Hypoxia and pulmonary acclimatisation at 4578 m. altitude: the role of acetazolamide and dexamethasone

To quantify the changes in ventilatory response and arterial blood gases in healthy male volunteers on acute ascent to 4578 meters altitude alongwith evaluating the role of acetazolamide and dexamethasone prophylaxis in acclimatisation. Forty four lowlander male subjects participated as two groups in the study. Twenty four lowlander healthy male adults [age mean + SE 27.8 + 1.24 years] comprised the non-acclimatised group. They were sub grouped in a double blind fashion into four. Each subgroup [n=6] received placebo [multivitamin] or acetazolamide [250 mg] or dexamethasone [4mg] or combined regimen of the two drugs twice daily for 5 days commencing 24 hours before ascent. The volunteers reached the altitude of 4578 meters within a span of one day. The second group [acclimatised] comprised of age and height matched twenty volunteers who had arrived 4 and 8 weeks earlier at the same altitude. Arterial PO2, PCO2, SO2 and minute respiratory rate pH were measured. The pulmonary functions [FVC,%FEV1 PEF, FE25-75% and MVV] were recorded by Compact Spirometer [Vitalograph]. Pre and post ascent measurements were carried out in non-acclimatised group whereas one measurement of the same parameters were made in acclimatised group. The study revealed a significant increase in respiratory rate min-1 after 24 hours of ascent alongwith reduction in PaO2 and SaO2. The gradual increase in PaO2 and SaO2 and reduction in PaCO2 was observed after 4 weeks at the same altitude. The reduction in FVC,%FEV1, PEF, FEF25-75% and MVV were recorded in our subjects after 24 hours of acute ascent. Nevertheless, all pulmonary parameters in volunteers having 8 weeks of stay at 4578 m altitude, were found equivalent to the non-acclimatised group. The greater increase in minute respiratory rate, PaO2, SaO2 and pulmonary functions was found in volunteers taking acetazolamide. It is concluded that hyperventilation and increase in lung volumes are the adaptive pulmonary responses which help in improving levels of PaO2 and SaO2. The acetazolamide-dexamethasone prophylaxis appears beneficial in promoting pulmonary acclimatisation during hypobaric hypoxia

Acute mountain sickness score and hypoxemia

Hypoxemia is the immediate consequence of hyobaric hypoxia, which is the crucial starting mechanism of acute mountain sickness [AMS]. The AMS is generally a benign and self-limiting condition which can be prevented by gradual ascent. However, ascent rates recommended for prophylaxis of AMS are far slower than those attempted during military operations and by climbers. The current study was carried out to quantify the relationship between AMS and hypoxemia alongwith evaluating the benefits of acetazolamide-dexamethasone chemoprophylaxis during acute ascent. Twenty-four low lander male adults [age mean +/- SE 27.8 +/- 1.24 years] were selected. They were grouped in a double-blind fashion into four groups and each group [n = 6] received placebo [multivitamin] or acetazolamide [250 mg] or dexamethasone [4 mg] or a combined regimen of the two drugs twice daily for 5 days, commencing 24 hours before ascent. The volunteers reached the altitude of 4578 meters within a span of one day. Their AMS symptoms were recorded on modified environmental symptoms questionnaire [ESQ], after 24 and 72 hours of ascent. Arterial PO2, SO2 and PCO2 were measured by GEMSTAT blood-gas analyzer [Mallincrodt-USA]. The ESQ, AMS-C [cerebral] and AMS-R [respiratory] scores of combined therapy group were significantly lower as compared to the other groups on the symptom rating scale. The significant finding amongst the volunteers taking acetazolamide was mild to moderate diuresis whereas severity of headache was markedly less in dexamethasone group. The commonest feature of combined therapy was that none of the volunteers complained of headache, dysponea, irritability and more than mild disturbance of sleep. The ESQ scores of volunteers were inversely correlated to PaO2 and SaO2 after 24 hours of ascent to 4578 meters. The study concludes that severity of AMS is closely related to hypoxemia and combination therapy of acetazolamide-dexamethasone may be effective in preventing AMS