As described previously, there are three methods of spontaneous breathing trials, T-piece trials, CPAP trials, and minimal PS trials (MacIntyre 2001). In the T-piece trial, the patient is removed from the ventilator, and humidified oxygen is provided through the T-piece. The flow should provide constant mist during both inspiration and expiration to match the patient’s minute ventilation. The minimal pressure support technique provides a minimal amount of pressure support estimated to overcome the resistance to breathing through an artificial airway and adjusted higher for smaller diameter endotracheal tubes. In CPAP trials, the patient is placed on a CPAP level of 4–5 cm H₂O. During all of these SBTs, indicators of oxygenation, ventilation, work of breathing, and patient distress are monitored.

Adult studies have demonstrated success using the spontaneous breathing trial and, more importantly, have shown that many patients are ready to be extubated without the need to wean. In a large RCT by Esteban et al. (1995), 76 % of patients evaluated for weaning readiness were extubated without weaning. In patients that failed an initial extubation evaluation, weaning methods were compared using daily T-piece trials, multiple SBTs, PSV, and intermittent ventilation. Patients were extubated successfully three times faster with a spontaneous breathing trial compared to intermittent ventilation and two times faster compared to pressure support ventilation (Esteban et al. 1997). Brouchard et al. (1994) compared weaning modalities using a T-piece, PSV, and SIMV. More patients were successfully weaned with PSV compared to SIMV. There was no difference in the rates of reintubation using PS compared to T-piece; however, more patients tolerated the PS trial and were extubated than the T-piece trial.

The ERT used by the PALISI Network in children consisted of first testing oxygenation and then, if oxygenation could be sustained on extubatable settings (FiO₂ 0.5, PEEP 5 cm H₂O), testing ventilatory support needs. The FiO₂ was dropped to 0.5 and the PEEP to 5 cm H₂O. If the patient was previously at these settings and maintaining peripheral oxygen saturations (SpO₂) ≥95 % on pulse oximetry, the settings were left unchanged. Patients unable to maintain an SpO₂ of ≥95 % failed the test. Those who maintained an SpO₂ of ≥95 % were placed on minimal PSV. Minimal pressure support was adjusted for the ETT size because of increasing resistance with lower ETT size (pressure support of 10 cm H₂O for an ETT size 3.0–3.5, 8 cm H₂O for an ETT size 4.0–4.5, and 6 cm H₂O for an ETT size ≥5.0). Exhaled tidal volumes were measured at the ETT with neonatal, pediatric, or adult sensors. Patients were monitored during the test for 2 h. Patients were classified as failing the test if at any time in the 2-h period their SpO₂ was less than 95 %, their exhaled tidal volume was less than 5 ml/kg ideal body weight, or their respiratory rate was outside of the acceptable range for their age (20–60/min for age ≤6 months, 15–45/min for 6 months–2 years, 10–35/min for age 2–5 years). As soon as any criteria for failure were met, the patient was removed from the test, placed back on previous ventilator settings, and randomized to PSV, VSV, or no protocol.

There are other studies of SBTs in children. In a large RCT by Farias et al. (2002), 77 % of children tested with a spontaneous breathing trial passed on the first attempt and were extubated without weaning. Like adults, the data supports that many pediatric patients are extubated successfully without weaning. In patients that failed an SBT, Farias et al. (2001) compared weaning modalities using pressure support of 10 cm H₂O to T-piece alone. There were no differences in 48 h extubation failure rates between the two groups. Respiratory rate, tidal volume, RSBI, and maximal negative inspiratory pressure (PI_max) were all poor predictors of extubation outcome. Chavez et al. (2006) evaluated the use of a 15 min SBT trial to test for extubation readiness. The SBT consisted of delivery of a continuous flow of oxygen sufficient to deliver a CPAP of 5 cm H₂O. Patients were tested when they were deemed ready to be extubated, rather than ready to be weaned. Ninety-one percent of patients passed the initial trial and were extubated; 7.8 % failed extubation. These studies indicate that the majority of children are ready to be extubated without the need to wean.

The 2001 task force identified eight specific predictors of extubation used in the literature, with varying predictive abilities, as shown in Table 57.2 (MacIntyre 2001). These indices were minute ventilation (V_e) 10–15 l/min, negative inspiratory force (NIF) 20–30, maximal inspiratory mouth pressures (PImax) −15 to −30, airway occlusion pressure (P₀₁)/PI_max (0.30), CROP score (dynamic compliance × maximal negative inspiratory pressure × (PaO₂/PAO₂)/respiratory rate), respiratory rate (RR) 30–38 breaths per minute (bpm), tidal volume (VT) 325–408, and rapid shallow breathing index or respiratory rate/VT ratio 60–105. Of these variables, RSBI <100 breaths/min/l, the CROP index, RR > 38 bpm, tidal volume standardized to body weight, and NIF 20–25 H₂O had the greatest predictive potential. The CROP index, RR, RSBI, and VT are indices that have been used in children (Newth et al. 2009).

In pooled adult studies, a RSBI <100 or 105 breaths/min/l had a sensitivity of 65–96 % and a specificity of 0–73 % to predict successful extubation. Respiratory rate (RR) <38 bpm had a sensitivity of 88 % and a specificity of 47 %. When both were pooled together, a RR >38 bpm and an RSBI < 100 reduces the probability of successful extubation. Given the high sensitivity but low specificity, the RSBI and RR indices may help screen those ready for extubation (Newth et al. 2009; MacIntyre 2001). Thiagarajan et al. (1999) evaluated potential predictors of extubation readiness in children. A RR ≤45 bpm, spontaneous tidal volume ≥ 5.5 ml/kg, RSBI ≤ 8 breaths/min/ml/kg body weight, and the CROP index ≥ 0.15 ml/kg body weight/breaths/min were good predictors of successful extubation. Leclerc et al. (2002) found the CROP index and the RSBI to have sensitivities of 97 and 94 %, respectively, with a specificity of 0 % in both. The area under the ROC curve was 0.8, suggesting that neither was a good predictor of extubation success. Manczur et al. (2000) found tidal volume and minute volume to be the best predictive indicator of extubation success, with low tidal volumes and minute volumes being the most predictive of extubation failure. In adults, poor cough strength and magnitude of endotracheal secretions has also been used (Khamiees et al. 2001). Cough strength was measured subjectively and objectively by measuring a patient’s ability to propel secretions onto a card placed 1–2 cm away from the endotracheal tube. Cough strength predicted extubation failure with a RR of 31.9 % (95 % CI 4.5–225 %). Despite the many indices used to predict extubation success, in multiple studies, none used individually have been shown to be superior to clinical judgment.