Portable, but suitable: devices in prehospital care might be hazardous to patient or to aviation safety.

INTRODUCTION: Devices used for support of patients requiring air rescue or conveyance are subjected to severe environments that may affect their ability to function when needed or may affect other systems within the transporting vehicle. METHODS: The ability of four portable ventilators, a suction device, and plastic and rubber tracheal tubes to withstand changes in temperature, vibration, sudden deceleration, and electromagnetic fields was studied in the laboratory setting. In addition, the effects of the operation of these devices on the flight instrumentation was investigated. RESULTS: All of the ventilators tested delivered stable minute volumes at temperatures above zero, but in sub-zero temperatures problems were encountered with the driving gas. Vibrations produced alterations in the performance of two of the ventilators, and resonant frequencies were detected that are identical to those produced by the rotors of the helicopter used. Suctioning became difficult at temperatures below -5 degrees C as the mucus froze in the collecting tubing. The motor produced electromagnetic fields that interfered with the aircraft instrumentation, and resonant frequencies had a deleterious effect on the circuit boards. Plastic tubes were adversely affected by cold, and these chilled tubes were excessively sensitive to vibration and shocks. CONCLUSIONS: The devices used in various aircraft influence certain vital maneuver systems of the craft. Studies on portable ventilators, a suction device, and tracheal tubes showed that, under specific conditions, the equipment was safe to patients and was not hazardous to the aviation safety. However, under certain conditions commonly encountered during air rescue operations, the equipment became dysfunctional or presented safety hazards to the aircraft, and, hence, the crew. The Swedish Air Force has adopted three different criteria constellations: 1) operative; 2) storing; and 3) transport environment.

Tracheal tubes in cold stress.

During rescues in cold climates, plastic tracheal tubes have fractured because of cold stress or mishandling. Susceptibility of rubber and plastic tracheal tubes to cold stress was tested in a climate chamber. Plastic tubes became stiffer when chilled, had greater resistance to reshaping and were more sensitive to shock and manipulation. They also need protection against cold and shock during transport. Rubber tubes were more tolerant of cold stress. Very cold rubber and plastic tubes may induce tissue damage. Rewarming to a nondangerous temperature was shown to be a quick procedure. It is suggested that the rescuer's own body heat be used.

Portable emergency ventilators. 2. Sensitivity to environment.

Three compact ventilators (Oxylog, Maxaman and Pneupac 2), commercially available in Sweden, were subjected to tests concerning sensitivity to environmental stress. The ventilators functioned very well at temperatures above 0 degree C. The Oxylog apparatus was very sensitive to subzero temperatures. It also had a spectrum of resonance frequencies when subjected to vibration testing that restricts its use outside the sheltered hospital environment. The Maxaman and Pneupac 2 in the modified version withstood the tests in a reliable way. The shock tests performed had no negative effects on any of the ventilators or their functions.