Optimal Positive End-expiratory Pressure Research Articles

Standard versus individualised positive end-expiratory pressure (PEEP) compared by electrical impedance tomography in neurocritical care: a pilot prospective single centre study

BackgroundIndividualised bedside adjustment of mechanical ventilation is a standard strategy in acute coma neurocritical care patients. This involves customising positive end-expiratory pressure (PEEP), which could improve ventilation homogeneity and arterial oxygenation. This study aimed to determine whether PEEP titrated by electrical impedance tomography (EIT) results in different lung ventilation homogeneity when compared to standard PEEP of 5 cmH2O in mechanically ventilated patients with healthy lungs.MethodsIn this prospective single-centre study, we evaluated 55 acute adult neurocritical care patients starting controlled ventilation with PEEPs close to 5 cmH2O. Next, the optimal PEEP was identified by EIT-guided decremental PEEP titration, probing PEEP levels between 9 and 2 cmH2O and finding the minimal amount of collapse and overdistension. EIT-derived parameters of ventilation homogeneity were evaluated before and after the PEEP titration and after the adjustment of PEEP to its optimal value. Non-EIT-based parameters, such as peripheral capillary Hb saturation (SpO2) and end-tidal pressure of CO2, were recorded hourly and analysed before PEEP titration and after PEEP adjustment.ResultsThe mean PEEP value before titration was 4.75 ± 0.94 cmH2O (ranging from 3 to max 8 cmH2O), 4.29 ± 1.24 cmH2O after titration and before PEEP adjustment, and 4.26 ± 1.5 cmH2O after PEEP adjustment. No statistically significant differences in ventilation homogeneity were observed due to the adjustment of PEEP found by PEEP titration. We also found non-significant changes in non-EIT-based parameters following the PEEP titration and subsequent PEEP adjustment, except for the mean arterial pressure, which dropped statistically significantly (with a mean difference of 3.2 mmHg, 95% CI 0.45 to 6.0 cmH2O, p < 0.001).ConclusionAdjusting PEEP to values derived from PEEP titration guided by EIT does not provide any significant changes in ventilation homogeneity as assessed by EIT to ventilated patients with healthy lungs, provided the change in PEEP does not exceed three cmH2O. Thus, a reduction in PEEP determined through PEEP titration that is not greater than 3 cmH2O from an initial value of 5 cmH2O is unlikely to affect ventilation homogeneity significantly, which could benefit mechanically ventilated neurocritical care patients.

Optimal Positive End-expiratory Pressure Levels in Tuberculosis-associated Acute Respiratory Distress Syndrome.

The objective is to assess lung compliance and identify the optimal positive end-expiratory pressure (PEEP) levels in patients with tuberculosis-associated Acute Respiratory Distress Syndrome (TB-ARDS) compared to non-TB-ARDS patients. This observational case-control study utilized electrical impedance tomography to evaluate lung mechanics in 20 TB-ARDS and 20 non-TB-ARDS patients. Participants underwent PEEP titration from 23 to 5 cm H2O in 2 cm H2O decrements. Lung compliance and the rates of hyperdistention and collapse were assessed at each PEEP level. Delta impedance values showed higher amounts in a PEEP range of 11-17 cm H2O and in patients with TB-ARDS (P > 0.05). In addition, both hyperdistention and collapse rates were nonsignificantly higher in TB-ARDS patients (P > 0.05), and the compromised levels of hyperdistention and collapse rates were at 15-17 cm H2O, indicating the most favorable PEEP level. The observed patterns of hyperdistention and collapse rates across various PEEP levels provide valuable insights into the susceptibility of TB-ARDS patients to barotrauma. Notably, the identified optimal PEEP range between 15 and 17 cm H2O may guide ventilator management strategies in mitigating both hyperdistention and collapse; nonetheless, due to the high variability of lung compliances within groups, we strongly recommend individualized consideration for tailored respiratory support and evaluation.

Tailoring the Best Positive End-Expiratory Pressure Through Invasive Right Ventricular Pressure-Volume Loops in a Patient Supported by Veno-Arterial Extracorporeal Membrane Oxygenation.

Patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO) typically suffer from cardiogenic pulmonary edema and lung atelectasis, which can exacerbate right ventricular (RV) dysfunction through an increase in lung elastance and RV afterload. Invasive mechanical ventilation settings, and positive end-expiratory pressure (PEEP) in particular, can help to improve RV performance by optimizing lung recruitment and minimizing alveolar overdistention. In this report, we present a VA-ECMO supported patient in whom in vivo RV pressure-volume (PV) loops were measured during a decremental PEEP trial, leading to the identification of an optimum PEEP level from a cardio-respiratory viewpoint. This innovative approach of tailoring mechanical ventilation settings according to cardio-respiratory physiology through in vivo RV PV loops may provide a novel way to optimize hemodynamics and patient outcomes.

Determination of optimal positive end-expiratory pressure using electrical impedance tomography in infants under general anesthesia: Comparison between supine and prone positions.

This study determined the optimal positive end-expiratory pressure levels in infants in supine and prone positions under general anesthesia using electrical impedance tomography (EIT). This prospective observational single-centre study included infants scheduled for surgery in the prone position. An electrical impedance tomography sensor was applied after inducing general anesthesia. The optimal positive end-expiratory pressure in the supine position was determined in a decremental trial based on EIT and compliance. Subsequently, the patient's position was changed to prone. Electrical impedance tomography parameters, including global inhomogeneity index, regional ventilation delay, opening pressure, the centre of ventilation, and pendelluft volume, were continuously obtained up to 1 h after prone positioning. The optimal positive end-expiratory pressure in the prone position was similarly determined. Data from 30 infants were analyzed. The mean value of electrical impedance tomography-based optimal positive end-expiratory pressure in the prone position was significantly higher than that in the supine position [10.9 (1.6) cmH2O and 6.1 (0.9) cmH2O, respectively (p < .001)]. Significant differences were observed between electrical impedance tomography- and compliance-based optimal positive end-expiratory pressure. Peak and mean airway, plateau, and driving pressures increased 1 h after prone positioning compared with those in the supine position. In addition, the centre of ventilation for balance in ventilation between the ventral and dorsal regions improved. The prone position required higher positive end-expiratory pressure than the supine position in mechanically ventilated infants under general anesthesia. EIT is a promising tool to find the optimal positive end-expiratory pressure, which needs to be individualized.

Bedside personalized methods based on electrical impedance tomography or respiratory mechanics to set PEEP in ARDS and recruitment-to-inflation ratio: a physiologic study

BackgroundVarious Positive End-Expiratory Pressure (PEEP) titration strategies have been proposed to optimize ventilation in patients with acute respiratory distress syndrome (ARDS). We aimed to compare PEEP titration strategies based on electrical impedance tomography (EIT) to methods derived from respiratory system mechanics with or without esophageal pressure measurements, in terms of PEEP levels and association with recruitability.MethodsNineteen patients with ARDS were enrolled. Recruitability was assessed by the estimated Recruitment-to-Inflation ratio (R/Iest) between PEEP 15 and 5 cmH2O. Then, a decremental PEEP trial from PEEP 20 to 5 cmH2O was performed. PEEP levels determined by the following strategies were studied: (1) plateau pressure 28–30 cmH2O (Express), (2) minimal positive expiratory transpulmonary pressure (Positive PLe), (3) center of ventilation closest to 0.5 (CoV) and (4) intersection of the EIT-based overdistension and lung collapse curves (Crossing Point). In addition, the PEEP levels determined by the Crossing Point strategy were assessed using different PEEP ranges during the decremental PEEP trial.ResultsExpress and CoV strategies led to higher PEEP levels than the Positive PLe and Crossing Point ones (17 [14–17], 20 [17–20], 8 [5–11], 10 [8–11] respectively, p < 0.001). For each strategy, there was no significant association between the optimal PEEP level and R/Iest (Crossing Point: r2 = 0.073, p = 0.263; CoV: r2 < 0.001, p = 0.941; Express: r2 < 0.001, p = 0.920; Positive PLe: r2 = 0.037, p = 0.461). The PEEP level obtained with the Crossing Point strategy was impacted by the PEEP range used during the decremental PEEP trial.ConclusionsCoV and Express strategies led to higher PEEP levels than the Crossing Point and Positive PLe strategies. Optimal PEEP levels proposed by these four methods were not associated with recruitability. Recruitability should be specifically assessed in ARDS patients to optimize PEEP titration.

Pulmonary response prediction through personalized basis functions in a virtual patient model

Background and ObjectiveRecruitment maneuvers with subsequent positive-end-expiratory-pressure (PEEP) have proven effective in recruiting lung volume and preventing alveoli collapse. However, determining a safe, effective, and patient-specific PEEP is not standardized, and this more optimal PEEP level evolves with patient condition, requiring personalised monitoring and care approaches to maintain optimal ventilation settings. MethodsThis research examines 3 physiologically relevant basis function sets (exponential, parabolic, cumulative) to enable better prediction of elastance evolution for a virtual patient or digital twin model of MV lung mechanics, including novel elements to model and predict distension elastance. Prediction accuracy and robustness are validated against recruitment maneuver data from 18 volume-controlled ventilation (VCV) patients at 7 different baseline PEEP levels (0 to 12 cmH2O) and 14 pressure-controlled ventilation (PCV) patients at 4 different baseline PEEP levels (6 to 12 cmH2O), yielding 623 and 294 prediction cases, respectively. Predictions were made up to 12 cmH2O of added PEEP ahead, covering 6 × 2 cmH2O PEEP steps. ResultsThe 3 basis function sets yield median absolute peak inspiratory pressure (PIP) prediction error of 1.63 cmH2O for VCV patients, and median peak inspiratory volume (PIV) prediction error of 0.028 L for PCV patients. The exponential basis function set yields a better trade-off of overall performance across VCV and PCV prediction than parabolic and cumulative basis function sets from other studies. Comparing predicted and clinically measured distension prediction in VCV demonstrated consistent, robust high accuracy with R2 = 0.90–0.95. ConclusionsThe results demonstrate recruitment mechanics are best captured by an exponential basis function across different mechanical ventilation modes, matching physiological expectations, and accurately capture, for the first time, distension mechanics to within 5–10 % accuracy. Enabling the risk of lung injury to be predicted before changing ventilator settings. The overall outcomes significantly extend and more fully validate this digital twin or virtual mechanical ventilation patient model.

Exploring phenotype-based ventilator parameter optimization to mitigate postoperative pulmonary complications: a retrospective observational cohort study.

To identify tidal volume (VT) and positive end-expiratory pressure (PEEP) associated with the lowest incidence and severity of postoperative pulmonary complications (PPCs) for each phenotype based on preoperative characteristics. The subjects of this retrospective observational cohort study were 34,910 adults who underwent surgery, using general anesthesia with mechanical ventilation. Initially, the least absolute shrinkage and selection operator regression was employed to select relevant preoperative characteristics. Then, the classification and regression tree (CART) was built to identify phenotypes. Finally, we computed the area under the receiver operating characteristic curves from logistic regressions to identify VT and PEEP associated with the lowest incidence and severity of PPCs for each phenotype. CARTs classified seven phenotypes for each outcome. A probability of the development of PPCs ranged from the lowest (3.51%) to the highest (68.57%), whereas the probability of the development of the highest level of PPC severity ranged from 3.3% to 91.0%. Across all phenotypes, the VT and PEEP associated with the most desirable outcomes were within a small range of VT 7-8ml/kg predicted body weight with PEEP of between 6 and 8 cmH2O. The ranges of optimal VT and PEEP were small, regardless of the phenotypes, which had a wide range of risk profiles.

Optimal positive end-expiratory pressure titration of intraoperative mechanical ventilation in different operative positions of female patients under general anesthesia

ObjectiveThis study aimed to compare the effectiveness and safety of different titrated methods used to determine individual positive end-expiratory pressure (PEEP) for intraoperative mechanical ventilation in female patients undergoing general anesthesia in different operative positions, and provide reference ranges of optimal PEEP values based on the titration. MethodsA total of 123 female patients who underwent elective open abdominal surgery under general anesthesia were included in this study. After endotracheal intubation, patients' body position was adjusted to the supine position, Trendelenburg positions at 10° and 20° respectively. PEEP was titrated from 20 cmH2O to 4 cmH2O, decreasing by 2 cmH2O every 1 min. Electrical impedance tomography (EIT), hemodynamic and respiratory mechanics parameters were continuously monitored and recorded. Optimal PEEP values and reference ranges were respectively calculated based on optimal EIT parameters, mean arterial pressure (MAP), and lung dynamic compliance (Cdyn). ResultsEIT-guided optimal PEEP was found to have higher values than those of the MAP-guided and Cdyn-guided methods for all three body positions (P < 0.001), and it was observed to more significantly inhibit hemodynamics (P < 0.05). The variable coefficients of EIT-guided optimal PEEP values were smaller than those of the other two methods, and this technique could provide better ventilation uniformity for dorsal/ventral lung fields and better balance for pulmonary atelectasis/collapse. The 95% reference ranges of EIT-guided optimal PEEP values were 4.6–13.8 cmH2O, 7.0–15.0 cmH2O and 8.6–17.0 cmH2O for the supine position, Trendelenburg 10°, and Trendelenburg 20° positions, respectively. ConclusionEIT-guided optimal PEEP titration was found to be a superior method for lung protective ventilation in different operative positions under general anesthesia. The calculated reference ranges of PEEP values based on the EIT-guided method can be used as a reference for intraoperative mechanical ventilation.

Setting the optimal positive end-expiratory pressure: a narrative review.

The primary goals of positive end-expiratory pressure (PEEP) are to restore functional residual capacity through recruitment and prevention of alveolar collapse. Through these mechanisms, PEEP improves arterial oxygenation and may reduce the risk of ventilator-induced lung injury (VILI). Because of the many potential negative effects associated with the use of PEEP, much research has concentrated on determining the optimal PEEP setting. Arterial oxygenation targets and pressure-volume loops have been utilized to set the optimal PEEP for decades. Several other techniques have been suggested, including the use of PEEP tables, compliance, driving pressure (DP), stress index (SI), transpulmonary pressures, imaging, and electrical impedance tomography. Each of these techniques has its own benefits and limitations and there is currently not one technique that is recommended above all others.

Methods for determination of optimal positive end-expiratory pressure: a protocol for a scoping review

IntroductionTitrated application of positive end-expiratory pressure (PEEP) is an important part of any mechanical ventilation strategy. However, the method by which the optimal PEEP is determined and titrated varies widely....

Effect of Lung Compliance-Based Optimum Pressure Versus Fixed Positive End-Expiratory Pressure on Lung Atelectasis Assessed by Modified Lung Ultrasound Score in Laparoscopic Gynecological Surgery: A Prospective Randomized Controlled Trial.

Lung protective ventilation during the intraoperative period is now well established. However, the additional role of positive end-expiratory pressure (PEEP) during the intraoperative period remains uncertain in major laparoscopic gynecological surgery. The authors hypothesized that compliance-based optimum PEEP titration reduces postoperative lung atelectasis and improves outcomes. Patients undergoing major laparoscopic pelvic gynecological surgeries with healthy lungs were randomized to the fixed PEEP group (PEEP 5 cm H2O and recruitment maneuver {RM}) and optimum PEEP group (compliance-based PEEP and RM). Lung ultrasound and arterial blood gas analysis were performed at four time points. Modified lung ultrasound scoring was done, and the same was used as means of assessing lung aeration and the amount of lung atelectasis. Postoperative supplemental oxygen requirement and duration were also assessed and compared. Lung ultrasound score (LUS) 30 minutes after extubation in fixed (Group F) and optimum (Group O) PEEP groups were median (interquartile range {IQR}) 3 (2-3) versus 1 (1-2),p=0.0001. Ventilatory parameters between Group F and Group Oafter lung recruitmentwere tidal volume (mean357 mL {SD: 35} versus 362 mL {SD: 22}, p=0.46), PEEP (median, 5 cm H2O {IQR: 5-5} versus median 16 cm H2O {IQR: 14-18}), peak airway pressure (median 26 cm H2O {IQR: 24-28} versus median30 cm H2O {IQR: 28-32} p<0.0001), plateau pressure (median22 cm H2O {IQR: 20-24} versus median26 cm H2O {IQR: 24-28} p<0.0001), static compliance (32.07±8.36 mL cm H2O-1 versus 39.58±8.99 mL cm H2O-1, p=0.0002). The number of patients requiring postoperative oxygen therapy to maintain SpO2>94% after extubation in postanesthesia care unit (PACU) was statistically significantly greater in group F (39/41 {95%} versus 30/41 {73%}, p=0.007). Median (IQR) duration of oxygenation therapy in the first 24 hours of the postoperative period between Group F and Group O differed with statistical significance, with the median (IQR) values being 25 (20-30) minutes versus 10 (0-15) minutes (p<0.0001). The modified lung ultrasound score significantly differed intraoperatively between the two groups, with lower scores in the optimum PEEP group. This has reflected improved postoperative outcomes in optimum PEEP group patients, with fewer patients requiring postoperative oxygen supplementation and reduced supplemental oxygen requirement duration.

Lung protection effect of EIT-based individualized protective ventilation strategy in patients with partial pulmonary resection.

This study aimed to evaluate the lung protection effect of an individualized protective ventilation strategy based on lung impedance tomography (EIT) technology in patients with partial pulmonary resection. Eighty patients of any gender, American Society of Anesthesiologists (ASA) classification I-II, age 30-64 years and body mass index (BMI) 18-28 kg/m2 who underwent elective thoracoscopic partial lung resection were selected and divided into 2 groups (n=40) using the random number table method: [positive end-expiratory pressure (PEEP) by electrical impedance tomography (EIT)] PEEPEIT group (experimental group) and control group. The PEEPEIT group used volume-controlled ventilation after one-lung ventilation, setting a tidal volume of 6 ml/kg and titrating the optimal PEEP value by EIT. Group C used volume-controlled ventilation after one-lung ventilation, setting a tidal volume of 6 ml/kg and a PEEP of 5 cm H2O. Clinical data were collected and recorded at 5 min after double lung ventilation (T0), single lung ventilation, 30 min after PEEP setting (T1), 60 min after PEEP setting (T2), the end of surgery, 10 min after resumption of double lung ventilation (T3) and 10 min after removal of the tracheal tube (T4), and serum surface active substance-associated protein-A (SP-A) concentrations were measured at T0, T3 and 1 d after surgery (T5). PEEP values were higher in the PEEPEIT group than in the control group at T1 and T2 (p-value <0.05); oxygenation index (OI) was higher in the PEEPEIT group compared to the control group at T2 and T3 (p-value <0.05); pulmonary dynamic compliance (Cdyn) was higher in the PEEPEIT group compared to the control group at T1 and T2 (p-value <0.05); intrapulmonary shunt rate (Qs/Qt) was lower in the PEEPEIT group compared to the control group at T1, T2 and at T3, the intrapulmonary shunt rate (Qs/Qt) was reduced in the PEEPEIT group compared to group C (p-value <0.05); at T5, the SP-A protein was reduced in the PEEPEIT group compared to group C. There was no statistically significant difference in the incidence of postoperative pulmonary complications between the two groups (p-value >0.05). The EIT-guided individualized protective ventilation strategy has a lung-protective effect in patients undergoing thoracoscopic partial lung resection.

Using lung ultrasound to guide PEEP determination in mechanically ventilated patients with acute respiratory distress syndrome

Supportive care with mechanical ventilation is the cornerstone of management for acute respiratory distress syndrome (ARDS). Positive end-expiratory pressure (PEEP) is often applied in mechanically ventilated patients with ARDS to improve oxygenation; however, determining the optimal PEEP level—the pressure that maximizes clinical benefit while minimizing risks of ventilator-induced lung injury and other harms—for each patient can be challenging. Recently, transthoracic lung ultrasonography (also called lung ultrasound) has been proposed as a tool to guide PEEP determination in patients with ARDS. This paper reviews the history of use of lung ultrasound as a method to guide PEEP determination and the four published studies which compared it to other techniques of PEEP determination, such as the oxygenation and PV-curve methods.

Optimal positive end-expiratory pressure obtained with titration of a fraction of inspiratory oxygen: a randomized controlled clinical trial.

Optimal intraoperative positive end-expiratory pressure (PEEP) improves patient outcomes. Pulse oximetry has been used to determine the lung opening and closing pressures. Therefore, we hypothesized that intraoperative optimal PEEP obtained by titrating inspiratory oxygen fraction (FiO2) guided with pulse oximetry could improve perioperative oxygenation. Forty-six males undergoing elective robotic-assisted laparoscopic prostatectomy were randomly assigned to either the optimal PEEP group (group O; n=23) or the fixed PEEP of 5 cmH2O group (group C; n=23). Optimal PEEP, defined as the PEEP with the lowest FiO2 or 0.21 to maintain SpO2 greater than or equal to 95%, was obtained in both groups after placing the patients in the Trendelenburg position and conducting intraperitoneal insufflation. Optimal PEEP was maintained for patients in group O. A PEEP of 5 cmH2O intraoperatively was maintained for patients in group C. Both groups were extubated in a semisitting position once the extubation criteria were met. The primary outcome was the arterial oxygen partial pressure (PaO2) divided by the inspiratory oxygen fraction (FiO2) prior to extubation. The secondary outcome was the incidence of postoperative hypoxemia (SpO2 less than 92% on room air after extubation) in the postanesthesia care unit (PACU). The median optimal PEEP was 16 cmH2O (IQR 12-18). The PaO2/FiO2 prior to extubation was significantly higher in group O than in group C (77.0±4.9 kPa vs. 60.6±5.9 kPa; P=0.04). PaO2/FiO2 was also significantly higher in group O 30 minutes after extubation (57.6±1.9 vs. 46.6±1.8 kPa; P=0.01). The incidence of hypoxemia on room air in the PACU was significantly lower in group O than in group C (4.3% vs. 30.4%; P=0.02). Intraoperative optimal PEEP can be achieved by a titration of FiO2 guided with SpO2. Maintaining intraoperative optimal PEEP improves intraoperative oxygenation and reduces the incidence of postoperative hypoxemia. The study was prospectively registered on September 10, 2021, in the Chinese Clinical Trial Registry (identifier: ChiCTR2100051010).

Optimal positive end-expiratory pressure reduces right ventricular dysfunction in COVID-19 patients on venovenous extracorporeal membrane oxygenation: A retrospective single-center study

While mechanical ventilation practices on venovenous extracorporeal membrane oxygenation (VV ECMO) are variable, most institutions utilize a lung rest strategy utilizing relatively low positive end-expiratory pressure (PEEP). The effect of PEEP titration using esophageal manometry during VV ECMO on pulmonary and cardiac function is unknown. This was a retrospective study of 69 patients initiated on VV ECMO between March 2020 through November 2021. Patients underwent standard PEEP (typically 10 cm H2O) or optimal PEEP (PEEP titrated to an end-expiratory transpulmonary pressure 0–3 cm H2O) throughout the ECMO run. The optimal PEEP strategy had higher levels of applied PEEP (17.9 vs. 10.8 cm H2O on day 2 of ECMO), decreased incidence of hemodynamically significant RV dysfunction (4.55% vs. 44.0%, p = 0.0001), and higher survival to decannulation (72.7% vs. 44.0%, p = 0.022). Survival to discharge did not reach statistical significance (61.4% vs. 44.0%, p = 0.211). In univariate logistic regression analysis, optimal PEEP was associated with less hemodynamically significant RV dysfunction with an odds ratio (OR) of 0.06 (95% confidence interval [CI] = 0.01–0.27, p = 0.0008) and increased survival to decannulation with an OR of 3.39 (95% CI 1.23–9.79), p = 0.02), though other confounding factors may have contributed.

Individualized positive end-expiratory pressure guided by respiratory mechanics during anesthesia for the prevention of postoperative pulmonary complications: a systematic review and meta-analysis.

The optimization of positive end-expiratory pressure (PEEP) according to respiratory mechanics [driving pressure or respiratory system compliance (Crs)] is a simple and straightforward strategy. However, its validity to prevent postoperative pulmonary complications (PPCs) remains unclear. Here, we performed a meta-analysis to assess such efficacy. We searched PubMed, Embase, and the Cochrane Library to identify randomized controlled trials (RCTs) that compared personalized PEEP based on respiratory mechanics and constant PEEP to prevent PPCs in adults. The primary outcome was PPCs. Fourteen studies with 1105 patients were included. Compared with those who received constant PEEP, patients who received optimized PEEP exhibited a significant reduction in the incidence of PPCs (RR = 0.54, 95% CI 0.42 to 0.69). The results of commonly happened PPCs (pulmonary infections, hypoxemia, and atelectasis but not pleural effusion) also supported individualized PEEP group. Moreover, the application of PEEP based on respiratory mechanics improved intraoperative respiratory mechanics (driving pressure and Crs) and oxygenation. The PEEP titration method based on respiratory mechanics seems to work positively for lung protection in surgical patients undergoing general anesthesia.

Evaluation of time constant, dead space and compliance to determine PEEP in COVID-19 ARDS: a prospective observational study

Multiple variables exist to identify optimal positive end-expiratory pressure (PEEP) to keep alveolar recruitment in acute respiratory distress syndrome (ARDS). These include increased respiratory system compliance (CRS ) and decreased dead space to tidal volume fraction (Vd/Vt). Increasing CRS reflects improved lung volume, whereas decreasing Vd/Vt reflects improved ventilation/perfusion matching. An increasing expiratory time constant (RCEXP ) reflects both, changes in CRS and alterations in tissue resistance. Whether RCEXP might reflect corresponding changes in Vd/Vt better than CRS during alveolar recruitment is unknown. This prospective observational study examined the correlation between these variables during ascending PEEP titration in patients with novel Coronavirus disease (COVID-19) related ARDS. PEEP titrations were performed in ten patients with COVID-19 ARDS under passive, pressure-controlled ventilation with a fixed driving pressure of 14 cmH2O. PEEP was increased stepwise between 5 and 20 cmH2O with 2 minutes allowed for Vd/Vt equilibration. RCEXP , Vd/Vt and CRS were recorded at each PEEP level and statistically assessed.The overall correlation between Vd/Vt and RCEXP was −0.72 (95% CI: −0.57 to −0.82); p &lt; 0.0001. CRS had a weaker correlation with Vd/Vt (−0.47 (95% CI: −0.25 to −0.64); p &lt; 0.0001). RCEXP was the highest at 12 cmH2O of PEEP whereas Vd/Vt was the lowest at 10 cmH2O of PEEP and CRS was the highest at PEEP of 15 cmH2O.Both parameters of exhalation, Vd/Vt and RCEXP, are strongly correlated which likely reflects corresponding mechanical and global ventilation/perfusion responses during ascending PEEP titration.

Time constant to determine PEEP levels in mechanically ventilated COVID-19 ARDS: a feasibility study

BackgroundWe hypothesized that the measured expiratory time constant (TauE) could be a bedside parameter for the evaluation of positive end-expiratory pressure (PEEP) settings in mechanically ventilated COVID-19 patients during pressure-controlled ventilation (PCV).MethodsA prospective study was conducted including consecutively admitted adults (n = 16) with COVID-19-related ARDS requiring mechanical ventilation. A PEEP titration using PCV with a fixed driving pressure of 14 cmH2O was performed and TauE recorded at each PEEP level (0 to 18 cmH2O) in prone (n = 29) or supine (n = 24) positions. The PEEP setting with the highest TauE (TauEMAX) was considered to represent the best tradeoff between recruitment and overdistention.ResultsTwo groups of patterns were observed in the TauE plots: recruitable (R) (75%) and nonrecruitable (NR) (25%). In the R group, the optimal PEEP and PEEP ranges were 8 ± 3 cmH2O and 6–10 cmH2O for the prone position and 9 ± 3 cmH2O and 7–12 cmH2O for the supine position. In the NR group, the optimal PEEP and PEEP ranges were 4 ± 4 cmH2O and 1–8 cmH2O for the prone position and 5 ± 3 cmH2O and 1–7 cmH2O for the supine position, respectively. The R group showed significantly higher optimal PEEP (p < 0.004) and PEEP ranges (p < 0.001) than the NR group. Forty-five percent of measurements resulted in the most optimal PEEP being significantly different between the positions (p < 0.01). Moderate positive correlation has been found between TauE vs CRS at all PEEP levels (r2 = 0.43, p < 0.001).ConclusionsTauE may be a novel method to assess PEEP levels. There was wide variation in patient responses to PEEP, which indicates the need for personalized evaluation.

Dynamic positive end-expiratory pressure strategies using time and pressure recruitment at birth reduce early expression of lung injury in preterm lambs.

Positive end-expiratory pressure (PEEP) is critical to the preterm lung at birth, but the optimal PEEP level remains uncertain. The objective of this study was to determine the effect of maximum PEEP levels at birth on the physiological and injury response in preterm lambs. Steroid-exposed preterm lambs (124-127 days gestation; n = 65) were randomly assigned from birth to either 1) positive pressure ventilation (PPV) at 8 cmH2O PEEP or 3-min dynamic stepwise PEEP strategy (DynPEEP), with either 2) 20 cmH2O maximum PEEP (10 PEEP second steps) or 3) 14 cmH2O maximum PEEP (20-s steps), all followed by standardized PPV for 90 min. Lung mechanics, gas exchange, regional ventilation and aeration (electrical impedance tomography), and histological and molecular measures of lung injury were compared between groups. Dynamic compliance was greatest using a maximum 20 cmH2O (DynPEEP). There were no differences in gas exchange, end-expiratory volume, and ventilator requirements. Regional ventilation became more uniform with time following all PEEP strategies. For all groups, gene expression of markers of early lung injury was greater in the gravity nondependent lung, and inversely related to the magnitude of PEEP, being lowest in the 20 cmH2O DynPEEP group overall. PEEP levels had no impact on lung injury in the dependent lung. Transient high maximum PEEP levels using dynamic PEEP strategies may confer more lung protection at birth.

Validation of lung sonography in the implementation of open lung strategy as a recruitment maneuver versus traditional sustained inflation in acute respiratory distress syndrome patients

Introduction Acute respiratory distress syndrome (ARDS) is a serious problem in critically ill patients with high mortality rates. Lung recruitment maneuvers (RM) are important in the treatment of ARDS with an aim to improve oxygenation. There are many approved methods for lung recruitment like the traditional sustained inflation technique and the stepladder positive end-expiratory pressure (PEEP) titration technique. The traditional methods to evaluate RM like computed tomography and pressure–volume curves showed some limitation and disadvantages. Thus, bedside ultrasonography (US) could be a safe bedside tool to evaluate lung aeration and the effectiveness of RM defining the optimum PEEP needed and preventing lung overdistension. Aim To evaluate the usefulness of lung US as a guide to follow up RM by PEEP titration technique in comparison to sustained inflation technique. Patients and methods In all, 40 ARDS patients were segregated into two groups: group 1 included 20 patients who were subjected to traditional sustained inflation RM and group 2 included 20 patients were subjected to sonar-guided lung recruitment. US scoring, PO2, PO2/FiO2, and lung compliance were used to evaluate the pulmonary recruitment end point defining the best PEEP. Results Lung compliance, PO2, and PO2/FiO2 were significantly increased after RM in both groups (P&lt;0.05); however, there was no statistically significant difference between the two groups. The best PEEP in group 1 and group 2 were 20.60±3.485 and 15.90±5.340, respectively, with a significant difference between the two groups (P=0.002). There was no statically significant difference between the two groups regarding complication, vent days and ICU days. Conclusion Bedside US can be very useful in the evaluation and management of mechanically ventilated patients in ICUs and to guide the RM in ARDS patients. There is no significant difference between the sustained inflation RM and the sonar-guided stepwise PEEP titration RM regarding oxygenation and compliance except for the level of PEEP reached, which is lower in the stepwise PEEP titration group giving less potentiality for complications.