title: [The influence of joining central venous catheter and pressure transducer with T-junctions on central venous pressure].
abstract: OBJECTIVE
  To 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, all P = 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.
  
  
  CONCLUSIONS
  After 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.
authors.affiliation: Department of Critical Care Medicine, the Fifth Center Hospital in Tianjin, Tianjin 300450, China. Corresponding author: Cheng Xiuling, Email: chengxiuling6630@sina.com.
authors.forename: Xiuling
authors.initials: X
authors.lastname: Cheng
authors.forename: Wanjie
authors.initials: W
authors.lastname: Yang
authors.forename: Youzhong
authors.initials: Y
authors.lastname: An
authors.forename: Hongyun
authors.initials: H
authors.lastname: Teng
authors.forename: Rumei
authors.initials: R
authors.lastname: Zhang
authors.forename: Yumei
authors.initials: Y
authors.lastname: Wang
authors.forename: Hailing
authors.initials: H
authors.lastname: Gao
authors.forename: Ning
authors.initials: N
authors.lastname: Hua
authors.forename: Yan
authors.initials: Y
authors.lastname: Song
mesh_terms: D002405:Catheterization, Central Venous / Q000295:instrumentation*; D062905:Central Venous Catheters; D002496:Central Venous Pressure / Q000502:physiology*; D002681:China; D004867:Equipment Design; D006801:Humans; D011446:Prospective Studies; D013997:Time Factors; D014160:Transducers, Pressure