Incidence and Operative Factors Associated With Discretional Postoperative Mechanical Ventilation After General Surgery.

BACKGROUND: Mechanical ventilation after general surgery is associated with worse outcomes, prolonged hospital stay, and increased health care cost. Postoperatively, patients admitted to the intensive care unit (ICU) may be categorized into 1 of 3 groups: extubated patients (EXT), patients with objective medical indications to remain ventilated (MED), and patients not meeting these criteria, called "discretional postoperative mechanical ventilation" (DPMV). The objectives of this study were to determine the incidence of DPMV in general surgery patients and identify the associated operative factors.

METHODS: At a large, tertiary medical center, we reviewed all surgical cases performed under general anesthesia from April 1, 2008 to February 28, 2015 and admitted to the ICU postoperatively. Patients were categorized into 1 of 3 cohorts: EXT, MED, or DPMV. Operative factors related to the American Society of Anesthesiologists Physical Status (ASA PS), duration of surgery, surgery end time, difficult airway management, intraoperative blood and fluid administration, vasopressor infusions, intraoperative arterial blood gasses, and ventilation data were collected. Additionally, anesthesia records were reviewed for notes indicating a reason or rationale for postoperative ventilation. Categorical variables were compared by χ test, and continuous variables by analysis of variance or Kruskal-Wallis H test. Categorical variables are presented as n (%), and continuous variables as mean ± standard deviation or median (interquartile range) as appropriate. Significance level was set at P≤ .05.

RESULTS: Sixteen percent of the 3555 patients were categorized as DPMV and 12.2% as MED. Compared to EXT patients, those classified as DPMV had received significantly less fluid (2757 ± 2728 mL vs 3868 ± 1885 mL; P < .001), lost less blood during surgery (150 [20-625] mL vs 300 [150-600] mL; P< .001), underwent a shorter surgery (199 ± 215 minutes vs 276 ± 143 minutes; P< .001), but received more blood products, 900 (600-1800) mL vs 600 (300-900) mL. The DPMV group had more patients with high ASA PS (ASA III-V) than the EXT group: 508 (90.4%) vs 1934 (75.6%); P< .001. Emergency surgery (ASA E modifier) was more common in the DPMV group than the EXT group: 145 (25.8%) vs 306 (12%), P< .001, respectively. Surgery end after regular working hours was not significantly higher with DPMV status compared to EXT. DPMV cohort had fewer cases with difficult airway when compared to EXT or MED. When compared to MED patients, those classified as DPMV received less fluid (2757 ± 2728 mL vs 4499 ± 2830 mL; P< .001), lost less blood (150 [20-625] mL vs 500 [200-1350] mL; P < .001), but did not differ in blood products transfused or duration of surgery.

CONCLUSIONS: In our tertiary medical center, patients often admitted to the ICU on mechanical ventilation without an objective medical indication. When compared to patients admitted to the ICU extubated, those mechanically ventilated but without an objective indication had a higher ASA PS class and were more likely to have an ASA E modifier. A surgery end time after regular working hours or difficult airway management was not associated with higher incidence of DPMV.