Factors associated with unanticipated day of surgery deaths in Department of Veterans Affairs hospitals.

BACKGROUND: Patients of ASA physical status 1, 2, and 3 undergoing elective surgery do not have underlying conditions that are a constant threat to life, and hence should not be expected to be at significant risk for death on the day of surgery. METHODS: We analyzed 815,077 ASA physical status 1, 2, and 3 elective surgery patients in the Department of Veterans Affairs National Surgical Quality Improvement Program database to identify patients who died on the day of surgery. We then attempted to identify factors predictive of unexpected death and to identify potential areas for improvement in care. A subset of the cases underwent individual chart review as well to identify areas for improvement in anesthesia care. RESULTS: Of the total patients, 0.08% died on the day of surgery. The strongest predictive factor by multiple variable regression was the type of surgery, with aortic surgery resulting in an odds ratio of 13.67, (95% CI 9.76-19.17). Other factors predictive of death were identified by multiple variable regressions and included low albumin, existence of dyspnea, and elevated bilirubin or creatinine. Chart reviews of 88 of the deaths found that opportunities for improved anesthesia care were present in 13 of the 88. We estimated that a death that might have been prevented by improved anesthesia care occurred in approximately 1/13,900 cases. Myocardial infarction and hemorrhage were frequently identified factors. An unexpected factor was that the period between the conclusion of surgery and the final transfer of care in recovery was a time when many of the deaths occurred. CONCLUSIONS: We conclude that, although patient and surgical factors lead to the vast majority of deaths on the day of surgery, there are identifiable areas for reducing the incidence of such deaths by improvements in anesthesia care.

Carbon dioxide added late in inspiration reduces ventilation-perfusion heterogeneity without causing respiratory acidosis.

We have shown previously that inspired CO2 (3-5%) improves ventilation-perfusion (Va/Q) matching but with the consequence of mild arterial hypercapnia and respiratory acidosis. We hypothesized that adding CO2 only late in inspiration to limit its effects to the conducting airways would enhance Va/Q matching and improve oxygenation without arterial hypercapnia. CO2 was added in the latter half of inspiration in a volume aimed to reach a concentration of 5% in the conducting airways throughout the respiratory cycle. Ten mixed-breed dogs were anesthetized and, in a randomized order, ventilated with room air, 5% CO2 throughout inspiration, and CO2 added only to the latter half of inspiration. The multiple inert-gas elimination technique was used to assess Va/Q heterogeneity. Late-inspired CO2 produced only very small changes in arterial pH (7.38 vs. 7.40) and arterial CO2 (40.6 vs. 39.4 Torr). Compared with baseline, late-inspired CO2 significantly improved arterial oxygenation (97.5 vs. 94.2 Torr), decreased the alveolar-arterial Po2 difference (10.4 vs. 15.7 Torr) and decreased the multiple inert-gas elimination technique-derived arterial-alveolar inert gas area difference, a global measurement of Va/Q heterogeneity (0.36 vs. 0.22). These changes were equal to those with 5% CO2 throughout inspiration (arterial Po2, 102.5 Torr; alveolar-arterial Po2 difference, 10.1 Torr; and arterial-alveolar inert gas area difference, 0.21). In conclusion, we have established that the majority of the improvement in gas exchange efficiency with inspired CO2 can be achieved by limiting its application to the conducting airways and does not require systemic acidosis.

Effects of perfluorohexane vapor on relative blood flow distribution in an animal model of surfactant-depleted lung injury.

OBJECTIVE: To test the hypothesis that treatment with vaporized perfluorocarbon affects the relative pulmonary blood flow distribution in an animal model of surfactant-depleted acute lung injury. DESIGN: Prospective, randomized, controlled trial. SETTING: A university research laboratory. SUBJECTS: Fourteen New Zealand White rabbits (weighing 3.0-4.5 kg). INTERVENTIONS: The animals were ventilated with an FIO(2) of 1.0 before induction of acute lung injury. Acute lung injury was induced by repeated saline lung lavages. Eight rabbits were randomized to 60 mins of treatment with an inspiratory perfluorohexane vapor concentration of 0.2 in oxygen. To compensate for the reduced FIO(2) during perfluorohexane treatment, FIO(2) was reduced to 0.8 in control animals. Change in relative pulmonary blood flow distribution was assessed by using fluorescent-labeled microspheres. MEASUREMENTS AND MAIN RESULTS: Microsphere data showed a redistribution of relative pulmonary blood flow attributable to depletion of surfactant. Relative pulmonary blood flow shifted from areas that were initially high-flow to areas that were initially low-flow. During the study period, relative pulmonary blood flow of high-flow areas decreased further in the control group, whereas it increased in the treatment group. This difference was statistically significant between the groups (p =.02) as well as in the treatment group compared with the initial injury (p =.03). Shunt increased in both groups over time (control group, 30% +/- 10% to 63% +/- 20%; treatment group, 37% +/- 20% to 49% +/- 23%), but the changes compared with injury were significantly less in the treatment group (p =.03). CONCLUSION: Short treatment with perfluorohexane vapor partially reversed the shift of relative pulmonary blood flow from high-flow to low-flow areas attributable to surfactant depletion.