Assisted mechanical ventilation promotes recovery of diaphragmatic thickness in critically ill patients: a prospective observational study

Abstract

Background: Diaphragm atrophy and dysfunction are consequences of mechanical ventilation and are determinants of clinical outcomes. We hypothesize that partial preservation of diaphragm function, such as during assisted modes of ventilation, will restore diaphragm thickness. We also aim to correlate the changes in diaphragm thickness and function to outcomes and clinical factors.

Methods: This is a prospective, multicentre, observational study. Patients mechanically ventilated for more than 48 h in controlled mode and eventually switched to assisted ventilation were enrolled. Diaphragm ultrasound and clinical data collection were performed every 48 h until discharge or death. A threshold of 10% was used to define thinning during controlled and recovery of thickness during assisted ventilation. Patients were also classified based on the level of diaphragm activity during assisted ventilation. We evaluated the association between changes in diaphragm thickness and activity and clinical outcomes and data, such as ventilation parameters.

Results: Sixty-two patients ventilated in controlled mode and then switched to the assisted mode of ventilation were enrolled. Diaphragm thickness significantly decreased during controlled ventilation (1.84 ± 0.44 to 1.49 ± 0.37 mm, p < 0.001) and was partially restored during assisted ventilation (1.49 ± 0.37 to 1.75 ± 0.43 mm, p < 0.001). A diaphragm thinning of more than 10% was associated with longer duration of controlled ventilation (10 [5, 15] versus 5 [4, 8.5] days, p = 0.004) and higher PEEP levels (12.6 ± 4 versus 10.4 ± 4 cmH2O, p = 0.034). An increase in diaphragm thickness of more than 10% during assisted ventilation was not associated with any clinical outcome but with lower respiratory rate (16.7 ± 3.2 versus 19.2 ± 4 bpm, p = 0.019) and Rapid Shallow Breathing Index (37 ± 11 versus 44 ± 13, p = 0.029) and with higher Pressure Muscle Index (2 [0.5, 3] versus 0.4 [0, 1.9], p = 0.024). Change in diaphragm thickness was not related to diaphragm function expressed as diaphragm thickening fraction.

Conclusion: Mode of ventilation affects diaphragm thickness, and preservation of diaphragmatic contraction, as during assisted modes, can partially reverse the muscle atrophy process. Avoiding a strenuous inspiratory work, as measured by Rapid Shallow Breathing Index and Pressure Muscle Index, may help diaphragm thickness restoration.

Keywords: Assisted mechanical ventilation; Diaphragm thickness; Diaphragm ultrasound.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Timeline of the study protocol. The day in which the patient was switched from controlled to assisted mechanical ventilation was marked as day 0. The study days before day 0 were numbered with negative numbers and correspond to the controlled ventilation days; the days after day 0 were numerated with positive numbers and correspond to the assisted mechanical ventilation period. MV, mechanical ventilation; ICU, intensive care unit

Fig. 2

Population selection. The population selection process which led to the final study population of 62 patients. ICU, intensive care unit; US, ultrasound; CMV, controlled mechanical ventilation; AMV, assisted mechanical ventilation

Fig. 3

Diaphragm thickening fraction over time. Diaphragm thickening fraction was lower during the days before day 0 (corresponding to the time spent by the patient ventilated in controlled modes) than during the days after day 0 (corresponding to the period spent with assisted ventilation modes)

Fig. 4

Diaphragm thickness over time. a The change in diaphragm thickness during the course of mechanical ventilation. Thickness is expressed as the percentage of the thickness in day 0 for every patient. Day 0 marks the switch from controlled to assisted mechanical ventilation mode. While during controlled ventilation (days before day 0), diaphragm thickness tends to decrease, during assisted ventilation partial restoration of the muscle thickness occurs. b The mean change in absolute diaphragm thickness from the beginning to the end of the study period. Tdi, diaphragm thickness; CMV, controlled mechanical ventilation; ICU, intensive care unit; SE, standard error; SD standard deviation

Fig. 5

Classification of patients based on the changes in diaphragmatic thickness during controlled and assisted mechanical ventilation. a Patients were classified into two groups based on the thinning of the diaphragm during controlled ventilation. Patients whose diaphragm thickness decreased by more than 10% are represented by the red line; patients whose diaphragm was unchanged are represented by the blue line. b Patients were classified into two groups based on the thickening of the diaphragm during assisted ventilation. Patients whose diaphragm thickness increased by more than 10% are represented by the orange line; patients whose diaphragm was unchanged are represented by the green line. CMV, controlled mechanical ventilation; AMV assisted mechanical ventilation: Tdi, diaphragm thickness; SE, standard error