To The Editor:
The very worthwhile, comprehensive, and long overdue paper "Accuracy
in the Measurement of Compartment Pressures: A Comparison of Three Commonly
Used Devices"
(2005;87:2415-22), by Boody and
Wongworawat, addresses important aspects about the accuracy of compartment
pressure measurements. While there are some interesting explanations about the
importance of a good tissue model and the effect of different needles and
catheters, the authors leave unanswered a number of important methodologic
questions.
Comprehensive details and references are given about where to find further
information about the Stryker system and the Whitesides method, but only the
phrase "arterial line manometer" is used to describe the third
device. What does this term mean? Is it a pressure transducer? If so, we need
more details about its manufacturer and its characteristics. How is it
connected to the needles?
This is important information to know because all of the associated
external plumbing with these systems can have a considerable effect on the
pressures recorded (possibly greater than the differences between the three
methods that were compared).
It is clearly stated that the needles used were 18 gauge, but the diameter
of the slit catheter is not stated. The diameter may have a substantial effect
on the pressure measured.
The authors are obviously aware of the effect that temperature changes can
have on the pressure recorded, but it is not clear how these were taken into
account. They state that normal saline solution was heated to 37°C to
mimic physiologic conditions. Was the whole system then maintained at 37°C
throughout the measurements, or was the temperature of the saline solution
measured each time that a pressure measurement was recorded? Did the entire
experimental setup gradually cool to room temperature as the pressure was
increased? The authors were measuring small differences between the different
devices, but the effects of changes in temperature could far outweigh these
measured differences.
Immediate atmospheric pressure changes could not have affected the results.
Since all of the pressures were measured with respect to atmospheric pressure,
they are not absolute values. If there was a change in atmospheric pressure
then it would affect both the measurement device and the source in exactly the
same way. I look forward to a clarification of these issues from the
authors.