Spontaneous breathing trial and post-extubation work of breathing in morbidly obese critically ill patients

Abstract

Background: Predicting whether an obese critically ill patient can be successfully extubated may be specially challenging. Several weaning tests have been described but no physiological study has evaluated the weaning test that would best reflect the post-extubation inspiratory effort.

Methods: This was a physiological randomized crossover study in a medical and surgical single-center Intensive Care Unit, in patients with body mass index (BMI) >35 kg/m2 who were mechanically ventilated for more than 24 h and underwent a weaning test. After randomization, 17 patients were explored using five settings : pressure support ventilation (PSV) 7 and positive end-expiratory pressure (PEEP) 7 cmH2O; PSV 0 and PEEP 7cmH2O; PSV 7 and PEEP 0 cmH2O; PSV 0 and PEEP 0 cmH2O; and a T piece, and after extubation. To further minimize interaction between each setting, a period of baseline ventilation was performed between each step of the study. We hypothesized that the post-extubation work of breathing (WOB) would be similar to the T-tube WOB.

Results: Respiratory variables and esophageal and gastric pressure were recorded. Inspiratory muscle effort was calculated as the esophageal and trans-diaphragmatic pressure time products and WOB. Sixteen obese patients (BMI 44 kg/m2 ± 8) were included and successfully extubated. Post-extubation inspiratory effort, calculated by WOB, was 1.56 J/L ± 0.50, not statistically different from the T piece (1.57 J/L ± 0.56) or PSV 0 and PEEP 0 cmH2O (1.58 J/L ± 0.57), whatever the index of inspiratory effort. The three tests that maintained pressure support statistically underestimated post-extubation inspiratory effort (WOB 0.69 J/L ± 0.31, 1.15 J/L ± 0.39 and 1.09 J/L ± 0.49, respectively, p < 0.001). Respiratory mechanics and arterial blood gases did not differ between the five tests and the post-extubation condition.

Conclusions: In obese patients, inspiratory effort measured during weaning tests with either a T-piece or a PSV 0 and PEEP 0 was not different to post-extubation inspiratory effort. In contrast, weaning tests with positive pressure overestimated post-extubation inspiratory effort.

Trial registration: Clinical trial.gov (reference NCT01616901 ), 2012, June 4th.

Keywords: Acute respiratory failure; Mechanical ventilation; Obese; Weaning; Work of breathing.

Figures

Fig. 1

Study design. Eleven morbidly obese patients ventilated in pressure support ventilation (PSV) and positive end-expiratory pressure (PEEP), considered as baseline settings, were included to randomly perform the five weaning test modalities of the study before extubation: PSV 7 cmH2O + PEEP 7 cm H2O; PSV 0 cmH2O + PEEP 7 cmH2O; PSV 7 cmH2O + PEEP 0 cmH2O; PSV 0 cmH2O + PEEP 0 cmH2O or the T piece. All measurements were obtained after 15 minutes of each test. A 10-minute period of return to baseline state (with initial settings of ventilation parameters before the first weaning test) was performed between each test and before extubation. WT weaning test

Fig. 2

Flow chart of the study. One patient fulfilled the inclusion criteria but was not included because of extubation during the weekend with no investigator available. BMI body mass index, SBT spontaneous breathing trial

Fig. 3

Esophageal (a) and trans-diaphragmatic (b) swings. Individual and mean changes in esophageal and trans-diaphragmatic swings during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduce respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O + positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation. Pdi transdiaphragmatic pressure, pes esophageal pressure

Fig. 4

Esophageal (a) and trans-diaphragmatic (b) pressure time products. Individual and mean changes in esophageal and trans-diaphragmatic pressure time products during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduce respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O+ positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation. PTPdi trans-diaphragmatic pressure-time product, PTPes trans-esophageal pressure-time product

Fig. 5

Work of breathing (WOB) in J/L (a) and in J/minute (b). Individual and mean changes in the WOB during the five weaning tests and 20 minutes after extubation. All the tests show that the weaning tests that best reproduced respiratory muscle work after extubation were pressure support ventilation (PSV) 0 cmH2O cmH2O + positive end-expiratory pressure (PEEP) 0 cmH2O and the T piece, with no statistically significant difference between the two. *p < 0.001 when compared with after extubation

Fig. 6

Ventilatory pattern during the five weaning tests and twenty minutes after extubation. One patient is presented with the acquisition of flow (L/s), esophageal (Pes, cmH2O), airway (Paw, cmH2O), gastric (Pga, cmH2O) and trans-diaphragmatic (Pdi, cmH2O) pressure signals. PSV pressure support ventilation, PEEP positive end-expiratory pressure