Final answer:
A pediatric complication requiring a knife for emergency situations is when there's an airway obstruction such as bronchospasm or laryngospasm, which can happen under anesthesia.
Step-by-step explanation:
The pediatric complication that would require the scrub person to have a knife ready for an emergency is an airway obstruction situation, such as in the case of bronchospasm, laryngospasm, or other similar conditions where the airway becomes compromised. When muscles necessary for breathing and securing the airway are impaired, such as under general anesthesia, procedures like endotracheal intubation ensure the patient maintains an open airway. However, if the patient's airway becomes obstructed post-surgery, and intubation cannot be performed or fails, an emergent tracheotomy may be necessary, thus requiring a knife.