Methods
Patients
All patients were admitted between February 2009 and September 2011, and permission was obtained from patients or their proxies if patients were unable to answer for themselves. The study was approved by the academic and ethics committee of the School of Medicine of the Universidad San Francisco de Quito. Three hospitals in Guayaquil, Ecuador participated in the study: Hospital Militar, Clinica Panamericana, and Clinica Santa Maria. A total of 22 patients were recruited for NIV and divided into two groups of 11.
Treatment Group Assignments
11 patients with infectious exacerbations of COPD and hypercapnic encephalopathy with GCS < 10 were designated to receive BiPAP S/T with AVAPS.
The control group was then selected from patients in the emergency unit with infectious exacerbations of COPD and encephalopathy (GCS < 10). Patients were treated immediately and referred to us by doctors who were unaware of the study. Each patient was treated with NIV and was selected according to: APACHE II score within 4 points, age within 10 points, pH within 0.04, GCS within 2 points, and BMI within 2 points.
Noninvasive Mechanical Ventilation: BiPAP S/T With AVAPS
Ventilatory parameters were initially programmed in the BiPAP S/T mode and AVAPS with an inspiratory positive airway pressure (IPAP) maximum programmed into the device of 26 cmH2O, to IPAP minimum programmed value of 12 cmH2O and an expiratory positive airway pressure (EPAP) of 6 cmH2O. The programmed tidal volume was at 8 to 12 ml/kg of IBW, and once the patient reached clinical stability and sensory, the target Vt in our patients were reprogrammed to 6–8 ml/kg/weight according to manufacturer's specifications, the decision was made by the expert physician in charge of patient case dependent, respiratory rate was 15 breaths/min, rise time set at 300–400 ms and inspiratory time was at a minimum of 0.6 s. Were given supplements O2 via an adapter circuit close to the facemask in order to maintain SaO2 above 90%. Patients were maintained on continuous NIV initially.
Maximum IPAP received delivered, exhaled tidal volume (EVT), Vmin, and leaks were monitored through the ventilator software. We used BiPAP Synchrony with AVAPS and Autotrak (Respironics Inc., Murrysville, Pennsylvania, USA) and a Mirage IV series facemask (Resmed).
Measurements
Arterial blood gases were measured at initial values and after 1 hour, 3 hours, 12 hours and then every 24 hours during NIV; the patient was assessed by a respiratory therapist under close supervision of a physician trained in NIV. Mask use, complications, and tolerance were also assessed.
Disease severity was assessed using the APACHE II score and GCS to determine the patient's level of consciousness. Maximum Vt, maximum IPAP, EVT, Vmin, leaks, respiratory rate, heart rate, systolic blood pressure, diastolic blood pressure, and IPAP were measured upon hospitalization, after 1 hour, 3 hours, and 12 hours, and then every 24 hours during NIV.
Exclusion criteria included facial deformity, obstruction in the upper airway from surgery or trauma, alterations of the central nervous system not related to hypercapnic encephalopathy, cardiogenic pulmonary edema, pneumothorax, pulmonary thromboembolism, hemoptysis or septic shock, emergency intubation due to cardiopulmonary arrest, and hemodynamic instability with systolic pressure below 80 mmHg.
Discontinuation of NIV
Treatment with NIV was initially used on a continuous regimen based on patient tolerance and after normalization of arterial pH > 7.35 ventilation was given in 3-hour blocks. The weaning process was initiated when clinical stability was achieved, which was defined as respiratory rate less than 24 breaths/min, a heart rate of 90 beats/min, and improved awareness and compensation from normalized pH values, with adequate SaO2 in ambient air and a low percentage of inspired O2 (3 liters). Once the patient remained stable, NIV was discontinued.
Control Group Ventilation Parameters: BiPAP S/T
Ventilatory parameters were initially programmed in BiPAP S/T mode. IPAP was programmed at 12 cmH2O, EPAP was programmed at 6 cmH2O. Respiratory rate was set at 15 breaths/min, rise time set at 300–400 ms, and inspiratory time was at a minimum of 0.6 s. Progressively increased levels were IPAP in increments of 2 cmH2O according to the discretion of the attending physician. Supplements were added O2 via an adapter circuit close to the facemask to maintain SaO2 above 90%. Patients were maintained on continuous NIV initially until normalized blood pH ( > 7.35). We monitored EVT, Vmin, and leakage. We used BiPAP Synchrony and Autotrak (Respironics Inc.), and two types of facemasks: Mirage IV series mask (Resmed) and Series II full facemask (Respironics). We monitored EVT, Vmin, and leakage in order to program inspiratory pressure Levels and adjust the mask.
In addition to ventilatory support, both groups received bronchodilators, intravenous corticosteroids, and antibiotic therapy consisting of beta-lactam (piperacillin/tazobactan at 4.5 g IV every 6 hours) in combination with a new fluoroquinolone (Levofloxacin 500 mg IV daily).
Primary analysis: level of consciousness (Glasgow Coma Scale score). Secondary analysis: duration of mechanical ventilation, hospital stay, and progression (exhaled tidal volume, inspiratory pressure, and arterial blood gases).
Statistical Analysis
All data were expressed as mean ± standard deviation (SD) for continuous variables and as percentages for categorical variables. Continuous variables with normal distribution were examined using the Kolmogorov-Smirnov test, and were compared using Student's t-test. For categorical variables, χ or Fisher's exact tests were used as appropriate. We used analysis of variance (ANOVA) with repeated measures to compare the ability of different variables (pH, pCO2, HCO3, heart rate, respiratory rate, systolic blood pressure, diastolic blood pressure, EVT, Vmin, leaks, maximum programmed IPAP, and GCS) to predict the outcome of therapy in experimental and control patients. A P value <.05 was considered statistically significant.