Download pheochromocytoma

Pheochromocytoma:
Definition:
Pheochromocytomas are catecholamine secreting tumours arising from cells of the
sympathoadrenal system.They are usually located in the adrenal medulla,however
they may occur in other sites containing chromaffin tissue such as:
Abdominal:
1 .paravertebral ganglia
2 .coeliac plexus
3.aorta at the level of the kidney(organs of zukerkandle)
Extra abdominal: 1. Chromaffin cells of the neck and thorax
2. chromaffin cells of the anal,vaginal and sacrococcygeal region.
Five per cent of cases are inherited as autosomal dominant.
Pheochromocytoma may occur as a part of multiple endocrine neoplasia syndrome
that is presnt as three types.
Type two A:
1.Pheochromocytoma
2.Medullary carcinoma of the thyroid
3. Parathyroid adenoma
Type two B:
1.Pheochromocytoma
2.Medullary carcinoma of the thyroid
3. Marfan syndrome
4. Mucosal adenoma
Von hippel-Lindau syndrome
1.Pheochromocytoma
2.hemangioblastoma of the retina ,cerebellum and CNS.
The tumour primarily secretes catecholamines that exert their effects by acting on
the alpha and beta adrenergic receptors.
The effect of catecholamines on the alpha receptors is mediated via phosphlipase c
that increased inositol triphosphate while their effect on beta receptors is mediated
via adenylate cuclase that increased cyclic AMP.
Clinical picture:
1.Hypertension that is usually paroxysmal in 65% of cases or sustained in 35% of
cases.
2.Fever and excessive sweating
3.Headache,nausea and vomiting
4.Elevated blood sugar
5.Visual disturbance
6.precordial pain
7.Pressor response to particular drugs such as histamine,glucagon droperidol
,metoclopramide, cytotoxic drugs, tricyclic anti depressant and phenothiazines.
Diagnosis:
1-The diagnosis is suspected from the clinical picture
2-Plasma catecholamine more than 2000 picogram/ml
3-Urinary catecholamine: they are generally considered superior to plasma test
because the tumour secretes catecholamine intermittently and the catecholamine in
plasma have short half life.
.catecholamine more than 1.2 mg per 24 h urine (most specific)
Valinyl mandelic acid more than 10 mg/24 h urine
VMA is used as an initial test due to its acceptable specificity and being
relatively inexpensive .However it is elevated in: carcinoid syndrome,carotid body
tumour,ganglioneuroblastoma and retinoblastoma.
4- Clonidine suppression test: the catecholamine secretion was not suppressed
after the administration of clonidine in patients with pheochromocytoma.
5-Abdominal ultrasound and CT scan.
6-CT scan with the use of iodine 131 labeled metaiodobenzylguanidine is extremely
accurate in diagnosing and localizing the tumour.
Preoperative preparation:
1-Control of blood pressure by the use of alpha blocking drugs:
. Phenoxybenzamine hydrochloride is the most effective drug,it is an alpha blocking
drug that act by irreversible alkylation of the alpha receptors,it have long duration
of action .
Dose: orally,10 to 20 mg three to four times daily
Side effects: postural hypotension and reflex tachycardia that can be treated by
administration of fluid and beta blickers.
.Prazosin: 2 to 5 mg /d can be used orally but it less effective than
Phenoxybenzamine.
.Beta blockers: propanolol is used to control the cardiac arrhythmias however it is
extremely important not to use the beta blickers alone before alpha blockers
otherwise the unopposed alpha receptors may result in hypertensive crisis.
.Alpha methyl paratyrosine that inhibit the tyrosine hydroxylase that is responsible
for the conversion of tyrosine to dopa as an initial step in the synthesis of
catecholamines.This drug can be given orally at adose of 0.5g to 4 g/d. Side effects of
the drug:.fatigue.diarrhea, anxiety ,agitated depression and tumours.
2- The patients have contracted blood volume also the alpha blockers may dilate the
vascular bed so 1 to 2 unnits of blood may be given to increase the intravascular
volume.
3-the criteria of adequate preparation:
1.Blood pressure not more than 160/90 for 48 h before surgery
2. Orthostatic hypotension should be present but the blood pressure should not
be less than 85/45
3. PVCS should be absent
4. ST segment changes absent 2 weeks before surgery.
Anaesthetic management:
The principle goal is to prevent the rise of blood pressure during induction and
manipulaton of the adrenal gland by the use of alpha blockers and smooth
induction. A secondry goal is to prevent falling of blood pressure after the surgical
removal of the tumour.
Premedication:
.Sedation by midazolam or valium
Avoidance of the following drugs:
1-Atropine:exacerbates the chronic effect of catecholamines due to vagal
inhibition.
2-Tricyclic antidepressant,phenothiazines,droperidol and metoclopramide as they
may stimulate the release of catecholamine from the tumour cells.
Monitoring:
1-Muli lead ECG 2-Invasive monitoring of the blood pressure 3-temperature
4-urine output 5-pulmonary artery pressure for patients with left ventricular
dysfunction.
Induction:
.Smooth induction should be done to avoid rise of the blood pressure
.Avoid rapid induction o f induction agents such as thiopentone or propofol.
.Avoid the use of droperidol ,ketamine,morphine.
Maintenance:
.Combined epidural and light GA can provide best control of blood pressure
Isoflurane and sevoflurane are safe,halothane is undesirable due to sensitization of
the heart to the catecholamines.
Vecuronium is the muscle relaxant of choice ,atracurium (histamine release) and
pancuronium(block muscarinic receptors) are better avoided.
Support anaesthesia by fentanyl and midazolam.
The fluid therapy is guided by cvp and urine output.
Intraoperative management of blood pressure:
Hypertension:
The intraoperative hypertension can result from surgical manipulation of the
tumour and can be controlled by anti hypertensive drugs and by surgical ligation of
the venous drainage of the tumour.
1-regitine is a short acting alpha blocking drug can be given 1 mg or 2mg
incremental dose .
2-Sodium nitroprusside and tridil are used as a second choice
3- Hydralazine in 2mg incremental dose ,it is along acting direct arteriolar
vasodilator.
4- labetalol combined alpha and beta blocker 10mg bolus to a total of 150 mg
Hypotension:
The most critical time is after surgical removal of the tumour ,a sudden fall of
the blood pressure may occur and this may cause severe impairement of the
coronary,cerebral an renal perfusion. The management of hypotension:
1-Discontinuation of the alpha blocking drugs after ligation of the venous drainage
of the tumour.
2- Expansion of the intravascular volume guided by CVP
3- The use of vasopressor drugs phenyl ephrine,ephedrine,levophed infusion and
adrenaline in fusion.
Management of arrhythmia:
1.lidocaine 2- amiodarone 3- DC shock should be available.
Post operative period:
1-Close monitoring of the blood pressure
2-Residual hypertension means incomplete removal of the tumour
3-persistant hyptension may require the continuation of vasopressors in the post
operative period and the exclusion of any surgical bleeding tha may need
exploration.
4-Gradual weaning of the vasopressor
5- Stop the vasopressor when the blood pressure are within the acceptable range
without support.
6-Somnolence may occur due to decrease in the circulating catecholamine level and
this may decrease the post operative narcotic requirement.
7-Hypoglycemia may occur due to rise of insulin as a result of loss of suppresion of
beta cell function. Therefore close monitoring of the blood sugar is needed for 24
hand switching to glucose containing containing solution.