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October 17-21, 2009 New Orleans, LA Home Abstract Archive Search Abstracts 2009 Session Grid 2009 Meeting Website Policy Statements ASA Website Feedback 
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A1470
October 21, 2009 9:00 AM - 11:00 AM Room Area F |
| Evaluation in Animals of a New Partial Rebreathing Cardiac Output Monitor |
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* Joseph A. Orr, Ph.D., Lara M. Brewer, M.S., Matthias Görges, M.S. Anesthesiology, University of Utah, Salt Lake City, Utah |
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Introduction:
The partial CO
2
rebreathing method uses a differential form of the Fick equation to calculate cardiac output noninvasively. This method uses a CO
2
and airflow sensor placed in the breathing circuit to measure end-tidal CO
2
(PetCO
2
) and CO
2
excretion (VCO
2
). The ratio of the change in these two signals in response to imposition of a rebreathing volume is used as the input to the differential Fick equation. This method assumes that the CO
2
excretion from the lungs as measured at airway is equal to the CO
2
excretion from the blood in the alveoli. This assumption is only true at steady state. The newer version of the partial rebreathing algorithm compensates for the non steady-state transfer of CO
2
between the blood and the FRC so that more accurate measurements are possible. This algorithm has been implemented in a new monitor (NM3, Philips, Wallingford, CT). The new monitor also incorporates improvements to the measurement of airway flow and pressure, making the measurements more reliable.
Methods: We evaluated the performance of a new monitor in five 30-40 kg pigs. Each animal was intubated and anesthetized using 1 MAC of isoflurane. The partial rebreathing sensor (flow, CO 2 and rebreathing volume) was placed in the breathing circuit between the endotracheal tube and the wye adapter. Rebreathing cardiac output measurements were taken automatically once every three minutes. The CO values reported by the NM3 were automatically saved to a laptop for later analysis. A pulmonary artery catheter was placed (Edwards Lifesciences, Irvine, CA) and reference cardiac output measurements were taken as the average of three to five bolus thermodilution measurements (10 ml iced 5% dextrose solution) which had been randomized with respect to respiration. Comparison between the two cardiac output measurements was made at baseline conditions, during infusions of either dobutamine or norepinephrine, and immediately following discontinuation of the drug infusions. Periodic arterial blood gas measurements were taken and PaCO 2 and hemoglobin values were manually entered into the NM3 monitor so that and estimate of shunt could be calculated and used to convert the directly measured pulmonary capillary blood flow to the reported cardiac output values. Noninvasive cardiac output measurements were compared against corresponding average bolus thermodilution measurements. Results: The average noninvasive measurement was 6.1 L/min and the average thermodilution measurement was 5.4 L/min (range of 1.9 to 10.6 L/min). The bias was 0.72 L/min. The standard deviation of the difference was 0.74 L/min. Figure 1 shows a scatter plot comparing the two methods R 2 = 0.95).[figure1] Discussion: The partial CO 2 rebreathing method as implemented in the new NM3 monitor measures cardiac output accurately as compared to bolus thermodilution measurements. The updated algorithm removes the need for steady state conditions during both rebreathing and non-rebreathing states and decreases the likelihood of error caused by venous blood recirculation during rebreathing. From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists. |
Figure 1
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