Pressure-controlled, inverse ratio ventilation that avoids air trapping in the adult respiratory distress syndrome

• Published in: Critical care medicine Vol. 23; no. 2; pp. 279 - 285
• Main Authors: Armstrong, Bruce W. Jr, MacIntyre, Neil R
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Williams & Wilkins 01-02-1995; Lippincott
• Subjects: Adult; Aged; Aged, 80 and over; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Emergency and intensive respiratory care; Female; Humans; Intensive care medicine; Male; Medical sciences; Middle Aged; Oxygen - blood; Positive-Pressure Respiration - adverse effects; Positive-Pressure Respiration - methods; Positive-Pressure Respiration, Intrinsic - prevention & control; Respiration, Artificial; Respiratory Distress Syndrome, Adult - blood; Respiratory Distress Syndrome, Adult - physiopathology; Respiratory Distress Syndrome, Adult - therapy; Retrospective Studies; Human; Lung disease; Intensive care; Treatment; Adult respiratory distress syndrome; Respiratory disease; Controlled mechanical ventilation; Artificial ventilation
• ISSN: 0090-3493; 1530-0293
• DOI: 10.1097/00003246-199502000-00013

OBJECTIVES To investigate physiologic and outcome data in patients switched from volume-cycled conventional ratio ventilation to pressure-controlled inverse ratio ventilation that did not produce air trapping and intrinsic positive end-expiratory pressure (PEEP).
SETTING Medical intensive care unit.
DESIGN Retrospective analysis of crossover data and outcome.
PATIENTS Fourteen patients with the adult respiratory distress syndrome who were receiving mechanical ventilation with volume-cycled, conventional ratio ventilation followed by pressure-controlled, inverse ratio ventilation.
INTERVENTIONS Our approach to pressure-controlled, inverse ratio ventilation was to use tidal volumes and applied PEEP values comparable to those volumes and values used on volume-cycled, conventional ratio ventilation, use inspiratory times to increase mean airway pressure instead of additional applied PEEP, and avoid air trapping (intrinsic PEEP).
MEASUREMENTS AND MAIN RESULTS With this approach, there was a reduction in peak airway pressure from 53 +/- 8.5 (SD) to 40 +/- 5.9 cm H2 O (p < .01), and an increase in mean airway pressure from 20 +/- 3.9 to 30 +/- 5.2 cm H2 O (p < .01). Tidal volume, mean inflation pressure, and compliance did not change. Oxygenation (PaO2) improved from 57 +/- 11.3 torr (7.6 +/- 1.5 kPa) to 94 +/- 40.2 torr (12.5 +/- 5.4 kPa) (p = .01) but the oxygenation index (mean airway pressure times FIO2 times 100/PaO2) did not change significantly (25.9 +/- 10.3 to 27.2 +/- 12.2). There was no significant change in PaCO2 or pH even though delivered minute ventilation decreased from 17.4 +/- 4.3 to 14.8 +/- 5.8 L/min (p = .02). Cardiac index slightly decreased, but hemodynamic values were otherwise stable. Only three of the 14 study patients survived.
CONCLUSIONS These data demonstrate that oxygenation is primarily a function of mean airway pressure, and that longer inspiratory times can be used as an alternative to applied PEEP to increase this oxygenation. If no air trapping develops, lung inflation pressures and delivered volumes remain constant with this approach. Because the technique was used only in patients refractory to conventional techniques, the poor outcome is not surprising.(Crit Care Med 1995; 23:279-285)