Respiratory system mechanics in sedated, paralyzed, morbidly obese patients

Physiological and clinical effects of trunk inclination adjustment in patients with respiratory failure: a scoping review and narrative synthesis

BACKGROUND

Adjusting trunk inclination from a semi-recumbent position to a supine-flat position or vice versa in patients with respiratory failure significantly affects numerous aspects of respiratory physiology including respiratory mechanics, oxygenation, end-expiratory lung volume, and ventilatory efficiency. Despite these observed effects, the current clinical evidence regarding this positioning manoeuvre is limited. This study undertakes a scoping review of patients with respiratory failure undergoing mechanical ventilation to assess the effect of trunk inclination on physiological lung parameters.

METHODS

The PubMed, Cochrane, and Scopus databases were systematically searched from 2003 to 2023.

INTERVENTIONS

Changes in trunk inclination.

MEASUREMENTS

Four domains were evaluated in this study: 1) respiratory mechanics, 2) ventilation distribution, 3) oxygenation, and 4) ventilatory efficiency.

RESULTS

After searching the three databases and removing duplicates, 220 studies were screened. Of these, 37 were assessed in detail, and 13 were included in the final analysis, comprising 274 patients. All selected studies were experimental, and assessed respiratory mechanics, ventilation distribution, oxygenation, and ventilatory efficiency, primarily within 60 min post postural change.

CONCLUSION

In patients with acute respiratory failure, transitioning from a supine to a semi-recumbent position leads to decreased respiratory system compliance and increased airway driving pressure. Additionally, C-ARDS patients experienced an improvement in ventilatory efficiency, which resulted in lower PaCO2 levels. Improvements in oxygenation were observed in a few patients and only in those who exhibited an increase in EELV upon moving to a semi-recumbent position. Therefore, the trunk inclination angle must be accurately reported in patients with respiratory failure under mechanical ventilation.

High Frequency Jet Ventilation or Mechanical Ventilation for Panendoscopy for Cervicofacial Cancer: A Retrospective Study

Introduction-the upper airway panendoscopy, performed under general anesthesia, is mandatory for the diagnosis of cervicofacial cancer. It is a challenging procedure because the anesthesiologist and the surgeon have to share the airway space together. There is no consensus about the ventilation strategy to adopt. Transtracheal high frequency jet ventilation (HFJV) is the traditional method in our institution. However, the COVID-19 pandemic forced us to change our practices because HFJV is a high risk for viral dissemination. Tracheal intubation and mechanical ventilation were recommended for all patients. Our retrospective study compares the two ventilation strategies for panendoscopy: high frequency jet ventilation (HFJV) and mechanical ventilation with orotracheal intubation (MVOI). Methods-we reviewed all panendoscopies performed before the pandemic in January and February 2020 (HFJV) and during the pandemic in April and May 2020 (MVOI). Minor patients, patients with a tracheotomy before or after, were excluded. We performed a multivariate analysis adjusted on unbalanced parameters between the two groups to compare the risk of desaturation. Results-we included 182 patients: 81 patients in the HFJV group and 80 in the MVOI group. After adjustments based on BMI, tumor localization, history of cervicofacial cancer surgery, and use of muscle relaxants, the patients from the HFJV group showed significantly less desaturation than the intubation group (9.9% vs. 17.5%, OR_a = 0.18, p = 0.047). Conclusion-HFJV limited the incidence of desaturation during upper airway panendoscopies in comparison to oral intubation.

Effect of Active Physiotherapy With Positive Airway Pressure on Pulmonary Atelectasis After Cardiac Surgery: A Randomized Controlled Study

OBJECTIVES

The authors investigated the effect of active work with positive airway pressure (PAP) in addition to chest physiotherapy (CP) on pulmonary atelectasis (PA) in patients undergoing cardiac surgery with cardiopulmonary bypass.

DESIGN

A randomized controlled study.

SETTING

At a single-center tertiary hospital.

PARTICIPANTS

Eighty adult patients undergoing cardiac surgery (coronary artery bypass grafting, valve surgery, or both), and presenting with PA after tracheal extubation on postoperative days 1 or 2, were randomized from November 2014 to September 2016.

INTERVENTION

Three days of CP, twice daily, associated with active work with PAP effect (intervention group) versus CP alone (control group). Pulmonary atelectasis was assessed by using the radiologic atelectasis score (RAS) measured from daily chest x-rays. All radiographs were reviewed blindly.

MEASUREMENTS AND MAIN RESULTS

Among included patients, 79 (99%) completed the trial. The primary outcome was mean RAS on day 2 after inclusion. It was significantly lower in the intervention group (mean difference and 95% CI: -1.1 [-1.6 to -0.6], p < 0.001). The secondary outcomes were the sniff nasal inspiratory pressure measured before and after CP and clinical variables. Sniff nasal inspiratory pressure was significantly higher in the intervention group on day 2 (7.7 [3.0-12.5] cmH₂O, p = 0.002). The respiratory rate was lower in the intervention group (-3.2 [95% CI -4.8 to -1.6] breaths/min, p < 0.001) on day 2. No differences were found between the 2 groups for percutaneous oxygen saturation/oxygen requirement ratio, heart rate, pain, and dyspnea scores.

CONCLUSIONS

Active work with the PAP effect, combined with CP, significantly decreased the RAS of patients undergoing cardiac surgery after 2 days of CP, with no differences observed in clinically relevant parameters.

Prolonged mechanical ventilation after lung transplantation: risks factors and consequences on recipient outcome

Background

Risk factors and the incidence of prolonged mechanical ventilation (PMV) after lung transplantation (LT) have been poorly described. The study assessed predictive factors of PMV after LT.

Methods

This observational, retrospective, monocentric study included all patients who received LT in Bichat Claude Bernard Hospital between January 2016 and December 2020. PMV was defined as a duration of MV > 14 days. Independent risk factors for PMV were studied using multivariate analysis. One-year survival depending on PMV was studied using Kaplan Meier and log-rank tests. A p value <0.05 was defined as significant.

Results

224 LT recipients were analysed. 64 (28%) of them received PMV for a median duration of 34 [26-52] days versus 2 [1-3] days without PMV. Independent risk factors for PMV were higher body mass index (BMI) (p = 0.031), diabetes mellitus of the recipient (p = 0.039), ECMO support during surgery (p = 0.029) and intraoperative transfusion >5 red blood cell units (p < 0.001). Increased mortality rates were observed at one-year in recipients who received PMV (44% versus 15%, p < 0.001).

Conclusion

PMV was associated with increased morbidity and mortality one-year after LT. Preoperative risk factors (BMI and diabetes mellitus) must be considered when selecting and conditioning the recipients.

Evaluation of the accuracy of established patient inspiratory effort estimation methods during mechanical support ventilation

There is a clinical need for monitoring inspiratory effort to prevent lung- and diaphragm injury in patients who receive supportive mechanical ventilation in an Intensive Care Unit. Different pressure-based techniques are available to estimate this inspiratory effort at the bedside, but the accuracy of their effort estimation is uncertain since they are all based on a simplified linear model of the respiratory system, which omits gas compressibility of air, and the viscoelasticity and nonlinearities of the respiratory system. The aim of this in-silico study was to provide an overview of the pressure-based estimation techniques and to evaluate their accuracy using a more sophisticated model of the respiratory system and ventilator. The influence of the following parameters on the accuracy of the pressure-based estimation techniques was evaluated using the in-silico model: 1) the patient's respiratory mechanics 2) PEEP and the inspiratory pressure of the ventilator 3) gas compressibility of air 4) viscoelasticity of the respiratory system 5) the strength of the inspiratory effort. The best-performing technique in terms of accuracy was the whole breath occlusion. The average error and maximum error were the lowest for all patient archetypes. We found that the error was related to the expansion of gas in the breathing set and lungs and respiratory compliance. However, concerns exist that other factors not included in the model, such as a changed muscle-force relation during an occlusion, might influence the true accuracy. The estimation techniques based on the esophageal pressure showed an error related to the viscoelastic element in the model which leads to a higher error than the occlusion. The error of the esophageal pressure-based techniques is therefore highly dependent on the pathology of the patient and the settings of the ventilator and might change over time while a patient recovers or becomes more ill.

Effect of continuous positive airway pressure on the respiratory system: a comprehensive review

Background

CPAP is characterized by the application of a constant and continuous positive pressure into the patient’s airway. By delivering a constant pressure during both inspiration and expiration, CPAP increases functional residual capacity and opens collapsed or under ventilated alveoli, thus decreasing right to left intrapulmonary shunt and improving oxygenation in obese individuals.

Main body of abstract

Obesity is characterized by several alterations in the mechanics of the respiratory system that tend to further exaggerate impairment of gas exchange rendering these patients prone to perioperative complications, such as hypoxemia, hypercapnia, and atelectasis. Interestingly, CPAP has been advocated as an efficacious modality for prevention and treatment of postoperative atelectasis considered to be the most common postoperative respiratory complication. In OSA, the CPAP device works to splint the airway open and prevent the collapse of the upper airway that is the cardinal event of OSA leading improvement of sleep, quality of life and the reduction of the risks of the cardiovascular and neurocognitive side effects associated with the disease. Besides such a beneficial effect, there are other physiological benefits to CPAP: greater end-expiratory lung volume and consequent increase in oxygen stores, increased tracheal traction to improve upper airway patency and decrease in cardiac after load.

Conclusion

Due to various physiological benefits on the respiratory system CPAP therapy is crucial for the prevention postoperative complications particularly related to obesity and the cornerstone for the treatment of moderate to severe obstructive sleep apnea.

A model-based approach to generating annotated pressure support waveforms

Large numbers of asynchronies during pressure support ventilation cause discomfort and higher work of breathing in the patient, and are associated with an increased mortality. There is a need for real-time decision support to detect asynchronies and assist the clinician towards lung-protective ventilation. Machine learning techniques have been proposed to detect asynchronies, but they require large datasets with sufficient data diversity, sample size, and quality for training purposes. In this work, we propose a method for generating a large, realistic and labeled, synthetic dataset for training and validating machine learning algorithms to detect a wide variety of asynchrony types. We take a model-based approach in which we adapt a non-linear lung-airway model for use in a diverse patient group and add a first-order ventilator model to generate labeled pressure, flow, and volume waveforms of pressure support ventilation. The model was able to reproduce basic measured lung mechanics parameters. Experienced clinicians were not able to differentiate between the simulated waveforms and clinical data (P = 0.44 by Fisher's exact test). The detection performance of the machine learning trained on clinical data gave an overall comparable true positive rate on clinical data and on simulated data (an overall true positive rate of 94.3% and positive predictive value of 93.5% on simulated data and a true positive rate of 98% and positive predictive value of 98% on clinical data). Our findings demonstrate that it is possible to generate labeled pressure and flow waveforms with different types of asynchronies.

Postoperative Recovery Outcomes for Obese Patients Undergoing General Anesthesia: A Meta-Analysis of Randomized Controlled Trials

Purpose

This study was performed to assess the postoperative recovery outcomes in obese patients undergoing general anesthesia.

Methods

The eligible studies were identified from PubMed, EmBase, and the Cochrane library until December 2020. The standard mean differences (SMDs) with 95% confidence intervals (CIs) were used to calculate the role of desflurane, sevoflurane, and propofol on recovery outcomes, and the analyses using the random-effects model.

Results

Eleven randomized controlled trials involving 713 obese patients undergoing general anesthesia were selected for final meta-analysis. We noted desflurane was associated with a shorter time to eye-opening than sevoflurane (SMD: −0.86; 95% CI, −1.43 to −0.28; P = 0.003). The use of desflurane with shorter time to extubation as compared with propofol (SMD: −1.13; 95% CI, −1.52 to −0.73; P < 0.001) or sevoflurane (SMD: −1.19; 95% CI, −2.15 to −0.22; P = 0.016), while sevoflurane was associated with longer time to extubation as compared with propofol (SMD: 1.47; 95% CI, 1.03 to 1.91; P < 0.001). Desflurane were associated with shorter time to stating name as compared with propofol (SMD: −1.40; 95% CI, −2.32 to −0.48; P = 0.003) or sevoflurane (SMD: −2.09; 95% CI, −3.33 to −0.85; P = 0.001). In addition, desflurane was associated with a longer time for orientation to place as compared with propofol (SMD: 0.65; 95% CI, 0.22 to 1.07; P = 0.003), while desflurane with shorter time for orientation to place as compared with sevoflurane (SMD: −0.88; 95% CI, −1.46 to −0.30; P = 0.003).

Conclusions

The use of desflurane could provide better recovery outcomes in obese patients undergoing general anesthesia. Further large-scale trials should be comparison the long-term effectiveness of various anesthetics.

Management of Respiratory Distress and Failure in Morbidly and Super Obese Patients During Critical Care Transport

Morbidly and super obese patients are a unique patient population that presents critical care transport providers with unique clinical and logistical challenges in the setting of respiratory distress and failure. These patients are more likely to have chronic respiratory issues at baseline, unique anatomic and physiologic abnormalities, and other comorbidities that leave them poorly able to tolerate respiratory illness or injury. This requires specialized understanding of their respiratory mechanics as well as how to tailor standard treatment modalities, such as noninvasive ventilation, to meet their needs. Also, careful and deliberate planning is required to address the specific anatomic and physiologic characteristics of this population if intubation and mechanical ventilation are needed. Finally, their dimensions and weight also have distinct consequences on transport vehicle considerations. This article reviews the pathophysiology, management, and critical care transport considerations for this unique patient population in respiratory distress and failure.

Monitoring postoperative lung recovery using electrical impedance tomography in post anesthesia care unit: an observational study

With electrical impedance tomography (EIT) recruitment and de-recruitment phenomena can be quantified and monitored at bedside. The aim was to examine the feasibility of EIT with respect to monitor atelectasis formation and resolution in the post anesthesia care unit (PACU). In this observational study, 107 postoperative patients were investigated regarding the presence and recovery of atelectasis described by the EIT-derived parameters Global Inhomogeneity Index (GI Index), tidal impedance variation (TIV), and the changes in end-expiratory lung impedance (ΔEELI). We examined whether the presence of obesity (ADP group) has an influence on pulmonary recovery compared to normal weight patients (NWP group). During the stay at PACU, measurements were taken every 15 min. GI Index, TIV, and ΔEELI were calculated for each time point. 107 patients were monitored and EIT-data of 16 patients were excluded for various reasons. EIT-data of 91 patients were analyzed off-line. Their length of stay averaged 80 min (25th and 75th quartile 52–112). The ADP group demonstrated a significantly higher GI Index at PACU arrival (p < 0.001). This finding disappeared during their stay at the PACU. Additionally, the ADP group showed a significant increase in ΔEELI between PACU arrival and discharge (p = 0.025). Furthermore, TIV showed a significantly lower value during the first 90 min of PACU stay as compared to the time period thereafter (p = 0.036). Our findings demonstrate that obesity has an influence on intraoperative atelectasis formation and de-recruitment during PACU stay. The application of EIT in spontaneously breathing PACU patients seems meaningful in monitoring pulmonary recovery.

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

OBJECTIVES

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

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

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

MEASUREMENTS

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

MAIN RESULTS

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

CONCLUSIONS

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

The Impact of Obesity in Critical Illness

The prevalence of obesity is rising worldwide. Adipose tissue exerts anatomic and physiological effects with significant implications for critical illness. Changes in respiratory mechanics cause expiratory flow limitation, atelectasis, and V̇/Q̇ mismatch with resultant hypoxemia. Altered work of breathing and obesity hypoventilation syndrome may cause hypercapnia. Challenging mask ventilation and peri-intubation hypoxemia may complicate intubation. Patients with obesity are at increased risk of ARDS and should receive lung-protective ventilation based on predicted body weight. Increased positive end expiratory pressure (PEEP), coupled with appropriate patient positioning, may overcome the alveolar decruitment and intrinsic PEEP caused by elevated baseline pleural pressure; however, evidence is insufficient regarding the impact of high PEEP strategies on outcomes. Venovenous extracorporeal membrane oxygenation may be safely performed in patients with obesity. Fluid management should account for increased prevalence of chronic heart and kidney disease, expanded blood volume, and elevated acute kidney injury risk. Medication pharmacodynamics and pharmacokinetics may be altered by hydrophobic drug distribution to adipose depots and comorbid liver or kidney disease. Obesity is associated with increased risk of VTE and infection; appropriate dosing of prophylactic anticoagulation and early removal of indwelling catheters may decrease these risks. Obesity is associated with improved critical illness survival in some studies. It is unclear whether this reflects a protective effect or limitations inherent to observational research. Obesity is associated with increased risk of intubation and death in SARS-CoV-2 infection. Ongoing molecular studies of adipose tissue may deepen our understanding of how obesity impacts critical illness pathophysiology.

Mortality and Healthcare Utilization of Patients with Compensated Hypercapnia

RATIONALE

Acute hypercapnic respiratory failure has been shown to be associated with worse outcomes for various disease states, but less is known about patients with compensated hypercapnic respiratory failure. Although these patients have a normal pH, it remains unknown whether chronically elevated partial pressures of carbon dioxide (PaCO2), irrespective of etiology, put patients at risk of adverse events.

OBJECTIVES

To understand the burden of and clinical factors associated with morbidity and mortality in patients with compensated hypercapnic respiratory failure.

METHODS

We performed a query of the electronic medical record (EMR) to identify patients hospitalized at the University of Michigan from January 1 - December 31, 2018 who had compensated hypercapnia, using a PaCO2 ≥ 50 mmHg and pH 7.35 - 7.45 on arterial blood gas (ABG). We obtained demographic and clinical data from the EMR. Survival probabilities for PaCO2 subgroups (50.0-54.9; 55.0-64.9; ≥65.0 mmHg) were determined using the Kaplan-Meier product limit estimator. Cox proportional hazard models were constructed to test the association between PaCO2 and all-cause mortality.

RESULTS

We identified 491 patients with compensated hypercapnia. The mean age was 60.5 ± 16.2. Patients were 57.4% male and 86.2% white. The mean pH and PaCO2 were 7.38 ± 0.03 and 58.8 ± 9.7 mmHg respectively. There were a total of 1,030 hospitalizations, with 44.4% of patients having 2 or more admissions. The median numbers of cumulative hospital and ICU days were 21.0 (IQR 11.0-38.0) and 7.0 (IQR 3.0-14.0) respectively. 217 patients (44.2%) died over a median of 592 days. In univariate analysis, every 5-mmHg increase in PaCO2 was associated with a higher risk of all-cause death (HR 1.09; 95% CI 1.03-1.16; p=0.004). This association was maintained after adjusting for age, sex, BMI, and the Charlson comorbidity index (HR 1.09 for every 5-mmHg increase in PaCO2; 95% CI 1.02-1.16; p=0.009). There was a statistically significant interaction between PaCO2 and BMI on mortality (p= 0.01 for the interaction term).

CONCLUSIONS

Patients with compensated hypercapnic respiratory failure have high mortality and healthcare utilization with higher PaCO2 associated with worse survival. Obese hypercapnic patients have higher risk of death with increases in PaCO2.

Multimorbidity and Critical Care Neurosurgery: Minimizing Major Perioperative Cardiopulmonary Complications

With increasing prevalence of chronic diseases, multimorbid patients have become commonplace in the neurosurgical intensive care unit (neuro-ICU), offering unique management challenges. By reducing physiological reserve and interacting with one another, chronic comorbidities pose a greatly enhanced risk of major postoperative medical complications, especially cardiopulmonary complications, which ultimately exert a negative impact on neurosurgical outcomes. These premises underscore the importance of perioperative optimization, in turn requiring a thorough preoperative risk stratification, a basic understanding of a multimorbid patient’s deranged physiology and a proper appreciation of the potential of surgery, anesthesia and neurocritical care interventions to exacerbate comorbid pathophysiologies. This knowledge enables neurosurgeons, neuroanesthesiologists and neurointensivists to function with a heightened level of vigilance in the care of these high-risk patients and can inform the perioperative neuro-ICU management with individualized strategies able to minimize the risk of untoward outcomes. This review highlights potential pitfalls in the intra- and postoperative neuro-ICU period, describes common preoperative risk stratification tools and discusses tailored perioperative ICU management strategies in multimorbid neurosurgical patients, with a special focus on approaches geared toward the minimization of postoperative cardiopulmonary complications and unplanned reintubation.

Effect of recumbency and body condition score on open-lung positive end-expiratory pressure and respiratory system compliance following a stepwise lung recruitment manoeuvre in healthy dogs during general anaesthesia

The aim was to assess the effects of recumbency and body condition score (BCS) on open-lung positive end-expiratory pressure (OL-PEEP) and quasistatic respiratory system compliance (Crs) following stepwise lung recruitment manoeuvre (RM) in healthy dogs under general anaesthesia. Thirty-four dogs were anaesthetised and mechanically ventilated (tidal volume of 10 mL/kg) without PEEP for 1 min (baseline). A stepwise RM was then performed and the individual OL-PEEP was subsequently applied. The Crs was registered at baseline and every 10-min for 50 min after RM. Dogs were classified into either dorsal or lateral recumbency groups, and as normal (score 4-5/9) or high (≥6/9) BCS groups. The OL-PEEP was higher in lateral than in dorsal recumbency (P = .002), but differences were not observed between normal and high BCS (P = .865). The Crs was increased from baseline at all time points after RM in all groups. The Crs did not differ between dorsally and laterally recumbent dogs at any time point. However, the baseline Crs was significantly lower in dogs with a high BCS than in those with a normal BCS (P < .001); therefore, the absolute change from baseline was considered when comparing Crs after the RM and it was similar in both BCS groups. In conclusion, in anaesthetised healthy dogs the OL-PEEP following RM was lower when dogs were positioned in dorsal than in lateral recumbency. The Crs after RM remained unchanged regardless of the dogs' recumbency. A stepwise RM followed by OL-PEEP could compensate for the potential negative impact of moderately increased BCS on Crs.

Effect of moderate elevated intra-abdominal pressure on lung mechanics and histological lung injury at different positive end-expiratory pressures

INTRODUCTION

Intra-abdominal hypertension (IAH) is a well-known phenomenon in critically ill patients. Effects of a moderately elevated intra-abdominal pressure (IAP) on lung mechanics are still not fully analyzed. Moreover, the optimal positive end-expiratory pressure (PEEP) in elevated IAP is unclear.

METHODS

We investigated changes in lung mechanics and transformation in histological lung patterns using three different PEEP levels in eighteen deeply anesthetized pigs with an IAP of 10 mmHg. After establishing the intra-abdominal pressure, we randomized the animals into 3 groups. Each of n = 6 (Group A = PEEP 5, B = PEEP 10 and C = PEEP 15 cmH2O). End-expiratory lung volume (EELV/kg body weight (bw)), pulmonary compliance (Cstat), driving pressure (ΔP) and transpulmonary pressure (ΔPL) were measured for 6 hours. Additionally, the histological lung injury score was calculated.

RESULTS

Comparing hours 0 and 6 in group A, there was a decrease of EELV/kg (27±2 vs. 16±1 ml/kg; p<0.05) and of Cstat (42±2 vs. 27±1 ml/cmH2O; p<0.05) and an increase of ΔP (11±0 vs. 17±1 cmH2O; p<0.05) and ΔPL (6±0 vs. 10±1 cmH2O; p<0.05). In group B, there was no significant change in EELV/kg (27±3 vs. 24±3 ml/kg), but a decrease in Cstat (42±3 vs. 32±1 ml/cmH20; p<0.05) and an increase in ΔP (11±1 vs. 15±1 cmH2O; p<0.05) and ΔPL (5±1 vs. 7±0 cmH2O; p<0.05). In group C, there were no significant changes in EELV/kg (27±2 vs. 29±3 ml/kg), ΔP (10±1 vs. 12±1 cmH2O) and ΔPL (5±1 vs. 7±1 cmH2O), but a significant decrease of Cstat (43±1 vs. 37±1 ml/cmH2O; p<0.05). Histological lung injury score was lowest in group B.

CONCLUSIONS

A moderate elevated IAP of 10 mmHg leads to relevant changes in lung mechanics during mechanical ventilation. In our study, a PEEP of 10 cmH2O was associated with a lower lung injury score and was able to overcome the IAP induced alterations of EELV.

[Preoperative risk and perioperative management of obese patients]

The obese patient is at an increased risk of perioperative complications. Most importantly, these include difficult access to the airways (intubation, difficult or impossible ventilation), and post-extubation respiratory distress secondary to the development of atelectasis or obstruction of the airways, sometimes associated with the use of morphine derivatives. The association of obstructive sleep apnea syndrome (OSA) with obesity is very common, and induces a high risk of peri- and postoperative complications. Preoperative OSA screening is crucial in the obese patient, as well as its specific management: use of continuous positive pre, per and postoperative pressure. For any obese patient, the implementation of protocols for mask ventilation and/or difficult intubation and the use of protective ventilation, morphine-sparing strategies and a semi-seated positioning throughout the care, is recommended, combined with close monitoring postoperatively. The dosage of anesthetic drugs should be based on the theoretical ideal weight and then titrated, rather than dosed to the total weight. Monitoring of neuromuscular blocking should be used where appropriate, as well as monitoring of the depth of anesthesia. The occurrence of intraoperative recall is indeed more frequent in the obese patient than in the non-obese patient. Appropriate prophylaxis against venous thromboembolic disease and early mobilization are recommended, as thromboembolic disease is increased in the obese patient. The use of non-invasive ventilation to prevent the occurrence of acute post-operative respiratory failure and for its treatment is particularly effective in obese patients. In case of admission to ICU, an individualized ventilatory management based on pathophysiology and careful monitoring should be initiated.

[The obese patient and acute respiratory failure, a challenge for intensive care]

As a result of the constantly increasing epidemic of obesity, it has become a common problem in the intensive care unit. Morbid obesity has numerous consequences for the respiratory system. It affects both respiratory mechanics and pulmonary gas exchange, and dramatically impacts on the patient's management and outcome. With the potential for causing devastating respiratory complications, the particular anatomical and physiological characteristics of the respiratory system of the morbidly obese subject should be carefully taken into consideration. The present article reviews the management of obese patients in respiratory failure, from noninvasive ventilation to tracheostomy, including postural and technical issues, and explains the physiologically based ventilatory strategy both for NIV and invasive mechanical ventilation up to the weaning from the ventilatory support.

Ventilation in patients with intra-abdominal hypertension: what every critical care physician needs to know

The incidence of intra-abdominal hypertension (IAH) is high and still underappreciated by critical care physicians throughout the world. One in four to one in three patients will have IAH on admission, while one out of two will develop IAH within the first week of Intensive Care Unit stay. IAH is associated with high morbidity and mortality. Although considerable progress has been made over the past decades, some important questions remain regarding the optimal ventilation management in patients with IAH. An important first step is to measure intra-abdominal pressure (IAP). If IAH (IAP > 12 mmHg) is present, medical therapies should be initiated to reduce IAP as small reductions in intra-abdominal volume can significantly reduce IAP and airway pressures. Protective lung ventilation with low tidal volumes in patients with respiratory failure and IAH is important. Abdominal-thoracic pressure transmission is around 50%. In patients with IAH, higher positive end-expiratory pressure (PEEP) levels are often required to avoid alveolar collapse but the optimal PEEP in these patients is still unknown. During recruitment manoeuvres, higher opening pressures may be required while closely monitoring oxygenation and the haemodynamic response. During lung-protective ventilation, whilst keeping driving pressures within safe limits, higher plateau pressures than normally considered might be acceptable. Monitoring of the respiratory function and adapting the ventilatory settings during anaesthesia and critical care are of great importance. This review will focus on how to deal with the respiratory derangements in critically ill patients with IAH.

Obesity in the critically ill: a narrative review

The World Health Organization defines overweight and obesity as the condition where excess or abnormal fat accumulation increases risks to health. The prevalence of obesity is increasing worldwide and is around 20% in ICU patients. Adipose tissue is highly metabolically active, and especially visceral adipose tissue has a deleterious adipocyte secretory profile resulting in insulin resistance and a chronic low-grade inflammatory and procoagulant state. Obesity is strongly linked with chronic diseases such as type 2 diabetes, hypertension, cardiovascular diseases, dyslipidemia, non-alcoholic fatty liver disease, chronic kidney disease, obstructive sleep apnea and hypoventilation syndrome, mood disorders and physical disabilities. In hospitalized and ICU patients and in patients with chronic illnesses, a J-shaped relationship between BMI and mortality has been demonstrated, with overweight and moderate obesity being protective compared with a normal BMI or more severe obesity (the still debated and incompletely understood "obesity paradox"). Despite this protective effect regarding mortality, in the setting of critical illness morbidity is adversely affected with increased risk of respiratory and cardiovascular complications, requiring adapted management. Obesity is associated with increased risk of AKI and infection, may require adapted drug dosing and nutrition and is associated with diagnostic and logistic challenges. In addition, negative attitudes toward obese patients (the social stigma of obesity) affect both health care workers and patients.

The Crashing Obese Patient

Emergency physicians (EP) frequently resuscitate and manage critically ill patients. Resuscitation of the crashing obese patient presents a unique challenge for even the most skilled physician. Changes in anatomy, metabolic demand, cardiopulmonary reserve, ventilation, circulation, and pharmacokinetics require special consideration. This article focuses on critical components in the resuscitation of the crashing obese patient in the emergency department, namely intubation, mechanical ventilation, circulatory resuscitation, and pharmacotherapy. To minimize morbidity and mortality, it is imperative that the EP be familiar with the pearls and pitfalls discussed within this article.

Acute Lobar Atelectasis

Lobar atelectasis (or collapse) is an exceedingly common, rather predictable, and potentially pathogenic companion to many forms of acute illness, postoperative care, and chronic debility. Readily diagnosed by using routine chest imaging and bedside ultrasound, the consequences from lobar collapse may be minor or serious, depending on extent, mechanism, patient vulnerability, abruptness of onset, effectiveness of hypoxic vasoconstriction, and compensatory reserves. Measures taken to reduce secretion burden, assure adequate secretion clearance, maintain upright positioning, reverse lung compression, and sustain lung expansion accord with a logical physiologic rationale. Both classification and logical approaches to prophylaxis and treatment of lobar atelectasis derive from a sound mechanistic knowledge of its causation.

VE/VCO2 slope in lean and overweight women and its relationship to lean leg mass

Ventilation/carbon dioxide production (VE/VCO2slope) is used clinically to determine cardiorespiratory fitness and morbidity in heart failure (HF). Previously, we demonstrated that lower lean leg mass is associated with high VE/VCO2slope during exercise in HF. In healthy individuals, we evaluated 1) whether VE/VCO2slope differed between lean and overweight women and 2) the relationship between lean leg mass and VE/VCO2slope in overweight sedentary (OWS), overweight trained (OWTR) and lean, trained (LTR) women.

METHODS

Gas exchange and ventilation were collected during a treadmill peak oxygen uptake test (VO2peak) in 40 women [26 OWS (29 ± 7 yrs., mean ± SD), 7 OWTR (33 ± 5 yrs) and 7 LTR (26 ± 6 yrs)]. Body composition was measured by dual X-ray absorptiometry.

RESULTS

VO2peak was highest in LTR (46.6 ± 8 ml/kg/min) compared with OWTR (38.1 ± 4.9 ml/kg/min) and OWS women (25.3 ± 4.8 ml/kg/min, p < 0.05). Lean leg mass was highest in OWTR and lowest in LTR women (p < 0.05). VE/VCO2slope was similar between groups (p > 0.05). Higher lean leg mass was associated with lower VE/VCO2slope in overweight women (OWS + OWTR: r = -0.55, p < 0.001), contrasting with higher VE/VCO2slope in LTR women (r = 0.86, p < 0.001).

CONCLUSIONS

These findings suggest VE/VCO2slope may not differentiate between low and high cardiorespiratory fitness in healthy individuals and muscle mass may play a role in determining the VE/VCO2slope, independent of disease.

The obesity supine death syndrome (OSDS)

The obesity supine death syndrome refers to a catastrophic cascade of cardiorespiratory complications resulting from the supine positioning of a morbidly obese subject which can ultimately lead to death. It was first described in 1977 in two massively obese patients who were forced to lie down for medical procedures. But surprisingly, despite the current worldwide epidemic of obesity, very few cases have been reported yet. It can be assumed that the syndrome is poorly recognized in clinical practice and may participate in the high rate of unexplained death in morbidly obese patients. Based on the previously published cases and on those we met, this review aims at helping clinicians to early detect at-risk patients, to correctly diagnose this dramatic syndrome and to understand the underlying pathophysiology. More importantly, the main objective is to convince the attending clinicians that they have to do everything in their power to prevent obesity supine death syndrome occurrence by maintaining morbidly obese patients in the sitting or upright position whenever possible. When the syndrome unfortunately occurs, the best therapeutic approach is based on the immediate return to sitting position.

Does Pulmonary Artery Systolic Pressure as Estimated by Transthoracic Echocardiography Alter the Effect of Positive End-Expiratory Pressure on Arterial Blood Gases and Hemodynamics in Morbidly Obese Patients?

Background

Positive end-expiratory pressure (PEEP) at the time of induction increases oxygenation by preventing lung atelectasis. However, PEEP may not prove beneficial in all cases. Factors affecting the action of PEEP have not been elucidated well and remain controversial. Pulmonary vasculature has direct bearing on the action of PEEP as has been proven in the previous studies. Thus, this prospective study was planned to evaluate the action of PEEP on the basis of pulmonary artery systolic pressure (PASP) which is noninvasive and easily measured by transthoracic echocardiography.

Materials and Methods

Seventy morbidly obese patients, the American Society of Anesthesiologists Grade II, or III, aged 20-65 years with body mass index >40 kg/m², scheduled for elective laparoscopic bariatric surgery were included. Patients who denied consent, those undergoing emergency and/or open surgery and those requiring >2 attempts for intubation were excluded from the study. Ten patients had to be excluded. Thus, a total of sixty patients participated in the study. Thirty patients received no PEEP at the time of induction while other thirty patients were given a PEEP of 10 cm of H₂O. Serial ABG samples were taken preoperatively, at the time of intubation, 5 min after intubation, and 10 min after intubation. Patients were then divided into four groups on the basis of PASP value of ≤30 mm Hg with and without PEEP or >30 mm Hg with and without PEEP.

Primary Outcome

The primary outcome was the effect of PEEP of 10 cm of H2 O on ABG and hemodynamics in morbidly obese patients.

Secondary Outcome

The secondary outcome was the effect of PASP on the action of PEEP in morbidly obese patients undergoing laparoscopic surgery.

Results

Patients having PASP of >30 mm Hg had significant improvement in oxygenation on PEEP application (270.11 ± 119.26 mm Hg) as compared to those without PEEP (157.57 ± 109.29 mm Hg) just after intubation. The increase in oxygenation remained significant at all time intervals. Patients with PASP ≤30 mm Hg did not show significant improvement in oxygenation with PEEP application (177.09 ± 85.85 mm Hg as compared to 226.27 ± 92.42 mm Hg without PEEP). Hemodynamic parameters did not show statistically significant alterations.

Conclusion

Morbidly obese patients who have PASP >30 mm Hg benefit most from the PEEP. Thus, PASP which is an easily measurable noninvasive parameter can be used as a criterion for selecting patients who benefit from PEEP application.

Controlled invasive mechanical ventilation strategies in obese patients undergoing surgery

INTRODUCTION

The obesity prevalence is increasing in surgical population. As the number of obese surgical patients increases, so does the demand for mechanical ventilation. Nevertheless, ventilatory strategies in this population are challenging, since obesity results in pathophysiological changes in respiratory function. Areas covered: We reviewed the impact of obesity on respiratory system and the effects of controlled invasive mechanical ventilation strategies in obese patients undergoing surgery. To date, there is no consensus regarding the optimal invasive mechanical ventilation strategy for obese surgical patients, and no evidence that possible intraoperative beneficial effects on oxygenation and mechanics translate into better postoperative pulmonary function or improved outcomes. Expert commentary: Before determining the ideal intraoperative ventilation strategy, it is important to analyze the pathophysiology and comorbidities of each obese patient. Protective ventilation with low tidal volume, driving pressure, energy, and mechanical power should be employed during surgery; however, further studies are required to clarify the most effective ventilation strategies, such as the optimal positive end-expiratory pressure and whether recruitment maneuvers minimize lung injury. In this context, an ongoing trial of intraoperative ventilation in obese patients (PROBESE) should help determine the mechanical ventilation strategy that best improves clinical outcome in patients with body mass index≥35kg/m².

Mechanical ventilation in obese ICU patients: from intubation to extubation

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

High Positive End-Expiratory Pressure Is Associated with Improved Survival in Obese Patients with Acute Respiratory Distress Syndrome

BACKGROUND

In acute respiratory distress syndrome, minimizing lung injury from repeated collapse and reopening of alveoli by applying a high positive end-expiratory pressure improves oxygenation without influencing mortality. Obesity causes alveolar atelectasis, thus suggesting that a higher positive end-expiratory pressure might be more protective among the obese. We hypothesized that the effect of applying a high positive end-expiratory pressure on mortality from acute respiratory distress syndrome would differ by obesity status.

METHODS

This was a retrospective analysis of 505 patients from the Assessment of Low tidal Volume and elevated End-expiratory volume to Obviate Lung Injury Trial, a multicenter randomized trial that compared a higher vs a lower positive end-expiratory pressure ventilatory strategy in acute respiratory distress syndrome. We examined the relationship between positive end-expiratory pressure strategy and 60-day mortality stratified by obesity status.

RESULTS

Among obese patients with acute respiratory distress syndrome, those assigned to a high positive end-expiratory pressure strategy experienced lower mortality compared with those assigned to a low strategy (18% vs 32%; P = .04). Among the nonobese, those assigned to high positive end-expiratory pressure strategy experienced similar mortality with those assigned to low strategy (34% vs 23%; P = .13). Multivariate analysis demonstrated an interaction between obesity status and the effect of positive end-expiratory pressure strategy on mortality (P <.01).

CONCLUSIONS

Ventilation with higher levels of positive end-expiratory pressure was associated with improved survival among the subgroup of patients with acute respiratory distress syndrome who are obese.

Single Minute of Positive End-expiratory Pressure at the Time of Induction: Effect on Arterial Blood Gases and Hemodynamics in Morbidly Obese Patients Undergoing Laparoscopic Bariatric Surgery

Background:

The effect of positive end-expiratory pressure (PEEP) has been studied in detail after induction of general anesthesia especially in obese individuals. However, sparse information can be gathered from the literature regarding its effect when applied at the time of induction and the time of onset of its effect. Thus, this study was planned to assess the effect of PEEP when applied for a single minute in morbidly obese patients.

Materials and Methods:

This was a randomized prospective study comprising seven morbidly obese patients (body mass index ≥40 kg/m²). Control group included 30 patients who received no PEEP at the time of induction. The study group consisted of thirty patients who were given a PEEP of 10 cmH₂O. Serial arterial blood gas samples were taken preoperatively, at the time of intubation, 5 min after intubation and 10 min after intubation.

Results:

PaO₂ was significantly higher in test group (242.0 ± 116.0 mmHg) than in control group (183.0 ± 107.0 mmHg) just after intubation. PaCO₂ was comparable in control group (43.73 ± 6.32 mmHg) and test group (44.52 ± 6.33 mmHg) just after intubation but was significantly less in test group than in control group at 5 and 10 min thereafter. Hemodynamic parameters were comparable in both groups at all time intervals.

Conclusion:

Application of even a single minute of PEEP at the time of induction improves oxygenation without any adverse effects on hemodynamics, in morbidly obese patients undergoing laparoscopic Bariatric surgery.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Determining respiratory system resistance and reactance by impulse oscillometry in obese individuals

Objective:

To evaluate peripheral respiratory system resistance and reactance (Rrs and Xrs, respectively) in obese individuals.

Methods:

We recruited 99 individuals, dividing them into four groups by body mass index (BMI): < 30.0 kg/m² (control, n = 31); 30.0-39.9 kg/m² (obesity, n = 13); 40.0-49.9 kg/m² (severe obesity, n = 28); and ≥ 50.0 kg/m² (morbid obesity, n = 13). Using impulse oscillometry, we measured total Rrs, central Rrs, and Xrs. Peripheral Rrs was calculated as the difference between total Rrs and central Rrs. All subjects also underwent spirometry.

Results:

Of the 99 individuals recruited, 14 were excluded because they failed to perform forced expiratory maneuvers correctly during spirometry. The individuals in the severe obesity and morbid obesity groups showed higher peripheral Rrs and lower Xrs in comparison with those in the two other groups.

Conclusions:

Having a BMI ≥ 40 kg/m² was associated with a significant increase in peripheral Rrs and with a decrease in Xrs.

Perioperative risk factors for postoperative pulmonary complications after major oral and maxillofacial surgery with microvascular reconstruction: A retrospective analysis of 648 cases

BACKGROUND

Postoperative pulmonary complications (PPCs) are common and result in prolonged hospital stays, higher costs and increased mortality. However, data on the incidence and predictors of PPCs after major oral and maxillofacial surgery with microvascular reconstruction are rare. This retrospective analysis identifies perioperative risk factors for postoperative pulmonary complications (PPCs) after major oral and maxillofacial surgery with microvascular reconstruction.

METHODS

Perioperative data and patient records of 648 subjects were analyzed in the period of June 2007 to May 2013. PPCs were defined as pneumonia, atelectasis, pleural effusions, pulmonary embolism, pulmonary oedema, pneumothorax or respiratory failure.

RESULTS

18.8% of all patients developed PPCs. Patient-related risk factors for PPCs were male sex, advanced age, smoking, alcohol abuse, a body mass index >30, American Society of Anaesthesiologists grade higher than 2, pre-existent pulmonary diseases and preoperative antihypertensive medication. Among the investigated procedure-related variables, the length of the operation, the amount of fluid administration and blood transfusion and an impaired oxygenation index during surgery were shown to be associated with the development of PPCs. Using a multivariable logistic regression model, we identified a body mass index >30, American Society of Anaesthesiologists grade higher than 2 and alcohol abuse as independent risk factors for PPCs.

CONCLUSIONS

Several perioperative factors can be identified that are associated with the development of PPCs. Patients having one or more of these conditions should be subjected to intensified postoperative pulmonary care.

Obesity in the intensive care unit: risks and complications

The steady growing prevalence of critically ill obese patients is posing diagnostic and management challenges across medical and surgical intensive care units. The impact of obesity in the critically ill patients may vary by type of critical illness, obesity severity (obesity distribution) and obesity-associated co-morbidities. Based on pathophysiological changes associated with obesity, predominately in pulmonary reserve and cardiac function, critically ill obese patients may be at higher risk for acute cardiovascular, pulmonary and renal complications in comparison to non-obese patients. Obesity also represents a dilemma in the management of other critical care areas such as invasive mechanical ventilation, mechanical ventilation liberation, hemodynamic monitoring and pharmacokinetics dose adjustments. However, despite higher morbidity associated with obesity in the intensive care unit (ICU), a paradoxical lower ICU mortality ("obesity paradox") is demonstrated in comparison to non-obese ICU patients. This review article will focus on the unique pathophysiology, challenges in management, and outcomes associated with obesity in the ICU.

Effect of body mass index in acute respiratory distress syndrome

BACKGROUND

Obesity is associated in healthy subjects with a great reduction in functional residual capacity and with a stiffening of lung and chest wall elastance, which promote alveolar collapse and hypoxaemia. Likewise, obese patients with acute respiratory distress syndrome (ARDS) could present greater derangements of respiratory mechanics than patients of normal weight.

METHODS

One hundred and one ARDS patients were enrolled. Partitioned respiratory mechanics and gas exchange were measured at 5 and 15 cm H2O of PEEP with a tidal volume of 6-8 ml kg(-1) of predicted body weight. At 5 and 45 cm H2O of PEEP, two lung computed tomography scans were performed.

RESULTS

Patients were divided as follows according to BMI: normal weight (BMI≤25 kg m(-2)), overweight (BMI between 25 and 30 kg m(-2)), and obese (BMI>30 kg m(-2)). Obese, overweight, and normal-weight groups presented a similar lung elastance (median [interquartile range], respectively: 17.7 [14.2-24.8], 20.9 [16.1-30.2], and 20.5 [15.2-23.6] cm H2O litre(-1) at 5 cm H2O of PEEP and 19.3 [15.5-26.3], 21.1 [17.4-29.2], and 17.1 [13.4-20.4] cm H2O litre(-1) at 15 cm H2O of PEEP) and chest elastance (respectively: 4.9 [3.1-8.8], 5.9 [3.8-8.7], and 7.8 [3.9-9.8] cm H2O litre(-1) at 5 cm H2O of PEEP and 6.5 [4.5-9.6], 6.6 [4.2-9.2], and 4.9 [2.4-7.6] cm H2O litre(-1) at 15 cm H2O of PEEP). Lung recruitability was not affected by the body weight (15.6 [6.3-23.4], 15.7 [9.8-22.2], and 11.3 [6.2-15.6]% for normal-weight, overweight, and obese groups, respectively). Lung gas volume was significantly lower whereas total superimposed pressure was significantly higher in the obese compared with the normal-weight group (1148 [680-1815] vs 827 [686-1213] ml and 17.4 [15.8-19.3] vs 19.3 [18.6-21.7] cm H2O, respectively).

CONCLUSIONS

Obese ARDS patients do not present higher chest wall elastance and lung recruitability.

Intrinsic positive end-expiratory pressure during ventilation through small endotracheal tubes during general anesthesia: incidence, mechanism, and predictive factors

STUDY OBJECTIVE

To assess the safety of mechanical ventilation and effectiveness of extrinsic positive end-expiratory pressure (PEEP) (PEEPe) in improving peripheral oxygen saturation (SpO2) during direct microlaryngeal laser surgery; to assess the incidence, amount, and nature (dynamic hyperinflation or airflow obstruction) of ensuing intrinsic PEEP (PEEPi); and to find a surrogate PEEPi indicator.

DESIGN

Quasiexperimental.

SETTING

S. Raffaele Hospital (Milano), November 2009 to December 2010.

PATIENTS

Fifty-two adults scheduled for direct microlaryngeal laser surgery. Exclusion criterion is pregnancy.

INTERVENTIONS

Twenty-one percent O2 mechanical ventilation through 4.5- to 5.5-mm internal diameter endotracheal tubes; in 29 patients, after measurement of PEEPi, an identical amount of PEEPe was added; and PEEPi.

MEASUREMENTS

SpO2, peak (Pawpeak) and plateau (Pawplateau) airway pressure, and end-expiratory carbon dioxide were measured every 5 minutes. Respiratory compliance (Crs) was computed. PEEPi was measured (end-expiratory occlusion method).

MAIN RESULTS

PEEPi ≥5 cm H2O occurred in 14 patients (27%) after intubation, in 16 (30%) at the beginning, and in 14 (27.3%) at the end of surgery. Thirty-one patients (59.4%) exhibited PEEPi ≥5 cm H2O on at least 1 time point. PEEPi at the beginning of surgery was positively correlated with Pawplateau, Crs, tidal volume, and body mass index. Body mass index was the only predictor for the occurrence of PEEPi ≥5 cm H2O. At the beginning of surgery, the Pawplateau receiver operating characteristic curve predicting PEEPi ≥5 cm H2O had area under the receiver operating characteristic curve of 0.85; best cutoff value of 15.5 cm H2O (sensitivity, 88.9%; specificity, 75%; correctly classified cases, 86.1%). When PEEPe was applied, in 23 cases (82.1%), total PEEP equaled PEEPe+ PEEPi; in 3 (10.7%), it was lower; and in 2 (7.1%), it was higher. Application of PEEPe increased SpO2 (P< .05) and Crs (P< .05).

CONCLUSIONS

During ventilation through small endotracheal tubes, PEEPi (mostly due to dynamic hyperinflation) is common. Hemodynamic complications, barotrauma, and O2 desaturation (reversible with PEEPe) are rare. Pawplateau provided by ventilators is useful in suspecting and monitoring the occurrence of PEEPi and allows detection of lung overdistension as PEEPe is applied.

Bronchospasm in obese patients undergoing elective laparoscopic surgery under general anesthesia

Background

Existing data suggest that obesity correlates with airway hyper-reactivity. However, the incidence of bronchospasm during bariatric surgery in obese patients has not been well studied.

Methods

This was a prospective observational study comparing 50 obese versus 50 non obese patients undergoing elective laparoscopic surgery over a 2 year period. Bronchospasm was detected clinically by auscultation and was confirmed by measuring peak airway pressure during mechanical ventilation. Blood gases were measured at predetermined time intervals intraoperatively. Categorical variables were analyzed using Fisher’s exact test, while numerical variables within and between groups were compared using repeated measures general linear model.

Results

The incidence of bronchospasm was significantly higher in obese compared to non obese patients (P = 0.027). Peak airway pressures and blood gases differed significantly when comparing non obese patients versus obese patients without bronchospasm versus obese patients with bronchospasm. Hypoventilation resulting in gradual increase of arterial PaCO₂ was noted in all groups during surgery.

Conclusion

The incidence of bronchospasm is higher in obese patients compared to non obese patients undergoing elective laparoscopic surgery. Airway pressures and blood gas values in obese patients are somewhere between values in non obese patients and values in patients with bronchospasm, thereby implying that obesity is associated with a state where bronchial smooth muscles are not fully relaxed. Consideration of increased airway reactivity in obese patients undergoing laparoscopic surgery is important for improved patient care and uneventful anesthetic course.

Brazilian recommendations of mechanical ventilation 2013. Part 2

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumologia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Epidural anesthesia for laparoscopic bariatric surgery: a case report

Background

Rapid and uneventful postoperative recovery following general anesthesia in morbidly obese patients undergoing bariatric surgery may offer challenges to anesthesiologists. With improved surgical techniques and shorter pneumoperitoneum, regional anesthesia may be considered for this laparoscopic procedure in selected cases.

Case description

The first patient was a 60-year-old male (body mass index: 39 kg/m²) who was scheduled for laparoscopic sleeve gastrectomy. The second patient was a 46-year-old female (body mass index: 47 kg/m²) who was scheduled for laparoscopic gastric bypass. After standard intraoperative monitoring was applied, epidural anesthesia was performed at thoracic level T9–T10. Surgical technique modification included insufflation of CO₂ at a low flow rate and avoidance of orogastric tube use. During the procedure, both patients breathed spontaneously without difficulty. One hypotension episode occurred and was successfully treated with a 12-mg bolus of ephedrine in case 1. Shoulder pain occurred intraoperatively in case 2 and was successfully treated with a 50-μg bolus of fentanyl. Postoperatively, 2 mg epidural morphine was administered for postoperative analgesia. Both patients were satisfied with the anesthesia technique and was discharged uneventfully.

Discussion and evaluation

This anesthetic technique may maintain pre-operative respiratory function, increase alertness, and reduce the use of rescue analgesics, which is crucial for optimal outcomes in morbidly obese patients. Conversion of epidural anesthesia to general anesthesia may be required if patients can not tolerate the laparoscopic procedure (e.g. intolerable shoulder pain) or the increased respiratory rate during pneumoperitoneum leading to difficulty in performing laparoscopic surgery. Further studies are needed to elucidate this issue.

Conclusions

General anesthesia is widely used for laparoscopic bariatric surgery, but epidural anesthesia may be a viable alternative to general anesthesia in selected cases. Further prospective studies may be required to elucidate the relative advantages and disadvantages of epidural anesthesia in this surgical population.

Physiological and management implications of obesity in critical illness

Obesity is highly prevalent in the United States and is becoming increasingly common worldwide. The anatomic and physiological changes that occur in obese individuals may have an impact across the spectrum of critical illness. Obese patients may be more susceptible to hypoxemia and hypercapnia. During mechanical ventilation, elevated end-expiratory pressures may be required to improve lung compliance and to prevent ventilation-perfusion mismatch due to distal airway collapse. Several studies have shown an increased risk of organ dysfunction such as the acute respiratory distress syndrome and acute kidney injury in obese patients. Predisposition to ventricular hypertrophy and increases in blood volume should be considered in fluid management decisions. Obese patients have accelerated muscle losses in critical illness, making nutrition essential, although the optimal predictive equation to estimate nutritional needs or formulation for obese patients is not well established. Many common intensive care unit medications are not well studied in obese patients, necessitating understanding of pharmacokinetic concepts and consultation with pharmacists. Obesity is associated with higher risk of deep venous thrombosis and catheter-associated bloodstream infections, likely related to greater average catheter dwell times. Logistical issues such as blood pressure cuff sizing, ultrasound assistance for procedures, diminished quality of some imaging modalities, and capabilities of hospital equipment such as beds and lifts are important considerations. Despite the physiological alterations and logistical challenges involved, it is not clear whether obesity has an effect on mortality or long-term outcomes from critical illness. Effects may vary by type of critical illness, obesity severity, and obesity-associated comorbidities.

Intraoperative mechanical ventilation strategies for obese patients: a systematic review and network meta-analysis

Several intraoperative ventilation strategies are available for obese patients. However, the same ventilation interventions have exhibited different effects on PaO2 /FIO2 concerning obese patients in different trials, and the issue remains controversial. Therefore, we conducted a network meta-analysis to identify the optimal mechanical ventilation strategy. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, Embase, MEDLINE, CINAHL and Web of Science for studies published up to June 2014, and the PaO2 /FIO2 in obese patients given different mechanical ventilation strategies was assessed. We assessed the studies for eligibility and extracted data and then pooled the data and used a Bayesian fixed-effect model to combine direct comparisons with indirect evidence. Eligible studies evaluated different ventilation strategies for obese patients and reported the intraoperative PaO2 /FIO2 ratio, atelectasis and pulmonary compliance. Thirteen randomized controlled trials were included for network meta-analysis, including 476 patients who received 1 of 12 ventilation strategies. Volume-controlled ventilation with higher PEEP plus single recruitment manoeuvres (VCV + higher PEEP + single RM) was associated with the highest PaO2 /FiO2 ratio, improving intraoperative pulmonary compliance and reducing the incidence of intraoperative atelectasis.