Acute abdominal pain

Introduction

Diagnosing acute abdominal pain in critically ill patients can be difficult if the clinician tries to work through a comprehensive list of differential diagnoses ( Fig. 25.1 ). The most common etiologies seen outside of the intensive care unit (ICU) also occur within it, but other diagnoses must be considered. Certain patient populations to include trauma patients, postoperative patients, and those who are immunosuppressed, to name a few, should illicit even broader differential diagnoses. This chapter focuses on the difficulties in diagnosing acute abdominal pain in the critically ill patient, highlighting those diagnoses most relevant in this population.

Initial approach

The top diagnoses on the differential list are rather different for patients who present to the hospital with acute abdominal pain and are critically ill than for those patients in an ICU who develop acute abdominal pain. Paramount to narrowing down the differential diagnosis for acute abdominal pain for either scenario is gathering as much information as reasonably possible. For patients presenting with abdominal pain, the history of the present illness with associated symptoms can be revealing. Providers should query the past medical history, current medications, prior surgical procedures, prior hospitalizations, and any recent courses of antibiotics. For those hospitalized critically ill patients who develop abdominal pain, a thorough understanding of their hospital course to date will help reorder a blind differential diagnosis. For patients in an ICU, the bedside nurse can be a wealth of knowledge, especially when patients are intubated or have altered sensorium. Events in the preceding 24 hours may likely be the trigger for acute abdominal pain. For example, diffuse abdominal pain after paracentesis or drain placement by interventional radiology might be concerning for an unsterile procedure seeding the abdomen or for iatrogenic bowel perforation. Mesenteric artery embolism is a rare complication of percutaneous coronary angioplasty.

Physical examination

In certain disease pathologies, the physical examination is not especially enlightening, but in others, the diagnosis might be made without further workup. For example, septic shock may develop from strangulated inguinal or incisional hernias with ischemic or necrotic bowel driving the underlying pathobiology. All surgical scars should be noted, as they may add or remove some of the diffferential diagnoses (internal hernia after gastric bypass surgery or acute cholecystitis after cholecystectomy as respective examples). Furthermore, pointing out surgical scars is sometimes the cue necessary for patients or family members to recall past surgical procedures not initially reported. Right upper quadrant (RUQ) tenderness may be indicative of biliary pathology. Suprapubic pain may be indicative of genitourinary causes of illness. All tubes, drains, and catheters present should be inspected for location and quality and quantity of output. Finally, an assessment of the patient’s vital signs and any hemodynamic-altering medications are important.

Diagnostic adjuncts

The evaluation of critically ill patients with abdominal pain almost universally entails obtaining laboratory and imaging studies based on the history and physical examination. Laboratory studies include, yet are not limited to, complete blood counts with leukocyte differentials, comprehensive metabolic panels including a liver function panel with conjugated bilirubin, coagulation studies, arterial or venous blood gases, and lactic acid measurements. Additional diagnostic studies to consider include urine analysis and cultures, blood cultures, stool cultures, and Clostridium difficile toxin assays if there is a concern for that infection.

Radiographic adjuncts include plain radiographs, ultrasonography, computed tomography (CT), and nuclear imaging studies. Plain radiographs may prove useful in diagnosing a perforated viscus (perforated ulcer or diverticulitis), cecal or sigmoid or volvulus, or toxic megacolon. Ultrasonography is the modality of choice if a biliary pathology or ovarian torsion is suspected. The mainstay of imaging modalities is the CT scan of the abdomen and pelvis, with intravenous (IV) contrast when possible. For critically ill patients being evaluated for acute abdominal pain, enteral contrast adds little in diagnostic value, but frequently delays the acquisition of images while exposing the patient to the risk for aspiration. Enteral contrast may be useful if the patient had an intraabdominal operation with anastomosis of gastrointestinal tract within the last 2–3 weeks and there is a concern for anastomotic leak or if there is a concern for esophageal perforation or peptic ulcer perforation.