Evaluation of the dead space to tidal volume ratio as a predictor of extubation failure

We measured the "effective" dead space of five commonly used respiratory valves: Hans Rudolph valve, two-way J valve, triple-J valve, and modified Otis-McKerrow valves without and with vane. The dead space was measured using a technique that mimicked the operation of valves during ordinary laboratory procedures. The valves were ventilated with tidal volumes ranging from 0.35-3.00 liters and at different frequencies. With all valves, there was a marked tendency for "effective" dead space to be tidal volume dependent. The measured dead space approached the water-displacement volume of the common chamber of the valve only at tidal volumes in excess of 2.0 liters. The relation between valve dead space and tidal volume was independent of frequency.

Download Full-text

Increased physiological dead space/tidal volume ratio during exercise in burned children

Burns ◽

10.1016/0305-4179(94)00017-4 ◽

1995 ◽

Vol 21 (5) ◽

pp. 337-339 ◽

Cited By ~ 7

Author(s):

R.P. Mlcak ◽

M.H. Desai ◽

E. Robinson ◽

R.L. McCauley ◽

J. Richardson ◽

...

Keyword(s):

Tidal Volume ◽

Dead Space ◽

Volume Ratio ◽

Physiological Dead Space

Download Full-text

Effect of common dead space on VA/Q distribution in the dog

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.6.2488 ◽

1990 ◽

Vol 68 (6) ◽

pp. 2488-2493 ◽

Cited By ~ 21

Author(s):

K. Tsukimoto ◽

J. P. Arcos ◽

W. Schaffartzik ◽

P. D. Wagner ◽

J. B. West

Keyword(s):

Blood Flow ◽

Tidal Volume ◽

Dead Space ◽

Volume Ratio ◽

Inert Gas ◽

Base Line ◽

Heavy Exercise ◽

The Common ◽

Technique Comparison ◽

Condition B

Several previous studies have shown worsening ventilation-perfusion (VA/Q) relationships in humans during heavy exercise at sea level. However, the mechanism of this deterioration remains unclear because of the correlation with ventilatory and circulatory variables. Our hypothesis was that the decrease in the series dead space-to-tidal volume ratio during exercise might be partly responsible because mixing in the common dead space can reduce apparent inequality. We tested this notion in 10 resting anesthetized normocapnic dogs passively hyperventilated by increase tidal volume and a) inspired CO2 or b) external dead space. We predicted less apparent VA/Q inequality in condition b because of mixing in the added dead space. After base-line measurements, conditions a and b were randomly assigned, and after a second set of base-line measurements they were repeated in the reverse order in each dog. VA/Q inequality was measured by the multiple inert gas elimination technique. Comparison of conditions a and b demonstrated that additional external dead space improved (P less than 0.001) the blood flow distributions as hypothesized [log standard deviation of perfusion = 0.49 +/- 0.02 (SE) in condition b and 0.61 +/- 0.03 in condition a with respect to 0.52 +/- 0.03 at base line]. This study suggests that the increased tidal volume during exercise could uncover VA/Q inequality not evident at rest because of the higher ratio of common dead space to tidal volume at rest.

Download Full-text