Specific Considerations with Renal Disease - Anesthetic Management

Preoperative Assessment

Preoperative Assessment. The etiology of renal disease should be elucidated (e.g., diabetes mellitus, glomerulonephritis, and polycystic kidney disease). Elective surgery should be postponed, therefore pending resolution of acute disease processes. The degree of residual renal function is best estimated by creatinine clearance and is the most important consideration for anesthetic management. A thorough, systems-based history and physical should be performed (see Chapter 1).

  1. History
    1. Signs and symptoms of polyuria, polydipsia, dysuria, edema, and dyspnea should be sought.
    2. Relevant medications should be detailed: diuretics, antihypertensives, potassium supplements, digitalis, and nephrotoxic agents (NSAIDs, aminoglycosides, exposure to heavy metals, and recent radiographic dye).
    3. Schedule of hemodialysis should be noted and coordinated with elective procedures.
  2. Physical examination
    1. Patients should be thoroughly examined for the stigmata of renal failure as described in section III.B.3.
    2. Arteriovenous fistula should be evaluated for patency (by the presence of a thrill or bruit). Intravenous access and blood pressure determinations should be performed on the opposite limb.
  3. Laboratory studies
    1. Urinalysis provides a qualitative assessment of general renal function.
      1. Findings suggestive of renal disease include abnormal pH, proteinuria, pyuria, hematuria, and casts.
      2. The kidney's ability to concentrate urine is often lost before other changes become apparent. A specific gravity of 1.018 or greater after an overnight fast suggests that concentrating ability is intact. However, radiographic dye and osmotic agents will elevate specific gravity and invalidate this test.
    2. Urine electrolytes, osmolality, and urine creatinine can help determine volume status and concentrating ability and are used to help differentiate between prerenal and intrarenal diseases (see Table 4.1).
    3. Blood urea nitrogen is an insensitive measure of GFR, because it is influenced by volume status, cardiac output, diet, and body habitus. The ratio of blood urea nitrogen to creatinine is normally 10–20:1; disproportionate elevation of the blood urea nitrogen may reflect hypovolemia, low cardiac output, gastrointestinal bleeding, or steroid use.
    4. Serum creatinine normally is 0.6 to 1.2 mg/dL but is affected by the patient's skeletal muscle mass and activity level. Creatinine concentration is inversely proportional to GFR so that a doubling of the creatinine generally corresponds to a 50% reduction in GFR.
    5. Creatinine clearance is used to estimate GFR and provides the best estimate of renal reserve. It is normally 80 to 120 mL/min. A gross estimate of creatinine clearance can be calculated with the following equation:{[140 − age (years)] × weight (kg)}/[72 × serum creatinine (mg/dL)]
    6. Multiply by 0.85 for women. In obese individuals, ideal body weight should be used to estimate creatinine clearance. This formula is invalid in the presence of gross renal insufficiency or changing renal function. Medications such as trimethoprim, H2receptor antagonists, and salicylates block the secretion of creatinine and may elevate serum creatinine and decrease creatinine clearance.
    7. Serum Na+, K+, Cl, and HCO3 concentrations usually will be normal until renal failure is advanced. Careful consideration of the risk and benefit of proceeding with elective surgery should be made if [Na+] is less than 131 or greater than 150 mEq/L or [K+] is less than 2.5 or greater than 5.9 mEq/L, because these abnormalities may exacerbate arrhythmias and compromise cardiac function.
    8. Serum Ca2+, PO4, and Mg2+ concentrations are altered.
    9. Hematologic studies should assess anemia and coagulation abnormalities.
    10. ECG may reveal myocardial ischemia or infarction, pericarditis, and the effects of electrolyte abnormalities.
    11. Chest radiographs may reveal evidence of fluid overload, pericardial effusion, infection, uremic pneumonitis, or cardiomegaly.
  4. Risk assessment. Risk factors for postoperative renal dysfunction are as follows:
    1. Preexisting renal insufficiency
    2. Diabetes mellitus, Types 1 and 2
    3. Age greater than 65 years due to an age-related decline in renal reserve and GFR.
    4. Congestive heart failure
    5. High-risk surgery such as renal artery surgery, thoracic and abdominal aortic surgery, and prolonged (>3 hours) cardiopulmonary bypass.
    6. Recent exposure to toxins
      1. Contrast media cause a decrease in O2 supply, by causing intrarenal vasoconstriction and a decreased medullary blood supply, and an increase in O2 demand. The osmotic load increases work to the medullary nephrons
      2. Bile pigments
      3. Endotoxemia
      4. Aminoglycoside antibiotics
      5. NSAID
    7. Prolonged renal hypoperfusion resulting from shock, sepsis, nephritic syndrome, and cirrhosis.
  5. Optimization
    1. Patients on hemodialysis should be dialyzed before surgery, allowing time between dialysis and surgery to permit equilibration of fluids and electrolytes. Blood samples taken immediately after hemodialysis may be inaccurate due to redistribution of fluid and electrolytes. Equilibration may take up to 6 hours.
    2. If the patient is on CRRT, the decision to continue intraoperatively must be based on the underlying reason for the CRRT, the duration of the procedure, and the type of procedure. Most patients will be able to tolerate discontinuation of CRRT before surgery and reinstitution afterward. However, certain patients may not be able to tolerate even a short period off CRRT, usually because of increased K+ or acidosis, and one may need to decide whether the surgery can be postponed or to arrange for CRRT in the operating room or even during transport to the operating room. Major surgical procedures or prolonged surgical procedures may also dictate the need for intraoperative CRRT.
    3. It may be prudent to postpone major elective vascular surgery for a few days after contrast media exposure. In addition, pretreatment with N-acetylcysteine (NAC) and sodium bicarbonate infusion (SBI) before radiographic contrast administration may prevent contrast-induced nephropathy.
      1. NAC 20% (200 mg/mL) 1,200 mg is given orally every 12 hours, on the day before and on the day of contrast administration, for a total of 2 days. There is conflicting data regarding the effectiveness of NAC in preventing contrast-induced nephropathy.
      2. SBI of 150 mEq/L of sodium bicarbonate (three ampules of 50 mEq sodium bicarbonate in 1 L of D5W or free water) is administered at 3 mL/kg/h for 1 hour before contrast administration and followed by an infusion of 1 mL/kg/h for 6 hours after the procedure.

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