In order to recognize complications, anesthetists should have extensive knowledge about monitoring machines, anesthetic drugs, anesthesia machines, etc. Complications can be related to the respiratory system, cardiovascular systems, mechanical system, and human error. In Part I, complications due to respiratory and cardiovascular systems will be reviewed.

Respiratory Complications

Apnea

Possible causes

 Anesthetic drugs: Anesthetic drugs suppress respiration in a dose-dependent manner. Suppressed respiration can be seen during induction when a high dose of anesthetics is used.

 Recent hyperventilation: CO₂ is a driving gas for respiration. Therefore, if CO₂ is low due to recent hyperventilation, patients may stop breathing.

Treatments

 A life-threatening situation should be confirmed.

 If it is cardiac arrest, CPR should be initiated immediately.

 Patients should be intubated when possible to provide 100% O₂ and ventilation.

 If recent hyperventilation is the cause, decreasing respiratory rate and volume (either from manual or mechanical ventilation) should be done.

Airway Obstruction

Clinical signs

 Dyspnea

 Stridor

 Abdominal breathing

Possible causes

 Laryngeal/bronchial spasm (cat)

 Airway masses, edema, mucus blockage (anticholinergic use)

 Kinking of endotracheal tube

Treatments

 Use lidocaine prior to endotracheal intubation or bronchodilator (aminophylline) for spasm

 Remove the causes (i.e., suction mucous)

 Use armoured endotracheal tube

 Use ETCO₂ to monitor CO₂ wave form

Hypoventilation (PaCO₂ > 40 mm Hg)

Possible causes

 CNS depression due to anesthetic depth or anesthetic drugs

 Limited thoracic wall movement (pneumothorax, obesity, GDV, pregnancy)

 Traumatic injuries, upper airway obstruction, etc.

Treatments

 Correct the causes

 Provide ventilation (manually or mechanically)

Hypoxemia (PaO₂ < 60 mm Hg)

Possible causes

 Hypoventilation - see above

 Low inspired O₂ - mechanical error

 Ventilation perfusion mismatching or shunt

Treatments

 Correct the causes

 Provide 100% O₂

 Check anesthetic machine

 Correct hypoventilation

 Provide ventilation (manually or mechanically)

 Complete surgery as soon as possible

Cardiovascular Complications

Hypotension

Clinical signs

 Mean arterial blood pressure < 70 mm Hg

 Systolic blood pressure < 80 mm Hg

 Increased heart rate

 Prolonged CRT

 Weak pulses

Possible causes

 Anesthetic overdose or high dose of anesthetics

 Deep anesthetic depth

 Hypovolemia or blood loss

 Increased abdominal pressure (i.e., pregnancy, GDV, etc.)

 Vasodilation (premedication, etc.)

 Cardiac arrhythmia

Treatments

 Decrease anesthetics (i.e., isoflurane level)

 Lighten up anesthetic depth

 Administer fluid prior to and during anesthesia; use fluid boluses (5–20 ml/kg) or blood transfusion when PCV < ~ 20%

 Correct the causes for increased abdominal pressure or cardiac arrhythmia

 Administer positive inotropic drugs (i.e., dobutamine [1–10 μg/kg/min], dopamine [1–10 μg/kg/min])

Premature Ventricular Contraction (PVC)

Possible causes

 Anesthetics

 High CO₂ level

 Hypoxia

 High level of circulating catecholamine (i.e., due to excitement during induction)

 Underlying cardiac problems

Treatments

 Check anesthetic depth

 Minimize the use of arrhythmogenic agents (i.e., thiopental or α-2 agonists)

 Check PaO₂, PaCO₂ and provide ventilation as needed

 Provide good premedication to minimize excitement

 Treat PVCs with lidocaine 1–2 mg/kg IV if they are multifocal and they run multiple PVCs/min

Tachycardia

Possible causes

 Too light anesthetic plane

 Drugs (i.e., ketamine, anticholinergics, etc.)

 Pain

 CO₂ retention

 Hypotension

Treatments

 Increase anesthetic plane

 If it is due to drugs, monitor patients closely until drug effects subside

 Treat pain with opioids

 Check CO₂ level, if CO₂ is high increase respiratory rate and/or volume

 For hypotension, please see hypotension

Bradycardia

Possible causes

 Deep anesthetic plane

 High vagal tone

 Drugs (i.e., opioids, α-2 agonists, etc.)

Treatment

 Lighten anesthetic plane

 Administer anticholinergics (i.e., atropine 0.02–0.04 mg/kg) if high vagal tone or opioid use

 For α-2 agonist use, administer anticholinergics if bradycardia is accompanied with hypotension

References

1.  Seymour C, Duke-Novakovski T. BSAVA Manual of Canine and Feline Anaesthesia and Analgesia. 2nd ed. Gloucester, UK: British Small Animal Veterinary Association; 2007.

2.  Greene SA. Veterinary Anesthesia and Pain Management Secrets. Philadelphia, PA: Hanley & Belfus; 2002:1–43.