Breathing After the airway has been evaluated and secured as necessary, breathing is assessed to assure adequate air exchange Continuous oxygen saturation measurement and endtidal carbon dioxide (ETCO2 ) monitoring in both intubated and nonintubated patients allows for continued assessment of oxygenation and ventilation The most common causes of hypoxemia in children are ventilation/perfusion (VQ) mismatch and hypoventilation ETCO2 may help distinguish between these two entities; providers will note normal or low ETCO2 in cases of primary VQ mismatch, while in cases of hypoventilation, physicians will often see hypercarbia out of proportion to hypoxemia It is important to note that in trauma patients, compromise of ventilatory function most often occurs secondary to a depressed sensorium rather than a primary pathology of the respiratory system itself Circulation Circulation is assessed by examining the character of the pulse, skin color, and capillary refill time There is no single physical or laboratory finding that will identify shock, however, the physical signs exhibited by the patient in shock are ultimately due to insufficient oxygen and substrate delivery to the tissues The physical manifestations vary with type of shock but include tachycardia, decreased skin perfusion, and hypotension (cold shock) or tachycardia, bounding pulses and flushed skin with hypotension (warm shock) If cardiogenic shock is present, HR may be normal or only modestly elevated Remember that in children, hypotension is a late finding requiring a 50% decrease in the circulating volume to affect a decrease in systolic pressure In trauma, external hemorrhage visualized during the primary survey should be controlled by direct pressure or pneumatic splints Disability CNS failure is manifested by altered MS or by the presence of focal neurologic deficit(s) Recall that the CNS is composed of the brain and meninges, the blood vessels, and the cerebrospinal fluid Many diseases that cause CNS failure are caused by compartment physiology, as in the case of elevated intracranial pressure (ICP) Examples of primary CNS disease include intracranial hypertension secondary to mass or hemorrhage, and status epilepticus The CNS may also be secondarily affected by respiratory or circulatory disease as oxygen delivery to the tissues of the CNS is impaired The AVPU scale and GCS ( Table 7.2 ) are used to measure level of consciousness in a standardized way Interventions to treat CNS failure include modest hyperventilation and hypertonic therapy (in the case of elevated ICP), maintenance of MAP and oxygenation to ensure adequate CNS perfusion, and avoidance of hyperthermia Other therapies aimed at the underlying cause of CNS failure include anticonvulsants, antimicrobials, and surgical decompression