At 8,100 feet, Vail Valley is nestled in the Colorado Rocky Mountains and draws millions of visitors a year. Recently, one of them, a 37-year-old man, walked into the local ED complaining of frothy cough, fatigue, and dyspnea. The patient had arrived three days earlier from sea level and immediately hit the ski slopes.
But after two days, he developed a dry cough and shortness of breath that did not improve with rest. His symptoms worsened until he couldn't sleep. Physical examination revealed tachypnea, tachycardia, and a room air pulse oximetry reading of 65%, but no jugular venous distention or lower-extremity edema. Auscultation and chest X-rays revealed diffuse wet crackles without wheezing through all lung fields and diffuse alveolar infiltrates.
This was a classic case of high-altitude pulmonary edema (HAPE), a noncardiogenic form that occurs when lowlanders rapidly ascend to high altitudes and exercise vigorously without allowing time to acclimate.
HAPE is only one of the conditions and factors that distinguish high-altitude hospital medicine from practice at sea level. Hospitalists working up high have learned the fine points of when to worry and take action and when to accept the normal responses of the human body to increased elevation.
As is typical in HAPE, the patient improved dramatically after about 36 hours of supplemental oxygen with a non-rebreather mask and twice-daily extended-release nifedipine (30 mg) to lessen his pulmonary hypertension, said Jamie Gray, MD, ACP Member, who has practiced hospital medicine at Vail Valley Medical Center for the past 11 years.
HAPE can send patients to the hospital even if they are young and healthy, without underlying cardiopulmonary disease, said Dr. Gray. While HAPE can resemble pneumonia, affected patients usually have oxygen saturation, pulmonary exam, and chest X-ray results that are “far out of proportion to their clinical picture,” she added. “I become very suspicious of HAPE in the two- to five-day window after arrival to altitude. A repeat chest X-ray at 24 hours showing near resolution of the infiltrates with oxygen and nifedipine confirms the diagnosis.”
Acute altitude-related illnesses tend to begin as a constellation of nonspecific signs and symptoms including headache, dizziness, gastrointestinal upset, fatigue, and sleep disturbances. Together, these are called acute mountain sickness. A rapid rate of ascent is the most important risk factor for this condition, explained Nicholas Kanaan, MD, an emergency medicine physician at the University of Utah in Salt Lake City (elevation 4,200 feet).
Travelers to high regions can help prevent acute mountain sickness by not ascending more than 1,500 feet in 24 hours, added Dr. Kanaan, who has worked in Nepal near Everest Base Camp and completed a wilderness medicine fellowship that focuses on high-altitude illnesses. “It can take an entire week to properly acclimatize to 15,000-feet elevation,” he emphasized. “Do not ascend any further if you start feeling symptoms of altitude illness.”
Individuals who don't follow this advice risk having their acute mountain sickness progress to HAPE or its relative, high-altitude cerebral edema (HACE), as in the case of a young Japanese ski racer whose nonspecific symptoms progressed until she reported intermittent troubles with vision. Imaging showed cerebral edema classic for HACE, said Mark A. Norden, MD, ACP Member, a hospitalist at St. Anthony Summit Medical Center in Frisco, Colo. (elevation 9,100 feet).
“Descent to lower altitude resolved her symptoms,” said Dr. Norden, noting that he and his colleagues also treat HAPE at least weekly. Most patients improve with high-flow oxygen, but many remain “very hypoxic after initial treatment and need to descend to a Denver-area hospital at lower altitude,” he added.
High altitude has been linked to other neurologic and visual conditions, including seizures, syncope, stroke, retinal hemorrhages, retinopathy, and ultraviolet keratitis, Dr. Kanaan said. Respiratory effects include pharyngitis, bronchitis, and periodic breathing, a type of central sleep apnea that affects even healthy individuals who sleep above 6,000 feet. At these altitudes, relative hypoxia triggers tachypnea, which in turn lowers blood levels of carbon dioxide and induces apnea. Treatment with acetazolamide helps stimulate breathing by inducing metabolic acidosis through increased renal excretion of bicarbonate, Dr. Kanaan explained.
In addition to its effects on healthy people, high altitude can significantly worsen chronic conditions. In a study of nearly 650 patients with moderate to severe obstructive sleep apnea, periodic breathing at altitudes of 4,500 to 7,000 feet approximately quadrupled the hourly number of apneic events and substantially complicated titration of positive airway pressure therapy, investigators reported in the December 2011 Journal of Clinical Sleep Medicine.
“At higher elevations, diseases related to sleep apnea, such as right-sided heart failure and pulmonary hypertension, are more common, have more significant sequelae on the body, and are more likely to be refractory to therapy. This makes managing them more challenging,” said Jacob Imber, MD, an assistant professor in the department of internal medicine at the University of New Mexico in Albuquerque (elevation 5,300 feet).
Dr. Gray offered the example of a patient with stable New York Heart Association Stage II congestive heart failure or minimally symptomatic chronic obstructive pulmonary disease at sea level traveling to 8,100 feet. “Within 48 hours, they are likely to end up in the hospital with worsening of their chronic condition,” she said. Likewise, a patient who has rate-controlled atrial fibrillation at sea level but travels to high altitude might end up hospitalized after developing atrial fibrillation with rapid ventricular response, she added.
Hospitalists who work at altitude need to be extra-vigilant about oxygen supplementation for patients with chronic obstructive pulmonary disease, interstitial lung disease, pulmonary hypertension, and obstructive sleep apnea, Dr. Imber added. He often sees patients who descend to Albuquerque from the mountains of New Mexico for treatment, he said. “It's very important to ask where your patient lives to understand how elevation may affect their illness. The amount of oxygen they require to maintain oxygenation during their hospital stay may be inadequate when they return home.”
Even patients with occult pulmonary disease who can maintain adequate oxygen saturation when breathing room air at sea level might not be able to do so at altitude, experts noted. In one case, a heavy smoker from Louisiana was hospitalized in Albuquerque with diverticulitis, said Dr. Imber. The patient had no pulmonary symptoms but needed nasal cannula oxygen therapy to maintain adequate oxygenation. As a commercial trucker, he was not allowed to use a supplemental oxygen tank on the job. He asked to be discharged without a tank. Dr. Imber agreed but recommended that the patient follow up with his primary care physician back home.
The lower effective oxygen percentage at altitude also can trigger sickle-cell crises, experts said. Dr. Imber described a young woman from Florida who rarely had sickle-cell crises at home but experienced three such exacerbations during her first four months at the University of New Mexico. “Her options were 24-hour oxygen supplementation—this did not appeal to her—or to transfer to a lower elevation,” he said.
Elevation does not directly affect medication efficacy but can alter treatment, even when hospital patients “live high” year-round. “At altitude, the air is drier and the effects of the sun are intensified by a thinner atmosphere,” said Dr. Kanaan. “As a result, the body experiences more insensible fluid loss, and people can become more profoundly dehydrated.”
Patients can be dehydrated without having tachycardia or ketonuria, Dr. Kanaan noted. Therefore, hospitalists who work at altitude are especially careful to assess hydration status and use IV fluids when indicated. “If you have access to an ultrasound machine, evaluating the inferior vena cava before and after passive leg raise will help guide how fluid-responsive patients may be,” he said.
Another consideration is that stable acclimatized patients often can be discharged without supplemental oxygen even if their oxygen saturation is somewhat low, said Daniel A. Kovnat, MD, FACP, a hospitalist at Christus St. Vincent Medical Center in Santa Fe, N.M. (elevation 7,200 feet). “It is not unusual for these patients to be doing well with an oxygen saturation of 88% or 89%,” he said.
These residents of high-altitude areas may have lower blood bicarbonate levels and lower pH on arterial blood gases, indicating an appropriate renal response to low-level chronic respiratory alkalosis resulting from mild hyperventilation, Dr. Kovnat noted. If their anion gap is normal, hospitalists should avoid overdiagnosing and overtreating renal tubular acidosis in patients with vague symptoms or slight abnormalities on blood chemistry, he said.
Conversely, however, long-term residents can develop acute mountain sickness or even HAPE after returning from a long trip to sea level. “I myself had a version of this after I came back to Santa Fe after an extended time at sea level,” said Dr. Kovnat. “Soon after flying in, I went for an aggressive mountain bike ride, only to find myself vomiting on the side of the trail, sick from the high altitude.” Likewise, Dr. Gray has treated severe HAPE in a patient who grew up in Vail and returned after attending college at sea level.
All these cases illustrate complexities that the experts said they often learned on the job. “I knew nothing about practicing medicine at altitude when I first moved to this hospital, but the learning curve was quick,” Dr. Gray noted. Some conferences focus on altitude medicine, as do many research articles and other opportunities for self-study, she said. “Generally, there is a wealth of information in the medical community that has been treating patients at altitude for decades.”