The effect of an intensive care unit staffing model on tidal volume in patients with acute lung injury

Abstract

Introduction: Little is known about the mechanisms through which intensivist physician staffing influences patient outcomes. We aimed to assess the effect of closed-model intensive care on evidence-based ventilatory practice in patients with acute lung injury (ALI).

Methods: We conducted a secondary analysis of a prospective population-based cohort of 759 patients with ALI who were alive and ventilated on day three of ALI, and were cared for in 23 intensive care units (ICUs) in King County, Washington.

Results: We compared day three tidal volume (VT) in open versus closed ICUs adjusting for potential patient and ICU confounders. In 13 closed model ICUs, 429 (63%) patients were cared for. Adjusted mean VT (mL/Kg predicted body weight (PBW) or measured body weight if height not recorded) for patients in closed ICUs was 1.40 mL/Kg PBW (95% confidence interval (CI) = 0.57 to 2.24 mL/Kg PBW) lower than patients in open model ICUs. Patients in closed ICUs were more likely (odds ratio (OR) = 2.23, 95% CI = 1.09 to 4.56) to receive lower VT (<or= 6.5 mL/Kg PBW) and were less likely (OR = 0.30, 95% CI = 0.17 to 0.55) to receive a potentially injurious VT (>or= 12 mL/Kg PBW) compared with patients cared for in open ICUs, independent of other covariates. The effect of closed ICUs on hospital mortality was not changed after accounting for delivered VT.

Conclusions: Patients with ALI cared for in closed model ICUs are more likely to receive lower VT and less likely to receive higher VT, but there were no other differences in measured processes of care. Moreover, the difference in delivered VT did not completely account for the improved mortality observed in closed model ICUs.

Figure 1

Cohort flowchart. ALI = acute lung injury; ICU = intensive care unit.

Figure 2

Sensitivity analysis for regression model of the effect of closed ICU on the odds of delivery of higher (≥ 12 mL/Kg predicted body weight (PBW), left panel) and lower (≤ 6.5 mL/Kg PBW, right panel) tidal volumes. Each covariate was sequentially added to the baseline model indicated in Table 3. Each point represents the odds ration (OR; closed versus open) after the addition of the covariate listed. Left of the dotted line indicates lower likelihood of the outcome for closed versus open ICU. Right of the dotted line indicates greater likelihood of the outcome.