[A study of mechanical ventilation pattern in different recovery stages of muscle relaxant after general anesthesia]

To observe the effects of intermittent positive pressure ventilation (IPPV), synchronized intermittent mandatory ventilation (SIMV), and biphasic intermittent positive airway pressure (BiPAP) on the recovery time of automatic breathing in patients in different stages of recovery of general anesthesia with muscle relaxant.

Thirty patients were randomly divided into three groups. The initial ventilation pattern was IPPV for all patients. After the last dose of muscle relaxant, the pattern of ventilation of group II and group III was adjusted to SIMV and BiPAP, respectively. The airway peak pressure(Ppeak), minute ventilation(MV), expiration carbon dioxide(P(Et)CO(2)), blood gases, and the interval between the last dose of muscle relaxant and automatic breathing(LR-S) was observed.

(1) When T(1) appeared, Ppeak of the BiPAP group was lower than that of the IPPV group and SIMV (all P<0.01). When T(R)=0.75, Ppeak of IPPV group was lower compared with the SIMV and BiPAP groups (all P<0.01). (2) When T(1) re-appeared, the MV of BiPAP was higher than that of the IPPV group (P<0.05), but was not different from that of the SIMV group (P>0.05). When T(4) appeared, T(R)=0.25, T(R)=0.75, MV of SIMV group and BiPAP group was higher than that of IPPV group (all P<0.01). (3) When T(R)=0.25, T(R)=0.75, the P(Et)CO(2) of the SIMV group and BiPAP group was lower than that of IPPV group (all P<0.05). (4) Partial pressure of carbon dioxide in artery (PaCO(2)) of the SIMV and BiPAP group was lower than that of the IPPV group (all P<0.05). (5) The LR-S before extubation was shorter in SIMV and BiPAP group than that in IPPV group (P<0.05).

SIMV and BiPAP have the advantages as follows: no confrontation between mechanical ventilation and autonomous breathing, quick recovery of autonomous breathing, little change in airway pressure, high MV and low P(Et)CO(2). So SIMV and BiPAP are more suitable for recovery from anesthesia. In addition, BiPAP can lower the airway's peak pressure and decrease the probability of barotrauma therefore it is more suitable for those patients with high airway pressure.