The Apnea-Hypopnea Index (AHI) is a critical tool used in the evaluation and management of patients with suspected obstructive sleep apnea (OSA). It quantifies the severity of sleep apnea based on the total number of complete cessations (apnea) and partial obstructions (hypopnea) of breathing occurring per hour of sleep. The AHI score is instrumental in determining the severity of OSA, with higher scores indicating more severe disease. 

This index is applicable to adult patients presenting with symptoms suggestive of OSA, such as excessive daytime sleepiness, loud snoring, observed episodes of breathing cessation during sleep, abrupt awakenings accompanied by gasping or choking, and morning headache. 

The AHI is not suitable for use in patients without symptoms of OSA, or in those with central sleep apnea, as it specifically measures obstructive events. Furthermore, it may not be accurate in patients with certain comorbid conditions that can affect respiratory function or sleep architecture, such as chronic obstructive pulmonary disease or neuromuscular disorders.