Equis ISSN 2398-2977

Muscle: myopathy - postanesthetic

Synonym(s): Postanesthetic muscle myopathy

Contributor(s): Keith Branson, Craig Johnson, Graham Munroe, Mark Senior, David Rendle

Introduction

  • First signs seen in the recovery period, but the damage occurs during the anesthetic procedure or during prolonged recumbency.
  • Signs:
    • Usually the muscle groups which were dependent during surgery, eg triceps after lateral recumbency or the gluteals after the horse has been in dorsal recumbency. Occasionally affects uppermost limbs, or generalized myopathy may occur.
    • In a myopathy case the affected muscles become hard, swollen and painful and this may result in anything from mild lameness to an inability to rise. Most commonly seen in fit, well-muscled, heavy horses and after prolonged anesthesia.
    • Neuropathy cases often do not exhibit any swelling just an inability to bear weight on one or more limbs.
  • Diagnosis: history and clinical signs and confirmed by the detection of high creatinine kinase (CK) values within a few hours of the end of anesthesia.
  • Prevention: maintaining adequate arterial blood pressure and by positioning in such a way as to minimize the pressure on dependent areas and the restriction of venous outflow.
  • Treatment: symptomatic, with non-steroidal anti-inflammatories (NSAIDs) and opiates to reduce the pain, and in severe cases diuresis using intravenous crystalloids.
  • See also Anesthesia: peri-operative complications - post-operative myopathy Anesthesia: peri-operative complications - post-operative myopathy.

Pathogenesis

Etiology

Predisposing factors

General

  • Heavy individual.
  • Prolonged anesthetic procedure (>2.5 h).

Specific

Pathophysiology

  • Pressure on compartmentalized muscle groups → compromised circulation → hypoxia of tissues → ischemia.
  • Hypotension Anesthesia: monitoring - cardiac output and blood pressure → decreased tissue perfusion → hypoxic muscle damage.
  • Hypotension Anesthesia: monitoring - cardiac output and blood pressure and increased intracompartmental pressure → ischemia → hypoxia → swelling of muscle cells → further increase in intracompartmental pressure may → affects on nerve transmission → neuropathy.
  • Necrotizing myositis may follow severe damage → bacterial infection → gas production (anaerobic) + liquefactive necrosis of muscle tissue.
  • Muscles most commonly affected:
    • Lateral recumbency:
      • Triceps brachii.
      • Pectoral.
      • Quadriceps femoris.
      • Hindlimb extensor muscles.
      • Masseter.
      • Flank muscles.
    • Dorsal recumbency:
      • Gluteals.
      • Longissimus dorsi.
      • Vastus lateralis.
      • Hindlimb adductor muscles.
  • Generalized myopathy (rare) resembles malignant hypothermia → myoglobinuria, renal nephrosis, shock and may → death. Signs are often evident before the end of anesthesia and may be caused by the anesthetic agent itself.

Timecourse

  • May be seen as soon as the horse begins to regain consciousness.
  • Occasionally takes several hours to develop.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Dugdale A H A, Obhrai J & Cripps P J (2016) Twenty years later: a single-centre, repeat retrospective analysis of equine perioperative mortality and investigation of recovery quality. Vet Anes & Analg 43, 171-178 PubMed.
  • Ragle C, Baetge C, Yiannikouris S, Dunigan D & Schneider R (2011) Development of equine post-anaesthetic myelopathy: Thirty cases (1979-2010). Equine Vet Educ 23 (12), 630-635 VetMedResource.
  • Johnson C B (1993) Positioning the anesthetized horse. Equine Vet Educ 5 (1), 57-60 WileyOnline.
  • Peek M L (1993) A case of post-anesthetic myopathy. Equine Vet Educ 5 (4), 183-186 WileyOnline.
  • Klein L (1990) Anesthetic complications in the horse. Vet Clin North Am Equine Pract 6 (3), 684-686 PubMed.
  • Young S (1989) Post-anesthetic myopathy. Equine Vet Educ 5 (4), 200-203 WileyOnline.
  • Dyson S, Taylor P & Whitwell K (1988) Femoral nerve paralysis after general anesthesia. Equine Vet 20 (5), 376-380 PubMed.

Other sources of information

  • Baxter G M & Turner A S (2002) Myopathy associated with prolonged recumbency or general anaesthesia. In: Adams Lameness in Horses. Ed: Stashak T D. Lippincott. pp 452-453. ISBN 0-7817-4195-5.
  • Pascoe P J (1990) Postanesthetic lameness. In: Current Practice of Equine Surgery. Eds: White N A & Moore J N. Lippincott. pp 115-120. ISBN: 0-397-50937-5.


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