Objectives: To evaluate the performance of a new device for noninvasive measurement of nonshunted pulmonary capillary blood flow (PCBF) by partial CO2 rebreathing.
Design and setting: Prospective clinical trial in an intensive care unit of a university hospital.
Patients and participants: Twenty mechanically ventilated patients with acute lung injury.
Interventions: Variations in PEEP of +/-3 cmH2O.
Measurements and results: Initially PCBF was measured invasively as cardiac output minus venous admixture (Q(VA)/Q(t)) flow, and by partial CO2 rebreathing at baseline PEEP (PEEP(b)). The PEEP was then reduced by 3 cmH2O (to PEEP(b-3)) and measurements were repeated after 30 min. PEEP was then increased by 6 cmH2O (to PEEP(b+3)), and measurements were repeated after 10, 20, and 30 min. The overall correlation coefficient between noninvasive and invasive PCBF measurements at PEEP(b) was high ( r=0.97), with close agreement between methods being observed (0.1+/-0.6 l/min, bias and precision, respectively). Accordingly, both the correlation coefficient and agreement between methods for changes in PCBF from PEEP(b-3) to PEEP(b+3) levels were satisfactory ( r=0.71; 0.2+/-0.5 l/min, bias and precision). The new device was able to detect the correct PCBF trend in 17 of 20 patients investigated and in all patients who showed invasive PCBF changes equal to or greater than 0.3 l/min ( n=12). Noninvasive PCBF changes were stable as early as 10 min after variation in PEEP, as compared to 30 min values.
Conclusions: The new device appears to be clinically useful for the monitoring of PCBF in patients suffering from acute lung injury. Our results suggest that titration of PEEP aimed at improving PCBF can be performed with the new device.