The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

'Use of Invasive Monitoring in a Patient in Acute Respiratory Failure'

John W. Hoyt, M.D., Sunday, December 7, 1997.

If one were to list the technologies that defined the practice of critical care over the last 30 years, included in that list would be the life-support technique of positive pressure ventilation and the monitoring technique of using a balloon-tip, flow-directed pulmonary artery catheter (PAC) to create a hemodynamic profile. The first technology arrived in the 1960s and became a standard by the 1970s and the second arrived in the early 1970s and became a standard in the 1980s. There has been much refining and adjustment of the early and primitive forms of positive pressure ventilation, but no clinician ever publicly suggested during the history of critical care that we should let a patient endure a relentless course of respiratory failure without the benefit of mechanical ventilation because that technology was too dangerous and might increase the death rate. Complications of positive pressure ventilation have always been known, but somehow the benefits always seemed to outweigh the risks. No investigator ever performed a perspective, randomized, controlled trial of 100 patients with respiratory failure treated with positive pressure ventilation and 100 matching patients without mechanical ventilation. The opposite is the case with the PAC. In fact, one public attack after another has been leveled at this diagnostic tool, claiming that it increases death rate by some ill-defined mechanism. It has been frequently suggested that the PAC should not be used in critical care because it worsens patient outcome.

The most recent of these attacks came from one investigator who over the years has done the most to construct circumstantial evidence about the value of the catheter, Alfred F. Connors, Jr., MD. His article in the Journal of the American Medical Association (JAMA) in September of 1996 reported a higher death rate when the PAC was used as a monitoring technique, and James E. Dalen, MD and Roger C. Bone, MD, suggested in an accompanying editorial that it was time to "pull the PAC" out of critical care. The report by Dr. Connors came from data collected as part of the Study to Understand Prognoses and Preferences for Outcome and Risks of Treatments (SUPPORT). In that study done at five academic institutions in this country, information was collected in the intensive care unit (ICU) to study patient preferences and outcome. One of the papers from these data demonstrated a poor level of communication between patients/families and physicians and poor-quality pain management.

One really needs an historical sense of critical care over the last 30 years to understand how the PAC came to occupy its position of prominence in the ICU community. One of the obsessions of early intensivists was to be able to measure intravascular volume to improve judgments about fluid administration versus diuresis. It was well understood from the early physiologic work of Starling that a full vascular space lead to a full heart and optimized cardiac performance. However, just the right level of fullness for the heart was needed because excessive fullness led to pulmonary edema and inadequate fullness led to hypovolemia and hypoperfusion of key organs such as the kidney. In the early days of the ICU, the measurement of central venous pressure (CVP) was used to make these judgments, but there was always a clinical sense that right-sided measurements might not reflect left-sided function and it was the powerful left ventricle that was responsible for peripheral organ perfusion. Thus, the 1970 article in the New England Journal of Medicine was warmly received because it delivered to critical care a monitoring tool to improve treatment decisions. Early reports demonstrate that patients with cardiac disease might have a wisely varying CVP while having a normal pulmonary capillary wedge pressure (PCWP). This information led to the widespread use of the PAC in both medical and surgical settings.

AARC 50th Anniversary, December 6 - 9, 1997, New Orleans, Louisiana.

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