Post Operative Nausea and Vomiting Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: This is one of the most common complaints you will receive from a post-operative patient on the ward. Managing it effectively prevents delays in oral intake, reduces patient distress, and avoids prolonged hospital stays.
High-Yield Definition: Postoperative nausea and/or vomiting is defined as any episode of nausea, retching, or vomiting occurring within the first 24 to 48 hours after a surgical procedure. (Source: UpToDate, 2024).
Clinical One-Liner: Basically, it's the patient feeling sick and throwing up after surgery because of the anaesthesia, the operation, and their own personal risk factors.
II. Etiology & Risk Factors
Etiology: PONV is multifactorial. The main triggers are stimulation of the chemoreceptor trigger zone (CTZ) and the brain's vomiting centre by anaesthetic agents, opioids, and substances released due to tissue trauma.
Risk Factors: We use the Apfel Score to predict risk. It's simple and validated. Just remember these four points:
Female gender
Non-smoker
History of PONV or motion sickness
Postoperative opioids
Apfel Score Interpretation:
0-1 point: Low risk (~10-20%)
2 points: Moderate risk (~40%)
3-4 points: High risk (~60-80%)
III. Quick Pathophysiology
Think of three main pathways being triggered:
Chemoreceptor Trigger Zone (CTZ): Located in the brainstem, it's sensitive to drugs like volatile anaesthetics (e.g., sevoflurane) and opioids.
Vestibular System: Movement after surgery, especially middle ear procedures, can trigger this pathway, leading to motion-sickness-like symptoms.
Vagal Afferents: Abdominal and laparoscopic surgeries can irritate nerves in the gut, sending signals straight to the vomiting centre.
Different antiemetics target different pathways, which is why a multimodal approach is best.
IV. Clinical Assessment
Red Flags & Immediate Actions:
Your main job is to differentiate simple PONV from something more sinister.
Abdominal distension or absent bowel sounds: Could be paralytic ileus. → Action: Keep patient nil by mouth (NBM), inform senior, consider ordering an abdominal X-ray (AXR).
Fever and severe abdominal pain: May indicate an anastomotic leak or intra-abdominal collection. → Action: Alert senior/surgical registrar immediately. This is a surgical emergency.
Vomiting bile or feces (feculent vomitus): Suggests bowel obstruction. → Action: NBM, insert a Ryle's tube for decompression, and escalate urgently.
Signs of dehydration (tachycardia, hypotension, low urine output): Requires aggressive fluid resuscitation. → Action: Check vital signs, start IV fluid bolus (e.g., 500ml Normal Saline over 30 mins), and monitor urine output.
History:
Common: Ask "Are you feeling sick to your stomach (nausea)?" "Have you vomited?" "How many times?"
Clarify the timing, volume, and content of the vomitus.
Check their Apfel score risk factors.
Review the anaesthetic and intra-operative charts: What anaesthetic agents were used? How much opioid was given?
Physical Examination:
General: Assess hydration status (check for dry mucous membranes, reduced skin turgor).
Abdomen: Palpate for tenderness, rigidity, or distension. Auscultate for bowel sounds.
Vitals: Check for tachycardia or hypotension.
Clinical Pearl: Prevention is always better than cure. If the patient is high-risk based on the Apfel score, prophylaxis should have been given. Check the anaesthetic chart to see what they received.
V. Diagnostic Workflow
Differential Diagnosis:
PONV is a diagnosis of exclusion in a post-op patient. Always consider:
Paralytic Ileus:
Points For: Absent bowel sounds, abdominal distension, failure to pass flatus.
Points Against: Simple nausea without distension.
How to Differentiate: AXR showing dilated bowel loops.
Bowel Obstruction (Mechanical):
Points For: Colicky abdominal pain, vomiting, absolute constipation.
Points Against: Nausea improving with simple antiemetics.
How to Differentiate: AXR and often a CT scan are required.
Anastomotic Leak:
Points For: Tachycardia, fever, localised or generalised peritonism, feeling of impending doom. Usually occurs day 5-7 post-op.
Points Against: Well-looking patient with isolated nausea.
How to Differentiate: Urgent CT abdomen with contrast.
Investigations Plan:
For uncomplicated PONV, no investigations are needed. If red flags are present:
Bedside: Vital signs monitoring.
First-Line Labs:
Renal Profile (Urea & Electrolytes): To check for hypokalaemia, hyponatremia, and dehydration-related kidney injury.
Full Blood Count (FBC): Look for elevated white cells (infection) or hemoconcentration (dehydration).
First-Line Imaging:
Abdominal X-Ray (Supine & Erect): To look for dilated bowel loops or air under the diaphragm.
VI. Staging & Severity Assessment
We use the Apfel risk score pre-operatively to guide prophylaxis.
Low Risk (0-1 factor): No routine prophylaxis needed.
Moderate Risk (2 factors): Dual prophylaxis with two different classes of antiemetics.
High Risk (3-4 factors): Triple or quadruple prophylaxis. Consider regional anaesthesia instead of general anaesthesia if possible.
The severity post-op is clinically assessed based on patient distress and the frequency of vomiting episodes.
VII. Management Plan
Immediate Stabilisation (Rescue Therapy on the Ward):
If a patient has breakthrough PONV, use an antiemetic from a class different from their prophylactic drug.
First-Line Rescue:
IV Metoclopramide (Maxolon) 10mg TDS. It's a dopamine D2 antagonist. Fast-acting.
Second-Line Rescue:
IV Ondansetron (Zofran) 4mg. A 5-HT3 antagonist. Very effective, but don't repeat if it was already given as prophylaxis within 6 hours.
Ensure adequate IV hydration to compensate for losses.
Definitive Treatment (Prophylaxis Plan - decided pre-op):
This is the domain of the anaesthetist but you need to know it. A multimodal approach is key.
Based on Apfel Score:
1 Risk Factor: Consider single agent.
2 Risk Factors (Dual Therapy): e.g., IV Dexamethasone 4-8mg (given after induction) + IV Ondansetron 4mg (given at end of surgery).
>2 Risk Factors (Triple Therapy): Dexamethasone + Ondansetron + one other agent like Droperidol or changing anaesthetic technique (e.g. Total Intravenous Anaesthesia - TIVA).
Long-Term & Discharge Plan:
The patient must be able to tolerate oral fluids without nausea or vomiting before being cleared for discharge.
Provide a short course of oral antiemetics (e.g., PO Metoclopramide 10mg) if they have a strong history of PONV.
VIII. Complications
Immediate: Dehydration, electrolyte disturbances (hypokalaemia, metabolic alkalosis), aspiration pneumonia.
Short-Term: Wound dehiscence or haematoma from forceful vomiting, delayed enteral feeding.
Long-Term: Generally none, but poor experience can lead to future anxiety about surgery.
IX. Prognosis
Prognosis is excellent. PONV is typically self-limiting within 24-48 hours.
The main prognostic factors for developing PONV are the Apfel score risks. Patients with 3-4 risk factors have a very high chance of experiencing it without aggressive prophylaxis.
X. How to Present to Your Senior
"Dr, for review please. This is Mdm. Lim in Bed 10, Day 1 post-laparoscopic cholecystectomy. She has been complaining of persistent nausea and has vomited twice in the last hour. She is a non-smoker with a history of motion sickness, Apfel score of 3. She received IV Ondansetron intra-op. I have given her one dose of IV Metoclopramide and ensured her IV drip is running. Her abdomen is soft and non-tender. Vital signs are stable. Could I get your advice on further management if she does not respond?"
XI. Summary & Further Reading
Top 3 Takeaways:
Risk Stratify Every Patient: Use the Apfel score (Female, Non-smoker, History of PONV, Post-op Opioids).
Prevention is Key: High-risk patients need multimodal prophylaxis. Check what the anaesthetist has already given.
Think Beyond PONV: If a patient has abdominal pain, distension, or fever with vomiting, you must rule out serious surgical complications.
Key Resources:
UpToDate: "Postoperative nausea and vomiting" (An excellent, evidence-based summary).
Amboss: "Postoperative Nausea and Vomiting" (Good for quick review).
Malaysian Society of Anaesthesiologists & College of Anaesthesiologists: Check their website for local guidelines on PONV management. https://www.msa.asm.org.my/guidelines.php
