Question 6.2
Look at the photo below (Figure 2), where is the zero point?
Figure 2:
For haemodynamic measurements? A, B, or C?
For intracranial pressure measurement? A, B, or C?
6.2 b) Assuming the item is correctly set-up and integrated within the appropriate system - how will the displayed value change if the device is raised by 13cm relative to the zero point?
College Answer
For haemodynamic measurements? A, B, or C?
Answer B
For intracranial pressure measurement? A, B, or C?
Answer C
6.2 b) Assuming the item is correctly set-up and integrated within the appropriate system - how will the displayed value change if the device is raised by 13cm relative to the zero point?
Fall in displayed pressure by 10 mmHg.
Discussion
B vaguely corresponds to the right atrium, and C vaguely corresponds to the circle of Willis.
Generally speaking, the circle of Willis is the appropriate place where one should zero one's transducer for the measurement of cerebral perfusion pressure. However, the Brain Trauma Foundation's guidelines regarding CPP use are all based on studies where the transducer was zeroed at the atrum. The controversial topic of where to properly "zero" one's CPP transducer is discussed in the chapter on the utility of the cerebral perfusion pressure as a therapeutic target.
The second part of the question calls upon the candidate to recall the conversion of cmH2O into mmHg. The conversion is, 1mmHg = 1.36cmH2O.
Thus, 13cm H2O = 10mmHg.