Nausea causes a person to not want to eat or drink anything and vomiting can cause dehydration. There is no magic pill that combats every type of mediator triggering nausea and/or vomiting. This is why it’s important to differentiate between the areas that feed into the vomiting center.

1.     Chemoreceptor trigger zone (CTZ):

The chemoreceptor trigger zone (CTZ) for emesis, is located outside the blood-brain barrier, on the floor of the fourth ventricle of the brain. The CTZ contains receptors that detect emetic agents in the blood and relays that information to the vomiting center, which is responsible for inducing the vomiting reflex. It’s critical to note that because it is outside the BBB, emetogenic stimuli can reach it through the bloodstream. Think of this area as a smoke detector. It is on the lookout for toxins, poisons, and ickies taking a swim in your bloodstream. It uses opioid mu, kappa, neurokinin-1, dopamine, and serotonin to mediate its effects.

2.     The Vomiting Centre:

Think of this as the sprinkler system located in the medulla oblongata. The vomiting centre, when stimulated, leads to the inevitable vomiting reflex. The mediators histamine and acetylcholine play the biggest role.

3.     Other areas that feed into the vomiting center:

1.     Vestibular System:

The vestibular apparatus is part of the inner ear that provides a sense of balance and is an inertial guidance device.  The “spinning room” after a heavy night out, labyrinthitis, or motion sickness all fall into this category. It is mediated by histamine and muscarinic receptors.

2.     Gastrointestinal tract:

Gastric distention, toxic stimulation of vagal afferents, or stimulation of glossopharyngeal nerve are all components. It is mainly mediated by 5HT3 and dopamine receptors.

3.     Cortex:

Fear, anxiety, apprehension, stress, and emotion are the major components.
This is mediated by GABA receptors.

It’s slightly more complicated than this but if your toolbox is loaded with this information, you will have better skills for managing and treating nausea and vomiting. Proper assessments are key along with history and physical.

How do you treat nausea and vomiting?

First, differentiate between GI and Non-GI causes.

GI Causes:

1.     Is it a mechanical problem?

a.     Examine underlying cause to plan for possible treatments

2.     Is it a motility problem?

a.     Use metoclopramide as a prokinetic

3.     Is it a gastrointestinal source? Is there damage to the GI lining? Radiotherapy, chemotherapy, gastroenteritis…

a.     5HT3 antagonist ondansetron

4.     Is there a suspicion of toxins?

a.     Has a new drug been introduced?

 i.     Opioids: Use metoclopramide, haloperidol, or Prochlorperazine SHORT- term as opioid induced nausea is usually transient and resolves in several days

ii.     Antibiotics: food/crackers can often help

b.     Uremia, sepsis, DKA: target the CTZ and block dopamine with haloperidol or metoclopramide

5.     Is there suspicion of inner ear issue, raised intracranial pressure, or intracerebral pressure?

a.     Target vestibular/cerebellar inputs and block histamine/acetylcholine receptors. Use  hyoscyamine, promethazine, or prochlorperazine

6.     Is the nausea due to a component of emotion or fear?

a.     This is often referred to as anticipatory nausea and vomiting. Benzodiazepines are helpful short-term. Long-term anxiety, fear, emotions require assessment for alternate medications and behavioral health input.

Drug notes:

·       Metoclopramide can be very useful because it is non-sedating and it targets 2 causes of nausea.

·       Avoid using multiple antinausea medications together as they can cause severe side-effects

·       Ondansetron/ 5HT3 antagonists: Very constipating! Commonly combined with opioids which leads to severe constipation and worsening nausea.

·       Phenothiazines (Prochlorperazine and Promethazine): Palliative care workhorse that hits most receptors in the vomiting set up. These drugs are very sedating and can cause postural hypotension. Use caution in patients with dementia and they are known to cause extrapyramidal side effects.

Remember non-pharmacological options:

·       Control odors

·       Eliminate offending foods, tastes, or smells

·       Small, frequent feedings

·       Get bowels moving

·       Treat dry mouth/candida

·       Position (raise head in ICP)

·       Relaxation techniques

Clinical pearl: inhaling isopropyl alcohol (alcohol swab) from the nares was shown to be superior to oral ondansetron in a small study. It’s a quick method (and inexpensive too) to treat transient nausea.

It’s important to assess the patient for the root cause of nausea/vomiting prior to treatment.
Don’t throw spaghetti at the wall and see what sticks. Choose wisely!

Pharmacists are your friend for side-effects and treatment options. Pick their brain!

References:

MacDougall MR, Sharma S. Physiology, Chemoreceptor Trigger Zone. 2020 Sep 27. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 30725818.

Takeda N, Morita M, Hasegawa S, Horii A, Kubo T, Matsunaga T. Neuropharmacology of motion sickness and emesis. A review. Acta Otolaryngol Suppl. 1993;501:10-5. doi: 10.3109/00016489309126205. PMID: 8447218.

April MD, Oliver JJ, Davis WT, Ong D, Simon EM, Ng PC, Hunter CJ. Aromatherapy Versus Oral Ondansetron for Antiemetic Therapy Among Adult Emergency Department Patients: A Randomized Controlled Trial. Ann Emerg Med. 2018 Aug;72(2):184-193. doi: 10.1016/j.annemergmed.2018.01.016. Epub 2018 Feb 17. Erratum in: Ann Emerg Med. 2019 May;73(5):552. PMID: 29463461.