Table 2.
Results of first SBT—comparison of patients with successful and unsuccessful SBT.
| First SBT | All patients (n = 130) |
SBT success (n = 100) |
SBT failure (n = 30) |
p valuea |
|---|---|---|---|---|
| Time from admission to first SBT (days) | 1 (0–3) | 1 (0–3) | 1 (1–3) | 0.638b |
| Hemoglobin on first SBT (g/dL) | 8.3 (± 1.2) | 8.3 (± 1.2) | 8.1 (± 1.3) | 0.266c |
| Ventilatory variables & MP indices | ||||
| FiO2 | 0.27 (± 0.05) | 0.27 (± 0.05) | 0.28 (± 0.04) | 0.156c |
| Tidal volume (mL) | 547 (± 86) | 547 (± 83) | 547 (± 97) | 0.459c |
| Minute ventilation (L/min) | 9.0 (± 1.9) | 9.0 (± 2.0) | 9.0 (± 1.7) | 0.676c |
| PaCO2 on MV (mmHg) | 35.0 (± 5.4) | 33.9 (± 4.8) | 38.8 (± 4.5) | < 0.001b |
| Ventilatory ratio | 1.19 (± 0.34) | 1.14 (± 0.34) | 1.38 (± 0.32) | < 0.001c |
| PEEP (cmH2O) | 6.0 (± 0.9) | 6.0 (± 0.9) | 6.0 (± 0.8) | 0.717c |
| Pmax (cmH2O) | 23.6 (± 4.2) | 22.8 (± 4.1) | 26.3 (± 3.5) | < 0.001b |
| ∆Paw (cmH2O) | 17.6 (± 4.0) | 16.8 (± 3.9) | 20.3 (± 3.4) | < 0.001c |
| LTCdyn (mL/cmH2O) | 32.8 (± 9.6) | 34.3 (± 9.6) | 27.9 (± 7.9) | < 0.001c |
| Mechanical power (J/min) | 21.0 (± 5.9) | 20.2 (± 5.7) | 23.6 (± 5.8) | 0.004c |
| PBW-MP (J/min/kg) | 0.3295 (± 0.1106) | 0.3111 (± 0.1033) | 0.3907 (± 0.1137) | < 0.001c |
| LTCdyn-MP (cmH2O2/min) | 7167 (± 3063) | 6569 (± 2885) | 9159 (± 2824) | < 0.001c |
| Power indexrs1.0 (cmH2O2/min) | 5696 (± 2884) | 5012 (± 2490) | 7978 (± 2971) | < 0.001c |
| Power indexrs2.0 (cmH2O2/min) | 4636 (± 2896) | 3902 (± 2323) | 7082 (± 3292) | < 0.001c |
| PaCO2 on ABG | ||||
| PaCO2 on MV pre-SBT (mmHg) | 35.0 (± 5.4) | 33.9 (± 4.8) | 38.8 (± 5.5) | 0.001b |
| PaCO2 on SB post-SBT (mmHg)* | 38.7 (± 7.0) | 36.3 (± 4.6) | 48.9 (± 6.5) | < 0.001b |
| ∆PaCO2 (post-/pre-SBT) | 3.9 (± 5.8) | 2.4 (± 4.4) | 10.2 (± 7.2) | < 0.001c |
| pH on ABG | ||||
| pH on MV pre-SBT | 7.50 (± 0.05) | 7.50 (± 0.05) | 7.48 (± 0.05) | 0.192c |
| pH on SB post-SBT* | 7.46 (± 0.06) | 7.48 (± 0.04) | 7.40 (± 0.07) | < 0.001c |
| ∆pH (post-/pre-SBT) | − 0.03 (± 0.06) | − 0.02 (± 0.05) | − 0.09 (± 0.07) | < 0.001c |
| PaO2 on ABG | ||||
| PaO2 on MV pre-SBT (mmHg) | 83.7 (± 15.9) | 85.0 (± 15.9) | 79.4 (± 15.5) | 0.069c |
| PaO2 on SB post-SBT (mmHg)* | 76.9 (± 18.1) | 77.4 (± 19.0) | 74.7 (± 13.8) | 0.790c |
| ∆PaO2 (post-/pre-SBT) | − 7.4 (± 21.0) | − 7.6 (± 22.2) | − 6.4 (± 15.0) | 0.506c |
| Duration of first SBT (min) | 30 (30–30) | 30 (30–30) | 30 (11–30) | < 0.001c |
Continuous variables are presented as arithmetic means values (± standard deviation) or median (– interquartile range [IQR]); categorical variables are presented as numbers (%).
SBT, spontaneous breathing trial; MP, mechanical power; FiO2, the fraction of inspired oxygen; MV, mechanical ventilation; PEEP, positive end-expiratory pressure; Pmax, the pre-set inspiratory positive airway pressure; ∆Paw, dynamic driving pressure (defined as Pmax—PEEP in the pressure-controlled ventilation mode); LTCdyn, dynamic lung-thorax compliance; PBW-MP, mechanical power normalized to predicted body weight; LTCdyn-MP, mechanical power normalized to dynamic lung-thorax compliance, ABG, arterial blood gas analysis.
*ABG at the end of the SBT was missing in seven patients due to severe respiratory distress, requiring immediate resumption of mechanical ventilation.
ap value for differences between patients with successful and unsuccessful SBT.
bStudent’s t-test.
cMann-Whitney U-test.
dChi-squared test.
Significant values are in Bold.