# Local anaesthetic safety calculations* Appendix 9

This nomogram calculates the maximum safe amount administered within an 8 HOUR period.

*Ropivacaine 0.2% is the preferred agent in Wellington for local anaesthetic wound catheters. See below for speciļ¬c 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.

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.

### 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:

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:

- Calculate the 24 hour maximum safe volume based on the patient's weight using this table:

- Divide this volume by
**4**to give the volume to be administered**every 6 hours** - Divide this volume by the
**number of wound catheters**to give the**volume per catheter**every 6 hours - Prescribe '
**Ropivacaine 0.2% q6 holy via wound catheters**' with the volume calculated in step 3

### SAFELY DOSING OTHER LOCAL ANAESTHETIC AGENTS

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.

Appendix 10 contains details on calculating drug concentrations from solutions expressed in percentages