Blunt abdominal trauma (BAT) comprises 75% of all blunt trauma and is the most common example of this injury. The majority occurs in motor vehicle accidents, in which rapid deceleration may propel the driver into the steering wheel, dashboard, or seatbelt causing contusions in less serious cases, or rupture of internal organs from briefly increased intraluminal pressure in the more serious, dependent on the force applied. It is important to note that initially there may be little in the way of overt clinical signs to indicate that serious internal abdominal injury has occurred, making assessment more challenging and requiring a high degree of clinical suspicion.
There are two basic physical mechanisms at play with the potential of injury to intra-abdominal organs: compression and deceleration. The former occurs from a direct blow, such as a punch, or compression against a non-yielding object such as a seat belt or steering column. This force may deform a hollow organ thereby increasing its intra-luminal or internal pressure, leading to rupture. Deceleration, on the other hand, causes stretching and shearing at the points at which mobile structures, such as the bowel, are anchored. This can cause tearing of the mesentery of the bowel, and injury to the blood vessels that travel within the mesentery. Classic examples of these mechanisms are a hepatic tear along the ligamentum teres and injuries to the renal arteries.
In rare cases, this injury has been attributed to medical techniques such as the Heimlich Maneuver, attempts at cardiopulmonary resuscitation and manual thrusts to clear an airway. Although these are rare examples, it has been suggested that they are caused by applying unnecessary pressure when administering such techniques. Finally, the occurrence of splenic rupture with mild blunt abdominal trama in those convalescing from infectious mononucleosis is well reported.
In all but the most obviously trivial injuries, the first concern is to exclude anything that might be quickly or immediately life-threatening. This is resolved by ascertaining that the subject's airway is open and competent, that breathing is unlabored, and that circulation—i.e. pulses that can be felt—is present. This is sometimes described as the "A, B, C's"—Airway, Breathing, and Circulation—and is the first step in any resuscitation or triage. Then, the history of the accident or injury is amplified with any medical, dietary (timing of last oral intake) and past history, from whatever sources such as family, friends, previous treating physicians that might be available. This method is sometimes given the mnemonic "SAMPLE". The amount of time spent on diagnosis should be minimized and expedited by a combination of clinical assessment and appropriate use of technology, such as diagnostic peritoneal lavage (DPL), or bedside ultrasound examination (FAST) before proceeding to laparotomy if required. If time and the patient's stability permits, CT examination may be carried out if available. Its advantages include superior definition of the injury, leading to grading of the injury and sometimes the confidence to avoid or postpone surgery. Its disadvantages include the time taken to acquire images, although this gets shorter with each generation of scanners, and the removal of the patient from the immediate view of the emergency or surgical staff.