RIGHT VENTRICULAR EJECTION FRACTION PULMONARY ARTERY CATHETERS

Although cardiovascular monitoring has focused predominantly on left ventricular performance, in some instances, right ventricular dysfunction may be the more important factor limiting the circulation.^{[687] [688] [689] [690]} Patient populations at increased risk for right ventricular dysfunction include those with chronic obstructive pulmonary disease, adult respiratory distress syndrome, pulmonary hypertension, and right ventricular ischemia and infarction.^[691]

Standard techniques are available for monitoring right ventricular performance in patients with acute myocardial infarction involving the right ventricle. ECG monitoring

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In intraoperative and critical care environments, measurement of the right ventricular ejection fraction (RVEF) with a specially designed PAC offers another method for evaluating right ventricular function. This method uses a standard PAC equipped with a rapid-response thermistor that detects and quantifies the small changes in pulmonary artery blood temperature that occur with each heartbeat.^{[700] [701]} The thermistor measures these temperature changes after bolus administration of an iced or room-temperature injectate, and the cardiac output computer measures the residual fraction of thermal signal after each heartbeat to determine the RVEF as 1 minus this average residual fraction.^[701] Clearly, all factors that confound standard thermodilution cardiac output measurement will also interfere with accurate determination of RVEF. In addition, because the temperature changes measured by the RVEF PAC are small, beat-to-beat changes, the method will not work if the ECG R waves cannot be detected accurately, the R-R interval is short as a result of tachycardia, or the cardiac rhythm is irregular.^[675] Comparison of PAC-based RVEF measurements with angiographic or nuclear techniques has yielded mixed results in terms of accuracy, but this may reflect, in part, the absence of a widely accepted reference standard for this measurement.^{[701] [702] [703]}

Intraoperative use of the RVEF PAC has focused primarily on detection of right ventricular dysfunction in patients with coronary artery disease undergoing surgical revascularization. Reduced RVEF has been noted after cardiopulmonary bypass, particularly in patients with preexisting right coronary artery obstruction.^{[704] [705] [706]} Anecdotally, an acute reduction in RVEF from its normal value of approximately 40% may provide an early sign of right ventricular ischemia.^[707] However, RVEF is an extremely load-dependent measurement of right ventricular performance, and the clinician must keep this fact in mind to interpret this measurement properly. ^{[675] [697] [698]}

Clinical use of the RVEF PAC appears to have found its greatest application to date in critically ill patients, especially those with respiratory failure.^{[675] [697] [698] [699] [708]} In these applications, the measurement of greatest interest has been right ventricular end-diastolic volume, which is derived mathematically from RVEF.





where RVEDV = right ventricular end-diastolic volume
SV = stroke volume
RVEF = right ventricular ejection fraction

Right ventricular end-diastolic volume appears to correlate better with cardiac output than do standard preload measurements such as CVP or PAWP.^{[675] [698] [699]} These findings are not surprising given all the interpretive problems associated with monitoring of cardiac filling pressure previously discussed. Furthermore, the better correlation between right ventricular end-diastolic volume and cardiac output may result from the mathematical coupling of measurements because both are derivatives of stroke volume determined with the PAC. As in the case of standard PAC monitoring, however, the benefit of RVEF PAC monitoring in terms of patient outcome remains unproven. ^[559]