Anesthetic Risk and Informed Consent

What are the 3 questions you should ask regarding anesthetic risk?

1. What complications can occur?

2. Which patients are at greatest risk of death?

3. How should that risk be communicated to an owner before euthanasia?

Describe the 5 categories of the ASA status

ASA status can identify patients at increased risk of mortality until 24-72 hours post-anesthesia

The higher the ASA score, the sicker the patient, the higher the anesthetic risk

ASA 1-2: generally describes healthy patients or patients with mild systemic disease

ASA 3-5: progressively more severe disease

ASA 5: moribund patient not expected to survive without the procedure

What else needs to be taken into consideration alongside the ASA classification?

Since the classification is somewhat subjective, it should be based on signalment, history, physical examination, and relevant diagnostic data rather than on a single isolated laboratory value. Identifying major physiologic abnormalities before induction lets the team anticipate which problems are most likely to occur during/after anesthesia

Contrast morbidity and mortality

Morbidity: refers to any disease, complication, or adverse effect resulting from anesthesia or the associated procedure that does not cause death. We clinically call them “complications”. Nonfatal adverse effects

The big 5 morbidities are hypoxemia, hypotension, hypothermia, bradycardia, and increased nociception

Mortality: refers to death resulting from anesthesia or the associated procedure. Anesthetic-related mortality is usually expressed as a rate -the number of deaths per number of anesthetized patients

Hypoxemia versus hypoxia

Hypoxemia is low oxygen in arterial blood

Hypoxia is inadequate oxygen delivery/availability at the tissue level

What are 5 broad mechanisms of hypoxemia?

1. Low inspired oxygen (altitude)

2. Hypoventilation

3. Right-to-left shunt

4. Ventilation-perfusion (V/Q) mismatch

5. Diffusion-related problems

Anesthesia worsens V/Q matching because positioning, recumbency, abdominal weight, and atelectasis can create areas that are perfused but poorly ventilated

Discuss anesthetic morbidity

Non-fatal complications occur more frequently than deaths - but are less often documented in veterinary literature

Reported small animal morbidity risk is about 2-10%

Consistent detection and recording of morbid events is genuinely difficult in practice

Monitoring standards can be superficial - unless a complication clearly disturbs the patient, it may go unnoticed. Be aware of detecting complications and be prepared to assess and respond to them