Nocturnal hypoxia Medical Assignment Help

It has been shown that patients with chronic bronchitis and emphysema who show severe arterial hypoxaemia also suffer from profound nocturnal hypoxaemia with a Pa02 as low as 2.5 kPa (19 mmHg), particularly during the rapid eye movement (REM) phase of sleep. Because patients with chronic bronchitis and emphysema are already hypoxic, the fall in Pao, produces a much larger fall in oxygen saturation (owing to the steepness of the oxyhaemoglobin dissociation curve) and desaturation of up to 50% occurs. The mechanism is alveolar hypoventilation due to:
• Inhibition of intercostal and accessory muscles in REM sleep
• Shallow breathing in REM sleep, which reduces ventilation, particularly in severe chronic bronchitis and emphysema
• An increase in upper airway resistance due to a reduction in muscle tone
These nocturnal hypoxaemic episodes are associated with a further rise in pulmonary arterial pressure, and the  majority of deaths in patients with chronic bronchitis and emphysema occur during the night, possibly due to cardiac arrhythmias. These patients additionally show severe secondary polycythaemia, partly as a result of the severe nocturnal hypoxaemia.
Each episode of desaturation is usually terminated by arousal from sleep, so that normal sleep is reduced and the patient suffers from daytime sleepiness. Patients with arterial hypoxaemia should never be given sleeping tablets, which will further depress respiratory drive. Treatment is with nocturnal administration of oxygen and ventilatory support.

VENTILATORY SUPPORT. Positive pressure ventilation can be administered non-invasively through a tightly fitting nasal mask with bilevel positive airway pressureinspiratory to provide inspiratory assistance and expiratory to prevent alveolar closure, each adjusted independently. The use of these devices to maintain adequate ventilation during sleep and allow respiratory muscles to rest at night, though effective in chronic chest wall (e.g. kyphoscoliosis) or neuromuscular disease (e.g. previous poliomyelitis) has not led to improvement in respiratory function, respiratory muscle strength, exercise tolerance or breathlessness in patients with chronic bronchitis and emphysema.

Obstructive sleep apnoea

This condition occurs most often in overweight middleaged men and affects 1-2% of the population. It can occur in children particularly with enlarged tonsils. The major symptoms and their frequency are: • Loud snoring (95%)
• Daytime sleepiness (90%)
• Unrefreshed sleep (40%)
• Restless sleep (40%)
• Morning headache (30%)
• Nocturnal choking (30%)
• Reduced libido (20%)
• Morning drunkenness (5%)
• Ankle swelling (50/0)
Apnoeas occur when the airway at the back of the throat is sucked closed when breathing in during sleep. When awake this tendency is overcome by the action of opening muscles of the upper airway-the genioglossus and palatal muscles, which become hypotonic during sleep. Partial narrowing results in snoring, occlusion in apnoea and critical narrowing in hypopnoeas. Patients are woken by the struggle to breathe against the blocked throat. The awakenings are so brief that the patient remains unaware of them but is woken thousands of times per night leading to daytime sleepiness and impaired performance. Important contributory factors are obesity, a small pharyngeal opening and chronic airflow limitation.
Correctable factors occur in about one-third of cases and include:
• Encroachment on pharynx: obesity, acromegaly, enlarged tonsils
• Nasal obstruction: nasal deformities, rhinitis, polyps, adenoids
• Respiratory depressant drugs: alcohol, sedatives, strong analgesics
The diagnosis can usually be made by non-invasive ear or finger oximetry, best performed at home, accompanied by observation of the pattern of the snore-silence-snore cycle by the patient’s family. Arterial oxygen saturation falls significantly in a cyclical manner. However, falsenegative or equivocal results may occur in 50% necessitating full polysomnographic studies. These involve:
• Electroencephalography to record patterns of sleep and arousal
• Recording of thoracoabdominal movements to assess breathing
• Oronasal flow
• Oximetry
The diagnosis of sleep apnoea/hypopnoea is made if there are more than 15 apnoeas or hypopnoeas in any 1 hour of sleep. Management consists of correction of treatable factors (see above) with, if necessary, continuous nasal positive airway pressure delivered by a nasal mask during sleep. Such systems raise the pressure in the pharynx by about I kPa, keeping the walls apart.

Section through head,

Section through head,

Bronchiectasis

Bronchiectasis may be defined simply as dilatation of the bronchi.
Bronchial walls become inflamed, thickened and irreversibly damaged. The mucociliary transport mechanism is impaired and frequent bacterial infections ensue. Clinically, the disease is characterized by cough productive of large amounts of sputum.

AETIOLOGY

Bronchial obstruction followed by infection plays a major role. In the past bronchiectasis frequently followed pneumonia in childhood. Bronchiectasis is still a rare complication of whooping cough and measles in the Western world. Localized bronchiectasis also rarely results from tuberculous enlargement of lymph nodes at the hilum of the lung, particularly around the origin of the middle-lobe bronchus. Bronchial obstruction in children from other causes (e.g. inhaled peanuts) can give rise to gross suppurative lung disease and residual bronchiectasis. Progressive bronchiectasis has been described in nonsmoking patients of both sexes, with no other underlying cause. This syndrome is known as chronic bronchial sepsis.
Cystic fibrosis  also leads to bronchiectasis, as over 75% of children with cystic fibrosis now survive to adult life. Occasionally cystic fibrosis may present with bronchiectasis in adults. Bronchiectasis can also be associated with other congenital abnormalities, e.g. Kartagener’s syndrome, which is characterized by sinusitis and transposinon of viscera with bronchiectasis, associated with ‘imrnotile cilia’. Immunoglobulin deficiencies particularly 19A or IgG4 can lead to recurrent infections and bronchiectasis.

CLINICAL FEATURES

Patients with mild bronchiectasis only produce yellow or green sputum after an infection, often viral. Localized areas of the lung may be particularly affected, when sputum production will depend on position. As the condition worsens, the patient suffers from persistent halitosis, recurrent febrile episodes with malaise, and episodes of pneumonia. Clubbing occurs, and coarse crackles can be heard over the infected areas, usually the bases of the lungs. When the condition is severe there is continuous production of foul-smelling, thick, khaki-coloured sputum. Haemoptysis, either as blood-stained sputum or as a massive haemorrhage, can occur. Breathlessness may result from airflow limitation.

INVESTIGATION

THE CHEST X-RAY may be quite normal or may show dilated bronchi with thickened bronchial walls and sometimes multiple cysts containing fluid.
HIGH-RESOLUTION CT SCANNING can show bronchial wall thickening and is the investigation of choice.
BRONCHOGRAMS. This investigation is uncomfortable for the patient and is only required if the diagnosis is in doubt or where there is reason to believe that the disease may be localized and therefore amenable to surgical treatment. The left lower lobe and lingula are the commonest sites for localized disease.
SPUTUM EXAMINATION with culture and sensitivity of the organisms is essential for adequate treatment. The major pathogens are Staph. aureus, Pseudomonas aeruginosa, H. infIuenzae and anaerobes. Other pathogens include Strep. pneumoniae and Klebsiella pneumoniae.  Aspergillus fumigatus can be isolated from 10% of sputum specimens in cystic fibrosis, but the role of this organism is uncertain.

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CT scan showing bronchiectasis in the right middle lobe.

CT scan showing bronchiectasis in the right middle lobe.

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