9.3 Preoperative Assessment, Surgical Site Infections & Fluid Management

Preoperative Risk Stratification: ASA Classification & Cardiovascular Indices

The fundamental goal of preoperative evaluation is to identify unrecognized medical comorbidities, optimize modifiable organ dysfunction, and stratify perioperative morbidity and mortality to guide anesthetic and surgical decision-making.

The American Society of Anesthesiologists (ASA) Physical Status Classification

The ASA classification serves as the worldwide metric for baseline physiological fitness prior to anesthesia and surgery:

• ASA I: A completely normal, healthy patient (non-smoking, no or minimal alcohol use, normal BMI).
• ASA II: A patient with mild systemic disease without substantive functional limitations (e.g., well-controlled hypertension, well-controlled non-insulin diabetes mellitus, mild obesity [30 <= BMI < 40], active social cigarette smoker).
• ASA III: A patient with severe systemic disease that causes substantive functional limitations (e.g., poorly controlled diabetes, stable angina, history of myocardial infarction > 3 months ago, chronic obstructive pulmonary disease [COPD], morbid obesity [BMI >= 40], chronic kidney disease on scheduled hemodialysis).
• ASA IV: A patient with severe systemic disease that is a constant, ongoing threat to life (e.g., recent myocardial infarction or stroke < 3 months ago, ongoing cardiac ischemia, severe calcific aortic stenosis, severe congestive heart failure with LVEF < 25%, end-stage renal disease not undergoing dialysis, septic shock).
• ASA V: A moribund patient who is not expected to survive without the planned surgical intervention (e.g., ruptured abdominal aortic aneurysm, massive intracranial hematoma with midline shift, extensive bowel ischemia with shock).
• ASA VI: A declared brain-dead patient whose organs are being retrieved for donor transplantation purposes.
• Emergency Modifier ('E'): Appended to any class when the operation must be performed emergently without delay (e.g., ASA III-E for an elderly patient with poorly controlled COPD undergoing emergency appendectomy).

The Revised Cardiac Risk Index (RCRI / Lee Index)

Cardiovascular complications—including perioperative myocardial infarction, ventricular fibrillation, complete heart block, and cardiac arrest—represent the leading cause of perioperative mortality following non-cardiac surgery. The Revised Cardiac Risk Index (RCRI) incorporates six independent clinical predictors:

1. High-risk surgical procedure: Intraperitoneal, intrathoracic, or suprainguinal vascular reconstruction.
2. History of ischemic heart disease: Prior MI, positive exercise test, ischemic chest pain/nitrate use or pathological Q waves; prior revascularization alone does not qualify without subsequent qualifying findings.
3. History of congestive heart failure: History of heart failure, pulmonary edema or PND; S3/bilateral rales, or pulmonary vascular redistribution on chest radiography.
4. History of cerebrovascular disease: Prior stroke or transient ischemic attack (TIA).
5. Preoperative insulin therapy for diabetes mellitus.
6. Preoperative serum creatinine > 2.0 mg/dL (> 177 mcmol/L).

Patients are risk-stratified based on the number of present predictors:

• 0 predictors: Class I (very low risk, ~0.4% rate of major adverse cardiac events [MACE])
• 1 predictor: Class II (low risk, ~0.9% MACE rate)
• 2 predictors: Class III (intermediate risk, ~6.6% MACE rate)

• = 3 predictors: Class IV (high risk, >= 11% MACE rate)

Patients with poor functional capacity (< 4 METs, indicating inability to climb two flights of stairs or carry a bag of groceries up a hill) and elevated RCRI scores require formal cardiology evaluation and potential non-invasive functional testing (e.g., dobutamine stress echocardiography) prior to elective major surgery.

Perioperative Medication Management & Anticoagulant Protocols

Reconciliation of chronic cardiovascular, endocrine, and anticoagulant medications requires strict adherence to evidence-based protocols to avoid severe intraoperative hypotension, metabolic decompensation, or hemorrhage.

Cardiovascular & Antihypertensive Medications

• Beta-Blockers: Patients on chronic beta-blocker therapy must continue their medication without interruption throughout the perioperative period (taken with a sip of water on the morning of surgery). Abrupt withdrawal triggers severe rebound hypertension, tachycardia, and acute myocardial ischemia. However, de novo initiation of high-dose beta-blockers on the day of surgery is dangerous, having been shown in the POISE trial to increase bradycardia, stroke, and overall mortality.
• Statins: Chronic statin therapy should be continued uninterrupted; statins confer plaque-stabilizing and anti-inflammatory properties that reduce perioperative cardiac events.
• ACE Inhibitors (ACEi) and Angiotensin Receptor Blockers (ARBs): For selected patients taking these agents for controlled hypertension and undergoing elevated-risk noncardiac surgery, omission 24 hours before surgery may limit intraoperative hypotension. For HFrEF, perioperative continuation is reasonable. Decide with the anesthetic team using the indication, blood pressure and surgical risk. RAAS blockade can contribute to vasodilatory hypotension; severe cases may require vasopressin. If withheld, restart when hemodynamics, renal function and oral intake permit.

Diabetic Medications & SGLT2 Inhibitor Alert

• SGLT2 Inhibitors (Empagliflozin, Dapagliflozin, Canagliflozin): Must be discontinued 3 to 4 days prior to major elective surgery. SGLT2 inhibitors trigger persistent glucosuria, shift cellular metabolism toward lipolysis and ketogenesis, and suppress endogenous insulin release. In the setting of surgical stress, dehydration, and fasting, continuing SGLT2 inhibitors induces euglycemic diabetic ketoacidosis (euDKA)—a life-threatening surgical complication marked by severe high anion gap metabolic acidosis and ketosis with completely normal or only mildly elevated serum glucose levels (< 11.1 mmol/L [200 mg/dL]), which frequently eludes early recognition.
• Metformin: Withheld 24 to 48 hours prior to surgery to minimize the risk of lactic acidosis in the event of perioperative renal hypoperfusion or intravenous iodinated contrast exposure.
• Basal Insulin: On the evening prior to or morning of surgery, patients on long-acting basal insulin (glargine, detemir, degludec) should receive 70% to 80% of their usual dose to prevent ketoacidosis while minimizing intraoperative hypoglycemia. Short-acting prandial insulins are held while fasting. Target perioperative blood glucose is 7.8 to 10.0 mmol/L (140 to 180 mg/dL).

Anticoagulation Management & Reversal

• Elective Warfarin Interruption: Warfarin is discontinued 5 days prior to elective surgery to permit spontaneous clearance of vitamin K-dependent clotting factors (target INR <= 1.4). Do not bridge routinely. Consider specialist-directed therapeutic LMWH bridging (e.g., enoxaparin 1 mg/kg twice daily once INR is subtherapeutic) only when thrombotic risk outweighs bleeding risk: examples include a mechanical mitral valve, recent VTE, or very-high-risk AF (CHA2DS2-VASc >= 7, or 5–6 with recent stroke/TIA). The final therapeutic LMWH dose is given 24 hours prior to surgery (12 hours for prophylactic doses) to prevent bleeding during surgery and spinal/epidural hematoma formation.
• Emergency Warfarin Reversal: For emergent, life-threatening operations, reversal cannot wait for days. Fresh Frozen Plasma (FFP) requires large volumes (15–30 mL/kg) and hours to thaw and infuse, risking fluid overload. The standard of care is intravenous 4-factor Prothrombin Complex Concentrate (4F-PCC) containing balanced concentrations of factors II, VII, IX, and X, alongside Protein C and S, dosed based on body weight and presenting INR. 4F-PCC is administered concurrently with slow intravenous Vitamin K 5 to 10 mg (which stimulates endogenous hepatic synthesis over the subsequent 12–24 hours, preventing rebound anticoagulation once PCC factors are cleared). 4F-PCC normalizes the INR within 10 to 15 minutes of infusion.
• Direct Oral Anticoagulants (DOACs: Apixaban, Rivaroxaban, Dabigatran): Because of predictable pharmacokinetics and short half-lives, DOACs are withheld 48 hours prior to high-bleeding-risk surgery (or 24 hours for low-risk procedures) in patients with normal renal function. Routine heparin bridging is unnecessary. For emergency reversal, Idarucizumab is the specific monoclonal antibody fragment antidote for dabigatran, while Andexanet alfa is the decoy receptor antidote for factor Xa inhibitors (apixaban, rivaroxaban).

Surgical Site Infection (SSI) Prevention Bundles & Prophylaxis Guidelines

Surgical site infections (SSIs) account for approximately 20% of all healthcare-associated infections. According to Centers for Disease Control and Prevention (CDC) criteria, SSIs are classified based on anatomical depth:

1. Superficial Incisional SSI: Involves only the skin and subcutaneous tissue; manifests within 30 days of the surgical procedure with purulent drainage, localized erythema, tenderness, or positive wound culture.
2. Deep Incisional SSI: Involves the deep soft tissue layers (fascia and muscle bellies); has a 30- or 90-day surveillance period determined by the NHSN operative procedure category, not simply implant presence.
3. Organ / Space SSI: Involves any anatomical space or organ opened or manipulated during the operative procedure (e.g., subphrenic abscess, pelvic abscess, peritonitis); has a 30- or 90-day surveillance period according to the NHSN operative procedure category.

The Evidence-Based SSI Prevention Bundle

Implementation of multifaceted perioperative bundles has dramatically decreased SSI rates:

• Hair Removal: Preoperative shaving with a traditional razor blade causes microscopic epidermal abrasions and cuts that become heavily colonized with skin flora (Staphylococcus aureus). Razor shaving is strictly contraindicated. Hair should either not be removed at all or clipped immediately prior to surgery using electric surgical clippers equipped with single-use disposable heads.
• Surgical Skin Antisepsis: Preoperative skin preparation using an alcohol-based chlorhexidine gluconate (CHG) solution is vastly superior to aqueous povidone-iodine. Alcohol provides immediate broad-spectrum bactericidal action, while chlorhexidine binds tenaciously to skin stratum corneum proteins, providing persistent antimicrobial suppression for up to 48 hours. The solution must be allowed to dry completely for a minimum of 3 minutes prior to surgical draping to eliminate operating room flash fire hazards.
• Maintenance of Perioperative Normothermia: Active patient warming with forced-air warming blankets and warmed intravenous fluids must maintain core body temperature >= 36.0°C. Intraoperative hypothermia induces cutaneous vasoconstriction, decreases subcutaneous oxygen tension, impairs neutrophil oxidative bacterial killing, and induces platelet dysfunction that increases blood loss and transfusion requirements.
• Strict Perioperative Glycemic Control: Hyperglycemia significantly impairs leukocyte phagocytosis and intracellular bacterial killing. Blood glucose should be maintained strictly < 10.0 mmol/L (< 180 mg/dL) in both diabetic and non-diabetic surgical patients.

Surgical Antimicrobial Prophylaxis Guidelines

Antibiotic prophylaxis is designed to establish therapeutic tissue drug concentrations in the surgical incision at the exact moment of skin incision to eliminate contaminating flora before bacterial adherence can occur:

1. Timing of Administration: Prophylactic antibiotics must be administered intravenously within 30 to 60 minutes prior to surgical incision. Agents requiring prolonged infusion times, specifically Vancomycin and Fluoroquinolones, must be initiated within 120 minutes prior to incision.
2. Antimicrobial Selection: Tailored to expected endogenous operative flora. For clean orthopedic, vascular, and breast surgery, Cefazolin (1st generation cephalosporin) provides excellent coverage against Staphylococcus aureus and Streptococcus. For clean-contaminated colorectal or appendiceal surgery, a second-generation cephalosporin with anaerobic coverage (e.g., Cefoxitin or Cefotetan), or Cefazolin combined with Metronidazole, is mandated.
3. Weight-Based Dosing: Cefazolin is dosed at 2 g for patients < 120 kg, and increased to 3 g for patients weighing >= 120 kg.
4. Intraoperative Redosing: Prophylactic antibiotics must be redosed intraoperatively if the duration of the surgical procedure exceeds two half-lives of the antimicrobial agent (e.g., Cefazolin must be redosed every 4 hours; Cefoxitin every 2 hours), or if acute intraoperative blood loss exceeds 1,500 mL.
5. Postoperative Discontinuation: Prophylactic antibiotics must be discontinued within 24 hours of surgery (or within 48 hours for cardiothoracic surgery). Continuing antibiotic administration beyond 24 hours provides no incremental reduction in SSI rates and exponentially drives antimicrobial resistance and Clostridioides difficile pseudomembranous colitis.

Perioperative Fluid Prescribing & ERAS Principles

Perioperative fluid prescribing must balance the prevention of hypovolemia-induced organ hypoperfusion against the morbidities of fluid overload, which causes pulmonary edema, impaired tissue oxygenation, and breakdown of gastrointestinal anastomoses.

The Hazard of 0.9% Normal Saline vs. Balanced Crystalloids

Standard "normal" saline (0.9% NaCl) contains supraphysiological concentrations of sodium (154 mmol/L) and chloride (154 mmol/L), with a pH of ~5.5 and zero buffer. Rapid infusion of large volumes of 0.9% saline drives excess circulating chloride, triggering hyperchloremic metabolic acidosis (via bicarbonate dilution and renal bicarbonate wasting). Elevated renal tubular chloride delivery to the macula densa activates tubuloglomerular feedback, triggering afferent renal arteriolar vasoconstriction, reducing renal blood flow and glomerular filtration rate (GFR). Furthermore, hyperchloremic acidosis induces delayed gastric emptying and postoperative paralytic ileus.

Consequently, balanced crystalloid solutions—predominantly Hartmann's solution or Ringer's lactate (containing Na+ 131 mmol/L, Cl- 111 mmol/L, K+ 5 mmol/L, and lactate buffer 29 mmol/L)—are preferred for many perioperative replacement and resuscitation needs. Routine daily maintenance requires a separate prescription meeting water, electrolyte and glucose requirements below; these solutions alone do not meet those needs.

Maintenance Fluid Prescribing Rules

Routine maintenance fluid therapy for an adult adheres to the following daily requirements:

• Water: 25 to 30 mL/kg/day (approximately 1 mL/kg/h)
• Sodium: 1 mmol/kg/day
• Potassium: 1 mmol/kg/day
• Glucose: 50 to 100 g/day (to suppress starvation ketosis and spare muscle protein catabolism)

The archaic practice of administering massive crystalloid fluid boluses to compensate for unmeasured, theoretical "third-space losses" during open abdominal surgery has been thoroughly discredited. Third-space fluid shifts represent iatrogenic endothelial glycocalyx disruption and interstitial edema caused by fluid overloading.

Enhanced Recovery After Surgery (ERAS) Pathway

The ERAS paradigm integrates multimodal perioperative interventions to attenuate the neuroendocrine surgical stress response, accelerate gastrointestinal recovery, and shorten hospital stay:

• Preoperative Phase: Minimizing fasting times (clear liquids containing complex carbohydrates allowed up to 2 hours prior to induction; light solid meals up to 6 hours prior); avoidance of routine mechanical bowel preparation.
• Intraoperative Phase: Goal-directed fluid therapy (GDFT) utilizing dynamic parameters (stroke volume variation or pulse contour analysis) to optimize end-diastolic volume without volume overload; multimodal opioid-sparing analgesia (paracetamol, NSAIDs, transversus abdominis plane [TAP] blocks, wound infiltration catheters); avoidance of routine nasogastric tubes and peritoneal drains.
• Postoperative Phase: Immediate cessation of maintenance intravenous crystalloids upon oral intake tolerance; early enteral feeding within hours of extubation; removal of Foley catheters on postoperative day 1; scheduled early ambulation on the day of surgery.