Non-Invasive Central Venous Pressure Measurement by Compression Ultrasound—A Step Into Real Life

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In a Swiss intensive care unit, 50 patients' central venous pressures (CVP) were compared using non-invasive and invasive techniques. The non-invasive technique consisted of compression ultrasound (CU) of a patient's forearm vein. The forearm was chosen for the non-invasive measurement as studies have found that when a patient is in a supine position, pressures are nearly the same in the cephalic, basilic, and brachial veins compared to the superior vena cava. The researchers investigated: 1) how feasible and accurate CVP measurements by vascular ultrasound were done by physicians with only a short training course; 2) simple ultrasound vs. a high-end duplex ultrasound system for measuring CVP; and 3) CU's ability to detect respiratory changes in CVP. Four different investigators took part in this study. The first investigator was a vascular expert with a high-end ultrasound system. The second investigator was a medical student with a high-end ultrasound system. The third investigator was a vascular expert with a portable ultrasound system, and the final investigator was an intensive care specialist with a portable ultrasound. The study was subdivided into two groups. The first one was the TeachPort study. This looked at the four investigators measuring CVP after the short training course. Four analyzers first went through three 1-h training sessions in which their technique was compared to experienced vascular ultrasonographers. Their technique was then adjusted until they obtained adequate results. Three of the four investigators then moved on to the surgical intensive care unit, where they were “blinded” for CVP, clinical diagnosis, therapy, and volume status. The fourth investigator was “blinded” only to current CVP values. The non-invasive measurement was done on the contralateral side of the subclavian catheter measuring the invasive CVP. A distal, superficial forearm vessel was examined for the CU part of the study. The second part of the study examined the influence of respiratory cycle on CVP measurement. The researchers used SPSS (SPSS Inc., Chicago, IL) to analyze the results. The study found that the ability to perform the ultrasound was comparable between the four investigators (88% and 92%). The average length of time to obtain the result was 4 min. There was a significant, linear correlation between non-invasive CVP measurements and invasive CVP measurements (r = 0.58–0.68; p < 0.001). There was no difference found between high-end ultrasounds and portable ultrasounds or between experts and trainees doing the measurements. Finally, CU was able to show differences in CVP during respiration.