Karen E. Raymer

Patients with aortic stenosis: Cardiac complications in non-cardiac surgery

PurposeTo reassess the risk of patients with aortic stenosis (AS) undergoing non-cardiac surgery.MethodsFollowing institutional approval, a retrospective chart audit of all patients with AS who underwent non-cardiac surgery in Hamilton between 1992 and 1994 was performed. For each AS case, a matching control was randomly selected. Data pertaining to pre-operative cardiac risk factors, intra-operative, and post-operative management were recorded. Complications were defined as the onset of congestive heart failure (CHF), myocardial infarction (M1), or dysrhythmias requiring cardioversion within seven post-operative days; unplanned or prolonged intensive care unit (ICU) stay due to cardiac cause; and cardiac death. Categorical data were compared using discordant data pairs and binomial distribution, with θ = 0.5. Parametric data were compared using students’ t test. All comparisons were two-tailed, with α < 0.05 considered significant.Results55 patients (32 male, 23 female, mean age 73 yr) with AS (mean aortic valve area 0.9 cm2) were studied. Cases and controls were identical for eight of nine pre-operative risk factors. Differences in perioperative management were found. Cardiac complications occurred in five cases and six control patients (P = 1.00).ConclusionsThe current study, involving 55 patients with AS undergoing non-cardiac surgery, showed no difference in the risk of cardiac complications compared with matched controls. However, the intensification of management in the AS patients may have attenuated the risk in this group. The sample size was adequate to detect a fourfold increase in risk.RésuméObjectifRéévaluer le risque, chez les patients présentant une sténose aortique (SA), de subir une chirurgie non cardiaque.MéthodeAprès avoir obtenu l’accord de l’institution, nous avons procédé à un audit rétrospectif des fiches de tous les patients souffrant de SA qui ont subi une chirurgie non cardiaque à Hamilton entre 1992 et 1994. Pour chacun des patients SA, il y a eu l’appariement au hasard d’un cas témoin. Des données relatives aux facteurs de risque cardiaque préopératoire, à la prise en charge intraopératoire et postopératoire ont été enregistrées. On a reconnu comme complications la survenue d’une insuffisance cardiaque congestive (ICC), l’infarctus du myocarde (IM) ou les troubles du rythme nécessitant une cardioversion dans les sept premiers jours postopératoires; un séjour non prévu ou prolongé à l’unité des soins intensifs (USI) en raison d’une cause cardiaque; l’arrêt cardiaque. Des données catégorielles ont été comparées en utilisant des paires de données discordantes et une distribution binomiale, avec θ = 0,5. Les données paramétriques ont été comparées selon le testt de Student. Toutes les comparaisons étaient bilatérales, avec α < 0,05 considéré comme significatif.Résultats55 patients (32 hommes, 23 femmes, dont l’âge moyen était de 73 ans) souffrant de SA (aire aortique moyenne de 0,9 cm2) ont été étudiés. Les patients et les témoins présentaient des fiches identiques pour huit des neuf facteurs de risque préopératoire. Des différences de mesures périopératoires ont été trouvées. Les complications cardiaques sont survenues chez cinq patients et six cas du groupe témoin (P = 1,00).ConclusionLa présente étude, réunissant 55 patients souffrant de SA et qui ont subi une chirurgie non cardiaque, n’a montré aucune différence de risque de complications cardiaques quand on les compare aux cas témoins qui leur sont appariés. Cependant, le renforcement des mesures thérapeutiques auprès des patients présentant une SA peut avoir atténué le risque dans ce groupe. Le nombre de sujets nécessaires à l’étude était suffisant pour détecter un accroissement de risque quatre fois plus grand.

Comparison of general anesthesia with and without lumbar epidural for total hip arthroplasty: Effects of epidural block on hip arthroplasty☆

STUDY OBJECTIVES To determine whether lumbar epidural anesthesia, when combined with general anesthesia, decreases perioperative blood loss, the incidence of postoperative deep vein thrombosis (DVT), cardiac dysrhythmias, and ischemia in patients undergoing total hip arthroplasty (THA). DESIGN Randomized, controlled study. SETTING A university hospital. PATIENTS 37 ASA physical status I, II, and III patients, undergoing elective THA. INTERVENTION Patients were divided into two statistically comparable groups: Group GA = general anesthesia; Group CEGA = general anesthesia plus lumbar epidural anesthesia. All patients had 48-hour perioperative Holter monitoring, applied on admission, the day prior to surgery. In both groups, general anesthesia was induced with thiopental sodium and muscle relaxant, and maintained with oxygen, nitrous oxide, isoflurane, opioid, and muscle relaxant. Group B received lumbar epidural anesthesia with 10 ml 0.5% bupivacaine with 1:200,000 epinephrine prior to anesthesia induction. Blood loss was measured by suction bottle contents, sponge weights, and collection drainage. DVT was assessed with postoperative leg scanning, plethysmography, and venogram. MEASUREMENTS AND MAIN RESULTS Intraoperative blood loss was less after combined epidural-general anesthesia (663.8 ml +/- 299.0 ml) than after general anesthesia alone (1,259.2 ml +/- 366.0 ml). The difference was found to be statistically significant (p < 0.00005). No difference was found between the two groups in postoperative blood loss, incidence of DVT, cardiac dysrhythmias, or ischemia. CONCLUSION Combined regional-general anesthesia decreases intraoperative blood loss in THA, and thereby offers an advantage over general anesthesia alone.

Concurrent subarachnoid haemorrhage and myocardial injury

PurposeSubarachnoid haemorrhage is frequently associated with myocardial injury and dysfunction. This report describes such a case, reviews the understanding of this phenomenon, and discusses the implications for timing of surgical clipping of intracranial aneurysm in patients with concurrent myocardial damage.Clinical FeaturesA 64-yr-old woman presented with syncope and congestive heart failure. A diagnosis of subarachnoid haemorrhage was made three days following the initial diagnosis of myocardial infarction. The patient presented for clipping of an intracranial aneurysm on day 36, after her cardiac status had stabilized. No new myocardial ischaemic events occurred, either intra-operatively or post-operatively. Ultimate neurological recovery was poor.ConclusionsThis case report demonstrates four important aspects of the clinical course of patients with concurrent subarachnoid haemorrhage and myocardial damage: 1) On presentation, cardiac features may predominate, and delay diagnosis and treatment of the underlying subarachnoid haemorrhage. 2) Left ventncular dysfunction, although dramatic, is usually transient. 3) There is confusion regarding the appropriate cardiac risk assessment and management in such patients when presenting for surgery. 4) Long-term morbidity is most often related to neurological, not medical, complications.RésuméObjectifL’hémorragie sous-arachnoïdienne s’accompagne souvent d’une lésion et d’un dysfonctionnement myocardiques. Ce compte rendu décnt un cas de cette affection, fait un survol de nos connaissances et discute de I’importance de ben planifier le moment de clamper I’anévrisme intracrânien chez des patients atteints d’une lésion myocardique.Éléments cliniquesUne femme de 64 ans se présente en état de syncope et d’insuffisance cardiaque. On constate qu’elle présente une hémorragie sous-arachnoïdienne trois jours après le diagnostic initial d’infarctus du myocarde. Trente-six jours plus tard, après stabilisation de la condition cardiaque, on insère un clip sur un col anévrismal. Elle ne présente pas de nouveaux épisodes d’ischémie myocardique peropératoires et postopératoires. La récupération neurologique définitive a été médiocre.ConclusionsCette observation illustre quatre aspect importants de I’évolution clinique de patients victimes d’hémorragie sous-arachnoïdienne et de lésion myocardique simultanées: 1) au départ, les éléments cardiaques peuvent prédominer et retarder le diagnostic et le traitement de l’hémorragie sous-arachnoïdienne sous-jacente. 2) L’insuffisance ventriculaire gauche tout en étant dramatique est transitoire. 3) L’évaluation du risque cardiaque et la prise en charge de ce type de patient pour la chirurgie prête à confusion. 4) la morbidité a long terme est plus souvent en rapport avec les complication neurologiques que cardiaques.

Anaesthesia monitor alarms: a theory-driven approach

The development of physiologic monitors has contributed to the decline in morbidity and mortality in patients undergoing anaesthesia. Diverse factors (physiologic, technical, historical and medico-legal) create challenges for monitor alarm designers. Indeed, a growing body of literature suggests that alarms function sub-optimally in supporting the human operator. Despite existing technology that could allow more appropriate design, most anaesthesia alarms still operate on simple, pre-set thresholds. Arguing that more alarms do not necessarily make for safer alarms is difficult in a litigious medico-legal environment and a competitive marketplace. The resultant commitment to the status quo exposes the risks that a lack of an evidence-based theoretical framework for anaesthesia alarm design presents. In this review, two specific theoretical foundations with relevance to anaesthesia alarms are summarised. The potential significance that signal detection theory and cognitive systems engineering could have in improving anaesthesia alarm design is outlined and future research directions are suggested. Practitioner Summary: The development of physiologic monitors has increased safety for patients undergoing anaesthesia. Evidence suggests that the full potential of the alarms embedded within those monitors is not being realised. In this review article, the authors propose a theoretical framework that could lead to the development of more ergonomic anaesthesia alarms.

Acid-induced fusion of liposomes: studies with 2,3-seco-5α-cholestan-2,3-dioic acid

The effect of 2,3-seco-5 alpha-cholestan-2,3-dioic acid on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine is markedly dependent on pH. Above pH 6.56, the 2,3-seco-5 alpha-cholestan-2,3-dioic acid raises the temperature of this transition, i.e., it stabilizes the bilayer phase. At pH 6.56 there is little effect of this sterol derivative on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine. However, below pH 6.56, the 2,3-seco-5 alpha-cholestan-2,3-dioic acid markedly lowers the temperature of this transition. The promotion of hexagonal phase formation increases both with increasing mol fraction of this sterol derivative and with lower pH, particularly in the range between pH 6.56 and pH 5.0. Below about pH 6, 2,3-seco-5 alpha-cholestan-2,3-dioic acid also induces vesicle fusion as measured both by lipid mixing as well as by mixing of aqueous contents. For these assays vesicles made of phosphatidylethanolamine (made from egg phosphatidylcholine) and extruded through 0.2 micron pore membranes were used. At higher concentrations or at lower pH the 2,3-seco-5 alpha-cholestan-2,3-dioic acid induces some leakage of the contents of these vesicles. Nevertheless, with vesicles containing only 2 weight% sterol derivative, it was possible to demonstrate substantial mixing of aqueous contents of the vesicles over the pH range 3.5 to 5.5. Several of the properties of 2,3-seco-5 alpha-cholestan-2,3-dioic acid indicate that this compound may be useful in sensitizing vesicles to acid-induced fusion for the purpose of endocytic drug delivery.

The shape of the gel to liquid crystalline phase transition of dielaidoylphosphatidylethanolamine is markedly dependent on the method of sample preparation

Abstract Phosphatidylethanolamines are known to exhibit asymmetric phase transitions with a low temperature shoulder. However, in this work we demonstrate that suspensions of dielaidoylphosphatidylethanolamine can be prepared which exhibit very sharp and only slightly asymmetric phase transitions. Such preparations are made either by isolating a rapidly sedimenting fraction of a vortexed suspension of this lipid or by dialyzing a suspension which had been hydrated at pH 9.2 to pH 7.2. Smaller aggregates of the lipid can be isolated from the supernate of a vortexed suspension of dielaidoylphosphatidylethanolamine after removal of the rapidly sedimenting fraction or it can be produced by sonication of a sample at pH 9.2 followed by dialysis to pH 7.2 Such preparations exhibit very broad transitions and the transition temperature is shifted to lower values. These results demonstrate that the shape of the phase transition of dielaidoylphosphatidylethanolamine is particularly sensitive to the method of sample preparation. Furthermore, an asymmetric phase transition with a low temperature shoulder is not necessarily an intrinsic property of phosphatidylethanolamines.

Why should we teach medical students

Brull and John Bradley1 entitled “The role of anesthesiologists in Canadian undergraduate medical education”. The article examines the timely issue of the involvement by anesthesiologists in undergraduate medical education (UME). Their findings indicate that although thirteen of sixteen medical schools have mandatory clerkship rotations, few anesthesiologists are engaged in preclerkship training. It is suggested that the pedagogic advantages of including anesthesiologists in UME are overlooked by medical schools or that anesthesiologists are themselves reluctant to assume pre-clerkship teaching responsibilities. The latter might imply that anesthesiologists do not view teaching medical students as worthwhile. In this editorial, we would like to explore why anesthesiologists should teach medical students. The involvement of anesthesiologists at the preclerkship level may be an important step in ensuring medical students make an informed career choice to enter anesthesia. Under the current Canadian Residents Matching Service (CaRMS), medical students must declare their specialty choices by October of their clerkship year although final choices may be changed, with some difficulty, right until January. Since clerkship usually continues until April or May, a considerable proportion of the students must finalize their specialty choices before their rotation in anesthesia. If one reason for anesthesiologists to teach medical students is to increase recruitment, then it would be appropriate to examine the evidence for that notion. In our previous national survey in 1994, the quantity of anesthesia exposure in a medical school did not correlate with the number of students in that school entering anesthesia.2 In a survey of 76 US medical schools which offered anesthesiology preceptorships, the percent of graduates entering anesthesiology after taking the preceptorships, on a per school basis, ranged from 0 to 80%.3 It would seem, therefore, that the mere exposure of medical students to anesthesia is not a de facto reason for medical students to choose anesthesia as a career. However, in the same study, when the total number of students (n=1480) who took the anesthesiology preceptorship were compared with the students who did not (n=26,662), the proportions of students who entered anesthesia were 11.5% and 2.3% respectively;3 i.e., students who entered anesthesia were more likely to have taken an anesthesia preceptorship. The notion that exposure to anesthesia leads to increased recruitment would seem to be too complex an issue to gather clear evidence on a medical school by medical school basis. However, when viewed from a broader national perspective, with a larger sample size, the evidence exists to show that students who enter anesthesia are more likely to have taken an anesthesia preceptorship. Another reason for anesthesiologists to teach medical students may be to influence student attitudes towards anesthesia. In one American study, the presence of certified registered nurse anesthetists was found to be a negative factor in medical students’ career choice for anesthesia.4 In another study, a survey of ten medical schools was conducted. Of the four medical schools whose students performed best on the anesthesia knowledge quiz, two provided routine exposure to anesthesia while the other two instituted a one-on-one preceptor-student relationship.5 More students in the schools with the routine anesthesia exposure had a negative attitude towards anesthesia. Another study found that the attitudes towards anesthesia after the clerkship rotation was more positive.6 It would seem that student attitudes towards anesthesia after an anesthesia rotation are perhaps more dependent on local factors within a medical school. In part, this is an issue of quantity vs quality. From the perspective of individual medical schools, there are no studies correlating the quality of exposure to the recruitment rate. From the perspective of role models, a recent study in Australia found that for those students who intended to enter anesthesia (18%), 94% identified a positive role model compared to 65% for EDITORIAL 115

User Image Mismatch in Anesthesia Alarms: A Cognitive Systems Analysis

In this study, principles of Cognitive Systems Engineering are used to better understand the human–machine interaction manifesting in the use of anaesthesia alarms. The hypothesis is that the design of the machine incorporates built-in assumptions of the user that are discrepant with the anaesthesiologists self-assessment, creating ‘user image mismatch’. Mismatch was interpreted by focusing on the ‘user image’ as described from the perspectives of both machine and user. The machine-embedded image was interpreted through document analysis. The user-described image was interpreted through user (anaesthesiologist) interviews. Finally, an analysis was conducted in which the machine-embedded and user-described images were contrasted to identify user image mismatch. It is concluded that analysing user image mismatch expands the focus of attention towards macro-elements in the interaction between man and machine. User image mismatch is interpreted to arise from complexity of algorithm design and incongruity between alarm design and tenets of anaesthesia practice. Practitioner Summary: Cognitive system engineering principles are applied to enhance the understanding of the interaction between anaesthesiologist and alarm. The ‘user image’ is interpreted and contrasted from the perspectives of machine as well as the user. Apparent machine–user mismatch is explored pertaining to specific design features.

Airway management of an open penetrating neck injury

Although penetrating neck injuries (PNIs) represent a small subset of patients presenting to the emergency department (ED), they can result in significant morbidity and mortality. The approach to airway management in PNI varies widely according to clinical presentation and local practice, such that global management statements are lacking. Although rapid sequence intubation (RSI) may be safe in most patients with PNI, the high-risk subset (10%) of patients with laryngotracheal injury require particularly judicious airway management. It is not known if RSI is safe in such patients, nor has there been reported use of videolaryngoscopy in patients with open PNI. Established principles of airway management in patients with an open airway injury include the avoidance of both positive pressure bag-mask ventilation and blind tube passage and the early consideration of a surgical airway. Because this high-risk subset may not be clinically apparent on initial presentation in the ED, such guiding principles apply to all patients with PNI until the nature of the injury is more accurately defined. In this report, we present the case of a patient who presented to the ED with a zone II open PNI, which occurred as a result of a stab wound.