To the Editor:—

I read with great interest the report by Cantillo et al ., 1regarding malfunction of flow sensors on the Datex-Ohmeda 7900 SmartVent (Madison, WI). Our department owns 15 such ventilators. We too experienced moisture buildup resulting in problems generating the desired tidal volume. Similar to the authors, our anesthesia assistants and engineers were asked to replace sensors, or the system integration board, on several occasions in 2000.

Our own experience differs from that reported in that we do not routinely use heated humidifiers. We did not experience this problem initially (1997–1999). During this period, the 7900s were located in the pediatric operating rooms, where the procedures are brief, and the ambient temperature warm. In 2000, these machines were placed in the adult orthopedic operating rooms where ambient temperatures are routinely low, the cases frequently exceed 3 h, and fresh gas flow is usually less than 2 l.

I believed that factors other than active humidification (low ambient temperature, low gas flows) contributed to this problem, and contacted Datex-Ohmeda. After several meetings with their engineers and customer representatives, they produced a flow sensor designed to minimize moisture buildup. As a result of this and nightly moisture inspections by our anesthesia assistants, the problem has all but vanished.

The authors suggest that Datex-Ohmeda issue a warning regarding heated, humidified circuits. I would be interested to learn if other anesthesiologists have experienced altered performance of this equipment as a result of cold operating rooms. If so, then perhaps the product warning should also include a statement to this effect.


Cantillo J, Domsky R, Gratz I, Goldgerg M: Ventilatory Failures with the Datex-Ohmeda 7900 SmartVent. A nesthesiology 2002; 96: 766–768