To the Editor

According to the proposed FDA checklist (APSF Newsletter, Winter 1992-1993: 47-51, 1992), it is advisable to use the negative pressure leak test with a suction bulb in order to maintain the safety and the reliability of the anesthetic machine.

Recently, we found this test to be impracticable in some anesthetic machines. It was found to be caused by the installed vaporizers in some of the machines, which are not designed to withstand a negative pressure. These vaporizers are the Tec 3 (Ohmeda Co., Ltd.) and the Acoma F-MKIII (Acoma Co., Ltd.), so far as we have investigated.

Concerning the leak check of machine low pressure system, ISO 5358 (anesthetic machines for use with humans) and JIS T 7201 (anesthetic machine) describe that the maximum leakage shall be 50 ml/min at pressure of 3kPa. However, this check needs the specific flowmeter and is time consuming to perform. Compared with this method, the negative pressure leak test is simple and easy to do, but it should be stressed that this test may be impracticable with some machines.

Satoshi Watanabe, M.D, Professor, Department of Clinical Engineering, Kitasato University School of Allied Health Sciences.

Kaoru Kobayashi, Clinical Engineering Technologist, Medical Engineering Center, Kitasato University East Hospital, Sagamihara, Kanagawa, Japan