PURPOSE: Appropriate respiratory muscle unloading with PSV is thought to be achieved using the following conventional method: Spontaneous breathing frequency (f) 15-25/min and tidal volume (VT) 6-8 ml/kg ideal body weight, absence of sternocleidiomastoid muscle contraction, and appearance of breathing comfortably. We evaluated this method.
METHODS: 115 adults (weight 91 ± 18 kg, age 50 ± 11 yrs) with varying degrees of respiratory failure were studied (IRB approved). Data from a combined pressure/flow sensor, positioned between the endotracheal tube and ventilator, were directed to a respiratory monitor (NICO, Respironics, Convergent Engineering) to measure power of breathing noninvasively (POBn) [work/minute, load on respiratory muscles, normal adult 4-8 Joules/min], f, and VT using the aforementioned method for setting PSV. Patients were divided into three groups, Group A: POBn < 5, Group B: POBn > 5 < 10, and Group C: POBn > 10. Data were analyzed using ANOVA; alpha was set at 0.05.
RESULTS: See table.
CONCLUSION: Although f and VT were in appropriate ranges most of the time for all groups, Group A was unloaded too much predisposing to disuse atrophy (largest group), Group C was not unloaded enough predisposing to muscle fatigue, and Group B (only 34% of patients) was unloaded appropriately.
CLINICAL IMPLICATIONS: These findings support the need to include both respiratory muscle load (POBn) and tolerance (f, VT) measurements to ensure appropriate unloading when using PSV.
DISCLOSURE: Carl Peters, University grant monies Grant support from Convergent Engineering for M.J. Banner; Shareholder N.R. Euliano is President of Convergent Engineering; Employee D. Martin is employed by Convergent Engineering; Product/procedure/technique that is considered research and is NOT yet approved for any purpose, Appropriate Pressure Support Ventilation.