Continuous Veno-Venous Filtration
Prescribing CVVH
In order to correctly prescribe CVVH you will need to know the patient's age and weight, the volume of intravenous fluids and drugs they are receiving, their haematocrit and their measured fluid losses.
The filtration fraction will be determined by the consultant, as will the hourly fluid balance to aim for. Similarly the type of replacement fluid to be used will be determined by the consultant - usually it is Monosol, but in patients with lactic acidosis or liver failure, lactate free solution will be used with a separate sodium bicarbonate infusion.
CVVH Calculator
This will make life easier for you prescribing correctly, but everything needs to be cross-checked with the nurse who will be supervising the CVVH.
It opens as an Excel spreadsheet. You enter the relevant values in the light blue cells and click enter. When you are finished, you will be asked if you want to save changes - click no.
Anticoagulation
If APTT is <60, give loading dose of heparin 10units/kg
Then make up an infsuion of heparin 500units/kg in 50mls of 0.9% saline - run this at 0.5 - 2mls/hr, adjusting according to the ACT.
In some patients with deranged coagulation, an infusion of Prostacyclin 2.5 - 5 nanograms/kg/min may be used, butthis is a consultant decision.
Using Lactate free replacement fluid
Lactate free solutions contain less sodium than Monosol, the usual replacement fluid. Lactate is present in monosol to prvide an acid-base buffer. When using Lactate free solutions, an infusion of sodium bicarbonate is used to increse the sodium content in replacement fluid, and to prvide the buffer.
The volume of sodium bicarbonate is given by:
{140 - [Na] in replacement fluid} X Ultrafiltration rate (L/hour) = Volume 8.4% Sodium Bicarbonate (ml/hour)
Thus for a patient receiving Baxter LF10 fluid ([Na]=110mmol/L) and an ultrafiltration rate (also called turnover rate) of 0.33 Litres/hr:
Voulme 8.4% Sodium bicarbonate = 0.33 X (140 - 110) = 10ml/hr