Respiratory dead space and arterial to end-tidal CO₂ tension difference in anesthetized man

TLDR

The study observed 12 anesthetized patients during spontaneous and artificial respiration to assess respiratory dead space. Anatomical dead space matched predictions above 350 ml and fell proportionally below that threshold, while physiological dead space remained about 0.3 × tidal volume and exceeded anatomical values; alveolar dead space ranged 15–231 ml, scaling with tidal volume, and the mean arterial‑to‑end‑tidal CO₂ difference was 4.6 mm Hg, unaffected by tidal volume, arterial CO₂, or respiration mode. Submitted September 25, 1959.

Abstract

Observations were made during both spontaneous and artificial respiration on 12 fit patients anesthetized for routine surgical procedures. Above a tidal volume of 350 ml (BTPS), the anatomical dead space was close to the predicted normal value for the subject. Below 350 ml, it was reduced in proportion to the tidal volume. The physiological dead space (below the carina) approximated to 0.3 times the tidal volume for tidal volumes between 163 and 652 ml (BTPS). Throughout the range the physiological dead space was considerably in excess of the anatomical dead space measured simultaneously. The difference (alveolar dead space) varied from 15 to 231 ml, being roughly proportional to the tidal volume. The mean arterial to end-tidal CO 2 tension difference was 4.6 (S.D. ±2.5) mm Hg and not related to tidal volume or arterial CO 2 tension. None of the findings appeared to depend on whether the respiration was spontaneous or artificial. Submitted on September 25, 1959