PERIOPERATIVE ASSESSMENT OF BLOOD LACTATE LEVELS AND LACTATE CLEARANCE IN PATIENTS UNDERGOING CARDIAC SURGERIES WITH CARDIOPULMONARY BYPASS

Abstract

Background: Cardiopulmonary bypass (CPB) is instituted, during various cardiac operations, to allow for
optimal systemic perfusion. Tissue hypoperfusion is associated with lactic acidosis secondary to anaerobic
metabolism. Measurement of blood lactate levels can hence be used as a marker to assess the adequacy of
tissue perfusion. In this study we tried to find out the association between various preoperative NYHA
classes and link their association with perioperative lactate and lactate clearance values.
Methods: 100 patients undergoing elective cardiac surgery under cardiopulmonary bypass were included in
this prospective observational study. Based on history, the patients were allocated to their respective class
as per the New York Heart Association (NYHA) functional classification. Patients aged between 18-80
years posted for elective cardiac surgery under cardiopulmonary bypass were included. For measuring
lactate levels, baseline arterial blood was collected from the intra-arterial catheter immediately after
induction of anaesthesia. Subsequent samples were collected at intervals of 15 minutes and 45 minutes after
institution of CPB, rewarming (at 35°C), immediately after termination of CPB, 24 hours and 48 hours
post-surgery.
Results: All four NYHA groups were comparable in terms of baseline lactate levels (P value 0.096). Higher
mean levels of lactate were seen in NYHA group 4 compared to other three groups during rewarming,
termination and post operatively (24 and 48 hours). After 45 minutes of CPB and during rewarming,
NYHA 4 group varied significantly from NYHA 1, 2 and 3. In terms of mean lactate clearance, Tukey
HSD (Assuming equal variances) post hoc test showed that both NYHA 3 and NYHA 4 were significantly
different from each other as well as NYHA group 2. At 24 hours postoperatively, NYHA 2 varied
significantly from NYHA 1, 3 and 4. After 48 hours, a significant difference in lactate clearance was seen
between NYHA 1 and 2. The duration of inotropic support as well as mechanical ventilation was more in
NYHA 3 and 4.
Conclusion: There is a definite association between higher mean lactate levels and lactate clearance with a
higher NYHA class during the perioperative period. Increased mean lactate levels and lactate clearance is
also associated with increased duration of mechanical ventilation and inotropic support. Higher
perioperative lactate levels also prolong the ICU and hospital stay in higher NYHA classes.