A transportable hyperbaric chamber with soda lime for the treatment of high-altitude disorders

Transcription

1 Journal ofwilderness Medicine, 5, (1994) ORIGINAL ARTICLE A transportable hyperbaric chamber with soda lime for the treatment of high-altitude disorders SHIGERU SAITO, MDI* HITOSHI SHIMADA, MDI and KINICHI YAMAMORF IDepartment ofanesthesiology and Reanimatology, Gunma University School ofmedicine, Maebashi, Japan, 2Himalayan Association ofjapan A transportable hyperbaric chamber called the GamoWffil bag has been reported to be effective in the treatment of high-altitude disorders in the alpine field. The problem with this device is that the operator has to endure a considerable amount of physical exercise -to prevent carbon dioxide accumulation in the bag and to supplement the consumed oxygen. To solve this problem, we have applied soda lime with a respiratory circuit. In preliminary experiments, pumping twice per minute was demonstrated to be sufficient to maintain the appropriate internal conditions of the bag for 90 min. Using this system, the amount of exercise by the operator could be reduced to approximately 10% of the original value. Following the experiments, this system was practically used in the treatment of high-altitude disorders at Mustagata and at Mt. Crown (Xinjang, China). Three patients with acute mountain sickness were successfully treated using this system. Considering further possible applications, this compact system is thought to be worthwhile to carry together with the Gamow bag in alpine expeditions. Key words: altitude illness, hyperbaric chamber, GamoWffil bag, soda lime, respiratory circuit Introduction High-altitude illness is commonly observed in people who ascend to altitudes above 2500 m without acclimatization. Although several sophisticated studies in the field and in experimental hypobaric chambers have suggested the possible pathophysiology of this disorder, the precise underlying mechanisms are not fully understood, and the absolute protocol for treatment is not yet established [1]. Oxygen supplementation and several medications have been proposed for effective treatment or for prophylaxis, but prompt descent is the most often recommended treatment. However, in the alpine setting, environmental factors such as weather and avalanche frequently make evacuation infeasible. Therefore, a transportable hyperbaric chamber is an effective and useful piece of equipment in such a severe environment [2]. Some groups have already reported the effectiveness of such equipment in clinical practice. Kasic et al. demonstrated that simulated descent in a fabric hyperbaric chamber (Gamow@J bag) is as effective as oxygen therapy for the immediate relief of acute mountain sickness [3]. The most serious problem with this device is that the operating staff has to undertake a considerable amount of physical work to maintain the appropriate internal conditions. Initial inflation of the bag *Address for correspondence: Department of Anesthesiology and Reanimatology, Gunma University School of Medicine, , Showa-machi, Maebashi, 371, Japan Chapman & Hall

2 296 Saito, Shimada and Yamamori requires the most heavy exercise but that can be accomplished in a few minutes. The trouble is that throughout the stay of a patient in the bag, attendants have to attend to the ventilation of the bag. According to data supplied by Gamow et at. to prevent accumulation of carbon dioxide, the operator has to depress the foot pump times per minute [2]. Considering that the therapy has to be continued for several hours in a severe case [4,5], this work is thought to be too heavy to be maintained at high altitude, especially in the case where the number of team members is small. To solve this problem, Gamow suggested the use of a "bladder mode" or "LiOH CO 2 scrubber" in his first report [2]. However, these instruments are not easy to obtain, especially outside the United States. Therefore, we tried to use soda lime, which is the most commonly used carbon dioxide absorber in operation units, with a respiratory circuit. This material is commercially available all over the world and the safety of this technique has been fully established due to the long history of usage in surgical anesthesia [6]. Assessment o(the performance of the respiratory circuit with soda lime in the Gamowbag Prior to clinical trials in the mountain field, the performance of soda lime and the usefulness of the respiratory circuit were assessed using human volunteers at sea level. The oxygen supplementation mode, which completely liberated the operator from pumping exercise, was also tested with the respiratory circuit. Materials and methods Following the approval by the local human ethics committee and informed consent, two healthy volunteers were studied. The subjects were placed in the Gamow@> bag (Du Pont Inc., Wilmington, DE) and breathed through a face mask and respiratory circuit which was equipped with a soda lime canister (Fig. la). The face mask was designed to fit to the face tightly by rubber strap and all of the expired air was drained into the soda lime canister Disp-COrSORB (Dryden Corp., Indianapolis, IN) used in the circuit without leakage. A pulse oximeter Pulsox-5 (Minolta Inc., Tokyo) and CO 2 meter, N-1000 (Nelcor Corp., Hayward CA), which could function with a battery power supply was attached to the subject's finger and to the inhalation hose (Fig. 1), respectively. Prior to the experiment, the CO 2 meter was calibrated according to the instruction manual. After the initial inflation to 2 psi, the bag was ventilated twice per minute with the foot pump, and throughout the experiment the arterial hemoglobin saturation and the CO 2 partial pressure of the inhaled air were monitored by the attending operator through the transparent window of the bag. Verbal communication between the subject and the operator was possible, even though speaking through the face mask made the words slightly difficult to understand. In the oxygen supplementation mode, oxygen was supplied from the compressed oxygen cylinder through a pressure regulator while ventilation of the bag by the foot pump was completely omitted. Other experimental procedures were the same as those described for the above case (Fig. IB).

3 Hyperbaric chamber with soda lime la) 297 Soda lime Canister Valve Air Inlet-;i Expiratory limb (8) Mask Oxygen Inlet '\ Inspiratory limb "'" Expiratory limb * Mask Fig. 1. (A) Respiratory circuit with soda lime and without oxygen supplementation. (B) Semiclosed respiratory circuit with soda lime and oxygen supplementation. The mask is closely fitted to the face by a rubber strap. The asterisk in the figure indicates the location where the COz concentration was measured. Results The COz partial pressure of the inhaled air was kept below detectable levels throughout the experiment while the arterial blood oxygen saturation value measured by pulse oximeter (SpOz) was maintained at a satisfactory level either with or without oxygen supplementation (Fig. 2). During the experiments, the subjects could respire through the face mask and the respiratory circuit without any difficulties. However, in the case of the oxygen supplementation mode, the subject complained about the coldness of the oxygen cylinder, which was located at his side. Case reports Case 1 A 35-year-old male climber suffered from a severe headache and peripheral edema in the face and lower extremities at 6500 m on Muztagata (Xinjiang Uygur, China). At the time, he had been above 4000 m for more than 10 days, but he was stricken just after his arrival at 6500 m. Following advice from the expedition leader, he descended to the base camp at 4300 m by foot. However, even after descent, the headache and the general fatigue

4 298 Saito, Shimada and Yamamori 90 Sp02 (%) Sp02 & C02 partial pressure in the Gamow bag 100 '\, IIJ IIJ o 80 "0 IIJ IIJ o IIJ 40 o 0 ; re~(iir:\iory drcuil with ~ lime (without oxreen cylinder) : semicloscd fc.'tpir.tlory circuli (with oxygen cylinder) o Time (minute) 30 C02 partial 20 pressure (mmhg) Fig. 2. CO2partial pressure of inhaled air and arterial blood oxygen saturation value measured by pulse oximeter (Sp02)' The open circles indicate CO2partial pressure ofinhaled air measured at the inlet side of the respiratory circuit presented in Fig. IA. Closed circles indicate those measured at the inlet side of the respiratory circuit presented in Fig. lb. Open squares indicate arterial blood oxygen saturation value measured by pulse oximeter for the subject respiring through the IA system in the GamoWffil bag, with closed squares indicating values for the subject respiring through the IB system. CO2partial pressures were below detectable levels throughout the experiments continued. His face ballooned because of severe edema, and he suffered from a slight cough. The pulse oximeter indicated that 74% of his arterial hemoglobin was saturated, a low value at this altitude. No rales were ausculated in his lungs. His condition was diagnosed as acute mountain sickness and suspected early high-altitude pulmonary edema. He was treated in the Gamow@l bag with the respiratory circuit and soda lime. The treatment in the bag was continued for 1 h without any trouble or discomfort. During his stay in the bag, an attending member ventilated the bag once or twice per minute by foot pump. About 5 min after entering the bag, the Sp02 value started to increase from the initial value, and after 30 min in the bag, the value was 85. At the end of the therapy, the Fig.3. A member preparing the respiratory circuit with soda lime (Fig. IB). The mask is fitted to the face by a rubber strap and the oxygen cylinder (which is not present in this photograph) is attached to the inlet channel of the canister.

5 Hyperbaric chamber with soda lime 299 value was 93 and he was completely cured of the headache, although the peripheral edema was not much improved. Even after decompression, no rebound effects were observed, and his SpOz value was maintained above 90. Within the 3-days at base camp, his peripheral edema improved and he returned to expedition activities as a member of the peak attack team. Case 2 A 33-year-old male had headache and insomnia at 4000 m on Mt. Crown (Xinjiang, China) after severe porter work between the camps. He had a fair appetite and was free from the symptoms suggesting high-altitude pulmonary edema. At his request, he was treated in the Gamow J bag with the respiratory circuit and soda lime for 45 min. Before the therapy, SpOz was shown to be 88% by pulse oximeter, and during therapy in the bag, the value increased to 95. After decompression, the value decreased from the maximum value to 91, but this level was maintained even 60 min after the treatment. His headache was ameliorated, and that night he slept sufficiently. During therapy in the bag, an attending member ventilated the bag twice per minute. With this amount of exercise, the operater was not exhausted, even at this high altitude. Case 3 A 36-year-old male suffered from general fatigue and severe peripheral edema in the face and extremities at 4000 m on Mt. Crown after severe porter work between camps. He lost his appetite and felt a slight headache. Cyanosis was also observed in the fingertips and lips; however, cough and dyspnea were absent. On ausculation, his lungs were shown to be almost normal and his SpOz value was 84%, slightly lower than the average value at this altitude. The patient was placed in the Gamow J bag for 45 min, respiring through the respiratory circuit with soda lime as a carbon dioxide absorber. During the treatment, the bag was ventilated twice per minute by another member of the climbing team. The operating member made no complaint about pumping for the ventilation. In the compressed bag, the maximum value of the SpOz of the patient was 97, and after the decompression the value decreased to 92. Sixty minutes after this therapy, the value was maintained between 90 and 92. After therapy, his general condition was moderately improved and the anorexia was ameliorated. Peripheral cyanosis was almost completely extinguished after this therapy; however, to improve the peripheral edema, administration of furosemide was necessary. Discussion After Gamow's first report in 1990 [2], several reports described the usefulness of this equipment as a therapy for high-altitude illnesses [3-5]. However, in those studies, this equipment was used in large teams, which had many members as operators. Recently, most expedition teams for high-altitude climbing consist of small numbers of members. At a high-altitude camp in particular, the members ofa party might only number two or three. Furthermore, in these conditions in which some of the members suffer from high-altitude sickness, the other members might not be completely healthy. Considering this situation, the rescue work with the Gamow J bag, which requires vigorous exercise, might not be useful as primary care for high-altitude illnesses. Although a private company started a rental service for this equipment to expedition teams in Japan, most of the expedition

6 300 Saito, Shimada and Yamamori teams hesitate to employ the equipment because of this potential factor. Therefore, some assisting device which reduces the large amount ofenergy expended in pumping is thought to be indispensable. The semiclosed respiratory circuit with soda lime is very commonly used in operation units and in intensive care units in hospitals all over the world. The disposable version of this system is very compact and weighs less than 1 kg. The performance and the safety of this equipment has been established [6,7]. One gram of soda lime can absorb ml (BTPS) of carbon dioxide at sea level. Therefore, 650 g of soda lime, which is packed in a disposable type of soda lime pack, can absorb the CO2 which is exhaled from a normal adult human for more than 10 h [8]. As expected from theoretical calculations, we did not observe any CO2accumulation in our experiments. In addition, within the duration of our experiments and clinical applications, oxygen consumption in the bag was thought to be compensated mostly by pumping twice per minute, namely, by the ventilation of 6 liters min-1, because the Sp02 values of the patients were maintained at a high level throughout their stay in the bag. With this system, the operator energy expenditure can be reduced to approximately 10% ofthat without the device. In our case, the operators never complained when pumping twice per minute. If an oxygen cylinder is attached to this system, the operator is totally free from the energy intensive exercise, even though carrying the oxygen cylinder requires considerable work (Fig. IB). Considering that most of the textbooks recommend minimization of physical work at high altitudes to prevent high-altitude disorders, this energy conservation must be extremely beneficial for the expedition party [1]. In this study, only a few and mild cases were examined; therefore, relatively short-time therapies by the GamoW bag were effective. Taber demonstrated that a min treatment was effective to resolve the symptoms of acute mountain sickness, and that with regard to high-altitude pulmonary edema and high-altitude cerebral edema, 4-6 h of treatment were beneficial [4]. Although we did not encounter a severe case which necessitated several hours in the bag, the energy-conserving system with soda lime may be especially useful on such an occasion. Further clinical experiences are required to establish a reliable treatment protocol for variable cases of high-altitude disorders. The precautionswhich should be noted in the use ofthis device are as follows: (1) If the mask is not fitted to the face and if the exhaled air does not flow into the soda lime canister, CO2may accumulate in the bag. (2) In the case where this system is used for a long and continuous period of time, oxygen supplementation by an oxygen cylinder or replacement ofthe inside air by intermittent large-volume ventilation might be necessary to prevent a decrease in oxygen concentration in the bag. (3) Some patients may note the respiration through the vinyl or the rubber mask to be uncomfortable. (4) For unconscious patients who cannot maintain their own airways, special care is necessary to keep the airway open with an artificial airway device, such as laryngeal mask or endotracheal tube. To obtain effective usage ofthis equipment and to avoid potential risks, it is recommended that trained staff use the system. In this report, we have only discussed use of the equipment for high-altitude disorders; however, further applications are now under consideration. In the field of emergency medicine, victims of carbon monoxide intoxication or of air embolization have been

7 Hyperbaric chamber with soda lime 301 treated by hyperbaric oxygen in the hospital [9]. Considering the fully accepted effectiveness of this therapy in these cases, the immediate application of this therapy using this transportable hyperbaric chamber is thought to be promising. In the near future, a more potent transportable hyperbaric chamber will be introduced into the clinical field as medical equipment for such cases. The CO 2 absorbing system which we applied in this study may also be useful in the new version ofthe bag. Acknowledgment We dedicate this paper to the memory of Mr Yuji Futamata, who cooperated fully in our study and was a victim of the avalanche at Mt. Crown. May his soul rest in peace. References 1. Ward, M.P., Milledge, J.S. and West, J.B., eds. High Altitude Medicine and Physiology. London: Chapman and Hall, Gamow, R.I., Geer, G.D., Kasic, J.F. and Smith, H.M. Methods ofgas-balance control to be used with a portable hyperbaric chamber in the treatment of high altitude illness. J Wilderness Med 1990; 1, Kasic, J.F., Yaron, M., Nicholas, R.A., Lickteig, J.A. and Roach, R. Treatment of acute mountain sickness: hyperbaric versus oxygen therapy.ann Emerg Med 1991; 20, Taber, R.L. Protocols for the use of a portable hyperbaric chamber for the treatment of high altitude disorders. J Wilderness Med 1990; 1, King, S.J. and Greenlee, R.R. Successful use of the Gamow hyperbaric bag in the treatment of altitude illness at Mount Everest. J Wilderness Med 1990; 1, Adriani, J. and Rovenstine, E.A. Experimental studies on carbon dioxide absorbers for anesthesia.anesthesiology 1941; 2, Brown, E.S. The activity and surface area of fresh soda lime. Anesthesiology 1957; 19, Andrews, J.J. Inhaled anesthetic delivery systems. In: Miller, R.D., ed. Anesthesia, 3rd ed. New York: Churchill Livingstone Inc, 1990: Jain, K.K. and Fischer, B., eds. Oxygen in Physiology and Medicine. Springfield, IL: Charles C Thomas, 1989.