7.5 Preoperative assessment and treatment of medical problems in renal failure 

• Fluid balance: In CRF sodium and water excretion is relatively fixed and often reduced. The kidneys can have difficulty handling both large fluid loads and dehydration. The degree of hydration should be assessed in the usual way using skin turgor, examination of the mucous membranes, jugular venous pressure, presence of dependent edema and presence of pulmonary edema on auscultation. The patient must be normovolemic prior to surgery. Fluid resuscitation should normally be with normal saline but if there has been blood loss this might also have to be replaced. 
• Acidosis can best be improved by dialysis (a procedure in which a membrane (e.g., peritoneum) is used as a filter to separate soluble waste substances from the blood). Administration of bicarbonate solution should be considered when the pH is <7.2. Side effects of bicarbonate solutions include hypernatremia and volume overload. 
• Cardiovascular status: Hypertension may be a primary problem, secondary to chronic salt and water retention or to excess renin production. Blood pressure must be controlled preoperatively. 
• Respiratory function: Pulmonary edema and pleural effusions both cause a decrease in lung compliance. All these increase the likelihood of hypoxia and are best treated by fluid removal with diuretics or dialysis. 
• Hematological function: Chronic anemia is common in patients with CRF is usually well tolerated. Unless the patient has ischemic heart disease the hemoglobin level may be maintained at around 7-8 g/dl. Uremic patients may have a bleeding tendency due to a decrease in platelet adhesion and fragility of the vessel walls. 
• Gastrointestinal system: Anorexia, nausea, vomiting, bleeding from stress ulceration, diarrhea and hiccups are all common symptoms. These can exacerbate dehydration. Nutrition is often poor and this can impair wound healing. 
• Central nervous system: Uremia causes malaise, fatigue, decreased mental ability and eventually coma. Severe uremia or fluid or electrolyte imbalance may cause convulsions. 
• Endocrine system: Hyperparathyroidism leads to demineralization of bone making patients more susceptible to fractures. Diabetic control may be difficult because of decreased sensitivity to insulin. 
• Multiple medications: Patients may be taking corticosteroids or other immune-suppressants which cannot be stopped. 
• Lab investigation (Biochemical balance): The most significant biochemical problems related to severe uncorrected renal disease are hyperkalemia and acidosis. Hyperkalemia is defined as a serum potassium of more than 5 mEq/l. ECG changes become apparent at 6-7 mmol/l and immediate treatment is needed if the serum potassium is over 7 mmol/l. ECG changes include tall peaked T waves, shortened QT intervals, widened QRS complexes and loss of P waves. Ventricular fibrillation may occur at serum concentrations over 10 mmol/l. 

Methods of treating high serum potassium in an emergency include: 

• Administration of 10 ml of 10% calcium gluconate over 10 minutes (max 20 ml). This has an immediate but transient stabilizing effect on the myocardial cells. 
• 50mls of 50% glucose +5-10units of Insulin as an intravenous bolus or infusion. Glucose and insulin will produce an immediate migration of potassium into the cells thus reducing the serum level 
• Nebulized salbutamol 2.5 - 5mg will assist in moving K+ into the cells.