Discussion
This study aimed to examine the impact of the PP on critically ill COVID-19 patients receiving invasive mechanical ventilation. We employed a matching technique to establish comparable groups. The findings revealed that PP has the potential to enhance the oxygenation levels and All-cause survival rate. Furthermore, a positive correlation was observed between the frequency of PP and the extent of oxygenation improvement. The potential mechanism underlying the effect of the PP may be associated with variations in lymphocyte count and the duration of PP.
According to our data, the utilization of PP appeared to enhance oxygenation and improve short-term survival rate in COVID-19 patients who are invasive mechanical ventilated. Within 10 days after ICU admission,, the survival rate of individuals in the PP group was notably higher compared to those in the non-PP group, 94.9% of patients received PP treatment. However, no significant disparity in survival rate was observed between the two groups at the 20-day and 30-day. 29.5% and 6.4% of patients in the PP group have undergone PP treatment for 10-20 days and 20-30 days, respectively. Notably, patients who underwent PP three times exhibited a 100.0% survival rate during their hospitalization period.
The survival rate during ICU stay was observed to be lower in patients with critical COVID-19 infection, ranging from 33.3% to 47.6% [11-13]. In a retrospective analysis conducted by Douglas, I.S et al [14], a total of 61 critically ill patients receiving invasive mechanical ventilation for COVID-19 were examined, revealing a hospital survival rate of 68.9% in the PP group. However, the study lacked a control group to ascertain whether the PP intervention influenced the survival rate. Similarly, Engerstrom, L et al [15] investigated 1714 patients on mechanical ventilation in the ICU with neocoronary, and determined that the PP did not have a significant impact on the 30-day survival rate. Hence, it can be inferred that the implementation of PP yields enhanced short-term survival rates, and the adoption of multiple PPs contributes to improved survival rates during hospitalization; however, their impact on long-term survival appears to be comparatively limited.
The data presented in our study indicates a positive correlation between the frequency of PP and the extent of improvement in oxygenation. Specifically, the oxygenation index continued to rise for a duration of 6 hours following the conclusion of the initial PP, with the most significant increase observed during the second PP. Among the 14 patients, the second PP resulted in the highest increase in oxygenation index (ranging from 109 mmHg to 373 mmHg), and 4 patients achieved normal levels of oxygenation index.
Previous research has established[16, 17] the efficacy of PP in enhancing the oxygenation index among patients. In a retrospective analysis conducted by Tyler T. Weiss et al [7], involving 42 COVID-19 patients receiving invasive mechanical ventilation, it was observed that repeated PP yielded a more significant improvement in oxygenation. However, the impact of varying frequencies of PP on oxygenation alteration remained inconclusive. Our study, on the other hand, determined that PP1 exhibited the longest duration of oxygenation, while PP2 demonstrated the most substantial increase in oxygenation levels for the majority of patients.
The current study provides evidence that PP can effectively mitigate the severity of COVID-19 in critically ill patients who require invasive mechanical ventilation. Previous research has demonstrated the utility of the SOFA score in evaluating disease severity among mechanically ventilated patients. In this study, approximately half of the patients experienced a decrease in their SOFA score following treatment with PP. Notably, nearly one-third of the patients exhibited a reduction in SOFA score exceeding 20%, while another one-third did not demonstrate any improvement in their SOFA score.
Patients who did not experience any improvement in SOFA score exhibited a significantly longer average duration between their admission to ICU and the commencement of PP (3day vs 1day). Additionally, these patients had a shorter average duration of each PP (15.5h vs22.0h). Previous research studies[20, 21] have demonstrated that PP enhances oxygenation in patients, yet it remains uncertain whether PP effectively reduces the severity of the disease. We hypothesize that the alteration in disease severity among patients may be associated with the start time and duration of PP interventions.
Furthermore, a comparison was conducted between patients who exhibited improvement and survival in the initial three PP oxygenation indices and those who did not. The findings revealed that the duration of PP was significantly longer in patients who demonstrated improvement in the initial three PP oxygenation indices. Previous studies [22, 23] have also reported that early and prolonged implementation of PP may yield enhanced oxygenation outcomes in individuals afflicted with COVID-19-induced lung infections.
Okin et al. [24] conducted a study involving 157 patients with neocoronary who were subjected to invasive mechanical ventilation. Their analysis revealed that extended durations of PP (≥24h) led to notable enhancements in respiratory compliance, oxygenation indices, as well as 30-day and 90-day survival rates. The researchers concluded that recurrent supine positioning could potentially exacerbate atelectasis injury and ventilator-induced lung injury. Consequently, they suggest that initiating and prolonging PP may offer greater benefits in terms of improving oxygenation.
In the present study, it was observed that lymphocyte counts could potentially serve as a useful indicator for assessing the efficacy of PP. The collected data revealed that patients who demonstrated improvement and survival after undergoing the initial three sessions of PP with oxygenation exhibited higher WBC and lymphocyte counts upon admission to the ICU compared to those who did not experience any enhancement in oxygenation. Furthermore, it was observed that the lymphocyte counts of patients who failed to exhibit any improvement in oxygenation were consistently ≤0.5 × 109/L. Previous studies [25, 26] have demonstrated that lymphocyte count serves as a valuable and dependable measure for assessing the severity of COVID-19. Patients with severe COVID-19 exhibit compromised cellular immune function, resulting in a diminished lymphocyte count.
However, the current body of academic literature exhibits a dearth of information pertaining to the correlation between lymphocyte counts and PP. In a prospective study undertaken by Coppo et al. [27], it was discovered that an active inflammatory response was linked to a more advantageous PP oxygenation index. Our contention is that PP might exhibit diminished efficacy in patients with diminished lymphocyte counts and compromised immune systems.
This study is a retrospective investigation conducted on a limited sample size. The participants of this study consisted of critically ill patients diagnosed with COVID-19, who were receiving invasive mechanical ventilation in ICU. These patients exhibited more severe and intricate medical conditions, as well as a higher number of influencing factors. However, we conducted the study in which we included PPs from three general hospitals simultaneously.The relevant information and inspection data was complete. Additionally, we employed a 1:1 PSM analysis to ensure comparability between the PP group and non-PP group, thereby minimizing differences in objective factors. We then dynamically compared the oxygenation index, disease severity, and survival rate between the two groups throughout their hospitalization, thus presenting the impact of PP in a comprehensive and multi-faceted manner across multiple centers.