Influence Of Small Dose Of Epidural Morphine On Minute Ventilatory Volume And Ventilatory Response To CO₂ In Rabbits

Objective: To study the influence of small dose of epidural morphine on minute ventilatory volume and ventilatory response to CO₂ in rabbits; Methods: 20 wealthy adult rabbits were assigned randomly into 4 groups, group A was control group, and others were experiment groups. All the rabbits received a epidural puncture, and after that, group A was given an epidural injection of normal saline and group B,C,D were given an epidural injection of morphine (0.25,0.35,0.50mg/kg), the volume was 0.5ml/kg. A pulmometer was used to measure the minute ventilatory volume of the rabbits after 3～6 hours, and artery blood was taken for blood gas analysis at the same time. And then the rabbits were laid in acomparative airtight box, in which CO₂ was ventilated and the concentration was measured at the same time. Minute ventilatory volume was measured when the concentration of CO₂ was 3%,5%,7%; And artery blood was taken again for blood gas analysis at the same time. Results: There were no difference of weight and volume of epidural injection in all the groups. After the epidural injection, there was no difference of minute ventilatory volume in groups when air was inhaled. There were differences of minute ventilatory volume between group A and B,group A and D when 3% of CO₂ was inhaled (P﹤0.05). There was no difference of ventilatory volume in groups when 5% and 7% of CO₂ were inhaled. There was difference in group A when air was inhaled compared with 5% of CO₂ (P﹤0.05), and there was difference in group B when 7% of CO₂ was inhaled compared with air and other concentration of CO₂ (P﹤0.05). There were differences in group C and D when 7% of CO₂ was inhaled compared with 3% of CO₂ (P﹤0.05). Studying the trendline of ventilatory response to CO₂ of all the groups, we found that the ventilatory volume in group A was in a direct ratio with the concentration of CO₂when 0～5% of CO₂ was inhaled while it was descending when the concentration of CO₂ was beyond 5%. However, there was no significant difference of ventilatory volume in group B,C,D when the concentration of CO₂ was under 3%, and the ventilatory volume was in a direct ratio with the concentration of CO₂ when it was beyond 3%. There was no significant difference in groups on the results of blood gas analysis. Conclusion: Small dose of epidural morphine makes no significant influence on minute ventilatory volume of rabbits; it can significantly restrain the ventilatory response to CO₂ of rabbits; and it makes no significant influence on the level of blood gas of rabbits.