Procedural pain: topical anaesthesia, preparation, distraction and non-pharmacological support — formative SAQs

SAQ 1 (10 marks)

A 6-month-old previously well infant is brought to the emergency department for a febrile illness and requires a venepuncture and cannulation as part of the workup. The infant is alert and being nursed by the mother, who is distressed by the thought of her baby being hurt. The team has about 70 minutes before the bloods must be taken. [1] [11]

1. Outline the structured pre-procedure comfort assessment and the multi-modal comfort bundle you will apply, naming the specific agents, their concentrations and timings. (5) [2] [9]
2. Give the exact oral sucrose dose and timing you would use, and explain why the dose must not be expressed as millilitres per kilogram. (3) [3]
3. Explain why you will combine the layers rather than rely on a single measure, and cite the evidence. (2) [1]

Model answer — SAQ 1

(1) Assessment and bundle (5). I run a short structured assessment covering the child, the procedure, the allergies and the time. The child is a 6-month-old with no prior needle trauma and a parent who can hold; the procedure is a venepuncture and cannulation of moderate, brief pain needing the arm still; the allergies are none, and at six months there is no methaemoglobinaemia contraindication, so EMLA is acceptable; the time is about 70 minutes, which allows a full EMLA hour. The bundle: I apply EMLA (lidocaine 2.5% and prilocaine 2.5%) under an occlusive dressing for at least 60 minutes at the likely site (or two sites), engage the parent in an honest explanation, plan an upright comfort position on the mother's lap (chest-to-chest), run an age-appropriate distraction (a tablet video), and offer breastfeeding during the procedure or oral sucrose as the sweet/oral layer. [2] [9]

(2) Sucrose dose and timing (3). If breastfeeding is not used, I give oral sucrose 24%, 0.1 to 2 mL (maximum about 2 mL) about two minutes before the procedure and again as the needle goes in, onto the anterior tongue or buccal mucosa. The dose is an absolute volume, never millilitres per kilogram, because dosing per kilogram or in large volumes risks aspiration, chloride loading and overload, while the effective analgesic window is a small volume engaging the taste-bud to endogenous-opioid pathway. Giving it only as the needle is inserted (rather than two minutes before) is under-effective. [3]

(3) Why combine the layers (2). Each layer acts on a different limb of the pain response — topical anaesthesia blocks the skin sodium channel, sweet taste recruits endogenous opioid and dopamine, and distraction and comfort positioning engage gate-control and attentional modulation — so no single agent abolishes procedural pain. The Cochrane review on non-pharmacological management of infant and young child procedural pain found that combining non-pharmacological with pharmacological measures reduces procedural pain better than either alone, which is why the fellowship answer is always a bundle. [1]

SAQ 2 (10 marks)

A 3-week-old term neonate on the postnatal ward needs a heel lance and venepuncture for a bilirubin and septic screen. The registrar applies an EMLA patch and returns 40 minutes later. The neonate looks dusky; supplemental oxygen does not improve the colour, and the blood appears chocolate-brown. [2]

1. What complication has occurred, who is at risk, and why did EMLA cause it in this neonate? (3) [2]
2. Give the immediate management, including the specific drug and dose. (3) [2]
3. State how this event should have been prevented, including the preferred topical agent and the non-pharmacological measures that should have accompanied it. (4) [3] [1]

Model answer — SAQ 2

(1) The complication and the at-risk group (3). This is prilocaine-induced methaemoglobinaemia from the EMLA patch. Prilocaine metabolism produces an oxidant metabolite that oxidises the iron in haemoglobin to the ferric state, forming methaemoglobin that cannot carry oxygen, producing cyanosis unresponsive to oxygen and chocolate-brown blood. The risk is concentrated in infants under three months, preterm babies, and children with G6PD deficiency or concurrent oxidant exposure, because the young infant's methaemoglobin-reductase pathway is immature. EMLA caused it here precisely because this neonate is under three months, the group in whom EMLA is contraindicated. [2]

(2) Immediate management (3). I remove the EMLA patch and stop any further oxidant exposure, give high-flow oxygen, confirm the diagnosis with a methaemoglobin level (here already 28 percent) and a venous blood gas, and treat symptomatic methaemoglobinaemia with methylene blue 1 to 2 mg per kilogram intravenously over five minutes, repeating once after 30 to 60 minutes if symptoms persist. I would seek urgent haematology or toxicology input and check a G6PD assay, because methylene blue can cause haemolysis in G6PD-deficient infants, in whom ascorbic acid or exchange transfusion may be needed. [2]

(3) Prevention and the correct neonatal bundle (4). EMLA should not have been used: in a neonate under three months the safer topical is amethocaine 4% gel (Ametop), an ester with a 30 to 45 minute onset that does not carry prilocaine's methaemoglobinaemia risk (except in known ester or PABA allergy, where an amide would be chosen). The neonatal comfort bundle should have been layered around the procedure: oral sucrose 24%, 0.1 to 2 mL about two minutes before, breastfeeding during the procedure, a dummy for non-nutritive sucking, swaddled containment and skin-to-skin, and clustering of samples to minimise repeated heel lances. The Cochrane evidence supports sucrose, breastfeeding and skin-to-skin for neonatal procedural pain, and combining these is the standard of care for every neonatal needle. [3] [1]