Give me a 10 marks answer about post operative nausea and vomiting under the headings of definition, mechanisms, risk factors, scoring systems, prevention, management from the above attached files for AIIMS md anaesthesia exams
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python3 << 'EOF' import pdfplumber for fname, path in [ ("Google 40", "/tmp/workspace/attachments/1e990600-86ba-45df-ab9f-5208a9334293/Google 40.pdf"), ("Google 41", "/tmp/workspace/attachments/1e990600-86ba-45df-ab9f-5208a9334293/Google 41.pdf"), ]: print(f"\n{'='*60}") print(f"FILE: {fname}") print('='*60) with pdfplumber.open(path) as pdf: print(f"Total pages: {len(pdf.pages)}") for i, page in enumerate(pdf.pages): text = page.extract_text() if text: print(f"\n--- Page {i+1} ---") print(text) EOF
Both PDFs have been fully extracted. Now I'll compile a comprehensive, exam-ready 10-mark answer.
POST-OPERATIVE NAUSEA AND VOMITING (PONV)
AIIMS MD Anaesthesia - 10 Marks Answer
1. DEFINITION
PONV is defined as any nausea, retching, or vomiting occurring during the first 24-48 hours after surgery in inpatients.
- Postdischarge nausea and vomiting (PDNV) refers to emetic symptoms after hospital discharge in ambulatory patients.
- Postoperative vomiting (POV) refers specifically to the vomiting component in children.
Incidence: Without prophylaxis, PONV occurs in 20-30% of all surgical patients under general anaesthesia and up to 70-80% in high-risk patients. After a first episode in the recovery room, the recurrence rate for PONV is 65-84%. PDNV occurs in approximately 37% of patients in the days after surgery. PONV is consistently rated as the anaesthesia outcome patients most want to avoid, with a high willingness-to-pay ($50-100) to prevent it.
Complications: Suture dehiscence, aspiration of gastric contents, oesophageal rupture, delayed discharge from PACU, unexpected hospital admissions in outpatients, increased healthcare costs.
2. MECHANISMS (Physiology/Pathophysiology)
The pathophysiology of PONV is complex. The brain structures involved are distributed throughout the medulla oblongata - there is no single anatomically defined "vomiting centre."
Key Structures:
Chemoreceptor Trigger Zone (CRTZ)
- Located at the caudal end of the fourth ventricle in the area postrema
- Lacks the blood-brain barrier, so it detects emetogenic toxins, metabolites, and drugs circulating in blood and CSF
- Receives vagal afferent input from the gastrointestinal tract
- Projects neurones to the Nucleus Tractus Solitarius (NTS)
Nucleus Tractus Solitarius (NTS)
- Located in the area postrema and lower pons
- Receives input from vagal afferents, vestibular system, and limbic system
- Triggers vomiting by stimulating the rostral nucleus, nucleus ambiguus, ventral respiratory group, and dorsal motor nucleus of the vagus
Neurotransmitter Pathways:
| Pathway | Receptors | Stimulus |
|---|---|---|
| GI enterochromaffin cells → vagus → CRTZ | 5-HT3 (serotonin) | Volatile anaesthetics, gut distension, opioids |
| CRTZ → NTS | D2 (dopamine) | Emetogenic drugs, toxins |
| Vestibular system → NTS | H1 (histamine) + mACh (muscarinic) | Motion, change in equilibrium |
| Cerebral cortex → NTS | Multiple neuroreceptors | Anticipatory/anxiety-induced nausea |
Opioid mechanism: Opioids reduce muscle tone and peristaltic activity, delay gastric emptying, cause gastric distension, and trigger the vomiting reflex via μ-opioid receptors in the CNS and peripherally in the GI tract.
Volatile anaesthetic mechanism: May decrease serum anandamide (endogenous cannabinoid neurotransmitter acting on CB-1 and TRPV-1 receptors that suppress nausea/vomiting). Effect is dose-dependent.
Nitrousoxide stimulates receptors in the vomiting centre and CRTZ; only 20-30% of patients respond to any single antiemetic, since multiple pathways are involved.
3. RISK FACTORS
A. Well-Established Independent Risk Factors
Patient-related:
- Female gender - strongest risk factor; OR = 3 (women are 3x more likely than men)
- Non-smoking status - OR = 2; smokers have lower risk, possibly due to cytochrome P450 induction by polycyclic aromatic hydrocarbons increasing metabolism of emetogenic volatiles
- History of PONV and/or motion sickness - OR = 2; indicates general susceptibility
- Age - in adults, incidence decreases with age (statistically relevant); in children >3 years, risk increases compared to <3 years; peak incidence ~40% in 11-14 year age group
Anaesthesia-related:
- Volatile anaesthetics - 2-fold increase; dose-dependent; most important factor for emesis in first 2 postoperative hours
- Nitrous oxide - relative risk increase of 1.4 (should be avoided in surgeries lasting >1 hour)
- Intraoperative and postoperative opioids - dose-dependent risk increase
- Duration of anaesthesia - describes cumulative exposure to emetogenic stimuli
B. Potential Risk Factors (Variable Association)
- Low ASA physical status (I-II)
- History of migraine
- Preoperative anxiety
- Locoregional vs general anaesthesia (GA associated with higher PONV; OR 1.3-10.6)
- Strabismus surgery (independent risk factor for POV in children)
- Gynaecological, ophthalmological, otological, thyroid surgery (in some studies)
C. Disproved Risk Factors
- Body mass index - no impact
- Menstrual cycle phase - no impact
- Remifentanil vs fentanyl - no significant difference
- Supplemental oxygen (FiO2 80%) - does not reduce PONV
- Nasogastric tube decompression - no effect on PONV
- Neostigmine - insufficient evidence to confirm increased risk (using sugammadex instead is associated with lower PONV incidence)
4. SCORING SYSTEMS
Risk scores are developed using multivariable analysis; validity is assessed by the AUC-ROC (Area Under Receiver Operating Characteristic Curve). AUC-ROC of 1 = perfect discrimination; 0.5 = no better than chance. Most scores achieve AUC-ROC of 0.65-0.80.
A. Apfel Simplified Score (Adults) - Most widely used
| Risk Factors (4 total) | Points |
|---|---|
| Female gender | 1 |
| History of PONV and/or motion sickness | 1 |
| Non-smoking status | 1 |
| Postoperative opioid use | 1 |
Predicted PONV incidence:
| Score | Risk |
|---|---|
| 0 | 10% |
| 1 | 20% |
| 2 | 40% |
| 3 | 60% |
| 4 | 80% |
AUC-ROC = 0.69
B. Koivuranta Score (Adults) - 5 risk factors
Factors: Female gender, non-smoking status, history of PONV, history of motion sickness, duration of surgery ≥60 min.
- 0/1/2/3/4/5 factors → 17%/18%/42%/54%/74%/87% PONV incidence
- AUC-ROC = 0.71
C. POVOC Score (Children)
Independent risk factors: Duration of surgery ≥30 min, age ≥3 years, strabismus surgery, history of POV in the child or PONV in relatives (4 factors).
- 0/1/2/3/4 factors → 9%/10%/30%/55%/70% POV incidence
Key principle: Multifactorial scores are significantly more accurate than single risk factors alone (AUC-ROC of surgery site = 0.68, history of PONV = 0.53, motion sickness = 0.58).
5. PREVENTION (Prophylaxis)
Step 1 - Reduce Baseline Risk
- Use locoregional anaesthesia instead of GA wherever possible
- If GA required, use TIVA with propofol (reduces PONV by ~30%, equivalent to one antiemetic drug)
- Avoid volatile anaesthetics (desflurane, sevoflurane, isoflurane) and nitrous oxide
- Minimise intraoperative and postoperative opioids; use multimodal opioid-sparing analgesia (NSAIDs, COX-2 inhibitors, paracetamol, gabapentin, regional nerve blocks)
- Adequate IV hydration with crystalloids/colloids (20-25 ml/kg) and vasopressors as needed
- Use sugammadex instead of neostigmine for neuromuscular block reversal
- Preoperative gabapentin 600-800 mg or pregabalin 150 mg reduce opioid consumption and PONV
Step 2 - Stratify Risk and Administer Prophylaxis
Based on number of Apfel risk factors:
- Low risk (0-1 factors): No prophylaxis or consider single drug
- Moderate risk (1-2 factors): 1-2 antiemetic interventions
- High risk (≥3 factors): 2-4 antiemetic interventions from different drug classes
Step 3 - Antiemetic Drug Classes
First-line drugs (each reduces PONV by ~25%):
| Drug | Class | Dose (Adult) | Timing | Notes |
|---|---|---|---|---|
| Ondansetron | 5-HT3 antagonist | 4-8 mg IV | End of surgery | QTc prolongation risk |
| Palonosetron | 5-HT3 antagonist (2nd gen) | 0.075 mg IV | After induction | 40h half-life; no QTc effect; 100x higher affinity |
| Granisetron | 5-HT3 antagonist | 0.3-1 mg IV | End of surgery | |
| Ramosetron | 5-HT3 antagonist (2nd gen) | 0.3 mg IV | End of surgery | Longer duration (6-9h) than ondansetron |
| Dexamethasone | Corticosteroid | 4-10 mg IV | After induction | Also reduces pain and fatigue; transient hyperglycaemia |
| Droperidol | D2 antagonist | 0.625-1.25 mg IV | End of surgery | Short half-life; FDA black box warning; QTc prolongation |
| Aprepitant | NK-1 antagonist | 40 mg oral / 32 mg IV | 1-2h before induction | 70-80% reduction in vomiting; useful in high-risk patients; no QTc effect |
Second-line drugs:
| Drug | Class | Notes |
|---|---|---|
| Metoclopramide | D2 antagonist | 10 mg dose ineffective; 25-50 mg effective; extrapyramidal side effects |
| Haloperidol | Butyrophenone | 1 mg IV; similar efficacy to 5-HT3 antagonists |
| Scopolamine (TD) | Anticholinergic | Patch applied evening before surgery; 40% risk reduction; visual disturbances |
| Dimenhydrinate | H1 antagonist | 25-50 mg IV; sedation, dry mouth |
| Midazolam | Benzodiazepine | 2 mg IV at induction; anxiolytic; not at end of surgery (causes sedation) |
| Amisulpride | D2/D3 antagonist | 5 mg IV; no QTc prolongation or sedation; useful in prophylaxis failures |
| Olanzapine | Antipsychotic | 10 mg oral; useful in multimodal regimen with ondansetron + dexamethasone |
| Gabapentin/Pregabalin | Gabapentinoids | Opioid-sparing; reduce PONV indirectly; risk of respiratory depression with CNS depressants |
Non-pharmacological:
- PC6 (Nei-Kuan) acupoint stimulation - 6th point of pericardial meridian at wrist; shown to reduce PONV without major side effects
- Chewing gum, aromatherapy (peppermint, lemon, isopropyl alcohol) - variable evidence
Combination/Multimodal Therapy
- Combining drugs from different classes produces additive effects (each targeting different receptor pathways)
- Ondansetron + dexamethasone is more effective than either alone
- Aprepitant + ondansetron or aprepitant + dexamethasone is more effective than single agents
- Olanzapine 10 mg + ondansetron + dexamethasone - additive efficacy
- Incremental antiemetic benefit decreases with each additional antiemetic added
ERAS Protocol Components for PONV Prevention:
Regional anaesthesia, opioid-sparing multimodal analgesia, adequate IV hydration, anxiolytics (midazolam), TIVA, double/triple antiemetic therapy based on Apfel score.
6. MANAGEMENT of Established PONV
Principles:
- First, rule out mechanical or medication causes (e.g., bowel obstruction)
- Rescue antiemetic should be from a different drug class than prophylaxis given
- Ondansetron given prophylactically - if PONV occurs within 6h, repeating ondansetron is no more effective than placebo
Algorithm:
If PONV within 6 hours of prophylaxis:
- Do NOT repeat the same prophylactic antiemetic
- Use an antiemetic from a different drug class
- Propofol bolus 20 mg IV in PACU has short but effective rescue antiemetic effect (comparable to ondansetron)
If PONV more than 6 hours after prophylaxis:
- Can repeat the same antiemetic, EXCEPT for long-acting agents (dexamethasone, aprepitant, palonosetron, TD scopolamine)
- Haloperidol 1 mg IV or amisulpride 10 mg IV can also be used
If NO prophylaxis was given:
- Begin with a 5-HT3 antagonist (ondansetron 4 mg IV)
Outpatients:
- Offer rescue therapy that can be administered orally or as a patch (e.g., transdermal scopolamine, ondansetron ODT, ramosetron ODT)
Combination therapy for rescue:
- More effective than single agents; use two drugs from different classes
Management in Children:
- For low risk: no prophylaxis or single 5-HT3 antagonist
- For medium risk: 5-HT3 antagonist + dexamethasone
- For high risk: 5-HT3 antagonist + dexamethasone + TIVA
- Rescue: droperidol, promethazine, dimenhydrinate, or metoclopramide (different class from prophylaxis); may consider acupuncture/acupressure
- Dexamethasone 0.15-1.0 mg/kg at induction reduces early and late PONV and postoperative pain
Summary Table - PONV Management Strategy
| Risk Level | Interventions |
|---|---|
| Low (0-1 factors, ~10-20%) | Baseline risk reduction only |
| Moderate (1-2 factors, ~20-40%) | TIVA or 1 antiemetic (ondansetron OR dexamethasone) |
| High (≥3 factors, 60-80%) | TIVA + 2-3 antiemetics from different classes (e.g., ondansetron + dexamethasone ± aprepitant/droperidol) |
Sources: Pierre S & Whelan R. "Nausea and vomiting after surgery." Continuing Education in Anaesthesia, Critical Care & Pain, Vol 13(1), 2013. | Kovac A & Choksi N. "Prophylaxis and treatment of postoperative nausea and vomiting." BJA Education, Vol 26(5), 2026.
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