Page 903 - Problem-Based Feline Medicine

41 – THE CAT WITH NECK VENTROFLEXION 895

– Losses can be determined more accurately – Where possible, give oral potassium prior to
measuring 24-hour urinary potassium loss. IV fluids.
– Oral administration of potassium is more
Electrodiagnostic testing may be normal, or may show
effective in normalizing potassium than IV
positive sharp waves and fibrillation potentials. Nerve
administration.
conduction velocities are normal.
– Only use fluids to administer potassium in the
Muscle biopsies may reveal normal muscle, or mild most severely affected cats.
myofiber necrosis, with little or no evidence of inflam- – When using fluids give a low volume with a high
mation. potassium concentration e.g. 160 mmol (Eq)/L
at 2.0 ml/kg/h. Ideally, do not exceed 0.5 mmol
(Eq)/kg/h or cardiac arrest may occur.
Differential diagnosis
Oral supplementation is necessary in all cases.
Myasthenia gravis, polymyositis and organophos- ● It should be started immediately, as IV administra-
phate toxicity can all cause similar clinical signs. tion is often not adequate to normalize potassium.
● Potassium gluconate solution (Kaon Elixir), tablets
Since hypokalemia is so readily detected by assessment
or powder (Tumil K) can be added to food (4–10
of serum biochemistry, more sophisticated diagnostics
mmol (Eq)/PO q 24 h, in divided doses).
are not usually required.
● Feeding a diet that is high in potassium can also
● If it becomes necessary to rule out specific differ-
help.
entials, electromyographic studies, IV edropho-
● The level of supplementation should be adjusted
nium (Tensilon test), assessment of serum
according to serum potassium levels.
anti-acetylcholine receptor antibodies and serum
● The duration of supplementation will depend on the
cholinesterase levels, toxoplasmosis serology
underlying cause.
and/or muscle biopsy may be required.
– Cats that had been fed an unsuitable diet, given
inappropriate IV fluids or excessive amounts of
frusemide will cease to require additional potas-
Treatment
sium once the precipitating cause has been cor-
Severely affected cases may require immediate IV rected.
potassium infusion. – Cats with chronic renal failure will require long-
● This requires the use of an infusion pump, constant term supplementation. Maintenance doses are
cardiac monitoring, and repeated evaluation of typically 2–5 mmol (Eq)/cat q 12–24 h.
serum potassium levels (every 2–4 hours until the – Some Burmese cease to need supplementation
serum level has risen to 3.5 mmol (Eq)/L). after they are about a year old, others need life-
● In severe cases, despite potassium supplementation, long supplementation, with an increasing need
IV fluid administration may result in hemodilution, during periods of stress.
diuresis with exacerbation of urinary potassium
Where possible, treat the underlying disease or cor-
loss, progressive hypokalemia, and worsening clin-
rect the dietary or fluid imbalance.
ical signs resulting in respiratory muscle paralysis
and respiratory arrest. Cats with hyperaldosteronism may benefit from
– Inappropriate fluid administration is the most spironolactone (an aldosterone antagonist; up to 50
common cause of death in hypokalemic cats. mg/kg PO q 24 h), in addition to potassium supple-
– It is therefore essential to monitor these patients mentation.
closely.
– Respiratory muscle paralysis typically occurs
when serum potassium levels fall below 2
Prognosis
mmol/L.
– Ventilatory support is required to save the cat Severely affected cats, particularly those with respira-
and may need to be continued for 24–48 hours. tory distress, carry a guarded short-term prognosis.