Correspondence

Mechanical Ventilation

N Engl J Med 1994; 331:549-550August 25, 1994

Article

To the Editor:

In his review of mechanical ventilation (April 14 issue),1 Tobin examines the new alternative methods of ventilation, including noninvasive ventilatory techniques. But he fails to mention a noninvasive method of ventilation that is based on the intermittent delivery of a negative pressure -- the iron lung.

In recent studies,2-5 the iron lung has been proposed as an alternative noninvasive method for the treatment of acute respiratory failure in patients with chronic obstructive pulmonary disease. Although these data are derived from uncontrolled clinical studies, the rates of long-term survival among the patients who, at the time of each disease exacerbation, were regularly treated with intermittent negative-pressure ventilation3,4 were considerably higher than those among patients treated by the standard techniques. When combined with long-term oxygen therapy, the iron lung may be particularly useful in patients with chronic obstructive pulmonary disease4. This method of ventilation helps patients recover the contractile strength of the respiratory muscles2 and averts the severe complications caused by mechanical ventilation with intubation6.

Although prospective controlled studies are still needed, we believe that the technique of intermittent negative-pressure ventilation has a role in mechanical ventilation.

Antonio Corrado, M.D.
Andrea Messori, Pharm.D.
Massimo Gorini, M.D.
Unita Sanitaria Locale 10/D, 50134 Florence, Italy

6 References

1. 1

   Tobin MJ. Mechanical ventilation. N Engl J Med 1994;330:1056-1061
   Full Text | Web of Science | Medline

2. 2

   Corrado A, Bruscoli G, De Paola E, Ciardi-Dupre GF, Baccini A, Taddei M. Respiratory muscle insufficiency in acute respiratory failure of subjects with severe COPD: treatment with intermittent negative pressure ventilation. Eur Respir J 1990;3:644-648
   Web of Science | Medline

3. 3

   Corrado A, Bruscoli G, Messori A, et al. Iron lung treatment of subjects with COPD in acute respiratory failure: evaluation of short- and long-term prognosis. Chest 1992;101:692-696
   CrossRef | Web of Science | Medline

4. 4

   Corrado A, De Paola E, Messori A, Bruscoli G, Nutini S. The effect of intermittent negative pressure ventilation and long-term oxygen therapy for patients with COPD: a 4-year study. Chest 1994;105:95-99
   CrossRef | Web of Science | Medline

5. 5

   Corrado A, De Paola E, Bruscoli G, Tozzi D, Gorini E, Nutini S. Iron lung treatment of hypoxic-hypercapnic coma in chronic respiratory insufficiency. Am J Respir Crit Care Med 1994;149:A637-A637 abstract.
   

6. 6

   Pingleton SK. Complications of acute respiratory failure. Am Rev Respir Dis 1988;137:1463-1493
   Web of Science | Medline

To the Editor:

I enjoyed Dr. Tobin's article on mechanical ventilation. However, I object to the practice of describing ventilation as either positive-pressure or negative-pressure. Dr. Tobin uses the term “positive-pressure ventilation,” implying a distinction between this type and another type of ventilation, namely, negative-pressure ventilation. Actually, all forms of ventilation involve positive pressure. A negative pressure is impossible to achieve and exists only as a mathematical abstraction. Of course, a negative pressure difference can occur, but if the word “negative” is to be used, the quantities being subtracted should be identified. A better way of describing different types of ventilation may be to use the terms “subambient pressure” and “supraambient pressure.”

Mark B. Mecikalski, M.D.
2224 N. Craycroft Rd., Tucson, AZ 85712

Author/Editor Response

Dr. Tobin replies:

To the Editor: Dr. Mecikalski makes a plea for the replacement of the term “negative pressure” by the term “subambient pressure.” Despite the justification for such a change, widespread use has firmly fixed the term “negative-pressure ventilation” in the lexicon, and I doubt that his recommendation can be successful.

I omitted discussion of negative-pressure ventilation from my article because of space constraints and my focus on critically ill patients. I am less enthusiastic than Dr. Corrado and his colleagues about the use of negative-pressure ventilation in patients with acute respiratory failure and chronic obstructive pulmonary disease. The studies they cite were retrospective and lacked control groups of patients treated with positive-pressure ventilation. During the poliomyelitis epidemic, mortality decreased from 87 percent to 40 percent when negative-pressure ventilation was replaced by positive-pressure ventilation1. Dr. Corrado indicates that negative-pressure ventilation averts severe complications. It is true that this technique averts the complications associated with endotracheal intubation, but it is not free of problems. Use of negative-pressure ventilation in patients with chronic obstructive pulmonary disease has been reported to result in rib fractures, pneumothorax, and upper-airway collapse and apnea2,3. Ventilator-induced injury is at least as common with negative-pressure ventilation as it is with positive-pressure ventilation3. In addition, negative-pressure ventilators are bulky and impede access to patients, many of whom consider them uncomfortable4. Despite these problems, negative-pressure ventilators are effective in patients with other disorders, such as chronic neuromuscular and chest-wall diseases5.

Martin J. Tobin, M.D.
Loyola University of Chicago Stritch School of Medicine, Maywood, IL 60153

5 References

1. 1

   Lassen HCA. A preliminary report on the 1952 epidemic of poliomyelitis in Copenhagen with special references to the treatment of acute respiratory insufficiency. Lancet 1953;1:37-41
   CrossRef | Medline

2. 2

   Levy RD, Cosio MG, Gibbons L, Macklem PT, Martin JG. Induction of sleep apnoea with negative pressure ventilation in patients with chronic obstructive lung disease. Thorax 1992;47:612-615
   CrossRef | Web of Science | Medline

3. 3

   Zibrak JD, Hill NS, Federman EC, Kwa SL, O'Donnell C. Evaluation of intermittent long-term negative-pressure ventilation in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1988;138:1515-1518
   Web of Science | Medline

4. 4

   Dreyfuss D, Soler P, Basset G, Saumon G. High inflation pressure pulmonary edema: respective effects of high airway pressure, high tidal volume, and positive end-expiratory pressure. Am Rev Respir Dis 1988;137:1159-1164
   Web of Science | Medline

5. 5

   Levine S, Henson D. Negative pressure ventilation. In: Tobin MJ, ed. Principles and practice of mechanical ventilation. New York: McGraw-Hill, 1994:393-411.