INFLUENCE OF GENDER AND ENDOTRACHEAL-TUBE SIZE ON PREEXTUBATION BREATHING PATTERN

An imbalance between work of breathing and respiratory muscle capacity often results in rapid, shallow breathing (increased respiratory rate /tidal volume [f/V-T]). Because this imbalance commonly causes unsucce ssful weaning from mechanical ventilation, it is not surprising that a n elevated f/VT accurately predicts weaning failure. However, while st udying extubation outcome, we observed that women and patients with na rrow endotracheal tubes are often successfully extubated with an eleva ted f/VT. We studied 218 medical patients in the intensive care unit w ho had a f/VT measured through an oral endotracheal tube (off of venti latory support) during 1 min of spontaneous respiration at the onset o f a weaning trial that culminated in extubation. Men and women were co mparable at the onset of mechanical ventilation and weaning trials in severity of illness, etiology of respiratory failure, ventilator setti ngs, and gas exchange data. Women were found to have a higher f/VT (79 +/- 5 versus 56 +/- 3 breaths/L, p < 0.001), lower tidal volumes (381 +/- 14 versus 494 +/- 13 mi, p < 0.001), and higher respiratory rate 26 +/- 1 versus 24 +/- 1, p < 0.05). The differences persisted after c ontrolling for extubation outcome. Smaller endotracheal tubes were ass ociated with a higher f/VT, especially for women (less than or equal t o 7 mm, 86 +/- 6 versus > 7 mm, 68 +/- 6, p < 0.05). Women were more l ikely to have a f/VT greater than or equal to 100 (19/82 [women] versu s 10/136 [men], p < 0.001). Although the overall incidence of extubati on failure was similar (11/82 [women] versus 23/136 [men], p = NS), am ong patients with f/VT >, 100, men were more likely to require reintub ation (3/19 [women] versus 5/10 [men], p = 0.08). We conclude that wom en, especially when breathing through small endotracheal tubes, have a higher f/VT (including likelihood of f/VT greater than or equal to 10 0) than men, independent of extubation outcome. Consideration of facto rs that elevate the f/VT, unrelated to physiologic work of breathing a nd respiratory muscle capacity, should improve application of this ind ex to extubation decision making.