Monitoring is an essential aspect to the practice of anesthesiology. The American Society of Anesthesiologists (ASA) has established basic monitoring criteria for circulation, ventilation, oxygenation, and temperature. These monitors allow the anesthesia provider to observe ECG changes, monitor oxygen and anesthetic gas concentrations, quantify oxygen saturation, and maintain normothermia. These “standard” ASA monitors represent the minimum monitoring required for each anesthetic delivered.
Unfortunately, these basic monitors may not provide enough information for the management of a complex patient. These standard monitors do not assess certain variables (e.g., stroke volume, systemic vascular resistance, preload, and afterload) which are essential to the maintenance of blood pressure. Additionally, the ASA does not formally endorse any method of measuring the depth of general anesthesia (DGA), the monitoring of which can help in the prevention of anesthesia awareness. Accordingly, devices have been developed to aid in the measurement of these variables. Anesthetic monitoring has developed into a billion-dollar industry.
Given the vast array of devices on the market, this chapter will only focus on the most commonly encountered technologies currently available. Cardiac output monitoring allows for the mathematical extrapolation of numerous other variables. Transesophageal echocardiogram allows for the direct visualization of the heart, allowing for the assessment of volume status and cardiac abnormalities on a rapid basis. DGA monitoring has to date focused on frontal lobe electroencephalogram analysis as a proxy for consciousness. Each technology carries its own limitations and indications, the knowledge of which is essential for their proper use.
Standard ASA monitors Ohm’s law Thermodilution Continuous cardiac output Pulse contour analysis Transesophageal echocardiography Depth of general anesthesia
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