Blocked Cats: Dispelling the Myhths

Blocked cats are arguably the most common condition seen in practice that is life threatening yet potentially curable. Success rates for unblocking and survival can and should approach 100%. This depends upon prompt and accurate assessment of each case, careful stabilisation and optimal treatment. Nevertheless, the majority can survive and moreover, go on to a full and happy life. Unfortunately the optimal management of the cat with urethral obstruction is marred by certain problems and popular misconceptions.

The most important things to consider to optimise success rates are:

1. An immediate and accurate assessment of the major body system abnormalities of the cat
2 Measurement of electrolyte and ideally acid base status
3 Electrocardiographic monitoring
4 Optimise initial stabilisation prior to unblocking: Aggressive fluid therapy is sometimes necessary and can be administered safely despite the obstruction. Use isotonic crystalloids NOT 0.18% saline (the Devil’s fluid!) Calcium gluconate is a wonder drug and should be used in preference to insulin/dextrose or bicarbonate for hyperkalaemia
5 Do not perform cystocentesis unless absolutely necessary
6 Optimise technique for urethral catheterisation to increase success rates and avoid urethral trauma - don’t use Walpole’s
7 Don’t use baseline azotaemia as a prognostic indicatorwe commonly see cats with creatinine >1000µmol/l that revert to normal within 12-36 hours.

Physical Exam

A streamlined, efficient major body system examination is performed to rapidly identify any imminently lifethreatening problems. The cardiovascular, respiratory and central nervous systems should be evaluated first, followed by abdominal palpation and body temperature. Stabilization measures should be initiated for any major problems prior to the remainder of the full physical evaluation. For the cardiovascular system, evaluation of the mucous membrane colour, capillary refill time (CRT) and vigour, pulse profile (height and width), heart rate, and cardiac auscultation should be performed. The astute clinician may be alerted to the possibility of hyperkalaemia following this initial cardiovascular assessment. A common finding is that the heart rate is inappropriately slow for the degree of hypoperfusion present. For example, a cat with very pale mucous membranes, absent capillary refill time, weak femoral pulses but a heart rate of only 100 - 140 has an inappropriate bradycardia. This finding should prompt an immediate electrocardiogram. Indeed an ECG is the quickest and easiest means of making the diagnosis of hyperkalaemia provided that one is familiar with the typical changes seen.

ECG

The cardinal signs of hyperkalaemia are relative bradycardia, peaked T waves, absent P waves and in severe cases, wide bizarre QRS complexes. The most severe ECG change seen is the so-called sine wave conformation (left). It is important to realise that individual animals vary in their ECG response to hyperkalaemia. For example, some blocked cats will be virtually normal with a potassium concentration of 7 mmol/L whereas others may be near death. Treatment should always be based upon the perfusion status of the animal and the electrocardiogram not the plasma potassium concentration. ECG showing bradycardia, absence of P waves and spiked T waves). [...]