Am. J. Respir. Crit. Care Med., Vol 149, No. 5, May 1994, 1085-1091.
Patient work of breathing during pressure support and volume-cycled mechanical ventilation
JW Kreit, MW Capper and WL Eschenbacher
Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh Medical Center, PA 15213.
A computer-assisted technique based on the equation of motion of the
respiratory system was used to measure inspiratory work of breathing in 11
patients during pressure support ventilation (PSV) and assisted,
volume-cycled mechanical ventilation (AMV). During both modes of
ventilation, patient work of breathing was calculated as the difference
between the total work performed on the respiratory system (as predicted by
the equation of motion) and the work performed by the ventilator. Patient
work of breathing during AMV was also calculated as the difference between
ventilator work measured during assisted and controlled mechanical breaths.
By either method of work calculation, patient work of breathing during AMV
was less than previously reported. In addition, when equal tidal volumes
were delivered, there was no significant difference between the work
performed by the patient during AMV and PSV. Patient work of breathing
during PSV was found, however, to vary inversely with the level of pressure
support. We conclude that: (1) patient work of breathing during AMV and PSV
can be calculated using a computer-assisted technique based on the equation
of motion of the respiratory system, and (2) depending on the amount of
pressure support provided, patient work of breathing during PSV may be
greater than, less than, or equal to the work performed during AMV.
