A 72 year old woman (55kg), Mrs X, with a history of severe emphysema and chronic bronchitis is intubated in the Emergency Department (ED) because of drowsiness associated with hypercarbia after her initial arterial blood gas analysis revealed:
- pH 7.219
- PC02 98mmHg
- PO2 48mmHg
- HC03 39mmol/l
- lactate 2.5 mmol/l
You are called to the ED to assess and admit this woman to ICU. The history from her daughter reveals that Mrs X lives independently but is limited by severe breathlessness with exercise.
(c)What are the effects of her lung disease on her respiratory physiology and how will this effect your management?
Although usually coexistent these problems (emphysema/chronic bronchitis) have theoretically different effects. Chronic bronchitis leads to increased airway resistance from mucosal oedema, secretions, bronchospasm, loss of elastic tissue supporting small airways leading to dynamic airway compression. Emphysema leads to loss of alveolar spaces and capillary bed. The end result is airflow limitation, prolonged expiration, hyperinflation (reducing diaphragm efficiency and increasing work of breathing), pulmonary hypertension, V/Q mismatch and tendency to degrees of hypoxia and hypercarbia. Chronic hypercarbia may lead to reliance on hypoxic drive and chronic hypoxia to cor pulmonale and polycythaemia. Skeletal muscle dysfunction may be prominent due to malnutrition, steroids, electrolyte abnormalities and reduced muscle blood flow.
These effect management by necessitating avoidance of gas trapping during ventilation (long exp time, bronchodilators etc), ensuring enteral nutrition and sputum clearance with physiotherapy, aiming to maintain the patient’s usual PCO2 and PO2 with a normal pH.
A systematic approach is called for:
- increased lung compliance
- decreased gas exchange surface
- increased dead space
- increased airway reactivity
- decreased airway diameter
COPD in general
- hyperinflation, decreased diaphragm excursion
- increased intrinsic PEEP
Consequences of chronic respiratory failure
- chronic hypercapnea
- decreased respiratory drive (reliance on hypoxic drive)
- chronically increased work of breathing, thus cachexia and malnutrition