Patients with a history of neck surgery should be warned of their potentially limited capacity to acclimatize and should ascend with caution.5,132 The drugs most commonly used to treat or prevent altitude-related illness are acetazolamide,133,134 nifedipine,133–136 and dexamethasone.133,134,137 Salmeterol,133,138 sildenafil,139,140 and tadalafil138 are occasionally used in the treatment and prevention Trametinib of HAPE. Patients with preexisting medical conditions or those who are taking other medications may have fewer medication options or elevated risk of experiencing adverse drug reactions. Luks and Swenson provide an excellent review of these issues, the main points

of which are summarized in Table 3.17 Tissot and colleagues found that patients taking warfarin were 2.7 times more likely to have a subtherapeutic international normalized ratio (INR) following ascent to altitude greater than 2,400 m. This risk is doubled in patients with atrial fibrillation. Thus, INR should be monitored closely following altitude travel to facilitate Palbociclib order early detection and compensation for subtherapeutic INR values. In patients with atrial fibrillation, it would be prudent to measure INR after arrival at altitude if this is practicable.141 Warfarin dosing and monitoring may be hindered by extended periods of remote travel, alterations in eating habits, travel-related illness, and physical exertion. Although it comes with the added inconvenience

of carrying and disposing of injection paraphernalia, low molecular weight Tangeritin heparin should be considered in patients where adherence to a warfarin regime is not practical but stable anticoagulation is critical. An additional, albeit expensive, option is a portable INR monitor which a suitably trained patient could use in conjunction with a nomogram for adjusting warfarin doses.121 Cortisol demands will increase in response to the hypobaric hypoxia at altitude. Patients taking glucocorticosteroids should

adjust their dose accordingly. It is recommended that the maintenance dose be doubled at altitudes above 3,000 m and tripled above 4,000 m. Supplemental injectable corticosteroids should also be available for administration in case of unexplained deterioration.142 Medications with a narrow therapeutic index that require toxicity monitoring (eg, lithium and certain anticonvulsant drugs) pose an additional limitation to prolonged remote travel at altitude. Passive ascent to altitude may result in sudden exposure to altitude without adequate time for acclimatization. This rapid change poses an additional physiologic challenge to people with compromised health and affects the safety of some medical devices. Cabin pressure in commercial aircraft is regulated at barometric pressures equivalent to altitudes between 1,500 and 2,500 m. In patients with reduced partial pressure of arterial oxygen at sea level, blood oxygen saturation can fall drastically at normal cabin pressures.