Technique and measurements: getting a line on the hemodynamic undercurrent

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Date: Jan. 2003
From: The Journal of Critical Illness(Vol. 18, Issue 1)
Publisher: CMP Medica, LLC
Document Type: Article
Length: 6,411 words

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ABSTRACT

Hemodynamic monitoring with the pulmonary artery catheter (PAC) can be an important diagnostic tool in the ICU. Correct use of the PAC in the critically ill patient requires an understanding of measured and calculated values and knowing how to identify errors in measurement and signal transduction. Errors can occur in making phlebostatic axis determinations and in obtaining cardiac output measurements. The most common insertion sites for the PAC are the internal jugular, subclavian, and femoral veins; the major complications associated with insertion include arterial puncture, bleeding, pneumothorax, arrhythmias, and air embolism. EGG tracings can help identify the portion of the cardiac cycle in which primary waveform measurements should be taken. The thermodilution technique, usually performed with a room-temperature solution, is used to measure cardiac output. (J Crit Illness. 2003;18(l):9-19)

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The right heart catheter, or the pulmonary artery catheter (PAC), has been under intense scrutiny since Connors and colleagues (1) questioned the value of its role in critically ill patients with shock, congestive heart failure, and renal failure. They reported that mortality was higher when the PAC was used, but the reason for this was unclear. Conversely, a meta-analysis by Ivanov and associates (2,3) showed no overall impact on mortality and a reduction in morbidity with PAC use.

Large, prospective, protocol-driven studies evaluating PAC use are needed to determine its value compared with that of central venous pressure (CVP) and to determine optimal management strategies in the critically ill patient. However, clinicians must first obtain reproducible and accurate measurements and understand the nuances of interpretation associated with measurements and derived values.

Iberti and coworkers (4) tested the knowledge of physicians in the United States and Canada regarding the PAC and reported a mean test score of 67%. The same questionnaire was applied to 535 European critical care physicians in 86 ICUs, and the mean score was about 72%. (5) Nurses who took the test had a mean score of 48.5%. (6) At best, half of the physicians and three fifths of the nurses surveyed could correctly determine the pulmonary artery occlusion pressure (PAOP) from a clear tracing, and a brief educational program had no impact on improving the interpretation of PAOP. (7)

In this article, I review technical aspects of the PAC, including insertion technique, associated complications, transducer zeroing and leveling, signal transduction, and interpreting primary and calculated measurements. In Part 2, to appear in an upcoming issue of The Journal of Critical Illness, I will discuss use of the PAC in the clinical setting--in ICU patients with shock, cardiac failure, and renal failure.

TECHNICAL ASPECTS

Proper use of the PAC requires understanding how measured values differ from predicted values and knowing how to identify errors in measurement and signal transduction. improper positioning of the patient or the PAC, or incorrect calibration or balancing of the transducer can render measurements invalid.

Many studies have identified frequent technical and interpretive errors made using the PAC. Morris and associates (8) evaluated 2711 PAOP measurements in 44 critically ill patients and found an...

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Source Citation   

Gale Document Number: GALE|A97113783