Body Positionings for Ventilation, Perfusion and its matching

I just wanted to have a review on the positioning for optimal ventilation, perfusion and ventilation and perfusion matching. Kindly discuss your clinical positioning for improving ventilation, perfusion and its matching. Now have a look over some detail to have a review of information regarding that.

The distribution of ventilation, perfusion and ventilation and perfusion matching in the lungs are primarily influenced by gravity, and hence by body position. The intrapleural pressure becomes less negative down the upright lung. Thus apices have a greater initial volume and reduced compliance than do the bases. Because the bases are more compliant, they exhibit greater volume changes during ventilation. In addition to these gravity dependent interregional differences in lung volume ventilation is influenced by intraregional differences which are dependent upon regional mechanical differences in the compliance of lung parenchyma and the resistance to air flow in air ways. Perfusion decreases down the upright lung such that ventilation/perfusion ratio in the apices is disproportionately high compared with that in the bases. Ventilation, perfusion matching is maximum in the mid lung region. Manipulating body position, however, alters both interregional and intraregional determinants of ventilation and perfusion and their matching. When considering specific positions to enhance arterial oxygenation for a given patient, one needs to consider the underlying pathophysiology impairing cardiopulmonary function, the effects of bed rest/recumbancy, immobility, and aspects of patient’s care, in addition to physiological consideration. Now have look over different positions.

Supine Position:

Although the negative effects of supine position have been well documented for several decades, supine and recumbent positions are frequently assumed by the patients in hospitals. These positions are associated with significant reduction in lung volumes and flow rates, and increased work of breathing. This decrease in functional residual capacity contributes to the closure of dependent air ways and reduced oxygenation. This effect is accentuated in older patients and patients with cardiopulmonary disease. The haemodynamic consequences of the supine position are also very remarkable. The gravity dependent increase in central blood volume may precipitate vascular congestion, reduced compliance and pulmonary oedema, and the commensurate increase in stroke volume increases the work of heart. Within 6 hours a compensatory diuresis can lead to a loss of circulating blood volume and orthostatic intolerance, i.e. haemodynamic intolerance to upright position. Bed rest deconditioning has been attributed to this reduction of blood volume and the impairment of volume regulating mechanism rather than physiological conditioning per se.

Upright Position:

Thus upright position is essential to maximize lung volume and flow rates, and this position is the only means of optimizing fluid shifts such that circulating blood volume and volume regulating mechanisms are maintained. The upright position coupled with movement is necessary to promote normal fluid regulation and balance.

Side lying Position:

Side to side positioning is frequently used in clinical setting. If applied in response to assessment rather than routinely, the benefits derived from such positioning could be enhanced. Adults patients with unilateral lung disease may derive greater benefit when the affected lung is uppermost. Arterial tension is increased secondary to improved ventilation of unaffected lung when this lung is dependent. Patients with uniformly distributed bilateral lung disease may derive greater benefit when the right lung is lower most. In this case arterial oxygen tension is increased secondary to improved ventilation of the right lung which may reflect the increased size of right lung compared with left, and in this position, the heart is subjected to less compression.

Prone Position:

The prone position has considerable physiological justification in patients with cardiopulmonary compromise. The beneficial effects of prone position on arterial oxygenation may reflect improved lung compliance, tidal ventilation, diaphragmatic excursion and FRC, and reduced air way closure. A variant of prone position, prone abdomen free, has shown additional benefit over prone abdomen restricted. In the prone abdomen free position, the patient is positioned such that the movement of abdomen is unencumbered by the bed. This can be achieved either by raising the patient body in relation to the bed so that abdomen falls free, or using the bed by a hole cut out at the level of abdomen. Despite compelling evidence to support the prone position, this position may be poorly tolerated in some patients, or may be contraindicated in the haemodynamically unstable patients. In these situations, intermediate positions approximating prone may produce many of the beneficial effects and minimize any potential hazard.

Positions for Postural drainage:

Positions for drainage of pulmonary secretions may be indicated in some patients. These positions have been based upon anatomical arrangement of bronchopulmonary segments to facilitate drainage of a particular segment. The bronchiole to the segment of interest is positioned perpendicular to facilitate drainage with use of gravity. The efficacy of postural drainage compared with deep breathing and coughing induced with mobilization and exercise has not been established.

The time which a patient spends for ventilation, perfusion and its matching positioning & positions for postural drainage, and the frequency with which the position is assumed over a period of time are based on indications for the position and outcome.