Advanced Hemodynamics - Orlando Health

Advanced Hemodynamic Monitoring
7. Before starting to monitor pressure, the stopcock
nearest the transducer must be placed at the level of
what is being measured. In most cases (other than
intracranial pressure monitoring) this is at the level
of the heart. Correct leveling is essential to achieve
accurate pressures and should be checked during
routine monitoring and troubleshooting of the
monitoring system. To level the transducer, place the
transducer at the level of the heart. This location is
called the phlebostatic axis, and is located at the 4 th
intercostal space, halfway between the anterior and
posterior chest (mid-chest). The mid-axillary line is
not accurate for patients with barrel chests or severe
chest deformities. To assure that the stopcock is
precisely leveled with this landmark, mark the position
of the phlebostatic axis on the patient’s chest with
permanent marker. The transducer can be taped
directly to this location, or it may be mounted on a
pole and leveled to the phlebostatic axis with a
carpenter’s or laser level. Re-level the transducer
phlebostatic axis
anytime the patient changes position or if the reading is in doubt or outside of prescribed
parameters.
x
From Techniques in Bedside Hemodynamic
Monitoring by E.K. Daily and J.S. Schroeder,
C.V. Mosby, 1981. Used with permission.
Technical Aspects of Leveling and Zeroing
A number of external factors may affect how accurately the hemodynamic monitoring system
reflects the pressures within the patient’s vascular system. There are two important pressures that
can affect hemodynamic readings.
Hydrostatic pressure is the force that is exerted by the fluid within the hemodynamic monitoring
system against the transducer. This pressure is the result of a combination of factors that include
gravity and the height and weight of the fluid column (in other words, the position or height of the
IV bag and length of tubing, which contains the fluid column), fluid density and positioning of the
transducer. Leveling the transducer to the phlebostatic axis eliminates inaccuracies in pressure
readings due to hydrostatic pressure. As long as the stopcock nearest the transducer is level with the
phlebostatic axis, the patient can be positioned as high as 60 degrees and still have generally
accurate pressure measurements. It is essential that pressures be measured at a consistent head-ofbed
elevation for trends to be valid.
Atmospheric pressure is the force that is exerted at the earth’s surface by the weight of the air that
surrounds the earth. At sea level this pressure is 760 mm Hg, but it varies depending on altitude.
Zeroing the monitor eliminates the effect of atmospheric pressure on the pressure readings.
Remember, zeroing can be accomplished even before the patient is attached to the system.
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