There is a growing interest in better understanding beneficial and/or potentially harmful effects associated with spontaneous breathing in mechanical ventilation. The concept of patient self-inflicted lung injury (P-SILI) that recently emerged from the literature, teaches us that assisted ventilation can be injurious when respiratory drive is high [
1,
2]. During assisted ventilation, high respiratory drive is associated with strong inspiratory efforts and very negative pleural pressure resulting in major stress applied to the lung parenchyma [
1]. Furthermore, both too low and too high respiratory drive are recognized as risk factors for diaphragmatic injury [
3]. In this context, the use of airway occlusion pressure at 100 ms (P0.1) which is usually considered as the simplest way to assess respiratory drive at the bedside, is of major interest for ventilated patients’ management [
4,
5]. P0.1 is defined as the negative pressure measured at the airway opening 100 ms after the initiation of an inspiratory effort performed against a closed respiratory circuit [
6‐
8]. P0.1 measurement is not perceived by the patient and does not influence respiratory pattern. More importantly, since P0.1 measurement is performed during an occlusion at the onset of the breath, flow and insufflated volume are equal to zero at the time of measurement and P0.1 is unrelated to respiratory mechanics. P0.1 measurement is feasible and reliable in presence of inspiratory muscle weakness [
5‐
7], abnormal respiratory compliance [
6‐
8] or intrinsic positive end expiratory pressure [
8‐
10]. P0.1 measurement was initially described in non-intubated spontaneously breathing patients. In these patients, it has been shown to be correlated with central respiratory drive and respiratory effort [
11]. In spontaneously breathing non-ventilated healthy subjects, low values around 2 cm H
2O are observed with normal respiratory drive whereas values greater than 10 cm H
2O are correlated with very high drive [
6]. P0.1 measurement was later used in intubated patient by occluding the ventilator circuit [
12,
13]. Automated measurement is now available in modern ICU ventilators either by default or on request using an easy-to-use and safe maneuver [
14]. However, the reliability of P0.1 automated measurements displayed by the different ICU ventilators has never systematically been studied. This study aimed at assessing the accuracy of ventilator automated P0.1 measurements. Using a lung model of an invasively ventilated spontaneously breathing patient, we compared the P0.1 displayed by several ventilators (P0.1
vent) to reference values of P0.1 (P0.1
ref) simulated on the lung model.