Abstract
Background: Exercising patients in the ICU receiving mechanical ventilation has shown to have positive outcomes; however, there is limited evidence as to which mode of ventilation to use during exercise. The purpose of this study was to evaluate the change in diaphragm thickness between expiration and inspiration (ΔDTE-I) during exercise in four modes of ventilation in normal subjects, to determine which mode had the smallest ΔDTE-I, indicating the lowest WOB. Methods: Following IRB approval, 16 subjects (8 male, 8 female) were ventilated with the PB 980 in VC A/C, VC + A/C, PC A/C and CPAP with PSV. Ventilator settings: PEEP 0 cm H2O in all modes, VT 8 mL/kg in VC A/C and VC + A/C, PSV 5 cm H2O in CPAP, PIP 5 cm H2O in PC A/C. While sitting on an exercise bike, subjects breathed on one of the 4 randomly assigned modes of ventilation for 2 minutes. At the end of two minutes, the diaphragm thickness was measured at end-expiration (DTE) and end-inspiration (DTI) on 3 breaths, when possible, by an experienced sonographer using a 9L3 linear transducer at 8 MHz. Heart rate (HR), SpO2, PEEP and Borg rating were recorded. Subjects remained in the same mode and started to pedal 50 RPM. At two minutes, subjects stopped pedaling, but continued to breathe on that mode while data were gathered. After the subject’s HR and SpO2 returned to baseline, the next randomly assigned mode was selected and the process was repeated until the subject breathed on all four modes. Results: VC A/C had the highest, and CPAP with PSV had the lowest, Borg rating during exercise, 6.25 and 1.94, respectively. During exercise, VC A/C had the most negative PEEP (-15.5 cm H2O), while PEEP in CPAP with PSV was least affected (-0.28 cm H2O). There was no statistically significant difference in DTI, DTE or ΔDTE-I when comparing VC A/C, VC + A/C and PC A/C to CPAP with PSV during exercise. Conclusions: VC A/C was shown to have the highest work of breathing via the Borg rating, the decrease in SpO2 and the decrease in PEEP. It is very difficult to measure the change in diaphragm thickness in a normal subject while exercising because of the chest movement and variation in VT causing the excursion of the diaphragm to move out of the range of the ultrasound transducer. There was no significant difference between DTI, DTE, ΔDTE-I between modes, during rest or exercise. Factors such as negative PEEP, SpO2 changes and the patient’s perceived WOB should be used to evaluate WOB during early mobility.
Footnotes
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