Section Two: Arterial Pressure Monitoring

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1 Section Two: Arterial Pressure Monitoring Indications An arterial line is indicated for blood pressure monitoring for the patient with any medical or surgical condition that compromises cardiac output, tissue perfusion, or fluid volume status. It is also helpful in the management of patients with acute respiratory failure who require frequent arterial blood gas measurements. With an arterial line in place, continuous measurement of the systolic, diastolic and mean arterial blood pressure is possible with alarms set to warn of change in patient status. Insertion Sites The most frequently used site is the radial artery. The major advantage of the radial artery is that collateral circulation to the hand is provided by the ulnar artery, in the event the radial artery becomes occluded due to the presence of the catheter. The patency of the ulnar artery should be assessed prior to cannulation of the radial artery, either with a Doppler flowmeter or by doing the Allen test. In the Allen s test the patient s hand is elevated with fist clenched, and both radial and ulnar arteries are compressed to block arterial flow (A). The hand is then lowered (B) and opened (C). Pressure is released over the ulnar artery only (D). Color should return to the hand within 6 seconds, indicating a patent ulnar artery and adequate collateral blood flow to the hand. (See diagram above.) If the radial artery is not available, the femoral, brachial, or dorsalis-pedis arteries may be used. The advantage of the femoral artery is that it is large and easy to cannulate. The disadvantage is that the site is difficult to maintain, more susceptible to contamination, and difficult to assess for loose connections and blood loss. Regardless of the site of insertion, insertion is done with sterile technique. The monitoring system is prepared as described in Section One and attached to the catheter. After the catheter is attached to the monitoring system the waveform and a dynamic response test are run and documented on a strip in the patient s record. Arterial Pressure Waveform The normal arterial waveform should have a rapid upstroke (systole), a clear dicrotic notch (closure of the aortic valve), and a definite downstroke (diastole). When compared with a simultaneous ECG recording, the peak of systole on the arterial waveform follows the QRS on the ECG (Fig 5). Figure 5. Arterial pressure waveform. 1=systole, 2=dicrotic notch, 3=diastole. B/P = 142/70 13

2 Cuff Blood Pressure vs. Arterial Line Pressure Differences in pressure between cuff and a-line are expected because the arterial catheter measures pressure within the artery, while the cuff pressure measures flow from the outside. In the normovolemic patient, differences of 5 to 10 mm Hg in the same arm are expected, with the arterial line value normally higher than the cuff pressure. If the patient has an abnormally large difference in blood pressure from one arm to the other due to arterial obstruction (rare), the arterial line should be on the side of the higher pressure to prevent false assumption of a hypotensive state. Accuracy of arterial line pressures should be assessed by checking leveling, zeroing and performance of a square wave test, not by comparing with the cuff pressure. In low cardiac output states and/or shock, the cuff pressure is less reliable than the arterial line pressure due to systemic vasoconstriction. Nursing Management Practice measures to ensure accuracy (zeroing, leveling, dynamic response test). Use sterile technique at all times during insertion and whenever entering the system. Apply sterile dressing. Set alarm parameters based on individual patient status. Record pressures according to policy. Monitor motor and sensory function to identify possible nerve damage. Monitor pulses, color, temperature, capillary refill of limb distal to the insertion site at least every 4 hours in order to identify ischemia or arterial spasm. Monitor insertion site for signs of infection and patency of dressing. Change flush bag and tubing according to policy. Current research recommendations for changing of tubing and flush solution are every 96 hours for arterial systems or with every change of the catheter. The flush solution should be changed only with the entire tubing system or when the bag is empty. The CDC has not specified recommendations related to tubing change frequency of hemodynamic monitoring systems. Label bag and tubing. Document waveform and dynamic response test every shift or when there is a change in patient condition or waveform morphology. Avoid flushing system with a syringe. Do not infuse medication or IV solution through the arterial line. Blood Sampling Ensure that sterile technique is used whenever entering the system. Determine what the deadspace volume of the catheter/flush system is. The deadspace volume is how many ml of fluid is needed to flush from the stopcock used to draw blood to the tip of the catheter. When obtaining blood for routine labs or ABGs, use a discard volume of two times the deadspace volume of the catheter and tubing to the site of sampling, then draw the amount of blood needed for the sample. When obtaining coagulation studies through a heparinized system, use a discard volume of six times the dead-space volume of the catheter and tubing to the site of sampling and then draw the amount of blood needed for the test. Removal of Arterial Catheter Immediately apply firm, continuous pressure just proximal to the insertion site after the catheter is removed. Continue to apply pressure until hemostasis is obtained. This is for a minimum of 5 minutes for a radial catheter site and > 15 minutes for a femoral catheter site. Do not release pressure to frequently assess for hemostasis because pressure must be continuous in order to be effective. Apply a pressure dressing and frequently check and document the pulses, color, temperature, capillary refill and monitor for bleeding at the site as specified in hospital policy. Standards may vary depending on insertion site and patient s coagulation status. (No research-based standard is currently 14

3 available for how frequent checks should be after catheter removal.) The table on page 73 of the workbook summarizes the AACN recommendations regarding protocols for arterial line use. Complications of Arterial Lines Complications are primarily infection, accidental blood loss, and impaired circulation to the extremity. Adherence to guidelines outlined above will help prevent complications. Complete the Self-Test that follows. 15

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5 Section Two: Arterial Pressure Monitoring Self-Test Match the following: 1. Less reliable measurement in low cardiac a) Allen s test output states. b) Dicrotic notch 2. Minimal frequency of extremity assessments c) Cuff pressure when a-line is in place. d) Every 96 hours 3. Recommended frequency of tubing/flush solution e) Every 4 hours changes according to some studies. 4. Used to assess ulnar artery patency. 5. Caused by closure of aortic valve. Review the following a-line strips and write in the pressure (systolic/diastolic) below each: Pressure = Pressure = 17

6 Section Two: Arterial Pressure Monitoring Match the following: Self-Test - Answers 1. C Less reliable measurement in low cardiac a) Allen s test output states. b) Dicrotic notch 2. E Minimal frequency of extremity assessments c) Cuff pressure when a-line is in place. d) Every 96 hours 3. D Recommended frequency of tubing/flush solution e) Every 4 hours changes according to some studies. 4. A Used to assess ulnar artery patency. 5. B Caused by closure of aortic valve. Review the following a-line strips and write in the pressure (systolic/diastolic) below each: Pressure = 195/120 1box=7.5mm Hg Pressure = 156/60 18

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