Physiology of gas exchange during anaesthesia:

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.

Analgesia-based Sedation for Oral Surgery in Patients With Chronic Respiratory Obstructive Disease

Chronic obstructive pulmonary disease (COPD) is a risk factor for postoperative cardiovascular and respiratory complications. Thus, intravenous sedation can be a better option than general anesthesia for surgery in patients with severe COPD. Herein, we present 2 cases of analgesia-based sedation in patients with severe COPD who underwent oral surgery. The current study aimed to discuss these cases to provide knowledge about the appropriate sedation management in patients with this disease. In the current cases, the patients received sufficient analgesia and minimum sedation (analgesia-based sedation). Moreover, dexmedetomidine was used for maintaining sedation and fentanyl for analgesic effects. Furthermore, we focused on providing the maximum analgesic effect of local anesthesia. The patients' vital signs were stable. They did not have any psychological or physical complaints, such as anxiety and pain, during the procedure. Then, they were discharged from the hospital without any complications. Thus, analgesia-based sedation can be an alternative option for oral surgery in patients with COPD.

Effect of differences in extubation timing on postoperative pneumonia following meningioma resection: a retrospective cohort study

Background

This study was designed to examine extubation time and to determine its association with postoperative pneumonia (POP) after meningioma resection.

Methods

We studied extubation time for 598 patients undergoing meningioma resection from January 2016 to December 2020. Extubation time was analysed as a categorical variable and patients were grouped into extubation within 21 minutes, 21–35 minutes and ≥ 35 minutes. Our primary outcome represented the incidence of POP. The association between extubation time and POP was assessed using multivariable logistic regression mixed-effects models which adjusted for confounders previously reported. Propensity score matching (PSM) was also performed at a ratio of 1:1 to minimize potential bias.

Results

Among 598 patients (mean age 56.1 ± 10.7 years, 75.8% female), the mean extubation time was 32.4 minutes. Extubation was performed within 21 minutes (32.4%), 21–35 minutes (31.2%) and ≥ 35 minutes (36.4%), respectively, after surgery. Older patients (mean age 57.8 years) were prone to delayed extubation (≥ 35 min) in the operating room, and more inclined to perioperative fluid infusion. When extubation time was analysed as a continuous variable, there was a U-shaped relation of extubation time with POP (P for nonlinearity = 0.044). After adjustment for confounders, extubation ≥35 minutes was associated with POP (odds ratio [OR], 2.73 95% confidence interval [CI], 1.36 ~ 5.47). Additionally, the results after PSM were consistent with those before matching.

Conclusions

Delayed extubation after meningioma resection is associated with increased pneumonia incidence. Therefore, extubation should be performed as early as safely possible in the operation room.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01836-w.

Regional Anaesthesia for Lower Extremity Amputation is Associated with Reduced Post-operative Complications Compared with General Anaesthesia

OBJECTIVE

Primary and secondary lower extremity amputation, performed for patients with lower extremity arterial disease, is associated with increased post-operative morbidity. The aim of the study was to assess the impact of regional anaesthesia vs. general anaesthesia on post-operative pulmonary complications.

METHODS

A retrospective analysis of 45 492 patients undergoing lower extremity amputation between 2005 and 2018 was conducted using data from the American College of Surgeons National Safety Quality Improvement Program database. Multivariable logistic regression was carried out to assess differences in primary outcome of post-operative pulmonary complications (pneumonia or respiratory failure requiring re-intubation) within 48 hours and 30 days after surgery between patients receiving regional (RA) or general anaesthesia (GA). Secondary outcomes included post-operative blood transfusion, septic shock, re-operation, and post-operative death within 30 days.

RESULTS

Of 45 492 patients, 40 026 (88.0%) received GA and 5 466 (12.0%) RA. Patients who received GA had higher odds of developing pulmonary complications at 48 hours (2.1% vs. 1.4%; adjusted odds ratio [aOR] 1.39, 95% confidence interval [CI] 1.09 - 1.78; p = .007) and within 30 days (6.3% vs. 5.9%; aOR 1.15, 95% CI 1.09 - 1.78; p = .039). The odds of blood transfusions (aOR 1.11, 95% CI 1.02 - 1.21; p = .017), septic shock (aOR 1.29, 95% CI 1.03 - 1.60; p = .025) and re-operation (OR 1.26, 95% CI 1.03 - 1.53; p = .023) were also higher for patients who received GA vs. patients who received RA. No difference in mortality rate was observed between patients who received GA and those who received RA (5.7% vs. 7.1%; odds ratio 0.95, 95% CI 0.84 - 1.07).

CONCLUSION

A statistically significant reduction in pulmonary complications was observed in patients who received RA for lower extremity amputation compared with GA.

Posttraumatic stress disorder prevalence in medical populations: A systematic review and meta-analysis

OBJECTIVE

PTSD is increasingly recognized following medical traumas although is highly heterogeneous. It is difficult to judge which medical contexts have the most traumatic potential and where to concentrate further research and clinical attention for prevention, early detection and treatment. The objective of this study was to compare PTSD prevalence in different medical populations.

METHODS

A systematic review of the literature on PTSD following medical traumas was conducted as well as a meta-analysis with final pooled result and 95% confidence intervals presented. A meta-regression was used to investigate the impact of potential effect modifiers (PTSD severity, age, sex, timeline) on study effect size between prevalence studies.

RESULTS

From 3278 abstracts, the authors extracted 292 studies reporting prevalence. Using clinician-administered reports, the highest 24 month or longer PTSD prevalence was found for intraoperative awareness (18.5% [95% CI=5.1%-36.6%]) and the lowest was found for epilepsy (4.5% [95% CI=0.2%-12.6%]). In the overall effect of the meta-regression, only medical events or procedures emerged as significant (p = 0.006) CONCLUSION: This review provides clinicians with greater awareness of medical contexts most associated with PTSD, which may assist them in the decision to engage in more frequent, earlier screening and referral to mental health services.

Effect of Long-Term Polytrauma on Ventilator-Induced Diaphragmatic Dysfunction in a Piglet Model

INTRODUCTION

Mechanical ventilation is known to activate oxidative stress and proteolytic pathways in the diaphragm. Trauma by inducing inflammation and activating proteolytic pathways may potentiate the effects of mechanical ventilation on the diaphragm. In a blunt chest trauma with concomitant injuries we tested the hypothesis that trauma via inflammation further activates the proteolytic pathways and worsens atrophy in the diaphragm.

MATERIAL AND METHODS

Piglets were separated into two groups and underwent 72 h of mechanical ventilation. One group received a polytrauma (PT) by unilateral femur fracture, blunt chest trauma with lung contusion, laparotomy with standardized liver incision, and a predefined hemorrhagic shock. The second mechanically ventilated group (MV) did not receive any trauma. A non-ventilated group (Con) served as control.Diaphragmatic fiber dimensions, Western Blot analyses of proteolytic pathways, and lipid peroxidation and messenger ribonucleic acid (mRNA) levels of cytokines and nuclear factor kappa b subunit p65 were measured.

RESULTS

Active Caspase-3 was significantly increased in MV (P = 0.019), and in PT (P = 0.02) compared with Con. Nuclear factor kappa b subunit p65, was upregulated in PT (P = 0.010) compared with Con. IL-6 mRNA increased significantly in PT compared with Con (P = 0.0024) but did not differ between Con and MV.

CONCLUSION

Trauma and mechanical ventilation induced proteolysis and atrophy in the diaphragm, but only polytrauma induced an inflammatory response in the diaphragm. The additional traumatic inflammatory stimulus did not increase the levels of the prementioned variables. These data underline that inflammation is not a major contributor to ventilator-induced diaphragmatic dysfunction.

TRIAL REGISTRY NUMBER

AZ 84-02.04.2014.A265 (Landesamt für Natur-, Umwelt- und Verbraucherschutz, LANUV NRW, Germany).

Successful 1:1 proportion ventilation with a unique device for independent lung ventilation using a double-lumen tube without complications in the supine and lateral decubitus positions. A pilot study

INTRODUCTION

Adequate blood oxygenation and ventilation/perfusion matching should be main goal of anaesthetic and intensive care management. At present, one of the methods of improving gas exchange restricted by ventilation/perfusion mismatching is independent ventilation with two ventilators. Recently, however, a unique device has been developed, enabling ventilation of independent lungs in 1:1, 2:1, 3:1, and 5:1 proportions. The main goal of the study was to evaluate the device's utility, precision and impact on pulmonary mechanics. Secondly- to measure the gas distribution in supine and lateral decubitus position.

MATERIALS AND METHODS

69 patients who underwent elective thoracic surgery were eligible for the study. During general anaesthesia, after double lumen tube intubation, the aforementioned control system was placed between the anaesthetic machine and the patient. In the supine and lateral decubitus (left/right) positions, measurements of conventional and independent (1:1 proportion) ventilation were performed separately for each lung, including the following: tidal volume, peak pressure and dynamic compliance.

RESULTS

Our results show that conventional ventilation using Robertshaw tube in the supine position directs 47% of the tidal volume to the left lung and 53% to the right lung. Furthermore, in the left lateral position, 44% is directed to the dependent lung and 56% to the non-dependent lung. In the right lateral position, 49% is directed to the dependent lung and 51% to the non-dependent lung. The control system positively affected non-dependent and dependent lung ventilation by delivering equal tidal volumes into both lungs with no adverse effects, regardless of patient's position.

CONCLUSIONS

We report that gas distribution is uneven during conventional ventilation using Robertshaw tube in the supine and lateral decubitus positions. However, this recently released control system enables precise and safe independent ventilation in the supine and the left and right lateral decubitus positions.

Perioperative Evaluation of Patients with Pulmonary Conditions Undergoing Non-Cardiothoracic Surgery

This review describes the perioperative management of patients with suspected or established pulmonary conditions undergoing non-cardiothoracic surgery, with a focus on common pulmonary conditions such as obstructive airway disease, pulmonary hypertension, obstructive sleep apnea, and chronic hypoxic respiratory conditions. Considering that postoperative pulmonary complications are common and given the increasing number of surgical procedures and the size of the aging population, familiarity with current guidelines for preoperative risk assessment and intra- and postoperative patient management is recommended to decrease the morbidity and mortality. In particular, smoking cessation and pulmonary rehabilitation are perioperative strategies for improving patients’ short- and long-term outcomes. Understanding the potential risk for pulmonary complications allows the medical team to appropriately plan the intra- and postoperative care of each patient.

[Diaphragm dysfunction : Facts for clinicians]

Diaphragm function is crucial for patient outcome in the ICU setting and during the treatment period. The occurrence of an insufficiency of the respiratory pump, which is predominantly formed by the diaphragm, may result in intubation after failure of noninvasive ventilation. Especially patients suffering from chronic obstructive pulmonary disease are in danger of hypercapnic respiratory failure. Changes in biomechanical properties and fiber texture of the diaphragm are further cofactors directly leading to a need for intubation and mechanical ventilation. After intubation and the following inactivity the diaphragm is subject to profound pathophysiologic changes resulting in atrophy and dysfunction. Besides this inactivity-triggered mechanism (termed as ventilator-induced diaphragmatic dysfunction) multiple factors, comorbidities, pharmaceutical agents and additional hits during the ICU treatment, especially the occurrence of sepsis, influence diaphragm homeostasis and can lead to weaning failure. During the weaning process monitoring of diaphragm function can be done with invasive methods - ultrasound is increasingly established to monitor diaphragm contraction, but further and better powered studies are in need to prove its value as a diagnostic tool.

[Ventilator-induced diaphragm dysfunction : clinically relevant problem]

Mechanical ventilation is a life-saving intervention for patients with respiratory failure or during deep sedation. During continuous mandatory ventilation the diaphragm remains inactive, which activates pathophysiological cascades leading to a loss of contractile force and muscle mass (collectively referred to as ventilator-induced diaphragm dysfunction, VIDD). In contrast to peripheral skeletal muscles this process is rapid and develops after as little as 12 h and has a profound influence on weaning patients from mechanical ventilation as well as increased incidences of morbidity and mortality. In recent years, animal experiments have revealed pathophysiological mechanisms which have been confirmed in humans. One major mechanism is the mitochondrial generation of reactive oxygen species that have been shown to damage contractile proteins and facilitate protease activation. Besides atrophy due to inactivity, drug interactions can induce further muscle atrophy. Data from animal research concerning the influence of corticosteroids emphasize a dose-dependent influence on diaphragm atrophy and function although the clinical interpretation in intensive care patients (ICU) patients might be difficult. Levosimendan has also been proven to increase diaphragm contractile forces in humans which may prove to be helpful for patients experiencing difficult weaning. Additionally, antioxidant drugs that scavenge reactive oxygen species have been demonstrated to protect the diaphragm from VIDD in several animal studies. The translation of these drugs into the IUC setting might protect patients from VIDD and facilitate the weaning process.

Patients with chronic pulmonary disease

Chronic pulmonary disease is common among the surgical population and the importance of a thorough and detailed preoperative assessment is monumental for minimizing morbidity and mortality and reducing the risk of perioperative pulmonary complications. These comorbidities contribute to pulmonary postoperative complications, including atelectasis, pneumonia, and respiratory failure, and can predict long-term mortality. The important aspects of the preoperative assessment for patients with chronic pulmonary disease, and the value of preoperative testing and smoking cessation, are discussed. Specifically discussed are preoperative pulmonary assessment and management of patients with chronic obstructive pulmonary disease, asthma, restrictive lung disease, obstructive sleep apnea, and obesity.

Respiratory anesthetic emergencies in oral and maxillofacial surgery

Respiratory anesthetic emergencies are the most common complications encountered during the administration of anesthesia in both the adult and pediatric populations. Regardless of the depth of anesthesia, a thorough review of the patients' health history, including the past medical history, edication list, prior anesthesia history, and complex physical examination, is critical in the promotion of safety in the oral and maxillofacial surgery office. The effective management of respiratory anesthetic emergencies includes both strong didactic and clinical skills.

Ventilation strategies in obese patients undergoing surgery: a quantitative systematic review and meta-analysis

BACKGROUND

Pathophysiological changes due to obesity may complicate mechanical ventilation during general anaesthesia. The ideal ventilation strategy is expected to optimize gas exchange and pulmonary mechanics and to reduce the risk of respiratory complications.

METHODS

Systematic search (databases, bibliographies, to March 2012, all languages) was performed for randomized trials testing intraoperative ventilation strategies in obese patients (BMI ≥ 30 kg m(-2)), and reporting on gas exchange, pulmonary mechanics, or pulmonary complications. Meta-analyses were performed when data from at least three studies or 100 patients could be combined.

RESULTS

Thirteen studies (505 obese surgical patients) reported on a variety of ventilation strategies: pressure- or volume-controlled ventilation (PCV, VCV), various tidal volumes, and different PEEP or recruitment manoeuvres (RM), and combinations thereof. Definitions and reporting of endpoints were inconsistent. In five trials (182 patients), RM added to PEEP compared with PEEP alone improved intraoperative PaO2/FIO2 ratio [weighted mean difference (WMD), 16.2 kPa; 95% confidence interval (CI), 8.0-24.4] and increased respiratory system compliance (WMD, 14 ml cm H(2)O(-1); 95% CI, 8-20). Arterial pressure remained unchanged. In four trials (100 patients) comparing PCV with VCV, there was no difference in PaO2/FIO2 ratio, tidal volume, or arterial pressure. Comparison of further ventilation strategies or combination of other outcomes was not feasible. Data on postoperative complications were seldom reported.

CONCLUSIONS

The ideal intraoperative ventilation strategy in obese patients remains obscure. There is some evidence that RM added to PEEP compared with PEEP alone improves intraoperative oxygenation and compliance without adverse effects. There is no evidence of any difference between PCV and VCV.

[Ventilation in acute respiratory distress. Lung-protective strategies]

Ventilation of patients suffering from acute respiratory distress syndrome (ARDS) with protective ventilator settings is the standard in patient care. Besides the reduction of tidal volumes, the adjustment of a case-related positive end-expiratory pressure and preservation of spontaneous breathing activity at least 48 h after onset is part of this strategy. Bedside techniques have been developed to adapt ventilatory settings to the individual patient and the different stages of ARDS. This article reviews the pathophysiology of ARDS and ventilator-induced lung injury and presents current evidence-based strategies for ventilator settings in ARDS.