CT Contrast in a Patient with Low eGFR, a Prior Reaction and No Documented Consent
A 67-year-old man is booked for CT abdomen and pelvis with IV iodinated contrast for a suspected intra-abdominal abscess. eGFR is 28 mL/min/1.73 m², he takes metformin, and he had urticaria after contrast 5 years ago. He is drowsy after IV morphine for pain, GCS 14, and no next of kin is present. The referral does not document any contrast discussion. A colleague starts the injection through a 22G antecubital cannula at 3 mL/s. At 3 minutes the patient becomes wheezy with facial urticaria, BP 88/50 mmHg, HR 122, and SpO2 89% on room air.
1. What are your immediate actions, in order, with doses? Justify why this is treated as anaphylaxis rather than a mild reaction.
Read the worked answer
Recognise: hypotension (88/50) plus bronchospasm (wheeze, SpO2 89%) plus urticaria after contrast is anaphylaxis with shock and respiratory compromise - not a 'mild rash'. The speed of onset (3 minutes) supports an IgE-mediated mechanism.
Actions, in order:
- Stop the injection and disconnect the giving set; keep IV access.
- Call for help - resuscitation team/code, and state 'anaphylaxis, CT scanner'.
- Position: lay him supine with legs elevated (Trendelenburg) to support venous return, unless vomiting necessitates a recovery position.
- Oxygen 15 L/min via non-rebreathe mask.
- Adrenaline 0.5 mg IM (1:1000) into the anterolateral thigh - first-line, no delay; repeat at 5-minute intervals if there is no improvement. Do not wait for antihistamines to work.
- IV crystalloid bolus 500–1000 mL rapidly, reassessing blood pressure.
- Secondary measures: chlorphenamine 10 mg and hydrocortisone 200 mg IV; prepare for airway support and, if refractory, adrenaline infusion per protocol.
- Document times, doses, route and response; send to ED/resus for observation even if he improves, because biphasic reactions occur.
Antihistamines treat skin, not airway or circulation - giving them first is the classic error this scenario is testing.
2. Looking back at the decision to give contrast: what was appropriate, what was missed, and what should have happened before the cannula was inserted?
Read the worked answer
Renal risk: eGFR 28 places him at meaningful risk of contrast-associated AKI. Contrast was not necessarily wrong - an abscess may need to be characterised, and the benefit can outweigh the risk - but it required a documented radiologist discussion, consideration of ultrasound or non-contrast CT first, volume optimisation, and the smallest adequate volume of low-osmolar contrast.
Metformin: should have been withheld at the time of the study and for 48 hours afterwards, with renal function rechecked before restarting, because AKI plus metformin risks lactic acidosis.
Prior reaction: urticaria alone 5 years ago is a mild reaction, not a contraindication. Premedication (for example oral prednisolone 40 mg at 13, 7 and 1 hour plus an antihistamine) is often used but is only partly effective and does not prevent breakthrough anaphylaxis - so the real preparation is having adrenaline, oxygen and a resuscitation plan immediately available, which is a departmental readiness issue, not just this patient's.
Practical miss: a 22G cannula at 3 mL/s carries a high extravasation risk in an elderly patient; a larger, more proximal cannula or a slower rate should have been used. All of this belongs in the pre-procedure checklist, not in hindsight.
3. The patient is drowsy with GCS 14 and no documented consent. How do you handle consent and documentation, and what do you do about the missing next of kin?
Read the worked answer
Consent: a patient with GCS 14 and recent IV morphine cannot be assumed to have capacity for a complex decision at this moment. The radiographer should not proceed on implied consent for a non-emergency examination. The correct sequence is to page the referring team and the radiologist, assess and document capacity and mental state, and delay a non-urgent study until capacity is restored or a lawful substitute decision-maker is identified under local health-authority rules.
Next of kin: attempt contact through the numbers on file and via the ward or ED, and record the attempts and times. Do not disclose clinical detail to an unidentified caller - verify identity and relationship first.
In this patient, though, the acute reaction overrides the consent question. Treat first under the emergency/best-interests principle, then document.
Documentation: the capacity assessment, the discussion attempted, the reason treatment proceeded, who was contacted, the reaction timeline with drug doses and times, and the handover to the receiving team. If a decision was made without consent, the note must explain why that was the least harmful option - an unexplained omission is what becomes indefensible later.