Support of Arterial Oxygenation

For circumstances in which patients who may otherwise be severely hypoxemic, such as cyanotic heart disease, HBO has been used to provide a margin of safety during anesthesia. Smith^[142] reported 45 cases of surgical correction of cyanotic heart disease in children operated on under HBO. Although most of these patients had a PaO₂ around 25 mm Hg or less while breathing 100% O₂ at 1 ATA, PaO₂ values increased to 50 mm Hg or greater in most patients at ambient pressures up to 4 ATA. Halothane anesthesia was used in most cases. No complications were reported, and it was concluded that HBO was useful to maintain PaO₂ in these critically ill infants. There was no evidence that increased concentrations of anesthetic were required to maintain anesthesia at the pressures used.

Li and coauthors^[143] reported a series of 48 cases of open heart surgery performed under HBO at 3 ATA with intravenous fentanyl anesthesia. In several of the patients, the blood Hb concentration could be safely reduced by phlebotomy to 3 to 4 g/dL during HBO. The authors pointed out that a major advantage of this technique is a reduction in transfusion requirements.

HBO has been reported to be a safe and effective method of supporting arterial oxygenation during therapeutic lung lavage performed under general anesthesia with one-lung ventilation.^{[48] [49]} In our experience of over 50 procedures, arterial oxygenation was satisfactorily maintained with no resulting complications ( Fig. 70-4 ). A reversible simulation of pulmonary gas exchange during the lavage procedure can be provided by temporarily ventilating the lung to be lavaged with 5% to 6% O₂ . Such ventilation reduces PAO₂ in that lung to approximately the level of mixed venous PO₂ , thereby confining O₂ exchange to the contralateral lung. If during a 5-minute period of unilateral hypoxic ventilation the patient's arterial Hb O₂ saturation drops below 90%, it is unlikely that lavage can be performed at 1 ATA without some technique to provide supplemental oxygenation (e.g., hyperbaric support).

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Figure 70-4 PaO₂ during unilateral lung lavage under hyperbaric conditions in eight patients. The open circles represent measured PaO₂ at various ambient pressures (abscissa). Solid circles represent the predicted PaO₂ at 1 ATA, calculated on the assumption of a constant PaO₂ /PAO₂ ratio.^[64] It can be seen that six of the eight patients would have had PaO₂ values less than 50 mm Hg had the procedure been performed at atmospheric pressure.