Positive end-expiratory pressure: how to set it at the individual level

Low-Cost, Open-Source Mechanical Ventilator with Pulmonary Monitoring for COVID-19 Patients

This paper shows the construction of a low-cost, open-source mechanical ventilator. The motivation for constructing this kind of ventilator comes from the worldwide shortage of mechanical ventilators for treating COVID-19 patients—the COVID-19 pandemic has been striking hard in some regions, especially the deprived ones. Constructing a low-cost, open-source mechanical ventilator aims to mitigate the effects of this shortage on those regions. The equipment documented here employs commercial spare parts only. This paper also shows a numerical method for monitoring the patients’ pulmonary condition. The method considers pressure measurements from the inspiratory limb and alerts clinicians in real-time whether the patient is under a healthy or unhealthy situation. Experiments carried out in the laboratory that had emulated healthy and unhealthy patients illustrate the potential benefits of the derived mechanical ventilator.

Lung protective ventilation in infants undergoing cardiopulmonary bypass surgery for congenital heart disease: A prospective randomized controlled trial

BACKGROUND

Lung protective ventilation (LPV) has been applied to surgical adults with normal pulmonary function for optimizing mechanical ventilation and reducing postoperative pulmonary complications. Few studies have reported the use of LPV in infants undergoing cardiac surgery with cardiopulmonary bypass (CPB).

AIMS

To explore safety and effectiveness of LPV in infants undergoing CPB surgery for congenital heart disease (CHD).

METHODS

Included in this study were 77 infants who underwent CPB surgery for CHD from November 2017 to September 2018. They were randomized into the LPV group and conventional ventilation (CV) group. In the LPV group, small-tidal-volume (6-8 ml/kg) ventilation, lung recruitment by PEEP increment to the maximum level of 15 cm H₂ O after CPB, and individualized optimal PEEP titration were applied. In the CV group, traditional tidal volume (10-12 ml/kg with zero PEEP) was applied. The primary outcome was the ratio of arterial partial pressure of oxygen to inspiratory oxygen fraction (PaO₂ /FiO₂ ). The secondary outcomes were respiratory dynamic parameters, hypoxemia, prognostic indexes, and postoperative pulmonary complications.

RESULTS

PaO₂ /FiO₂ in the LPV group (416.86, 95%CI: 381.60-452.12) was significantly higher than that in the CV group (263.37, 95%CI: 227.65-299.09) after intervention (P < .001). There was a significant difference in the trend of change in dynamic compliance, alveolar-arterial oxygen difference, arterial-end-expired carbon dioxide difference, driving pressure, and respiratory index between the two groups at different time points from weaning from CPB to 2 hours after operation. There was no significant difference in PaO₂ /FiO₂ , alveolar-arterial oxygen difference, respiratory index, and dynamic compliance 2 hours postoperative and in the incidence of postoperative pulmonary complications, prognostic indexes between the two groups.

CONCLUSIONS

LPV could be used safely in infants undergoing CPB in that it can improve oxygenation, alveolar aeration, and dynamic compliance, and reduce driving pressure, pulmonary shunting, and dead space. Its effect on oxygenation, pulmonary gas exchange, and pulmonary compliance was relatively short, and had less impact on postoperative pulmonary complications and prognosis.

Lung Recruitability in Severe Acute Respiratory Distress Syndrome Requiring Extracorporeal Membrane Oxygenation

OBJECTIVES

Quantification of potential for lung recruitment may guide the ventilatory strategy in acute respiratory distress syndrome. However, there are no quantitative data on recruitability in patients with severe acute respiratory distress syndrome who require extracorporeal membrane oxygenation. We sought to quantify potential for lung recruitment and its relationship with outcomes in this cohort of patients.

DESIGN

A single-center, retrospective, observational cohort study.

SETTING

Tertiary referral severe respiratory failure center in a university hospital in the United Kingdom.

PATIENTS

Forty-seven adults with severe acute respiratory distress syndrome requiring extracorporeal membrane oxygenation.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

In patients with severe acute respiratory distress syndrome-mainly of pulmonary origin (86%)-the potential for lung recruitment and the weight of nonaerated, poorly aerated, normally aerated, and hyperaerated lung tissue were assessed at low (5 cmH2O) and high (45 cmH2O) airway pressures. Patients were categorized as high or low potential for lung recruitment based on the median potential for lung recruitment value of the study population. The median potential for lung recruitment was 24.3% (interquartile range = 11.4-37%) ranging from -2% to 76.3% of the total lung weight. Patients with potential for lung recruitment above the median had significantly shorter extracorporeal membrane oxygenation duration (8 vs 13 d; p = 0.013) and shorter ICU stay (15 vs 22 d; p = 0.028), but mortality was not statistically different (24% vs 46%; p = 0.159).

CONCLUSIONS

We observed significant variability in potential for lung recruitment in patients with severe acute respiratory distress syndrome requiring extracorporeal membrane oxygenation. Patients with high potential for lung recruitment had a shorter ICU stay and shorter extracorporeal membrane oxygenation duration.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

PEEP guided by electrical impedance tomography during one-lung ventilation in elderly patients undergoing thoracoscopic surgery

Background

To examine the influence of positive end-expiratory pressure (PEEP) settings on lung mechanics and oxygenation in elderly patients undergoing thoracoscopic surgery.

Methods

One hundred patients aged >65 years were randomly allocated into either the PEEP₅ or the electrical impedance tomography (EIT) group (PEEP_EIT). Each group underwent volume-controlled ventilation (tidal volume 6 mL/kg predicted body weight) with the PEEP either fixed at 5 cmH₂O or set at an individualized EIT setting. The primary endpoint was the ratio of the arterial oxygen partial pressure to the fractional inspired oxygen (PaO₂/FiO₂). The secondary endpoints included the driving pressure, and dynamic respiratory system compliance (C_dyn). Other outcomes, such as the mean airway pressure (P_mean), mean arterial pressure (MAP), lung complications and the length of hospital stay were explored.

Results

The optimal PEEP set by EIT was significantly higher (range from 9-13 cmH₂O) than the fixed PEEP. PaO₂/FiO₂ was 47 mmHg higher (95% CI: 7-86 mmHg; P=0.021), C_dyn was 4.3 mL/cmH₂O higher (95% CI: 2.1-6.7 cmH₂O; P<0.001), and the driving pressure was 3.7 cmH₂O lower (95% CI: 2.2-5.1 mmH₂O; P<0.001) at 0.5 h during one-lung ventilation (OLV) in the PEEP_EIT group than in the PEEP₅ group. At 1 h during OLV, PaO₂/FiO₂ was 93 mmHg higher (95% CI: 58-128 mmHg; P<0.001), C_dyn was 4.4 mL/cmH₂O higher (95% CI: 1.9-6.9 mL/cmH₂O; P=0.001), and the driving pressure was 4.9 cmH₂O lower (95% CI: 3.8-6.1 cmH₂O; P<0.001) in the PEEP_EIT group than in the PEEP₅ group. PaO₂/FiO₂ was 107 mmHg higher (95% CI: 56-158 mmHg; P<0.001) in the PEEP_EIT group than in the PEEP₅ group during double-lung ventilation at the end of surgery.

Conclusions

PEEP values determined with EIT effectively improved oxygenation and lung mechanics during one lung ventilation in elderly patients undergoing thoracoscopic surgery.

High positive end expiratory pressure levels affect hemodynamics in elderly patients with hypertension admitted to the intensive care unit: a prospective cohort study

Background

To study the effects of different positive end expiratory pressure (PEEP) on blood pressure and heart function in elderly patients with hypertension.

Methods

Forty elderly patients above 65 years of age treated with mechanical ventilation were divided into two groups: a control group of non-hypertensive subjects (n = 18) and a hypertension group (n = 22) patients with essential hypertension. Changes in blood pressure, central venous pressure (CVP), central venous oxygen saturation (ScvO₂), heart rate, and airway pressure were determined in response to different selected PEEP levels of 0, 2, 4, 6, 8, 10 and 12 cm H₂O under SIMV(PC) + PSV mode throughout the study.

Results

In both groups, the increase in PEEP led to an increase in CVP and airway pressure. When PEEP was above 4 cm H₂O in the hypertension group, a decrease in blood pressure and ScvO₂, and an increase of heart rate were observed. These results indicated that cardiac output significantly decreased.

Conclusion

High levels of PEEP can significantly influence changes in blood pressure and heart function in elderly patients with hypertension.

Trial registration

This trial was retrospectively registered, The Chinese trial registration number is ChiCTR-ROC-17012873. The date of registration is 10-2-2017.

Medical Optimization and Liberation of Adult Patients From VA-ECMO

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) can be an efficacious cardiopulmonary support for adults as rescue from refractory cardiogenic shock. It is best employed as a bridging strategy to recovery or alternative support rather than sustained, long-term mechanical circulatory support. The purpose of this paper is to discuss strategies to optimize patient management on VA-ECMO and approaches to promote successful separation from support. Rapid medical optimization will assist in reducing the time on VA-ECMO, thereby improving the likelihood of patient salvage. Suitably trained physicians and personnel, guided by structured protocols, can promote excellence in team care and provision of consistent management. Focusing on anticoagulation, careful neurologic monitoring, prevention of leg ischemia, awareness of differential hypoxemia, optimizing mechanical ventilation, identifying and timely intervention for left-ventricular distension (LVD), along with a strategic weaning algorithm, can prevent significant morbidity and mortality. LVD physiology, diagnosis, and risk factors are reviewed. Indications for LV decompression, along with medical and mechanical management options, are elucidated.

Comparative effects of open-lung positive end-expiratory pressure (PEEP) and fixed PEEP on respiratory system compliance in the isoflurane anaesthetised healthy dog

This study was performed to assess the effects of open-lung positive end-expiratory pressure (OL-PEEP) following stepwise recruitment manoeuvre (RM) and those of a fixed PEEP of 5 cm H₂O without previous RM on respiratory system compliance (Crs) and selected cardiovascular variables in healthy dogs under general anaesthesia. Forty-five healthy client-owned dogs undergoing surgery were anaesthetised and mechanically ventilated (tidal volume, VT = 10-12 mL/kg; PEEP = 0 cm H₂O) for 1 min (baseline) and randomly allocated into zero positive end-expiratory pressure (ZEEP), PEEP (5 cm H₂O) and OL-PEEP treatment groups. In the OL-PEEP group, a stepwise RM was performed and the individual OL-PEEP was subsequently applied. The Crs, heart rate (HR) and non-invasive mean arterial pressure (NIMAP) were registered at baseline and then every 10 min during 60 min. In the ZEEP group, Crs decreased from baseline. In the PEEP group, Crs was not different from either baseline or ZEEP group values. In the OL-PEEP group, Crs was higher than both baseline and ZEEP group values at all time points as well as of those in the PEEP group during at least 20 min after RM. There were no differences for HR and NIMAP between groups. A clinically relevant hypotension following RM was observed in 40% of dogs. Therefore, an individually set OL-PEEP following stepwise RM improved Crs in anaesthetised healthy dogs, although transient but clinically relevant hypotension was observed during RM in some dogs. Fixed PEEP of 5 cm H₂O without previous RM did not improve Crs, although it prevented it from decreasing.

Critical Care of Patients After Pulmonary Thromboendarterectomy

Pulmonary thromboendarterectomy (PTE) remains the only curative surgery for patients with chronic thromboembolic pulmonary hypertension (CTEPH). Postoperative intensive care unit care challenges providers with unique disease physiology, operative sequelae, and the potential for detrimental complications. Central concerns in patients with CTEPH immediately after PTE relate to neurologic, pulmonary, hemodynamic, and hematologic aspects. Institutional experience in critical care for the CTEPH population, a multidisciplinary team approach, patient risk assessment, and integration of current concepts in critical care determine outcomes after PTE surgery. In this review, the authors will focus on specific aspects unique to this population, with integration of current available evidence and future directions. The goal of this review is to provide the cardiac anesthesiologist and intensivist with a comprehensive understanding of postoperative physiology, potential complications, and contemporary intensive care unit management immediately after pulmonary endarterectomy.

Positive end-expiratory pressure titration with electrical impedance tomography and pressure-volume curve in severe acute respiratory distress syndrome

BACKGROUND

The study objective was to compare titration of positive end-expiratory pressure (PEEP) with electrical impedance tomography (EIT) and with ventilator-embedded pressure-volume loop in severe acute respiratory distress syndrome (ARDS).

METHODS

We have designed a prospective study with historical control group. Twenty-four severe ARDS patients (arterial oxygen partial pressure to fractional inspired oxygen ratio, PaO₂/FiO₂ < 100 mmHg) were included in the EIT group and examined prospectively. Data from another 31 severe ARDS patients were evaluated retrospectively (control group). All patients were receiving medical care under identical general support guidelines and protective mechanical ventilation. The PEEP level selected in the EIT group was the intercept point of cumulated collapse and overdistension percentages curves. In the control group, optimal PEEP was selected 2 cmH₂O above the lower inflection point on the static pressure-volume curve.

RESULTS

Patients in the EIT group were younger (P < 0.05), and their mean plateau pressure was 1.5 cmH₂O higher (P < 0.01). No differences in other baseline parameters such as APACHE II score, PaO₂/FiO₂, initial PEEP, driving pressure, tidal volume, and respiratory system compliance were found. Two hours after the first PEEP titration, significantly higher PEEP, compliance, and lower driving pressure were found in the EIT group (P < 0.01). Hospital survival rates were 66.7% (16 of 24 patients) in the EIT group and 48.4% (15 of 31) in the control group. Identical rates were found regarding the weaning success rate: 66.7% in the EIT group and 48.4% in the control group.

CONCLUSION

In severe ARDS patients, it was feasible and safe to guide PEEP titration with EIT at the bedside. As compared with pressure-volume curve, the EIT-guided PEEP titration may be associated with improved oxygenation, compliance, driving pressure, and weaning success rate. The findings encourage further randomized control study with a larger sample size and potentially less bias in the baseline data. Trial Registration NCT03112512.

Biologic Impact of Mechanical Power at High and Low Tidal Volumes in Experimental Mild Acute Respiratory Distress Syndrome

Background

The authors hypothesized that low tidal volume (VT) would minimize ventilator-induced lung injury regardless of the degree of mechanical power. The authors investigated the impact of power, obtained by different combinations of VT and respiratory rate (RR), on ventilator-induced lung injury in experimental mild acute respiratory distress syndrome (ARDS).

Methods

Forty Wistar rats received Escherichia coli lipopolysaccharide intratracheally. After 24 h, 32 rats were randomly assigned to be mechanically ventilated (2 h) with a combination of different VT (6 ml/kg and 11 ml/kg) and RR that resulted in low and high power. Power was calculated as energy (ΔP,L2/E,L) × RR (ΔP,L = transpulmonary driving pressure; E,L = lung elastance), and was threefold higher in high than in low power groups. Eight rats were not mechanically ventilated and used for molecular biology analysis.

Results

Diffuse alveolar damage score, which represents the severity of edema, atelectasis, and overdistension, was increased in high VT compared to low VT, in both low (low VT: 11 [9 to 14], high VT: 18 [15 to 20]) and high (low VT: 19 [16 to 25], high VT: 29 [27 to 30]) power groups. At high VT, interleukin-6 and amphiregulin expressions were higher in high-power than in low-power groups. At high power, amphiregulin and club cell protein 16 expressions were higher in high VT than in low VT. Mechanical energy and power correlated well with diffuse alveolar damage score and interleukin-6, amphiregulin, and club cell protein 16 expression.

Conclusions

In experimental mild ARDS, even at low VT, high mechanical power promoted ventilator-induced lung injury. To minimize ventilator-induced lung injury, low VT should be combined with low power.