Oertzenweg 19 b
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History and signalment:
This patient was a 8-year-old mare (~700 kg) with colon obstruction exhibiting signs of severe abdominal pain nonresponsive to analgesic therapy (sweating, restlessness, distension of the abdomen, bright red gums, capillary refilling time 4 s, pulse 60bpm, hematocrit 0.44 l/l, total protein: 66 g/l).
Before and after the infusion venous blood was taken. The acid-base parameters included electrolytes and protein were determined within 30 min and the Stewart-variables (Strong ion difference=SID and Acid total=Atot) were calculated (Tab.1).
Tab.1: Equations for calculation of the Stewart-variables
1 Serum-[SID4] mmol/l = ([Na] + [K]) - ([Cl] + [Lactate]) mmol/l
2 Serum-[Atot] mmol/l = (0.225 x [Albumin] g/l + 0.14 x [Globulin] g/l) + 1.828 x [Phosphate] mmol/l
Therapy: focussed on infusion
Before surgery the mare was degassed and received 5 L isotonic sodium-chloride solution ([SID4]=0mmol/l, [Atot]=0mmol/l) and 1 L sodium-bicarbonate solution (4.2%, [SID4]=500mmol/l, [Atot]=0mmol/l) within 45 min for stabilization. By surgery the cause of this colic was found (Retroflexio coli) and the colon was replaced.
Discussion about the acid-base status:
Before fluid therapy the patient showed a metabolic acidosis caused by hyperlactemia and increased unmeasured organic ions .Therefore after infusion the hyperlactemic acidosis was decreased (increased [SID4] and decreased lactate compared to before), but a mild alkalosis was induced that results in a corrected blood pH. This fact is hidden by observation with the traditional Henderson-Hasselbalch model.
In order to determine the cause of metabolic acidosis and alkalosis (aetiopathogenesis) the Stewart parameters [SID] and [Atot] are necessary which show the relationship between electrolytes, proteins and acid-base status. Therefore the SID- and Atot concentrations of the plama as well as of infusion solutions must be considered to administer an effective fluid therapy.