Observing the cat undisturbed in its cage allows assessment of its demeanor and resting respiratory rate and effort, all of which may change upon handling. Unless there are specific indications otherwise, physical examination is best completed on the examination table. Physical examination has been described in Chapter 1. For patients with reduced mobility or where handling causes discomfort, the bedding can be used to support the patient during transfer from the cage (Fig. 3-1). Cats should be weighed using scales that are accurate for small patients, such as pediatric scales (Fig. 3-2). A fall in body weight can accompany dehydration or catabolism, whereas a rapid increase can signal occult effusion. Surgical wounds, drains and feeding tube sites and intravenous (IV) catheter sites should be inspected for discharge, redness, swelling, or evidence of self-trauma. Gentle palpation of surgical sites can assist with pain scoring. The cage should be checked for evidence of urination (estimated volume, color), defecation (amount, color, consistency, presence of mucus, blood), vomitus or hemorrhage. Food and water intake should be recorded. For cats on IV fluids, the rate and type of fluid being administered should be confirmed. Patients receiving IV fluids typically have hematocrit, total plasma protein (TP), electrolytes and, where available, blood gases monitored every 24 hours. Judicious sampling minimizes handling and restraint and avoids exacerbating anemia. Using an insulin syringe for venipuncture is well tolerated, minimally traumatic and provides sufficient sample for microhematocrit, TP, electrolytes, blood glucose and blood film preparation.

Figure 3-1 Using the bedding to transport a weak, immobile or painful patient.

Figure 3-2 Pediatric scales for accurate weighing.

Assessment

Subjective and objective data form the basis of the patient assessment. All problems identified should be ranked and assessed (Chapter 1) and an overall assessment of the cat’s status as stable, improving or deteriorating made. Consideration should be given to the pain score, hydration/nutritional status, changes in body weight, new problems, or problems that cannot be accounted for.

Plan

The plan schedules investigations, treatments and ongoing monitoring, including adjustments to fluid therapy, nutrition, the analgesia plan, other medications (type, dose, route and frequency) and care of surgical drains, feeding tubes, venous access or closed urine collection systems. Environmental adjustments, such as a litter tray with low sides or a privacy area (a sleeping box or a curtain over part of the cage door) for timid cats undergoing less intensive monitoring, are included.

Fluid therapy

The goals of fluid therapy are to maintain hydration and effective circulating volume and to contribute to acid–base and electrolyte balance. Evidence on which to base recommendations for fluid therapy in the postoperative feline patient is limited, mainly comprising extrapolation of data relating to other species and pathophysiological justification. The volume, composition and rate of IV fluids should be tailored to the individual based on serial monitoring of physical and laboratory parameters.

Route of fluid administration

A pump should be used to deliver IV fluids and a peripheral catheter is suitable for most purposes. Where a fluid pump is not available, a pediatric burette (Fig. 3-3) is preferable to a standard giving set to avoid fluid overload. The required rate is converted to the number of drips/minute for the giving set:

Figure 3-3 A pediatric burette prevents fluid overload when a fluid pump is not available.

Subcutaneous (SC) administration is not suitable for irritant solutions and an unpredictable rate of absorption can precipitate congestive heart failure or hypokalemia. Administration via a feeding tube or the intraosseous route may be indicated.

Volume of fluid administration

The volume of fluid required for a 24 hour period is the sum of current deficits, maintenance requirements, and ongoing losses (Box 3-2). Losses during surgery include hemorrhage, evaporation from serous surfaces, transudation from traumatized tissues, and gastrointestinal sequestration. The maintenance requirement for an adult cat is approximately 60 mL/kg/day.¹ Ongoing losses include those associated with vomiting, diarrhea, polyuria, surgical drains, and transudation into body cavities or externally. Hydration status is estimated based on the patient’s history, physical findings and laboratory data. Changes from objective baseline data such as weight, hematocrit, TP and creatinine are particularly useful.

Box 3-2 Example of a fluid replacement calculation

A 5 kg cat is estimated to be 5% dehydrated. The cat is vomiting four times per day, approximately 10 mL per vomit

Maintenance requirement (60 mL/kg/day) for this cat is 60 × 5 = 300 mL in 24 hours, or 150 mL in 12 hours

Fluids deficit (in mL) is body weight (kg) × % dehydration (as a decimal) × 1000

This cat’s fluid deficit is (5 × 0.05 × 1000) = 250 mL

The ongoing losses are 40 mL in 24 hours, or 20 mL in 12 hours

So, if the fluid deficit is replaced over 12 hours, the total volume of fluid to be delivered in 12 hours is 150 + 250 + 20 = 420 mL, or (420/12) = 35 mL/hour

Rate of fluid administration

The rate at which fluid is administered depends on the severity and clinical consequences of the deficit, taking into account pre-existing conditions, which may predispose to fluid overload. Deficits are usually replaced over six to 12 hours.

The maximum rate of infusion for cats, 60 mL/kg/hour (90 mL/kg/hour in the dog), is reserved for patients with non-cardiogenic shock, and even then, is given as smaller boluses, repeated as necessary (see below, Management considerations for the septic cat). Care should be taken to avoid interstitial fluid overload, the consequences of which include pulmonary edema, pleural effusion and delayed healing due to prolonged ileus, edema and poor tissue oxygenation. Compensated cardiac and renal disease, chronic anemia, and colloid administration all increase the risk of fluid overload. Urine output should be monitored and maintained above 1–2 mL/kg/hour (or higher where there is obligatory polyuria). Compensated cardiac disease is difficult to detect without echocardiography. Detection of a murmur is neither sensitive nor specific for this purpose.² Assessment of vertebral heart score, atrial size, and pulmonary vasculature on thoracic radiographs can assist. However, in contrast to dogs, hypertrophic cardiomyopathies are common in cats and significant structural changes can produce minimal change in the cardiac silhouette. Where an increased risk of fluid overload is identified, for example in a cat with advanced hyperthyroidism where significant structural cardiac disease might be predicted despite medical stabilization, conservative fluid rates and additional monitoring should be instituted. Resting respiratory rate and effort can be recorded cage-side, hourly. Increased rate and effort from baseline should prompt assessment for jugular distension or pulsation, thorough auscultation for signs of pulmonary edema or pleural effusion and, if necessary, thoracic radiographs. Serial central venous pressure (CVP) monitoring is useful for avoiding volume overload (normal CVP 0–10 cmH₂O).³ As maintenance needs are gradually met from other sources, such as enteral feeding or voluntary food intake, fluid rates should be reduced and then ceased.

Fluid composition

The exact composition of the fluid administered will depend on individual requirements. In humans and dogs, anesthesia and surgery are associated with a transient increase in antidiuretic hormone (ADH) secretion lasting from one to four days.⁴ ADH promotes fluid retention and natriuresis. The administration of hypotonic, maintenance solutions in the immediate postsurgical period has been associated with dilutional hyponatremia and fluid overload, which can be severe.⁵ Assuming that the same is true in cats, then even in a well-hydrated patient, a rehydration solution, such as 0.9% saline or Hartmann solution, is recommended in the initial postsurgical period. Since high rates of potassium-free crystalloids are often administered during surgery, prompt supplementation of fluids after surgery with potassium is necessary to prevent iatrogenic hypokalemia.

Electrolyte abnormalities

It is essential to monitor for postoperative electrolyte abnormalities. Hypokalemia is common after surgery, particularly in cats that have been inappetent preoperatively.

Hypokalemia

Hypokalemia results from reduced intake, increased losses or redistribution in alkalosis. In the postsurgical patient, reduced food intake, inadequate supplementation of fluids, solute diuresis, diarrhea, chronic vomiting and diuretic use (loop and thiazide diuretics) can contribute. Other causes of hypokalemia, including primary hyperaldosteronism (Conn syndrome) (Chapter 35), a condition likely underdiagnosed in the cat,⁶ and breed-associated hypokalemia of Burmese cats, will be identified preoperatively. Intracellular potassium concentrations are actively maintained at much higher levels than extracellular levels and this potassium gradient contributes to the resting membrane potential of excitable cells. When IV fluids are delivered at maintenance rates, supplementation with potassium chloride at 20 mmol/L usually maintains normokalemia. The clinical consequences of severe hypokalemia (<3 mmol/L) include generalized weakness, cervical ventroflexion and reduced gastrointestinal motility. Where the potassium deficit is mild, oral or enteral supplementation can be used (4–10 mmol of potassium gluconate/cat/day divided) or the concentration of potassium in the fluids can be increased up to 40 mmol/L. Where potassium is added to a bag of fluids in use, the fluids must be turned ‘off’ to the patient while adding concentrated potassium solution to prevent infusion until the solution is adequately mixed. The maximum rate of potassium supplementation, 0.5 mmol/kg/hour, should not be exceeded or life-threatening cardiotoxicity can result. If plasma potassium is <3.0 mmol/L, a maximum-rate potassium infusion can be delivered using a syringe driver (Fig. 3-4), or as a secondary infusion on a pump, for one hour, after which electrolytes should be retested and the infusion repeated if necessary (Box 3-3).

Box 3-3 Preparing a maximum-rate potassium infusion

A 10 mL quantity of a 1 mmol/mL solution of potassium chloride is added to 10 mL of 0.9% sodium chloride. The resulting 0.5 mmol/mL solution is delivered using a syringe driver (Fig. 3-4) at 1 mL/kg/hour for one hour only. Plasma potassium is re-measured. The infusion can be repeated until normokalemia is achieved, but this rate should not be exceeded.