Objectives: (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.
Prospective, controlled laboratory study.
Large animal laboratory.
Subjects: Five Yorkshire
Interventions: 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°, and Trendelenburg 25° positions with a
transducer placed level to each access site while in every
Measurements and main 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