Hypoxemic Episodes of Patients in a Postanesthesia Care Unit: Discussion

Hypoxemic episodes have been demonstrated to occur commonly in the immediate postoperative recovery period in both adult and pediatric patients breathing room air. In the present study with patients evaluated during prophylactic oxygen administration by aerosol face tent, desaturations occurred in a minimum 25 percent of patients. The large number of recorded desaturations excluded from the study suggest that this is the minimum number of hypoxemic episodes since true desaturations may have been occurring at the same time as poor pulse oximeter tracking. The high percentage of oximeter-perceived desaturations that could not be substantiated after review of the pulse amplitude tracings demonstrates the difficulty of documenting true desaturations with pulse oximetry in the acute postoperative situation when there are active changes in the patient s physical condition and movements, as well as nursing activity.
Causes of Postoperative Hypoxemia
Postoperative hypoxemia has been evaluated previously from multiple perspectives. The underlying pathophysiologic state of hypoxemia has been concluded to include the following: (1) inhomogeneity of pulmonary ventilation and perfusion; (2) decreased functional residual capacity, with increased closing volume; and (3) a postoperative increase in venoarterial shunting. Associated with this are decreased mixed venous oxygen saturation and decreased alveolar ventilation from either respiratory depression or blunted airway reflexes and upper airway obstruction. This study did not evaluate these possible physiologic disruptions as underlying causes for the hypoxemic episodes. Paresthesia
Narcotics can result in respiratory depression as well as decrease the ventilatory response to hypercap-nea and hypoxemia. However, in this study, narcotic dosages did not correlate with hypoxemia in this patient population.
Preventing and Treating Postoperative Hypoxemia
Oxygen therapy has become routine practice during PAR care. Because of this, Conway and Payne found that patients breathing oxygen 2 L/min by facemask increased their Sa02 from 88.98 ±4.88 percent to 94.30 ±4.89 percent; removing the face mask decreased Sa02 falling to 88.69 ±5.32 percent. All children studied by Tomkins et al responded to oxygen administration with improved Sa02. Only 1.6 percent of patients receiving oxygen at 2 L/min by nasal catheter, studied by Smith et al, desaturated. Hudes et al studied 161 ASA class 1 to 3 elective surgical patients and found that 21 percent had arrived in PAR with a Sa02 <90 percent (mean = 85.2 percent). Oxygen delivery at 4 L/min by nasal catheter and 40 percent oxygen administered at 8 L/min by Venturi mask both increased SaOz values to normal and desaturations were detected on only 1 of the 161 patients when saturation was measured again 15 min after admission. Desaturations correlated positively with age, weight, use of premedication, and use of positive pressure ventilation intraoperatively.

This entry was posted in Hypoxemic Episodes and tagged abdominal surgery, anesthesia, hypoxemia, oxygen saturation, postoperative hypoxemia.