure variation observed in any patient will be influenced by positive-pressure ventilation parameters, including tidal volume and peak inspiratory pressure. SPV and PPV cannot be used reliably in patients with cardiac arrhythmias or significant changes in chest wall or lung compliance.
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197. As noted earlier, respiratory cycle–induced variations in arterial pressure are not solely related to changes in left ventricular preload but depend in part on afterload influences. Although it is clear that the magnitude of SPV and PPV predict fluid responsiveness, precise threshold values remain uncertain, and the variety of techniques described have not been standardized.[83] Perhaps most important, all these measures have been validated only in mechanically ventilated patients and are not applicable to spontaneously breathing subjects, thereby precluding their use in many anesthetized and critically ill patients.
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