## 4 Discussion
A study on animals found that histopathologic changes in the lung with a tidal volume of 15 mL/kg induced a PIP of 40 cm H\({}_{2}\)O for up to 32 h [30]. Unlike other research carried out in this area, we find a significant difference in PIP according to the endotracheal tube's ventilation area and pulmonary mechanics during closed suction with different modes. The optimal OD of suction catheters can be extended to the ventilation area; this is critical for the efficacy and effectiveness of PIP management during closed endotracheal suction. Using PC-CMV mode can avoid raising transpulmonary pressure during closed suction. A maximum airway pressure alarm was set in advance for barotrauma incidents through a higher PIP in patients with deteriorating pulmonary mechanics. A higher PEEP level (intrinsic PEEP) than the set level was observed in severe R\({}_{\text{aw}}\) cases during PC-CMV. PC-CMV is advantageous since the operator can control inspiratory pressure ventilation directly. During suctioning, the inspiratory pressure decreased significantly with a 14 Fr suction catheter in CSS. The ventilator has to provide extra flow to compensate for the loss of inspiratory pressure in PC-CMV. The PEEP level in breathing circuits rose when the inflow volume exceeded gas outflow during catheter suction. Our study demonstrates that in the obstructive respiratory system, when undergoing PC-CMV with closed suction, the rise of R\({}_{\text{aw}}\) may worsen, resulting in an intrinsic PEEP effect. In the clinical setting, for COPD patients with dynamic hyperinflation, it is necessary to generate high pleural pressure swings for patients undertaking mechanical ventilation to a level higher than intrinsic PEEP before triggering the activation of the ventilator [31; 32]. However, the ventilator will be ineffective for this triggering function if patients have a weakness in fatigue of the respiratory muscle [33]. New monitoring waveform systems can be used with other inputs, helping detection and improving triggering synchrony management. These results show that careful attention must be paid to the PEEP level when obstructive respiratory system patients are undergoing closed suction. PEEP levels decreased significantly for 14 Fr of SC in VC-CMV, a PEEP level lower than the set level observed for the severe C\({}_{\text{rs}}\) pulmonary mechanics during PC-CMV. This PEEP effect was at odds with the results of previous studies. A prior review of CSS's effectiveness shows that the prevention of lung collapse can be helped by performing suction without interrupting mechanical ventilation to maintain PEEP [7]. In this way, the decline of PaO\({}_{2}\) in mechanical ventilation patients can be improved [4; 17; 34; 35]. There is a possible explanation for the result in this study: 14 Fr SC has a higher cross-section area conducive to removing more airflow in the airway, especially in VC-CMV, which can control the tidal volume. It can thus be reasonably assumed that VC-CMV with less than 14 Fr CSS or PC-CMV was applied to patients with high PEEP to preserve more alveoli volume during suction at the end of expiration. Approximately 5% of patients with COVID-19 eventually develop ARDS, septic shock, and/or multiple organ failure. The mainstay of clinical treatment for patients with respiratory failure is mechanical ventilation [36]. CSS can decrease the clinical signs of hypoxemia by creating a small volume loss to preserve PEEP. It can also be used during suction to limit the spread of Severe Acute Respiratory Syndrome Coronavirus 2 into the environment, and contamination of the person during suction [37]. Therefore, there are significant advantages to the clinical practitioner adopting CSS for critically ill patients with COVID-19. This study found that the conserved ventilation volume was affected by the OD size of suction catheters in PC-CMV. Vexp decreased with suction catheters with larger ODs, but this was less noticeable when respiratory systems were severe.