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Nasal ventilation
  1. A M ZEDAN
  1. The Royal National Throat, Nose & Ear Hospital
  2. Grays Inn Road, London WC1X 8DA, UK

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    Sir,In a paper in the June issue of this journal,1 the author mentioned briefly the “crucial recognition” that continuous positive airway pressure (CPAP) “is effective therapy for obstructive sleep apnoea”.

    Although CPAP is a well-established management option for sleep apnoea, its limitations and lack of universal acceptance should be borne in mind. Other modalities of treatment should also be considered when appropriate. Definition of sleep apnoea, determining its severity, and management options remain unclear to many healthcare providers. Sleep apnoea is the periodic cessation (apnoea) or reduction (to 50% of tidal volume or less) of air flow at the nostrils and mouth during sleep. The number of apnoeic–hypopnoeic episodes per hour of sleep (called the apnoea–hypopnoea index, or AHI) is used to indicate the severity of the syndrome (mild: 5–20, moderate: 21–50, severe: >50). It is usually caused by nasopharyngeal narrowing or collapse (peripheral or obstructive sleep apnoea) and much less commonly due to disturbance of the neurological control of respiration (central sleep apnoea). It is thought that obstructive sleep apnoea (OSA, the more common type of sleep apnoea) affects 2–4% of males and 1–2% of females in middle age.

    The syndrome presents clinically with observed apnoea, disturbed sleep and, in OSA, loud snoring. Daytime somnolence is a significant part of the syndrome2 and is used with other parameters to indicate its severity. OSA is also associated with cognitive impairment and increased susceptibility to road traffic accidents.3Claims that OSA is a cause of ischaemic heart disease, cerebrovascular accidents and pulmonary hypertension are based on very weak evidence.4 Risk factors include obesity, male gender, alcohol ingestion, nasal obstruction and retrognathia. The most common cause of paediatric OSA is adenotonsillar hypertrophy.

    History and clinical examination are aimed at identifying the syndrome components, severity, causes and associated risk factors. The severity of the syndrome may be assessed from a parents' or a partner's account or a tape recording of breathing during sleep. The Epworth Sleepiness Scale is being used by some units to quantify the problem. This scale assesses daytime tendency to doze in eight different situations and, indirectly, measures the quality of night-time sleep. The chance of dozing is scored as slight (1), moderate (2), or high (3). The situations covered are: watching TV, sitting inactive, sitting and reading, sitting and talking to someone, sitting quietly after lunch without alcohol, lying down in the afternoon, as a passenger in a car for an hour without a break and in a car whilst stopped for a few minutes in traffic. Some hospital units have restricted management of sleep apnoea in adults to cases with Epworth Sleepiness Scale scores of 12 or more.

    At this point, it may be obvious that a specific cause is responsible, eg, nasal obstruction, large tonsils, long redundant soft palate, small receding mandible or other craniofacial abnormalities. It would seem logical to address the obvious cause(s) directly by surgery, orthodontic devices or weight reduction as appropriate.

    Polysomnography is the overnight sleep study used to assess different parameters related to OSA syndrome. Other versions of the investigation include pulse oximetry and home sleep study. Polysomnography is resorted to if the diagnosis needs to be confirmed, if central apnoea is suspected, if there are severe symptoms with respiratory or cardiovascular complications, and if there are contraindications to, refusal or failure of other options, such as surgery. In other words, when the management choices have been narrowed to the use of CPAP. Other uses for polysomnography include pre-operative assessment if post-operative failure to restore spontaneous breathing is anticipated. In such cases, arrangements for post-operative assisted ventilation in the intensive care unit should be made. Polysomnography is also used to monitor the efficacy of a certain modality of management.

    Polysomnography consists of simultaneous measurement during sleep of eye movements (electro-oculogram), electro-encephalogram, electrocardiogram, chest and abdominal respiratory movements, nasal and oral air flow and oxygen saturation with finger or ear lobe oximeter. The following information is available from the study:

    • the AHI

    • the drop in oxygen saturation during the apnoeic/hypopnoeic episodes. This is also used to grade the syndrome, ie, >85%: mild, 80–85%: moderate, <80%: severe

    • duration of periods of oxygen desaturation

    • sleep efficiency, ie, the proportion of the study spent asleep

    • associated cardiovascular complications, eg, arrhythmias.

    CPAP ventilation during sleep is the treatment option in severe cases of obstructive sleep apnoea and in less severe cases if other modalities of treatment have failed, been rejected or are contraindicated. Central apnoea may be managed more effectively with intermittent rather than continuous positive airway pressure ventilation.5 Positive pressure ventilation acts as a pneumatic splint for the airways. Air is generated by a ‘blower’ and is delivered by means of a tight fitting mask placed on the nose and mouth. The appropriate pressure, between 7–15 cmH2O, is determined during a night stay in a sleep laboratory.

    CPAP is effective in improving the AHI and the oxygen saturation but has the following disadvantages: life-long treatment, cumbersome noisy machine, uncomfortable mask, nasal and pharyngeal irritation, sore eyes from leakage around the mask, abdominal bloating from leakage into the oesophagus, a feeling of claustrophobia experienced by many patients and overall compliance of 50–90%. New developments include customised masks, smaller quieter machines and nasal BiPAP (bi-level positive airway pressure) in which the pressure is reduced during expiration thus improving comfort and compliance.

    Surgery may be used if a specific obstruction is detected in the nose or pharynx during clinical or endoscopic examination under simulated sleep induced by light general anaesthesia (sleep naso-endoscopy). Surgical management for OSA aims to relieve the obstruction by increasing the surface area, to bypass the pharyngeal airway, or to remove a specific pathological lesion. Papers on the outcome of surgery are usually based on reporting particular procedures and/or related modifications rather than on randomised controlled trials.

    The following are some of the surgical procedures and their indication or rationale:

    • adeno-tonsillectomy for adenoid and tonsillar hypertrophy

    • uvulo-palato-pharyngoplasty (UPPP) which consists of excision of the uvula, redundant part of the soft palate and the tonsills in case of obstruction caused by these structures. Modifications and improvements to this procedure include laser-assisted uvulo-palatoplasty (LAUP)

    • nasal surgery to relieve nasal obstruction caused, for example, by nasal septal deviation, polyps or large inferior turbinates

    • tracheostomy to bypass pharyngeal obstruction

    • inferior sagittal mandibular osteotomy and genio-glossal advancement with hyoid myotomy and suspension (GAHM) to create an enlarged retro-lingual airway

    • laser mid-line glossectomy and linguoplasty to create an enlarged retro-lingual airway

    • maxillo-mandibular osteotomy and advancement to enlarge both retro-lingual and retro-palatal airways

    • epiglottoplasty in selected cases of laryngomalacia.

    Mandibular advancement prostheses (oral appliances), provided by an orthodontist, are worn at night to pull the mandible and tongue base forward if the oropharynx is narrowed by retrognathia or tongue base hypertrophy. They are less effective than CPAP in improving the AHI and oxygen saturation but are better tolerated and accepted by patients.6

    Conservative measures include weight loss, medications to relieve nasal obstruction, modification of sleep position, and avoidanace of evening alcohol and hypnotics.

    In conclusion, effective management of sleep apnoea will depend on careful assessment of its severity, identification of its causes and risk factors and awareness of the available management options.

    References

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