Energy Gains and Losses from Glucose Fluxes During Dialysis

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Energy requirements for CAPD patients are partially met from absorbed dialysate glucose. Requirements from dietary intake are therefore lower at 30 kcal/kg body weight (25 kcal/kg if obese) and 25-30 kcal/kg body weight if older than 65 years (21).

Patients absorb approximately 70% of dialysate glucose, amounting to 300600 kcal or 2.5-17 g of glucose per hour during dwell times (22) (See table 15.4). Bag volumes range from 1 to 3 litres, with higher dextrose concentrations and larger volumes used to maximize solute clearance and ultrafiltration. The exact amount of glucose absorbed will depend on the dialysate glucose concentration and volume, the number of exchanges, the dwell time between each exchange and the permeability of the patient's peritoneal membrane. Membrane permeability is likely to be increased in people with diabetes. Increasing glucose loads can predispose to hyperglycaemia, hyperinsulinaemia, hyper-lipidaemia, and obesity.

On the basis of a 70% absorption rate of glucose from dialysate fluid, between 2.5-17 g of glucose can be absorbed per hour during dwell times. This glucose load can predispose to hyperglycaemia, leading in turn to hyper-insulinaemia, hyperlipidaemia and obesity.

During HD blood values frequently fall below 4.0mmol/l when patients are dialysed against a glucose-free dialysate (23).

Such patients should be advised to either eat a snack before or during dialysis. The choice of a slowly absorbed, low-glycaemia snack is ideal for this purpose.

Due to the metabolic problems associated with glucose as the main osmotic agent for inducing ultrafiltration in PD, alternative osmotic agents are now becoming available. High molecular weight glucose polymer solutions such as Icodextrin appear to be safe and effective. Icodextrin has the advantage of a reduced glucose and calorific load but requires dwell times of between 8-12 h and is therefore often left in situ overnight. No studies of use in diabetic patients have so far been published (24).

Table 15.4 Approximate energy provided by glucose-containing dialysate

Dialysate (1 l)

Grams of absorbed glucose

Energy provided (kcal)

1.36% dextrose

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