Stress response during weaning after cardiac surgery

We compared the effects of weaning using synchronized intermittent mandator y ventilation (SIMV) with the use of biphasic positive airway pressure (BIP AP) on the stress response, oxygen uptake ((V)over dot(O 2)) and work of br eathing (WOB) in 10 patients after aortocoronary bypass surgery. All three ventilatory settings were investigated in each patient, for example, volume -controlled mechanical ventilation immediately before weaning was followed, in randomized order, by both SIMV and BIPAP. In addition to routine monito ring of continuous and respiratory state, we measured (V)over dot(O 2), WOB , and pressure-time product (PTP) as well as the plasma concentrations of e pinephrine, norepinephrine, ACTH, cortisol, vasopressin, and prolactin. Alt hough respiratory rate (f), WOB and PTP were greater with both SIMV and BIP AP when compared with control, other variables did not change with the vent ilatory mode. In conclusion, weaning from mechanical ventilation using part ial support modes does not affect the postoperative stress response in pati ents who have had uncomplicated cardiac surgery.