The upper airway during anaesthesia

The Postoperative Airway Compromise Score-First Steps to Developing a Postoperative Tool for the Assessment of Upper Airway-Related Complications Following Anterior Cervical Spine Surgery

BACKGROUND

Acute upper airway compromise is a rare but catastrophic complication after anterior cervical discectomy and fusion. This study aims to develop a score to identify patients at risk of acute postoperative airway compromise (PAC).

METHODS

Potential risk factors for acute PAC were selected by a modified Delphi process. Ten patients with acute PAC were identified of 1466 patients who underwent elective anterior cervical discectomy and fusion between July 2014 and May 2019. A comparison group was created by a randomized selection process (non-PAC group). Factors associated with PAC and a P value of < 0.10 were entered into a logistic regression model and coefficients contributed to each risk factor's overall score. Calibration of the model was evaluated using the Hosmer-Lemeshow goodness-of-fit test. Quantitative discrimination was calculated, and the final model was internally validated with bootstrap sampling.

RESULTS

We identified 18 potential risk factors from our Delphi process, of which 6 factors demonstrated a significant association with airway compromise: age >65 years, current smoking status, American Society of Anesthesiologists class >2, history of a bleeding disorder, surgery of upper subaxial cervical spine (above C4), and duration of surgery >179 minutes. The final prediction model included 5 predictors with very strong performance characteristics. These 5 factors formed the PAC score, with a range from 0 to 100. A score of 20 yielded the greatest balance of sensitivity (80%) and specificity (88%).

CONCLUSIONS

The acute PAC score demonstrates strong performance characteristics. The PAC score might help identify patients at risk of upper airway compromise caused by surgical site abnormalities.

A pilot observation using ultrasonography and vowel articulation to investigate the influence of suspected obstructive sleep apnea on upper airway

Failure to employ suitable measures before administering full anesthesia to patients with obstructive sleep apnea (OSA) who are undergoing surgery may lead to developing complications after surgery. Therefore, it is very important to screen OSA before performing a surgery, which is currently done by subjective questionnaires such as STOP-Bang, Berlin scores. These questionnaires have 10-36% specificity in detecting sleep apnea, along with no information given on anatomy of upper airway, which is important for intubation. To address these challenges, we performed a pilot study to understand the utility of ultrasonography and vowel articulation in screening OSA. Our objective was to investigate the influence of OSA risk factors in vowel articulation through ultrasonography and acoustic features analysis. To accomplish this, we recruited 18 individuals with no risk of OSA and 13 individuals with high risk of OSA and asked them to utter vowels, such as /a/ (as in "Sah"), /e/ (as in "See"). An expert ultra-sonographer measured the parasagittal anterior-posterior (PAP) and transverse diameter of the upper airway. From the recorded vowel sounds, we extracted 106 features, including power, pitch, formant, and Mel frequency cepstral coefficients (MFCC). We analyzed the variation of the PAP diameters and vowel features from "See: /i/" to "Sah /a/" between control and OSA groups by two-way repeated measures ANOVA. We found that, there was a variation of upper airway diameter from "See" to "Sah" was significantly smaller in OSA group than control group (OSA: ∆12.8 ± 5.3 mm vs. control: ∆22.5 ± 3.9 mm OSA, p < 0.01). Moreover, we found several vowel features showed the exact same or opposite trend as PAP diameter variation, which led us to build a machine learning model to estimate PAP diameter from vowel features. We found a correlation coefficient of 0.75 between the estimated and measured PAP diameter after applying four estimation models and combining their output with a random forest model, which showed the feasibility of using acoustic features of vowel sounds to monitor upper airway diameter. Overall, this study has proven the concept that ultrasonography and vowel sounds analysis may be useful as an easily accessible imaging tool of upper airway.

Anesthesia management in a child with mucopolysaccharidosis and toxic epidermal necrolysis: A case report

Toxic epidermal necrolysis and mucopolysaccharidosis are both rare diseases that pose significant airway maintenance challenges to anesthesiologists. In this report, we describe the anesthesia management in a 4-year-old male with mucopolysaccharidosis type II who developed toxic epidermal necrolysis and presented for ophthalmic surgical procedures. Combined use of propofol and ketamine with the support of high-flow nasal oxygen enabled adequate analgesia and sedation while maintaining spontaneous ventilation and airway patency. The strategy presented in this report may contribute to enhancing the safety of sedation in spontaneously breathing children with abnormal airways.

The Modulation by Anesthetics and Analgesics of Respiratory Rhythm in the Nervous System

Rhythmic eupneic breathing in mammals depends on the coordinated activities of the neural system that sends cranial and spinal motor outputs to respiratory muscles. These outputs modulate lung ventilation and adjust respiratory airflow, which depends on the upper airway patency and ventilatory musculature. Anesthetics are widely used in clinical practice worldwide. In addition to clinically necessary pharmacological effects, respiratory depression is a critical side effect induced by most general anesthetics. Therefore, understanding how general anesthetics modulate the respiratory system is important for the development of safer general anesthetics. Currently used volatile anesthetics and most intravenous anesthetics induce inhibitory effects on respiratory outputs. Various general anesthetics produce differential effects on respiratory characteristics, including the respiratory rate, tidal volume, airway resistance, and ventilatory response. At the cellular and molecular levels, the mechanisms underlying anesthetic-induced breathing depression mainly include modulation of synaptic transmission of ligand-gated ionotropic receptors (e.g., γ-aminobutyric acid, N-methyl-D-aspartate, and nicotinic acetylcholine receptors) and ion channels (e.g., voltage-gated sodium, calcium, and potassium channels, two-pore domain potassium channels, and sodium leak channels), which affect neuronal firing in brainstem respiratory and peripheral chemoreceptor areas. The present review comprehensively summarizes the modulation of the respiratory system by clinically used general anesthetics, including the effects at the molecular, cellular, anatomic, and behavioral levels. Specifically, analgesics, such as opioids, which cause respiratory depression and the "opioid crisis", are discussed. Finally, underlying strategies of respiratory stimulation that target general anesthetics and/or analgesics are summarized.

Predicting obstructive sleep apnoea and perioperative respiratory adverse events in children: role of upper airway collapsibility measurements

BACKGROUND

Obstructive sleep apnoea (OSA) and perioperative respiratory adverse events are significant risks for anaesthesia in children undergoing adenotonsillectomy. Upper airway collapse is a crucial feature of OSA that contributes to respiratory adverse events. A measure of upper airway collapsibility to identify undiagnosed OSA can help guide perioperative management. We investigated the utility of pharyngeal closing pressure (PCLOSE) for predicting OSA and respiratory adverse events.

METHODS

Children scheduled for elective adenotonsillectomy underwent in-laboratory polysomnography 2-12 weeks before surgery. PCLOSE measurements were obtained while the child was anaesthetised and breathing spontaneously just before surgery. Logistic regression was used to assess the predictive performance of PCLOSE for detecting OSA and perioperative respiratory adverse events after adjusting for potential covariates.

RESULTS

In 52 children (age, mean [standard deviation] 5.7 [1.8] yr; 20 [38%] females), airway collapse during PCLOSE was observed in 42 (81%). Of these, 19 of 42 (45%) patients did not have OSA, 15 (36%) had mild OSA, and eight (19%) had moderate-to-severe OSA. All 10 children with no evidence of airway collapse during the PCLOSE measurements did not have OSA. PCLOSE predicted moderate-to-severe OSA (odds ratio [OR] 1.71; 95% confidence interval [CI]: 1.2-2.8; P=0.011). All children with moderate-to-severe OSA could be identified at a PCLOSE threshold of -4.0 cm H2O (100% sensitivity), and most with no or mild OSA were ruled out (64.7% specificity; receiver operating characteristic/area under the curve=0.857). However, there was no significant association between respiratory adverse events and PCLOSE (OR 1.0; 95% CI: 0.8-1.1; P=0.641).

CONCLUSIONS

Measurement of PCLOSE after induction of anaesthesia can reliably identify moderate or severe OSA but not perioperative respiratory adverse events in children before adenotonsillectomy.

CLINICAL TRIAL REGISTRATION

ANZCTR ACTRN 12617001503314.

Effects of the Lubo cervical collar on airway patency in awake adults - A magnetic resonance imaging study

Introduction: Intended for use by prehospital first responders, the Lubo ^TM cervical collar is an adjustable, radiolucent, single-use device that incorporates a mechanical jaw thrust mechanism. The combination enables non-invasive airway management in cases of trauma where cervical motion restriction is necessary. The potential benefits include use as an airway adjuvant maintaining upper airway patency, reducing provider task loading. The limited research on the device efficacy and safety requires further investigation.

Methods: A randomized, crossover, interventional study was performed to compare mean differences in airway patency at the level of the uvula, epiglottis, tongue and soft palate with and without the Lubo collar in awake volunteers using magnetic resonance imaging (MRI). Fourteen participants each underwent two MRI scans of the upper airway: A control scan with no Lubo collar, and an intervention scan with the Lubo collar applied and jaw thrust mechanism activated. Two independent radiologists measured anterior-posterior diameter of the airway at four anatomical levels on the resulting MRI images.

Results: There was no significant difference in mean airway diameter between the control and intervention measurements at any level. Mean (SD; 95% CI: p-value) differences were 0.9 mm (-2.38; 2.3 to 0.5; p=0.17) at the epiglottis, 0.5 mm (1.6; -0.5 to 1.4; p=0.29) at the soft palate, 0.2 mm (2.86; -1.4 to 1.9; p = 0.78) at the tongue, 0.4 mm (4.04; -1.9 to 2.7; p = 0.72) at the uvula.

Conclusion: The Lubo ^TM airway collar did not show a significant change in upper airway patency at four anatomical levels measured in awake adult participants. Further research is required to investigate its clinical use in patients that are unable to maintain upper airway tone. Groups of interest would include trauma, obstructive sleep apnoea, obesity and patients under general anaesthesia.

Lubo Airway Collar as a Rescue in Magnetic Resonance Imaging

Adverse respiratory events in the out-of-operation theatre premises can be challenging to anesthesiologists. Manual jaw thrust application by anesthesiologists can be a temporary solution during an adverse airway event in remote locations. This report highlights the utility of a novel collar in alleviating upper airway obstruction in a patient in the MRI suite under IV sedation. The Lubo collar provides an automated jaw thrust and can also be applied electively for patients undergoing MRI under sedation and who are at risk of upper airway obstruction.

Comparison of the effectiveness of two-handed mask ventilation techniques (C-E versus V-E) in obese patients requiring general anesthesia in an Indian population

Background:

Two-handed mask ventilation techniques are often used in cases of difficult mask ventilation scenarios. A comparison of two methods of two-handed techniques in terms of tidal volume was undertaken in the context of the obese population.

Aims and Objectives:

To determine and compare the effectiveness of mask ventilation in obese Indian adult subjects by using either the C-E technique or the V-E technique after induction of general anaesthesia.

Material and Methods:

This was a randomised interventional study conducted on eighty obese patients. They were randomized into Group A ventilated with C-E technique and Group B with V-E technique. Expired tidal volume (VTe), Peak inspiratory pressure (PIP), SpO₂, EtCO₂ and vital signs were noted.

Results:

The BMI and hemodynamic parameters were comparable between the two groups. The expired tidal volume of 702 ± 77 mL with the V-E technique was significantly more than the C-E technique, which was 492 ± 71 mL. The ventilatory failure rate with the C-E technique was 15% and 0% with the V-E technique. There was no significant difference between the peak airway pressures for the two techniques: 20.3 ± 1.5 mm H₂O for Group A and 20.5 ± 1.2 mm H₂O for Group B.

Conclusions:

Mask ventilation with the two-handed V-E technique is associated with better tidal volumes and reduced failure rates in the obese population. So the V-E technique should be attempted first as a rescue measure in obese adult patients if the return of spontaneous breathing and tracheal intubation is impossible.

High flow versus conventional nasal cannula for oxygenation and ventilation maintenance during surgery with intravenous deep sedation by propofol: a randomized controlled study

Background

The dead space washout and provision of some level of positive airway pressure by nasal high-flow (NHF) cannula could improve the efficiency of ventilation, oxygenation and maintenance of the upper airway in patients undergoing deep sedation. This study aimed to compare the incidences of events represented oxygenation and ventilation, i.e. desaturation and upper airway obstruction, and arterial blood gas (ABG) levels between using NHF cannula and conventional nasal cannula (NC2) during deep sedation of adult surgical patients.

Methods

In this prospective randomized single-blinded study, the patients who were 20–80 years old, ASA physical status of 1 to 3, scheduled for surgery under intravenous sedation (IVS) were included. The patients were randomly divided into two groups, i.e., NC2 or NHF groups. Propofol infusion was given to maintain deep sedation. The desaturation (SpO₂ < 92%) and upper airway obstruction events (presence of snoring with paradoxical breathing) after application of NC2 or NHF were observed and collected. Other outcomes included interventions during IVS, such as jaw lifting or airway instrument insertion, mouth dryness, and post- ABG analyses were also collected and compared.

Results

Thirty-six patients undergoing endovascular surgery were randomized into NC2 or NHF groups (18 in each group). No patients dropped out of the study. There were no significant differences in age, sex, ASA physical status, pre-sedation and pre-application of NC2 and NHF ABG analyses (PaO₂, SaO₂, pH, PaCO₂, and PaO₂/FiO₂). NHF group had significantly lower in the incidence of desaturation [5 (27.78%) vs 13 (72.22%), p = 0.008], upper airway obstruction [4 (22.22%) vs 13 (72.22%), p = 0.003], and airway maneuver [6 (33.33%) vs 13 (72.22%), p = 0.019] than NC2 group. There were no differences in the ABG analyses after oxygen supplementation and no significant differences in mouth dryness between groups.

Conclusion

The use of NHF cannula in patients undergoing endovascular surgery under deep sedation reduced desaturation events and required fewer airway interventions than NC2 with no difference in arterial blood gas analyses and mouth dryness.

Body position and the effectiveness of mask ventilation in anaesthetised paralysed obese patients: A randomised cross-over study

BACKGROUND

Airway management is more challenging in the obese. Compared with the supine position, the sitting position can decrease the collapsibility of the upper airway and improve respiratory mechanics.

OBJECTIVE

The aim of this study was to evaluate the 25° semisitting position on the effectiveness of mask ventilation in anaesthetised paralysed obese patients.

DESIGN

A randomised, cross-over study.

SETTING

Medical centre managed by a university tertiary hospital.

PATIENTS

Thirty-eight obese adults scheduled for general anaesthesia.

METHODS

After anaesthesia and paralysis, two-handed mask ventilation was performed in the supine and 25° semi-sitting positions with a cross-over, in a randomised order. During mask ventilation, mechanical ventilation was delivered with a pressure-controlled mode with a peak inspiratory pressure of 15 cmH2O, a respiratory rate of 15 bpm, and no positive end-expiratory pressure. Ventilatory outcomes were based upon lean body weight.

MAIN OUTCOMES

Exhaled tidal volume (ml kg-1), respiratory minute volume (ml kg-1 min-1), and the occurrence of inadequate ventilation, defined as an exhaled tidal volume less than 4 ml kg-1, or absence of end-tidal CO2 recording.

RESULTS

Exhaled tidal volume (mean ± SD) in the 25° semi-sitting position was higher than in the supine position, 9.3 ± 2.7 vs. 7.6 ± 2.4 ml kg-1; P less than 0.001. Respiratory minute volume was improved in the 25° semisitting position compared with that in the supine position, 139.6 ± 40.7 vs. 113.4 ± 35.7 ml kg-1 min-1; P less than 0.001.

CONCLUSION

The 25° semisitting position improved mask ventilation compared with the supine position in anaesthetised paralysed obese patients.

TRIAL REGISTRY NUMBER

ClinicalTrials.gov (NCT03996161).

Acute upper airway obstruction due to tonsillitis necessitating emergency cricothyroidotomy

A 17-year-old man was admitted to Accident & Emergency out of hours with unilateral tonsillar enlargement covering more than 75% of his oropharyngeal inlet. He appeared calm and stable on initial presentation, but in a short span of time rapidly deteriorated, leading to near complete airway obstruction necessitating an emergency awake cricothyroidotomy. Tracheostomy and tonsillectomy were done after this, he was ventilated postoperatively in intensive therapy unit and discharged home in a week. This is a rare clinical scenario in a patient presenting with palatine tonsillitis. A few subtle points in the history and examination alerted the team and prevented a risky inter hospital transfer for ear, nose and throat review. This is the first reported case in UK of palatine tonsillitis not due to infectious mononucleosis presenting with acute upper airway obstruction in a patient with no airway anomalies. It may also have been a varied presentation of COVID-19.

Pharmacologically Induced Ventilatory Depression in the Postoperative Patient: A Sleep-Wake State-Dependent Perspective

Pharmacologically induced ventilatory depression (PIVD) is a common postoperative complication with a spectrum of severity ranging from mild hypoventilation to severe ventilatory depression, potentially leading to anoxic brain injury and death. Recent studies, using continuous monitoring technologies, have revealed alarming rates of previously undetected severe episodes of postoperative ventilatory depression, rendering the recognition of such episodes by the standard intermittent assessment practice, quite problematic. This imprecise description of the epidemiologic landscape of PIVD has thus stymied efforts to understand better its pathophysiology and quantify relevant risk factors for this postoperative complication. The residual effects of various perianesthetic agents on ventilatory control, as well as the multiple interactions of these drugs with patient-related factors and phenotypes, make postoperative recovery of ventilation after surgery and anesthesia a highly complex physiological event. The sleep-wake, state-dependent variation in the control of ventilation seems to play a central role in the mechanisms potentially enhancing the risk for PIVD. Herein, we discuss emerging evidence regarding the epidemiology, risk factors, and potential mechanisms of PIVD.

Effects of continuous positive airway pressure administered by a helmet in cats under general anaesthesia

OBJECTIVES

The aim of this study was to evaluate the respiratory effects of non-invasive continuous positive airway pressure (CPAP) administered by a helmet in healthy cats under anaesthesia.

METHODS

Fifteen healthy male cats scheduled for castration were anaesthetised with medetomidine (20 µg/kg), ketamine (10 mg/kg) and buprenorphine (20 µg/kg) intramuscularly. When an adequate level of anaesthesia was achieved, a paediatric helmet was placed on all subjects. The helmet was connected to a Venturi valve supplied with medical air and cats received the following phases of treatments: 0 cmH2O (pre-CPAP), 5 cmH2O (CPAP) and 0 cmH2O (post-CPAP). Each treatment lasted 10 mins. At the end of each phase an arterial blood sample was drawn. The following data were also collected: mean arterial pressure, respiratory rate, heart rate and the anaesthesia level score (0 = awake, 10 = deep anaesthesia). The alveolar to arterial oxygen gradient (P[A-a]O2) and the venous admixture (Fshunt) were also estimated. Data were analysed with two-way ANOVA (P <0.05).

RESULTS

The arterial partial pressure of oxygen was higher (P <0.001) at CPAP (103.2 ± 5.1 mmHg) vs pre-CPAP (77.5 ± 7.4 mmHg) and post-CPAP (84.6 ± 8.1 mmHg). The P(A-a)O2 and the Fshunt were lower (P <0.001) at CPAP (4.4 ± 2.3 mmHg; 7.4 ± 3.1%) vs pre-CPAP (18.9 ± 6.4 mmHg; 22.8 ± 4.6%) and post-CPAP (15.6 ± 7.3 mmHg; 20.9 ± 4.6 %). No other parameters differed between groups.

CONCLUSIONS AND RELEVANCE

Non-invasive CPAP applied by a helmet improves oxygenation in cats under injectable general anaesthesia.

Ocular complications of perioperative anesthesia: a review

Ocular complications associated with anesthesia in ocular and non-ocular surgeries are rare adverse events which may present with clinical presentations vacillating between easily treatable corneal abrasions to more serious complication such as irreversible bilateral vision loss. In this review, we outline the different techniques of anesthetic delivery in ocular surgeries and highlight the incidence and etiologies of associated injuries. The changes in vision in non-ocular surgeries are mistaken for residual sedation or anesthetics, therefore require high clinical suspicion on part of the treating ophthalmologists, to ensure early diagnosis, adequate and swift management especially in surgeries such as cardiac, spine, head and neck, and some orthopedic procedures, that have a comparatively higher incidence of ocular complications. In this article, we review the literature for reports on the clinical incidence of different ocular complications associated with anesthesia in non-ocular surgeries and outline the current understanding of pathophysiological processes associated with these adverse events.

Comparison of CPAP and oxygen therapy for treatment of postoperative hypoxaemia in dogs

OBJECTIVE

To compare 5 cmH₂ O of continuous positive airway pressure with oxygen therapy in dogs recovering from general anaesthesia with low SpO₂ values. continuous positive airway pressure is more effective than oxygen therapy in restoring normoxaemia (SpO₂ ≥95%).

MATERIALS AND METHODS

Prospectively, dogs recovering from anaesthesia, with SpO₂ <95% after extubation (T0), were randomised and treated with continuous positive airway pressure (FiO₂ 0.21) or oxygen (O₂ ; FiO₂ 0.35-0.40) therapy. Dogs were monitored with SpO₂ every 15 minutes for 1 hour (T15, T30, T45, T60). Data from normoxaemic dogs (SpO₂ >95%) were used as control (CTR).

RESULTS

Of the 42 dogs enrolled, 34 completed the study. Eleven dogs were treated with O₂ , 10 with continuous positive airway pressure and 13 were CTR. The SpO₂ values at T0 were similar in the continuous positive airway pressure and O₂ groups and were lower than in the CTR group. At T15, T30, T45 and T60, the SpO₂ values in the continuous positive airway pressure group were higher than at T0; these were similar to those of the CTR group at the same time-points. In the O₂ group, SpO₂ values were significantly higher at T45 and T60 than at T0; 45.5% of dogs became normoxaemic at T45 and the remaining dogs became normoxaemic at T60. The average time to reach normoxaemia in the O₂ group (53.1±7.3 minutes) was longer than in the continuous positive airway pressure group (15.0±0.0 minutes).

CLINICAL SIGNIFICANCE

In dogs recovering from general anaesthesia with pulmonary gas exchange impairment, normoxaemia is restored more effectively and rapidly by using continuous positive airway pressure than by oxygen therapy.

Experiential learning in simulated parapharyngeal abscess in breathing cadavers

Purpose

Education in airway management is a fundamental component of anesthesiology training programs. There has been a shift towards the use of simulation models of higher fidelity for education in airway management. The goal of this study was to create a novel cadaveric model of a simulated parapharyngeal abscess with features of a difficult airway such as distorted anatomy and narrow airway passages presenting as stridor. The model was further assessed for its suitability for enhanced experiential learning in the management of difficult airways.

Methods

Cadaver heads were modified surgically to simulate parapharyngeal abscess. Airtight torso of the cadaver was connected to an Oxylog ventilator to simulate respiratory movements—the opening and closing of air channels with breaths in a patient with parapharyngeal abscess. Advanced airway workshop facilitators conducted directed one-to-one learning, and provided feedback to participants. A paper-based feedback was obtained from 72 participants on their confidence level, and the realism, attractiveness, beneficial, and difficulty levels of the simulated cadaveric models.

Results

The modified cadavers were reliable in simulating difficult airways. The majority of participants (91%) reported an increase in confidence level for management of the difficult airway after the experience with the modified cadavers and found the models realistic (93%), attractive (92%), beneficial (93%), and difficult (85%).

Conclusions

Surgical modifications of cadavers to simulate difficult airways such as parapharyngeal abscess with edema and stridor can be incorporated into advanced airway management courses to enhance experiential learning in airway management by awake fibreoptic intubation, and promote patient safety.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00540-021-02904-0.

Breathing Re-Education and Phenotypes of Sleep Apnea: A Review

Four phenotypes of obstructive sleep apnea hypopnea syndrome (OSAHS) have been identified. Only one of these is anatomical. As such, anatomically based treatments for OSAHS may not fully resolve the condition. Equally, compliance and uptake of gold-standard treatments is inadequate. This has led to interest in novel therapies that provide the basis for personalized treatment protocols. This review examines each of the four phenotypes of OSAHS and explores how these could be targeted using breathing re-education from three dimensions of functional breathing: biochemical, biomechanical and resonant frequency. Breathing re-education and myofunctional therapy may be helpful for patients across all four phenotypes of OSAHS. More research is urgently needed to investigate the therapeutic benefits of restoring nasal breathing and functional breathing patterns across all three dimensions in order to provide a treatment approach that is tailored to the individual patient.

Canadian Airway Focus Group updated consensus-based recommendations for management of the difficult airway: part 2. Planning and implementing safe management of the patient with an anticipated difficult airway

PURPOSE

Since the last Canadian Airway Focus Group (CAFG) guidelines were published in 2013, the published airway management literature has expanded substantially. The CAFG therefore re-convened to examine this literature and update practice recommendations. This second of two articles addresses airway evaluation, decision-making, and safe implementation of an airway management strategy when difficulty is anticipated.

SOURCE

Canadian Airway Focus Group members, including anesthesia, emergency medicine, and critical care physicians were assigned topics to search. Searches were run in the Medline, EMBASE, Cochrane Central Register of Controlled Trials, and CINAHL databases. Results were presented to the group and discussed during video conferences every two weeks from April 2018 to July 2020. These CAFG recommendations are based on the best available published evidence. Where high-quality evidence is lacking, statements are based on group consensus.

FINDINGS AND KEY RECOMMENDATIONS

Prior to airway management, a documented strategy should be formulated for every patient, based on airway evaluation. Bedside examination should seek predictors of difficulty with face-mask ventilation (FMV), tracheal intubation using video- or direct laryngoscopy (VL or DL), supraglottic airway use, as well as emergency front of neck airway access. Patient physiology and contextual issues should also be assessed. Predicted difficulty should prompt careful decision-making on how most safely to proceed with airway management. Awake tracheal intubation may provide an extra margin of safety when impossible VL or DL is predicted, when difficulty is predicted with more than one mode of airway management (e.g., tracheal intubation and FMV), or when predicted difficulty coincides with significant physiologic or contextual issues. If managing the patient after the induction of general anesthesia despite predicted difficulty, team briefing should include triggers for moving from one technique to the next, expert assistance should be sourced, and required equipment should be present. Unanticipated difficulty with airway management can always occur, so the airway manager should have a strategy for difficulty occurring in every patient, and the institution must make difficult airway equipment readily available. Tracheal extubation of the at-risk patient must also be carefully planned, including assessment of the patient's tolerance for withdrawal of airway support and whether re-intubation might be difficult.

Comparing two airway management strategies for moderately sedated patients undergoing awake craniotomy: A single-blinded randomized controlled trial

BACKGROUND

In the monitored anesthesia care (MAC) setting for awake craniotomy (AC), maintaining airway patency in sedated patients remains challenging. This randomized controlled trial aimed to compare the validity of the below-epiglottis transnasal tube insertion (the tip of the tube placed between the epiglottis and vocal cords) and the nasopharyngeal airway (simulated by the above-epiglottis transnasal tube with the tip of the tube placed between the epiglottis and the free edge of the soft palate) with respect to maintaining upper airway patency for moderately sedated patients undergoing AC.

METHODS

Sixty patients scheduled for elective AC were randomized to receive below-epiglottis (n = 30) or above-epiglottis (n = 30) transnasal tube insertion before surgery. Moderate sedation was maintained in the pre- and post-awake phases. The primary outcome was the upper airway obstruction (UAO) remission rate (relieved obstructions after tube insertion/the total number of obstructions before tube insertion).

RESULTS

The UAO remission rate was higher in the below-epiglottis group [100% (12/12) vs 45% (5/11); P = .005]. The tidal volume values monitored through the tube were greater in the below-epiglottis group during the pre-awake phase (P < .001). End-tidal carbon dioxide (EtCO₂ ) monitored through the tube was higher in the below-epiglottis group at bone flap removal (P < .001). During the awake phase, patients' ability to speak was not impeded. No patient had serious complications related to the tube.

CONCLUSION

The below-epiglottis tube insertion is a more effective method to maintain upper airway patency than the nasopharyngeal airway for moderately sedated patients undergoing AC.

A novel algorithm to predict oxygen desaturation in sedated patients with obstructive sleep apnea utilizing polysomnography: A STROBE-compliant article

This retrospective study aimed at identifying the predictors of oxygen desaturation (OD) (i.e., SpO2 < 95%) in patients with obstructive sleep apnea (OSA) requiring deep sedation and developing an algorithm to predict OD.We studied 66 OSA patients undergoing propofol-induced deep sedation for drug-induced sleep endoscopy (DISE). The patients were divided into prediction (n = 35) and validation (n = 31) groups. Patient characteristics and polysomnographic parameters were analyzed with receiver operating characteristic curve and Chi-squared test to identify significant predictors of OD for developing an algorithm in the prediction group. The predictive accuracy, sensitivity, positive predictive value, and negative predictive value of the algorithm were determined in the validation group.Six polysomnographic predictors of OD were identified, including Apnea-Hypopnea Index of total sleep time (AHI-TST), AHI at the stage of rapid eye movement (AHI-REM), percentage of time with oxygen saturation <90% (mO2 < 90%), average SpO2, lowest SpO2, and desaturation index. Stepwise multiple logistic regression analysis demonstrated that low average SpO2 (<95.05%) and high AHI-REM (>16.5 events/h) were independent predictors of OD. The algorithm thus developed showed that patients with an average SpO2 < 95.05% and those with an average SpO2 ≥ 95.05% together with an AHI-REM > 16.5 events/h would be at risk of OD under sedation. The predictive accuracy, sensitivity, positive predictive value, and negative predictive value were 84%, 100%, 83%, 100%, respectively.For patients with OSA, average SpO2 and AHI-REM may enable clinicians to predict the occurrence of oxygen desaturation under deep sedation. Future large-scale studies are needed to validate the findings.

Evaluation of the effects of helmet continuous positive airway pressure on laryngeal size in dogs anesthetized with propofol and fentanyl using computed tomography

OBJECTIVE

To evaluate the effect of 5 cm H₂ O of continuous positive airway pressure (CPAP) on laryngeal size in spontaneously breathing anesthetized dogs via computed tomography (CT).

DESIGN

Prospective, randomized, cross-over clinical study.

SETTING

University teaching hospital and referral private practice.

ANIMALS

Eight healthy client-owned dogs undergoing CT.

INTERVENTIONS

Dogs were sedated with acepromazine 20 μg/kg IM and induced with fentanyl 2 μg/kg and propofol 3-5 mg/kg IV before being maintained on fentanyl (5 μg/kg/h) and propofol (0.3 mg/kg/min) constant rate infusion. Dogs received an air/oxygen mixture with (CPAP) and without (NO-CPAP) 5 cm H₂ O of CPAP in a random order. Each study step lasted 15 minutes.

MEASUREMENTS AND MAIN RESULTS

Ten minutes after the beginning of each study period, a CT scan of the laryngeal region was obtained at end-expiration. CT images were analyzed to determine the laryngeal cross-sectional area (CSA; cm² ), total volume (V_TOT ; cm³ ), and laterolateral and dorsoventral diameters (D_LL and D_DV , respectively; cm). Differences between the 2 treatments were analyzed with t-test for paired data (P < 0.05). Compared to the NO-CPAP, during CPAP the CSA increased by 53.3 ± 23.1% (ie, from 3.3 ± 0.8 to 5.1 ± 1.3 cm² , P = 0.0004), V_TOT increased by 52.4 ± 13.6% (from 6.2 ± 1.7 to 9.4 ± 2.4 cm³ , P < 0.0001), and D_LL and D_DV were 55.5 ± 13.3% (3.6 ± 0.8 vs 2.4 ± 0.5 cm, P = 0.006) and 20.3 ± 8.8% larger (3.2 ± 0.7 vs 2.7 ± 0.6 cm, P = 0.0002), respectively.

CONCLUSIONS

Laryngeal volume and cross sectional area increased during the application of 5 cm H₂ O of helmet CPAP in spontaneously breathing anesthetized dogs.

Total Intravenous Anaesthesia for Fibre Optic-Aided Nasal Endotracheal Intubation in a Toddler with Anticipated Difficult Mask Ventilation

Paediatric airway tumours can prove to be quite challenging for anaesthesiologists. We attempted to secure airway in a toddler with a large tongue haemangioma using total intravenous anaesthesia (TIVA) with dexmedetomidine and propofol while preserving spontaneous ventilation.

Preoperative identification of children at high risk of obstructive sleep apnea

Obstructive sleep apnea is a common childhood disorder which can lead to serious health problems if left untreated. Enlarged adenoid and tonsils are the commonest causes, and adenotonsillectomy is the recommended first line of treatment. Obstructive sleep apnea poses as an anesthetic challenge, and it is a well-known risk factor for perioperative adverse events. The presence and severity of an obstructive sleep apnea diagnosis will influence anesthesia, pain management, and level of monitoring in recovery period. Preoperative obstructive sleep apnea assessment is necessary, and anesthetists are ideally placed to do so. Currently, there is no standardized approach to the best method of preoperative screening for obstructive sleep apnea. Focused history, clinical assessments, and knowledge regarding the strengths and limitations of available obstructive sleep apnea assessment tools will help recognize a child with obstructive sleep apnea in the preoperative setting.

Effect of oxygen fraction on airway rescue: a computational modelling study

BACKGROUND

During induction of general anaesthesia, patients frequently experience apnoea, which can lead to dangerous hypoxaemia. An obstructed upper airway can impede attempts to provide ventilation. Although unrelieved apnoea is rare, it continues to cause deaths. Clinical investigation of management strategies for such scenarios is effectively impossible because of ethical and practical considerations.

METHODS

A population-representative cohort of 100 virtual (in silico) subjects was configured using a high-fidelity computational model of the pulmonary and cardiovascular systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway, during induction of general anaesthesia. Apnoea continued throughout the protocol. When arterial oxygen saturation (Sao₂) reached 20%, 40%, or 60%, airway obstruction was relieved. We examined the effect of varying supraglottic oxygen fraction (Fo₂) on the degree of passive re-oxygenation occurring without tidal ventilation.

RESULTS

Relief of airway obstruction during apnoea produced a single, passive inhalation (caused by intrathoracic hypobaric pressure) in all cases. The degree of re-oxygenation after airway opening was markedly influenced by the supraglottic Fo₂, with a supraglottic Fo₂ of 100% providing significant and sustained re-oxygenation (post-rescue Pao₂ 42.3 [4.4] kPa, when the airway rescue occurred after desaturation to Sao₂ 60%).

CONCLUSIONS

Supraglottic oxygen supplementation before relieving upper airway obstruction improves the effectiveness of simulated airway rescue. Management strategies should be implemented to assure a substantially increased pharyngeal Fo₂ during difficult airway management.

Current concepts of perioperative monitoring in high-risk surgical patients: a review

A substantial number of patients are at high-risk of intra- or post-operative complications or both. Most perioperative deaths are represented by patients who present insufficient physiological reserve to meet the demands of major surgery. Recognition and management of critical high-risk surgical patients require dedicated and effective teams, capable of preventing, recognize, start treatment with adequate support in time to refer patients to the satisfactory ICU level provision. The main task for health-care planners and managers is to identify and reduce this severe risk and to encourage patient’s safety practices. Inadequate tissue perfusion and decreased cellular oxygenation due to hypovolemia, heart dysfunction, reduced cardiovascular reserve, and concomitant diseases are the most common causes of perioperative complications. Hemodynamic, respiratory and careful sequential monitoring have become essential aspects of the clinical practice both for surgeons and intensivists. New monitoring techniques have changed significantly over the past few years and are now able to rapidly identify shock states earlier, define the etiology, and monitor the response to different therapies. Many of these techniques are now minimally invasive or non-invasive. Advanced hemodynamic and respiratory monitoring combines invasive, non-invasive monitoring skills. Non-invasive ultrasound has emerged during the last years as an essential operative and perioperative evaluation tool, and its use is now rapidly growing. Perioperative management guided by appropriate sequential clinical evaluation combined with respiratory and hemodynamic monitoring is an established tool to help clinicians to identify those patients at higher risk in the attempt to reduce the complications rate and potentially improve patient outcomes. This review aims to provide an update of currently available standard concepts and evolving technologies of the various respiratory and hemodynamic monitoring systems for the high-risk surgical patients, highlighting their potential usefulness when integrated with careful clinical evaluation.

Comparison of the Baska and I-gel supraglottic airway devices: a randomized controlled study

BACKGROUND

Laryngeal masks are increasingly used in place of endotracheal intubation or face masks for maintaining the airway during surgery.

OBJECTIVES

Compare the insertion time and other features of the Baska and I-gel masks in patients undergoing general anesthesia for urological surgery.

DESIGN

Randomized-controlled, single-blind study.

SETTINGS

Urology surgical operating rooms of a tertiary care hospital.

SUBJECTS AND METHODS

We enrolled concomitant patients whose surgery was expected to last less than two hours. Following premedication and adequate relaxation, subjects were randomly allocated to the I-gel mask or the Baska mask. Computer-generated random numbers were used for randomization with sealed opaque envelopes for allocation concealment.

MAIN OUTCOME MEASURES

The primary outcome measure of the study was the time required for laryngeal mask airway (LMA) insertion. Also, the number of device placement attempts, the number of postoperative signs and symptoms (cough, breath holding, laryngeal spasm, lip trauma, blood on the mask), and laryngopharyngeal morbidity scores at 1 and 24 hours postoperatively.

SAMPLE SIZE

211 met inclusion criteria, 200 participants completed the study.

RESULTS

Compared to I-gel, the Baska mask required a longer time for insertion, and its airway pressure was higher. The median (minimum-maximum) duration of LMA insertion in the Baska and I-gel groups was 14 (6-25) and 7 (5-12) seconds, respectively (z=-10.934; P<.001). The mean (SD) airway pressures were significantly different between the two groups (15.8 [1.9] and 14.9 [1.7] cm/H2O for Baska and I-gel, respectively; t=3.668; P<.001). Seal pressure was not significantly different between the groups (0.08 [0.2] vs. 0.07 [0.2] cm/H2O in the Baska and I-gel groups, respectively, (t=1.35; P=.194).

CONCLUSIONS

The Baska and I-gel masks are similar in most respects. Both have reasonably acceptable insertion times and can be used for selected surgical procedures.

LIMITATIONS

The requirement for more vigorous training is a limitation of the Baska mask. Results could differ with patients younger than 18 years of age or obese patients.

CONFLICT OF INTEREST

None.

CLINICAL TRIAL REGISTRY

Not registered.

Changes in the upper airway following induction of anaesthesia: a prospective observational study protocol to determine the use of ultrasound in the assessment of a difficult airway in China

INTRODUCTION

Difficult airway management is closely related to the safety and quality of medical care. However, the low incidence of correct prediction of difficult airway in clinical screening tests presents physicians with a dilemma. Depressed airway neuromuscular tension during sleep and anaesthesia tends to cause collapse of fragile parts of the upper airway. Although previous studies have confirmed that anterior cervical tissue thickness is associated with difficult airways, there is no evidence to support a correlation between a difficult airway and specific patterns or findings of anaesthesia-induced airway collapse. Thus, this study aims to examine changes in airway dimensions before and after induction of general anaesthesia to explore whether it could provide useful information regarding the specific anatomic changes occurring which may cause difficult airways.

METHODS AND ANALYSIS

This will be a single-centre prospective observational single-blinded study, conducted in a tertiary teaching hospital in Guangzhou, China. Subjects will be recruited from patients (aged 18-65 years) scheduled for elective surgery under general anaesthesia. Sonographic measurement will be performed to detect changes in the thickness of the anterior cervical soft tissue before and after anaesthetic induction. Based on the resulting data distribution, analyses will initially compare these changes using a paired t-test or the Wilcoxon signed-rank test. The correlation of sonographic changes and Cormack-Lehane grade will be evaluated by using receiver-operating characteristic curves to detect the sensitivity and specificity of a measurement for detecting difficulties. Linear stepwise regression analysis will be used to assess the correlation between airway changes and demographic variables as well as clinical tests.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Ethics Committee of the First Affiliated Hospital of Guangzhou University of Chinese Medicine (ZYYECK (2018) 041). The results will be disseminated through conference presentations, professional journals and peer-reviewed publications.

TRIAL REGISTRATION NUMBER

ChiCTR1900021123; Pre-results.

Fibreoptic Orotracheal Intubation of Obese Patients Using Parker Flex-Tip vs. Standard Endotracheal Tube

Objective

Advancement of the endotracheal tube through a fibreoptic scope can sometimes prove to be challenging in obese patients. The Parker Flex-Tip endotracheal tube was developed with a curved and tapered distal tip to facilitate easier placement in the trachea. This study examined the use of the Parker Flex-Tip tube as compared to standard endotracheal tubes in patients with a body mass index of 30 or greater.

Methods

Sixty patients undergoing surgery requiring general anaesthesia were randomised into two groups. Using the fibreoptic scope, one group was intubated with the Parker Flex-Tip tube and the other group with a standard polyvinyl Portex tube. The time for intubation and the number of attempts required to place the endotracheal tube were measured and recorded.

Results

Using the Mann-Whitney U rank sum test, the median time needed for intubation with the two types of endotracheal tubes did not show a significant difference. The chi-square analyses were conducted for the number of attempts needed to place the endotracheal tubes, which also did not demonstrate any significant difference.

Conclusions

Parker Flex-Tip endotracheal tube was not superior to the standard endotracheal tubes for fibreoptic intubation in obese patients.

Comparison of lateral and supine positions for tracheal extubation in children : A randomized clinical trial

BACKGROUND

The lateral position is known to be advantageous for maintaining airway patency. This study compared the lateral and supine positions for tracheal extubation in pediatric patients when performing deep extubation.

OBJECTIVE

The hypothesis was that tracheal extubation in the lateral position would improve airway obstruction that often occurs immediately after extubation and can be a practical method.

MATERIAL AND METHODS

This prospective randomized trial was performed in operating rooms in a tertiary care hospital and included 92 patients (3-12 years old) undergoing elective strabismus surgery. The patients were randomly divided into two groups: deep extubation in the supine position (group S) and deep extubation in the lateral position (group L). Oxygen saturation (SpO₂) and the incidence of stridor, laryngospasm, and coughing after tracheal extubation were assessed.

RESULTS

The mean ± standard deviation of the lowest SpO₂ values within 5 min after extubation was significantly higher in group L (98.3 ± 2.1%) than in group S (96.8 ± 2.5%, mean difference 1.5, 95% confidence interval, CI 0.5-2.5, p = 0.003). The incidences of stridor and laryngospasm of group L were significantly lower than those of group S (1/45, 2% vs. 8/45, 18%, respectively; relative risk 1.9, 95% CI 1.4-2.7, p = 0.03). The incidence of desaturation and coughing were not significantly different between groups.

CONCLUSION

In pediatric patients deep extubation in the lateral position improved SpO₂ and reduced the incidence of stridor and laryngospasm in the early emergence period when compared to extubation in the supine position.

A prospective cohort study of awake fibreoptic intubation practice at a tertiary centre

Contemporary data are lacking for procedural practice, training provision and outcomes for awake fibreoptic intubation in the UK. We performed a prospective cohort study of awake fibreoptic intubations at a tertiary centre to assess current practice. Data from 600 elective or emergency awake fibreoptic intubations were collected to include information on patient and operator demographics, technical performance and complications. This comprised 1.71% of patients presenting for surgery requiring a general anaesthetic, with the majority occurring in patients presenting for head and neck surgery. The most common indication was reduced mouth opening (26.8%), followed by previous airway surgery or head and neck radiotherapy (22.5% each). Only five awake fibreoptic intubations were performed with no sedation, but the most common sedative technique was combined target-controlled infusions of remifentanil and propofol. Oxygenation was achieved with high-flow, heated and humidified oxygen via nasal cannula in 49.0% of patients. Most operators had performed awake fibreoptic intubation more than 20 times previously, but trainees were the primary operator in 78.6% of awake fibreoptic intubations, of which 86.8% were directly supervised by a consultant. The failure rate was 1.0%, and 11.0% of awake fibreoptic intubations were complicated, most commonly by multiple attempts (4.2%), over-sedation (2.2%) or desaturation (1.5%). The only significant association with complications was the number of previous awake fibreoptic intubations performed, with fewer complications occurring in the hands of operators with more awake fibreoptic intubation experience. Our data demonstrate that awake fibreoptic intubation is a safe procedure with a high success rate. Institutional awake fibreoptic intubation training can both develop and maintain trainee competence in performing awake fibreoptic intubation, with a similar incidence of complications and success compared with consultants.

SponTaneous Respiration using IntraVEnous anaesthesia and Hi-flow nasal oxygen (STRIVE Hi) maintains oxygenation and airway patency during management of the obstructed airway: an observational study

Background. High-flow nasal oxygen (HFNO) has been shown to benefit oxygenation, ventilation and upper airway patency in a range of clinical scenarios, however its use in spontaneously breathing patients during general anaesthesia has not been described. Spontaneous respiration using i.v. anaesthesia is the primary technique used at our institution for tubeless airway surgery. We hypothesized that the addition of HFNO would increase our margin of safety, particularly during management of an obstructed airway.

Methods. A retrospective observational study was conducted using a SponTaneous Respiration using IntraVEnous anaesthesia and High-flow nasal oxygen (STRIVE Hi) technique to manage 30 adult patients undergoing elective laryngotracheal surgery.

Results. Twenty-six patients (87%) presented with significant airway and/or respiratory compromise (16 were stridulous, 10 were dyspnoeic). No episodes of apnoea or complete airway obstruction occurred during the induction of anaesthesia using STRIVE Hi. The median [IQR (range)] lowest oxygen saturation during the induction period was 100 [99–100 (97–100)] %. The median [IQR (range)] overall duration of spontaneous ventilation was 44 [40–49.5 (18–100)] min. The median [IQR (range)] end-tidal carbon dioxide (ETCO₂) level at the end of the spontaneous ventilation period was 6.8 [6.4–7.1 (4.8–8.9)] kPa. The mean rate of increase in ETCO₂ was 0.03 kPa min⁻¹.

Conclusions. STRIVE Hi succeeded in preserving adequate oxygen saturation, end-tidal carbon dioxide and airway patency. We suggest that the upper and lower airway benefits attributed to HFNO, are ideally suited to a spontaneous respiration induction, increasing its margin of safety. STRIVE Hi is a modern alternative to the traditional inhalation induction.

Mask ventilation

Effective mask ventilation is an essential skill for any practitioner engaged in airway management. Recent methods to objectively describe mask ventilation using waveform capnography help practitioners to monitor and communicate the effectiveness of mask ventilation.

Gentle mask ventilation is now considered acceptable during rapid sequence induction/intubation after loss of consciousness, hence reducing the incidence of hypoxia prior to tracheal intubation. Mask ventilation can be enhanced with muscle relaxation, a double C-E grip, and jaw thrust. This is particularly relevant for patients with reduced apnoea time.

An awareness of the complications associated with mask ventilation may help reduce the morbidity associated with this technique. Effective ventilation technique and optimum device selection are important aspects for resuscitation of the newborn. Teaching correct establishment and maintenance of mask ventilation is essential for safe patient care.

This review will examine some of the latest developments concerning mask ventilation for adult and paediatric patients.

The effect of head rotation on efficiency of face mask ventilation in anaesthetised apnoeic adults: A randomised, crossover study

BACKGROUND

Upper airway obstruction occurs commonly after induction of general anaesthesia. It is the major cause of difficult mask ventilation.

OBJECTIVES

The aim of this study was to determine whether head rotation improves the efficiency of mask ventilation of anaesthetised apnoeic adults.

DESIGN

A randomised, crossover study.

SETTING

Single university teaching hospital.

PATIENTS

Forty patients, aged 18 to 75 years with a BMI 18.5 to 35.0 kg m requiring general anaesthesia for elective surgery were recruited and randomised into two groups.

INTERVENTIONS

Once apnoeic after induction of general anaesthesia, face mask ventilation began with pressure controlled ventilation, at a peak inspiratory pressure of 15 cmH2O. Each patient was ventilated for three 1-min intervals with the head position alternated every minute: group A, mask ventilation was performed with a neutral head position for 1 min, followed by an axial head position rotated 45° to the right for 1 min and then returned to the neutral position for another 1 min. In group B, the sequence of head positioning was rotated → neutral → rotated.

MAIN OUTCOME MEASURES

Expiratory tidal volume, measured with a respiratory inductive plethysmograph.

RESULTS

Two patients were excluded due to protocol violation; thus, data from 38 patients were analysed. The mean expiratory tidal volume was significantly higher in the rotated head position than in the neutral position (612.6 vs. 544.0 ml: difference [95% confidence interval], 68.6 [46.8 to 90.4] ml, P < 0.0001).

CONCLUSION

Head rotation of 45° in anaesthetised apnoeic adults significantly increases the efficiency of mask ventilation compared with the neutral head position. Head rotation is an effective alternative to improve mask ventilation if airway obstruction is encountered.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02755077.

Biomechanics of the soft-palate in sleep apnea patients with polycystic ovarian syndrome

Highly compliant tissue supporting the pharynx and low muscle tone enhance the possibility of upper airway occlusion in children with obstructive sleep apnea (OSA). The present study describes subject-specific computational modeling of flow-induced velopharyngeal narrowing in a female child with polycystic ovarian syndrome (PCOS) with OSA and a non-OSA control. Anatomically accurate three-dimensional geometries of the upper airway and soft-palate were reconstructed for both subjects using magnetic resonance (MR) images. A fluid-structure interaction (FSI) shape registration analysis was performed using subject-specific values of flow rate to iteratively compute the biomechanical properties of the soft-palate. The optimized shear modulus for the control was 38 percent higher than the corresponding value for the OSA patient. The proposed computational FSI model was then employed for planning surgical treatment for the apneic subject. A virtual surgery comprising of a combined adenoidectomy, palatoplasty and genioglossus advancement was performed to estimate the resulting post-operative patterns of airflow and tissue displacement. Maximum flow velocity and velopharyngeal resistance decreased by 80 percent and 66 percent respectively following surgery. Post-operative flow-induced forces on the anterior and posterior faces of the soft-palate were equilibrated and the resulting magnitude of tissue displacement was 63 percent lower compared to the pre-operative case. Results from this pilot study indicate that FSI computational modeling can be employed to characterize the mechanical properties of pharyngeal tissue and evaluate the effectiveness of various upper airway surgeries prior to their application.

Postoperative Respiratory Impairment Is a Real Risk for Our Patients: The Intensivist's Perspective

Postoperative respiratory impairment occurs as a result of a combination of patient, surgical, and management factors and contributes to both surgical and anesthetic risk. This complication is challenging to predict and has been associated with an increase in mortality and hospital length of stay. There is mounting evidence to suggest that patients remain vulnerable to respiratory impairment well into the postoperative period, with the vast majority of adverse events occurring during the first 24 hours following discharge from anesthesia care. At present, preoperative risk stratification scores may be able to identify patients who are particularly prone to respiratory complications but cannot consistently and globally predict risk in an ongoing fashion as they do not incorporate the impact of intra- and postoperative events. Current postoperative monitoring strategies are not always continuous or comprehensive and do not dependably identify all cases of respiratory impairment or mitigate their sequelae, which may be severe and require the use of increasingly limited intensive care unit resources. As a result, postoperative respiratory impairment has the potential to cause significant downstream effects that can increase cost and adversely impact the care of other patients.

Deep or awake removal of laryngeal mask airway in children at risk of respiratory adverse events undergoing tonsillectomy-a randomised controlled trial

BACKGROUND

Laryngeal mask airways (LMA) are widely used during tonsillectomies. Contrasting evidence exists regarding the timing of the removal and the risk of perioperative respiratory adverse events. We assessed whether the likelihood of perioperative respiratory adverse events is influenced by the timing of LMA removal in children with at least one risk factor for these events.

METHODS

Participants (n=290, 0-16 yr) were randomised to have their LMA removed either deep (in theatre by anaesthetist at end-tidal sevoflurane >1 minimum alveolar concentration) or awake (in theatre by anaesthetist or in postanaesthesia care unit by anaesthetist or trained nurse). The primary outcome was the occurrence of perioperative respiratory adverse events over the whole emergence and postanaesthesia care unit phases of anaesthesia. The secondary outcome was the occurrence of perioperative respiratory adverse events over the distinct phases of emergence and postanaesthesia care unit.

RESULTS

Data from 283 participants were analysed.

PRIMARY OUTCOME

even though a higher occurrence of adverse events was observed in the awake group, no evidence for a difference was found [45% vs 35%, odds ratio (OR): 1.5, 95% confidence interval (CI): 0.9-2.5, P=0.09]. Secondary outcome: there was no evidence for a difference between the groups during emergence [19 (14%) deep vs 25 (18%) awake, OR: 0.74, 95%CI: 0.39-1.42, P=0.37]. However, in the postanaesthesia care unit, children with an awake rather than deep removal experienced significantly more adverse events [55 (39%) vs 37 (26%); OR: 1.85, 95%CI: 1.12-3.07, P=0.02].

CONCLUSION

We found no evidence for a difference in the timing of the LMA removal on the incidence of respiratory adverse events over the whole emergence and postanaesthesia care unit phases. However, in the postanaesthesia care unit solely, awake removal was associated with significantly more respiratory adverse events than deep removal.

TRIAL REGISTRATION NUMBER

ACTRN12609000387224 (www.anzctr.org.au).

Comparison of Arndt-endobronchial blocker plus laryngeal mask airway with left-sided double-lumen endobronchial tube in one-lung ventilation in thoracic surgery in the morbidly obese

This study aimed to evaluate the feasibility and performance of Arndt-endobronchial blocker (Arndt) combined with laryngeal mask airway (LMA) compared with left-sided double-lumen endobronchial tube (L-DLT) in morbidly obese patients in one-lung ventilation (OLV). In a prospective, randomized double-blind controlled clinical trial, 80 morbidly obese patients (ASA I-III, aged 20-70) undergoing general anesthesia for elective thoracic surgeries were randomly allocated into groups Arndt (n=40) and L-DLT (n=40). In group Arndt, a LMA™ Proseal was placed followed by an Arndt-endobronchial blocker. In group L-DLT, patients were intubated with a left-sided double-lumen endotracheal tube. Primary endpoints were the airway establishment, ease of insertion, oxygenation, lung collapse and surgical field exposure. Results showed similar ease of airway establishment and tube/device insertion between the two groups. Oxygen arterial pressure (PaO2) of patients in the Arndt group was significantly higher than L-DLT (154±46 vs 105±52 mmHg; P<0.05). Quality of lung collapse and surgical field exposure in the Arndt group was significantly better than L-DLT (effective rate 100 vs 90%; P<0.05). Duration of surgery and anesthesia were significantly shorter in the Arndt group (2.4±1.7 vs 3.1±1.8 and 2.8±1.9 vs 3.8±1.8 h, respectively; P<0.05). Incidence of hoarseness of voice and incidence and severity of throat pain at the post-anesthesia care unit and 12, 24, 48, and 72 h after surgery were significantly lower in the Arndt group (P<0.05). Findings suggested that Arndt-endobronchial blocker combined with LMA can serve as a promising alternative for morbidly obese patients in OLV in thoracic surgery.

Improving patient safety during procedural sedation via respiratory volume monitoring: A randomized controlled trial

STUDY OBJECTIVE

Assess the utility of a respiratory volume monitor (RVM) to reduce the incidence of low minute ventilation events in procedural sedation.

DESIGN

Randomized control trial SETTING: Endoscopy suite PATIENTS: Seventy-three total patients (ASA Physical Status 1-3) undergoing upper endoscopies were analyzed.

INTERVENTION

Patients were randomized into two groups using a computer generated randomization table: Control (n=41): anesthesia provider was unable to see the screen of the RVM; RVM (n=32): anesthesia provider had access to RVM data to assist with management of the case.

MEASUREMENTS

Minute ventilation (MV), tidal volume, and respiratory rate were continuously recorded by the RVM. MV is presented as percent of Baseline MV (MV_Baseline), defined during a 30s period of quiet breathing prior to sedation. We defined Low MV as MV<40% MV_Baseline, and calculated the percentage of procedure spent with Low MV. Patients in the RVM group were stratified based on whether the anesthesiologist rated the RVM as "not useful", "somewhat useful", or "very useful" during the case.

MAIN RESULTS

Control patients experienced twice as much Low MV compared to RVM patients (15.3±2.8% vs. 7.1±1.4%, P=0.020). The "not useful" (13.7±3.8%) group showed no improvement over the Control group (p=0.81). However, both the "very useful" (4.7±1.4%) and "somewhat useful" (4.9±1.7%) groups showed significant improvement over the "not useful" group (p<0.05).

CONCLUSIONS

Patients in the Control group spent more than double the amount of time with Low MV compared to the RVM group. This difference became more pronounced when the anesthesiologist found the RVM useful for managing care, lending credibility to the usage of minute ventilation monitoring in procedural sedation.

Enhancing airway assessment of patients with head and neck pathology using virtual endoscopy

Studies have demonstrated that poor assessment and planning contribute to airway complications and that current airway assessment strategies have a poor diagnostic accuracy in predicting difficult intubation in the general population. Patients with head and neck pathology are at higher risk for difficulties during airway management and are more likely to need emergency surgical access. Therefore, thorough assessment of this group of patients is mandatory. The addition of virtual endoscopy (VE) to clinical history and computerised tomography imaging has been shown to improve diagnostic accuracy for supraglottic, glottic and infraglottic lesions and has a positive influence in formulating a more cautious and thorough airway management strategy in this high-risk group of patients. This article reviews whether VE can enhance airway assessment in patients with head and neck pathology and help reduce airway complications.