To the Editor:—

Safe delivery of a general anesthetic requires an intact anesthesia respiratory circuit. An anesthesia circuit leak test is recommended as part of the routine preoperative anesthesia machine check. *However, a negative leak test preoperatively does not guarantee that a significant respiratory circuit leak will not develop during the case.

We report here a series of 13 cases of anesthesia circuit failure resulting from circuit leaks found in the tubing of a (click-expandable) poppel 96-in adult anesthesia circuit (catalog No. K150E6000; Mallinckrodt Inc., St. Louis, MO). These cases occurred over a 1-month period at the Johns Hopkins Hospital (Baltimore, Maryland). It is of interest that the circuit design had recently been modified without notification from Mallinckrodt. These newer circuits are of wider diameter and narrower wall thickness.

In all 13 instances of circuit failure, a leak check was performed by the anesthesiologist prior to the case. In three cases, the leak test results were positive, with the magnitude of the anesthesia circuit leak greater than 10–15 l/min fresh gas flow. These circuits were replaced prior to the start of the cases. In 10 cases, although the preoperative leak test was negative, a leak and anesthesia circuit failure developed after the induction of general anesthesia. Two of these circuit failures occurred well into the operative cases, at approximately 45 min and 2 h, respectively. All 10 postinduction circuit failures were associated with an inability to ventilate the patients. Nine cases of circuit leak occurred either during or sometime after placement of the circuit tubing into the tube tree holder. In four cases, circuit failure occurred after the patient's head was repositioned. Each patient was rescued through emergent replacement of the respiratory circuit.

Upon inspection of the 13 failed circuits, 11 had a crack or tear in an inner fold of expandable circuit tubing (fig. 1). The other two circuit leaks were manifestations of longitudinal tears in the circuit tubing at the joint between the tubing and the end connector. On two occasions, the respiratory circuits severed into two separate pieces of hosing at an inner fold of circuit tubing. These were respiratory circuits that had passed preoperative leak tests but subsequently developed large and unacceptable leaks during routine manipulations and use.

Fig. 1. Defective anesthesia circuit.

Fig. 1. Defective anesthesia circuit.

A self-inflating bag and an additional anesthesia circuit were immediately available in all situations. No patient experienced significant oxygen desaturation or injury. In spite of this, anesthesia respiratory circuit failure did occur at critical times and added risk.