Beyond the Basics: Acute Abdominal Pain

CEU Review Form Beyond the Basics: Acute Abdominal Pain (PDF) Valid until September 5, 2008

     Acute abdominal pain is a common presenting complaint encountered by prehospital care personnel. It can be an indication of a number of diseases and conditions involving abdominal organs and structures or associated with referred pain from organs and structures outside the borders of the abdominal cavity. However, a sudden onset and severe abdominal pain is almost always caused by some type of intra-abdominal pathology.

     Using your critical thinking skills, you will develop a list of possible conditions, commonly referred to as possibilities, that the patient may be experiencing. As you continue to collect information through the history, physical examination and diagnostic equipment, you will build a shorter list of more probable conditions (probabilities) that are likely causing the abdominal pain. Because abdominal pain can be a common finding in so many different conditions, a single differential field diagnosis may or may not be completely possible, or even necessary. The primary goal in assessing the patient complaining of acute abdominal pain is to recognize an acute abdomen and determine if any life-threatening or potentially life-threatening conditions exist.

ANATOMY AND PHYSIOLOGY
     Reviewing the anatomy and physiology of the abdominal cavity and its contents helps with the understanding of the pathophysiology and presentation of conditions.

     The superior border of the abdominal cavity is the diaphragm, which separates it from the thoracic cavity. The diaphragm is located at approximately the fifth intercostal space anteriorly. The rib cage extends inferiorly into the abdominal cavity and protects the liver on the right and the spleen on the left. This area is commonly known as the thoracoabdominal region. Because the floor of the pelvis forms the inferior border, the abdominal cavity is often referred to as the abdominopelvic cavity. The anterior border is primarily comprised of abdominal wall muscles; the posterior border also consists of muscles in addition to the lumbar spine.

     The abdominal cavity is frequently divided into four quadrants: right upper (RUQ), left upper (LUQ), right lower (RLQ) and left lower (LLQ).¹ The umbilicus (navel) is the center point of intersection of the horizontal and vertical lines separating the four quadrants. When documenting or describing the location of abdominal pain or other physical findings, use the umbilicus as the center point of a clock. A 12 o'clock position is superior and a 6 o'clock position is inferior on a vertical line, while 3 o'clock is right lateral and 9 o'clock is left lateral on a horizontal line. Describe the point of pain, discoloration, mass or other finding by describing it as being so many centimeters or inches from the umbilicus at a particular o'clock position. For example, you might describe a point location of pain as being 6 cm at a 2 o'clock position from the umbilicus. This puts the pain at a very specific location within the left upper quadrant. Another method used to describe locations within the abdominal cavity is to separate it into nine different regions.¹ These regions provide a more precise identification of location than the less descript four quadrants.

     The abdominal and pelvic cavities are lined by a serous membrane called the peritoneum. The outer layer of the peritoneum is referred to as the parietal peritoneum. It also forms the innermost layer of the abdominal wall. The visceral peritoneum is the innermost lining that covers the abdominal organs (viscera). Serous fluid located between the layers acts as a lubricant to reduce friction from organ movement. The mesenteries are double sheets or folds of peritoneum that suspend the stomach, intestines and some other organs. The mesenteries also contain blood vessels responsible for perfusing the intestines. A posterior portion of the abdominopelvic cavity is not lined by peritoneum and is referred to as the retroperitoneal space. Some organs, such as the kidneys and ureters, are located completely in the retroperitoneal space, whereas organs like the pancreas are located in both the peritoneal and retroperitoneal spaces.

     Abdominal organs are classified as hollow or solid (see Table I). Hollow organs are usually less vascular and contain a chemical-like or bacterial substance that may spew into the abdominal cavity if ruptured or lacerated. Solid organs are typically more vascular and may lead to more aggressive blood loss if ruptured or lacerated. Also contained within the abdominal cavity are large vascular structures such as the abdominal aorta and inferior vena cava. Rupture of a vascular structure will produce significant blood loss and severe hypovolemia.

PATHOPHYSIOLOGY OF ABDOMINAL PAIN
     Pain is the hallmark symptom of an acute abdominal condition. Understanding the pathophysiology and presentation of abdominal pain may heighten your suspicion of a progressing disease state or enable you to recognize a change that points to an acute abdominal condition.

     The pain is usually caused by one of the following mechanisms:

• Ischemia (lack of adequate oxygenation of tissue) of the intestines or associated structures
• Distention of the organs or associated structures
• Inflammation or irritation of the peritoneal lining due to chemical or infectious substances
• Mechanical stretch of tissues.

     The source of abdominal pain can originate from the organ itself, the mesentery, peritoneum, abdominal wall muscle, skin or subcutaneous tissue, or it can be referred from organs or structures outside the abdominal cavity. The abdominal organs are not sensitive to cutting or tearing, with the exception of the aorta; however, stretching or distention of the organ, the fibrous capsule of some solid organs, and the peritoneum will stimulate nerve fibers and produce pain. Rapid distention usually produces significant pain, while a gradual distention may be associated with little pain. Pain is not considered an early sign in chronic conditions like cirrhosis of the liver, which is usually associated with a gradual organ distention. A patient may be experiencing a significant chronic condition that may be life-threatening; however, if the distention occurs over a period of time, the pain will not be as evident on assessment. Therefore, less pain is not necessarily correlated with a less severe condition.

     Prostaglandins, histamine, bradykinin and serotonin are chemical mediators related to an inflammatory response. These may stimulate nerve endings and cause the patient to experience abdominal pain. Edema linked to bacterial, chemical or viral inflammation will stretch the organ walls, stimulate the nerve endings and result in pain.

     If blood flow to an organ is obstructed, the tissue becomes ischemic. Metabolites and waste products have a tendency to build up within the tissue and organ, which in turn stimulates the pain receptors. As ischemia progresses, the pain tends to worsen in intensity.

     Abdominal pain can be classified as visceral, parietal or somatic, or referred.

•      Visceral pain originates from the stimulation of nerve fibers within the organ itself, hence the name visceral, referring to viscera (organs). Visceral pain is usually the earliest manifestation of an abdominal condition. It is usually felt in the midline in the epigastric or umbilical areas and is poorly localized, meaning the patient will have difficulty pointing to the pain with one finger. Most often, the patient will wave his or her hand over the area indicating a general or more diffuse pain. This is due to the sparse number of nerve endings in the organ and afferent nerve fibers that enter the spinal cord at multiple levels.
•      The pain is often described as dull, aching and crampy. If hollow organs are involved, the pain is often described as crampy, colicky, dull and intermittent. Solid organs usually produce dull but constant pain. The vague pain will often trigger the sympathetic nervous system and produce associated nausea, vomiting, diaphoresis and tachycardia.
•      Parietal or somatic pain is produced when the parietal peritoneum pain nerve fibers are activated. This pain is much more localized. If asked, the patient will typically be able to point to the pain with one finger. The more precise localization of pain is a result of the parietal peritoneum nerve fibers traveling along very specific peripheral nerves that enter the spinal cord in precise areas that directly correspond with the skin dermatomes between T6 and L1. The pain is usually unilateral (on one side) because the parietal peritoneum is innervated only from one side of the nervous system.
  
•      Parietal pain is normally described as sharp, intense and constant. These patients usually lie very still with the legs drawn up toward the chest in what appears to be a fetal position. By doing so, the parietal peritoneum is more relaxed, which reduces pain. Also, the patient will breathe shallow and fast to reduce movement of the diaphragm and subsequent aggravation of the peritoneum.
  
•      Bacterial and chemical irritants cause somatic pain and peritonitis. Bacteria may leak from an infected organ such as the appendix or large intestine, while chemical irritation may arise from leakage of irritating chemical substances like highly acidic gastric juices from the stomach, duodenum or ileum, or from digestive enzymes spewing from the pancreas. Peritonitis can lead to sepsis. When visceral pain is replaced by parietal pain, it is typically an indication that the condition has progressed and is potentially worsening.
•      Referred pain is a type of visceral pain that is felt away from the actual affected organ site, even though the patient is complaining of discomfort or pain in that particular area.¹ This type of pain is usually well localized in the skin or deeper tissue. The referred pain is produced when neural pathways of the affected organ follow or share a central afferent (toward spinal cord) nerve pathway that may have been common during embryonic development. As an example, afferent neural pathways from the diaphragm enter the spinal column at C4. Irritation of the diaphragm will produce referred pain in the neck or shoulder on the same side of the diaphragm irritation. As the intensity of visceral pain increases, the patient may begin to experience referred pain.

     Just as abdominal conditions may cause referred pain outside of the abdominal cavity, the same is true for some extra-abdominal conditions. As an example, pneumonia or an acute myocardial infarction may cause diffuse abdominal pain; however, there is no tenderness on palpation.

     To apply the pain classifications to a clinical situation and to help clarify how understanding this information may assist you in recognizing an acute abdominal condition, take the case of appendicitis. As the appendix becomes infected, it begins to fill with purulent fluid that stretches and distends the organ, creating visceral pain. As you recall, the visceral pain is described as intermittent, dull pain that is usually felt around the umbilicus. This pain may be annoying but not a real concern for the patient, even though he may have an inflamed and distended appendix. As the purulent fluid filled with bacteria penetrates the wall of the appendix and contacts the parietal peritoneum, the characteristics of the pain gradually change to become sharper, more intense, constant and localized to the right lower quadrant, making the patient want to draw his knees up to his chest to reduce the abdominal wall tension. You may also note an increase in respiratory rate with a decrease in tidal volume in an attempt to reduce the diaphragmatic excursion into the abdominal cavity. You would recognize the change in the pain pattern from visceral to parietal pain indicating a progressive disease condition.

PATIENT ASSESSMENT
     Assessment of the patient complaining of acute abdominal pain follows the typical medical assessment format: scene size-up, initial assessment, focused history and physical exam, and ongoing assessment.

SCENE SIZE-UP
     The scene size-up may provide information regarding the patient prior to even asking the first question or obtaining physical examination findings. This may be especially useful in the patient who has an altered mental status.

     Upon entering the scene, look for evidence of buckets, basins or other collection devices that may indicate the patient was nauseated and vomiting. This is especially true if one is found next to the patient or where he or she was just sitting or lying. Look at the contents in the bucket to determine the color, consistency and content. Dark "coffee-ground" emesis may indicate a slower upper gastrointestinal bleed with partially digested blood; bright red blood in the vomitus may indicate a more active bleed in the upper gastrointestinal tract, gastritis or an esophageal bleed, along with other potential conditions. Vomiting is usually associated with a condition involving the stomach, liver, gallbladder or appendix.

     The patient's posture may also provide some clues. The patient who presents in a fetal position is likely experiencing parietal pain from peritoneal irritation; the patient who is lying supine with the legs outstretched is more likely experiencing visceral pain. The patient who wants to be upright and walk or continues to pace likely has an obstruction to a hollow organ, such as a bowel obstruction, gallstone or kidney stone.

     Look for any other evidence that may provide clues to the etiology of the abdominal pain such as liquor bottles, syringes, drug paraphernalia, poisons and other substances that might irritate the gastrointestinal tract.

INITIAL ASSESSMENT
     An altered mental status may be an early indication of a poor perfusion state. In the acute abdomen patient, this may be due to a significant hemorrhage. The effects may have accumulated from the patient gradually bleeding over a period of time or from an acute severe hemorrhage.

     An elevated respiratory rate with a decreased tidal volume (shallow respirations) may result from parietal pain, peritoneal irritation or a limited excursion of the diaphragm from an upward compression from a bowel obstruction or ascites, which is a collection of fluid in the intraperitoneal space. Tachypnea with a normal or slightly deeper tidal volume, often referred to as quiet tachypnea, may be an indication of metabolic acidosis or may result from an increase in sympathetic stimulation from pain or hypovolemia.

     Tachycardia may reflect compensation for hypovolemic shock or from pain. Weak peripheral pulses and pale, cool and clammy skin would be clear indicators of poor perfusion. Vasoconstriction with shunting of blood from the capillary beds causes the skin to become pale and cool. This is most often related to stimulation of the vessels by the sympathetic nervous system and the release of epinephrine and norepinephrine from the adrenal medulla. The alpha properties in epinephrine and norepinephrine stimulate the sweat glands and produce clammy skin. Flushed skin would indicate vasodilation produced by the release of chemical mediators potentially associated with an infectious process. Infection may also cause the skin to become pale if shunting occurs. Suspect hypoxemia or poor perfusion if cyanosis is noted. Circumoral (around the mouth) cyanosis may appear earlier than in other areas of the body. Mottling, which is often described as grayish, purplish and bluish skin color, is typically seen with blood pooling in capillary beds that may occur from inadequate perfusion from blood loss or long-term vasodilation. Pale and mottled skin is normally cool to touch. Flushed skin is usually warm and may be an indication of infection and associated fever.

HISTORY
     A patient history will likely provide the most valuable information in determining potential life-threats and in working through the possible to probable conditions. The typical SAMPLE history information must be collected.

•      Signs and symptoms
       The most common symptom is pain. It is important to also collect other associated symptoms, such as nausea, weakness, lightheadedness, shortness of breath and chest discomfort.
•      Allergies
       Determine if the patient has any allergies to prescription medication, especially pain medication in this case, or over-the-counter medications.
•      Medications
       The medications the patient is taking may provide some clues to his medical history, current treatment of a related condition, or the possible cause for pain. Be sure to collect information on both prescription and nonprescription medications like over-the-counter antacids.
•      Past medical history
       Ascertain the past medical history to include any abdominal surgeries.
•      Last oral intake
       Determine when the patient last had anything to eat or drink. It is also helpful to ask questions about dietary habits, especially the most recent eating habits. What the patient ate may provide an explanation in some cases, such as a severe case of gastritis from recent ingestion of hot and spicy foods.
•      Events prior to the episode
       Ask about the patient's activity prior to the onset of pain and other signs or symptoms. This may include physical activity, ingestion of certain food substances, use of certain medication or work around chemicals.

     Because pain is the most common complaint associated with an acute abdomen, it is necessary to collect additional information to determine if a potential life-threat exists and to assist with the critical thinking process of drilling down to probabilities. A common mnemonic used is OPQRST:

•      Onset

       Determine if the onset was sudden or gradual. A sudden onset of severe pain with significant weakness, lightheadedness or syncope (fainting) may indicate a perforated organ, ruptured aneurysm or ruptured ovary or fallopian tube in an ectopic pregnancy. A gradual onset with less descriptive symptoms that suddenly become more intense, localized and constant may indicate the progression from visceral to parietal pain with leakage of blood, bacteria or biochemicals with peritoneal irritation. Also ascertain if this is the first episode or if this pain has occurred before. If so, did the patient seek medical treatment and what was the outcome? If this is not the first episode of pain, ask what was different that caused the patient to call EMS this time.

•      Palliation or provocation

       What makes the pain better and what makes it worse? If the patient experiences some relief when lying still with the knees drawn up toward the chest, suspect peritoneal irritation. If the patient prefers to continue walking or moving, it is likely an obstruction of the bowel or bile duct. Antacids may relieve the pain associated with gastritis or peptic ulcer.

•      Quality

       How does the patient describe the pain? Sharp, constant, knife-like pain may be due to peritoneal irritation. Dull pain is likely from organ distention. Crampy or colicky pain is most often produced by a hollow organ.

•      Radiation

       Does the patient experience pain away from the abdomen? Most often this is referred pain and is not pathologic itself; however, it may provide significant clues to the organ involved. For example, inflammation of the gallbladder will cause right scapular pain.

•      Severity

       Quantify the pain by asking on a scale of 1 to 10 how bad the pain is, with 10 being the worst. Realize, though, that this is extremely subjective, since patients have different reference points for pain. The elderly and those with diabetes mellitus may have a reduced sensitivity to pain. Thus, do not judge the criticality of the condition based solely on the severity of pain.

•      Time

       Attempt to determine as exactly as possible when the pain began and how long each episode lasted. Progression of the condition may be identified by episodes that occurred more frequently with greater intensity, and lasted longer.

PHYSICAL EXAM
     Do not develop tunnel vision when performing a physical exam by focusing on only the abdomen. Because abdominal pain may arise from extra-abdominal causes, it is important to assess other organ systems along with the abdomen. The physical exam will also provide additional evidence of real or potential life-threats, such as poor perfusion, or it may heighten or eliminate your suspicion of a traumatic etiology of the pain. The physical exam should be conducted in an organized and systematic manner. Begin with the head, moving downward toward the feet and ending with the posterior body. Sluggish pupils may indicate poor perfusion. Hypovolemic shock may produce pale conjunctiva, while the hypoxic patient may present with cyanotic conjunctiva. Yellow sclera (icterus) may heighten your suspicion of liver disease. Inspect the oral mucosa for signs of adequate perfusion.

     Auscultate the chest for any abnormal breath sounds. Rales or crackles, rhonchi or wheezing may be signs of pneumonia producing referred pain to the abdomen. Wheezing may also be produced from a distended abdomen that triggers bronchospasm in the terminal bronchioles from compression.

     Inspect the abdomen, looking for distention from air or fluid collection, discoloration, scars or evidence of trauma. Ecchymotic (black and blue) discoloration around the umbilicus (Cullen's sign) or to the flank areas (Grey-Turner's sign) indicates bleeding that has occurred over several hours.

     Auscultation of the abdomen has very little use in the prehospital setting. To be done accurately, the abdomen must be auscultated for three to five minutes in each quadrant in an extremely quiet environment. The information provided will also be of limited use, and treatment will not change based on the presence or absence of bowel sounds.

     Prior to palpation of the abdomen, ask the patient to point with one finger to where the pain is greatest. This will assist you in determining whether the pain is localized or diffuse. Begin palpation at the point farthest away from that location, assessing for guarding, rigidity, masses, tenderness, enlarged organs or abnormal pulsations. Assess for rebound tenderness by having the patient cough. A heel-drop (Markle test) or a heel-jar test can also be done to assess for rebound tenderness. The heel-drop is done by having the patient lift up on the balls of his feet while in a standing position, then drop down on his heels. Alternatively, you can strike the heel of the foot with a closed fist when assessing the lower extremities. Be sure to watch the patient's face for a grimace or listen for complaints of pain to the abdomen when doing either test. If the patient feels dizzy, lightheaded or has a syncopal episode when changing his position from lying to sitting or sitting to standing, suspect hypovolemia.

     Inspect the upper and lower extremities for abnormal skin color or edema. Determine skin temperature and condition, and assess for distal pulses. Compare the pulse amplitudes between lower and upper extremities. Pale or mottled and cool lower extremities with lower pulse amplitudes than those found in the upper extremities in a patient complaining of abdominal and lower lumbar pain should lead you to suspect an abdominal aortic aneurysm. Male patients may also complain of scrotal or testicular pain.

     Inspect and palpate the posterior body, paying particular attention to the flank and lumbar regions. Look for any evidence of trauma. Inspect for an ecchymotic discoloration to the flank areas (Grey-Turner's sign), especially if the patient has been in a supine position.

VITAL SIGNS
     Assess heart rate; respirations; skin color, temperature and condition; blood pressure and pupils. Many of the abnormal findings were discussed previously as part of the initial assessment. Although tachycardia is a true sign of shock, it may not be present in many patients. If the patient takes beta blockers or calcium channel blockers, the heart rate may remain much lower than would be expected, even though he is truly in hypovolemic shock.

     Once a baseline is established, frequently reassess the vital signs, looking for trends that may indicate deterioration or improvement of the patient's condition. Auscultate the blood pressure so you can obtain both a systolic and a diastolic reading. A decreasing systolic blood pressure may suggest reduced cardiac output associated with hypovolemia. As cardiac output falls, the sympathetic nervous system, along with many circulating hormones, constricts the vessels and increases systemic vascular resistance (SVR). A measure of SVR is the diastolic blood pressure. A fall in cardiac output will cause the systolic blood pressure to decrease, while an increase in SVR will cause the diastolic blood pressure to increase or be maintained. This produces a narrowing pulse pressure (difference when the diastolic blood pressure is subtracted from the systolic blood pressure), which is a sign of hypovolemia.

     Orthostatic vital signs should also be assessed. An increase in heart rate is a much more sensitive finding than a decrease in systolic blood pressure. An increase in the heart rate of 30 bpm or greater may signify a substantial volume loss.

     When assessing for shock, be sure to consider signs of perfusion in addition to just taking the vital signs. As noted earlier, the heart rate may remain normal or only slightly increased, and the systolic blood pressure may appear fairly normal, even though the patient is in serious shock. Assess the skin signs and mental status for evidence of poor perfusion.

EMERGENCY CARE
     Emergency care for the patient experiencing abdominal pain is dependent somewhat on the complaint, severity of the condition and signs of shock. Most of the care is supportive and involves ensuring an adequate airway, ventilation and oxygenation; maintaining circulation through administration of normal saline or lactated Ringer's; placing the patient in a position of comfort; relieving pain with the use of analgesics based on the physiologic stability of the patient and your protocol; and rapidly transporting. Septic shock patients may require vasopressors such as dopamine to raise and maintain blood pressure.

     Using your critical thinking skills, it may be possible to work toward a differential field diagnosis; however, without laboratory and diagnostic tests, it is unlikely the condition can be conclusively identified in the field. It is most important for EMS providers to recognize the complaint, assess and manage any life-threats, and provide competent supportive care to the patient.

CEU Review Form Beyond the Basics: Acute Abdominal Pain (PDF) Valid until September 5, 2008

Reference
     Dalton AL, Limmer D, Mistovich JJ, Werman HA. Advanced Medical Life Support: A Practical Approach to Adult Medical Emergencies, 3rd edition, p. 317, figure 8-2a and figure 8-2b; and page, 321, figure 8-4. Upper Saddle River, NJ: Prentice Hall, 2007.

Joseph J. Mistovich, MEd, NREMT-P, is a professor and chair of the Department of Health Professions at Youngstown (OH) State University.

William S. Krost, MBA, NREMT-P, is director of Emergency Services & Health System Access for Blanchard Valley Health System in Findlay, OH.

Daniel D. Limmer, AS, EMT-P, is a paramedic with Kennebunk Fire-Rescue in Kennebunk, ME.