The Journal of critical illness
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Most modern ventilators have several key features in common: microprocessor control of operational and monitoring functions; electromechanical valves to control and adjust gas flow patterns; and extensive monitoring systems. In addition, these machines can provide a number of different modes of ventilation (including pressure support). Though not microprocessor-controlled, the Siemens Servo 900 series ventilators use feedback electronics to adjust inspiratory flow based on expiratory flow to meet preset volumes. In contrast, the Bennett 7200 units use microprocessor-regulated solenoid valves to deliver preset tidal volume. High-frequency ventilators deliver smaller tidal volumes at rates greater than 60 bpm.
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In the ICU, both transthoracic and transesophageal echocardiography can assist in the acute management of a number of different disorders. In hypotensive patients, echocardiography helps distinguish between cardiogenic shock (resulting from acute myocardial infarction), septic shock, and circulatory shock (associated with a reduction in circulating blood volume); it can also help determine whether pericardial effusion or obstruction to valvular flow is producing the hypotension and suggesting pulmonary embolus. Other roles for echocardiography include differentiating left- and right-sided heart failure, assessing the extent of pericardial disease, diagnosing disorders of the thoracic aorta, and evaluating traumatic heart disease.