Three Safety Devices for the Heart-Lung Machine

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THE most important single cause of pulmonary damage arising from the use of a heart-lung machine is overfilling of the pulmonary vascular bed.1 To avoid such overfilling, the following methods and devices have been developed and are described in this paper: (1) a precise automatic control of blood volume in the oxygenator to prevent forward overloading of the lungs by changes in volume; (2) an open reservoir in the venous line to preclude the possibility of drawing the walls of the venae cavae into the openings of the cannulae, thereby occluding them; (3) a cannula in the left atrium (a) to monitor left atrial pressure, and (b) to permit release of blood from the left atrium to avert build-up of pressure and retrograde overfilling of the pulmonary vascular bed.

Automatic Control of Pump

The blood level or volume in most oxygenation chambers cannot be assessed with sufficient accuracy by the unaided eye. Since the azygos flow or “small” flow principle2 is no longer used, large blood flows make it exceedingly trying to maintain both a smooth perfusion and a stable blood volume in the machine by manual control. At times of abrupt changes of pressure in the line, which occasionally occur, satisfactory manual control is impossible. At a flow of five liters of blood per minute, a disturbance lasting 24 seconds can increase or decrease a patient’s blood volume by two liters. At the onset or at the end of a cardiac bypass, when there are no occluding tapes around. . .



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