Derivation of Stroke Volume from Pulmonary Artery Pressures

Introduction Intermittent cardiac output (CO) studies using thermodilution is considered the gold standard. We have developed a stroke volume (SV) calculator from pulmonary pulse pressure (PP) to allow continuous monitoring of SV and CO from PP.

Methods Haemodynamic data on 169 patients following orthotopic heart transplantation were used to compare our calculator-derived SV (and SV index, or SVi) against thermodilution-derived SV on admission into intensive care unit immediately following heart transplantation (T0) and six hours after admission (T6).

Results The calculated SV correlated with thermodilution-derived SV T0 (r=0.920, p<0.001, coefficient of 0.539 and the constant of 2.06). The median calculator SV, adjusted for coefficient and constant was 48.4ml (37.7, 60.7), comparable to the median thermodilution-derived SV 47.9ml (37.5, 61.0), p= 0.737 with acceptable agreement on Bland-Altman plots. The thermodilution derived SVi was 28.1ml (19.7, 38.7) and adjusted calculator derived SVi 28.9ml (19.7, 39.9), p= 0.781. At T6, median thermodilution-derived SVi was 27.7ml (19.5, 35.9) compared to the calculator SVi median of 26.1ml (17.7, 37.7), p= 0.203.

Conclusions Changes in PP can be used to track changes in SV using this calculator. Changes in PP may be used to assess response to treatment in the early post-operative period.