Measurement of Arterial Pressure

Measurement of Blood Pressure We will discuss the following Rapid Assessment Sphygmomanometer Arterial Lines

Rapid Assessment If Systolic pressure is less than the following you will not feel a pulse in that region: No pulse in the radial: > 80 mmHg - possible altered mental status No pulse in the femoral: > 60 mmHg –Unresponsive No pulse in the carotid: > 40 mmHg – Perform CPR

Cuff Pressure Sphygmomanometer invented in 1896 Artery is compressed with high enough pressure to occlude the artery completely at the level of the heart. Remember Systole is the pressure created during the beat of the heart. Diastole is the resting pressure.

Cuff Pressure Systolic Pressure: As pressure is slowly decreased blood can start getting by the cuff during systole only….at this point you hear the heart rate with your stethoscope, just distal to the cuff. During diastole, though, the artery slams shut.

Cuff Pressure Diastolic Pressure: Eventually, as the pressure is slowly lowered, until the artery no long slams shut, and you can’t hear the pulsation. This point is the diastolic pressure.

Cuff Pressure Although blood pressure cuff readings are very reliable, there may be considerable variation between what our ears detect. Still, cuff pressure is considerably accurate. Allowing a computer to analyze the sound removes this human error and is much more reliable.

Cuff Pressure Pressures below 80 mmHg may be difficult to detect with a stethoscope over the brachial artery. In this case a doppler may be used. When pressures are below 80 mmHg sounds may be heard all the way to down to zero, so there is no diastolic reading.

Using Doppler Device to Identify Posterior Tibial Artery http://medicine.ucsd.edu/clinicalmed/extremities.htm

Doppler Stethoscope

Doppler Doppler’s work on ultrasonic sound waves that detect blood movement Always use ultrasonic gel with doppler equipment Listen for “swish…swish…swish” sound

An introduction to “Fluid Filled Monitoring Systems” Arterial Lines An introduction to “Fluid Filled Monitoring Systems”

Arterial Line Definition: An indwelling catheter used to detect the pulsations that can then be converted to arterial pressure readings. These lines can also be used to acquire arterial blood for laboratory analysis.

Arterial Line How do fluid filled systems work? A continuous column of heparinized fluid is dripping at a slow rate through a 3-inch plastic catheter which is inserted in the artery. The pulsation of blood slams against the tip of the catheter where the fluid is coming out, causing the column of fluid to transmit sound vibrations all the way back up the line. Eventually the vibrations reach a small inline microphone called a “Transducer”.

Measurement of Arterial Pressure The transducer is hooked up, electrically, to the processor which converts the sound vibration into a pressure reading. Transducer must be level with the heart Transducer must be calibrated by “Zeroing”

Measurement of Arterial Pressure Also: The bag of drip fluid must be pressurized at least higher than the patients potential blood pressure For example: (next slide)

Indications for Arterial Line Individuals that need continuous assessment of blood pressure because the likelihood of hemodynamic instability is high. Individuals suffering from hemodynamic instability. Persons need frequent ABG’s.

Measurement of Arterial Pressure Cuff Pressure Case Study: Jim is a 67 y/o patient being worked up for possible MI. He is in ICU with a blood pressure cuff in place. The cuff is set to measure the maximum of 12 measurements per hour (every 5 minutes). Immediately after his reading of 100/ 55 is displayed, Jim converts to 3rd degree block and his blood pressure plummets to ~60 mmHg. After a four minutes of this dangerously low level of blood pressure, Jim converts to asystole. CPR is started and Jim does not recover.

Measurement of Arterial Pressure Arterial line Case Study: Jim is a 67 y/o patient being worked up for possible MI. He is in ICU with a blood pressure cuff in place. The cuff is set to measure the maximum of 12 measurements per hour (every 5 minutes). Immediately after his reading of 100/ 55 is displayed, Jim converts to 3rd degree block and his blood pressure plummets to ~60 mmHg, however his Arterial line starts alarming immediately notifying the personnel. Emergency therapy is administered and a Code Blue is narrowly averted. Jim expires later that day.

5 minutes between blood pressures is too long for a critical patient! The bottom line: 5 minutes between blood pressures is too long for a critical patient!

Measurement of Arterial Pressure Arterial line Hazards Disconnect exsanguinations Infection Arterial thrombosis Damage to the artery

Measurement of Arterial Pressure Arterial line readings can be subject to error: Abnormally low: Damping Clot in line Catheter is Positional Transducer too high Not “Zeroed” Abnormally high Transducer too low.

The bottom line: Arterial lines are prone to multiple problems. Despite the difference in hearing, cuff pressures are still considered more reliable than A-lines.

Blood Pressure Analysis Systolic < 100 mmHg is considered hypotensive Pulse Pressure is the difference between the systolic and diastolic pressure and is increased by stroke volume and decreased by vascular system compliance.

Aortic Compliance As we age, the aorta becomes less compliant and this tends to increase the pulse pressure Pulse pressure has recently been identified as a predictor of cardiovascular health.

Hypertension Stage 1 140-159 or 90-99 Stage 2 160-179 or 100-109 Systolic Diastolic Stage 1 140-159 or 90-99 Stage 2 160-179 or 100-109 Stage 3 >180 or >110 http://www.emedmag.com/html/pre/cov/covers/101500.asp Adapted from Joint Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The Sixth Report. Arch Intern Med 157: 2413, 1997.

Hypertension Causes Increase in Cardiac output (Q) Hypervolemia Stress Increase in Systemic Vascular resistance Idiopathic: essential or primary hypertension (95% of cases) no unidentified cause. Atherosclerosis Diabetes Etc…

Hypotension Causes Decreased Systemic Vascular Resistance Decrease in Cardiac Output (Q) Changes in H.R. or conduction Bradycardia Inefficient rhythms: ie..freqent PVC’s Decrease in volume Hypovolemia Heart failure

A-Line Insertion See notes

A-Line Insertion Direct Transfixation Modified Seldinger

Seldinger The catheter surrounds a needle and is connected to a guide wire system. Needle is inserted into the artery until a blood return is seen. Guidewire is threaded into the artery. Needle is withdrawn leaving the catheter in place. Catheter is threaded down the guidewire into the artery The guidewire is removed. The catheter is connected and secured.