Mean Airway Pressure As a Predictor of 90-Day Mortality in Mechanically Ventilated Patients

Sarina K. Sahetya, MD, MHS; T. David Wu, MD, MHS; Brooks Morgan, MSPH; Phabiola Herrera, MD; Rollin Roldan, MD; Enrique Paz, MD; Amador A. Jaymez, MD; Eduardo Chirinos, MD; Jose Portugal, MD; Rocio Quispe, MD; Roy G. Brower, MD; William Checkley, MD, PhD

Disclosures

Crit Care Med. 2020;48(5):688-695. 

In This Article

Abstract and Introduction

Abstract

Objectives: To determine the association between mean airway pressure and 90-day mortality in patients with acute respiratory failure requiring mechanical ventilation and to compare the predictive ability of mean airway pressure compared with inspiratory plateau pressure and driving pressure.

Design: Prospective observational cohort.

Setting: Five ICUs in Lima, Peru.

Subjects: Adults requiring invasive mechanical ventilation via endotracheal tube for acute respiratory failure.

Interventions: None.

Measurements and Main Results: Of potentially eligible participants (n = 1,500), 65 (4%) were missing baseline mean airway pressure, while 352 (23.5%) were missing baseline plateau pressure and driving pressure. Ultimately, 1,429 participants were included in the analysis with an average age of 59 ± 19 years, 45% female, and a mean PaO 2/FIO 2 ratio of 248 ± 147 mm Hg at baseline. Overall, 90-day mortality was 50.4%. Median baseline mean airway pressure was 13 cm H2O (interquartile range, 10–16 cm H2O) in participants who died compared to a median mean airway pressure of 12 cm H2O (interquartile range, 10–14 cm H2O) in participants who survived greater than 90 days (p < 0.001). Mean airway pressure was independently associated with 90-day mortality (odds ratio, 1.38 for difference comparing the 75th to the 25th percentile for mean airway pressure; 95% CI, 1.10–1.74) after adjusting for age, sex, baseline Acute Physiology and Chronic Health Evaluation III, baseline PaO 2/FIO 2 (modeled with restricted cubic spline), baseline positive end-expiratory pressure, baseline tidal volume, and hospital site. In predicting 90-day mortality, baseline mean airway pressure demonstrated similar discriminative ability (adjusted area under the curve = 0.69) and calibration characteristics as baseline plateau pressure and driving pressure.

Conclusions: In a multicenter prospective cohort, baseline mean airway pressure was independently associated with 90-day mortality in mechanically ventilated participants and predicts mortality similarly to plateau pressure and driving pressure. Because mean airway pressure is readily available on all mechanically ventilated patients and all ventilator modes, it is a potentially more useful predictor of mortality in acute respiratory failure.

Introduction

Approximately 40% of all patients admitted to ICUs require mechanical ventilation for acute respiratory failure (ARF) during their hospitalization.[1,2] As the population ages, the frequency of respiratory failure is projected to rise by 80% by 2026.[3] Ventilation guidelines for ARF are frequently extrapolated from evidence-based recommendations for acute respiratory distress syndrome (ARDS) that center on reducing tidal volumes (VTs) and inspiratory airway pressures.[4] Plateau pressure (Pplat), the airway pressure during a brief inspiratory pause, is one of the primary measurements that guide ventilator management. Recent evidence also suggests that driving pressure (Pdriv), measured as the Pplat minus positive end-expiratory pressure (PEEP), may be a more useful target.[5] However, recent large observational studies suggest that clinicians fail to measure Pplat, and subsequently Pdriv, in over 50% of ARDS patients on controlled modes of ventilation and 60% of ARF patients receiving mechanical ventilation.[1,2]

Mean airway pressure (Pmean) is determined by the peak inspiratory pressure (PIP), PEEP, and the inspiratory to expiratory time ratio (e-Figure 1, Supplemental Digital Content 1, http://links.lww.com/CCM/F323; legend, Supplemental Digital Content 2, http://links.lww.com/CCM/F324). It is a commonly available pressure measurement that has received relatively little attention in the literature. In contrast to Pplat and Pdriv, Pmean is measured and reported by most mechanical ventilators automatically with every breath and is thus more easily obtained.[6] Under normal conditions, Pmean closely correlates with mean alveolar pressure[7] and thus may represent the stresses applied to the lung parenchyma with ventilation. Furthermore, unlike Pplat and Pdriv, Pmean is affected by minute ventilation and therefore may reflect dead space, acidosis, and other aspects of critical illness severity. We hypothesize that elevations in Pmean are associated with higher mortality and that Pmean will perform similarly to Pplat and Pdriv to predict mortality in ARF. To evaluate this hypothesis, we analyzed a prospective observational cohort of critically ill participants with ARF requiring mechanical ventilation admitted to ICUs in Lima, Peru.

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