Management of diabetic patients requiring nutritional support. Nutrition 1992; 8: 316, 320.
Diabetes and Renal ReplacementTherapy MARIE KELLY AND THUSHARA DASSANAYAKE Hammersmith Hospital, London, UK
INTRODUCTION
The renal dietitian is an important member of the clinical team looking after patients with diabetes and end stage renal failure (ESRF). An understanding of the metabolic and nutritional changes that occur prior to and during ESRF is essential in order to provide nutritional advice to these patients. This is applicable irrespective of whether they are treated with haemodialysis (HD), peritoneal dialysis (PD) or renal transplantation.
PREVALENCE
Diabetes has become the commonest cause of ESRF in Western countries. In the UK around 16% of patients starting renal replacement therapy (RRT) have ESRF due to diabetic nephropathy (1). This figure is considerably higher in areas of the country where there are ethnic populations with an increased susceptibility to diabetes (2).
DIALYSIS INITIATION
Ideally, all diabetic patients approaching ESRF should be involved in the development of their own personalised care plan. This will enable a negotiation
Nutritional Management of Diabetes Mellitus. Edited by G. Frost, A. Dornhorst and R. Moses & 2003 John Wiley & Sons, Ltd. ISBN 0 471 49751 7
232 NUTRITIONAL MANAGEMENT OF DIABETES MELLITUS
of the necessary dietary changes leading up to and extending to the initiation of elective dialysis (3).
Dialysis guidelines from the National Kidney Foundation promote the early initiation of RRT for diabetic patients, due to an increased susceptibility to uraemic symptoms at lower serum creatinine levels than non-diabetic subjects (4).
Early RRT for diabetic renal failure not only relieves the symptoms of nausea, anorexia and vomiting but also helps reduce overall mortality.
However, despite these recommendations, dialysis is frequently delayed due to either personal resistance or inadequate dialysis resources.
Some diabetic patients with already compromised renal function, will require the emergency initiation of dialysis during an intercurrent illness.
However, this does not mean that all will require long-term RRT.
GLYCAEMIC CONTROL Achieving good glycaemic control is important for all patients with ESRF as this can retard the progression of the microvascular and macrovascular complications (5).
Good glycaemic control at the start of dialysis has also been shown to improve mortality risk.
For patients on continuous ambulatory peritoneal dialysis (CAPD) hyperglycaemia increases circulating advanced glycation end products (AGE), which have been implicated in causing endothelium and peritoneal membrane damage with loss of ultrafiltration capacity.
Good glycaemic control reduces thirst, which in turn helps to reduce fluid associated weight gain.
RENAL REPLACEMENT THERAPY
A brief outline on the principles of RRT is given below. Most patients with ESRF initially require dialysis, either haemodialysis or peritoneal dialysis. Only a minority of individuals, usually those with a suitable relative willing to donate a kidney, will have immediate access to a renal transplant.
DIALYSIS While survival on dialysis continues to improve, diabetic patients still do less well than non-diabetic patients (6). Results from the Italian Cooperative Peritoneal Study Group Registry show the 10-year patient survival for the 301 diabetic patients to be less than half that of the 1689 non-diabetic subjects (20.6% vs 55.6%) (7). Higher mortality rates among diabetic patients receiving HD also occur (8), but with good glycaemic control these rates can be improved (9).
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Peritoneal dialysis is the preferred mode of treatment for diabetic patients with microvascular and macrovascular co-morbidities.
Continuous ambulatory peritoneal dialysis allows for a slow ultrafiltration process that provides greater cardiovascular stability than HD.
Blood pressure control is easier and residual renal function is preserved for longer.
It also provides incidentally for an alternative route of insulin administration.
Initial concerns that diabetic CAPD patients may have higher dialysis-associated infection rates have not been confirmed (10,11).
DIALYSIS PROCEDURES Continuous Ambulatory Peritoneal Dialysis CAPD is a method of long-term dialysis that requires a permanent intra- peritoneal catheter. The peritoneum acts as a semi-permeable membrane that allows diffusion of solutes and facilitates the removal of water by ultrafiltra- tion. The daily CAPD regimen comprises a drain-in period, followed by a dwell time of approximately 4 h and a drain-out period. This cycle is usually repeated four times each day (12,13).
Haemodialysis Haemodialysis requires the surgical construction of an arterio-venous fistula that is usually sited in the non-dominant forearm using the cephalic vein and either the radial or brachial artery.
After six to eight weeks the fistula has usually thickened sufficiently to allow it to be cannulated with two large-bore needles that take blood to and from the dialysis machine.
Blood is pumped through a semi-permeable membrane filter in the dialysis machine allowing removal of excess solutes and fluid.
Haemodialysis is repeated every two to three days with the time on dialysis dependent on the patient’s body size and residual renal function.
If a patient has no permanent access and requires emergency dialysis this can be done through a temporary neckline or a semi- permanent catheter in a central vein (14).
FACTORS INFLUENCING NUTRITIONAL STATUS IN DIALYSIS PATIENTS Approximately 40% of dialysis patients exhibit some degree of protein and energy malnutrition and this is associated with an increased risk of morbidity and mortality. In the Modification in Renal Disease Feasibility Study (MDRD) in which 840 patients were prospectively studied, 42% of CAPD patients and 30% of HD patients were considered to be malnourished (15). Contributing factors to protein energy malnutrition occurring in dialysed patients are shown in Table 15.1.
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Table 15.1 Factors implicated in protein, energy malnutrition in dialysis patients
Factors Comments
Reduced nutritional intake Energy and protein intakes consistently lower than requirements Uraemic symptoms can continue for upto three months after starting dialysis
Underdialysis Nutritional intake deteriorates with inadequate dialysis
Gastroparesis Abdominal distension Vomiting Early satiety
Dialysis-related effects Abdominal discomfort with infusion of PD dialysate Protein losses, 6, 12 g amino acids during one HD session Daily protein losses on CAPD of 5, 15 g/day Peritonitis protein losses up to 20 g/day
Metabolic/endocrine Hyperparathyroidism factors Hyperglucagonaemia Insulin resistance Vitamin D deficiency
Co-morbidity and IHD and episodes of hypotension limiting dialysis time infections PVD can limit vascular access for HD Infections of vascular access in HD patients and peritonitis in PD
NUTRITIONAL ASSESSMENT/SCREENING
Ideally the nutritional status of patients approaching ESRF and starting dialysis should be monitored.
As a single marker of nutritional status is unreliable, a number of nutritional parameters, as outlined in Chapter 14, can help identify those who are malnourished.
Dual-energy X-ray absorptometry remains a useful method for assessment of lean body mass (15).
Nutrition scores such as subjective global nutrition assessment (SGA), based on clinical, physical and subjective measures are useful tools.
The SGA is considered better suited to assessing study populations.
Serial biochemical flow charts are useful in assessing nutritional status (see Table 15.3).
A decline in pre-dialysis serum urea, creatinine, potassium and phosphate may be indicative of a loss of lean body mass, rather than an improvement in nutritional status (17).
Additional points to consider in the nutritional assessment of dialysis patients are given in Table 15.2.
DIABETES AND RENAL REPLACEMENT THERAPY 235
Table 15.2 Additional factors in the nutritional assessment of dialysis patients
Factors Comment
Anthropometry Ensure measurements are taken at patient’s dry weight: Post-dialysis for the HD patient After drained-out period for CAPD Adjust for oedema
Serum biochemistry Serial biochemical measurements are useful in monitoring nutritional status
Protein catabolic rate An indirect marker of protein intake in stable dialysis (nPCR) patients The nPCR for stable HD patients 41.2 g/kg/day The nPCR for stable PD patients 1.3 g/kg/day Patients with nPCR50.8 g/kg/day require a dietary intake assessment
NUTRITIONAL REQUIREMENTS
Prior to dialysis most diabetic patients will have followed a diet that attempted to balance their carbohydrate intake with other aspects of their diabetes management.
Many will already be on a diet that is low in phosphate and potassium and some will also be on a low-protein diet.
Prior to dialysis, nutritional intake is usually inadequate with most patients having a negative energy balance (18).
Intensive dietetic counselling is required for all patients starting dialysis to help them improve their dietary intake within the constraints of the combined diabetic/renal diet.
Energy Requirements for Dialysis Patients Energy requirements to achieve neutral nitrogen balance in stable diabetic dialysis patients are similar to those of healthy non-diabetic adults (35 kcal/kg body weight), with lower requirements for subjects over 65 years of age (30, 35 kcal/kg body weight) (19).
Patients on CAPD receive part of their energy requirements from dialysate glucose (see below) (20).
If CAPD patients have difficulty in meeting their recommended dietary energy intakes due to early satiety, they should be encouraged to eat after ‘drain-out’ and to wait 20, 30 min before commencing the next dialysate bag.
Avoiding fluids at mealtimes can also improve appetite by minimising stomach distension.
If energy requirements are not achieved despite dietetic input, nutritional supplements should be considered (21).
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Table 15.3 A checklist for interpreting blood results of dialysis patients
Biochemistry Low Good Acceptable High (normal range)
Urea (mmol/l) 520 20, 28 28, 32 432 (2.5, 5.5) vegetarian check dialysis high protein intake status adequacy or inadequate poor appetite urea reduction dialysate residual ratio to ensure drugs, i.e. steroids function patient not catabolism underdialysed acidosis