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October 16-20, 2010 San Diego, CA Home Abstract Archive Search Abstracts 2010 Session Grid 2010 Meeting Website Policy Statements ASA Website Feedback 
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A1291
October 20, 2009 2:00 PM - 4:00 PM Room Area M |
| Effect of Ventilatory Parameters on the Quantification of Anatomical Dead Space |
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Fangping Bao, M.D., Lin Zhang, M.D., Yafen Liang, M.D., Robert M. Kacmarek, Ph.D., R.R.T., Yandong Jiang, Ph.D., M.D. Anesthesia and Critical Care and Respiratory Care, Massacbhsetts General Hospital and Harvard Medical School, Boston, Massachusetts |
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Background:
The anatomical dead space (VDan) is frequently used to calculate alveolar dead space which has been associated with mortality in critical ill patient. However, the interface of fresh gas and CO
2
containing gas is a moving target and as a result, VDan may not be constant as previously thought. Therefore, accurate quantification of the VDan is challenging as many factors may affect VDan. The goal of this study was to determine the effects of commonly used ventilatory parameters on the quantification of VDan in the absence of intrinsic spatial and sequential characteristics of the lungs.
Methods: A mechanical model lung and a plastic tube serving as a trachea with precisely set and variable VDan volumes (46, 106, 173 and 240 ml) were used. There was no alveolar dead space or intra-pulmonary shunt in this model. A flow and infrared CO 2 sensor were placed between the tracheal and the ventilator, and continuously measured flow rate, end tidal CO 2 and CO 2 concentration profile. From this data tidal volume (V T ) and VDan were calculated. The VDan volume was calculated using a modification of the Bohr method VDan= V T e*(1-Mean CO 2 /ETCO 2 ) where V T e, Mean CO 2 and ETCO 2 represent the expired tidal volume per breath, the volume of CO 2 removed per breath divided by V T e, and end tidal CO 2 respectively. The VDan was determined at variable V T (250, 500 and 750 ml), breathing frequencies (10 and 20 breaths/min), end tidal CO 2 levels (ETCO 2 , 20, 40 and 60 mmHg) and end inspiratory pause times (0.2 to 1 second). The effect of constant alveolar V T at variable set VDan was also determined. Results: At a constant alveolar V T , measured VDan and set VDan were linearly correlated, VDan mea=1.03*VDan set + 45.09, r 2 =0.999.[figure1]Increases in V T resulted in increases in the measured VDan (p<0.01).[figure2]Increasing the end inspiratory pause reduced measured Vdan, Vdan mea=-36.92T 2 + 14.12T + 118.52 (T is inspiratory pause from 0.2 to 1.0 second, Vdan was set at 46 ml). Change in ventilation frequency and ETCO 2 in the tested range did not significantly affect measurement of Vdan (p>0.05). Conclusions: Vdan is proportional to alveolar V T and inversely related to the end inspiratory pause time. Breathing frequency and ETCO 2 in a clinically relevant range did not affect measurement of Vdan. From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists. |
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