Canadian Airway Focus Group updated consensus-based recommendations for management of the difficult airway: part 1. Difficult airway management encountered in an unconscious patient

PURPOSE

Since the last Canadian Airway Focus Group (CAFG) guidelines were published in 2013, the literature on airway management has expanded substantially. The CAFG therefore re-convened to examine this literature and update practice recommendations. This first of two articles addresses difficulty encountered with airway management in an unconscious patient.

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 was lacking, statements are based on group consensus.

FINDINGS AND KEY RECOMMENDATIONS

Most studies comparing video laryngoscopy (VL) with direct laryngoscopy indicate a higher first attempt and overall success rate with VL, and lower complication rates. Thus, resources allowing, the CAFG now recommends use of VL with appropriately selected blade type to facilitate all tracheal intubations. If a first attempt at tracheal intubation or supraglottic airway (SGA) placement is unsuccessful, further attempts can be made as long as patient ventilation and oxygenation is maintained. Nevertheless, total attempts should be limited (to three or fewer) before declaring failure and pausing to consider "exit strategy" options. For failed intubation, exit strategy options in the still-oxygenated patient include awakening (if feasible), temporizing with an SGA, a single further attempt at tracheal intubation using a different technique, or front-of-neck airway access (FONA). Failure of tracheal intubation, face-mask ventilation, and SGA ventilation together with current or imminent hypoxemia defines a "cannot ventilate, cannot oxygenate" emergency. Neuromuscular blockade should be confirmed or established, and a single final attempt at face-mask ventilation, SGA placement, or tracheal intubation with hyper-angulated blade VL can be made, if it had not already been attempted. If ventilation remains impossible, emergency FONA should occur without delay using a scalpel-bougie-tube technique (in the adult patient). The CAFG recommends all institutions designate an individual as "airway lead" to help institute difficult airway protocols, ensure adequate training and equipment, and help with airway-related quality reviews.

A NEW SEMI-EMPIRICAL AMBIENT TO EFFECTIVE DOSE CONVERSION MODEL FOR THE PREDICTIVE CODE FOR AIRCREW RADIATION EXPOSURE (PCAIRE)

The Predictive Code for Aircrew Radiation Exposure (PCAIRE) is a semi-empirical code that estimates both ambient dose equivalent, based on years of on-board measurements, and effective dose to aircrew. Currently, PCAIRE estimates effective dose by converting the ambient dose equivalent to effective dose (E/H) using a model that is based on radiation transport calculations and on the radiation weighting factors recommended in International Commission on Radiological Protection (ICRP) 60. In this study, a new semi-empirical E/H model is proposed to replace the existing transport calculation models. The new model is based on flight data measured using a tissue-equivalent proportional counter (TEPC). The measured flight TEPC data are separated into a low- and a high-lineal-energy spectrum using an amplitude-weighted ¹³⁷Cs TEPC spectrum. The high-lineal-energy spectrum is determined by subtracting the low-lineal-energy spectrum from the measured flight TEPC spectrum. With knowledge of E/H for the low- and high-lineal-energy spectra, the total E/H is estimated for a given flight altitude and geographic location. The semi-empirical E/H model also uses new radiation weighting factors to align the model with the most recent ICRP 103 recommendations. The ICRP 103-based semi-empirical effective dose model predicts that there is a ∼30 % reduction in dose in comparison with the ICRP 60-based model. Furthermore, the ambient dose equivalent is now a more conservative dose estimate for jet aircraft altitudes in the range of 7-13 km (FL230-430). This new semi-empirical E/H model is validated against E/H predicted from a Monte Carlo N-Particle transport code simulation of cosmic ray propagation through the Earth's atmosphere. Its implementation allows PCAIRE to provide an accurate semi-empirical estimate of the effective dose.

Impact of oxaliplatin-induced neuropathy in patients with colorectal cancer: a prospective evaluation at a single institution

Oxaliplatin plays a major role in the treatment of colorectal cancer (crc), but is associated with the development of neuropathies. The main objective of the present prospective study was to estimate the proportion of participants with grade 1, 2, 3, or 4 peripheral sensory neuropathies according to the U.S. National Cancer Institute's Common Terminology Criteria for Adverse Events (version 4) among crc patients treated with oxaliplatin (adjuvant or metastatic, folfox or xelox regimens) at the Centre hospitalier universitaire de Sherbrooke. Among the 57 patients so treated between May 2012 and April 2013, about 60% reported grade 2 neuropathy, at maximum, during treatment. About 25% of patients had to stop treatment because of neuropathies. In a subset of patients contacted approximately 22 months after treatment cessation, neuropathies persisted in 70%. Oxaliplatin-induced neuropathy affects a significant number of crc patients and can influence the course of treatment and outcomes.

Palliative chemotherapy for patients 70 years of age and older with metastatic colorectal cancer: a single-centre experience

BACKGROUND

Metastatic colorectal cancer (mcrc) commonly affects elderly people, an understudied subset of patients. We analyzed the survival impact of the first and subsequent lines of chemotherapy in eligible non-trial patients 70 years of age and older with mcrc treated between 2004 and 2012.

METHODS

This single-centre retrospective analysis estimated overall survival (os) and progression-free survival (pfs) using the Kaplan-Meier method. Multivariate analysis was used to adjust for age, sex, Eastern Cooperative Oncology Group performance status, score on the Charlson comorbidity index, dependency in activities of daily living, and exposure to 1 or more chemotherapy doublets, capecitabine alone, or best supportive care (bsc).

RESULTS

Of 109 patients identified, 29 elected bsc, and 80 received chemotherapy. In multivariate analysis, age was not associated with os [hazard ratio (hr): 0.99; 95% confidence interval (ci): 0.92 to 1.05], but a performance status of 2 or higher was associated with a decreased likelihood of survival (hr: 3.12; 95% ci: 1.87 to 5.76), and exposure to 1 or more doublets was associated with improved survival (hr: 0.33; 95% ci: 0.17 to 0.66). In univariate analysis, a trend toward improved os was observed for first-line doublet chemotherapy compared with capecitabine (hr: 0.66; 95% ci: 0.41 to 1.07), and pfs was superior (hr: 0.46; 95% ci: 0.26 to 0.84). Compared with exposure to 1 doublet, exposure to the 3 potential cytotoxic chemotherapies was not associated with improved os (hr: 0.77; 95% ci: 0.41 to 1.43). The incidence of neutropenia with first-line folfiri was 40%; the incidences of bevacizumab-related arterial and venous thrombosis were both 8%.

CONCLUSIONS

Exposure to 1 or more doublet chemotherapies for mcrc was associated with better outcomes in non-trial patients 70 years of age and older. Elderly patients treated with palliative chemotherapy and bevacizumab should be monitored carefully for arterial and venous thrombotic events.

Combined HER2 analysis of biopsies and surgical specimens to optimize detection of trastuzumab-eligible patients in eso-gastric adenocarcinoma: a GERCOR study

BACKGROUND

HER2 is overexpressed in 10 to 20% of gastro-esophageal adenocarcinoma (GE-ADK), and is a target for trastuzumab in metastatic patients. We conducted a study to compare HER2 expression between diagnostic biopsies (DBs) and surgical specimens (SSs) of GE-ADK, and to determine the influence of non-trastuzumab containing neoadjuvant chemotherapy (NAC) on this expression.

PATIENTS AND METHODS

Pathological specimens from biopsies of 228 patients operated on between 2004 and 2011 were collected. Two cohorts treated (n = 141) or not (n = 87) with a NAC were constituted. Two blind independent pathological HER2 analyses on DB and on SS were carried out using immunohistochemistry (IHC) and colorimetric in situ hybridization (CISH). HER-2 overexpression (HER2+) was defined by a score 3+ in IHC, or 2+ with a positive CISH test, according to the specific HER2 scoring guidelines for GE-ADK.

RESULTS

Paired HER2 status could be determined for 218 out of the 228 patients (95.6%). HER2+ rates were 13.3% on DB (29/218) and 14.7% on SS (32/218). HER2+ tumors were mainly cardial or esophageal adenocarcinomas, with a well-differentiated, intestinal histological type. HER2 status differed between DB and SS in 6% of cases. When DB analyses were added to SS analyses, the relative increase in HER2+ cases was 13.5% (17.1% for patients with NAC and 23.5% for patients with histological response to NAC, versus 7.1% for patients without NAC, P = 0.4, NS). Differences between DB and SS HER2 expression could be explained by intratumoral heterogeneity and by a HER2 expression decrease in SS after NAC in responding patients possibly due to a higher chemosensitivity of HER2-positive clones.

CONCLUSION

The determination of HER2 status on DB provides results that complete those obtained with SS. Combining the analysis of DB and of SS enables to optimize the selection of trastuzumab-eligible patients in case of metastatic relapse, and particularly in previously NAC-responding patients.

Multichannel statistical analysis of low-level radioactivity in the presence of background counts

This paper presents a multichannel extension to the Poisson-based Bayesian statistical analysis of the net count rate in a sample. The derivation gives the net count rate probability density distribution in analytical form. In addition, it presents a Normal approximation that is appropriate when the number of counts is large. The new analysis can exhibit a lower false positive probability than methods that consider the counts for each peak separately or sum the counts for all the expected peaks associated with a radioactive substance.

A weight of evidence approach for the assessment of the ototoxic potential of industrial chemicals

There is accumulating epidemiological evidence that exposure to some solvents, metals, asphyxiants and other substances in humans is associated with an increased risk of acquiring hearing loss. Furthermore, simultaneous and successive exposure to certain chemicals along with noise can increase the susceptibility to noise-induced hearing loss. There are no regulations that require hearing monitoring of workers who are employed at locations in which occupational exposure to potentially ototoxic chemicals occurs in the absence of noise exposure. This project was undertaken to develop a toxicological database allowing the identification of possible ototoxic substances present in the work environment alone or in combination with noise exposure. Critical toxicological data were compiled for chemical substances included in the Quebec occupational health regulation. The data were evaluated only for noise exposure levels that can be encountered in the workplace and for realistic exposure concentrations up to the short-term exposure limit or ceiling value (CV) or 5 times the 8-h time-weighted average occupational exposure limit (TWA OEL) for human data and up to 100 times the 8-h TWA OEL or CV for animal studies. In total, 224 studies (in 150 articles of which 44 evaluated the combined exposure to noise and a chemical) covering 29 substances were evaluated using a weight of evidence approach. For the majority of cases where potential ototoxicity was previously proposed, there is a paucity of toxicological data in the primary literature. Human and animal studies indicate that lead, styrene, toluene and trichloroethylene are ototoxic and ethyl benzene, n-hexane and p-xylene are possibly ototoxic at concentrations that are relevant to the occupational setting. Carbon monoxide appears to exacerbate noise-induced hearing dysfunction. Toluene interacts with noise to induce more severe hearing losses than the noise alone.

Development of a predictive code for aircrew radiation exposure

Using the empirical data measured by the Royal Military College with a tissue equivalent proportional counter, a model was derived to allow for the interpolation of the dose rate for any global position, altitude and date. Through integration of the dose-rate function over a great circle flight path or between various waypoints, a Predictive Code for Aircrew Radiation Exposure (PCAire) was further developed to provide an estimate of the total dose equivalent on any route worldwide at any period in the solar cycle.

Ethyl benzene should be considered ototoxic at occupationally relevant exposure concentrations

Organic solvents can produce ototoxic effects in both man and experimental animals. The objective of this study was to review the literature on the effects of low-level exposure to ethyl benzene on the auditory system and consider its relevance for the occupational settings. Both human and animal investigations were evaluated only for realistic exposure concentrations based on the permissible exposure limits. In Quebec, the Time-Weighed Average Exposure Value for 8A h (TWAEV) is 100A ppm (434A mg/m(3)) and the Short-Term Exposure Value for 15A min (STEV) is 125A ppm (543A mg/m(3)). In humans, the upper limit for considering ototoxicity data relevant to the occupational exposure situation was set at STEV. Animal data were evaluated only for exposure concentrations up to 100 times the TWAEV. In workers, there is no evidence of either ethyl benzene-induced hearing losses or ototoxic interaction after combined exposure to ethyl benzene and noise. In rats, ethyl benzene affects the auditory function mainly in the cochlear mid-frequency range and ototoxic interaction was observed after combined exposure to noise and ethyl benzene. Further studies with sufficient data on the ethyl benzene exposure of workers are necessary to make a definitive conclusion. Given the current evidence from animal studies, we recommend considering ethyl benzene as an ototoxic agent.

Ototoxicity of trichloroethylene in concentrations relevant for the working environment

Organic solvents can cause hearing loss themselves or promote noise-induced hearing loss. The objective of this study was to review the literature on the effects of low-level exposure to trichloroethylene on the auditory system and consider its relevance for the occupational settings. Both human and animal investigations were evaluated only for realistic exposure concentrations based on the Quebec permissible exposure limits: 50 ppm 8-h time-weighed average exposure value (TWAEV) and 200 ppm short-term exposure value (STEV). In humans, the upper limit for considering ototoxicity data relevant to the occupational exposure situation was set at the STEV. Animal data were evaluated only for exposure concentrations up to 100 times the TWAEV. There is no convincing evidence of trichloroethylene-induced hearing losses in workers. In rats, trichloroethylene affects the auditory function mainly in the cochlear mid- to high-frequency range with a lowest observed adverse effect level (LOAEL) of 2000 ppm. No studies on ototoxic interaction after combined exposure to noise and trichloroethylene were identified in humans. In rats, supra-additive interaction was reported. Further studies with sufficient data on the trichloroethylene exposure of workers are necessary to make a definitive conclusion. In the interim, we recommend considering trichloroethylene as an ototoxic agent.

Adjustment of permissible exposure values to unusual work schedules

Research activities sought development of a method to adjust exposure limits for 694 substances for unusual work schedules. A consensus was established on the basic toxicological principle for adjustment; criteria for adjustment were selected by a panel of scientists coordinated by a committee of international experts and supported by toxicokinetic modeling; and a group of toxicologists attributed primary health effects and related adjustment category to each substance. A consensus among scientists and employers' and workers' representatives was established on the protocol of the application, in the field, of the adjusted exposure limits. The guiding toxicological principle for adjusting exposure standards to unusual work schedules is to guarantee an equivalent degree of protection for workers with unusual schedules as for workers with a conventional schedule of 8 hours per day, 5 days per week. The process of the adjustment is inspired from the Occupational Safety and Health Administration logic for attribution of primary health effects and adjustment categories ranging from no adjustment to daily or weekly adjustments. The adjusted exposure limits are calculated according to Haber's rule. Decisions on attribution of adjustment categories for the following toxicological effects were reached: respiratory sensitizers (asthma); skin sensitizers; tissue irritants versus tissue toxicants; methemoglobinenia-causing agents; cholinesterase inhibitors; and reproductive system toxicants and teratogens. A simple procedure is presented to facilitate the calculation, application, and interpretation of the adjusted exposure limits.

Structural requirements for molecular recognition by the Neurokinin receptors

Populations of lower energy conformers have been generated by conformational energy calculations, using empirical energy functions, for the C-terminal pentapeptide of Substance P (CH3-CO-Phe-Phe-Gly-Leu-Met-NH2), Neurokinins A and B (CH3-CO-Phe-Val-Gly-Leu-Met-NH2), and Eledoisin (CH3-CO-Phe-Ile-Gly-Leu-Met-NH2). The C-terminal sequences are greatly conserved in the Neurokinin and Tachychinin families of peptides and are mainly responsible for the molecular recognition. These sequences differ in the nature of the second residue. This substitution interferes with the recognition processes and modulates the specificities. A procedure based on a random generation of conformers, followed by energy minimizations, has been applied to produce the populations of conformers for the three pentapeptides. The conformational properties of the lower energy conformers have been analysed and compared with respect to the substitution of the second residue. Earlier nuclear magnetic resonance data as well as structure–activity relationship results have been interpreted in light of the proposed stable conformers. It is shown that the selectivity towards the NK3 receptor requires a structure with a restrained flexibility introduced at the second N-terminal residue. The selectivity towards the NK1 receptor is shown to be related to the presence of a constrained structure at the Gly residue. These structures suggest further chemical modifications be introduced in order to produce more selective and stable analogues. Keywords: peptide conformation, empirical energy, Neurokinin, molecular recognition.