Monitoring of Patient-Ventilator Interaction at the Bedside

Abstract

Introduction Trigger Asynchrony Flow Asynchrony Cycling Asynchrony SummaryMonitoring of patient-ventilator interactions at the bedside involves evaluation of patient breathing pattern on ventilator settings. One goal of mechanical ventilation is to have ventilator-assisted breathing coincide with patient breathing. The objectives of this goal are to have patient breath initiation result in ventilator triggering without undue patient effort, to match assisted-breath delivery with patient inspiratory effort, and to have assisted breathing cease when the patient terminates inspiration, thus avoiding ventilator-assisted inspiration during patient exhalation. Asynchrony can occur throughout the respiratory cycle, and this paper describes common asynchronies. The types of asynchronies discussed are trigger asynchrony (ie, breath initiation that may manifest as ineffective triggering, double-triggering, or auto-triggering); flow asynchrony (ie, breath-delivery asynchrony, which may manifest as assisted-breath delivery being faster or slower than what patient desires); and cycling asynchronies (ie, termination of assisted inspiration does not coincide with patient breath termination, which may manifest as delayed cycling or premature cycling). Various waveforms are displayed and graphically demonstrate asynchronies; basic principles of waveform interpretation are discussed.

Identifying Patient-Ventilator Asynchrony Using Waveform Analysis

“…The difference, with the double triggering, is that in premature cycling the inspiratory effort of the patient is not enough to trigger a second breath. Premature cycling produces a significant decrease in airway pressure, which can be seen immediately after the end of the inspiratory phase programmed in the ventilator, accompanied by an increase of the inspiratory flow which can be seen in the flow/time waveform [32][ Figure 6]. This type of PVA could be confused with an ineffective effort during the expiratory phase, with the difference that premature cycling responds to changes in programmed inspiratory time or cycling; where as ineffective efforts responds to changes in the level of PEEP, sensitivity or assistance levels [23].…”

“…This means that the system continues in the inspiratory phase, once the patient's inspiratory effort has ended, which decreases the time available for the expiratory phase. This may produce an activation of the patient's expiratory muscles before the established cycling criteria (active exhalation), air trapping, dynamic hyperinflation and PEEPi, which may increase the work of breathing and cause ineffective efforts [32][33][34]. Parthasarathy et al mentioned that "a delay in relaxation of the expiratory muscles could cause them to remain active during the early phase of the next inspiration, and by opposing the downward motion of the diaphragm could hinder the efficacy of the subsequent inspiratory effort.…”

Proportional Assist Ventilation and Neurally Adjusted Ventilatory Assist

“…1 As discussed in other papers from this conference, patient-ventilator asynchrony is a very common problem. 2,3 Ventilator manufacturers have developed new ventilation modes that target both pressure and volume and have added adjuncts to pressure-targeted ventilation that are designed to improve synchrony: rise time and breath-termination (ie, cycle) criteria. 4 Some ventilator manufacturers have tried to automate these functions to ensure that gas delivery changes as patient demand changes, 4 but despite these new options, asynchrony is still a major problem.…”

Patient-Ventilator Interaction

“…In her discussion of the bedside assessment and monitoring of PVI, 6 Marjolein de Wit drew primarily from the large patient series she and her colleagues have collected in their medical intensive care unit (ICU). It may be the largest and most extensively documented observational study on PVI anywhere: 80 patients (without critical hypoxemia, on no more than 8 cm H 2 O of PEEP, and capable of making inspiratory efforts) who were observed and their bedside ventilator graphics recorded for more than 50 hours and 60,000 individual breaths.…”

“…This paper summarizes what I took to be the most important messages of the individual presentations and the discussions that followed them, and offers some of my own observations on this central component of the management of patients with acute respiratory failure. With a few exceptions I will not attempt to cite the most important primary work that has been done in this field; the individual papers in these 2 special issues [1][2][3][4][5][6][7][8][9][10][11][12][13][14] provide a comprehensive and authoritative review of the literature pertaining to PVI.…”