Anesthesia at altitude and in the hyperbaric chamber
Stem
A 29-year-old woman, 61 kg, visiting from sea level for a ski trip, needs open reduction and internal fixation of a tibial plateau fracture at a mountain hospital at 2,900 m (9,500 ft). She arrived two days ago and has a headache and poor sleep. SpO2 is 90% on room air, heart rate 104. The anesthesia workstation has sevoflurane and desflurane vaporizers and a rotameter backup flowmeter.
Question
What does the altitude change about your anesthetic?
Ideal answer
HeadlineLess oxygen and lower partial pressures: I favor a spinal, give oxygen throughout, and dose volatile agent by effect, not by the dial's percentage.
- Spinal with light sedation, because it keeps her breathing spontaneously and works well at altitude.1
- Supplemental oxygen from start to discharge, at least 30% inspired above 5,000 ft and 40% above 10,000 ft.1
- If general: sevoflurane as dialed; desflurane dialed higher, because the desflurane vaporizer holds fraction, not partial pressure: sea-level % × 760/barometric pressure, about ×1.4 here.1
- No nitrous oxide, because it loses potency and takes the place of oxygen.1
- Careful with fluids and opioids, given her risk of pulmonary edema and hypoventilation.1
Watch for: depth on processed EEG, and a gas analyzer reading low until recalibrated.
Breaking down the answer
- The physiology — alveolar oxygen falls about 20% at 5,500 ft and 40% at 11,800 ft; her headache and poor sleep after two days suggest she is still acclimatizing.1
- Flow and analyzers — rotameter bobbins rise less in thin gas, so delivered flow is about 1% higher than displayed per 1,000 ft (~10% here); fixed Venturi masks deliver more oxygen than labeled.1
- MAC as a percentage misleads — in one study more than half of patients were deep by BIS at standard MAC values.1 Changes if: no processed EEG, then I titrate to clinical signs and use partial-pressure thinking.
- Ketamine and blocks — ketamine with caution if high-altitude pulmonary edema is a risk; brachial plexus and stellate blocks threaten the phrenic nerve, and a high neuraxial block impairs breathing.1
- Blood — altitude adds hypercoagulability, so thromboprophylaxis matters after a leg fracture.1
- Any remote site is a NORA site — the ASA requires reliable oxygen with a backup full E cylinder, suction, scavenging, a self-inflating bag delivering at least 90%, capnography, emergency power, battery lighting, a defibrillator cart and two-way communication.2
Follow-up question
A different patient: an intubated 40-year-old man with carbon monoxide poisoning, carboxyhemoglobin 32% and a period of unconsciousness, is to be treated in a multiplace hyperbaric chamber, and you will accompany him. What do you prepare?
Follow-up answer
HeadlineEvery gas space shrinks and re-expands with pressure; I fix each one before we go down.
I replace the cuff air with saline, and ENT places tympanostomy tubes because he cannot equalize his own ears.3 Any pneumothorax is drained first, onto Heimlich valves.3 I cap unneeded lines, vent gas-filled bags, bring only a chamber-rated ventilator and pumps, recalibrate transducers at depth and check delivered volume with a spirometer.3 Fire is the chamber's lethal hazard, so electrical devices and defibrillation follow chamber rules. An oxygen-toxicity seizure, 1–4 per 10,000 treatments, means cutting inspired oxygen at the same pressure, never decompressing mid-seizure.3
Pitfalls that cost points
- Taking an implanted pump or epidural pain pump into the chamber without the manufacturer's pressure limits.4
- Missing prior bleomycin, doxorubicin or cisplatin: relative contraindications that change the risk of hyperbaric oxygen.4
Rapid-fire
Q: What is the absolute contraindication to hyperbaric oxygen? A: Untreated pneumothorax, which can become tension on decompression; treat it with a chest tube first.4
Q: What is the most common complication? A: Middle ear barotrauma; patients learn autoinsufflation, and tympanostomy tubes are placed if that fails.3
Q: What defines hyperbaric oxygen therapy? A: 100% oxygen at 1.4 atmospheres absolute or more.4
Q: Above what altitude is nitrous oxide largely ineffective? A: About 10,000 ft (3,048 m); it is only partly effective at 5,000 ft.1
Q: Is active cancer a contraindication to hyperbaric oxygen? A: No.4
Numbers to know
| Item | Value |
|---|---|
| Alveolar oxygen fall | ~20% at 5,500 ft; ~40% at 11,800 ft1 |
| Minimum inspired oxygen | 30% above 5,000 ft; 40% above 10,000 ft1 |
| Rotameter error | Delivered ~1% above displayed per 1,000 ft1 |
| Desflurane dial | Sea-level % × 760/barometric pressure (~×1.4 at 2,900 m), since the dial holds fraction1 |
| NORA backup oxygen | At least a full E cylinder2 |
| Hyperbaric definition | ≥1.4 ATA with 100% oxygen4 |
| Oxygen-toxicity seizures | 1–4 per 10,000 treatments3 |
Links
- Anesthesia in MRI and remote locations, Methemoglobinemia and carbon monoxide, Volatile agents and nitrous oxide: when and when not, Anesthesia machine checkout and intraoperative failures, Spinal anesthesia: dosing, spread, hypotension
- ASA Statement on Nonoperating Room Anesthesia Services (amended 2023)
Sources
- 1.Anesthetic Management at High Altitude · OpenAnesthesia, 2026 · openanesthesia.orgLast updated 02/17/2026.
- 2.Statement on Nonoperating Room Anesthesia Services · ASA, 2023 · asahq.orgLast amended October 18, 2023.
- 3.Hyperbaric oxygen · Life in the Fast Lane (Critical Care Compendium) · litfl.com
- 4.Hyperbaric Oxygen Therapy Contraindications · StatPearls (NCBI Bookshelf), 2025 · ncbi.nlm.nih.govGawdi R, Yrastorza J, Cooper JS. Last update May 27, 2025.
Facts on this page were checked against these sources on Oct 22, 2026. Guidelines change; confirm doses against current institutional protocols.