Friday, November 5, 2010


In patients who failed wean criteria, our standard of ventilator management utilized PC-CMV. However, it is well-known that positive pressure ventilation can profoundly alter cardiovascular function.
Admitted to our ICU was an 85 y/o male with an extensive cardiac history significant for Sick Sinus Syndrome, Paroxysmal Atrial Fibrillation, and Atherosclerotic Coronary Artery Disease, with an estimated Left Ventricular ejection fraction of 25%. The patient’s surgical history was significant for pacemaker placement and percutaneous coronary intervention. On ventilator day 3, the patient’s ventilator mode was changed from PC-CMV to Proportional Assist Ventilation (PAV) to allow for unhindered spontaneous breathing in an effort to increase cardiac output (C.O.)/index (C.I.).
Case Summary
The patient was intubated due to hypoxic ventilatory failure secondary to decompensated congestive heart failure. Immediately following the application of mechanical ventilation, the hypoxemia was reversed, yet the cardiac instability persisted and prevented the patient from progressing to spontaneous breathing trials. Initial ventilator settings were PC-CMV, Vt 450, RR 14, FiO2 30%, & PEEP of 5. Respiratory and hemodynamic measurements were obtained before switching the mode to PAV, 80% support, FiO2 30%, & PEEP of 5 and the patient was allowed one hour to stabilize after modality change before obtaining an additional set of parameters. Pharmacological agents included a Dobutamine infusion @ 4mcg/min and a Propofol infusion @ 5cc/hr. No pharmacological changes were completed during data collection or alternating between ventilator modes.
 Our patient’s initial C.O. on PC-CMV was 3.06 L/Min with a C.I. of 1.56 L/Min/M2. Upon conversion to PAV, the patient’s C.O. & C.I. increased by ~27% while the PaO2 increased by ~17% (Table 1). After observing hemodynamic improvement with PAV, the patient was maintained on PAV and the Propofol infusion was rapidly terminated. On ventilator day six, the Dobutamine infusion was discontinued and the patient was extubated without complication.
 In our patient PAV produced a higher C.O. & C.I. over PC-CMV which is similar to the results Kondili documented when comparing PAV to pressure-support ventilation. Conversely, spontaneous variability of C.O. should be considered when evaluating two measurements taken at separate times. Sasse revealed that variability of C.O. may differ as much as 10%.  

1. Proportional Assist Ventilation: Guidelines for Using PAV+