Monitoring of the Risk Patient - The Clinical Opportunity
'High risk' surgery patients subjected to a reduction in global oxygen delivery are known to have increased levels of morbidity and mortality. Increasing global oxygen delivery results in a dramatic improvement in outcome in these patients. For example in the USA there are over 30 million operations performed annually, 10-15% of which are deemed to be 'high risk' - approximately 3 million operations. These 'high risk' patients have an increased risk of death. Analysis of 17 studies designed to evaluate the effects of peri-operative optimization of 'high risk' patients suggests that for every 100 patients undergoing such surgery 11 lives would be saved if optimization had taken place.1
Limitations of Invasive Arterial Blood Pressure Monitoring
Invasive arterial blood pressure monitoring is used in virtually all
'high risk' surgery patients, post-operative high dependency wards and the general intensive
care unit. Invasive arterial blood pressure monitoring provides continuous hemodynamic data
with an acceptable level of risk. As a consequence, continuous blood pressure monitoring is
used to provide a practical 'Early Warning' of hemodynamic change. However, by necessity
rapid changes in arterial blood pressure are mostly interpreted as resulting from changes
in systemic blood flow. Unfortunately, marked changes in systemic vascular resistance, that
occur in sick patients, invariably result in a poor correlation between changes in arterial
pressure and blood flow (r = 0.22). Therefore, if the therapeutic intervention is solely
targeted at achieving a normal blood pressure this may, in fact, obscure an underlying/occult
low cardiac output status. In many patients the combination of sub-optimal blood flow and
oxygen content may lead to the build-up of a potentially life-threatening oxygen debt. The
concern is that in elderly patients and/or patients with a co-existing cardiac problem,
the repayment of such a debt may prove beyond the actual physiological reserve of the patient.
The measurement of cardiac output is therefore a requirement within a large expanded group of
'risk' patients currently indicated for arterial line replacement.
References
- Special Report: Consensus Meeting: Management of the High Risk Surgical Patient. Clinical Intensive Care, September 2000; 11:1-19
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