Endocrine Abstracts

OBJECTIVE Induction of anaesthesia and surgical stress, factors known to trigger catecholamine release from phaeochromocytomas, are believed to result in elevated levels in the postoperative period even in the absence of such tumours, and biochemical screening is usually deferred for two or more weeks following surgery. The aim of this study was to determine patterns of peri-operative urinary catecholamine excretion in otherwise healthy subjects undergoing a single type of major surgical procedure.

DESIGN AND SUBJECTS Five patients undergoing elective coronary artery bypass graft surgery were studied prospectively. None of them was administered exogenous catecholamines and all had a routine post-operative recovery. Catecholamine-to-creatinine ratios measured in single-voided urine samples are convenient, eliminate sampling errors of timed collections and have reported sensitivity of 97-100% and specificity of 98-100%; we obtained random (mid-day) specimens acidified to pH < 4.0 on one pre-operative and four post-operative days. 33 healthy volunteers served as controls for determination of reference ranges (mean plus/minus 2SD).

MEASUREMENTS Epinephrine (E), norepinephrine (NE) dopamine (DA), metanephrine (MN) and normetanephrine (NMN) were measured using HPLC with electrochemical detection and vanillylmandelic acid (VMA) by gas chromatography of trimethyl silyl derivatives (Pisano reaction). Creatinine was measured by a kinetic colorimetric modified Jaffe method.

RESULTS NMN was elevated up to 2x upper reference limit (0.0-190.9 micromol/mol) on post-op days 1-3 returning towards normality by day 4. Other catecholamines remained within the reference range (E=0.0-11.2 nanomol/mol; NE=0.0-96.6 nanomol/mol; DA=0.0-434.7 nanomol/mol; MN=0.0-381.1 micromol/mol; VMA=0.0-4.9 millimol/mol).

CONCLUSIONS These preliminary data show no significant deviation from normality in urinary excretion of catecholamines, barring normetanephrine, in the early post-operative period in people undergoing elective surgery employing modern anaesthetic and analgesic techniques. It may therefore be possible to investigate patients for possible phaeochromocytoma in the immediate post-operative phase by simple screening. This requires corroboration by further study.When hypertension is first observed or is difficult to control in a previously well-controlled hypertensive during the intra-/post- operative period, the anaesthetist or physician is often prompted to seek exclusion of phaeochromocytoma, among other causes of secondary hypertension. At the present time there is little known about how soon after surgery such patients can undergo biochemical screening tests; but it is generally believed that biochemical tests should be deferred until at least 2 weeks have elapsed since the date of surgery as levels as likely to be elevated due to the stress of surgery. We report that levels are not significantly different from normality in patients undergoing surgery employing modern anaesthetic techniques. This finding, if corroborated, would enable screening for possible catecholamine-secreting tumours in the immediate post-op period.