Effect of weaning on oxygen consumption and cardiovascular function A comparison of continuous flow and demand valve systems

Abstract

SummaryIn critically ill patients with septicaemia, the increased that the time delay between the instigation of the patient's oxygen requirements demand increased oxygen delivery inspiratory effort and the onset of inspiratory gas flow is and a reduction in the metabolic demands of tissues. minimal, thus avoiding an intrapulmonary pressure drop Respiratory muscles in particular can utilise large amounts which will greatly increase the work of breathing. A survey of oxygen when the work of breathing is increased. A of 55 major intensive care units in the United Kingdom in reduction in the work of breathing leads to a reduced 1984 found that this physiological goal was achieved in oxygen cost of breathing, thus avoiding 'oxygen steal' from 82% of units by custom-made CPAP circuits, while 78% nonrespiratory tissues and consequent impairment of vital had ventilators equipped with a CPAP facility [4]. Of the organ function.CPAP systems investigated, the most acceptable adult Continuous positive airways pressure (CPAP) is a widely CPAP delivery system was the traditional custom-made used technique for respiratory support in patients with type with a high flow (greater than 301.min-'), a large respiratory failure. With CPAP, a significant decrease inspiratory reservoir, and a water bottle. (25%) in the work of breathing has been demonstrated in These considerations led us to compare the CPAP mode babies [l], and a similar decrease suggested in adults [2]. To of the Engstrom Erica ventilator with a custom-made minimise the work of breathing during CPAP, the airway continuous flow CPAP system in terms of measured and pressure must be maintained at a near constant value derived haemodynamic variables and oxygen consumption throughout the respiratory cycle [3]. It is also important and delivery during weaning from mechanical ventilation.