Adjunts to Anesthesia

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Questions and Answers

What effect do antacids have on the absorption of digoxin?

They enhance its absorption.

They slow down its absorption. (correct)

They eliminate it completely.

They have no effect on its absorption.

Which of the following conditions is NOT treated by metoclopramide?

Prophylaxis for aspiration pneumonia

Severe obstipation (correct)

Gastroesophageal reflux disease (GERD)

Diabetic gastroparesis

What mechanism does metoclopramide use to increase lower esophageal sphincter tone?

Facilitating acetylcholine transmission. (correct)

Inhibit gastric acid secretion.

Antagonism of serotonin receptors.

Inhibition of acetylcholine breakdown.

What is a common side effect from rapid intravenous injection of metoclopramide?

Abdominal cramping Signup and view all the answers

What happens to the elimination rate of phenobarbital when antacids are used?

It is quickened. Signup and view all the answers

Which patient condition should metoclopramide be avoided in due to its side effects?

Parkinson disease Signup and view all the answers

What kind of effects does metoclopramide produce through its action on dopamine receptors?

Antiemetic effects Signup and view all the answers

What are the possible effects of prolonged treatment with metoclopramide?

Tardive dyskinesia Signup and view all the answers

What effect do antimuscarinic drugs have on metoclopramide?

Block the GI effects of metoclopramide Signup and view all the answers

Which condition can proton pump inhibitors (PPIs) help treat more rapidly than H2-receptor blockers?

Gastroesophageal reflux disease (GERD) Signup and view all the answers

What is the mechanism of action of proton pump inhibitors?

Inhibit the secretion of hydrogen ions Signup and view all the answers

Which of the following is a potential adverse effect of proton pump inhibitors?

Increased risk of pneumonia Signup and view all the answers

How does metoclopramide interact with cimetidine?

Inhibits absorption of cimetidine Signup and view all the answers

Which of the following conditions is NOT a clinical use for proton pump inhibitors?

Chronic fatigue syndrome Signup and view all the answers

In which situation should metoclopramide dosage be decreased?

In patients with kidney dysfunction Signup and view all the answers

Which drug can have its clearance decreased by proton pump inhibitors?

Warfarin Signup and view all the answers

What is the primary mechanism of action of 5-HT3-receptor antagonists?

They inhibit serotonin 5-HT3 receptors. Signup and view all the answers

Which of the following agents is known for having an extended duration of action compared to others?

Palonosetron Signup and view all the answers

Which risk factor is associated with a higher incidence of postdischarge nausea and vomiting (PDNV)?

Use of opioids in the PACU Signup and view all the answers

What is the most commonly reported side effect of 5-HT3-receptor antagonists?

Headache Signup and view all the answers

Which statement is true regarding the QT interval effect of 5-HT3-receptor antagonists?

Dolasetron may cause a slight prolongation of the QT interval. Signup and view all the answers

Which of the following statements about 5-HT3-receptor antagonists is NOT accurate?

They cause sedation in most patients. Signup and view all the answers

In patients taking antiarrhythmic drugs, which consideration is important when prescribing 5-HT3-receptor antagonists?

Increased risk of QT interval prolongation Signup and view all the answers

What role do 5-HT3 receptors play in vomiting?

They contribute to the initiation of the vomiting reflex. Signup and view all the answers

Study Notes

Adjuncts to Anesthesia

Diphenhydramine competitively blocks H₁ receptors, has antimuscarinic and antiserotonergic activity.
H₂ blockers decrease perioperative risk of aspiration pneumonia by decreasing gastric fluid volume and raising pH.
Metoclopramide increases lower esophageal sphincter tone, speeds gastric emptying, and lowers gastric fluid volume.
Ondansetron, granisetron, tropisetron, and dolasetron block serotonin 5-HT3 receptors, with minimal effect on dopamine receptors.
Ketorolac is a nonsteroidal anti-inflammatory drug that inhibits prostaglandin synthesis, providing analgesia.
Clonidine is an antihypertensive agent used in anesthesia for epidural, caudal, and peripheral nerve block, and pain management.
Dexmedetomidine is a selective a₂-agonist with sedative properties.
Doxapram stimulates carotid chemoreceptors stimulating hypoxic drive, increasing tidal volume.
Naloxone reverses opioid agonist activity.
Flumazenil reverses benzodiazepine sedation.
Aspiration of gastric contents is a rare, potentially fatal event in anesthesia. Factors increasing the risk include full stomach, intestinal obstruction, hiatal hernia, obesity, pregnancy.
Many drugs are used perioperatively to protect against aspiration, nausea, vomiting, or respiratory depression.

Aspiration

Aspiration of gastric contents can complicate anesthesia, often resulting in aspiration pneumonia.
Risk factors include a "full" stomach, intestinal obstruction, hiatal hernia, obesity, pregnancy, and inadequate anesthesia depth.
Many approaches aim to reduce the risk, such as Sellick maneuver, rapid sequence induction.
Anesthetized patients are at risk of passive aspiration due to reduced lower esophageal sphincter tone and gag reflex suppression.

Histamine-Receptor Antagonists

Histamine is found in the central nervous system, gastric mucosa and other peripheral tissues.
It is synthesized from the amino acid histidine.
Histamine plays a role in HCl acid secretion in the stomach
Histamine release can be stimulated by chemical, mechanical or immunological stimulation.
H₁ receptors activate phospholipase C, while H₂ receptors increase intracellular cyclic adenosine monophosphate.
H₃ receptors are primarily located on histamine-secreting cells and mediate negative feedback.
H₁-receptor antagonists, including diphenhydramine, have multiple therapeutic uses, including allergic reactions, upper respiratory tract infections, vertigo, nausea, sedation, cough suppression, and dyskinesias..

H₂-Receptor Antagonists

H₂-receptors, found in parietal cells, increase gastric acid secretion.
H₂-receptor antagonists inhibit histamine binding to H₂ receptors, reducing gastric acid output.
Cimetidine, famotidine, nizatidine, and ranitidine are H₂-receptor antagonists.
These agents are used to treat peptic ulcers, hypersecretory states, gastroesophageal reflux disease (GERD), and prevent aspiration pneumonia perioperatively.

Proton Pump Inhibitors

PPIs inhibit the proton pump of parietal cells, decreasing gastric hydrogen ion secretion.
Omeprazole, lansoprazole, rabeprazole, esomeprazole, and pantoprazole are examples.
PPIs are used for peptic ulcer disease, GERD, and Zollinger-Ellison syndrome.
Potential side effects include hepatotoxicity, interstitial nephritis, and interactions with other drugs.

Post Operative Nausea & Vomiting (PONV)

PONV occurs in approximately 30-80% of patients.
Risk factors include female gender, history of PONV/motion sickness, nonsmoker, use of opioids and duration of surgery
Risk factors for children include age, surgery > 30 minutes, and history of PONV.
Prophylactic antiemetics, including 5-HT3 antagonists, butyrophenones (dexamethasone), NK1-receptor antagonists, antihistamines and scopolamine are used.

Butyrophenones

Droperidol is a butyrophenone used for PONV prophylaxis.
This drug is no longer commonly used due to concerns about QT prolongation, Torsades de Pointes, and cardiac effects.
Other phenothiazines, such as promethazine, may be alternative options, however, are not commonly used for prophylaxis of PONV.

Doxapram

Doxapram is a peripheral and central nervous system stimulant
It selectively activates carotid chemoreceptors.
It is not a reversal agent and thus should not replace standard supportive therapies.
Stimulation leads to an increase in tidal volume and respiratory rate.
The drug should not be used in patients with underlying conditions such as epilepsy, cerebrovascular disease, acute head injury, or bronchial asthma.

Naloxone

Naloxone is a competitive opioid receptor antagonist with high affinity for µ receptors.
It reverses the effects of opioid-induced respiratory depression.
It is used in emergency situations involving overdose or opioid-related respiratory issues.
Rapid reversal can lead to a surge in sympathetic activity.

Flumazenil

Flumazenil is a benzodiazepine receptor antagonist.
It reverses benzodiazepine-induced sedation and overdose.
It should be used cautiously, especially in patients with pre-existing conditions, including head injuries.

Dexamethasone

Dexamethasone is a synthetic corticosteroid that reduces the incidence of PONV.
Its mechanism of action is not fully understood, but it may have analgesic and mild euphoric effects.
It may increase postoperative blood glucose.
It should be administered at induction, not at the end of surgery.

Neurokinin-1 Receptor Antagonists

Aprepitant is a neurokinin-1 receptor antagonist that reduces PONV.
It's often used in combination with other agents given its additive effect.

Ketorolac

Ketorolac is a nonsteroidal anti-inflammatory drug (NSAID).
Decreases postoperative need for opioid analgesics as it inhibits prostaglandin synthesis.
It has minimal central nervous system side effects and is commonly used post-operatively.

Clonidine

Clonidine is an imidazoline derivative with prominent α2-adrenergic agonist activity.
It reduces sympathetic tone by decreasing systemic vascular resistance, heart rate, and blood pressure.
It has analgesic effects, especially during epidural/caudal/peripheral nerve blocks, thus decreasing the need for opioids.
It is also indicated in chronic neuropathic pain management.

Dexmedetomidine

Dexmedetomidine is a selective α2-agonist with sedative properties.
It causes dose-dependent sedation, anxiolysis, analgesia, and blunting of sympathetic responses.
It spares opioids and is particularly useful in mechanically ventilated patients.
Side effects include bradycardia, heart block, and hypotension.

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