copd_2008

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ED: Prabhu

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LWW_MEJ_200300 Original article 1

Noninvasive mechanical ventilation in patients with chronic obstructive pulmonary disease and severe hypercapnic neurological deterioration in the emergency room Killen Harold Briones Claudetta, Mo´nica H. Briones Claudettb, Miguel A. Chung Sang Wongb, Michelle Grunauer Andradec, Cristian X. Cruzd, Antonio Esquinase and Gumersindo Gonzalez Diaze Objectives The objective of this study was to assess the effectiveness of noninvasive motion ventilation (NIMV) in patients with chronic obstructive pulmonary disease (COPD), having infectious exacerbation and severe hypercapnic neurological dysfunction in the emergency room.

groups, respectively (P = 0.01). Days of IMV were 5.60 ± 1.2 versus 3.6 ± 1.1 for NIMV (P = 0.006). Days of hospitalization were 11.1 ± 4.7 for the IMV group and 6.5 ± 1.9 for the NIMV group (P = 0.001). The cumulative survival rates at 6 months were 71.4 and 80% for the IMV and NIMV groups, respectively (P = 0.80).

Design This is a prospective interventional study.

Conclusions We consider that severe neurological dysfunction and pH of less than 7.25 do not constitute absolute contraindications to the use of NIMV. This kind of management can be implemented in the emergency room with favorable results. European Journal of Emergency c 2008 Wolters Kluwer Health | Medicine 00:000–000 Lippincott Williams & Wilkins.

Setting The study setting was the emergency room at the Military Hospital in Guayaquil-Ecuador.

Patients A total of 24 patients were studied. Twelve patients had acute exacerbation of their chronic obstructive pulmonary disease: they presented at the emergency room with severe neurological dysfunction, with a Glasgow Coma Scale (GCS) score of less than 8 and a pH of less than 7.25. These patients were compared with 12 controls who were being treated with invasive mechanical ventilation (IMV), who were then matched according to their GCS scores, pH status, Acute Physiology and Chronic Health Evaluation II (APACHE II) scores, and age.

Interventions We evaluated the effectiveness and safety of applying a ventilatory strategy based on a biphasic positive airway pressure protocol in the emergency room.

Measurements and results The pH, PCO2, and GCS scores, measured during the first 3 h, were predictors of success for the application of NIMV treatment (P < 0.05).

Mortality was 33.3 and 16.7% for the IMV and the NIMV

Introduction Several meta-analyses establish the clear benefits of noninvasive mechanical ventilation (NIMV) over routine medical treatments in patients with an exacerbation of chronic obstructive pulmonary disease (COPD) [1–3].

The recruitment criteria for patients vary in several studies that evaluate the effectiveness of NIMV. Some studies enroll patients with infectious exacerbation of their hypercapnic COPD, whereas others enroll a mixed c 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 0969-9546

European Journal of Emergency Medicine 2008, 00:000–000 Keywords: bilevel positive airway pressure, chronic obstructive pulmonary disease, noninvasive mechanical ventilation, severe hypercapnic neurological dysfunction a Pneumology Department of Military Hospital, bPneumology Department and Intensive Care Unit of Military Hospital, cIntensive Care Unit of Military Hospital, Guayaquil, Ecuador, dUniversity Of San Francisco De Quito in Cumbaya and e Intensive Care Unit and Pneumology Services of the Hospital JM Morales, Meseguer Murcia, Spain

Correspondence to Killen Harold Briones Claudett, MD, Chief Pneumology Department, Hospital De Divisio´n II-DE, Av Pedro Menendez Gilbert y Av Democracia, Guayaquil, Guayas, Ecuador, 5934 Tel: + 59342897236; fax: + 59342897238; e-mail: kyllenb@interactive.net.ec Received 16 February 2007 Accepted 19 July 2007

population (patients without hypercapnia, with a normal pH, and without neurological deterioration) [4–6]. In their study, Plant et al. [7] included patients with a slight deterioration of their pH levels (7.32), who had been admitted to the general medical floor. In contrast, the majority of authors, in their studies, involve patients with infectious exacerbation of their COPD, suffering severe respiratory distress, and having a pH level of less than 7.25, who have been admitted exclusively to the ICU [8– 14]. The international consensus is that therapy with

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NIMV is contraindicated in patients presenting with an infectious exacerbation of their COPD, a Glasgow Coma Scale (GCS) score of less than 10, and a pH level of less than 7.25 [15–17].

Few studies have been reported of cases comparing the use of NIMV and invasive mechanical ventilation (IMV) in patients with severe hypercapnic neurological dysfunction and COPD. This study, however, includes patients who had not been prematurely treated with NIMV, who failed to respond to routine therapies, and even some patients with community-acquired pneumonia [14,18– 20].

The objectives of our study were as follows: 1. To evaluate the safety and effectiveness of using NIMV in patients with severe hypercapnic neurological deterioration and a pH level of less than 7.25, by instituting a biphasic positive airway pressure (BIPAP) protocol both in the emergency department (ED) and during hospitalization. In addition, we compared this group with a mixed control group who had been administered IMV immediately on arrival at the ED. 2. To evaluate the confounding variables that predicted the failure of the NIMV therapy.

GCS score of less than 8, and a pH level of less than 7.25, were treated immediately with NIMV. Patients were admitted to the ED and treated with NIMV during a 6-h period. Subsequently, they were transferred either to the pulmonary medicine floor or to the ICU, depending on the improvement in their levels of consciousness and arterial blood gases (ABGs). None of the patients presented with any additional organ failures: only respiratory and neurological dysfunctions were reported.

The exclusion criteria were as follows: 1. a face deformity; 2. obstruction of the upper respiratory tract owing to recent surgery or trauma; 3. alterations in the central nervous system not related to a hypercapnic encephalopathy; 4. cardiogenic pulmonary edema, pneumothorax, pulmonary thromboembolism, hemoptysis, or septic shock; 5. urgent intubation owing to cardiac and/or respiratory arrest, and hemodynamic instability with a systolic arterial blood pressure (BP) of less than 80 mmHg;

NIMV protocol

Materials and methods Patients

All patients were admitted during the period 1 December 1999 to 1 December 2004 to the ‘Hospital Division IID.E – LIBERTAD’ in Guayaquil, Ecuador. Permission was obtained from the patients, or from their related subrogates if they were not capable of granting it themselves. This study was approved by the ethics committees of the University of San Francisco de Quito in Cumbaya, Ecuador and of the Military Hospital in Ecuador.

Patients with infectious exacerbation of their COPD, arriving at the ED with a pH level of 7.25 or less, and with neurological deterioration, as estimated by a GCS score of less than 8, were recruited.

COPD was diagnosed on the basis of the recommendations of the American Thoracic Society [21], with the pH level being less than 7.25 and PCO2 being more than 60 mmHg. Case designation

Patients with an acute exacerbation of their COPD from December 2002 to December 2004, who presented to the ED with severe hypercapnic neurological dysfunction, a

The initial inspiratory positive airway pressure (IPAP) was programmed in 12 cm of H2O and the expiratory positive airway pressure (EPAP) in 6 cm of H2O. Supplementary oxygen was added by face mask, to maintain an O2 saturation of over 90%.

Patients were initially maintained in continuous-mode NIMV for a 6-h period at the ED, with continuous monitoring and ABGs evaluation.

We used a BIPAP S (Duet System with autotrack, manufactured by Respironics Murrysville Inc., Pennsylvania, USA), initially graduated with an IPAP of 12 cm of H2O and an EPAP of 12 cm of H2O. The mask used for the study was a Mirage Phase Series II (Respironics Inc.).

A nasogastric tube was inserted in all patients, O2 saturation monitored constantly, and supplementary oxygen given to maintain an O2 saturation of over 90%.

Criteria of transferring patients either to the ICU or to the general medical floor

After 6–12 h of exposure to NIMV in the ED, monitored by a physician specialized in NIMV, and after a subsequent substantial improvement in their pH and PCO2 levels, and an improvement in their GCS scores of more than 10, patients were transferred to a general

Noninvasive mechanical ventilation in patients with COPD Briones Claudett et al. 3

medical room, where care with NIMV continued under the supervision of nurses and the respiratory therapist. If there was no improvement during this time, the patient was transferred back to the ICU. Measurements

ABGs and levels of consciousness (evaluated by a GCS score) were measured after 1, 3, 6, 12, and 24 h of exposure to NIMV. Mask use and mask tolerability evaluation

During the first 6 h, patients were evaluated by respiratory therapists, under the strict surveillance of physicians trained in NIMV. Additionally, the hours on BIPAP were recorded. Complications owing to use of the mask were as follows: excessive discomfort, nasal ulcers, gastric distention, and claustrophobia. Comfort was assessed by the respiratory therapist or the nurse in charge on a five-point scale: (i) poor, (ii) very bad, (iii) competent, (iv) good, and (v) excellent [22].

The severity of the disease was evaluated by means of the Acute Physiology and Chronic Health Evaluation (APACHE) II score [23]. Limitations of daily activities caused by COPD were evaluated according to information presented by Seneff et al. [24]. These data were obtained directly from the patients or from their family members. A nasogastric tube was inserted in all patients to minimize the risk of bronchial aspiration.

pH within 0.04, and GCS score within 2 points of the former’s corresponding scores.

Patients were intubated with an endotracheal tube (7.5– 8 mm in diameter); the initial ventilator programming was assist controlled at 8 ml/kg weight, with an RR of 10–14 breaths/min, and an FiO2 of 35%. The positive end expiratory pressure (PEEP) was programmed at 5 cm of H2O, with a trigger of – 1 cm of H2O for all patients. The head of the bed was maintained at a 45-degree angle, to diminish the risk of aspiration.

The criteria for intubation used for the control group was a GCS score of less than 8, severe acidosis (pH < 7.25), hypercapnia, and signs of severe respiratory insufficiency.

The two groups of patients received, in addition to the ventilatory support, medication in the form of bronchodilators, intravenous corticosteroids, and antibiotic therapy based on a third-generation cephalosporin in combination with a fluoroquinolone.

Results measurement

The primary outcome measured was mortality rate. The secondary outcomes were days of hospital stay, days in mechanical ventilation, and days of permanence at the ICU. Tolerability was assessed, as well as the complications owing to the use of the facial mask. Improvements in the ABG values were evaluated in all cases, as well as whether or not the patient was transferred to the ICU.

Discontinuation of the NIMV therapy

NIMV was used initially for a minimum of 6 h and maintained according to the patient’s tolerance level. A 3h time-out from NIMV was allowed between sessions.

The weaning process began once clinical stability was achieved. Clinical stability was defined as follows: respiratory rate (RR) of less than 24 breaths/min, heart rate (HR) of 90 beats/min, an improvement in the level of consciousness (GCS score of 15/15), and a compensated arterial pH with adequate O2 saturation at room air or with the use of a low percentage of inspired oxygen (less than 3 l). If the patient remained stable, the NIMV therapy was not restored. If the patient seemed fatigued at the end of the day, NIMV was initiated for short periods during the night.

Controls selection

The control group was selected from a previous group admitted to the ED with a diagnosis of acute exacerbation of COPD from December 1999 to December 2004.

These patients were treated immediately with IMV and transferred to the ICU. The physician who selected the controls was blinded to the study results. For each patient treated with NIMV, a control was selected according to the following criteria: disease severity evaluated with the APACHE II score, within 4 points, age within 10 points,

Statistical analyses

All the data were expressed as means ± standard deviations (SDs) for continuous variables and as percentages for nominal variables. Normal distribution variables were compared with the Student’s test. The normality in the distribution of continuous variables was determined with the Kolmogorov–Smirnov test. For nonparametric distribution variables, w2 test or the Fisher’s exact test were used, depending on the case.

To compare the results of the different variables (pH, PCO2, HCO3, HR, RR, BP, and GCS scores) in predicting the success of the NIMV therapy in the experimental group, the variance analysis of repeated measurements was used. A P value of less than 0.05 was considered to be of statistical significance. The out-of-hospital survival rate for all the patients was evaluated after 6 months of home care. The Kaplan–Meier method [25] was used to determine the out-of-hospital survival rate in the experimental and control groups, and the log-rank test to establish differences between the groups. A P value of less than 0.05 was considered to be of statistical significance.

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4 European Journal of Emergency Medicine 2008, Vol 00 No 00

Results Group characteristics

The two groups of patients (12 patients in each group), who were assigned either to NIMV or to IMV, exhibited similar characteristics that are shown in Tables 1 and 2.

The evolution of the parameters (pH, PCO2, HCO3, RR, and HR) in the patients of the NIMV group was Table 1

Primary outcome

Characteristics of hospitalized patientsa Invasive mechani- Noninvasive mecal ventilation chanical ventilation N = 12 n = 12

Variables Age (years) GCS* score APACHE II** score Previous exacerbations in the course of 1 year Arterial blood pH*** PCO2 (mmHg) HCO3 (mmol/L) PO2 (mmHg) Heart rate (beats/min) Respiratory rate (breaths/min) SO2 (%) Mean blood pressure systolic (mmHg) Mean blood pressure diastolic (mmHg)

evaluated at 1, 3, 6, 12, and 24 h. The pH, PCO2, and GCS scores, measured during the first 3 h, were considered to be predictors of success of the NIMV therapy (ANOVA; P < 0.05). One patient presented nasal irritation and another presented gastric distention during the use of NIMV, but these were not severe enough to stop the intervention. The evaluation of parameters in patients undergoing NIMV is shown in Table 3.

P value

70.1 ± 8.9 6.3 ± 1.3 25.7 ± 1.8 2.3 ± 0.4

71.2 ± 5.3 5.58 ± 1.3 26.2 ± 2.0 1.9 ± 0.6

0.61 0.85 0.64 0.81

7.15 ± 0.07 85.1 ± 14.6 39.5 ± 4.1 109.1 ± 80.9 102.6 ± 14.1 31.8 ± 14.6

7.18 ± 0.05 75.3 ± 13.8 32.3 ± 8.3 103 ± 43.3 100.2 ± 18.3 34.4 ± 15.1

0.67 0.53 0.13 0.51 0.12 0.56

94.5 ± 3.1 114 ± 16.4

95.6 ± 4 130.8 ± 22.7

0.41 0.45

69 ± 7.3

79.5 ± 9.7

0.44

a

Data are presented as numbers and percentages unless otherwise specified.

ANOVA, analysis of variance; APACHE II, acute physiology chronic health evaluation; GCS, Glasgow Coma Scale score; HR, heart rate; PCO2, arterial blood–carbon dioxide partial pressure; pH, arterial blood pH; PO2, arterial blood– oxygen partial pressure; RR, respiratory rate; SO2%, percentage of oxygen saturation. *P < 0.05 = statistically significant.

The mortality rate was 33.3% for the IMV group and 16.7% for the NIMV group (P = 0.01). Two patients were intubated, one after 6 h and the other after 72 h in the NIMV group.

Secondary outcomes

The number of days on mechanical ventilation were 5.6 ± 1.2 and 3.6 ± 1.1 for the IMV and NIMV groups, respectively (P = 0.006). Days of hospitalization were 11.1 ± 4.7 and 6.5 ± 1.9 for the IMV and NIMV groups, respectively (P = 0.001). These results are shown in Table 4.

Long-term survival

Long-term survival is defined as survival rate, beginning at the point of hospital admission. Cumulative survival rates at 6 months were 71.4% for the IMV group and 80.0% for the NIMV group. The log-rank test analysis of these results is depicted in Fig. 1 (P = 0.80).

Table 4

Table 2

Spirometry values at stability, in 12 patients under NIMVa

FVC (% predicted) FVC–ML FEV1 (% predicted) FEV1–ML FEV1/CVF

55.5% 1195 ml 30.9% 651.3 ml 0.54

(Range: 42–71) (Range: 570–1860) (Range: 24–38) (Range: 350–1000) (0.46–0.62)

a Data are presented as numbers and percentages unless otherwise specified.

FEV1, forced vital capacity in the first second; FEV1/CVF, FEV1/CVF ratio; FVC, forced vital capacity.

Table 3

Outcome Mortality (%) Duration of hospital stay (days) Duration of mechanical ventilation (days)

IMV n = 12

NIMV n = 12

P value

33.33 5.6 ± 1.2

16.70 3.6 ± 1.1

0.01* 0.006*

11.1 ± 4.7

6.5 ± 1.9

0.001*

a Data are presented in number and percentages unless otherwise specified.

IMV, invasive mechanical ventilation; NIMV, non-invasive mechanical ventilation. *P < 0.05 = statistically significant.

Evaluation of parameters in patients under NIMVa

Variables Arterial blood, pH PaCO2, mmHg HCO3, mmol/l PO2, mmHg SO2, % HR beats/min RR, breaths/min Systolic blood pressure, mmHg Diastolic blood pressure, mmHg GCS score a

Final outcome evaluation in studied groupsa

Baseline

1h

3h

6h

12 h

24 h

ANOVA

7.18 ± 0.05 75.3 ± 13.8 32.3 ± 8.3 103 ± 43.3 95.6 ± 4 98.9 ± 19 37.8 ± 10.5 130.8 ± 22.7

7.24 ± 0.03 60.2 ± 12.4 30.1 ± 8 82.2 ± 13.5 96.1 ± 2 93.9 ± 12.7 27 ± 5.9 128 ± 11.3

7.28 ± 0.03 56.4 ± 12.4 28 ± 5.5 84.6 ± 10.3 94.7 ± 2.5 91 ± 12.7 26.6 ± 6.6 128 ± 10.4

7.30 ± 0.06 54.4 ± 15.3 28.6 ± 4.2 87.9 ± 12.7 97.7 ± 2.4 89.7 ± 14.6 24.2 ± 6 129.6 ± 8.8

7.36 ± 0.04 49.9 ± 7.9 28.4 ± 4.7 75.8 ± 13.8 94 ± 2.7 85 ± 7.6 25.4 ± 4.4 127.2 ± 6.4

7.39 ± 0.04 44.7 ± 11.6 25.3 ± 6.1 86.2 ± 18 95 ± 3.4 79.1 ± 11.1 22.7 ± 2.2 128.1 ± 7

0.01* 0.005* 0.7 0.5 0.3 0.7 0.5 0.6

79.5 ± 9.7

79 ± 5.3

76.9 ± 5.8

78.5 ± 4.9

79.0 ± 3

5.5 ± 1.3

9.4 ± 0.9

11.2 ± 1.3

12.9 ± 2.3

14.8 ± 0.4

Data are presented as numbers and percentages unless otherwise specified.

NIMV, Noninvasive mechanical ventilation. *P < 0.05 = statistically significant.

GCS, Glasgow Coma Scale score.

76.3 ± 6.7 15

0.5 0.02*

Noninvasive mechanical ventilation in patients with COPD Briones Claudett et al. 5

to the inclusion of patients with pneumonia, the ventilatory strategy associated with the primary disease, the interphase, or the manufacturer model of the ventilators used. In addition, all the patients included in our study showed a decline in their levels of consciousness (GCS scores of less than 8), owing to a hypercapnic encephalopathy. Patients with a pH level of less than 7.25 and with psychomotor stress tolerated NIMV to a lesser degree.

Fig. 1

Survival functions

1.0

Log rank test (P= 0.80)

0.9 Cumulative survival

0.8 0.7 0.6 0.5 Groups

0.4 0.3

NIMV

0.2

IMV

0.1 0.0 3.0

3.5

4.0 4.5 5.0 Time (months)

5.5

6.0

Cumulative survival rate at 6 months. Survival rate was 71.4% for IMV group and 80% for the NIMV group. IMV, invasive mechanical ventilation; NIMV, noninvasive motion ventilation.

Discussion We found a clear benefit for early intervention with NIMV in the ED, in patients with severe hypercapnic neurological dysfunction and a pH of less than 7.25. Our study demonstrated a significant reduction in mortality, days of hospital stay, and days on mechanical ventilation, compared with conventional IMV therapy.

The mortality rate observed in the IMV group was 33.3%.

The severity of the COPD varies from study to study, with mortality percentages ranging from 28 to 82% [26– 33]. Soo Hoo et al. [34] describe a 70% mortality rate in 16 patients with hypercapnic episodes and pH levels of less than 7.25. In contrast, early intubated patients, within the first 2 ± 2 h (mean ± SD), presented an increased mortality rate of 27%.

In a randomized trial in which Conti [14] compared the use of NIMV versus IMV, no differences in mortality were found. We should consider that in this study NIMV was not used early on and that most of the patients presented with pneumonia, which added up to a less favorable prognosis with the use of NIMV [35]. Squadrone [19] compared 64 COPD patients presenting advanced respiratory failure with 64 mixed controls, and find a high percentage (62.5%) of treatment failure with NIMV. This work, nonetheless, also includes patients with pneumonia as a cause of respiratory failure. In this study, 37.5% of the patients who failed to respond to NIMV showed mask intolerance and discomfort.

The differences observed between our study and those of Conti [14] and Squadrone [19] are related to an early implementation of NIMV; however, they are not related

Randomized studies [8–11] showing benefits with the early use of NIMV enrolled patients who had mild-tomoderate respiratory failure and an average pH level of ± 7.27. Furthermore, these studies were also carried out on hospitalized [6,7,36] patients presenting with pH values of more than 7.30 and without any severe neurological deficit.

We found a significant improvement in the PCO2, pH, and GCS scores in patients undergoing NIMV after the first 3 h of treatment (ANOVA; P < 0.05). Some studies report changes in the pH, PCO2, and neurological statuses that related to the success or failure of the NIMV therapy during the initial hours [35,37]. Adnet [38] described favorable results after treating a patient with a GCS score of 3, a pH of 7.06, and a PCO2 of 185 mmHg with NIMV for 12 h.

Corrado et al. [18] described 150 patients with acute respiratory failure and hypoxemic hypercapnic coma, who were retrospectively evaluated. Of these patients, 79% had COPD associated with a decompensated acidosis (pH 7.13, GCS score ranging from 3 to 8). All patients received intermittent positive-pressure ventilation with a mechanical ventilator. Forty-five patients failed to respond to the treatment (30%) and 36 (24%) died.

Gonzalez et al. [20] described a total of 76 patients in coma. Of these, 80% responded to noninvasive positivepressure ventilation (NPPV) therapy, and 25 of them died during their hospital stay. Our results, in contrast to the observations of Corrado and Gonzalez, show a less-thanaverage PCO2 (72.31 ± 13.8), but similar values in GCS scores. The results obtained from our patients are perhaps on account of the geographical area of their origin (the Ecuadorian highlands region), where altitude can influence the ABG values.

Benhamou et al. [39] obtained a favorable response with the use of NIMV therapy in two of three patients with COPD and with a GCS score of less than 3. In our study, two patients failed the NIMV treatment: the first one during the first 6 h of NIMV, and the second, after 72 h of NIMV in the general medical ward.

Using the protocol described previously, we found an 83.4% effectiveness, similar to that in studies reporting

6 European Journal of Emergency Medicine 2008, Vol 00 No 00

patients with pH values of more than 7.25 and mild-tosevere neurological deterioration [8–10].

Our ventilatory strategy was safe and effective, with strict control of the GCS score and ABGs (PCO2 and pH), which allowed us to decide on an early transfer to the ICU in nonresponsive patients, as well as an early resolution to initiate IMV for a maximum period of 6 h.

Anto´n et al. [40] reported an improvement in levels of consciousness, pH, and PCO2 during the initial hours of NIMV therapy, thereby predicting a favorable outcome.

We should, however, be cautious with patients who might present with delayed failure (patients with episodes of acute respiratory failure, limitation of daily activities, and a low initial pH), as described by Moretti et al. [41].

One patient presented a limitation of 2 on his functional activity, a pH of 7.10, hyperglycemia of > 250 mg/dl, and developed cardiac arrhythmia after 72 h of admission.

Moretti et al. [41] described the presence of metabolic complications in 20% of patients with delayed failure.

Senef et al. [24] observed the presence of respiratory abnormalities in patients with COPD, which they associated with the worst prognosis.

In our study, patients treated with NIMV had a forced expiratory volume in 1 s (FEV1) of 30.9% [26,40]. This severe obstruction implied major stress in their ventilatory capacity and ventilatory muscle strength. Some authors report that patients with low levels of FEV1 [40,42] might show better results.

We also demonstrated, as Plant et al. [7] did, that no differences existed in the mortality rate at 6 months. This is different from the results reported by Confalonieri et al.

[43], who found differences at the 1-year mark.

Additional variables that influence the results and should be evaluated and studied are levels of PCO2 at home [44], functional status, nutritional status, and home oxygen administration.

This study has some considerations worth mentioning, which did not limit the effectiveness of our observations: 1. Some patients (41.6%) in the IMV group, who did not have an actual COPD diagnosis, established a previous spirometry record.

2. We did not quantify some of the factors that could influence the results, such as comorbidity and the use of home oxygen before admissions.

3. As our study had been carried out in one center only, our findings could not be applied to other populations.

4. We only studied a small group of patients with similar characteristics of hypercapnic neurological

deterioration, dysfunction of no more than two organs, and with COPD. Despite these limitations, our study has contributed important data. It is the first study that tries to establish the effect of the early use of NIMV in selected patients with severe acute respiratory failure (pH < 7.25). It also establishes a strategy for maintaining patients with COPD and hypercapnic neurological deficits in the ED, improving by these means the use of economic and human resources, and limiting admissions to the ICU, which is the most expensive option [45,46].

This study compares the use of NIMV versus IMV in patients with severe respiratory acidosis and hypercapnic neurological deterioration. Both therapies were implemented immediately after the admission of the patient, to diminish the effects that usual therapeutical measurements might involve (use of high concentrations of oxygen and an excess of alveolar ventilation in patients with a severe airway obstruction) [42].

In view of our results, we consider that a severe neurological dysfunction and a pH level of less than 7.25 do not constitute absolute contraindications to the early use of NIMV. NIMV can be used with favorable results following an adequate guided strategy, to be accomplished in the ED. Randomized multicentric trials involving a larger number of patients, will, however, clarify this observation.

Acknowledgement The authors thank Michele Vitacca, MD, for his helpful suggestions and for his assistance in preparing the manuscript.

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