Episode 27: Wilderness medicine with Ross Hofmeyr

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Management of an alpine medicine scene including discussion of HAPE (High Altitude Pulmonary Edema), HACE (High Altitude Cerebral Edema), and suspension syndrome, with Dr. Ross Hofmeyr (@rosshofmeyr), anesthesiologist in the Department of Anaesthesia and Perioperative Medicine at the University of Cape Town, as well as cofounder and medical director of WildMedix, the oldest wilderness medicine support group in South Africa.

Takeaway lessons

1. Scene safety comes first, which in a high-altitude setting includes consideration for the acclimatization of your team.
2. Other than ABCs, think WMX:
   1. W= Factors of the Wilderness environment, such as altitude and exposure.
   2. M= Materials and Manpower; what’s needed for the rescue and what’s available?
   3. X= Exit strategy; from the start, think about how (and how rapidly) you’re getting out.
3. Spinal stabilization is not feasible until a suspended patient can reach a stable location.
4. Suspension syndrome (aka harness suspension syndrome, harness hang syndrome, suspension trauma) is a phenomenon of reduced venous return due to immobility while suspended in a vertical position (exacerbated by, although not requiring, a restrictive harness). Similar orthostasis can occur in healthy individuals forced to stand upright and immobile (at parade rest) without active muscle pumps, except they will then fall and self-reperfuse. In suspended patients, cardiac arrest can occur during suspension due to loss of preload, and further instability can occur after flow is restored due to a crush-syndrome-like reperfusion phenomenon with cold, acidotic blood. A hanging patient may be temporized by lifting their legs to a more horizontal position.
5. Lowering a suspended patient is always easier than lifting them.
6. If possible, consider deferring intubation in very austere settings, unless you realistically have the equipment, manpower, and space to transport a sedated, apneic patient while continuously ventilating them.
7. Optic nerve sheath ultrasound can be a big diagnostic aid for ruling in cerebral edema in the setting of HACE or head trauma. A diameter >9–10 mm is suspicious for elevated ICP, >15 mm is a reliable rule-in, 6–9 mm is unclear. Differences between the two sides are concerning.
8. The first treatment for any altitude sickness is oxygen; the second is descent. Everything else is temporizing or supportive.
9. HACE is part of the spectrum of acute mountain sickness, and is caused by increased hydrostatic pressure and capillary permeability, leading to vasogenic edema. It tends to be caused by hypobaric hypoxemia, causing an afferent–efferent imbalance in cerebral vasculature.
10. HAPE is caused by hypoxic pulmonary vasoconstriction and perhaps increased vascular permeability. It can cause severe hemorrhagic pulmonary edema.
11. Give dexamethasone 8 mg IV (IM is okay too) for suspected HACE. No mannitol. Hypertonic saline can be considered but is poorly studied, and probably not smart while still far from help.
    1. Portable hyperbaric chambers can provide a substantial relative decrease in a patient’s altitude (the difference is more dramatic at higher altitudes), useful for temporization when immediate descent is impossible. However, they are bulky and completely envelope the patient, limiting further access for care. Provide other measures first, pressurize them therapeutically, then generally remove them from the bulky device for transport.
12. Acetazolamide may help accelerate the acclimatization process, but can only do so much, and has no role in treating acute mountain sickness.
13. >5,000 ft (1,500 m) or so is considered “high altitude” (some purists call 1,500–2,500 m/5,000–8,200 ft “intermediate altitude”). However, true altitude illness usually occurs above 3,500 m (11,500 ft), aka “very high altitude,” as above this level, it becomes impossible to hyperventilate enough to normalize alveolar oxygen concentration (PAO2).
14. Above this level (~10,000 ft), gradual acclimatization is recommended. Sleeping altitude should only increase by about 500 m (1500–2000 ft) per day, and every second day should be a rest day.