1.11: RENAL DISEASE

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

 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 glomerulonephritis,diabetes, polycystic renal disease, pyelonephritis, hypertensive vascular disease, nephrotoxin 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 tumors, 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.

Chronic Renal Failure

Chronic renal failure is irreversible and often follows acute renal failure. The most common cause is glomerulonephritis. Other causes include pyelonephritis, diabetes, polycystic renal disease, vascular disease and hypertension.These patients have many changes to their health, which are important for the anesthetist to identify and treat if possible before surgery.

Preoperative Assessment 

Patients with chronic 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 hyponatremia .Increased blood levels of parathyroid hormone may cause hypocalcaemia and hyperphosphataemia. Acidosis is common. Patients may have a normocytic normochromic anaemia caused by reduced erythropoietin production, reduced red cell survival and bone marrow depression. These patients may also have prolonged bleeding time due to decreased platelet adhesiveness. Chronic 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 anesthetist must take a complete history and examination and look at all investigations. The anesthetist 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 anesthetist 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 anesthetist 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. Chronic anaemia rarely needs transfusion.

The anesthetist 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 treatedas if they have normal renal function.

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

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

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

 

 Premedication

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

The anaesthetist may wish to give an antacid and histamine (H-2) blocker as delayedgastric 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 aselectrolyte abnormalities.

 Anaesthetic Maintenance

The anaesthetist must avoid hypovolaemia.

Potassium-containing intravenous fluids should not be given. Drugs, which accumulatein 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 inductionagents 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 notcontraindicated unless there is hyperkalaemia (greater than 5.5 mmol/l) or peripheralneuropathy. Atracurium and cis-atracurium are a good choice of muscle relaxants astheir metabolism is generally unaffected in renal failure. Methoxyflurane can cause renaldamage by increasing blood fluoride levels. Though both enflurane and sevoflurane canincrease blood fluoride they have not been shown to decrease renal function. Themetabolite of pethidine (nor-pethidine) may accumulate in renal failure. NSAIDs should be avoided.

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