Positive end-expiratory pressure prevents atelectasis during general anaesthesia even in the presence of a high inspired oxygen concentration

Effects of individualized positive end-expiratory pressure on intraoperative oxygenation in thoracic surgical patients: study protocol for a prospective randomized controlled trial

BACKGROUND

Intraoperative hypoxemia and postoperative pulmonary complications (PPCs) often occur in patients with one-lung ventilation (OLV), due to both pulmonary shunt and atelectasis. It has been demonstrated that individualized positive end-expiratory pressure (iPEEP) can effectively improve intraoperative oxygenation, increase lung compliance, and reduce driving pressure, thereby decreasing the risk of developing PPCs. However, its effect during OLV is still unknown. Therefore, we aim to investigate whether iPEEP ventilation during OLV is superior to 5 cmH2O PEEP in terms of intraoperative oxygenation and the occurrence of PPCs.

METHODS

This study is a prospective, randomized controlled, single-blind, single-center trial. A total of 112 patients undergoing thoracoscopic pneumonectomy surgery and OLV will be enrolled in the study. They will be randomized into two groups: the static lung compliance guided iPEEP titration group (Cst-iPEEP Group) and the constant 5 cmH2O PEEP group (PEEP 5 Group). The primary outcome will be the oxygenation index at 30 min after OLV and titration. Secondary outcomes are oxygenation index at other operative time points, PPCs, postoperative adverse events, ventilator parameters, vital signs, pH value, inflammatory factors, and economic indicators.

DISCUSSION

This trial explores the effect of iPEEP on intraoperative oxygenation during OLV and PPCs. It provides some clinical references for optimizing the lung protective ventilation strategy of OLV, improving patient prognosis, and accelerating postoperative rehabilitation.

TRIAL REGISTRATION

www.Chictr.org.cn ChiCTR2300073411 . Registered on 10 July 2023.

Effect of Lung Compliance-Based Optimum Pressure Versus Fixed Positive End-Expiratory Pressure on Lung Atelectasis Assessed by Modified Lung Ultrasound Score in Laparoscopic Gynecological Surgery: A Prospective Randomized Controlled Trial

BACKGROUND

 Lung protective ventilation during the intraoperative period is now well established. However, the additional role of positive end-expiratory pressure (PEEP) during the intraoperative period remains uncertain in major laparoscopic gynecological surgery. The authors hypothesized that compliance-based optimum PEEP titration reduces postoperative lung atelectasis and improves outcomes.

METHODS

 Patients undergoing major laparoscopic pelvic gynecological surgeries with healthy lungs were randomized to the fixed PEEP group (PEEP 5 cm H₂O and recruitment maneuver {RM}) and optimum PEEP group (compliance-based PEEP and RM). Lung ultrasound and arterial blood gas analysis were performed at four time points. Modified lung ultrasound scoring was done, and the same was used as means of assessing lung aeration and the amount of lung atelectasis. Postoperative supplemental oxygen requirement and duration were also assessed and compared.

RESULTS

Lung ultrasound score (LUS) 30 minutes after extubation in fixed (Group F) and optimum (Group O) PEEP groups were median (interquartile range {IQR}) 3 (2-3) versus 1 (1-2), p=0.0001. Ventilatory parameters between Group F and Group O after lung recruitment were tidal volume (mean 357 mL {SD: 35} versus 362 mL {SD: 22}, p=0.46), PEEP (median, 5 cm H₂O {IQR: 5-5} versus median 16 cm H₂O {IQR: 14-18}), peak airway pressure (median 26 cm H₂O {IQR: 24-28} versus median 30 cm H₂O {IQR: 28-32} p<0.0001), plateau pressure (median 22 cm H₂O {IQR: 20-24} versus median 26 cm H₂O {IQR: 24-28} p<0.0001), static compliance (32.07±8.36 mL cm H₂O-1 versus 39.58±8.99 mL cm H₂O-1, p=0.0002). The number of patients requiring postoperative oxygen therapy to maintain SpO₂ >94% after extubation in postanesthesia care unit (PACU) was statistically significantly greater in group F (39/41 {95%} versus 30/41 {73%}, p=0.007). Median (IQR) duration of oxygenation therapy in the first 24 hours of the postoperative period between Group F and Group O differed with statistical significance, with the median (IQR) values being 25 (20-30) minutes versus 10 (0-15) minutes (p<0.0001).

CONCLUSIONS

 The modified lung ultrasound score significantly differed intraoperatively between the two groups, with lower scores in the optimum PEEP group. This has reflected improved postoperative outcomes in optimum PEEP group patients, with fewer patients requiring postoperative oxygen supplementation and reduced supplemental oxygen requirement duration.

Lung ultrasound score-based assessment of postoperative atelectasis in obese patients according to inspired oxygen concentration: A prospective, randomized-controlled study

BACKGROUND

According to a recent meta-analysis, in patients with a body mass index (BMI) ≥ 30, a high fraction of inhaled oxygen (FiO2) did not increase postoperative atelectasis. However, a high FiO2 generally increases the risk of postoperative atelectasis. Therefore, this study aimed to evaluate the effect of FiO2 on the development of atelectasis in obese patients using the modified lung ultrasound score (LUSS).

METHODS

Patients were assigned to 4 groups: BMI ≥ 30: group A (n = 21) and group B (n = 20) and normal BMI: group C (n = 22) and group D (n = 21). Groups A and C were administered 100% O2 during preinduction and emergence and 50% O2 during anesthesia. Groups B and D received 40% O2 for anesthesia. The modified LUSS was assessed before and 20 min after arrival to the postanesthesia care unit (PACU).

RESULTS

The difference between the modified LUSS preinduction and PACU was significantly higher in group A with a BMI ≥ 30 (P = .006); however, there was an insignificant difference between groups C and D in the normal BMI group (P = .076).

CONCLUSION

High FiO2 had a greater effect on the development of atelectasis in obese patients than did low FiO2; however, in normal-weight individuals, FiO2 did not have a significant effect on postoperative atelectasis.

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

BACKGROUND

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

AIM

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

METHOD

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

RESULT

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

CONCLUSION

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

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.

The Influence of Positive End-Expiratory Pressure on Leakage and Oxygenation Using a Laryngeal Mask Airway: A Randomized Trial

BACKGROUND

The value of positive end-expiratory pressure (PEEP) in maintaining oxygenation during ventilation with a laryngeal mask airway (LMA) mask is unclear. To clarify the potential benefit or harm to PEEP application during positive pressure ventilation with a ProSeal LMA® mask, we compared the effect of PEEP versus zero end-expiratory pressure (ZEEP) on gas leakage and oxygenation. We hypothesized that a PEEP of 8 mbar (8.2 cm H2O) would be associated with an increased incidence of gas leakage compared to ZEEP.

METHODS

We designed a prospective, controlled, randomized, single-blinded, multicenter clinical trial. Patients >18 years of age with an American Society of Anesthesiologists (ASA) physical status I/II without increased risk of aspiration were enrolled if they were scheduled for elective surgery under general anesthesia with an LMA mask. Patients were randomized to a control group managed with ZEEP or an intervention group managed with a PEEP of 8 mbar. Both groups received positive pressure ventilation. The primary end point was the occurrence of gas leakage. The Student t test and χ2 test were used for statistical analysis.

RESULTS

A total of 174 patients were enrolled in the ZEEP group, and 208 were enrolled in the PEEP group. The incidence of gas leakage did not differ between the 2 groups (ZEEP: 23/174, 13.2%; PEEP: 42/208, 20.2%; P = .071; odds ratio [OR], 1.611; 95% confidence interval [CI], 0.954-2.891). However, more patients required reseating of the LMA mask in the PEEP group (ZEEP: 5/174, 2.9%; PEEP: 18/208, 8.7%; P = .018; OR, 3.202; 95% CI, 1.164-8.812). The need for endotracheal intubation did not differ between groups (ZEEP: 2/174, 1.1%; PEEP: 7/208, 3.4%; P = .190; OR, 2.995; 95% CI, 0.614-14.608). After positive pressure ventilation for 25 minutes, the mean peripheral oxygen saturation (Spo2) was higher in the PEEP than in the ZEEP group (98.5 [1.9]% vs 98.0 [1.4]%; P = .01). Peak inspiratory pressure (PIP; 16 [2] vs 12 [4] mbar; P < .001) and dynamic compliance (57 [14] vs 49 [14] mL/mbar; P < .001) were both higher in the PEEP group than in the ZEEP group.

CONCLUSIONS

Use of PEEP did not affect the overall incidence of gas leakage. However, PEEP did result in a higher incidence of attempts to reseat the LMA mask compared to ZEEP, whereas the incidence of rescue intubation did not differ between groups. We concluded that a PEEP of 8 mbar did not increase overall gas leakage during positive pressure ventilation with an LMA mask, but it did slightly improve gas exchange and compliance. Overall, our study does not provide strong arguments for using PEEP during ventilation with an LMA mask in elective surgery.

Lung Navigation Ventilation Protocol to Optimize Biopsy of Peripheral Lung Lesions

BACKGROUND

Computed tomography-to-body divergence caused by respiratory motion, atelectasis, diaphragmatic motion and other factors is an obstacle to peripheral lung biopsies. We examined a conventional ventilation strategy versus a lung navigation ventilation protocol (LNVP) optimized for intraprocedural 3-dimensional image acquisition and bronchoscopic biopsy of peripheral lung nodules.

METHODS

A retrospective, single center study was conducted in consecutive subjects with peripheral lung lesions measuring <30 mm. Effects of ventilation strategies including atelectasis and tool-in-lesion confirmation were assessed using cone beam computed tomography images. Diagnostic yield was also evaluated. Complications were assessed through 7 days.

RESULTS

Fifty subjects were included (25 per group) with 27 nodules in the conventional group and 25 nodules in the LNVP group. Atelectasis was assessed by 2 blinded readers: [reader 1 (R1) and reader 2 (R2)]. Atelectasis was more prevalent in the conventional ventilation group, both for dependent atelectasis (R1: 64% and R2: 68% vs. R1: 36% and R2: 16%, P=0.00014) and sublobar/lobar atelectasis (R1: 48% and R2: 56% vs. R1: 20% and R2: 32%, P=0.01). Similarly, the target lesion was obscured due to atelectasis more often in the conventional ventilation group (R1: 36% and R2: 36% vs. R1: 4% and R2: 8%, P=0.01). Diagnostic yield was 70% for conventional ventilation and 92% for LNVP (P=0.08).

CONCLUSION

LNVP demonstrated markedly reduced dependent and sublobar/lobar atelectasis and lesions either partially or completely obscured by atelectasis compared with conventional ventilation. Future prospective studies are necessary to understand the impact of protocolized ventilation strategies for bronchoscopic biopsy of peripheral lung lesions.

Carbon Dioxide Changes during High-flow Nasal Oxygenation in Apneic Patients: A Single-center Randomized Controlled Noninferiority Trial

BACKGROUND

Anesthesia studies using high-flow, humidified, heated oxygen delivered via nasal cannulas at flow rates of more than 50 l · min-1 postulated a ventilatory effect because carbon dioxide increased at lower levels as reported earlier. This study investigated the increase of arterial partial pressure of carbon dioxide between different flow rates of 100% oxygen in elective anesthetized and paralyzed surgical adults before intubation.

METHODS

After preoxygenation and standardized anesthesia induction with nondepolarizing neuromuscular blockade, all patients received 100% oxygen (via high-flow nasal oxygenation system or circuit of the anesthesia machine), and continuous jaw thrust/laryngoscopy was applied throughout the 15-min period. In this single-center noninferiority trial, 25 patients each, were randomized to five groups: (1) minimal flow: 0.25 l · min-1, endotracheal tube; (2) low flow: 2 l · min-1, continuous jaw thrust; (3) medium flow: 10 l · min-1, continuous jaw thrust; (4) high flow: 70 l · min-1, continuous jaw thrust; and (5) control: 70 l · min-1, continuous laryngoscopy. Immediately after anesthesia induction, the 15-min apnea period started with oxygen delivered according to the randomized flow rate. Serial arterial blood gas analyses were drawn every 2 min. The study was terminated if either oxygen saturation measured by pulse oximetry was less than 92%, transcutaneous carbon dioxide was greater than 100 mmHg, pH was less than 7.1, potassium level was greater than 6 mmol · l-1, or apnea time was 15 min. The primary outcome was the linear rate of mean increase of arterial carbon dioxide during the 15-min apnea period computed from linear regressions.

RESULTS

In total, 125 patients completed the study. Noninferiority with a predefined noninferiority margin of 0.3 mmHg · min-1 could be declared for all treatments with the following mean and 95% CI for the mean differences in the linear rate of arterial partial pressure of carbon dioxide with associated P values regarding noninferiority: high flow versus control, -0.0 mmHg · min-1 (-0.3, 0.3 mmHg · min-1, P = 0.030); medium flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.002); low flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.003); and minimal flow versus control, -0.1 mmHg · min-1 (-0.4, 0.2 mmHg · min-1, P = 0.004).

CONCLUSIONS

Widely differing flow rates of humidified 100% oxygen during apnea resulted in comparable increases of arterial partial pressure of carbon dioxide, which does not support an additional ventilatory effect of high-flow nasal oxygenation.

EDITOR’S PERSPECTIVE

Evaluation of atelectasis using electrical impedance tomography during procedural deep sedation for MRI in small children: A prospective observational trial

STUDY OBJECTIVE

To investigate the variation of poorly ventilated lung units (i.e., silent spaces) in children undergoing procedural sedation in a day-hospital setting, until discharge home from the Post-Anesthesia Care Unit (PACU).

DESIGN

Prospective, single-center, observational cohort trial.

SETTING

This study was conducted at the radiology department and in PACU at Bern University Hospital (Switzerland), a tertiary care hospital.

PATIENTS

We included 25 children (1-6 years, ASA I-III) scheduled for cerebral magnetic resonance imaging scan, spontaneously breathing under deep sedation. Children planned for tracheal intubation, supraglottic airway insertion, or with contraindication for propofol were excluded.

INTERVENTION

After intravenous or inhaled induction, deep sedation was performed with 10 mg/kg/h Propofol. All children received nasal oxygen 0.3 ml/kg/min.

MEASUREMENTS

The proportion of silent spaces and the global inhomogeneity index were determined at each of five procedural points, using electrical impedance tomography: before induction (T1); before (T2) and after (T3) magnetic resonance imaging; at the end of sedation before transport to the PACU (T4); and before hospital discharge (T5).

MAIN RESULTS

The median [interquartile range (IQR)] proportion of silent spaces at the five analysis points were: T1, 5% [2%-14%]; T2, 10% [7%-14%]; T3, 12% [5%-23%]; T4, 12% [7%-24%]; and T5, 3% [2%-11%]. These defined significant changes in silent spaces over the course of sedation (p = 0.009), but no differences in silent spaces from before induction to before discharge from the PACU (T1 vs. T5; p = 0.29). Median [IQR] global inhomogeneity indices were 0.57 [0.55-0.58], 0.56 [0.53-0.59], 0.56 [0.54-0.59], 0.57 [0.54-0.60] and 0.56 [0.54-0.57], respectively (p = 0.93). None of the children reported anesthesia-related complications.

CONCLUSION

Deep sedation results in significantly increased poorly ventilated lung units during sedation. However, this does not significantly affect ventilation homogeneity, which was fully resolved at discharge from the PACU.

TRIAL REGISTRATION

clinicaltrials.gov, identifier NCT04507581.

Phrenic nerve stimulation prevents diaphragm atrophy in patients with respiratory failure on mechanical ventilation

BACKGROUND

Diaphragm atrophy and dysfunction is a major problem among critically ill patients on mechanical ventilation. Ventilator-induced diaphragmatic dysfunction is thought to play a major role, resulting in a failure of weaning. Stimulation of the phrenic nerves and resulting diaphragm contraction could potentially prevent or treat this atrophy. The subject of this study is to determine the effectiveness of diaphragm stimulation in preventing atrophy by measuring changes in its thickness.

METHODS

A total of 12 patients in the intervention group and 10 patients in the control group were enrolled. Diaphragm thickness was measured by ultrasound in both groups at the beginning of study enrollment (hour 0), after 24 hours, and at study completion (hour 48). The obtained data were then statistically analyzed and both groups were compared.

RESULTS

The results showed that the baseline diaphragm thickness in the interventional group was (1.98 ± 0.52) mm and after 48 hours of phrenic nerve stimulation increased to (2.20 ± 0.45) mm (p=0.001). The baseline diaphragm thickness of (2.00 ± 0.33) mm decreased in the control group after 48 hours of mechanical ventilation to (1.72 ± 0.20) mm (p<0.001).

CONCLUSIONS

Our study demonstrates that induced contraction of the diaphragm by pacing the phrenic nerve not only reduces the rate of its atrophy during mechanical ventilation but also leads to an increase in its thickness - the main determinant of the muscle strength required for spontaneous ventilation and successful ventilator weaning.

TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov (18/06/2018, NCT03559933, https://clinicaltrials.gov/ct2/show/NCT03559933 ).

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

A prospective, assessor-blinded, randomised controlled trial.

SETTING

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

PATIENTS

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

INTERVENTION

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSION

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

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03160144.

Individualized positive end-expiratory pressure following alveolar recruitment manoeuvres in lung-healthy anaesthetized dogs: a randomized clinical trial on early postoperative arterial oxygenation

OBJECTIVE

To assess and compare the effect of intraoperative stepwise alveolar recruitment manoeuvres (ARMs), followed by individualized positive end-expiratory pressure (PEEP), defined as PEEP at maximal respiratory system compliance + 2 cmH₂O (PEEP_maxCrs+2), with that of spontaneous ventilation (SV) and controlled mechanical ventilation (CMV) without ARM or PEEP on early postoperative arterial oxygenation in anaesthetized healthy dogs.

STUDY DESIGN

Prospective, randomized, nonblinded clinical study.

ANIMALS

A total of 32 healthy client-owned dogs undergoing surgery in dorsal recumbency.

METHODS

Dogs were ventilated intraoperatively (inspired oxygen fraction: 0.5) with one of the following strategies: SV, CMV alone, and CMV with PEEP_maxCrs+2 following a single ARM (ARM1) or two ARMs (ARM2, the second ARM at the end of surgery). Arterial blood gas analyses were performed before starting the ventilatory strategy, at the end of surgery, and at 5, 10, 15, 30 and 60 minutes after extubation while breathing room air. Data were analysed using Kruskal-Wallis and Friedman tests (p < 0.050).

RESULTS

At any time point after extubation, PaO₂ was not significantly different between groups. At 5 minutes after extubation, PaO₂ was 95.1 (78.1-104.0), 93.8 (88.3-104.0), 96.9 (86.6-115.0) and 89.1 (87.6-102.0) mmHg in the SV, CMV, ARM1 and ARM2 groups, respectively. PaO₂ decreased at 30 minutes after extubation in the CMV, ARM1 and ARM2 groups (p < 0.050), but it did not decrease after 30 minutes in the SV group. Moderate hypoxaemia (PaO₂, 60-80 mmHg) was observed in one dog in the ARM1 group and two dogs each in the SV and ARM2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Intraoperative ARMs, followed by PEEP_maxCrs+2, did not improve early postoperative arterial oxygenation compared with SV or CMV alone in healthy anaesthetized dogs. Therefore, this ventilatory strategy might not be clinically advantageous for improving postoperative arterial oxygenation in healthy dogs undergoing surgery when positioned in dorsal recumbency.

Assessment of the Effect of Recruitment Maneuver on Lung Aeration Through Imaging Analysis in Invasively Ventilated Patients: A Systematic Review

Background: Recruitment maneuvers (RMs) have heterogeneous effects on lung aeration and have adverse side effects. We aimed to identify morphological, anatomical, and functional imaging characteristics that might be used to predict the RMs on lung aeration in invasively ventilated patients.

Methods: We performed a systemic review. Studies included invasively ventilated patients who received an RM and in whom re-aeration was examined with chest computed tomography (CT), electrical impedance tomography (EIT), and lung ultrasound (LUS) were included.

Results: Twenty studies were identified. Different types of RMs were applied. The amount of re-aerated lung tissue after an RM was highly variable between patients in all studies, irrespective of the used imaging technique and the type of patients (ARDS or non-ARDS). Imaging findings suggesting a non-focal morphology (i.e., radiologic findings consistent with attenuations with diffuse or patchy loss of aeration) were associated with higher likelihood of recruitment and lower chance of overdistention than a focal morphology (i.e., radiological findings suggestive of lobar or segmental loss of aeration). This was independent of the used imaging technique but only observed in patients with ARDS. In patients without ARDS, the results were inconclusive.

Conclusions: ARDS patients with imaging findings suggestive of non-focal morphology show most re-aeration of previously consolidated lung tissue after RMs. The role of imaging techniques in predicting the effect of RMs on re-aeration in patients without ARDS remains uncertain.

[Intraoperative Ventilation in Adults]

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

Cone beam CT imaging for bronchoscopy: a technical review

Cone beam computed tomography (CBCT) is a well-established imaging modality with numerous proven applications across multiple clinical disciplines. More recently, CBCT has emerged as an important imaging tool for bronchoscopists, primarily used during transbronchial biopsy of peripheral pulmonary lesions (PPLS). For this application CBCT has proved useful in navigating devices to a target lesion, in confirming device tool-in-lesion, as well as during tissue acquisition. In addition, CBCT is poised to play an important role in trials evaluating bronchoscopic ablation by helping to determine the location of the ablative probe relative to the target lesion. Before adopting this technology, it is key for bronchoscopists to learn some basic concepts that will allow them to have a safer and more successful experience with CBCT. Hence, in the current manuscript, we will focus on both technical and practical aspects of CBCT imaging, ranging from systems considerations, image quality, radiation dose and dose-reduction strategies, procedure room set-up, and best practices for CBCT image acquisition.

Atelectasis prevention during anaesthesia using high-flow nasal cannula therapy: A paediatric randomised trial using MRI images

BACKGROUND

Atelectasis frequently occurs early on during anaesthesia in children. We hypothesised that positive expiratory pressure (PEP) generated via high-flow nasal cannula (HFNC) could prevent atelectasis in non-intubated children under general anaesthesia. The objective was to compare the volume of atelectasis present in patients treated via HFNC to that of patients treated via a face bag-mask without PEP. The outcome used for this comparison was the ratio of the atelectasis volume to the total pulmonary volume.

METHODS

A prospective single-centre, single-blind, randomised trial was conducted in a tertiary hospital from November 2018 through May 2019. The trial subjects were infants and children between six months and six years of age who required anaesthesia for an MRI. The children were randomised to receive sevoflurane for maintenance of anaesthesia either via a classic face bag-mask or by HFNC. The atelectasis volume was measured from thoracic MRI images. The judgement criterion was the ratio of the atelectasis volume to the lung volume.

RESULTS

Of a trial group of 42 patients, 21 received anaesthesia via a face bag-mask and 21 via HFNC. After three patients were excluded for technical issues, the data for 39 patients were analysed. The atelectasis volume to the lung volume ratio in the HFNC group was significantly smaller than the ratio for the face bag-mask group (1.6% vs 6.8%, respectively; p=0.002).

CONCLUSION

HFNC was associated with a lower atelectasis lung ratio compared to using a face bag-mask during anaesthesia for children maintained with spontaneous ventilation. Registered on Clinicaltrials.gov: NCT03592589.

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.

Effect of Different Levels of Positive End-Expiratory Pressure (PEEP) on Respiratory Status during Gynecologic Laparoscopy

Background

During gynecologic laparoscopy, pneumoperitoneum, and the position of the patient's head can lead to pathophysiologic changes in cardiovascular and respiratory systems, complicating the management of anesthesia in these patients. One of the strategies for improving the respiratory status of patients undergoing laparoscopy is the use of Positive End-Expiratory Pressure (PEEP).

Objectives

This study aimed to evaluate the effect of different levels of PEEP on the respiratory status of patients undergoing gynecologic laparoscopy.

Methods

In this clinical trial, 60 patients with ASA I were randomly assigned to three groups to control anesthesia: ZEEP (PEEP 0 cmH₂O; 20 cases), PEEP₅ (PEEP 5 cmH₂O; 20 cases), and PEEP₁₀ (PEEP 10 cmH₂O; 20 cases). Respiratory and hemodynamic variables of patients were compared before general anesthetic induction and immediately after CO₂ insufflation at intervals of 5, 10, 20, 30, and 60 min and the end of the operation in the three study groups.

Results

The PEEP application improved pH, PaCO₂, and PaO₂ levels at the end of pneumoperitoneum compared to baseline when compared with the non-use of PEEP (ZEEP group). Also, the frequency of dysrhythmia in the use of PEEP in controlled ventilation was significantly lower in patients with PEEP₁₀ (P < 0.05). The application of PEEP₅ resulted in similar effects to PEEP₁₀ in the levels of respiratory variables.

Conclusions

The PEEP application is associated with improved arterial blood gas in patients with gynecologic laparoscopy. The use of PEEP₁₀ has a greater effect on the improvement of respiratory parameters and complications of pneumoperitoneum.

Perioperative Hyperoxyphobia: Justified or Not? Benefits and Harms of Hyperoxia during Surgery

The use of an inspiratory oxygen fraction of 0.80 during surgery is a topic of ongoing debate. Opponents claim that increased oxidative stress, atelectasis, and impaired oxygen delivery due to hyperoxic vasoconstriction are detrimental. Proponents point to the beneficial effects on the incidence of surgical site infections and postoperative nausea and vomiting. Also, hyperoxygenation is thought to extend the safety margin in case of acute intraoperative emergencies. This review provides a comprehensive risk-benefit analysis for the use of perioperative hyperoxia in noncritically ill adults based on clinical evidence and supported by physiological deduction where needed. Data from the field of hyperbaric medicine, as a model of extreme hyperoxygenation, are extrapolated to the perioperative setting. We ultimately conclude that current evidence is in favour of hyperoxia in noncritically ill intubated adult surgical patients.

Driving Pressure During General Anesthesia for Open Abdominal Surgery (DESIGNATION): study protocol of a randomized clinical trial

BACKGROUND

Intraoperative driving pressure (ΔP) is associated with development of postoperative pulmonary complications (PPC). When tidal volume (V_T) is kept constant, ΔP may change according to positive end-expiratory pressure (PEEP)-induced changes in lung aeration. ΔP may decrease if PEEP leads to a recruitment of collapsed lung tissue but will increase if PEEP mainly causes pulmonary overdistension. This study tests the hypothesis that individualized high PEEP, when compared to fixed low PEEP, protects against PPC in patients undergoing open abdominal surgery.

METHODS

The "Driving prESsure durIng GeNeral AnesThesIa for Open abdomiNal surgery trial" (DESIGNATION) is an international, multicenter, two-group, double-blind randomized clinical superiority trial. A total of 1468 patients will be randomly assigned to one of the two intraoperative ventilation strategies. Investigators screen patients aged ≥ 18 years and with a body mass index ≤ 40 kg/m², scheduled for open abdominal surgery and at risk for PPC. Patients either receive an intraoperative ventilation strategy with individualized high PEEP with recruitment maneuvers (RM) ("individualized high PEEP") or one in which PEEP of 5 cm H₂O without RM is used ("low PEEP"). In the "individualized high PEEP" group, PEEP is set at the level at which ΔP is lowest. In both groups of the trial, V_T is kept at 8 mL/kg predicted body weight. The primary endpoint is the occurrence of PPC, recorded as a collapsed composite of adverse pulmonary events.

DISCUSSION

DESIGNATION will be the first randomized clinical trial that is adequately powered to compare the effects of individualized high PEEP with RM versus fixed low PEEP without RM on the occurrence of PPC after open abdominal surgery. The results of DESIGNATION will support anesthesiologists in their decisions regarding PEEP settings during open abdominal surgery.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03884543. Registered on 21 March 2019.

Comparative effects of open-lung positive end-expiratory pressure (PEEP) and fixed PEEP on respiratory system compliance in the isoflurane anaesthetised healthy dog

This study was performed to assess the effects of open-lung positive end-expiratory pressure (OL-PEEP) following stepwise recruitment manoeuvre (RM) and those of a fixed PEEP of 5 cm H₂O without previous RM on respiratory system compliance (Crs) and selected cardiovascular variables in healthy dogs under general anaesthesia. Forty-five healthy client-owned dogs undergoing surgery were anaesthetised and mechanically ventilated (tidal volume, VT = 10-12 mL/kg; PEEP = 0 cm H₂O) for 1 min (baseline) and randomly allocated into zero positive end-expiratory pressure (ZEEP), PEEP (5 cm H₂O) and OL-PEEP treatment groups. In the OL-PEEP group, a stepwise RM was performed and the individual OL-PEEP was subsequently applied. The Crs, heart rate (HR) and non-invasive mean arterial pressure (NIMAP) were registered at baseline and then every 10 min during 60 min. In the ZEEP group, Crs decreased from baseline. In the PEEP group, Crs was not different from either baseline or ZEEP group values. In the OL-PEEP group, Crs was higher than both baseline and ZEEP group values at all time points as well as of those in the PEEP group during at least 20 min after RM. There were no differences for HR and NIMAP between groups. A clinically relevant hypotension following RM was observed in 40% of dogs. Therefore, an individually set OL-PEEP following stepwise RM improved Crs in anaesthetised healthy dogs, although transient but clinically relevant hypotension was observed during RM in some dogs. Fixed PEEP of 5 cm H₂O without previous RM did not improve Crs, although it prevented it from decreasing.

Positive End-expiratory Pressure Alone Minimizes Atelectasis Formation in Nonabdominal Surgery: A Randomized Controlled Trial

BACKGROUND

Various methods for protective ventilation are increasingly being recommended for patients undergoing general anesthesia. However, the importance of each individual component is still unclear. In particular, the perioperative use of positive end-expiratory pressure (PEEP) remains controversial. The authors tested the hypothesis that PEEP alone would be sufficient to limit atelectasis formation during nonabdominal surgery.

METHODS

This was a randomized controlled evaluator-blinded study. Twenty-four healthy patients undergoing general anesthesia were randomized to receive either mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index (n = 12) or zero PEEP (n = 12). No recruitment maneuvers were used. The primary outcome was atelectasis area as studied by computed tomography in a transverse scan near the diaphragm, at the end of surgery, before emergence. Oxygenation was evaluated by measuring blood gases and calculating the ratio of arterial oxygen partial pressure to inspired oxygen fraction (PaO2/FIO2 ratio).

RESULTS

At the end of surgery, the median (range) atelectasis area, expressed as percentage of the total lung area, was 1.8 (0.3 to 9.9) in the PEEP group and 4.6 (1.0 to 10.2) in the zero PEEP group. The difference in medians was 2.8% (95% CI, 1.7 to 5.7%; P = 0.002). Oxygenation and carbon dioxide elimination were maintained in the PEEP group, but both deteriorated in the zero PEEP group.

CONCLUSIONS

During nonabdominal surgery, adequate PEEP is sufficient to minimize atelectasis in healthy lungs and thereby maintain oxygenation. Thus, routine recruitment maneuvers seem unnecessary, and the authors suggest that they should only be utilized when clearly indicated.

VISUAL ABSTRACT

An online visual overview is available for this article at http://links.lww.com/ALN/B728.

Analysis of different levels of positive end-expiratory pressure during lung retrieval for transplantation: an experimental study

Atelectasis and inadequate oxygenation in lung donors is a common problem during the retrieval of these organs. Nevertheless, the use of high positive end-expiratory pressure (PEEP) is not habitual during procedures of lung retrieval. Twenty-one Sprague-Dawley male consanguineous rats were used in the study. The animals were divided into 3 groups according to the level of PEEP used: low (2 cmH2O), moderate (5 cmH2O), and high (10 cmH2O). Animals were ventilated with a tidal volume of 6 mL/kg. Before lung removal, the lungs were inspected for the presence of atelectasis. When atelectasis was detected, alveolar recruitment maneuvers were performed. Blood gasometric analysis was performed immediately. Finally, the lungs were retrieved, weighed, and submitted to histological analysis. The animals submitted to higher PEEP showed higher levels of oxygenation with the same tidal volumes PO2=262.14 (PEEP 2), 382.4 (PEEP 5), and 477.0 (PEEP 10). The occurrence of atelectasis was rare in animals with a PEEP of 10 cmH2O, which therefore required less frequent recruitment maneuvers (need for recruitment: PEEP 2=100%, PEEP 5 =100%, and PEEP 10=14.3%). There was no change in hemodynamic stability, occurrence of pulmonary edema, or other histological injuries with the use of high PEEP. The use of high PEEP (10 cmH2O) was feasible and probably a beneficial strategy for the prevention of atelectasis and the optimization of oxygenation during lung retrieval. Clinical studies should be performed to confirm this hypothesis.

Effectiveness and pulmonary complications of perioperative laryngeal mask airway used in elderly patients (POLMA-EP trial): study protocol for a randomized controlled trial

Background

With the increasing amount of geriatric surgery, it has become a great challenge for anesthesiologists to reduce the incidence of postoperative pulmonary complications (PPCs). The two most popular airway management methods, laryngeal mask airway (LMA) and endotracheal intubation (ETI), both have their unique advantages in specific clinical settings. For the purpose of helping clinicians make better decisions on airway management during geriatric surgery, we designed this multi-center clinical trial to compare the influence of LMA and ETI on PPCs.

Methods/design

In this multi-center, randomized, parallel clinical trial, a total of 6000 elderly patients, aged ≥ 70 years, with an American Society of Anesthesiologists classification level of 1–2 and a body mass index ≤ 35 kg/m², undergoing elective surgery will be enrolled and randomized into the LMA or the ETI group. Both groups will receive usual perioperative care except for the adoption of LMA/ETI. Primary outcomes are the occurrence of PPCs and patients’ perioperative mortality rates. Ease of intubation, anesthetics consumption, treatment for PPCs, duration of surgery, anesthesia recovery time and performance, time of PPC onset, postanesthesia care unit stay, intensive care unit admission and stay, in-hospital days, re-admission rates, hospitalization cost, and patients’ satisfactory scores will be secondary outcomes. Follow-up will be conducted through phone-call visits until 12 weeks after discharge.

Discussion

This trial will assess the possible benefits or disadvantages of perioperative LMA use in elderly patients compared with ETI regarding the occurrence of PPCs and clinical prognosis. We expect that this trial will also add to the current understanding of PPCs in geriatric populations and contribute to the international recommendations of geriatric surgery management.

Trial registration

ClinicalTrials.gov, NCT02240901. Registered on 16 September 2014.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3351-2) contains supplementary material, which is available to authorized users.

Respiratory complications of anaesthesia

Postoperative pulmonary complications are a major determinant of outcome for patients and consume huge resources within hospital, particularly in critical care. Prediction and anticipation of postoperative pulmonary complications are vital for patient selection and, in some cases, for informed patient consent. Being able to assess the likelihood of postoperative pulmonary complications also allows research into methods to reduce them by allowing allocation of patients to the appropriate arms of research trials. Some patients have pre-operative characteristics or belong to patient groups such as those with chronic obstructive pulmonary disease or obstructive sleep apnoea, where techniques and evidence-based guidance to avoid or reduce complications are becoming established. Intra-operative ventilation and the use of lung-protective ventilation may be helpful during major surgery, but studies looking at reduced tidal volumes, recruitment and levels of positive end-expiratory pressure, have this far only led to a degree of consensus in terms of tidal volume, although parameters that predispose to postoperative pulmonary complications are becoming clearer. Optimal postoperative care in terms of analgesia, positioning, physiotherapy and mobilisation is another developing area. Techniques such as continuous positive airways pressure, non-invasive ventilation and high-flow nasal humidified oxygen appear to show some benefit, but the exact roles, pressures and timings of each are currently being explored. Much remains to be researched and developed into evidence-based practice.

Low tidal volume ventilation strategy and organ functions in patients with pre-existing systemic inflammatory response

Background and Aims

Ventilation can induce increase in inflammatory mediators that may contribute to systemic organ dysfunction. Ventilation-induced organ dysfunction is likely to be accentuated if there is a pre-existing systemic inflammatory response.

Material and Methods

Adult patients suffering from intestinal perforation peritonitis-induced systemic inflammatory response syndrome and scheduled for emergency laparotomy were randomized to receive intraoperative ventilation with 10 ml.kg^-1 tidal volume (Group H) versus lower tidal volume of 6 ml.kg^-1 along with positive end-expiratory pressure (PEEP) of 10 cmH₂O (Group L), (n = 45 each). The primary outcome was postoperative organ dysfunction evaluated using the aggregate Sepsis-related Organ Failure Assessment (SOFA) score. The secondary outcomes were, inflammatory mediators viz. interleukin-6, tumor necrosis factor-α, procalcitonin, and C-reactive protein, assessed prior to (basal) and 1 h after initiation of mechanical ventilation, and 18 h postoperatively.

Results

The aggregate SOFA score (3[1-3] vs. 1[1-3]); and that on the first postoperative day (2[1-3] vs. 1[0-3]) were higher for group L as compared to group H (P < 0.05). All inflammatory mediators were statistically similar between both groups at all time intervals (P > 0.05).

Conclusions

Mechanical ventilation with low tidal volume of 6 ml/kg^-1 along with PEEP of 10 cmH₂O is associated with significantly worse postoperative organ functions as compared to high tidal volume of 10 ml.kg^-1 in patients of perforation peritonitis-induced systemic inflammation undergoing emergency laparotomy.

Comparison of the effects of different positive end-expiratory pressure levels on respiratory mechanics and oxygenation in laparoscopic surgery: A protocol for systematic review and network meta-analyses

BACKGROUND

Several studies have observed the good effects of positive end-expiratory pressure (PEEP) application in laparoscopic surgeries, such as counteracted intraoperative atelectasis, improved respiratory mechanics, and gas exchange. However, evidence of systematic comparisons of different PEEP levels is short, and the optimal level of PEEP during laparoscopy remains unknown and controversial. The study aims to compare the effects of different PEEP levels on respiratory mechanics and oxygenation in laparoscopic surgery using network meta-analyses.

METHODS

To identify relevant studies, a systematic search will be conducted among electronic databases, including PubMed, Cochrane Library, EMBASE, and Web of Science. We will include randomized controlled trials (RCTs). The risk of bias in the included RCTs will be assessed using the Cochrane bias risk tool. Network meta-analysis will be performed using STATA 15.0, and R 3.4.1 software.

RESULTS

This study is ongoing and the results will be published in a peer-reviewed journal.

CONCLUSION

The results of this study will be sent to clinicians and healthcare providers in the National Health Service, which is expected to help clinicians make more informed treatment decisions and facilitate further research on the use of PEEP during surgery.

PROSPERO REGISTRATION NUMBER

CRD42018093537.

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.

Increasing positive end-expiratory pressure (re-)improves intraoperative respiratory mechanics and lung ventilation after prone positioning

BACKGROUND

Turning a patient prone, changes the respiratory mechanics and potentially the level of positive end-expiratory pressure (PEEP) that is necessary to prevent alveolar collapse. In this prospective clinical study we examined the impact of PEEP on the intratidal respiratory mechanics and regional lung aeration in the prone position. We hypothesized that a higher PEEP is required to maintain compliance and regional ventilation in the prone position.

METHODS

After ethical approval, 45 patients with healthy lungs undergoing lumbar spine surgery were examined in the supine position at PEEP 6 cm H2O and in the prone position at PEEP (6, 9 and 12 cm H2O). Dynamic compliance (CRS) and intratidal compliance-volume curves were determined and regional ventilation was measured using electrical impedance tomography. The compliance-volume curves were classified to indicate intratidal derecruitment, overdistension, or neither.

RESULTS

CRS did not differ between postures and PEEP levels (P>0.28). At a PEEP of 6 cm H2O a compliance-volume profile indicating neither derecruitment nor overdistension was observed in 38 supine, but only in 20 prone positioned patients (P<0.001). The latter increased to 33 and 37 (both P<0.001) when increasing PEEP to 9 and 12 cm H2O, respectively. Increasing PEEP from 6 to 9 cm H2O in the prone position increased peripheral ventilation significantly.

CONCLUSIONS

Respiratory system mechanics change substantially between supine and prone posture, which is not demonstrated in routine measurements. The intratidal compliance analysis suggests that in most patients a PEEP above commonly used settings is necessary to avoid alveolar collapse in the prone position.

CLINICAL TRIAL REGISTRATION

DRKS 00005692.

The effect of positive end-expiratory pressure during anesthesia on arterial oxygen saturation after surgery in patient undergoing cesarean section

One of the major complications of general anesthesia in the recovery room is arterial oxygen desaturation and hypoxemia. Positive end-expiratory pressure (PEEP) can improve arterial oxygen saturation by increasing FRC. This study aims to evaluate the effects of applying PEEP on arterial oxygen saturation and hemodynamic parameters in the patient undergoing cesarean section in VALIASR hospital. In this double blind clinical trial we randomly allocated 120 patients of class1 and 2 ASA scheduled to undergoing cesarean section into 3 group (in 40).Different levels of PEEP (0, 5 and 10 CmH2o) were applied to each group while zero PEEP was established as control. All other variables (anesthesia and surgery techniques) were the same for all patients SPO2, noninvasive mean arterial pressure and heart rate were measured before, during and after surgery (Recovery room). The comparison of noninvasive arterial blood pressure and heart rate during and after surgery did not show significant differences but mean o2 saturation in group B (5 cmH2o PEEP) and C (10 cm H2o PEEP) in PACU was higher than control group (98.30±0.93 and 98.50±0.90 as opposed to97.12±1.15 respectively) P<0.001. In light of results applying PEEP is effective in preventing desaturation after surgery and improving respiratory indexes without the significant hemodynamic changes, the result of using five cmH2o PEEP is more efficient and satisfying.

Intraoperative low tidal volume ventilation strategy has no benefits during laparoscopic cholecystectomy

Background and Aims:

Benefits of intraoperative low tidal volume ventilation during laparoscopic surgery are not conclusively proven, even though its advantages were seen in other situations with intraoperative respiratory compromise such as one-lung ventilation. The present study compared the efficacy of intraoperative low tidal volume ventilatory strategy (6 ml/kg along with positive end-expiratory pressure [PEEP] of 10 cmH₂O) versus one with higher tidal volume (10 ml/kg with no PEEP) on various clinical parameters and plasma levels of interleukin (IL)-6 in patients undergoing laparoscopic cholecystectomy.

Material and Methods:

A total of 58 adult patients with American Society of Anesthesiologists physical status I or II, undergoing laparoscopic cholecystectomy were randomized to receive the low or higher tidal volume strategy as above (n = 29 each). The primary outcome measure was postoperative PaO₂. Systemic levels of IL-6 along with clinical indices of intraoperative gas exchange, pulmonary mechanics, and hemodynamic consequences were measured as secondary outcome measures.

Results:

There was no statistically significant difference in oxygenation; intraoperative dynamic compliance, peak airway pressures, or hemodynamic parameters, or the IL-6 levels between the two groups (P > 0.05). Low tidal volume strategy was associated with significantly higher mean airway pressure, lower airway resistance, greater respiratory rates, and albeit clinically similar, higher PaCO₂and lower pH (P < 0.05).

Conclusion:

Strategy using 6 ml/kg tidal volume along with 10 cmH₂O of PEEP was not associated with any significant improvement in gas exchange, hemodynamic parameters, or systemic inflammatory response over ventilation with 10 ml/kg volume without PEEP during laparoscopic cholecystectomy.

Associations between positive end-expiratory pressure and outcome of patients without ARDS at onset of ventilation: a systematic review and meta-analysis of randomized controlled trials

Background

The aim of this investigation was to compare ventilation at different levels of positive end-expiratory pressure (PEEP) with regard to clinical important outcomes of intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) at onset of ventilation.

Methods

Meta-analysis of randomized controlled trials (RCTs) comparing a lower level of PEEP with a higher level of PEEP was performed. The primary outcome was in-hospital mortality.

Results

Twenty-one RCTs (1393 patients) were eligible. PEEP ranged from 0 to 10 cmH₂O and from 5 to 30 cmH₂O in the lower PEEP and the higher PEEP arms of included RCTs, respectively. In-hospital mortality was not different between the two PEEP arms in seven RCTs (risk ratio [RR] 0.87; 95% confidence interval [CI] 0.62–1.21; I² = 26%, low quality of evidence [QoE]), as was duration of mechanical ventilation in three RCTs (standardized mean difference [SMD] 0.68; 95% CI −0.24 to 1.61; I² = 82%, very low QoE). PaO₂/FiO₂ was higher in the higher PEEP arms in five RCTs (SMD 0.72; 95% CI 0.10–1.35; I² = 86%, very low QoE). Development of ARDS and the occurrence of hypoxemia (2 RCTs) were lower in the higher PEEP arms in four RCTs and two RCTs, respectively (RR 0.43; 95% CI 0.21–0.91; I² = 56%, low QoE; RR 0.42; 95%–CI 0.19–0.92; I² = 19%, low QoE). There was no association between the level of PEEP and any hemodynamic parameter (four RCTs).

Conclusion

Ventilation with higher levels of PEEP in ICU patients without ARDS at onset of ventilation was not associated with lower in-hospital mortality or shorter duration of ventilation, but with a lower incidence of ARDS and hypoxemia, as well as higher PaO₂/FiO₂. These findings should be interpreted with caution, as heterogeneity was moderate to high, the QoE was low to very low, and the available studies prevented us from addressing the effects of moderate levels of PEEP.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0208-7) contains supplementary material, which is available to authorized users.

Effects of positive end-expiratory pressure and 30% inspired oxygen on pulmonary mechanics and atelectasis in cats undergoing non-bronchoscopic bronchoalveolar lavage

Objectives The objective of this study was to determine if modification of inspired oxygen concentration or positive end-expiratory pressure (PEEP) would alter bronchoalveolar lavage (BAL)-induced changes in pulmonary mechanics or atelectasis, as measured using ventilator-acquired pulmonary mechanics and thoracic CT. Methods Six experimentally asthmatic cats underwent anesthesia and non-bronchoscopic BAL, each under four randomized treatment conditions: 100% oxygen, zero PEEP; 30% oxygen, zero PEEP; 100% oxygen, PEEP 2 cmH₂O; and 30% oxygen, PEEP 2 cmH₂O. Pulse oximetry was used to estimate oxygen saturation (SpO₂). Ventilator-acquired pulmonary mechanics and thoracic CT scans were collected prior to BAL and at 1, 5 and 15 mins post-BAL. Results While receiving 100% oxygen, no cat had SpO₂ <91%. Some cats receiving 30% oxygen had decreased saturation immediately post-BAL (mean ± SD 70.8 ± 31%), but 6/8 of these had SpO₂ >90% by 1 min later. There was a significant increase in airway resistance and a decrease in lung compliance following BAL, but there was no significant difference between treatment groups. Cats receiving no PEEP and 30% oxygen conserved better aeration of the lung parenchyma in BAL-sampled areas than those receiving no PEEP and 100% oxygen. Conclusions and relevance Alterations in pulmonary mechanics or atelectasis may not be reflected by SpO₂ following BAL. The use of 30% inspired oxygen concentration failed to show any significant improvement in pulmonary mechanics but did diminish atelectasis. In some cats, it was also associated with desaturation of hemoglobin. The use of PEEP in this study did not show any effect on our outcome parameters. Further studies using higher PEEP (5-10 cmH₂O) and intermediate inspired oxygen concentration (40-60%) are warranted to determine if they would confer clinical benefit in cats undergoing diagnostic BAL.

Effect of positive end-expiratory pressure on blood loss during retropubic and robot-assisted laparoscopic radical prostatectomy

OBJECTIVES

To study the effect of end-expiratory pressure used during anesthesia on blood loss during radical prostatectomy.

METHODS

We evaluated 247 patients who underwent either radical retropubic prostatectomy or robot-assisted laparoscopic prostatectomy at a single institution from 2008 to 2013 by one of four surgeons. Patient characteristics were compared using t-tests, rank sum or χ(2) -tests as appropriate. The association between positive end-expiratory pressure and estimated blood loss was tested using linear regression.

RESULTS

Patients were classified into high (≥4 cmH2 O) and low (≤1 cmH2 O) positive-end expiratory pressure groups. Estimated blood loss in radical retropubic prostatectomy was higher in the high positive end-expiratory pressure group (1000 mL vs 800 mL, P = 0.042). Estimated blood loss in robot-assisted laparoscopic prostatectomy was lower in the high positive end-expiratory pressure group (150 mL vs 250 mL, P = 0.015). After adjusting for other factors known to influence blood loss, a 5-cmH2 O increase in positive end-expiratory pressure was associated with a 34.9% increase in estimated blood loss (P = 0.030) for radical retropubic prostatectomy, and a 33.0% decrease for robot-assisted laparoscopic prostatectomy (P = 0.038).

CONCLUSIONS

In radical retropubic prostatectomy, high positive end-expiratory pressure was associated with higher estimated blood loss, and the benefits of positive end-expiratory pressure should be weighed against the risk of increased estimated blood loss. In robot-assisted laparoscopic prostatectomy, high positive end-expiratory pressure was associated with lower estimated blood loss, and might have more than just pulmonary benefits.

Mechanical ventilation strategies for the surgical patient

PURPOSE OF REVIEW

To summarize clinical evidence for intraoperative ventilation settings, which could protect against postoperative pulmonary complications (PPCs) in surgical patients with uninjured lungs.

RECENT FINDINGS

There is convincing evidence for protection against PPCs by low tidal volumes: benefit was found in several randomized controlled trials, and was recently confirmed in meta-analyses. Evidence for protection against PPCs by high levels of positive end-expiratory pressure (PEEP) is less definite. Although benefit was found in several randomized controlled trials, most of them compared a bundle of low tidal volume and high level of PEEP with conventional ventilation; one recent large randomized controlled trial that compared high with low levels of PEEP showed that ventilation with high level of PEEP did not protect against PPCs but caused intraoperative complications instead. A recent individual patient data meta-analysis of trials comparing bundles of low tidal volume and high levels of PEEP to conventional intraoperative ventilation suggested that protection against PPCs comes from tidal volume reductions, and not from increasing levels of PEEP.

SUMMARY

The understanding on the protective roles of tidal volume and PEEP settings against PPCs has rapidly expanded. During intraoperative ventilation, low tidal volumes are protective, the protective role of high levels of PEEP is uncertain.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.