Pulmonary Artery Catheterization

Chapter 50 Pulmonary Artery Catheterization



Benjamin M. Brainard, VMD, DACVA, DACVECC, Deborah C. Mandell, VMD, DACVECC



KEY POINTS



• Pulmonary artery catheters (PACs) are placed through the right side of the heart and the right ventricular outflow tract, into a pulmonary artery (PA).

• PACs may be used to measure cardiac output by thermodilution, to calculate systemic vascular resistance, and to sample mixed venous blood.

• Information from a PAC may be used to tailor fluid or pressor choices in the anesthesia or intensive care setting.

• A PAC may be placed by following pressure tracings or by using fluoroscopy.

• PA catheterization is not a benign procedure and may be associated with significant morbidity, requiring a thorough evaluation of the risk-to-benefit ratio.

• Many alternative techniques for measuring cardiac output that do not require a PAC are available for use in veterinary patients.


INTRODUCTION


Pulmonary artery (PA) catheterization is a technique that places a catheter through the right heart and right ventricular outflow tract into the PA. It is used to measure cardiac output by thermodilution, to calculate systemic vascular resistance, and to sample mixed venous blood. Often, placement is assisted by a latex balloon at the tip of the catheter that allows its course to follow the flow of blood (flow-directed catheter placement).



TYPES OF CATHETERS AND USES


There are many types of pulmonary artery catheters (PACs) designed for angiographic studies or for measuring the blood pressure in the pulmonary arteries. These catheters may be single-lumen or double-lumen catheters.1 Some catheters designed to be introduced into the PA have sensors 4 cm distal to the tip of the catheter that allow temperature measurement (e.g., the Swan-Ganz type catheter). Other catheters may measure blood oxygenation (e.g., the oximetry thermodilution catheter) (Tables 50-1, 50-2, and 50-3). Diameters of thermodilution catheters range from 5 to 7.5 Fr. Angiographic catheters are available from 4 to 8 Fr. Most Swan-Ganz catheters are made of polyvinyl chloride (PVC) and are available in lengths of 75 or 110 cm, which are adequate for most small animal species, but which may not be of sufficient length for horses or other large animals. Other thermodilution catheters are made of polyurethane, which has the characteristic of softening at body temperature.



Table 50-1 Pulmonary Arterial Catheter Types, Sizes, and Manufacturers: Angiographic Catheters

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Table 50-2 Pulmonary Arterial Catheter Types, Sizes, and Manufacturers: Thermodilution Catheters

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Table 50-3 Pulmonary Arterial Catheter Types, Sizes, and Manufacturers: Other Catheters

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Because of the wide diameter, complicated placement, and need to adjust the depth of catheter insertion, it is necessary to place PACs via a catheter introducer sheath. The introducer sheath should be at least one size larger than the catheter itself. For example, a 7 Fr catheter will fit through an 8 or 8.5 Fr introducer sheath, while a 6 or 6.5 Fr introducer sheath is adequate for the 5 Fr catheter. For sterility, a plastic sleeve attached to the sheath covers the catheter and keeps the catheter sterile while the PAC is moved into and out of the vessel.


Most commercial catheters designed for thermodilution measurement of cardiac output have multiple ports and lumens (Color Plate 50-1). The proximal port, or central venous pressure (CVP) port, is used to measure right atrial or central venous pressure. This port is also used for fluid boluses during cardiac output determination in humans, dogs, and cats. Because the proximal port is located 30 cm from the tip of the catheter where the thermistor is located, it is necessary to have a separate catheter advanced into the right atrium (RA) in large animals for the purpose of injecting fluid for thermodilution measurements (the proximal port will be located in the right ventricle [RV] in the horse).2 Separate RA catheters have also been used in cats and small dogs, where the proximal port would be located outside of the RA.3 When using separate injection catheters, it is important that the catheter volume be the same as the injection port on the Swan-Ganz catheter, because the K2 constant of the Stewart-Hamilton equation used by cardiac output computers is specific for the catheter type.4 The distal port of the catheter is the central lumen and is used to measure both PA pressure and pulmonary capillary wedge pressure (PCWP) or PA occlusion pressure. Mixed venous blood is also sampled from this port. The balloon port allows for inflation of the balloon tip of the catheter with a small amount of air (usually ≤1.5 ml) for flow-directed catheter placement, and measurement of PCWP. The catheter will also have an electronic thermistor connection for temperature measurement.



Cardiac Output


A PA catheter is necessary for evaluation of cardiac output using some thermodilution techniques (see Chapter 212, Cardiac Output Monitoring). Briefly, 1.5 ml/kg of saline (or 5% dextrose in water) of a known temperature is injected into the proximal port of the multilumen catheter.4 In most animals, this proximal port (30 cm proximal to the tip of the catheter) will sit either in the RA or in the jugular vein, where it is appropriate to inject the indicator bolus. As mentioned previously, placement of a second injection catheter in the RA may be necessary to perform thermodilution in smaller or larger animals.2,3 The thermistor probe on the distal end of the catheter will measure the change in blood temperature over time and will calculate cardiac output based on the area under the temperature curve. Newer Swan-Ganz catheters have thermistor probes near the junction of the proximal port and the catheter to more accurately measure the temperature of the injectate (it may warm significantly during injection). For larger animals such as horses, it is necessary to use chilled injectate, because subtle changes in blood temperature may not be sensed by the thermistor probe because of the relatively large cardiac output and blood volume in these animals. The indicator bolus must also be administered quickly, because a slow injection will minimize the change in temperature that is recognized by the thermistor and cause inaccurate readings (if injected too slowly, falsely low cardiac output measurement will be displayed). The use of a power injector pump is recommended for these measurements in large animals, and the bolus should be injected as quickly as possible in small animals.



Pulmonary Capillary Wedge Pressure


Measurement of PCWP via a PAC enables an estimation of left ventricular preload, because it can correlate with the left ventricular end-diastolic pressure. This correlation may not be reliable in patients with pulmonary hypertension, mitral regurgitation, or decreased ventricular compliance.5,6 Airway and intrathoracic pressure can also affect this relationship. The methods for determination of the PCWP are discussed below. The PCWP may also be used to derive the pulmonary transcapillary pressure in dogs and cats.4



Right Ventricular End-Diastolic Volume


Right ventricular end-diastolic volume and index are used increasingly in human medicine to estimate volume status, especially in patients who are receiving positive-pressure ventilation with positive end-expiratory pressure, or other scenarios in which the PCWP does not accurately indicate left ventricular end-diastolic pressure. These values may be measured via catheters with special rapid-response thermistors that will sense small beat-to-beat changes in temperature induced by an upstream heat filament. These catheters need to be synchronized with the electrocardiogram, and patients need to have a regular R-R interval.7 This same rapid-response thermistor and filament combination is used in catheters that will continuously measure cardiac output without the need for bolus injection (CCO PA catheter, CCOmbo Continuous Cardiac Output catheter, Baxter Healthcare Corporation, Edwards Critical Care Division, Irvine, CA).7



Selective Pulmonary Angiography


Selective pulmonary angiography via a PA catheter is sometimes indicated to elucidate complex congenital defects of the cardiopulmonary system in veterinary species.1 Presurgical right heart catheterization for angiographic purposes is performed commonly in humans before cardiac surgery.1 In animals, congenital defects such as stenosis of the pulmonic valve may be delineated via angiography and managed with balloon valvuloplasty by inflating a balloon catheter across the stenotic area.8

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Pulmonary Artery Catheterization
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