Circulation 60,475 • Volume 14, No. 1 • Spring 1999

ASA Amends Monitoring Standards to Make End-Trial CO 2 More Specific, But Temp. More General

John H. Eichhorn, M.D.

Two substantive amendments to the “Standards for Basic Anesthetic Monitoring” of the American Society of Anesthesiologists (ASA) that have patient safety implications were adopted by the ASA House of Delegates in October and become effective July 1, 1999. All those interested will find the full text of all the monitoring standards on pages 462-463 of the ASA’s 1999 Directory of Members and on the ASA website:

New Mandate on Expired CO2: Capnography for Face-Mask GA

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.” In addition to promoting internal consistency in the standards and also reflecting common practice, this change was made to include specifically inhalation anesthesia via face mask when saying, “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.)

Failure of the adequacy of the patient’s ventilation or of anesthesia personnel to ventilate the patient has traditionally accounted for the greatest number and most severe overt anesthesia catastrophes. The strengthening of ventilation monitoring serves as both recognition of the extremely valuable role of capnography as a critical component of “safety monitoring”1 and programmatically as a logical lead-in to the standard which follows in the ASA set that had been previously modified to require identification of expired CO2 to verify correct positioning of an endotracheal tube or laryngeal mask.

Issues raised during the process of proposal and evaluation of this change centered on two basic points. With the recent potential blurring of the distinction between IV sedation and general anesthesia, it was recommended that a clear definition of general anesthesia be developed, particularly because this standard applies to “every patient receiving general anesthesia.” Also, concern was expressed about whether capnography will be required in brief, entirely noninvasive procedures such as cardioversion or ECT during which an anesthesia machine may not even be used. The ASA Committee on Standards of Care noted that the caveat included in the standard regarding the nature of the procedure and the equipment likely will allow the responsible anesthesiologist to use his/her own judgement as to the validity of capnography for those procedures, thus facilitating the decision as to whether the standard would apply and capnography would be required.

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 specific patient-safety orientation, particularly the detection of inadequacy or overt failure of ventilation, was seen as key point – 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?”

New Temperature Monitoring Controversy

Attempting to update the temperature monitoring standard (unchanged since 1986) proved to be more complex. The ASA had received extensive input over many years suggesting that temperature monitoring should be mandatory during all anesthetics because of the risk of malignant hyperthermia. However, there had been a consistent feeling that almost always a temperature increase is a late-developing clinical sign appearing only after the syndrome is well underway, limiting the value of temperature monitoring as a safety screen intended to provide warning. In the last two years, even greater input was received regarding accidental hypothermia during anesthesia (and the multiple adverse consequences attributed by various authors to this hypothermia) and the resulting suggestion that temperature monitoring should be required for this reason. The ASA committee evaluated the extensive documentation submitted regarding the potentially deleterious effects of accidental hypothermia and eventually agreed that an update of the standard was indicated. Importantly, assertions that the standard should include language about maintaining a minimum acceptable temperature were not adopted because this is a standard specifically for monitoring and not therapy.

One central idea from the original 1986 standard became the opening of the proposed update: “Every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated, or suspected.” After much deliberation, it was decided to propose adding more specificity to the standard due to the documented likelihood of significant heat loss (after an equilibration period of 30-40 minutes) during general anesthesia and a second mandate was included in the proposal: “Every patient receiving general anesthesia lasting more than a short duration (for example, more than 45 minutes) shall have body temperature continually monitored.” This latter proposed standard generated many opinions and significant testimony, both pro and con.

The ASA Reference Committee evaluating the proposal at the beginning of the Annual Meeting recommended approval of the proposed revision containing both ideas but debate on the floor of the House of Delegates led to a vote to delete the second part, leaving the general introductory statement as the full text of the standard as of July 1, 1999: “Every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated, or suspected.” Clearly this standard is open to interpretation in the clinical setting. Some authors and experts would state that all patients receiving general anesthesia, or, possibly, any anesthetic for that matter, for more than a brief duration would be anticipated to develop clinically significant hypothermia while others might argue that in the large majority of cases, any drop in temperature is not really significant, while still others might hold that modern methods of attempting to avoid hypothermia make the issue virtually moot.

The ASA Committee on Standards of Care has not decided whether to consider the temperature monitoring question again for 2000. Reader input on this point, especially with specific suggestions for topics and wording, is actively welcomed and will be forwarded to the ASA.

Dr. Eichhorn, Chairman of Anesthesiology at the University of Mississippi, is Chairman of the Committee on Standards of Care of the ASA and Editor of the APSF Newsletter.


  1. Eichhorn JH. Prevention of intraoperative anesthesia accidents and related severe injury through safety monitoring. Anesthesiology 1989;70:572-577.