Hemodynamic Monitoring: Techniques & Troubleshooting

Since its introduction in 1970, the pulmonary artery (PA) catheter has become commonplace in intensive care units. The PA catheter is used to provide information about right and left intracardiac pressures as well as cardiac output. Specially designed catheters can also monitor mixed venous oxygen saturation, assess right ventricular volumes and ejection fraction, and provide temporary atrial or ventricular pacing.1

The critical care nurse plays a vital role in the process of maintaining and troubleshooting the PA catheter system, as well as monitoring, measuring and recording readings from the catheter. In order to provide meaningful information, the critical care nurse should be knowledgeable regarding techniques to obtain accurate data and about troubleshooting the system when problems arise.

Preventing Infection
The critical care nurse's role in preventing infection related to the presence of the PA catheter begins with the initial setup of the hemodynamic monitoring system and continues until removal of the central venous catheter. Recommendations from the Centers for Disease Control and Prevention for the prevention of infection related to intravascular devices2 should be incorporated into your institution's policies related to hemodynamic monitoring.

Handwashing, maximal barrier precautions during insertion, aseptic insertion and care techniques, continuous flush devices, use of disposable (rather than reusable) transducers and minimizing entry into the system are important aspects of care. A sterile sleeve should be used to protect the pulmonary artery catheter from contamination. The transducers and other components of the system should be replaced at 96-hour intervals. Cap all stopcocks that are not in use. Do not routinely replace pulmonary artery catheters to prevent a catheter-related infection. 2

Gauze dressings should be replaced every 2 days and transparent dressings every 7 days. Replace the dressing more frequently if it is soiled or damp or if it becomes loose.2

Obtaining Accurate Information
There are several variables that must be taken into account when obtaining hemodynamic data. Leveling, zero referencing, dynamic response, patient position, the effects of ventilation, catheter location in a physiological lung zone and proper balloon inflation must be considered by the critical care nurse.

Leveling. Inaccuracies in data obtained from the PA catheter can occur if the system is incorrectly leveled. The stopcock nearest the transducer is known as the air-fluid interface. This component of the monitoring system is positioned level with the patient's left atrium.

Hydrostatic pressure is the weight of blood in the vasculature. When the air-fluid interface is not in the correct position, the effects of hydrostatic pressure cause an inaccurate estimate of left atrial pressure.3 For every 1 cm above the left atrium the catheter is referenced, the pressure measurement is underestimated by 0.74 mm Hg; the reverse is true for systems that are referenced below the left atrium.4 The reference point for the left atrium in patients in the supine position is the phlebostatic axis. A measuring device should be used to locate the reference point. "Eyeballing" the level of the monitoring system and estimating measurements can result in referencing errors.

The phlebostatic axis is externally landmarked on the patient as the intersection of two points. The first point is found where the fourth intercostal space joins the sternum. An imaginary line is drawn out to the side of body and marked. From that mark, measure the distance between the anterior and posterior surfaces of the chest, again drawing an imaginary line. The midpoint of the second line on the lateral chest surface (midanteroposterior diameter) is the landmark for the left atrium. Using a skin marker, Place a mark on the patient to identify the reference point. The midaxillary line should not be used for landmarking the phlebostatic axis, as the result may be a measurement error of up to 6 mm Hg.4 The air-fluid interface will have to be leveled whenever the patient is repositioned.

Zero Referencing. Zeroing calibrates the hemodynamic monitoring system to read only the pressure generated within the patient without the interference of external factors. When the transducer is isolated from the effect of hydrostatic pressure on its diaphragm, the monitoring system can be zeroed.5

To zero the transducer, the stopcock closest to the transducer is closed to the patient. Remove the sterile protective cap from the stopcock port, exposing the hemodynamic monitoring system to air. The monitor's zero function key is activated to offset pressure in the transducer, setting the pressure to zero. Open the stopcock to the patient and replace the sterile cap on the stopcock port. Zeroing ensures that when the transducer stopcock is open to the patient and closed to air, the only pressure on the transducer will be from the vessel/heart chamber being monitored.5

Transducer "drift" from the zero reference point occurs over time. To ensure accurate readings from the monitoring system, the transducer should be leveled and zero referenced every 8 hours or whenever measurements are in question.5 

Dynamic Response. Dynamic response is the ability of the transducer system to measure physiologic pressure changes.5 To ensure an adequate dynamic response, it is important that the tubing is the correct type and length. Tubing used for hemodynamic monitoring systems is less compliant than regular intravenous tubing. The length should be no more than 4 feet.5 Long tubing, tubing that has had too many components added (e.g., excessive stopcocks, extensions), or tubing that is too flexible can interfere with dynamic response.

Air bubbles in the system can also affect dynamic response. Flush all air out of the system at the time of setup and reassess periodically for the presence of air bubbles for the duration of monitoring.5

Patient Position. Critically ill patients do not always tolerate supine positioning with the backrest flat (0 degrees elevation). If the monitoring system's air-fluid interface is correctly referenced, the supine patient's backrest may be positioned up to 60 degrees without affecting the accuracy of measurements.5-7 Because some patients may produce variable readings in different positions, it is a good idea to compare measurements in a variety of positions as a baseline. Wait 5 minutes after a position change before measuring pulmonary artery pressure. Consistency should be used in patient position when obtaining hemodynamic readings. Any variation in the patient's position at different data collection times should be documented.5 6

The Effects of Ventilation. Hemodynamic measurements should be obtained at end expiration for patients who are breathing spontaneously as well as those receiving positive pressure mechanical ventilatory support. 6-8 End expiration is the point in the ventilation cycle where there is the least effect of pleural pressure on intracardiac pressures.6 Using a respiratory or airway pressure monitor can help identify end expiration when obtaining hemodynamic data.

Use of positive end expiratory pressure (peep) in excess of 10 cm H2O may affect the accuracy of pulmonary artery wedge pressure (PAWP) to serve as an indicator of left atrial pressure.4,6 Removing the patient from the ventilator does not improve accuracy of PA readings and is not recommended because it may be detrimental to the patient.6

Lung Zones. Lung zones are physiologic states related to blood distribution rather than anatomic locations within the lung. Pressures vary from zone to zone (see Table 1). The optimal pressure state for obtaining hemodynamic data exists in zone 3, which is generally considered to be found in the area of the lung below the left atrium. 6,9

Table 1: Characteristics of Lung Zones

 

Zone 1

Zone 2

Zone 3

Blood Flow

Absent

Intermittent

Constant

Pressures

Alveolar >
Arterial and
Venous

Arterial >
Alveolar and Venous

Arterial and
Venous > Alveolar

Balloon Inflation. Overinflation of the balloon can cause damage to the pulmonary artery and to the balloon itself. The balloon should be inflated with a volume of 1.5 mL of air or less. As the inflated balloon floats into small vessels, the flow of blood is stopped and the PA waveform dampens. Stop balloon inflation as soon as dampening occurs. The balloon should not remain inflated for more than four respiratory cycles. Allow passive balloon deflation - do not pull back on the balloon plunger to deflate. Always ensure that the PA waveform reappears on the monitor following balloon deflation. When the balloon is deflated, remove the syringe and expel the air before reattaching it to the balloon inflation port. Ensuring that there is no air in the syringe and that the gate valve is closed with the syringe in place decreases the chance of accidental wedging of the PA catheter.1

Graphic vs. Digital Readings
Use of graphic strip recordings to obtain hemodynamic measurements improves the accuracy of the data. Digital measurement has been found to be inaccurate in measuring data with or without variations in the respiratory pattern because the reading reflects pressures obtained throughout the respiratory cycle.7,10

Troubleshooting
Problems obtaining accurate hemodynamic data occur for two reasons: human error and monitoring system problems. Always obtain and record baseline data. If you suspect a problem, comparing the current situation to previous data is important. The hemodynamic profile should reflect the patient's clinical picture. The critical care nurse is clued in that troubleshooting is necessary when the clinical status and the hemodynamic data conflict. Troubleshooting always begins with patient assessment. After assessing the patient, review the techniques used to obtain the data. If any errors in technique were present, repeat data collection. If correct techniques were used, review the monitoring system (see Table 2).

Table 2: Troubleshooting Hemodynamic Monitoring Problems

Problem

Possible Causes

Troubleshooting

Dampened Waveform

Incorrect scale selected on monitor

Incorrect leveling

Air in the system

Spontaneous wedging of catheter

Check the monitor to ensure
the correct scale is in use

Check transducer level

Check pressure in bag
Check for loose connections
Remove air bubbles
Flush system

See below-Spontaneous Wedge

Overdamping
(diminished systolic peak,
loss of dicrotic notch, rounder wave forms)

Compliant tubing


Large air bubbles

Clots/blood in system

Loose connections

Kinked catheter or catheter tip against vessel wall

Check tubing-right tubing, no air, no clots, no blood

Aspirate air/blood clots from system then flush

Check for loose connections
Flush tubing

Perform square wave test

Collaborate with physician/APN as
needed to reposition/remove
catheter as indicated

Underdamping
(falsely high systolic peak,
falsely low diastolic value, artifact)

Pressure tubing is too long

Too many components
(i.e., stopcocks)
Small air bubbles
Defective transducer

Ensure that the correct tubing is in use - shorten if necessary
Ensure that there are no tubing extensions added
Remove extra components

Remove air bubbles
Change transducer

Erratic Waveform
With Highly Variable
Pressures (catheter whip/fling)


External noise


Hyperdynamic heart

Excessive movement of the catheter tip within the vessel

Excessive catheter length in ventricle

Place tubing away from motion sources
Use mean PA pressure reading

The catheter will probably have to be repositioned to a less turbulent area of the vessel

Collaborate with physician/APN to reduce length of catheter in ventricle

Spontaneous Wedge

Catheter is advanced too far or is too flexible

Do not flush catheter
Assess for other causes of
dampened waveform-see above
Reposition or ask the patient
to cough
Catheter will require repositioning -pull back slowly until PA waveform appears (if allowed by institution P&P)
Notify physician/APN of need to
reposition catheter

Unable to Obtain Wedge

Air returns to syringe - catheter is probably not advanced far enough
into the PA

Air does not return to syringe - balloon is probably ruptured

Catheter will require repositioning as permitted by institution P&P
Notify physician/APN of need to
reposition catheter

Notify physician/APN of need to remove catheter

Overwedging

Excessive air volume is injected
into the balloon

Catheter is advanced too far

Observe waveform on monitor
while injecting air - stop injecting
as soon as the waveform dampens

Allow passive deflation of balloon
Catheter will require repositioning
- pull back slowly until PA wave-
form appears (if allowed by
institution P&P)
Notify physician/APN of need to
reposition catheter

Absent Waveform

Disconnect of monitoring system

Incorrect scale in use

Loose or cracked transducer dome or air in dome

Defective transducer

Inadequate pressure in pressure bag

Check for kinks in the system

Catheter tip or lumen totally occluded

Check connections

Set correct scale on monitor

Change transducer


Change transducer

Adjust pressure to 300 mm Hg


Remove kinks

Slowly aspirate to check for blood
return - if no blood return, notify physician/APN of need to remove catheter

Damping. Damping is a term used to describe alterations in the dynamic response of the monitoring system. The dynamic response may be evaluated by performing a square wave test. Fast flush the catheter. A characteristic square wave appears on the monitor, indicating an appropriate dynamic response. Normal dynamic response is indicated by an immediate rapid downstroke below baseline with 1-2 oscillations within 0.12 seconds and a quick return to baseline. An overdamped waveform will produce no downward spike following the square wave. An underdamped waveform will produce multiple spikes/oscillations following the square wave before returning to the PA waveform.5 When damping problems occur, check to ensure that the balloon is deflated. Verify that the correct scale is set on the monitor and that the air-fluid interface is referenced correctly. Check the pressure bag to ensure that it is inflated to 300 mm Hg, remove any air from the system, and flush.

Catheter Whip/Fling. Catheter whip (fling) may be caused by external noise brought about by movement (i.e., breathing, shivering), a hyperdynamic heart, turbulent flow in the vessel near the tip of the catheter, or excess catheter length in the ventricle. There is an erratic waveform with artifact on the oscilloscope. The monitored numbers are often highly variable and inaccurate. Ensure that the system tubing and connections are positioned away from areas of patient movement. In patients with a hyperdynamic heart, use the mean PA pressure to estimate hemodynamic status. To eliminate catheter whip, the catheter may have to be repositioned to a less turbulent area of the vessel or the length of tubing in the ventricle may need to be reduced. 6

Spontaneous/Continuous Wedge. A spontaneous wedge occurs with the balloon deflated. A spontaneous or continuous wedge may be seen if the PA catheter is advanced too far or if the catheter is flexible. Ensure that the balloon is deflated by removing the syringe from the open inflation port. Assess for other causes of dampening. Assist the patient to a different position or ask the patient to cough, if possible, to help float the catheter out of the wedge position. Do not flush a wedged catheter, as flushing may lead to PA rupture. If there are no other reasons for the waveform to dampen, the catheter will have to be withdrawn until the PA waveform appears on the monitor. 11

Inability to Obtain Wedge. When you are unable to obtain a wedge tracing on the monitor, deflate the balloon. If the air returns to syringe, the PA catheter is probably not in far enough and will require repositioning. If the air does not return to the syringe, the balloon is probably ruptured and will need to be removed. 11

Overwedging. Overwedging occurs when too much air is injected into the balloon or when the catheter is in too far. When an overwedge is detected, remove the syringe from the inflation port and allow passive deflation of the balloon. Reconnect the air-filled syringe and slowly inflate while watching the waveform. Stop air injection when the waveform dampens (even if the full volume of air in the syringe has not been injected) and measure wedge pressure.11

Absent Waveform. The waveform may be absent when there is a disconnection or a problem with the monitoring system. A large leak in the system, use of the incorrect monitor scale, loose or defective monitoring system components, incorrect stopcock position, inadequate pressure on the continuous flush bag, kinks in the system, or occlusion of the catheter are all factors that may lead to loss of the waveform. 11 Check the transducer, all connections, the monitor setup, the pressure bag and stopcock positions to correct the problem. Aspirate through the catheter stopcock to verify patency. Replace system components. If you are still unable to obtain a waveform, notify the physician or APN.

Conclusion
Hemodynamic monitoring can provide valuable information about the critically ill patient. An understanding of proper techniques for maintenance of the system can improve patient outcomes through data accuracy.

Janice M. Wojcik is an advanced practice nurse, critical care, at St. Joseph's Regional Medical Center, Paterson, NJ.


Hemodynamic Monitoring: Techniques & Troubleshooting

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