Complications in Equine Surgery. Группа авторов

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Complications in Equine Surgery - Группа авторов


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hematocrit values can be influenced by splenic contractions and low protein concentrations can be due to primary hypoproteinemia rather than overhydration. Urine output is a good marker for hydration status. When adequate urine output (min, 1 mL/kg/h, approx. 500 mL/h or 12 L/day for a 500 kg horse) occurs after initiation of fluid therapy and urine specific gravity returns to normal (reference range 1,020–1,040), dehydration is likely resolved and fluid rates should be reduced to cover maintenance and ongoing losses. Repeated weighing of the patient as an objective determination of adequate fluid administered has limited value. For instance, horses with colitis may accumulate fluid in the colon, and gain weight rapidly while still being dehydrated. Continuous daily weight gain should alert for fluid overload in a horse with normal hydration status; however, severely dehydrated horses usually appropriately gain weight. Other techniques providing a more accurate estimation of fluid therapy include central venous pressure monitoring, bioimpedance analysis and pulse pressure variation [8–11]. These techniques are not routinely used in practice and are usually restricted to large referral or university hospitals.

       Diagnosis

Photo depicts frothy nasal discharge due to pulmonary edema from fluid overload in a horse.

       Treatment

      Once fluid overload is recognized, measures should aim at reducing the total amount of body fluid. Treatment options depend on severity of the case. If mild signs of pulmonary (mild tachypnea but no signs of respiratory distress or nasal discharge) or of cardiovascular impairment (mildly elevated heart rate but no overt signs of heart failure) are present and renal function is normal, the kidneys are likely to excrete the excessive amounts of fluid as long as no additional excessive fluid amount is administered.

Photo depicts ventral edema as a consequence of fluid overload in a horse. Photo depicts chemosis as a consequence of fluid overload in a horse.

       Discontinue or decrease administration of fluid, depending on whether the underlying clinical problem requires additional fluid therapy (e.g. electrolyte imbalances).

       Increase renal excretion of fluid: Furosemide 1–2 mg/kg IV as a bolus. In case of severe pulmonary edema, up to 4 mg/kg.

       Drain excessive fluid from pleural and peritoneal spaces if present.

       Reassess hydration status initially every 2–4 hours, later every 6–12 hours, using the clinical and laboratory parameters described above until hydration status is normal.

       Expected outcome

      The outcome depends on the inciting cause and underlying disease. If the inciting cause (such as inadvertent over‐administration to a healthy patient) can be resolved, prognosis is good. If renal failure is the cause for fluid overload, prognosis is poorer and guarded. Horses with pulmonary edema can die within a short period of time, or can recover fully depending on severity and initiation of treatment.

      Fluid therapy can lead to acid–base and electrolyte imbalances when given to a healthy animal, but also overcorrections of pre‐existing abnormalities can lead to severe side effects if not performed correctly. Sodium and potassium mainly, but also chloride, calcium, magnesium and phosphor homeostasis, are important.

      Many different crystalloid fluids are available commercially, containing varying concentrations of different electrolytes and base equivalents. Few formulations are currently available in 3–5 L bags, while 1 L bags usually are available but are often cost‐prohibitive and cumbersome to be administered to a normal sized horse. Depending on the country and legislation, these fluids differ slightly in their composition. Every clinic/hospital/practitioner should attempt to get an overview of formulations available in his/her country for administration to horses and should know content and concentrations including osmolality of the fluids.

      Replacement fluid therapy should be considered separately from maintenance fluid therapy, especially the type of fluid chosen. In general, replacement fluids (e.g. Lactated Ringer’s, isotonic saline, Normosol‐RTM, Plasmalyte ATM) are very close to serum concentrations for sodium, chloride and potassium, whereas maintenance fluids contain much lower amounts of sodium and chloride and higher amounts of potassium as well as other electrolytes and sometimes glucose (e.g. Normosol MTM).

      Sodium Imbalance

       Definition

       Increased (hypernatremia) or decreased (hyponatremia) blood sodium levels (reference range: 139–147 mmol/L)

       Acute (<24–48 h) and chronic (>40 h) conditions are recognized

       Risk factors

       Administration of intravenous sodium‐bicarbonate (hypernatremia)

       Administration of hypertonic saline (hypernatremia)

       Peritoneal lavage or colon lavage with water or low sodium fluids (hyponatremia)

       Reflux and diarrhea (usually hyponatremia)

       Renal disease, interfering with sodium excretion (usually hyponatremia, except if large amounts of sodium are administered when hypernatremia can occur)

       Small patients (neonates, ponies): these have a smaller margin of safety (both)

       Pre‐existing blood sodium abnormalities (both)


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