ABSTRACT
A mechanical lung was used to evaluate the pressure and flow characteristics of four demand and two continuous flow intermittent mandatory ventilation (IMV) systems. The amount of negative pressure required to initiate inspiratory flow and peak expiratory resistance were measured. The inspiratory pressure required to initiate flow in the demand mode was also compared to pressures generated in the assist mode. In addition, the peak expiratory resistance was measured with four commercially available exhalation valves. Results showed that the ventilator manometer measuring internal machine pressures significantly underestimated the amount of negative pressure required to open the demand valve (p less than 0.01). There are major differences in the flow and pressure characteristics among demand and continuous flow IMV systems. Systems that impose high inspiratory elastic threshold loads and expiratory flow resistive loads may have a deleterious effect on the mechanics of breathing, and thereby limit weaning success and eventually impair the recovery of certain patients in respiratory failure. The basic methodology, especially the simple technique of inserting an aneroid manometer in line next to a patient's ET tube, for measuring proximal negative inspiratory force (NIF test) can be easily applied to any and all ventilators at any practitioner's individual institution.
Subject(s)
Intermittent Positive-Pressure Ventilation , Lung Diseases, Obstructive/therapy , Positive-Pressure Respiration , Respiration , Acute Disease , Airway Resistance , Evaluation Studies as Topic , Humans , Intermittent Positive-Pressure Breathing , Intermittent Positive-Pressure Ventilation/instrumentation , Intermittent Positive-Pressure Ventilation/standards , Lung Diseases, Obstructive/physiopathology , Positive-Pressure Respiration/instrumentation , Positive-Pressure Respiration/standards , Pulmonary Ventilation , Respiratory Insufficiency/physiopathology , Respiratory Insufficiency/therapy , Transducers, Pressure , Work of BreathingABSTRACT
A 1-year survey of patients in three hospitals identified 936 patients who had one predisposition and 57 who had several predispositions to the adult respiratory distress syndrome. From the total predisposed population of 993 patients, 68 subsequently developed the syndrome. An additional 20 patients developed the syndrome from causes other than eight identified predispositions, to bring the total of patients studied to 88. A highly significant difference (p less than 0.0001) was found in the incidence rates of the syndrome between patients with one and several predispositions (5.8 versus 24.6 per 100 patients). Within 72 hours of onset of predisposition, 89.5% of patients who developed the syndrome had been intubated and placed on mechanical ventilation. Fifty-seven of the 88 patients (64.8%) with the syndrome died. By the 14th day 90% of deaths had occurred. There were no age- or sex-specific differences in either incidence or mortality rates. Case fatality rates of the syndrome were high in all predisposed groups.
