Invasive Hemodynamic Monitoring

CHAPTER 7 Invasive Hemodynamic Monitoring



S. Kay Sedlak, RN, MS, CEN



MAJOR TOPICS



Invasive Hemodynamic Monitoring Basics


Concepts

Types of Monitoring Systems

Pressure Monitoring System Components

Obtain Accurate Data

Setting Up Pressure Monitoring System with Transducer

Leveling the Transducer and Zeroing the Monitor

Complications

Specific Pressure Monitoring Systems


Central Venous Pressure Monitoring

Arterial Pressure Monitoring

Pulmonary Artery Pressure Monitoring

Intracranial Pressure Monitoring


I. INVASIVE HEMODYNAMIC MONITORING BASICS


Critically ill patients have dynamic and rapidly changing profiles that require monitoring parameters beyond the physical examination, imaging, and laboratory results. The practice of placing devices into the vascular system or the brain allows the bedside clinician to rapidly and accurately identify and manage changes as they occur in the patient. This is referred to as hemodynamic monitoring or studying the variables of circulation. Analysis of the hemodynamic parameters assists the nurse in assessing the accuracy of circulation, perfusion, and oxygenation of the body. Whenever possible, consent should be obtained prior to performing these invasive procedures.



A. Concepts




1. Pascal’s law


a. A pressure change at any given point in a confined fluid space results in a similar pressure change to the entire fluid volume

b. In a fluid-filled tube, pressure at both ends of the tube is equal

2. Pressure signal transmission


a. Pressure changes in a vessel can be sent through fluid-filled tubing to a monitor and displayed as a numeric value, waveform, or both


B. Types of Monitoring Systems




1. Fluid-filled system attached to water manometer ( Fig. 7-1)


a. Requires minimal monitoring equipment; electronic signals are not required

b. Pressure equalizes within the fluid-filled system and is reflected as a rise or fall in water level of manometer

c. Currently used primarily for central venous pressure (CVP) readings

d. Pressures are measured in terms of centimeters of water

2. Fluid system with transducer, amplifier, and monitor ( Fig. 7-2)


a. The transducer receives pressure signals and converts to electronic signals

b. The amplifier enhances transducer-generated signals and filters out unwanted artifact

c. The monitor displays amplifier-enhanced signals on an oscilloscope

1) Vertical axis represents pressure

2) Horizontal axis moves with time

d. Used for arterial, pulmonary artery (PA), and intracranial pressure (ICP) monitoring

3. Fiberoptic monitoring systems ( Fig. 7-3)


a. Pressure signal is sent by fragile fiberoptics to monitor

b. Increased accuracy and decreased complexity compared with transducer system

c. Currently used primarily for ICP monitoring

image

FIGURE 7-1 The stopcock is turned to fill the manometer to 25 cm H2O.


(From Roberts, J., & Hedges, J. [2004]. Clinical procedures in emergency medicine [4th ed.]. Philadelphia: Saunders.)


image

FIGURE 7-2 A fluid system of pulmonary artery pressure monitoring coupled with electronic instrumentation.


(From Darovic, G. O. [2004]. Handbook of hemodynamic monitoring [2nd ed.]. Philadelphia: Saunders.)


image

FIGURE 7-3 Fiberoptic monitoring system using the subarachnoid bolt (patient), disposable catheter connected to preamplifier cable with continuous visual intracranial pressure (ICP) waveform display on the bedside monitor (upper left), and a continuous digital readout of ICP (lower monitor) with ICP waveform printout.


(Courtesy of Integra Neurosciences, Camino, San Diego, California.)



C. Pressure Monitoring System Components




1. Catheter: provides access to patient’s vessels/brain for monitoring pressure


2. Stopcock(s)


a. Allows clinician to isolate infusing fluid and transmit pressure signals directly from vessel to transducer

b. Allows flush solution to flow continuously and reduces the risk of clot formation at catheter tip

c. Allows clinician to open system to atmospheric pressure for zeroing

d. Allows blood to be withdrawn from vessel without dilution from flush solution

Note: Review the directions of stopcocks to open/close because they vary among manufacturers

3. Rigid pressure tubing (for fluid-filled transducer system): optimizes physiologic signal transmission


a. Compliant tubing distorts pressure signals and causes overdamped tracings

b. Long tubing also distorts tracing; allow no greater than 4 feet of tubing between catheter and transducer

4. Flush device with capillary restrictors: keeps system patent by allowing a continuous flow of solutions through line


a. Capillary restrictor limits flow of solution

b. An activator (fast flush device) can bypass the restrictor to allow rapid flow of flush solution through line (e.g., while priming the line and to clear line after blood draws)

5. Dead-end caps (nonvented): maintain sterility of stopcock ports


6. Transducer: senses physiologic pressure signals and converts them to an electrical signal with proportionate changes


a. Pretested, precalibrated, presterilized disposable transducers are preferred over reusable transducers

7. Monitor and amplifier: creates readable signals, filters out unwanted “noise,” and displays waveform on oscilloscope


8. Flush solution: keeps line patent


a. Water manometer: normal saline or intravenous solution at prescribed flow rate

b. Transducer system

1) 300 mm Hg pressure overcomes resistance of pressure tubing and allows a continuous flush at 1 to 5 mL per hour and prevents backflow.

2) Heparinized solution (0.5 to 1 unit/mL, according to institutional policies) reduces the risk of clot formation at catheter tip. Premixed heparin may be available.

Note: Do not use heparin if patient is allergic or if the transducer system is being used for ICP monitoring.

9. Pressure-infuser bag or cuff: capable of providing 300 mm Hg pressure



D. Obtain Accurate Data


The clinician must take measures to ensure that the data obtained from invasive monitoring systems are accurate and reflective of the patient’s physiologic status. Box 7-1 identifies the characteristics of a reliable monitoring system. Other variables to consider are patient position, height of the transducer, zero referencing, and dynamic response testing.



Box 7-1 CHARACTERISTICS OF A RELIABLE MONITORING SYSTEM




The system should be as simple as possible. Extra stopcocks and manifolds decrease the fidelity of the monitoring system and increase the risk of fluid leak, microbial line contamination, and air bubble collection.


The bores of monitoring catheters should be no smaller than 18 gauge or 7 French. Small bores result in overdamping.


All connecting tubing should be of low compliance (stiff) and no longer than 3 to 4 feet. Low-compliance tubing is identified on packaging as “monitoring tubing.”


Tubing connectors should be tight. Use Luer-Lok connections, and inspect frequently for fluid leaks.


The catheter and connection tubing must be patent. Use a continuous-flush device for cardiovascular pressure monitoring, and inspect frequently to see that the pressure bag is inflated to 300 mg Hg. Routinely fast flush the monitoring systems of hypercoagulable patients.


The system must be free of air bubbles or clots. Even pinpoint air bubbles decrease the fidelity of monitoring systems.


Keep the connecting tubing away from areas of patient movement. Jostling of tubing results in an externally induced whip artifact.


From Davoric, G. O. (2004). Handbook of hemodynamic monitoring (2nd ed.). Philadelphia: Saunders.




1. Dynamic response testing: a means to assess the transducer’s ability to accurately reproduce variations in the patient’s vascular pressures


a. Activate the fast flush device and observe the characteristics of the waveform produced on the monitor

b. Resulting waveform described as (Box 7-2)

1) Optimally damped

2) Overdamped

3) Underdamped


Box 7-2 DYNAMIC RESPONSE TESTING (SQUARE WAVE, FREQUENCY RESPONSE TESTING) USING THE FAST FLUSH SYSTEM


From Davoric GO (2004). Handbook of hemodynamic monitoring (ed. 2). Philadelphia: Saunders.



Optimally Damped System


When the fast flush of the continuous flush system is activated and quickly released, a sharp upstroke terminates in a flat line at the maximal indicator on the monitor and hard copy. This is then followed by an immediate rapid downstroke extending below baseline with just one or two oscillations within 0.12 seconds (minimal ringing) and a quick return to baseline. The patient’s pressure waveform is also clearly defined, with all components of the waveform, such as the dicrotic notch on an arterial waveform, clearly visible.



image

Intervention: There is no adjustment in the monitoring system required.



Overdamped System


The upstroke of the square wave appears somewhat slurred, the waveform does not extend below the baseline after the fast flush, and there is no ringing after the flush. The patient’s waveform displays a falsely decreased systolic pressure and false high diastolic pressure as well as poorly defined components of the pressure tracing, such as a diminished or absent dicrotic notch on arterial waveforms.



image

Intervention: To correct for the problem:




1. Check for the presence of blood clots, blood left in the catheter after blood sampling, or air bubbles at any point from the catheter tip to the transducer diaphragm and eliminate these as necessary.


2. Use low-compliance (rigid), short (less than 3-4 ft) monitoring tubing.


3. Connect all line components securely.


4. Check for kinks in the line.



Underdamped System


The waveform is characterized by numerous amplified oscillations above and below the baseline after the fast flush. The monitored pressure wave displays false high systolic pressure (overshoot), possibly false low diastolic pressure, and “ringing” artifacts on the waveform.



image

Intervention: To correct the problem, remove all air bubbles (particularly pinpoint air bubbles) in the fluid system; use large-bore, shorter tubing; or use a damping device



E. Setting Up Pressure Monitoring System with Transducer (see CVP section for water manometer setup and ICP section for fiberoptic setup).


Note: Individual systems may have specific requirements. Always review manufacturer’s guidelines to ensure that all requirements are met.





1. Turn monitor on. Some monitors require time to warm-up.

2. Gather supplies specific to type of system being used and physician request.

3. Exchange vented caps on stopcocks with dead-end caps to ensure sterility.

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Nov 8, 2016 | Posted by in NURSING | Comments Off on Invasive Hemodynamic Monitoring

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