Use of CPAP for Post-Operative Hypoxemia
Abstract & Commentary
Dean R. Hess, PhD, RRT, Respiratory Care, Massachusetts General Hospital, Department of Anesthesiology, Harvard Medical School, is Associate Editor for Criticall Care Alert.
Synopsis: CPAP may decrease the incidence of endotracheal intubation and other severe complications in patients who develop hypoxemia after elective major abdominal surgery.
Source: Squadrone V, et al. JAMA. 2005;293:589-595.
The objective of this study was to determine the effectiveness of continuous positive airway pressure (CPAP) compared with standard treatment in preventing the need for intubation and mechanical ventilation in patients who develop acute hypoxemia after elective major abdominal surgery. It was a randomized, controlled trial with concealed allocation conducted in 15 intensive care units in Italy. Patients who developed severe hypoxemia (PaO2/FIO2 300 mm Hg or less) after major elective abdominal surgery were enrolled. The trial was stopped for efficacy after 209 patients had been enrolled (n = 104 received oxygen and n = 105 received oxygen plus CPAP). The primary end point was incidence of endotracheal intubation. Secondary end points were intensive care unit and hospital lengths of stay, incidence of pneumonia, infection and sepsis, and hospital mortality.
Patients who received oxygen plus CPAP had a lower intubation rate (1% vs 10%; relative risk, 0.099; 95% CI, 0.01-0.76; P = 0.005) and had a lower occurrence rate of pneumonia (2% vs 10%; RR, 0.19; 95% CI, 0.04-0.88; P =.02), infection (3% vs 10%; RR, 0.27; 95% CI, 0.07-0.94; P = 0.03), and sepsis (2% vs 9%; RR, 0.22; 95% CI, 0.04-0.99; P = 0.03) than patients treated with oxygen alone. Patients who received oxygen plus CPAP spent fewer days in the intensive care unit (1.4, 1.6 vs 2.6, 4.2; P = 0.09) than patients treated with oxygen alone. Use of CPAP did not affect the time that patients spent in the hospital (15 ±13 days vs 17 ± 15 days, respectively; P = 0.10). None of those treated with oxygen plus CPAP died in the hospital and 3 deaths occurred among those treated with oxygen alone (P = 0.12). CPAP was applied for 19-22 hours and interrupted only when the oxygenation target for stopping treatment was reached (PaO2/FIO2 > 300).
COMMENT BY DEAN R. HESS, PhD, RRT
Recovery from abdominal surgery is usually uncomplicated, but postoperative hypoxemia complicates 30% to 50% of cases even in patients undergoing uneventful procedures. Oxygen therapy and deep breathing are effective in treating most cases of postoperative hypoxemia. However, respiratory failure may require endotracheal intubation and mechanical ventilation in 8% to 10% of patients.1 This is usually attributed to a loss of lung volume (atelectasis) but might also be due, in part, to pulmonary edema resulting from intraoperative fluid administration. With CPAP, the patient breathes spontaneously through a pressurized circuit that maintains a positive airway pressure. Although several studies have demonstrated the efficacy of CPAP to reduce atelectasis and improve oxygenation in patients after abdominal surgery,2-4 no clinical trials have confirmed that the improvement in oxygenation with CPAP results in a reduced need for intubation and mechanical ventilation in patients who develop hypoxemia after abdominal surgery.
This study demonstrates that early treatment with CPAP may reduce the need for intubation, the ICU length of stay and the incidence of pneumonia, infection, and sepsis in patients who develop acute hypoxemia after elective major abdominal surgery. In this study, 209/1322 (16%) of patients met criteria for enrollment in the study, suggesting that the use of CPAP in such patients may be indicated relatively frequently.
A helmet device was used as the interface to apply CPAP. This interface is not available in the United States and, moreover, has recently been shown to be associated with the potential for carbon dioxide rebreathing.5 In the United States, respiratory therapists and physicians are more familiar with using a face mask (nasal or oronasal) to apply CPAP and noninvasive ventilation.6
The results of this study should not be extrapolated to all patients with acute hypoxemic respiratory failure. In a study of 123 patients with hypoxemia from diverse etiologies, Delclaux et al7 reported no difference in intubation rate or hospital mortality between patients receiving CPAP or oxygen therapy alone. Moreover, they reported a higher number of adverse events occurred in patients receiving CPAP. Thus, although the current study reports benefit for CPAP in patients developing hypoxemia after abdominal surgery, the results may not apply to other patient populations.
The mechanism whereby CPAP was beneficial in this study is unclear and was not examined in the study design. Squadrone and associates speculate that the CPAP improved the impairment in ventilation-perfusion ratio due to atelectasis caused by recumbent position, high oxygen concentration, temporary diaphragmatic dysfunction, impairment of pulmonary secretion clearance, and pain. However, it is also possible that CPAP improved hypoxemia secondary to pulmonary edema resulting from intra-operative fluid administration. It is well known that CPAP is effective in patients with acute cardiogenic pulmonary edema.8,9 Regardless of the mechanism, this well designed study provides evidence to support the use of CPAP in patients who develop hypoxemia following major abdominal surgery.
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9. Park M, et al. Crit Care Med. 2004;32:2407.