Arterial Catheters Systemic arterial blood pressure is most accurately measured by placing a catheter directly into a peripheral artery. Peripheral arterial lines should be used in patients with hemodynamic instability. Along with the measurement of blood pressure, these lines provide a direct route for the frequent blood samples drawn from these patients. The most common peripheral artery sites are as follows –Radial: most common because of easy access and good collateral circulation (with ulnar artery). The Allen test must be performed before puncture to determine whether collateral circulation is present. –Brachial –Femoral

Arterial Catheters Sterile technique should be used when the 18- or 20- gauge catheter is placed into the artery by either surgical cutdown or percutaneous puncture. The catheter is connected to a system that delivers a continuous flow of fluid from an IV bag to maintain patency of the system. The IV bag, which should contain normal saline with added heparin, is pressurized by a hand-bulb pressure pump. The system is also equipped with stopcocks to allow for calibration with atmospheric pressure and for arterial sampling. A strain gauge pressure transducer (the most commonly used transducer) is connected to the system to provide a display of the pressure waveform and a digital reading of the arterial pressure in millimeters of mercury.

Pressures Measured on an Arterial Waveform Systolic pressure: equal to the peak of the waveform (normally 90 to 140 mm Hg). Diastolic pressure: measured at the lowest point of the waveform (normally 60 to 90 mm Hg). Pulse pressure: the difference between the systolic and diastolic pressures (normally about 40 mm Hg). Mean arterial pressure: represents the average pressure during the cardiac cycle (normally 80 to 100 mm Hg). Note the dicrotic notch on the waveform. It represents the closing of the aortic valve. –If the dicrotic notch is not visible, the pressure is most likely inaccurate, in that the values are lower than the patient's actual pressure. –The dicrotic notch may disappear when the systolic pressure drops below 50 to 60 mm Hg. At this point it is difficult to palpate or hear a cuff pressure.

Arterial Waveform

Complications Infection: risk may be reduced with removal of the catheter within 4 days. Hemorrhage: make sure all connections in the system are tight. Ischemia: note the color and temperature of the skin distal to the insertion site to determine distal perfusion. Thrombosis and embolization: a weak pulse distal to the puncture site may indicate thrombosis. A continuous flush of saline and heparin through the system helps to avoid clot formation.

Troubleshooting “Damped” pressure tracing; causes include –Occlusion of the catheter tip by a clot: correct by aspiration of the clot and flushing with heparinized saline. –Catheter tip resting against the wall of the vessel: correct by repositioning catheter while observing waveform. –Clot in transducer or stopcock: correct by flushing system and, if no improvement is seen in the waveform tracing, change the stopcock and transducer. –Air bubbles in the line: correct by disconnecting transducer and flushing out air bubbles.

Troubleshooting Abnormally high or low pressure readings; causes include –Improper calibration: correct by recalibration of monitor and strain gauge. –Improper transducer position: correct by ensuring the transducer is kept at the level of the patient's heart. No pressure reading; causes include –Improper scale selection: correct by selecting appropriate scale. –Transducer not open to catheter: correct by checking system and making sure the transducer is open to the catheter.

(Persing, Gary. Respiratory Care Exam Review: Review for the Entry Level and Advanced Exams, 3rd Edition. Elsevier Health Sciences, ).