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.

Appropriate suction device in rescue medicine.

In rescue medicine, a suction apparatus must function in a variety of environmental conditions. To find an appropriate device for the Swedish Air Force air rescue service the Laerdal suction device 790,000 was selected for further testing according to international standards for aviation safety. Tests showed that vibrations had deleterious effects on the internal construction of the suction device. In addition, an electromagnetic field was generated affecting the navigation, autopilot, and communication systems. We conclude that the suction apparatus and probably other devices as well must be tested for their functioning in adverse environments and their ability to meet international aviation safety regulations.

Public opinion on the ambulance service in a rural and an urban region.

Two groups of parents to schoolchildren (7 y and 15 y) were formed. The aim was to study if there were any differences in attitudes and knowledge concerning ambulance services in rural and urban areas. The results showed that knowledge about the ambulance service is good. Further, that day to day activities were considered more important than security measures to be used in emergencies. Parents living in rural parts considered the ambulance "near" but not as "near" as the parents in urban districts.

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.

Ambulance utilization in Sweden: analysis of emergency ambulance missions in urban and rural areas.

Data concerning ambulance utilization in a rural and an urban region were registered in a computer. In both regions approximately 30% of missions were emergencies. In the urban area, 20% of the emergency missions were due to trauma, compared with 10% in the rural area (P less than .01). The major symptoms were unconsciousness (34%) and shortness of breath (24%) in the rural region, while in the urban region pain (32%) was the dominating symptom. The response time in emergency missions, used as a measure of the service level of the emergency medical system, was shorter in the urban area than in the rural area (P less than .01): less than 15 minutes in 93% of emergencies in the urban area (mean time, 8.1 minutes) and in 78% of emergencies in the rural area (mean time, 10.2 minutes). Ambulance utilization was higher (P less than .01) in the urban region (0.37 missions/ambulance/hour) than in the rural region (0.22 missions/ambulance/hour). The study indicates that there are great differences between urban and rural areas with respect to the incidence and character of ambulance missions. This difference must be considered when analyzing the cost effectiveness of emergency medical services.

Training of emergency dispatch-center personnel in Sweden.

The ability to recognize symptoms, to make priority decisions, to dispatch suitable ambulance transport and inform the crews, and finally, to initiate first aid via the caller is essential for optimum care of severely injured or ill patients outside the hospital. In Sweden, a special job-related course trains dispatch-center personnel to think in terms of symptoms and evolution of the victim's status, and to assess the level of seriousness.

Portable emergency ventilators. A lung model study.

The ventilatory performance of four portable emergency ventilators (Logic 07, Motivus, Oxylog and Pneupac II) was tested on a lung model. The model consisted of one common (tracheal) tube, two separate (bronchial) tubes in which different obstructions could be applied, and two glass jars filled with water to suitable compliances. Dialled volume was compared to measured volume. The gas distribution produced by the different ventilators was also studied. It was found that all four ventilators could distribute gas to the lungs. The ventilators Logic 07 and Oxylog had acceptable relationships between dialled and measured volume/frequency and they also produced a good final distribution.

Portable emergency ventilators. Sensitivity to environment.

The function in various types of climate of three ventilators which are commercially available in Sweden: Motivus, Pneupac 2 and Logic 07, was tested as well as their sensitivity to vibration. The ventilators functioned in subzero temperatures only if the driving gas had a low humidity content. They also required an increased driving gas pressure. Only Logic 07 would function below -20 degrees C. In a hot climate there were no functional disturbances. Motivus and Pneupac 2 had few resonance frequencies during the vibration tests. Logic 07 had a very marked resonance frequency at 60 Hz, as well as in other ranges, which disturbed the ventilatory function since the vibration affected the ventilatory frequency regulator. All three ventilators functioned without any complaints after being subjected to vibration tests for at least 15 min at the observed resonance frequencies, or to shock tests. The results suggest that a through scrutiny should be carried out of the function of compact ventilators in various environments.

Hepatic and renal effects of low concentrations of methoxyflurane in exposed delivery ward personnel.

During five alternating three-week periods either methoxyflurane-nitrous oxide or nitrous oxide alone was used for obstetrical analgesia. Delivery ward personnel were followed by venous blood samples once a week. Analyses of blood urea nitrogen, serum uric acid, SGOT and SGPT showed significantly elevated levels three days after exposure to methoxyflurane. This study demonstrates the importance of the scavenging of anesthetic gases to reduce the exposure of personnel to inhalational agents used in delivery suites. Since definite alterations in the indices of both hepatic and renal functions were recognized in obstetrical personnel following exposure, a re-evaluation of the use of methoxyflurane for obstetrical analgesia is suggested.

A comparison of the analgesic effects of methoxyflurane-nitrous oxide and nitrous oxide alone during labour related to the Eysenck personality inventory test.

One hundred and thirty-three paturients who had received either methoxyflurane-nitrous oxide or nitrous oxide analgesia with or without pudendal block, underwent the Eysenck Personality Inventory Test on the second postpartum day and evaluated their memory of the pain (Subjectively Evaluated Pain Suffering Scores) during labor. Parturients who had received methoxyflurance-nitrous oxide analgesia reported significantly lower pain suffering than parturients who had had nitrous oxide analgesia. Subdivision according to Personality Inventory factors showed that at the introvert end of the Extroversion-Introversion scale, methoxyflurance-nitrous oxide analgesia with or without additional pudendal block resulted in significantly lower pain suffering than did not nitrous oxide analgesia. On the other hand, nitrous oxide analgesia without additional pudendal block gave significantly lower pain suffering at the extrovert end of the scale. Among the extroverts there was a tendency, though not statistically significant, towards non-approval of the pudendal block.

Fluoride concentrations in urine of delivery ward personnel following exposure to low concentrations of methoxyflurane.

Midwives and other delivery ward personnel exposed to methoxyflurane do not have measurable traces of the agent in expired air when examined soon after exposure. This may imply a rapid uptake of the anesthetic. If this is the case, then the products of the metabolism of methoxyflurane, such as fluoride, may appear in the urine of such personnel. The present study investigated urinary fluoride levels in 24 delivery ward personnel and compared the values found after methoxyflurane/nitrous oxide analgesia with those measured in the same individuals after exposure to nitrous oxide alone. A highly significant difference was observed. Thus it would appear that, in spite of an apparently adequate system of environmental ventilation, there is a significant uptake of methoxyflurane by delivery ward personnel when this agent is employed for obstetrical analgesia.

Pollution of delivery ward air by nitrous oxide--methoxyflurane.

Pollution of delivery ward atmosphere by analgesic gases and vapors has not been studied as extensively as pollution of operating theaters. This study shows that delivery room atmosphere is polluted by methoxyflurane (0.5--0.8 ppm) and nitrous oxide (300--540 ppm) and that a local gas exhaust system reduces the concentration by half.

Influence of methoxyflurane-nitrous oxide analgesia during childbirth on renal and hepatic function.

Blood urea content and the serum concentrations of sodium, creatinine, uric acid, glutamic oxaloacetic transaminase (g.o.t.), glutamic pyruvate transaminase (g.p.t.) and bilirubin were measured before delivery, on the 2nd and 3rd days and on the 5th day after delivery. In two groups of mothers, one receiving nitrous oxide analgesia and the other a combination of nitrous oxide and methoxyflurane, blood urea and serum sodium and g.o.t. were increased following labour and nitrous oxide analgesia; s.g.p.t. was increased only in the late post-partum period. Serum sodium, creatinine, uric acid, urea, g.o.t. and g.p.t. increased following exposure to methoxyflurance. The increase in serum sodium, uric acid and urea was dose-dependent. Capillary concentrations of uric acid in the neonates showed dose-dependent changes in response to methoxyflurane.

Changes in kidney and liver function after methoxyflurane (penthrane) anaesthesia.

Three groups of patients receiving methoxyflurane or halothane or pethidine after thiopentone suxamethonium induction were compared. Using multivariate Student t tests with simultaneous confidence intervals, significant differences in the test battery of uric acid, creatinine, blood urea nitrogen and sodium in the methoxyflurane series compared with the other series was found, indicating transient impaired kidney function. Likewise, there was a significant difference between the methoxyflurane and the other series in the s.g.p.t., s.g.o.t., alkaline phosphatase and bilirubin test battery, indicating impaired liver function. This was found after doses less than 16 ml which, so far, had been considered to be without any toxic effects.