Correspondence

Noninvasive Positive-Pressure Ventilation

N Engl J Med 1999; 340:150-151January 14, 1999

Article

To the Editor:

Antonelli et al. (Aug. 13 issue)1 concluded that noninvasive positive-pressure ventilation was as effective as conventional mechanical ventilation in patients with acute respiratory failure and was associated with fewer serious complications and shorter stays in the intensive care unit.

With regard to the duration of ventilation, the timing of the initiation and the mode of weaning differed in the two groups. Patients assigned to receive noninvasive positive-pressure ventilation were “evaluated daily . . . without ventilatory support for 15 minutes,” and ventilatory support was discontinued if they met certain criteria. This trial of spontaneous breathing is equivalent to a T-piece trial and should also have been used in the patients assigned to receive conventional ventilation. Instead, the level of pressure support and the intermittent-mandatory-ventilation rate were reduced in a uniform fashion in these patients until they could tolerate a ventilatory rate of 0.5 per minute and a pressure-support level of 8 cm of water, at which point a T-piece trial was performed. With the use of a daily T-piece trial after 24 hours of ventilation, it is likely that the mean duration of mechanical ventilation would have been shortened in these patients.2,3 The authors do not state how long these patients had to “tolerate” such settings. Unnecessarily prolonged intubation itself would increase the frequency of infectious complications in this group.4

Without the use of objective criteria for discharge from the intensive care unit in both groups, the finding of shorter stays in the noninvasive-ventilation group may be biased. The mean interval between the discontinuation of ventilation and discharge from the intensive care unit was 3.6 days in the noninvasive-ventilation group and 8 days in the conventional-ventilation group, with no explanation given for the prolonged stays in the intensive care unit after extubation. This finding also raises the question of bias.

Sangeeta Mehta, M.D.
Stephen E. Lapinsky, M.B., B.Ch.
Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada

4 References

1. 1

   Antonelli M, Conti G, Rocco M, et al. A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure. N Engl J Med 1998;339:429-435
   Full Text | Web of Science | Medline

2. 2

   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
   Full Text | Web of Science | Medline

3. 3

   Ely EW, Baker AM, Dunagan DP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med 1996;335:1864-1869
   Full Text | Web of Science | Medline

4. 4

   Fagon JY, Chastre J, Domart Y, et al. Nosocomial pneumonia in patients receiving continuous mechanical ventilation: prospective analysis of 52 episodes with use of a protected specimen brush and quantitative culture techniques. Am Rev Respir Dis 1989;139:877-884
   Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: We do not believe that our weaning protocol unnecessarily prolonged intubation in the patients who were treated with conventional mechanical ventilation. We did not use the T-piece trial alone for weaning in patients in the conventional-ventilation group, because Brochard et al.1 demonstrated that pressure-support ventilation was superior to a T-piece trial in shortening the weaning period, with a better outcome. Our weaning protocol combined pressure-support ventilation with intermittent mandatory ventilation. Esteban and colleagues2 applied intermittent mandatory ventilation at a rate of 10±2 breaths per minute without pressure support, whereas we usually started with a rate of 5 breaths per minute (range, 4 to 7) with pressure support (range, 14 to 20 cm of water); thus, the two weaning procedures are not comparable. Moreover it is not known whether the combination of intermittent mandatory ventilation and pressure-support ventilation is a better method of weaning patients from mechanical ventilation than a once-daily trial of spontaneous breathing with a T piece.3

Our chief concern about the once-daily T-piece trial is the abrupt transition from full, positive-pressure ventilation to unassisted breathing, which leads to sudden changes in mean intrathoracic pressure and to hemodynamic effects.4 Patients who are unable to tolerate sudden volume shifts may be better served by gradual weaning accompanied by diuresis.

In accordance with the study by Brochard et al.,1 patients in our study had to “tolerate” for a 24-hour period an intermittent-mandatory-ventilation rate of 0.5 breath per minute, a pressure-support level of 8 cm of water, and a fraction of inspired oxygen of 0.5 or less before the 2-hour T-piece trial and extubation. A pressure-support level of 8 cm of water is in fact sufficient to compensate for the additional workload imposed by the use of the endotracheal tube and the demand valve.5

The longer interval between the discontinuation of ventilation and discharge in the conventional-ventilation group was due to the higher rate of complications in this group (66 percent, vs. 38 percent in the noninvasive-ventilation group; P=0.02), including pneumonia, sepsis, polyneuropathy of the critically ill, and renal failure. The longer stays in the intensive care unit after extubation in this group reflected the need for clinical stabilization before discharge.

Massimo Antonelli, M.D.
Giorgio Conti, M.D.
Università La Sapienza, 00161 Rome, Italy

5 References

1. 1

   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
   Web of Science | Medline

2. 2

   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
   Full Text | Web of Science | Medline

3. 3

   Weinberger SE, Weiss JW. Weaning from ventilatory support. N Engl J Med 1995;332:388-389
   Full Text | Web of Science | Medline

4. 4

   Pinsky MR. Cardiopulmonary interactions: the effects of negative and positive changes in pleural pressure on cardiac output. In: Dantzker ER, ed. Cardiopulmonary critical care. 2nd ed. Philadelphia: W.B. Saunders, 1991:87-120.
   

5. 5

   Brochard L, Rua F, Lorino H, Lemaire F, Harf A. Inspiratory pressure support compensates for the additional work of breathing caused by the endotracheal tube. Anesthesiology 1991;75:739-745
   CrossRef | Web of Science | Medline