KEY POINTS

1. HBO exposure (breathing oxygen at increased ambient pressure, typically 2 to 3 ATA) causes an increase in arterial and tissue PO₂ and no significant change in arterial pH or PCO₂ .

---

2695

2. During HBO therapy, cardiac output is reduced, systemic vascular resistance is increased, and pulmonary vascular resistance is decreased.
3. Acute illnesses for which HBO is indicated include carbon monoxide poisoning (based on randomized, controlled studies), gas bubble disease (gas embolism and decompression sickness), and soft tissue necrotizing infections (the latter two based on clinical experience and meta-analysis).
4. The decision to use HBO to treat a patient with arterial gas embolism or decompression sickness should be based on clinical criteria, including the presence of symptoms, abnormal physical examination, or a history of arterial gas embolism within a few hours, even in the absence of symptoms. Neither neurophysiologic testing nor radiographic imaging are useful except, rarely, to exclude other pathologies.
5. The decision to use HBO to treat a patient with carbon monoxide poisoning should be based on clinical criteria, including a history of impaired consciousness or other neurologic manifestations, pregnancy, or severe exposure (e.g., HbCO >25%). The HbCO level is generally useful only to make the diagnosis; it correlates poorly with the severity of the illness.
6. Oxygen-induced seizures are rare and self-limited. Appropriate management includes discontinuation of inhaled oxygen. Chamber pressure should not be altered during the seizure. Decompression can result in pulmonary barotrauma.
7. The principles of treatment of acute altitude illness include descent and supplemental oxygen. If these options are not available, dexamethasone and acetazolamide are recommended for acute mountain sickness or high-altitude cerebral edema; for high-altitude pulmonary edema, drugs that lower pulmonary artery pressure, such as nifedipine, are recommended.
8. When providing anesthesia for otherwise healthy acclimatized patients at altitude, supplemental oxygen should be used only to maintain arterial oxygen saturation at baseline (not normal levels). Liberal administration of oxygen may reverse acclimatization.
9. As ambient pressure is altered, anesthetic vaporizers deliver a variable concentration but fixed partial pressure. Therefore, it is not necessary to adjust vaporizer settings when delivering anesthesia in a hyperbaric chamber or at altitude.
10. The physiologic changes that may accompany neuraxial or general anesthesia during or after space flight are poorly understood. Extreme attention to cardiovascular parameters is warranted.