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Determining CSCI Volume — SCE Palliative Medicine MCQ

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EasySyringe Driver & Drug CompatibilityDetermining CSCI VolumeSCE Palliative Medicine

A patient’s CSCI is prescribed as “morphine 40 mg + midazolam 10 mg + haloperidol 3 mg / 24 h in water for injection via McKinley T34.” The community nurse asks what volume of water for injection to add. What determines the final volume?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Add WFI to achieve a volume that balances adequate dilution (to reduce site reaction) and compatibility, typically ~17 mL in 20 mL or ~22 mL in 30 mL syringes, per current guidance.

Explanation lettering: D = shown as A · A = shown as B · E = shown as D · B = shown as E

Option E is correct. UK CSCI practice with the McKinley T34 emphasises choosing a diluent volume that ensures adequate dilution—thereby reducing risk of local tissue irritation and maintaining drug stability and compatibility—while fitting within the calibrated syringe volumes. Standard guidance recommends approximately 17 mL total volume in a 20 mL syringe, or around 22 mL in a 30 mL syringe. Options A–D are incorrect: A may over-dilute and cause pump inaccuracy; B ignores compatibility and site safety; C is arbitrary and unsuitable for typical drug loads; D risks precipitation, incompatibility and irritation due to high concentration.

Reference: Shrops Community Health NHS Trust McKinley T34 guidance (2019); BNSSG McKinley T34 policy (circa 2023); Scottish Palliative Care Guidelines (setting up a syringe pump section, 2026) – all showing 20 mL volume ≈ 17 mL fill, 30 mL ≈ 22 mL.