Case 30: Blood Pressure Difference Between a Noninvasive and an Invasive Blood Pressure Measurement
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A 54-year-old male (ASA3) is scheduled to undergo an automated implantable cardioverter-defibrillator (AICD) change under general anesthesia. His past history is remarkable for coronary artery disease, hypertension, and insulin-dependent diabetes mellitus. He is 230 lbs. and 5′5″. You meet him in the catheterization laboratory. As usual the place is in partial darkness and you are asked not to put on the light. So in the darkness you place noninvasive monitors. A right radial arterial line is secured prior to induction of anesthesia (Transpac IV monitoring kit. 84″ disposable transducers with a 3 ml squeeze flush. Abbott Critical Care System, Abbott Laboratory, North Chicago, IL.60064). A seemingly normal-appearing arterial waveform is present with a blood pressure of 149/116 mmHg and a mean of 129 mmHg. A simultaneous noninvasive blood pressure of 105/70 with a mean of 82 mmHg is obtained in the left arm. You change the noninvasive cuff to the right arm and get the same reading as in the left arm. The transducer is located in the midaxillary line and has been zeroed by you just before the arterial line was placed. Since you have just zeroed the transducer, you dismiss that as a cause for this difference in blood pressure reading. Furthermore, you did not see any offset when the stopcock was opened to atmosphere.