Page 15 - Medicine and Surgery

P1: JYS
BLUK007-01 BLUK007-Kendall May 12, 2005 17:17 Char Count= 0

Chapter 1: Fluid and electrolyte balance 11

respiratory compensation). Causes of metabolic aci- Pathophysiology
dosisincludesalicylatepoisoning(seepage528),lactic Hypercalcaemia prevents membrane depolarisation
acidosis or diabetic ketoacidosis (see page 460). Al- leadingtocentralnervoussystemeffects,decreasedmus-
ternatively failure to excrete acid or increased loss of cle power and reduced gut mobility. It also has multiple
HCO 3 ,such as renal tubular disease (see page 251) effects on the kidney: it reduces the glomerular filtration
−
and diarrhoea. Hyperkalaemia may occur as an im- rate;it can cause acute or chronic renal failure; it can also
portant complication (see page 7) particularly if there causenephrogenicdiabetesinsipidus(seepage445),uri-
is also acute renal failure. nary stones (see page 270) and calcium deposition in the
Alkalosiswithalowcarbondioxidedefinesrespiratory kidney and other tissues. Hypercalcaemia causes short-

alkalosis. This may result from any cause of hyperven- ening of the Q–T interval but this is not associated with
tilation including stroke, subarachnoid haemorrhage, an increased risk of cardiac arrhythmias.
meningitis, pyrexia, hyperthryoidism, pregnancy or
anxiety. It is generally an acute condition and so little
compensation occurs.
Clinical features
Alkalosis with a high bicarbonate and a positive base

The condition may be asymptomatic and diagnosed in-
excess defines metabolic alkalosis. It is rare and may
cidentally on calcium measurement. Early symptoms
be caused by loss of acid from the gastrointestinal
are often insidious, including loss of appetite, fatigue,
tract (e.g. vomiting) or from the kidney (e.g. Cush-
lethargy, weakness, constipation and thirst. The symp-
ing or Conn’s syndrome). Hypokalaemia may occur
toms of hypercalcaemia can be summarised as bones,
(see page 8).
stones, moans and groans:
Bone pain may be due to metastases, multiple

Hypercalcaemia myeloma or bone disease as a complication of hyper-
parathyroidism.
Definition
Urinary stones.
Aserum calcium level of >2.6 mmol/L.
Moans due to confusion and drowsiness. Depression
and acute psychosis can also occur.
Incidence Groans due to abdominal symptoms such as nausea,
Relatively common. vomiting, pain and constipation.
Deposition of calcium in heart valves, coronary
Aetiology arteries and other blood vessels may occur. Hyper-
Important causes of hypercalcaemia are given in tension is relatively common, possibly due to renal im-
Table 1.5. More than 80% of cases are due to malignancy pairment and also related to calcium-induced vasocon-
or primary hyperparathyroidism (see page 446). striction.

Table 1.5 Important causes of hypercalcaemia
Increased bone Increased GI
resorption absorption Decreased output
Hyperparathyroidism Excess calcium intake (milk-alkali Renal failure
syndrome): Thiazide diuretics
Malignancy (3 mechanisms): Calcium supplements Familial hypocalciuric
Osteolytic metastases Antacids hypercalcaemia (FHH)
PTH-like peptide Excess vitamin D:
Osteoclast activating factors Vitamin D supplements
(multiple myeloma, lymphoma) Increased production of active Vitamin D
Paget’s disease metabolites occurs in granulomatosis
Immobilisation disorders (e.g. sarcoidosis, TB) and in
lymphoma