Effect Of Mechanical Ventilation With Different Tidal Volumes On The Intrancranial Pressure During General Anesthesia

Objective:To investigate the influence of mechanical ventilation with different tidal volumes on the intracranial pressure and the relativity of the pressure of lumbar subarachnoid space and sigmoid sinus in patients undergoing selective craniocerebral operations.Methods:Thirty adult patients of cerebral tumor (aged 18—55,ASAⅠ—Ⅱ,cardiac functionⅠ-Ⅱ) scheduled for neurosurgery under general anesthesia were randomized to two groups(n=15) according to different tidal volumes(group A with a conventional tidal volume of 12 ml/Kg, group B with a low-tidal volume of 7 ml/Kg) and ventilated with intermittent positive pressure, PETCO2 was kept on 30-40mmHg according to blood gas analysis by adjusting respiratory frequency for an equivalent ventilation in the two groups. The limbar subarachnoid pressure,the pressure of sigmoid sinus,Pplat,Ppeak,Pmean,HR,Rf and MAP were measured after intubation of lumbar subarachnoid space(T0),after intubation of internal jugular vein(T1),afer incision of skin (T2),after boring of skull(T3),after removement of skull (T4),after scission of endocranium(T5),after resection of tumor(T6),after suture of endocranium (T7) and at the end of operation(T8). Blood samples were drawn synchronously from sigmoid sinus and dorsal artery of foot peripheral vein at different time points including T1,T5,T8 and then detected blood gas analysis.Result:①comparison among groups:Ppeak,Pplat and Pmean were significantly higher in group A than those in group B; Rf were significantly lower in group A than those in group B; blood gas analysis,liquid intake and output volume,anesthetic depth and electrolyte concentration had no significant differences between the two groups;②comparison among groups:The pressure of lumbar subarachnoid space had no significant differences between the two groups at T0,T1,T5,T6,T7,T8(P>0.05),and had significant differences at T2,T3,T4 (p<0.05); The pressure of sigmoid sinus had significant differences at all the other time points except T1.③Interclass comparison:Compared with T0,the pressure of lumbar subarachnoid space had significant differences at all the other points except T1 in both group A and B (P>0.05); compared with Tl,the pressure of sigmoid sinus had significant differences at all the points both in group A and in group B; The pressure of sigmoid sinus is higher than the pressure of sigmoid sinus;④Relativity:The correlation relativity of the pressure of lumbar subarachnoid space and sigmoid sinus were significant before scission of endocranium,intermediate after suture of endocranium and not after scission of endocranium. The correlation coefficient was 0.934 and the regression equation was Y=0.787X+1.657 before scission of endocranium and the correlation coefficient was 0.604 and the regression equation was Y=0.7085X+2.3123 after sutue of endocranium. The correlation coefficient was-0.021 after scission of endocranium.Conclusion:①The effect of Low-volume mechanical ventilation on the intrancranial pressure is lesser and low-volume mechanical ventilation is better to craniocerebral operations under general anesthesia.②the correlation relativity of the pressure of lumbar subarachnoid space and sigmoid sinus is significant and the pressure of lumbar subarachnoid space is higher than the pressure of sigmoid sinus before scission of endocranium.