Changes in dead space components during pressure-controlled inverse ratio ventilation: A secondary analysis of a randomized trial

Abstract

Background We previously reported that there were no differences between the lung-protective actions of pressure-controlled inverse ratio ventilation and volume control ventilation based on the changes in serum cytokine levels. Dead space represents a ventilation-perfusion mismatch, and can enable us to understand the heterogeneity and elapsed time changes in ventilation-perfusion mismatch. Methods This study was a secondary analysis of a randomized controlled trial of patients who underwent robot-assisted laparoscopic radical prostatectomy. The inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave in the pressure-controlled inverse ratio ventilation group (n = 14) and was set to 1:2 in the volume-control ventilation group (n = 13). Using volumetric capnography, the physiological dead space was divided into three dead space components: airway, alveolar, and shunt dead space. The influence of pressure-controlled inverse ratio ventilation and time factor on the changes in each dead space component rate was analyzed using the Mann-Whitney U test and Wilcoxon’s signed rank test. Results The physiological dead space and shunt dead space rate were decreased in the pressure-controlled inverse ratio ventilation group compared with those in the volume control ventilation group (p < 0.001 and p = 0.003, respectively), and both dead space rates increased with time in both groups. The airway dead space rate increased with time, but the difference between the groups was not significant. There were no significant changes in the alveolar dead space rate. Conclusions Pressure-controlled inverse ratio ventilation reduced the physiological dead space rate, suggesting an improvement in the total ventilation/perfusion mismatch due to improved inflation of the alveoli affected by heterogeneous expansion disorder without hyperinflation of the normal alveoli. However, the shunt dead space rate increased with time, suggesting that atelectasis developed with time in both groups.

Effects of volume-targeted pressure-controlled inverse ratio ventilation on functional residual capacity and dead space in obese patients undergoing robot-assisted laparoscopic radical prostatectomy

“…Thus, VD alv and VD shunt improve significantly when the open-lung approach ventilation strategy improves the heterogeneous distribution of alveolar units with relative hyperinflation and hyperperfusion, resulting in minimised VD phys . 10 , 12 , 19 , 20 , 21 …”

“…We cannot rule out this possibility. However, 12 VD phys and VD shunt increased within 2 h intraoperatively, and atelectasis probably developed in ventilator conditions with an I:E ratio of 1:2 or 2:1, suggesting that FRC may decrease, and the dead space components may increase with time. Therefore, it is conceivable that our findings of IRV acutely increasing FRC and decreasing VD phys and VD shunt were attributable to ventilator settings, rather than time-dependent changes.…”

“…We previously reported that the physiological dead space (VD phys ) in robot-assisted laparoscopic radical prostatectomy improved with volume-targeted pressure-controlled inverse-ratio ventilation (vtPC-IRV). 10 , 11 , 12 vtPC-IRV with a prolonged plateau time promotes sufficient opening of the slow-opening alveoli and facilitates diffusion of gases from the pulmonary capillaries to the alveoli, resulting in reduced VD phys . However, VD phys increases with time, suggesting that atelectasis develops with time during surgery.…”