ABSTRACT
RATIONALEProne positioning has been shown to have significant survival benefits in Adult Respiratory Distress Syndrome (ARDS). There is little evidence in the literature assessing its effect on patients with Covid-19. With this in mind, we performed a retrospective study of patients receiving treatment with prone-position in the context of Covid-19, and have assessed its impact on efficiency of ventilation (dead space ratio), oxygenation (P/F ratio) and mortality. METHODS We included all patients admitted to our 18 bed ICU with either PCR-confirmed or clinically presumed diagnosis of Covid-19 pneumonia, who were under mechanical ventilation and completed two or more full proning cycles in the period 03/12/2020-04/12/2020. Demographic characteristics, data on mechanical ventilation, patient position, end tidal CO2 and arterial blood gas were obtained from patient charts. Pa/FiO2 ratios (P/F) were calculated as a marker of oxygenation and dead space fraction (Vd/Vt) to assess ventilation. RESULTS Twelve patients were studied. There was a statistically significant improvement in P/F ratio when prone compared to supine (Wilcoxon signed-rank Z=12, p<0.01) with more than a 20% increase. There was no statistically significant change in Vd/Vt ratio on proning (p>0.05). Over time, Vd/Vt increased in non-survivors (Rs=0.48, p<0.01), whilst remained flat in survivors (Rs=0.002, p=0.97). See Figure 1. CONCLUSION Our findings indicate that prone position in patients with Covid-19 has little effect on dead space fraction, but does improve oxygenation. This poses the question as to whether this therapy adds anything to the management of Covid-19 patients-aside from a transient improvement in oxygenation that would buy time for additional therapies to succeed. In non-survivors, we observed a progressive rise in Vd/Vt over time. This was not the case in survivors, as seen in ARDS, where a rise in Vd/Vt has been shown to be a prognostic marker for death. With regards to response to prone position, only improvements in Vd/Vt (but not in P/F ratio) have been shown to be prognostic. Our findings seem to replicate this in Covid-19 patients. We propose the regular calculation of Vd/Vt as an easy tool to assess the progress of Covid-19 patients. Our sample size was small and contained mainly our sickest Covid-19 patients due a high number of inter-trust bed pressure transfers. Drawing firm conclusions from this data is thus not possible however we believe it to still be valuable. Further work is required to show a replication of our findings on a larger scale. (Table Presented).
ABSTRACT
Little is known about the impact of proning on oxygenation and ventilatory efficiency on patients with severe Covid-19. In this retrospective observational study we calculated Pa/FiO2 ratio (P/F) as a marker of oxygenation and dead space fraction (Vd/Vt) to assess ventilation. 12 patients who were proned twice or more were included. There was a significant improvement in P/F ratio when prone (110.18 ± 28.11) compared to supine (88.95 ± 19.34) (p < 0.01). There was no improvement in Vd/Vt on proning (p > 0.05). Vd/Vt as a function of time displayed a positive linear correlation in those who did not survive (n = 9) (Rs = 0.48, p < 0.01) but no observed correlation in those who survived (n = 3) (Rs = 0.002, p = 0.97). Our findings indicate that prone position in patients with Covid-19 has little effect on dead space fraction but does improve oxygenation. Rise in dead space with time appears to be a prognostic factor for death in patients with severe Covid- 19.