Lactate concentration gradient from right atrium to pulmonary artery

Area of Science:

• Cardiology
• Intensive Care Medicine
• Physiology

Background:

• Simultaneous blood lactate concentration ([Lac]) measurements in the right atrium (RA) and pulmonary artery (PA) were compared.
• Investigated if mixing of RA blood with lower [Lac] coronary venous blood causes detectable RA to PA [Lac] decreases.

Purpose of the Study:

• To determine if blood lactate concentration decreases from the right atrium to the pulmonary artery in critically ill patients.
• To assess the physiological basis of observed lactate gradients.

Main Methods:

• Prospective, observational study in a medical-surgical intensive care unit.
• 45 critically ill adults requiring pulmonary artery catheters (PACs) were enrolled.
• Paired blood samples from PAC ports measured [Lac], O2 saturation (SO2); Delta[Lac], DeltaSO2, and DeltaVO2 were calculated.

Main Results:

• Right atrial O2 saturation (SraO2) was higher than pulmonary artery O2 saturation (SpaO2) (74.2% vs. 69.0%, p < 0.001).
• [Lac] in the RA was higher than in the PA (3.9 vs. 3.7 mmol x L-1, p < 0.001).
• Delta[Lac] showed a significant correlation with DeltaVO2 (r² = 0.34, p < 0.001).

Conclusions:

• Decreases in [Lac] from RA to PA were observed in critically ill individuals.
• Parallel decreases in SO2 and [Lac] support the hypothesis of mixing with lower-SO2 and [Lac] coronary venous blood.
• Further research is needed to define the physiological and clinical significance of these lactate gradients (Delta[Lac]).