Magnitude and time to peak oxygenation effect of prone positioning in ventilated adults with COVID-19 related acute hypoxemic respiratory failure.

BACKGROUND: Prone positioning may improve oxygenation in acute hypoxemic respiratory failure and was widely adopted in COVID-19 patients. However, the magnitude and timing of its peak oxygenation effect remain uncertain with the optimum dosage unknown. Therefore, we aimed to investigate the magnitude of the peak effect of prone positioning on the PaO2 :FiO2 ratio during prone and secondly, the time to peak oxygenation. METHODS: Multi-centre, observational study of invasively ventilated adults with acute hypoxemic respiratory failure secondary to COVID-19 treated with prone positioning. Baseline characteristics, prone positioning and patient outcome data were collected. All arterial blood gas (ABG) data during supine, prone and after return to supine position were analysed. The magnitude of peak PaO2 :FiO2 ratio effect and time to peak PaO2 :FIO2 ratio effect was measured. RESULTS: We studied 220 patients (mean age 54 years) and 548 prone episodes. Prone positioning was applied for a mean (±SD) 3 (±2) times and 16 (±3) hours per episode. Pre-proning PaO2 :FIO2 ratio was 137 (±49) for all prone episodes. During the first episode. the mean PaO2 :FIO2 ratio increased from 125 to a peak of 196 (p < .001). Peak effect was achieved during the first episode, after 9 (±5) hours in prone position and maintained until return to supine position. CONCLUSIONS: In ventilated adults with COVID-19 acute hypoxemic respiratory failure, peak PaO2 :FIO2 ratio effect occurred during the first prone positioning episode and after 9 h. Subsequent episodes also improved oxygenation but with diminished effect on PaO2 :FIO2 ratio. This information can help guide the number and duration of prone positioning episodes.

Neuromuscular blockade and oxygenation changes during prone positioning in COVID-19.

PURPOSE: Neuromuscular blockers (NMBs) are often used during prone positioning to facilitate mechanical ventilation in COVID-19 related ARDS. However, their impact on oxygenation is uncertain. METHODS: Multi-centre observational study of invasively ventilated COVID-19 ARDS adults treated with prone positioning. We collected data on baseline characteristics, prone positioning, NMB use and patient outcome. We assessed arterial blood gas data during supine and prone positioning and after return to the supine position. RESULTS: We studied 548 prone episodes in 220 patients (mean age 54 years, 61% male) of whom 164 (75%) received NMBs. Mean PaO2:FiO2 (P/F ratio) during the first prone episode with NMBs reached 208 ± 63 mmHg compared with 161 ± 66 mmHg without NMBs (Δmean = 47 ± 5 mmHg) for an absolute increase from baseline of 76 ± 56 mmHg versus 55 ± 56 mmHg (padj < 0.001). The mean P/F ratio on return to the supine position was 190 ± 63 mmHg in the NMB group versus 141 ± 64 mmHg in the non-NMB group for an absolute increase from baseline of 59 ± 58 mmHg versus 34 ± 56 mmHg (padj < 0.001). CONCLUSION: During prone positioning, NMB is associated with increased oxygenation compared to non-NMB therapy, with a sustained effect on return to the supine position. These findings may help guide the use of NMB during prone positioning in COVID-19 ARDS.

Ventilation management in Victorian intensive care unit patients without acute respiratory distress syndrome.

BACKGROUND: The setting of tidal volume (VT) during controlled mechanical ventilation (CMV) in critically ill patients without acute respiratory distress syndrome (ARDS) is likely important but currently unknown. We aimed to describe current CMV settings in intensive care units (ICUs) across Victoria. METHODS: We performed a multicentre, prospective, observational study. We collected clinical, ventilatory and arterial blood gas data twice daily for 7 days. We performed subgroup analysis by sex and assessment of arterial partial pressure of carbon dioxide (PaCO2) management where hypercapnia was potentially physiologically contraindicated. RESULTS: We recorded 453 observational sets in 123 patients across seven ICUs. The most commonly selected initial VT was 500 mL (33%), and this proportion did not differ according to sex (32% male, 34% female). Moreover, 38% of patients were exposed to initial VT per predicted body weight (VT-PBW) > 8.0 mL/kg. VT-PBW in this range were more likely to occur in females, those with a lower height, lower ideal body weight or in those for whom hypercapnia was potentially physiologically contraindicated. As a consequence, females were more frequently exposed to a lower PaCO2 and higher pH. CONCLUSIONS: In adults without ARDS undergoing CMV in Australian ICUs, the initial VT was a stereotypical 500 mL in one-third of participants, irrespective of sex. Moreover, around 40% of patients were exposed to an initial VT-PBW > 8.0 mL/kg. Finally, women were more likely to be exposed to a high VT and hyperventilation.