The primary goals of mechanical ventilation are to restore adequate gas exchange, unload the over-tasked respiratory muscles, and prevent ventilator-related complications while allowing the underlying disease process to resolve. Clinicians have become attuned to the management of abnormal blood gases and the complications associated with mechanical ventilation. Bedside assessment of the degree of ventilator unloading has been limited, however, by the inability to make a convenient estimation of the patient's work of breathing or breathing effort. Breathing effort can be defined as the product of pressure generated by the contracting respiratory muscles and the duration of contraction, quantified as the pressure–time product (PTP).<sup>20 Field S., Grassino A., Sanci S. Respiratory muscle oxygen consumption estimated by the diaphragm pressure-time index J Appl Physiol 1984 ;  57 : 44-51

Cliquez ici pour aller à la section Références</sup> The degree of ventilator unloading and the load imposed by the ventilator are determinants of patient–ventilator interaction during acute respiratory failure and discontinuation from mechanical ventilation. Despite the appearance of patient–ventilator synchrony, estimation of PTP actually may reveal considerable patient effort.<sup>29 Jubran A., Van De Graaff W.B., Tobin M.J. Variability of patient–ventilator interaction with pressure support ventilation in patients with chronic obstructive pulmonary disease Am J Respir Crit Care Med 1995 ;  152 : 129-136

Cliquez ici pour aller à la section Références</sup> In cases of extreme discordance, these interactions commonly are described as “fighting the ventilator.”

When the patient is completely passive, without patient-initiated breaths, the ventilator assumes the entire workload. With patient-triggered breaths, however, the degree of ventilatory unloading by the machine depends on the matching between the ventilator-delivered gas flow and the patient's ventilatory demand—i.e., patient–ventilator synchrony. Ideally, the ventilator shouldadjust flow delivery instantaneously in response to the patient's changing respiratory drive and workload. Although proportional-assist ventilation would appear to meet the aforementioned requirement,<sup>97 Younes M. Proportional assist ventilation, a new approach to ventilatory support. Theory Am Rev Respir Dis 1992 ;  145 : 114-120  [cross-ref]

Cliquez ici pour aller à la section Références99 Younes M., Puddy A., Roberts D. , et al. Proportional assist ventilation. Results of an initial clinical trial Am Rev Respir Dis 1992 ;  145 : 121-129  [cross-ref]

Cliquez ici pour aller à la section Références</sup> unfortunately, proportional-assist ventilation is not available commercially.

Failure to achieve patient–ventilator synchrony may result in impaired gas exchange, with hypoxemia and hypercapnia; increased load to the respiratory muscles; and increased intrathoracic pressure, compromising cardiovascular function.<sup>88 Tobin M.J., Fahey P.J. Management of the patient who is “fighting the ventilator.” Principles and Practice of Mechanical Ventilation New York: McGraw-Hill (1994).  1149-1162

Cliquez ici pour aller à la section Références</sup> Factors inherent to the patient and the ventilator determine patient–ventilator interaction.

In this review, the authors focus on the determinants of patient–ventilator interactions and the strategies to improve the interaction in terms of its effect on the work of breathing or breathing effort.