Washout of Anatomical Dead Space. Design of a Method and Experimental Study Using an External Dead Space

Effect of Washout of Anatomical Dead Space on Ventilation, pH and Blood Gas Composition in Anesthetized Dogs

“…Dead space washout substitutes fresh air for dead air and thus removes exhaled C 0 2 from the anatomical dead space, as ascertained in previous experiments [2]. Lowering of minute ventilation in this study was connected to a decrease in breathing rate.…”

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Elimination of dead air from the anatomical dead space by insufflation during expiration (washout) has recently been studied in emphysematous patients with COa retention [1], Experimental work has also been done on the influence of washout of dead air from an added dead space in normal subjects [2]. The method of washout of dead air as practised in these studies served for assessing the effect of such measure on various physiological parameters in the normal dog under anesthesia.

Methods

7 mongrel dogs weighing between 7 and 16 kg (mean 11 kg) were anesthetized in 12 separate experiments using 30 mg/kg sod.

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“…Another catheter of the same caliber extended only 5 to 7 cm down the proximal lumen of the tube and served for transmitting to the sensing device air flow as produced by the animal's breath ing. Flow rates were sensed by a thermistor flow meter which was made to phase insufflation of air into the dead space strictly during exhalation as described elsewhere [2]. Minute ventilation was measured on a Wright respirometer, calibrated on a spirometer (Godart, Pulmonet) at flow rates in the range of 400 ml/sec and found to read 3.1 °/o low.…”

Washout of Anatomical Dead Space for Alveolar Hypoventilation

“…Air or oxygen was then delivered via this catheter to flush dead space at rates of approxi mately 100-200 ml/s either during expiration only or during the entire respiratory cycle. The equipment used for flushing the dead space solely during exhalation has been described elsewhere [8], For the dead space washout throughout the respiratory cycle a constant flow of humidified air or oxygen was used. When washout was done in conjunction with IPPB, the described catheter was passed into the trachea via the tracheal cannula.…”

“…This promotes elimination from the upper airways of C 0 2, the rebreathing of which contributes to inefficiency of ventilation in these patients. The rationale and technique as well as the results of dead space washout using an added dead space model have re cently been described [8]. It was demonstrated that flushing an added dead space of approximately 100 ml with air during exhalation at flow rates of 200 ml/sec leads to a nearly complete washout of dead air.…”