Page 709 - Small Animal Clinical Nutrition 5th Edition

736 Small Animal Clinical Nutrition

body mass is a negative predictor of survival (Freeman and Abnormalities in electrolyte and magnesium homeostasis can
VetBooks.ir Roubenoff, 1994). Systems for accurately assessing and scoring cause or contribute to the progression or severity of cardiac dys-
rhythmias, and decreased myocardial contractility associated
body condition are available for dogs and cats (Chapter 1). The
body condition of dogs and cats with cardiovascular disease
with severe electrolyte abnormalities may cause profound heart
should be followed closely as part of reassessment. muscle weakness. Electrolyte and magnesium abnormalities
can also potentiate adverse effects from cardiac glycosides and
Laboratory and Other Clinical Information other cardiac drugs. Unfortunately, the precise diagnosis of
Measurement of Systemic Blood Pressure potassium and magnesium depletion can be difficult to make
Hypertension is often defined as that blood pressure two stan- because these are primarily intracellular constituents. Normal
dard deviations above the mean for the population (Littman serum potassium and magnesium concentrations can occur in
and Drobatz, 1995). Most investigators agree that the systemic the presence of total body depletion of these elements; there-
systolic/diastolic blood pressure in awake, untrained dogs and fore, serum potassium and magnesium concentrations do not
cats normally should not exceed 180/100 millimeters of mercu- always reflect total body stores.
ry (mm Hg), with values up to 200/110 mm Hg considered
borderline or mild hypertension (Littman and Drobatz, 1995), TAURINE
especially in cats. Plasma and whole blood taurine concentrations are routine-
Direct blood pressure measurement is obtained by inserting ly measured to evaluate the taurine status of cats and dogs.
a needle or catheter into an artery. The needle or catheter is Most early experimental and clinical studies used plasma tau-
connected to a pressure transducer and the result displayed on rine concentration to define taurine status. Values for plasma
an oscilloscope/recording device. Anxiety and pain may falsely taurine of less than 20 to 30 nmol/ml (µmol/l) have been asso-
elevate the blood pressure of awake, restrained or uncooperative ciated with deficiency in clinical studies involving client-owned
patients when measured by direct techniques. cats (Pion et al, 1987; Sisson et al, 1991) and dogs (Kramer et
Indirect blood pressure measurement is noninvasive and al, 1995).
obtained with a cuff constricting a peripheral artery (leg or tail). Studies involving laboratory cats have shown that plasma,
An ultrasonic, oscillometric or photoplethysmographic trans- but not whole blood taurine concentrations are affected by
ducer distal to the cuff is used to detect blood flow or arterial meals and food deprivation (Trautwein and Hayes, 1991; Pion
wall motion (Hansen, 1995). Blood pressure values obtained by et al, 1991). Therefore, whole blood taurine concentration is a
direct and indirect methods generally correlate well, but indi- more reliable index of taurine status in cats. In general, the
rect methods may produce values less than those obtained whole blood taurine pool is remarkably stable and declines only
simultaneously by direct methods. In general, blood pressure during prolonged depletion, whereas plasma taurine concentra-
measurements obtained routinely during hospital visits are rea- tions fluctuate acutely depending on availability in food. Cats
sonable estimates of a dog’s true blood pressure (Remillard et al, with whole blood taurine concentrations consistently less than
1991). Uncooperative, anxious patients may have elevated 150 nmol/ml should be considered taurine deficient (Pion et al,
blood pressure measurements in the hospital setting that do not 1989, 1991). Whole blood taurine concentrations have also
reflect normal values. A review of blood pressure measurements been adopted by the Association of American Feed Control
describes these techniques (Hansen, 1995). Comprehensive, Officials (AAFCO) as part of its feeding protocols for cats. To
current guidelines for the diagnosis and management of hyper- successfully complete an AAFCO feeding protocol, no individ-
tension have recently been published (Brown et al, 2007). ual cat, kitten or queen can have a whole blood taurine concen-
tration less than 200 nmol/ml (AAFCO, 2008).
Screening for Concomitant Disease Assessment of urinary taurine excretion has also been advo-
Cardiovascular disease is frequently associated with or exacerbat- cated as an alternative to measuring plasma or whole blood tau-
ed by underlying chronic renal disease in dogs and cats. All rine concentrations (Glass et al, 1992). Urinary taurine excretion
patients with cardiovascular disease should be screened for con- may provide vital information in the experimental setting for
comitant renal disease.This is best accomplished with a urinalysis proper formulation of feline foods, but this assessment is prob-
and a serum biochemistry profile, which includes urea nitrogen, ably not a practical technique for use with client-owned cats.
creatinine, electrolyte, calcium and phosphorus concentrations. In North America, several laboratories routinely perform
Hyperthyroidism in cats is a risk factor for secondary thyro- plasma and whole blood taurine assays. These laboratories are
toxic cardiomyopathy and systemic hypertension. Cats over the most easily accessed through regional veterinary reference lab-
age of seven years with evidence of cardiovascular disease oratories that perform routine diagnostic services.
should be screened for hyperthyroidism (Chapter 29).
CARNITINE
Measuring and Interpreting Tissue Nutrients and Many investigators have reported blood and tissue carnitine
Hormones concentrations in animals. The lowest levels are usually found
ELECTROLYTES AND MAGNESIUM in serum; in contrast, heart and skeletal muscle contain very
Serum electrolyte and magnesium concentrations are impor- high levels of carnitine, which underscores its importance in
tant factors to assess in patients with cardiovascular disease. these tissues. Normal canine and feline values are similar for