I. Problem. A 3-year-old boy who was recently admitted from the emergency department with respiratory distress has a room-air pulse-oximetry reading of 89%.
A. Is patient truly hypoxic or is the pulse-oximetry reading an artifact of measurement? Motion and improper oximeter probe placement may lead to falsely low readings. If pulse tracing is strong and corresponds to the heart rate, and the reading remains low, provide oxygen and examine patient.
B. What is patient's ventilation and hemoglobin saturation state? Pulse oximeters reflect only oxygenation and do not measure ventilation. Altered hemoglobin saturation states (eg, methemoglobin and carboxyhemoglobin) may lead to false oxime-ter readings.
C. How severe and prolonged has hypoxia been? This decision must be made early in the evaluation, always assessing and correcting airway, breathing, and circulation (ABCs) initially.
III. Differential Diagnosis
A. Airway Obstruction. In the lower airway, consider asthma; in the upper airway, choanal atresia.
B. Decreased Diffusion of Gas From Alveoli to Capillaries. Includes pneumonia and aspiration.
C. Abnormal Cardiopulmonary Blood Flow. Includes cyanotic congenital heart disease and pulmonary embolus.
D. Alteration in Neuromuscular Control of Respiration. Includes drugs and muscular dystrophy.
A. Physical Exam Key Points. Observation of general appearance (including level of alertness) is important. Evaluate for cyanosis, airway patency, respiratory rate and effort, and cardiac abnormalities. Listen for snoring, stridor, wheezing, rales, and adequacy of air movement.
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