Complications

What do we need to do to prepare?

Look at

• species, breed

• pre-existing conditions

• type of surgery

• drugs used

• positioning

Hypoxemia

Mild → PaO2 < 80 mmHg or SpO2 <95%

Moderate → PaO2 < 60 mmHg or SpO2 < 90%

Severe → PaO2 < 40-45 mmHg or SpO2 < 80%

Cyanosis

5 g/dL of deoxyhemoglobin or more

• SpO2 of < 85% if Hb is normal

• Lower if patient is anemic

Causes of hypoxemia

• V/Q Mismatch: Atelectasis, pulmonary edema, pulmonary contusions,

  thromboembolism, asthma…

• R-L shunt: intra-cardiac or intra-pulmonary

• Diffusion impairment: pneumonia, interstitial lung disease…

• Hypoventilation (severe)

• Decreased FiO2

Treat hypoxemia

Treat underlying problem → pay special attention during induction and recovery

• inc FiO2 and check O2 source

• lung re-expansion

• bronchodilators

• support and optimize ventilation

• diuretic

• surgical correction

Apnea

> 1min without spontaneous breathing → common after induction → prevent by pre-oxygenating animal

• excessive depth

• additional drugs

• hypocarbia → ventilating too much

• excessive work to ventilate

• inability to ventilate

• cardiopulmonary arrest

Hypoventilation

Happens the most because the drugs we give cause this

• Alveolar hypoventilation as insufficient ventilation leading to hypercapnia

• ETCO2 3-5 mmHg <PaCO2

• caused by decrease in tidal volume (not taking enough breaths, or not fast enough), RR, inc dead space, or combo

Physiological effects of hypercapnea

• stimulation of respiratory drive

• respiratory acidosis

• inc cerebral blood flow

• CNS depression

• sympathetic stimulation → inc HR & BP

• hypoxemia

Causes of hypercapnea

• anesthetic drug

• obesity

• inc abdominal pressure

• neuro disorders

• pathologies of thoracic wall or lungs, pneumothorax, pleural disorders, mass, trauma

• age

• hypothermia

• positioning

• equipment → dead space

• inc CO2 production → hyperthermia, systemic absorption during lap spay

Treat hypercapnea

• find underlying cause

• know pre-existing conditions

• measure ETCO2 and/or PaCO2

• check drugs, anesthetic depth

• correct body temp

• equipment

• support with ventilation

Hyperventilation

From inc respiratory rate → lead to hypocapnea and respiratory alkalosis

• light plane

• nociception

• hypercapnia

• hypoxemia

• metabolic acidosis

Airway obstruction

Partial or total obstruction → Brachycephalic breeds predisposed

• underlying isues

• airway swelling

• surgery

• trauma

• aspiration of foreign material

• external pressure

• equipment problems

Diagnose airway obstruction

• Paradoxic breathing → thoracic wall sucks in, abdominal wall expands, open mouth breaking, nostril flare, neck flexed, stridor

• prolonged inspiratory time

• hypoxemia and/or cyanosis

• rebreathing bag not working

• capnograph wave abnormal or disappears

• high pressure when trying to ventilate

Brachycephalic syndrome

Upper airway disease

Problems at intubation or recovery → pre-oxygenate, small tube, local anesthetic application

• laryngeal paralysis

• laryngeal hemiplegia

• laryngospasm

Lower airway disease

Problems during anesthetic maintenance if endo tube does not pass lesion

• tracheal mass

• tracheal stenosis

• tracheal collapse

• bronchospasm → asthma, reactive airway, anaphylaxis, bronchitis → when animal is intubated

Airway inflammation cause and treatment

Cause → respiratory distress/effort, surgery, trauma

treat → corticosteroids, local vasoconstrictors, dextrose 50%

Equipment problems

• kinked, twisted ET tube

• kinked breathing circuit

• mucus/blood ET tube obstruction

• pop-off closed → tension pneumothorax

Airway obstruction

Tension pneumothorax

If can’t hear lung sounds, tap the chest!!

What do we consider for HR?

• age

• Size/breed

• Resting HR

Why is HR so important?

• Determines CO

• O2 content

• Blood pressure

What happens with slow HR?

• Diastolic filling volume (preload), time (HR)

• Too low will directly Dec CO and BP

What causes inc parasympathetic activity - Bradycardia?

• Vagal tone → eye reflex, inc GI pressure, expiration

• Drug induced → Alpha 2, opioids

• Reflex mechanism due to hypertension → baroreflex response

• Cardiac disease

• Inc intracranial pressure → Cushing response

• Electrolyte abnormalities

• Hypothermia

When do we treat bradycardia?

Only if marked and affecting CO

• look at blood pressure

• Treat if rhythm is markedly irregular

How can we treat bradycardia?

• vagal tone → Anticholinergics

• Drug induced → reversal, lidocaine(for alpha 2), anticholinergics(not during hypertensive phase)

• Reflex mechanism due to hypertension → control hypertension → baroreflex response Cardiac disease

• Cardiac disease → anticholinergics, isoproterenol, pace maker

• Intracranial pressure → control ICP

• Electrolytes → Dec K, calcium gluconate

• Hypothermia → warm up

Tachycardia

fast HR → SV Dec because it is not effectively filling, Dec CO, Dec BP

• Inc O2 consumption → myocardial ischemia and arrhythmia

Tachycardia causes

Inc sympathetic activity

• superficial anesthetic plane

• Hypotension/hypovolemia

• Hypercapnia/hyperthermia

• Drug induced → ketamine, sympothomimetics, anticholinergics

• Hyperthyroidism

• Hypoxia/shock

• Heart disease

Treat tachycardia

• superficial plane/pain → check depth/analgesia

• Hypotension/hypovolemia → correct fluids

• Hypercapnia/hyperthermia Drug→ cool down, adjust ventilation

• Drug induced → stop giving

• Hypoxia/shock → improve oxygen delivery

How to recognize sinus rhythm?

ECG

• regular rhythm?

• All waves resent and normal?

• P & QRS are associated

Common dysrhythmias

Atrioventricular (AV) block*

▪ Atrial premature contractions (APC)

▪ Atrial fibrillation (AF)

▪ Ventricular premature contractions (VPC)*

▪ Ventricular tachycardia (VT)*

▪ Ventricular fibrillation (VF)

AV blocks

Conduction from atria to ventricles is not working

• slow conduction → 1st degree AV black

• P waves not followed by QRS complex (2nd & 3rd degree)

• Bradycardia is common

• Due to inc vagal tone

• Drug induced → alpha 2, anticholinergics

• Intrinsic cardiac disease

Treat AV blocks

• reverse alpha 2

• Anticholinergics

• Isoproterenol

• 3rd degree needs a pacemaker

Ventricular premature contraction VPC

Ventricle is contracting during the wrong time - not following normal path, taking longer

• No P waves

• Premature

• Bizarre QRS

Premature nature prevents adequate diastolic filling

• pulse deficit

What causes VPC?

• Heart disease, cardiomyopathies

• Catecholamine release: pain, stress, inappropriate anesthetic plane

• Myocardial hypoxia

• Electrolytic abnormalities (Hypomagnesemia, hypokalemia, hypercalcemia)

• Myocardial depressant factors (GDV, splenic tumors)

• Arrhythmogenic drugs (thiopental, B1-agonists-sympathomimetics)

• Irritation of ventricle, mechanical stimulation

Treat VCP

If blood pressure and CO affected

• oxygenate

• Improve cantractility

• Control underlying cause → electrolytes, surgery

• Lidocaine

• Procainamide

• Magnesium sulfate

• Beta blockers

• Amiodarone

Ventricular tachycardia

Lots of VPCs in sequence → high HR

• can become ventricular fibrillation → always treat

• Tachycardia is part of dysrhythmia

• Some ethnology and treatment as for VPCs

Hypotension

Most common during general anesthesia → can cause Dec perfusion to tissues, damage to kidneys, muscles

• measure with Doppler and oscillometric

Normal BP values

If your animal is healthy and is hypotension, what is the most common reason for this?

too much gas

Hypotension causes

• excessive depth

• Hypovolemia

• Peripheral vasodilation

• Cardiac dysrhythmia

• Dec cardiac contractility

• Bradycardia

• Tachycardia

Treat hypotension

• too deep → check plane

• Dehydrated → correct fluid

• Bradycardia → anticholinergics

• Tachycardia → hypovolemia, analgesia, anesthetic plane, beta blockers

• Inc contractility → dopamine, NE

• Vasodilation → inc vascular resistance → dopamine, NE, phenylephrine, epinephrine

Hypertension

usually associated with tachycardia initial phase

• less common than hypotension

• More common in cats

• Inadequate depth

• Drug induced

• Hypercapnia

• Hypoxia

• Underlying disease

Hypovolemia

Hypovolemia leads to hypotension

• hypotentive patient is not always hypovolemia

• Results in Dec blood flow

• Hypotension does not always result in Dec blood flow

Estimate blood loss

• amount in suction bottle, lap sponges, gauze, hemodynamic state

• HR inc

• BP Dec

• CO Dec

• Hemodilution PCV & TS dec

Treat hypovolemia

Volume → isotonic crystalloids, colloids, hypertonic saline, blood products

Contractility → inotropes, balanced anesthesia → Dec cardiac depression

Vasoconstriction without fluid replacement will not inc CO

Dosing errors

• wrong concentration

• Math errors

• Drawing up wrong drugs

• Giving wrong drug

• Do not wait until peak effect of the drug

Precautions to avoide dosing errors

• Check label syringe

• Check concentration

• Double check volume math

• Have reversal available

IV catheter complications

• Non patent

• Phlebitis from long term catheter

• Leaky vein

• Propofol and cats

Intubation problems

• lack of visualization → use guide tube, look for condensation, CO2 monitor, scope to visualize

• Esophageal intubation

  • Lack of movement of bag

  • Very low or no CO2 wave

  • Inability to seal cuff

  • Animal waking up

  • Hypoxemia

Hypothermia

< 36 C

• temp drop with GA in 1st hr

• Loss of temp regulation ability under GA

• Vasodilation → acepromazine, inhalants

• Large surface area:body mass ratio

• Cold fluids

• Cool operating room

• Alcohol prep

• Lavage during surgery

Why is hypothermia bad?

▪ Decrease metabolism leads to less anesthetic requirements: risk of anesthetic

overdose

▪ Prolonged recovery

▪ Postoperative wound infection

▪ Impairment of coagulation

▪ Increased shivering and discomfort during recovery,

▪ Increased blood viscosity

▪ Bradycardia, non responsive to anticholinergics

▪ Cardiac arrhythmias and arrest < 23 C

Prevent hypothermia

• prevent heart loss → keep patient covered, avoid cold surfaces

• Active warming → forced air blankets, water circulating heating pads, oat bags, hot dog, warm lavage, warm Iv fluids

Causes of hyperthermia

• Iatrogenic

  • Warming devices

  • Large heavy coated animal undergoing diagnostics procedures associated with little heat loss

• Metabolic derangement or disease

  • Malignant hyperthermia

  • Serotonin syndrome

  • Hyperthyroidism & Cushing

  • HYPP

  • Seizures

  • Opioids → cats

Hyperthermia consequences

• hyper metabolism

• Inc HR & RR

• Metabolic acidosis

• Seizures

• Organ dysfunction

Treat by stopping warming devices

Regurgitation

Small ruminants will regurgitate the whole time

• anesthetic drugs will relax LES

• Can lead to aspiration pneumonia

• Ulcerative esophagitis and stricture

• Nasal and pharyngeal irritation

• Prevent with cisapride and metoclopramide

• Treat with anti acids, head down to drain, suction, lavage

Hypoglycemia

<4 mmol/L

• in pediatric patients or small patients fasted for too long

• Diabetes

• Insulinoma

• Hepatic disease

• Prolonged recovery

• Seizures

• Treat with dextrose

Seizures

• idiopathic epilepsy

• Intracranial disease/trauma

• Metabolic disease

• Cerebral ischemia

• Severe hyperthermia

• Post myelogram contrast inj

• Treat with → benzodiazepine, propofol, barbiturates, inhalants anesthetic, provide oxygen, check temp, glucose, electrolytes

Awake/moving

• Inadequate depth monitoring

• Apnea

• Hypoventilation

• Accidental extubation/loss of IV

• Forget to turn vaporizer

• Safety hazard

• Always have induction top up available

• Continuous monitoring

Poor recovery problems

1. Pain

2. Emergence delirium → waking up too fast, anxious animals, no sedative, noises and stimulation

3. Dysphoria → excitement, vocalization, lack of response to interaction after opioid administration

4. Horses

How do we treat delirium?

Give more sedation

How do we treat Dysphoria?

Titrate to effect with opiate reversal → naloxone