ACUTE MOUNTAIN SICKNESS (AMS)

GENERAL APPROACH TO AMS

During the mission planning phase, prioritize risk mitigation strategies. While at altitude, continue to reassess for AMS, considering differentials that may mimic AMS. Untreated AMS increases risk of HACE, whether AMS is diagnosed or not. Mild AMS can be treated in place with constant monitoring and re-evaluation. Higher risk AMS should be evacuated to lower altitude with repeat evaluations. Use pharmaceuticals and adjuncts listed above if the operational environment prevents rapid evacuation. More severe disease will require more aggressive therapy. There is an extreme risk to forces if AMS increases and or left untreated. Commanders should consider prophylaxis treatment, acclimatization, and if needed aggressive treatment.

#### Acute Mountain Sickness Diagnosis Criteria

at altitude (2500M or higher) Headache plus at least one of these:

- Weakness/lightheadedness
- Nausea/vomiting
- Anorexia
- Fatigue

AMS EVALUATION

AMS typically presents within 1-6 hours of altitude exposure although delayed presentations can occur at up to 48 hours. This is a clinical diagnosis of a syndrome consisting of headache, in addition to one or more additional symptoms including: lassitude/ fatigue/ weakness, nausea/ vomiting, anorexia, fatigue, and dizziness/ lightheadedness. Physical exam findings are nonspecific. See Appendix A for a scoring scale that can help with trending severity.32 AMS generally does not occur below an altitude of 2000m. When diagnosing AMS, consider ruling out other differentials with similar presentations: dehydration, head trauma, caffeine withdrawal, migraine, alcohol hangover (veisalgia), carbon monoxide poisoning, viral syndrome, emotional stress, hyperthermia, and hypothermia.

AMS PREVENTION

Mission planning, pre-acclimatization strategy, nutrition, and hydration are discussed above and will mitigate incidence and severity of AMS. If the aforementioned risk mitigation approaches cannot be implemented due to mission constraints, consider pharmacologic therapy as described below.

Acetazolamide: There is strong evidence for the use of acetazolamide in preventing all HAI, including AMS. Reports on exercise performance deterioration at altitude secondary to acetazolamide are mixed, some reporting mild impairment and others reporting no change. A 2020 study done by the U.S. Army Research Institute of Environmental Medicine has shown no detrimental effect from acetazolamide at altitude.33 The benefits of avoiding AMS and decreasing the likelihood of progression to HACE outweigh the risks of unlikely minor depression in exertional capacity.33 For individuals with moderate to high risk of AMS, the recommended adult dose is 125 mg oral every 12 hours, and the pediatric dose is 1.25 mg/kg every 12 hours (max 125 mg/dose). Individuals should begin taking acetazolamide 24 hours prior to high altitude exposure and continue for 2 days at stable altitude if the rate of ascent was < 500m per day. If the rate of ascent was > 500m per day, then continue acetazolamide for 4 days once at stable maximum altitude. If symptoms of AMS return after acetazolamide has been stopped, then it can be restarted for an additional 2-4 days. Acetazolamide can be discontinued once steady descent has been initiated. (Luks AM, 2019, Davis C, 2020) For small units making rapid ascent to altitudes >3500 with high risk of HAI and expectations of immediate execution of specialized tasks, increase the dosage of acetazolamide to 250 mg orally every 12 hours beginning 24 hours prior to exposure.34

Dexamethasone: There is strong evidence for the use of dexamethasone in preventing AMS.17,34-35 However, given its significant side effect profile (ex. adrenal suppression) and ability to mask AMS symptoms without aiding in acclimatization it should be considered only as second line to acetazolamide, and/ or reserved as a treatment of severe AMS. It can also be used in addition to acetazolamide for otherwise unavoidable missions with a very high risk of AMS. For those at moderate to high risk of AMS, the recommended dose of dexamethasone is 4 mg orally every 12 hours starting the day of ascent and continuing until at a stable altitude for 2 days. Higher doses may be required by some individuals and units at very high-risk for AMS; increase dosing to 4 mg every 6 hours. If dexamethasone is used for greater than 10 days, consider a 7-day taper. There is no recommendation for use of dexamethasone for AMS in the pediatric population. 3-4,17

AMS TREATMENT

Descent: This is the first line and the definitive treatment of nearly all HAI. Symptoms of AMS will typically resolve after descent of 300 - 1000 m from altitude of symptom onset. With increasing severity more urgent descent is advised. (See Appendix A.) With isolated AMS without progression to HACE or HAPE, individuals can be treated with arrest of ascent and rest at their current altitude for 1-2 days. Ascent may be resumed, at a rate no greater than 500m per day, once the individual is asymptomatic.

Oxygen: Oxygen is beneficial, titrate to SpO2>90%. Hypoxia reaches a peak during sleep; if possible, provide low flow oxygen (<2 L/min) by mask or nasal cannula during sleep to treat and prevent progression of AMS.3,17 The logistics of carrying large amounts of oxygen are generally not feasible in the operational environment, thus oxygen should be reserved for severe AMS, HACE, and HAPE cases as an adjunctive therapy pending evacuation.

Portable hyperbaric chambers: Strong evidence exists for the effectiveness of portable hyperbaric chambers (PHCs) in treating severe HAI.3,17,36 If immediate descent is not an option, individuals with severe AMS and at risk of progression to HACE should be treated with a PHC per the chamber’s protocol. Descent and evacuation should be a priority for these individuals and the PHC should be viewed as a temporary stopgap.

Acetazolamide: Acetazolamide can be given to treat AMS in adults at a dose of 250 mg orally every 12 hours. In pediatrics, the dosing is 2.5 mg/kg orally every 12 hours (max 250 mg/dose).17 In severe AMS, it should be used as an adjunct to dexamethasone.

Dexamethasone: There is strong evidence for the treatment of AMS with dexamethasone.3,17 Dexamethasone should be given to individuals with severe AMS as well as moderate AMS who are at risk of progression towards HACE if descent is not an option. Although giving dexamethasone can improve symptoms of AMS, continuing altitude exposure can cause disease progression. Dosing for AMS treatment is 4mg every 6 hours until asymptomatic.17

If Dexamethasone is utilized for treatment of AMS, it should be limited to only a few doses and the individual should not ascend again until asymptomatic off dexamethasone for at least 48 Hours.

Ibuprofen/Acetaminophen: Ibuprofen and acetaminophen can be used to treat headache symptoms of AMS at their usual dosing for headache therapy.