Post-operative Nausea and Vomiting (PONV)

Last updated: March 9, 2026Bookmark

Table Of Contents

Overview
Antiemetics

Overview

Post-operative Nausea and Vomiting is the leading cause of delayed discharge from PACU. Current recommendations is at least 2 prophylactic drugs for patients with at least 1 risk factor for PONV. Combinations should be with drugs that have different mechanism of action.

Chemoreceptor Trigger Zone

Major Risk Factors for PONV

Risk factor	Examples
Patient-related	Female, History of PONV or motion sickness, young, non-smoker
Anaesthetic related	Volatile agents, Nitric Oxide, Post-op narcotics, Neostigmine, Aggressive hydration (gut oedema)
Surgery-related	Duration of surgery (> 2 hours), laparoscopic, bariatric, gynaecological, cholecystectomy

Risk factors for PONV in adults
- Age < 50 years
- Female gender
- History of PONV/Motion sickness
- Non-smoking status
Risk factors for PONV in children
- Age > 3 years
- History of nausea/vomiting (in the child or relative)
- Strabismus surgery
- Surgery > 30 minutes
Factors that increase the incidence of PONV
- Duration of anaesthesia
- Post-operative opioid use
- Laparoscopic, cholecystectomy, gynaecological
- Nitrous oxide and volatile agents
Strategies for reducing PONV
- Regional anaesthesia
- Using propofol for induction and maintenance of anaesthesia (TIVA)
- Avoid nitrous oxide and volatile agents
- Minimising intra-operative and post-operative opioids use
- Adequate hydration
- Avoid hypotension and cerebral hypoxia
- Use a combination of antiemetics in different classes
- Use sugammadex instead of neostigmine for reversal
Consequences of PONV
- Aspiration risk and airway compromise
- Dehydration and electrolyte changes
- Increased CVP, ICP, suture or mesh disruption, venous hypertension and bleeding, or wound dehiscence

Antiemetics

5-HT3 Antagonists (Ondansetron, Granisetron)

These are more effective at preventing emesis than just preventing nausea. They are usually given approximately 30 minutes before emergence

Side effects of 5-HT3 Antagonists
- Headache
- QT prolongation

Steroids (Dexamethasone)

Steroids are cheap and effective and give prolonged PONV relief. There mechanism of action is uncertain. Dexamethasone (4 -10mg) can be given IV after induction.

Side effects
- Can cause severe perineal itching or discomfort in awake patients
- A single does does not cause a significant increase in blood glucose (for diabetes), infection, or cancer recurrence

IV Induction agents (Propofol)

Propofol can be given as a low-dose bolus (10-20 mg) in PACU or as low-dose infusion during the case to prevent PONV.

Anticholinergics (Scopolamine patch)

Scopolamine patch can be given 2-4 hours pre-op. A patch (1.5 mg) can also be given TD q72h (placed in the posterior ear lobe)

Side effects
- Anticholinergic side effects are potentially worse than nausea and vomiting in some patients
- Can cause post-op confusion/delirium in elderly patients
- Mydriasis if the patient touches the patch and wipes their eyes

Phenothiazines (Promethazine, Prochlorperazine)

These are dopamine antagonists (promethazine also has H1 antagonism). They can be given IV or IM. Usually given IV at the end of a case.

Side effects
- Sedation
- Extrapyramidal side effects

Gastrokinetic (Metoclopramide)

Metoclopromide is a dopamine antagonist. Dose required may exceed 25 mg which can increase the risk of extrapyramidal side effects.

Side effects
- Extrapyramidal side effects
- Increased GI motility and LES tone (avoid in patients with bowel obstruction)
Contraindications
- Patients with Parkinson Disease
- Bowel obstruction

Butyrophenones (Droperidol, Haloperidol)

These are central dopamine anatagonist. Droperidol is especially cheap and very effective, however it can cause arrhythmia when given at much higher doses. Haloperidol (at 1mg) is just as effective as Ondansetron with a similar side effect profile.

Side effects
- QT prolongation
Contraindications
- Patients with Parkinson Disease

Substance P Antagonists (Aprepitant, Fosaprepitant)

These are Neurkinin 1 Receptor Antagonists. They are more effective when given with Ondansetron. The downside is that they are expensive (reserved for posterior fossa neurosurgery and chemotherapy related PONV). PO is preferred since it is more cost effective. The can also be used for patients with refractory PONV.

Other Antiemetic Agents

Class	Description
Vasopressors	Prevents intestinal hypoperfusion. Ephedrine 50mg IM
Antihistamines (H2-blockers)	Often given pre-operatively. Cimetidine 300mg IV, Ranitidine 50 mg IV
Gabapentin	Given 600 – 800 mg preoperatively
Midazolam	Effective is given at the end of surgery but less favourable since it causes sedation

Reference Intervals ›

Biochemistry

ACTH	P: <80 ng/L
ALT	P: 5–35 U/L
Albumin	P: 35–50 g/L
Aldosterone	P: 100–500 pmol/L
Alk. phosphatase	P: 30–130 U/L
α-Amylase	P: 0–180 IU/dL
α-Fetoprotein	S: <10 kU/L
Angiotensin II	P: 5–35 pmol/L
ADH	P: 0.9–4.6 pmol/L
AST	P: 5–35 U/L
Bicarbonate	P: 24–30 mmol/L
Bilirubin	P: 3–17 μmol/L
BNP	P: <50 ng/L
CRP	P: <10 mg/L
Calcitonin	P: <0.1 mcg/L
Calcium (ionized)	P: 1.0–1.25 mmol/L
Calcium (total)	P: 2.12–2.60 mmol/L
Chloride	P: 95–105 mmol/L
Cholesterol	P: <5.0 mmol/L
VLDL	P: 0.128–0.645 mmol/L
LDL	P: <2.0 mmol/L
HDL	P: 0.9–1.93 mmol/L
Cortisol AM	P: 450–700 nmol/L
Cortisol Midnight	P: 80–280 nmol/L
CK ♂	P: 25–195 U/L
CK ♀	P: 25–170 U/L
Creatinine	P: 70–100 μmol/L
Ferritin	P: 12–200 mcg/L
Folate	S: 2.1 mcg/L
FSH	P: 2–8 U/L ♂; >25 menopause
GGT ♂	P: 11–51 U/L
GGT ♀	P: 7–33 U/L
Glucose (fasting)	P: 3.5–5.5 mmol/L
Growth hormone	P: <20 mu/L
HbA1C (DCCT)	B: 4–6%
HbA1C (IFCC)	B: 20–42 mmol/mol
Iron ♂	S: 14–31 μmol/L
Iron ♀	S: 11–30 μmol/L
Lactate (venous)	P: 0.6–2.4 mmol/L
Lactate (arterial)	P: 0.6–1.8 mmol/L
LDH	P: 70–250 U/L
LH	P: 3–16 U/L
Magnesium	P: 0.75–1.05 mmol/L
Osmolality	P: 278–305 mosmol/kg
PTH	P: 0.8–8.5 pmol/L
Potassium	P: 3.5–5.3 mmol/L
Prolactin ♂	P: <450 U/L
Prolactin ♀	P: <600 U/L
PSA	P: 0–4 mcg/mL
Protein (total)	P: 60–80 g/L
Red cell folate	B: 0.36–1.44 μmol/L
Renin (erect)	P: 2.8–4.5 pmol/mL/h
Renin (recumbent)	P: 1.1–2.7 pmol/mL/h
Sodium	P: 135–145 mmol/L
TBG	P: 7–17 mg/L
TSH	P: 0.5–4.2 mU/L
T4	P: 70–140 nmol/L
Free T4	P: 9–22 pmol/L
TIBC	S: 54–75 μmol/L
Triglycerides	P: 0.50–2.3 mmol/L
T3	P: 1.2–3.0 nmol/L
Troponin T	P: <0.1 mcg/L
Urate ♂	P: 210–480 μmol/L
Urate ♀	P: 150–390 μmol/L
Urea	P: 2.5–6.7 mmol/L
Vitamin B12	S: 0.13–0.68 nmol/L
Vitamin D	S: 50 nmol/L

Arterial Blood Gases

pH	7.35–7.45
PaCO₂	4.7–6.0 kPa
PaO₂	>10.6 kPa
Base excess	±2 mmol/L

Urine

Cortisol (free)	<280 nmol/24h
Hydroxyindole acetic acid	16–73 μmol/24h
Hydroxymethylmandelic acid	16–48 μmol/24h
Metanephrines	0.03–0.69 μmol/mmol cr.
Osmolality	350–1000 mosmol/kg
17-Oxogenic steroids ♂	28–30 μmol/24h
17-Oxogenic steroids ♀	21–66 μmol/24h
17-Oxosteroids ♂	17–76 μmol/24h
17-Oxosteroids ♀	14–59 μmol/24h
Phosphate (inorganic)	15–50 mmol/24h
Potassium	14–120 mmol/24h
Protein	<150 mg/24h
Protein/creatinine ratio	<3 mg/mmol
Sodium	100–250 mmol/24h

Haematology

WCC	4.0–11.0 ×10⁹/L
RBC ♂	4.5–6.5 ×10¹²/L
RBC ♀	3.9–5.6 ×10¹²/L
Hb ♂	130–180 g/L
Hb ♀	115–160 g/L
PCV ♂	0.4–0.54 L/L
PCV ♀	0.37–0.47 L/L
MCV	76–96 fL
MCH	27–32 pg
MCHC	300–360 g/L
RDW	11.6–14.6%
Neutrophils	2.0–7.5 ×10⁹/L (40–75%)
Lymphocytes	1.0–4.5 ×10⁹/L (20–45%)
Eosinophils	0.04–0.44 ×10⁹/L (1–6%)
Basophils	0–0.10 ×10⁹/L (0–1%)
Monocytes	0.2–0.8 ×10⁹/L (2–10%)
Platelets	150–400 ×10⁹/L
Reticulocytes	0.8–2.0% / 25–100 ×10⁹/L
Prothrombin time	10–14 s
APTT	35–45 s

Paediatric

Pulse Rate (bpm)
Neonate	140–160
Infant <1yr	120–140
1–5 years	110–130
5–12 years	80–120
>12 years	70–100
Respiratory Rate (tachypnoea)
0–2 months	≥60/min
2–12 months	≥50/min
1–5 years	≥40/min
>5 years	≥30/min
Blood Pressure (mmHg)
Term	65/45
1 year	75/50
4 years	85/60
8 years	95/65
10 years	100/70
Weight Formulas
3–12 months	(a + 9)/2 kg
1–6 years	2a + 8 kg
>6 years	(7a − 5)/2 kg
Haemoglobin (g/dL)
Term newborn	13–20
1 month	11–18
2 months	10–15
1–2 years	10–13
>2 years	11–14
MUAC (6 months–5 years)
Obese	>17.5 cm
Normal	13.5–17.4 cm
At risk	12.5–13.4 cm
Moderate malnutrition	11.5–12.4 cm
Severe malnutrition	<11.5 cm
Developmental Milestones
Social smile	1.5 months
Head control	4 months
Sits unsupported	7 months
Crawls	10 months
Stands unsupported	10–12 months
Walks	12–13 months
Talks	18 months
CSF WBC (/mm³)
Term newborn	0–25
>2 weeks	0–5

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