Failure of non-invasive ventilation in patients with acute lung injury: observational cohort study

Vol10No3 Failure of non-invasive ventilation in patients with acute lung injury: observational cohort study Sameer Rana1, Hussam Jenad1, Peter C Gay1, Curtis F Buck2, Rolf D Hubmayr1 and Ognjen Gajic1 Corresponding author: Ognjen Gajic 0 Department of Anesthesiology, Division of Intensive Care and Respiratory Care, Mayo Clinic , Rochester, Minnesota USA 1 Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, Mayo Clinic , Rochester, Minnesota USA Introduction The role of non-invasive positive pressure ventilation (NIPPV) in the treatment of acute lung injury (ALI) is controversial. We sought to assess the outcome of ALI that was initially treated with NIPPV and to identify specific risk factors for NIPPV failure. Methods In this observational cohort study at the two intensive care units of a tertiary center, we identified consecutive patients with ALI who were initially treated with NIPPV. Data on demographics, APACHE III scores, degree of hypoxemia, ALI risk factors and NIPPV respiratory parameters were recorded. Univariate and multivariate regression analyses were performed to identify risk factors for NIPPV failure. Results Of 79 consecutive patients who met the inclusion criteria, 23 were excluded because of a do not resuscitate order - Introduction Non-invasive positive pressure ventilation (NIPPV) is the accepted initial mode of treatment in subsets of patients with acute respiratory failure, the foremost exacerbation of chronic obstructive pulmonary disease with hypercarbia [1], and also in immunocompromised hosts [2,3], patients with cardiogenic pulmonary edema [4,5] and as a weaning aid in chronic obstructive pulmonary disease [6]. The efficacy of NIPPV in the initial management of other forms of hypoxemic respiratory failure, such as acute lung injury (ALI), pneumonia or postextubation respiratory failure, remains controversial [7-9]. Continuous positive airway pressure (CPAP) has been shown to be of no benefit in non-selected patients with acute hypoxemic resand two did not give research authorization. Of the remaining 54 patients, 38 (70.3%) failed NIPPV, among them all 19 patients with shock. In a stepwise logistic regression restricted to patients without shock, metabolic acidosis (odds ratio 1.27, 95% confidence interval (CI) 1.03 to 0.07 per unit of base deficit) and severe hypoxemia (odds ratio 1.03, 95%CI 1.01 to 1.05 per unit decrease in ratio of arterial partial pressure of O2 and inspired O2 concentration PaO2/FiO2) predicted NIPPV failure. In patients who failed NIPPV, the observed mortality was higher than APACHE predicted mortality (68% versus 39%, p < 0.01). Conclusion NIPPV should be tried very cautiously or not at all in patients with ALI who have shock, metabolic acidosis or profound hypoxemia. piratory failure and was associated with a higher number of adverse events [10]. While a prospective multicenter study identified ALI as an independent predictor of failure of NIPPV [11], specific underlying risk factors, such as presence of shock or metabolic acidosis, have not been evaluated in this group of patients. The uncertainty of the benefit of NIPPV in patients with ALI is reflected in a recent survey of NIPPV practice in which less than 40% of providers consider NIPPV to be beneficial in this group of patients [12]. The present study was undertaken to evaluate the outcome of patients with ALI treated with NIPPV as the initial mode of therapy and to identify factors predicting success/failure of NIPPV in this group of patients. ALI = acute lung injury; APACHE = Acute Physiology and Chronic Health Assessment; CI = confidence interval; CPAP = continuous positive airway pressure; DNR/DNI = do not resuscitate/do not intubate; ICU = intensive care unit; NIPPV = non-invasive positive pressure ventilation. Outline of the study. CPAP, continuous positive airway pressure; DNI, do not intubate; DNR, do not resuscitate; NIPPV, non-invasive positive pressure ventilation. PaO2/FiO2, ratio of arterial partial pressure of O2 and inspired O2 concentration Materials and methods The present study was undertaken in two intensive care units (ICUs) of a tertiary care center. The institutional review board waved the informed consent requirement. Consecutive critically ill medical patients who met ALI criteria and who were treated with NIPPV as the initial mode of therapy between March and October of 2004 were included. The decision to intubate was left to the discretion of the treating intensivist. ALI was defined according to the American-European Consensus Conference definition [13]. Sepsis and shock were defined according to the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference definition [14]. Patients who had 'do not resuscitate/do not intubate' preferences (DNR/DNI) or refused research authorization were excluded (Figure 1). The main outcome measure was failure of NIPPV defined as subsequent intubation and invasive mechanical ventilation. Secondary outcomes were hospital mortality and ICU length of stay. Data on demographics, DNR status, diagnoses, acute physiology parameters (vital signs, arterial blood gases, blood urea nitrogen, creatinine, bilirubin and hematocrit), severity of illness scores, mortality and length of ICU stay were prospectively collected by the bedside nurse into the Acute Physiology and Chronic Health Assessment (APACHE) III database. The characteristics of the ICU and the APACHE database have been previously described [15]. NIPPV was delivered through a full face mask in all patients. Patients who received bi-level pressure ventilation were ventilated with the 'Vision' NIPPV ventilator (Respironics Inc., Carlsbad, CA, USA). Data on inspiratory and expiratory pressure and estimated tidal volume were prospectively collected four times a day and documented in the respiratory therapy electronic medical record. The respiratory therapist confirmed the absence of air leak prior to recording the tidal volume value. The minority of patients in whom the initial mode of ventilation was CPAP, positive pressure was delivered by either 'Vision' NIPPV ventilator or a custom CPAP delivery system (Down's Flow Generator, Vital Signs Inc., Totowa, NJ, USA). In this group of patients the respiratory rate and airway pressure but not tidal volume were recorded. Categorical variables were compared using standard Chi square and Fisher's exact tests as appropriate. Wilcoxon rank sum test was used to compare continuous variables. To evaluate the risk factors for NIPPV failure, a multivariate logistic regression model was created. Variables that were associated with NIPPV failure in univariate analysis (p < 0.1) were entered and a forward selection process identified the final model containing no more than three predictor variables. JMP statistical Clinical characteristics of medical ICU patients with ALI receiving NIPPV. NIPPV failure (n = 38) NIPPV success (n = 16) Lacta (...truncated)