William P. McKay

Resting muscle sounds in anesthetized patients

It is known that contracting muscle makes low frequency sound vibrations. Small vibrations of uncertain origin are found over resting muscle. These could be shown to be of muscle origin if they significantly diminish in response to agents expected to decrease muscle activity. Thiopental, propofol, and neuromuscular-junction blocking muscle relaxants have such properties. Twenty-one subjects slated for elective surgery for which they would routinely be anesthetized and paralysed gave informed consent to having a small accelerometer taped upon their supine biceps (9 subjects), or volar forearm (12 subjects). Recordings were made in four stages while subjects: (i) lifted a 2-kg weight just off the sponge armrest on which their outstretched arm lay; (ii) relaxed their arm in the awake state prior to anesthesia; (iii) had anesthesia induced with intravenous thiopental (n = 11) or propofol (n = 10); and (iv) were paralysed. Recordings were digitised at 172-Hz and 6-s segments fast Fourier transformed (FFT). Total signal power, as determined by the area under the power spectrum, was significantly different (p < 0.05) in all stages for the biceps and in all but stages (iii) from (iv) in the forearm. It appears that resting muscle generates measurable vibrations.

Distribution of ran-domised controlled trials of drugs for post-operative nausea and vomiting

Purpose: Randomised controlled trials (RCTs) guide therapeutic decisions. But which RCTs are done; which omitted; and which should be done? This study illustrates a method to explore these questions applied to drugs for post-operative nausea and vomiting (PONV).Methods: Review artides listed 18 drugs for PONV. All RCTs of these drugs for PONV were sought. The first drug mentioned in an RCT was counted and tabulated against others in all the arms of the RCT (against itself in a dose-ranging RCT). Additional drugs mentioned in these RCTs were added to the study, for a total of 40 drugs.Results: Drugs involved in the most RCTs were: ondansetron 131 RCTs; propofol 118; droperidol 74; metoclopramide 67; granisetron 52; scopolamine 22; tropisetron 16. Drugs involved in the fewest RCTs: two drugs with 2 RCTs; twelve drugs with one; three with none. Probability that this distribution occurred by chance:P<0.00001; that the distribution of dose-ranging RCTs occurred by chance:P<0.001. Regression of RCT numbers on cost: R=0.86,P<0.0001; on year of drug introduction: R=0.14. Of 1600 possible comparisons of drugs for PONV, (including dose-ranging) 97.8% have never been published.Conclusion: Although some antiemetic drugs for PONV have been studied in large numbers of RCTs, many have not been adequately evaluated. Finding relevant RCTs and tabulating their comparison arms is useful for directing future research, and is applicable to any symptom or disorder.RésuméObjectif: Les essais contrôlés randomisés (ECR) guident les choix thérapeutiques, mais quels ECR sont réalisés, omis ou devraient être faits? L’étude actuelle illustre une méthode pour explorer ces questions appliquées aux médicaments contre les nausées et vomissements postopératoires (NVPO).Méthode: L’examen des articles a donné une liste de 18 médicaments contre les NVPO. Tous les ECR de ces médicaments contre les NVPO ont été recherchés. Le premier médicament mentionné dans un ECR était pris en compte et dassifié pour être comparé aux autres dans tous les groupes de l’ECR (comparé à lui-même dans un ECR portant sur un éventail de doses). Les médicaments additionnels mentionnés dans ces ECR ont été ajoutés à l’étude, amenant le total à 40 médicaments.Résultats: Les médicaments étudiés dans le plus grand nombre d’ECR ont été: l’ondansétron, 131 ECR; le propofol, 118; le dropéridol, 74; le métoclopramide, 67; le granisétron, 52; la scopolamine, 22; le tropisétron, 16. Les médicaments qu’on retrouve dans le plus petit nombre d’ECR: deux médicaments dans deux ECR; douze médicaments dans un; trois dans aucun. La probabilité que cette distribution soit l’effet du hasard:P<0,00001; que la distribution d’essais sur des doses multiples soit aléatoire:P<0,001. La régression du nombre des ECR selon le coût: R=0,86,P<0,0001; selon l’année d’introduction du médicament: R=0,14. Sur 1 600 comparaisons possibles de médicaments contre les NVPO (y compris les comparaisons de doses), 97,8 % n’ont jamais été publiées.Conclusion: Même si certains médicaments antiémétisants contre les NVPO ont été étudiés dans un grand nombre d’ECR, beaucoup n’ont pas été complètement évalués. La découverte d’ECR pertinents et le classement de leurs groupes comparatifs est utile en vue de recherches ultérieures et s’applique à tout symptôme ou tout dérèglement.

Reactive hyperemia increases forearm vein area.

PurposeTo determine the effect of reactive hyperemia on human forearm vein area.MethodsAfter obtaining ethics approval and informed consent, an automatic tourniquet was applied to the forearms of 20 healthy subjects for one, two, and three minutes, at pressures of 25 mmHg, 200 mmHg, then 25 mmHg. A blinded radiographer measured the cross-sectional area of the cephalic vein at the wrist using ultrasonography. Measurements were recorded prior to tourniquet application and every minute thereafter for ten minutes, at each pressure setting and each time interval.ResultsThe mean vein cross-sectional area (mm2) increased from 8.22 ± 3.09 to 10.77 ± 3.50 after one minute of ischemia, from 8.31 ± 2.78 to 10.61 ± 2.77 after two minutes of ischemia, and from 8.39 ± 3.34 to 10.94 ± 3.46 after three minutes of ischemia (P < 0.05 for all). A tourniquet inflated to 25 mmHg for 13 min produced a mean vein cross-sectional area of 10.71 ± 3.25 mm2.ConclusionsReactive hyperemia causes human forearm vein cross-sectional area to increase. A low pressure tourniquet will also increase forearm vein area, but veins dilate more quickly during reactive hyperemia. This may have important clinical implications for attempting venous cannulation in patients with difficult venous access.RésuméObjectifDéterminer l’effet de l’hyperémie réactionnelle sur l’aire veineuse de l’avant-bras humain.MéthodeAyant obtenu l’accord du comité d’éthique et le consentement éclairé des participants, nous avons appliqué un garrot automatique à l’avant-bras de 20 sujets sains pendant une, deux et trois minutes, à des pressions de 25 mmHg, 200 mmHg, puis 25 mmHg. Un radiologue impartial a mesuré, par échographie, l’aire transversale de la veine céphalique au poignet. Les mesures ont été enregistrées avant la pose du garrot et à chaque minute par la suite pendant dix minutes, pour chaque pression établie et chaque intervalle de temps.RésultatsL’aire veineuse transversale moyenne (mm2) a augmenté de 8,22 ± 3,09 à 10,77 ± 3,50 après une minute d’ischémie, de 8,31 ± 2,78 à 10,61 ± 2,77 après deux minutes d’ischémie et de 8,39 ± 3,34 à 10,94 ± 3,46 après trois minutes d’ischémie (P < 0,05 pour toutes les mesures). Un garrot gonflé à 25 mmHg pendant 13 min a produit une aire veineuse transversale moyenne de 10,71 ± 3,25 mm2.ConclusionL’hyperémie réactionnelle augmente l’aire veineuse transversale de l’avant-bras chez l’homme. Un garrot basse pression l’augmente aussi, mais les veines se dilatent plus rapidement pendant l’hyperémie réactionnelle. Cela pourrait avoir d’importantes implications cliniques pour les essais de canulation veineuse en cas d’accès veineux difficile.

Dexmedetomidine during total knee arthroplasty performed under spinal anesthesia decreases opioid use: a randomized-controlled trial.

BackgroundIt remains unclear whether the opioid-sparing effects of dexmedetomidine seen in patients undergoing general anesthesia are reproducible in patients undergoing spinal anesthesia. We hypothesized that the administration of intravenous dexmedetomidine for sedation during total knee arthroplasty under spinal anesthesia would decrease postoperative morphine consumption in the first 24 hr following surgery.MethodsWe conducted this prospective double-blind randomized-controlled trial in 40 patients (American Society of Anesthesiologists physical status I-III) undergoing total knee arthroplasty with a standardized spinal anesthetic. Patients were randomized to receive either a dexmedetomidine loading dose of 0.5 µg·kg−1 over ten minutes, followed by an infusion of 0.5 µg·kg·hr−1 for the duration of the surgery, or a normal saline loading dose and an infusion of an equivalent volume. The primary outcome was the consumption of morphine delivered via patient-controlled analgesia in the first 24 hr following surgery.ResultsThe mean (SD) cumulative morphine at 24 hr in the dexmedetomidine group was 29.2 (11.2) mg compared with 61.2 (17.2) mg in the placebo group (mean difference, 32.0 mg; 95% confidence interval, 22.7 to 41.2; P < 0.001). In the dexmedetomidine group, there was a delay in the time to first analgesic request (P = 0.003) and a reduction in the mean morphine use at six and 12 hr following surgery (both P < 0.001).ConclusionsDexmedetomidine was associated with a significant decrease in morphine use in the first 24 hr following total knee arthroplasty. Our study shows that an intraoperative infusion of dexmedetomidine for sedation in patients receiving spinal anesthesia can produce postoperative analgesic effects. This offers another potential adjunct in the multimodal pain management of these patients. This trial was registered at ClinicalTrials.gov (identifier NCT02026141).RésuméContexteNous ne savons pas si les effets de réduction de la consommation d’opioïdes qu’on observe lors de l’administration de dexmédétomidine aux patients subissant une anesthésie générale s’appliquent également chez les patients subissant une rachianesthésie. Nous avons émis l’hypothèse que l’administration de dexmédétomidine par voie intraveineuse pour la sédation pendant une arthroplastie totale du genou sous rachianesthésie réduirait la consommation postopératoire de morphine au cours des premières 24 h après la chirurgie.MéthodeNous avons réalisé cette étude randomisée contrôlée prospective à double insu chez 40 patients (statut physique I-III selon l’American Society of Anesthesiologists) subissant une arthroplastie totale du genou avec un anesthésique rachidien standardisé. Les patients ont été randomisés à recevoir soit une dose de charge de dexmédétomidine de 0,5 µg·kg−1 sur une période de 10 minutes, suivie par une perfusion de 0,5 µg·kg·h−1 pour la durée de la chirurgie, ou une dose de charge de sérum physiologique et une perfusion de volume équivalent. Le critère d’évaluation principal était la consommation de morphine administrée par analgésie contrôlée par le patient au cours des premières 24 h suivant la chirurgie.RésultatsLa dose cumulative moyenne (ÉT) de morphine consommée à 24 h dans le groupe dexmédétomidine était de 29,2 (11,2) mg, par rapport à 61,2 (17,2) mg dans le groupe placebo (différence moyenne, 32,0 mg; intervalle de confiance 95 %, 22,7 à 41,2; P < 0,001). Dans le groupe dexmédétomidine, on a observé un délai jusqu’au moment de première demande d’analgésique (P = 0,003) et une réduction de l’utilisation moyenne de morphine à six et 12 h après la chirurgie (les deux P < 0,001).ConclusionLa dexmédétomidine a été associée à une réduction significative de la consommation de morphine au cours des premières 24 h suivant une arthroplastie totale du genou. Notre étude montre qu’une perfusion peropératoire de dexmédétomidine pour la sédation de patients recevant une rachianesthésie peut avoir des effets analgésiques postopératoires. Voici donc un autre adjuvant potentiel à la prise en charge multimodale de la douleur de ces patients. Cette étude est enregistrée au ClinicalTrials.gov (identifiant NCT02026141).

Three‐finger tracheal palpation to guide endotracheal tube depth in children

Accurate endotracheal tube (ETT) depth is critical, especially in children. The current tools used to guide appropriate ETT depth have significant limitations.

Tracheal ultrasound to assess endotracheal tube depth: an exploratory study

To the Editor, This letter outlines an observational study to assess endotracheal tube (ETT) depth using ultrasound. Ideal ETT tip position is in the mid-trachea, and malpositioning can result in unintended extubation, hypoxia, or barotrauma. Transverse plane ultrasound of the saline-filled ETT cuff has been reported to determine ETT depth in children and esophageal placement in adults. Although the use of measurement marks (MM) at the teeth (21 cm for females, 23 cm for males) is simple and commonly employed, this method is unreliable for ensuring adequate ETT tip placement. We explored the concept of ETT positioning using longitudinal ultrasound while watching the movement (undulation) of the tracheal rings as the ETT tip slides forward. We hypothesized that ultrasound observation of the ETT tip while it is moving slowly down the trachea would improve correct placement (ETT tip[ 2.5 cm from the carina with the cuff still below the cords) compared with the conventional MM technique. With University of Saskatchewan Ethics Board approval (May 2012), consent was obtained from adult elective surgery patients where routine tracheal intubation was planned. Non-elective and physiologically unstable patients were excluded. Following induction of anesthesia, the attending anesthesiologist was instructed to ‘‘advance the ETT slowly once the tip is through the cords’’ while an investigator viewed the trachea in the long axis using ultrasound (MicroMaxx with MSK L25e/13-6 MHz transducer; SonoSite Inc. Bothell, WA, USA). Disposable cuffed ETTs (8-mm internal diameter for females, 9-mm for males) were used for all intubations. When the ultrasound image of the tracheal ring undulation – caused by the advancing ETT – showed that the ETT tip had reached the sternal notch, the ETT was fixed at that depth. In addition, the depth marking at the upper incisors was noted in order to calculate where the ETT tip placement would have been if MM had been used. The ETT was carefully kept at that depth while an investigator evaluated (using flexible bronchoscopy) the ETT depth as ‘‘too shallow’’, ‘‘too deep’’, or ‘‘correct’’. A Chi square test was used to compare the MM vs the ultrasound method and intent-to-treat analysis was performed on the bronchoscopic evaluations. A sample size of 40 patients was based on a previous study. Fifty-three patients were approached; three declined consent, and seven were excluded because a bronchoscope was not available. This left 43 subjects (24 females and 19 males) to be evaluated. Sixteen patients had a BMI [ 30 kg m, including four subjects with a BMI [ 40 kg m. Movement of the ETT tip was visualized in 42 (98%) subjects. Using ultrasound resulted in 38 of 43 (88%) patients with a correct ETT position compared with 24 (56%) correct if only the conventional MM method had been used (mean difference 32%; 95% confidence interval [CI] 18 to 46%; P = 0.002). There were no endobronchial intubations, whereas two would have resulted with MM. Tracheal ultrasound was more successful than MM for proper ETT tip placement, but tracheal ultrasound was similar to results using palpation of the ETT tip during advancement, as previously reported, which resulted in 85% (95% CI 77 to 92) correct tip placements. W. P. McKay, MD (&) A. Wang, MD K. Yip, MD M. Raazi, MBChB Department of Anesthesiology, Perioperative Medicine and Pain Management, University of Saskatchewan, Saskatoon, SK, Canada e-mail: bill.mckay@usask.ca

Epidural loss-of-resistance biomechanics: an open pilot cadaver study

Purpose We measured dynamic biomechanics of loss-of-resistance (LOR) epidural placement in prone cadavers, focussing on the period immediately following LOR, to estimate forces acting on the tissue of the epidural space. Methods An epidural syringe with 17G Hustead needle was instrumented to track force on the plunger, pressure in the chamber, and movement of barrel and plunger. Insertions were attempted in five formalin-preserved cadavers from T2–3 to L4–5, using LOR with saline or air, and confirmed with X-ray. Results Sixteen insertions were successful. Soft tissues in formalin-preserved cadavers are much harder than in living humans. With continuous pressure on the plunger, fluid thrust through the needle at the point of LOR was significantly greater (P = 0.005) with saline (mean ± standard deviation [95% confidence intervals]: 19.3 ± 14.9 [8.3 to 30.3] N); than with air (0.17 ± 0.25 [0 to 0.39] N). Stress exerted on epidural tissue was similar (air = 7792 ± 920 [6986 to 8598] Pa; saline = 7378 ± 3019 [5141 to 9614] Pa); and in both cases was greater than the stress exerted by cerebrospinal fluid pushing outwardly on the dura (4800 Pa). Conclusion Formalin-preserved cadavers are too stiff to make them an experimental model from which we can generalize to live humans, although we were successful in entering the epidural space and testing the instrumentation for further studies on live animals or humans. Continuous pressure on the plunger while advancing the epidural needle may “blow” the dura away from the needle tip and help prevent dural puncture. Better results are seen with saline rather than air.

Peripheral venous pressure predicts central venous pressure poorly in pediatric patients

PurposeUsing peripheral venous pressure (PVP) instead of central venous pressure (CVP) as a volume monitor decreases patient risks and costs, and is convenient. This study was undertaken to determine if PVP predicts CVP in pediatric patients.MethodsWith ethical approval and informed consent, 30 pediatric patients aged neonate to 12 yr requiring a central venous line were studied prospectively in a tertiary care teaching hospital. In the supine position, PVP and CVP were simultaneously transduced. Ninety-six paired recordings of CVP and PVP were made. Correlation and Bland-Altman analysis of agreement of end-expiratory measurements were performed.ResultsThe mean (SD; range) CVP was 10.0 mmHg (6.0; −1.0 to 27.0); the mean PVP was 13.7 mmHg (6.3; 0.0 to 33.0); offset (bias) of PVP > CVP was 3.7 mmHg with SD 2.6. The 95% confidence intervals (CI) for the bias were 3.2 to 4.1 mmHg. In the Bland-Altman analysis, lower and upper limits of agreement (LOA; CI in parentheses) were −1.5 (−2.3 to −0.7) and 8.8 (8.1 to 9.6) mmHg. Eight of 96 points were outside the limits of agreement. The correlation of PVP on CVP was r = 0.92,P < 0.0001. For a subset of ten patients (20 simultaneous recordings) withiv atheters proximal to the hand, limits of agreement were better — offset: 3.8 mmHg (± 1.4); lower LOA: 1.2 mmHg (0.25 to 2.1); upper LOA: 6.6 mmHg (5.7 to 7.5).ConclusionPeripheral venous pressure measured from aniv catheter in the hand predicts CVP poorly in pediatric patients.RésuméObjectifLa tension veineuse périphérique (TVP) est une façon pratique de remplacer la tension veineuse centrale (TVC) comme indicateur de la réplétion volémique, à moindre risque et à meilleur coût. l’objectif de cette étude était de déterminer si la TVP est un bon reflet de la TVC chez les enfants.MéthodeAprès l’approbation du comité d’éthique et l’obtention du consentement, 30 sujets de 0 à 12 ans chez qui un cathéter veineux central était indiqué ont été recrutés de façon prospective dans un hôpital universitaire de soins tertiaires. On a mesuré la TVP et la TVC simultanément en position dorsale à 96 reprises. On a réalisé des analyses de corrélation et de Bland-Altman pour les mesures télé-expiratoires.RésultatsLa TVC moyenne (ET; extrêmes) était de 10,0 mmHg (6,0; −1,0 à 27,0); la TVP était de 13,7 mmHg (6,3; 0,0 à 33,0); la TVP était de 3,7 mmHg (ET 2,6) supérieure à la TVC. Les intervalles de confiance à 95% (IC) pour cet écart (biais) étaient de 3,2 à 4,1 mmHg. Selon l’analyse Bland-Altman, les limites de concordance inférieure et supérieure (LDC; CI entre parenthèses) étaient de −1,5 (−2,3 à −0,7) et 8,8 (8,1 à 9,6) mmHg. Huit des 96 points étaient à l’extérieur des limites de concordance. La corrélation entre PVP et TVC était r = 0,92, P < 0,0001. Dans un sous-groupe de dix patients (20 mesures pairées) avec des cathéters iv plus proximaux que la main, la concordance était meilleure — biais: 3,8 mmHg (± 1,4); LDC inférieure: 1,2 mmHg (0,25 à 2,1); supérieure: 6,6 mmHg (5,7 à 7,5).ConclusionLa tension veineuse périphérique mesurée à partir d’un cathéter installé sur la main ne reflète pas bien la TVC chez les enfants.

A randomized trial of three lubrication strategies on sore throat after insertion of the LMA ® Classic™ supraglottic airway

To the Editor, The laryngeal mask supraglottic airway (SGA) is commonly used in anesthesiology and is often lubricated for easy insertion. We studied sore throat (primary outcome), cough, and laryngospasm after insertion of the LMA Classic (Teleflex Inc.; Morrisville, NC, USA) comparing three lubricating strategies: water-soluble medical lubricant (M) (Muko; Source Medical, Mississauga ON, Canada) or 2% lidocaine jelly (L) (Lidodan; Odan Laboratories, Montreal QC, Canada) vs no lubricant control (C). After institutional ethical approval, consenting American Society of Anesthesiologists physical status I-II adult patients having elective surgery where an LMA was planned were recruited. Those with asthma, sore throat, cough, or allergy to lidocaine or Muko were excluded. Participants were randomly assigned after anesthesia induction by opening an opaque envelope, prepared by the research pharmacist, that contained a 3-mL syringe with Muko, lidocaine jelly, or nothing, with instructions to apply the lubricant to the entire inflatable surface of the LMA. Patients, investigators, and other caregivers were blinded to group assignment. The anesthesiologist was blinded to the lubricants, but not to lubricant vs. controls. Anesthesia was induced with 1 ug kg fentanyl and propofol and maintained with sevoflurane in air-oxygen with additional fentanyl as needed (up to 4 lg kg hr). Antiemetics were given according to guidelines by Gan et al. Morphine was used in the postanesthetic care unit (PACU) as needed. Patients were assessed for coughing and laryngospasm as well as for sore throat in the PACU and on the first postoperative day. Demographics, concurrent diseases, cigarette use, medications, number of attempts to insert the LMA, and any complications were recorded. The anesthesiologist graded severity of coughing on emergence on the validated five-point Breathlessness, Cough, and Sputum Scale (where 0 is no cough and 4 is a prolonged distressing coughing spell resulting in breathlessness), so for simplicity we used a similarly rated scale for throat pain in PACU. Continuous variables were compared using KruskalWallis analysis of variance on ranks; categorical variables using Chi-squared. An intention-to-treat analysis was used, with removal of one patient from analysis whose surgery was cancelled and one where the pharmacy was unable to provide the envelope in time. Two hundred participants were recruited from 4 June 2004 to 28 February 2007 (see Table). Pain scores on day zero and day one were low and not different (Table). One participant in group M had severe throat pain (score = 4) in PACU; no one had severe throat pain on postoperative day 1. There was no significant difference in difficulty with LMA insertion. Laryngospasm on LMA removal occurred in two controls and once in each lubricated group. This letter is accompanied by an editorial. Please see Can J Anesth 2018; 65: this issue.

Erratum to: Tracheal palpation to assess endotracheal tube depth: an exploratory study

In the article entitled: ‘‘Tracheal palpation to assess endotracheal tube depth: an exploratory study’’ published in the March 2014 issue, Can J Anesth 2014; DOI: 10.1007/s12630-013-0079-4, Table 3 contained several typographical errors that have now been corrected by the authors. In addition, the first column of Fig. 2 also contained an error that has also been corrected. The authors apologize most sincerely for these errors. Table 3 Comparison of tracheal palpation (TP) with measurement method (MM)