Volatile Agent Monitoring

A case for routine monitoring of volatile anesthetic agents (halocarbons) is based on presumptions of enhanced patient safety, quality patient care, and economy. The patient under anesthesia stands to benefit when halocarbon concentrations in anesthetic gas mixtures are precisely known. Although dial settings of halocarbon vaporizers may roughly approximate halocarbon concentrations present in anesthetic breathing systems, several factors contribute to discrepancies between dial-set concentrations and directly measured concentrations. These discrepancies are often clinically significant. The variables causing discrepancies are complex, being influenced by multiple factors such as the duration of anesthesia, flow rates of gases employed with halocarbons, and vaporizer accuracy. These variables are often difficult to predict and correct for. Therefore, the continuous monitoring of halocarbon concentrations in anesthetic breathing systems offers the most viable method of assessing the halocarbon concentrations present. Halometry is likely to prove cost-effective on at least two counts, including facilitation of economical reduced flow-rate anesthetic techniques, which conserve expensive halocarbons, and decreased anesthetic mishaps due to over- and underdosage, which may reduce litigation and insurance rates. Halometers are readily available for routine use. Clinically useful features include frequency response sufficient for breath-by-breath analysis, as end-tidal concentrations are related to anesthetic depth. Readability to two significant figures is also useful. The capability of specific agent recognition seems important primarily when vaporizers are easily misfilled with wrong agents. The overall complexity of patient monitoring need not be objectionably increased by routine halometry. The time may be appropriate for a halometry standard.