Hypotension

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Hypotension in dogs is a relatively rare circulatory disorder characterized by arterial blood pressure < 90 mm Hg[1].

This disorder is frequently associated with general anesthesia, cardiac abnormalities such as ventricular fibrillation, sepsis[2] or shock.

In dogs, volatile anesthetics (e.g. isoflurane) decrease myocardial contractility and cardiac output, which results in dose-dependent hypotension[3] which is not counteracted by administering intravenous isotonic fluids in dogs anesthetized at a surgical depth of anesthesia, even under conditions of surgical stimulation[4][5].

However, unlike arterial blood pressure, cardiac output can be positively influenced by administering intravenous fluid. By increasing circulating volume and therefore venous return (preload), it is possible to increase stroke volume, which contributes significantly to changes in cardiac output[6].

Therefore, intravenous fluid therapy is often recommended in anesthetized hypotensive patients to increase blood pressure since hypovolemia may be the cause of the hypotension and volume replacement will therefore benefit the patient.

Intravenous isotonic crystalloids fluids is recommended in most cases[7].

Drugs which counteract hypotension in dogs include dopamine, vasopressin and ephedrine[8].

References

  1. Valverde A et al (2012) Effects of high-volume, rapid-fluid therapy on cardiovascular function and hematological values during isoflurane-induced hypotension in healthy dogs. Can J Vet Res 76(2):99-108
  2. Conti-Patara A et al (2012) Changes in tissue perfusion parameters in dogs with severe sepsis/septic shock in response to goal-directed hemodynamic optimization at admission to ICU and the relation to outcome. J Vet Emerg Crit Care (San Antonio) 22(4):409-418
  3. Kazama T & Ikeda K (1988) The comparative cardiovascular effects of sevoflurane with halothane and isoflurane. J Anesth 2:63–68
  4. Aarnes TK et al (2009) 3rd Effect of intravenous administration of lactated Ringer’s solution or hetastarch for the treatment of isoflurane-induced hypotension in dogs. Am J Vet Res 70:1345–1353
  5. Hauptman JG et al (2000) Effects of anesthesia, surgery, and intravenous administration of fluids on plasma antidiuretic hormone concentrations in healthy dogs. Am J Vet Res 61:1273–1276
  6. Reuter DA et al (2002) Stroke volume variations for assessment of cardiac responsiveness to volume loading in mechanically ventilated patients after cardiac surgery. Intensive Care Med 28:392–398
  7. Silverstein DC et al (2012) Effectiveness of intravenous fluid resuscitation in the emergency room for treatment of hypotension in dogs: 35 cases (2000-2010). J Vet Emerg Crit Care (San Antonio) 22(6):666-673
  8. Sinclair MD & Dyson DH (2012) The impact of acepromazine on the efficacy of crystalloid, dextran or ephedrine treatment in hypotensive dogs under isoflurane anesthesia. Vet Anaesth Analg 39(6):563-573
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