National Board Ex- 6 Book .pmd - National Board Of Examination

Excretion of catecholamines and their metabolites in a 24 hour sampleof urine (moreàphaeochromocytoma)Epinephrine (Ep)5 mgNorepinephrine (Nep)30 mgConjugated (Ep + Nep)100 mgTotal metanephrines65 mgTotal normetanephrines100 mgVannilyl mandelic acid (VMA)1 – 1.2 mgCatecholamine/ metaboliteEpinephrine 40 - 100Norepinephrine 200 - 400Dopamine < 1400Metanephrine < 2000Normetanephrine < 5000Ultrasound may demonstratelarge adrenal / intrabdominaltumours. Intravenous pyelographymay also be done.Other tests, of academic importancebut negligible clinical significanceinclude selective adrenalor renal venous sampling;adrenal provocation tests usingglucagons and histamine, andsuppression tests using clonidine;angiography; DSA etc.Pre - operative managementa - adrenergic blockers- Phenoxybenzamine - Noncompetitive á-blocker, withlong half life.Dose is 10 mgbd orally, increasing by 10-20mg/day, until postural hypotensionand resolution ofadrenergic symptoms occurs.Plasma levels (pg/ml)- Prazosin- 6-10 mg of thisalpha-1 selective blocker.- Doxazosin.b- adrenergic blockers- Propranolol is added at dosesof 40-80 mg/day, can beincreased to120-480 mg/dayif required. b-blockers shouldnever be started tilladequate á-blockade has beenobtained, otherwise they willprecipitate hypertensive crisis.- Esmolol is used mostly tocontrol heart rate duringacute crises in the operatingroom.Labetalol - Combined á and b-blocker, with greater b than áeffect. Care should be taken whileusing this drug that an adequateá-blockade has been obtained.This is used more in acute crisesand in the operating room.Others - Magnesium, CalciumChannel Blockers, Clonidine,Alpha Methyl Para Tyrosine –These are not very commonlyused.Pre-operative control of bloodpressure is an essentialcomponent of preparing thesepatients. Preoperative alphaadrenergicblockade is essentialusing phenoxybenzamine 10 mgtwice a day increasing daily untilblood pressure is controlled, i.e.till postural hypotension occursor till adrenergic symptomsresolve 3,4,5 . If tachycardiadevelops, propranolol, a betablocker,is added (40-80 mg/day) 4 . Patients should be givenplenty of fluids as a relativehypovolaemia is exposed. Aminimal of 7 to 10 days treatmentis required for most patients;longer for severe disease or ifthere is a cardiomyopathy. Betablockage should never becommenced before alphablockade, as this will precipitatea hypertensive crisis.Roizen’s Criteria (for adequatepre-operative control) 6lllBlood pressure < 165 / 90 atall timesPostural BP fall to not below80 / 45ECG free of ST changes for2 weeksl < 1 VEB over 5 minutesAnaesthetic goals:l Optimum pre–operativepreparationl Alleviation of anxiety –drugs, good communicationwith anaesthesiologist &surgeon, informed consent66Journal of Postgraduate Medical Education, Training & ResearchVol. II, No. 5, September-October 2007