Effect of low tidal volume ventilation on atelectasis in patients during general anesthesia: a computed tomographic scan

Quantitative assessment of atelectasis formation under high frequency jet ventilation during liver tumour ablation-A computer tomography study

BACKGROUND

High frequency jet ventilation (HFJV) can be used to minimise sub-diaphragmal organ displacements. Treated patients are in a supine position, under general anaesthesia and fully muscle relaxed. These are factors that are known to contribute to the formation of atelectasis. The HFJV-catheter is inserted freely inside the endotracheal tube and the system is therefore open to atmospheric pressure.

AIM

The aim of this study was to assess the formation of atelectasis over time during HFJV in patients undergoing liver tumour ablation under general anaesthesia.

METHOD

In this observational study twenty-five patients were studied. Repeated computed tomography (CT) scans were taken at the start of HFJV and every 15 minutes thereafter up until 45 minutes. From the CT images, four lung compartments were defined: hyperinflated, normoinflated, poorly inflated and atelectatic areas. The extension of each lung compartment was expressed as a percentage of the total lung area.

RESULT

Atelectasis at 30 minutes, 7.9% (SD 3.5, p = 0.002) and at 45 minutes 8,1% (SD 5.2, p = 0.024), was significantly higher compared to baseline 5.6% (SD 2.5). The amount of normoinflated lung volumes were unchanged over the period studied. Only a few minor perioperative respiratory adverse events were noted.

CONCLUSION

Atelectasis during HFJV in stereotactic liver tumour ablation increased over the first 45 minutes but tended to stabilise with no impact on normoinflated lung volume. Using HFJV during stereotactic liver ablation is safe regarding formation of atelectasis.

Tidal Volume and Positive End-Expiratory Pressure and Postoperative Hypoxemia during General Anesthesia: A Single Center Multiple Cross-over Factorial Cluster Trial

BACKGROUND

Intraoperative mechanical ventilation is a major component of general anesthesia. The extent to which various intraoperative tidal volumes and positive end-expiratory pressures (PEEP) on postoperative hypoxia and lung injury remains unclear. We hypothesized that adult patients having orthopedic surgery, ventilation using different tidal volumes and PEEP levels affects the oxygenation within first hour in the postoperative care unit.

METHODS

We conducted a 2 by 2 factorial cross-over cluster trial at the Cleveland Clinic Main Campus. We enrolled patients having orthopedic surgery with general anesthesia who were assigned to factorial clusters with tidal volumes of 6 or 10 ml/kg of predicted body weight and to PEEP of 5 or 8 cm H20 in one-week clusters The primary outcome was the effect of tidal volume or PEEP on time-weighted average peripheral oxygen saturation divided by the fraction of inspired oxygen (SpO2/FiO2 ratio) during the initial postoperative hour.

RESULTS

We enrolled 2860 patients who had general anesthesia for orthopedic surgery from September 2018 through October 2020. The interaction between tidal volume and PEEP was not significant (p = 0.565). The mean (SD) time-weighted average of SpO2/FiO2 ratio was 353 (47) and not different in patients assigned to high and low tidal volume (estimated effect 3.5% (97.5%CI: -0.4%,7.3%;P=0.042), and for those assigned to high and low PEEP (-0.2% (97.5%CI: -4.0%,3.6%;P=0.906). We did not find significant difference in ward SpO2/FiO2 ratio, pulmonary complications, and duration of hospitalization among patients assigned to various tidal volumes and PEEP levels.

CONCLUSION

Among adults having major orthopedic surgery, pulse oximetry oxygenation is similar with tidal volumes between 6 and 10 ml/kg and PEEP between 5 and 8 cm H20. Our results suggest that any combination of tidal volumes between 6 and 10 ml/kg and PEEP between 5 vs. 8 mL cmH20 can be used safely for orthopedic surgery.Trial Registration ClinicalTrials.gov Identifier: NCT03657368.

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.

Assessment of Perioperative Atelectasis Using Lung Ultrasonography in Patients Undergoing Pneumoperitoneum Surgery in the Trendelenburg Position: Aspects of Differences according to Ventilatory Mode

BACKGROUND

During robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position, aeration loss leads to perioperative atelectasis. Recently developed ventilator mode pressure-controlled ventilation volume-guaranteed (PCV-VG) mode could provide adequate ventilation with lower inspiratory pressure compared to volume-controlled ventilation (VCV); we hypothesized that PCV-VG mode may be beneficial in reducing perioperative atelectasis via low tidal volume (V_T) of 6 mL/kg ventilation during robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position. We applied lung ultrasound score (LUS) for detecting perioperative atelectasis. We aimed to compare perioperative atelectasis between VCV and PCV-VG with a low V_T of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position using LUS.

METHODS

Patients scheduled for robotic gynecologic surgery were randomly allocated to the VCV (n = 41) or PCV-VG group (n = 41). LUS, ventilatory, and hemodynamic parameters were evaluated at T1 (before induction), T2 (10 minutes after induction in the supine position), T3 (10 minutes after desufflation of CO₂ in the supine position), and T4 (30 minutes after emergence from anesthesia in the recovery room).

RESULTS

Eighty patients (40 with PCV-VG and 40 with VCV) were included. Demographic data showed no significant differences between the groups. The total LUS has changed from baseline to T4, 0.63 (95% confidence interval [CI], 0.32, 0.94) to 1.77 (95% CI, 1.42, 2.21) in the VCV group and 0.86 (95% CI, 0.56, 1.16) to 1.43 (95% CI, 1.08, 1.78) in the PCV-VG group (P = 0.170). In both groups, total LUS increased significantly compared to the baseline values.

CONCLUSION

Using a low V_T of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position, our study showed no evidence that PCV-VG ventilation was superior to VCV in terms of perioperative atelectasis.

TRIAL REGISTRATION

Clinical Research Information Service Identifier: KCT0006404.

Effect of Intraoperative Ventilation Strategies on Postoperative Pulmonary Complications: A Meta-Analysis

Introduction: The role of intraoperative ventilation strategies in subjects undergoing surgery is still contested. This meta-analysis study was performed to assess the relationship between the low tidal volumes strategy and conventional mechanical ventilation in subjects undergoing surgery. Methods: A systematic literature search up to December 2020 was performed in OVID, Embase, Cochrane Library, PubMed, and Google scholar, and 28 studies including 11,846 subjects undergoing surgery at baseline and reporting a total of 2,638 receiving the low tidal volumes strategy and 3,632 receiving conventional mechanical ventilation, were found recording relationships between low tidal volumes strategy and conventional mechanical ventilation in subjects undergoing surgery. Odds ratio (OR) or mean difference (MD) with 95% confidence intervals (CIs) were calculated between the low tidal volumes strategy vs. conventional mechanical ventilation using dichotomous and continuous methods with a random or fixed-effect model. Results: The low tidal volumes strategy during surgery was significantly related to a lower rate of postoperative pulmonary complications (OR, 0.60; 95% CI, 0.44-0.83, p < 0.001), aspiration pneumonitis (OR, 0.63; 95% CI, 0.46-0.86, p < 0.001), and pleural effusion (OR, 0.72; 95% CI, 0.56-0.92, p < 0.001) compared to conventional mechanical ventilation. However, the low tidal volumes strategy during surgery was not significantly correlated with length of hospital stay (MD, -0.48; 95% CI, -0.99-0.02, p = 0.06), short-term mortality (OR, 0.88; 95% CI, 0.70-1.10, p = 0.25), atelectasis (OR, 0.76; 95% CI, 0.57-1.01, p = 0.06), acute respiratory distress (OR, 1.06; 95% CI, 0.67-1.66, p = 0.81), pneumothorax (OR, 1.37; 95% CI, 0.88-2.15, p = 0.17), pulmonary edema (OR, 0.70; 95% CI, 0.38-1.26, p = 0.23), and pulmonary embolism (OR, 0.65; 95% CI, 0.26-1.60, p = 0.35) compared to conventional mechanical ventilation. Conclusions: The low tidal volumes strategy during surgery may have an independent relationship with lower postoperative pulmonary complications, aspiration pneumonitis, and pleural effusion compared to conventional mechanical ventilation. This relationship encouraged us to recommend the low tidal volumes strategy during surgery to avoid any possible complications.

Effects of positive end-expiratory pressure/recruitment manoeuvres compared with zero end-expiratory pressure on atelectasis in children: A randomised clinical trial

BACKGROUND

Atelectasis is a common postoperative complication. Peri-operative lung protection can reduce atelectasis; however, it is not clear whether this persists into the postoperative period.

OBJECTIVE

To evaluate to what extent lung-protective ventilation reduces peri-operative atelectasis in children undergoing nonabdominal surgery.

DESIGN

Randomised, controlled, double-blind study.

SETTING

Single tertiary hospital, 25 July 2019 to 18 January 2020.

PATIENTS

A total of 60 patients aged 1 to 6 years, American Society of Anesthesiologists physical status 1 or 2, planned for nonabdominal surgery under general anaesthesia (≤2 h) with mechanical ventilation.

INTERVENTIONS

The patients were assigned randomly into either the lung-protective or zero end-expiratory pressure with no recruitment manoeuvres (control) group. Lung protection entailed 5 cmH2O positive end-expiratory pressure and recruitment manoeuvres every 30 min. Both groups received volume-controlled ventilation with a tidal volume of 6 ml kg-1 body weight. Lung ultrasound was conducted before anaesthesia induction, immediately after induction, surgery and tracheal extubation, and 15 min, 3 h, 12 h and 24 h after extubation.

MAIN OUTCOME MEASURES

The difference in lung ultrasound score between groups at each interval. A higher score indicates worse lung aeration.

RESULTS

Patients in the lung-protective group exhibited lower median [IQR] ultrasound scores compared with the control group immediately after surgery, 4 [4 to 5] vs. 8 [4 to 6], (95% confidence interval for the difference between group values -4 to -4, Z = -6.324) and after extubation 3 [3 to 4] vs. 4 [4 to 4], 95% CI -1 to 0, Z = -3.161. This did not persist from 15 min after extubation onwards. Lung aeration returned to normal in both groups 3 h after extubation.

CONCLUSIONS

The reduced atelectasis provided by lung-protective ventilation does not persist from 15 min after extubation onwards. Further studies are needed to determine if it yields better results in other types of surgery.

TRIAL REGISTRATION

Chictr.org.cn (ChiCTR2000033469).

Lung-protective mechanical ventilation for patients undergoing abdominal laparoscopic surgeries: a randomized controlled trial

Background

Pneumoperitoneum and Trendelenburg position in laparoscopic surgeries could contribute to postoperative pulmonary dysfunction. In recent years, intraoperative lung-protective mechanical ventilation (LPV) has been reportedly able to attenuate ventilator-induced lung injuries (VILI). Our objectives were to test the hypothesis that LPV could improve intraoperative oxygenation function, pulmonary mechanics and early postoperative atelectasis in laparoscopic surgeries.

Methods

In this randomized controlled clinical trial, 62 patients indicated for elective abdominal laparoscopic surgeries with an expected duration of greater than 2 h were randomly assigned to receive either lung-protective ventilation (LPV) with a tidal volume (Vt) of 7 ml kg^− 1 ideal body weight (IBW), 10 cmH₂O positive end-expiratory pressure (PEEP) combined with regular recruitment maneuvers (RMs) or conventional ventilation (CV) with a Vt of 10 ml kg^− 1 IBW, 0 cmH₂O in PEEP and no RMs. The primary endpoints were the changes in the ratio of PaO₂ to FiO₂ (P/F). The secondary endpoints were the differences between the two groups in PaO₂, alveolar-arterial oxygen gradient (A-aO₂), intraoperative pulmonary mechanics and the incidence of atelectasis detected on chest x-ray on the first postoperative day.

Results

In comparison to CV group, the intraoperative P/F and PaO₂ in LPV group were significantly higher while the intraoperative A-aO₂ was clearly lower. C_dyn and C_stat at all the intraoperative time points in LPV group were significantly higher compared to CV group (p < 0.05). There were no differences in the incidence of atelectasis on day one after surgery between the two groups.

Conclusions

Lung protective mechanical ventilation significantly improved intraoperative pulmonary oxygenation function and pulmonary compliance in patients experiencing various abdominal laparoscopic surgeries, but it could not ameliorate early postoperative atelectasis and oxygenation function on the first day after surgery.

Trial registration

https://www.clinicaltrials.gov/identifier: NCT04546932 (09/05/2020).

Effects of Intraoperative Ventilation Strategy on Perioperative Atelectasis Assessed by Lung Ultrasonography in Patients Undergoing Open Abdominal Surgery: a Prospective Randomized Controlled Study

BACKGROUND

Protective mechanical ventilation using low tidal volume has been introduced to surgical patients to reduce the incidence of postoperative pulmonary complications. We investigated the effects of protective ventilation (PV) techniques on anesthesia-induced atelectasis identified via lung ultrasonography in patients undergoing abdominal surgery.

METHODS

A total of 42 adult patients who were scheduled for open abdominal surgery with an expected duration > 2 hours were included in the study. Patients were randomized to receive either conventional ventilation (CV; tidal volume of 9-10 mL/kg predicted body weight [PBW] with no positive end-expiratory pressure [PEEP]) or PV (tidal volume of 6-8 mL/kg PBW and 5 cmH₂O PEEP) via pressure-controlled ventilation with volume guaranteed. Lung ultrasonography was performed at four predefined time points to assess perioperative atelectasis by dividing each hemithorax into six quadrants based on a modified lung ultrasound (LUS) scoring system.

RESULTS

The tidal volume delivered to patients was 9.65 ± 1.65 mL/kg PBW in the CV group and 6.31 ± 0.62 mL/kg PBW in the PV group. Ventilation using low tidal volume led to similar LUS scores in all lung areas and at all time points compared to ventilation using high tidal volume. There was no significant difference between the groups in the number of patients requiring recruitment maneuvers at the end of surgery.

CONCLUSION

Ventilation with low tidal volume combined with 5 cmH₂O PEEP did not cause further loss of aeration compared to ventilation with high tidal volume. Low tidal volume ventilation can be used in patients without lung injury based on lung assessment by bedside lung ultrasonography.

TRIAL REGISTRATION

Clinical Research Information Service Identifier: KCT0003746.

Association of tidal volume during mechanical ventilation with postoperative pulmonary complications in pediatric patients undergoing major scoliosis surgery

BACKGROUND

The use of lung-protective ventilation strategies with low tidal volumes may reduce the occurrence of postoperative pulmonary complications. However, evidence of the association of intraoperative tidal volume settings with pulmonary complications in pediatric patients undergoing major spinal surgery is insufficient.

AIMS

This study examined whether postoperative pulmonary complications were related to tidal volume in this population and, if so, what factors affected the association.

METHODS

In this retrospective cohort study, data from pediatric patients (<18 years old) who underwent posterior spinal fusion between 2016 and 2018 were collected from the hospital electronic medical record. The associations between tidal volume and the clinical outcomes were examined by multivariate logistic regression and stratified analysis.

RESULTS

Postoperative pulmonary complications occurred in 41 (16.1%) of 254 patients who met the inclusion criteria. For the entire cohort, tidal volume was associated with an elevated risk of pulmonary complications (adjusted odds ratio [OR] per 1 mL/kg ideal body weight [IBW] increase in tidal volume, 1.28; 95% confidence interval [CI], 1.01-1.63, P = .038). In subgroup analysis, tidal volume was associated with an increased risk of pulmonary complications in patients older than 3 years (adjusted OR per 1 mL/kg IBW increase in tidal volume, 1.43, 95% CI: 1.12-1.84), but not in patients aged 3 years or younger (adjusted OR, 0.78, 95% CI: 0.46-1.35), indicating a significant age interaction (P = .035).

CONCLUSION

In pediatric patients undergoing major spinal surgery, high tidal volume was associated with an elevated risk of postoperative pulmonary complications. However, the effect of tidal volume on pulmonary outcomes in the young subgroup (≤3 years) differed from that in the old (>3 years). Such information may help to optimize ventilation strategy for children of different ages.

Perioperative interventions for prevention of postoperative pulmonary complications: systematic review and meta-analysis

OBJECTIVE

To identify, appraise, and synthesise the best available evidence on the efficacy of perioperative interventions to reduce postoperative pulmonary complications (PPCs) in adult patients undergoing non-cardiac surgery.

DESIGN

Systematic review and meta-analysis of randomised controlled trials.

DATA SOURCES

Medline, Embase, CINHAL, and CENTRAL from January 1990 to December 2017.

ELIGIBILITY CRITERIA

Randomised controlled trials investigating short term, protocolised medical interventions conducted before, during, or after non-cardiac surgery were included. Trials with clinical diagnostic criteria for PPC outcomes were included. Studies of surgical technique or physiological or biochemical outcomes were excluded.

DATA EXTRACTION AND SYNTHESIS

Reviewers independently identified studies, extracted data, and assessed the quality of evidence. Meta-analyses were conducted to calculate risk ratios with 95% confidence intervals. Quality of evidence was summarised in accordance with GRADE methods. The primary outcome was the incidence of PPCs. Secondary outcomes were respiratory infection, atelectasis, length of hospital stay, and mortality. Trial sequential analysis was used to investigate the reliability and conclusiveness of available evidence. Adverse effects of interventions were not measured or compared.

RESULTS

117 trials enrolled 21 940 participants, investigating 11 categories of intervention. 95 randomised controlled trials enrolling 18 062 participants were included in meta-analysis; 22 trials were excluded from meta-analysis because the interventions were not sufficiently similar to be pooled. No high quality evidence was found for interventions to reduce the primary outcome (incidence of PPCs). Seven interventions had low or moderate quality evidence with confidence intervals indicating a probable reduction in PPCs: enhanced recovery pathways (risk ratio 0.35, 95% confidence interval 0.21 to 0.58), prophylactic mucolytics (0.40, 0.23 to 0.67), postoperative continuous positive airway pressure ventilation (0.49, 0.24 to 0.99), lung protective intraoperative ventilation (0.52, 0.30 to 0.88), prophylactic respiratory physiotherapy (0.55, 0.32 to 0.93), epidural analgesia (0.77, 0.65 to 0.92), and goal directed haemodynamic therapy (0.87, 0.77 to 0.98). Moderate quality evidence showed no benefit for incentive spirometry in preventing PPCs. Trial sequential analysis adjustment confidently supported a relative risk reduction of 25% in PPCs for prophylactic respiratory physiotherapy, epidural analgesia, enhanced recovery pathways, and goal directed haemodynamic therapies. Insufficient data were available to support or refute equivalent relative risk reductions for other interventions.

CONCLUSIONS

Predominantly low quality evidence favours multiple perioperative PPC reduction strategies. Clinicians may choose to reassess their perioperative care pathways, but the results indicate that new trials with a low risk of bias are needed to obtain conclusive evidence of efficacy for many of these interventions.

STUDY REGISTRATION

Prospero CRD42016035662.

Temporal Changes in Ventilator Settings in Patients With Uninjured Lungs: A Systematic Review

In patients with uninjured lungs, increasing evidence indicates that tidal volume (VT) reduction improves outcomes in the intensive care unit (ICU) and in the operating room (OR). However, the degree to which this evidence has translated to clinical changes in ventilator settings for patients with uninjured lungs is unknown. To clarify whether ventilator settings have changed, we searched MEDLINE, Cochrane Central Register of Controlled Trials, and Web of Science for publications on invasive ventilation in ICUs or ORs, excluding those on patients <18 years of age or those with >25% of patients with acute respiratory distress syndrome (ARDS). Our primary end point was temporal change in VT over time. Secondary end points were changes in maximum airway pressure, mean airway pressure, positive end-expiratory pressure, inspiratory oxygen fraction, development of ARDS (ICU studies only), and postoperative pulmonary complications (OR studies only) determined using correlation analysis and linear regression. We identified 96 ICU and 96 OR studies comprising 130,316 patients from 1975 to 2014 and observed that in the ICU, VT size decreased annually by 0.16 mL/kg (-0.19 to -0.12 mL/kg) (P < .001), while positive end-expiratory pressure increased by an average of 0.1 mbar/y (0.02-0.17 mbar/y) (P = .017). In the OR, VT size decreased by 0.09 mL/kg per year (-0.14 to -0.04 mL/kg per year) (P < .001). The change in VTs leveled off in 1995. Other intraoperative ventilator settings did not change in the study period. Incidences of ARDS (ICU studies) and postoperative pulmonary complications (OR studies) also did not change over time. We found that, during a 39-year period, from 1975 to 2014, VTs in clinical studies on mechanical ventilation have decreased significantly in the ICU and in the OR.

Perioperative anaesthetic management of patients with or at risk of acute distress respiratory syndrome undergoing emergency surgery

Patients undergoing emergency surgery may present with the acute respiratory distress syndrome (ARDS) or develop this syndrome postoperatively. The incidence of ARDS in the postoperative period is relatively low, but the impact of ARDS on patient outcomes and healthcare costs is relevant Aakre et.al (Mayo Clin Proc 89:181-9, 2014).The development of ARDS as a postoperative pulmonary complication (PPC) is associated with prolonged hospitalisation, longer duration of mechanical ventilation, increased intensive care unit length of stay and high morbidity and mortality Ball et.al (Curr Opin Crit Care 22:379-85, 2016). In order to mitigate the risk of ARDS after surgery, the anaesthetic management and protective mechanical ventilation strategies play an important role. In particular, a careful integration of general anaesthesia with neuraxial or locoregional techniques might promote faster recovery and reduce opioid consumption. In addition, the use of low tidal volume, minimising plateau pressure and titrating a low-moderate PEEP level based on the patient's need can improve outcome and reduce intraoperative adverse events. Moreover, perioperative management of ARDS patients includes specific anaesthesia and ventilator settings, hemodynamic monitoring, moderately restrictive fluid administration and pain control.The aim of this review is to provide an overview and evidence- and opinion-based recommendations concerning the management of patients at risk of and with ARDS who undergo emergency surgical procedures.

Oxygenation Impairment during Anesthesia

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Anesthesia is increasingly common in elderly and overweight patients and prompted the current study to explore mechanisms of age- and weight-dependent worsening of arterial oxygen tension (Pao2).

Methods

This is a primary analysis of pooled data in patients with (1) American Society of Anesthesiologists (ASA) classification of 1; (2) normal forced vital capacity; (3) preoxygenation with an inspired oxygen fraction (Fio2) more than 0.8 and ventilated with Fio2 0.3 to 0.4; (4) measurements done during anesthesia before surgery. Eighty patients (21 women and 59 men, aged 19 to 69 yr, body mass index up to 30 kg/m2) were studied with multiple inert gas elimination technique to assess shunt and perfusion of poorly ventilated regions (low ventilation/perfusion ratio []) and computed tomography to assess atelectasis.

Results

Pao2/Fio2 was lower during anesthesia than awake (368; 291 to 470 [median; quartiles] vs. 441; 397 to 462 mm Hg; P = 0.003) and fell with increasing age and body mass index. Log shunt was best related to a quadratic function of age with largest shunt at 45 yr (r2 =0.17, P = 0.001). Log shunt was linearly related to body mass index (r2 = 0.15, P &lt; 0.001). A multiple regression analysis including age, age2, and body mass index strengthened the association further (r2 = 0.27). Shunt was highly associated to atelectasis (r2 = 0.58, P &lt; 0.001). Log low showed a linear relation to age (r2 = 0.14, P = 0.001).

Conclusions

Pao2/Fio2 ratio was impaired during anesthesia, and the impairment increased with age and body mass index. Shunt was related to atelectasis and was a more important cause of oxygenation impairment in middle-aged patients, whereas low, likely caused by airway closure, was more important in elderly patients. Shunt but not low increased with increasing body mass index. Thus, increasing age and body mass index impaired gas exchange by different mechanisms during anesthesia.

Evaluation of Perioperative Ventilation Strategies: National Survey Study

OBJECTIVE

Lung injury can develop in the perioperative period due to ventilation management techniques. Thus, the attitude of anaesthetists on protective ventilation (PV) practice comes into question. In our study, we aimed to evaluate the perioperative ventilation practice of anaesthetists and trainees on anaesthesiology by a survey study.

METHODS

Survey form was sent to all doctors registered to TARD via electronic mail. The participants were asked questions involving PV parameters such as low tidal volume (TV) according to ideal body weight (BW), positive end-expiratory pressure (PEEP), FiO2 use and recruitment manoeuvre (RM) application. In total, 411 doctors who answered the survey were included to the study. Application rates of PV parameters and causes were compared within the answers obtained. P<0.05 was accepted statistically significant.

RESULTS

PV was practised by 19.4% of the participants. Those who preferred low TV used ideal BW more frequently (p<0.001). PEEP of 4-6 cm H2O was commonly used (p<0.001). The participants mostly preferred FiO2 of 1.0 (60.4%), and application rate of RM was found to be 17.2%. The use of all PV parameters was detected to be higher among instructors than among other groups.

CONCLUSION

In our study, application ratio of PV with all its parameters was found to be lower. Among the parameters, while low TV according to ideal BW and PEEP were applied at higher ratios, the use of RM and low oxygen percentage were applied less frequently. While PV was found to be useful in terms of perioperative ventilation strategies, low practice rates may result from habits besides lack of knowledge and experience; comprehensive and quality education studies are needed to overcome this.

Perioperative lung protective ventilation

Perioperative lung injury is a major source of postoperative morbidity, excess healthcare use, and avoidable mortality. Many potential inciting factors can lead to this condition, including intraoperative ventilator induced lung injury. Questions exist as to whether protective ventilation strategies used in the intensive care unit for patients with acute respiratory distress syndrome are equally beneficial for surgical patients, most of whom do not present with any pre-existing lung pathology. Studied both individually and in combination as a package of intraoperative lung protective ventilation, the use of low tidal volumes, moderate positive end expiratory pressure, and recruitment maneuvers have been shown to improve oxygenation and pulmonary physiology and to reduce postoperative pulmonary complications in at risk patient groups. Further work is needed to define the potential contributions of alternative ventilator strategies, limiting excessive intraoperative oxygen supplementation, use of non-invasive techniques in the postoperative period, and personalized mechanical ventilation. Although the weight of evidence strongly suggests a role for lung protective ventilation in moderate risk patient groups, definitive evidence of its benefit for the general surgical population does not exist. However, given the shift in understanding of what is needed for adequate oxygenation and ventilation under anesthesia, the largely historical arguments against the use of intraoperative lung protective ventilation may soon be outdated, on the basis of its expanding track record of safety and efficacy in multiple settings.

Effect of lung protective ventilation on coronary heart disease patients undergoing lung cancer resection

Background

Mechanical ventilation, especially large tidal volume (Vt) one-lung ventilation (OLV), can cause ventilator-induced lung injury (VILI) that can stimulate cytokines. Meanwhile, cytokines are considered very important factor influencing coronary heart disease (CHD) patient prognosis. So minimization of pulmonary inflammatory responses by reduction of cytokine levels for CHD undergoing lung resection during OLV should be a priority. Because previous studies have demonstrated that lung-protective ventilation (LPV) reduced lung inflammation, this ventilation approach was studied for CHD patients undergoing lung resection here to evaluate the effects of LPV on pulmonary inflammatory responses.

Methods

This is a single center, randomized controlled trial. Primary endpoint of the study are plasma concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-10 and C-reactive protein (CRP). Secondary endpoints include respiratory variables and hemodynamic variables. 60 CHD patients undergoing video-assisted thoracoscopic lung resection were randomly divided into conventional ventilation group [10 mL/kg Vt and 0 cmH₂O positive end-expiratory pressure (PEEP), C group] and protective ventilation group (6 mL/kg Vt and 6 cmH₂O PEEP, P group; 30 patients/group). Hemodynamic variables, peak inspiratory pressure (Ppeak), dynamic compliance (Cdyn), arterial oxygen tension (PaO₂) and arterial carbon dioxide tension (PaCO₂) were recorded as test data at three time points: T1-endotracheal intubation for two-lung ventilation (TLV) when breathing and hemodynamics were stable; T2-after TLV was substituted with OLV when breathing and hemodynamics were stable; T3-OLV was substituted with TLV at the end of surgery when breathing and hemodynamics were stable. The concentrations of TNF-α, IL-6, IL-10 and CRP in patients' blood in both groups at the very beginning of OLV (beginning of OLV) and the end moment of the surgery (end of surgery) were measured.

Results

The P group exhibited greater PaO₂, higher Cdyn and lower Ppeak than the C group at T2, T3 (P<0.05). At the end moment of the surgery, although the P group tended to exhibit higher TNF-α and IL-10 values than the C group, the differences did not reach statistical significance(P=0.0817, P=0.0635). Compared with C group at the end moment of the surgery, IL-6 and CRP were lower in P group, the differences were statistically significant (P=0.0093, P=0.0005). There were no significant differences in hemodynamic variables between the two groups (P>0.05).

Conclusions

LPV can effectively reduce the airway pressure, improve Cdyn and PaO₂, reduce concentrations of IL-6 and CRP during lung resection of CHD patients.Trial registration: The trial was registered in the Chinese Clinical Trial Registry.

Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in adults without acute lung injury

BACKGROUND

Since the 2000s, there has been a trend towards decreasing tidal volumes for positive pressure ventilation during surgery. This an update of a review first published in 2015, trying to determine if lower tidal volumes are beneficial or harmful for patients.

OBJECTIVES

To assess the benefit of intraoperative use of low tidal volume ventilation (less than 10 mL/kg of predicted body weight) compared with high tidal volumes (10 mL/kg or greater) to decrease postoperative complications in adults without acute lung injury.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2017, Issue 5), MEDLINE (OvidSP) (from 1946 to 19 May 2017), Embase (OvidSP) (from 1974 to 19 May 2017) and six trial registries. We screened the reference lists of all studies retained and of recent meta-analysis related to the topic during data extraction. We also screened conference proceedings of anaesthesiology societies, published in two major anaesthesiology journals. The search was rerun 3 January 2018.

SELECTION CRITERIA

We included all parallel randomized controlled trials (RCTs) that evaluated the effect of low tidal volumes (defined as less than 10 mL/kg) on any of our selected outcomes in adults undergoing any type of surgery. We did not retain studies with participants requiring one-lung ventilation.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the quality of the retained studies with the Cochrane 'Risk of bias' tool. We analysed data with both fixed-effect (I² statistic less than 25%) or random-effects (I² statistic greater than 25%) models based on the degree of heterogeneity. When there was an effect, we calculated a number needed to treat for an additional beneficial outcome (NNTB) using the odds ratio. When there was no effect, we calculated the optimum information size.

MAIN RESULTS

We included seven new RCTs (536 participants) in the update.In total, we included 19 studies in the review (776 participants in the low tidal volume group and 772 in the high volume group). There are four studies awaiting classification and three are ongoing. All included studies were at some risk of bias. Participants were scheduled for abdominal surgery, heart surgery, pulmonary thromboendarterectomy, spinal surgery and knee surgery. Low tidal volumes used in the studies varied from 6 mL/kg to 8.1 mL/kg while high tidal volumes varied from 10 mL/kg to 12 mL/kg.Based on 12 studies including 1207 participants, the effects of low volume ventilation on 0- to 30-day mortality were uncertain (risk ratio (RR) 0.80, 95% confidence interval (CI) 0.42 to 1.53; I² = 0%; low-quality evidence). Based on seven studies including 778 participants, lower tidal volumes probably reduced postoperative pneumonia (RR 0.45, 95% CI 0.25 to 0.82; I² = 0%; moderate-quality evidence; NNTB 24, 95% CI 16 to 160), and it probably reduced the need for non-invasive postoperative ventilatory support based on three studies including 506 participants (RR 0.31, 95% CI 0.15 to 0.64; moderate-quality evidence; NNTB 13, 95% CI 11 to 24). Based on 11 studies including 957 participants, low tidal volumes during surgery probably decreased the need for postoperative invasive ventilatory support (RR 0.33, 95% CI 0.14 to 0.77; I² = 0%; NNTB 39, 95% CI 30 to 166; moderate-quality evidence). Based on five studies including 898 participants, there may be little or no difference in the intensive care unit length of stay (standardized mean difference (SMD) -0.06, 95% CI -0.22 to 0.10; I² = 33%; low-quality evidence). Based on 14 studies including 1297 participants, low tidal volumes may have reduced hospital length of stay by about 0.8 days (SMD -0.15, 95% CI -0.29 to 0.00; I² = 27%; low-quality evidence). Based on five studies including 708 participants, the effects of low volume ventilation on barotrauma (pneumothorax) were uncertain (RR 1.77, 95% CI 0.52 to 5.99; I² = 0%; very low-quality evidence).

AUTHORS' CONCLUSIONS

We found moderate-quality evidence that low tidal volumes (defined as less than 10 mL/kg) decreases pneumonia and the need for postoperative ventilatory support (invasive and non-invasive). We found no difference in the risk of barotrauma (pneumothorax), but the number of participants included does not allow us to make definitive statement on this. The four studies in 'Studies awaiting classification' may alter the conclusions of the review once assessed.

Interaction between peri-operative blood transfusion, tidal volume, airway pressure and postoperative ARDS: an individual patient data meta-analysis

Background

Transfusion of blood products and mechanical ventilation with injurious settings are considered risk factors for postoperative lung injury in surgical Patients.

Methods

A systematic review and individual patient data meta-analysis was done to determine the independent effects of peri-operative transfusion of blood products, intra-operative tidal volume and airway pressure in adult patients undergoing mechanical ventilation for general surgery, as well as their interactions on the occurrence of postoperative acute respiratory distress syndrome (ARDS). Observational studies and randomized trials were identified by a systematic search of MEDLINE, CINAHL, Web of Science, and CENTRAL and screened for inclusion into a meta-analysis. Individual patient data were obtained from the corresponding authors. Patients were stratified according to whether they received transfusion in the peri-operative period [red blood cell concentrates (RBC) and/or fresh frozen plasma (FFP)], tidal volume size [≤7 mL/kg predicted body weight (PBW), 7-10 and >10 mL/kg PBW] and airway pressure level used during surgery (≤15, 15-20 and >20 cmH₂O). The primary outcome was development of postoperative ARDS.

Results

Seventeen investigations were included (3,659 patients). Postoperative ARDS occurred in 40 (7.2%) patients who received at least one blood product compared to 40 patients (2.5%) who did not [adjusted hazard ratio (HR), 2.32; 95% confidence interval (CI), 1.25-4.33; P=0.008]. Incidence of postoperative ARDS was highest in patients ventilated with tidal volumes of >10 mL/kg PBW and having airway pressures of >20 cmH₂O receiving both RBC and FFP, and lowest in patients ventilated with tidal volume of ≤7 mL/kg PBW and having airway pressures of ≤15 cmH₂O with no transfusion. There was a significant interaction between transfusion and airway pressure level (P=0.002) on the risk of postoperative ARDS.

Conclusions

Peri-operative transfusion of blood products is associated with an increased risk of postoperative ARDS, which seems more dependent on airway pressure than tidal volume size.

Quick reference tidal volume cards reduce the incidence of large tidal volumes during surgery

Ventilation with large tidal volumes (V _T), greater than 10 ml/kg of predicted body weight (PBW), is associated with worse outcomes in critically ill and surgical patients. We hypothesized that the availability of quick reference cards with proposed V _T ranges specific to gender and different heights would reduce the intraoperative use of large V _T during prolonged abdominal surgery. We compared retrospectively the incidence of median V _T used during prolonged (≥4-h-long) abdominal surgery before ("before") and after ("after") the quick reference V _T cards were made available in all anesthesia machines in operating rooms of a single academic US medical center. We evaluated the effect of the intervention on the primary outcome while adjusting for previously identified risk factors of large V _T use: female gender, obesity (body mass index, BMI > 30), and short height (< 165 cm). The frequency of V _T > 10 ml/kg PBW was 15.1% in the before group and 4.3% in the after group (p < 0.001). The frequency of large V _T used during abdominal surgery was significantly decreased after the intervention even after adjusting for female gender, obesity or short height [adjOR 0.11 (95% CI 0.04-0.30)]. Our quick reference V _T cards significantly reduced the frequency of large V _T use during abdominal surgery.

[Does intraoperative lung-protective ventilation reduce postoperative pulmonary complications?]

BACKGROUND

Recent studies show that intraoperative protective ventilation is able to reduce postoperative pulmonary complications (PPC).

OBJECTIVES

This article provides an overview of the definition and ways to predict PPC. We present different factors that lead to ventilator-induced lung injury and explain the concepts of stress and strain as well as driving pressure. Different strategies of mechanical ventilation to avoid PPC are discussed in light of clinical evidence.

MATERIALS AND METHODS

The Medline database was used to selectively search for randomized controlled trials dealing with intraoperative mechanical ventilation and outcomes.

RESULTS

Low tidal volumes (VT) and high levels of positive end-expiratory pressure (PEEP), combined with recruitment maneuvers, are able to prevent PPC. Non-obese patients undergoing open abdominal surgery show better lung function with the use of higher PEEP levels and recruitment maneuvers, however such strategy can lead to hemodynamic impairment, while not reducing the incidence of PPC, hospital length of stay and mortality. An increase in the level of PEEP that results in an increase in driving pressure is associated with a greater risk of PPC.

CONCLUSIONS

The use of intraoperative VT ranging from 6 to 8 ml/kg based on ideal body weight is strongly recommended. Currently, a recommendation regarding the level of PEEP during surgery is not possible. However, a PEEP increase that leads to a rise in driving pressure should be avoided.

Protective Ventilation Improves Gas Exchange, Reduces Incidence of Atelectases, and Affects Metabolic Response in Major Pancreatoduodenal Surgery

Background

Protective perioperative ventilation has been shown to improve outcomes and reduce the incidence of postoperative pulmonary complications. The goal of this study was to assess the effects of ventilation with low tidal volume (V_T) either alone or in a combination with moderate permissive hypercapnia in major pancreatoduodenal interventions.

Materials and methods

Sixty adult patients scheduled for elective pancreatoduodenal surgery with duration >2 h were enrolled into a prospective single-center study. All patients were randomized to three groups receiving high V_T [10 mL/kg of predicted body weight (PBW), the HVT group, n = 20], low V_T (6 mL/kg PBW, the LVT group, n = 20), and low V_T combined with a moderate hypercapnia and hypercapnic acidosis (6 mL/kg PBW, PaCO₂ 45–60 mm Hg, the LVT + HC group, n = 20). Cardiopulmonary parameters and the incidence of complications were registered during surgery and postoperatively.

Results and discussion

The values of V_T were 610 (563–712), 370 (321–400), and 340 (312–430) mL/kg for the HVT, the LVT, and the LVT + HC groups, respectively (p < 0.001). Compared to the HVT group, PaO₂/FiO₂ ratio was increased in the LVT group by 15%: 333 (301–381) vs. 382 (349–423) mm Hg at 24 h postoperatively (p < 0.05). The HVT group had significantly higher incidence of atelectases (n = 6), despite lower incidence of smoking compared with the LVT (n = 1) group (p = 0.017) and demonstrated longer length of hospital stay. The patients of the LVT + HC group had lower arterial lactate and bicarbonate excess values by the end of surgery.

Conclusion

In major pancreatoduodenal interventions, preventively protective V_T improves postoperative oxygenation, reduces the incidence of atelectases, and shortens length of hospital stay. The combination of low V_T and permissive hypercapnia results in hypercapnic acidosis decreasing the lactate concentration but adding no additional benefits and warrants further investigations.

Performance of Lung Ultrasound in Detecting Peri-Operative Atelectasis after General Anesthesia

The aim of this prospective observational study was to evaluate the performance of lung ultrasound (LUS) in detecting post-operative atelectasis in adult patients under general anesthesia. Forty-six patients without pulmonary comorbidities who were scheduled for elective neurosurgery were enrolled in the study. A total of 552 pairs of LUS clips and thoracic computed tomography (CT) images were ultimately analyzed to determine the presence of atelectasis in 12 prescribed lung regions. The accuracy of LUS in detecting peri-operative atelectasis was evaluated with thoracic CT as gold standard. Levels of agreement between the two observers for LUS and the two observers for thoracic CT were analyzed using the κ reliability test. The quantitative correlation between LUS scores of aeration and the volumetric data of atelectasis in thoracic CT were further evaluated. LUS had reliable performance in post-operative atelectasis, with a sensitivity of 87.7%, specificity of 92.1% and diagnostic accuracy of 90.8%. The levels of agreement between the two observers for LUS and for thoracic CT were both satisfactory, with κ coefficients of 0.87 (p < 0.0001) and 0.93 (p < 0.0001), respectively. In patients in the supine position, LUS scores were highly correlated with the atelectasis volume of CT (r = 0.58, p < 0.0001). Thus, LUS provides a fast, reliable and radiation-free method to identify peri-operative atelectasis in adults.

Preventing Ventilator-Associated Lung Injury: A Perioperative Perspective

Introduction

Research into the prevention of ventilator-associated lung injury (VALI) in patients with acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU) has resulted in the development of a number of lung protective strategies, which have become commonplace in the treatment of critically ill patients. An increasing number of studies have applied lung protective ventilation in the operating room to otherwise healthy individuals. We review the history of lung protective strategies in patients with acute respiratory failure and explore their use in patients undergoing mechanical ventilation during general anesthesia. We aim to provide context for a discussion of the benefits and drawbacks of lung protective ventilation, as well as to inform future areas of research.

Methods

We completed a database search and reviewed articles investigating lung protective ventilation in both the ICU and in patients receiving general anesthesia through May 2015.

Results

Lung protective ventilation was associated with improved outcomes in patients with acute respiratory failure in the ICU. Clinical evidence is less clear regarding lung protective ventilation for patients undergoing surgery.

Conclusion

Lung protective ventilation strategies, including low tidal volume ventilation and moderate positive end-expiratory pressure, are well established therapies to minimize lung injury in critically ill patients with and without lung disease, and may provide benefit to patients undergoing general anesthesia.

Association between driving pressure and development of postoperative pulmonary complications in patients undergoing mechanical ventilation for general anaesthesia: a meta-analysis of individual patient data

BACKGROUND

Protective mechanical ventilation strategies using low tidal volume or high levels of positive end-expiratory pressure (PEEP) improve outcomes for patients who have had surgery. The role of the driving pressure, which is the difference between the plateau pressure and the level of positive end-expiratory pressure is not known. We investigated the association of tidal volume, the level of PEEP, and driving pressure during intraoperative ventilation with the development of postoperative pulmonary complications.

METHODS

We did a meta-analysis of individual patient data from randomised controlled trials of protective ventilation during general anesthaesia for surgery published up to July 30, 2015. The main outcome was development of postoperative pulmonary complications (postoperative lung injury, pulmonary infection, or barotrauma).

FINDINGS

We included data from 17 randomised controlled trials, including 2250 patients. Multivariate analysis suggested that driving pressure was associated with the development of postoperative pulmonary complications (odds ratio [OR] for one unit increase of driving pressure 1·16, 95% CI 1·13-1·19; p<0·0001), whereas we detected no association for tidal volume (1·05, 0·98-1·13; p=0·179). PEEP did not have a large enough effect in univariate analysis to warrant inclusion in the multivariate analysis. In a mediator analysis, driving pressure was the only significant mediator of the effects of protective ventilation on development of pulmonary complications (p=0·027). In two studies that compared low with high PEEP during low tidal volume ventilation, an increase in the level of PEEP that resulted in an increase in driving pressure was associated with more postoperative pulmonary complications (OR 3·11, 95% CI 1·39-6·96; p=0·006).

INTERPRETATION

In patients having surgery, intraoperative high driving pressure and changes in the level of PEEP that result in an increase of driving pressure are associated with more postoperative pulmonary complications. However, a randomised controlled trial comparing ventilation based on driving pressure with usual care is needed to confirm these findings.

FUNDING

None.

Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in patients without acute lung injury

BACKGROUND

During the last decade, there has been a trend towards decreasing tidal volumes for positive pressure ventilation during surgery. It is not known whether this new trend is beneficial or harmful for patients.

OBJECTIVES

To assess the benefit of intraoperative use of low tidal volume ventilation (< 10 mL/kg of predicted body weight) to decrease postoperative complications.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 9), MEDLINE (OvidSP) (from 1946 to 5 September 2014) and EMBASE (OvidSP) (from 1974 to 5 September 2014).

SELECTION CRITERIA

We included all parallel randomized controlled trials (RCTs) that evaluated the effect of low tidal volumes (defined as < 10 mL/kg) on any of our selected outcomes in adult participants undergoing any type of surgery. We did not retain studies with participants requiring one-lung ventilation.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the quality of the retained studies with the Cochrane 'Risk of bias' tool. We analysed data with both fixed-effect (I(2) statistic < 25%) or random-effects (I(2) statistic > 25%) models based on the degree of heterogeneity. When there was an effect, we calculated a number needed to treat for an additional beneficial outcome (NNTB) using the odds ratio. When there was no effect, we calculated the optimal size information.

MAIN RESULTS

We included 12 studies in the review. In total these studies detailed 1012 participants (499 participants in the low tidal volume group and 513 in the high volume group). All studies included were at risk of bias as defined by the Cochrane tool. Based on nine studies including 899 participants, we found no difference in 0- to 30-day mortality between low and high tidal volume groups (risk ratio (RR) 0.79, 95% confidence interval (CI) 0.40 to 1.54; I(2) statistic 0%; low quality evidence). Based on four studies including 601 participants undergoing abdominal or spinal surgery, we found a lower incidence of postoperative pneumonia in the lower tidal volume group (RR 0.44, 95% CI 0.20 to 0.99; I(2) statistic 19%; moderate quality evidence; NNTB 19, 95% CI 14 to 169). Based on two studies including 428 participants, low tidal volumes decreased the need for non-invasive postoperative ventilatory support (RR 0.31, 95% CI 0.15 to 0.64; moderate quality evidence; NNTB 11, 95% CI 9 to 19). Based on eight studies including 814 participants, low tidal volumes during surgery decreased the need for postoperative invasive ventilatory support (RR 0.33, 95% CI 0.14 to 0.80; I(2) statistic 0%; NNTB 36, 95% CI 27 to 202; moderate quality evidence). Based on three studies including 650 participants, we found no difference in the intensive care unit length of stay (standardized mean difference (SMD) -0.01, 95% CI -0.22 to 0.20; I(2) statistic = 42%; moderate quality evidence). Based on eight studies including 846 participants, we did not find a difference in hospital length of stay (SMD -0.16, 95% CI -0.40 to 0.07; I(2) statistic 52%; moderate quality evidence). A meta-regression showed that the effect size increased proportionally to the peak pressure measured at the end of surgery in the high volume group. We did not find a difference in the risk of pneumothorax (RR 2.01, 95% CI 0.51 to 7.95; I(2) statistic 0%; low quality evidence).

AUTHORS' CONCLUSIONS

Low tidal volumes (defined as < 10 mL/kg) should be used preferentially during surgery. They decrease the need for postoperative ventilatory support (invasive and non-invasive). Further research is required to determine the maximum peak pressure of ventilation that should be allowed during surgery.

Protective versus Conventional Ventilation for Surgery: A Systematic Review and Individual Patient Data Meta-analysis

BACKGROUND

Recent studies show that intraoperative mechanical ventilation using low tidal volumes (VT) can prevent postoperative pulmonary complications (PPCs). The aim of this individual patient data meta-analysis is to evaluate the individual associations between VT size and positive end-expiratory pressure (PEEP) level and occurrence of PPC.

METHODS

Randomized controlled trials comparing protective ventilation (low VT with or without high levels of PEEP) and conventional ventilation (high VT with low PEEP) in patients undergoing general surgery. The primary outcome was development of PPC. Predefined prognostic factors were tested using multivariate logistic regression.

RESULTS

Fifteen randomized controlled trials were included (2,127 patients). There were 97 cases of PPC in 1,118 patients (8.7%) assigned to protective ventilation and 148 cases in 1,009 patients (14.7%) assigned to conventional ventilation (adjusted relative risk, 0.64; 95% CI, 0.46 to 0.88; P < 0.01). There were 85 cases of PPC in 957 patients (8.9%) assigned to ventilation with low VT and high PEEP levels and 63 cases in 525 patients (12%) assigned to ventilation with low VT and low PEEP levels (adjusted relative risk, 0.93; 95% CI, 0.64 to 1.37; P = 0.72). A dose-response relationship was found between the appearance of PPC and VT size (R2 = 0.39) but not between the appearance of PPC and PEEP level (R2 = 0.08).

CONCLUSIONS

These data support the beneficial effects of ventilation with use of low VT in patients undergoing surgery. Further trials are necessary to define the role of intraoperative higher PEEP to prevent PPC during nonopen abdominal surgery.

Intraoperative protective mechanical ventilation for prevention of postoperative pulmonary complications: a comprehensive review of the role of tidal volume, positive end-expiratory pressure, and lung recruitment maneuvers

Postoperative pulmonary complications are associated with increased morbidity, length of hospital stay, and mortality after major surgery. Intraoperative lung-protective mechanical ventilation has the potential to reduce the incidence of postoperative pulmonary complications. This review discusses the relevant literature on definition and methods to predict the occurrence of postoperative pulmonary complication, the pathophysiology of ventilator-induced lung injury with emphasis on the noninjured lung, and protective ventilation strategies, including the respective roles of tidal volumes, positive end-expiratory pressure, and recruitment maneuvers. The authors propose an algorithm for protective intraoperative mechanical ventilation based on evidence from recent randomized controlled trials.

Intraoperative mechanical ventilation strategies to prevent postoperative pulmonary complications in patients with pulmonary and extrapulmonary comorbidities

A variety of patient characteristics and comorbidities have been identified, which increase the risk of postoperative pulmonary complications (PPCs), including smoking, age, chronic obstructive pulmonary disease, pulmonary hypertension, obstructive sleep apnea, cardiac and neurologic diseases as well as critical illness. In contrast to the variety of conditions, evidence for specific intraoperative ventilation strategies to reduce PPC is very limited for most comorbidities. Here, we provide an overview of and discuss possible implications for the intraoperative ventilatory management of patients with comorbidities.

Lung protective ventilation in patients undergoing major surgery: a systematic review incorporating a Bayesian approach

OBJECTIVE

Protective ventilation (PV) has been validated in patients with acute respiratory distress syndrome. However, the effect of PV in patients undergoing major surgery is controversial. The study aimed to explore the beneficial effect of PV on patients undergoing a major operation by systematic review and meta-analysis.

SETTING

Various levels of medical centres.

PARTICIPANTS

Patients undergoing general anaesthesia.

INTERVENTIONS

PV with low tidal volume.

PRIMARY AND SECONDARY OUTCOME MEASURES

Study end points included acute lung injury (ALI), pneumonia, atelectasis, mortality, length of stay (LOS) in intensive care unit (ICU) and hospital.

METHODS

Databases including PubMed, Scopus, EBSCO and EMBASE were searched from inception to May 2015. Search strategies consisted of terms related to PV and anaesthesia. We reported OR for binary outcomes including ALI, mortality, pneumonia, atelectasis and other adverse outcomes. Weighted mean difference was reported for continuous outcomes such as LOS in the ICU and hospital, pH value, partial pressure of carbon dioxide, oxygenation and duration of mechanical ventilation (MV).

MAIN RESULTS

A total of 22 citations were included in the systematic review and meta-analysis. PV had protective effect against the development of ALI as compared with the control group, with an OR of 0.41 (95% CI 0.19 to 0.87). PV tended to be beneficial with regard to the development of pneumonia (OR 0.46, 95% CI 0.16 to 1.28) and atelectasis (OR 0.68, 95% CI 0.46 to 1.01), but statistical significance was not reached. Other adverse outcomes such as new onset arrhythmia were significantly reduced with the use of PV (OR 0.47, 95% CI 0.48 to 0.93).

CONCLUSIONS

The study demonstrates that PV can reduce the risk of ALI in patients undergoing major surgery. However, there is insufficient evidence that such a beneficial effect can be translated to more clinically relevant outcomes such as mortality or duration of MV.

TRIAL REGISTRATION NUMBER

The study was registered in PROSPERO (http://www.crd.york.ac.uk/PROSPERO/) under registration number CRD42013006416.

Effect of lung-protective ventilation with lower tidal volumes on clinical outcomes among patients undergoing surgery: a meta-analysis of randomized controlled trials

BACKGROUND

In anesthetized patients undergoing surgery, the role of lung-protective ventilation with lower tidal volumes is unclear. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the effect of this ventilation strategy on postoperative outcomes.

METHODS

We searched electronic databases from inception through September 2014. We included RCTs that compared protective ventilation with lower tidal volumes and conventional ventilation with higher tidal volumes in anesthetized adults undergoing surgery. We pooled outcomes using a random-effects model. The primary outcome measures were lung injury and pulmonary infection.

RESULTS

We included 19 trials (n=1348). Compared with patients in the control group, those who received lung-protective ventilation had a decreased risk of lung injury (risk ratio [RR] 0.36, 95% confidence interval [CI] 0.17 to 0.78; I2=0%) and pulmonary infection (RR 0.46, 95% CI 0.26 to 0.83; I2=8%), and higher levels of arterial partial pressure of carbon dioxide (standardized mean difference 0.47, 95% CI 0.18 to 0.75; I2=65%). No significant differences were observed between the patient groups in atelectasis, mortality, length of hospital stay, length of stay in the intensive care unit or the ratio of arterial partial pressure of oxygen to fraction of inspired oxygen.

INTERPRETATION

Anesthetized patients who received ventilation with lower tidal volumes during surgery had a lower risk of lung injury and pulmonary infection than those given conventional ventilation with higher tidal volumes. Implementation of a lung-protective ventilation strategy with lower tidal volumes may lower the incidence of these outcomes.

Incidence of mortality and morbidity related to postoperative lung injury in patients who have undergone abdominal or thoracic surgery: a systematic review and meta-analysis

BACKGROUND

Lung injury is a serious complication of surgery. We did a systematic review and meta-analysis to assess whether incidence, morbidity, and in-hospital mortality associated with postoperative lung injury are affected by type of surgery and whether outcomes are dependent on type of ventilation.

METHODS

We searched MEDLINE, CINAHL, Web of Science, and Cochrane Central Register of Controlled Trials for observational studies and randomised controlled trials published up to April, 2014, comparing lung-protective mechanical ventilation with conventional mechanical ventilation during abdominal or thoracic surgery in adults. Individual patients' data were assessed. Attributable mortality was calculated by subtracting the in-hospital mortality of patients without postoperative lung injury from that of patients with postoperative lung injury.

FINDINGS

We identified 12 investigations involving 3365 patients. The total incidence of postoperative lung injury was similar for abdominal and thoracic surgery (3·4% vs 4·3%, p=0·198). Patients who developed postoperative lung injury were older, had higher American Society of Anesthesiology scores and prevalence of sepsis or pneumonia, more frequently had received blood transfusions during surgery, and received ventilation with higher tidal volumes, lower positive end-expiratory pressure levels, or both, than patients who did not. Patients with postoperative lung injury spent longer in intensive care (8·0 [SD 12·4] vs 1·1 [3·7] days, p<0·0001) and hospital (20·9 [18·1] vs 14·7 [14·3] days, p<0·0001) and had higher in-hospital mortality (20·3% vs 1·4% p<0·0001) than those without injury. Overall attributable mortality for postoperative lung injury was 19% (95% CI 18-19), and differed significantly between abdominal and thoracic surgery patients (12·2%, 95% CI 12·0-12·6 vs 26·5%, 26·2-27·0, p=0·0008). The risk of in-hospital mortality was independent of ventilation strategy (adjusted HR 0·71, 95% CI 0·41-1·22).

INTERPRETATION

Postoperative lung injury is associated with increases in in-hospital mortality and durations of stay in intensive care and hospital. Attributable mortality due to postoperative lung injury is higher after thoracic surgery than after abdominal surgery. Lung-protective mechanical ventilation strategies reduce incidence of postoperative lung injury but does not improve mortality.

FUNDING

None.

Effect of protective ventilation on postoperative pulmonary complications in patients undergoing general anaesthesia: a meta-analysis of randomised controlled trials

OBJECTIVE

To determine whether anaesthetised patients undergoing surgery could benefit from intraoperative protective ventilation strategies.

METHODS

MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were searched up to February 2014. Eligible studies evaluated protective ventilation versus conventional ventilation in anaesthetised patients without lung injury at the onset of mechanical ventilation. The primary outcome was the incidence of postoperative pulmonary complications. Included studies must report at least one of the following end points: the incidence of atelectasis or acute lung injury or pulmonary infections.

RESULTS

Four studies (594 patients) were included. Meta-analysis using a random effects model showed a significant decrease in the incidence of atelectasis (OR=0.36; 95% CI 0.22 to 0.60; p<0.0001; I(2)=0%) and pulmonary infections (OR=0.30; 95% CI 0.14 to 0.68; p=0.004; I(2)=20%) in patients receiving protective ventilation. Ventilation with protective strategies did not reduce the incidence of acute lung injury (OR=0.40; 95% CI 0.07 to 2.15; p=0.28; I(2)=12%), all-cause mortality (OR=0.77; 95% CI 0.33 to 1.79; p=0.54; I(2)=0%), length of hospital stay (weighted mean difference (WMD)=-0.52 day, 95% CI -4.53 to 3.48 day; p=0.80; I(2)=63%) or length of intensive care unit stay (WMD=-0.55 day, 95% CI -2.19 to 1.09 day; p=0.51; I(2)=39%).

CONCLUSIONS

Intraoperative use of protective ventilation strategies has the potential to reduce the incidence of postoperative pulmonary complications in patients undergoing general anaesthesia. Prospective, well-designed clinical trials are warranted to confirm the beneficial effects of protective ventilation strategies in surgical patients.

The postoperative airway: unique challenges?

PURPOSE OF REVIEW

The review is focused on the challenge of managing airway and ventilation in the intraoperative and postoperative period.

RECENT FINDINGS

In past years, a lot of attention was focused on tracheal intubation in difficult airway, whereas only in recent years extubation time of difficult airway is also covering an important role. Protective ventilation strategies have been studied in acute respiratory distress syndrome and then in general anesthesia, either for thoracic or bariatric surgery, whereas in general abdominal surgery, in healthy lung, few studies are present demonstrating the effective protective role of low tidal volume, lung recruitment maneuvers (LRM) and positive end-expiratory pressure (PEEP). In the early postoperative period, the role of noninvasive ventilation is growing as it reduces postoperative pulmonary complications, postoperative length of stay and costs.

SUMMARY

The combination of planning extubation of predicted and unpredicted difficult airway, both intraoperative low tidal volume and low FiO2 with LRM and PEEP at different points of surgery and postoperative noninvasive ventilation should be considered in patients undergoing surgery to decrease the rate of postoperative pulmonary complications and major fatal complications such as brain damage and death.

Regional lung derecruitment and inflammation during 16 hours of mechanical ventilation in supine healthy sheep

BACKGROUND

Lung derecruitment is common during general anesthesia. Mechanical ventilation with physiological tidal volumes could magnify derecruitment, and produce lung dysfunction and inflammation. The authors used positron emission tomography to study the process of derecruitment in normal lungs ventilated for 16 h and the corresponding changes in regional lung perfusion and inflammation.

METHODS

Six anesthetized supine sheep were ventilated with VT=8 ml/kg and positive end-expiratory pressure=0. Transmission scans were performed at 2-h intervals to assess regional aeration. Emission scans were acquired at baseline and after 16 h for the following tracers: (1) F-fluorodeoxyglucose to evaluate lung inflammation and (2) NN to calculate regional perfusion and shunt fraction.

RESULTS

Gas fraction decreased from baseline to 16 h in dorsal (0.31±0.13 to 0.14±0.12, P<0.01), but not in ventral regions (0.61±0.03 to 0.63±0.07, P=nonsignificant), with time constants of 1.5-44.6 h. Although the vertical distribution of relative perfusion did not change from baseline to 16 h, shunt increased in dorsal regions (0.34±0.23 to 0.63±0.35, P<0.01). The average pulmonary net F-fluorodeoxyglucose uptake rate in six regions of interest along the ventral-dorsal direction increased from 3.4±1.4 at baseline to 4.1±1.5 10(-3)/min after 16 h (P<0.01), and the corresponding average regions of interest F-fluorodeoxyglucose phosphorylation rate increased from 2.0±0.2 to 2.5±0.2 10(-2)/min (P<0.01).

CONCLUSIONS

When normal lungs are mechanically ventilated without positive end-expiratory pressure, loss of aeration occurs continuously for several hours and is preferentially localized to dorsal regions. Progressive lung derecruitment was associated with increased regional shunt, implying an insufficient hypoxic pulmonary vasoconstriction. The increased pulmonary net uptake and phosphorylation rates of F-fluorodeoxyglucose suggest an incipient inflammation in these initially normal lungs.

Intraoperative ventilatory strategies to prevent postoperative pulmonary complications: a meta-analysis

PURPOSE OF REVIEW

It is uncertain whether patients undergoing short-lasting mechanical ventilation for surgery benefit from lung-protective intraoperative ventilatory settings including the use of lower tidal volumes, higher levels of positive end-expiratory pressure (PEEP) and/or recruitment maneuvers. We meta-analyzed trials testing the effect of lung-protective intraoperative ventilatory settings on the incidence of postoperative pulmonary complications.

RECENT FINDINGS

Eight articles (1669 patients) were included. Meta-analysis showed a decrease in lung injury development [risk ratio (RR) 0.40; 95% confidence interval (CI) 0.22-0.70; I 0%; number needed to treat (NNT) 37], pulmonary infection (RR 0.64; 95% CI 0.43-0.97; I 0%; NNT 27) and atelectasis (RR 0.67; 95% CI 0.47-0.96; I 48%; NNT 31) in patients receiving intraoperative mechanical ventilation with lower tidal volumes. Meta-analysis also showed a decrease in lung injury development (RR 0.29; 95% CI 0.14-0.60; I 0%; NNT 29), pulmonary infection (RR 0.62; 95% CI 0.40-0.96; I 15%; NNT 33) and atelectasis (RR 0.61; 95% CI 0.41-0.91; I 0%; NNT 29) in patients ventilated with higher levels of PEEP, with or without recruitment maneuvers.

SUMMARY

Lung-protective intraoperative ventilatory settings have the potential to protect against postoperative pulmonary complications.

Acute respiratory distress syndrome after pulmonary resection

Postoperative acute respiratory distress syndrome (ARDS) is a recognized complication of pulmonary resection. It is characterized by the acute onset of hypoxemia with radiographic infiltrates consistent with pulmonary edema, without elevations in the pulmonary capillary wedge pressure. Many studies suggest that around 2-5 % of patients develop some degree of lung injury, and the mortality from ARDS following pulmonary resection remains high. ARDS following thoracotomy and lung resection has a miserable prognosis, with overall hospital mortality rates over 25 %. The present review evaluates the evidence available in the literature tracking perioperative mortality and morbidity as well as the pathogenesis and management of ARDS in patients undergoing pulmonary resection.

Application of PEEP using the i-gel during volume-controlled ventilation in anesthetized, paralyzed patients

PURPOSE

This prospective, randomized trial was designed to assess whether the i-gel supraglottic airway device is suitable for volume-controlled ventilation while applying positive end-expiratory pressure (PEEP) of 5 cmH(2)O under general anesthesia. It was believed that this device might improve arterial oxygenation.

METHODS

Forty adult patients (aged 20-60 years) scheduled for elective orthopedic surgery were enrolled in this study. Twenty patients were ventilated without external PEEP [zero positive end-expiratory pressure (ZEEP) group], and the other 20 were ventilated with PEEP 5 cmH(2)O (PEEP group) after placing an i-gel device. Volume-controlled ventilation at a tidal volume (TV) of 8 ml/kg of ideal body weight, leak volume, and arterial blood gas analysis were investigated.

RESULTS

The incidences of a significant leak were similar in the ZEEP and PEEP groups (3/20 and 1/20, respectively; P = 0.605), as were leak volumes. No significant PaO(2) difference was observed between the two groups at 1 h after satisfactory i-gel insertion (215 ± 38 vs. 222 ± 54; P = 0.502).

CONCLUSIONS

The use of an i-gel during PEEP application at 5 cmH(2)O did not increase the incidence of a significant air leak, and a PEEP of 5 cmH(2)O failed to improve arterial oxygenation during controlled ventilation in healthy adult patients.

A 5-year observational study of lung-protective ventilation in the operating room: a single-center experience

PURPOSE

We assessed the evolution of lung-protective ventilation strategies during anesthesia and identified factors associated with the selection of a nonprotective ventilation strategy.

METHODS

This retrospective observational study covered a 5-year period from March 2006 to March 2011. It included 45575 adult patients who underwent intubation de novo in the operating room. We considered a tidal volume (VT) greater than 10 mL/kg of ideal body weight (IBW) and/or positive end-expiratory pressure (PEEP) less than 5 cm H2O as not lung protective. We evaluated the use of nonprotective ventilation strategies over time in men and women, by American Society of Anesthesiologists classification, and for elective vs emergent surgery.

RESULTS

Over the duration of the study, there was a significant reduction in the percentage of patients receiving a VT greater than 10 mL/kg IBW (28.5%-16.3%, P < .001), zero PEEP (27.5%-18.2%, P < .001), and VT greater than 10 mL/kg IBW with PEEP less than 5 cm H2O (13.4%-8.0%, P < .001). The odds of receiving nonprotective ventilation were greater for women than for men, in the first year compared with the last year, and for elective compared with emergent surgery.

CONCLUSION

Although use of nonprotective ventilation decreased over time, an important percentage of patients continue to receive nonprotective ventilation.