Wellington ICU Drug Manual: Appendices

appendix 9:
Local anaesthetic safety calculations

Wellington ICU Drug Manual - Local anaesthetic safety calculations

Dosing nomogram

This nomogram calculates the maximum safe amount of common local anaesthetics that can be administered within an 8 HOUR period.

Ropivacaine 0.2% is the preferred agent in Wellington for local anaesthetic wound catheters. See below for specific ropivacaine dosing guidelines.

HOW TO USE THIS NOMOGRAM:
  • Take a ruler or straight edge
  • Place one end on scale 1 on the relevant value for the patient's body weight*
  • Place the other end on line 2 crossing the preferred local anaesthetic agent & concentration
  • The maximum volume in millilitres that can be safely administered is shown where the straight line crosses the middle scale (marked 3)

*For patients > 70 kg, use 70 kg. For obese patients, use ideal body weight.
If body weight or maximum volume values fall between scale graduations, use next LOWEST values on each scale.

This nomogram is a guide and does not replace calculations for maximum dose toxicity.
See table below for guidance with this calculation.

Source: A nomogram for calculating maximum dose of local anaesthetic. Williams et al. Anaesthesia 2014

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Ropivacaine 0.2% dosing

This is the preferred local anaesthetic agent for administration through wound catheters (usually rectus sheath catheters) in Wellington Regional Hospital.

Ropivacaine 0.2% contains 2 mg / ml. The maximum safe dose in 24 hours is 8 mg / kg
Consider reduction in elderly patients

Follow steps 1-4 below to prescribe ropivacaine safely:

  1. Calculate the 24 hour maximum safe volume based on the patient's weight, using the table below
  2. Divide this volume by four to give the volume to be administered every 6 hours
  3. Divide this volume by the number of wound catheters to give the volume per catheter every 6 hours
  4. Prescribe 'Ropivacaine 0.2% q6 hourly via wound catheters' with the volume calculated in the previous step

Safely dosing other local anaesthetic agents

Use the table to calculate the maximum safe dose for other local anaesthetic agents in both plain preparation and preparations with adrenaline added.

This is the maximum safe dose that can be administered every 8 hours (TDS).

The maximum stated dose assumes normal plasma protein binding, normal hepatic & renal function, and no interactions with other co-administered drugs. If variants in these factors are known or suspected then the administered dose should be reduced accordingly. Dose reduction should also be considered in elderly patients.

Wellington ICU Drug Manual - Local anaesthetic safety calculations
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Appendix 10 contains details on calculating drug concentrations from solutions expressed in percentages