RESUMO
ObjectiveTo investigate the influence of the number of T-junctions between central venous catheter and pressure transducer on measurement of central venous pressure (CVP) in patients.Methods A prospective controlled study was conducted. The patients with CVP monitoring in Department of Critical Care Medicine of the Fifth Center Hospital in Tianjin from February to October in 2014 were enrolled. The patients were divided into three groups according to the number of T-junction between central venous catheter and pressure transducer: without T-junction control group and 1, 2, 3 T-junctions groups. In each patient, corresponding CVP values with different number of T-junctions placed between the central venous catheter and pressure sensors were determined within a certain period, and a square-wave graphic was obtained and preserved on the monitor. The own frequency (fn) and the attenuation coefficient (D) of the system of pressure measurement were calculated after measurement of the shock wave following a square-wave to obtain the distance between two vibrations and the amplitude of the shock wave. The difference in CVP, fn and D were compared among the groups.Results A total of 20 cases were enrolled, and 150 groups of data were collected.① With the increase in the number of T-junction, CVP showed a tendency of gradual reduction. The CVP of the groups of control and 1, 2, 3 T-junctions was (7.00±1.60), (7.00±3.00), (5.00±2.00), and (4.00±1.00) mmHg (1 mmHg = 0.133 kPa), respectively. The CVP of 3 T-junctions group was significantly lower than that of the control group (F = 9.333,P = 0.015).② With an increase in the number of T-junction, fn showed a tendency of gradual increase. The fn of groups control and 1, 2, 3 T-junctions was (12.30±0.79), (16.00±0.91),(18.10±1.75), (20.90±2.69) Hz, respectively. The fn of 1, 2, 3 T-junctions group was significantly higher than that of the control group (F1 = 45.962,F2 = 45.414,F3 = 46.830, allP = 0.000); the fn of groups 2 and 3 T-junctions was significantly higher than that of 1 T-junction group (F1 = 5.827,P1 = 0.042;F2 = 15.038,P2 = 0.004), but there was no significant difference between the groups of 2 T-junctions and 3 T-junctions (F = 3.800,P = 0.087).③ With an increase of the number of T-junction, D also showed a tendency of gradual increase. The D of 1, 2, 3 T-junction group was 1.62±0.27, 1.60±0.22, 1.82±0.25, and 2.15±0.58, respectively. There were no differences among four groups.ConclusionAfter the application of T-junctions between central venous catheter and pressure transducer, CVP values will be underestimated, the reason of which is considered to be the increase in length and thinner lumen of the T-junctions.
RESUMO
Objective To determine the appropriate size of the tube for the thoracic drainage in good efficiency by the experimental study in the influence of the tube size on the flow rate of the fluid with different properties.Methods Three groups were divided according to the different components in the fluid:group A,whole blood with 30％ hematocrit; group B,2.5％ albumin solution; and group C,0.9％ normal saline.The total volume of the fluid was 1000 mL in each group in the experiment.Different sorts of fluids were drained with the chest tubes with different diameters (6F,8F,10F,12F,14F,16F,18F,20F,22F,24F,26F,28F,30F,32F,34F,36F of French F) separately,and the flow rate was calculated.ANOVA was used for the comparison of the differences in flow rate among the groups with given fluid property.Twofactor analysis of variance was used for the analysis of flow rates of fluid with different fluid properties.Curve fitting was performed according to the Poiseuille formula.Results The flow rate was positively correlated with the size of the chest drainage tube.The difference in flow rate among the tubes with difference in size was statistically significant (P ＜ 0.05) but there was no noticeable difference in flow rate between 6F and 8F (P =0.513).The flow rate of the 6F and 8F tubes was higher than that of the control (3.33 mL/min) but there was no significant difference between them (P ＞ 0.05).The flow rate of the tubes in 10F and above was obviously higher than that of control (P ＜ 0.05).The curve was estimated that group A was Q =0.002 9x4,R2 =0.991; group B Q=0.003 2x4,R2 =0.981; group C Q =0.003 4x4,R2 =0.975.When the flow rate was fixed at 3.33 mL/min,the estimated curve in group A was X ≈ 5.82F.Conclusions Our experiment indicated that the chest tube with small diameters (6F-14F) could meet the demand of high efficient drainage in the patients with hemothorax or pleural effusion.