Nausea & Vomiting
Nausea and vomiting comes into every area of Medicine. Knowledge of the basic concepts is key.
- GI Disease
- Raised Intracranial Pressure
- Opioids - 1/3 of patients started on opioids will have chemically mediated nausea, most of these patients will develop tolerance to this within 5–7 days as the body adapts. Haloperidol at a low dose can be prescribed alongside the opiate for the first week to relieve this nausea.
- Psychogenic - situational, fear, anger
Gastric stasis is classically nausea that is relieved by vomiting and is caused by opioids, liver mets and ascites.
Physiology and Treatment
There are 5 main pathways that cause nausea and vomiting:
- Vestibular Nucleus
- This is the area that responses to motion and changes in the middle ear
- Neurotransmitters - AChm (muscarinic acetylcholine) and H1 (Histamine)
- If the vestibular nucleus is the proplem then treat with Hyoscine Hydrobromide, Cyclizine
- Vagus Nerve Stimulation (Autonomic)
- This is stimulated by stretch - e.g. in bowel obstruction, liver capsule stretch
- Use Cyclizine
- Chemoreceptor Trigger Zone (CTZ)
- Anatomically, this is part of the area postrema - the posterior and inferior part of the fourth ventricle. This part of the brain is special as it is not separated by the blood-brain barrier.
- As it sits outside the blood brain barrier it can easily detect abnormalities in the bloodstream (e.g. drugs, toxins, electrolyte disturbances - high calcium/low sodium) and refer them directly to other parts of the brain.
- Neurotransmitters - 5HT3 (serotonin), D2 (dopamine), α2
- Use Ondansetron, Haloperidol
- Cerebral Cortex - Higher centre causes including situational, fear, anger, depression
- Neurotransmitters - GABA, 5HT3
- GI Tract - e.g. gastric stasis
- Neurotransmitters - 5HT3
- Use Metoclopramide
The final common pathway is that of the Vomiting Centre in the brain. This is where the above 5 pathways converge. It uses the neurotransmitters AChm, H1, 5HT. Use cyclizine, benzodiazepine.
These are drugs used to reduce the feelings of nausea and vomiting. It might be a good idea to start the antiemetic parentally as if you give it orally the patient might throw it up before it works! You can always switch the drug to oral later on when the patient feels better.
- Hyoscine Hydrobromide - anticholinergic
- Cyclizine - anticholinergic and antihistamine - note that the dose should be reduced in elderly patients and patients with impaired renal function
- Ondansetron - works against 5HT3
- Haloperidol - antidopaminergic
- Metoclopramide - antidopaminergic and works against 5HT3 - take care as in bowel obstruction can increase colic and pain