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* From the Department of Medicine (Drs. Cook, Meade, Guyatt, and Aldawood), McMaster University, Hamilton, Ontario, Canada; the Department of Anesthesia (Dr. Butler), University of Western Ontario, London, Ontario, Canada; and the Department of Medicine (Dr. Epstein), New England Medical Center, Tufts University, Boston, MA.
Correspondence to: Deborah J. Cook, MD, McMaster University, Faculty of Health Sciences Center, Department of Clinical Epidemiology & Biostatistics, 1200 Main St West, Hamilton, Ontario, Canada; e-mail: debcook{at}mcmaster.ca
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Key Words: acupuncture • biofeedback • capnography • enteral nutrition • growth hormone • mechanical ventilation • meta-analysis • noninvasive ventilation • oximetry • systematic reviews • weaning
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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For example, the thermal effect of nutrition increases CO2 production in healthy patients and in those experiencing disease states. CO2 production may be determined in part by the composition of enteral or parental nutrition, which in turn may affect the weaning process.2 Other strategies to help achieve the goal of the safe and timely discontinuation of mechanical ventilation may involve devices and computers to monitor or drive the process of discontinuation,3 pharmacologic approaches to hasten it, and noninvasive ventilation to prevent extubation failure.4 5 Alternative strategies may focus on the provision of physiologic or psychological support during weaning.6
The objective of this systematic review is to examine the experimental evidence arising from randomized trials about miscellaneous interventions such as these designed to facilitate the process of weaning from mechanical ventilation.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Eligibility Criteria
For this section on miscellaneous interventions influencing the
weaning process, we included only published randomized controlled
trials (RCTs) of interventions not addressed in earlier sections in
this supplement. Studies reporting both clinical and physiologic
outcomes were included. We excluded interventions whose influence on
the duration of ventilation already has been summarized in a recent
systematic review (eg, sedation in the ICU7
).
Search for Relevant Studies
To identify relevant studies, we searched MEDLINE, Excerpta
Medica Database, HEALTHStar, Cumulative Index to Nursing and Allied
Health Literature, the Cochrane Controlled Trials Registry, and the
Cochrane Data Base of Systematic Reviews from 1971 to 1999, and we
examined the reference lists of all included articles.
Data Abstraction and Assessment of Methodological Quality
Data abstraction and methodological quality assessment were
performed in duplicate by two members of a team of five respiratory
therapists and five intensivists. The design features of RCTs
that we abstracted included the following: the method of randomization
and whether randomization was concealed; the definitions of weaning,
extubation, and reintubation; the extent to which groups were similar
with respect to important prognostic factors; whether investigators
conducted an intention-to-treat analysis; whether patients, clinicians,
and those assessing outcome were blind to allocation; the extent to
which the groups received similar cointerventions; and reporting of the
reasons for study withdrawal.
Statistical Analysis
We present both binary and continuous outcome variables.
Differences in means, relative risks, and their 95% confidence
intervals are reported. We did not pool results across studies due to
the diverse interventions incorporated in this review.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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E) was < 12 L/min (if their
PaO2 at the fraction of inspired
oxygen [FIO2] was > 60 mm Hg),
when their PaCO2 was 38 to 45 mm Hg,
and when their pH was 
7.3. The study was terminated as soon as
patients were able to tolerate 3 h of spontaneous breathing.
Patients were comparable at baseline with respect to basic demographics
and the preintervention duration of ventilation (approximately 64 and
70 h, respectively). Only one patient in the high-fat group developed delayed gastric emptying (feeds were held for 2 h, but recommenced with no further problem). The PaCO2 decreased significantly in the high-fat feeding group just prior to weaning but increased slightly in patients receiving the isocaloric feed (p = 0.003), whereas there was no difference in PaO2 and tidal volume (VT) or respiratory rate. The time from feeding commencement to successful weaning was significantly shorter in the high-fat group than the isocaloric feeding group (86.1 ± 17.8 h vs 148.7 ± 36.7 h, respectively).
In a second randomized unblinded enteral nutrition trial,9 32 medical ICU patients were allocated to (1) a high-fat/low-carbohydrate enteral feeding solution (Pulmocare; Ross Products [17% protein, 55% fat, and 28% carbohydrates]) or (2) isocaloric feeds (Ensure Plus; Ross Products [17% protein, 30% fat, ad 53% carbohydrates]). Nutritional requirements were calculated as per the previous trial. Patients were eligible if they had COPD, neurologic disease, or pneumonia without COPD. Patients were excluded if they had renal failure, hepatic failure, diabetes mellitus, or respiratory failure "without a prospect of weaning from the ventilator." Patients received mechanical ventilation using volume control. Weaning was started using continuous positive airway pressure (CPAP) when patients were afebrile, in hemodynamically stable condition, required positive end-expiratory pressure of < 10 cm H2O on FIO2, and when their bicarbonate level was < 28 mmol/L. CPAP continued for a maximum of 3 h until patients were too dyspneic or tired too continue; specific failure criteria were not reported. Rest periods lasted for 4 to 6 h between CPAP trials. The study was terminated when patients were able to tolerate 3 h of spontaneous breathing.
Adherence to the feeding regimens was successful in all but one patient in each group, in whom feeding was discontinued because of gastric distention. Patients were comparable at baseline with respect to illness severity and nutritional status. There were similar numbers of COPD patients in each arm of the study; however, in the high-fat group, 10 of 11 patients with COPD received mechanical ventilation for acute or chronic respiratory failure, vs 5 of 13 patients in the isocaloric feeding group.
The respiratory quotient was significantly lower in patients receiving
the high-fat/low-carbohydrate feed compared with the isocaloric feed
(0.72 ± 0.02 vs 0.86 ± 0.02, respectively; p < 0.01). The
E during weaning was also lower (8.8 ± 0.9 vs
10.5 ± 0.8, respectively; p < 0.01). A similar proportion of
patients in both arms of the study had a successful 3-h trial of
spontaneous breathing on CPAP (12 of 14 patients vs 13 of 16 patients,
respectively; p = 0.74).
Postextubation Noninvasive Ventilation
The hypothesis of this RCT is that functional residual capacity
after spontaneous breathing with a T-piece may be better restored with
noninvasive positive-pressure ventilation (NPPV) and CPAP than with
spontaneous breathing and physiotherapy, thereby minimizing pulmonary
edema and extubation failure. In a randomized unblinded trial of 75
cardiac surgery patients,10
three postextubation
interventions were evaluated after 10 to 14 h of controlled
ventilation and 30 min of T-piece breathing. Patients were extubated,
then randomized to the following: (1) NPPV (n = 25) involving bilevel
pressure ventilation using the spontaneous timed mode (S/T) via
nasal mask with an inspiratory positive airway pressure of 10 cm
H2O, an expiratory positive airway pressure of 5
cm H2O, and 10 L/min oxygen via nasal mask for 30
min; (2) CPAP at 7.5 cm H2O and
FIO2 at 0.5 for 30 min (n = 25);
and (3) chest physiotherapy for 10 min and oxygen via nasal mask at 6
L/min for 30 min (n = 25).
Left ventricular function and inotropic support were comparable across groups. Cardiac surgical, anesthetic, and preextubation ICU management for the entire cohort are well-described. No patients were unavailable for follow-up, and the analysis was intention-to-treat. All three groups had the following increases in pulmonary blood volume index (PBVI) over time: bilevel pressure ventilation, 17 mL/m2; CPAP, 9 mL/m2; and chest physiotherapy, 17 mL/m2. Following 30 min of each intervention, however, PBVI in the bilevel pressure ventilation group was significantly lower than that in the other two groups (p < 0.05). Extravascular lung water (EVLW) increased significantly from extubation through the 30-min intervention to 90 min following extubation in the chest physiotherapy group, compared to the other two groups (p < 0.05). All patients in each group underwent sustained extubation.
In the second randomized trial by Jiang and colleagues,11 NPPV was evaluated among 93 extubated patients, 56 of whom were electively extubated and 37 of whom underwent unplanned extubations. Patients were randomized to either (1) bilevel pressure ventilation delivering inspiratory positive airway pressure of 12 cm H2O and expiratory positive airway pressure of 4 cm H2O by face mask, which was temporarily removed for suctioning and eating, for up to 72 h or (2) oxygen therapy. All patients had blood gas values measured 1 to 3 h after extubation. Bilevel pressure ventilation was terminated, and patients were intubated if their blood gas levels deteriorated, or if labored breathing or hemodynamic stability developed.
Extubation failure was defined as the need for reintubation as judged by the attending physician. Patients had similar preextubation blood gas levels. Seven of 46 patients in the oxygen therapy group underwent reintubation, whereas 13 of 47 patients in the bilevel pressure ventilation group underwent reintubations (not significantly different). Postextubation management, with or without NPPV, therefore did not influence outcome; however, compared with the elective extubation patients (6 of 56 patients), the unplanned extubation patients were more likely to be reintubated (14 of 37 patients).
Oximetry and Capnography
The rationale for this study12
was that arterial
blood gas analysis may not be needed often if continuous monitoring of
oxygenation and ventilation is provided during weaning. This trial was
not designed to test the accuracy or utility of oximetry and
capnography (which has been evaluated in the technology-assessment
literature) but to evaluate its utility as a weaning adjunct.
In a randomized unblinded trial, 24 postoperative cardiac patients were
allocated to (1) pulse oximetry and capnography or (2) to periodic
arterial blood gas measurements. Intermittent mandatory ventilation
(IMV) was used for weaning, but stepwise decrements were not specified.
Patients in the oximetry-and-capnography group had arterial blood gas
measurements taken on ICU admission, just before extubation, and if
their arterial oxygen saturation was at < 95% or their
end-expiratory PCO2 was < 26
mm Hg or > 40 mm Hg, and as clinically indicated. The blood-gas group
was weaned from ventilatory support if
PaCO2 was at 35 to 45 mm Hg, pH was
at 7.35 to 7.45, PaO2 was 70 mm
Hg, and respiratory rate was 
30 breaths/min.
There were fewer blood gas analyses performed in the oximetry-and-capnography group (5.9 ± 2.7 vs 10.1 ± 1.8 analyses, respectively; p < 0.01). The duration of ventilation was similar (18.8 ± 2.0 h vs 19.7 ± 1.9 h, respectively). One patient in the blood-gas group did not get extubated and was excluded from analysis. No patients required reintubation.
Growth Hormone
The catabolism of critical illness, and the functional and
structural neuromuscular abnormalities that occur in mechanically
ventilated patients have prompted investigators to study the influence
of growth hormones on weaning from mechanical ventilation.
In a randomized double-blinded trial, 20 patients requiring ventilation
for > 7 days were allocated to either (1) 0.43 IU recombinant growth
hormone/kg/d administered subcutaneously for 12 days or (2) normal
saline solution.13
Patients were excluded if they had
known myopathy, neuropathy, or a risk factor for neuromuscular
abnormalities. Weaning began for all patients when the following
conditions occurred: E < 10 L/min; vital capacity,
> 1 L; PaO2 60 with
FIO2 0.4; or if a T-piece trial
was tolerated for 30 min. Weaning began with synchronized IMV, and
pressure support was added when spontaneous breathing developed and was
gradually lowered. At a pressure support of 10 cm
H2O, patients underwent a T-piece trial. After
12 h of spontaneous breathing, patients were extubated. Parenteral
nutrition was provided for the first 48 h, at which time enteral
nutrition was instituted.
After 12 days, the growth-hormone group had higher levels of growth hormone, insulin-like growth hormone factor-1, and insulin. Fat-free mass was increased in the treated group compared to the untreated group. The cumulative duration of weaning for > 12 days was similar (235.6 ± 17.6 h vs 245.4 ± 14.7 h, respectively). A similar proportion of patients continued to receive mechanical ventilation at 12 days (7 of 10 and 7 of 10, respectively).
Relaxation Biofeedback
To induce anxiolysis and to minimize muscle fatigue, the effect of
relaxation biofeedback on respiratory mechanics and weaning was tested
by Holliday and Hyers.14
In an unblinded randomized trial,
40 patients ventilated for 7 days were allocated to either (1)
relaxation biofeedback or (2) a control group. The biofeedback group
received a multifaceted intervention, which consisted of communication
(ie, the patient was asked about feelings, breathing, and
sleeping, and was encouraged), VT feedback
(ie, auditory and visual feedback on a computer screen
containing data on the patient’s VT compared to
a threshold VT), and computerized visual feedback
of frontalis muscle tension by electromyogram, for 30 to 50 min per day
on CPAP (5 cm H2O) 5 days per week until study
termination.
Cointerventions during the weaning process are not
well-described. Four patients who had been randomized to the
control group died and were not included in the analysis. Within-group
changes in maximal inspiratory pressure, VT, and
E were no different. The duration of ventilation was
12 days shorter in the biofeedback group than in the control group
(20.6 ± 8.9 days vs 32.6 ± 17.6 days, respectively; p = 0.01).
Nonextubation rates were the same. The undisclosed weaning protocol
using T-piece or IMV in this unblinded study, which found a 12-day
difference in the duration of ventilation, makes interpretation
difficult; moreover, the generalizability of this technologically
complex intervention also is limited.
Acupuncture
The potential benefit of acupuncture in averting largyngospasm was
tested in 76 children who had undergone surgery and who had been
randomized to receive either acupuncture with bloodletting at the Shao
Shang acupoint on both thumbs just prior to extubation or to a control
group.15
Patients undergoing oropharyngeal surgery
were not enrolled. Laryngospasm was defined as occurring within 2 min
of extubation, and was characterized by stridor, silence due to total
closure of the vocal cords, and cyanosis. Among the patients in the
acupuncture group, 2 of 38 (5.3%) developed laryngospasm, whereas 9 of
38 (23.7%) in the control group developed laryngospasm. No patients
required reintubation.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The two RCTs of high-fat/low-carbohydrate enteral nutrition enrolled a
total of 52 patients. One study8
found a significant
decrease in PaCO2, while the
other9
found a significantly lower respiratory quotient
and E in patients receiving the high-fat feeds. The
time from feeding commencement to successful weaning was significantly
shorter in the high-fat group than in the isocaloric feeding
group,8
but in the unblinded study9
the rate
of successful 3-h spontaneous breathing trials was the same. High-fat
feeds appear to have favorable physiologic effects on
CO2 production and may be useful in patients with
impaired ventilatory reserves. However, these studies were underpowered
for clinically important outcomes, and their results require
confirmation or refutation. Future RCTs in this area should enroll
large numbers of difficult-to-wean COPD patients and should measure
both physiologic and clinically important outcomes, such as the
duration of mechanical ventilation. The influence of enteral vs
parenteral nutrition on weaning success and the duration of ventilation
in patients receiving long-term ventilation would be
useful.16
The total calories may be as important as the
composition of enteral feeding. Feasible but accurate methods to
measure caloric needs also are needed.
The two RCTs of patients after extubation that evaluate NPPV have conflicting results. The study by Gust et al10 in patients following coronary artery bypass grafting tested the following three strategies: NPPV; CPAP; and chest physiotherapy. All three groups had an increase in PBVI over time, but PBVI was lower in the NPPV group after 30 min, and the level of EVLW was higher following extubation in the chest physiotherapy group. Although these physiologic responses potentially have important clinical implications in some patients, all patients in this trial achieved successful extubation. In the randomized trial by Jiang et al,11 patients who were managed using NPPV after extubation did not have lower reintubation rates than did patients managed with oxygen therapy alone. The two small trials of NPPV postextubation that are included in this systematic review generate results that are less promising than other studies demonstrating the effectiveness of NPPV to prevent the initial intubation in patients with an exacerbation of COPD.17 However, it will be very challenging to detect a possible benefit of NPPV application following extubation, since the vast majority of patients who are extubated, including those who extubate themselves, do not require reintubation. Thus, trials of NPPV postextubation should focus on patients either at the highest risk of the need for reintubation or on those patients showing early signs of postextubation distress.
The four other miscellaneous interventions provide us with insight into some nonpulmonary approaches to weaning. The double-blind trial of 12 days of recombinant growth hormone failed to show any significant improvement in the rate or success of weaning.13 Future research might include more chronic and difficult-to-wean patients, in whom the effect might be greater. However, a multicenter RCT18 showed that growth hormone therapy was associated with increased ICU mortality, seriously questioning the ethics of future investigations using this hormone.
In the RCT of oximetry and capnography to monitor patients during weaning,12 approximately half as many blood gas analyses were performed compared to the control arm. However, the control patients were already getting approximately one blood gas analysis every 2 h. Such a dramatic benefit is unlikely to be seen in practice today, since this baseline blood gas frequency is highly atypical except for unstable or very difficult-to-wean patients.
The hypothesis that biofeedback could enhance safe and rapid weaning is attractive, although the feasibility of this approach is questionable in clinical practice. The study by Holliday and Hyers14 showed a dramatic difference of 12 days in the duration of ventilation; however, the weaning methods were not described in this unblinded study, and it is possible that the estimated treatment is slightly inflated. One component of this multimethod intervention that could have been responsible for some of the benefit was actually a behavioral technique of positive verbal reinforcement. Encouragement has been shown to favorably influence functional health outcomes such as those for the 6-min walk test in ambulatory patients with severe COPD.19 Depending on a patient’s alertness, motivation, and sense of self-efficacy, strategies such as classic biofeedback, operant conditioning, or the behavioral approach used in this study could prove to be effective if studied in suitable populations.
Multidisciplinary, patient-centered, holistic medicine is more embraced in the ICU today than in the past. Nontraditional medicine is increasingly subject to hypothesis-driven investigation.20 In the future, we may read more research reports on less technologic and more nonpulmonary approaches to weaning from mechanical ventilation. These may suggest additional safe and effective adjunctive methods of hastening liberation from mechanical ventilation.
The data included in this systematic review and a more comprehensive discussion of the original articles are included in an Evidence Report of the Agency for Healthcare Research and Quality.21
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Footnotes |
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E = minute
ventilation; VT = tidal volume This article is based on work performed by the McMaster University Evidence-based Practice Center, under contract to the Agency for Healthcare Research and Quality (Contract No. 290-97-0017), Rockville, MD.
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