Canadian Journal of Anesthesia, Vol 17, 119-128, Copyright © 1970 by Canadian Anesthesiologists' Society

The Reliability and Usefulness of the Suwa Nomogram in Patients in Respiratory Failure

¹ Department of Anaesthesia, University of Toronto

The Suwa nomogram was devised to predict the amount of mechanical dead space which must be added to a ventilated patient's breathing circuit to achieve a normal arterial carbon dioxide tension of 40 mm Hg from a hypocapnoeiac level. The reliability of the mathematical analysis from which the nomogram was derived, together with the Suwa nomogram itself, were assessed in nine patients in respiratory failure. The results from 26 samples verified the mathematical analysis with a difference of ± 1 mm Hg from the predicted value of 40 mm Hg for arterial carbon dioxide tension when mechanical dead space was added. The mechanical dead space predicted by the Suwa nomogram to achieve an arterial carbon dioxide tension of 40 mm Hg was shown to have a potential error of ± 3.23 mm Hg. It was shown that the mathematical analysis warranted more use than the Suwa nomogram because of superior accuracy.