Читать книгу Small Animal Surgical Emergencies - Группа авторов - Страница 137

The ultimate goal of stabilizing any patient with major body system abnormalities is maximizing oxygen delivery. The total oxygen delivery depends on both cardiac output and the oxygen content of the arterial blood (CaO₂), and compromise of either will contribute to tissue hypoxia. Initial treatment for hypovolemia includes rapid intravenous fluid replacement to optimize preload and cardiac output, and initial oxygen therapy to maximize blood oxygen content. Before volume resuscitation, the patient's heart and lungs should be ausculted critically to rule out any primary cardiac abnormality that could be contributing to the shock state (cardiogenic shock). At the time of intravenous catheter placement and before fluid administration, blood samples for an emergency database should be obtained, including packed cell volume (PCV) and total solids, blood glucose concentration, blood lactate concentration, and arterial or venous blood gas with electrolytes, blood urea nitrogen (BUN), and creatinine. A full diagnostic panel including complete blood count, serum biochemical profile, and urinalysis should also be performed as early as possible to aid in identification of comorbid conditions and organ dysfunction(s), as well as to direct additional diagnostics. In addition, coagulation testing and a blood smear (or complete blood count) for platelet estimate are indicated before taking a patient to surgery.

Replacement fluid options for volume expansion include isotonic crystalloid solutions (0.9% saline; lactated Ringer's solution; Plasma‐Lyte A, Baxter Healthcare Ltd; Normosol‐R, Hospira, Inc.; hypertonic crystalloid solution; 7–7.5% saline; colloids e.g., hetastarch), blood and plasma products. The initial choice of fluid type depends largely on the cause of hypovolemia, as well as concurrent disease processes, patient electrolyte status, and coagulation status. In the emergent situation, shock doses of isotonic crystalloids can be administered as intravenous boluses. The total shock dose for a dog is approximately equal to one blood volume, or 90 ml/kg body weight, with the shock dose for a cat being approximately 40–60 ml/kg body weight. One‐quarter of the total shock dose (20–25 ml/kg for dogs, 10–15 ml/kg for cats) may be administered over approximately 15 minutes, with repeated assessment of the patient's perfusion parameters. Once there is improvement and/or normalization of heart rate, pulse quality, mucous membrane color, and capillary refill time, fluid rates can be tapered accordingly.

Blood products including whole blood and packed red blood cells may be indicated in cases of acute hemorrhage, and/or when the hematocrit is below 20%, as there is inadequate oxygen delivery because of decreased oxygen‐carrying capacity. It is important to also recognize that dogs and cats can exsanguinate with a normal hematocrit. Furthermore, in acute hemorrhage, the hematocrit may in fact be normal and a decrease in total solids may be apparent first. With this in mind, early clinical identification of large volume blood loss, coupled with early intervention, is critical. This is especially relevant in patients with acute abdomen secondary to a bleeding abdominal mass or injured abdominal organ. In these patients, the source of hemorrhage must be identified and controlled while crystalloids and blood products are administered pre‐ and perioperatively as needed to maintain euvolemia and a hematocrit above 20%.

Hypertonic crystalloids can also be used for rapid intravascular volume expansion. Hypertonic crystalloid solutions (7–7.5% saline) are used to raise the intravascular concentration of sodium ions, which in turn draws water out of the interstitial space to increase intravascular fluid volume. Hypertonic saline should be administered slowly at a rate of not more than 1 ml/kg/minute for a total dose of 4 ml/kg. Administration of hypertonic saline should be followed with isotonic crystalloids to replace the interstitial volume as fluid shifts quickly into intracellular and interstitial spaces.

Stabilization of the patient in distributive shock also initially includes fluid resuscitation to optimize intravascular volume and oxygen supplementation. Fluid requirements are often very high owing to the vasodilation that may occur with severe systemic inflammation. Arterial blood pressure monitoring is helpful for guiding early goal‐directed fluid therapy. Even after appropriate fluid resuscitation, patients with distributive shock will often require circulatory support in the form of positive inotropes and/or pressor agents to increase cardiac output and/or blood pressure. If the source of distributive shock is infectious, identification and source control are critical. Early initiation of broad‐spectrum antimicrobial therapy is critical in all cases of suspected sepsis, in addition to taking necessary steps toward source identification and control (i.e., diagnostic abdominocentesis and abdominal exploratory surgery in cases of septic peritonitis).