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Distributive shock is defined as a maldistribution of blood flow, most commonly due to altered systemic vascular resistance (SVR). Decreased SVR is the most common SVR alteration, and vasodilatory shock secondary to sepsis is one of the most readily recognized forms of distributive shock. Distributive shock can also be secondary to obstructive disease processes, such as gastric dilation and volvulus, pericardial effusion, and neoplasia causing vascular obstruction (such as adrenal tumors with invasion into the vena cava) [25]. The clinical signs of distributive shock in dogs are often very different from other forms of shock. In dogs, the mucous membranes are often bright pink (Figure 1.5), CRT is decreased (< 2 seconds), and peripheral pulses can be bounding or more prominent than normal. Cats with septic shock generally do not demonstrate the hyperdynamic signs seen in dogs and instead have pale mucous membranes, bradycardia, and decreased rectal temperature [60].

Many patients with distributive shock also have a component of hypovolemic shock (absolute or relative), so fluid therapy to correct intravascular volume deficit is essential. In humans with severe sepsis and septic shock, early goal‐directed therapy is shown to improve patient outcome when compared to traditional management strategies. In two landmark human studies, hemodynamic parameters such as direct arterial blood pressure, CVP, and S_CVO2 measurement, and treatment with crystalloids, colloids, pRBC, and catecholamines to improve cardiac contractility and/or vasomotor tone were used until prescribed endpoints were achieved [61, 62]. Standardized goal‐directed therapy does not yet exist for veterinary patients, therefore, normalization of routinely monitored cardiovascular and perfusion parameters, including heart rate and rhythm, rectal temperature, mucous membrane color and CRT, blood pressure, CVP, PCV/TS, lactate and base deficit are recommended [31, 63, 64].

Figure 1.5 Bright pink mucous membranes in a dog with septic peritonitis.

When fluid therapy fails to normalize hemodynamic parameters, particularly blood pressure in septic patients, vasoactive catecholamines may be necessary [65, 66]. Commonly used vasoactive catecholamines used in critical care are dopamine, dobutamine, and norepinephrine (Table 1.1). Vasopressin, also known as antidiuretic hormone, is a peptide synthesized in the pituitary that binds vasopressin specific receptors on vascular smooth muscle. Vasopressin stores can become depleted with prolonged shock or sepsis resulting in vasoplegia despite intravenous fluid and vasoactive catecholamine therapy. Vasopressin deficiency has been documented in people with refractory hypotension, and positive benefit has been shown with the addition of intravenous administration of vasopressin. Experience with vasopressin is growing in veterinary medicine [67, 68].

Early administration of broad‐spectrum antibiotics has been shown to improve survival in human patients with sepsis and septic shock when combined with early goal‐directed therapy. When antibiotics were given within one hour of triage in combination with early goal‐directed therapy, mortality decreased from 33.3% to 19.5% [69]. In veterinary patients with septic shock, antimicrobials should be given as soon as reasonably possible, especially for those that will undergo emergency anesthesia and surgery. In critically ill septic patients anticipated to undergo surgery, 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).