Increase in intra-abdominal pressure during airway suctioning-induced cough after a successful spontaneous breathing trial is associated with extubation outcome

This is a single-center, prospective, cohort study. The study was approved by the Institutional Review Board at Tokyo Bay Urayasu Ichikawa Medical Center (TBUIMC). A waiver of informed consent was obtained because the study exposed patients to less than minimal risk.

The study was performed in the medical–surgical ICU during the period from April 2015 through November 2015. All mechanically ventilated patients 18 years or older who had been endotracheally intubated and had passed an SBT of longer than 30 min were eligible for inclusion. The SBT was conducted on pressure support ventilation with a pressure support of 5 cm H₂O, a positive end-expiratory pressure (PEEP) of ≤ 8 cm H₂O, and a fraction of inspiratory oxygen (FiO₂) of ≤ 0.50. Patients were excluded from the study if they had “comfort care” or “do not re-intubate” status or had been previously extubated during the same hospitalization. Patients were also excluded if they had documented or suspected upper airway obstruction, end-stage renal disease requiring hemodialysis, or no Foley catheter at the time of extubation. Successful completion of an SBT was determined using the standard Tokyo Bay Urayasu Ichikawa Medical Center (TBUIMC) Respiratory Care Weaning Protocols (no evidence of severe anxiety, dyspnea, or excessive accessory muscle use; a rapid shallow breathing index [RSBI] of ≤ 105 breaths/min/L; and adequate gas exchange, i.e., SaO₂ ≥ 90% with FiO₂ ≤ 0.50 and PEEP ≤ 8 cm H₂O).

A water-column technique was used to measure IAP [17], which was determined in the ICU by resident physicians using the following protocol, after all sedatives and analgesics were discontinued for at least 60 min: (1) the drainage tube of the patient’s Foley bladder catheter was clamped; (2) sterile normal saline (20 ml) was instilled into the bladder via the aspiration port of the Foley catheter with a needleless connection system; (3) a fluid column consisting of two extension tubes (length 75 cm, inner diameter 3.1 mm; Terumo, Tokyo, Japan) was constructed, connected to the aspiration port of the Foley catheter, and then placed at the level of the mid-axillary line; (4) with the patient in supine position, fluid level in the absence of cough at end expiration was marked on the extension tube and recorded as the baseline bladder pressure; (5) airway suctioning was performed by advancing the closed-system suction catheter while the patient was connected to the ventilator, which is part of the standard pre-extubation procedure; and (6) the recorder observed changes in fluid level and marked the highest fluid level on the extension tube during successive coughs, which was recorded as the highest bladder pressure. The patient was extubated within 10 min after IAP measurement. Attending physicians and fellows responsible for clinical decisions, including extubation, were blinded to the results of the IAP and ΔIAP measurements.

Successful extubation was defined as the absence of the need for re-intubation within 72 h after extubation. Extubation failure was defined as re-intubation within 72 h after extubation. Patients were followed until hospital discharge or death. The use of prophylactic or therapeutic noninvasive positive pressure ventilation without consequent re-intubation was not considered as extubation failure.

Because at least 10 episodes of extubation failure were required in order to conduct multiple regression analysis adjusted for APACHE II score—the most important confounding factor for extubation outcomes—the estimated minimum sample size needed for the statistical analysis was 135 with a predicted extubation failure rate of 8%, as indicated by the past extubation failure rate in this ICU [18]. With a planned study duration of 9 months, the predicted number of patients to be recruited in the study was 400, assuming an average of approximately 45 extubations per month in our ICU.

The primary outcome of this study was extubation failure. Secondary outcomes included in-hospital mortality, ICU days, and length of hospital stay. A ΔIAP cutoff value for extubation failure was estimated with receiver operator characteristic (ROC) analysis. A multivariable-adjusted logistic regression model was used to calculate the odds ratio for extubation failure based on ΔIAP adjusted for APACHE II score. Mean baseline IAP, ΔIAP, and other variables were compared in relation to extubation success and failure. The Student t test was used to compare the means for variables. The Fisher exact test was used to compare grouped data such as sex, Confusion Assessment Method for the Intensive Care Unit (CAM-ICU), and mortality. For measures of association, 95% confidence intervals (CI) were computed, and statistical significance was defined as a two-tailed p value of less than .05. Using a multivariable-adjusted logistic regression model, we estimated the odds ratio (OR) for re-intubation adjusted for APACHE II score. We also conducted a secondary analysis to investigate the relationship between ΔIAP and extubation outcomes in patients who were mechanically ventilated for longer than 72 h. All statistical analyses, except for sample size estimation, were performed with the IBM Statistical Package for the Social Sciences version 22.0 (IBM, Corp, Armonk, NY, USA).

A total of 335 patients were included in the analyses (Fig. 1), 24 (7.2%) of whom were re-intubated within 72 h after extubation. Tables 1 and 2 show patient baseline characteristics and indications for intubation, respectively. Univariate analysis showed that CAM-ICU, APACHE II score, Simplified Acute Physiology Score II score, intubation days, length of ICU stay, length of hospital stay, 28-day mortality, and in-hospital mortality were significantly higher, and P/F ratio was significantly lower, in the extubation failure group than in the extubation success group. Figures 2 and 3 show the distributions of baseline IAP and ΔIAP for the patients. The median (interquartile range) baseline IAP was 8 (4–11) cm H₂O, and the median (interquartile range) ΔIAP was 38 (23–55) cm H₂O (range, 0–120 cm H₂O).

ΔIAP was significantly higher in the extubation success group than in the extubation failure group (p = 0.012; median, 39.00 vs 25.50 cm H₂O, respectively). Figure 4 shows the ROC curve between ΔIAP and extubation failure. The area under the ROC curve was 0.654 (95% CI 0.544–0.764), and the cutoff value was 30 cm H₂O (sensitivity, 64%; specificity, 67%). ΔIAP was classified as ≤ 30 cm H₂O (low ΔIAP group) or > 30 cm H₂O (high ΔIAP group). Table 3 shows that low ΔIAP was significantly associated with extubation failure after adjusting for APACHE II score (adjusted OR, 3.40; 95% CI, 1.39–8.26, p = .007). The positive predictive value and negative predictive value of a ΔIAP value of ≤ 30 cm H₂O for extubation failure were 1.85 and 0.52, respectively.

A secondary analysis including only patients who were mechanically ventilated for longer than 72 h (124 patients with successful extubation and 17 patients with extubation failure) yielded an AUC of 0.708 (95% CI 0.571–0.845) with a cutoff value of 29 cm H₂O (Fig. 5). Multiple regression analysis (Table 4) showed that a low ΔIAP (≤ 29 cm H₂O) was significantly associated with extubation failure, after adjusting for APACHE II score (adjusted OR, 3.79; 95% CI, 1.32–10.75, p = 0.01). The positive predictive value and negative predictive value of a ΔIAP value of ≤ 29 cm H₂O for extubation failure were 2.21 and 0.56, respectively.