BACKGROUND: Nursing textbooks and tradition suggest that the high-Fowler's position is best to optimize diaphragmatic excursion and effective breathing pattern. The optimal position for intubated patients with obesity, ascites or abdominal distention has yet to be determined but is important because weaning trial outcomes may reflect the effect of position rather than weaning trial tolerance. OBJECTIVE: To determine the body position that optimizes breathing pattern (tidal volume and respiratory rate) in spontaneously breathing, intubated patients with a large abdomen. METHODS: Nineteen intubated patients with abdominal distention, ascites or obesity who were on continuous positive airway pressure or the pressure support ventilation mode were studied in the 0 degrees, 45 degrees, 90 degrees and reverse Trendelenburg's at 45 degrees positions for 5 minutes prior to data collection. RESULTS: The RT at 45 degrees position resulted in a significantly larger tidal volume and lower respiratory rate than the 90 degrees position in intubated, spontaneously breathing patients with a large abdomen. The 45 degrees position resulted in a significantly lower respiratory rate than at 90 degrees; however, no difference in tidal volume was demonstrated. DISCUSSION: A high respiratory rate and low tidal volume potentiates atelectasis and ultimately failure to wean. It is important that the effect of positioning on breathing pattern in intubated patients be determined so that care planning results in optimal outcomes. CONCLUSIONS: The results of this study have implications for the selection of chair and bed positioning during weaning trials.