الفهرس 
Pathophysiology of Obstructive Sleep ApneaOnly 14 pages are availabe for public view
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Abstract
It is generally agreed that an apnea, defined as a cessation of airflow, has to exceed 10sec. duration to be considered significant.
The apneas may be obstructive, central or mixed.
Obstructive apneas are characterized by persistent effort without airflow, while with central apnea, effort is absent.
Abnormalities of airway structure, such as enlarged tonsils and uvula, and abnormal airway function (primarily a reduction in the activity of the dilator muscles of the pharynx) may contribute to the problem in varying degrees. Progressive upper-airway closure during the transition to sleep is accompanied by complete obstruction of airflow (apnea) or partial obstruction (hypopnea). Hypercapnia and acidosis resulting from hypoventilation stimulate arousal centers in the central nervous system, leading to increased respiratory and pharyngeal-muscle activity. The patient then returns to sleep, the pharyngeal musculature relaxes, and the cycle repeats itself.
Central sleep apnea may occur in association with disorders of ventilatory control or neuromuscular function or where the respiratory musculature is excessively loaded. Patients with such conditions have diminished ventilatory capacity that results in hypoventilation during sleep when the drive to ventilation is reduced and the compensatory mechanisms fail.
Symptoms of sleep apnea syndrome include snoring, witnessed apneas, nocturnal shoking or gasping, insomnia, excessive daytime sleepiness, fatigue, memory impairment, personality changes, morning nausea, morning headaches, and depression.
By examination, patients of OSA are usually obese with specific craniofacial anatomy including retrognathia, micrognathia, tonsillar hypertrophy, macroglossia, and inferior displacement of the hyoid.
Sequelae of sleep apnoea syndrome include daytime sleepiness, insulin resistence and type 2 diapetes, hypertention, atherogenesis, CV events, and mortality.
Management of sleep apnea syndrome include weight reduction, avoidance of alcohol intake, oral Appliances. However the most important line is the CPAP which acts physiologically as a pneumatic splint, inducing patency of the upper airway during inspiration and expiration.
OSA and Anesthesia Creates a Multidimensional Problem: The disastrous respiratory outcomes during the perioperative management of patients with OSA are a major and increasing problem for the anesthesia community. The disastrous outcomes are due to:
- Failure to secure the airway during the induction of anesthesia.
- Respiratory obstruction soon after extubation.
- Respiratory arrest after the administration of opioids and/or sedation to postoperative extubated patients (personal observation).
Preoperative preparation of a patient with OSAS include determination of the causes of OSA, establishment of a well defined diagnosis, determination of severity of the condition, determination of perioperative risk of OSA then perioperative management including premedication in which sedatives should be avoided, regional anaesthesia whenever possible, preparation for difficult intubation considering awake intubation as the choice, during general anaesthesia both opioids and muscle relaxants should be used judiciously.
One of the major concerns in patients with OSA is the risk of airway obstruction after tracheal extubation. Thus, prior to tracheal extubation the patient must be fully awake, alert, and following commands, and complete reversal of neuromuscular blockade should be established. Extubation should be performed in a semi-upright (30º head-up) position, when possible.
The patient then will be transfered to PACU as postoperative complications are more frequent in patients with OSA. These include airway obstruction, oxygen desaturation, and the need for reintubation as well as systemic hypertension, cardiac dysrhythmias. Once in the PACU, patients should be maintained in a semi-upright (30º head-up) position, if possible. It is recommended that patients who use CPAP preoperatively should wear their CPAP masks postoperatively.
Post operative opioids and PCA should be used judiciously, both NSAIDS and paracetamol have an opioid sparing action and decreases its post operative requirments.
Post operative observation together with SPO2 monitoring are mandatory either in a private room or in ICU.