Disorders of Ventilation

ALVEOLAR HYPOVENTILATION

• When there is alveolar hypoventilation, arterial PC0₂ increases above the range of 37 – 43 mmHg.
• PaC0₂ may be 50 – 80 mmHg.
• The respiratory system is dependent upon a complex system of ventilatory control to ensure appropriate and adequate ventilation in order to supply oxygen, remove carbon dioxide, and maintain acid-base homeostasis.

CHRONIC HYPOVENTILATION Etiologic   :

• · Obesity
• · COPD
• · Myasthenia gravis
• · Motor neuron disease
• · Poliomyelitis
• · Brain stem infarction and haemorrhage
• · Metabolic alkalosis
• · High cervical hauma
• · Obstructive sleep apnea
• · Cystic fibrosis
• · Kyphoscoliosis.

Clinical Features of Disorders of Ventilation :

• · Cyanosis
• · Secondary polycythemia
• · Pulmonary hypertension
• · RVH (Right Ventricular Hypertrophy)
• · CHF (Congestive Heart Failure)
• · Morning headache
• · Fatigue
• · Somnolence
• · Mental confusion
• ·Intellectual impairment.

Treatment of Disorders of Ventilation

• Treat the cause
• Correction of metabolic acidosis Supplemental oxygen Progesterone may be of benefit Mechanical ventilatory support Diaphragmatic pacing
• Bipap ventilation – non-invasive positive pres­sure ventilation.

HYPOVENTILATION SYNDROMES Primary alveolar hypoventilation

• · It is a disorder of unknown cause
• · There is chronic hypercapnia and hypoxaemia
• · There is no neuromuscular disease.

Respiratory neuromuscular disorders

• · Disease of spinal cord, peripheral respiratory nerves and disease of respiratory muscles pro­duce a chronic hypoventilation syndrome over a • period of months to years e.g. MND (Motor Neu­ron Disease), myasthenia gravis, muscular dystrophy.

Obesity hypoventilation syndrome

•  Massive obesity causes a load on the respiratory system due to weight on the rib cage and abdo­men reducing the compliance of the chest wall.
• Treatment is reduction of weight, cessation of smoking in smokers, treatment of sleep apnea, enhancement of respiratory drive by progesterone.

HYPERVENTILATION AND ITS SYNDROMES

• Alveolar hyperventilation is PaC0₂ below range of 37­.- 43 mmHg.

Causes are Disorders of Ventilation :

• High altitude
• Pulmonary disease – Cardiac shunts
• – Chest wall disorder
• – CHF
• Diabetic acidosis ./ Hepatic failure ../ Psychogenic
• Salicylate induced ‘IT Fever
• Sepsis
• Pain
• Pregnancy.
• Treatment is removal of underlying cause. Usually alveolar hyperventilation has no clinical consequence and may not require treatment.