## 4 Discussion  
This study examined the effects of ventilator-related parameters during closed endotracheal suctioning; even CSS used for 15 s of suctioning had advantages in clinical practice. The study found that CSS of endotracheal suction caused increased respiratory resistance (R\({}_{\text{INSP}}\) and R\({}_{\text{EXP}}\)), mainly due to the effects of positive pressure ventilation, suction catheter insertion into endotracheal tubes, and patients' pulmonary mechanics. VC-CMV offers a pre-set tidal volume and minute ventilation safety. It also requires set inspiratory flow, flow waveform, and inspiratory time for delivering tidal volume. However, airway pressure increases in response to reduced lung compliance or increased airway resistance during VCV-CMV. In PC-CMV, the ventilator provides a high inspiratory flow rate to achieve the pre-set pressure and time during the inspiration phase. However, tidal volume is dependent on the pulmonary mechanics. Additionally, R\({}_{\text{aw}}\) is the opposition to flow caused by the forces of friction. It is usually defined as the ratio of driving pressure to the airflow rate during the mechanical ventilation, R\({}_{\text{aw}}\) = \(\Delta\)P/Flow (\(\Delta\)P is the pressure applied to the airway above PEEP). Expiratory flow is normally passive and is determined by alveolar pressure, as well as R\({}_{\text{aw}}\), the elapsed time since initiation of exhalation, and constant time. Lung units with higher resistance and/or compliance will have a longer time constant and require more time to fill and empty. End-expiratory flow is limited if R\({}_{\text{aw}}\) is high and expiratory time is not sufficient, indicating the presence of air trapping (auto-PEEP). The rise in PIP is a significant ventilator-related parameter during VC-CMV with closed suction. It is a phenomenon that can be aggravated when the pulmonary mechanics of the respiratory system was compromised. PEEP changed in 14 Fr SC of CSS, with a more significant reduction in VC-CMV than in PC-CMV. PEEP was at an increased level in severely R\({}_{\text{aw}}\) pulmonary mechanics during PC-CMV, but a decreased level was found in severely C\({}_{\text{rs}}\) pulmonary mechanics. Additionally, minute volume was a critical ventilator-related parameter in PC-CMV. The change of Vexp was associated with larger ODs of suction catheters and with pulmonary mechanics. The amount of the decrease in Vexp reduced in severely C\({}_{\text{rs}}\) pulmonary mechanics. The study shows that a change of \(\triangle\)PIP% during VC-CMV hinges on the ventilation area of the endotracheal tubes. For instance, the change of \(\triangle\)PIP% for a 12 Fr suction catheter paired with a 7.0 mm endotracheal tube was greater than for an 8.0 mm endotracheal tube (50% versus 30%) in 0.03 L-cm H\({}_{2}\)O\({}^{-1}\) of C\({}_{\text{rs}}\). These results were consistent with a previous cardiac surgery study, which showed that the airway pressure in volume-controlled mode peaks when the insertion of 14 Fr SC into an endotracheal tube reaches an 8.0 mm depth position [21]. This earlier research pointed to changes in the radius ofthe tube, which had a significant effect on resistance [22]. Due to this higher resistance, a ventilator needs more energy (positive pressure) to expand the lungs [23; 24; 25]. A previous bench study put forth an alternative solution for pairing suction catheters with endotracheal tubes, suggesting a volume or area ratio of SC/ETT 50%, in correspondence with a diameter ratio of 70% SC/ETT ratio [26]. Clinical studies have associated R\({}_{\text{aw}}\)'s rise in CSS with a practice-related factor and the effect of the reduced area of the artificial airway tube [27; 28]. When closed suction was underway for patients with a progressive decline in pulmonary mechanics with VC-CMV, PIP rose more significantly. In addition, a higher PIP resulting from higher trans-airway pressure can cause barotrauma to the detriment of the lung, especially for patients with COPD [8; 29].