Current issues of ACP Journal Club are published in Annals of Internal Medicine


Therapeutics

Pressure support ventilation improved weaning from mechanical ventilation

ACP J Club. 1995 Mar-April;122:34. doi:10.7326/ACPJC-1995-122-2-034


Source Citation

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 Oct;150:896-903.


Abstract

Objective

To compare spontaneous intermittent T-piece, synchronized intermittent mandatory ventilation (SIMV), and pressure support ventilation (PSV) for rates of successful weaning.

Design

Randomized controlled trial.

Setting

3 medical-surgical intensive care units in Europe.

Patients

109 patients (mean age 59 y, 74 men) on mechanical ventilation (MV) for > 24 hours who had recovered from acute-phase disease and who did not tolerate 2 hours of spontaneous breathing on a T-piece. Patients met ≥ 3 of 4 criteria: maximal inspiratory pressure ≤ -25 cm H2O; spontaneous breathing frequency ≤ 35 breaths/min; vital capacity ≥ 10 mL/kg; and arterial oxygen saturation ≥ 90% at 40% inspired oxygen.

Intervention

35 patients were allocated to T-piece trials of gradually lengthening daily disconnection from MV. Trials ranged from 3 to 8/d until 2 hours were successfully tolerated at least once. 43 patients were allocated to SIMV without PSV. The SIMV rate was decreased, when considered appropriate, by 2 to 4 breaths/min twice daily until ≤ 4 IMV breaths. 31 patients were allocated to PSV with initial pressure adjusted so that 20 to 30 breaths/min occurred. PSV was decreased, when considered appropriate, in 2- or 4-cm increments twice daily until the 8-cm level was reached. When this goal was reached in each group, extubation was attempted. Enteral nutrition support was given. 4 cm of water-positive, end-expiratory pressure could be applied.

Main outcome measures

Failed weaning defined as 1) failure to separate from MV at 21 days or tracheal reintubation ≤ 48 hours after extubation or 2) intercurrent myocardial ischemia or ventilator-associated pneumonia, which led to withdrawal of weaning procedures.

Main results

At 21 days, the proportion of patients who were not separated from MV was 43% for T-piece trial, 42% for SIMV, and 23% for PSV (P = 0.05 for comparisons with PSV) (Table). Excluding patients with non-ventilator-related complications, only 8% of PSV weans failed compared with 33% of those for T-piece and 39% of those for SIMV (P < 0.02) (Table). In the same subgroup, weaning was successful after only 5.7 days in the PSV group compared with T-piece (8.3 d) and SIMV (9.9 d) (P < 0.05). The groups did not differ for mortality, although a nonsignificant trend favored PSV.

Conclusion

Pressure support ventilation provided more rapid and more frequently successful weaning than either a protocol using multiple disconnections on a T-piece or synchronized intermittent mandatory ventilation.

Source of funding: Not stated.

For article reprint: Dr. L. Brochard, Service de Réanimation Médicale, Hôpital Henri Mondor, 94010 Créteil-Cedex, France. FAX 33-1-4207-9943.


Table. Spontaneous intermittent T-piece, synchronized intermittent mandatory ventilation (SIMV), and pressure support ventilation (PSV) for weaning from mechanical ventilation (MV)*

Outcome Comparisons Event rates RRR (95% CI) NNT (CI)
Failed weaning† PSV vs T-piece 23% vs 43% 47% (-8 to 76) Not significant
PSV vs SIMV 23% vs 42% 46% (-8 to 75) Not significant
PSV vs T-piece† 8% vs 33% 77% (18 to 94) 4 (2 to 23)
PSV vs SIMV† 8% vs 39% 80% (33 to 95) 3 (2 to 9)

*Abbreviations defined in Glossary; RRR, NNT, and CI calculated from data in article.
†1) Failure to separate from MV at 21 days or tracheal intubation ≤ 48 hours after extubation or 2) intercurrent myocardial ischemia or ventilator-assisted pneumonia.
†Excluding patients with non-ventilator-related complications.


Commentary

PSV is widely used for MV support because it offers advantages in response to patient demands (e.g., the high inspiratory flows demanded by patients with chronic obstructive pulmonary disease who are in distress) and, hence, increases patient comfort when used as primary support. Moreover, PSV is routinely used at many, if not most, hospitals as an adjunct to SIMV to reduce the resistive work of breathing caused by endotracheal intubation that must be overcome during a patient's spontaneous breath. The study by Brochard and colleagues additionally validates the use of PSV as a stand-alone method to provide safe, successful, and rapid weaning of patients who have difficulty separating from MV.

When patients are strong and the cause of their respiratory failure is largely resolved, the mode of weaning makes little difference. Other patients require us to be diligent in our weaning efforts to avoid the major causes of failure: myocardial dysfunction, ventilator-associated pneumonia, inadequate nutrition support, and impaired function of the muscles of respiration. Myocardial ischemia and respiratory muscle fatigue frequently are caused by misjudgment during weaning that leads to tachypnea, tachycardia, and a downward spiral of excessive work of breathing and inadequate cardiac reserve. These results are different from the randomized trial by Esteban and colleagues (1) which showed that daily 2-hour spontaneous breathing trials led to extubation much more quickly than SIMV or PSV. However, in another trial by Esteban and colleagues (2), patients having a 2-hour spontaneous breathing trial with PSV of 7 cm were more likely to succeed than patients undergoing a spontaneous breathing test with a T piece.

These findings suggest that the results regarding the merit of PSV differ because of different protocols for using PSV rather than innate features of the mode itself.

Christopher M. Hughes, MD
Monongahela Valley HospitalMonongahela, Pennsylvania, USA


References

1. Esteban A, Frutos F, Tobin MJ, et al., for the Spanish Lung Failure Collaborative Group. A comparison of four methods of weaning patients from mechanical ventilation. N Engl J Med. 1995;332:345-50.

2. Esteban A, Alía I, Gordo F, et al., for the Spanish Lung Failure Collaborative Group. Extubation outcome after spontaneous breathing trials with T-tube or pressure support ventilation. Am J Respir Crit Care Med. 1997;156:459-65.