Anaesthesia and analgesia for the collapsed patient

• Approach to the collapsed patient

  Most of the time you don’t have a definitive diagnosis for the problem.

  Many sedative drugs and anaesthetic can make things worse.

  But oxygen always works.

  Often general anaesthetic is safer than heavy sedation as it ensures a secured airway (ET tube).
• What’s the difference between hypoxaemia and hypoxia

  Hypoxia is low oxygen levels in the tissues and hypoxaemia is low oxygen levels in the blood. Hypoxia is often caused by hypoxaemia but not always. You can be hypoxaemia and vice versa.
• Hypoxaemia categories

  Hypoxic hypoxia - not enough oxygen available to lungs. Low FiO2, hypoventilation, pulmonary disease, BOAS, PDA, fibrosis.

  Anaemic hypoxia - reduced haemoglobin content, e.g. IMHA and haemorrhage.

  Circulatory hypoxia - cardiovascular impairment e.g. Hypovolaemic, septic shock, PTE, DCM and systolic failure.

  Histotoxic hypoxia - cells can’t use the oxygen, e.g. mitochondrial problem, cyanide.
• What devices can help you with the diagnosis of hypoxaemia?

  Pulse oximeter, & or blood gas analyser.

  Visual observation of mucous membrane colour (not very accurate).

  If below 93% then need to do something additional.
• Treating animals with low SPO2

  Provide oxygen enriched environment (mask, flow by, nasal tube, oxygen cage, incubator).

  Is suction of the airway/mouth necessary? Are ‘drying agent’ indicated?

  Ensure patient does not overheat.

  Consider low dose sedation if patient is agitated too (midazolam 0.3 to 0.5mg/kg and butorphanol 0.2 to 0.3mg/kg).

  Consider analgesia if patient is in pain.

  Be prepared to induce anaesthesia and intubate the trachea.
• Dogs receiving oxygen by flow by.

  This is modestly enriches the FiO2, but only 25-40% if high oxygen flow rates are used (2-3L/min).

  Often not well tolerated at all.

  Can further contribute to anxiety.
• Dogs receiving oxygen via mask.

  Simple, but may not be well tolerated in anxious patients.

  The FiO2 varies depending on how tightly fitting the face mask is and the flow rate.

  Hither oxygen flow rates achieve and FiO2 of 35% to 60%.

  Rebreathing of carbon dioxide can occur with tightly fitting masks, and periodically switching out the mask is recommended.
• Oxygen cages

  Pros and cons:

  • Physical separation of the clinical team from the patient.
  • Reduces anxiety.
  • Disadvantage is this approach may miss changes in the animal (not as closely monitored).
  • Expensive.
  • Patients can overheat.
• Nasal lines

  Dual line enable flow to be reduced improving comfort.

  1 line achieves FiO2 30-50%

  2 line achieves FiO2 30-70%

  Can be placed under minor sedation.
• Premedication/ sedation in the collapsed patient

  As animals become more compromised so avoid:

  • NSAIDs
  • Alpha 2 agonists
  • Acepromazine

  Communicate the risk to the owner.

  Oxygen and IV acces

  Analgesia

  Pre calculate IV fluid rescuscitaion/ challenges.

  Opioids:

  • Methadone (IM or slow IV)
  • Fentanyl (very potent short acting opioid, tends not to be available in first opinion).
  • Consider lidocaine bolus then CRI (constant rate infusion).
• Fluid resuscitation prior to anaesthesia

  Assess patient and where possible commence IVFT to improve haemodynamic status.

  Hypotensive resuscitation? (not CPR - resuscitating fluid volume)
• induction of anaesthesia in the collapsed patient

  As animals become more compromised always continue to administer oxygen during induction.

  Administer drugs slowly as vein to brain time has increased with low cardiac outputs.

  Option:

  • Propofol or Alfaxalone (low end of dose range).
  • Propofol or Alfaxalone then benzodiazepine then more propofol or Alfaxalone.
  • Ketamine and benzodiazipine.
• Maintenance of the collapsed patient

  Measure ET tubes, reduce dead space, inflate cuff with care, secure well (tie to patient).

  Use lowest % of sevoflurane or isoflurane.

  Supplemenet with CRI.

  Use local anaesthesia where possible (topical, PNB, into abdomen or thorax, wounds, incisions).

  Aim to reduce MAC of volatile.