P. Christensen et al., Thermodilution versus inert gas rebreathing for estimation of effective pulmonary blood flow, CRIT CARE M, 28(1), 2000, pp. 51-56
Objective: To compare measurements of the effective pulmonary blood flow (Q
(ep), i,e,, nonshunted fraction of cardiac output, Q(t)) by the inert gas r
ebreathing (RB) method and the thermodilution (TD) technique in critically
ill patients.
Design: Prospective, comparative study of a noninvasive method and an estab
lished invasive technique.
Setting: An 11-bed general intensive care unit in a university hospital. Pa
tients: A total of 14 critically ill patients, all mechanically ventilated
and monitored with systemic and pulmonary artery catheters,
Measurements and Main Results; Q(ep) was determined in duplicate by RE usin
g a mass spectrometer for gas analysis. For each determination, Q(t) was me
asured in triplicate by the cold water bolus TD technique and averaged. Sim
ultaneously mixed venous and arterial blood samples were analyzed to calcul
ate the intrapulmonary shunt fraction and thereby convert estimates of Q(t)
to Q(ep). Mean difference between paired estimates (RB - TD) was 0.01 L/mi
n, So for differences was 1,19 L/min, and 95% confidence interval for the b
ias was -0.45 to 0.47 L/min, Coefficients of variation for repeated Q(ep) e
stimates were 8% (RB) and 12% (TD), respectively, Coefficients of variation
for RE estimates of functional residual capacity and lung tissue volume we
re 6% and 17%, respectively.
Conclusions: The RE method is a promising method for simultaneous noninvasi
ve estimation of Q(ep) and functional residual capacity in mechanically ven
tilated patients. However, further investigations are needed to evaluate po
tential problems of the method before it can be recommended for clinical pu
rposes.