Preoperative assessment

The etiology of renal disease should be elucidated (eg, diabetes mellitus, hypertension). Elective surgery should be postponed in the setting of an acute, unoptimized disease process (eg, new type 1 hepatorenal syndrome). The degree of residual renal function is best estimated by creatinine clearance (see Section IV.A.3.b). A thorough, systems-based history and physical should be performed (see Chapter 1).

1. History
   1. Signs and symptoms can be varied depending on the cause of renal failure but may include polyuria, polydipsia, dysuria, edema, dyspnea, arrhythmia, and mental status changes.
   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 for coordination with procedures. Dry weight should be confirmed.
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 to preserve the fistula.
   3. Avoid inserting peripherally inserted central venous catheters in patients with CKD given the risk of upper-extremity venous thrombosis and central venous stenosis, which impairs future RRT vascular access.
   4. For central lines in CKD, if clinically appropriate, choose smaller-bore catheters to preserve the veins. Internal jugular vein sites rather than subclavian veins are also less prone to thrombose or permanently damage vessels.
3. Laboratory studies
   1. Serum creatinine (SCr) is normally 0.6 to 1.2 mg/dL but is affected by the patient’s skeletal muscle mass and activity level. SCr concentration is inversely proportional to GFR; thus, a doubling of SCr generally corresponds to a 50% reduction in GFR. In pregnancy, physiologic increase in GFR and expansion of extracellular fluid volume mean normal SCr is 0.4 to 0.8 mg/dL (thus SCr of 1.0 mg/dL in pregnancy may mean renal failure, the etiology of which must be investigated).
   2. 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 by: {[140-age (years)] × weight (kg)}/[72 × serum creatinine (mg/dL)]. Multiply by 0.85 for women. Ideal body weight should be used in obesity. This formula is invalid with gross renal insufficiency or changing renal function. Medications such as trimethoprim, H₂ receptor antagonists, and salicylates block the secretion of creatinine and may elevate serum creatinine and decrease creatinine clearance.
   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 to 20:1; disproportionate elevation of the blood urea nitrogen may reflect hypovolemia, low cardiac output, gastrointestinal bleeding, or steroid use.
   4. Electrolytes: Serum Na⁺, K⁺, Cl⁻, and HCO₃⁻ concentrations will usually 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 if [K⁺] is less than 2.5 or greater than 5.9 mEq/L, because these abnormalities may exacerbate arrhythmias and compromise cardiac function. Serum Ca²⁺, PO₄⁻, and Mg²⁺ concentrations are altered in renal failure.
   5. 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.
   6. Urine electrolytes, osmolality, urine creatinine, and urine urea can help determine volume status and concentrating ability and are used to help differentiate between prerenal and intrarenal diseases (see Table 5.2).
   7. Hematologic studies should assess anemia and coagulation abnormalities.
   8. ECG may reveal myocardial ischemia or infarction, pericarditis, and the effects of electrolyte abnormalities (see Section II.B).
   9. Imaging may show evidence of fluid overload, pericardial effusion, infection, uremic pneumonitis, or cardiomegaly.
4. Risk assessment for postoperative renal dysfunction
   1. Patient factors:
      1. Demographics: age >65 years, male gender, higher ASA score, ICU patient
      2. Acute Pathology: sepsis, trauma, abdominal hypertension
      3. Comorbidities: CKD, obesity, hypertension, diabetes mellitus, vascular disease, liver disease, cardiac dysfunction
   2. Potential nephrotoxins
      1. NSAIDs: associated with increased risk of perioperative AKI in patients with underlying risk factors (age, higher burden of comorbidity). Consider avoiding or dose-reducing.
      2. ARB/ACEI: Angiotensin II increases efferent arteriolar vasoconstriction to maintain glomerular filtration pressure. However, in patients taking ACEI or ARB, this compensatory mechanism may be decreased, which could cause a decrease in renal perfusion pressure and urine production. Consider stopping these on the day of surgery.
      3. Antibiotics: aminoglycosides, multitherapy versus monotherapy.
      4. Contrast media: These cause a decrease in O₂ supply by causing intrarenal vasoconstriction, decreased medullary blood supply, and an increase in O₂ demand. The osmotic load increases work to the medullary nephrons.
   3. High-risk surgery: renal artery surgery, thoracic and abdominal aortic surgery, nonrenal organ transplantation, surgery with large blood loss, and prolonged (>3 hours) cardiopulmonary bypass.
5. Preoperative 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 owing 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.
   3. It may be prudent to postpone major elective vascular surgery for a few days after contrast media exposure. In addition, pretreatment with isotonic crystalloid for volume expansion, NAC, or sodium bicarbonate infusion (SBI) before radiographic contrast administration may prevent contrast-induced (CI) nephropathy in patients at increased risk of CI-AKI.
      1. Volume expansion with crystalloid has been shown to be beneficial. There is no clear consensus on optimal rate or duration of infusion.
      2. NAC 20% (200 mg/mL) 1200 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 are conflicting data regarding the effectiveness of NAC in preventing CI-nephropathy.
      3. 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, followed by an infusion of 1 mL/kg/h for 6 hours after the procedure. Most likely the benefit is from crystalloid volume expansion rather than the bicarbonate component.