Anesthetic Management in Renal Patients

Preoperative Management
General
Causes of postoperative renal failure
Prophylaxis against postoperative renal failure

Intraoperative Mangement
Monitoring
Induction
Maintenance
Fluid therapy

PREOPERATIVE MANAGEMENT IN RENAL FAILURE PATIENTS

General
-signs of fluid overload or hypovolemia should be investigated
-compare the patients current weight with pre and post dialysis weights to help assess intravascular volume trends
-chest films help asses fluid overload possibilities
-ABG will help asses hypoxemia and acid base status
-ECG will help asses for electrolye abnormalities such as hyperkalemia and hypocalcemia
-ECG asses cardiac issues such as ischemia, condution blocks, and LVH
-echocardiography help assess the function of the heart and any wall motion abnormalities
-CBC hemoglobin/hematocrit status. usually not transfused unless the hemoglobin < 6-7 g/dL or expectant large blood loss
-coagulation profile especially if regional anethesia is being performed
-electrolyes, BUN/Cr: help asses the adequacy of dialysis
-glucose levels help assess for the need of intraoperative insulin needs

Acute renal failure
-most patients requiring surgery while in acute renal failure are critically ill
-pts with ARF are generally caused by or associated with postoperative complications or trauma

Chronic renal failure
-most patients requiring surgery while in chronic renal failure are for creation or revision of an AV fistula
-usually under local or regional anesthesia
-all reversible manifestations of uremia should be controlled
-preoperative dialysis on the day of surgery or previous day of surgery is usually recommended
-normal GFR ranges from 95 - 120 ml/min
-GFR can decrease from 120 to 60 ml/min without any percieved clinical changes of renal function
-often patients who have Cr clearance of 40- 60 ml/min are asymtomatic although may have mild renal impairment
-patients with mild renal impairment may have decreased renal reserve therefore care must be taken to preserve remaining function
-Cr clearance of 25 - 40 ml/min may signify moderate renal impairment and therefore have renal insufficieny
-patients with renal insufficieny fenerally have significant azotemia along with hypertension and anemia

Possible causes of postoperative renal failure
Relatively high incidence of postoperative renal failure in:
-cardiac or aortic reconstructive surgery
-intravascular volume depletion
-sepsis
-obstructive jaundice
-crush injuries leading to myoglobinuria
-contrast dye injections
-aminoglycoside administration
-treatment with ACE inhibitors
-treatment with NSAIDs

Prophylaxis against renal failure
-indicated in high risk patients undergoing cardiac and major reconstructive surgery of the aorta
-solute diuresis appears effective
ex. mannitol (0.5 mg/kg) is generally given either before or during induction of anethesia
-intravenous fluids should be given during diuresis in order to prevent intravascular volume depletion
-intravenous dopamine may assist in renal perfusion by vasodilating with dopamine receptors on renal vessels
-in order to prevent fluid overload and maintain an adedquate urine output a loop diuretic may be considered

INTRAOPERATIVE MANAGEMENT IN RENAL FAILURE PATIENTS

Monitoring
-surgical procedure and patients overall condition guide to what degree of monitoring is needed
-due to occlusion potential, blood pressure cuff should not be placed on the side where the AV fistula is present
-cases involving major fluid shifts: A-line, CVP, and PAC are generally indicated
-diabetic patients with advanced renal disease undergoing major surgery have increased risk of perioperative morbidity
-increased risk of perioperative morbidity (vs nl renal functioning diabetic patients) is upto 10 times more

Induction
-patients with nasusea, vomiting or GI bleeding should be induced with rapid sequence intubation with cricoid pressure
-in debilitaed or critically ill patients: induction dose of agents should generally be reduced
ex. Thiopental: 2-3 mg/kg Propofol : 1-2 mg/kg Etomidate: 0.2 - 0.4 mg/kg
-blunting the hypertensive response to intubation the following may be useful: opiods, betablocker(ex.esmolol) and lidocaine
-patients with potassium < 5 mEq/L: succinylcholine usually may be suffice
-patients with potassium > 5 mEq/L: avoid succinlycholine and perhaps may use a nondepolarizing muscle relaxant

Maintenance
-ideally should entail controlled hypertension with minimal effects on cardiac output
-renal patients generally have increased cardiac output in order to compensate for the underlying anemia (anemia of chronic dis.)

Generally satisfactory agents:
-volatile anesthetics
-nitrous oxide
-propofol
-fentanyl
-sufentanil
-alfentanil
-remifentanil
-hydromorphone
-morphine
-isoflurane and desflurane have the least effect on cardiac output therefore may be the preferred volatile anesthetics in renal patients
-anemic renal patietns with hemoglobin < 7 g/dL should avoid nitrous oxide in order to allow for 100% 02 with volatile anethetic
-nitrous oxide should be used cautiously if at all in patients with poor ventricular function
-meperidine because of its potential accumulation of metabolite should be avoided
-morphine may have an additional prolonged effect

Fluid Therapy
superficial operations: generally require replacement of insensible fluid loss with D5W
complex operations: generally require replacement with isotonic crystalloids, colloids or both

-large volumes of lactated ringer's administration should be avoided in hyperkalemic patients due to potassium content (4 mEq/L)
-increased volume resusitation may generally be managed better with normal saline to avoid glucose intolerance in uremic patients
-increased blood loss should generally be replaced with packed reb blood cells (PRBC)