Effects of the heart-lung machine on melatonin metabolism and mood disturbances

Cardiothoracic surgery using the heart-lung machine (HLM) provokes a pronounced endocrine-metabolic response leading to circadian rhythm disturbances that affect postoperative morbidity. Focus has been laid on changes in melatonin metabolism. The effects of an extra-corporal artificial circulation have not been adequately addressed.

Seventeen patients scheduled for open heart surgery using the HLM were compared with 15 patients undergoing major surgery without cardiopulmonary bypass (non-HLM). Late afternoon and night urinary 6-sulfatoxymelatonin were measured at baseline, immediately after the operation and on return to the normal ward. Mood disturbances were assessed at baseline and final sampling times using a standardized questionnaire (arbitrary units).

Vital signs were comparable between groups. The difference (delta) between day and night melatonin levels was similar at baseline (HLM group 1.1 ng/ml, non-HLM group 1.4 ng/ml, p=0.25). Immediately following surgery melatonin day-night deltas were unchanged to baseline (HLM 1.0 ng/ml, p=0.67; non-HLM 0.8 ng/ml, p=0.46) but at final sampling normal circadian melatonin profile was abolished (-0.3 ng/ml, p=0.001 and 0.0 ng/ml, p=0.07). However, this effect was not different between the two studied groups (p=0.17). No mood disorders were detectable at baseline (HLM 8.0 vs non-HLM 7.0, p=0.97) and no changes occurred after surgery (7.0 vs 6.5, p=0.33). Overall, patients with a worsening psychological score had pronounced postoperative washout of afternoon-night melatonin delta (p=0.04).

We found no relevant influence of the HLM on perioperative circadian melatonin profiles. Additionally, no alterations in mood assessment before and after surgery were observed. However, worsening of psychological score was associated with a pronounced disruption of the normal circadian melatonin profile.