Post-operative Nausea and Vomiting Flashcards
(12 cards)
What is PONV?
post-operative nausea and vomiting
What is the definition of PONV?
PONV is an umbrella term that covers nausea, retching and vomiting that occurs within the 24-48 hours after surgery.
Give examples of PONV consequences if left untreated. Include rationale
- bleeding - reopening of surgical wounds
- wound dehiscence - retching causes intra-abdominal pressure which can cause sutures to separate and blood vessels to rupture
- pulmonary aspiration - PONV weakens the reflexes and consciousness due to anaesthesia which cause stomach acid to expel into the lungs thus lead to irritation and inflammation
- oesophageal perforation - also called boerhaave’s syndrome where a strong, involuntary expulsion of gastric contents increases intra-oesophageal pressure which leads to a tear in the oesophageal wall
- dehydration or electrolyte imbalance - fluid loss from vomiting or reduced fluid intake
- increased recovery or hospital stay - delays recovery as requiring medical attention and leads to complications
What is pathophysiology of PONV?
The chemoreceptor trigger zone (CTZ) lies outside the blood brain barrier and plays an integral role in detecting substances in the blood. Three significant neurotransmitters such as serotonin, dopamine and histamine gets detected by its receptors and stimulates the CTZ. Opioids in the blood are detected by both opioid receptors in the CTZ and dopamine receptors. Whereas, serotonin is detected by both peripheral receptors and central receptors. The stimulation of CTZ sends emetogenic triggers to the brainstem’s vomiting centre to activate the vomiting reflex.
How do you conduct a physical assessment for PONV? include rationale
- assess onset, duration, frequency and quantity of vomit - to check severity
- medication - opioids can exasperate condition
How do you conduct a holistic assessment of PONV? include rationale
- history of smoking - non-smokers are more at risk
- history of motion sickness - increases risk
- history of anxiety/migraine - risk factor
- history of PONV - risk factor
What are the red flags when assessing PONV? include rationale
- absence of bowel sounds/flatus - may indicate ileus
- blood in vomit - indicates perforation
- confusion/agitation - represents dehydration/electrolyte imbalance
- signs of anaemia/blood loss - indicates perforation
What is the first line of treatment recommended for PONV? include rationale
Serotonin receptor antagonists - recommended as first line of treatment as the body have serotonin receptors both peripherally and centrally, which acts as a powerful anti-emetic effect as they block both receptors.
What is the pharmacodynamics of serotonin receptor antagonists?
Serotonin receptor antagonists are effective anti-emetics as they block serotonin receptors which are located in peripheral (GI tract) and central nervous system. By blocking serotonin peripheral action, it prevents signals from the GI tract/peripheral nervous system to reach the CNS. In the CNS, serotonin receptors are located in the chemoreceptor trigger zone and the vomiting centre. By blocking these receptors, the signals are reduced between the CTZ and vomiting centre which prevents nausea and vomiting from being triggered.
What is unique about the positioning of the CTZ compared to the rest of the brainstem?
It lies outside the blood brain barrier which allows it to detect the chemicals/toxins in our blood.
Which receptors on the CTZ detect opioids?
Opioid and dopamine receptors
Where does the CTZ relay messages to trigger vomiting?
The CTZ relays messages to the vomiting centre of the brain which then triggers the vomiting reflex
