![]() ![]() Therefore, expecting a normal physiology in patients on invasive mechanical ventilation is further not possible as during normal quiet breathing air passes through various humidification systems through the nose and sinuses to reach the trachea, whereas the air/oxygen in ventilation is pushed through a turbine/piston/bellows to the trachea directly through a narrow tube, generating flows up to 240L/min. Table 1 highlights the key factors why vesicular breath sounds cannot be heard in patients on mechanical ventilation. In most ventilators, inspiratory pause is set, again different from the described lack of inspiratory pause in normal vesicular breath sounds. Moreover, the I:E ratio set by default in ICU/OR ventilator is 1:2, inverse of the described I:E ratio in vesicular breath sounds. ![]() ![]() Normal physiological flow pattern is sinusoidal but usual flow patterns in various ventilators are of descending ramp or square wave flow pattern or rarely ascending ramp, gas delivery is altered, and turbulent flow is generated, which is unlikely to result in soft and low-pitched sounds which are characteristic of vesicular breath sounds. In addition, with added leaks of up to 25% and in cases with coexisting acute respiratory distress syndromes (ARDS), very high peak inspiratory flow rates up to 200 L/min may be needed. In mechanically ventilated patients with normal lungs, the minimal inspiratory flow rate range between 45 and 60 L/min (Table 1). As described classically, vesicular breath sounds as soft, low-pitched ( 400 Hz), heard normally over the trachea. ![]()
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