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Clinical Investigations in Critical CareNoninvasive Positive-Pressure Ventilation To Treat Hypercapnic Coma Secondary to Respiratory Failure
Section snippets
Materials and Methods
This prospective, observational study was carried out between January 1, 1997, and May 31, 2002, in patients who were admitted to the ICU with ARF and a severe deterioration of consciousness (GCS score ≤ 8). The study was approved by the ethics committee at our institution, and written consent was obtained from patients or their next of kin.
Patients Included
Consecutive patients presenting with ARF were treated with NPPV for the following standard indications: moderate-to-severe respiratory distress accompanied by tachypnea (for hypoventilatory causes, > 24 breaths/min; for hypoxemic causes, > 29 breaths/min) and acute or acute-on-chronic CO2 retention (Paco2, > 45 mm Hg; pH < 7.35); or severe hypoxemia coma (Pao2/fraction of inspired oxygen [Fio2] ratio, < 200). Patients with coma (GCS score, ≤ 8) and CO2 retention formed one group, and those
Patients Excluded
Contraindications to the use of NPPV therapy were agonal breathing and apnea, recent facial, esophageal, or upper airway surgery, uncontrolled GI hemorrhaging, excessive airway secretions, or a facial deformity preventing the application of the mask. Hemodynamic instability that is responsive to treatment with fluid resuscitation and vasoactive drugs was not considered to be a contraindication to NPPV therapy. Patients were excluded if another etiology of coma, such as a hypoglycemic,
Ventilator, Ventilation Mode, and Interface
NPPV therapy was administered using bilevel positive airway ventilation (BiPAP ST-D or VISION Ventilator Support Systems; Respironics, Inc; Murrysville, PA) via a properly fitted face mask (Respironics). The head of the bed was raised to 45° in order to minimize the risk of pulmonary aspiration. The face mask was attached by means of head straps and was tightened to minimize leaks, although care was taken to avoid excessive tightening. Artificial skin was applied over the bridge of the nose in
Noninvasive Ventilation Protocol
On admission to the ICU, a nasogastric tube was placed in all patients to minimize the risk of gastric distension and vomiting. The ventilator was set in the spontaneous/timed mode, with a minimum respiratory rate (RR) of 20 to 25 breaths/min. The initial inspiratory positive airway pressure (IPAP) was set at 12 cm H2O. IPAP levels were raised by 2 to 3 cm H2O every 4 h as tolerated in order to keep pH at > 7.3 but did not exceed 30 cm H2O.
Expiratory positive airway pressure (EPAP) was begun at
Criteria for Intubation
Patients who had not declined such a procedure were intubated endotracheally if any of the following conditions occurred: worsening respiratory distress despite NPPV therapy; respiratory arrest; unmanageable airway secretions; uncontrolled ventricular arrhythmias; hemodynamic instability that was unresponsive to therapy with fluid resuscitation and/or vasoactive drugs (with a maximum norepinephrine dose of 0.3 μg/kg/min); RR persistently > 40 breaths/min despite optimized interface and
Effectiveness of the Technique
NPPV therapy was held to be successful when the patient avoided endotracheal intubation, completely recovered consciousness, was discharged from the ICU, and remained alive and conscious on a hospital ward for at least 24 h without requiring the resumption of NPPV therapy. Patients were considered to be intolerant to therapy if they were unable to cooperate with the technique, pulling the mask off and refusing to continue. Lack of response to NPPV therapy occurred if patients experienced a
Measurements
At the start of NPPV therapy, the following variables were also recorded: age; sex; indicators of severity with APACHE (acute physiologic and chronic health evaluation) II score and simplified acute physiologic score (SAPS) II; original location of the patient (ie, emergency department or hospital ward); underlying disease; and premorbid respiratory status. RR, heart rate, arterial BP, continuous arterial oxygen saturation, GCS score, temperature, and urine output were measured hourly. Also
Statistical Analysis
Continuous variables were expressed as the mean ± SD, and categoric variables were recorded as percentages. The relationship between two qualitative variables was tested using the χ2 test or the Fisher exact test. The Kolmogorov-Smirnov test was used to identify variables with a normal distribution. In these cases, mean values were compared using the Student t test for independent data, while a paired t test was applied to compare the data of each patient before and after treatment. Variables
Results
During the period of the study, 2,865 ARF patients were admitted to the ICU, of whom 958 (33.4%) were treated with NPPV. Of these patients, 95 (10.1%) had GCS scores on ICU admission ≤ 8, and 863 had GCS scores > 8. The global success rate of NPPV therapy was slightly higher in coma patients than in patients with GCS scores > 8 (80.0% and 70.1%, respectively; p = 0.0434). Despite this, the hospital mortality rate was not significantly different between the two groups. The mortality rate of
Characteristics of Comatose Patients
The group of comatose patients consisted of 46 men and 49 women. The mean age was 73 ± 9 years (men, 70 ± 12 years; women, 74 ± 12 years; age range, 42 to 88 years), the mean APACHE II score was 29 ± 7, and the mean SAPS II was 53 ± 13. The mean GCS score of these 95 patients on ICU admission was 6.5 ± 1.7. In 11.6% of cases, the GCS score was 3, in 40.1% of cases the score was 4 to 7, and in 45.3% of cases the score was 8. The etiology for ARF was COPD in 66 patients, pneumonia in 4 patients,
Physiologic Measurements
At study entry, all comatose patients had severe respiratory failure. Most were hypercapnic, but some were hypoxemic initially, developed muscular fatigue, and became hypercapnic. The mean Pao2/Fio2 ratio on ICU admission was 139 ± 43, the mean Paco2 was 99 ± 19 mm Hg (range, 60 to 166 mm Hg), and the mean pH was 7.13 ± 0.06 (range, 6.93 to 7.23). Physiologic parameters, with the exception of RR and systolic BP, improved significantly after 1 h of NPPV therapy (Table 2)
Outcomes of Patients
The mean duration of NPPV therapy for the comatose patients was 2.0 ± 1.3 days, totaling 27 ± 19 h of NPPV treatment. Complete recovery of consciousness (GCS score, 15) was achieved in 81 patients (85.3%), within a mean time of 4.1 ± 2.4 h from the start of NPPV. In addition, there was a weak but statistically significant correlation (r = 0.22; p = 0.048) between the Paco2 level on ICU admission and the time needed to recover consciousness (GCS score = 15)
A positive response to therapy (ie,
Complications
Complications attributable to NPPV were observed in 29 patients (30.5%) but did not lead to the lack of response to NPPV therapy (Table 3). The most frequent complication (affecting 23 patients [24.2%]) was skin ulceration on the nose or forehead. Gastric distension was observed in five patients, even though all patients had a nasogastric tube in place. In three of these patients, vomiting occurred, and one patient experienced pulmonary aspiration necessitating endotracheal intubation.
Factors Predicting Success of NPPV
A univariate analysis that was performed to identify factors that correlated with the response or lack of response to NPPV therapy demonstrated that neither gender nor age was related to a response to NPPV therapy (Table 4). Not surprisingly, lack of response was more likely among patients with higher acuity of illness and organ failure scores. GCS score, RR, pH, Paco2, and Pao2/Fio2 ratio on ICU admission did not correlate with response to therapy, but, with the exception of RR, improvements
Factors Predicting Hospital Survival in Comatose Patients Using NPPV
A separate univariate analysis (Table 6) demonstrated that hospital survival was significantly associated with lower ICU admission APACHE II score, SAPS II, and SOFA score, with less tachypnea at the start of NPPV, with the initiation of therapy taking in an emergency department rather than on an inpatient ward (84% vs 59%, respectively; p = 0.007), and the absence of DNI orders. Patients with DNI orders had a hospital mortality rate of 52%, as opposed to 24% when there were no such orders (p =
Discussion
This study shows that NPPV use in patients with acute severe respiratory insufficiency causing severe encephalopathy, and even coma, is associated with high response and hospital survival rates, improving gas exchange and consciousness with few serious side effects. These results are at odds with the conventional wisdom, considering that most previous trials of NPPV, including a number of randomized, controlled trials, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 have deemed coma to be a
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Drs. Gonzalez Dyaz and Carillo Alcarez belong to the Spanish Investigation Net in Acute Respiratory Failure (RED GIRA)