To the Editor:—
Electrical power failure in the hospital presents a severe challenge to intensive care unit patients.1We recently experienced electrical backup failure in an Evita 4® ventilator (Dräger Medizintechnik, Lübeck, Germany), which was caused by the internal erosion of a connecting cable of an adjunct battery Dryfit A512® (Sonnenschein, Budingen, Germany) to the ventilator.
Because of renovation of the power supply system in our hospital, the temporary interruption of electrical supply in the intensive care unit was scheduled. According to an advance notice from the hospital management division, the electrical supply would be stopped for only several minutes before the emergency electrical generator would start up to supply electricity. At the time of power interruption, three patients were ventilator dependent. The ventilators used in our intensive care unit are checked annually, and adjunct batteries are replaced by engineers from the manufacturers. At the time of power stoppage, two ventilators continued to function, but an Evita 4® ventilator shut down instantly without any alarm. An attending nurse noticed the incident and ventilated the patient manually using a resuscitation bag. Electricity was reestablished quickly, and the ventilator restarted immediately. The patient had no identifiable injury as a result of the shutdown.
The AC and DC power modules of the ventilator were 8 yr old. The ventilator functioned steadily with an external power supply. Because the Evita 4® is normally configured to function for 10 min with backup from a fully charged battery in case of a power cut, the battery assembly was suspected to be responsible for the problem. The ventilator was sent to the manufacturers for close inspection to identify the source of the power backup failure. Dräger Germany found that the cable connector to an adjunct battery was eroded by leaked battery solution. Inside the moist electronic unit, the minor erosion had degraded the connecting cable over time and increased the electrical resistance, leading to the malconduction to the ventilator system and power failure even though the adjunct battery was properly charged (figs. 1–3). Close examination of the manufacturer’s database for batteries of approximately 10,000 serial numbers showed that the erosion occurred rarely. The current case was formally registered in the manufacturer’s incident list. The manufacturer replaced the emergency power unit of the ventilator with a Panasonic lead–acid battery (Mastushita Battery Industrial, Osaka, Japan). Dräger Japan explained that all Evita 4® ventilators used in Japan would be inspected eventually, and batteries would be replaced, because there was a risk of leakage with the current battery unit.
The internal component of life-supporting devices including ventilators is a “black box” to medical users. We have no precise information about battery life. Depending on the rate of deterioration over time, the life of a battery is usually within 3–5 yr. Regular checkup and periodical replacement of the battery assembly by trained technicians are mandatory. Moreover, we have to be aware that without reliable power supply, life-supporting machines such as ventilators would be lethal.2
*Yamagata Prefectural Shinjo Hospital, Shinjo, Yamagata, Japan. email@example.com