Influence of gas composition on recurrence of atelectasis after a reexpansion maneuver during general anesthesia

Closed-loop oxygen control for critically ill patients--A systematic review and meta-analysis

BACKGROUND

The impact of closed-loop control systems to titrate oxygen flow in critically ill patients, including their effectiveness, efficacy, workload and safety, remains unclear. This systematic review investigated the utilization of closed-loop oxygen systems for critically ill patients in comparison to manual oxygen titration systems focusing on these topics.

METHODS AND FINDINGS

A search was conducted across several databases including MEDLINE, CENTRAL, EMBASE, LILACS, CINAHL, LOVE, ClinicalTrials.gov, and the World Health Organization on March 3, 2022, with subsequent updates made on June 27, 2023. Evidence databases were searched for randomized clinical parallel or crossover studies investigating closed-loop oxygen control systems for critically ill patients. This systematic review and meta-analysis was performed following the Preferred Reporting Items for Systematic Review and Meta-analysis guidelines. The analysis was conducted using Review Manager software, adopting the mean difference or standardized mean difference with a 95% confidence interval (95% CI) for continuous variables or risk ratio with 95% CI for dichotomous outcomes. The main outcome of interest was the percentage of time spent in the peripheral arterial oxygen saturation target. Secondary outcomes included time for supplemental oxygen weaning, length of stay, mortality, costs, adverse events, and workload of healthcare professional. A total of 37 records from 21 studies were included in this review with a total of 1,577 participants. Compared with manual oxygen titration, closed-loop oxygen control systems increased the percentage of time in the prescribed SpO2 target, mean difference (MD) 25.47; 95% CI 19.7, 30.0], with moderate certainty of evidence. Current evidence also shows that closed-loop oxygen control systems have the potential to reduce the percentage of time with hypoxemia (MD -0.98; 95% CI -1.68, -0.27) and healthcare workload (MD -4.94; 95% CI -7.28, -2.61) with low certainty of evidence.

CONCLUSION

Closed-loop oxygen control systems increase the percentage of time in the preferred SpO2 targets and may reduce healthcare workload.

TRIAL REGISTRATION

PROSPERO: CRD42022306033.

Effects of different fractions of inspired oxygen on gas embolization during hysteroscopic surgery: A double-blind, randomized, controlled trial

OBJECTIVE

Gas embolism is a common complication of hysteroscopic surgery that causes serious concern among gynecologists and anesthesiologists due to the potential risk to patients. The factors influencing gas embolism in hysteroscopic surgery have been extensively studied. However, the effect of the oxygen concentration inhaled by patients on gas embolism during hysteroscopic surgery remains elusive. Therefore, we designed a double-blind, randomized, controlled trial to determine whether different inhaled oxygen concentrations influence the occurrence of gas embolism during hysteroscopic surgery.

METHODS

This trial enrolled 162 adult patients undergoing elective hysteroscopic surgery who were randomly divided into three groups with inspired oxygen fractions of 30%, 50%, and 100%. Transthoracic echocardiography (four-chamber view) was used to evaluate whether gas embolism occurred. Before the start of surgery, the four-chamber view was continuously monitored.

RESULTS

The number of gas embolisms in the 30%, 50%, and 100% groups was 36 (69.2%), 30 (55.6%), and 24 (44.4%), respectively. The incidence of gas embolism gradually decreased with increasing inhaled oxygen concentration (P = 0.031).

CONCLUSION

In hysteroscopic surgery, a higher oxygen concentration inhaled by patients may reduce the incidence of gas embolism, indicating that a higher inhaled oxygen concentration, especially 100%, could be recommended for patients during hysteroscopic surgery.

TRIAL REGISTRATION

Chinese Clinical Trial Registry (https://www.chictr.org.cn/showproj.html?proj=53779, Registration number: ChiCTR2000033202).

The effect of high perioperative inspiratory oxygen fraction for abdominal surgery on surgical site infection: a systematic review and meta-analysis

Guidelines from the World Health Organization strongly recommend the use of a high fraction of inspired oxygen (FiO2) in adult patients undergoing general anesthesia to reduce surgical site infection (SSI). However, previous meta-analyses reported inconsistent results. We aimed to address this controversy by focusing specifically on abdominal surgery with relatively high risk of SSI. Medline, EMBASE, and Cochrane CENTRAL databases were searched. Randomized trials of abdominal surgery comparing high to low perioperative FiO2 were included, given that the incidence of SSI was reported as an outcome. Meta-analyses of risk ratios (RR) were performed using a fixed effects model. Subgroup analysis and meta-regression were employed to explore sources of heterogeneity. We included 27 trials involving 15977 patients. The use of high FiO2 significantly reduced the incidence of SSI (n = 27, risk ratio (RR): 0.87; 95% confidence interval (CI): 0.79, 0.95; I2 = 49%, Z = 3.05). Trial sequential analysis (TSA) revealed that z-curve crossed the trial sequential boundary and data are sufficient. This finding held true for the subgroup of emergency operations (n = 2, RR: 0.54; 95% CI: 0.35, 0.84; I2 = 0%, Z = 2.75), procedures using air as carrier gas (n = 9, RR: 0.79; 95% CI: 0.69, 0.91; I2 = 60%, Z = 3.26), and when a high level of FiO2 was maintained for a postoperative 6 h or more (n = 9, RR: 0.68; 95% CI: 0.56, 0.83; I2 = 46%, Z = 3.83). Meta-regression revealed no significant interaction between SSI with any covariates including age, sex, body-mass index, diabetes mellitus, duration of surgery, and smoking. Quality of evidence was assessed to be moderate to very low. Our pooled analysis revealed that the application of high FiO2 reduced the incidence of SSI after abdominal operations. Although TSA demonstrated sufficient data and cumulative analysis crossed the TSA boundary, our results should be interpreted cautiously given the low quality of evidence.Registration: https://www.crd.york.ac.uk/prospero (CRD42022369212) on October 2022.

Higher versus lower fractions of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit

BACKGROUND

This is an updated review concerning 'Higher versus lower fractions of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit'. Supplementary oxygen is provided to most patients in intensive care units (ICUs) to prevent global and organ hypoxia (inadequate oxygen levels). Oxygen has been administered liberally, resulting in high proportions of patients with hyperoxemia (exposure of tissues to abnormally high concentrations of oxygen). This has been associated with increased mortality and morbidity in some settings, but not in others. Thus far, only limited data have been available to inform clinical practice guidelines, and the optimum oxygenation target for ICU patients is uncertain. Because of the publication of new trial evidence, we have updated this review.

OBJECTIVES

To update the assessment of benefits and harms of higher versus lower fractions of inspired oxygen (FiO2) or targets of arterial oxygenation for adults admitted to the ICU.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, Science Citation Index Expanded, BIOSIS Previews, and LILACS. We searched for ongoing or unpublished trials in clinical trial registers and scanned the reference lists and citations of included trials. Literature searches for this updated review were conducted in November 2022.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared higher versus lower FiO2 or targets of arterial oxygenation (partial pressure of oxygen (PaO2), peripheral or arterial oxygen saturation (SpO2 or SaO2)) for adults admitted to the ICU. We included trials irrespective of publication type, publication status, and language. We excluded trials randomising participants to hypoxaemia (FiO2 below 0.21, SaO2/SpO2 below 80%, or PaO2 below 6 kPa) or to hyperbaric oxygen, and cross-over trials and quasi-randomised trials.

DATA COLLECTION AND ANALYSIS

Four review authors independently, and in pairs, screened the references identified in the literature searches and extracted the data. Our primary outcomes were all-cause mortality, the proportion of participants with one or more serious adverse events (SAEs), and quality of life. We analysed all outcomes at maximum follow-up. Only three trials reported the proportion of participants with one or more SAEs as a composite outcome. However, most trials reported on events categorised as SAEs according to the International Conference on Harmonisation Good Clinical Practice (ICH-GCP) criteria. We, therefore, conducted two analyses of the effect of higher versus lower oxygenation strategies using 1) the single SAE with the highest reported proportion in each trial, and 2) the cumulated proportion of participants with an SAE in each trial. Two trials reported on quality of life. Secondary outcomes were lung injury, myocardial infarction, stroke, and sepsis. No trial reported on lung injury as a composite outcome, but four trials reported on the occurrence of acute respiratory distress syndrome (ARDS) and five on pneumonia. We, therefore, conducted two analyses of the effect of higher versus lower oxygenation strategies using 1) the single lung injury event with the highest reported proportion in each trial, and 2) the cumulated proportion of participants with ARDS or pneumonia in each trial. We assessed the risk of systematic errors by evaluating the risk of bias in the included trials using the Risk of Bias 2 tool. We used the GRADEpro tool to assess the overall certainty of the evidence. We also evaluated the risk of publication bias for outcomes reported by 10b or more trials.

MAIN RESULTS

We included 19 RCTs (10,385 participants), of which 17 reported relevant outcomes for this review (10,248 participants). For all-cause mortality, 10 trials were judged to be at overall low risk of bias, and six at overall high risk of bias. For the reported SAEs, 10 trials were judged to be at overall low risk of bias, and seven at overall high risk of bias. Two trials reported on quality of life, of which one was judged to be at overall low risk of bias and one at high risk of bias for this outcome. Meta-analysis of all trials, regardless of risk of bias, indicated no significant difference from higher or lower oxygenation strategies at maximum follow-up with regard to mortality (risk ratio (RR) 1.01, 95% confidence interval (C)I 0.96 to 1.06; I2 = 14%; 16 trials; 9408 participants; very low-certainty evidence); occurrence of SAEs: the highest proportion of any specific SAE in each trial RR 1.01 (95% CI 0.96 to 1.06; I2 = 36%; 9466 participants; 17 trials; very low-certainty evidence), or quality of life (mean difference (MD) 0.5 points in participants assigned to higher oxygenation strategies (95% CI -2.75 to 1.75; I2 = 34%, 1649 participants; 2 trials; very low-certainty evidence)). Meta-analysis of the cumulated number of SAEs suggested benefit of a lower oxygenation strategy (RR 1.04 (95% CI 1.02 to 1.07; I2 = 74%; 9489 participants; 17 trials; very low certainty evidence)). However, trial sequential analyses, with correction for sparse data and repetitive testing, could reject a relative risk increase or reduction of 10% for mortality and the highest proportion of SAEs, and 20% for both the cumulated number of SAEs and quality of life. Given the very low-certainty of evidence, it is necessary to interpret these findings with caution. Meta-analysis of all trials indicated no statistically significant evidence of a difference between higher or lower oxygenation strategies on the occurrence of lung injuries at maximum follow-up (the highest reported proportion of lung injury RR 1.08, 95% CI 0.85 to 1.38; I2 = 0%; 2048 participants; 8 trials; very low-certainty evidence). Meta-analysis of all trials indicated harm from higher oxygenation strategies as compared with lower on the occurrence of sepsis at maximum follow-up (RR 1.85, 95% CI 1.17 to 2.93; I2 = 0%; 752 participants; 3 trials; very low-certainty evidence). Meta-analysis indicated no differences regarding the occurrences of myocardial infarction or stroke.

AUTHORS' CONCLUSIONS

In adult ICU patients, it is still not possible to draw clear conclusions about the effects of higher versus lower oxygenation strategies on all-cause mortality, SAEs, quality of life, lung injuries, myocardial infarction, stroke, and sepsis at maximum follow-up. This is due to low or very low-certainty evidence.

Changes in lung volume estimated by electrical impedance tomography during apnea and high-flow nasal oxygenation: A single-center randomized controlled trial

Background

Previous studies concerning humidified, heated high-flow nasal oxygen delivered in spontaneously breathing patients postulated an increase in functional residual capacity as one of its physiological effects. It is unclear wheter this is also true for patients under general anesthesia.

Methodology

The sincle-center noninferiority trial was registered at ClinicalTrials.gov (NCT NCT03478774). This secondary outcome analysis shows estimated differences in lung volume changes using electrical impedance tomography between different flow rates of 100% oxygen in apneic, anesthetized and paralyzed adults prior to intubation. One hundred and twenty five patients were randomized to five groups with different flow rates of 100% oxygen: i) minimal-flow: 0.25 l.min-1 via endotracheal tube; ii) low-flow: 2 l.min-1 + continuous jaw thrust; iii) medium-flow: 10 l.min-1 + continuous jaw thrust; iv) high-flow: 70l.min-1 + continuous jaw thrust; and v) control: 70 l.min-1 + continuous video-laryngoscopy. After standardized anesthesia induction with non-depolarizing neuromuscular blockade, the 15-minute apnea period and oxygen delivery was started according to the randomized flow rate. Continuous electrical impedance tomography measurements were performed during the 15-minute apnea period. Total change in lung impedance (an estimate of changes in lung volume) over the 15-minute apnea period and times to 25%, 50% and 75% of total impedance change were calculated.

Results

One hundred and twenty five patients completed the original study. Six patients did not complete the 15-minute apnea period. Due to maloperation, malfunction and artefacts additional 54 measurements had to be excluded, resulting in 65 patients included into this secondary outcome analysis. We found no differences between groups with respect to decrease in lung impedance or curve progression over the observation period.

Conclusions

Different flow rates of humidified 100% oxygen during apnea result in comparable decreases in lung volumes. The demonstrated increase in functional residual capacity during spontaneous breathing with high-flow nasal oxygenation could not be replicated during apnea under general anesthesia with neuromuscular blockade.

Effect of sigh in lateral position on postoperative atelectasis in adults assessed by lung ultrasound: a randomized, controlled trial

Background

Postoperative atelectasis occurs in 90% of patients receiving general anesthesia. Recruitment maneuvers (RMs) are not always effective and frequently associated with barotrauma and hemodynamic instability. It is reported that many natural physiological behaviors interrupted under general anesthesia could prevent atelectasis and restore lung aeration. This study aimed to find out whether a combined physiological recruitment maneuver (CPRM), sigh in lateral position, could reduce postoperative atelectasis using lung ultrasound (LUS).

Methods

We conducted a prospective, randomized, controlled trial in adults with open abdominal surgery under general anesthesia lasting for 2 h or longer. Subjects were randomly allocated to either control group (C-group) or CPRM-group and received volume-controlled ventilation with the same ventilator settings. Patients in CPRM group was ventilated in sequential lateral position, with the addition of periodic sighs to recruit the lung. LUS scores, dynamic compliance (Cdyn), the partial pressure of arterial oxygen (PaO₂) and fraction of inspired oxygen (FiO₂) ratio (PaO₂/FiO₂), and other explanatory variables were acquired from each patient before and after recruitment.

Results

Seventy patients were included in the analysis. Before recruitment, there was no significant difference in LUS scores, Cdyn and PaO₂/FiO₂ between CPRM-group and C-group. After recruitment, LUS scores in CPRM-group decreased significantly compared with C-group (6.00 [5.00, 7.00] vs. 8.00 [7.00, 9.00], p = 4.463e-11 < 0.05), while PaO₂/FiO₂ and Cdyn in CPRM-group increased significantly compared with C-group respectively (377.92 (93.73) vs. 309.19 (92.98), p = 0.008 < 0.05, and 52.00 [47.00, 60.00] vs. 47.70 [41.00, 59.50], p = 6.325e-07 < 0.05). No hemodynamic instability, detectable barotrauma or position-related complications were encountered.

Conclusions

Sigh in lateral position can effectively reduce postoperative atelectasis even without causing severe side effects. Further large-scale studies are necessary to evaluate it’s long-term effects on pulmonary complications and hospital length of stay.

Trial registration

ChiCTR1900024379. Registered 8 July 2019, 

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01748-9.

Impact of airway and a standardized recruitment maneuver on CT chest imaging quality in a pediatric population: A retrospective review

INTRODUCTION

When performing computerized tomography chest imaging in children, obtaining high quality, motion-free images is important in the accurate diagnosis of underlying pathology. General anesthesia is associated with the development of atelectasis, which can impair accurate diagnosis by obscuring or altering the appearance of the lung parenchyma or airways. Recruitment maneuvers, performed by anesthesiologists, can be used to effectively re-expand atelectatic lung.

METHODS

The computerized tomography chest imaging in 44 children aged between 2 months and 7 years, undergoing serial imaging for monitoring of cystic fibrosis, were reviewed and graded for atelectasis. The first scan performed on each child was performed with a supraglottic airway device and a non-standardized recruitment maneuver. The second scan on each child was performed with a cuffed endotracheal tube and a standardized recruitment maneuver.

RESULTS

When a supraglottic airway device and a non-standardized recruitment maneuver were used, 77% of patients demonstrated atelectasis of any degree on their computerized tomography chest imaging, compared with only 39% when a cuffed endotracheal tube and standardized recruitment maneuver were used. The percentage of computerized tomography chest scans that were scored acceptable (with either a total combined lung atelectasis score of 0 or 1) improved from 37% to 75% when a cuffed endotracheal tube and standardized recruitment maneuver were used. In particular, the mean atelectasis score for both lungs improved from 2.91 (SD ± 2.6) to 1.11 (SD ± 1.9), with a mean difference of 1.8 (95% CI 0.82-2.77; p: .0004).

CONCLUSION

The use of a cuffed endotracheal tube and a standardized recruitment maneuver is an effective way to reduce atelectasis as a result of general anesthesia. Anesthesiologists can actively contribute toward improved image quality through their choice of airway and recruitment maneuver.

Atelectasis and lung recruitment in pediatric anesthesia: An educational review

General anesthesia is associated with development of pulmonary atelectasis. Children are more vulnerable to the development and adverse effects of atelectasis. We review the physiology and risk factors for the development of atelectasis in pediatric patients under general anesthesia. We discuss the clinical significance of atelectasis, the use and value of recruitment maneuvers, and other techniques available to minimize lung collapse. This review demonstrates the value of a recruitment maneuver, maintaining positive end-expiratory pressure (PEEP) until extubation and lowering FiO₂ where possible in the daily practice of the pediatric anesthetist.

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.

Perioperative Pulmonary Atelectasis: Part I. Biology and Mechanisms

Pulmonary atelectasis is common in the perioperative period. Physiologically, it is produced when collapsing forces derived from positive pleural pressure and surface tension overcome expanding forces from alveolar pressure and parenchymal tethering. Atelectasis impairs blood oxygenation and reduces lung compliance. It is increasingly recognized that it can also induce local tissue biologic responses, such as inflammation, local immune dysfunction, and damage of the alveolar-capillary barrier, with potential loss of lung fluid clearance, increased lung protein permeability, and susceptibility to infection, factors that can initiate or exaggerate lung injury. Mechanical ventilation of a heterogeneously aerated lung (e.g., in the presence of atelectatic lung tissue) involves biomechanical processes that may precipitate further lung damage: concentration of mechanical forces, propagation of gas-liquid interfaces, and remote overdistension. Knowledge of such pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should guide optimal clinical management.

Comparison of Positive End-Expiratory Pressure versus Tidal Volume-Induced Ventilator-Driven Alveolar Recruitment Maneuver in Robotic Prostatectomy: A Randomized Controlled Study

Background: We evaluated the pulmonary effects of two ventilator-driven alveolar recruitment maneuver (ARM) methods during laparoscopic surgery. Methods: Sixty-four patients undergoing robotic prostatectomy were randomized into two groups: incrementally increasing positive end-expiratory pressure in a stepwise manner (PEEP group) versus tidal volume (V_T group). We performed each ARM after induction of anesthesia in the supine position (T1), after pneumoperitoneum in the Trendelenburg position (T2), and after peritoneum desufflation in the supine position (T3). The primary outcome was change in end-expiratory lung impedance (EELI) before and 5 min after ARM at T3, measured by electrical impedance tomography. Results: The PEEP group showed significantly higher increasing EELI 5 min after ARM than the V_T group at T1 and T3 (median [IQR] 460 [180,800] vs. 200 [80,315], p = 0.002 and 280 [170,420] vs. 95 [55,175], p = 0.004, respectively; PEEP group vs. V_T group). The PEEP group showed significantly higher lung compliance and lower driving pressure at T1 and T3. However, there was no significant difference in EELI change, lung compliance, or driving pressure after ARM at T2. Conclusions: The ventilator-driven ARM by the increasing PEEP method led to greater improvements in lung compliance at the end of laparoscopic surgery than the increasing V_T method.

Perioperative high inspired oxygen fraction induces atelectasis in patients undergoing abdominal surgery: A randomized controlled trial

STUDY OBJECTIVE

We evaluated the feasibility of use and effects on postoperative atelectasis and complications of lower inspired oxygen fraction (FIO₂) compared to conventional oxygen therapy.

DESIGN

Single center, randomized clinical trial.

SETTING

University hospital, operating room and postoperative recovery area.

PATIENTS

One hundred ninety patients aged ≥50 with an American Society of Anesthesiologists physical status of I-III who underwent abdominal surgery with general anesthesia.

INTERVENTIONS

Participants were randomly assigned to either the low FIO₂ group (intraoperative: FIO₂ 0.35, during induction and recovery: FIO₂ 0.7) or the conventional FIO₂ group (intraoperative: FIO₂ 0.6, during induction and recovery: FIO₂ 1.0).

MEASUREMENTS

The primary outcome was postoperative atelectasis measured with lung ultrasonography at postoperative 30 min in the post-anesthesia care unit (consolidation score: each region 0-3, 12 region, total score range of 0 to 36, a lower score indicating better aeration).

MAIN RESULTS

Seven patients in the low FIO₂ group were omitted from the study due to changing FIO₂ during intervention (7/95 (8.4%) vs. 2/95 (2.1%), p = 0.088; low FIO₂ group vs. conventional FIO₂ group). Overall, atelectasis was detected in 29.7% (51/172) of patients 30 min after surgery by lung ultrasound and 40.1% (69/172) of patients after 2 days after surgery by chest X-ray. The scores of lung ultrasonography and the incidence of significant atelectasis (consolidation score ≥ 2 at any region) were lower in the low FIO₂ group than in the conventional FIO₂ group (median [IQR]: 3 [1,6] vs. 7 [3,9], p < 0.001 and 17/85 (20%) vs. 34/87 (39%), RR: 0.512 [95% CI: 0.311-0.843], p = 0.006, respectively). The incidence of surgical site infection and length of hospitalization were not significantly different between the two groups.

CONCLUSIONS

Based on our findings, decreased inspired oxygen fraction during anesthesia and recovery did not cause hypoxic events, but instead reduced immediate postoperative atelectasis. The use of intraoperative conventional higher inspired oxygen did not afford any clinical advantages for postoperative recovery in abdominal surgery.

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).

Perioperative Lung Protection: Clinical Implications

In the past, it was common practice to use a high tidal volume (VT) during intraoperative ventilation, because this reduced the need for high oxygen fractions to compensate for the ventilation-perfusion mismatches due to atelectasis in a time when it was uncommon to use positive end-expiratory pressure (PEEP) in the operating room. Convincing and increasing evidence for harm induced by ventilation with a high VT has emerged over recent decades, also in the operating room, and by now intraoperative ventilation with a low VT is a well-adopted approach. There is less certainty about the level of PEEP during intraoperative ventilation. Evidence for benefit and harm of higher PEEP during intraoperative ventilation is at least contradicting. While some PEEP may prevent lung injury through reduction of atelectasis, higher PEEP is undeniably associated with an increased risk of intraoperative hypotension that frequently requires administration of vasoactive drugs. The optimal level of inspired oxygen fraction (FIO2) during surgery is even more uncertain. The suggestion that hyperoxemia prevents against surgical site infections has not been confirmed in recent research. In addition, gas absorption-induced atelectasis and its association with adverse outcomes like postoperative pulmonary complications actually makes use of a high FIO2 less attractive. Based on the available evidence, we recommend the use of a low VT of 6-8 mL/kg predicted body weight in all surgery patients, and to restrict use of a high PEEP and high FIO2 during intraoperative ventilation to cases in which hypoxemia develops. Here, we prefer to first increase FIO2 before using high PEEP.

Measurement of airway pressure during high-flow nasal therapy in apnoeic oxygenation: a randomised controlled crossover trial. Anaesthesia 2020;76:27-35. [PMID: 32776518 DOI: 10.1111/anae.15224]

It is recognised that high-flow nasal therapy can prevent desaturation during airway management. Studies in spontaneously breathing patients show an almost linear relationship between flow rate and positive airway pressure in the nasopharynx. Positive airway pressure has been suggested as one of the possible mechanisms explaining how high-flow nasal therapy works. However, data on pressures generated by high-flow nasal therapy in apnoeic adults under general anaesthesia are absent. This randomised controlled crossover trial investigated airway pressures generated by different flow rates during high-flow nasal therapy in anaesthetised and paralysed apnoeic patients, comparing pressures with closed and open mouths. Following induction of anaesthesia and neuromuscular blockade, a continuous jaw thrust was used to enable airway patency. Airway pressure was measured in the right main bronchus, the middle of the trachea and the pharynx, using a fibreoptically-placed catheter connected to a pressure transducer. Each measurement was randomised with respect to closed or open mouth and different flow rates. Twenty patients undergoing elective surgery were included (mean (SD) age 38 (18) years, BMI 25.0 (3.3) kg.m^-2 , nine women, ASA physical status 1 (35%), 2 (55%), 3 (10%). While closed mouths and increasing flow rates demonstrated non-linear increases in pressure, the pressure increase was negligible with an open mouth. Airway pressures remained below 10 cmH₂ O even with closed mouths and flow rates up to 80 l.min^-1 ; they were not influenced by catheter position. This study shows an increase in airway pressures with closed mouths that depends on flow rate. The generated pressure is negligible with an open mouth. These data question positive airway pressure as an important mechanism for maintenance of oxygenation during apnoea.

Lung ultrasound score to determine the effect of fraction inspired oxygen during alveolar recruitment on absorption atelectasis in laparoscopic surgery: a randomized controlled trial

Background

Although the intraoperative alveolar recruitment maneuver (RM) efficiently treats atelectasis, the effect of Fio₂ on atelectasis during RM is uncertain. We hypothesized that a high Fio₂ (1.0) during RM would lead to a higher degree of postoperative atelectasis without benefiting oxygenation when compared to low Fio₂ (0.4).

Methods

In this randomized controlled trial, patients undergoing elective laparoscopic surgery in the Trendelenburg position were allocated to low- (Fio₂ 0.4, n = 44) and high-Fio₂ (Fio₂ 1.0, n = 46) groups. RM was performed 1-min post tracheal intubation and post changes in supine and Trendelenburg positions during surgery. We set the intraoperative Fio₂ at 0.4 for both groups and calculated the modified lung ultrasound score (LUSS) to assess lung aeration after anesthesia induction and at surgery completion. The primary outcome was modified LUSS at the end of the surgery. The secondary outcomes were the intra- and postoperative Pao₂ to Fio₂ ratio and postoperative pulmonary complications.

Results

The modified LUSS before capnoperitoneum and RM (P = 0.747) were similar in both groups. However, the postoperative modified LUSS was significantly lower in the low Fio₂ group (median difference 5.0, 95% CI 3.0–7.0, P < 0.001). Postoperatively, substantial atelectasis was more common in the high-Fio₂ group (relative risk 1.77, 95% CI 1.27–2.47, P < 0.001). Intra- and postoperative Pao₂ to Fio₂ were similar with no postoperative pulmonary complications. Atelectasis occurred more frequently when RM was performed with high than with low Fio₂; oxygenation was not benefitted by a high-Fio_2.

Conclusions

In patients undergoing laparoscopic surgery in the Trendelenburg position, absorption atelectasis occurred more frequently with high rather than low Fio₂. No oxygenation benefit was observed in the high-Fio₂ group.

Trial registration

ClinicalTrials.gov, NCT03943433. Registered 7 May 2019,

Higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the intensive care unit

BACKGROUND

The mainstay treatment for hypoxaemia is oxygen therapy, which is given to the vast majority of adults admitted to the intensive care unit (ICU). The practice of oxygen administration has been liberal, which may result in hyperoxaemia. Some studies have indicated an association between hyperoxaemia and mortality, whilst other studies have not. The ideal target for supplemental oxygen for adults admitted to the ICU is uncertain. Despite a lack of robust evidence of effectiveness, oxygen administration is widely recommended in international clinical practice guidelines. The potential benefit of supplemental oxygen must be weighed against the potentially harmful effects of hyperoxaemia.

OBJECTIVES

To assess the benefits and harms of higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU.

SEARCH METHODS

We identified trials through electronic searches of CENTRAL, MEDLINE, Embase, Science Citation Index Expanded, BIOSIS Previews, CINAHL, and LILACS. We searched for ongoing or unpublished trials in clinical trials registers. We also scanned the reference lists of included studies. We ran the searches in December 2018.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that compared higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU. We included trials irrespective of publication type, publication status, and language. We included trials with a difference between the intervention and control groups of a minimum 1 kPa in partial pressure of arterial oxygen (PaO2), minimum 10% in fraction of inspired oxygen (FiO2), or minimum 2% in arterial oxygen saturation of haemoglobin/non-invasive peripheral oxygen saturation (SaO2/SpO2). We excluded trials randomizing participants to hypoxaemia (FiO2 below 0.21, SaO2/SpO2 below 80%, and PaO2 below 6 kPa) and to hyperbaric oxygen.

DATA COLLECTION AND ANALYSIS

Three review authors independently, and in pairs, screened the references retrieved in the literature searches and extracted data. Our primary outcomes were all-cause mortality, the proportion of participants with one or more serious adverse events, and quality of life. None of the trials reported the proportion of participants with one or more serious adverse events according to the International Conference on Harmonisation Good Clinical Practice (ICH-GCP) criteria. Nonetheless, most trials reported several serious adverse events. We therefore included an analysis of the effect of higher versus lower fraction of inspired oxygen, or targets using the highest reported proportion of participants with a serious adverse event in each trial. Our secondary outcomes were lung injury, acute myocardial infarction, stroke, and sepsis. None of the trials reported on lung injury as a composite outcome, however some trials reported on acute respiratory distress syndrome (ARDS) and pneumonia. We included an analysis of the effect of higher versus lower fraction of inspired oxygen or targets using the highest reported proportion of participants with ARDS or pneumonia in each trial. To assess the risk of systematic errors, we evaluated the risk of bias of the included trials. We used GRADE to assess the overall certainty of the evidence.

MAIN RESULTS

We included 10 RCTs (1458 participants), seven of which reported relevant outcomes for this review (1285 participants). All included trials had an overall high risk of bias, whilst two trials had a low risk of bias for all domains except blinding of participants and personnel. Meta-analysis indicated harm from higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation regarding mortality at the time point closest to three months (risk ratio (RR) 1.18, 95% confidence interval (CI) 1.01 to 1.37; I2 = 0%; 4 trials; 1135 participants; very low-certainty evidence). Meta-analysis indicated harm from higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation regarding serious adverse events at the time point closest to three months (estimated highest proportion of specific serious adverse events in each trial RR 1.13, 95% CI 1.04 to 1.23; I2 = 0%; 1234 participants; 6 trials; very low-certainty evidence). These findings should be interpreted with caution given that they are based on very low-certainty evidence. None of the included trials reported any data on quality of life at any time point. Meta-analysis indicated no evidence of a difference between higher fraction of inspired oxygen or targets as compared with lower fraction or targets of arterial oxygenation on lung injury at the time point closest to three months (estimated highest reported proportion of lung injury RR 1.03, 95% CI 0.78 to 1.36; I2 = 0%; 1167 participants; 5 trials; very low-certainty evidence). None of the included trials reported any data on acute myocardial infarction or stroke, and only one trial reported data on the effects on sepsis.

AUTHORS' CONCLUSIONS

We are very uncertain about the effects of higher versus lower fraction of inspired oxygen or targets of arterial oxygenation for adults admitted to the ICU on all-cause mortality, serious adverse events, and lung injuries at the time point closest to three months due to very low-certainty evidence. Our results indicate that oxygen supplementation with higher versus lower fractions or oxygenation targets may increase mortality. None of the trials reported the proportion of participants with one or more serious adverse events according to the ICH-GCP criteria, however we found that the trials reported an increase in the number of serious adverse events with higher fractions or oxygenation targets. The effects on quality of life, acute myocardial infarction, stroke, and sepsis are unknown due to insufficient data.

Effect of different fraction of inspired oxygen on development of atelectasis in mechanically ventilated children: A randomized controlled trial

BACKGROUND

The use of high fraction of inspired oxygen (F_I O₂ ) can cause direct pulmonary toxicity and pulmonary complications. The purpose of this study was to evaluate the effect of different F_I O₂ on development of intraoperative atelectasis in mechanically ventilated children using lung ultrasound.

METHODS

In this randomized controlled, patient- and sonographer-blinded trial, 86 children (≤6 years) undergoing noncardiac surgery were allocated into a low (n = 43) or high (n = 43) F_I O₂ group. The low F_I O₂ group consistently received 30% air-oxygen mixture during preoxygenation, ultrasound-guided recruitment maneuver, and mechanical ventilation. The high F_I O₂ group received 100% oxygen during preoxygenation and ultrasound-guided recruitment maneuver and 60% air-oxygen mixture during mechanical ventilation. Positive end-expiratory pressure of 5 cm H₂ O was applied in both groups. Lung ultrasound was performed one minute after the start of mechanical ventilation and at the end of surgery in both groups. Primary outcome was significant atelectasis incidence (consolidation score of ≥2 in any region) on the postoperative lung ultrasound. Secondary outcomes included significant atelectasis incidence on the preoperative lung ultrasound, incidences of intra- and postoperative desaturation, and incidences of postoperative fever and postoperative pulmonary complications.

RESULTS

Significant atelectasis incidence on the postoperative lung ultrasound was similar between the low and high F_I O₂ groups (28% vs 37%; Pearson chi-square value = 0.847; P = .357; OR 1.531; 95% CI 0.617-3.800). Significant atelectasis incidence on the preoperative lung ultrasound was also similar between the groups (12% vs 9%; Pearson chi-square value = 0.124; P = .725; OR 0.779; 95% CI 0.194-3.125). There were no statistically significant differences in the other secondary outcomes.

CONCLUSIONS

F_I O₂ did not affect significant atelectasis formation in mechanically ventilated children who received ultrasound-guided recruitment maneuver and positive end-expiratory pressure.

Effects of inspired oxygen concentration during emergence from general anaesthesia on postoperative lung impedance changes evaluated by electrical impedance tomography: a randomised controlled trial

We evaluated the effects of three different inspired oxygen concentrations (40%, 80%, and 100%) at anaesthesia emergence on postoperative lung volumes as measured by global impedance of electrical impedance tomography (EIT). This is a randomised, controlled, and assessor-blinded study in single-centre from May 2017 to August 2017. Seventy-one patients undergoing elective laparoscopic colorectal surgery with healthy lung condition were randomly allocated into the three groups based on the concentration of inspired oxygen applied during anaesthesia emergence: 40%-, 80%- or 100%-oxygen. End-expiratory lung impedance (EELI) with normal tidal ventilation and total lung impedance (TLI) with full respiratory effort were measured preoperatively and before discharge in the post-anaesthesia care unit by EIT, and perioperative changes (the ratio of difference between preoperative and postoperative value to preoperative value) were compared among the three groups. Postoperative lung impedances were significantly reduced compared with preoperative values in all patients (P < 0.001); however, perioperative lung impedance reduction (%) did not differ among the three oxygen groups. The mean reduction ratio in each 40%-, 80%-, and 100%-oxygen group were 37% ± 13%, 41% ± 14%, and 46% ± 14% for EELI (P = 0.125) and 40% ± 20%, 44% ± 17% and 49% ± 20% for TLI (P = 0.276), respectively. Inspired oxygen concentrations applied during anaesthesia emergence did not show a significant difference in postoperative lung volume as measured by EIT in patients undergoing laparoscopic colorectal surgery with healthy lungs.Trial registration cris.nih.go.kr (KCT0002642).

Handling Oxygenation Targets in the Intensive Care Unit (HOT-ICU)-Protocol for a randomised clinical trial comparing a lower vs a higher oxygenation target in adults with acute hypoxaemic respiratory failure

BACKGROUND

Acutely ill adults with hypoxaemic respiratory failure are at risk of life-threatening hypoxia, and thus oxygen is often administered liberally. Excessive oxygen use may, however, increase the number of serious adverse events, including death. Establishing the optimal oxygenation level is important as existing evidence is of low quality. We hypothesise that targeting an arterial partial pressure of oxygen (PaO₂ ) of 8 kPa is superior to targeting a PaO₂ of 12 kPa in adult intensive care unit (ICU) patients with acute hypoxaemic respiratory failure.

METHODS

The Handling Oxygenation Targets in the ICU (HOT-ICU) trial is an outcome assessment blinded, multicentre, randomised, parallel-group trial targeting PaO₂ in acutely ill adults with hypoxaemic respiratory failure within 12 hours after ICU admission. Patients are randomised 1:1 to one of the two PaO₂ targets throughout ICU stay until a maximum of 90 days. The primary outcome is 90-day mortality. Secondary outcomes are serious adverse events in the ICU, days alive without organ support and days alive out of hospital in the 90-day period; mortality, health-related quality-of-life at 1-year follow-up as well as 1-year cognitive and pulmonary function in a subgroup; and an overall health economic analysis. To detect or reject a 20% relative risk reduction, we aim to include 2928 patients. An interim analysis is planned after 90-day follow-up of 1464 patients.

CONCLUSION

The HOT-ICU trial will test the hypothesis that a lower oxygenation target reduces 90-day mortality compared with a higher oxygenation target in adult ICU patients with acute hypoxaemic respiratory failure.

Conservative versus conventional oxygen therapy for cardiac surgical patients: A before-and-after study

Avoiding hypoxaemia is considered crucial in cardiac surgery patients admitted to the intensive care unit (ICU). However, avoiding hyperoxaemia may also be important. A conservative approach to oxygen therapy may reduce exposure to hyperoxaemia without increasing the risk of hypoxaemia. Using a before-and-after design, we evaluated the introduction of conservative oxygen therapy (target SpO₂ 88%-92% using the lowest FiO₂) for cardiac surgical patients admitted to the ICU. We studied 9041 arterial blood gas (ABG) datasets: 4298 ABGs from 245 'conventional' and 4743 ABGs from 298 'conservative' oxygen therapy patients. During mechanical ventilation (MV) and while in the ICU, compared to the conventional group, conservative group patients had significantly lower FiO₂ exposure and PaO₂ values ( P < 0.001 for each). Accordingly, using the mean PaO₂ during MV, more conservative group patients were classified as normoxaemic (226 versus 62 patients, P < 0.01), fewer as hyperoxaemic (66 versus 178 patients, P < 0.01) and no patient in either group as hypoxaemic or severely hypoxaemic. Moreover, more ABG samples were hyperoxaemic or severely hyperoxaemic during conventional treatment ( P < 0.001). Finally, there was no difference in ICU or hospital length of stay, ICU or hospital mortality or 30-day mortality between the groups. Our findings support the feasibility and physiological safety of conservative oxygen therapy in patients admitted to ICU after cardiac surgery.

Controversies when using mechanical ventilation in obese patients with and without acute distress respiratory syndrome

INTRODUCTION

As the prevalence of obesity increases, so does the number of obese patients undergoing surgical procedures and being admitted into intensive care units. Obesity per se is associated with reduced lung volume. The combination of general anaesthesia and supine positioning involved in most surgeries causes further reductions in lung volumes, thus resulting in alveolar collapse, decreased lung compliance, increased airway resistance, and hypoxemia. These complications can be amplified by common obesity-related comorbidities. In otherwise healthy obese patients, mechanical ventilation strategies should be optimised to prevent lung damage; in those with acute distress respiratory syndrome (ARDS), strategies should seek to mitigate further lung damage. Areas covered: This review discusses non-invasive and invasive mechanical ventilation strategies for surgical and critically ill adult obese patients with and without ARDS and proposes practical clinical insights to be implemented at bedside both in the operating theatre and in intensive care units. Expert opinion: Large multicentre trials on respiratory management of obese patients are required. Although the indication of lung protective ventilation with low tidal volume is apparently translated to obese patients, optimal PEEP level and recruitment manoeuvres remain controversial. The use of non-invasive respiratory support after extubation must be considered in individual cases.

Post–suction Recruitment Manoeuvre Restores Lung Function in Healthy, Anaesthetized Pigs

Endotracheal suction can cause partial lung collapse and hypoxia and alter lung mechanics. We investigated the effects of adding a recruitment manoeuvre directly after endotracheal suction to restore lung volume in volume-controlled ventilation and pressure-controlled ventilation modes. Five anaesthetized pigs were investigated. The effects of endotracheal suction with or without a recruitment manoeuvre were compared in random order. In volume-controlled ventilation, compliance decreased after suction from 33±5 to 26±6 ml.cmH2O–1 (P<0.05), and 30 minutes later it remained decreased at 25±6 ml.cmH2O–1. Venous admixture increased after suction from 5±2 to 8±4% (P<0.05), but had recovered at 30 minutes. In pressure-controlled ventilation, compliance decreased after suction from 34±3 to 25±7 ml.cmH2O–1 (P<0.05), and 30 minutes later it remained decreased at 25±7 ml.cmH2O–1. Venous admixture increased after suction from 5±2 to 13±7% (P<0.05), and had not recovered after 30 minutes, 10±4%. When a recruitment manoeuvre was applied directly after suction, no negative side-effects were registered in volume-controlled ventilation or pressure-controlled ventilation. We conclude that the impairment of lung mechanics and gas exchange induced by endotracheal suction can be prevented by a simple post-suction recruitment manoeuvre. Further studies are needed to identify a suitable suction recruitment manoeuvre in patients with diseased lungs.

Mechanical ventilation management during cardiothoracic surgery: an open challenge

Mechanical ventilation during surgery is a highly complex procedure, particularly in cardiothoracic surgery, where patients need to undergo substantial hemodynamic management, involving large fluid exchanges and pharmacological manipulation of vascular resistance, as well as direct manipulation of the lungs themselves. Cardiothoracic surgery is burdened by a high rate of postoperative pulmonary complication (PPC), comorbidity, and mortality. Recent trials have examined various techniques to preserve lung function, although consensus on best practice has yet to be reached. This might be due to the close relationship between the circulatory and pulmonary systems. The use of a technique designed to prevent pulmonary complication might negatively impact the hemodynamics of an already critical patient. Stress-induced lung injury can occur during surgery for various reasons, some of which have yet to be fully investigated. In cardiac surgery, this damage is mainly ascribed to two events: cardiopulmonary bypass (CPB) and sternotomy. In thoracic surgery, on the other hand, overdistention and permissive hyperoxia, both routinely used on one lung to compensate for the collapse of the other, are generally to blame for lung injury. In recent years "protective" ventilation strategies have been proposed to spare lung parenchyma from stress-induced damage. Despite the growing interest in protective ventilation techniques, there are still no clear international guidelines for mechanical ventilation in cardiothoracic surgery. However, some recent progress has been made, with positive clinical outcomes.

Effect of intraoperative hyperoxia on the incidence of surgical site infections: a meta-analysis

BACKGROUND

Whether supplemental intraoperative oxygen reduces surgical site infections remains unclear. Recent recommendations from the World Health Organization and Center for Disease Control to routinely use high inspired oxygen concentrations to reduce infection risk have been widely criticized. We therefore performed a meta-analysis to evaluate the influence of inspired oxygen on infection risk, including a recent large trial.

METHODS

A systematic literature search was performed. Primary analysis included all eligible trials. Sensitivity analyses distinguished studies of colorectal and non-colorectal surgeries, and excluded studies with high risk of bias. Another post-hoc sensitivity analysis excluded studies from one author that appear questionable.

RESULTS

The primary analysis included 26 trials (N=14,710). The RR [95%CI] for wound infection was 0.81 [0.70, 0.94] in the high vs. low inspired oxygen groups. The effect remained significant in colorectal patients (N=10,469), 0.79 [0.66, 0.96], but not in other patients (N=4,241), 0.86 [0.69, 1.09]. When restricting the analysis to studies with low risk of bias, either by strict inclusion criteria (N=5,047) or by researchers' judgment (N=12,547), no significant benefit remained: 0.84 [0.67, 1.06] and 0.89 [0.76, 1.05], respectively.

CONCLUSIONS

When considering all available data, intraoperative hyperoxia reduced wound infection incidence. However, no significant benefit remained when analysis was restricted to objective- or investigator-identified low-bias studies, although those analyses were not as well-powered. Meta-analysis of the most reliable studies does not suggest that supplemental oxygen substantively reduces wound infection risk, but more research is needed to fully answer this question.

Specific anesthesia-induced lung volume changes from induction to emergence: a pilot study

BACKGROUND

Studies aimed at maintaining intraoperative lung volume to reduce post-operative pulmonary complications have been inconclusive because they mixed up the effect of general anesthesia and the surgical procedure. Our aims were to study: (1) lung volume during the entire course of anesthesia without the confounding effects of surgical procedures; (2) the combination of three interventions to maintain lung volume; and (3) the emergence phase with focus on the restored activation of the respiratory muscles.

METHODS

Eighteen ASA I-II patients undergoing ENT surgery under general anesthesia without muscle relaxants were randomized to an intervention group, receiving lung recruitment maneuver (LRM) after induction, 7 cmH₂ O positive end-expiratory pressure (PEEP) during anesthesia and continuous positive airway pressure (CPAP) during emergence with 0.4 inspired oxygen fraction (FiO₂ ) or a control group, ventilated without LRM, with 0 cmH₂ O PEEP, and 1.0 FiO₂ during emergence without CPAP application. End-expiratory lung volume (EELV) was continuously estimated by opto-electronic plethysmography. Inspiratory and expiratory ribcage muscles electromyography was measured in a subset of seven patients.

RESULTS

End-expiratory lung volume decreased after induction in both groups. It remained low in the control group and further decreased at emergence, because of active expiratory muscle contraction. In the intervention group, EELV increased after LRM and remained high after extubation.

CONCLUSION

A combined intervention consisting of LRM, PEEP and CPAP during emergence may effectively maintain EELV during anesthesia and even after extubation. An unexpected finding was that the activation of the expiratory muscles may contribute to EELV reduction during the emergence phase.

Associations between intraoperative ventilator settings during one-lung ventilation and postoperative pulmonary complications: a prospective observational study

Background

The interest in perioperative lung protective ventilation has been increasing. However, optimal management during one-lung ventilation (OLV) remains undetermined, which not only includes tidal volume (V_T) and positive end-expiratory pressure (PEEP) but also inspired oxygen fraction (F_IO₂). We aimed to investigate current practice of intraoperative ventilation during OLV, and analyze whether the intraoperative ventilator settings are associated with postoperative pulmonary complications (PPCs) after thoracic surgery.

Methods

We performed a prospective observational two-center study in Japan. Patients scheduled for thoracic surgery with OLV from April to October 2014 were eligible. We recorded ventilator settings (F_IO₂, V_T, driving pressure (ΔP), and PEEP) and calculated the time-weighted average (TWA) of ventilator settings for the first 2 h of OLV. PPCs occurring within 7 days of thoracotomy were investigated. Associations between ventilator settings and the incidence of PPCs were examined by multivariate logistic regression.

Results

We analyzed perioperative information, including preoperative characteristics, ventilator settings, and details of surgery and anesthesia in 197 patients. Pressure control ventilation was utilized in most cases (92%). As an initial setting for OLV, an F_IO₂ of 1.0 was selected for more than 60% of all patients. Throughout OLV, the median TWA F_IO₂ of 0.8 (0.65-0.94), V_T of 6.1 (5.3-7.0) ml/kg, ΔP of 17 (15-20) cm H₂O, and PEEP of 4 (4-5) cm H₂O was applied. Incidence rate of PPCs was 25.9%, and F_IO₂ was independently associated with the occurrence of PPCs in multivariate logistic regression. The adjusted odds ratio per F_IO₂ increase of 0.1 was 1.30 (95% confidence interval: 1.04-1.65, P = 0.0195).

Conclusions

High F_IO₂ was applied to the majority of patients during OLV, whereas low V_T and slight degree of PEEP were commonly used in our survey. Our findings suggested that a higher F_IO₂ during OLV could be associated with increased incidence of PPCs.

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0476-x) contains supplementary material, which is available to authorized users.

Are we fully utilizing the functionalities of modern operating room ventilators?

PURPOSE OF REVIEW

The modern operating room ventilators have become very sophisticated and many of their features are comparable with those of an ICU ventilator. To fully utilize the functionality of modern operating room ventilators, it is important for clinicians to understand in depth the working principle of these ventilators and their functionalities.

RECENT FINDINGS

Piston ventilators have the advantages of delivering accurate tidal volume and certain flow compensation functions. Turbine ventilators have great ability of flow compensation. Ventilation modes are mainly volume-based or pressure-based. Pressure-based ventilation modes provide better leak compensation than volume-based. The integration of advanced flow generation systems and ventilation modes of the modern operating room ventilators enables clinicians to provide both invasive and noninvasive ventilation in perioperative settings. Ventilator waveforms can be used for intraoperative neuromonitoring during cervical spine surgery.

SUMMARY

The increase in number of new features of modern operating room ventilators clearly creates the opportunity for clinicians to optimize ventilatory care. However, improving the quality of ventilator care relies on a complete understanding and correct use of these new features. VIDEO ABSTRACT: http://links.lww.com/COAN/A47.

The New World Health Organization Recommendations on Perioperative Administration of Oxygen to Prevent Surgical Site Infections: A Dangerous Reductionist Approach?

In October 2016, the World Health Organization (WHO) published recommendations for preventing surgical site infections (SSIs). Among those measures is a recommendation to administer oxygen at an inspired fraction of 80% intra- and postoperatively for up to 6 hours. SSIs have been identified as a global health problem, and the WHO should be commended for their efforts. However, this recommendation focuses only on the patient's "wound," ignores other organ systems potentially affected by hyperoxia, and may ultimately worsen patient outcomes.The WHO advances a "strong recommendation" for the use of a high inspired oxygen fraction even though the quality of evidence is only moderate. However, achieving this goal by disregarding other potentially lethal complications seems inappropriate, particularly in light of the weak evidence underpinning the use of high fractions of oxygen to prevent SSI. Use of such a strategy thus should be intensely discussed by anesthesiologists and perioperative physicians.Normovolemia, normotension, normoglycemia, normothermia, and normoventilation can clearly be safely applied to most patients in most clinical scenarios. But the liberal application of hyperoxemia intraoperatively and up to 6 hours postoperatively, as suggested by the WHO, is questionable from the viewpoint of anesthesia and perioperative medicine, and its effects will be discussed in this article.

Efficacy of continuous positive airway pressure and incentive spirometry on respiratory functions during the postoperative period following supratentorial craniotomy: A prospective randomized controlled study

STUDY OBJECTIVE

Volume controlled ventilation with low PEEP is used in neuro-anesthesia to provide constant PaCO₂ levels and prevent raised intracranial pressure. Therefore, neurosurgery patients prone to atelectasis formation, however, we could not find any study that evaluates prevention of postoperative pulmonary complications in neurosurgery.

DESIGN

A prospective, randomized controlled study.

SETTING

Intensive care unit in a university hospital in Istanbul.

PATIENTS

Seventy-nine ASAI-II patients aged between 18 and 70years scheduled for elective supratentorial craniotomy were included in the study.

INTERVENTIONS

Patients randomized into 3 groups after surgery. The Group IS (n=20) was treated with incentive spirometry 5 times in 1min and 5min per hour, the Group CPAP (n=20) with continuous positive airway pressure 10 cmH₂O pressure and 0.4 F_iO₂ via an oronasal mask 5min per hour, and the Group Control (n=20) 4L·min^-1O₂ via mask; all during the first 6h postoperatively. Respiratory functions tests and arterial blood gases analysis were performed before the induction of anesthesia (Baseline), 30min, 6h, 24h postoperatively.

MAIN RESULTS

The IS and CPAP applications have similar effects with respect to FVC values. The postoperative 30min FEV₁ values were statistically significantly reduced compared to the Baseline in all groups (p<0.0001). FEV₁ values were statistically significantly increased at the postoperative 24h compared to the postoperative 30min in the Groups IS and CPAP (p<0.0001). This increase, however, was not observed in the Group Control, and the postoperative 24h FEV₁ values were statistically significantly lower in the Group Control compared to the Group IS (p=0.015).

CONCLUSION

Although this study is underpowered to detect differences in FEV₁ values, the postoperative 24h FEV₁ values were significantly higher in the IS group than the Control group and this difference was not observed between the CPAP and Control groups. It might be evaluate a favorable effect of IS in neurosurgery patients. But larger studies are needed to make a certain conclusion.

Perioperative hyperoxia: perhaps a malady in disguise

Oxygen is an element, which is used liberally during several medical procedures. The use of oxygen during perioperative care is a controversial issue. Anesthesiologists use oxygen to prevent hypoxemia during surgical procedures, but the effects of its liberal use can be harmful. Another argument for using high oxygen concentrations is to prevent surgical site infections by increasing oxygen levels at the incision site. Although inconclusive, literature concerning the use of high oxygen concentrations during anesthesia show that this approach may cause hemodynamic changes, altered microcirculation and increased oxidative stress. In intensive care it has been shown that high oxygen concentrations may be associated with increased mortality in certain patient populations such as post cardiac arrest patients. In this paper, a review of literature had been undertaken to warn anesthesiologists about the potential harmful effects of high oxygen concentrations.

Use of manual alveolar recruitment maneuvers to eliminate atelectasis artifacts identified during thoracic computed tomography of healthy neonatal foals

OBJECTIVE To evaluate use of single manual alveolar recruitment maneuvers (ARMs) to eliminate atelectasis during CT of anesthetized foals. ANIMALS 6 neonatal Standardbred foals. PROCEDURES Thoracic CT was performed on spontaneously breathing anesthetized foals positioned in sternal (n = 3) or dorsal (3) recumbency when foals were 24 to 36 hours old (time 1), 4 days old (time 2), 7 days old (time 3), and 10 days old (time 4). The CT images were collected without ARMs (all times) and during ARMs with an internal airway pressure of 10, 20, and 30 cm H₂O (times 2 and 3). Quantitative analysis of CT images measured whole lung and regional changes in attenuation or volume with ARMs. RESULTS Increased attenuation and an alveolar pattern were most prominent in the dependent portion of the lungs. Subjectively, ARMs did not eliminate atelectasis; however, they did incrementally reduce attenuation, particularly in the nondependent portion of the lungs. Quantitative differences in lung attenuation attributable to position of foal were not identified. Lung attenuation decreased significantly (times 2 and 3) and lung volume increased significantly (times 2 and 3) after ARMs. Changes in attenuation and volume were most pronounced in the nondependent portion of the lungs and at ARMs of 20 and 30 cm H₂O. CONCLUSIONS AND CLINICAL RELEVANCE Manual ARMs did not eliminate atelectasis but reduced attenuation in nondependent portions of the lungs. Positioning of foals in dorsal recumbency for CT may be appropriate when pathological changes in the ventral portion of the lungs are suspected.

Preoxygenation and intraoperative ventilation strategies in obese patients: a comprehensive review

PURPOSE OF REVIEW

Obesity along with its pathophysiological changes increases risk of intraoperative and perioperative respiratory complications. The aim of this review is to highlight recent updates in preoxygenation techniques and intraoperative ventilation strategies in obese patients to optimize gas exchange and pulmonary mechanics and reduce pulmonary complications.

RECENT FINDINGS

There is no gold standard in preoxygenation or intraoperative ventilatory management protocol for obese patients. Preoxygenation in head up or sitting position has been shown to be superior to supine position. Apneic oxygenation and use of continuous positive airway pressure increases safe apnea duration. Recent evidence encourages the intraoperative use of low tidal volume to improve oxygenation and lung compliance without adverse effects. Contrary to nonobese patients, some studies have reported the beneficial effect of recruitment maneuvers and positive end-expiratory pressure in obese patients. No difference has been observed between volume controlled and pressure controlled ventilation.

SUMMARY

The ideal ventilatory plan for obese patients is indeterminate. A multimodal preoxygenation and intraoperative ventilation plan is helpful in obese patients to reduce perioperative respiratory complications. More studies are needed to identify the role of low tidal volume, positive end-expiratory pressure, and recruitment maneuvers in obese patients undergoing general anesthesia.

Zero expiratory pressure and low oxygen concentration promote heterogeneity of regional ventilation and lung densities

Background

It is not well known what is the main mechanism causing lung heterogeneity in healthy lungs under mechanical ventilation. We aimed to investigate the mechanisms causing heterogeneity of regional ventilation and parenchymal densities in healthy lungs under anesthesia and mechanical ventilation.

Methods

In a small animal model, synchrotron imaging was used to measure lung aeration and regional‐specific ventilation (sV̇). Heterogeneity of ventilation was calculated as the coefficient of variation in sV̇ (CV_sV̇). The coefficient of variation in lung densities (CV_D) was calculated for all lung tissue, and within hyperinflated, normally and poorly aerated areas. Three conditions were studied: zero end‐expiratory pressure (ZEEP) and F_IO₂ 0.21; ZEEP and F_IO₂ 1.0; PEEP 12 cmH₂O and F_IO₂1.0 (Open Lung‐PEEP = OLP).

Results

The mean tissue density at OLP was lower than ZEEP‐1.0 and ZEEP‐0.21. There were larger subregions with low sV̇ and poor aeration at ZEEP‐0.21 than at OLP: 12.9 ± 9.0 vs. 0.6 ± 0.4% in the non‐dependent level, and 17.5 ± 8.2 vs. 0.4 ± 0.1% in the dependent one (P = 0.041). The CV_sV̇ of the total imaged lung at PEEP 12 cmH₂O was significantly lower than on ZEEP, regardless of F_IO₂, indicating more heterogeneity of ventilation during ZEEP (0.23 ± 0.03 vs. 0.54 ± 0.37, P = 0.049). CV_D changed over the different mechanical ventilation settings (P = 0.011); predominantly, CV_D increased during ZEEP. The spatial distribution of the CV_D calculated for the poorly aerated density category changed with the mechanical ventilation settings, increasing in the dependent level during ZEEP.

Conclusion

ZEEP together with low F_IO₂ promoted heterogeneity of ventilation and lung tissue densities, fostering a greater amount of airway closure and ventilation inhomogeneities in poorly aerated regions.

Effect of low inspired oxygen fraction on respiratory indices in mechanically ventilated horses anaesthetised with isoflurane and medetomidine constant rate infusion

Horses may become hypoxaemic during anaesthesia despite a high inspired oxygen fraction (FiO2). A lower FiO2 is used commonly in human beings to minimise atelectasis and to improve lung function, and previously has been shown to be of potential benefit in horses in experimental conditions. Other studies suggest no benefit to using a FiO2 of 0.5 during clinically relevant conditions; however, low FiO2 (0.65) is commonly used in practice and in a large number of studies. The present study was performed to compare the effect of a commonly used FiO2 of 0.65 versus 0.90 on calculated respiratory indices in anaesthetised mechanically ventilated horses in a clinical setting. Eighteen healthy Thoroughbred horses anaesthetised for experimental laryngeal surgery were recruited into a prospective, non-blinded, randomised clinical study. Before anaesthesia, the horses were randomly allocated into either low (0.65) or high (0.90) FiO2 groups and arterial blood gas (ABG) analysis was performed every 30 min during anaesthesia to allow for statistical analysis of respiratory indices. As expected, PaO2 was significantly lower in horses anaesthetised with a low FiO2, but was sufficient to fully saturate haemoglobin. There were no significant improvements in any of the other respiratory indices. There is no obvious benefit to be gained from the use of a FiO2 of 0.65 compared to 0.90 for mechanically ventilated Thoroughbred horses anaesthetised in lateral recumbency with isoflurane and a medetomidine constant rate infusion.

Mild loss of lung aeration augments stretch in healthy lung regions

Inspiratory stretch by mechanical ventilation worsens lung injury. However, it is not clear whether and how the ventilator damages lungs in the absence of preexisting injury. We hypothesized that subtle loss of lung aeration during general anesthesia regionally augments ventilation and distension of ventilated air spaces. In eight supine anesthetized and intubated rats, hyperpolarized gas MRI was performed after a recruitment maneuver following 1 h of volume-controlled ventilation with zero positive end-expiratory pressure (ZEEP), FiO2 0.5, and tidal volume 10 ml/kg, and after a second recruitment maneuver. Regional fractional ventilation (FV), apparent diffusion coefficient (ADC) of (3)He (a measurement of ventilated peripheral air space dimensions), and gas volume were measured in lung quadrants of ventral and dorsal regions of the lungs. In six additional rats, computed tomography (CT) images were obtained at each time point. Ventilation with ZEEP decreased total lung gas volume and increased both FV and ADC in all studied regions. Increases in FV were more evident in the dorsal slices. In each lung quadrant, higher ADC was predicted by lower gas volume and by increased mean values (and heterogeneity) of FV distribution. CT scans documented 10% loss of whole-lung aeration and increased density in the dorsal lung, but no macroscopic atelectasis. Loss of pulmonary gas at ZEEP increased fractional ventilation and inspiratory dimensions of ventilated peripheral air spaces. Such regional changes could help explain a propensity for mechanical ventilation to contribute to lung injury in previously uninjured lungs.