CSE Dosing Interval — FRCA Final MCQ

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ModerateRegional AnaesthesiaCSE Dosing IntervalFRCA Final

A 55-year-old woman (ASA II) is undergoing bilateral knee replacement under combined spinal-epidural anaesthesia. After intrathecal injection, the epidural catheter is threaded. The anaesthetic team plan to use the epidural for post-operative analgesia. What is the minimum recommended interval between spinal injection and the first epidural dose?

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Correct answer: A — No interval required

There is no mandatory interval between a spinal injection and subsequent use of an epidural catheter placed as part of a combined spinal-epidural (CSE) technique. The epidural catheter can be dosed at any time based on clinical need. In practice, the spinal provides initial surgical anaesthesia, and the epidural is typically first used as the spinal block regresses. However, caution is needed when dosing the epidural while the spinal is still active, as the combined effect may produce an excessively high block. The volume-extension phenomenon means epidural volume can extend a subarachnoid block.

Reference: RCOA – 2023 – Regional anaesthesia module; Cook TM – 2009 – Combined spinal-epidural techniques