Arterial pressure monitoring Direct arterial pressure monitoring permits continuous measurement of systolic, diastolic, and mean pressures and allows

Transcription

1 Arterial pressure monitoring Direct arterial pressure monitoring permits continuous measurement of systolic, diastolic, and mean pressures and allows arterial blood sampling. Because direct measurement reflects systemic vascular resistance as well as blood flow, it s generally more accurate than indirect methods (such as palpation and auscultation of Korotkoff s, or audible pulse, sounds), which are based on blood flow. Direct monitoring is indicated when highly accurate or frequent blood pressure measurements are required for example, in patients with low cardiac output and high systemic vascular resistance. It also may be used for hospitalized patients who are obese or have severe edema, if these conditions make indirect measurement hard to perform. What s more, it may be used for patients who are receiving titrated doses of vasoactive drugs or who need frequent blood sampling. Indirect monitoring, which carries few associated risks, is commonly performed by applying pressure to an artery (such as by inflating a blood pressure cuff around the arm) to decrease blood flow. As pressure is released, flow resumes and can be palpated or auscultated. Korotkoff s sounds presumably result from a combination of blood flow and arterial wall vibrations; with reduced flow, these vibrations may be less pronounced. EQUIPMENTFor catheter insertion: Gloves gown mask protective eye wear sterile gloves 16G to 20G catheter (type and length depend on the insertion site, patient s size, and other anticipated uses of the line) preassembled preparation kit (if available) sterile drapes sheet protector sterile towels prepared pressure transducer system ordered local anesthetic sutures syringe and needle (21G to 25G, 1") I.V. pole tubing and medication labels site care kit (containing sterile dressing, antimicrobial ointment, and hypoallergenic tape) armboard and soft wrist restraint (for a femoral site, an ankle restraint) optional: shaving kit (for femoral artery insertion). For blood sample collection: If an open system is in place: gloves gown mask protective eyewear sterile 4" 4" gauze pads sheet protector 500-ml I.V. bag 5- to 10-ml syringe for discard sample syringes of appropriate size and number for ordered laboratory tests laboratory request forms and labels 16G or 18G needles (depending on your facility s policy) Vacutainers. If a closed system is in place: gloves gown mask protective eyewear syringes of appropriate size and number for ordered laboratory tests laboratory request forms and labels alcohol swab blood transfer unit Vacutainers. For arterial line tubing changes: Gloves gown mask protective eyewear sheet protector preassembled arterial pressure tubing with flush device and disposable pressure transducer sterile gloves 500-ml bag of I.V. flush solution (such as D5W or normal saline solution) 500 or 1,000 units of heparin syringe and needle (21G to 25G, 1") alcohol swabs medication label pressure bag site care kit tubing labels. For arterial catheter removal: Gloves mask gown protective eyewear two sterile 4" 4" gauze pads sheet protector sterile suture removal set dressing alcohol swabs hypoallergenic tape. For femoral line removal: Additional sterile 4" 4" gauze pads small sandbag (which you may wrap in a towel or place in a pillowcase) adhesive bandage. For a catheter-tip culture: Sterile scissors a sterile container. PREPARATION OF EQUIPMENTBefore setting up and priming the monitoring system, wash your hands thoroughly. Maintain asepsis by wearing personal protective equipment throughout preparation. (For instructions on setting up and priming the monitoring system, see the section on transducer system setup.) When you ve completed the equipment preparation, set the alarms on the bedside monitor according to your facility s policy. IMPLEMENTATIONExplain the procedure to the patient and his family, including the purpose of arterial pressure monitoring and the anticipated duration of catheter placement. Make sure the patient signs a consent form. If he s unable to sign,

2 ask a responsible family member to give written consent. Check the patient s history for an allergy or a hypersensitivity to iodine or the ordered local anesthetic. Maintain asepsis by wearing personal protective equipment throughout all procedures described below. Position the patient for easy access to the catheter insertion site. Place a sheet protector under the site. If the catheter will be inserted into the radial artery, perform Allen s test to assess collateral circulation in the hand. (See the Specimen Collection and Testing section.) Inserting an arterial catheter Using a preassembled preparation kit, the doctor prepares and anesthetizes the insertion site. He covers the surrounding area with either sterile drapes or towels. The catheter is then inserted into the artery and attached to the fluid-filled pressure tubing. While the doctor holds the catheter in place, activate the fastflush release to flush blood from the catheter. After each fast-flush operation, observe the drip chamber to verify that the continuous flush rate is as desired. A waveform should appear on the bedside monitor. The doctor may suture the catheter in place, or you may secure it with hypoallergenic tape. Apply antimicrobial ointment and cover the insertion site with a dressing, as specified by facility policy. Immobilize the insertion site. With a radial or brachial site, use an arm board and soft wrist restraint (if the patient s condition so requires). With a femoral site, assess the need for an ankle restraint; maintain the patient on bed rest, with the head of the bed raised no more than 15 to 30 degrees, to prevent the catheter from kinking. Level the zeroing stopcock of the transducer with the phlebostatic axis. Then zero the system to atmospheric pressure. Activate monitor alarms, as appropriate. Obtaining a blood sample from an open system Assemble the equipment, taking care not to contaminate the dead-end cap, stopcock, and syringes. Turn off or temporarily silence the monitor alarms, depending on your facility s policy. (However, some facilities require that alarms be left on.) Locate the stopcock nearest the patient. Open a sterile 4" 4" gauze pad. Remove the dead-end cap from the stopcock and place it on the gauze pad. Insert the syringe for the discard sample into the stopcock. (This sample is discarded because it s diluted with flush solution.) Follow your facility s policy on how much discard blood to collect. Usually, you ll withdraw 5 to 10 ml through a 5- or 10-ml syringe. Next, turn the stopcock off to the flush solution. Slowly retract the syringe to withdraw the discard sample. If you feel resistance, reposition the affected extremity and check the insertion site for obvious problems (such as catheter kinking). After correcting the problem, resume blood withdrawal. Then turn the stopcock halfway back to the open position to close the system in all directions. Remove the discard syringe, and dispose of the blood in the syringe, observing universal precautions. Place the syringe for the laboratory sample in the stopcock, turn the stopcock off to the flush solution, and slowly withdraw the required amount of blood. For each additional sample required, repeat this procedure. If the doctor has ordered coagulation tests, obtain blood for this sample from the final syringe to prevent dilution from the flush device. After you ve obtained blood for the final sample, turn the stopcock off to the syringe and remove the syringe. Activate the fast-flush release to clear the tubing. Then turn off the stopcock to the patient, and repeat the fast flush to clear the stopcock port. Turn the stopcock off to the stopcock port, and replace the dead-end cap. Reactivate the monitor alarms. Attach needles to the filled syringes, and transfer the blood samples to the appropriate Vacutainers, labeling them according to facility policy. Send all samples to the laboratory with appropriate documentation. Check the monitor for return of the arterial waveform and pressure reading. (See Understanding the arterial waveform.) Obtaining a blood sample from a closed system Assemble the equipment, maintaining

3 aseptic technique. Locate the closed-system reservoir and blood sampling site. Deactivate or temporarily silence monitor alarms. (However, some facilities require that alarms be left on.) Clean the sampling site with an alcohol swab. Holding the reservoir upright, grasp the flexures and slowly fill the reservoir with blood over 3 to 5 seconds. (This blood serves as discard blood.) If you feel resistance, reposition the affected extremity, and check the catheter site for obvious problems (such as kinking). Then resume blood withdrawal. Turn the one-way valve off to the reservoir by turning the handle perpendicular to the tubing. Using a syringe with attached cannula, insert the cannula into the sampling site. (Make sure the plunger is depressed to the bottom of the syringe barrel.) Slowly fill the syringe. Then grasp the cannula near the sampling site, and remove the syringe and cannula as one unit. Repeat the procedure, as needed, to fill the required number of syringes. If the doctor has ordered coagulation tests, obtain blood for those tests from the final syringe to prevent dilution from the flush solution. After filling the syringes, turn the one-way valve to its original position, parallel to the tubing. Now smoothly and evenly push down on the plunger until the flexures lock in place in the fully closed position and all fluid has been reinfused. The fluid should be reinfused over a 3- to 5-second period. Then activate the fast-flush release to clear blood from the tubing and reservoir. Clean the sampling site with an alcohol swab. Reactivate the monitor alarms. Using the blood transfer unit, transfer blood samples to the appropriate Vacutainers, labeling them according to facility policy. Send all samples to the laboratory with appropriate documentation. Changing arterial line tubing Wash your hands and follow standard precautions. Assemble the new pressure monitoring system. Consult your facility s policy and procedure manual to determine how much tubing length to change. Inflate the pressure bag to 300 mm Hg, and check it for air leaks. Then release the pressure. Prepare the I.V. flush solution and prime the pressure tubing and transducer system. At this time, add both medication and tubing labels. Apply 300 mm Hg of pressure to the system. Then hang the I.V. bag on a pole. Place the sheet protector under the affected extremity. Remove the dressing from the catheter insertion site, taking care not to dislodge the catheter or cause vessel trauma. Turn off or temporarily silence the monitor alarms. (However, some facilities require that alarms be left on.) Turn off the flow clamp of the tubing segment that you ll change. Disconnect the tubing from the catheter hub, taking care not to dislodge the catheter. Immediately insert new tubing into the catheter hub. Secure the tubing and then activate the fast-flush release to clear it. Reactivate the monitor alarms. Apply an appropriate dressing. Level the zeroing stopcock of the transducer with the phlebostatic axis, and zero the system to atmospheric pressure. Removing an arterial line Consult facility policy to determine if you re permitted to perform this procedure. Explain the procedure to the patient. Assemble all equipment. Wash your hands. Observe standard precautions, including wearing personal protective equipment, for this procedure. Record the patient s systolic, diastolic, and mean blood pressures. If a manual, indirect blood pressure hasn t been assessed recently, obtain one now to establish a new baseline. Turn off the monitor alarms. Then turn off the flow clamp to the flush solution. Carefully remove the dressing over the insertion site. Remove any sutures, using the suture removal kit, and then carefully check that all sutures have been removed. Withdraw the catheter using a gentle, steady motion. Keep the catheter parallel to the artery during withdrawal to reduce the risk of traumatic injury. Immediately after withdrawing the catheter, apply pressure to the site with a sterile 4" 4" gauze pad. Maintain pressure for at least 10 minutes (longer if bleeding or oozing persists). Apply

4 additional pressure to a femoral site or if the patient has coagulopathy or is receiving anticoagulants. Cover the site with an appropriate dressing and secure the dressing with tape. If stipulated by facility policy, make a pressure dressing for a femoral site by folding in half four sterile 4" 4" gauze pads, and apply the dressing. Cover the dressing with a tight adhesive bandage; then cover the bandage with a sandbag. Maintain the patient on bed rest for 6 hours with the sandbag in place. If the doctor has ordered a culture of the catheter tip (to diagnose a suspected infection), gently place the catheter tip on a 4" 4" sterile gauze pad. Once the bleeding is under control, hold the catheter over the sterile container. Using sterile scissors, cut the tip so it falls into the sterile container. Label the specimen and send it to the laboratory. Observe the site for bleeding. Assess circulation in the extremity distal to the site by evaluating color, pulses, and sensation. Repeat this assessment every 15 minutes for the first 4 hours, every 30 minutes for the next 2 hours, then hourly for the next 6 hours. UNDERSTANDING THE ARTERIAL WAVEFORM Normal arterial blood pressure produces a characteristic waveform, representing ventricular systole and diastole. The waveform has five distinct components: the anacrotic limb, systolic peak, dicrotic limb, dicrotic notch, and end diastole. Normal arterial waveform The anacrotic limb marks the waveform s initial upstroke, which results as blood is rapidly ejected from the ventricle through the open aortic valve into the aorta. The rapid ejection causes a sharp rise in arterial pressure, which appears as the waveform s highest point. This is called the systolic peak. As blood continues into the peripheral vessels, arterial pressure falls, and the waveform begins a downward trend. This part is called the dicrotic limb. Arterial pressure usually will continue to fall until pressure in the ventricle is less than pressure in the aortic root. When this occurs, the aortic valve closes. This event appears as a small notch (the dicrotic notch) on the waveform s downside. When the aortic valve closes, diastole begins, progressing until the aortic root pressure gradually descends to its lowest point. On the waveform, this is known as end diastole. SPECIAL CONSIDERATIONSObserving the pressure waveform on the monitor can enhance assessment of arterial pressure. An abnormal waveform may reflect an arrhythmia (such as atrial fibrillation) or other cardiovascular problems, such as aortic stenosis, aortic insufficiency, pulsus alternans, or pulsus paradoxus. (See Recognizing abnormal waveforms.) Change the pressure tubing every 2 to 3 days, according to facility policy. Change the dressing at the catheter site at intervals specified by facility policy. Regularly assess the site for signs of infection, such as redness and swelling. Notify the doctor immediately if you note any such signs. Be aware that erroneous pressure readings may result from a catheter that is clotted or positional, loose connections, addition of extra stopcocks or extension tubing, inadvertent entry of air into the system, or improper calibration, leveling, or zeroing of the monitoring system. If the catheter lumen clots, the flush system may be improperly pressurized. Regularly assess the amount of flush solution in the I.V. bag, and maintain 300 mm Hg of pressure in the pressure bag. RECOGNIZING ABNORMAL WAVEFORMS Understanding a normal arterial waveform is relatively straightforward. But an abnormal waveform is more difficult to decipher. Abnormal patterns and markings, however, may provide important diagnostic clues to the patient s cardiovascular status, or they may simply signal trouble in the monitor. Use this chart to help you recognize and resolve waveform abnormalities. AbnormalityPossible causesnursing interventions Alternating high and low waves in a regular pattern Ventricular bigeminy Check the patient s electrocardiogram (ECG) to confirm ventricular bigeminy. The tracing should reflect

5 premature ventricular contractions every second beat. Flattened waveform Overdamped waveform or hypotensive patient Check the patient s blood pressure with a sphygmomanometer. If you obtain a reading, suspect overdamping. Correct the problem by trying to aspirate the arterial line. If you succeed, flush the line. If the reading is very low or absent, suspect hypotension. Slightly rounded waveform with consistent variations in systolic height Patient on ventilator with positive end-expiratory pressure Check the patient s systolic blood pressure regularly. The difference between the highest and lowest systolic pressure reading should be less than 10 mm kg. If the difference exceeds that amount, suspect pulsus paradoxus, possibly from cardiac tamponade. Slow upstroke Aortic stenosis Check the patient s heart sounds for signs of aortic stenosis. Also notify the doctor, who will document suspected aortic stenosis in his notes. Diminished amplitude on inspiration Pulsus paradoxus, possibly from cardiac tamponade, constrictive pericarditis, or lung disease Note systolic pressure during inspiration and expiration. If inspiratory pressure is at least 10 mm Hg less than expiratory pressure, call the doctor. If you re also monitoring pulmonary artery pressure, observe for a diastolic plateau. This occurs when the mean central venous pressure (right atrial pressure), mean pulmonary artery pressure, and mean pulmonary capillary wedge pressure (pulmonary artery obstructive pressure) are within 5 mm Hg of one another. COMPLICATIONSDirect arterial pressure monitoring can cause such complications as arterial bleeding, infection, air embolism, arterial spasm, or thrombosis. DOCUMENTATIONDocument the date of system setup so that all caregivers will know when to change the components. Document systolic, diastolic, and mean pressure readings as well. Record circulation in the extremity distal to the site by assessing color, pulses, and sensation. Carefully document the amount of flush solution infused to avoid hypervolemia and volume overload, and to ensure accurate assessment of the patient s fluid status. Make sure the position of the patient is documented when each blood pressure reading is obtained. This is important for determining trends.