Anesthesia Complications and Prevention

• Anesthetic complications can be prevented through patient stabilization, appropriate drug selection, equipment preparation, patient support, and physiological monitoring
• Veterinary professionals should respond to changes before they become complications by monitoring patients
• Excessive anesthetic depth can lead to other complications
• Analgesia and premedication are critical for optimal anesthetic events

Anesthesia-Related Deaths

• Death can occur within 48 hours in small animals, or up to 7 days in horses
• In dogs, cats and rabbits, roughly 50% of postoperative deaths happen within 3 hours after anesthesia ends
• In horses, 92% of complications during recovery are neuromuscular or respiratory
• Additional complications like decreased renal/hepatic function, can occur weeks after anesthesia

Safety Checklists

• It is critical to confirm patient identity, procedure, and consent before anesthesia
• The surgical team must introduce themselves by name and role
• Patient name, consent, and procedure must be confirmed prior to induction
• IV cannulation is essential
• Airway equipment must be readily available and functional
• Endotracheal tube cuffs need to be checked
• Anesthetic machines should be checked daily
• Adequate oxygen supply is required for the procedure
• The breathing system should be connected, leak-free, with the APL valve open
• A designated person should monitor the patient
• Risks should be identified and communicated and emergency interventions readily available
• Patient name and procedure, depth of anesthesia and safety concerns must all be communicated before the procedure
• Safety concerns must be communicated during recovery
• Airway, breathing, circulation(fluid balance), body temperature, and pain levels need to be assessed
• An assessment and intervention plan needs to be confirmed
• An analgesic plan needs to be confirmed
• A person must be assigned to monitor the patient

Common Complications

• Hypoventilation
• Hypotension
• Hypothermia
• Hypoxemia
• CV complications
• Respiratory issues
• CNS issues
• Problems with anesthetic depth
• Issues with temperature regulation
• Dysphoric recovery
• Gastroesophageal Reflux (GER) that can lead to aspiration

Uncommon Complications

• Metabolic issues
• Neuromuscular issues
• Post-anesthesia cortical blindness

CV Complications

• Hypotension is defined as a MAP < 60 mmHg or <90 mmHg on Doppler
• It can be caused by drugs, the patient's physical status, or vasodilation
• Treatment includes decreasing depth, fluid therapy, vasopressors, or positive inotropes
• Severe decreases in BP reduce perfusion to the optic nerve and kidneys
• Can cause post-anesthetic blindness especially in cats
• Hypertension is defined as a MAP of > 150 mmHg
• Hypovolemia from hemorrhage causes an increased HR to compensate
• Can lead to cardiac arrest

Arrhythmias

• Treat if blood pressure is affected, but look for the underlying cause
• Can be Tachyarrhythmias vs. Bradyarrhythmias
• Can be Atrial vs. ventricular
• AV blocks (1st, 2nd, 3rd degree)
• Sinus arrhythmia may be normal in dogs, but abnormal in cats
• Often related to anesthetic drugs unless there is direct heart manipulation

Donkey Case Example

• An 8 year-old male donkey, weighing 150 kg and undergoing a castration, was given 1 mg/kg xylazine IV as premedication, was induced with IV thiopental at 5 mg/kg and intubated and placed on 2.5% Isoflurane in 100% O2
• The vitals were: pulse = 42 bpm, resp = 12 bpm, BP on Doppler = 80 mmHg (= low), rectal temp = 97°F, ETCO2 = 35 mmHg

Decision Tree for Hypotension

• Recognize hypotension
• Check anesthesia depth and other causes
• Assess heart rate
• Determine if anticholinergics are warranted
• Consider IVF bolus up to 2 times at 4.5ml/kg
• Give fluids safely at an hourly rate not exceeding 15 min
• Consider inotrope or vasopressor therapy
• Administer colloidal support (transfusion of blood products is also an option)
• Discontinue the anesthesia as soon as possible

Respiratory Complications

• Hypoventilation
• Apnea
• Tachypnea
• Dyspnea
• Ventilation to perfusion (V/Q) mismatch
• Atelectasis
• Airway obstruction
• Pulmonary embolism
• Hypoxemia
• Brachycephalic syndrome
• Pneumothorax/pneumomediastinum
• Tracheal tear
• Aspiration
• Acute Respiratory Distress Syndrome (ARDS)

Hypoventilation

• Defined as ETCO2 over 55 mmHg while under anesthesia
• Potentially caused by anesthetic drugs or excessive anesthetic depth, also due to other comorbidities
• May result in respiratory acidosis, hypoxemia, and raised intracranial pressure
• Check depth and adjust as appropriate, and provide IPPV; and reposition the patient, and check equipment

Hypoxemia

• Unlikely if intubated and on 100% O2, but can become life-threatening
• SpO2 of 95% = PaO2 of 80 mmHg
• SpO2 of 90% = PaO2 of 60 mmHg
• Patients can be hypoxemic without showing cyanosis
• Treatment involves checking O2 flow rate, ETT placement, and anesthesia machine, and giving IPPV, and adding PEEP
• Assess perfusion and offer cardiac support, and reposition the animal, and discontinue anesthesia if no improvement is seen with other interventions -Not always indicated (ex. Cat neuters)

Causes for Hypoxemia

• Hypoventilation
• V/Q mismatch
• Decreased FiO2
• Right-to-left shunt
• Diffusion impairment

Preoxygenation

• Is related to increasing oxygen supplementation
• Using an oxygen cage will get you aprox 40-50% oxygen, 10-12 l/min Suggested 02 flow rate
• Using a mask will get you aprox 40-50% oxygen, 2-5l/min Suggested 02 flow rate
• Using Hood will get you aprox 30-40% oxygen, 2-5l/min Suggested 02 flow rate
• Using Flow-by will get you aprox 30-40% oxygen, 2-10l/min Suggested 02 flow rate
• Using Nasal tube will get you aprox 30-50% oxygen, 50–100 ml/kg/min Suggested 02 flow rate
• Using Transtracheal will get you aprox 40-60% oxygen, 10–50 ml/kg/min Suggested 02 flow rate
• Using Endotracheal Tube circuit will get you aprox 100% oxygen, Dependent on anaesthetic circuit used

Goat Case Example

• A 1.5-year old castrated goat is waking up after a tube cystotomy
• They were premedicated with acepromazine and morphine, and induced with propofol and maintained with sevoflurane in 100% oxygen
• Surgery was uneventful
• The goat woke quickly and chewed the ETT tube in half and aspirated the distal piece

Thermoregulation Complications

• Can be caused by Hypothermia and hyperthermia
• It is important to check for proper causes, concerns, and corrections
• Can be caused by Malignant hyperthermia
• Is a rare but life threatening phenomena, that may be inherited
• It is Reported in pigs, dogs (Greyhounds), horses and cats

GER

• Gastro-Esophageal Reflux occurs when gastric contents pass into the esophagus and fluid comes out of the nose and mouth
• 50-60% of dogs get it, up to 33% incidence in cats.
• Can lead to esophagitis, esophageal stricture formation, or aspiration pneumonia

GER Risks

• Pregnancy (later stage)
• Abdominal and orthopedic surgery
• Length of preop fasting time & type of food
• Breed (brachycephalic, large, or deep-chested dogs)
• Pre-existing conditions (Gl disease, megaesophagus, dysphagia, regurgitation)
• Anesthetic drug protocol
• Recumbency and changes in body position during anesthesia
• prolonged duration of anesthesia
• Older dogs

GER Treatment

• Be sure that the ETT cuff is sealed; check pH
• Suction & lavage the esophagus with water and bicarbonate
• Sucralfate and H2-receptor antagonists may be considered (e.g. famotidine)
• Metoclopramide bolus and CRI may reduce incidence, but does not totally prevent GER -> Oral omeprazole 4 hours prior
• Maropitant (Cerenia) will NOT prevent GER

Metabolic Complications

• Can cause Hypoglycemia or hyperglycemia
• Glycemic control is very important in patients with diabetes Monitor BG at intervals and be ready to treat
• Can cause Acid-base disturbance

Hyperkalemia

• Calcium gluconate: dose - 50-150 mg/kg, IV slowly over 5 min
• Protects the heart
• 0.9% NaCl (or isotonic crystalloid): dose - Diuresis 10–15 ml/kg IV (over 20 min)
• Dextrose 50%: dose- 0.25-0.5 gram/kg IV (over 5 min) -Promotes release of insulin and uptake of K+ into the cells
• Regular insulin: dose - 1 unit IV -Shifts K+ into the cells
• Sodium bicarbonate: dose - 1 mEq/kg IV slowly (over 5 min) Alkalinizing blood promotes K+ influx intracellularly only if severe hyperkalemia

Neurologic & Musculoskeletal Complications

• Myopathy
• Neuropathy
• Prolonged or weak recovery
• Myoclonus
• Seizures
• Post-anesthetic cortical blindness

Myopathy and Neuropathy

• Myopathy can be caused by ischemic muscle damage linked to prolonged compression or inadequate padding and/or prolonged hypotension
• Peripheral neuropathy is caused by stretching, compression, ischemia, surgical resections; metabolic derangement
• Prevention is better than treatment.

Blindness

• May be seen after dental cleanings
• Likely due to mouth gags causing cerebral ischemia to due maxillary artery blood flow compression
• Neuro deficits may resolve in some patients, giving a good prognosis
• caused by severe hypotension and/or CPA

Prolonged Recovery

• Dependent on the situation
• Recheck vitals (especially temp, BP, ETCO2), SpO2, blood gases
• Review any drugs previously given - are any reversible?
• Gentle stimulation of patient
• Continue heat support and IV fluids -> Adding dextrose and calcium gluconate fluids is helpful

Dysphoria

Signs may include:

• Vocalization
• Panting
• Restlessness
• Urination/defecation
• Salivation

Treatment

• Must distinguish dysphoria from pain If in doubt always give analgesic drug
• Have concern or awareness of drug-induced (Further) dysphoria
• Several causes
• full bladder
• drug related
• metabolic
• respiratory problems Keep safety of patient and personnel in mind
• provide a quiet environment- dim lights First-treat any underlying problems and if dysphoria does not readily subdue-consider other drugs

Drugs to Treat Dysphoria

• Dexmedetomidine (at a low dose to start)
• Can be given as CRI if needed- (0.5-3 mcg/kg, IV)
• Acepromazine-(0.01-0.025 mg/kg, IV)
• Benzodiazepine: flumazenil- (0.01 mg/kg, IV) maybe considered
• Severe dysphoria- consider Propofol- give up to 1 mg/kg, IV-and allow to wake slowly again
• Consider Naloxone for reversal
• Use Butorphanol instead, if continued analgesia is desired (0.1 mg/kg, IV

Examples of Preventable Complications

• Human Error Leaving pop off valve closed Intracarotid or perivascular injection Walking away from patient where it falls off the table Tracheal tear- from turning intubated patient- still attached
• Drug Related

Miscalculation and administration of drugs that can be given incorrectly- route or reconstitution Wrong drug selected for a debilitated patient

Equipment Malfunction

SodaSorb expires or undergoes channeling

• Oxygen tank runs out of gas, or has a line that is disrupted
• Misassembly of a machine or breathing system
• Sticking of exhalation values, or kinking/obstruction

Tracheal Tears in Cats

Caused by: Over inflation when cuff is inflated during turning Stylet puncture Extubation that is still inflated

• Often seen during dental procedures
• Clinical Signs; Subcutaneous emphysema- dyspnea and stridor Look for any signs of pneomediastinum or pneumothorax

• Inspect ETT for blood on it after it is deflated for extubation Look for symptoms in hours or even days (coughing- not eating etc)

Treatment

• Either surgical or medical
• Prevention Use a small ETT- fill slowly with no more than cc's

Other Possible Complications

• Swollen feet or stiff joints from positioning on surgery table
• Corneal Ulcers
• Over administration of fluids
• Epidural needle or anesthetic is accidently placed in a nerve

BOAS Syndrome

• Smaller ETT
• challenging intubation
• Preoxygenate
• Use antiemetics with a concern of regurgitations and aspirating- so avoid prolonged fasting times
• Anticholinergics are very effective because of their high vagal tone
• bulging and protecting the eyes is key
• careful drug selection and titration of drugs
• Injectable steroid will help with airway inflimation
• Close monitoring, be prepared to leave the EXT in longer if can be tolerated

Summary

• PREVENTION is the best option
• Human error is never if it will occur, but when
• LABEL SYRINGES
• The selected drugs have to be selected correctly-
• Stabilize the patient and stay on them until the procedure is complete
• If there is complication- communicate quickly to the peri operative team at hand
• discuss the complications afterwards- and find better solutions