Use Of Positive End-expiratory Pressure Research Articles

Impact of zero-positive end-expiratory pressure on blood transfusion rates in off-pump coronary artery bypass surgery: a retrospective cohort study

BackgroundBleeding are common in cardiac surgery, with significant impacts on transfusion-related complications and patient prognosis. This study aimed to determine the differences in perioperative blood loss, transfusion rates, and the incidence of postoperative pulmonary complications (PPCs) with and without the use of positive end-expiratory pressure (PEEP) in patients undergoing off-pump coronary artery bypass graft surgery (OPCAB).MethodsThis single-center, retrospective study included 106 adult patients undergoing coronary artery bypass surgery without cardiopulmonary bypass from January 2018 to March 2022. The patients were divided into two groups based on intraoperative ventilator settings: the zero-PEEP (ZEEP) group and the PEEP group. The primary outcome was the perioperative transfusion rate from the intraoperative period to postoperative 7 day. The incidence of PPCs was recorded for 1 week post-operatively. Logistic regression analysis was performed for statistical analysis.ResultsThe average PEEP in the PEEP group was 4.92 ± 0.42 cmH2O. Multiple regression analysis indicated that lower mean airway pressure during surgery tend to associate with intraoperative lower blood loss. The intraoperative transfusion rates in the ZEEP group were significantly lower than those in the PEEP group (ZEEP:14%, PEEP 38.4%, P = 0.02). Logistic regression analysis revealed that ZEEP (adjusted odds ratio [OR] 0.13, 95% confidence interval [CI] 0.04–0.78) and Society of Thoracic Surgeons(STS) scores (adjusted OR 2.31, 95% CI 1.53–3.49) were significantly associated with a reduced requirement for perioperative transfusions. No significant difference was observed between the two groups in terms of PPCs (p = 0.824). Atelectasis was the most common complication in both groups (ZEEP: 35.7%, PEEP: 40%, P = 0.832).ConclusionsZEEP and STS scores were associated with significantly reduced requirement for perioperative transfusion rates during elective OPCAB surgery. However, ZEEP did not significantly affect the incidence of PPCs.

Investigating the effects of pressure support ventilation and positive end-expiratory pressure during extubation on respiratory system complications

BackgroundPostoperative extubation is a critical phase. Various medications and different ventilation modes are employed during extubation to minimize potential issues. This study aimed to observe the early effects of the concurrent use of positive end-expiratory pressure (PEEP) and pressure support ventilation (PSV) modes during the extubation-emerge period on the respiratory system.MethodsAfter laparoscopic cholecystectomy, patients were administered a remifentanil infusion following the cessation of inhalation agents. PSV and PEEP modes were used on the mechanical ventilator, and the patients were extubated upon awakening. Hemodynamic and respiratory parameters, as well as complications during intraoperative and extubation periods, were recorded.ResultsA total of 199 patients were evaluated. Patients with complications were defined as group I (n = 37), and those without complications as group 0 (n = 167). Post-extubation complications included cough (3 or more, persistent or repetitive coughing) in 12 patients (6.04%), desaturation (SPO2 < 90% for 10 s) in nine patients (4.53%), bronchospasm in eight patients (4.02%), agitation (5 and above on the agitation scale) in three patients (1.5%), need for rescue mask ventilation (SPO2 < 90% lasting longer than 10 s) in three patients (1.5%), and airway obstruction (2 and above according to laryngospasm score) in two patients (1%). Statistically significant differences were observed between the two groups for ASA III (p = 0.0365).ConclusionsThe use of PSV and PEEP modes during extubation-emergence period in laparoscopic cholecystectomy results in a low rate of respiratory system complications, which are mostly minor. These modes can be safely used during the extubation phase. However, since these complications are seen in patients with high ASA physical scores, further studies are needed for these patients.Trial registrationNCT06356649.

The relationship between positive end-expiratory pressure (PEEP) and intra-abdominal pressure (IAP) in mechanically ventilated patients: A prospective observational study.

Positive end-expiratory pressure is a crucial mechanical breathing parameter. Intra-abdominal hypertension is well defined as a sustained increase in the intra-abdominal pressure ≥12 mmHg. There are still controversies about mechanical ventilation's effect and use of positive end-expiratory pressure on intra-abdominal pressure. We aimed to delineate the relationship between positive end-expiratory pressure and intra-abdominal pressure in mechanically ventilated patients admitted to the intensive care units of a large tertiary hospital in Upper Egypt. This study was a prospective observational study. The study was conducted at a university hospital from October 2023 to February 2024. The enrolled adult patients were allocated into two groups based on their positive end-expiratory pressure: group I, low pressure (<8 cm H2O) and group II, high pressure (8-10 cm H2O). A total of 120 patients were enrolled, 60 patients in each group. The most commonly encountered diagnoses were pneumonia (32/120, 26.7%) and acute respiratory distress syndrome (ARDS) (31/120, 25.8%), respectively. There was a significant difference between the intra-abdominal pressure mean values of the two patient groups, 18.9 ± 3.3 versus 24.4 ± 5.9 mmHg in the group of low versus high pressure (correlation value of .454, p < .001), respectively. There were highly significant correlations between intra-abdominal pressure categories and the patient groups (correlation value of .495, p < .001). There were 24 (40%) versus 0 (0%) patients of high pressure versus low pressure within the category IV group of intra-abdominal hypertension (>25 mmHg). We observed a significant relationship between positive end-expiratory pressure and intra-abdominal pressure in mechanically ventilated patients. The patient group with high pressure had higher mean values compared with the group with low pressure. The study highlights the importance of closely monitoring intra-abdominal pressure in mechanically ventilated patients who receive positive end-expiratory pressure. Further studies are warranted. The relationship between positive end-expiratory pressure and intra-abdominal pressure is an essential issue in daily critical care nursing clinical practice. Considering the occurrence of multiple organ dysfunction as a result of a non-detected increase in intra-abdominal pressure, critical care nurses should pay attention to measuring this pressure to maintain intra-abdominal pressures that are safe for mechanically ventilated and critically ill intensive care unit patients, thereby preventing these undue effects.

Implementation of Continuous Capnography Protocol in a Postanesthesia Care Unit for Adult Patients at High-risk of Postoperative Respiratory Depression

PurposeThis project aimed to implement a continuous capnography protocol in the postanesthesia care unit (PACU) for postoperative adult patients who are at high risk for respiratory failure. DesignA preintervention and postintervention quality improvement design with retrospective chart reviews evaluated patient demographics (age, weight, body mass index [BMI], perioperative fluid intake and output, use of intraoperative positive-end expiratory pressure), length of surgery, average length of PACU stay, incidence of respiratory events, and adherence to a PACU capnography protocol. MethodsPreimplementation data were collected from retrospective chart reviews over a 3-month period. A continuous capnography protocol was implemented for same-day surgery patients with a BMI of 35 kg/m2 or greater and who received general anesthesia. Postimplementation data were collected over 3 months in addition to adherence to the capnography protocol. This was presented using descriptive statistics. FindingsAge, length of surgery, weight, BMI, perioperative fluid intake and output, and use of positive-end expiratory pressure did not impact PACU length of stay. The average PACU length of stay decreased from 76.76 to 71.82 minutes postimplementation but was not statistically significant (P = .470). The incidence of respiratory events was 6% (n = 3). After the implementation of the continuous capnography protocol, adherence to the continuous capnography monitoring was 86% (n = 43). ConclusionsPatients who are at high risk for postoperative respiratory failure may benefit from continuous capnography monitoring in the PACU. Capnography monitoring may decrease PACU length of stay and provide earlier detection of pending respiratory depression or failure than pulse oximetry alone.

Exploring alveolar recruitability using positive end-expiratory pressure in mice overexpressing TGF-β1: a structure–function analysis

Pre-injured lungs are prone to injury progression in response to mechanical ventilation. Heterogeneous ventilation due to (micro)atelectases imparts injurious strains on open alveoli (known as volutrauma). Hence, recruitment of (micro)atelectases by positive end-expiratory pressure (PEEP) is necessary to interrupt this vicious circle of injury but needs to be balanced against acinar overdistension. In this study, the lung-protective potential of alveolar recruitment was investigated and balanced against overdistension in pre-injured lungs. Mice, treated with empty vector (AdCl) or adenoviral active TGF-β1 (AdTGF-β1) were subjected to lung mechanical measurements during descending PEEP ventilation from 12 to 0 cmH2O. At each PEEP level, recruitability tests consisting of two recruitment maneuvers followed by repetitive forced oscillation perturbations to determine tissue elastance (H) and damping (G) were performed. Finally, lungs were fixed by vascular perfusion at end-expiratory airway opening pressures (Pao) of 20, 10, 5 and 2 cmH2O after a recruitment maneuver, and processed for design-based stereology to quantify derecruitment and distension. H and G were significantly elevated in AdTGF-β1 compared to AdCl across PEEP levels. H was minimized at PEEP = 5–8 cmH2O and increased at lower and higher PEEP in both groups. These findings correlated with increasing septal wall folding (= derecruitment) and reduced density of alveolar number and surface area (= distension), respectively. In AdTGF-β1 exposed mice, 27% of alveoli remained derecruited at Pao = 20 cmH2O. A further decrease in Pao down to 2 cmH2O showed derecruitment of an additional 1.1 million alveoli (48%), which was linked with an increase in alveolar size heterogeneity at Pao = 2–5 cmH2O. In AdCl, decreased Pao resulted in septal folding with virtually no alveolar collapse. In essence, in healthy mice alveoli do not derecruit at low PEEP ventilation. The potential of alveolar recruitability in AdTGF-β1 exposed mice is high. H is optimized at PEEP 5–8 cmH2O. Lower PEEP folds and larger PEEP stretches septa which results in higher H and is more pronounced in AdTGF-β1 than in AdCl. The increased alveolar size heterogeneity at Pao = 5 cmH2O argues for the use of PEEP = 8 cmH2O for lung protective mechanical ventilation in this animal model.

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.

Editor's Choice Articles for June.

Editor's Choice Articles for June.

Effect of different titration methods on right heart function and prognosis in patients with acute respiratory distress syndrome

BackgroundAcute respiratory distress syndrome (ARDS) is a common disease in intensive critical care(ICU), and the use of positive end-expiratory pressure(PEEP) during mechanical ventilation can increase the right heart afterload and eventually cause right heart dysfunction. For these factors causing acute cor pulmonale(ACP), especially inappropriate mechanical ventilation settings, it is important to explore the effect of PEEP on right heart function. ObjectiveTo investigate the effects of three titration methods on right heart function and prognosis in patients with ARDS. MethodsObservational, prospective study in which ARDS patients were enrolled into three distinct PEEP-titration strategies groups: guide, transpulmonary pressure-oriented and driving pressure-oriented. Prognostic indicators, right heart systolic and diastolic echocardiographic function indices, ventilatory parameters, blood gas analysis results, and respiratory mechanics Monitoring indices were collated and analyzed statistically by STATA 15 software. ResultsA total of 62 ARDS patients were enrolled into guide (G) group (n=40) for whom titrated PEEP values were 9±2cm H2O, driving pressure-oriented (DPO) group (n=12) with titrated PEEP values of 10±2cm H2O and transpulmonary pressure-oriented (TPO) group (n=10) with titrated PEEP values of 12±3cm H2O. Values were significantly higher for TPO than for G (p=0.616) or DPO (p=0.011). Compliance was significantly increased after 72 h in the TPO and DPO groups compared with the G group (p<0.001). Mean airway pressure at end-inspiratory obstruction (p=0.047), tricuspid annular plane systolic excursion (TAPSE, p<0.001) and right ventricular area change fraction (RVFAC, p=0.049) were all higher in the TPO and DPO groups than in the G group. E/A indices were significantly better in the TPO group than in the G or DPO groups (p=0.046). No significant differences in 28 day mortality were found among the three groups. Multivariate logistic regression analysis revealed that lung compliance and transpulmonary pressure-oriented PEEP titration method was negatively correlated to the increase in right ventricular systolic dysfunction. ConclusionTranspulmonary pressure-oriented PEEP titration improves oxygenation and pulmonary function and causes less right heart strain when compared to other PEEP-titration methods during mechanical ventilation of ARDS patients.

Taking a Big Breath: Identifying and Preventing Pulmonary Complications After Liver Transplantation.

In this issue of Transplantation, Oh et al1 describe the results of a retrospective study of postoperative pulmonary complications (PPCs) in 608 patients who underwent living donor liver transplantation over a period of 9 y. More than half of the patients developed pulmonary complications defined as respiratory failure, pneumonia, pulmonary edema, moderate-severe atelectasis, or pleural effusions within 7 d after the transplant. The authors found that a large number of intraoperative variables were associated with PPC including (not surprisingly) Model for End-stage Liver Disease score, ventilator driving pressures, positive end-expiratory pressure (PEEP) and compliance, fluid and blood administration, and duration of anesthesia. However, when using a multivariate analysis and focusing on intraoperative factors, greater driving pressure, and albumin levels at the end of surgery, prolonged hypotension and larger tidal volumes (but not PEEP) remained independently associated with PPC. Patient with PPCs had worse outcomes such as longer intensive care unit stay and worse graft and patient survival. This is the first, larger study of PPC after liver transplantation that investigates the effect of intraoperative variables and therefore factors that may be modifiable. Although any retrospective study can only identify associations and not prove causal relationships, this study provides us with evidence that may influence how we manage patients. Specifically, the association of driving pressures at the end of surgery confirms what we have learned from the nontransplant anesthesiology literature: intraoperative ventilator management matters. Almost 10 y ago, Futier et al2 demonstrated the benefit of intraoperative lung-protective ventilation including the use of PEEP to prevent PPC after abdominal surgery with the landmark randomized, controlled Intraoperative Protective Ventilation trial. The benefit of using PEEP shown in the Intraoperative Protective Ventilation trial could not be replicated in the present study. This may reflect more recent evidence that suggests that high driving pressure (and tidal volumes) and not just low PEEP are actually harmful,3 and PEEP should be individualized to the patient’s static compliance. The ongoing Prime-Air study (ClinicalTrials.gov Identifier: NCT04108130) is a large, multicenter, randomized, controlled trial of an anesthetic-center bundle of interventions that includes individualized PEEP. This study will likely provide us with a better understanding if and how individualized PEEP may be beneficial. Other factors identified by this study associated with PPCs such as low albumin levels at the end of surgery and intraoperative hypotension require more complex physiologic explanations and are not as easily modifiable. PPCs are usually defined as any serious respiratory complications after surgery independent of their etiology.4 Cardiogenic pulmonary edema, pneumonias, and pleural effusions are all considered PPCs, although they represent very different pathologies. PPC is a syndrome with often vague and subjective definitions. For example, the severity of atelectasis or pleural effusion is difficult to quantify and what some may consider normal postoperative changes may be considered PPC by others. The elegant solution to this problem by the present study was to assess for PPCs with radiograph and chart review by 2 pulmonologists. Although this method allows for the application of some common sense in the diagnosis of PPC, it is harder to quantify severity. For example, is severe atelectasis equally harmful than pneumonia? Unlike other organ injuries such as acute kidney injury or liver failure, there are no proven sensitive and specific biomarkers that allow us to identify PPCs and assess its severity. This should not discourage us as it is a great opportunity for future research that may dramatically transform clinical studies of PPCs and possible interventions. The present study is further encouraging as it demonstrates that interventions in the operating room affect complications and the anesthesiologist as an integral member of transplant team can contribute to better outcomes for our patients.

Positive end-expiratory pressure and postoperative complications in patients with obesity: a review and meta-analysis.

In patients with obesity, use of positive end-expiratory pressure (PEEP) > 5 cm H2 O (centimeters of water) has been shown to prevent intraoperative atelectasis. This study compares the rate of postoperative pulmonary complications (PPCs) associated with PEEP > 5 cm H2 O and PEEP ≤ 5 cm H2 O in patients with obesity who underwent surgery under general anesthesia with mechanical ventilation. This study searched Medline, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) using the terms "PEEP," "anesthesia," and "ventilation." Cochrane ReviewManager (RevMan) version 5 was used for data analysis. The primary outcome was a composite of PPCs, including atelectasis, pneumonia, pneumothorax, and acute respiratory failure. The initial search identified 903 titles and abstracts, and 4 randomized controlled trials were included for analysis. We included a total of 2116 participants from four randomized controlled trials that compared PEEP ≤ 5 cm H2 O with PEEP > 5 cm H2 O in adult patients with obesity. There was no statistically significant difference in PPCs between the PEEP ≤ 5 cm H2 O and PEEP > 5 cm H2 O groups (risk ratio=2.21, 95% CI: 0.41-11.83; p=0.35). However, a significant heterogeneity was found within included studies (I2 = 53%). It is unclear whether PEEP > 5 cm H2 O improves the postoperative clinical outcome in patients with obesity, which is in contrast to previously established evidence that it reduces atelectasis in patients with obesity.

Invasive Ventilatory Support in Patients With Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference.

To provide evidence for the Second Pediatric Acute Lung Injury Consensus Conference updated recommendations and consensus statements for clinical practice and future research on invasive mechanical ventilation support of patients with pediatric acute respiratory distress syndrome (PARDS). MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost). We included clinical studies of critically ill patients undergoing invasive mechanical ventilation for PARDS, January 2013 to April 2022. In addition, meta-analyses and systematic reviews focused on the adult acute respiratory distress syndrome population were included to explore new relevant concepts (e.g., mechanical power, driving pressure, etc.) still underrepresented in the contemporary pediatric literature. Title/abstract review, full text review, and data extraction using a standardized data collection form. The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations, good practice statements and research statements. We identified 26 pediatric studies for inclusion and 36 meta-analyses or systematic reviews in adults. We generated 12 recommendations, two research statements, and five good practice statements related to modes of ventilation, tidal volume, ventilation pressures, lung-protective ventilation bundles, driving pressure, mechanical power, recruitment maneuvers, prone positioning, and high-frequency ventilation. Only one recommendation, related to use of positive end-expiratory pressure, is classified as strong, with moderate certainty of evidence. Limited pediatric data exist to make definitive recommendations for the management of invasive mechanical ventilation for patients with PARDS. Ongoing research is needed to better understand how to guide best practices and improve outcomes for patients with PARDS requiring invasive mechanical ventilation.

Effects of positive end-expiratory pressure and oxygen concentration on non-hypoxemic apnea time during face mask ventilation of anesthesia induction: A randomized controlled trial.

Background: The optimal ventilatory strategy for the face mask ventilation during anesthesia induction is still unknow. Methods: We evaluated the effect of two positive end-expiratory pressure (PEEP) levels (0cmH2O and 6cmH2O) and two oxygen concentration levels (1.0 and .6) on non-hypoxemic apnea time during face mask ventilation of anesthesia induction. Sixty adult patients scheduled for elective surgery were enrolled in this study. The patients were randomized to receive anesthesia induction with four different ventilation strategy under volume-controlled ventilation. Patients assigned to the LOZP group received low fraction of inspiration O2 (FiO2 = .6) and 0 PEEP. Patients assigned to the LOHP group received low fraction of inspiration O2 (FiO2 = .6) and 6cmH2O PEEP. Patients assigned to the HOZP group received high fraction of inspiration O2 (FiO2 = 1.0) and 0 PEEP. Patients assigned to the HOHP group received high fraction of inspiration O2 (FiO2 = 1.0) and 6cmH2O PEEP. After 3min of ventilation, the patient was intubated but disconnected from the breathing circuit. Ventilation was not initiated until the pulse oximetry dropped to 90%. The primary outcome was non-hypoxemic apnea time defined as the time from cessation of ventilation to a pulse oximeter reading of 90%. The secondary outcome was the PaO2/FiO2 ratio immediately after ventilation. Results: The non-hypoxemic apnea time was significantly longer in the group of HOHP when compared to the other three groups (192s ± 70s, 221s ± 74s, 284s ± 101s, and 353s ± 85s in the LOZP, LOHP, HOZP, and HOHP group, respectively). The PaO2/FiO2 ratio immediately after ventilation was significantly higher in the group of LOHP when compared to the other three groups (LOZP 393 ± 130, LOHP 496 ± 97, HOZP 335 ± 58, HOHP 391 ± 50). When compared the PaO2/FiO2 ratio immediately after ventilation to its value before administration of anesthesia, the PaO2/FiO2 ratio in the group of LOHP was improved, the group LOZP and HOHP remained the same, while the group HOZP significantly decreased. Conclusion: Application of PEEP and 100% of oxygen during face mask ventilation of induction could maximize the non-hypoxemic apnea time. However, the use of PEEP and 60% of oxygen during preoxygenation resulted in improved PaO2/FiO2 ratio.

Respiratory function under anaesthesia

General anaesthesia can affect every aspect of ventilation. It produces dose dependent depression of control of respiration. Carbon dioxide response curve is shifted to the right. Muscle tone is reduced and the airway can get obstructed. One of the most prominent changes is reduction in functional residual capacity (FRC) with the adoption of supine function and induction of anaesthesia. The closing capacity increases with age. The atelectasis that occurs consequent to the fall in FRC and increasing age is compounded by the use of high concentrations of oxygen, cephalad movement of the diaphragm, residual effect of muscle relaxants and inadequate analgesia after thoracic or abdominal surgery. One of the important causes of ventilation perfusion mismatch during anaesthesia is atelectasis. This has been shown to contribute to hypoxia as well as increased postoperative pulmonary complications. A lot of research is being conducted as to reduce the effects of atelectasis during anaesthesia, including the best ventilator strategy during anaesthesia. Most inhalation anaesthetics are good bronchodilators. Inhalation anaesthetics depress hypoxic pulmonary vasoconstriction (HPV) beyond 1 MAC. The movement of ciliary movements is reduced with the use of dry gases. All these can increase postoperative pulmonary complications which are important causes of postoperative morbidity. Appropriate preoperative preparation has to be combined with optimal management of ventilation intraoperatively to minimise postoperative pulmonary complications. The role of lower tidal volume, use of positive end-expiratory pressure, limiting oxygen concentrations and the utility of recruitment manoeuvres are increasingly being recognised and have been the topics of recent research.

Effect of positive end-expiratory pressure on pulmonary compliance and pulmonary complications in patients undergoing robot-assisted laparoscopic radical prostatectomy: a randomized control trial

BackgroundTo observe the effects of different positive end-expiratory pressure (PEEP) ventilation strategies on pulmonary compliance and complications in patients undergoing robotic-assisted laparoscopic prostate surgery.MethodsA total of 120 patients with the American Society of Anesthesiologists Physical Status Class I or II who underwent elective robotic-assisted laparoscopic prostatectomy were enrolled. We randomized the patients divided into divided into three groups of 40 patients each: PEEP0, PEEP5, or PEEP10. Master Anesthetist used volume control ventilation intraoperatively with an intraoperative deep muscle relaxation strategy. Respiratory mechanics indexes were recorded at six time-points: 10 mimuts after anaesthesia induction, immediately after pneumoperitoneum establishment, 30 min, 60 min, 90 min, and at the end of pneumoperitoneum. Arterial blood gas analysis and oxygenation index calculation were performed 10 mimuts after anaesthesia induction, 60 mimuts after pneumoperitoneum, and after tracheal extubation. Postoperative pulmonary complications were also recorded.ResultsAfter pneumoperitoneum, peak inspiratory pressure (Ppeak), plateau pressure (Pplat), mean pressure (Pmean), driving pressure (ΔP), and airway resistance (Raw) increased significantly, and pulmonary compliance (Crs) decreased, persisting during pneumoperitoneum in all groups. Between immediately after pneumoperitoneum establishment, 30 min, 60 min, and 90 min, pulmonary compliance in the 10cmH2OPEEP group was higher than in the 5cmH2OPEEP (P < 0.05) and 0cmH2OPEEP groups(P < 0.05). The driving pressure (ΔP) immediately after pneumoperitoneum establishment, at 30 min, 60 min, and 90 min in the 10cmH2OPEEP group was lower than in the 5cmH2OPEEP (P < 0.05) and 0cmH2OPEEP groups (P < 0.05). Sixty min after pneumoperitoneum and tracheal extubation, the PaCO2 did not differ significantly among the three groups (P > 0.05). The oxygenation index (PaO2/FiO2) was higher in the PEEP5 group than in the PEEP0 and PEEP10 groups 60 min after pneumoperitoneum and after tracheal extubation, with a statistically significant difference (P < 0.05). In postoperative pulmonary complications, the incidence of atelectasis was higher in the PEEP0 group than in the PEEP5 and PEEP10 groups, with a statistically significant difference (p < 0.05).ConclusionThe use of PEEP at 5cmH2O during RARP increases lung compliance, improves intraoperative oxygenation index and reduces postoperative atelectasis.Trial registrationThis study was registered in the China Clinical Trials Registry on May 30, 2020 (Registration No. ChiCTR2000033380).

Hyperoxemia in invasively ventilated COVID–19 patients–Insights from the PRoVENT–COVID study

ObjectiveWe determined the prevalences of hyperoxemia and excessive oxygen use, and the epidemiology, ventilation characteristics and outcomes associated with hyperoxemia in invasively ventilated patients with coronavirus disease 2019 (COVID–19). MethodsPost hoc analysis of a national, multicentre, observational study in 22 ICUs. Patients were classified in the first two days of invasive ventilation as ‘hyperoxemic’ or ‘normoxemic’. The co–primary endpoints were prevalence of hyperoxemia (PaO2 > 90 mmHg) and prevalence of excessive oxygen use (FiO2 ≥ 60% while PaO2 > 90 mmHg or SpO2 > 92%). Secondary endpoints included ventilator settings and ventilation parameters, duration of ventilation, length of stay (LOS) in ICU and hospital, and mortality in ICU, hospital, and at day 28 and 90. We used propensity matching to control for observed confounding factors that may influence endpoints. ResultsOf 851 COVID–19 patients, 225 (26.4%) were classified as hyperoxemic. Excessive oxygen use occurred in 385 (45.2%) patients. Acute respiratory distress syndrome (ARDS) severity was lowest in hyperoxemic patients. Hyperoxemic patients were ventilated with higher positive end–expiratory pressure (PEEP), while rescue therapies for hypoxemia were applied more often in normoxemic patients. Neither in the unmatched nor in the matched analysis were there differences between hyperoxemic and normoxemic patients with regard to any of the clinical outcomes. ConclusionIn this cohort of invasively ventilated COVID–19 patients, hyperoxemia occurred often and so did excessive oxygen use. The main differences between hyperoxemic and normoxemic patients were ARDS severity and use of PEEP. Clinical outcomes were not different between hyperoxemic and normoxemic patients.

High PEEP Levels during CPR Improve Ventilation without Deleterious Haemodynamic Effects in Pigs.

Background: Invasive ventilation during cardiopulmonary resuscitation (CPR) is very complex due to unique thoracic pressure conditions. Current guidelines do not provide specific recommendations for ventilation during ongoing chest compressions regarding positive end-expiratory pressure (PEEP). This trial examines the cardiopulmonary effects of PEEP application during CPR. Methods: Forty-two German landrace pigs were anaesthetised, instrumented, and randomised into six intervention groups. Three PEEP levels (0, 8, and 16 mbar) were compared in high standard and ultralow tidal volume ventilation. After the induction of ventricular fibrillation, mechanical chest compressions and ventilation were initiated and maintained for thirty minutes. Blood gases, ventilation/perfusion ratio, and electrical impedance tomography loops were taken repeatedly. Ventilation pressures and haemodynamic parameters were measured continuously. Postmortem lung tissue damage was assessed using the diffuse alveolar damage (DAD) score. Statistical analyses were performed using SPSS, and p values <0.05 were considered significant. Results: The driving pressure (Pdrive) showed significantly lower values when using PEEP 16 mbar than when using PEEP 8 mbar (p = 0.045) or PEEP 0 mbar (p < 0.001) when adjusted for the ventilation mode. Substantially increased overall lung damage was detected in the PEEP 0 mbar group (vs. PEEP 8 mbar, p = 0.038; vs. PEEP 16 mbar, p = 0.009). No significant differences in mean arterial pressure could be detected. Conclusion: The use of PEEP during CPR seems beneficial because it optimises ventilation pressures and reduces lung damage without significantly compromising blood pressure. Further studies are needed to examine long-term effects in resuscitated animals.

The Influence of Positive End-Expiratory Pressure on Leakage and Oxygenation Using a Laryngeal Mask Airway: A Randomized Trial.

The value of positive end-expiratory pressure (PEEP) in maintaining oxygenation during ventilation with a laryngeal mask airway (LMA) mask is unclear. To clarify the potential benefit or harm to PEEP application during positive pressure ventilation with a ProSeal LMA® mask, we compared the effect of PEEP versus zero end-expiratory pressure (ZEEP) on gas leakage and oxygenation. We hypothesized that a PEEP of 8 mbar (8.2 cm H 2 O) would be associated with an increased incidence of gas leakage compared to ZEEP. We designed a prospective, controlled, randomized, single-blinded, multicenter clinical trial. Patients >18 years of age with an American Society of Anesthesiologists (ASA) physical status I/II without increased risk of aspiration were enrolled if they were scheduled for elective surgery under general anesthesia with an LMA mask. Patients were randomized to a control group managed with ZEEP or an intervention group managed with a PEEP of 8 mbar. Both groups received positive pressure ventilation. The primary end point was the occurrence of gas leakage. The Student t test and χ 2 test were used for statistical analysis. A total of 174 patients were enrolled in the ZEEP group, and 208 were enrolled in the PEEP group. The incidence of gas leakage did not differ between the 2 groups (ZEEP: 23/174, 13.2%; PEEP: 42/208, 20.2%; P = .071; odds ratio [OR], 1.611; 95% confidence interval [CI], 0.954-2.891). However, more patients required reseating of the LMA mask in the PEEP group (ZEEP: 5/174, 2.9%; PEEP: 18/208, 8.7%; P = .018; OR, 3.202; 95% CI, 1.164-8.812). The need for endotracheal intubation did not differ between groups (ZEEP: 2/174, 1.1%; PEEP: 7/208, 3.4%; P = .190; OR, 2.995; 95% CI, 0.614-14.608). After positive pressure ventilation for 25 minutes, the mean peripheral oxygen saturation (Sp o2 ) was higher in the PEEP than in the ZEEP group (98.5 [1.9]% vs 98.0 [1.4]%; P = .01). Peak inspiratory pressure (PIP; 16 [2] vs 12 [4] mbar; P < .001) and dynamic compliance (57 [14] vs 49 [14] mL/mbar; P < .001) were both higher in the PEEP group than in the ZEEP group. Use of PEEP did not affect the overall incidence of gas leakage. However, PEEP did result in a higher incidence of attempts to reseat the LMA mask compared to ZEEP, whereas the incidence of rescue intubation did not differ between groups. We concluded that a PEEP of 8 mbar did not increase overall gas leakage during positive pressure ventilation with an LMA mask, but it did slightly improve gas exchange and compliance. Overall, our study does not provide strong arguments for using PEEP during ventilation with an LMA mask in elective surgery.

Cardiovascular and Gas Exchange Effects of Individualized Positive End-Expiratory Pressures in Cats Anesthetized With Isoflurane.

ObjectivesTo compare the effects of four levels of end-expiratory pressure [zero (ZEEP) and three levels of positive end-expiratory pressure (PEEP)] on the cardiovascular system and gas exchange of cats anesthetized with isoflurane and mechanically ventilated for 3 h with a tidal volume of 10 ml/kg.Study DesignProspective, randomized, controlled trial.AnimalsSix healthy male neutered purpose-bred cats.MethodsAnesthesia was induced with isoflurane and maintained at 1.3 minimum alveolar concentration. PEEP of maximal respiratory compliance (PEEPmaxCrs) was identified in a decremental PEEP titration, and cats were randomly ventilated for 3 h with one of the following end-expiratory pressures: ZEEP, PEEPmaxCrs minus 2 cmH2O (PEEPmaxCrs−2), PEEPmaxCrs, and PEEPmaxCrs plus 2 cmH2O (PEEPmaxCrs+2). Cardiovascular and gas exchange variables were recorded at 5, 30, 60, 120, and 180 min (T5 to T180, respectively) of ventilation and compared between and within ventilation treatments with mixed-model ANOVA followed by Dunnet's and Tukey's tests (normal distribution) or Friedman test followed by the Dunn's test (non-normal distribution). Significance to reject the null hypothesis was considered p < 0.05.ResultsMean arterial pressure (MAP—mmHg) was lower in PEEPmaxCrs+2 [63 (49–69); median (range)] when compared to ZEEP [71 (67–113)] at T5 and stroke index (ml/beat/kg) was lower in PEEPmaxCrs+2 (0.70 ± 0.20; mean ± SD) than in ZEEP (0.90 ± 0.20) at T60. Cardiac index, oxygen delivery index (DO2I), systemic vascular resistance index, and shunt fraction were not significantly different between treatments. The ratio between arterial partial pressure and inspired concentration of oxygen (PaO2/FIO2) was lower in ZEEP than in the PEEP treatments at various time points. At T180, DO2I was higher when compared to T5 in PEEPmaxCrs. Dopamine was required to maintain MAP higher than 60 mmHg in one cat during PEEPmaxCrs and in three cats during PEEPmaxCrs+2.ConclusionIn cats anesthetized with isoflurane and mechanically ventilated for 3 h, all levels of PEEP mildly improved gas exchange with no significant difference in DO2I when compared to ZEEP. The PEEP levels higher than PEEPmaxCrs−2 caused more cardiovascular depression, and dopamine was an effective treatment. A temporal increase in DO2I was observed in the cats ventilated with PEEPmaxCrs. The effects of these levels of PEEP on respiratory mechanics, ventilation-induced lung injury, as well as in obese and critically ill cats deserve future investigation for a better understanding of the clinical use of PEEP in this species.

Intraoperative Protective Mechanical Ventilation in Dogs: A Randomized Clinical Trial.

ObjectiveTo evaluate gas exchange, respiratory mechanics, and hemodynamic impact of mechanical ventilation with low tidal volume (VT) in dogs with the use of positive end-expiratory pressure (PEEP) or preceded by alveolar recruitment maneuver (ARM).Study DesignProspective randomized clinical trial.AnimalsTwenty-one healthy client-owned mesocephalic healthy dogs, 1–7 years old, weighing 10–20 kg, and body condition scores 4–6/9 admitted for periodontal treatment.MethodsIsoflurane-anesthetized dogs in dorsal recumbency were ventilated until 1 h with a volume-controlled ventilation mode using 8 mL kg−1 of VT. The dogs were distributed in 2 groups: in the ARM group, PEEP starts in 0 cmH2O, increasing gradually 5 cmH2O every 3 min, until reach 15 cmH2O and decreasing in the same steps until 5 cmH2O, maintaining this value until the end; and PEEP group, in which the pressure 5 cmH2O was instituted from the beginning of anesthesia and maintained the same level up to the end of the anesthesia. Cardiopulmonary, metabolic, oxygenation parameters, and respiratory mechanics were recorded after the anesthesia induction (baseline—BL), 15, 45, and 75 min after BL and during the recovery.ResultsThe ARM increased the static compliance (Cst) (15 min after baseline) when compared with baseline moment (24.9 ± 5.8 mL cmH20−1 vs. 20.7 ± 5.4 mL cmH20−1–p = 0.0364), oxygenation index (PaO2/FIO2) (505.6 ± 59.2 mmHg vs. 461.2 ± 41.0 mmHg—p = 0.0453) and reduced the shunt fraction (3.4 ± 2.4% vs. 5.5 ± 1.6%—p = 0.062). In the PEEP group, no statistical differences were observed concerning the variables evaluated. At the beginning of the evaluation, the driving pressure (DP) before ARM was significantly greater than all other evaluation time points (6.9 ± 1.8 cmH20).Conclusions and Clinical RelevanceThe use of 8 mL kg−1 of VT and 5 cmH20 PEEP without ARM maintain adequate oxygenation and mechanical ventilation in dental surgeries for up to 1 h. The use of ARM slightly improved compliance and oxygenation during the maneuver.

Effects of intraoperative positive end-expiratory pressure and fraction of inspired oxygen on postoperative oxygenation in dogs undergoing stifle surgery

ObjectiveTo compare the effects of fraction of inspired oxygen (FiO2) with the addition of positive end-expiratory pressure (PEEP) during anesthesia on arterial oxygenation in the first 4 postoperative hours in dogs. We hypothesized that compared with dogs breathing FiO2 ≥ 0.95 and no PEEP (ZEEP), the use of intraoperative PEEP would improve postoperative oxygenation, and that the use of PEEP combined with an FiO2 of 0.4 would further improve it. Study designProspective, randomized study. AnimalsA total of 30 dogs undergoing unilateral stifle surgery. MethodsUsing a standardized anesthetic protocol, dogs were assigned to either FiO2 ≥ 0.95 and ZEEP, FiO2 ≥ 0.95 and 5 cmH2O PEEP or FiO2 0.4 and 5 cmH2O PEEP. All dogs were mechanically ventilated with a tidal volume of 12 mL kg–1. Dogs breathed room air after recovery from anesthesia. Arterial blood gases were measured during surgical closure and 10, 120 and 240 minutes after extubation. Demographic characteristics were compared with Kruskal–Wallis tests. The effects of treatment and time on the PaO2, PaCO2, PaO2:FiO2 and shunt fraction (F-shunt) were assessed with mixed-effect models. ResultsThe PaO2 and F-shunt were lower during anesthesia for dogs breathing FiO2 0.4. No differences among groups were measured after extubation for any variable. Conclusions and clinical relevanceCompared with dogs ventilated with FiO2 ≥ 0.95 and ZEEP, application of 5 cmH2O PEEP did not improve intraoperative gas exchange. The combination of 5 cmH2O PEEP and FiO2 0.4 resulted in lower intraoperative F-shunt values. However, no benefits from those maneuvers on postoperative PaO2 and F-shunt were recorded after extubation, suggesting that alterations in pulmonary function imposed by anesthesia were reversed soon after extubation.