Patients undergoing abdominal surgery necessitate a complete history and physical examination as outlined in Chapter 1. Additional concerns germane to abdominal surgery should be considered including:

1. Preoperative volume status. Surgery in the abdomen has the potential to cause severe derangements in volume status and fluid homeostasis. The main sources of perioperative fluid deficits include preoperative fasting, interstitial sequestration of intravascular volume (via inflammation or edema), and surgical bleeding.
   1. Assessment of volume status
      1. Postural changes in vital signs (increased heart rate and decreased blood pressure) and clinical signs including dry mucous membranes, decreased skin turgor or mottling, and delayed capillary refill may suggest hypovolemia or dehydration.
      2. Laboratory analysis of base excess or deficit, hematocrit, serum osmolality, BUN (blood urea nitrogen) to creatinine ratio, serum and urine electrolyte concentrations, and urine output may be helpful in estimating volume deficits.
      3. Dynamic hemodynamic monitoring may also be considered to guide assessment of intravascular volume status. Pulse pressure variation (PPV) and systolic pressure variation (SPV) obtained from an arterial catheter waveform may aid in estimating volume-responsiveness. Generally, a delta-down component of 5 mm Hg for SPV or 13% to 15% for PPV is indicative of volume-responsiveness. Traditional assessments of volume status including central venous pressure (CVP) and pulmonary artery occlusion pressures have been questioned in the context of guiding intraoperative fluid management.
   2. Etiologies of hypovolemia
      1. Reduced oral intake, malabsorption, or gastrointestinal tract dysmotility may predispose a patient to hypovolemia or dehydration in the perioperative period.
      2. Emesis, gastric drainage, or diarrhea may produce significant fluid and electrolyte derangements. Monitoring the quantity, quality, duration, and frequency of output is recommended.
      3. Bleeding from the gastrointestinal tract may be occult and include sources like ulcers, neoplasms, esophageal varices, diverticula, angiodysplasia, and hemorrhoids.
      4. Sequestration of fluid may occur either into the bowel lumen from ileus or into the interstitium from peritonitis.
      5. Fever increases insensible fluid loss.
2. Metabolic derangements occur frequently in patients requiring emergency abdominal surgery. Hypokalemic metabolic alkalosis is common in patients with large gastric losses (emesis or nasogastric [NG] tube drainage). Severe hypovolemia or septicemia may cause profound metabolic acidosis.
3. Length of surgery is influenced by the history of previous abdominal surgery, intra-abdominal infection, radiation therapy, steroid use, surgical technique, and surgeon experience.
4. All patients for emergency abdominal procedures should be considered as high risk for aspiration and induced as a “full stomach.” A rapid sequence induction (RSI) is indicated with the goal of minimizing aspiration risk. Cricoid pressure is an area of active controversy with respect to its role and efficacy in minimizing aspiration. Premedication with histamine (H₂) antagonists and oral nonparticulate antacids may decrease gastric acidity.