Anesthetic Complications Flashcards
(41 cards)
The most effective way to prevent complications are as follows:
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
most common anesthetic complication
- hypoventilation
what is hypoventilation
- numerical def based on PaCO2
- leads to?
- 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.
can a patient be breathing fast but still hypoventilating?
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.
Causes of hypoventilation or apnea
- drugs
- 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
what do we do if we notice hypoventilation under anesthesia?
the inhalant level should be reduced
Physical or physiologic issues causing hypoventilation includes
systemic disease, CNS disease, upper airway problems and lower airway diseases.
Common equipment problems leading to hypoventilation
kinked or plugged endotracheal tubes, malfunctioning inspiratory/expiratory valves, exhausted CO2 absorbent canisters, and or disconnections and premature extubations.
hyperventilation PaCO2 definition
PaCO2 or ETCO2 < 25-30 mmHg
hyperventilation under anesthesia cause, possible outcomes
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.
hypoxemia under anesthesia
- how common?
- definition
- 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.
hypoxemia under anesthesia causes
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.
bradycardia values for dogs (small, acerage, giant) and cats
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
main cause of bradycardia under GA
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.
The decision to treat the bradycardia should be based on:
the underlying cause and the significane of the bradycardia or bradyarrhythmias to the patient.
significance of bradycardia during surgery
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.
bradycardia under GA Tx
Most causes of bradycardia are responsive to anticholinergic treatment with either atropine or glycopyrrolate.
potential side effects of treating bradycardia with anticholinergic
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.
if bradycardia is from alpha-2-agonsit, should we use anticholinergic? why?
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.
tachycardia for small, average, large, dogs, and cats
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
tachycardia issues
An elevation in heart rate increases myocardial workload of the heart, oxygen consumption and reduces the time for relaxation and filling of the heart.
Increases in heart rate under general anesthesia are most commonly associated with
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.
tachycardia treatment
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.
normal blood pressures in adults, acceptable and optimal for GA
ACCEPTABLE:
Systolic (SAP) - 90
Mean (MAP) - 60
Diastolic (DAP) - 40
OPTIMAL:
Systolic (SAP) - 120
Mean (MAP) - 80
Diastolic (DAP) - 60
