Manual of Equine Anesthesia and Analgesia. Группа авторов

it only comprises 50–60% of the total protein content of plasma.

       The oncotic effect of albumin is enhanced by its ability, due to its negative charge, to attract cations, particularly Na+.This is termed the Gibbs‐Donnan effect.

        Albumin is the smallest plasma protein in molecular weight (~66 kDa).

       Albumin binds water, ions, fatty acids, hormones, bilirubin, and therapeutic compounds.

       It is synthetized by the liver and has a plasma half‐life of approximately 19 days in the horse.

       Albumin is classified as a negative acute phase reactant because its production is down‐regulated during inflammation.

       Hypoalbuminemia can result from:

       Increased loss (most common cause).Gastrointestinal (GI) (e.g., bacterial‐induced colitis).Vasculitis, peritonitis, and pleuritis.Renal – due to glomerular disease.

       Reduced synthesis.End‐stage or diffuse liver disease.Chronic inflammation.

       Excessive catabolismMost likely due to starvation.Plasma proteins are a rapid source of replacement for tissue proteins.

       Low dietary protein intake.

       Hypoalbuminemia may result in edema depending on the severity of albumin loss and rapidity of onset.

      B Globulins

       The reference range is 2.1–3.2 g/dl.

       The globulin fraction of plasma proteins comprises dozens of proteins including:Carrier proteins.Complement.Immunoglobulins (IgGs).Enzymes.

       Includes α, β, and γ globulins, from smallest to largest.

       Globulins are large molecules (~90–150 kDa) in comparison to albumin.

       Reference range for α1 is 0.1–0.2 g/dl and for α2 is 0.6–0.8 g/dl.

       Reference range for β1 is 0.3–0.8 g/dl and for β2 is 0.2–0.9 g/dl.

       Reference range for γ is 0.5–1.3 g/dl.

       α and β globulins are synthetized in the liver.

       γ globulins are synthetized in lymphoid tissue by plasma cells.

       γ globulins are a major class of IgG.

       Hyperglobulinemia

       Is associated with chronic disease, such as the presence of as an abscess, intestinal parasites, or a tumor.

       Hypoglobulinemia

       Malnutrition can result in a decrease in total globulins due to decreased synthesis.

       In rare cases, a congenital immune deficiency might be the cause of hypoglobulinemia.

C Fibrinogen

       Fibrinogen is an important soluble glycoprotein that is synthetized by the liver.

       It is a plasma clotting factor precursor which is converted to fibrin on contact with a sticky surface.The fibrin threads formed in this way trap platelets to form the primary platelet clot on which a stable blood clot is formed by the process of coagulation.

       Fibrinogen is a positive acute phase reactant, and it can be used to diagnose and monitor inflammatory conditions.

       Reference range is 2–4 g/l.

       Plasma fibrinogen concentrations can increase up to 10‐fold in an inflammatory process.The half‐life of fibrinogen is ~three days.

       Foals may have increased concentrations up to six months of age.

       Pregnant mares may have increases of up to 40%, and fibrinogen may further increase in the immediate postpartum period, before returning to normal in about two weeks post‐foaling.

      IV Lactate

       Hyperlactatemia (>2 mmol/l)Type AIs due to inadequate tissue perfusion and oxygen depletion.e.g. hypovolemia, septic shock, anemia.Type BIs associated with increased lactate production in patients with underlying diseases, but with normal tissue perfusion.Type B1Is associated with sepsis, neoplasia, endocrine disease, hepatic disease, and renal failure.Type B2Is associated with a number of toxins and pharmaceuticals.e.g. salicylates, epinephrine, norepinephrine, bicarbonate.Type B3Results from genetic metabolic abnormalities.e.g. glycogen storage disease.

       L‐lactateIt is produced by mammalian cells, and can be used as a marker of hypoxia or decreased tissue perfusion.It is the form of lactate measured by POC analyzers.In colic cases, a high lactate concentration in blood and peritoneal fluid is indicative of a surgical lesion.In horses with colic, increases in L‐lactate concentrations in the peritoneal fluid and plasma are associated with intestinal ischemia and increased mortality.L‐lactate measurement has potential application for diagnosis, monitoring, and prognostication.

       D‐lactate (not routinely measured)It is a stereoisomer of mammalian L‐lactate.It is not produced by mammalian cells.Rather, it is product of bacterial fermentation.D‐lactate is not metabolized in mammals.D‐lactate produced in the gut can be measured unchanged in peripheral blood.D‐lactate concentrations in the blood may increase in patients with intestinal ischemia.In colic cases, plasma D‐lactate is poorly correlated with plasma L‐lactate.On the other hand, peritoneal D‐lactate concentration has a strong correlation with peritoneal L‐lactate.Furthermore, peritoneal fluid D‐lactate is highly sensitive in detecting horses with strangulating obstructions of the intestine.

Suggested Reading

      1 DeNotta, S. and Divers, T. (2020). Clinical pathology in the adult sick horse: the gastrointestinal system and liver. Vet. Clin. North Am. Equine. Pract. 36: 105–120.

      2 Lester, S., Mollat, W., and Bryant, J. (2015). Overview of clinical pathology and the horse. Vet. Clin. North Am. Equine. Pract. 31: 247–268.

      3 Newman, A. (2020). Practical tips on sample handling for hematology, chemistry, and cytology testing for equine patients: getting more bang for your buck. Vet. Clin. North Am. Equine. Pract. 36: 1–14.

      4 Tennet‐Brown, B. (2012). Interpreting lactate measurement in critically ill horses: diagnosis, treatment, and prognosis. Compend. Contin. Educ. Vet. 34: E2.

      3

       The Cardiovascular System: Physiology of the Cardiovascular System

       Tamara Grubb

       The cardiovascular system consists of three components (heart, vessels, blood/plasma) whose ultimate goal is to work in concert with the respiratory system to deliver oxygen to the working cells.

       Tissue oxygen delivery (DO2) is determined by both the volume of blood pumped to the cells (cardiac output or “Q”) and the oxygen content of the blood (CaO2).

       Anesthetic drugs can drastically alter cardiovascular function and have a global impact on organ function via decreased DO2.

      I Anatomy

      A Chambers

       The equine heart is a typical mammalian heart with four chambers: two atria and two ventricles.