Nausea

• Emetic response involves the coordination of central and peripheral pathways
• Central pathway signals come directly from the brain, including the cerebral cortex, thalamus, hypothalamus, and vestibular system
• Peripheral pathway involves long fibers acting on peripheral nerves such as vagus and splanchnic nerves
• Chemoreceptor Trigger Zone (CRTZ) is located outside the blood-brain barrier and is exposed to toxins
• Abnormal absorption of toxins can activate components of CRTZ, including neurotransmitters like neurokinin 1 (NK-1), dopamine, serotonin, acetylcholine, and substance P
• Substance P binds to NK-1 receptor, resulting in the activation of the vomiting response
• There are 3 phases of the vomiting reflex: Pre-ejection, Ejection, and Post-ejection
• Other symptoms associated with nausea include increased salivation, shivering, fast heart rate, palpitations, and slowed stomach movements
• After nausea, retching occurs, followed by vomiting
• Reverse peristalsis leads to the movement of food content from the small intestine back to the stomach
• Retching is the start of the ejection phase, involving intense rhythmic contractions of chest, abdominal muscles, and diaphragm
• During retching, the pyloric sphincter relaxes, allowing food to move from the intestine to the stomach
• Intense contraction during retching forces stomach contents into the esophagus, leading to vomiting
• The glottis closes to prevent food from entering the airway during vomiting
• Fatigue and muscle weakness may signal the beginning of the post-ejection phase
• Nausea is defined as the inclination to vomit, while vomiting is the forceful expulsion of gastric contents through the mouth
• The three consecutive phases of emesis are nausea, retching, and vomiting
• Vomiting is triggered by afferent impulses to the vomiting center in the medulla, integrating signals from sensory centers like the chemoreceptor trigger zone, cerebral cortex, and visceral afferents
• Efferent impulses from the vomiting center lead to salivation, respiratory changes, and muscle contractions for vomiting
• Specific Etiologies of Nausea and Vomiting
• Treatment of simple nausea or vomiting may involve antacids or antihistaminic-anticholinergic agents like dimenhydrinate, diphenhydramine, hydroxyzine, meclizine, scopolamine, and trimethobenzamide
• Antihistaminic-anticholinergic agents are used for motion sickness and simple nausea and vomiting
• Benzodiazepines are weak antiemetics used for anxiety or anticipatory nausea and vomiting
• Phenothiazines are useful for simple nausea and vomiting, with rectal administration as an alternative route
• Dexamethasone is commonly used for chemotherapy-induced nausea and vomiting
• Metoclopramide is used for diabetic gastroparesis and prophylaxis of delayed nausea and vomiting with chemotherapy
• Neurokinin 1 receptor antagonists like aprepitant and fosaprepitant are indicated for prophylaxis of nausea and vomiting with high-dose cisplatin-based chemotherapy
• 1. HT3 receptor antagonists like dolasetron, granisetron, ondansetron, and palonosetron are used for CINV, PONV, and radiation-induced nausea and vomiting
• Scopolamine is effective for motion sickness prevention
• During pregnancy, management of nausea and vomiting may involve dietary changes, pyridoxine, doxylamine, IV fluid replacement with thiamine, and medications like ondansetron, promethazine, and metoclopramide
• In children, corticosteroids plus 5-HT3 receptor antagonists are administered for chemotherapy-induced nausea and vomiting