Page 568 - Problem-Based Feline Medicine

560 PART 8 CAT WITH ABNORMAL LABORATORY DATA

– Pale mucus membranes and increased capillary ● Replacement fluids include lactated Ringer’s,
refill time (> 2 s). Normosol-R or Plasma-Lyte A.
– Cold extremities.
If ongoing maintenance fluids are required over several
– Anuria or oliguria (<1 ml/kg/h urine produced).
days because fluid intake is inadequate or there are con-
– Decreased central venous pressure (< 5 cmH O).
2 tinuing fluid losses, change to a maintenance fluid that
● Inadequate interstitial hydration is evident as tacky
resembles the amount of free water and electrolytes that
mucus membranes, skin tenting and sunken eyes.
would be consumed daily and are being lost.
Crystalloids can be used alone, but colloids and hyper- Maintenance solutions are hypotonic crystalloids that
tonic saline result in much more rapid restoration of are lower in sodium and chloride but higher in potas-
normal perfusion, because only small volumes need to sium concentration than plasma, such as Plasma-Lyte
be administered (3–5 ml/kg), and they act immediately 56, Normosol M, 0.45% NaCl with added potassium, or
to attract water into the vascular space. 0.45% NaCl with 2.5% dextrose and added potassium.
● When tissue perfusion is inadequate, for example ● Maintenance fluid rates are 70 ml/kg/day, but if
from severe dehydration or shock, crytalloids there are ongoing fluid losses from polyuria, diar-
administered alone can be infused at 40–55 rhea or vomiting, then calculate an additional
ml/kg/h for a total dose of 45–60 ml/kg to restore 5%/kg requirement (or 50 ml/kg/day), which is
circulating intravascular volume. This volume nearly equivalent to doubling the daily maintenance
should be reduced by 40–60% if colloids are rate. Fever can increase fluid requirements by
administered together with crytalloids. 15–20 ml/kg/day.
– In general, the patient should be reassessed after
Potassium is usually added to fluids at the following
1/4 to 1/3 is administered or after 15 min,
rates, and the infusion rate of the fluid is adjusted so the
because IV fluids administered too rapidly can
rate does not exceed 0.5 mmol (mEq)/kg/h.
cause pulmonary edema. Intravascular volume is
usually restored over the first 2 hours. Serum potassium Potassium
● If the electrolyte status of the patient is unknown, use concentration supplementation
a crystalloid most like plasma in sodium and potas- (mmol or mEq/L) to 1 L of IV fluids
sium content, pH and osmolality, such as lactated
>3.5 20 mEq
Ringer’s, Normosol-R or Plasma-Lyte A. These
30 mEq 3.0–3.5
have an alkalizing effect which is useful because
40 mEq 2.5–3.0
patients with reduced circulating blood volume are
60 mEq 2.0–2.5
usually acidotic. 0.9% NaCl can also be used.
80 mEq < 2.0
For hemodynamically stable patients with dehydra-
tion, fluid deficits are corrected over the first 12–24
Prognosis
hours, followed by maintenance fluid rates. Maintenance
rates of 70 ml/kg/day (3 ml/kg/h) are calculated, and The prognosis ultimately depends on the inciting con-
the dehydration fluid deficit is added to the mainten- dition, but acute dehydration treated with prompt and
ance figure. Dehydration fluid deficit is calculated by vigorous fluid therapy has an excellent prognosis.
the following formula: % dehydration × body weight
(kg) = fluid deficit (liters).
HYPERTHYROIDISM**
● For example, a 5 kg cat that is 10% dehydrated
requires 500 ml (0.1 × 5 L) to correct the fluid
Classical signs
deficit and 350 ml (70 × 5 ml) for maintenance,
which is 850 ml in the first 24 h, or 35 ml/h or 0.59 ● Weight loss despite polyphagia.
ml/min. Using a microdrip set with 60 drops per ml, ● Polyuria/polydipsia.
the infusion rate is 35 drops per minute (0.59 ml × ● Tachycardia, sometimes with a gallop
60 drops/ml), or just over one every 2 seconds. This rhythm.
rate may be increased in the first 4–6 h to correct ● Mild erythrocytosis in some cases.
the fluid deficit more rapidly.