Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + INTRODUCTION Download Section PDF Listen +++ ++ Pharmacology. Oxygen is a necessary oxidant to drive biochemical reactions. Room air contains 21% oxygen. Hyperbaric oxygen (HBO), which is 100% oxygen delivered to the patient in a pressurized chamber at 2–3 atm of pressure, may be beneficial for patients with severe carbon monoxide (CO) poisoning. It can hasten the reversal of CO binding to hemoglobin and intracellular myoglobin and provide oxygen independently of hemoglobin, and it may have protective actions in reducing postischemic brain damage. Randomized controlled studies have reported conflicting outcomes with HBO treatment, but there may be a marginal benefit in preventing subtle neuropsychiatric sequelae. Indications Supplemental oxygen is indicated when normal oxygenation is impaired because of pulmonary injury, which may result from aspiration (chemical pneumonitis) or inhalation of toxic gases. The PO2 should be maintained at 70–80 mm Hg or higher if possible. Supplemental oxygen usually is given empirically to patients with altered mental status or suspected hypoxemia. Oxygen (100%) is indicated for patients with carbon monoxide poisoning to increase the conversion of carboxyhemoglobin and carboxymyoglobin to hemoglobin and myoglobin, respectively, and to increase the oxygen saturation of the plasma and subsequent delivery to tissues. Hyperbaric oxygen may be beneficial for patients with severe carbon monoxide poisoning, although the clinical evidence is mixed. Potential indications include history of a loss of consciousness, metabolic acidosis, age more than 36 years, pregnancy, carboxyhemoglobin level greater than 25%, and cerebellar dysfunction (eg, ataxia; see Table II-20). Hyperbaric oxygen has also been advocated for the treatment of poisoning with carbon tetrachloride, cyanide, and hydrogen sulfide and for severe methemoglobinemia, but the experimental and clinical evidence is scanty. Contraindications In paraquat poisoning, oxygen may contribute to lung injury. In fact, slightly hypoxic environments (10-12% oxygen) have been advocated to reduce the risk for pulmonary fibrosis from paraquat (see Paraquat and Diquat). Relative contraindications to hyperbaric oxygen therapy include a history of recent middle ear or thoracic surgery, untreated pneumothorax, seizure disorder, and severe sinusitis. Adverse effects. Caution: Oxygen is extremely flammable. Prolonged high concentrations of oxygen are associated with pulmonary alveolar tissue damage. In general, the fraction of inspired oxygen (FIO2) should not be maintained at greater than 80% for more than 24 hours. Oxygen therapy may increase the risk for retrolental fibroplasia in neonates. Administration of oxygen at high concentrations to patients with severe chronic obstructive pulmonary disease and chronic carbon dioxide retention who are dependent on hypoxemia to provide a drive to breathe may result in respiratory arrest. Hyperbaric oxygen treatment can cause hyperoxic seizures, aural trauma (ruptured tympanic membrane), and acute anxiety resulting from claustrophobia. Seizures are more likely at higher atmospheric pressures (eg, ≥3 atm). Oxygen may potentiate toxicity via enhanced generation of free radicals with some chemotherapeutic agents (eg, bleomycin, Adriamycin, and daunorubicin). Use in pregnancy. No known adverse effects. Drug or laboratory interactions. None known. Dosage and method of administration Supplemental oxygen. Provide supplemental oxygen to maintain a PO2 of at least 70–80 mm Hg. If a PO2 above 50 mm Hg cannot be maintained with an FIO2 of at least 60%, consider positive end-expiratory pressure or continuous positive airway pressure. Carbon monoxide poisoning. Provide 100% oxygen by tight-fitting mask or via endotracheal tube. Consider hyperbaric oxygen therapy if the patient has serious poisoning (see "Indications" above) and can be treated within 6 hours of the exposure. Consult with a poison center (1-800-222-1222) or a hyperbaric specialist to determine the location of the nearest HBO facility. Usually, three HBO treatments at 2.5–3 atm are recommended over a 24-hour period. Formulations Nasal cannula. Provides 24-40% oxygen, depending on the flow rate and patient's breathing pattern. Ventimask. Provides variable inspired oxygen concentrations from 24 to 40%. Nonrebreathing reservoir mask. Provides inspired oxygen concentrations of 60-90%. Hyperbaric oxygen. One hundred percent oxygen can be delivered at a pressure of 2–3 atm.