Tension pneumothorax

In the case of a one-way valve mechanism only a part of the inspired volume can be exhaled and the remaining volume is trapped in the pleural space. Thus the intrapleural gas accumulates and tension pneumothorax develops. Intrapleural pressure which exceeds ambient pressure throughout expiration is the specific characteristic of tension pneumothorax. Increased pleural pressure and volume results in a displacement of the mediastinal structures and the heart, and probably also in compression of the opposite lung. Venous return, and hence cardiac output, will be decreased by the increased intrathoracic pressure and/or by kinking of the vena cava due to the mediastinal shift. However, animal studies suggest that the major consequence of tension pneumothorax is not a decrease in cardiac output but severe hypoxemia due to increased intrapulmonary shunt (Guslman. e,t,..al 1983). These animal studies were conducted in spontaneous breathing sheep; thus inspiratory pleural pressure was lower than ambient pressure. Therefore venous return might be influenced less than during positive-pressure ventilation when pleural pressure exceeds ambient pressure even during inspiration. This is supported by observation of decreased cardiac output after the animals were artificially hyperventilated. Moreover, hemodynamic measurements during tension pneumothorax in a mechanically ventilated patient revealed a significant decrease of about 45 per cent in cardiac output and a reduction of PaO2 from 10.1 to 6.1 kPa (76 to 46 mmHg (Connolly.1993). Likewise, central venous pressure increased threefold, indicating venous congestion by the high intrathoracic pressure.

Tension pneumothorax is rare in spontaneous breathing individuals and is usually a complication during positive-pressure ventilation. However, significant tension pneumothorax can occur even during spontaneous breathing in patients with asthma or exacerbated chronic obstructive pulmonary disease with severe hyperinflation and intrinsic PEEP.

Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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