Understanding Anti-Diuretic Hormone Dynamics in Off pump Coronary Artery Bypass Grafting (OPCABG) Patients: A Case...

The conundrum of Polyuria witnessed post-cardiac surgery has been attributed to altered antidiuretic hormone (ADH) release secondary to both osmotic and non-osmotic stimulus. This transient DI-like state is more often seen in on-bypass cardiac surgeries but a few off-bypass occurrences have also been reported. A lot of conflicting evidence has accumulated trying to explain this altered water balance but a broader conceptual framework is lacking, which we have attempted to provide, with an objective of designing a future prospective study.

This prospective observational case-series included 12 cases, who underwent off pump coronary artery bypass grafting (OPCABG) at a single tertiary care hospital. All were operated and managed by the same anesthetist-cardiac surgeon team following a structured protocol, hence negating various confounders. Serum and urine osmolality samples were collected post-Intubation (Baseline) and within 1 hour of ICU-transfer and all relevant data associated with these cases was recorded for analysis.

The data was systematically analyzed in terms of descriptives, paired T-test and correlation statistics. The pre-post serum osmolality was found to increase (P value 0.389, Cohen's d -0.26) whereas urine osmolality decreased significantly (P value 0.013, Cohen's d 0.85). This mean fall in urine osmolality was much higher compared to the rise seen in serum osmolality, both being negatively correlated (r -0.59, P value 0.04).

This case series investigating the changes in osmolality alongside pre-perfusion reduced urine output and post-perfusion a state of polyuria, is our primer for a future assay-based objective study. We have created a framework of concepts that provide clarity to the dynamics of ADH-release in OPCABG patients. Furthermore, we are presenting a different hypothesis to explain increase in ADH-release that is evidence-based and open to critical comments.