Final answer:
The most likely cause of the child's acute deterioration is a physiological shunt. This occurs when there is obstruction in the lung, leading to decreased ventilation without affecting perfusion. As a result, the V/Q ratio changes and gas exchange is affected, causing hypoxemia and cyanosis.
Step-by-step explanation:
A physiological shunt can develop if there is infection or edema in the lung that obstructs an area. This will decrease ventilation but not affect perfusion; therefore, the V/Q ratio changes and gas exchange is affected.
Based on the information provided, the most likely cause of the child's acute deterioration is a physiological shunt. A physiological shunt occurs when there is obstruction in the lung, leading to a decrease in ventilation but not affecting perfusion. This results in a change in the V/Q ratio (ventilation/perfusion ratio) and impaired gas exchange, causing hypoxemia and cyanosis.
In this case, the child's cyanosis, decreased heart rate, and low oxygen saturation (spO2) levels indicate poor oxygenation. The diminished breath sounds on the left side suggest a problem with ventilation in that area, which could be caused by an obstruction.