Wac. Mutch et al., Biologically variable ventilation prevents deterioration of gas exchange during prolonged anaesthesia, BR J ANAEST, 84(2), 2000, pp. 197-203
Citations number
26
Categorie Soggetti
Aneshtesia & Intensive Care","Medical Research Diagnosis & Treatment
We have studied the time course of changes in gas exchange and respiratory
mechanics using two different modes of ventilation during 7 h of isoflurane
anaesthesia in pigs. One group received conventional control mode ventilat
ion (CV). The other group received biologically variable ventilation (BW) w
hich simulates the breath-to-breath variation in ventilatory frequency cn t
hat characterizes normal spontaneous ventilation. After baseline measuremen
ts with CV, animals were allocated randomly to either CV or BW (Fl(O2) 1.0
with 1.5% end-tidal isoflurane). With BW, there were 376 changes in f and t
idal volume (V-T) over 25.1 min. Ventilation was continued over the next 7
h and blood gases and respiratory mechanics were measured every 60 min. The
modulation file used to control the ventilator for BW used an inverse powe
r law frequency distribution (1/f(a) with a = 2.3 +/- 0.3). After 7 h, at a
similar delivered minute ventilation, significantly greater Pa-O2 (mean 72
.3 (SD 4.0) vs 63.5 (6.5) kPa) and respiratory system compliance (1.08 (0.0
8) vs 0.92 (0.16) mi cm H2O-1 kg(-1)) and lower Pa-CO2 (6.5 (0.7) vs 8.7 (1
.5) kPa) and shunt fraction (7.2 (2.7)% vs 12.3 (6.2)%) were seen with BW,
with no significant difference in peak airway pressure (16.3 (1.2) vs 15.3
(3.7) cm H2O). A deterioration in gas exchange and respiratory mechanics wa
s seen with conventional control mode ventilation but not with BW in this e
xperimental model of prolonged anaesthesia.