Body assessment

Many assessment protocols for humans use the body mass index (BMI), which is weight (kg)/height(m)², and anthropometric measurements such as midarm muscle circumference.⁶ A feline version of BMI has been developed and validated by dual energy X-ray absorptiometry (DEXA) for healthy cats weighing between 3 kg and 9 kg.¹⁴ The feline BMI uses the rib cage circumference in cm and the leg index measurement (LIM), which is the hind leg length in cm from the middle of the patella to the dorsal tip of the calcaneal process. The amount of body fat is estimated using the equation in Box 6-2. This calculation has not been validated in ill cats, and feline BMI is not widely used in clinical practice.

Body condition scores (BCS) provide a semi-quantitative method for evaluating fat and lean body tissue percentages.15,16 Scoring systems have been developed using systems of 1 to 5, 6, or 9 points, with lower numbers representing thinner cats and higher numbers indicating fatter animals. A feline BCS system using a 9-point scale has shown good correlation (0.91) with percentage of body fat as determined by DEXA.¹⁶ This BCS system, using pictures and descriptions, shows good repeatability within and between observers. A score of five out of nine is optimal (Table 6-1).

The BCS systems do not take into account muscle wasting, and many ill cats have muscle loss disproportionate to fat loss due to the metabolic changes of stress. Consequently, a 4-point feline muscle mass scoring (MSS) system has been developed based on palpation of muscles over the skull, scapulae, spine, and pelvis¹⁷ (Table 6-2). Animals with no muscle wasting are scored as a 3, mild wasting is 2, moderate wasting is 1, and a 0 score represents severe wasting. There was a fair correlation between the feline MMS system and cats’ lean body mass as determined by DEXA.¹⁷

Multi-frequency bioelectrical impedance has been used experimentally to assess body composition in healthy cats,¹⁸ but is not used in the clinical setting. Disturbances of water and electrolyte metabolism in the ill patient limit the usefulness of this technique in the hospital.⁶ In research settings, DEXA is used for determination of body composition. It has good accuracy but requires anesthesia and is not practical for most patients.¹⁹

Nutritional assessment in humans has included measurements of serum albumin and other proteins, including acute phase reactants. These parameters are affected by factors other than nutrition, including metabolic changes of illness, hydration, and vascular permeability. Serum albumin does not correlate well with other nutritional assessments or with starvation in people,6,20 although in cats admitted to a referral practice there was a positive correlation of serum albumin with body condition score.²¹ This was likely due to decreases in serum albumin and BCS both reflecting the underlying disease.^20,21 Serum insulin-like growth factor (IGF)-I concentrations are reduced by short-term dietary restriction and restored by re-feeding in cats,²² but this parameter is not widely available for daily use in practice.

While there appear to be no reliable, widely available laboratory markers for assessment of nutritional status, the identification of specific nutrient deficiencies, such as folate, cobalamin, and iron can be useful. The most practical preoperative nutritional assessment in practice combines the history of acute or chronic weight loss, dietary intake, body condition score, and muscle mass score.

Obesity concerns

Due to the potential for obese cats to have higher risks of complications with anesthesia and surgery, it may be prudent to postpone elective procedures until the cat loses weight. For more urgent procedures, the fat cat should be provided with adequate nutritional support to decrease the loss of lean body tissue and the risk of hepatic lipidosis.

Daily monitoring of the cat’s nutritional status while hospitalized will help to ensure adequate intake. Cats should be weighed daily (Fig. 6-1), although day-to-day weight fluctuations are influenced by fluid balance.

Adult cats

Fasting has been recommended prior to general anesthesia to minimize gastric content volume and thereby decrease the risk of regurgitation and aspiration. Gastroesophageal reflux during general anesthesia is considered to be a common cause of esophagitis, and can cause esophageal strictures. The incidence of gastroesophageal reflux during anesthesia in dogs has been reported as 16.3%.²³ In another canine study, the rate of esophageal stricture caused by gastroesophageal reflux during anesthesia was 0.13%, and 30% of these cases died.²⁴ Studies in cats are not available.

The traditional practice in veterinary medicine has been to starve patients overnight or for at least six to 12 hours prior to anesthesia. However, canine studies have shown that prolonged fasting neither diminishes gastric volume nor decreases gastric acidity.²⁵ An increased duration of fasting is actually associated with an increased incidence of reflux in dogs. None of 30 dogs fasted for two to four hours refluxed during anesthesia, while 13.3% of the ones fasted for 12 to 18 hours had an episode of reflux.²³ In another study, none of 31 dogs fasted for three hours refluxed, while 16.3% of those fasted for ten hours had an episode. Dogs fasted for three hours after a canned food meal did not have a significantly increased gastric volume compared to those dogs fasted for 20 hours. Further, gastric acidity was reduced in the dogs with a three hour fast compared to those with a 20 hour fast.²⁶ Morphine also decreases the lower esophageal pressure; its use in combination with acetylpromazine (acepromazine) prior to anesthesia increased the incidence of gastroesophageal reflux in dogs from 27% to 60%.²⁷ Further, in humans, providing oral fluids and carbohydrates up to two hours before surgery attenuates postoperative insulin resistance. As dietary fat slows the rate of gastric emptying, feeding a small, low fat meal may be the best option.²⁸ Recent recommendations for otherwise healthy dogs undergoing elective procedures are to allow water up to two hours prior to induction, and a light meal three to four hours before induction.²⁹ While no feline studies are available to provide specific protocols, similar recommendations are reasonable.

Kittens

No studies provide good evidence for the most appropriate preoperative fasting times for kittens. Similar to current recommendation for adult animals, many clinicians provide a small morning feed three to four hours prior to anesthesia to decrease the risk of hypoglycemia.³⁰ Checking blood glucose concentration at induction and intermittently during a procedure and treating as needed may be recommended for very young kittens, especially for longer procedures.

Diabetic cats

Where possible, surgery should be delayed until the cat’s diabetic state is stable and reasonably well controlled with insulin. While surgery itself is not a greater risk for a well-controlled diabetic patient than for a healthy animal, the preoperative fast and the anesthetic drugs may cause problems, as can stresses which cause release of counter-regulatory (diabetogenic) hormones promoting insulin resistance and ketogenesis.³¹ Even short hypoglycemic episodes may cause brain damage and hyperglycemia can cause an osmotic diuresis.¹¹

Various different options are available for diabetic cats (Chapter 2); ultimately, careful monitoring of blood glucose is essential in all cases. One option is to provide food and insulin in the morning as normal and anesthetize in the afternoon. Otherwise, insulin should be administered in the morning, but if the cat will not be fed, the insulin dose should be adjusted³¹ as recommended in Table 6-3.

During anesthesia the cat’s blood glucose concentrations should be monitored every 30 to 60 minutes and dextrose administered to maintain a blood glucose concentration between 8.5 and 14 mmol/L. If the cat’s blood glucose remains persistently above 17 mmol/L, regular crystalline insulin may be administered at 20% of the cat’s normal dose. The following day, the usual schedule can be maintained unless the cat is not eating. If that occurs, it may be necessary to use intravenous dextrose and subcutaneous regular crystalline insulin (every six to eight hours) until the cat is eating regularly.