Influence of temperature on leukocyte kinetics during cardiopulmonary bypass and postoperative organ damage: an experimental study

Objectives

To Study the influence of core temperature during cardiopulmonary bypass (CPB) on leukocyte kinetics and perioperative organ damage.

Methods

Eighteen young pigs (weight 40 kg) were randomly assigned to a temperature (T°) group during CPB: normothermia (group 1, T° = 37°C, n = 6), mild hypothermia (group 2, T° = 28°C, n = 6) and deep hypothermia (group 3, T° = 20°C, n = 6). CPB was conducted with full flow in group 1 (2.7 l/m²/min) and with reduced flow in group 2 and 3 (60% and 50% of full flow, respectively), for a duration of 120 min. Aorta was cross-clamped for 60 min and cardioplegia achieved with a single dose of 4°C cold Bretschneider solution. Leukocyte count was determined before, during and after CPB.

At the end of the experimentation (6 h after CPB) tissue probes of heart, lung, liver, kidney and intestine were taken for histological examination.

Results

In all groups, there was a significant fall of total leucocyte count at induction of CPB, without any intergroup difference (leukocytes=7800 ± 1150 cells/ml). Leukocyte count continued to decrease till clamping of the aorta in group 2 (4980 ± 513 cells/ml) and further till myocardial reperfusion in group 3 (3880 ± 625 cells/ml). In contrast, in group 1, leukocyte count increased significantly before myocardial ischemia and further at myocardial reperfusion (10 700 ± 803 and 14 100 ± 1960 cells/ml, respectively) (intergroup difference: P < 0.005 and < 0.001, respectively). Group 1 pigs had the highest transcoronary leukocyte gradient before clamping of the aorta (850 ± 454 cells/ml vs 150 ± 117 cells/ml in group 2 and 150 ± 159 cells/ml in group 3). At the end of CPB, there was no difference in leukocyte count between groups.

Results of the histological examination show that the most important tissue damage in terms of interstitial oedema and leukostasis in heart, lung, liver and intestine but not kidney was seen in group 1 followed by group 3 while the least important damage was present in group 2.

Conclusions

In our experimental series, CPB conducted under normothermia was associated with higher circulating leukocyte levels and higher intramyocardial leukostasis when compared with CPB conducted under mild or deep hypothermia. Mild hypothermia (28°C) but not normothermia or deep hypothermia (20°C) is associated with lower postoperative organ damage.