Pulmonary Function after Emergence on 100% Oxygen in Patients with Chronic Obstructive Pulmonary Disease

Weaning from mechanical ventilation in the operating room: a systematic review

BACKGROUND

Postoperative pulmonary complications (PPCs) are associated with postoperative mortality and prolonged hospital stay. Although intraoperative mechanical ventilation (MV) is a risk factor for PPCs, strategies addressing weaning from MV are understudied. In this systematic review, we evaluated weaning strategies and their effects on postoperative pulmonary outcomes.

METHODS

Our protocol was registered on PROSPERO (CRD42022379145). Eligible studies included randomised controlled trials and observational studies of adults weaned from MV in the operating room. Primary outcomes included atelectasis and oxygenation; secondary outcomes included lung volume changes and PPCs. Risk of bias was assessed using the Cochrane Risk of Bias (RoB2) tool, and quality of evidence with the GRADE framework.

RESULTS

Screening identified 14 randomised controlled trials including 1719 patients; seven studies were limited to the weaning phase and seven included interventions not restricted to the weaning phase. Strategies combining pressure support ventilation (PSV) with positive end-expiratory pressure (PEEP) and low fraction of inspired oxygen (FiO2) improved atelectasis, oxygenation, and lung volumes. Low FiO2 improved atelectasis and oxygenation but might not improve lung volumes. A fixed-PEEP strategy led to no improvement in oxygenation or atelectasis; however, individualised PEEP with low FiO2 improved oxygenation and might be associated with reduced PPCs. Half of included studies are of moderate or high risk of bias; the overall quality of evidence is low.

CONCLUSIONS

There is limited research evaluating weaning from intraoperative MV. Based on low-quality evidence, PSV, individualised PEEP, and low FiO2 may be associated with reduced postoperative pulmonary outcomes.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO (CRD42022379145).

Effects of an open lung extubation strategy compared with a conventional extubation strategy on postoperative pulmonary complications after general anesthesia: a single-centre pilot randomized controlled trial

PURPOSE

Postoperative pulmonary complications (PPCs) are a common cause of morbidity. Postoperative atelectasis is thought to be a significant risk factor in their development. Recent imaging studies suggest that patients' extubation may result in similar postoperative atelectasis regardless of the intraoperative mechanical ventilation strategy used. In this pilot trial, we hypothesized that a study investigating the effects of an open lung extubation strategy compared with a conventional one on PPCs would be feasible.

METHODS

We conducted a pilot, single-centre, double-blinded randomized controlled trial. Adult patients at moderate to high risk of PPCs and scheduled for elective surgery were eligible. Patients were randomized to an open lung extubation strategy (semirecumbent position, fraction of inspired oxygen [FIO2] 50%, pressure support ventilation, unchanged positive end-expiratory pressure) or to a conventional extubation strategy (dorsal decubitus position, FIO2 100%, manual bag ventilation). The primary feasibility outcome was global protocol adherence while the primary exploratory efficacy outcome was PPCs.

RESULTS

We randomized 35 patients to the conventional extubation group and 34 to the open lung extubation group. We observed a global protocol adherence of 96% (95% confidence interval, 88 to 99), which was not different between groups. Eight PPCs occurred (two in the conventional extubation group vs six in the open lung extubation group). Less postoperative supplemental oxygen and better lung aeration were observed in the open lung extubation group.

CONCLUSIONS

In this single-centre pilot trial, we observed excellent feasibility. A multicentre pilot trial comparing the effect of an open lung extubation strategy with that of a conventional extubation strategy on the occurrence of PPCs is feasible.

STUDY REGISTRATION DATE

ClinicalTrials.gov (NCT04993001); registered 6 August 2021.

Sevoflurane Exposure in Neonates Perturbs the Expression Patterns of Specific Genes That May Underly the Observed Learning and Memory Deficits

Exposure to commonly used anesthetics leads to neurotoxic effects in animal models-ranging from cell death to learning and memory deficits. These neurotoxic effects invoke a variety of molecular pathways, exerting either immediate or long-term effects at the cellular and behavioural levels. However, little is known about the gene expression changes following early neonatal exposure to these anesthetic agents. We report here on the effects of sevoflurane, a commonly used inhalational anesthetic, on learning and memory and identify a key set of genes that may likely be involved in the observed behavioural deficits. Specifically, we demonstrate that sevoflurane exposure in postnatal day 7 (P7) rat pups results in subtle, but distinct, memory deficits in the adult animals that have not been reported previously. Interestingly, when given intraperitoneally, pre-treatment with dexmedetomidine (DEX) could only prevent sevoflurane-induced anxiety in open field testing. To identify genes that may have been altered in the neonatal rats after sevoflurane and DEX exposure, specifically those impacting cellular viability, learning, and memory, we conducted an extensive Nanostring study examining over 770 genes. We found differential changes in the gene expression levels after exposure to both agents. A number of the perturbed genes found in this study have previously been implicated in synaptic transmission, plasticity, neurogenesis, apoptosis, myelination, and learning and memory. Our data thus demonstrate that subtle, albeit long-term, changes observed in an adult animal's learning and memory after neonatal anesthetic exposure may likely involve perturbation of specific gene expression patterns.

Pressure Support versus Spontaneous Ventilation during Anesthetic Emergence-Effect on Postoperative Atelectasis: A Randomized Controlled Trial

BACKGROUND

Despite previous reports suggesting that pressure support ventilation facilitates weaning from mechanical ventilation in the intensive care unit, few studies have assessed its effects on recovery from anesthesia. The authors hypothesized that pressure support ventilation during emergence from anesthesia reduces postoperative atelectasis in patients undergoing laparoscopic surgery using the Trendelenburg position.

METHODS

In this randomized controlled double-blinded trial, adult patients undergoing laparoscopic colectomy or robot-assisted prostatectomy were assigned to either the pressure support (n = 50) or the control group (n = 50). During emergence (from the end of surgery to extubation), pressure support ventilation was used in the pressure support group versus intermittent manual assistance in the control group. The primary outcome was the incidence of atelectasis diagnosed by lung ultrasonography at the postanesthesia care unit (PACU). The secondary outcomes were Pao2 at PACU and oxygen saturation measured by pulse oximetry less than 92% during 48 h postoperatively.

RESULTS

Ninety-seven patients were included in the analysis. The duration of emergence was 9 min and 8 min in the pressure support and control groups, respectively. The incidence of atelectasis at PACU was lower in the pressure support group compared to that in the control group (pressure support vs. control, 16 of 48 [33%] vs. 28 of 49 [57%]; risk ratio, 0.58; 95% CI, 0.35 to 0.91; P = 0.024). In the PACU, Pao2 in the pressure support group was higher than that in the control group (92 ± 26 mmHg vs. 83 ± 13 mmHg; P = 0.034). The incidence of oxygen saturation measured by pulse oximetry less than 92% during 48 h postoperatively was not different between the groups (9 of 48 [19%] vs. 11 of 49 [22%]; P = 0.653). There were no adverse events related to the study protocol.

CONCLUSIONS

The incidence of postoperative atelectasis was lower in patients undergoing either laparoscopic colectomy or robot-assisted prostatectomy who received pressure support ventilation during emergence from general anesthesia compared to those receiving intermittent manual assistance.

EDITOR’S PERSPECTIVE

Effects of high versus low inspiratory oxygen fraction on postoperative clinical outcomes in patients undergoing surgery under general anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To determine whether high perioperative inspired oxygen fraction (FiO₂) compared with low FiO₂ has more deleterious postoperative clinical outcomes in patients undergoing non-thoracic surgery under general anesthesia.

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

High perioperative FiO₂ (≥0.8) vs. low FiO₂ (≤0.5).

MEASUREMENTS

The primary outcome was mortality within 30 days. Secondary outcomes were pulmonary outcomes (atelectasis, pneumonia, respiratory failure, postoperative pulmonary complications [PPCs], and postoperative oxygen parameters), intensive care unit (ICU) admissions, and length of hospital stay. A subgroup analysis was performed to explore the treatment effect by body mass index (BMI).

MAIN RESULTS

Twenty-six trials with a total 4991 patients were studied. The mortality in the high FiO₂ group did not differ from that in the low FiO₂ group (risk ratio [RR] 0.91, 95% confidence interval [CI] 0.42-1.97, P = 0.810). Nor were there any significant differences between the groups in such outcomes as pneumonia (RR 1.19, 95% CI 0.74-1.92, P = 0.470), respiratory failure (RR 1.29, 95% CI 0.82-2.04, P = 0.270), PPCs (RR 1.05, 95% CI 0.69-1.59, P = 0.830), ICU admission (RR 0.94, 95% CI 0.55-1.60, P = 0.810), and length of hospital stay (mean difference [MD] 0.27 d, 95% CI -0.28-0.81, P = 0.340). The high FiO₂ was associated with postoperative atelectasis more often (risk ratio 1.27, 95% CI 1.00-1.62, P = 0.050), and lower postoperative arterial partial oxygen pressure (MD -5.03 mmHg, 95% CI -7.90- -2.16, P < 0.001)_. In subgroup analysis of BMI >30 kg/m², these parameters were similarly affected between the groups.

CONCLUSIONS

The use of high FiO₂ compared to low FiO₂ did not affect the short-term mortality, although it may increase the incidence of atelectasis in adult, non-thoracic patients undergoing surgical procedures. Nor were there any significant differences in other secondary outcomes.

The Effects of Intraoperative Inspired Oxygen Fraction on Postoperative Pulmonary Parameters in Patients with General Anesthesia: A Systemic Review and Meta-Analysis

High intraoperative inspired oxygen concentration is applied to prevent desaturation during induction and recovery of anesthesia. However, high oxygen concentration may lead to postoperative pulmonary complications. The purpose of this study is to compare the postoperative pulmonary parameters according to intraoperative inspired oxygen fraction in patients undergoing general anesthesia. We identified all randomized controlled trials investigating postoperative differences in arterial gas exchange according to intraoperative fraction of inspired oxygen (FiO₂). A total of 10 randomized controlled trials were included, and 787 patients were analyzed. Postoperative PaO₂ was lower in the high FiO₂ group compared with the low FiO₂ group (mean difference (MD) −4.97 mmHg, 95% CI −8.21 to −1.72, p = 0.003). Postoperative alveolar-arterial oxygen gradient (AaDO₂) was higher (MD 3.42 mmHg, 95% CI 0.95 to 5.89, p = 0.007) and the extent of atelectasis was more severe (MD 2.04%, 95% CI 0.14 to 3.94, p = 0.04) in high intraoperative FiO₂ group compared with low FiO₂ group. However, postoperative SpO₂ was comparable between the two groups. The results of this meta-analysis suggest that high inspired oxygen fraction during anesthesia may impair postoperative pulmonary parameters. Cautious approach in intraoperative inspired oxygen fraction is required for patients susceptible to postoperative pulmonary complications.

Tracheal extubation with suction vs. positive pressure during emergence from general anaesthesia in adults: A randomised controlled trial

BACKGROUND

After general anaesthesia (GA) in adults, the optimal tracheal extubation technique (positive pressure or suctioning) remains debated. The primary endpoint of this study was to assess the effects of these techniques on onset time of desaturation (SpO₂<92%).

METHODS

Sixty-nine patients with a body mass index<30 scheduled for elective orthopaedic surgery were allocated to positive pressure (PP) or suctioning (SUC) group. GA was standardised with propofol and remifentanil via target-controlled infusion. A morphine bolus of 0.15mg/kg was administered 20-30mins before the end of surgery. The effect of extubation technique on onset time of desaturation (T92) was assessed during the first 10mins after extubation during the spontaneous air breathing. Secondary endpoints included: frequency of desaturation, respiratory complications, need to use oxygen therapy and SpO₂ at the end of the first hour while breathing in air (ClinicalTrials.gov identifier: NCT01323049).

RESULTS

Baseline patient characteristics and intraoperative management data for the 68 patients included had no relevant clinical difference between groups. T92 (sec) after tracheal extubation was 214 (168) vs. 248 (148) in the PP and SUC groups, respectively (P=0.44). In the PP and SUC groups, 50 and 43% reached a SpO₂<92% within the first 10mins after extubation respectively (P=0.73). There were no statistically significant differences between groups for any secondary endpoints.

CONCLUSIONS

Positive pressure extubation as compared with suctioning extubation did not seem to delay onset time of desaturation after GA in standard weight adult patients.

Effects of dexmedetomidine on oxygenation and lung mechanics in patients with moderate chronic obstructive pulmonary disease undergoing lung cancer surgery: A randomised double-blinded trial

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a risk factor that increases the incidence of postoperative cardiopulmonary morbidity and mortality after lung resection. Dexmedetomidine, a selective α₂-adrenoreceptor agonist, has been reported previously to attenuate intrapulmonary shunt during one-lung ventilation (OLV) and to alleviate bronchoconstriction.

OBJECTIVE

The objective is to determine whether dexmedetomidine improves oxygenation and lung mechanics in patients with moderate COPD during lung cancer surgery.

DESIGN

A randomised, double-blinded, placebo-controlled study.

SETTING

Single university hospital.

PARTICIPANTS

Fifty patients scheduled for video-assisted thoracoscopic surgery who had moderate COPD. Patients were randomly allocated to a control group or a Dex group (n = 25 each).

INTERVENTIONS

In the Dex group, dexmedetomidine was given as an initial loading dose of 1.0 μg kg⁻¹ over 10 min followed by a maintenance dose of 0.5 μg kg⁻¹ h⁻¹ during OLV while the control group was administered a comparable volume of 0.9% saline. Data were measured at 30 min (DEX-30) and 60 min (DEX-60) after dexmedetomidine or saline administration during OLV.

MAIN OUTCOME MEASURES

The primary outcome was the effect of dexmedetomidine on oxygenation. The secondary outcome was the effect of dexmedetomidine administration on postoperative pulmonary complications.

RESULTS

Patients in the Dex group had a significantly higher PaO₂/FiO₂ ratio (27.9 ± 5.8 vs. 22.5 ± 8.4 and 28.6 ± 5.9 vs. 21.0 ± 9.9 kPa, P < 0.05), significantly lower dead space ventilation (19.2 ± 8.5 vs. 24.1 ± 8.1 and 19.6 ± 6.7 vs. 25.3 ± 7.8%, P < 0.05) and higher dynamic compliance at DEX-30 and DEX-60 (P = 0.0001 and P = 0.0184) compared with the control group. In the Dex group, the PaO₂/FiO₂ ratio in the postoperative period was significantly higher (P = 0.022) and the incidence of ICU admission was lower than in the control group.

CONCLUSION

Dexmedetomidine administration may provide clinically relevant benefits by improving oxygenation and lung mechanics in patients with moderate COPD undergoing lung cancer surgery.

TRIAL REGISTRATION

ClinicalTrial.gov identifier: NCT 02185430.

Preserved oxygenation in obese patients receiving protective ventilation during laparoscopic surgery: a randomized controlled study

BACKGROUND

Venous admixture from atelectasis and airway closure impedes oxygenation during general anaesthesia. We tested the hypothesis that continuous positive airway pressure (CPAP) during pre-oxygenation and reduced fraction of inspiratory oxygen (FIO2 ) during emergence from anaesthesia can improve oxygenation in patients with obesity undergoing laparoscopic surgery.

METHODS

In the intervention group (n = 20, median BMI 41.9), a CPAP of 10 cmH2 O was used during pre-oxygenation and induction of anaesthesia, but no CPAP was used in the control group (n = 20, median BMI 38.1). During anaesthesia, all patients were ventilated in volume-controlled mode with an FIO2 of 0.4 and a positive end-expiratory pressure (PEEP) of 10 cmH2 O. During emergence, before extubation, the control group was given an FIO2 of 1.0 and the intervention group was divided into two subgroups, which were given an FIO2 of 1.0 or 0.31. Oxygenation was assessed perioperatively by the estimated venous admixture (EVA).

RESULTS

The median EVA before pre-oxygenation was about 8% in both groups. During anaesthesia after intubation, the median EVA was 8.2% in the intervention vs. 13.2% in the control group (P = 0.048). After CO2 pneumoperitoneum, the median EVA was 8.4% in the intervention vs. 9.9% in the control group (P > 0.05). One hour post-operatively, oxygenation had deteriorated in patients given an FIO2 of 1.0 during emergence but not in patients given an FIO2 of 0.31.

CONCLUSIONS

A CPAP of 10 cmH2 O during pre-oxygenation and induction, followed by PEEP after intubation, seemed to preserve oxygenation during anaesthesia. Post-operative oxygenation depended on the FIO2 used during emergence.