Volume 2, No. 2 • Summer 1987

From the Literature: Views of Minimal Monitoring

J. S. Gravenstein; James H. Philip, M.D.

Editor’s note: In each APSF Newsletter, a pertinent publication from the anesthesia patient safety literature ,will be summarized. Suggestions for future issues are welcome.

Gravenstein, J.S.: Essential monitoring examined through different lenses. I Clin Mon 1986; 2:22-29.

Dr. Gravenstein examines monitoring through three different lenses. Each reveals a different view as he scrutinizes the variables we monitor and how we have chosen them. Through @his examination we are shown the various forces which specify and mold our clinical practice.

Monitoring is classified according to its purpose, either to aid clinical management or to assist detecting and diagnosing physiologic aberrations. This paper concentrates on the latter.

Essential monitoring is equated with minimal monitoring and may be measured by the prevalence of monitor use. “Once a monitoring practice has been adopted by the majority of anesthesiologists, 51% to 99% that practice becomes a standard”.

The first lens allows us to view monitoring as it affects outcome. Outcomes from anesthesia are classified as unremarkable or adverse. An outcome is adverse if it is remarkable because of prolonged hospital stay or impaired post-operative well-being (ill-being). Onset of ill-being is usually acute, but infections and other complications can have delayed onset. Duration can be either transient or prolonged.

Through one portion of this first lens, we see that it was not scientific data concerning outcome that led us to our current choice of monitors. Indeed, even after years of common use, we find no scientific evidence of improved outcome attributable to any of them. Nonetheless, some of our present monitors do stand the test of logical analysis. They seem to be measures of well-being or ill-being. They provide quantifiable data that guide us in protecting or improving our patient’s state.

Unfortunately, for many measured variables, it is difficult to define the point at which well-being slips into ill-being. We have little data to determine what range of blood pressure is acceptable in any patient or population of patients. Indeed, thresholds for clinical action vary even among experts. As years have passed, our collective wisdom has shifted. Unacceptable hypotension of the 1940’s (below 120180) became the acceptable hypotension of the 60’s, 70’s and 80’s.

Thus, clinical practice has evolved extensively despite the lack of scientific data documenting changes in outcome.

The second lens explores the relationship between the variables we monitor and true measures of the patient’s state. Dr. Gravenstein defines the patient’s state as the state of the vital cell, a hypothetical cell which represents the heart and the brain. None of the variables we monitor let us view the actual state of the vital cell. At best, we view its input cascade. For the vital variable ‘cellular oxygen tension’, we monitor a series of variables which begin with pipeline oxygen pressure, pass through flow meters and a circuit-pressure gauge, and end with arterial oxygen saturation. Although we monitor numerous precursor variables, we are blind to the crucial variables that measure the state of the vital cell.

We thus acquiesce to monitor only the output of the vital cell to evaluate its state. Ideally, we would measure aggregate cellular output which represents electrical or chemical activity and is independent of organs and systems. Examples include the ECG which demonstrates electrical activity and is independent of mechanical performance. Temperature is another example. Instead, we usually measure integrated organ function (output) which fails to detect or identify specific state derangements. We do so because “monitoring has grown topsy-turvy and without the guidance of logic or insight”.

The third tens clarifies the actual factors which have molded our monitoring practices; most are non-clinical. Anesthesiologists have been rigid in their ways and have resisted change. With many modalities, there has been a long delay from demonstration to adoption. This is because each newly offered variable was of questionable utility in clinicians’ minds. Even capnography failed to gain acceptance in the U.S. until pulse oximetry eclipsed its impact.

To some degree, pressures from society, especially the legal community, have caused us to reassess our practices. “Lawsuits result as soon as the public recognizes that mistakes rather than fate may be responsible for an adverse outcome.. A verdict can firmly set a minimal standard.”

In summary, most monitors considered essential were adopted by anesthesiologists because they believed that these monitors improved the outcome for the patient, even without scientific evidence. Only now are investigators beginning to measure the impact of monitoring on outcome.

Abstracted by James H. Philip, M.D., Director, Biomedical Engineering, Brigham and Women’s Hospital, Boston, MA.