Elaine C. Gonçalves

Low pressure support changes the rapid shallow breathing index (RSBI) in critically ill patients on mechanical ventilation

BACKGROUND The rapid shallow breathing index (RSBI) is the most widely used index within intensive care units as a predictor of the outcome of weaning, but differences in measurement techniques have generated doubts about its predictive value. OBJECTIVE To investigate the influence of low levels of pressure support (PS) on the RSBI value of ill patients. METHOD Prospective study including 30 patients on mechanical ventilation (MV) for 72 hours or more, ready for extubation. Prior to extubation, the RSBI was measured with the patient connected to the ventilator (DragerTM Evita XL) and receiving pressure support ventilation (PSV) and 5 cmH2O of positive end expiratory pressure or PEEP (RSBI_MIN) and then disconnected from the VM and connected to a Wright spirometer in which respiratory rate and exhaled tidal volume were recorded for 1 min (RSBI_ESP). Patients were divided into groups according to the outcome: successful extubation group (SG) and failed extubation group (FG). RESULTS Of the 30 patients, 11 (37%) failed the extubation process. In the within-group comparison (RSBI_MIN versus RSBI_ESP), the values for RSBI_MIN were lower in both groups: SG (34.79±4.67 and 60.95±24.64) and FG (38.64±12.31 and 80.09±20.71; p<0.05). In the between-group comparison, there was no difference in RSBI_MIN (34.79±14.67 and 38.64±12.31), however RSBI_ESP was higher in patients with extubation failure: SG (60.95±24.64) and FG (80.09±20.71; p<0.05). CONCLUSIONS In critically ill patients on MV for more than 72h, low levels of PS overestimate the RSBI, and the index needs to be measured with the patient breathing spontaneously without the aid of pressure support.

Comparison of Energy Expenditure and Oxygen Consumption of Spontaneous Breathing Trial Conducted With and Without Automatic Tube Compensation

Background Weaning from mechanical ventilation is defined as the process of release of ventilatory support and how the evaluation of this phase is conducted in the spontaneous breathing trial (SBT). One of the most used modes of SBT is the continuous positive airway pressure (CPAP), which applies a continuous positive pressure in both inspiration and expiration. However, together with the mechanical ventilation modes, the automatic tube compensation (ATC) can be used, which compensates the resistance imposed by the endotracheal tube. The objective of this study was to compare oxygen consumption (VO2) and energy expenditure (EE) during SBT conducted with and without ATC. Methods The study was prospective, randomized and crossover. Forty mechanically ventilated patients were admitted to an intensive care unit of a university tertiary hospital. The participants were randomly allocated in group 1, in which SBT was initiated with CPAP and ATC, followed by CPAP without ATC or in group 2, in which SBT was initiated with CPAP without ATC, followed by CPAP with ATC. Indirect calorimetry helped to measure VO2 and EE during SBT. Results The differences between VO2 and EE obtained during SBT with ATC and without ATC were -1.6 mL/kg/min (95% CI: -4.36 - 1.07) and 5.4 kcal/day (95% CI: -21.67 - 10.79), respectively. Conclusions We concluded that VO2 and EE obtained during SBT with and without ATC were not different.

Spontaneous breathing test conducted with and without automatic tube compensation does not differ from a metabolic standpoint

Weaning from mechanical ventilation is defined as the process of release of ventilatory support and how the evaluation of this phase is conducted in the Spontaneous Breathing Test (SBT). One of the most used modes of SBT is the Continuous Positive Airway Pressure (CPAP). However, together with the mechanical ventilation modes it can be used the Automatic Tube Compensation (ATC), which compensates the resistance imposed by the endotracheal tube.