11. RENAL DISEASE

Patients with renal disease may have many medical problems. Renal failure may be acute or chonic. All patients require careful preoperative assessment. The anaesthetist must consider how the anaesthetic might affect the renal disease and how the renal disease might affect the anaesthetic.

Acute Renal Failure

Acute renal failure usually occurs over a few days. The patient may have had normal or reduced renal function previously. The patient’s urine output may be normal, reduced or absent.

Acute renal failure may be due to a decreased blood flow to the kidney (prerenal), renal disease (renal) or an obstruction in the urinary collecting system (post renal).

Causes of prerenal acute renal failure include shock, hypovolaemia, cardiac failure and renal artery stenosis. If the blood flow to the kidney is quickly restored the kidney function usually returns to normal but if the poor blood flow continues there may be permanent renal damage. Causes of renal acute renal failure include glomerulonephitis, diabetes, polycystic renal disease, pyelonephitis, hypertensive vascular disease, nephotoxins and acute tubular necrosis (ATN). ATN accounts for 75% of hospital admissions for acute renal failure. Post renal acute renal failure may occur from any obstruction in the urinary collecting system like bladder tumours, renal stones or prostate disease. If the cause of the obstruction can be quickly treated then the renal function should return to normal.

The death rate from acute renal failure is high (30%) in surgical and trauma patients.

Preoperative Assessment

Patients with acute renal failure usually have decreased urine output. They have increased blood levels of urea and other substances that cause nausea, vomiting, and tiredness. They may also have increased bleeding and are at increased risk of infections. Sodium and water excretion is reduced so the patients develop oedema, hypertension, acidosis and hyperkalaemia.

Chonic Renal Failure

Chonic renal failure is irreversible and often follows acute renal failure. The most common cause is glomerulonephitis. Other causes include pyelonephitis, diabetes, polycystic renal disease, vascular disease and hypertension.

These patients have many changes to their health, which are important for the anaesthetist to identify and treat if possible before surgery.

Preoperative Assessment

Patients with chonic renal failure may be tired, confused and finally convulsing and in coma. They may have hypertension, pericarditis and pericardial effusions (which may cause a pericardial tamponade), peripheral vascular disease and cardiac failure. They will usually have hyperkalaemia, hypermagnesaemia and hyponatraemia. Increased blood levels of parathyroid hormone may cause hypocalcaemia and hyperphosphataemia. Acidosis is common. Patients may have a normocytic normochomic anaemia caused by reduced erythopoietin production, reduced red cell survival and bone marrow depression. These patients may also have prolonged bleeding time due to decreased platelet adhesiveness. Chonic renal failure can cause both peripheral and autonomic neuropathy. The autonomic neuropathy can cause delayed gastric emptying.

The effects of drugs on the patient (pharmacokinetics) will also be changed due to changes in body water, pH, electrolytes, total protein and rates of excretion.

Anaesthetic Management

As with all patients, the anaesthetist must take a complete history and examination and look at all investigations. The anaesthetist must decide if the patient’s health can be improved before surgery, whether the surgery should be delayed and what the best anaesthetic for that patient will be.

When assessing the patient the anaesthetist should take a history and examination looking for both the severity of the renal disease and the severity of the cause of the renal disease (e.g. diabetes, vascular disease, hypertension). In particular, the anaesthetist should assess cardiovascular complications, fluid and electrolyte and acid base changes.

If the patient has signs or symptoms of autonomic neuropathy, the patient may be at an increased risk of aspiration of gastric contents. Chonic anaemia rarely needs transfusion.

The anaesthetist should also check the drugs the patient is taking.

Laboratory investigations are important. If available, ideally the patient’s sodium, potassium, chloride, bicarbonate, haemoglobin and coagulation should be tested.

Patients with a sodium less than 130 mmol/l or greater than 150 mmol/l, or a potassium less than 2.5 mmol/l or greater than 5.0 mmol/l will probably need treatment before surgery because these abnormalities may cause dangerous heart arrhythmias and reduced heart function.

An electrocardiogram is useful to look for signs of myocardial ischaemia, electrolyte changes and pericarditis. A chest X-ray may show signs of heart failure, pericardial effusions or pneumonia.

It is also important to check the renal function. Blood urea is not a good measure of renal function, as it will change with cardiac output, diet, body size and dehydration. Blood creatinine also is not a good measure as it is affected by skeletal muscle mass and the patient’s activity level. The rate at which creatinine is excreted by the kidneys is a good measure of renal function. It can be measured by collecting the patient’s urine for 12 or 24 hours and measuring the creatinine concentration in the urine, the urine volume and the creatinine level in the blood.

Estimated creatinine clearance ml/min

 = (140 – age) x weight in kilograms

          72 x blood creatinine mg/dl

Recommendation

Patients with an estimated creatinine clearance of greater than 50 ml/min can be treated as if they have normal renal function.

Patients with an estimated creatinine clearance of between 30 to 50 ml/min have decreased renal function and the anaesthetist must avoid dehydration and nephotoxins.

Patients with an estimated creatinine clearance of between 10 to 30 ml/min have severe renal disease and may need preoperative dialysis.

Patients with an estimated creatinine clearance of less than 10 ml/min have severe renal disease and should have dialysis within 24 hours preoperatively.

Premedication

The dose of central nervous system depressant premedications should be reduced, as renal failure patients are more sensitive to them.

The anaesthetist may wish to give an antacid and histamine (H-2) blocker as delayed gastric emptying and increased gastric volume are common.

Patients on dialysis must be dialysed before major surgery.

Check the hydration status of the patient (weight, central venous pressure, lung fields). Patients who have not been recently dialysed may have fluid overload as well as electrolyte abnormalities.

Anaesthetic Maintenance

The anaesthetist must avoid hypovolaemia.

Potassium-containing intravenous fluids should not be given. Drugs, which accumulate in renal failure, should be avoided (e.g. gallamine). Drugs that can reduce renal function (e.g. gentamicin, NSAID, radioactive dye) should not be given. The dose of induction agents may need to be reduced and should be given slowly to avoid hypotension. Renal patients are more sensitive to opioids, benzodiazepines, phenothiazines, barbiturates and propofol. These drugs should be given in reduced dosages. Suxamethonium is not contraindicated unless there is hyperkalaemia (greater than 5.5 mmol/l) or peripheral neuropathy. Atracurium and cis-atracurium are a good choice of muscle relaxants as their metabolism is generally unaffected in renal failure. Methoxyflurane can cause renal damage by increasing blood fluoride levels. Though both enflurane and sevoflurane can increase blood fluoride they have not been shown to decrease renal function. The metabolite of pethidine (nor-pethidine) may accumulate in renal failure. NSAIDs should be avoided.

The anaesthetist may choose general or regional anaesthesia. (Patients for regional anaesthesia should have normal coagulation).