Anesthetic Complications

Question 1

The most effective way to prevent complications are as follows:

Answer 1

1) Stabilize the patient in the peri-anesthetic period as required
2) Adhere to appropriate fasting times recommended for the species
3) Choose appropriate anesthetics and doses for the individual patient ensuring no mistakes are made
4) Understanding and checking the anesthetic machine and monitoring equipment prior to each case
4) Adequate monitoring in the pre-intra-and post-operative periods

Question 2

most common anesthetic complication

Answer 2

• hypoventilation

Question 3

what is hypoventilation
- numerical def based on PaCO2
- leads to?

Answer 3

• Hypoventilation (PaCO2 or ETCO2 > 55 mmHg) is the most common reported anesthetic complication.
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  Hypoventilation means that the overall gas exchange, removal of CO2 and uptake of O2 is impaired. Hypoventilation leads to hypercarbia (high CO2), which causes a respiratory acidosis (pH <7.4).
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  Normal CO2 is typically reported as 40 mmHg. A slight permissive hypercarbia (PaCO2 >40-55 mmHg) is acceptable under general anesthesia in routine elective cases, but is contraindicated in neurologic cases, certain ocular disease, or septic, acidotic patients.

Question 4

can a patient be breathing fast but still hypoventilating?

Answer 4

A patient can be breathing rapid and shallow and still be hypoventilating as alveolar ventilation is inadequate. Hypoventilation is best evaluated by measuring the CO2 level in blood.

Question 5

Causes of hypoventilation or apnea
- drugs

Answer 5

• The main cause of hypoventilation during anesthesia are the anesthetic drugs.
  > It is most commonly noted during bolus doses of thiopental, alfaxalone, or propofol with induction and with all inhalant anesthetics
  > Opioids can also cause mild hypoventilation when used alone but this effect is more pronounced when they are combined with other sedatives or inhalant anesthetic
  > Ketamine benzodiazepine inductions can also result in hypoventilation with higher doses

Question 6

what do we do if we notice hypoventilation under anesthesia?

Answer 6

the inhalant level should be reduced

Question 7

Physical or physiologic issues causing hypoventilation includes

Answer 7

systemic disease, CNS disease, upper airway problems and lower airway diseases.

Question 8

Common equipment problems leading to hypoventilation

Answer 8

kinked or plugged endotracheal tubes, malfunctioning inspiratory/expiratory valves, exhausted CO2 absorbent canisters, and or disconnections and premature extubations.

Question 9

hyperventilation PaCO2 definition

Answer 9

PaCO2 or ETCO2 < 25-30 mmHg

Question 10

hyperventilation under anesthesia cause, possible outcomes

Answer 10

Hyperventilation is generally due to an underlying cause like pain, inadequate anesthetic depth and elevated CO2. In anesthetized animals, their ability to increase ventilation secondary to hypercarbia will be reduced, however, it is important to assess the patient’s depth and not administer additional anesthetics if the patient’s RR is increased. This could indicate a high CO2 and the animal responding properly, or they could also be on hypoxic drive to ventilate. Hyperventilation leads to respiratory alkalosis.

Question 11

hypoxemia under anesthesia
- how common?
- definition

Answer 11

• rare in healthy anesthetized small animals
• Hypoxemia is defined as relative hypoxemia (PaO2 <80 mmHg) or absolute hypoxemia (PaO2 < 60 mmHg) and requires management.
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  Inhalant anesthetics are delivered in 100% oxygen, so outside of pre-medication, induction and recovery phases, you should expect the maintenance phase to have a PaO2 > 200 mmHg.

Question 12

hypoxemia under anesthesia causes

Answer 12

Hypoxemia can be due to hypoventilation, low FIO2, ventilation- perfusion mismatch, impaired diffusion of oxygen across the alveolar/arterial membrane, or anatomical shunting of blood. Hypoxemia may occur with significant hypoventilation, however, this is more common in sedated or anesthetized animals breathing room air (FiO2=0.21) versus those animals, which are intubated and maintained under inhalant anesthetics delivered with 100% oxygen.
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In most cases, hypoxemia is the result of a prolonged or difficult intubation, failed intubation, inadvertent extubation, airway obstruction, apnea during induction of anesthesia, recovery complications and aspiration, or underlying respiratory disease. Airway obstructions can occur due to kinked or twisted tubes, excessive secretions occluding the lumen of the tube or a twisted/kinked breathing circuit. Kinked endotracheal tubes happen with manipulation of the patient for surgery, dental procedures or positioning for diagnostics. The patient and machine should always be checked after they are moved or during or after extreme patient movements.

Question 13

bradycardia values for dogs (small, acerage, giant) and cats

Answer 13

Small Breed Dogs <10-15 kg
- <80 bpm

Average Size Dogs (15-50 kg)
- <60bpm

Giant breed Dogs (> 50 kg)
- <50bpm
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Cats <100bpm

Question 14

main cause of bradycardia under GA

Answer 14

The main cause of bradycardia under general anesthesia is from increased parasympathetic tone (vagal stimulation) or a reduction in sympathetic tone. This can be the result of sedative (opioids, alpha2- agonists), anesthetic drug administration and unconsciousness (inhalants), or from any reflex that increases vagal tone (visceral traction, endotracheal intubation, oculocardiac reflex). Other causes include hypothermia, or hyperkalemia.

Question 15

The decision to treat the bradycardia should be based on:

Answer 15

the underlying cause and the significane of the bradycardia or bradyarrhythmias to the patient.

Question 16

significance of bradycardia during surgery

Answer 16

This significance of bradycardia under general anesthesia is multiple;
1) Reduced cardiac output and hence blood pressures, which reduces organ perfusion and results in morbidities and/or worsening of the
animal’s primary condition (CKD, liver disease, etc).
2) Bradycardia may result in associated bradyarrhythmias (1st, 2nd, 3rd
degree AV heart block, which will further reduce cardiac output and
lead to other more significant or fatal arrhythmias.
3) Bradycardia could lead to sinus arrest if left untreated.

Question 17

bradycardia under GA Tx

Answer 17

Most causes of bradycardia are responsive to anticholinergic treatment with either atropine or glycopyrrolate.

Question 18

potential side effects of treating bradycardia with anticholinergic

Answer 18

Side effects of anticholinergic treatment are a potential worsening of the bradycardia or bradyarrhythmias, a tachycardia, and reduced gi motility. An initial bradycardia can be seen if lowered doses are administered, or if the drug is not given as a bolus. The animals’s heart rate and ECG should be monitored following treatment.

Question 19

if bradycardia is from alpha-2-agonsit, should we use anticholinergic? why?

Answer 19

If the cause of the bradycardia is from alpha2-agonist administration, and hypertension is also noted, even in the face of inhalant administration, then treatment specifically for the bradycardia with an anticholinerigic is not warranted. This is because the anticholinergic with the alpha2-agonist increased BP, will increase myocardial oxygen demand.
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Once under inhalant and a decrease in the peripheral vascoconstriction or blood pressure, the bradycardia resulting from general anesthesia, opioid and alpha2-administration may require treatment with an anticholinergic.

Question 20

tachycardia for small, average, large, dogs, and cats

Answer 20

Small Breed Dogs <10-15 kg: >180bpm

Average Size Dogs (15-50 kg): >150 bpm

Giant breed Dogs (> 50 kg): > 130-150bpm
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cats: >240bpm

Question 21

tachycardia issues

Answer 21

An elevation in heart rate increases myocardial workload of the heart, oxygen consumption and reduces the time for relaxation and filling of the heart.

Question 22

Increases in heart rate under general anesthesia are most commonly associated with

Answer 22

inadequate depth/analgesics, hypoventilation (increased CO2), hypovolemia, ketamine induction (first 20 minutes form induction only), or high doses or inadvertent boluses of sympathomimetic drugs such as dopamine. Hypoxemia or hyperthermia may also cause increases in heart rate.

Question 23

tachycardia treatment

Answer 23

Treatment will always be directed at identifying and correcting the underlying cause. For example, if the animal has manual monitoring signs consistent with inadequate depth and the anesthetic record confirms it has been 3 hours since the last administration of hydromorphone (which has a duration of effect of 2-4 hrs), than an additional IV dose of hydromorphone is warranted. If blood loss has occurred, then administering fluids to replace the blood loss is necessary.

Question 24

normal blood pressures in adults, acceptable and optimal for GA

Answer 24

ACCEPTABLE:
Systolic (SAP) - 90
Mean (MAP) - 60
Diastolic (DAP) - 40

OPTIMAL:
Systolic (SAP) - 120
Mean (MAP) - 80
Diastolic (DAP) - 60

Question 25

hypotension definition under GA

Answer 25

ACCEPTABLE:

Systolic (SAP) - 90
Mean (MAP) - 60
Diastolic (DAP) - 40
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Hypotension under general anesthesia in veterinary medicine is defined as lower than the ACCEPTABLE normal in each age category listed above.

Question 26

how do anesthetics cause hypotension

Answer 26

by; reducing myocardial contractility, cardiac output, and vascular responsiveness (baroreceptor reflexes), causing vasodilation and in general an overall reduction in sympathetic tone.

Question 27

drugs affecting cardiovascular function

Answer 27

Inhalant anesthetics have the greatest negative impact on cardiovascular function. Opioids increase vagal tone, and thereby lower heart rate. If the bradycardia from an opioid is not treated in the face of inhalant anesthesia, then hypotension can result.

Question 28

Hypotension is most commonly associated with :
and other considerations

Answer 28

anesthetic drug induced cardiovascular depression and excessive anesthetic depth, especially when without surgical stimulation. Excessive depth may not always be the main cause of hypotension. In some cases, the animal is as light as possible to maintain a surgical depth, however, the cardio-depressive anesthetic effects combined with the patient’s primary condition or problem, hypovolemia, dorsal recumbency, or obesity result in hypotension.

Question 29

In all situations of hypotension, the following treatment and sequence of interventions is required:

Answer 29

1) Assess patient’s depth – reduce if possible or add additional analgesics or other drugs to assist in lowering the inhalant level.
2) Assess accuracy of monitors – cuff size and replace/retighten, restart, count HR manually, palpate pulse.
3) Assess heart rate. If the patient is bradycardic, treat with an anticholinergic.
4) Consider a fluid bolus if patient had signs of dehydration prior to anesthesia, or has evidence of blood loss intra-operatively.
5) If the previous 4 options were not possible or did not assist in improving blood pressure, than an inotrope is required to continue and maintain surgery for a longer period. Commonly used sympathomimetics include dopamine, dobutamine or ephedrine.

Question 30

hypertension definition

Answer 30

Hypertension – SBP >180 mmHg; MBP > 100 mmHg; DAP >60 mmHg

Question 31

In most situations, hypertension is associated with

Answer 31

a light plane of anesthesia, inadequate analgesics, or alpha2-agonist pre-medication.

Question 32

how fast does the hypertension from alpha-2 agonists wear off?

Answer 32

The hypertension from alpha2-agonist pre-medication typically declines to normal or even to levels of hypotension during the first 30-45 minutes of general anesthesia (inhalant or maintenance with injectables)

Question 33

primary conditions that can contibute to hypertension

Answer 33

Hypertension can also be secondary to the patients primary condition; CKD, hyperadrenocorticism, pheochromocytoma, or increased intracranial pressure.

Question 34

premature ventricular contractions (PVC’s). Occasional PVC’s do not necessarily require treatment, however, consistent or frequent PVC’s leading to ventricular tachycardia are cause for treatment:

Answer 34

Lidocaine at 2 mg/kg, then infusion

Question 35

hypothermia definition

Answer 35

F. Hypothermia (Body Temperature < 36.5 OC

Question 36

why do we get hypothermia, what are the trends
- what contributes

Answer 36

Body temperature drops steadily with heavy sedation or induction of general anesthesia during the first hour. From there, the temperature will continue to drop but at a slower rate.
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The drop and resultant hypothermia is most significant in the smallest (<5kg), low body fat, thin hair and neonatal patients. In addition, administration of cold fluids, cool operating rooms, and cold inhalant gases add to the temperature loss. Supplemental support with blankets, warm water bottles, warm air forced blankets or electric methods are required to maintain body temperature.

Question 37

problems that arise due to hypothermia

Answer 37

Hypothermia contributes to poor wound healing, risk of infection, and increased incidence of adverse cardiovascular effects (bradycardia and associated bradyarrhythmias). It is important to note that hypothermia reduces the anesthetic requirements and drug metabolism.

Question 38

hyperthermia definition

Answer 38

Body Temperature > 39OC

Question 39

why do we see hyperthemia under anesthesia

Answer 39

Increases in body temperature may be noted during anesthesia and are most commonly due to a febrile condition, pre-operative stress and anxiousness, especially in an animal used to Canadian outdoor temperatures vs. the clinic, or inadvertent overwarming. It may also be due to malignant hyperthermia, which although uncommon, should be ruled out immediately.

Question 40

Hyperthermia post-operatively is most commonly a result of:

Answer 40

pure-mu agonist administration or with ketamine IM in healthy cats undergoing elective procedures. Hydromorphone is most commonly reported to cause this effect with temperatures in the post-operative phase > 40.5 OC. This does not mean that analgesia with opioids in cats be withheld, but that temperature should be monitored and treated as necessary.

Question 41

hyperthermia post-op treatment

Answer 41

Treatment includes sedation with acepromazine, which causes vasodilation and assists with heat loss. It also calms the animal and prevents excessive movement that the cat will want to do when hyperthermic. The cats paws should be wet, fleeces removed to allow the cat to sit on the cold metal cage surface and a fan should be available.