Table 3.
Breath components and oxygenation during weaning trials without (Control day) and with (Study day) nitroglycerin
| Variable | Mechanical ventilation | Spontaneous breathing trial | P valuea | ||
|---|---|---|---|---|---|
| Start | End | ||||
| VT, Ml | Control day | 617 ± 103 | 289 ± 123b | 298 ± 114b | 0.18 |
| Study day | 608 ± 88 | 343 ± 114b | 365 ± 73b | ||
| Frequency, beats/minute | Control day | 16 ± 3.8 | 29 ± 7.7b | 29 ± 7.8b | 0.44 |
| Study day | 16 ± 4.1 | 25 ± 5b | 26 ± 5b | ||
| VE, L/minute | Control day | 9.7 ± 2.9 | 8.1 ± 3.6 | 8.3 ± 3.3 | 0.51 |
| Study day | 9.7 ± 3.2 | 8.8 ± 3.3 | 9.4 ± 2.6 | ||
| f/VT, beats/minute per liter | Control day | 26 ± 8 | 114 ± 48b | 108 ± 42b | 0.03 |
| Study day | 27 ± 7 | 82 ± 29b,c | 73 ± 19b,c | ||
| PaO2, mm Hg | Control day | 130 ± 35 | 65 ± 18b | 66 ± 17b | 0.23 |
| Study day | 132 ± 35 | 85 ± 18c,d | 89 ± 23c,d | ||
| PaCO2, mm Hg | Control day | 51 ± 10 | 69 ± 13b | 70 ± 13b | 0.20 |
| Study day | 49 ± 11 | 61 ± 13b,c | 64 ± 16b | ||
| pHa | Control day | 7.41 ± 0.06 | 7.32 ± 0.07b | 7.30 ± 0.07b | 0.20 |
| Study day | 7.42 ± 0.05 | 7.34 ± 0.06d | 7.34 ± 0.07b | ||
| SaO2, percentage | Control day | 98.3 ± 1.6 | 89.2 ± 6.2b | 88.8 ± 4.7b | 0.01 |
| Study day | 98.2 ± 1.5 | 95.3 ± 2.2c | 94.9 ± 2.2c | ||
| SvO2, percentage | Control day | 75.7 ± 3.5 | 67.3 ± 7.2d | 69.3 ± 7.5d | 0.04 |
| Study day | 73 ± 4.1 | 72.3 ± 4.3c | 74.6 ± 4.3c | ||
| Qs/Qt, percentage | Control day | 15.0 ± 6.0 | 37.8 ± 17.8b | 39.5 ± 13.8b | 0.04 |
| Study day | 14.3 ± 5.9 | 25.7 ± 6.6c | 28.5 ± 8.1d | ||
| O2ER, percentage | Control day | 24.4 ± 3.3 | 24.7 ± 8.4 | 22.9 ± 8.5 | 0.32 |
| Study day | 27 ± 4.1 | 24.8 ± 4.4 | 22.1 ± 4.5 | ||
Values are presented as mean ± standard deviation. aP value of the interaction (day × time) of the repeated-measures two-way analysis of variance comparison between the Control day and Study day across time (that is, during mechanical ventilation, the second minute [for breath components] or 10th minute [for oxygenation variables] [Start], and the last minute [End] of the spontaneous breathing trial). bP < 0.001 versus mechanical ventilation. cP < 0.05 versus control day. dP < 0.05 versus mechanical ventilation. f/VT, frequency/tidal volume (index of rapid shallow breathing); O2ER, oxygen extraction ratio; PaCO2, arterial carbon dioxide partial pressure; PaO2, arterial oxygen partial pressure; pHa, arterial pH; Qs/Qt, venous admixture; SaO2, arterial oxygen saturation; SvO2, mixed venous oxygen saturation; VE, minute ventilation; VT, tidal volume.