Objective To evaluate the influence of tidal volume on the accuracy of stroke volume variation ( SVV) to predict volume state of pigs with ventilation.Methods Thirty-six healthy pigs were anesthetized after tracheal intubation and ventilated. With the envelope method, they were randomized into a normovolemia group, a hemaerrhagic shock group, and a hypervolemia group, with 12 pigs in each group. The pigs in the hemaerrhagic shock group were removed 20 percent of blood, and the pigs in the hypervolemia group received additional infusion of 20 percent 6% hydroxyethyl starch. In each group, ventilator settings were changed in a randomized order by changing VT [ VT = 5 mL/kg ( VT5 ) , VT =10 mL/kg ( VT10 ) , and VT =15 mL/kg ( VT15 ) ] . Hemodynamic measurements [ heart rate ( HR) , mean arterial boold pressure ( MAP) , systemic vascular resistance index ( SVRI) , cardiac index ( CI) , stroke volume index ( SVI) , intrathoracic blood volume index( ITBVI) , and SVV] were obtained after 10 minutes of stabilization. Results SVV was increased in the hemaerrhagic shock group comparing with the normovolemia group for VT10 [ ( 21 ±5) % vs. ( 11 ±2) % , P lt;0. 05] , but SVV was decreased in the hypervolemia group comparing with the normovolemia group [ ( 7 ±2) % vs. ( 11 ±2) % , P lt; 0. 05] . The variation tendency for VT15 was the same with VT10 , moreover SVV were all above 12% for the hemaerrhagic shock group, the normovolemia group, and the hypervolemia group [ ( 30 ±7) % , ( 19 ±3) % , and ( 15 ±4) % ] . There were no significant diffrences among the hemaerrhagic shock group, hypervolemia group and normovolemia group [ ( 8 ±6) % ,( 7 ±5) % , and ( 7 ±4) % , P gt; 0. 05] for VT5 . Conclusions SVV was a precise indicator of cardiac preload, but SVV was less sensitive to the changes of volume during low tidal volume ( 5 mL/kg) ventilation. The threshold of SVV for predicting fluid responsiveness maybe above 12% with a high tidal volume ( 15 mL/kg) ventilation.
ObjectiveTo evaluate the effect of different rehydration strategies on the incidence of spinal anesthesia-induced hypotension and neonatal outcomes during elective cesarean section.MethodsWe searched PubMed, Embase, the Cochran Library, China National Knowledge Internet, VIP database, Wanfang database, and China Biology Medicine database from inception to January 2018, to collect randomized controlled trials (RCTs) about the incidence of spinal anesthesia-induced hypotension during elective cesarean section and neonatal outcomes of preloading or coloading. Two researchers independently screened the literature, extracted data, and evaluated the risk of bias in the study. Meta-analysis was conducted using RevMan 5.3 software.ResultsA total of 11 RCTs were included, including 894 parturients, of whom 448 cases in the preload group and 446 cases in the coload group. Comparing with the preload group, the incidence of spinal anesthesia-induced hypotension during cesarean section in the coload group significantly decreased [risk ratio (RR)=1.27, 95% confidence interval (CI) (1.13, 1.43), P<0.000 1]. Subgroup analysis showed that in the crystalloid fluid group, the difference in the incidence of hypotension between the preload group and the coload group was statistically significant [RR=1.48, 95%CI (1.26, 1.73), P<0.000 01]; while in the colloidal fluid group, the difference in the the incidence of hypotension between the preload group and the coload group was not significant [RR=1.00, 95%CI (0.85, 1.17), P=0.96]. The lowest systolic blood pressure, the incidence of nausea and vomiting, and neonatal outcomes had no significant difference between the two groups.ConclusionsComparing with preloading crystalloid fluid, rapid infusion of crystalloid fluid at the same time implementation of spinal anesthesia could significantly reduce the incidence of hypotension during cesarean section while there was no superiority in infusion of colloid fluid. There was no significant effect on the severity of hypotension, nausea and vomiting, and neonatal outcomes. Due to the limitation of the quantity and quality of the included studies, the above conclusions need to be verified by more high-quality studies.