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Questions and Answers
What should be the first step in treatment for a hypotensive patient with a fluid deficit?
What should be the first step in treatment for a hypotensive patient with a fluid deficit?
- Administer a fluid bolus based on estimated deficit. (correct)
- Start constant rate infusions immediately.
- Assess the patient’s age and comorbidities.
- Double the constant rate infusion rate.
How should the rate of norepinephrine infusion be adjusted if a patient's blood pressure does not improve after 5 minutes?
How should the rate of norepinephrine infusion be adjusted if a patient's blood pressure does not improve after 5 minutes?
- Double the rate to enhance blood pressure response. (correct)
- Stop the infusion and reassess the patient.
- Keep the rate the same and monitor for additional signs.
- Decrease the rate by half to minimize side effects.
What is the free water deficit for a 20 kg dog estimated to be 7% dehydrated?
What is the free water deficit for a 20 kg dog estimated to be 7% dehydrated?
- 2 L free water deficit.
- 1 L free water deficit.
- 0.7 L free water deficit.
- 1.4 L free water deficit. (correct)
When initiating treatment for hypotension in patients, which factor should influence the approach taken?
When initiating treatment for hypotension in patients, which factor should influence the approach taken?
If a patient's blood pressure improves after a bolus but declines later, what is the next recommended step?
If a patient's blood pressure improves after a bolus but declines later, what is the next recommended step?
What is the definition of tachycardia in small breed dogs?
What is the definition of tachycardia in small breed dogs?
What is one of the first steps in treating tachycardia under general anesthesia?
What is one of the first steps in treating tachycardia under general anesthesia?
How does the intravascular volume affect blood pressure?
How does the intravascular volume affect blood pressure?
What should be suspected when a patient is moderately tachycardic and hypotensive?
What should be suspected when a patient is moderately tachycardic and hypotensive?
What is the effect of larger breed dogs on tolerance to higher heart rates?
What is the effect of larger breed dogs on tolerance to higher heart rates?
What was the initial dose of propofol required for induction of anesthesia?
What was the initial dose of propofol required for induction of anesthesia?
What is one method used to correct hypoventilation in animals under general anesthesia?
What is one method used to correct hypoventilation in animals under general anesthesia?
What was the depth of anesthesia immediately after induction?
What was the depth of anesthesia immediately after induction?
What does the administration of ephedrine primarily aim to address?
What does the administration of ephedrine primarily aim to address?
What should be prioritized to ensure adequate oxygen delivery during anesthesia?
What should be prioritized to ensure adequate oxygen delivery during anesthesia?
What role does vascular resistance play in blood pressure?
What role does vascular resistance play in blood pressure?
Which receptor does acepromazine antagonize?
Which receptor does acepromazine antagonize?
What kind of effects does dexmedetomidine have on the cardiovascular system?
What kind of effects does dexmedetomidine have on the cardiovascular system?
What is the minimum systolic blood pressure (SBP) for adequate end-organ perfusion?
What is the minimum systolic blood pressure (SBP) for adequate end-organ perfusion?
What complication is the most commonly reported from general anesthesia in dogs and cats?
What complication is the most commonly reported from general anesthesia in dogs and cats?
How is the treatment threshold for hypotension often affected?
How is the treatment threshold for hypotension often affected?
What is the primary goal of monitoring cardiovascular stability during anesthesia?
What is the primary goal of monitoring cardiovascular stability during anesthesia?
What is the standard definition of bradycardia in dogs?
What is the standard definition of bradycardia in dogs?
Which medications are typically used for treating bradycardia?
Which medications are typically used for treating bradycardia?
How is cardiac output calculated?
How is cardiac output calculated?
What should be done in cases of hypotensive patients with bradycardia?
What should be done in cases of hypotensive patients with bradycardia?
Which is NOT a factor that influences heart rate variability among different dog breeds?
Which is NOT a factor that influences heart rate variability among different dog breeds?
What is a common characteristic of pediatric patients regarding cardiovascular stability?
What is a common characteristic of pediatric patients regarding cardiovascular stability?
What might indicate the need for treating bradycardia in a patient?
What might indicate the need for treating bradycardia in a patient?
What is a potential complication of hypotension during anesthesia?
What is a potential complication of hypotension during anesthesia?
How does vasoconstriction affect blood pressure and perfusion?
How does vasoconstriction affect blood pressure and perfusion?
What is the recommended starting dose for a beta agonist at 5 kg?
What is the recommended starting dose for a beta agonist at 5 kg?
What intervention may be necessary for cats experiencing hypotension under general anesthesia?
What intervention may be necessary for cats experiencing hypotension under general anesthesia?
What statistical outcome is associated with cats experiencing hypotension during anesthesia?
What statistical outcome is associated with cats experiencing hypotension during anesthesia?
What condition does hypotension NOT commonly lead to in humans post-anesthesia?
What condition does hypotension NOT commonly lead to in humans post-anesthesia?
What should be adjusted every 3-5 minutes when administering a beta agonist for hypotension?
What should be adjusted every 3-5 minutes when administering a beta agonist for hypotension?
During the presentation of a healthy 26 kg Golden for surgery, which parameter was abnormal?
During the presentation of a healthy 26 kg Golden for surgery, which parameter was abnormal?
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Study Notes
Cardiovascular Consequences
- Oxygen Delivery to Tissues (DO2) is calculated by multiplying Cardiac Output (CO) by Arterial Oxygen Content (CaO2).
- Cardiac Output is determined by heart rate (HR) and stroke volume.
- Bradycardia: Heart rate below the normal range for the species and breed.
- Dogs: HR < 50-80 bpm, with smaller breeds having a higher baseline.
- Cats: HR < 110-120 bpm.
- Tachycardia: Heart rate above the normal range for the species and breed.
- Dogs: HR > 140-180 bpm, with smaller breeds tolerating higher heart rates.
- Cats: HR > 200-220 bpm.
Bradycardia / Bradyarrhythmias - Treatment
- Treat bradycardia in hypotensive patients, patients with certain cardiac diseases, and pediatric patients.
- Identify the cause of bradycardia before treating.
- Consider adjusting anesthetic depth and ensure adequate oxygenation.
- Anticholinergics can be administered to increase heart rate.
- Atropine: 0.02-0.04 mg/kg IV/IM, lasts 30-40 minutes.
- Glycopyrrolate: 0.005-0.01 mg/kg IV/IM, lasts 45-60 minutes.
Tachycardia / Tachyarrythmias under GA - Treatment
- Evaluate anesthetic depth and ensure optimal analgesia.
- Address hypoventilation by initiating IPPV if EtCO2 is elevated (e.g., > 60 mmHg).
- Moderate tachycardia might not require intervention if adequate perfusion is maintained.
- Moderate to severe tachycardia with hypotension requires immediate attention:
- Evaluate for hypovolemia and consider a fluid bolus (e.g., 10 ml/kg over 10 minutes).
- Reduce or discontinue sympathomimetic drugs (e.g., dobutamine, ephedrine).
- Consider beta-blockers (e.g., esmolol) or opioids.
Blood Pressure and Anesthesia
- Blood pressure is an easily measured indicator of cardiovascular function during anesthesia.
- Maintaining adequate oxygen delivery to tissues under anesthesia is the primary goal.
- Blood pressure is proportional to both cardiac output (CO) and vascular resistance (VR).
- Hypotension is the most common anesthetic-related complication.
- Regional vascular resistance dictates organ perfusion. Vasoconstriction can improve blood pressure but compromise perfusion in some organs.
Hypotension as an Adverse Effect
- Hypotension is associated with increased morbidity and mortality in human patients.
- Cats that experience hypotension under general anesthesia have a 2.6 times higher risk of death.
- Hypotension can lead to acute kidney injury (AKI), even in healthy adults.
- Treatment of hypotension requires addressing the underlying cause.
- Norepinephrine can be administered as a continuous rate infusion (CRI) to support blood pressure.
Case Example: Hypotension Management
- A 26 kg Golden Retriever undergoing elective OHE exhibits hypotension after general anesthesia induction.
- Initial Assessment: 1st oscillatory BP 109/60 (71) mmHg, HR 77, RR 7-9 bpm.
- Treatment: Ephedrine 0.1 mg/kg IV was administered.
- Monitoring: Blood pressure and heart rate are closely monitored.
- Treatment Options: Repeated ephedrine boluses, ephedrine CRI, or norepinephrine CRI can be considered.
Acepromazine and Hypotension
- Acepromazine is an alpha-1 adrenergic receptor antagonist, reducing venous tone and exacerbating blood volume shifts.
- Acepromazine can contribute to hypotension by decreasing preload and cardiac output.
Dexmedetomidine and Hypotension
- Dexmedetomidine is an alpha-2 agonist with both peripheral and central effects.
- Peripheral effects: Vasoconstriction and reflex bradycardia.
- Central effects: Reduced sympathetic tone, leading to decreased heart rate, vascular tone, and contractility.
Hypotension in Anesthesia: Summary
- Blood pressure is a key indicator of cardiovascular health under general anesthesia.
- Maintaining adequate perfusion is critical.
- Hypotension is a common complication with associated risks.
- Treatment strategies should target the primary cause of hypotension.
- Fluid boluses are indicated for volume deficits, but not as preventative measures.
- Interventions should be individualized based on patient factors (e.g., age, comorbidities).
Volume Deficits
- Patients with dehydration may require fluid boluses in addition to maintenance intravenous fluids (IVF).
- Example: 20 kg dog with a 7% free water deficit.
- Initial fluid bolus: 20 ml/kg (400 ml) over 10-15 minutes.
- Re-evaluate blood pressure and heart rate after the bolus.
- Repeat boluses or consider vasopressors if necessary.
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