Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

Highlighted lines and questions below provide links to the pertinent description of criteria in The EBM User's Guide, now available at the Canadian Centres for Health Evidence

Article Reviewed:

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Is there a preferred technique for weaning the difficult-to-wean patient? A systematic review of the literature.

Butler R, Keenan SP, Inman KJ, Sibbald WJ, Block G.

Crit Care Med 1999;27:2331-2336 [abstract]

Reviewed by Al Torres, MD, MS and Julie Wohrley, MD, University of Illinois College of Medicine at Peoria

Review posted April 14, 2000

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I. Are the results of the study valid?

A. Primary questions:

1. Did the overview address a focused clinical question?

Yes. The authors ask the specific question "...In difficult-to-wean (adult) patients, which of the three commonly used techniques to weaning (T-piece, synchronized intermittent mandatory ventilation (SIMV), or pressure support ventilation) leads to the highest proportion of successfully weaned patients and the shortest weaning time?"

2. Were the criteria used to select articles for inclusion appropriate?

Yes. the authors included studies that fulfilled the following criteria:

1. Population: patients requiring a gradual weaning process from the ventilator (either requiring prolonged initial ventilation of > 72 hours or failed trial of spontaneous breathing after > 24 hours of ventilation);
2. Interventions: at least two of the following three modes of weaning from mechanical ventilation must have been compared (T-piece, SIMV, or pressure support ventilation [PSV]);
3. Outcomes: at least one of the following: weaning time (time from initiation of weaning to extubation) or successful weaning rate (successfully off the ventilator for > 48 hours);
4. Study design: controlled clinical trial.

B. Secondary questions:

3. Is it unlikely that important, relevant studies were missed?

Maybe. The authors did not make personal contact with any of the authors of published studies. Since positive results are more likely to be published, publication bias may exist. However, the authors did review a total of 667 published studies from three major databases (MEDLINE, Cinahl, Healthplan) making it appear unlikely any major weaning studies were not included.

4. Was the validity of the included studies appraised?

Yes. The criteria the authors used addressed whether or not the studies reviewed satisfied the selection criteria (e.g., criteria for determining when patients were ready for weaning, well-defined extubation criteria, reintubation criteria, etc.). Almost all of the validity criteria for a therapy article as defined by the Centres for Health Evidence were also addressed. The authors did assess for adequacy of randomization, use of an intention-to-treat analysis to compensate for loss of subjects, complete follow-up, and standardization of co-interventions. Whether the groups compared in each study were similar at the start of the trial was not a criterion. Blinding of study personnel is not feasible in this type of controlled trial and was, therefore, not one of the selection criteria.

5. Were assessments of studies reproducible?

Yes. The two reviewers agreed on all validity criteria assessment with the exception of initial disagreement over whether one trial was truly randomized. Consensus was achieved after further discussion.

6. Were the results similar from study to study?

Not really. The authors assessed the four studies that met some of the selection criteria for clinical heterogeneity and statistical heterogeneity. There was clinical heterogeneity amongst the trials. Not all modes were compared in each study, reporting of weaning time and criteria used for weaning varied, and even definitions of success and failure were not consistent. This makes interpretation of pooled results difficult.

II. What are the results?

1. What are the overall results of the review?

The four studies selected for review only satisfied between three and seven of the validity criteria. Two of the studies (2,3) compared all 3 modes of weaning (T-piece vs. PSV, T-piece vs. SIMV, PSV vs. SIMV). The fourth study (4) only compared PSV vs. SIMV.

There was no significant difference in TIME TO EXTUBATION (days) amongst the various weaning groups compared in all 4 studies. SIMV did appear to lead to the longest weaning time.

Study/Modes	T-piece	PSV	SIMV
Tomlinson et al. (1)	18.3 +/- 6.3	Not studied	15.9 +/- 5.9
Brochard et al (2)	8.5 +/- 8.3	5.7 +/- 3.7	9.9 +/- 8.2
Esteban et al. (3)	3 (1 - 6)	4 (1 - 12)	5 (3 - 11)
Esen et al. (4)	Not studied	6.3 +/- 3.1	9.9 +/- 2.7

No mode of weaning was superior in % of subjects successfully weaned. In one of the four studies,(1) SUCCESSFUL WEAN (%) was unclear because the modes of weaning used in each group were not clearly presented.

Study/Modes	T-piece	PSV	SIMV
Brochard et al (2)	20/35 (57)	24/31 (77)	25/43 (58)
Esteban et al. (3)	47/62 (76)	23/37 (62)	20/29 (69)
Esen et al. (4)	Not studied	17/20 (85)	15/20 (75)

The authors expressed RISK DIFFERENCE (%) as the difference in proportions of successfully weaned between respective weaning modes:

Study/Modes	T-piece vs PSV	T-piece vs. SIMV	PSV vs. SIMV
Brochard et al (2)	- 20 (-42, 2)	-1 (-23, 21)	19 (-2, 40)
Esteban et al. (3)	14 (-5, 32)	7 (-13, 27)	-7 (-20, 16)
Esen et al. (4)	Not studied	Not studied	10 (-15, 35)
Pooled risk difference for successful wean	- 3 (-36, 30)	3 (-11, 18)	8 (-7, 23)

The authors pointed out the most important difference between the 4 studies was in how the weaning modes were applied. For example, in two of the studies (2,3) pressure support was adjusted according to different upper limit spontaneous respiratory rates. In three of the studies (2-4), SIMV was used differently. A lack of standardization of the weaning modes across studies partially explains the lack of evidence supporting one mode as superior. The authors state that "it would appear that how the technique of weaning is applied has at least as great an effect on the likelihood of successful weaning as the technique itself".

2. How precise were the results?

The 95% confidence intervals for the risk differences (especially the pooled risk difference) were not only large, but also included zero risk reduction when comparing all the modes of weaning. These results do not support any mode being more superior than the others.

III. Will the results help me in caring for my patients?

1. Can the results be applied to my patient care?

No. Besides a lack of pediatric patients in these studies, the few studies reviewed did not provide sufficient evidence to identify a clearly superior mode for weaning the difficult-to-wean patient.

2. Were all clinically important outcomes considered?

Yes. The authors were primarily interested in weaning time, successful extubation rate, and reintubation rate. One of the studies quoted but not reviewed (5) demonstrated that protocol-directed weaning by non-physicians was more successful in than physician-directed weaning regardless of mode used. A large randomized, controlled trial of protocol-directed weaning versus physician-directed weaning in difficult-to-wean children is warranted.

3. Are the benefits worth the harms and costs?

Unclear. Benefit of one weaning mode versus another was not clearly demonstrated. The study (3) which used a more aggressive approach to extubation (only 2 hours at the final level of suggested support) had a higher rate of reintubation, ranging from 14 to 23%, compared with 9 to 10% for a less aggressive approach (2). Clinicians considering weaning protocols as a means of shortening duration of ventilation and ICU length of stay must be willing to accept a higher rate of reintubation.

References

1. Tomlinson JR, Miller KS, Lorch DG, et al. A prospective comparison of IMV and T-piece weaning from mechanical ventilation. Chest 1989;96:348-352. [abstract]
2. Brochard L, Rauss A, Benito S, et al. Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation. Am J Respir Crit Care Med 1994;150:896-903. [abstract]
3. Esteban A, Frutos F, Tobin MJ, et al. A comparison of four methods of weaning patients from mechanical ventilation. N Engl J Med 1995;332:345-350. [abstract]
4. Esen F, Denkel T, Telci L, et al. Comparison of pressure support ventilation (PSV) and intermittent mandatory ventilation (IMV) during weaning patients with acute respiratory failure. Adv Exp Med Biol 1992;317:371-376. [citation]
5. Kollef MH, Shapiro SD, Silver P, et al. A randomized controlled trial of protocol- directed versus physician-directed weaning from mechanical ventilation. Crit Care Med 1997; 25:567-574. [abstract]

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