Background: The effects of awake prone position on the breathing pattern of hypoxemic patients need to be better understood. We conducted a crossover trial to assess the physiological effects of awake prone position in patients with acute hypoxemic respiratory failure. Methods: Fifteen patients with acute hypoxemic respiratory failure and PaO₂/FiO₂ < 200 mmHg underwent high-flow nasal oxygen for 1 h in supine position and 2 h in prone position, followed by a final 1-h supine phase. At the end of each study phase, the following parameters were measured: arterial blood gases, inspiratory effort (ΔP_ES), transpulmonary driving pressure (ΔP_L), respiratory rate and esophageal pressure simplified pressure–time product per minute (sPTP_ES) by esophageal manometry, tidal volume (V_T), end-expiratory lung impedance (EELI), lung compliance, airway resistance, time constant, dynamic strain (V_T/EELI) and pendelluft extent through electrical impedance tomography. Results: Compared to supine position, prone position increased PaO₂/FiO₂ (median [Interquartile range] 104 mmHg [76–129] vs. 74 [69–93], p < 0.001), reduced respiratory rate (24 breaths/min [22–26] vs. 27 [26–30], p = 0.05) and increased ΔP_ES (12 cmH₂O [11–13] vs. 9 [8–12], p = 0.04) with similar sPTP_ES (131 [75–154] cmH₂O s min⁻¹ vs. 105 [81–129], p > 0.99) and ΔP_L (9 [7–11] cmH₂O vs. 8 [5–9], p = 0.17). Airway resistance and time constant were higher in prone vs. supine position (9 cmH₂O s arbitrary units⁻³ [4–11] vs. 6 [4–9], p = 0.05; 0.53 s [0.32–61] vs. 0.40 [0.37–0.44], p = 0.03). Prone position increased EELI (3887 arbitrary units [3414–8547] vs. 1456 [959–2420], p = 0.002) and promoted V_T distribution towards dorsal lung regions without affecting V_T size and lung compliance: this generated lower dynamic strain (0.21 [0.16–0.24] vs. 0.38 [0.30–0.49], p = 0.004). The magnitude of pendelluft phenomenon was not different between study phases (55% [7–57] of V_T in prone vs. 31% [14–55] in supine position, p > 0.99). Conclusions: Prone position improves oxygenation, increases EELI and promotes V_T distribution towards dependent lung regions without affecting V_T size, ΔP_L, lung compliance and pendelluft magnitude. Prone position reduces respiratory rate and increases ΔP_ES because of positional increases in airway resistance and prolonged expiratory time. Because high ΔP_ES is the main mechanistic determinant of self-inflicted lung injury, caution may be needed in using awake prone position in patients exhibiting intense ΔP_ES. Clinical trail registeration: The study was registered on clinicaltrials.gov (NCT03095300) on March 29, 2017.

Purpose Personalized positive end-expiratory pressure (PEEP) might foster lung and diaphragm protection in patients with acute respiratory distress syndrome (ARDS) who are undergoing pressure support ventilation (PSV). We aimed to compare the physiologic effects of personalized PEEP set according to synchronized electrical impedance tomography (EIT) and driving transpulmonary pressure (∆PL) monitoring against a classical lower PEEP/FiO₂ table in intubated ARDS patients undergoing PSV. Methods A cross-over randomized multicenter study was conducted in 30 ARDS patients with simultaneous recording of the airway, esophageal and transpulmonary pressure, together with EIT during PSV. Following a decremental PEEP trial (18 cmH₂O to 4 cmH₂O), PEEP_EIT-∆PL was identified as the level with the smallest difference between lung overdistension and collapse. A low PEEP/FiO₂ table was used to select PEEP_TABLE. Each PEEP strategy was applied for 20 min, and physiologic data were collected at the end of each step. Results The PEEP trial was well tolerated. Median PEEP_EIT-∆PL was higher than PEEP_TABLE (10 [8–12] vs. 8 [5–10] cmH₂O; P = 0.021) and, at the individual patient level, PEEP_EIT-∆PL level differed from PEEP_TABLE in all patients. Overall, PEEP_EIT-∆PL was associated with lower dynamic ∆PL (P < 0.001) and pressure–time product (P < 0.001), but there was variability among patients. PEEP_EIT-∆PL also decreased respiratory drive and effort (P < 0.001), improved regional lung mechanics (P < 0.05) and reversed lung collapse (P = 0.007) without increasing overdistension (P = 0.695). Conclusion Personalized PEEP selected using synchronized EIT and transpulmonary pressure monitoring could be associated with reduced dynamic lung stress and metabolic work of breathing in ARDS patients undergoing PSV.

Acute respiratory distress syndrome (ARDS) is a leading cause of disability and mortality worldwide, and while no specific etiologic interventions have been shown to improve outcomes, noninvasive and invasive respiratory support strategies are life-saving interventions that allow time for lung recovery. However, the inappropriate management of these strategies, which neglects the unique features of respiratory, lung, and chest wall mechanics may result in disease progression, such as patient self-inflicted lung injury during spontaneous breathing or by ventilator-induced lung injury during invasive mechanical ventilation. ARDS characteristics are highly heterogeneous; therefore, a physiology-based approach is strongly advocated to titrate the delivery and management of respiratory support strategies to match patient characteristics and needs to limit ARDS progression. Several tools have been implemented in clinical practice to aid the clinician in identifying the ARDS sub-phenotypes based on physiological peculiarities (inspiratory effort, respiratory mechanics, and recruitability), thus allowing for the appropriate application of personalized supportive care. In this narrative review, we provide an overview of noninvasive and invasive respiratory support strategies, as well as discuss how identifying ARDS sub-phenotypes in daily practice can help clinicians to deliver personalized respiratory support and potentially improve patient outcomes.

Background: Positive end-expiratory pressure (PEEP) benefits in acute respiratory distress syndrome are driven by lung dynamic strain reduction. This depends on the variable extent of alveolar recruitment. The recruitment-to-inflation ratio estimates recruitability across a 10–cm H₂O PEEP range through a simplified maneuver. Whether recruitability is uniform or not across this range is unknown. The hypotheses of this study are that the recruitment-to-inflation ratio represents an accurate estimate of PEEP-induced changes in dynamic strain, but may show nonuniform behavior across the conventionally tested PEEP range (15 to 5 cm H₂O). Methods: Twenty patients with moderate-to-severe COVID-19 acute respiratory distress syndrome underwent a decremental PEEP trial (PEEP 15 to 13 to 10 to 8 to 5 cm H₂O). Respiratory mechanics and end-expiratory lung volume by nitrogen dilution were measured the end of each step. Gas exchange, recruited volume, recruitment-to-inflation ratio, and changes in dynamic, static, and total strain were computed between 15 and 5 cm H₂O (global recruitment-to-inflation ratio) and within narrower PEEP ranges (granular recruitment-to-inflation ratio). Results: Between 15 and 5 cm H₂O, median [interquartile range] global recruitment-to-inflation ratio was 1.27 [0.40 to 1.69] and displayed a linear correlation with PEEP-induced dynamic strain reduction (r = –0.94; P < 0.001). Intraindividual recruitment-to-inflation ratio variability within the narrower ranges was high (85% [70 to 109]). The relationship between granular recruitment-to-inflation ratio and PEEP was mathematically described by a nonlinear, quadratic equation (R ² = 0.96). Granular recruitment-to-inflation ratio across the narrower PEEP ranges itself had a linear correlation with PEEP-induced reduction in dynamic strain (r = –0.89; P < 0.001). Conclusions: Both global and granular recruitment-to-inflation ratio accurately estimate PEEP-induced changes in lung dynamic strain. However, the effect of 10 cm H₂O of PEEP on lung strain may be nonuniform. Granular recruitment-to-inflation ratio assessment within narrower PEEP ranges guided by end-expiratory lung volume measurement may aid more precise PEEP selection, especially when the recruitment-to-inflation ratio obtained with the simplified maneuver between PEEP 15 and 5 cm H₂O yields intermediate values that are difficult to interpret for a proper choice between a high and low PEEP strategy. Editor’s Perspective: What We Already Know about This Topic: What This Article Tells Us That Is New:

Background: Noninvasive respiratory support (NRS), including high-flow nasal oxygen therapy (HFNOT), noninvasive ventilation (NIV) and continuous positive airway pressure (CPAP), are routinely used in the perioperative period. Objectives: This narrative review provides an overview on the perioperative use of NRS. Preoperative, intraoperative, and postoperative respiratory support is discussed, along with potential future areas of research. Results: During induction of anesthesia, in selected patients at high risk of difficult intubation, NIV is associated with improved gas exchange and reduced risk of postoperative respiratory complications. HFNOT demonstrated an improvement in oxygenation. Evidence on the intraoperative use of NRS is limited. Compared with conventional oxygenation, HFNOT is associated with a reduced risk of hypoxemia during procedural sedation, and recent data indicate a possible role for HFNOT for intraoperative apneic oxygenation in specific surgical contexts. After extubation, “preemptive” NIV and HFNOT in unselected cohorts do not affect clinical outcome. Postoperative “curative” NIV in high-risk patients and among those exhibiting signs of respiratory failure can reduce reintubation rate, especially after abdominal surgery. Data on postoperative “curative” HFNOT are limited. Conclusions: There is increasing evidence on the perioperative use of NRS. Use of NRS should be tailored based on the patient’s specific characteristics and type of surgery, aimed at a personalized cost-effective approach.

Acute hypercapnic respiratory failure is a life-threatening condition caused by alveolar hypoventilation. It is mostly caused by an acute exacerbation of chronic obstructive pulmonary disease or conditions yielding muscle dysfunction. Noninvasive ventilation through a facemask is the cornerstone first-line strategy to support hypercapnic patients with acidemia, and current guidelines strongly recommend this intervention to improve survival and long-term clinical outcomes. Because of its benefits related to carbon dioxide washout from the upper airways and the enhanced comfort, high-flow nasal oxygen has been proposed as a respiratory support strategy in patients with hypercapnic respiratory failure, both as an alternative to and in combination with noninvasive ventilation. When compared to noninvasive ventilation as a first-line intervention, high-flow nasal oxygen shows a higher rate of failure. Hence, if not contraindicated, the use of noninvasive ventilation should be preferred. After the resolution of acidemia with noninvasive ventilation, high-flow nasal oxygen showed promising physiological effects compared to conventional oxygen. During weaning from mechanical ventilation in patients with or at risk of developing hypercapnia, high-flow nasal oxygen showed encouraging results, especially when applied alternating with sessions of noninvasive ventilation. Optimal settings of high-flow nasal oxygen in hypercapnic patients include the use of a smaller-size cannula, flows ranging between 30 and 40 L/min, and FiO₂ adjusted to obtain SpO₂ between 88% and 92%. Specific interfaces, such as asymmetric cannulas, may further enhance the benefits of a high flow in terms of carbon dioxide clearance. In this narrative review, we provide an updated overview of the physiological rationale and clinical evidence concerning the use of high-flow nasal oxygen in patients with acute hypercapnic respiratory failure.