INTRODUCTION: Determination of the volume of respiratory dead space can be clinically useful. Measurements made with a Deltatrac metabolic cart were used to determine dead-space-to-tidal-volume ratio (VD/VT) and were compared to VD/VT determination by a standard method using a Douglas bag. MATERIALS & METHOD: Thirty studies were performed on 26 mechanically ventilated patients in the Medical/Surgical Intensive Care Unit. VD/VT was calculated using the Enghoff modification of the Bohr equation. RESULTS: Values obtained using the Douglas bag ranged from 0.37 to 0.74. Simultaneous measurements using the metabolic cart ranged from 0.40 to 0.78. The correlation coefficient was 0.92, the mean difference was 0.004 and the standard deviation of the difference was 0.034. CONCLUSION: These data show that the metabolic cart is as accurate as the Douglas-bag method for determination of VD/VT.
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References
1.
WestJB. Assessing pulmonary gas exchange (editorial). N Engl J Med1987;316(21):1336–1338.
2.
ShikoraSA, BistrianBR, BorlaseBC, BlackburnGL, StoneMD, BenottiPN. Work of breathing: Reliable predictor of weaning and extubation. Crit Care Med1990;18(2):157–162.
3.
SwinamerDL, GraceMG, HamiltonSM, JonesRL, RobertsP, KingEG. Predictive equation for assessing energy expenditure in mechanically ventilated critically ill patients. Crit Care Med1990;18(6):657–661.
4.
NunnJF. Applied respiratory physiology, third edition. Bristol: Butterworths, 1987:158–179.
5.
MakitaK, NunnJF, RoystonB.Evaluation of metabolic measuring instruments for use in critically ill patients. Crit Care Med1990;18(6):638–644.
6.
PhangPT, RichT, RoncoJ.A validation and comparison study of two metabolic monitors. J Parenter Enteral Nutr1990;14(3):259–261.
7.
RuppelGE. Manual of pulmonary function testing, sixth ed. St Louis: Mosby-Year Book Inc; 1994:34–37.
8.
BlandJM, AltmanDG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet1986;1(8476):307–310.
9.
TakalaJ, KeinanenO, VaisanenP, KariA.Measurement of gas exchange in intensive care: Laboratory and clinical validation of a new device. Crit Care Med1989;17(10):1041–1047.
10.
BredbackaS, KawachiS, NorlanderO, KirkB.Gas exchange during ventilator treatment: a validation of a computerized technique and its comparison with the Douglas Bag method. Acta Anaesthesiol Scand1984;28(4):462–468.
11.
SnyderJV. The development of supported ventilation: a critical summary. In: SnyderJV, PinskyMR (editors). Oxygen transport in the critically ill. Chicago: Year Book Publishers; 1987.
