title: Invasive arterial BP monitoring in trauma and critical care: effect of variable transducer level, catheter access, and patient position.
abstract: OBJECTIVE
  (1) To determine the validity of current recommendations for direct arterial BP measurement that suggest that the transducer (zeroed to atmosphere) be placed level with the catheter access regardless of subject positioning: and (2) to investigate the effect of transducer level, catheter access site, and subject positioning on direct arterial BP measurement.
  
  
  METHODS
  Prospective, controlled laboratory study.
  
  
  METHODS
  Large animal laboratory.
  
  
  METHODS
  Five Yorkshire pigs.
  
  
  METHODS
  Anesthetized animals had 16F catheters placed at three access sites: aortic root, femoral artery, and distal hind limb. Animals were placed in supine, reverse Trendelenburg 35 degrees, and Trendelenburg 25 degrees positions with a transducer placed level to each access site while in every position.
  
  
  RESULTS
  For each transducer level, five systolic and diastolic pressures were measured and used to calculate five corresponding mean arterial pressures (MAPs) at each access site. When transducers were at the aortic root, MAP corresponding to aortic root pressure was obtained in all positions regardless of catheter access site. When transducers were moved to the level of catheter access, as current recommendations suggest, significant errors in aortic MAP occurred in the reverse Trendelenburg position. The same trend for error was noted in the Trendelenburg position but did not reach statistical significance.
  
  
  CONCLUSIONS
  (1) Current recommendations that suggest placing the transducer at the level of catheter access regardless of patient position are invalid. Significant errors occur when subjects are in nonsupine positions. (2) Valid determination of direct arterial BP is dependent only on transducer placement at the level of the aortic root, and independent of catheter access site and patient position.
authors.affiliation: Cardiopulmonary and Critical Care Laboratory, SUNY Upstate Medical University, University Hospital, Syracuse, NY, USA.
authors.forename: U G
authors.initials: UG
authors.lastname: McCann
authors.forename: H J
authors.initials: HJ
authors.lastname: Schiller
authors.forename: D E
authors.initials: DE
authors.lastname: Carney
authors.forename: J
authors.initials: J
authors.lastname: Kilpatrick
authors.forename: L A
authors.initials: LA
authors.lastname: Gatto
authors.forename: A M
authors.initials: AM
authors.lastname: Paskanik
authors.forename: G F
authors.initials: GF
authors.lastname: Nieman
mesh_terms: D000818:Animals; D001158:Arteries; D015924:Blood Pressure Monitors; D002408:Catheters, Indwelling; D003422:Critical Care; D003971:Diastole / Q000502:physiology; D018475:Head-Down Tilt / Q000502:physiology; D006801:Humans; D011446:Prospective Studies; D016683:Supine Position / Q000502:physiology; D013552:Swine; D013599:Systole / Q000502:physiology; D014160:Transducers, Pressure; D014947:Wounds and Injuries / Q000503:physiopathology*