Sleep-Disordered Breathing in ICU: Causes, Diagnosis & Life-Saving Management Guide

 Sleep-Disordered Breathing in ICU: Causes, Diagnosis & Life-Saving Management Guide

Sleep-Disordered Breathing in the Intensive Care Unit

Sleep has a wide range of effects on respiratory physiology in healthy individuals. In patients with underlying comorbidities such as severe chronic obstructive pulmonary disease or neuromuscular disease, these changes in respiratory physiology can compromise cardiopulmonary status. Additionally, sleep-related breathing disorders may lead to respiratory failure.

Sleep-related breathing disorders occur during sleep and include obstructive sleep apnea (OSA), central sleep apnea (CSA), and sleep-related obesity hypoventilation. Apneic events during sleep may be either obstructive or central in nature. Obstructive events are associated with continued respiratory effort, whereas central events occur without respiratory effort.

Obstructive sleep apnea occurs due to narrowing of the upper airway during sleep, often caused by excessive soft tissue or structural abnormalities. This leads to limitation or cessation of airflow and is commonly associated with arousals and oxygen desaturation. OSA is linked with increased risk of excessive daytime sleepiness, hypertension, stroke, and heart failure. The prevalence of obstructive sleep apnea–hypopnea syndrome (OSAHS) is approximately 4% in men and 2% in women.

Central sleep apnea may occur in conditions such as severe heart failure (Cheyne–Stokes respiration), stroke, or narcotic use. The severity of obstructive sleep apnea is quantified using the apnea–hypopnea index (AHI), which measures the number of apnea and hypopnea events per hour.

Obesity hypoventilation syndrome (OHS) is used to describe hypoventilation during sleep in obese individuals, leading to daytime hypercapnia. The prevalence of OHS is unclear, and its definition varies in the literature. However, diagnostic criteria include features such as hypercapnia during sleep or wakefulness.

Effects of Sleep on Respiratory Physiology:

During sleep, several physiological changes occur. There is a decrease in hypoxic ventilatory response and hypercapnic ventilatory response. Muscle tone is reduced, leading to increased airway resistance. Additionally, the arousal threshold increases, meaning that stronger stimuli are required to awaken the individual, especially during REM sleep.

Severity of Obstructive Sleep Apnea:

Obstructive sleep apnea is classified based on the apnea–hypopnea index (AHI). Mild OSA is defined by an AHI of 5–15 and is associated with impairment during sedentary activities requiring minimal attention, such as watching television or reading. Moderate OSA (AHI 15–30) affects activities requiring some attention, such as attending meetings. Severe OSA (AHI >30) affects activities requiring active attention, such as conversation, eating, or driving.

Diagnostic Criteria for Sleep Hypoventilation Syndrome:

Patients may present with signs such as cor pulmonale, pulmonary hypertension, unexplained excessive daytime sleepiness, erythrocytosis, and waking hypercapnia (PaCO₂ >45 mm Hg). Monitoring findings include an increase in PaCO₂ during sleep by more than 10 mm Hg compared to awake supine values and oxygen desaturation during sleep not associated with apneas or hypopneas. At least one criterion from each category is required for diagnosis.

Signs and Symptoms of OSAHS and OHS:

Common features include obesity, snoring, awakening with snorting or gasping, witnessed apneas, excessive daytime sleepiness, and morning headaches. Patients may also have a short neck circumference, unrefreshing sleep, poorly controlled hypertension, and craniofacial abnormalities such as micrognathia, retrognathia, or macroglossia. Other findings include nocturnal oxygen desaturation, unexplained hypercapnia, and hypothyroidism.