Physiologic effects of prone positioning on gas exchange and ventilation-perfusion matching in awake patients with AHRF

doi:10.21203/rs.3.rs-4645709/v1

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Research Article

Physiologic effects of prone positioning on gas exchange and ventilation-perfusion matching in awake patients with AHRF

https://doi.org/10.21203/rs.3.rs-4645709/v1

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Background

Prone positioning (PP) improves oxygenation in awake patients with acute hypoxemic respiratory failure (AHRF). However, the underlying mechanisms remain unclear in patients with diverse lung morphology. We aimed to determine the short-term effects of awake prone positioning (APP) in AHRF patients with focal and non-focal lung morphology.

Methods

This is a prospective physiological study. Twenty-four non-intubated patients with PaO₂/FiO₂ ≤ 300 mm Hg were included. Gas exchange, ventilation and perfusion distribution, and hemodynamics variables were recorded in the supine position (SP1), 2 h after PP, and 1 h after re-supine (SP2). Lung morphology was classified as focal and non-focal patterns using computed tomography.

Results

Twelve of the included patients were classified to the focal group and 12 to the non-focal group. PaO₂/FiO₂ improved after PP in all patients (161 [137, 227] mmHg vs. 236 [202, 275] mmHg, p < 0.001). Ventilation-perfusion (V/Q) matching increased after PP in all patients (61.9 [53.9, 66.5] vs. 77.5 [68.3, 80.0], p < 0.001). Shunt exhibited a significant decrease in patients of the non-focal group (28.6 [22.5, 30.3] vs. 11.3 [9.0, 14.5], p < 0.001), whereas no difference was found in the focal group after PP. Dead space decreased significantly in patients of the focal group (25.6 [21.5, 28.4] vs. 12.0 [10.8, 14.1], p < 0.001), whereas no difference was found in the non-focal group after PP.

Conclusions

APP improves V/Q matching by decreasing dead space in patients with focal lung morphology, and by decreasing shunt in patients with non-focal lung morphology.

Trial registration:

The study is registered in ClinicalTrials.gov (NCT04754113).

Awake prone positioning

ventilation-perfusion matching

shunt

dead space

acute hypoxemic respiratory failure

Acute respiratory distress syndrome (ARDS) was first described in the 1960s [1]. Since then, prone positioning has become an established evidence-based practice for mechanically ventilated patients with moderate-to-severe ARDS, which has been proven to decrease mortality [2]. Physiologically, prone positioning improves oxygenation by promoting lung recruitment and generating a more homogeneous ventilation distribution. Consequently, it reduces ventilation-perfusion (V/Q) mismatch and mitigates ventilator-induced lung injury among these patients [3–5].

Following the onset of the COVID-19 pandemic, the use of awake prone positioning in non-intubated patients has attained more urgency and has been subsequently implemented in clinical practice due to its beneficial effect on the oxygenation [6–9]. However, the exact mechanisms leading to the oxygenation improvement remain unclear. Only few studies have addressed the physiological effects of prone positioning in awake patients, most of which have only demonstrated the change of regional distribution of ventilation and effort-to-breathe after proning [10–12]. As oxygenation improvement may involve changes in the distribution of either ventilation and/or perfusion that may both affect regional ventilation/perfusion (V/Q) matching, it is essential to consider the distribution of regional pulmonary blood flow following awake prone positioning [13]. Meanwhile, lung recruitment has been proposed as one of the mechanisms for the beneficial effects of prone positioning [14]. Lung morphology, as assessed by thoracic computed tomography (CT), has been shown to predict lung recruitability in ARDS patients [15]. Subsequent multi-center study conducted in France was able to determine that the lung imaging morphology guided ventilator settings in ARDS patients also reduced mortality [16]. These findings suggested that lung morphology is a crucial aspect in distinguishing specific ARDS phenotypes. However, whether lung morphology impacts the effects of awake prone positioning on patients with acute hypoxemic respiratory failure (AHRF) has never been explored.

Electrical impedance tomography (EIT) has the capability for real-time visualization of ventilation and hence expands our understanding of the physiology effects of prone positioning [12, 13, 17]. Additionally, EIT has been identified to detect pulmonary blood flow, particularly when using hypertonic saline as a “conductive” contrast agent [18]. Therefore, EIT is a useful tool for assessing the potential mechanisms affecting the distribution of both ventilation and perfusion during awake prone positioning. In this study, we use EIT to continuously record regional lung ventilation and perfusion in patients with AHRF and we hypothesize that the effects of awake prone positioning in improving V/Q matching by reducing shunt and dead space may differ among patients exhibiting diverse lung morphology.

This prospective observation study was performed in the medical ICU at Zhongda Hospital, Southeast University from May 2021 to March 2022. The study protocol was granted approval by the Institutional Ethics Committee of Zhongda hospital (2020ZDSYLL057-P01). Written informed consent was obtained from all patients or their legal representatives prior to the study. This was a prospective, observational cohort study registered in ClinicalTrials.gov (NCT04754113, the Registration Date: June 02, 2021).

Study population

All adults (> 18 years) admitted to our ICU were enrolled if they met the following criteria: 1) a ratio of the partial pressure of arterial oxygen (PaO₂) to the FiO₂ (PaO₂/FiO₂) ≤ 300 mm Hg while the patient was breathing oxygen at a flow rate of 10 liters per minute or more for at least 15 minutes [19], 2) evidence of bilateral pulmonary infiltrates on a chest radiograph or a CT scan, 3) an acute onset (< 1 week) of respiratory distress, 4) a partial pressure of arterial carbon dioxide (PaCO₂) ≤ 45 mm Hg, and 5) no history of chronic respiratory failure. Exclusion criteria were as follows: contraindication to EIT use (presence of pacemaker), prior intubation, contraindications to prone positioning, poor tolerance and/or severe worsening of clinical conditions during study phases necessitating prone positioning discontinuation, a lack of ability to hold the breath, a lack of central venous catheter, and refusal to participate in this study.

Study protocol

Demographic data (age, sex, body mass index [BMI]), cause of AHRF, type of supplemental oxygen, time from symptoms onset to hospital admission and ICU admission, and time from hospital admission to awake prone positioning were collected. Chest CT scan in the supine position was collected at enrollment. Upon enrollment, each patient was assigned to either standard oxygen therapy or high-flow nasal cannula (MR860 or ARIVO2, Fisher and Paykel healthcare), which remained unchanged during the study period. All patients were examined in the supine position at baseline (SP1), 2 hours after prone positioning initiation (PP), and 1 hour after re-positioning to the supine posture (SP2). The respiratory rate (RR), peripheral capillary oxygen saturation (SpO₂), arterial blood gas analysis (pH, PaO₂, PaCO₂, PaO₂/FiO₂), hemodynamic parameters (heart rate and mean arterial pressure), and EIT data were recorded during the last five-minute period of each of the three phases. The use of sedative or analgesic agents which could have interfered with the breathing pattern was not allowed during the study period.

EIT data

EIT measurements were performed using PulmoVista 500 (Dräger Medical GmbH, Lübeck, Germany) at 50 Hz and the data were stored for offline analysis. The 16-electrode EIT belt was placed along the fourth to fifth intercostal space and kept in the same position during the whole study period. The patients were asked to perform an end-expiratory breath-hold for 8–12 s, and then a bolus of 10 mL of 10% NaCl solution was quickly injected through a central venous catheter 2 seconds after the voluntary onset of airway occlusion. Regional ventilation maps were calculated by averaging tidal impedance variation (the difference between end-inspiratory and end-expiratory impedance) after the bolus during the last 1 minute of the 5-min long data acquisition. Regional perfusion maps were generated by the slope of the impedance decrease following a saline bolus injection during an end-expiratory breath-hold [20]. The following parameters were calculated in the last minute of each study phase: 1) the percentage of total ventilated lung area that is located in the dorsal half of the thorax [21], 2) the percentage of total perfused lung area that is located in the dorsal half of the thorax [21], 3) the global inhomogeneity (GI) index [22]. Subsequently, the following regions were identified [21]: 1) shunt %: all pixels that were only perfused, divided by the total number of pixels classified as ventilated or perfused. 2) dead space %: all pixels that were only ventilated, divided by the total number of pixels classified as ventilated or perfused. 3) V/Q matching %: corresponding to the pixels that were both ventilated and perfused divided by the total number of pixels ventilated or perfused.

Lung morphology assessment

The chest CT was obtained within 48 hours prior to or following the onset of study period. All CT scans were performed in the supine position. CT images were analyzed by two intensivists and one radiologist who were blinded to patient’s history. Patterns of lung morphology were considered as “focal” in the presence of consolidations localized only in the lower lobes or gravitationally dependent parenchyma, and as “non-focal” if diffuse or patchy consolidations were identified in the lung parenchyma [23].

Endpoints

The primary endpoint was the degree of V/Q matching in different body positions. The secondary endpoints were the percentage of shunt, the percentage of dead space, the percentage of dorsal ventilated area, the percentage of dorsal perfused area, the GI index, pH, PaO₂, PaO₂/FiO₂, PaCO₂, RR, heart rate, and mean arterial pressure in different positions. A patient was considered to be an oxygenation responder when a relative increase in PaO₂/FiO₂ by 20% or more was noted after prone positioning [11].

Statistical analysis

Considering the lack of previous studies’ results, sample size calculation was unattainable in our study. Data were tested for normality distribution by Shapiro-Wilk test. Continuous variables were reported as mean (± standard deviation) or median (interquartile range [IQR]) for continuous variables, as appropriate. Categorical variables were reported as numbers (percent). For the analysis of variables with normal distribution, Mauchly’s test was performed for sphericity, and repeated measures ANOVA was used with post hoc Bonferroni’s multiple comparisons. If not normally distributed, the change of variables at the different timepoints were compared using Kruskal-Wallis test. Greenhouse-Geisser method was applied for correction when Mauchly’s test p value was < 0.05. A level of two-tailed p < 0.05 was considered as statistically significant. Statistical analyses were conducted using STATA version 19.0 (Statacorp, College Station, TX, USA) and Prism (GraphPad Prism v9.3, La Jolla, CA).

Patients’ characteristics

Twenty-four patients were enrolled in the study. Twelve patients were classified to the focal lung morphology group and twelve to the non-focal lung morphology group. The patients had a median age of 67 years (IQR 56–73 years), and 17 (70.8%) were male. The main cause of AHRF in this study was COVID-19 and more than half of the patients needed HFNC (70.8%) to maintain oxygenation. The patients in the non-focal group were older than patients in the focal group (73 [62, 75] vs. 61 [54, 68] years, P = 0.037). However, there were no significant differences in the causes of AHRF, type of supplemental oxygen and other characteristics between the two groups. Additional details are summarized in Table 1.

Table 1

Baseline characteristics of the study patients
Variable	Overall N = 24	Focal group N = 12	Non-focal group N = 12	P
Age (years)	67 [56, 73]	61 [54, 68]	73 [62, 75]	0.037
Sex, male, n (%)	17 (70.8)	7 (58.3)	10 (83.3)	0.178
BMI (kg/m²)	24.1 [22.8, 26.4]	23.8 [21.7, 26.8]	24.5 [23.3, 25.3]	0.885
Cause of AHRF				0.319
Community-acquired pneumonia	8	4	4
COVID-19	14	8	6
Extrapulmonary sepsis	2	0	2
Type of supplemental oxygen				0.653
Nasal tube oxygen, n (%)	7 (29.2)	4 (33.3)	3 (25.0)
HFNC, n (%)	17 (70.8)	8 (66.7)	9 (75.0)
FIO₂, %	41.2 ± 11.4	39.7 ± 13.6	42.8 ± 8.9	0.519
HFNC gas flow, L/min	48.5 ± 4.9	47.5 ± 4.6	49.2 ± 5.1	0.461
Time from syndrome onset to hospital admission, d	5.5 [3, 8]	5.5 [3.5, 8]	5 [3, 7]	0.640
Time from syndrome onset to ICU admission, d	6 [3, 8.5]	6.5 [3.5, 8]	5.5 [3, 11]	0.793
Time from hospital admission to awake prone position, d	0.8 [0.5, 3.5]	0.8 [0.5, 2.5]	0.8 [0.5, 4.0]	0.908
Length of ICU stay, d	18 [14, 22.5]	19.5 [15, 28.5]	17.5 [14, 21.5]	0.506
28-day mortality	0	0	0	1.00
BMI, body mass index; AHRF, acute hypoxemic respiratory failure; HFNC, high-flow nasal cannula

Comparisons between PP and SP1

Gas exchange and hemodynamics variables

After proning, PaO₂/FiO₂ improved in both group (both P < 0.01) (Fig. 1A). Seven (54%) patients in the focal group and ten patients (91%) in the non-focal group were classified as oxygenation responders (Figure E1). pH and PaCO₂ did not significantly change after PP in both groups. RR did not change between SP1 and PP (Table 2). For the hemodynamics variables, both heart rate and mean arterial pressure were not affected by the body position in both groups (Table 2).

Table 2

Gas exchange, EIT-related variables, and hemodynamics variables during the study period
	Focal group, N = 12			P	Non-focal group, N = 12			P
	SP1	PP	SP2	P	SP1	PP	SP2	P
Gas exchange
pH	7.46 ± 0.06	7.45 ± 0.05	7.45 ± 0.05	0.144	7.43 ± 0.06	7.44 ± 0.04	7.44 ± 0.04	0.521
PaO₂, mmHg	73.7 [58.5, 80.2]	89.2 [75.0, 99.2]^*	74.8 [60.1, 80.4]^#	< 0.001	68.6 [58.5, 81.8]	94.0 [78.8, 106.8]^*	82.0 [68.8, 89.8]^#	< 0.001
PaO₂/FIO₂, mmHg	191 [143, 240]	237 [196, 270]^*	212 [144, 254]^#	< 0.001	142 [129, 208]	235 [202, 282]^*	205 [153, 224]^#	< 0.001
PaCO₂, mmHg	35.9 ± 4.1	38.2 ± 3.1	37.4 ± 3.0	0.221	33.6 ± 7.3	33.2 ± 6.2	34.0 ± 5.5	0.635
Respiratory rate, breaths/min	23 ± 5	24 ± 4	25 ± 6	0.337	25 ± 6	24 ± 3	25 ± 6	0.563
EIT-based measures
Global inhomogeneity index	0.40 [0.36, 0.50]	0.41 [0.36, 0.47]	0.42 [0.38, 0.46]	0.913	0.39 [0.36, 0.44]	0.40 [0.37, 0.43]	0.39 [0.36, 0.48]	0.913
Ventilated area, dorsal, %	52.9 ± 13.1	56.9 ± 10.4	50.8 ± 12.9	0.132	47.4 ± 17.4	53.5 ± 14.4	46.6 ± 18.7	0.428
Perfused area, dorsal, %	54.8 ± 14.0	52.4 ± 11.9	50.4 ± 15.9	0.606	44.1 ± 9.5	51.4 ± 11.1	46.7 ± 11.5	0.126
Shunt, %	10.8 [5.5, 20.5]	11.5 [7.4, 16.8]	11.1 [5.0, 24.2]	0.558	28.6 [22.5, 30.3]	11.3 [9.0, 14.5]^*	16.9 [9.5, 25.1]^*	< 0.001
Dead space, %	25.6 [21.5, 28.4]	12.0 [10.8, 14.1]^*	20.3 [14.7, 27.8]	< 0.001	13.6 [6.8, 17.8]	12.5 [7.4, 19.0]	15.0 [10.1, 19.1]	0.472
Ventilation-perfusion matching, %	62.6 [52.6, 71.9]	78.6 [69.7, 81.4]^*	65.1 [58.2, 73.6]^#	< 0.001	61.9 [54.3, 63.1]	76.0 [68.7, 79.0]^*	62.5 [61.0, 69.2]^#	< 0.001
Hemodynamic data
Heart rate, beats/min	87 ± 14	85 ± 15	80 ± 13^*	0.033	90 ± 15	94 ± 15	90 ± 17	0.146
Mean arterial pressure, mmHg	86 ± 11	88 ± 10	88 ± 13	0.582	86 ± 11	85 ± 10	84 ± 10	0.707
SP1, supine at baseline; PP, prone position; SP, re-supine. ^* p < 0.05 supine versus prone, ^# p < 0.05 prone versus re-supine.

Ventilation, perfusion, and V/Q distribution

GI index remained constant and did not differ between SP1 and PP in both groups. The ventilated and perfused lung areas at the dorsal image region did not change significantly with the position in both groups (Table 2). The change in the V/Q matching after PP is presented in the Table 2 and Fig. 1B. V/Q matching increased significantly in both groups after proning (both p < 0.001). The percentages of shunt in SP1 and PP are presented in the Table 2. The percentage of shunt did not change after PP for the patients in the focal group. For patients in the non-focal group, it decreased significantly (28.6 [22.5, 30.3] vs. 11.3 [9.0, 14.5], P < 0.001) following PP (Fig. 2A). The percentages of dead space at different positions are presented in the Table 2 and Fig. 2B. For patients in the focal group, a significant decrease in the percentage of dead space was detected after proning (p < 0.001). For patients in the non-focal group, there was no change in the percentage of dead space after proning.

Comparisons between PP and SP2

Gas exchange and hemodynamics variables

For patients in both groups, PaO₂/FiO₂ decreased significantly in the SP2 when compared with PP (Fig. 1A). Patients in both groups were not different in the PaCO₂ and RR between PP and SP2 (Table 2). Regarding the hemodynamics, neither heart rate nor mean arterial pressure in both groups showed any changes in the SP2 compared to PP (Table 2).

Ventilation, perfusion, and V/Q distribution

GI index did not differ between PP and SP2 in both groups. The ventilated and perfused dorsal lung areas did not significantly change from PP to SP2 in both groups (Table 2). From PP to SP2, V/Q matching had significantly decreased in patients with both groups (Fig. 1B). For the percentage of shunt dead space, patients in both groups did not change from PP to SP2 (Fig. 2B).

The physiologic effects of awake prone positioning on the distribution of pulmonary ventilation and perfusion in two representative patients determined by EIT, are presented in the Figure E2 and Figure E3.

Correlations between change in PaO₂/FiO₂ and V/Q distribution

The relative variations in the PaO₂/FiO₂ during the PP session were inversely correlated with change in the percent of shunt (r = -0.46, P = 0.025) (Fig. 3B). However, no correlation was observed between the relative variations in the PaO₂/FiO₂ and the change in the percentage of V/Q matching (Fig. 3A) and dead space (Fig. 3C).

The primary findings of this study are as follows: Awake prone positioning improved both V/Q matching and oxygenation in patients with AHRF, irrespective of lung morphology. Among patients with focal lung morphology, V/Q matching was improved by the reduced percentage of lung units with dead space ventilation. Among patients with non-focal lung morphology, V/Q matching was improved by the decreased percentage of shunt lung units.

The beneficial effect of awake prone positioning on the oxygenation improvement has been explored in several studies, especially in the context of the COVID-19 pandemic [11–13]. Nevertheless, discrepancies persist concerning oxygenation endpoints, the duration of prone positioning, and the respiratory support devices used in these studies [6, 9, 24]. A previous study reported that awake prone positioning induced a marked increase of PaO₂/FiO₂ of 20% or more in up to 85% of patients [25]. In the present study, we observed a significant increase in the PaO₂/FiO₂ at pp. Consistent with previous studies, our current study revealed that oxygenation improvement was independent of the baseline degree of hypoxemia, suggesting that basing the decisions on implementation of awake prone positioning on PaO₂/FiO₂ levels may not be reliable[25]. Furthermore, we confirmed that the effect of awake prone positioning on the oxygenation improvement was lost after repositioning to the supine posture, which was in line with previous studies [12, 13, 26]. Almost 70% of patients were classified as responders, showing a clinically significant increase in PaO₂/FiO₂ of 20% or more in the present study. This is comparable to the 65% reported in the previous study [11].

The physiological effects of awake prone positioning in the non-intubated patients with AHRF are not yet fully understood. The fact that oxygenation improved in awake patients after prone positioning may suggest that similar pathophysiological considerations are valid as in the case of intubated patients, irrespective of the nature triggering the underlying lung injury. Following PP, the decrease of pleural pressure gradient from non-dependent to dependent regions reopens non-aerated or poorly aerated regions, therefore, reinforcing a more homogeneous ventilation with subsequent favorable effect on V/Q matching [17]. In the present study, V/Q matching increased in all patients after awake prone positioning regardless of the lung morphology.

However, there were still some differences in the effects of awake prone positioning among patients with different lung morphology, which were revealed in our study. According to morphological patterns, the majority of patients with a non-focal pattern (91%) were responders, whereas only half of those with a focal pattern (54%) were responders. This indicated that identification of patients who were likely to benefit from awake prone positioning on the oxygenation improvement could be achieved by the lung morphology. In the present study, awake prone positioning improved V/Q matching mainly by decreasing the shunt fraction in patients with non-focal pattern, while decreasing the dead space fraction in patients with focal pattern. One possible explanation for this discrepancy is that non-aerated lung tissue, which can be reopened with prone positioning (PP), is more prevalent in AHRF patients with non-focal patterns. Pervious study has shown that non-focal pattern is associated with elevated lung inflammation, potentially resulting in increased lung injury [27, 28]. Moreover, compared to focal pattern, non-focal pattern had a lower overinflation and a higher lung recruitability. This can be attributed to the higher amount of lung edema which represents tissue that can be re-opened [29]. These features suggested awake prone positioning may be likely to recruit the non-aerated tissue and further decrease the percentage of shunt in non-intubated patients with AHRF. For patients with focal morphology pattern, the overinflation may be the main feature. This indicated that V/Q matching improved in the patients with focal pattern after awake prone positioning may be mainly governed by a decrease in overinflated lung tissue.

To date, the effect of awake prone positioning on the work of breathing (WOB) in non-intubated patients was controversial. Most patients with AHRF are characterized by vigorous breathing efforts and a higher RR. Several studies have reported that awake prone positioning, in combination with non-invasive ventilation in non-intubated patients with COVID-19, decreased RR and excessive WOB, further resulting in a trend towards reduced intubation rate [11, 23, 30]. The decrease of RR after awake prone positioning may be generated by the decrease in the respiratory strain, and this is clinically important in avoiding intubation. In contrast, RR was not different after awake prone positioning in the present study. The contrary results may be associated with the respiratory support and patients’ tolerance.

Our study has some limitations. First, the respiratory parameters, including esophageal pressure, trans-diaphragmatic pressure, tidal volume, and work of breathing was not measured which may affect the evaluation of the effects of awake prone positioning. Second, the long-term effects of awake prone positioning are missing, whether the short-term beneficial effects translate into improved clinically relevant outcome is unclear. Third, EIT cannot provide images of the whole lung, so the assessment of the entire spectrum of V/Q matching in the whole lung was not accessible.

Awake prone positioning improves oxygenation and V/Q matching in AHRF patients regardless of lung morphology. In patients with focal lung morphology, V/Q matching improved by decreasing the percentage of dead space lung units. In patients with non-focal lung morphology, V/Q matching improved by decreasing the percentage of shunt lung units.

PP Prone positioning

APP Awark prone positioning

AHRF Acute hypoxemic respiratory failure

SP Supine positioning

PaO₂ Partial pressure of arterial oxygen

PaCO₂ Partial pressure of arterial carbon dioxide

EIT Eletrical impedance tomography

Ventilation-perfusion V/Q

BMI Body mass index

Data availability statement

The data that support the findings of this study are available upon reasonable request from the corresponding author.

Acknowledgements

All authors were responsible for data interpretation, revised the manuscript critically, and approved the version submitted for publication.

Funding

This work was funded by National Science and Technology Major Project of China (2022YFC2504400), the National Natural Science Foundation of China (82341032 and 81930058), the Second Level Talents of the “333 High Level Talents Training Project” in the sixth phase in Jiangsu (LGY2022025), and Jiangsu Provincial Key Laboratory of Critical Care Medicine (BM2020004).

Ethical statement

The study protocol was approved by the Institutional Ethics Committee of Zhongda hospital (2020ZDSYLL057-P01).

Conflict of interest

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

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No competing interests reported.

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You are reading this latest preprint version

Physiologic effects of prone positioning on gas exchange and ventilation-perfusion matching in awake patients with AHRF

Status:

Version 1

Abstract

Background

Methods

Results

Conclusions

Trial registration:

Figures

Introduction

Methods

Study population

Study protocol

EIT data

Lung morphology assessment

Endpoints

Statistical analysis

Results

Patients’ characteristics

Comparisons between PP and SP1

Gas exchange and hemodynamics variables

Ventilation, perfusion, and V/Q distribution

Comparisons between PP and SP2

Gas exchange and hemodynamics variables

Ventilation, perfusion, and V/Q distribution

Correlations between change in PaO₂/FiO₂ and V/Q distribution

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Physiologic effects of prone positioning on gas exchange and ventilation-perfusion matching in awake patients with AHRF

Status:

Version 1

Abstract

Background

Methods

Results

Conclusions

Trial registration:

Figures

Introduction

Methods

Study population

Study protocol

EIT data

Lung morphology assessment

Endpoints

Statistical analysis

Results

Patients’ characteristics

Comparisons between PP and SP1

Gas exchange and hemodynamics variables

Ventilation, perfusion, and V/Q distribution

Comparisons between PP and SP2

Gas exchange and hemodynamics variables

Ventilation, perfusion, and V/Q distribution

Correlations between change in PaO2/FiO2 and V/Q distribution

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Correlations between change in PaO₂/FiO₂ and V/Q distribution