Time required for equilibration of arterial oxygen pressure after setting optimal positive end-expiratory pressure in acute respiratory distress syndrome

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

BACKGROUND

Individualised 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.

METHODS

In 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.

RESULTS

The 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).

CONCLUSION

Adjusting 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.

Use of Lung Ultrasound for Assessment of Lung Recruitment Maneuvers in Patients with ARDS

BACKGROUND: Positive pressure mechanical ventilation is a non-physiological intervention that saves lives but is not free of important side effects. It invariably results in different degrees of collapse of small airways. Recruitment maneuver (RM) aims to resolve lung collapse by a brief and controlled increment in airway pressure while positive end-expiratory pressure (PEEP) afterward keeps the lungs open. Therefore, ideally RM and PEEP selection must be individualized and this can only be done when guided by specific monitoring tools since lung’s opening and closing pressures vary among patients with different lung conditions. AIM: The aim of this study was to explore the clinical value of ultrasonic monitoring in the assessment of pulmonary recruitment and the best PEEP. PATIENTS AND METHODS: This study was conducted on 120 patients, 30 were excluded as in whom lung collapse cannot be confirmed then the rest were 90 patients from whom another 25 patients excluded as they were hemodynamically unstable the rest 65 patients were divided into two groups: Group A: Included 50 mechanically ventilated patients with ARDS, underwent lung recruitment using lung ultrasound and Group B: Included 15 mechanically ventilated patients with ARDS, underwent lung recruitment using oxygenation index. This prospective study was held at many critical care departments around Egypt. RESULTS: We noticed that lung recruitment in both groups significantly increased Pao2/Fio2 ratio immediately after recruitment compared with basal state and also significantly increase dynamic compliance compared with basal state. The increase in PF ratio immediately was significantly more in ultrasound group than in oxygenation group. Furthermore, we noticed that that P/F ratio 12 h after recruitment decreased compared with P/F ratio immediately after recruitment but significantly increased compared with basal state before recruitment and also we found that the increase in P/F ratio 12 h after recruitment was more significantly in lung ultrasound group than in oxygenation group. Furthermore, we noticed that lung recruitment (both lung ultrasound and oxygenation group) significantly increase RV function using TAPSE compared with basal state. Both opening pressure and optimal PEEP were significantly higher in lung ultrasound group than in oxygenation group. In our study, opening pressure was 37.28 ± 1.25 in lung ultrasound group and was 36.67±0.98 in oxygenation group and optimal PEEP was 14.64 ± 1.08 in lung ultrasound group and was 13.13 ± 0.74 in oxygenation group. CONCLUSION: Lung US is an effective mean of evaluating and guiding alveolar recruitment in ARDS. Compared with the maximal oxygenation–guided method, the protocol for reaeration in US-guided lung recruitment achieved a higher opening pressure, resulted in greater improvements in lung aeration, and substantially reduced lung heterogeneity in ARDS.

Equilibration Time Required for Respiratory System Compliance and Oxygenation Response Following Changes in Positive End-Expiratory Pressure in Mechanically Ventilated Children

OBJECTIVES

Increases in positive end-expiratory pressure are implemented to improve oxygenation through the recruitment and stabilization of collapsed alveoli. However, the time it takes for a positive end-expiratory pressure change to have maximum effect upon oxygenation and pulmonary compliance has not been adequately described in children. Therefore, we sought to quantify the time required for oxygenation and pulmonary system compliance changes in children requiring mechanical ventilation.

DESIGN

Retrospective analysis of continuous data.

SETTINGS

Multidisciplinary ICU of a pediatric university hospital.

PATIENTS

Mechanically ventilated pediatric subjects.

INTERVENTIONS

A case was eligible for analysis if during a 90-minute window following an increase in positive end-expiratory pressure, no other changes to the ventilator were made, ventilator and physiologic data were continuously available and a positive oxygenation response was observed. Time to 90% (T90) of the maximum change in oxygenation and compliance was computed. Differences between oxygenation and compliance T90 were compared using a paired t test. The effect of severity of illness (by oxygen saturation index) upon oxygenation and compliance was analyzed.

MEASUREMENTS AND MAIN RESULTS

A total of 200 subjects were enrolled and 1,150 positive end-expiratory pressure change cases were analyzed. Of these, 54 subjects with 171 positive end-expiratory pressure change case were included in the analysis (67% were responders).Changes in dynamic compliance (T90 = 38 min) preceded changes in oxygenation (T90 = 71 min; p < 0.001). Oxygenation response differed depending on severity of illness quantified by oxygen saturation index; lung dysfunction was associated with a longer response time (p = 0.001).

CONCLUSIONS

T90 requires 38 and 71 minutes for dynamic pulmonary compliance and oxygenation, respectively; the latter was directly observed to be dependent upon severity of illness. To our knowledge, this is the first report of oxygenation and compliance equilibration data following positive end-expiratory pressure increases in pediatric mechanically ventilated subjects.

Positive End-Expiratory Pressure Lower Than the ARDS Network Protocol Is Associated with Higher Pediatric Acute Respiratory Distress Syndrome Mortality

RATIONALE

The ARDS Network (ARDSNet) used a positive end-expiratory pressure (PEEP)/Fi_O2 model in many studies. In general, pediatric intensivists use less PEEP and higher Fi_O2 than this model.

OBJECTIVES

To evaluate whether children managed with PEEP lower than recommended by the ARDSNet PEEP/Fi_O2 model had higher mortality.

METHODS

This was a multicenter, retrospective analysis of patients with pediatric acute respiratory distress syndrome (PARDS) managed without a formal PEEP/Fi_O2 protocol. Four distinct datasets were combined for analysis. We extracted time-matched PEEP/Fi_O2 values, calculating the difference between PEEP level and the ARDSNet-recommended PEEP level for a given Fi_O2. We analyzed the median difference over the first 24 hours of PARDS diagnosis against ICU mortality and adjusted for confounding variables, effect modifiers, or factors that may have affected the propensity to use lower PEEP.

MEASUREMENTS AND MAIN RESULTS

Of the 1,134 patients with PARDS, 26.6% were managed with lower PEEP relative to the amount of Fi_O2 recommended by the ARDSNet protocol. Patients managed with lower PEEP experienced higher mortality than those who were managed with PEEP levels in line with or higher than recommended by the protocol (P < 0.001). After adjustment for hypoxemia, inotropes, comorbidities, severity of illness, ventilator settings, nitric oxide, and dataset, PEEP lower than recommended by the protocol remained independently associated with higher mortality (odds ratio, 2.05; 95% confidence interval, 1.32-3.17). Findings were similar after propensity-based covariate adjustment (odds ratio, 2.00; 95% confidence interval, 1.24-3.22).

CONCLUSIONS

Patients with PARDS managed with lower PEEP relative to Fi_O2 than recommended by the ARDSNet model had higher mortality. Clinical trials targeting PEEP management in PARDS are needed.

Using machine learning models to predict oxygen saturation following ventilator support adjustment in critically ill children: A single center pilot study

BACKGROUND

In an intensive care units, experts in mechanical ventilation are not continuously at patient's bedside to adjust ventilation settings and to analyze the impact of these adjustments on gas exchange. The development of clinical decision support systems analyzing patients' data in real time offers an opportunity to fill this gap.

OBJECTIVE

The objective of this study was to determine whether a machine learning predictive model could be trained on a set of clinical data and used to predict transcutaneous hemoglobin oxygen saturation 5 min (5min SpO2) after a ventilator setting change.

DATA SOURCES

Data of mechanically ventilated children admitted between May 2015 and April 2017 were included and extracted from a high-resolution research database. More than 776,727 data rows were obtained from 610 patients, discretized into 3 class labels (< 84%, 85% to 91% and c92% to 100%).

PERFORMANCE METRICS OF PREDICTIVE MODELS

Due to data imbalance, four different data balancing processes were applied. Then, two machine learning models (artificial neural network and Bootstrap aggregation of complex decision trees) were trained and tested on these four different balanced datasets. The best model predicted SpO2 with area under the curves < 0.75.

CONCLUSION

This single center pilot study using machine learning predictive model resulted in an algorithm with poor accuracy. The comparison of machine learning models showed that bagged complex trees was a promising approach. However, there is a need to improve these models before incorporating them into a clinical decision support systems. One potentially solution for improving predictive model, would be to increase the amount of data available to limit over-fitting that is potentially one of the cause for poor classification performances for 2 of the three class labels.

Use of Lung Ultrasound to Assess the Efficacy of an Alveolar Recruitment Maneuver in Rabbits With Acute Respiratory Distress Syndrome

OBJECTIVES

To investigate the application of lung ultrasound (US) in the evaluation and implementation of alveolar recruitment maneuvers in acute respiratory distress syndrome (ARDS).

METHODS

Twelve rabbits with saline lavage-induced lung injury were randomly divided into 2 groups: one with alveolar recruitment guided by lung US and the other with alveolar recruitment guided by maximal oxygenation. Recruitment maneuvers were applied according to a stepwise incremental positive end-expiratory pressure method in both groups. In the oxygenation group, a sum of the partial pressures of oxygen and carbon dioxide exceeding 400 mm Hg was used to define adequate recruitment. In the lung US group, a new protocol for reaeration in US-guided lung recruitment was used to guide treatment. Evaluation by lung US, respiratory mechanical parameters, the Smith pathologic score (Crit Care Med 1997; 25:1888-1897), and wet-to-dry ratio were compared between the groups.

RESULTS

Opening pressure was significantly higher in the lung US group (mean ± SD, 23.4 ± 3.4 cm H2O) than the oxygenation group (18.7 ± 2.1 cm H2O; P < .05). The reaeration score in the lung US group significantly increased during alveolar recruitment (6.5 ± 1.6 points at baseline versus 13.8 ± 3.0 points after completion; P < .05). Lung compliance, dead space shunts, the Smith pathologic score, and tissue wet-to-dry ratio, however, were not significantly different between the groups.

CONCLUSIONS

Lung US is an effective means of evaluating and guiding alveolar recruitment in ARDS. Compared with the maximal oxygenation-guided method, the protocol for reaeration in US-guided lung recruitment achieved a higher opening pressure, resulted in greater improvements in lung aeration, and substantially reduced lung heterogeneity in ARDS.

Inhaled β2-Agonist Therapy Increases Functional Residual Capacity in Mechanically Ventilated Children With Respiratory Failure

OBJECTIVES

To test the hypothesis that in mechanically ventilated children with respiratory failure, aerosolized albuterol modifies functional residual capacity, lung mechanics, oxygen consumption, and hemodynamics.

DESIGN

Prospective, self-control clinical trial.

SETTING

A 24-bed PICU in a quaternary care, academic children's hospital.

PATIENTS

25 children (age range, 1-18 yr) undergoing mechanical ventilation to treat respiratory failure. Entry criteria included previously prescribed inhaled β2 agonists. Physiologic measurements were performed prior to and 20 minutes after administration of aerosolized albuterol solution. Functional residual capacity was determined via nitrogen washout.

INTERVENTIONS

Functional residual capacity, oxygen consumption, respiratory mechanics, and vital signs were measured were measured prior to and 20 minutes after administration of aerosolized albuterol solution. Functional residual capacity was determined via nitrogen washout.

MEASUREMENT AND MAIN RESULTS

At baseline, functional residual capacity is only 53% of predicted. After aerosolized albuterol, functional residual capacity increased by 18.3% (p = 0.008). Overall, aerosolized albuterol had no effect on airway resistance. However, in patients with an endotracheal tube size of more than or equal to 4.0 mm, resistance decreased from 33 ± 3 to 25 ± 3 (p < 0.02). Inhaled albuterol administration had no effect on oxygen consumption despite an increase in heart rate from 116 ± 2 to 128 ± 2 beats/min (p < 0.0001).

CONCLUSIONS

In pediatric patients with respiratory failure, aerosolized albuterol increases functional residual capacity without a decrease in resistance. In infants and children, aerosolized albuterol might favorably enhance pulmonary mechanics and thereby represent a novel strategy for lung recruitment in children with respiratory failure.

Positive end-expiratory pressure titration at bedside using electrical impedance tomography in post-operative cardiac surgery patients

BACKGROUND

Post-operative positive end-expiratory pressure (PEEP) setting to minimize the risk of ventilator-associated lung injury is still controversial. Assessment of regional ventilation distribution by electrical impedance tomography (EIT) might be superior as compared with global parameters. The aim of this prospective observational study was to compare global dynamic compliance (CRS ) with different EIT indices during a short clinical applicable descending PEEP trial.

METHODS

Twenty mechanically ventilated patients after elective cardiac surgery received a standard recruitment manoeuvre (RM) following descending PEEP trial in steps of 2 cmH2 O from PEEP 14 cmH2 O to 6 cmH2 O. During baseline and all PEEP steps, CRS was assessed and regional ventilation distribution was measured by means of EIT. The individual 'best' PEEP values for the derived EIT indices and CRS were calculated and compared.

RESULTS

The descending PEEP trial lasted less than 10 min. CRS increased after the RM and showed a maximum value at PEEP 8 cmH2 O. Ventilation distribution shifted more to dependent lung regions after RM and back to more non-dependent regions during the PEEP trial. Individual 'best' PEEP by CRS showed significantly lower values than 'best' PEEP by ventilation distribution measured with EIT indices.

CONCLUSION

During a short descending PEEP trial at bedside, EIT is capable of following the status of regional ventilation distribution in ventilated patients. The 'best' PEEP value identified by individual maximum CRS was lower than optimal PEEP levels as determined by means of EIT indices. EIT could help setting PEEP in post-operative ventilated patients.

Physiological predictors of survival during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

INTRODUCTION

Data that provide clinical criteria for the identification of patients likely to respond to high-frequency oscillatory ventilation (HFOV) are scarce. Our aim was to describe physiological predictors of survival during HFOV in adults with severe acute respiratory distress syndrome (ARDS) admitted to a respiratory failure center in the United Kingdom.

METHODS

Electronic records of 102 adults treated with HFOV were reviewed retrospectively. We used logistic regression and receiving-operator characteristics curve to test associations with oxygenation and mortality.

RESULTS

Patients had severe ARDS with a mean (SD) Murray's score of 2.98 (0.7). Partial pressure of oxygen in arterial blood to fraction of inspired oxygen (PaO2/FiO2) ratio and oxygenation index improved only in survivors. The earliest time point at which the two groups differed was at three hours after commencing HFOV. An improvement of >38% in PaO2/FiO2 occurring at any time within the first 72 hours, was the best predictor of survival at 30 days (area under the curve (AUC) of 0.83, sensitivity 93%, specificity 78% and a positive likelihood ratio (LR) of 4.3). These patients also had a 3.5 fold greater reduction in partial pressure of carbon dioxide in arterial blood (PaCO2). Multivariate analysis showed that HFOV was more effective in younger patients, when instituted early, and in patients with milder respiratory acidosis.

CONCLUSIONS

HFOV is effective in improving oxygenation in adults with ARDS, particularly when instituted early. Changes in PaO2/FiO2 during the first three hours of HFOV can identify those patients more likely to survive.

Oxygenation equilibration time after alteration of inspired oxygen in critically ill patients

To determine the time required for arterial oxygen partial pressure (Pao(2)) equilibration after a change in fractional inspired oxygen (Fio(2)) in intensive care unit (ICU) patients, a prospective study in a 7-bed university ICU was performed. Forty adult patients were examined using sequential arterial blood gas measurements after a .3 alteration in Fio(2). The Pao(2) value measured at 30 minutes after a step change in Fio(2) in both periods was accepted as representative of the equilibrium value for Pao(2). The mean equilibration time was 8.26+/-5.6 minutes and 4.5+/-2.65 minutes for increases and decreases in Pao(2), respectively (P=.003). The constant k values were .44 +/- .31 minutes and .72 +/- .7 minutes for increases and decreases in Pao(2), respectively. There was no significant difference between the increase and the decrease of 90% oxygenation times in the 2 groups (P=.150 and P=.446, respectively). The study confirms that a period of less than 10 minutes is adequate for 90% of the equilibration of Pao(2) to occur after an Fio(2) change in ICU patients.

Relationship between dynamic respiratory mechanics and disease heterogeneity in sheep lavage injury*

OBJECTIVE

Acute respiratory distress syndrome and acute lung injury are characterized by heterogeneous flooding/collapse of lung tissue. An emerging concept for managing these diseases is to set mechanical ventilation so as to minimize the impact of disease heterogeneity on lung mechanical stress and ventilation distribution. The goal of this study was to determine whether changes in lung mechanical heterogeneity with increasing positive end-expiratory pressure in an animal model of acute lung injury could be detected from the frequency responses of resistance and elastance.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a veterinary hospital.

SUBJECTS

Female sheep weighing 48 +/- 2 kg.

INTERVENTIONS

In five saline-lavaged sheep, we acquired whole-lung computed tomography scans, oxygenation, static elastance, and dynamic respiratory resistance and elastance at end-expiratory pressure levels of 7.5-20 cm H2O.

MEASUREMENTS AND MAIN RESULTS

As end-expiratory pressure increased, computed tomography-determined alveolar recruitment significantly increased but was accompanied by significant alveolar overdistension at 20 cm H2O. An optimal range of end-expiratory pressures (15-17.5 cm H2O) was identified where alveolar recruitment was significantly increased without significant overdistension. This range corresponded to the end-expiratory pressure levels that maximized oxygenation, minimized peak-to-peak ventilation pressures, and minimized indexes reflective of the mechanical heterogeneity (e.g., frequency dependence of respiratory resistance and low-frequency elastance). Static elastance did not demonstrate any significant pressure dependence or reveal an optimal end-expiratory pressure level.

CONCLUSIONS

We conclude that dynamic mechanics are more sensitive than static mechanics in the assessment of the functional trade-off of recruitment relative to overdistension in a sheep model of lung injury. We anticipate that monitoring of dynamic respiratory resistance and elastance ventilator settings can be used to optimize ventilator management in acute lung injury.

Effect of inspired oxygen fraction on alveolar derecruitment in acute respiratory distress syndrome

OBJECTIVE

High fractions of inspired oxygen (FIO(2)) used in acute lung injury (ALI) may promote resorption atelectasis. The impact of derecruitment related to high FIO(2) in ALI is debated. We evaluated derecruitment with 100% vs. 60% FIO(2) at two levels of positive end-expiratory pressure (PEEP).

PATIENTS

Fourteen consecutive patients with ALI were studied.

INTERVENTIONS

Recruited volume at two PEEP levels was computed from two pressure-volume curves, recorded from PEEP and from zero end-expiratory pressure, using the sinusoidal flow modulation method. PEEP-induced recruitment was measured during prolonged expiration as the difference between the two curves at a given pressure. PaO(2)/FIO(2) was also measured. PEEP was 5 +/- 1 or 14 +/- 3 cmH(2)O and FIO(2) was 60% or 100%, yielding four combinations. We looked for differences between the beginning and end of a 30-min period with each combination.

MEASUREMENT AND RESULTS

With low PEEP and 100% FIO(2), recruited volume decreased significantly from 68 +/- 53 to 39 +/- 43 ml and PaO(2)/FIO(2) from 196 +/- 104 to 153 +/- 83 mmHg. With the three other combinations (low PEEP and 60% FIO(2) or high PEEP and 60% or 100% FIO(2)) none of the parameters decreased significantly.

CONCLUSION

In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP.