Abstract
Prolonged duration of endotracheal mechanical ventilation (ETMV) is associated with an increased morbidity and mortality in intensive care unit (ICU) patients. The aim of this study was to assess the usefulness of noninvasive ventilation (NIV) as a systematic extubation and weaning technique to reduce the duration of ETMV in acute-on-chronic respiratory failure (ACRF). Among 53 consecutively intubated patients admitted for ACRF, we conducted a prospective, randomized controlled trial of weaning in 33 patients who failed a 2-h T-piece weaning trial (2 h-WT) although they met simple criteria for weaning. Conventional invasive pressure support ventilation (IPSV) was used as the control weaning technique in 16 patients (IPSV group), and NIV was applied immediately after extubation in 17 patients (NIV group). The two weaning groups were similar for type of chronic respiratory failure (CRF), pulmonary function data, age, Simplified Acute Physiology Score (SAPS II), and severity of ACRF on admission. The characteristics of the two groups were also similar at randomization. In the IPSV group, 12 of 16 patients (75%) were successfully weaned and extubated, versus 13 of 17 (76.5%) in the NIV group (p = NS). NIV like IPSV significantly and similarly improved gas exchange in relation to that achieved during 2 h-WT (p < 0.05). The duration of ETMV was significantly shorter in the NIV (4.56 ± 1.85 d) than in the IPSV group (7.69 ± 3.79 d) (p = 0.004). NIV also reduced the mean period of daily ventilatory support, but increased the total duration of ventilatory support related to weaning (3.46 ± 1.42 d, versus 11.54 ± 5.24 d with NIV; p = 0.0001). Most patients in the IPSV group developed complications related to ETMV and / or the weaning process, but the difference was not significant (nine of 16 versus six of 17). The durations of ICU and hospital stays and the 3-mo survival were similar in the two groups. In conclusion, NIV permits earlier removal of the endotracheal tube than with conventional IPSV, and reduces the duration of daily ventilatory support without increasing the risk of weaning failures. NIV should be considered as a new and useful systematic approach to weaning in patients with ACRF who are difficult to wean.
The clinical efficacy of noninvasive ventilation (NIV) has been demonstrated in the management of acute-on-chronic respiratory failure (ACRF) of various and particularly of obstructive etiology (1-5). The main objective of NIV is to avoid the need for intubation or endotracheal mechanical ventilation (ETMV) while ensuring effective alveolar ventilation and oxygenation. During ACRF, NIV could therefore avoid the need for intubation in 60 to 70% of cases in selected patients, consequently reducing these patients' morbidity, mortality, and length of hospital stay (4, 5). Apart from its multiple specific complications (6), ETMV can lead to excess morbidity or even mortality by inducing weaning difficulties, especially in chronic respiratory failure (CRF) (7-9), and nosocomial pneumonia, which is often related to prolonged ETMV (10, 11). Thus, prolonged ETMV, whose economic implications are far from negligible (12), can considerably decrease patient survival (9, 10). To improve the prognosis, it might be useful to reduce the duration of ETMV by delivering effective ventilatory support without an endotracheal prosthesis, such as with NIV. NIV could be useful in two circumstances of extubation and weaning from ETMV: when adopting a systematic approach to a weaning procedure that must be considered for patients who are difficult to wean, or for a practical approach to weaning when the clinician faces difficulties with conventional weaning techniques leading to prolonged ETMV. Several uncontrolled studies (13, 14) have reported the clinical benefits of NIV in cases of failure with conventional weaning techniques; the most useful technique of weaning appears to be pressure-support ventilation (PSV) and spontaneous breathing with a T-piece (15-17). On the other hand, only one previous study has to our knowledge specifically evaluated NIV as a technique for early extubation and weaning from ETMV (18).
The aim of the present study was to assess the usefulness of NIV as a systematic extubation and weaning technique for reducing the duration of ETMV in difficult-to-wean patients intubated for ACRF, in comparison with conventional weaning through invasive PSV (IPSV).
The study was a randomized prospective study conducted from February 1996 to June 1997 at the Charles Nicolle University Hospital, and was approved by the local ethics committee. Selected patients were those admitted consecutively to our 22-bed medical intensive care unit (ICU) for ACRF requiring ETMV in the assisted-controlled ventilatory mode (ACV) immediately or in the few hours after admission. Chronic respiratory failure was defined on the basis of clinical history, chest X-ray, and/or previous pulmonary function tests. Selected patients were randomized only when they met simple weaning criteria but failed a 2-h T-piece weaning trial of spontaneous breathing (2 h-WT). Patients also had to give their written informed consent. Patients with chronic respiratory failure receiving ETMV and presenting one of the following criteria were not included: difficult intubation during ETMV, presence of swallowing disorders, ineffective cough or persistence of bronchial congestion at the time of weaning, lack of cooperativity, and history of recent gastrointestinal surgery or intestinal ileus.
The following protocol was observed. All patients were screened daily after 48 h on ETMV. Weaning from ETMV was considered when the criteria described subsequently were met. The variables for weaning, evaluated daily, were (19): maximal inspiratory pressure (MIP) measured on the inspiratory circuit with an aneroid manometer; minute ventilation (V˙e), vital capacity (VC), tidal volume (Vt), respiratory frequency (f), and the f/Vt ratio measured with a portable spirometer during the first 2 min after disconnecting the ventilator (20, 21), and arterial oxygen saturation (SaO2 ) during ACV. The 2 h-WT with additional O2 and air humidification was then performed within 24 h if at least three of the following criteria were met (15-17, 19): MIP ⩽ −25 cm H2O, V˙e ⩽ 10 L/min, VC ⩾ 10 ml/kg, Vt ⩾ 5 ml/ kg, f ⩽ 35/min, f/Vt ⩽ 105 cycles/min/L, and SaO2 > 90% for an Fi O2 of 40% in ACV. If these criteria were not met, ETMV in ACV was continued and the criteria were reevaluated daily. The success or failure of the 2 h-WT was assessed on the basis of clinical and hemodynamic tolerance and arterial blood gas measurements made at the end of the 2 h-WT or at any time before they were clinically required. In the case of satisfactory tolerance, patients were simply extubated and given nasal oxygen therapy. Otherwise, patients were included in the study when they presented one of the following signs at the end of or at any time during the 2 h-WT (15-17): sweating and/or agitation, drowsiness, f > 35/min or increase in f ⩾ 50%, decrease in SaO2 of ⩾ 5%, increase in heart rate or systolic blood pressure of ⩾ 20%, and PaO2 ⩽ 8 kPa and/or pH ⩽ 7.35. For the purpose of this study, these patients were considered as difficult to wean from mechanical ventilation. Randomization and introduction of the weaning procedure with IPSV (IPSV group) or NIV (NIV group) were done during the 24 h after failure in the 2 h-WT. In the NIV group, extubation was followed immediately by introduction of NIV. All patients were monitored continuously with a cardioscope, oximeter, and noninvasive blood pressure measurement during the weaning process. Ventilatory support in both groups was gradually decreased according to clinical and hemodynamic tolerance and with arterial blood gas control by the attending physician, who was not involved in the study. Criteria for poor tolerance were the same as those described for the 2 h-WT. The decrease in ventilatory support was continued until extubation in the IPSV group, and until withdrawal of all ventilatory support in the NIV group whenever possible. In both groups, home NIV was considered by the attending physician before hospital discharge when the patient was clinically stable and when supplementary nasal oxygen therapy failed to increase the daytime PaO2 by > 7.5 kPa without an increase in the awake PaCO2 of > 8 kPa.
During ETMV and the weaning period, all patients were ventilated with the same type of ventilator (Evita; Dräger Medical, Lübeck, Germany), allowing the use of a flow or pressure mode and application of the two weaning techniques. These two modalities were clearly explained to the patient before randomization. NIV was delivered with a nasal or face mask and in flow or pressure mode, depending on the patient's facial morphology and clinical tolerance (22). Intermittent periods of NIV, initially lasting from 2 to 4 h, were separated by periods of spontaneous breathing with nasal oxygen therapy, initially lasting from 1 to 2 h and then being gradually increased throughout the day according to the patient's autonomous breathing, arterial blood gas values, and clinical tolerance, to finally achieve a nocturnal period of exclusive NIV, followed by the withdrawal of NIV whenever possible. The ventilatory mode used with NIV (flow or pressure mode) and its settings were continuously adjusted according to the patient's respiratory comfort, the presence of air leaks, and the regular monitoring of arterial blood gas values (22). In the IPSV group, the initial pressure support level was selected in order to obtain an f between 20 and 30 cycles/min (15). Invasive PSV was delivered with a rapid initial flow rate of 0.1 to 0.25 s, which generates less of a respiratory workload in patients with chronic respiratory failure (23). The IPSV level was then gradually decreased by 3 to 5 cm H2O according to the patient's clinical tolerance of the previous level of IPSV as assessed for at least 2 h. Extubation was performed when the patient tolerated an IPSV level ⩽ 8 cm H2O (24). In order to follow a similar strategy of decreasing ventilatory support in the IPSV and NIV groups, the attending physician was asked to observe at least two periods of increased spontaneous breathing in the NIV group and at least two periods decrease in the level of IPSV in the IPSV group during the day, depending on patients' arterial blood gas values and clinical tolerance. The Fi O2 used during the initial phase of the weaning procedure in both groups, was the same as that used during the last period of ACV, and was then subsequently adjusted according to arterial blood gas controls. During periods of spontaneous breathing in the NIV group, the nasal oxygen flow rate was adjusted in order to obtain an SaO2 ⩾ 92%. Regardless of the weaning technique used, positive end-expiratory pressure (PEEP) could be used to facilitate ventilator triggering when intrinsic PEEP (iPEEP) was suspected, particularly in patients with chronic obstructive pulmonary disease (COPD). The external PEEP applied should not have exceeded 80% of the dynamic iPEEP measured during ETMV in ACV (25). Additionally, the sensitivity of the ventilator trigger was set to a maximum level with the two techniques.
During the weaning period, optimal respiratory (β2-mimetics, corticosteroids, antibiotic therapy, mucolytics, physiotherapy) and cardiac medical treatment were given when necessary (26). Enteral feeding via a nasogastric tube was always preferred in the IPSV group, at a rate of 30 to 35 kcal/kg/d, and oral feeding (from the 24th hour after extubation) was preferred in the NIV group.
The patient's clinical and demographic characteristics were recorded on admission. The two primary evaluation criteria were the total duration of ETMV prior to extubation and the success or failure rate of weaning with the two techniques. Successful weaning in both groups was defined as the absence of reintubation within 5 d after extubation. Weaning failure was defined as the need to reintubate the patient within 5 d after extubation in both groups, or when extubation was impossible 5 d after the start of weaning in the IPSV group. We also examined the total duration of ventilatory support related to the weaning procedure. This was defined as the duration of ventilatory support from randomization until extubation in the IPSV group, until withdrawal of ventilatory support in the NIV group, or until the decision for home NIV in both groups. The other evaluation criteria were complications related to ETMV and/or weaning procedure, length of ICU stay, length of hospital stay, and patient's outcome after 3 mo. Discharge from the ICU to another general hospital ward was authorized under the following conditions: when the patient's clinical status remained stable for at least 48 h after extubation in the IPSV group; when the clinical status remained stable for at least 48 h after extubation in the NIV group, whether or not the patient required intermittent diurnal and/or nocturnal NIV.
Quantitative data for the two groups were compared with Student's t test, and qualitative data were compared with the chi-square test. The comparison of gas exchange in each group was done with Wilcoxon's test. The cumulative probability of remaining on ETMV and on ventilatory support was calculated with the Kaplan–Meier method, and the comparison between groups was made with the log-rank test. The results are expressed as mean ± SD. A difference was considered statistically significant when the alpha probability was less than 0.05 (p < 0.05).
Throughout the study period, 20 (38%) of the 53 selected patients tolerated the 2 h-WT and were simply extubated. Two of these patients had to be reintubated at 4 h and 48 h after extubation because of laryngeal edema and cardiogenic pulmonary edema, respectively. The 2 h-WT failed in the remaining 33 patients, and 16 were randomized to the IPSV group and 17 to the NIV group. The main clinical and functional characteristics of the two weaning groups at the time of their hospital admission are summarized in Table 1. No difference was observed between the two groups, and arterial blood gas analyses showed similarly severely decompensated respiratory acidosis in both groups. Table 2 illustrates the patients' ventilatory characteristics and weaning criteria at randomization. There was no difference between the two weaning groups for any of the clinical or physiologic parameters. Ventilator settings were initially set at a level of 17.5 ± 2.8 cm H2O with an Fi O2 of 43 ± 5% in the IPSV group. The initial ventilator settings for the NIV group were Vt = 625 ± 41.83 ml, f = 16.5 ± 2.7, and Fi O2 = 45 ± 5% for six patients using the assist-control mode, and a pressure support level of 14 ± 3.63 cm H2O and Fi O2 of 43 ± 7% for 11 patients using the pressure-support mode. An external PEEP was applied for six patients in each group, with a similar mean level (4 ± 1 cm H2O). As in the IPSV group, the gas exchange control showed a significant improvement in response at up to 1 h of NIV after extubation as compared with the values obtained during the 2 h-WT, with no difference between the two weaning groups (Table 3). Table 4 shows that weaning with NIV significantly decreased the total duration of ETMV as compared with weaning in the IPSV group, and the difference between the two groups extended to more than 3 d (p = 0.004) (Table 4). The day-to-day analysis shown in Figure 1 confirmed this result, and the cumulative probability of remaining on ETMV was lower in the NIV group than in the IPSV group (p = 0.004). Importantly, these results were obtained with a similar weaning success or failure rate in both groups (Table 4). In contrast, the total duration of ventilatory support related to the weaning procedure was greater in the NIV group than in the IPSV group (Table 4 and Figure 2). However, the mean time per day spent on ventilatory support was greater in the IPSV group during the first 5 d of the weaning period (Figure 3). Most patients in the IPSV group developed complications related to the ETMV and/or the weaning process (one or several per patient), but the difference between the two groups in this respect was not significant (Table 4). The complications are summarized in Table 5. All patients classified as experiencing weaning failure in both groups were reintubated within 5 d after extubation. No patient in the IPSV group received NIV after extubation. The mean durations of ICU and hospital stay were also similar in both groups. The same results were observed when weaning failures were excluded from the two groups (11.75 ± 5.17 d versus 10.15 ± 3.83 d, and 23.58 ± 6.33 d versus 22.62 ± 7.83 d, respectively, for the IPSV and NIV groups). The 3 mo survival of the patients was comparable, at 87% for the IPSV group and 100% for the NIV group, respectively. The two in-hospital deaths observed in the IPSV group were attributed to the severity of the underlying respiratory disease, but were not considered to be directly related to ETMV or to the weaning procedure. One patient was tracheostomized and had diffuse bronchiectasis, and the other had refused tracheostomy because of advanced emphysema. However, the two groups differed in terms of their ventilatory treatment after hospital discharge, as seven patients (41%) in the NIV group were treated with home NIV and no patient in the IPSV group met the criteria for home NIV (p = 0.03) (Table 4).
| IPSV Group (n = 16) | NIV Group (n = 17) | p Value | ||||
|---|---|---|---|---|---|---|
| Age, yr | 64.94 ± 9.09 | 63.59 ± 14.62 | NS | |||
| Type of CRF | NS | |||||
| COPD | 8 | 9 | ||||
| Restrictive | 4 | 4 | ||||
| Mixed | 4 | 4 | ||||
| Previous conditions | NS | |||||
| LTO | 4 | 6 | ||||
| Home NIV | 0 | 1 | ||||
| Intubation* | 5 | 7 | ||||
| FEV1, L† | 0.8 ± 0.28 | 0.95 ± 0.45 | NS | |||
| FEV1, % pred† | 30.4 ± 12.07 | 38 ± 14 | NS | |||
| VC, L† | 1.69 ± 0.62 | 1.89 ± 0.88 | NS | |||
| VC, % pred† | 48.45 ± 15.56 | 64 ± 24.33 | NS | |||
| FEV1/VC† | 45.3 ± 13.43 | 49.64 ± 10.77 | NS | |||
| TLC, L† | 5.41 ± 2.31 | 4.54 ± 2.77 | NS | |||
| TLC, % pred† | 89.7 ± 36.1 | 80.09 ± 35.66 | NS | |||
| SAPS II | 39.25 ± 11.66 | 37.59 ± 9.77 | NS | |||
| PaO2 , kPa‡ | 8.61 ± 6.10 | 9.76 ± 6.14 | NS | |||
| PaCO2 , kPa‡ | 10.93 ± 4.05 | 11.40 ± 4.41 | NS | |||
| pH‡ | 7.24 ± 0.12 | 7.26 ± 0.10 | NS |
| IPSV Group (n = 16) | NIV Group (n = 17) | p Value | ||||
|---|---|---|---|---|---|---|
| Duration of ETMV, d | 4.50 ± 2.99 | 4.56 ± 1.85 | NS | |||
| SaO2 , % | 93.31 ± 1.96 | 93.65 ± 1.84 | NS | |||
| MIP, cm H2O | 29.25 ± 4.61 | 29.47 ± 5.86 | NS | |||
| VE, L/min | 7.35 ± 2.7 | 7.86 ± 2.49 | NS | |||
| VC, ml/kg | 15.66 ± 12.23 | 11.92 ± 9.11 | NS | |||
| Vt, ml/kg | 5.55 ± 1.3 | 4.93 ± 1.75 | NS | |||
| f, breaths/min | 23.06 ± 4.09 | 23.18 ± 3.84 | NS | |||
| f/Vt, breaths/min/L | 71.12 ± 19.54 | 67.65 ± 21.55 | NS | |||
| PaO2 , kPa* | 9.27 ± 1.29 | 11.37 ± 3.15 | NS | |||
| PaCO2 , kPa* | 8.14 ± 1.33 | 8.68 ± 0.84 | NS | |||
| pH* | 7.35 ± 0.06 | 7.33 ± 0.03 | NS | |||
| 2 h-WT tolerance, min | 65 ± 43.7 | 88.24 ± 35.92 | NS |
| 2 h-WT | 1 h Postrandomization | p Value | ||||
|---|---|---|---|---|---|---|
| IPSV group (n = 16) | ||||||
| PaO2 , kPa | 9.27 ± 1.29 | 11.26 ± 2.22 | 0.005 | |||
| SaO2 , % | 92.64 ± 2.57 | 97.10 ± 3.25 | 0.001 | |||
| PaCO2 , kPa | 8.14 ± 1.33 | 7.72 ± 0.90 | 0.03 | |||
| pH | 7.35 ± 0.06 | 7.37 ± 0.03 | 0.002 | |||
| HCO3 −, mmol/L | 33.14 ± 4.05 | 32.75 ± 2.92 | NS | |||
| NIV group (n = 15) | ||||||
| PaO2 , kPa | 11.37 ± 3.15 | 13.60 ± 1.92 | 0.006 | |||
| SaO2 , % | 93.12 ± 7.5 | 97.24 ± 0.97 | 0.001 | |||
| PaCO2 , kPa | 8.68 ± 0.84 | 8.13 ± 1.10 | 0.02 | |||
| pH | 7.33 ± 0.03 | 7.36 ± 0.04 | 0.002 | |||
| HCO3 −, mmol/L | 32.67 ± 2.88 | 33.25 ± 3.33 | NS |
| IPSV group (n = 16) | NIV group (n = 17) | p Value | ||||
|---|---|---|---|---|---|---|
| Total duration of ETMV, d | 7.69 ± 3.79 | 4.56 ± 1.85 | 0.004 | |||
| Weaning | ||||||
| Success rate | 12 (75%) | 13 (76.5%) | NS | |||
| Failure rate | 4 (25%) | 4 (23.5%) | NS | |||
| Total duration of ventilatory | ||||||
| support, d* | 3.46 ± 1.42 | 11.54 ± 5.24 | 0.0001 | |||
| Complications (patients) | ||||||
| Related to ETMV and weaning | 9 (56.3%) | 6 (35.3%) | NS | |||
| Related to weaning alone | 7 (43.7%) | 3 (17.5%) | NS | |||
| Length of ICU stay, d | 14.06 ± 7.54 | 12.35 ± 6.82 | NS | |||
| Length of hospital stay, d | 27.69 ± 13.09 | 27.12 ± 14.33 | NS | |||
| Outcome | ||||||
| In-hospital death | 2 | 0 | NS | |||
| Treatment after discharge | 0.03 | |||||
| SB/LTO | 7/6 | 6/4 | ||||
| NIV/Trach | 0/1 | 7/0 | ||||
| 3-mo survival | 14 (87.5%) | 17 (100%) | NS |
Fig. 1. Cumulative probability of remaining on ETMV in the IPSV and NIV weaning groups. IPSV = invasive pressure support ventilation; NIV = noninvasive ventilation; ETMV = endotracheal mechanical ventilation; analysis through Kaplan–Meier curves and p from log-rank test.
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Fig. 2. Cumulative probability of remaining on ventilatory support related to weaning in the IPSV and NIV groups. IPSV = invasive pressure support ventilation; NIV = noninvasive ventilation; analysis through Kaplan–Meier curves and p from log-rank test.
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Fig. 3. Time of daily ventilatory support during the first 5 d of the weaning period. IPSV = invasive pressure support ventilation; NIV = noninvasive ventilation; ( ) = number of patients in each group (**p = 0.0001; *p = 0.0005).
[More] [Minimize]| IPSV Group (n = 16) | NIV Group (n = 17) | |||
|---|---|---|---|---|
| Nosocomial pneumonia | 1 | 1 | ||
| Sinusitis | 0 | 1 | ||
| Bronchial congestion | 2 | 2 | ||
| Intestinal ileus | 2 | 1 | ||
| Subacute CPE | 2 | 0 | ||
| Arrhythmia | 1 | 0 | ||
| Hypercapnic encephalopathy | 1 | 0 | ||
| Reintubation < 5 d | 4 | 4 | ||
| Self-extubation | 1 | 1 | ||
| Arterial hypotension | 0 | 1 | ||
| Tube obstruction | 0 | 1 | ||
| Total number of complications | 14 | 12 |
This study shows that NIV, used as an early extubation and weaning technique, can reduce the duration of ETMV (i.e., permits earlier removal of the endotracheal tube) as compared with conventional IPSV weaning in intubated patients with ACRF who are difficult to wean. Furthermore, the benefit from the reduced duration of ETMV is obtained without any increased risk of weaning failures as compared with IPSV weaning. The study also shows that weaning with NIV reduces the period of daily ventilatory support during the first 5 d of the weaning period, but does not reduce the total duration of ventilatory support related to weaning. To our knowledge, this is one of the first controlled randomized prospective studies to demonstrate the value of NIV in this situation (18). Moreover, the study suggests that NIV could reduce ETMV-related morbidity by decreasing the duration of ETMV.
The role of NIV as an extubation and weaning technique can be justified by the various pathophysiologic mechanisms occurring in passage from ETMV to spontaneous breathing. In the case of weaning difficulties, these mechanisms essentially involve respiratory muscle fatigue and altered gas exchange, which are interdependent (27). Therefore, the patient will tend to adapt by modifying his or her breathing pattern, usually by increasing f and decreasing Vt (20). These mechanisms correspond to those most often observed during acute exacerbations in COPD patients. However, it is now clearly demonstrated that NIV with either the flow or pressure mode allows respiratory muscle rest (22, 28-30), and improves the patient's breathing pattern (22, 29, 30) and gas exchange (1-5, 22, 29, 30) in this situation. Furthermore, the patients most likely to benefit from NIV would be those with hypercapnic acute respiratory failure (31), a frequent situation in cases of weaning failure (20). Our results confirm these data by demonstrating diminished alveolar hypoventilation in response to NIV following extubation. From a clinical viewpoint, the value of NIV as an early extubation and weaning technique can also be justified by the weaning difficulties observed in 20 to 80% of patients, depending on the series and the underlying disease (7, 8), and by the capacity for ventilator dependency of approximately 25 to 45% of these patients for more than 21 d (9) regardless of the weaning technique used (15-17). These difficulties in weaning therefore require prolonged ETMV and hospitalization, with consequently increased morbidity and mortality (9-11) and inevitable major human as well as economic repercussions (12, 32).
Our results confirm those of previously published studies. Although retrospective and uncontrolled, these studies have nevertheless demonstrated the feasibility and clinical value of NIV in facilitating weaning from prolonged ETMV in cases of difficulties with conventional weaning techniques (13, 14), and in preventing reintubation in cases of acute postextubation respiratory failure (1). Favorable results were also obtained by simple application of an external PEEP with a mask after extubation or decannulation in patients with CRF (33-35). Apart from its methodology, our study also differs from these previous studies in its systematic approach, in the use of NIV when a weaning procedure was considered, and not only when the clinician was faced with weaning difficulties with conventional techniques. The study suggests that an average of 3 d can be saved from the total duration of ETMV, and that it is probably unnecessary to wait for failure of other weaning techniques, such as IPSV, before considering NIV in this situation.
These results would appear to be critically important in view of the increased morbidity and mortality related to prolonged ETMV (9, 10). In contrast to the shorter duration of ETMV with NIV, we also found a shorter period of daily ventilatory support in the first 5 d of the weaning period but a greater total duration of ventilatory support related to the weaning process in the NIV group. These results could be explained not only by the weaning technique used, since NIV was intermittently applied, but probably also by the variable delay involved in stabilizing patients with severe ACRF of various etiologies with NIV (2, 36). Nevertheless, it seems to us more important to reduce the duration of ETMV rather than the total duration of mechanical ventilation without intubation in relation to the weaning process, since the duration of ETMV appears to be an important risk factor for complications related to mechanical ventilation, and especially for nosocomial pneumonia (37). Most of the patients in our study who developed ETMV or weaning-related complications were in the IPSV group, but we failed to demonstrate any statistically significant difference in this from the NIV group, probably because of the sample size of the two groups. Complications related to ETMV that affect the duration of mechanical ventilation are essentially related to nosocomial pneumonia. Its impact on mortality nevertheless remains highly controversial (10, 11). In our population, only one patient in each group developed nosocomial pneumonia, and both were alive after 3 mo.
In a recently reported multicenter, randomized controlled trial involving 50 COPD patients, Nava and colleagues (18) also showed that NIV can be used as an early extubation and weaning technique. They also reported that NIV reduced the duration of mechanical ventilation and of ICU stay, and the occurrence of complications such as nosocomial pneumonia, and that it was associated with an improved 2-mo survival rate in comparison with conventional IPSV weaning. The discrepancy in our results and theirs could be explained by the way in which the two weaning techniques were applied, by the conditions of ICU discharge, and by the number of patients involved in each of the studies.
Other reported studies have shown that NIV applied in ACRF can reduce the duration of ICU and hospital stay (4). The authors who found this (15) also demonstrated favorable effect of IPSV weaning on the duration of ICU stay (17.5 ± 10.2 d), as compared with other weaning techniques using a T-tube or synchronized intermittent mandatory ventilation (SIMV) (27.8 ± 18.3 d). Although the difference between our two weaning groups in the duration of ICU stay was approximately 2 d, we failed to demonstrate any statistical significance in this respect. The time gained in reducing the total duration of ETMV with NIV therefore could not influence the duration of either ICU stay or of hospital stay. This must be interpreted with caution, since several explanations could be proposed for it. In the context of the protocol of our study, we insisted on observing most of our patients until the end of the 5-d period selected for the definition of weaning success or failure. Additionally, discharge of patients from our medical ICU depends mainly on the space available for these patients in other, general hospital wards, and on the ward capacity to continue NIV. The similar duration of hospital stay after ICU discharge in both our IPSV and NIV groups could reflect the difficulty of stabilizing the patient's respiratory status at an advanced stage of his or her disease and the time required to organize modalities for the patient's return home. In contrast, regardless of the weaning technique used, our results confirm those reported by Ely and coworkers (38), who found that the systematic use of simple objective criteria to decide whether or not to wean the patient, although decreasing the duration of ETMV, did not significantly influence either the duration of ICU or of hospital stay.
In contrast, the ventilatory treatment after hospital discharge differed between our two study groups, since almost 41% of the patients in the NIV group were discharged with home NIV. These data could reflect a selection bias in our randomization, since a double-blind control study could not be performed. This nevertheless appears unlikely, because only one patient in the NIV group had previously received home nocturnal NIV for obstructive sleep apnea syndrome. Furthermore, home NIV was selected according to strict criteria defined in the general hospital ward by the patient's attending physician, who was not involved in the study. Despite similar clinical and functional characteristics of patients in the IPSV and NIV groups on admission, these data may simply suggest more severe chronic respiratory failure in the NIV-group patients as reflected by the previous conditions in this group.
Several studies have shown that the duration of ETMV depends not only on the weaning strategy used and the way in which it is applied (15-17), but also on daily objective evaluation of the predictive criteria for weaning (38). Our systematic approach combined both objective evaluation and comparison of two weaning techniques. Because evaluation was the same in the two groups, with a similar duration of ETMV prior to weaning, the difference observed for the total duration of ETMV could only be attributed to the technique used. This difference was nevertheless expected, since we used two very different techniques in that NIV requires extubation. However, it appeared essential to demonstrate that the benefit in terms of duration of ETMV was not obtained at the expense of greater complication and/or reintubation rates in the NIV group. Under these conditions, the criticism that could be formulated in relation to our results would apply to the way in which we used conventional IPSV, owing to the impossibility of conducting a double-blind control trial. Although this type of bias cannot be formally excluded, it is unlikely to have significantly influenced our results, because in order to reduce to a minimum the subjective nature of medical decisions, we adopted a similar strategy of decrease in ventilatory support in the two groups, and set strict evaluation criteria for tolerance of ventilatory support in each group. Furthermore, the patient's daily attending physician was not directly involved in the study, but was only required to comply with these criteria. Additionally, with regard to conventional weaning using IPSV in practice, the mean duration of our procedure was shorter (3.19 ± 1.35 d) than that reported either by Brochard and colleagues (5.7 ± 3.7 d) (15) or Esteban and associates (4 d) (16). Therefore, our results and those of previous studies (15-18) emphasize the need for protocol guidelines to improve weaning practices. Our systematic approach, using NIV as an early extubation and weaning technique, could be included in these guidelines to reduce the duration of ETMV (18, 38, 39).
In conclusion, we have shown that it is possible to use NIV immediately as an early extubation and weaning technique in intubated ACRF patients who are difficult to wean. In this situation, NIV permits earlier removal of the endotracheal tube and reduces the duration of daily ventilatory support during the weaning period without increasing the risk of weaning failure over that with conventional weaning using IPSV. However, NIV does not reduce the total duration of ventilatory support related to the weaning process. A decrease in ETMV-related morbidity or mortality could therefore be expected with NIV (9, 10, 18, 37). Our results are certainly dependent on the weaning strategy and ventilatory techniques applied. However, in general practice, these results should permit a more active approach to weaning, and should prevent hesitation in the extubation of “borderline” patients with chronic respiratory failure after a 2 h-WT.
The authors thank Richard Medeiros for his advice in editing the manuscript, and Marie France Hellot for her statistical assistance.
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Presented in part at the Annual International Conference of the American Lung Association and American Thoracic Society, April 24–29, 1998, Chicago.
