Question

For each aspect of the treatment of renal failure by haemodialysis or peritoneal dialysis A–E, select the best matching option from the following list of problems caused by renal failure. 

1. Raised blood urea. 

2. Abnormal arterial blood pressure. 

3. Abnormal cardiac rhythms. 

4. Hyperventilation. 

5. Anaemia. 

6. Impaired consciousness. 

A. Removal of a variety of toxins, many unidentified, and correction of a variety of metabolic disturbances. 

B. Dialysing with fluid with a potassium level well below the normal plasma value. 

C. Manipulating pressures and osmolalities in the dialysis fluid to reduce or increase the patient’s body fluid content. 

D. Dialysing with fluid with a higher pH than the normal plasma level. E. Dialysing to lower the osmolality of the body fluids, irrespective of any change in electrolytes.

Answer 1

A. Option 6 Impaired consciousness. Drowsiness and coma are related to a variety of disturbances; dialysis reduces toxins by creating a gradient for passive diffusion, it can also correct electrolyte and acid–base disturbances. 

B. Option 3 Abnormal cardiac rhythms. Although these too are related to a variety of disturbances, a very high extracellular/plasma potassium level is the major cause. 

C. Option 2 Abnormal arterial blood pressure. The pressure may be too high or too low; in both cases it may be corrected by increasing or decreasing extracellular and hence blood volume; this may be done by ‘sucking’ fluid out of the patient’s blood by a raised dialysate osmolality or by lowering the dialysing equipment (or drainage bag with peritoneal dialysis) to remove fluid by gravity. 

D. Option 4 Hyperventilation. Hyperventilation is a sign of serious acidosis, so the pH of the dialysate fluid should be increased. 

E. Option 1 Raised blood urea. A raised urea raises total osmolality; as an extreme example, a rise of 30 mmol per litre would increase the normal osmolality (around 290 mosmol/kg) by just over 10 per cent; having the dialysate fluid free of urea allows a gradient for diffusion out of the patient’s blood.