perioperative first‐ and second‐generation cephalosporins likely do not provide adequate antimicrobial coverage and should not be used in favor of more broad‐spectrum medications. In the absence of confirmatory culture and sensitivity testing, broad‐spectrum therapy should be used until a diagnostic culture result is obtained and antimicrobial therapy can be de‐escalated. Intravenous administration is preferred in all cardiovascularly unstable and critically ill patients as oral, intramuscular, and subcutaneous absorption may not be predictable. Antibiotics that can be considered for first‐line broad‐spectrum therapy include ampicillin and clavulanate (Unasyn®, Pfizer, 22–30 mg/kg IV every 8 hours); ampicillin (18–22 mg/kg IV every 8 hours) combined with enrofloxacin (10–15 mg/kg IV every 24 hours), cefoxitin (30 mg/kg IV every 6 hours), and clindamycin (10 mg/kg IV every 12 hours) combined with cefotaxime (40–50 mg/kg IV every 6 hours), or ceftazidime (30–50 mg/kg IV every 6–8 hours with dosing at the lower end of the range for cats and higher end for dogs).
Metabolic Shock
Metabolic shock is defined as dysfunction of cellular metabolism, which generally occurs in the face of adequate perfusion and oxygenation. Examples include severe pH derangements, hypoglycemia, adrenal insufficiency, and certain toxicities such as cyanide. The clinical signs seen with metabolic shock closely resemble those in hypovolemic shock and are related to the underlying etiology. Mental depression is the most universally recognized sign of metabolic shock. The same diagnostics used for patients in hypovolemic shock are indicated for the patient in metabolic shock. Treatment may include correction of acid–base derangements with IV fluids and/or bicarbonate, dextrose supplementation, and steroid administration, if adrenal dysfunction is demonstrated or highly suspected [70–74].
Dehydration
The management of hypovolemic shock focuses on restoration of intravascular volume for improvement in cardiovascular function, rather than normalization of hydration. Dehydration is a reflection of interstitial fluid balance, and while imperative to assess, treat, and monitor for improvement, treating hypovolemic shock must take priority. Interstitial fluid losses are generally gradual and are therefore corrected over time. Prolonged or severe dehydration can lead to hypovolemic shock. The percentage of dehydration (5–12%) is estimate based on physical exam (skin turgor, sunken eyes, urine output) and objective criteria, such as PCV/TS, loss of body weight, and urine specific gravity. The fluid deficit is determined using the percentage of dehydration and the patient's lean body weight. Estimation of lean body weight is imperative when determining the fluid prescription for obese patients, especially cats, as significant overhydration can result if overweight or obese body weight is used. The deficit is then corrected over a period of 12–48 hours depending on chronicity, patient's tolerance to fluid therapy, maintenance fluid needs, and any continuing fluid losses (Box 1.2). In small animal patients, maintenance fluid rates are generally 2–3 ml/kg/hour in dogs and 1–2 ml/kg/hour in cats [75].
Table 1.1 Commonly used vasopressors used in the emergency room and intensive care unit.
Source: Adapted from Simmons and Wohl [65]. CRI = constant rate infusion.
| CRI dose | Effect | Additional information | |
|---|---|---|---|
| Dopamine | 1–4 μg/kg/minute | Vasodilation (renal) | Mixed data for renal effects |
| 5–10 μg/kg/minute | Increased contractility, some vasoconstriction | ||
| 10–20 μg/kg/minute | Vasoconstriction, variable contractility effects | ||
| Dobutamine | 2–20 μg/kg/minute (dogs) | Increased contractility, little vasoconstriction | |
| 2–5 μg/kg/minute (cats) | Increased contractility, little vasoconstriction | Can cause seizures in cats | |
| Norepinephrine | 0.05–2 μg/kg/minute | Potent vasoconstriction | |
| Vasopressin | 0.5–2 mU/kg/minute (dogs) | Potent vasoconstriction (even in acidosis) | Limited clinical experience in dogs, no dose established for cats |
Box 1.2 Fluid Therapy Prescription Formula
This formula incorporates fluid deficit (dehydration), ongoing losses, and maintenance fluid needs. It should be used only after intravascular volume deficits (hypovolemic shock) have been corrected.
Rate of deficit correction is generally over 12–36 hours depending on patient stability, chronicity of dehydration, and tolerance for IV fluids.
Maintenance needs are generally 2–3 ml/kg/hour for dogs and 1–2 ml/kg/hour for cats.
Example Fluid Prescription Calculation
25 kg mixed breed dog (lean body condition)
Estimated to be 8% dehydrated based on physical exam findings (tacky mucous membranes, prolonged skin tent, slightly sunken globes, hyperviscous saliva in the corner of the mouth).
No conditions that would make the patient fluid intolerant; plan to correct over 24 hours.
The dog is losing approximately 60 ml in vomit every hour, no excessive gastrointestinal or urinary losses.
Deficit = 0.08 × 25
Deficit = 2000 ml
Rate of deficit correction = 2000/24 = 83 ml/hour
Fluid prescription (per hour) = 83 ml (deficit) + 60 ml (losses) + 50 ml (maintenance)
Fluid prescription = 193 ml/hour
Electrolyte monitoring should be performed routinely (Table 1.2) in patients with dehydration and shock. This is particularly true in anorexic patients or those with renal dysfunction, which may require supplementation with potassium and/or phosphorus. Additionally, as many fluids used in veterinary medicine are designed as “replacement” and not “maintenance” fluids, sodium values may increase in patients receiving prolonged intravenous fluid therapy, particularly in patients with continued free water loss, such as renal, gastrointestinal, skin, and respiratory loss. Fluids with lower sodium concentrations such as Normosol‐M, 0.45% NaCl, and dextrose 5% in water (D5W) may be necessary to prevent or manage hypernatremia associated with prolonged fluid therapy and/or concurrent hypotonic fluid losses.
Table 1.2 Monitoring parameter guidelines and frequencies for