Multicenter Evaluation of a Novel Surveillance Definition for Complications of Mechanical Ventilation

Background: Surveillance for ventilator-associated pneumonia (VAP) is time consuming, subjective, inaccurate, and inconsistently predicts patients’ outcomes. Shifting the emphasis of surveillance from pneumonia in particular to complications of mechanical ventilation in general has many advantages including a) circumventing the inaccuracy of clinical signs to diagnose VAP, b) facilitating an objective surveillance definition that can be easily applied using electronically collectible data, and c) emphasizing the importance of preventing all complications of mechanical ventilation rather than pneumonia alone.

Objective:   To evaluate a novel surveillance paradigm for complications of mechanical ventilation based upon unexpected increases in patients’ ventilator settings after a period of stable ventilator support.

Methods:   We defined a ventilator-associated complication (VAC) as an increase in a patient’s daily minimum positive-end-expiratory pressure by 2.5cm H₂O or fraction of inspired oxygen by 15 points, occurring after ≥48 hours of stable or decreasing ventilator settings, and persisting for ≥48 hours. We retrospectively applied this definition to randomly selected medical and surgical patients in three large hospitals: each hospital included 100 patients ventilated 2-7 days and 100 patients ventilated for >7 days.  All patients were also assessed by infection preventionists for VAP using the CDC surveillance definition. We compared patients’ length-of-stay on the ventilator, in the intensive care unit, and in hospital using the Wilcoxon signed rank test and hospital mortality using Fisher’s exact test to determine how well each definition predicted patients’ outcomes.

Results:   Data were available for 597 patients. Median durations of mechanical ventilation, length-of-stay in the ICU, and length-of-stay in the hospital are summarized below for patients meeting criteria for VAC and CDC criteria for VAP.  Differences in length-of-stay for patients defined by either method were highly significant (P<.0001) but only VAC was significantly associated with hospital mortality. 

 

	VAC+	VAC-	P	VAP+	VAP-	P
Number of patients	136	461	--	56	541	--
Duration of ventilation(median days)	13	6	<.0001	13.5	7	<.0001
ICU length-of-stay(median days)	16.3	8	<.0001	18	9	<.0001
Hospital length-of-stay(median days)	21	16	<.0001	24.6	17	<.0001
Hospital mortality (% of pts)	38%	23%	.0005	27%	26%	NS

Conclusions:   A simple, rapid, objective, and electronically collectible surveillance definition predicted patient outcomes for ventilated patients more robustly than the conventional suveillance definition for VAP:  both methods distinguished between patients with long and short lengths of stay but only the novel method predicted hospital mortality.