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OSA (Obstructive Sleep Apnea)


A normal human being spends 1/3rd of life in sleeping. But, isn’t it surprising that, we are still not aware about the majority of sleep disorders! This must be the reason that although, we have huge numbers of Ischemic heart disease, Hypertension and Diabetes mellitus, still we don’t have major epidemic data from India about this root disease, OSA (Obstructive Sleep Apnea).

Is it that we have very limited number of patients or we are not aware about the disease or we don’t know how to diagnose it, although we have clinical suspicion! Diagnosing OSA should not be a challenge, as we have various parameters like clinical, laboratory, Sleep questionnaire and of course, sleep study to arrive to exact diagnosis.

CLINICAL DIAGNOSIS-

As with majority of the medical conditions, the key to suspect the diagnosis of sleep apnea syndromes and various other sleep related disorders is History, History and History.

While evaluating the patient of suspected sleep disorder, always divide the patients into 3 broad subgroups-

The common symptoms are-

In any of these consistent symptomatology, irrespective of age and gender, a thorough clinical check up and a visit to sleepexpert is essential. With vast array of these symptoms, these patients often present to ENT specialist, Neurologist, Pulmonologist or a psychiatrist and the diagnosis may need a multidisciplinary approach.

BMI- Body mass index of more than 27 may predispose a person to develop OSA, but the absence of OSA can't certainly rule out OSA. Neck girth- Neck girth more than 17 inches in males and more than 15 inches in females predispose the person for developing OSA. Similarly, mentohyoid distance of less than 3 finger width has more chances of developing OSA.

Upper airawy evaluation for presence of tonsillar and adenoid hypertrophy, high arched palate, Septal deviation of the nasal bone, Macroglossia, Retrognathia, Long bulky uvula and facial structure predispose the patients for developing OSA irrespective of the BMI and hence, should be carefully evaluated.

SLEEP QUIESTIONNAIRE-

In a suspected OSA patient, these questionnaires can predict the probability of diagnosing the OSA before sending the patient to full night polysomnography. Epworth sleepiness scale, Berlin Questionnaire are widely used for assessing the sleepiness scale. One such scale is Sleep Apnea Clinical Score which is based on neck circumference, snoring, witnessed apneas and systemic hypertension. A score of more than 15 gives high likelihood of diagnosing moderate to severe OSA. A simple way of using adjusted neck circumference is as- measured neck circumference in cm and adding 3cm for snoring, 3cm for witnessed apneas, 4cm for systemic hypertension. Adjusted neck circumference of <43, 43-47.9 and >48 cm indicate mild, moderate and severe risk of OSA. Sleep questionnaires are simple OPD tools for assessing the patients for sleep apnea evaluation and must be practiced very routinely by all pulmonologist.

LABORATORY PARAMETERS-

Evaluation for Thyroid functions, hematocrit, ECG, 2D-Echo, Pulmonary function Test and arterial blood gas analysis may add to the diagnosis. The presence of saw-tooth pattern on the flow-volume loop can clinch the diagnosis and presence of pulmonary hypertension and hypercapnea will add in the severity of the diagnosis and concomitant lung problems.

POLYSOMNOGRAPHY (PSG)-
PSG remains the gold-standard for diagnosis and has an advantage of assessing the severity of the disease. It comprises of evaluation of the person's sleep pattern by using multiple parameters like sleep cycle, sleep staging, oximetry, apneas and hypopneas, cardiac function etc.

Various parameters in PSG are-

As per the American Academy Of The Sleep Medicine, PSG can be classified as 4 types-

Type 1 and Type 2 are Gold-standards for the diagnosis of OSA. By doing only nocturnal oximetry, around 50-60% cases of OSA can be misdiagnosed and hence, the use should be restricted only when facilities are not available. Type 1 study is of certain benefit only when parasomnias, REM- Behavioral disorders are sought.
A grading of more than 5 obstructive apneas and hypopneas (AHI >5) along with excessive daytime sleepiness or witnessed episodes of apneas, choking episodes at night are sufficient to make the diagnosis.

A typical polysomnogram looks like-
An obstructive apnea is defined as cessation of airflow for more than 10 seconds, when inspiratory efforts are made against a closed upper airway with continued presence of respiratory drive. I t looks like this-

A central apnea is cessation of respiratory drive resulting in absence of airflow. It looks like this-
Ideally, PSG should be done for 2 nights in sleep laboratory. However, in the presence of AHI more than 40 or AHI between 20-40 with certainty to prescribe CPAP, split night study can be done, where manual CPAP scoring can be done in later half of night.

Excessive daytime sleepiness (EDS)-5% of the population suffers from EDS. These can be patients due to OSA, narcolepsy, idiopathic hypersomnolence etc. The tests which are widely used are Multiple sleep latency test (MSLT) and Maintenance of Wakefulness Test (MWT). The test is done in sleep lab on the day following PSG and consists of allowing the patient to nap at intervals of 2 hours for 5 consecutive occasions. If mean sleep latency is less than 8 minutes, diagnosis of EDS is made.

SLEEP-MRI-A modality used by ENT surgeons to assess the operability in a patient of OSA. It can accurately calculate the level of obstruction in the upper airway and can help surgeons in predicting the benefits of surgery against long term use of CPAP in young patients.

Upper Airway Resistance Syndrome-It is a condition which common in habitual snorers and have typically, AHI<5 events per hour along with >10 RERAs (Respiratory Effort Related Arousals). These patients have partial collapse of the airway resulting in increased airway resistance. These are typically young females with low BMI and have problems in initiating sleep.
Sleep disorders are commonly missed diagnosis and need suspicion, detailed history from the patient and bed partner, careful clinical evaluation, assessment by sleep questionnaire and an overnight PSG to come to a diagnosis.