Individualised positive end-expiratory pressure guided by electrical impedance tomography for robot-assisted laparoscopic radical prostatectomy: a prospective, randomised controlled clinical trial

Effect of flow-optimized pressure control ventilation-volume guaranteed (PCV-VG) on postoperative pulmonary complications: a consort study

BACKGROUND

Postoperative pulmonary complications (PPCs) after one-lung ventilation (OLV) significantly impact patient prognosis and quality of life.

OBJECTIVE

To study the impact of an optimal inspiratory flow rate on PPCs in thoracic surgery patients.

METHODS

One hundred eight elective thoracic surgery patients were randomly assigned to 2 groups in this consort study (control group: n = 53 with a fixed inspiratory expiratory ratio of 1:2; and experimental group [flow rate optimization group]: n = 55). Measurements of Ppeak, Pplat, PETCO2, lung dynamic compliance (Cdyn), respiratory rate, and oxygen concentration were obtained at the following specific time points: immediately after intubation (T0); immediately after starting OLV (T1); 30 min after OLV (T2); and 10 min after 2-lung ventilation (T4). The PaO2:FiO2 ratio was measured using blood gas analysis 30 min after initiating one-lung breathing (T2) and immediately when OLV ended (T3). The lung ultrasound score (LUS) was assessed following anesthesia and resuscitation (T5). The occurrence of atelectasis was documented immediately after the surgery. PPCs occurrences were noted 3 days after surgery.

RESULTS

The treatment group had a significantly lower total prevalence of PPCs compared to the control group (3.64% vs. 16.98%; P = 0.022). There were no notable variations in peak airway pressure, airway plateau pressure, dynamic lung compliance, PETCO2, respiratory rate, and oxygen concentration between the two groups during intubation (T0). Dynamic lung compliance and the oxygenation index were significantly increased at T1, T2, and T4 (P < 0.05), whereas the CRP level and number of inflammatory cells decreased dramatically (P < 0.05).

CONCLUSION

Optimizing inspiratory flow rate and utilizing pressure control ventilation -volume guaranteed (PCV-VG) mode can decrease PPCs and enhance lung dynamic compliance in OLV patients.

A stepwise lung recruitment maneuver using I-gel can improve respiratory parameters: A prospective observational study

I-gel has been used in various clinical situations. The study investigated alterations in respiratory parameters following a stepwise lung recruitment maneuver (LRM) using the i-gel. The research involved 60 patients classified as American Society of Anesthesiologists class I-II, aged 30 to 75 years, undergoing elective urologic surgery. Various respiratory parameters, including lung compliance, airway resistance, leak volume, airway pressure, and oxygen reserve index, were recorded at different time points: before LRM, immediately after LRM, and at 5, 15, and 30 minutes after LRM, as well as at the end of the surgery. The primary outcome was to assess an improvement in lung compliance. Dynamic lung compliance (mean ± SD) was significantly increased from 49.2 ± 1.8 to 70.15 ± 3.2 mL/cmH2O (P < .05) after LRM. Static lung compliance (mean ± SD) was increased considerably from 52.4 ± 1.7 to 65.0 ± 2.5 mL/cmH2O (P < .05) after the LRM. Both parameters maintained a statistically significant increased status for a certain period compared to baseline despite a decreased degree of increment. Airway resistance (mean ± SD) was significantly reduced after the LRM from 12.05 ± 0.56 to 10.41 ± 0.64 L/cmH2O/s (P < .05). Stepwise LRM using i-gel may improve lung compliance and airway resistance. Repeated procedures could lead to prolonged improvements in respiratory parameters.

Mechanical power during robotic-assisted laparoscopic prostatectomy: an observational study

BACKGROUND

Robotic-assisted laparoscopic radical prostatectomy (RALP) requires pneumoperitoneum and steep Trendelenburg position. Our aim was to investigate the influence of the combination of pneumoperitoneum and Trendelenburg position on mechanical power and its components during RALP.

METHODS

Sixty-one prospectively enrolled patients scheduled for RALP were studied in supine position before surgery, during pneumoperitoneum and Trendelenburg position and in supine position after surgery at constant ventilatory setting. In a subgroup of 17 patients the response to increasing positive end-expiratory pressure (PEEP) from 5 to 10 cmH2O was studied.

RESULTS

The application of pneumoperitoneum and Trendelenburg position increased the total mechanical power (13.8 [11.6 - 15.5] vs 9.2 [7.5 - 11.7] J/min, p < 0.001) and its elastic and resistive components compared to supine position before surgery. In supine position after surgery the total mechanical power and its elastic component decreased but remained higher compared to supine position before surgery. Increasing PEEP from 5 to 10 cmH2O within each timepoint significantly increased the total mechanical power (supine position before surgery: 9.8 [8.4 - 10.4] vs 12.1 [11.4 - 14.2] J/min, p < 0.001; pneumoperitoneum and Trendelenburg position: 13.8 [12.2 - 14.3] vs 15.5 [15.0 - 16.7] J/min, p < 0.001; supine position after surgery: 10.2 [9.4 - 10.7] vs 12.7 [12.0 - 13.6] J/min, p < 0.001), without affecting respiratory system elastance.

CONCLUSION

Mechanical power in healthy patients undergoing RALP significantly increased both during the pneumoperitoneum and Trendelenburg position and in supine position after surgery. PEEP always increased mechanical power without ameliorating the respiratory system elastance.

Individualized PEEP guided by EIT in patients undergoing general anesthesia: A systematic review and meta-analysis

BACKGROUND

The determination of optimal positive end-expiratory pressure (PEEP) values in patients undergoing general anesthesia remains controversial. Electrical impedance tomography (EIT) directed individualized PEEP has emerged as a novel approach to PEEP setting and has garnered increasing attention. This meta-analysis aims to systematically assess the effect of EIT-guided PEEP setting compared to traditional fixed PEEP values or other PEEP titration strategies in patients undergoing general anesthesia.

METHODS

A comprehensive search of electronic databases, including PubMed, Web of Science, EMBASE, and the Cochrane Library, was conducted from inception to January 2023, with no language restrictions. The search terms used were "EIT"and "PEEP" with their corresponding free words. Two researchers independently conducted literature screening, data extraction, and quality evaluation. The primary outcomes of interest were oxygenation index (OI), lung compliance, and number of postoperative pulmonary complications (PPCs). The secondary outcomes included mean arterial blood pressure (MAP) and number of vasoactive drug injections. RevMan 5.3 software was used to analyze the data and draw the forest plot, and Stata 14.2 software was used to conduct sensitivity analysis to assess the stability of the results.

RESULTS

5 studies involving 272 participants were included in this meta-analysis. Our findings suggest that EIT-guided individualized PEEP setting is superior to traditional fixed PEEP values and other individualized PEEP titration methods in terms of intraoperative OI(OR = 95.73, 95%CI: (49.10, 142.37); P < 0.0001) and lung compliance(OR = 7.69, 95%CI: (5.55, 9.83); P < 0.00001), without affecting intraoperative hemodynamic parameters such as MAP(OR = 2.07, 95%CI: (-1.00, 5.13); P = 0.19) and the number of intravenous vasoactive drugs(OR = 1.22, 95%CI: (0.68, 2.21); P = 0.51) or increasing the incidence of postoperative PPCs(OR = 0.87, 95%CI: (0.41, 1.82); P = 0.71).

CONCLUSIONS

Our meta-analysis suggests potential benefits of EIT-guided individualized PEEP setting in improving intraoperative oxygenation and lung compliance in patients undergoing general anesthesia. However, further research is needed to establish conclusive evidence, and caution should be exercised in interpreting these findings as the current literature remains inconclusive regarding the impact on intraoperative hemodynamics and postoperative complications.

Risk factors for pulmonary complications after colorectal cancer surgery: a Japanese multicenter study

PURPOSE

Pulmonary complications (PC) are a serious condition with a 20% mortality rate. However, few reports have examined risk factors for PC after colorectal surgery. This study investigated the frequency, characteristics, and risk factors for PC after colorectal cancer surgery.

METHODS

Between January 2016 and December 2022, we retrospectively reviewed 3979 consecutive patients who underwent colorectal cancer surgery in seven participating hospitals. Patients were divided into patients who experienced PC (PC group, n = 54) and patients who did not (non-PC group, n = 3925). Clinical and pathological features were compared between groups.

RESULTS

Fifty-four patients (1.5%) developed PC, of whom 2 patients (3.7%) died due to PC. Age was greater (80 years vs 71 years; p < 0.001), frequency of chronic obstructive pulmonary distress was greater (9.3% vs 3.2%; p = 0.029), performance status was poorer (p < 0.001), the proportion of underweight was higher (42.6% vs 13.4%, p < 0.001), frequency of open surgery was greater (24.1% vs 9.3%; p < 0.001), and blood loss was greater (40 mL vs 22 mL; p < 0.001) in the PC group. Multivariate analysis revealed male sex (odds ratio (OR) 2.165, 95% confidence interval (CI) 1.176-3.986; p = 0.013), greater age (OR 3.180, 95%CI 1.798-5.624; p < 0.001), underweight (OR 3.961, 95%CI 2.210-7.100; p < 0.001), and poorer ASA-PS (OR 3.828, 95%CI 2.144-6.834; p < 0.001) as independent predictors of PC.

CONCLUSION

Our study revealed male sex, greater age, underweight, and poorer ASA-PS as factors associated with development of PC, and suggested that pre- and postoperative rehabilitation and pneumonia control measures should be implemented for patients at high risk of PC.

Intraoperative lung protection: strategies and their impact on outcomes

PURPOSE OF REVIEW

The present review summarizes the current knowledge and the barriers encountered when implementing tailoring lung-protective ventilation strategies to individual patients based on advanced monitoring systems.

RECENT FINDINGS

Lung-protective ventilation has become a pivotal component of perioperative care, aiming to enhance patient outcomes and reduce the incidence of postoperative pulmonary complications (PPCs). High-quality research has established the benefits of strategies such as low tidal volume ventilation and low driving pressures. Debate is still ongoing on the most suitable levels of positive end-expiratory pressure (PEEP) and the role of recruitment maneuvers. Adapting PEEP according to patient-specific factors offers potential benefits in maintaining ventilation distribution uniformity, especially in challenging scenarios like pneumoperitoneum and steep Trendelenburg positions. Advanced monitoring systems, which continuously assess patient responses and enable the fine-tuning of ventilation parameters, offer real-time data analytics to predict and prevent impending lung complications. However, their impact on postoperative outcomes, particularly PPCs, is an ongoing area of research.

SUMMARY

Refining protective lung ventilation is crucial to provide patients with the best possible care during surgery, reduce the incidence of PPCs, and improve their overall surgical journey.

Electrical impedance tomography as a bedside assessment tool for COPD treatment during hospitalization

For patients with chronic obstructive pulmonary disease (COPD), the assessment of the treatment efficacy during hospitalization is of importance to the optimization of clinical treatments. Conventional spirometry might not be sensitive enough to capture the regional lung function development. The study aimed to evaluate the feasibility of using electrical impedance tomography (EIT) as an objective bedside evaluation tool for the treatment of acute exacerbation of COPD (AECOPD). Consecutive patients who required hospitalization due to AECOPD were included prospectively. EIT measurements were conducted at the time of admission and before the discharge simultaneously when a forced vital capacity maneuver was conducted. EIT-based heterogeneity measures of regional lung function were calculated based on the impedance changes over time. Surveys for attending doctors and patients were designed to evaluate the ease of use, feasibility, and overall satisfaction level to understand the acceptability of EIT measurements. Patient-reported outcome assessments were conducted. User's acceptance of EIT technology was investigated with a five-dimension survey. A total of 32 patients were included, and 8 patients were excluded due to the FVC maneuver not meeting the ATS criteria. Spirometry-based lung function was improved during hospitalization but not significantly different (FEV1 %pred.: 35.8% ± 6.7% vs. 45.3% ± 8.8% at admission vs. discharge; p = 0.11. FVC %pred.: 67.8% ± 0.4% vs. 82.6% ± 5.0%; p = 0.15. FEV1/FVC: 0.41 ± 0.09 vs. 0.42 ± 0.07, p = 0.71). The symptoms of COPD were significantly improved, but the correlations between the improvement of symptoms and spirometry FEV1 and FEV1/FVC were low (R = 0.1 and -0.01, respectively). The differences in blood gasses and blood tests were insignificant. All but one EIT-based regional lung function parameter were significantly improved after hospitalization. The results highly correlated with the patient-reported outcome assessment (R > 0.6, p < 0.001). The overall acceptability score of EIT measurement for both attending physicians and patients was high (4.1 ± 0.8 for physicians, 4.5 ± 0.5 for patients out of 5). These results demonstrated that it was feasible and acceptable to use EIT as an objective bedside evaluation tool for COPD treatment efficacy.

Evaluation of adjacent and opposite current injection patterns for a wearable chest electrical impedance tomography system

Objective.Wearable electrical impedance tomography (EIT) can be used to monitor regional lung ventilation and perfusion at the bedside. Due to its special system architecture, the amplitude of the injected current is usually limited compared to stationary EIT system. This study aims to evaluate the performance of current injection patterns with various low-amplitude currents in healthy volunteers.Approach.A total of 96 test sets of EIT measurement was recorded in 12 healthy subjects by employing adjacent and opposite current injection patterns with four amplitudes of small current (i.e. 1 mA, 500 uA, 250 uA and 125 uA). The performance of the two injection patterns with various currents was evaluated in terms of signal-to-noise ratio (SNR) of thorax impedance, EIT image metrics and EIT-based clinical parameters.Main results.Compared with adjacent injection, opposite injection had higher SNR (p< 0.01), less inverse artifacts (p< 0.01), and less boundary artifacts (p< 0.01) with the same current amplitude. In addition, opposite injection exhibited more stable EIT-based clinical parameters (p< 0.01) across the current range. For adjacent injection, significant differences were found for three EIT image metrics (p< 0.05) and four EIT-based clinical parameters (p< 0.01) between the group of 125 uA and the other groups.Significance.For better performance of wearable pulmonary EIT, currents greater than 250 uA should be used in opposite injection, 500 uA in adjacent one, to ensure a high level of SNR, a high quality of reconstructed image as well as a high reliability of clinical parameters.

Intraoperative individualization of positive-end-expiratory pressure through electrical impedance tomography or esophageal pressure assessment: a systematic review and meta-analysis of randomized controlled trials

PURPOSE

This systematic review of randomized-controlled trials (RCTs) with meta-analyses aimed to compare the effects on intraoperative arterial oxygen tension to inspired oxygen fraction ratio (PaO2/FiO2), exerted by positive end-expiratory pressure (PEEP) individualized trough electrical impedance tomography (EIT) or esophageal pressure (Pes) assessment (intervention) vs. PEEP not tailored on EIT or Pes (control), in patients undergoing abdominal or pelvic surgery with an open or laparoscopic/robotic approach.

METHODS

PUBMED®, EMBASE®, and Cochrane Controlled Clinical trials register were searched for observational studies and RCTs from inception to the end of August 2022. Inclusion criteria were: RCTs comparing PEEP titrated on EIT/Pes assessment vs. PEEP not individualized on EIT/Pes and reporting intraoperative PaO2/FiO2. Two authors independently extracted data from the enrolled investigations. Data are reported as mean difference and 95% confidence interval (CI).

RESULTS

Six RCTs were included for a total of 240 patients undergoing general anesthesia for surgery, of whom 117 subjects in the intervention group and 123 subjects in the control group. The intraoperative mean PaO2/FiO2 was 69.6 (95%CI 32.-106.4 ) mmHg higher in the intervention group as compared with the control group with 81.4% between-study heterogeneity (p < 0.01). However, at meta-regression, the between-study heterogeneity diminished to 44.96% when data were moderated for body mass index (estimate 3.45, 95%CI 0.78-6.11, p = 0.011).

CONCLUSIONS

In patients undergoing abdominal or pelvic surgery with an open or laparoscopic/robotic approach, PEEP personalized by EIT or Pes allowed the achievement of a better intraoperative oxygenation compared to PEEP not individualized through EIT or Pes.

PROSPERO REGISTRATION NUMBER

CRD 42021218306, 30/01/2023.

The intraoperative management of robotic-assisted laparoscopic prostatectomy

PURPOSE OF REVIEW

Robotic-assisted laparoscopic radical prostatectomy has become the second most commonly performed robotic surgical procedure worldwide, therefore, anesthesiologists should be aware of the intraoperative pathophysiological consequences. The aim of this narrative review is to report the most recent updates regarding the intraoperative management of anesthesia, ventilation, hemodynamics and central nervous system, during robotic-assisted laparoscopic radical prostatectomy.

RECENT FINDINGS

Surgical innovations and the advent of new technologies make it imperative to optimize the anesthesia management to provide the most holistic approach possible. In addition, an ageing population with an increasing burden of comorbidities requires multifocal attention to reduce the surgical stress.

SUMMARY

Total intravenous anesthesia (TIVA) and balanced general anesthesia are similar in terms of postoperative complications and hospital stay. Reversal of rocuronium is associated with shorter hospital stay and postanesthesia recovery time. Adequate PEEP levels improve oxygenation and driving pressure, and the use of a single recruitment maneuver after the intubation reduces postoperative pulmonary complications. Restrictive intravenous fluid administration minimizes bladder-urethra anastomosis complications and facial edema. TIVA maintains a better autoregulation compared with balanced general anesthesia. Anesthesiologists should be able to optimize the intraoperative management to improve outcomes.

Effects of driving pressure-guided ventilation by individualized positive end-expiratory pressure on oxygenation undergoing robot-assisted laparoscopic radical prostatectomy: a randomized controlled clinical trial

PURPOSE

Patients with robot-assisted laparoscopic radical prostatectomy (RALP) need to be placed in Trendelenburg position, which results in cranial displacement of the diaphragm and decreases functional residual capacity and pulmonary compliance. Positive end-expiratory pressure (PEEP) can increase ventilation in the dorsal area, reduce the occurrence of atelectasis and improve oxygenation. However, due to individual differences, inappropriate PEEP will cause lung injury and even hemodynamic instability. Therefore, our study is to evaluate the efficacy of individualized PEEP in RALP.

METHODS

We randomly recruited 48 patients and divided them into driving pressure-guided individualized PEEP group (P group, individualized PEEP) or traditional lung-protective ventilation strategy group (C group, tidal volume 8 mL/kg combined with PEEP of 5cmH2O). The primary outcome was the PaO2/FiO2 before extubation. The secondary outcomes included individualized PEEP values in the P group, the results of arterial blood gas analysis, respiratory mechanics parameters and vital sign parameters. Other measurements included intraoperative vasoactive drug dosage, length of stay, postoperative SpO2, leukocyte count, temperature, serum inflammatory factors and soluble receptor for advanced glycation end products (sRAGE).

RESULTS

Individualized PEEP improved the PaO2/FiO2 before extubation (P = 0.034) and decreased driving pressure (P = 0.011). The PEEP valued in the P group was 14 [10-14] cmH2O. The lung compliance of the P group was significantly higher than that in the C group (P = 0.013). There was no significant difference in other measurements.

CONCLUSIONS

Individualized PEEP could improve PaO2/FiO2 in patients who underwent RALP and do not increase the dosage of intraoperative vasoactive drug and the release of inflammatory factors.

TRIAL REGISTRATION

www.chictr.org.cn (registration no. ChiCTR2100047271).

Impact of a positive end-expiratory pressure strategy on oxygenation, respiratory compliance, and hemodynamics during laparoscopic surgery in non-obese patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Higher positive end-expiratory pressure (PEEP) during laparoscopic surgery may increase oxygenation and respiratory compliance. This meta-analysis aimed to compare the impact of different intraoperative PEEP strategies on arterial oxygenation, compliance, and hemodynamics during laparoscopic surgery in non-obese patients.

METHODS

We searched RCTs in PubMed, Cochrane Library, Web of Science, and Google Scholar from January 2012 to April 2022 comparing the different intraoperative PEEP (Low PEEP (LPEEP): 0-4 mbar; Moderate PEEP (MPEEP): 5-8 mbar; high PEEP (HPEEP): >8 mbar; individualized PEEP - iPEEP) on arterial oxygenation, respiratory compliance (Cdyn), mean arterial pressure (MAP), and heart rate (HR). We calculated mean differences (MD) with 95% confidence intervals (CI), and predictive intervals (PI) using random-effects models. The Cochrane Bias Risk Assessment Tool was applied.

RESULTS

21 RCTs (n = 1554) met the inclusion criteria. HPEEP vs. LPEEP increased PaO2 (+ 29.38 [16.20; 42.56] mmHg, p < 0.0001) or PaO2/FiO2 (+ 36.7 [+ 2.23; +71.70] mmHg, p = 0.04). HPEEP vs. MPEEP increased PaO2 (+ 22.00 [+ 1.11; +42.88] mmHg, p = 0.04) or PaO2/FiO2 (+ 42.7 [+ 2.74; +82.67] mmHg, p = 0.04). iPEEP vs. MPEEP increased PaO2/FiO2 (+ 115.2 [+ 87.21; +143.20] mmHg, p < 0.001). MPEEP vs. LPEP, and HPEEP vs. MPEEP increased PaO2 or PaO2/FiO2 significantly with different heterogeneity. HPEEP vs. LPEEP increased Cdyn (+ 7.87 [+ 1.49; +14.25] ml/mbar, p = 0.02). MPEEP vs. LPEEP, and HPEEP vs. MPEEP did not impact Cdyn (p = 0.14 and 0.38, respectively). iPEEP vs. LPEEP decreased driving pressure (-4.13 [-2.63; -5.63] mbar, p < 0.001). No significant differences in MAP or HR were found between any subgroups.

CONCLUSION

HPEEP and iPEEP during PNP in non-obese patients could promote oxygenation and increase Cdyn without clinically significant changes in MAP and HR. MPEEP could be insufficient to increase respiratory compliance and improve oxygenation. LPEEP may lead to decreased respiratory compliance and worsened oxygenation.

PROSPERO REGISTRATION

CRD42022362379; registered October 09, 2022.

Effect of driving pressure-guided positive end-expiratory pressure on postoperative pulmonary complications in patients undergoing laparoscopic or robotic surgery: a randomised controlled trial

BACKGROUND

Individualised positive end-expiratory pressure (PEEP) improves respiratory mechanics. However, whether PEEP reduces postoperative pulmonary complications (PPCs) remains unclear. We investigated whether driving pressure-guided PEEP reduces PPCs after laparoscopic/robotic abdominal surgery.

METHODS

This single-centre, randomised controlled trial enrolled patients at risk for PPCs undergoing laparoscopic or robotic lower abdominal surgery. The individualised group received driving pressure-guided PEEP, whereas the comparator group received 5 cm H2O fixed PEEP during surgery. Both groups received a tidal volume of 8 ml kg-1 ideal body weight. The primary outcome analysed per protocol was a composite of pulmonary complications (defined by pre-specified clinical and radiological criteria) within 7 postoperative days after surgery.

RESULTS

Some 384 patients (median age: 67 yr [inter-quartile range: 61-73]; 66 [18%] female) were randomised. Mean (standard deviation) PEEP in patients randomised to individualised PEEP (n=178) was 13.6 cm H2O (2.1). Individualised PEEP resulted in lower mean driving pressures (14.7 cm H2O [2.6]), compared with 185 patients randomised to standard PEEP (18.4 cm H2O [3.2]; mean difference: -3.7 cm H2O [95% confidence interval (CI): -4.3 to -3.1 cm H2O]; P<0.001). There was no difference in the incidence of pulmonary complications between individualised (25/178 [14.0%]) vs standard PEEP (36/185 [19.5%]; risk ratio [95% CI], 0.72 [0.45-1.15]; P=0.215). Pulmonary complications as a result of desaturation were less frequent in patients randomised to individualised PEEP (8/178 [4.5%], compared with standard PEEP (30/185 [16.2%], risk ratio [95% CI], 0.28 [0.13-0.59]; P=0.001).

CONCLUSIONS

Driving pressure-guided PEEP did not decrease the incidence of pulmonary complications within 7 days of laparoscopic or robotic lower abdominal surgery, although uncertainty remains given the lower than anticipated event rate for the primary outcome.

CLINICAL TRIAL REGISTRATION

KCT0004888 (http://cris.nih.go.kr, registration date: April 6, 2020).

Effects of individualised positive end-expiratory pressure titration on respiratory and haemodynamic parameters during the Trendelenburg position with pneumoperitoneum: A randomised crossover physiologic trial

BACKGROUND

The Trendelenburg position with pneumoperitoneum during surgery promotes dorsobasal atelectasis formation, which impairs respiratory mechanics and increases lung stress and strain. Positive end-expiratory pressure (PEEP) can reduce pulmonary inhomogeneities and preserve end-expiratory lung volume (EELV), resulting in decreased inspiratory strain and improved gas-exchange. The optimal intraoperative PEEP strategy is unclear.

OBJECTIVES

To compare the effects of individualised PEEP titration strategies on set PEEP levels and resulting transpulmonary pressures, respiratory mechanics, gas-exchange and haemodynamics during Trendelenburg position with pneumoperitoneum.

DESIGN

Prospective, randomised, crossover single-centre physiologic trial.

SETTING

University hospital.

PATIENTS

Thirty-six patients receiving robot-assisted laparoscopic radical prostatectomy.

INTERVENTIONS

Randomised sequence of three different PEEP strategies: standard PEEP level of 5 cmH 2 O (PEEP 5 ), PEEP titration targeting a minimal driving pressure (PEEP ΔP ) and oesophageal pressure-guided PEEP titration (PEEP Poeso ) targeting an end-expiratory transpulmonary pressure ( PTP ) of 0 cmH 2 O.

MAIN OUTCOME MEASURES

The primary endpoint was the PEEP level when set according to PEEP ΔP and PEEP Poeso compared with PEEP of 5 cmH 2 O. Secondary endpoints were respiratory mechanics, lung volumes, gas-exchange and haemodynamic parameters.

RESULTS

PEEP levels differed between PEEP ΔP , PEEP Poeso and PEEP5 (18.0 [16.0 to 18.0] vs. 20.0 [18.0 to 24.0]vs. 5.0 [5.0 to 5.0] cmH 2 O; P  < 0.001 each). End-expiratory PTP and lung volume were lower in PEEP ΔP compared with PEEP Poeso ( P  = 0.014 and P  < 0.001, respectively), but driving pressure, lung stress, as well as respiratory system and dynamic elastic power were minimised using PEEP ΔP ( P  < 0.001 each). PEEP ΔP and PEEP Poeso improved gas-exchange, but PEEP Poeso resulted in lower cardiac output compared with PEEP 5 and PEEP ΔP .

CONCLUSION

PEEP ΔP ameliorated the effects of Trendelenburg position with pneumoperitoneum during surgery on end-expiratory PTP and lung volume, decreased driving pressure and dynamic elastic power, as well as improved gas-exchange while preserving cardiac output.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00028559, date of registration 2022/04/27). https://drks.de/search/en/trial/DRKS00028559.

Individualized PEEP without Recruitment Maneuvers Improves Intraoperative Oxygenation: A Randomized Controlled Study

Individualized positive end-expiratory pressure (PEEP) combined with recruitment maneuvers improves intraoperative oxygenation in individuals undergoing robot-assisted prostatectomy. However, whether electrical impedance tomography (EIT)-guided individualized PEEP without recruitment maneuvers can also improve intraoperative oxygenation is unknown. To test this, fifty-six male patients undergoing elective robot-assisted laparoscopic prostatectomy were randomly assigned to either individualized PEEP (Group PEEPIND, n = 28) or a control with a fixed PEEP of 5 cm H2O (Group PEEP5, n = 28). Individualized PEEP was guided by EIT after placing the patients in the Trendelenburg position and performing intraperitoneal insufflation. Patients in Group PEEPIND maintained individualized PEEP without intermittent recruitment maneuvers, and those in Group PEEP5 maintained a PEEP of 5 cm H2O intraoperatively. Both groups were extubated in a semi-sitting position once the extubation criteria were met. The primary outcome was arterial oxygen partial pressure (PaO2)/inspiratory oxygen fraction (FiO2) prior to extubation. Other outcomes included intraoperative driving pressure, plateau pressure and dynamic, respiratory system compliance, and the incidence of postoperative hypoxemia in the post-operative care unit (PACU). Our results showed that the intraoperative median for PEEPIND was 16 cm H2O (ranging from 12 to 18 cm H2O). EIT-guided PEEPIND was associated with higher PaO2/FiO2 before extubation compared to PEEP5 (71.6 ± 10.7 vs. 56.8 ± 14.1 kPa, p = 0.003). Improved oxygenation extended into the PACU with a lower incidence of postoperative hypoxemia (3.8% vs. 26.9%, p = 0.021). Additionally, PEEPIND was associated with lower driving pressures (12.0 ± 3.0 vs. 15.0 ± 4.4 cm H2O, p = 0.044) and better compliance (44.5 ± 12.8 vs. 33.6 ± 9.1 mL/cm H2O, p = 0.017). Our data indicated that individualized PEEP guided by EIT without intraoperative recruitment maneuvers also improved perioperative oxygenation in patients undergoing robot-assisted laparoscopic radical prostatectomy, which could benefit patients with the risk of intraoperative hemodynamic instability caused by recruitment maneuvers. Trial registration: China Clinical Trial Registration Center Identifier: ChiCTR2100053839. This study was registered on 1 December 2021. The first patient was recruited on 15 December 2021.

Ventilation strategy during urological and gynaecological robotic-assisted surgery: a narrative review

Robotic-assisted surgery has improved the precision and accuracy of surgical movements with subsequent improved outcomes. However, it requires steep Trendelenburg positioning combined with pneumoperitoneum that negatively affects respiratory mechanics and increases the risk of postoperative respiratory complications. This narrative review summarises the state of the art in ventilatory management of these patients in terms of levels of positive end-expiratory pressure (PEEP), tidal volume, recruitment manoeuvres, and ventilation modes during both urological and gynaecological robotic-assisted surgery. A review of the literature was conducted using PubMed/MEDLINE; after completing abstract and full-text review, 31 articles were included. Although different levels of PEEP were often evaluated within a protective ventilation strategy, including higher levels of PEEP, lower tidal volume, and recruitment manoeuvres vs a conventional ventilation strategy, we conclude that the best PEEP in terms of lung mechanics, gas exchange, and ventilation distribution has not been defined, but moderate PEEP levels (4-8 cm H2O) could be associated with better outcomes than lower or highest levels. Recruitment manoeuvres improved intraoperative arterial oxygenation, end-expiratory lung volume and the distribution of ventilation to dependent (dorsal) lung regions. Pressure-controlled compared with volume-controlled ventilation showed lower peak airway pressures with both higher compliance and higher carbon dioxide clearance. We propose directions to optimise ventilatory management during robotic surgery in light of the current evidence.

Individualized Positive End-expiratory Pressure on Postoperative Atelectasis in Patients with Obesity: A Randomized Controlled Clinical Trial

BACKGROUND

Individualized positive end-expiratory pressure (PEEP) guided by dynamic compliance improves oxygenation and reduces postoperative atelectasis in nonobese patients. The authors hypothesized that dynamic compliance-guided PEEP could also reduce postoperative atelectasis in patients undergoing bariatric surgery.

METHODS

Patients scheduled to undergo laparoscopic bariatric surgery were eligible. Dynamic compliance-guided PEEP titration was conducted in all patients using a downward approach. A recruitment maneuver (PEEP from 10 to 25 cm H2O at 5-cm H2O step every 30 s, with 15-cm H2O driving pressure) was conducted both before and after the titration. Patients were then randomized (1:1) to undergo surgery under dynamic compliance-guided PEEP (PEEP with highest dynamic compliance plus 2 cm H2O) or PEEP of 8 cm H2O. The primary outcome was postoperative atelectasis, as assessed with computed tomography at 60 to 90 min after extubation, and expressed as percentage to total lung tissue volume. Secondary outcomes included Pao2/inspiratory oxygen fraction (Fio2) and postoperative pulmonary complications.

RESULTS

Forty patients (mean ± SD; 28 ± 7 yr of age; 25 females; average body mass index, 41.0 ± 4.7 kg/m2) were enrolled. Median PEEP with highest dynamic compliance during titration was 15 cm H2O (interquartile range, 13 to 17; range, 8 to 19) in the entire sample of 40 patients. The primary outcome of postoperative atelectasis (available in 19 patients in each group) was 13.1 ± 5.3% and 9.5 ± 4.3% in the PEEP of 8 cm H2O and dynamic compliance-guided PEEP groups, respectively (intergroup difference, 3.7%; 95% CI, 0.5 to 6.8%; P = 0.025). Pao2/Fio2 at 1 h after pneumoperitoneum was higher in the dynamic compliance-guided PEEP group (397 vs. 337 mmHg; group difference, 60; 95% CI, 9 to 111; P = 0.017) but did not differ between the two groups 30 min after extubation (359 vs. 375 mmHg; group difference, -17; 95% CI, -53 to 21; P = 0.183). The incidence of postoperative pulmonary complications was 4 of 20 in both groups.

CONCLUSIONS

Postoperative atelectasis was lower in patients undergoing laparoscopic bariatric surgery under dynamic compliance-guided PEEP versus PEEP of 8 cm H2O. Postoperative Pao2/Fio2 did not differ between the two groups.

EDITOR’S PERSPECTIVE

Effect of individualized PEEP titration by ultrasonography on perioperative pulmonary protection and postoperative cognitive function in patients with chronic obstructive pulmonary disease

OBJECTIVE

To evaluate the effect of the individualized positive end-expiratory pressure (PEEP) lung protection ventilation strategy by combining driving pressure (ΔP) and pulmonary ultrasound (LUS)-based titration on lung function and postoperative cognitive function in patients with chronic obstructive pulmonary disease (COPD) during laparoscopic surgery.

METHODS

A total of 108 patients with COPD undergoing laparoscopic gastrointestinal surgery under general anesthesia were included in this study. They were randomly divided into three groups (n = 36): traditional volume ventilation group (Group C), fixed PEEP 5 cmH₂O group (Group P), and ΔP combined with LUS-based PEEP titration in the resuscitation room group (Group T). All three groups were given volume ventilation mode, I:E = 1:2; In group C, VT was 10 mL/kg and PEEP was 0 cmH₂O; In groups P and T, VT was 6 mL/kg and PEEP was 5 cmH₂O; After mechanical ventilation for 15 min in Group T, ΔP in combination with LUS was used to titrate PEEP. The oxygenation index (PaO2/FiO2), airway platform pressure (Pplat), dynamic lung compliance (Cdyn), Montreal Cognitive Assessment (MoCA), and venous interleukin-6(IL-6) were recorded at the corresponding time points, and the final PEEP value in Group T was recorded.

RESULTS

The final PEEP value of Group T was (6.4 ± 1.2) cmH₂O; Compared with groups C and P: PaO₂/FiO₂ and Cdyn in Group T were significantly increased (P < 0.05) and value of IL-6 was significantly decreased (P < 0.05) at the corresponding time points. Compared with group C, the MoCA score on day 7 after surgery in Group T was significantly higher (P < 0.05).

CONCLUSION

Compared with the traditional ventilation strategy, the individualized ΔP combined with LUS-based PEEP titration in patients with COPD during the perioperative period of laparoscopic surgery can play a better role in lung protection and can improve postoperative cognitive function.

Effect of driving pressure on early postoperative lung gas distribution in supratentorial craniotomy: a randomized controlled trial

BACKGROUND

Neurosurgical patients represent a high-risk population for postoperative pulmonary complications (PPCs). A lower intraoperative driving pressure (DP) is related to a reduction in postoperative pulmonary complications. We hypothesized that driving pressure-guided ventilation during supratentorial craniotomy might lead to a more homogeneous gas distribution in the lung postoperatively.

METHODS

This was a randomized trial conducted between June 2020 and July 2021 at Beijing Tiantan Hospital. Fifty-three patients undergoing supratentorial craniotomy were randomly divided into the titration group or control group at a ratio of 1 to 1. The control group received 5 cmH₂O PEEP, and the titration group received individualized PEEP targeting the lowest DP. The primary outcome was the global inhomogeneity index (GI) immediately after extubation obtained by electrical impedance tomography (EIT). The secondary outcomes were lung ultrasonography scores (LUSs), respiratory system compliance, the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO₂/FiO₂) and PPCs within 3 days postoperatively.

RESULTS

Fifty-one patients were included in the analysis. The median (IQR [range]) DP in the titration group versus the control group was 10 (9-12 [7-13]) cmH₂O vs. 11 (10-12 [7-13]) cmH₂O, respectively (P = 0.040). The GI tract did not differ between groups immediately after extubation (P = 0.080). The LUS_S was significantly lower in the titration group than in the control group immediately after tracheal extubation (1 [0-3] vs. 3 [1-6], P = 0.045). The compliance in the titration group was higher than that in the control group at 1 h after intubation (48 [42-54] vs. 41 [37-46] ml·cmH₂O^-1, P = 0.011) and at the end of surgery (46 [42-51] vs. 41 [37-44] ml·cmH₂O^-1, P = 0.029). The PaO₂/FiO₂ ratio was not significantly different between groups in terms of the ventilation protocol (P = 0.117). At the 3-day follow-up, no postoperative pulmonary complications occurred in either group.

CONCLUSIONS

Driving pressure-guided ventilation during supratentorial craniotomy did not contribute to postoperative homogeneous aeration, but it may lead to improved respiratory compliance and lower lung ultrasonography scores.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT04421976.

Effects of Individualised High Positive End-Expiratory Pressure and Crystalloid Administration on Postoperative Pulmonary Function in Patients Undergoing Robotic-Assisted Radical Prostatectomy: A Prospective Randomised Single-Blinded Pilot Study

OBJECTIVES

Robotic-assisted laparoscopic prostatectomy (RALP) is typically conducted in steep Trendelenburg position (STP). The aim of the study was to evaluate whether crystalloid administration and individual management of positive end-expiratory pressure (PEEP) improve peri- and post-operative pulmonary function in patients undergoing RALP.

DESIGN

Prospective randomised single-centre single-blinded explorative study.

SETTING

Patients were either allocated to a standard PEEP (5 cmH₂O) group or an individualised high PEEP group. Furthermore, each group was divided into a liberal and a restrictive crystalloid group (8 vs. 4 mL/kg/h predicted body weight). Individualised PEEP levels were determined by means of preoperative recruitment manoeuvre and PEEP titration in STP.

PARTICIPANTS

Informed consent was obtained from 98 patients scheduled for elective RALP.

INTERVENTIONS

The following intraoperative parameters were analysed in each of the four study groups: ventilation setting (peak inspiratory pressure [PIP], plateau pressure, driving pressure [P_driv], lung compliance [LC] and mechanical power [MP]) and postoperative pulmonary function (bed-side spirometry). The spirometric parameters Tiffeneau index (FEV₁/FVC ratio) and mean forced expiratory flow (FEF_25-75) were measured pre- and post-operatively. Data are shown as mean ± standard deviation (SD), and groups were compared with ANOVA. A p-value of <0.05 was considered significant.

RESULTS

The two individualised high PEEP groups (mean PEEP 15.5 [±1.71 cmH₂O]) showed intraoperative significantly higher PIP, plateau pressure and MP levels but significantly decreased P_driv and increased LC. On the first and second postoperative day, patients with individualised high PEEP levels had a significantly higher mean Tiffeneau index and FEF_25-75. Perioperative oxygenation and ventilation and postoperative spirometric parameters were not influenced by restrictive or liberal crystalloid infusion in either of the two respective PEEP groups.

CONCLUSIONS

Individualised high PEEP levels (≥14 cmH₂O) during RALP improved intraoperative blood oxygenation and resulted in more lung-protective ventilation. Furthermore, postoperative pulmonary function was improved for up to 48 h after surgery in the sum of the two individualised high PEEP groups. Restrictive crystalloid infusion during RALP seemed to have no effect on peri- and post-operative oxygenation and pulmonary function.

Driving pressure-guided ventilation improves homogeneity in lung gas distribution for gynecological laparoscopy: a randomized controlled trial

To investigate whether driving pressure-guided ventilation could contribute to a more homogeneous distribution in the lung for gynecological laparoscopy. Chinese patients were randomized, after pneumoperitoneum, to receive either positive end expiratory pressure (PEEP) of 5 cm H₂O (control group), or individualized PEEP producing the lowest driving pressure (titration group). Ventilation homogeneity is quantified as the global inhomogeneity (GI) index based on electrical impedance tomography, with a lower index implying more homogeneous ventilation. The perioperative arterial oxygenation index and respiratory system mechanics were also recorded. Blood samples were collected for lung injury biomarkers including interleukin-10, neutrophil elastase, and Clara Cell protein-16. A total of 48 patients were included for analysis. We observed a significant increase in the GI index immediately after tracheal extubation compared to preinduction in the control group (p = 0.040) but not in the titration group (p = 0.279). Furthermore, the GI index was obviously lower in the titration group than in the control group [0.390 (0.066) vs 0.460 (0.074), p = 0.0012]. The oxygenation index and respiratory compliance were significantly higher in the titration group than in the control group. No significant differences in biomarkers or hemodynamics were detected between the two groups. Driving pressure-guided PEEP led to more homogeneous ventilation, as well as improved gas exchange and respiratory compliance for patients undergoing gynecological laparoscopy.Trial Registration: ClinicalTrials.gov NCT04374162; first registration on 05/05/2020.

Distribution of ventilation and oxygenation in surgical obese patients ventilated with high versus low positive end-expiratory pressure: A substudy of a randomised controlled trial

BACKGROUND

Intra-operative ventilation using low/physiological tidal volume and positive end-expiratory pressure (PEEP) with periodic alveolar recruitment manoeuvres (ARMs) is recommended in obese surgery patients.

OBJECTIVES

To investigate the effects of PEEP levels and ARMs on ventilation distribution, oxygenation, haemodynamic parameters and cerebral oximetry.

DESIGN

A substudy of a randomised controlled trial.

SETTING

Tertiary medical centre in Geneva, Switzerland, between 2015 and 2018.

PATIENTS

One hundred and sixty-two patients with a BMI at least 35 kg per square metre undergoing elective open or laparoscopic surgery lasting at least 120 min.

INTERVENTION

Patients were randomised to PEEP of 4 cmH 2 O ( n  = 79) or PEEP of 12 cmH 2 O with hourly ARMs ( n  = 83).

MAIN OUTCOME MEASURES

The primary endpoint was the fraction of ventilation in the dependent lung as measured by electrical impedance tomography. Secondary endpoints were the oxygen saturation index (SaO 2 /FIO 2 ratio), respiratory and haemodynamic parameters, and cerebral tissue oximetry.

RESULTS

Compared with low PEEP, high PEEP was associated with smaller intra-operative decreases in dependent lung ventilation [-11.2%; 95% confidence interval (CI) -8.7 to -13.7 vs. -13.9%; 95% CI -11.7 to -16.5; P  = 0.029], oxygen saturation index (-49.6%; 95% CI -48.0 to -51.3 vs. -51.3%; 95% CI -49.6 to -53.1; P  < 0.001) and a lower driving pressure (-6.3 cmH 2 O; 95% CI -5.7 to -7.0). Haemodynamic parameters did not differ between the groups, except at the end of ARMs when arterial pressure and cardiac index decreased on average by -13.7 mmHg (95% CI -12.5 to -14.9) and by -0.54 l min -1  m -2 (95% CI -0.49 to -0.59) along with increased cerebral tissue oximetry (3.0 and 3.2% on left and right front brain, respectively).

CONCLUSION

In obese patients undergoing abdominal surgery, intra-operative PEEP of 12 cmH 2 O with periodic ARMs, compared with intra-operative PEEP of 4 cmH 2 O without ARMs, slightly redistributed ventilation to dependent lung zones with minor improvements in peripheral and cerebral oxygenation.

TRIAL REGISTRATION

NCT02148692, https://clinicaltrials.gov/ct2.

Recruitable alveolar collapse and overdistension during laparoscopic gynecological surgery and mechanical ventilation: a prospective clinical study

Background

Laparoscopic surgery in Trendelenburg position may impede mechanical ventilation (MV) due to positioning and high intra-abdominal pressure. We sought to identify the positive end-expiratory pressure (PEEP) levels necessary to counteract atelectasis formation (“Open-Lung-PEEP”) and to provide an equal balance between overdistension and alveolar collapse (“Best-Compromise-PEEP”).

Methods

In 30 patients undergoing laparoscopic gynecological surgery, relative overdistension and alveolar collapse were assessed with electrical impedance tomography (EIT) during a decremental PEEP trial ranging from 20 to 4 cmH₂O in supine position without capnoperitoneum and in Trendelenburg position with capnoperitoneum.

Results

In supine position, the median Open-Lung-PEEP was 12 (8–14) cmH₂O with 8.7 (4.7–15.5)% of overdistension and 1.7 (0.4–2.2)% of collapse. Best-Compromise-PEEP was 8 (6.5–10) cmH₂O with 4.2 (2.4–7.2)% of overdistension and 5.1 (3.9–6.5)% of collapse. In Trendelenburg position with capnoperitoneum, Open-Lung-PEEP was 18 (18–20) cmH ₂ O (p < 0.0001 vs supine position) with 1.8 (0.5–3.9)% of overdistension and 0 (0–1.2)% of collapse and Best-Compromise-PEEP was 18 (16–20) cmH₂O (p < 0.0001 vs supine position) with 1.5 (0.7–3.0)% of overdistension and 0.2 (0–2.7)% of collapse. Open-Lung-PEEP and Best-Compromise-PEEP were positively correlated with body mass index during MV in supine position but not in Trendelenburg position.

Conclusion

The PEEP levels required for preventing alveolar collapse and for balancing collapse and overdistension in Trendelenburg position with capnoperitoneum were significantly higher than those required for achieving the same goals in supine position without capnoperitoneum. Even with high PEEP levels, alveolar overdistension was negligible during MV in Trendelenburg position with capnoperitoneum.

Trial registration

This study was prospectively registered at German Clinical Trials registry (DRKS00016974).

Methods for Determination of Individual PEEP for Intraoperative Mechanical Ventilation Using a Decremental PEEP Trial

(1) Background: Individual PEEP settings (PEEPIND) may improve intraoperative oxygenation and optimize lung mechanics. However, there is uncertainty concerning the optimal procedure to determine PEEPIND. In this secondary analysis of a randomized controlled clinical trial, we compared different methods for PEEPIND determination. (2) Methods: Offline analysis of decremental PEEP trials was performed and PEEPIND was retrospectively determined according to five different methods (EIT-based: RVDI method, Global Inhomogeneity Index [GI], distribution of tidal ventilation [EIT VT]; global dynamic and quasi-static compliance). (3) Results: In the 45 obese and non-obese patients included, PEEPIND using the RVDI method (PEEPRVD) was 16.3 ± 4.5 cm H2O. Determination of PEEPIND using the GI and EIT VT resulted in a mean difference of −2.4 cm H2O (95%CI: −1.2;−3.6 cm H2O, p = 0.01) and −2.3 cm H2O (95% CI: −0.9;3.7 cm H2O, p = 0.01) to PEEPRVD, respectively. PEEPIND selection according to quasi-static compliance showed the highest agreement with PEEPRVD (p = 0.67), with deviations > 4 cm H2O in 3/42 patients. PEEPRVD and PEEPIND according to dynamic compliance also showed a high level of agreement, with deviations > 4 cm H2O in 5/42 patients (p = 0.57). (4) Conclusions: High agreement of PEEPIND determined by the RVDI method and compliance-based methods suggests that, for routine clinical practice, PEEP selection based on best quasi-static or dynamic compliance is favorable.

Positive end-expiratory pressure and risk of postoperative pulmonary complications in patients living at high altitudes and undergoing surgery at low altitudes: a single-centre, retrospective observational study in China

OBJECTIVES

To examine whether a high positive end-expiratory pressure (PEEP ≥5 cmH₂O) has a protective effect on the risk of postoperative pulmonary complications (PPCs) in a cohort of patients living at high altitudes and undergoing general anaesthesia.

DESIGN

Retrospective, observational study.

SETTING

A tertiary hospital in China.

PARTICIPANTS

Adult Tibetan patients living at high altitudes (≥3000 m) and who went to the low-altitude plain to undergo non-cardiothoracic surgery under general anaesthesia, from January 2018 to April 2020.

MEASUREMENTS

This study included 1905 patients who were divided according to the application of an intraoperative PEEP: low PEEP (<5 cmH₂O, including 0 cmH₂O) or high PEEP (≥5 cmH₂O). The primary outcome was a composite of PPCs within the first 7 postoperative days. The secondary outcomes included reintubation and unplanned intensive care unit (ICU) admission within the first 7 postoperative days and total hospital stays (day).

RESULTS

The study included 1032 patients in the low PEEP group and 873 in the high PEEP group. There were no differences in the incidence of PPCs between the high and low PEEP groups (relative risk (RR) 0.913; 95% CI 0.716 to 1.165; p=0.465). After propensity score matching, 643 patients remained in each group, and the incidence of PPCs in the low PEEP group (18.0%) was higher than in the high PEEP group (13.7%; RR 0.720; 95% CI 0.533 to 0.974; p=0.033). There were no differences in the incidence of reintubation, unplanned ICU admission or hospital stays. The risk factors of PPCs derived from multiple regression showed that the application of >5 cmH₂O PEEP during intraoperative mechanical ventilation was associated with a significantly lower risk of PPCs in patients from a high altitude (OR=0.725, 95% CI 0.530 to 0.992; p=0.044).

CONCLUSIONS

The application of PEEP ≥5 cmH₂O during intraoperative mechanical ventilation in patients living at high altitudes and undergoing surgery at low altitudes may be associated with a lower risk of PPCs. Prospective longitudinal studies are needed to further investigate perioperative lung protection ventilation strategies for patients from high altitudes.

TRIAL REGISTRATION NUMBER

Chinese Clinical Trial Registry (ChiCTR2100044260).

Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

Positive end-expiratory pressure individualization guided by continuous end-expiratory lung volume monitoring during laparoscopic surgery

To determine whether end-expiratory lung volume measured with volumetric capnography (EELV_CO2) can individualize positive end-expiratory pressure (PEEP) setting during laparoscopic surgery. We studied patients undergoing laparoscopic surgery subjected to Fowler (F-group; n = 20) or Trendelenburg (T-group; n = 20) positions. EELV_CO2 was measured at 0° supine (baseline), during capnoperitoneum (CP) at 0° supine, during CP with Fowler (head up + 20°) or Trendelenburg (head down - 30°) positions and after CP back to 0° supine. PEEP was adjusted to preserve baseline EELV_CO2 during and after CP. Baseline EELV_CO2 was statistically similar to predicted FRC in both groups. At supine and CP, EELV_CO2 decreased from baseline values in F-group [median and IQR 2079 (768) to 1545 (725) mL; p = 0.0001] and in T-group [2164 (789) to 1870 (940) mL; p = 0.0001]. Change in body position maintained EELV_CO2 unchanged in both groups. PEEP adjustments from 5.6 (1.1) to 10.0 (2.5) cmH₂O in the F-group (p = 0.0001) and from 5.6 (0.9) to 10.0 (2.6) cmH₂O in T-group (p = 0.0001) were necessary to reach baseline EELV_CO2 values. EELV_CO2 increased close to baseline with PEEP in the F-group [1984 (600) mL; p = 0.073] and in the T-group [2175 (703) mL; p = 0.167]. After capnoperitoneum and back to 0° supine, PEEP needed to maintain EELV_CO2 was similar to baseline PEEP in F-group [5.9 (1.8) cmH₂O; p = 0.179] but slightly higher in the T-group [6.5 (2.2) cmH₂O; p = 0.006]. Those new PEEP values gave EELV_CO2 similar to baseline in the F-group [2039 (980) mL; p = 0.370] and in the T-group [2150 (715) mL; p = 0.881]. Breath-by-breath noninvasive EELV_CO2 detected changes in lung volume induced by capnoperitoneum and body position and was useful to individualize the level of PEEP during laparoscopy.Trial registry: Clinicaltrials.gov NCT03693352. Protocol started 1st October 2018.

Intra-operative open-lung ventilatory strategy reduces postoperative complications after laparoscopic colorectal cancer resection: A randomised controlled trial

BACKGROUND

The role of the positive end-expiratory pressure (PEEP) and lung recruitment manoeuvre (LRM) combination (termed open-lung strategy, OLS) during intra-operative mechanical ventilation is not clear.

OBJECTIVE

To determine whether an open-lung strategy constituting medium PEEP (6-8 cmH2O) and repeated LRMs protects against postoperative complications in at-risk patients undergoing laparoscopic colorectal cancer resection under low-tidal-volume ventilation.

DESIGN

A prospective, assessor-blinded, randomised controlled trial.

SETTING

Single university-affiliated hospital, conducted from January 2017 to October 2018.

PATIENTS

A total of 280 patients at risk of pulmonary complications, scheduled for laparoscopic colorectal cancer resection under general anaesthesia and low-tidal-volume (6-8 ml kg-1 predicted body weight) ventilation.

INTERVENTION

The patients were randomly assigned (1 : 1) to a PEEP of 6-8 cmH2O with LRMs repeated every 30 min (OLS group) or a zero PEEP without LRMs (non-OLS group).

MAIN OUTCOME MEASURES

The primary outcome was a composite of major pulmonary and extrapulmonary complications occurring within 7 days after surgery. The secondary outcomes included intra-operative potentially harmful hypotension and the need for vasopressors.

RESULTS

A total of 130 patients from each group were included in the primary outcome analysis. Primary outcome events occurred in 24 patients (18.5%) in the OLS group and 43 patients (33.1%) in the non-OLS group [relative risk, 0.46; 95% confidence interval (CI), 0.26 to 0.82; P = 0.009). More patients in the OLS group developed potentially harmful hypotension (OLS vs. non-OLS, 15% vs. 4.3%; P = 0.004) and needed vasopressors (25% vs. 8.6%; P < 0.001).

CONCLUSION

Among at-risk patients undergoing laparoscopic colorectal cancer resection under low-tidal-volume ventilation, an open-lung strategy with a PEEP of 6-8 cmH2O and repeated LRMs reduced postoperative complications compared with a strategy using zero PEEP without LRMs. Of note, LRMs should be used with caution in patients with haemodynamic instability.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03160144.

Individualized versus Fixed Positive End-expiratory Pressure for Intraoperative Mechanical Ventilation in Obese Patients: A Secondary Analysis

BACKGROUND

General anesthesia may cause atelectasis and deterioration in oxygenation in obese patients. The authors hypothesized that individualized positive end-expiratory pressure (PEEP) improves intraoperative oxygenation and ventilation distribution compared to fixed PEEP.

METHODS

This secondary analysis included all obese patients recruited at University Hospital of Leipzig from the multicenter Protective Intraoperative Ventilation with Higher versus Lower Levels of Positive End-Expiratory Pressure in Obese Patients (PROBESE) trial (n = 42) and likewise all obese patients from a local single-center trial (n = 54). Inclusion criteria for both trials were elective laparoscopic abdominal surgery, body mass index greater than or equal to 35 kg/m2, and Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score greater than or equal to 26. Patients were randomized to PEEP of 4 cm H2O (n = 19) or a recruitment maneuver followed by PEEP of 12 cm H2O (n = 21) in the PROBESE study. In the single-center study, they were randomized to PEEP of 5 cm H2O (n = 25) or a recruitment maneuver followed by individualized PEEP (n = 25) determined by electrical impedance tomography. Primary endpoint was Pao2/inspiratory oxygen fraction before extubation and secondary endpoints included intraoperative tidal volume distribution to dependent lung and driving pressure.

RESULTS

Ninety patients were evaluated in three groups after combining the two lower PEEP groups. Median individualized PEEP was 18 (interquartile range, 16 to 22; range, 10 to 26) cm H2O. Pao2/inspiratory oxygen fraction before extubation was 515 (individual PEEP), 370 (fixed PEEP of 12 cm H2O), and 305 (fixed PEEP of 4 to 5 cm H2O) mmHg (difference to individualized PEEP, 145; 95% CI, 91 to 200; P < 0.001 for fixed PEEP of 12 cm H2O and 210; 95% CI, 164 to 257; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Intraoperative tidal volume in the dependent lung areas was 43.9% (individualized PEEP), 25.9% (fixed PEEP of 12 cm H2O) and 26.8% (fixed PEEP of 4 to 5 cm H2O) (difference to individualized PEEP: 18.0%; 95% CI, 8.0 to 20.7; P < 0.001 for fixed PEEP of 12 cm H2O and 17.1%; 95% CI, 10.0 to 20.6; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Mean intraoperative driving pressure was 9.8 cm H2O (individualized PEEP), 14.4 cm H2O (fixed PEEP of 12 cm H2O), and 18.8 cm H2O (fixed PEEP of 4 to 5 cm H2O), P < 0.001.

CONCLUSIONS

This secondary analysis of obese patients undergoing laparoscopic surgery found better oxygenation, lower driving pressures, and redistribution of ventilation toward dependent lung areas measured by electrical impedance tomography using individualized PEEP. The impact on patient outcome remains unclear.

EDITOR’S PERSPECTIVE

Management of Intraoperative Mechanical Ventilation to Prevent Postoperative Complications after General Anesthesia: A Narrative Review

Mechanical ventilation (MV) is still necessary in many surgical procedures; nonetheless, intraoperative MV is not free from harmful effects. Protective ventilation strategies, which include the combination of low tidal volume and adequate positive end expiratory pressure (PEEP) levels, are usually adopted to minimize the ventilation-induced lung injury and to avoid post-operative pulmonary complications (PPCs). Even so, volutrauma and atelectrauma may co-exist at different levels of tidal volume and PEEP, and therefore, the physiological response to the MV settings should be monitored in each patient. A personalized perioperative approach is gaining relevance in the field of intraoperative MV; in particular, many efforts have been made to individualize PEEP, giving more emphasis on physiological and functional status to the whole body. In this review, we summarized the latest findings about the optimization of PEEP and intraoperative MV in different surgical settings. Starting from a physiological point of view, we described how to approach the individualized MV and monitor the effects of MV on lung function.

[Intraoperative Ventilation in Adults]

Avoiding postoperative pulmonary complications (PPC) is an important goal for anesthesiologists during general anesthesia, and ventilation strategies may play a role. It seems reasonable to apply knowledge from lessons we learned from ventilation of intensive care unit patients aiming at avoiding ventilator associated lung injury. Ventilation associated lung injuries occur frequently and are associated with substantial morbidity and mortality. Strategies of lung protective ventilation, like lower tidal volumes and the use of positive end-expiatory pressure (PEEP), can usually be transferred safely to perioperative ventilation, although some issues such as hemodynamic side effects must be considered. For some reasons, however, current evidence is conflicting and there is no consensus on ventilatory perioperative management to avoid PPCs so far. This paper briefly summarizes physiological backgrounds in a functional context, current evidence, and provides some recommendations at "expert" opinion level for perioperative ventilation procedures.Especially in patients at risk and/or during surgery with higher surgical trauma and inflammation, we recommend limiting tidal volume to 6 - 8 ml/kg predicted body weight and the use of PEEP, which should be individualized e.g. by minimizing driving pressure. Recruitment maneuvers may be considered and should be carried out by using the ventilator.Obese patients are an increasing entity and can be challenging during anesthesia and ventilation. From a physiological point of view, these patients require much higher ventilation pressures as currently used, although recent evidence is not in favor of using moderately higher PEEP, which is matter of discussion.

Regional ventilation distribution in healthy lungs: can reference values be established for electrical impedance tomography parameters?

Background

Although electrical impedance tomography (EIT) is widely used for monitoring regional ventilation distribution, reference values have yet to be established for clinical use. The present study aimed to evaluate the feasibility of creating reference values for standard EIT parameters for potential clinical application.

Methods

A total of 75 participants with healthy lungs were included in this prospective study (male:female, 48:27; age, 34±14 years; height, 172±7 cm; weight, 73±12 kg). The subjects were examined during spontaneous breathing in the supine position. EIT measurements were performed at the level of the 4^th intercostal space. Commonly used EIT-based parameters, including the center of ventilation (CoV), dorsal and most dorsal fractions of ventilation distribution (TV_D and TV_ROI4 respectively), global inhomogeneity (GI) index, and standard deviation of regional ventilation delay index (RVD_SD) were calculated.

Results

Following outlier detection, EIT data from 71 subjects were finally evaluated. The values of the evaluated parameters were: CoV, 48.7%±1.7%; TVD, 48.1%±5.4%; TV_ROI4, 7.1%±1.8%; GI, 0.49±0.04; and RVD_SD, 7.0±2.0. The coefficients of variation for CoV and GI were low (0.03 and 0.07, respectively), but those for TV_ROI4 and RVD_SD were comparatively high (0.26 and 0.28, respectively). None of the evaluated parameters showed a significant correlation with age. The GI index showed a weak but significant correlation with body mass index (R=0.29, P=0.01). The RVD_SD was slightly higher in males than in females.

Conclusions

Our study indicated that CoV and GI were stable parameters with small coefficients of variation in participants with healthy lungs. The creation of EIT parameter reference values for setting treatment targets may be feasible.

The Effect of Ventilation with Individualized Positive End-Expiratory Pressure on Postoperative Atelectasis in Patients Undergoing Robot-Assisted Radical Prostatectomy: A Randomized Controlled Trial

For patients undergoing robot-assisted radical prostatectomy, the pneumoperitoneum with a steep Trendelenburg position could worsen intraoperative respiratory mechanics and result in postoperative atelectasis. We investigated the effects of individualized positive end-expiratory pressure (PEEP) on postoperative atelectasis, evaluated using lung ultrasonography. Sixty patients undergoing robot-assisted radical prostatectomy were randomly allocated into two groups. Individualized groups (n = 30) received individualized PEEP determined by a decremental PEEP trial using 20 to 7 cm H₂O, aiming at maximizing respiratory compliance, whereas standardized groups (n = 30) received a standardized PEEP of 7 cm H₂O during the pneumoperitoneum. Ultrasound examination was performed on 12 sections of thorax, and the lung ultrasound score was measured as 0–3 by considering the number of B lines and the degree of subpleural consolidation. The primary outcome was the difference between the lung ultrasound scores measured before anesthesia induction and just after extubation in the operating room. An increase in the difference means the development of atelectasis. The optimal PEEP in the individualized group was determined as the median (interquartile range) 14 (12–18) cm H₂O. Compared with the standardized group, the difference in the lung ultrasound scores was significantly smaller in the individualized group (−0.5 ± 2.7 vs. 6.0 ± 2.9, mean difference −6.53, 95% confidence interval (−8.00 to −5.07), p < 0.001), which means that individualized PEEP was effective to reduce atelectasis. The lung ultrasound score measured after surgery was significantly lower in the individualized group than the standardized group (8.1 ± 5.7 vs. 12.2 ± 4.2, mean difference −4.13, 95% confidence interval (−6.74 to −1.53), p = 0.002). However, the arterial partial pressure of the oxygen/fraction of inspired oxygen levels during the surgery showed no significant time-group interaction between the two groups in repeated-measures analysis of variance (p = 0.145). The incidence of a composite of postoperative respiratory complications was comparable between the two groups. Individualized PEEP determined by maximal respiratory compliance during the pneumoperitoneum and steep Trendelenburg position significantly reduced postoperative atelectasis, as evaluated using lung ultrasonography. However, the clinical significance of this finding should be evaluated by a larger clinical trial.