Page 137 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

However, one study (Flanders, 1999) showed that there Cats with tetany or seizures should be treated to
was no difference in the incidence of hypocalcaemia when effect with a slow intravenous bolus of calcium.
VetBooks.ir simultaneous thyroidectomy was performed using an intra- and the effects of the bolus may last only 1–2 hours.
Twitching or panting may take up to an hour to resolve,
the operations were staged by 3–4 weeks, or if bilateral
Ongoing management should be instigated as soon as
capsular technique.
calcium injections are less beneficial than constant rate
PRACTICAL TIPS the initial crisis is under control. Multiple intermittent
infusion as the former cause large serum calcium
• Haemostasis is particularly important in those cats fluctuations and will significantly delay recovery. Oral
that have received methimazole or carbimazole calcium and vitamin D supplementation should be
• Do not take jugular blood samples in the days started and a continuous calcium infusion used until
preceding thyroid surgery the oral supplementation is able to maintain calcium
• Sometimes the cranial thyroid artery travels levels adequately. Oral supplementation of calcium is
through the parenchyma of the thyroid gland prior absorbed through passive mechanisms and is not
to supplying the parathyroid gland. In this situation, dependent on the activity of the vitamin D supplemen-
the parathyroid gland is unlikely to be salvaged tation; it is therefore particularly important in an
and there is an increased risk of postoperative anorexic cat. As the activity of the vitamin D supple-
hypocalcaemia. Staged thyroidectomy or mentation takes effect, the calcium supplementation
autotransplantation of parathyroid tissue should be may be tapered or stopped (Figure 10.6).
considered • Cardiac or renal disease: Thyrotoxic cardiac changes
• Examine both thyroid glands closely before will resolve postoperatively; persistent clinical signs
deciding which gland to start with. Remove the usually indicate primary cardiac disease. In cats where
thyroid on which the parathyroid is most likely to hyperthyroidism has masked the presence of renal
be saved first, and then remove the second thyroid disease, the urea and creatinine levels will rise
gland if that procedure went well postoperatively as the GFR falls. This complication is
irreversible, and conventional management of renal
failure is instigated (see the BSAVA Manual of Canine
If inadvertent complete parathyroidectomy occurs, and Feline Nephrology and Urology).
resolution of postoperative hypocalcaemia may be quicker • Laryngeal paralysis: Retraction of the tissues during
if the parathyroid gland is immediately reimplanted into surgery can cause trauma to the recurrent laryngeal
well vascularized tissue such as muscle. nerve, resulting in laryngeal paralysis. Unilateral paresis
may not cause clinical signs, but acute bilateral paresis
Postoperative complications: can cause significant laryngeal obstruction
• Hypoparathyroidism: Bilateral thyroidectomy can
result in iatrogenic damage to the parathyroid glands,
resulting in hypoparathyroidism. Anecdotal reports of Drug Dose rate Comments
hypoparathyroidism in cases of unilateral thyroidec- Calcium lo i.v. Monitor heart rate
tomy may be due to over-vigorous retraction of tissues, borogluconate 1 . 1. ml/kg to effect during initial
damaging the contralateral parathyroid gland or its Available elemental if seizuring, over treatment and
blood supply. Loss of PTH secretion causes increased calcium .3 mg/ml 3 minutes. monitor serum
1 mg/kg/h ionized calcium levels
urinary loss of calcium, reduced mobilization of elemental calcium i.v. regularly
calcium from bone and decreased intestinal absorption
of calcium. Postoperative anorexia may exacerbate Calcium chloride 1 lo i.v. 1 mg/kg/h Vascular irritant – use
this. Secondary effects result from increased phos- Available elemental ith caution
calcium 7. mg/ml
phate and decreased renal synthesis of calcitriol.
Clinical signs are related to hypocalcaemia. Low
levels of ionized calcium result in increased excitability Calcium carbonate Oral treatment Other oral calcium
of neuromuscular tissue and in muscle fasciculations, mg/kg h supplements may also
twitching, irritability and disorientation, leading up to be used at the same
seizures. Facial trembling and pruritus are particularly dose
common signs in cats. Diagnosis is confirmed by Vitamin D analogues
measurement of serum calcium (measurement of
ionized calcium will detect subtle changes earlier) and Dihydrotachysterol . . 3 mg/kg Onset 1–7 days
Discontinuation time
q24h initially, reduce
serum phosphate. to . 1 . mg/kg of 1 3 eeks for
It is important to instigate specific treatment as soon every 1–2 days serum calcium levels
as possible to prevent the onset of seizures or, in severe to normalize
cases, respiratory arrest and death. The aim is to Overdosing may result
increase calcium levels to physiological levels without in hypercalcaemia
causing hypercalcaemia (vitamin D toxicosis), keeping 1,25-Dihydroxy - 1 1 ng/kg orally uicker onset 1
calcium levels at the low end of normal to stimulate cholecalciferol 1 h for 3 days days; short half-life,
compensatory ectopic parathyroid hypertrophy. In cats then reduce to reduces risk of
whose calcium levels are steadily or rapidly declining, or . 7. ng 1 h for 3 overdose and
days, then give q24h. iatrogenic
those where there is severe hypocalcaemia but no Higher doses have hypercalcaemia
clinical signs, treatment should be started immediately. also been reported
Frequent measurements (e.g. 2–4 times daily) of serum Treatments for hypocalcaemia follo ing parathyroid gland
ionized calcium levels are necessary to keep serum 10.6 damage or removal. btain o ner consent to use drugs not
calcium levels on the low end of the reference range to licensed for veterinary use.
allow recovery of normal homeostatic mechanisms. (Data from the BSAVA Small Animal Formulary, 9th edn, Part A: Canine and Feline)

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