Pressure-targeted modes of ventilation and acute respiratory distress syndrome are associated with higher above-target tidal volumes
CCCF ePoster library. Khan Y. Oct 3, 2017; 198194; 50
Dr. Yasin Khan
Dr. Yasin Khan
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Abstract
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Pressure-targeted modes of ventilation and acute respiratory distress syndrome are associated with higher above-target tidal volumes

Khan, Yasin1; McKown, Andrew2; Semler, Matthew2; Rice, Todd2; deBoisblanc, Bennett3; Janz, David3



1Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada; 2Division of Allergy, Pulmonary & Critical Care Medicine, Vanderbilt University, Nashville, TN, USA; 3Section of Pulmonary/Critical Care & Allergy/Immunology, Louisiana State University, New Orleans, LA, USA


Introduction
 
Lung protective ventilation is a life saving intervention in acute respiratory distress syndrome (ARDS). Lung protective tidal volumes (VT) can be achieved by using volume-targeted modes or by adjusting the driving pressure on pressure-targeted modes. However, the actual VT delivered to a patient may be affected by both the mode of ventilation and by patient-ventilator interactions. It is unknown which modes better achieve desired VT and avoid potentially injurious above-target VT. The impact of ARDS on the ability of different ventilator modes to deliver desired VT and avoid above-target VT is also unknown.
 
Objectives
 
To determine the association between ventilator mode and the delivery of above-target VT, and to determine how ARDS influences this association.
 
Methods
 
We performed a prospective, single-centre, observational cohort study of all invasively ventilated patients admitted to two intensive care units during a 30-day period. The level of sedation, the ventilator settings, and fifty consecutive exhaled VT (VTe) were recorded once daily for each patient. Patients were ventilated with modes of the provider’s choosing. Patients on spontaneous breathing trials were excluded. For volume-targeted modes (assist control [AC], assist control-volume control plus [ACVC+], synchronized intermittent mandatory ventilation [SIMV]), the target VT was that which was set on the ventilator. For pressure-targeted modes (pressure support [PS], proportional assist ventilation [PAV], bilevel, pressure control [PC]), the target VT was obtained from the provider’s orders. Above-target VT was calculated as VTe normalized for predicted body weight (PBW) minus the target VT normalized for PBW. Patients with ARDS were identified by retrospective review of medical records using the Berlin Definition. 
 
Results
 
A total of 68 patients contributed 220 ventilator-days and 11,000 VTe. Volume-targeted modes included AC (n=46), ACVC+ (n=7) and SIMV (n=3). Pressure-targeted modes included PS (n=7), bilevel (n=4), PAV (n=2) and PC (n=1). There were no differences in baseline characteristics, admitting ICU service, APACHE II or SOFA scores between the volume-targeted and pressure-targeted groups. Among all patients, volume-targeted modes were associated with lower, above-target VTe (median 0.36 cc/kg of PBW above set VT, IQR 0.2 - 0.87) compared with pressure-targeted modes (1.24 cc/kg PBW, 0.51 - 2.83, p = <0.001) (Figures 1 & 2). Thirty-two patients had a diagnosis of ARDS, and contributed 85 ventilator-days. For patients ventilated with volume-targeted modes, ARDS diagnosis was associated with higher above-target VTe (0.45 cc/kg PBW, 0.24 - 1.08) compared to no ARDS (0.3 cc/kg PBW, 0.17 - 0.72, p = <0.001). Likewise, for patients ventilated with pressure-targeted modes, ARDS diagnosis was associated with higher above-target VTe (1.82 cc/kg PBW, 0.56 - 0.3.95) compared to no ARDS (1.14 cc/kg PBW, 0.49 - 1.71, p = <0.001) (Figure 3).
 
Conclusions
 
Volume-targeted modes of ventilation are associated with lower, above-target VTe compared with pressure-targeted modes of ventilation. ARDS is associated with significantly higher, above-target VTe in both volume-targeted and pressure-targeted modes, with greater above-target VTe noted among pressure-targeted modes.

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