We sought to investigate factors that affect the difference between the peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions (resistive pressure
) during pressure controlled ventilation
across a range of endotracheal tube sizes, respiratory mechanics, and ventilator settings.
In vitro study.
An in vitro bench model of the intubated respiratory system during pressure controlled ventilation
was used to obtain the difference between peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions across a range of endotracheal tubes sizes (3.0–8.0 mm). Measurements were taken at combinations of pressure above positive end-expiratory pressure (10, 15, and 20 cm H2
O), airway resistance (no, low, high), respiratory system compliance (ranging from normal to extremely severe), and inspiratory time at constant positive end-expiratory pressure (5 cm H2
O). Multiple regression analysis was used to construct models predicting resistive pressure
stratified by endotracheal tube size.
Measurements and Main Results:
On univariate regression analysis, respiratory system compliance (β –1.5; 95% CI, –1.7 to –1.4; p
< 0.001), respiratory system resistance (β 1.7; 95% CI, 1.5–2.0; p
< 0.001), pressure above positive end-expiratory pressure (β 1.7; 95% CI, 1.4–2.0; p
< 0.001), and inspiratory time (β –0.7; 95% CI, –1.0 to –0.4; p
< 0.001) were associated with resistive pressure
. Multiple linear regression analysis showed the independent association between increasing respiratory system compliance, increasing airway resistance, increasing pressure above positive end-expiratory pressure, and decreasing inspiratory time and resistive pressure
across all endotracheal tube sizes. Inspiratory time was the strongest variable associated with a proportional increase in resistive pressure
. The contribution of airway resistance became more prominent with increasing endotracheal tube size.
Peak inspiratory pressures measured during pressure controlled ventilation
overestimated plateau pressure irrespective of endotracheal tube size, especially with decreased inspiratory time or increased airway resistance.