NUTRITION & HYDRATION

HYDRATION: Bicarbonate diuresis in response to respiratory alkalosis as well as venous constriction with suppression of antidiuretic hormone and aldosterone are normal physiologic responses to ascent, and the resulting hemoconcentration can increase blood oxygen carrying capacity.3-4 These responses plus the lower humidity and the lower atmospheric pressure of higher altitude alpine environments predispose individuals to dehydration. Dehydration can be further exacerbated if patients are taking diuretic medications, such as acetazolamide. Signs and symptoms of dehydration can mimic those of AMS and HACE; however, dehydration itself has not been shown to increase the incidence of AMS.21,22 Thus, dehydration should be avoided and guided by thirst and appropriate urine output. Overhydration and forced hydration has not been shown to be helpful.7,23 Consider dehydration as a differential diagnosis or co-presentation when evaluating for AMS/HACE.

NUTRITION: Multiple studies have shown both men and women tend to reduce their energy intake after acute ascent to over 4,300m.24-26 Acute high-altitude exposure alone has been demonstrated to increase basal metabolic rate and energy demand by 30%.26 AMS can cause nausea, further exacerbating anorexia. One study showed that reduced calorie intake at altitude was independently associated with the presence of AMS symptoms.24 Data on any specific type of diet having a benefit in performance or decreasing incidence of HAI are mixed.28 Prolonged physical exertion at a caloric deficit will likely lead to performance deterioration. Considering the above, individuals should be encouraged to intentionally increase energy intake above sea-level when ascending to altitude; although the specific amount of caloric increase to optimize performance is likely determined by complex unique factors and there is not enough data to make a specific recommendation at this time.

IRON: Pulmonary hypertension from any cause is a strong risk factor for HAPE..4 Iron infusions in healthy adult males lowered pulmonary artery systolic pressures by 6 mmHg 3 days after moving from sea level to 4340m as well as a separate study showing decreased pulmonary vascular reactivity in acute hypoxia.29,30 Both those studies used one time dose of Iron Sucrose 200mg IV. Maximum oral iron absorption was shown to be limited at 25mg/day.31 A small single randomized, double-blinded, placebo-controlled study did show a lower rate of AMS with iron infusions at 24hrs of altitude exposure, but it did not reach significance (P = .097).21 Based on the above, consider screening personnel, especially those with a history of pulmonary arterial hypertension or HAPE, for iron deficiency prior to high altitude operations and treat iron deficiency with iron supplementation. Iron infusions are currently being studied at USAREIM at time of this CPG publication. Update required upon completion of their study.