ASA Standards of monitoring during anesthesia 

Bhavani Shankar Kodali MD

 

ASA Standards of Care - Capnography

Standard for "every patient receiving general anesthesia

Continual monitoring for the presence of expired carbon dioxide

Identification of expired CO2 to verify correct positioning of an endotracheal tube or laryngeal mask

 

In 1998, the ASA (American Society of Anesthesiologists) Committee on Standards of Care continued its ongoing efforts to refine and update the ASA "Standards for Basic Anesthetic Monitoring," which were first adopted in their original form in 1986 and have been modified several times since. Two substantive amendments that were somewhat different from the Committee's proposals were adopted by the ASA House of Delegates in October 1998 and become effective July 1, 1999. Members and other interested parties will find the full text of all the monitoring standards on pages 462-463 of the 1999 ASA Directory of Members.

Mandatory Monitoring of Expired CO2

The first and most general point in the "methods" section of the ventilation monitoring standard was modified in such a way as to include capnography as a standard for "every patient receiving general anesthesia." This includes inhalation anesthesia via face mask: "Continual monitoring for the presence of expired carbon dioxide shall be performed unless invalidated by the nature of the patient, procedure, or equipment. Quantitative monitoring of the volume of expired gas is strongly encouraged.*" (As usual, this standard has the asterisk referring to the ability of the responsible anesthesiologist to waive the requirements under extenuating circumstances.)

This strengthening of ventilation monitoring was intended by the committee as both recognition of the extremely valuable role of capnography and as a logical lead-in to the following standard previously modified to require identification of expired CO2 to verify correct positioning of an endotracheal tube or laryngeal mask. Testimony during the proposal and evaluation process raised two main issues. With the recent potential blurring of the distinction between intravenous sedation and general anesthesia, it was recommended that a clear definition of general anesthesia be developed. Also, concern was expressed about whether capnography will be required in brief, entirely noninvasive procedures such as cardioversion or electroconvulsive therapy during which an anesthesia machine may not even be used. The committee notes that the caveat about the nature of the procedure and the equipment likely will allow the responsible anesthesiologist to use his/her own judgment as to the validity of capnography for those procedures.

Further, the committee acknowledged the fact that the "end-tidal CO2" numerical value displayed on a monitor during mask anesthesia often may be influenced by gas mixing in the patient's airway and in the mask. However, the patient-safety orientation, particularly the detection of the failure of ventilation, was seen as key, with the integral role of capnography relating to the basic questions: "Is there expired CO2? Is it clearly too high or too low?" and "Is there any trend?"

John H. Eichhorn, M.D., is Professor and Chair of Anesthesiology, University of Mississippi School of Medicine/ Medical Center, Jackson, Mississippi.