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Anaesthesia for Phaeochromocytoma 1) Incidence Rare catecholamine-secreting tumours which may present at any age, but usually 40-50; female > male; 0.5% of all hypertensives. Only 10% occur in childhood, in this age group phaeos are twice as common in boys than girls, 20% are bilateral, and the tumour is more malignant. Occurs in chromaffin tissue of neural crest origin, usually abdominal, 85% are adrenal. Other sites include Coeliac, Renal, Hypogastric, Sympathetic chain ganglia, and the organ of Zuckerkandl. 15% have metastatised at the time of diagnosis (35% in kids and 8% in adults). 2) Symptoms Classic episodes of headache (hypertension), sweating, axiety, pallor, and palpitation (arrythmias), provoked by posture, exercise, anxiety, pain, and drugs, occur in only 50% of phaeos. Most of these do not have elevated resting BP's; the others are found during investigation of hypertension. Postural hypotension is common (70%) in Phaeo's and suggests the diagnosis in an untreated hypertensive. It should also be considered in pre-eclampsia, thyotoxicosis, and malignant hypertension. 3) Associated disesases Medullary thyroid cancer, parathyroid adenoma, other neuromas. Von Recklinghausens in 5% of Phaeo's, but Phaeo's seen in only 1% of Von Recklinghausens. 5% inherited. 4) Diagnosis a) Urine metanephrine, VMA and catecholamines
b) Plasma catecholamines
Catecholamines are generally the most accurate, but owing to short half-life may get false negatives if tumour hasn't recently been stimulated. Significant Adrenaline production strongly implies adrenal location. c) Provocation Glucagon or histamine provocation of catechol release then blood levels taken - little used these days. d) Suppression Clonidine 300μg has no effect on plasma Nad in phaeo but suppresses normal. 5) Tumour localisation IVP: Positive in only 40% 6) Preoperative drug management a) Phenoxybenzamine: Non competitive α-blocker, with long (24 hr) half life. Allows plasma volume re-expansion, but some hypertension on handling may still occur. Dose is 20 mg/day orally, increasing by 10-20mg/day, until desired effect. Overdose causes toxic megacolon and postural hypotension. b) β-Blockers Added to manage persistent tachycardia, arrythmias, angina. May worsen BP and LV performance unless adequately α-blocked. c) Prazosin: 6-10mg of this α-1 selective blocker used with propranolol in high doses (120-480 mg/day) d) Labetolol: Has been decribed but is probably inadequate alone. Good for resting rather than paroxysmal hypertension; frequently need Nad postop. e) Magnesium: MgSO4 > 2g IV may be useful for managing acute episodes. 7) Anaesthetic management Aim is to avoid excessive sympathetic stimulation, hypoxia, and hypercarbia, and to be able to cope with the acute changes (ie, hypertension, arrythmias, etc) which may arise. Several weeks of bedrest and preoperative drug treatment in hospital are usually required. a) Assessment Roizens criteria for adequate preoperative control are: Blood pressure < 165/90 Look for significant LV compromise or dysfunction, and consider S-G catheterisation if present. Book an ICU bed postop. Check BSL, K+. Crossmatch blood. b) Premedication Relief of anxiety is important, deep premeds usually advocated. Almost all drugs have been used without problems, however Droperidol has been associated with some idiosyncratic responses, and Atropine is often not recommended. α-blockers and other short acting drugs are usually given on the same day, but not phenoxybenzamine. c) Choice of anaesthesia Intubation and muscle relaxation is required for access, and anaesthesia with volatile agents, narcotic, and neurolept techniques have all been used. Gallamine, pancuronium, and suxamethonium have disadvantages, and Halothane may worsen arrythmias. Agents that release Histamine best avoided (morphine). Relaxant, nitrous, narcotic, and Enflurane or Isoflurane supplementation are recommended. d) Monitoring equipment CVP (for monitoring and vasoactive infusions) and Arterial line (essential). Swan-Ganz / TOE if LV dysfunction or other indications present. Usual equipment for a long case with bloodloss, ie ECG, IV, warming blanket, blood warmer, humidifier, temperature probe, HiLo cuffed ETT with pressure monitor, NGT, Urinary catheter, etc. e) Induction Major danger period, requiring profound reflex supression prior to intubation. Insert arterial line prior to induction and ensure an adequate CVP. Avoid Ketamine; use a large dose of thiopentone, +/- Fentanyl, Diazepam, IV or topical lignocaine, MgSO4 etc. f) Hypertensive crises Provoked by noxious stimuli or tumour palpation, usually best managed by removing the stimulus. SNP bolus, Phentolamine 1-5 mg IV bolus or by infusion, MgSO4 2g IV, Lignocaine 1-2 mg/kg, Esmolol, Labetalol, etc are all useful. g) Postoperative hypotension Very common, due to combination of residual α and β blockade, fall in circulating catecholamine levels, receptor downgrading, and diminished blood volume. 50% have significant hypotension for 3 days. Management requires good pain relief, adequate fluid load, IV infusions of catecholamines, ICU observation and monitoring. Always be wary of an Addisonian crisis. Management requires good pain relief, adequate fluid load, IV infusions of catecholamines, ICU observation and monitoring. Always be wary of an Addisonian crisis. 8) Phaeochromocytoma in pregnancy 25-50% mortality if untreated in 1967; tumour excision mid-pregnancy or simultaneous Caesarian Section and excision have been advocated, although several cases of successful epidural C.S. and vaginal delivery with later excision have been described. More information: EndoText.Org - chapter on Phaeochromocytoma Wikipedia chapter on Paragangliomas.
Last updated Tuesday, December 15, 2020 |
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