Page 448 - Medicine and Surgery

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444 Chapter 11: Endocrine system

flankincisionfollowingremovalofarib.Thediaphragm,
pleura and peritoneum are left intact wherever possible. Inappropriate ADH Secretion
Aposterior approach through the bed of the 11th or
12 rib is more difficult, but has a lower morbid-
Increased water reabsorption from renal collecting ducts
ity. Lifelong corticosteroid (both glucocorticoid and
mineralocorticoid with hydrocortisone and fludocorti-
sone) replacement therapy is needed following bilateral Increased blood volume
adrenalectomy. Laparoscopic adrenalectomy is increas-
ingly being used.
Increased glomerular filtration rate
Replacementismonitoredbybloodpressuremeasure-
ment, serum electrolytes and patient well-being. Stress,
infection and surgery may all increase corticosteroid re- Continued water reabsorption leads to
quirements, and may precipitate an Addisonian crisis production of highly concentrated urine
(see page 441). Patients need to be advised of the signs
and symptoms and management of such events.
Hyponatraemia, low plasma osmolality

Thirst axis Shift of fluid from extracellular space into cells
e.g. in the brain causing cerebral oedema
Syndrome of inappropriate
anti-diuretic hormone secretion Figure 11.12 Pathophysiology of SIADH.
(SIADH)
Definition
Pathophysiology
SIADH is characterised by the persistence of ADH secre-
ADH is a peptide hormone similar to oxytocin which
tion despite decreased plasma osmolality and normal or
is normally secreted from the posterior pituitary, in re-
increased extracellular fluid volume.
sponse to an increase in plasma osmolality. It acts on
the collecting tubules in the kidney to make them more
Aetiology permeable to water molecules. Hence its secretion causes
See Table 11.13. water retention (see Fig. 11.12).

Table 11.13 Causes of syndrome of inappropriate anti-diuretic hormone secretion (SIADH)
Ectopic secretion Small-cell bronchial carcinoma
Rarely carcinoma of the thymus, prostate, pancreas, duodenum, adrenal, ureter
or nasopharynx
Lymphoma, leukaemia
Inappropriate secretion (hypothalamus)
Lung disease Pneumonia, tuberculosis, aspergillosis
Positive pressure mechanical ventilation (stretch receptors)
Neurological Trauma (including neurosurgery or major surgery)
Encephalitis, post-meningitis
Ischaemia (stroke, vasculitis)
Tumours
Drugs Carbamazepine, chlorpropamide, tricyclics, phenothiazines, syntocinon, narcotics
and cytotoxic drugs (vinca alkaloids – cyclophosphamide, vincristine)
Other Pain, intermittent acute porphyria, Guillain–Barr´e syndrome, hypothyroidism,
symptomatic HIV infection or AIDS