Ventilatory management during routine general anaesthesia

An in vitro technique to measure resistance to compression and kinking of endotracheal tubes

Background

During intraoperative care, ventilatory parameters including peak inflating pressure (PIP) and exhaled tidal volumes are continuously monitored to assess changes in respiratory resistance and compliance. Changes in these parameters, such as an increase in PIP or a decrease in the exhaled tidal volume, may indicate various pathologic processes that may require immediate attention to prevent inadequate ventilation resulting in hypoxemia or hypercarbia. A kinked endotracheal tube (ETT) may mimic other pathologic processes including bronchospasm, mainstem intubation, or ventilator malfunction. As newer ETTs are developed, a key factor in their design should be resistance to kinking or occlusion due to patient positioning.

Methods

The current project developed and describes the process for using a repeatable in vitro mechanical test to determine resistance to kinking by an ETT.

Results

The mechanical testing procedure can be used to determine the compression force and distance required to kink an ETT under different conditions including temperature. The force required to induce devastating kink failure was lower during heated testing conditions. The addition of airflow through the ETTs during compression testing confirms the occurrence of airway obstruction at approximately the same time a mechanical kink is observed on the force-versus-distance curves.

Conclusions

These procedures may be used to characterize and evaluate ETT designs under in vitro conditions mimicking those in the clinical practice.

Comparison of the respiratory effects of commonly utilized general anaesthesia regimes in male Sprague-Dawley rats

Background: Respiratory parameters in experimental animals are often characterised under general anaesthesia. However, anaesthesia regimes may alter the functional and mechanical properties of the respiratory system. While most anaesthesia regimes have been shown to affect the respiratory system, the effects of general anaesthesia protocols commonly used in animal models on lung function have not been systematically compared. Methods: The present study comprised 40 male Sprague-Dawley rats divided into five groups (N = 8 in each) according to anaesthesia regime applied: intravenous (iv) Na-pentobarbital, intraperitoneal (ip) ketamine-xylazine, iv propofol-fentanyl, inhaled sevoflurane, and ip urethane. All drugs were administered at commonly used doses. End-expiratory lung volume (EELV), airway resistance (Raw) and tissue mechanics were measured in addition to arterial blood gas parameters during mechanical ventilation while maintaining positive end-expiratory pressure (PEEP) values of 0, 3, and 6 cm H2O. Respiratory mechanics were also measured during iv methacholine (MCh) challenges to assess bronchial responsiveness. Results: While PEEP influenced baseline respiratory mechanics, EELV and blood gas parameters (p < 0.001), no between-group differences were observed (p > 0.10). Conversely, significantly lower doses of MCh were required to achieve the same elevation in Raw under ketamine-xylazine anaesthesia compared to the other groups. Conclusion: In the most frequent rodent model of respiratory disorders, no differences in baseline respiratory mechanics or function were observed between commonly used anaesthesia regimes. Bronchial hyperresponsiveness in response to ketamine-xylazine anaesthesia should be considered when designing experiments using this regime. The findings of the present study indicate commonly used anaesthetic regimes allow fair comparison of respiratory mechanics in experimental animals undergoing any of the examined anaesthesia protocols.

Management of Intraoperative Mechanical Ventilation to Prevent Postoperative Complications after General Anesthesia: A Narrative Review

Mechanical ventilation (MV) is still necessary in many surgical procedures; nonetheless, intraoperative MV is not free from harmful effects. Protective ventilation strategies, which include the combination of low tidal volume and adequate positive end expiratory pressure (PEEP) levels, are usually adopted to minimize the ventilation-induced lung injury and to avoid post-operative pulmonary complications (PPCs). Even so, volutrauma and atelectrauma may co-exist at different levels of tidal volume and PEEP, and therefore, the physiological response to the MV settings should be monitored in each patient. A personalized perioperative approach is gaining relevance in the field of intraoperative MV; in particular, many efforts have been made to individualize PEEP, giving more emphasis on physiological and functional status to the whole body. In this review, we summarized the latest findings about the optimization of PEEP and intraoperative MV in different surgical settings. Starting from a physiological point of view, we described how to approach the individualized MV and monitor the effects of MV on lung function.

Efficacy of Oscillation and Lung Expansion in Reducing Postoperative Pulmonary Complication

BACKGROUND

Postoperative pulmonary complications (PPCs) cause high morbidity and mortality. Targeted treatment for patients at risk for PPCs can improve outcomes. This multicenter prospective trial examined the impact of oscillation and lung expansion (OLE) therapy, using continuous high-frequency oscillation and continuous positive expiratory pressure on PPCs in high-risk patients.

METHODS

In stage I, CPT and ICD codes were queried for patients (n = 210) undergoing thoracic, upper abdominal, or aortic open procedures at 3 institutions from December 2014 to April 2016. Patients were selected randomly. Age, comorbidities, American Society of Anesthesiologists physical status classification scores, and PPC rates were determined. In stage II, 209 subjects were enrolled prospectively from October 2016 to July 2017 using the same criteria. Stage II subjects received OLE treatment and standard respiratory care. The PPCs rate (prolonged ventilation, high-level respiratory support, pneumonia, ICU readmission) were compared. We also compared ICU length of stay (LOS), hospital LOS, and mortality using t-tests and analysis of covariance. Data are mean ± SD.

RESULTS

There were 419 subjects. Stage II patients were older (61.1 ± 13.7 years vs 57.4 ± 15.5 years; p < 0.05) and had higher American Society of Anesthesiologists scores. Treatment with OLE decreased PPCs from 22.9% (stage I) to 15.8% (stage II) (p < 0.01 adjusted for age, American Society of Anesthesiologists score, and operation time). Similarly, OLE treatment reduced ventilator time (23.7 ± 107.5 hours to 8.5 ± 27.5 hours; p < 0.05) and hospital LOS (8.4 ± 7.9 days to 6.8 ± 5.0 days; p < 0.05). No differences in ICU LOS, pneumonia, or mortality were observed.

CONCLUSIONS

Aggressive treatment with OLE reduces PPCs and resource use in high-risk surgical patients.

Comparison of the diagnostic accuracy of dynamic and static preload indexes to predict fluid responsiveness in mechanically ventilated, isoflurane anesthetized dogs

OBJECTIVE

To compare the diagnostic accuracy of pulse pressure variation (PPV), stroke volume variation from pulse contour analysis (SVV_PCA), plethysmographic variability index (PVI), central venous pressure (CVP) and global end-diastolic volume index measured by transpulmonary thermodilution (GEDVI_TPTD) to predict fluid responsiveness (FR) in dogs.

STUDY DESIGN

Prospective study.

ANIMALS

A group of 40 bitches (13.8-26.8 kg) undergoing ovariohysterectomy.

METHODS

Anesthesia was maintained with isoflurane under volume-controlled ventilation (tidal volume 12 mL kg^-1; inspiratory pause during 40% of inspiratory time; inspiration:expiration ratio 1:1.5). Transpulmonary thermodilution cardiac output was recorded through a femoral artery catheter. FR was evaluated by a fluid challenge (lactated Ringer's, 20 mL kg^-1 over 15 minutes) administered once (n = 21) or twice (n = 18) before surgery. Individuals were responders if stroke volume index measured by transpulmonary thermodilution increased >15% after the last fluid challenge.

RESULTS

Of the 39 animals studied, 21 were responders and 18 were nonresponders. Area under the receiver operating characteristics curve (AUROC) was 0.976, 0.906, 0.868 and 0.821 for PPV, PVI, CVP and SVV_PCA, respectively (p < 0.0001 from AUROC = 0.5). GEDVI_TPTD failed to predict FR (AUROC: 0.660, p = 0.078). Best cut-off thresholds discriminating responders and nonresponders, with respective zones of diagnostic uncertainty (gray zones) were: PPV >16% (15-16%), PVI >11% (10-13%), SVV_PCA >10% (9-18%) and CVP ≤1 mmHg (0-3 mmHg). Percentage of animals within gray zone limits was 13% (PPV), 28% (PVI), 51% (SVV_PCA) and 67% (CVP).

CONCLUSIONS AND CLINICAL RELEVANCE

PPV has better diagnostic accuracy to predict FR (conclusive results in nearly 90% of population) than other preload indexes in healthy dogs. When invasive blood pressure is unavailable, PVI will predict FR with reasonable accuracy (conclusive results in approximately 70% of the population). PPV and PVI values above gray zone limits (>16% and >13%, respectively) can reliably predict responders to volume expansion.

Standard perioperative management in gastrointestinal surgery

INTRODUCTION

The outcome of patients who are scheduled for gastrointestinal surgery is influenced by various factors, the most important being the age and comorbidities of the patient, the complexity of the surgical procedure and the management of postoperative recovery. To improve patient outcome, close cooperation between surgeons and anaesthesiologists (joint risk assessment) is critical. This cooperation has become increasingly important because more and more patients are being referred to surgery at an advanced age and with multiple comorbidities and because surgical procedures and multimodal treatment modalities are becoming more and more complex.

OBJECTIVE

The aim of this review is to provide clinicians with practical recommendations for day-to-day decision-making from a joint surgical and anaesthesiological point of view. The discussion centres on gastrointestinal surgery specifically.