Page 15 - Delaware Medical Journal - September 2016

SCIENTIFIC ARTICLE
measured and estimated values,9-11

subsequent hemodynamic and valve area calculations.12,13
Portable devices are available that measure breath-by-breath oxygen and carbon dioxide levels using a facemask and provide direct continuous VO2 measurements. These devices are well validated to produce very reliable VO2 assessment similar to these assessed by Douglas bag while being less cumbersome to patients and staff.14 Importantly,
VO2 can vary during the course of a catheterization. We hypothesized that measuring CO at a time when the VO2 was not only stable but precisely known (i.e., not an average over time) might give the most reliable calculations of aortic valvular dimensions. We investigated
the correlation of the CO based on direct continuous VO2 measurement by this device to the more commonly used techniques of estimated VO2 and thermodilution CO.15,16
METHODS AND MATERIALS
This study was approved by the institutional review board (IRB) of Christiana Care Health System. Seventeen patients scheduled for right and left heart catheterization were included in the study. Catheterization was performed in the usual fashion including measurement of right and left sided pressures. Intravenous midazolam and fentanyl were given to patients as needed. Patients were not placed on supplemental oxygen.
In order to measure VO2 directly and

facemask with an airtight seal over the nose and mouth, which was connected to Ultima CardiO2 breathing analyzer (Medgraphics, St. Paul, Minnesota). The
FIGURE 1
Correlation of AVA based on direct continuous VO2, assumed VO2 and TD CO. A - Correlation of direct continuously measured VO2 based AVA with assumed VO2 based AVA. B - Correlation of direct continuously measured VO2 based AVA with TD based AVA.
device allows comparison of inspired
and expired air to determine VO2. To minimize the time of mask use, it was placed only after all catheters were in place for pressure measurements. After a baseline of at least three minutes to assure patient comfort and a steady-state VO2, immediate measurements of femoral artery and pulmonary artery saturations were obtained in triplicate, immediately followed by three thermodilution CO measurements. We could complete
these measurements in approximately 90-120 seconds. We waited until the continuous VO2 was relatively stable before performing the CO determinations in triplicate. If the VO2 became variable
subsequently, we waited for a return of a relatively stable VO2 before performing the repeat CO determinations.
Oxygen consumption was measured continuously for these two minutes with the mean VO2 over that time period used for analysis. The aortic valve
area was determined by computerized integration (Xper, Phillips, Miami, Fla). The Gorlin formula was used:
Ao Valve Area in cm2 = CO (l/min)/ [HR(bpm) x SEP (mSec)]
Where SEP = Systolic ejection period, K (Empiric Constant) = 44.3
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