The effects of laryngeal mask versus endotracheal tube on atelectasis after general anesthesia induction assessed by lung ultrasound: A randomized controlled trial

STUDY OBJECTIVE

This study aims to evaluate the impact of Supreme™ laryngeal masks versus endotracheal tubes on atelectasis during general anesthesia using lung ultrasound (LUS), and provide evidence for respiratory management.

DESIGN

A single-center, double-blind, randomized controlled trial was conducted.

SETTING

The study was conducted in both the operating room and the post-anesthesia care unit, with follow-up assessments performed in the ward.

PATIENTS

Enrollment included 180 cases undergoing non-laparoscopic surgeries in gynecology, urology, and orthopedic limb surgeries.

INTERVENTIONS

Patients were randomly assigned 1:1 to the endotracheal intubation or laryngeal mask group.

MEASUREMENTS

LUS scores were recorded across 12 lung regions at baseline, 15 min after airway establishment, at the end of surgery, and 30 min following airway removal. Outcome measures encompassed the oxygenation index, dynamic lung compliance, incidence of postoperative pulmonary complications, throat pain, and other postoperative complications assessed at 24 and 48 h postoperatively. The primary outcome focused on the LUS score in all 12 lung regions at 15 min after airway establishment.

MAIN RESULTS

Intention-to-treat analysis of 177 subjects revealed endotracheal intubation led to significantly higher LUS scores at 15 min {P < 0.001, mean difference 4.15 ± 0.60, 95% CI [2.97, 5.33]}, end of surgery (P < 0.001, mean difference 3.37 ± 0.68, 95% CI [2.02, 4.72]), and 30 min post-removal (P < 0.001, mean difference 2.63 ± 0.48, 95% CI [1.68, 3.58]). No major complications occurred in the two groups.

CONCLUSIONS

Compared to endotracheal intubation, laryngeal masks effectively reduce atelectasis formation and progression in gynecological, urological non-laparoscopic, and orthopedic limb surgeries. However, caution is warranted when generalizing these findings to surgeries with a higher risk of laryngeal mask leakage or obese patients. Additionally, the efficacy of laryngeal masks in reducing postoperative atelectasis remains uncertain when comprehensive monitoring of muscle relaxation and reversal therapy is employed.

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.

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.

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

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.

Application of a High-Flow Nasal Cannula for Prevention of Postextubation Atelectasis in Children Undergoing Surgery: A Randomized Controlled Trial

BACKGROUND

General anesthesia-induced atelectasis is common, and persistent postoperative atelectasis is associated with pulmonary complications. We aimed to evaluate the preventive effects of a high-flow nasal cannula (HFNC) on postoperative atelectasis and respiratory complications in infants and small children.

METHODS

In this prospective randomized controlled trial, children (≤2 years) receiving general anesthesia (>2 hours) were randomized into the control and HFNC groups. At the end of the surgery, the first lung ultrasound evaluation was performed in both groups. In the postanesthetic care unit (PACU), the control group received conventional oxygen therapy, while the HFNC group received oxygen via HFNC, with a flow rate of 2 L kg-1 min-1. Before discharge to the ward, a second lung ultrasound examination was performed. The primary outcome was the lung ultrasound score at PACU discharge. The secondary outcomes included the lung ultrasound score at the end of surgery, the incidence of significant atelectasis at PACU discharge, and other postoperative outcomes.

RESULTS

Lung ultrasound score and the incidence of atelectasis at the end of surgery did not differ significantly between the control (n = 38) and HFNC (n = 40) groups. After staying in the PACU, both groups showed a reduced lung ultrasound score and atelectasis incidence. However, the HFNC group had a significantly lower consolidation score than the control group (0; interquartile range [IQR] = 0-1 vs 3; IQR = 2-4; P< .001). Additionally, none of the patients had significant atelectasis in the HFNC group, compared to 6 patients in the control group (0% vs 15.8%; odds ratio [OR] = 0.444; 95% confidence interval for OR, 0.343-0.575; P = .011). Incidence of desaturation (oxygen saturation [Spo2] ≤ 95%), postoperative complications, and the length of hospital stay did not differ between the groups.

CONCLUSIONS

Preventive use of HFNC after surgery improves the lung ultrasound score and reduces postoperative atelectasis compared to conventional oxygen therapy in infants and small children.

Alveolar recruitment manoeuvre results in improved pulmonary function in obese patients undergoing bariatric surgery: a randomised trial

Perioperative ventilation is an important challenge of anaesthesia, especially in obese patients: body mass index is correlated with reduction of the pulmonary volume and they develop significantly more perioperative atelectasis and pulmonary complications. The alveolar recruitment manoeuvre is the most effective technique to reverse atelectasis. However, the clinical benefit on lung function in the perioperative period is not clear. The aim of the present study is to assess the perioperative clinical results of systematic alveolar recruitment manoeuvre associated with protective ventilation in patients undergoing laparoscopic bariatric surgery. It was a single-centre, randomised, double blind, superiority trial: control group with standard protective ventilation and recruitment group with protective ventilation and systematic recruitment manoeuvre. The primary outcome was a composite clinical criterion of pulmonary dysfunction including oxygen saturation, oxygen needs and dyspnoea in recovery room and at day 1. Secondary outcomes were recruitment manoeuvre tolerance, pulmonary and non-pulmonary complications, length of hospital stay and proportion of Intensive Care Unit admission. Two hundred and thirty patients were included: 115 in the recruitment manoeuvre group and 115 in the control group, 2 patients were excluded from the analysis in the control group. Patients in the recruitment manoeuvre group had significantly lower rate of pulmonary dysfunction in the recovery room (73% versus 84% (p =  0.043) and 77% versus 88% at postoperative day 1 (p =  0.043)). No significant differences were found for secondary outcomes. No patient was excluded from the recruitment manoeuvre group for intolerance to the manoeuvre. Recruitment manoeuvre is safe and effective in reducing early pulmonary dysfunction in obese patients undergoing bariatric surgery.

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).

Post-extubation continuous positive airway pressure improves oxygenation after pediatric laparoscopic surgery: A randomized controlled trial

BACKGROUND

Effects of intraoperative recruitment maneuvers (RMs) on oxygenation and pulmonary compliance are lost during recovery if high inspired oxygen and airway suctioning are used. We investigated the effect of post-extubation noninvasive CPAP mask application on the alveolar arterial oxygen difference [(A-a) DO₂ ] after pediatric laparoscopic surgery.

METHODS

Sixty patients (1-6 years) were randomly allocated to three groups of 20 patients, to receive zero end-expiratory pressure (ZEEP group), RM with decremental PEEP titration only (RM group), or followed with post-extubation CPAP for 5 minutes (RM-CPAP group). Primary outcome was [(A-a) DO₂ ] at 1 hour postoperatively. Secondary outcomes were respiratory mechanics, arterial blood gas analysis, hemodynamics, and adverse events.

RESULTS

At 1 hour postoperatively, mean [(A-a) DO₂ ] (mm Hg) was lower in the RM-CPAP group (41.5 ± 13.2, [95% CI 37.6-45.8]) compared to (80.2 ± 13.7 [72.6-87.5], P < 0.0001] and (59.2 ± 14.6, [54.8-62.6], P < 0.001) in the ZEEP and RM groups. The mean PaO₂ (mm Hg) at 1 hour postoperatively was higher in the RM-CPAP group (156.2 ± 18.3 [95% CI 147.6-164.7]) compared with the ZEEP (95.9 ± 15.9 [88.5-103.3], P < 0.0001) and RM groups (129.1 ± 15.9 [121.6-136.5], P < 0.0001). At 12 hours postoperatively, mean [(A-a) DO₂ ] and PaO₂ were (9.6 ± 2.1 [8.4-10.8]) and (91.9 ± 9.4 [87.5-96.3]) in the RM-CPAP group compared to (25.8 ± 5.5 [23.6-27.6]) and (69.9 ± 5.5 [67.4-72.5], P < 0.0001) in the ZEEP group and (34.3 ± 13.2, [28.4-40.2], P < 0.0001) and (74.03 ± 9.8 [69.5-78.6], P < 0.0001) in the RM group. No significant differences of perioperative adverse effects were found between groups.

CONCLUSIONS

An RM done after pneumoperitoneum inflation followed by decremental PEEP titration improved oxygenation at 1 hour postoperatively. The addition of an early post-extubation noninvasive CPAP mask ventilation improved oxygenation at 12 hours postoperatively.

Effects of lowering inspiratory oxygen fraction during microvascular decompression on postoperative gas exchange: A pre-post study

BACKGROUND

Despite many previous studies, the optimal oxygen fraction during general anesthesia remains controversial. This study aimed to evaluate the effects of lowering intraoperative fraction of inspired oxygen on postoperative gas exchange in patients undergoing microvascular decompression (MVD).

METHODS

We conducted a pre-post study to compare postoperative gas exchange with different intraoperative oxygen fractions. From April 2010 to June 2017, 1456 consecutive patients who underwent MVD were enrolled. Starting in January 2014, routine oxygen fraction was lowered from 1.0 to 0.3 during anesthetic induction/awakening and from 0.5 to 0.3 during anesthetic maintenance. Postoperative gas exchange, presented as the minimum value of PaO2/FIO2 ratio within 48 hours, were compared along with adverse events.

RESULTS

Among 1456 patients, 623 (42.8%) patients were stratified into group H (high FIO2) and 833 (57.2%) patients into group L (low FIO2). Intraoperative positive end-expiratory pressure was used in 126 (15.1%) patients in group H and 90 (14.4%) patients in group L (p = 0.77).The minimum value of PaO2/ FIO2 ratio within 48 hours after surgery was significantly greater in the group L (226.13 vs. 323.12; p < 0.001) without increasing any adverse events.

CONCLUSION

In patients undergoing MVD, lowering routine FIO2 and avoiding 100% O2 improved postoperative gas exchange.

Ventilation with high versus low peep levels during general anaesthesia for open abdominal surgery does not affect postoperative spirometry: A randomised clinical trial

BACKGROUND

Invasive mechanical ventilation during general anaesthesia for surgery typically causes atelectasis and impairs postoperative lung function.

OBJECTIVE

We investigated the effect of intraoperative ventilation with high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RMs) on postoperative spirometry.

DESIGN

This was a preplanned, single-centre substudy of an international multicentre randomised controlled trial, the PROVHILO trial.

SETTING

University hospital from November 2011 to January 2013.

PATIENTS

Nonobese patients scheduled for major abdominal surgery at a high risk of postoperative pulmonary complications (PPCs).

INTERVENTION

Intraoperative low tidal volume ventilation with PEEP levels of 12 cmH2O and RM (the high PEEP group) or with PEEP levels of 2 cmH2O or less without RM (the low PEEP group).

MAIN OUTCOME MEASURES

Time-weighted averages (TWAs) of the forced expiratory volume in 1 s (FEV1) and the forced vital capacity (FVC) up to postoperative day five.

RESULTS

Thirty-one patients were allocated to the high PEEP group and 32 to the low PEEP group. No postoperative spirometry test results were available for 6 patients. In both groups, TWA of FEV1 and FVC until postoperative day five were lower than preoperative values. Postoperative spirometry test results were not different between the high and low PEEP group; Data are median [interquartile range], TWA FVC 1.8 [1.6 to 2.4] versus 1.7 [1.2 to 2.4] l (P = NS) and TWA FEV1 1.2 [1.1 to 2.5] versus 1.2 [0.9 to 1.9] l (P = NS). Patients who developed PPCs had lower FEV1 and FVC on postoperative day five; 1.1 [0.9 to 1.6] versus 1.6 [1.4 to 1.9] l (P = 0.001) and 1.6 [1.2 to 2.6] versus 2.3 [1.7 to 2.6] l (P = 0.036), respectively.

CONCLUSION

Postoperative spirometry is not affected by PEEP and RM during intraoperative ventilation for open abdominal surgery in nonobese patients at a high risk of PPCs, but rather is associated with the development of PPCs.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01441791.

Perioperative lung protective ventilation

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

The effect of high-flow nasal oxygen on hospital length of stay in cardiac surgical patients at high risk for respiratory complications: a randomised controlled trial

There has been increased interest in the prophylactic and therapeutic use of high‐flow nasal oxygen in patients with, or at risk of, non‐hypercapnic respiratory failure. There are no randomised trials examining the efficacy of high‐flow nasal oxygen in high‐risk cardiac surgical patients. We sought to determine whether routine administration of high‐flow nasal oxygen, compared with standard oxygen therapy, leads to reduced hospital length of stay after cardiac surgery in patients with pre‐existing respiratory disease at high risk for postoperative pulmonary complications. Adult patients with pre‐existing respiratory disease undergoing elective cardiac surgery were randomly allocated to receive high‐flow nasal oxygen (n = 51) or standard oxygen therapy (n = 49). The primary outcome was hospital length of stay and all analyses were carried out on an intention‐to‐treat basis. Median (IQR [range]) hospital length of stay was 7 (6–9 [4–30]) days in the high‐flow nasal oxygen group and 9 (7–16 [4–120]) days in the standard oxygen group (p=0.012). Geometric mean hospital length of stay was 29% lower in the high‐flow nasal group (95%CI 11–44%, p = 0.004). High‐flow nasal oxygen was also associated with fewer intensive care unit re‐admissions (1/49 vs. 7/45; p = 0.026). When compared with standard care, prophylactic postoperative high‐flow nasal oxygen reduced hospital length of stay and intensive care unit re‐admission. This is the first randomised controlled trial examining the effect of prophylactic high‐flow nasal oxygen use on patient‐centred outcomes in cardiac surgical patients at high risk for postoperative respiratory complications.

Intraoperative Ventilation of Morbidly Obese Patients Guided by Transpulmonary Pressure

BACKGROUND

Bariatric surgery has proven a successful approach in the treatment of morbid obesity and its concomitant diseases such as diabetes mellitus and arterial hypertension. Aiming for optimal management of this challenging patient cohort, tailored concepts directly guided by individual patient physiology may outperform standardized care. Implying esophageal pressure measurement and electrical impedance tomography-increasingly applied monitoring approaches to individually adjust mechanical ventilation in challenging circumstances like acute respiratory distress syndrome (ARDS) and intraabdominal hypertension-we compared our institutions standard ventilator regimen with an individually adjusted positive end expiratory pressure (PEEP) level aiming for a positive transpulmonary pressure (P _L) throughout the respiratory cycle.

METHODS

After obtaining written informed consent, 37 patients scheduled for elective bariatric surgery were studied during mechanical ventilation in reverse Trendelenburg position. Before and after installation of capnoperitoneum, PEEP levels were gradually raised from a standard value of 10 cm H₂O until a P _L of 0 +/- 1 cm H₂O was reached. Changes in ventilation were monitored by electrical impedance tomography (EIT) and arterial blood gases (ABGs) were obtained at the end of surgery and 5 and 60 min after extubation, respectively.

RESULTS

To achieve the goal of a transpulmonary pressure (P _L) of 0 cm H₂O at end expiration, PEEP levels of 16.7 cm H₂O (95% KI 15.6-18.1) before and 23.8 cm H₂O (95% KI 19.6-40.4) during capnoperitoneum were necessary. EIT measurements confirmed an optimal PEEP level between 10 and 15 cm H₂O before and 20 and 25 cm H₂O during capnoperitoneum, respectively. Intra- and postoperative oxygenation did not change significantly.

CONCLUSION

Patients during laparoscopic bariatric surgery require high levels of PEEP to maintain a positive transpulmonary pressure throughout the respiratory cycle. EIT monitoring allows for non-invasive monitoring of increasing PEEP demand during capnoperitoneum. Individually adjusted PEEP levels did not result in improved postoperative oxygenation.

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.

Direct extubation onto high-flow nasal cannulae post-cardiac surgery versus standard treatment in patients with a BMI ≥30: a randomised controlled trial

PURPOSE

Patients with a body mass index (BMI) ≥30 kg/m(2) experience more severe atelectasis following cardiac surgery than those with normal BMI and its resolution is slower. This study aimed to compare extubation of patients post-cardiac surgery with a BMI ≥30 kg/m(2) onto high-flow nasal cannulae (HFNC) with standard care to determine whether HFNC could assist in minimising post-operative atelectasis and improve respiratory function.

METHODS

In this randomised controlled trial, patients received HFNC or standard oxygen therapy post-extubation. The primary outcome was atelectasis on chest X-ray. Secondary outcomes included oxygenation, respiratory rate (RR), subjective dyspnoea, and failure of allocated treatment.

RESULTS

One hundred and fifty-five patients were randomised, 74 to control, 81 to HFNC. No difference was seen between groups in atelectasis scores on Days 1 or 5 (median scores = 2, p = 0.70 and p = 0.15, respectively). In the 24-h post-extubation, there was no difference in mean PaO2/FiO2 ratio (HFNC 227.9, control 253.3, p = 0.08), or RR (HFNC 17.2, control 16.7, p = 0.17). However, low dyspnoea levels were observed in each group at 8 h post-extubation, median (IQR) scores were 0 (0-1) for control and 1 (0-3) for HFNC (p = 0.008). Five patients failed allocated treatment in the control group compared with three in the treatment group [Odds ratio 0.53, (95 % CI 0.11, 2.24), p = 0.40].

CONCLUSIONS

In this study, prophylactic extubation onto HFNC post-cardiac surgery in patients with a BMI ≥30 kg/m(2) did not lead to improvements in respiratory function. Larger studies assessing the role of HFNC in preventing worsening of respiratory function and intubation are required.

A ventilation strategy during general anaesthesia to reduce postoperative atelectasis

BACKGROUND

Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy, without recruitment manoeuvres, using a combination of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and a reduced end-expiratory oxygen fraction (FETO2) before ending mask ventilation with CPAP after extubation would reduce the area of postoperative atelectasis.

METHODS

Thirty patients were randomized into three groups. During induction and emergence, inspiratory oxygen fractions (FIO2) were 1.0 in the control group and 1.0 or 0.8 in the intervention groups. No CPAP/PEEP was used in the control group, whereas CPAP/PEEP of 6 cmH2O was used in the intervention groups. After extubation, FIO2 was set to 0.30 in the intervention groups and CPAP was applied, aiming at FETO2 < 0.30. Atelectasis was studied by computed tomography 25 min postoperatively.

RESULTS

The median area of atelectasis was 5.2 cm(2) (range 1.6-12.2 cm(2)) and 8.5 cm(2) (3-23.1 cm(2)) in the groups given FIO2 1.0 with or without CPAP/PEEP, respectively. After correction for body mass index the difference between medians (2.9 cm(2)) was statistically significant (confidence interval 0.2-7.6 cm(2), p = 0.04). In the group given FIO2 0.8, in which seven patients were ex- or current smokers, the median area of atelectasis was 8.2 cm(2) (1.8-14.7 cm(2)).

CONCLUSION

Compared with conventional ventilation, after correction for obesity, this ventilation strategy reduced the area of postoperative atelectasis in one of the intervention groups but not in the other group, which included a higher proportion of smokers.

Post-operative atelectasis - a randomised trial investigating a ventilatory strategy and low oxygen fraction during recovery

BACKGROUND

Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy with a combination of 1) continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and 2) a reduced end-expiratory oxygen concentration during recovery would reduce post-operative atelectasis.

METHODS

Sixty patients were randomized into two groups. During anaesthesia induction, inspiratory oxygen fraction (FIO2) was 1.0, and depending on weight, CPAP 6, 7 or 8 cmH2O was applied in both groups via facemask. During maintenance of anaesthesia, a laryngeal mask airway (LMA) was used, and PEEP was 6-8 cmH2O in both groups. Before removal of the LMA, FIO2 was set to 0.3 in the intervention group and 1.0 in the control group. Atelectasis was studied by computed tomography (CT) approximately 14 min post-operatively.

RESULTS

In one patient in the group given an FIO2 of 0.3 before removal of the LMA a CT scan could not be performed so the patient was excluded. The area of atelectasis was 5.5, 0-16.9 cm(2) (median and range), and 6.8, 0-27.5 cm(2) in the groups given FIO2 0.3 or FIO2 1.0 before removal of the LMA, a difference that was not statistically significant (P = 0.48). Post-hoc analysis showed dependence of atelectasis on smoking (despite all were clinically lung healthy) and American Society of Anesthesiologists class (P = 0.038 and 0.015, respectively).

CONCLUSION

Inducing anaesthesia with CPAP/PEEP and FIO2 1.0 and deliberately reducing FIO2 during recovery before removal of the LMA did not reduce post-operative atelectasis compared with FIO2 1.0 before removal of the LMA.

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

Background:

During emergence from anesthesia, breathing 100% oxygen is frequently used to provide a safety margin toward hypoxemia in case an airway problem occurs. Oxygen breathing has been shown to cause pulmonary gas exchange disorders in healthy individuals. This study investigates how oxygen breathing during emergence affects lung function specifically whether oxygen breathing causes added hypoxemia in patients with chronic obstructive pulmonary disease.

Methods:

This trial has been conducted in a parallel-arm, case-controlled, open-label manner. Fifty-three patients with chronic obstructive pulmonary disease were randomly allocated (computer-generated lists) to breathe either 100 or 30% oxygen balanced with nitrogen during emergence from anesthesia. Arterial blood gas measurements were taken before induction and at 5, 15, and 60 min after extubation.

Results:

All participants tolerated the study well. Patients treated with 100% oxygen had a higher alveolar–arterial oxygen pressure gradient (primary outcome) compared with patients treated with 30% oxygen (25 vs. 20 mmHg) and compared with their baseline at the 60-min measurement (25 vs. 17 mmHg). At the 60-min measurement, arterial partial pressure of oxygen was lower in the 100% group (62 vs. 67 mmHg). Arterial partial pressure of carbon dioxide and pH were not different between groups or measurements.

Conclusions:

In this experiment, the authors examined oxygen breathing during emergence—a widely practiced maneuver known to generate pulmonary blood flow heterogeneity. In the observed cohort of patients already presenting with pulmonary blood flow disturbances, emergence on oxygen resulted in deterioration of oxygen-related blood gas parameters. In the perioperative care of patients with chronic obstructive pulmonary disease, oxygen breathing during emergence from anesthesia may need reconsideration.

[Do anesthetic techniques influence postoperative outcomes? Part I]

The influence of anesthetic technique on postoperative outcomes has opened a wide field of research in recent years. High-risk patients undergoing non-cardiac surgery are those who have higher incidence of postoperative complications and mortality. A proper definition of this group of patients should focus maximal efforts and resources to improve the results. In view of the significant reduction in postoperative mortality and morbidity in last 20 years, perioperative research should take into account new indicators to investigate the role of anesthetic techniques on postoperative outcomes. Studies focused on the evaluation of intermediate outcomes would probably discriminate better effectiveness differences between anesthetic techniques. We review some of the major controversies arising in the literature about the impact of anesthetic techniques on postoperative outcomes. We have grouped the impact of these techniques into 9 major investigation areas: mortality, cardiovascular complications, respiratory complications, postoperative cognitive dysfunction, chronic postoperative pain, cancer recurrence, postoperative nausea/vomiting, surgical outcomes and resources utilization. In this first part of the review, we discuss the basis on postoperative outcomes research, mortality, cardiovascular and respiratory complications.

Perioperative oxygen toxicity

This article challenges the use of hyperoxia in the perioperative period. It describes the biochemical and physiologic basis for both the direct and indirect adverse effects of oxygen. The reasons for using hyperoxia in the perioperative period are critically evaluated, and the evidence and guidelines for oxygen use in common acute medical conditions are reviewed.

Oxygen and anesthesia: what lung do we deliver to the post-operative ward?

Anesthesia is safe in most patients. However, anesthetics reduce functional residual capacity (FRC) and promote airway closure. Oxygen is breathed during the induction of anesthesia, and increased concentration of oxygen (O(2) ) is given during the surgery to reduce the risk of hypoxemia. However, oxygen is rapidly adsorbed behind closed airways, causing lung collapse (atelectasis) and shunt. Atelectasis may be a locus for infection and may cause pneumonia. Measures to prevent atelectasis and possibly reduce post-operative pulmonary complications are based on moderate use of oxygen and preservation or restoration of FRC. Pre-oxygenation with 100% O(2) causes atelectasis and should be followed by a recruitment maneuver (inflation to an airway pressure of 40 cm H(2) O for 10 s and to higher airway pressures in patients with reduced abdominal compliance (obese and patients with abdominal disorders). Pre-oxygenation with 80% O(2) may be sufficient in most patients with no anticipated difficulty in managing the airway, but time to hypoxemia during apnea decreases from mean 7 to 5 min. An alternative, possibly challenging, procedure is induction of anesthesia with continuous positive airway pressure/positive end-expiratory pressure to prevent fall in FRC enabling use of 100% O(2) . A continuous PEEP of 7-10 cm H(2) O may not necessarily improve oxygenation but should keep the lung open until the end of anesthesia. Inspired oxygen concentration of 30-40%, or even less, should suffice if the lung is kept open. The goal of the anesthetic regime should be to deliver a patient with no atelectasis to the post-operative ward and to keep the lung open.

Protocol for a randomised controlled trial of nasal high flow oxygen therapy compared to standard care in patients following cardiac surgery: the HOT-AS study

BACKGROUND

Postoperative respiratory complications following cardiac surgery may increase morbidity, mortality and length of stay. Non-invasive respiratory support therapies can be used prophylactically or curatively to reduce respiratory complications. One system, nasal high flow oxygen therapy, is in use in many intensive care units (ICUs) however there is a lack of information regarding its clinical utility and efficacy.

OBJECTIVES

This paper outlines the study protocol and methodology for a study designed to determine if the prophylactic use of nasal high flow oxygen therapy can improve pulmonary function in patients following cardiac surgery.

METHODS/DESIGN

A prospective randomised controlled trial will be conducted of adult patients scheduled for cardiac surgery and admitted to the Cardiothoracic Intensive Care Unit of a tertiary hospital. Study participants will be assigned to receive either nasal high flow or standard oxygen therapy (oxygen therapy at 2-4 L/min via either simple facemask or nasal cannulae) at extubation. The primary outcome measure is improved pulmonary function demonstrated by SpO2/FiO2 ratio >445 on post-operative day 3. Secondary outcome measures include atelectasis score on chest X-ray; spirometry; readmission to ICU for respiratory causes; ICU and hospital length of stay; mortality and incidence of respiratory complications at day 28; oxygenation variables; use of adjunctive respiratory support therapies; escalation of respiratory support; adverse events and patient comfort during administration of oxygen therapy.

SAMPLE SIZE

It was calculated that 340 patients will be required--170 per arm of study--to give a 90% power to detect a 15% treatment effect.

RESULTS

This study started recruiting in March 2011. It is anticipated that enrollment will be complete in April 2012 and results available towards the end of 2012.

CONCLUSION

This study will provide evidence of any benefits in the use of prophylactic nasal high flow therapy in post-operative cardiac surgical patients.

TRIAL REGISTRATION

This trial is registered with the Australian New Zealand Clinical Trials Registry www.anzctr.org.au (ACTRN12610000973011).

One-lung ventilation and arterial oxygenation

PURPOSE OF REVIEW

Hypoxemia during one-lung ventilation (OLV) has become less common; however, it may still occur in about 10% of cases. We review recent developments which may affect the incidence and treatment of hypoxemia during OLV.

RECENT FINDINGS

Changes in surgical techniques are affecting oxygenation during OLV. The increased use of the supine position may adversely affect the prevalence of hypoxemia, whereas the increased application of thoracoscopic techniques is limiting the treatment options. Treatment options such as global or selective recruitment maneuvers and drug effects of dexmedetomidine and epoprostenol on arterial oxygenation during OLV are discussed. Capnometry prior to, or early during OLV, may in fact be able to predict the degree of hypoxemia during OLV. Persistent controversies surrounding the effect of epidural anesthesia, ventilatory modalities and gravity are reviewed.

SUMMARY

Interesting concepts have emerged from case reports and small studies on the treatment and prediction of hypoxemia during OLV. Definitive studies on the most effective ventilatory mode remain elusive. End-organ effects of OLV are an exciting new concept that may shape clinical practice and research going forward.