Stephan K. W. Schwarz

Case series : Anesthesia for retrograde percutaneous aortic valve replacement -experience with the first 40 patients

Purpose: To describe both the evolution and the main associated complications in the anesthetic management of the initial 40 patients at our centre who underwent percutaneous retrograde aortic valve replacement, a novel technique utilizing a catheterguided femoral artery approach.Clinical features: With institutional Research Ethics Board approval, we retrospectively reviewed the medical records of the first 40 patients who underwent percutaneous retrograde aortic valve replacement between January 2005 and March 2006. Information obtained included patient characteristics, anesthetic management, details of the procedure, and complications. All procedures were scheduled to be performed in the cardiac catheterization laboratory. The first four patients received monitored anesthesia care, and the subsequent 36 underwent general anesthesia. There were no anesthesia-related adverse events. The prosthetic valve was placed successfully in 33/40 patients (83%). Median anesthetic time was 3.5 hr (range, 1.25–7.25 hr). Thirty-two/40 patients required vasopressor support. The most common, serious procedural complications were myocardial ischemia and arrhythmia following rapid ventricular pacing, hemorrhage from vascular injury secondary to the placement and removal of the large-bore sheath in the ilio-femoral artery, aortic rupture, and prosthetic valve maldeployment; 30-day mortality was 13% (n=5/40).Conclusions: Percutaneous retrograde aortic valve replacement is a novel procedure that presents the anesthesiologist with unique challenges. Careful preoperative assessment, intraoperative monitoring appropriate for a major vascular procedure, and meticulous management of hemodynamics are imperative for a successful outcome. Serious complications, including major hemorrhage from vascular injury as well as arrhythmia and myocardial ischemia following rapid ventricular pacing, must be anticipated and managed in an expeditious fashion.RésuméObjectif: Décrire l’évolution et les principales complications associées à la prise en charge anesthésique des premiers 40 patients de notre centre à subir un remplacement valvulaire aortique percutané rétrograde, une technique innovante utilisant une approche échoguidée par l’artère fémorale.Éléments cliniques: Une fois le consentement du Comité d’éthique de la recherche obtenu, nous avons révisé de façon rétrospective les dossiers médicaux des 40 premiers patients à avoir subi un remplacement valvulaire aortique percutané rétrograde entre janvier 2005 et mars 2006. Les caractéristiques des patients, la prise en charge anesthésique, les détails de l’intervention et les complications faisaient partie des renseignements obtenus. Toutes les interventions étaient prévues dans le laboratoire de cathétérisation cardiaque. Les quatre premiers patients ont reçu une sédation sous surveillance, et les 36 suivants une anesthésie générale. Il n’y a pas eu d’événements indésirables provoqués par l’anesthésie. La prothèse valvulaire a été positionnée avec succès chez 33/40 patients (83 %). Le temps d’anesthésie médian était de 3,5 h (extrêmes, 1,25 – 7, 25 h). Un vasopresseur a été nécessaire chez 32/40 patients. Suite à l’intervention, les complications graves les plus fréquentes étaient l’ischémie myocardique et l’arythmie à la suite d’un entraînement ventriculaire rapide, l’hémorragie provoquée par une lésion vasculaire due au positionnement et au retrait de la gaine à grand diamètre dans l’artère ilio-fémorale, la rupture aortique et le mauvais déploiement de la prothèse valvulaire. La mortalité à 30 jours était de 13 % (5/40).Conclusion: Le remplacement valvulaire aortique percutané rétrograde est une intervention nouvelle qui présente à l’anesthésiologiste des défis spéciaux. Une évaluation préopératoire attentive, un monitorage peropératoire adapté à une intervention vasculaire majeure et une prise en charge méticuleuse de l’hémodynamie sont absolument nécessaires à un devenir réussi. Des complications graves, notamment une hémorragie majeure causée par une lésion vasculaire ainsi que de l’arythmie et une ischémie myocardique suite à un entraînement ventriculaire rapide doivent être anticipés et pris en charge rapidement.

QX-314 Produces Long-lasting Local Anesthesia Modulated by Transient Receptor Potential Vanilloid Receptors in Mice

Background:The quaternary lidocaine derivative QX-314 is now known to produce long-lasting local anesthesia despite its positive charge. However, recent research suggests that the transient receptor potential vanilloid receptor agonist, capsaicin, should reduce the onset and offset times, whereas the transient receptor potential vanilloid receptor antagonist, capsazepine, should delay the onset time of sensory blockade by QX-314. Methods:Sensory blockade in the tail of the conscious mouse was investigated using QX-314 2.5% in combination with capsaicin 0.1% and/or capsazepine (50 &mgr;g/ml). After tail injection, onset and offset times of local anesthesia were measured using the hot water tail-flick latency test. Results:Capsaicin reduced the onset time of local anesthesia by QX-314 by more than 75% (Mann–Whitney test, P = 0.007; n = 10 per group) with no effect on the offset time of QX-314. For QX-314 without capsaicin, the onset and offset times were 23 min (interquartile range 15–30 min) and 300 min (interquartile range 285–375 min), respectively. For QX-314 with capsaicin, the onset and offset times were 4 min (interquartile range 3–8 min) and 360 min (interquartile range 285–435 min), respectively. In the antagonist study, capsazepine without added capsaicin decreased QX-314’s efficacy, as 6 out of 9 mice did not develop sensory blockade after 90 min (Fisher exact test, P = 0.009). Conclusion:We have confirmed in a sensory blockade model that QX-314 is a local anesthetic with a slow onset and a long duration of reversible blockade. Capsaicin, a transient receptor potential vanilloid receptor agonist, accelerated QX-314’s onset kinetics, whereas capsazepine, a transient receptor potential vanilloid receptor antagonist, decreased QX-314’s efficacy. These observations raise the possibility that endovanilloids may modulate cell entry of QX-314.

A Novel Vibrotactile Display to Improve the Performance of Anesthesiologists in a Simulated Critical Incident

BACKGROUND: Current methods of information transfer in the operating room between monitor and anesthesiologist rely on visual and auditory modalities. These modalities can easily become overloaded in a high cognitive workload situation, such as in a critical incident. The use of vibrotactile communication has been shown to improve information transfer in other high cognitive workload environments such as aviation. We designed a novel waist-mounted vibrotactile display to be worn by the anesthesiologist to test if a vibrotactile display could improve the clinical response time to begin treating a simulated case of anaphylaxis when compared with a group using traditional information displays. In addition, we evaluated differences in situational awareness (SA) between the two groups. METHODS: Twenty-four volunteer anesthesiologists were randomized to diagnose and treat a simulated case of anaphylaxis using the vibrotactile display and standard monitoring (vibrotactile display group) or standard monitoring alone (control group). The time taken to administer epinephrine was measured, and objective post hoc analysis of participant SA was performed. RESULTS: Participants in the vibrotactile group took 4.08 min (95% CI = 1.22) to deliver definitive treatment compared with 7.21 min (95% CI = 2.07) for the control group (P < 0.05). Despite the reduced time to treatment, no improvement in SA was measured. CONCLUSION: Our study provides evidence that vibrotactile communication can reduce response time to critical incidents.

Spontaneous recovery from a spinal epidural hematoma with atypical presentation in a nonagenarian

PurposeSpinal epidural hematoma following epidural anesthesia is extraordinarily rare in association with low-dose sc heparin, and the prognosis for neurologic recovery without rapid surgical decompression poor. We report a case of spinal epidural hematoma in a nonagenarian who received low-dose sc unfractionated heparin postoperatively in accordance with standard guidelines, presented with no back pain, and made full neurologic recovery without surgical intervention.Clinical featuresA 90-yr-old female with gastric adenocarcinoma presented for subtotal gastrectomy. Her past medical history and physical examination were largely unremarkable and she had no bleeding diathesis. She took no medications other than preoperative ranitidine, and had a normal coagulation profile. A thoracic epidural catheter was placed uneventfully before induction of general anesthesia. Postoperatively, low-dose sc unfractionated heparin was started 12 hr after the epidural catheter insertion. On postoperative day two, the patient developed flaccid lower extremity paralysis and paresthesia without back pain. Her coagulation profile remained normal. Subsequent magnetic resonance imaging showed a large epidural hematoma extending from T3 to T11. With conservative treatment and no surgery, the patient slowly made full neurologic recovery and was discharged home on postoperative day 56.ConclusionComplete neurologic recovery from flaccid paralysis following spinal epidural hematoma occurred without surgical decompression in a nonagenarian. Low-dose sc heparin may be a greater risk factor for spinal epidural hematoma than previously assumed, and the absence of back pain does not rule out this diagnosis.RésuméObjectifL’hématome épidural rachidien postanesthésie péridurale est extrêmement rare en association avec une faible dose d’héparine sc et, sans décompression chirurgicale rapide, le pronostic de récupération est pauvre. Nous présentons un cas d’hématome épidural rachidien chez une nonagénaire qui a reçu de faibles doses sc d’héparine standard postopératoire selon les directives uniformisées, ne présentait pas de dorsalgie et a connu une récupération neurologique complète sans intervention chirurgicale.Éléments cliniquesUne femme de 90 ans atteinte d’adénocarcinome gastrique s’est présentée pour une gastrectomie partielle. Les antécédents médicaux et l’examen physique étaient sans particularité et sans diathèse hémorragique. Elle n’avait pris d’autres médicaments que la ranitidine préopératoire et présentait un profil de coagulation normal. Un cathéter épidural thoracique a été inséré sans problème avant l’induction de l’anesthésie générale. Après l’opération, l’administration sc d’héparine standard a été amorcée 12 h après l’insertion du cathéter. Au jour deux postopératoire, la patiente présentait une paralysie flasque et une paresthésie des membres inférieurs sans dorsalgie. Son profil de coagulation est demeuré normal. Un examen d’imagerie par résonance magnétique a montré un important hématome épidural s’étendant de T3 à T11. Un traitement conservateur, sans chirurgie, a permis une récupération neurologique complète et un retour à domicile 56 jours après l’opération.ConclusionLa récupération neurologique complète d’une paralysie flasque suivant un hématome épidural rachidien est survenue sans décompression chirurgicale chez une nonagénaire. L’administration sc de faibles doses d’héparine peut présenter un risque plus important d’hématome épidural rachidien qu’on ne l’avait d’abord cru et l’absence de dorsalgie n’exclut pas ce diagnostic.

Addition of femoral 3-in-1 blockade to intra-articular ropivacaine 0.2% does not reduce analgesic requirements following arthroscopic knee surgery.

PurposeTo test the hypothesis that the addition of a preincisional femoral 3-in-1 block to intra-articular instillation with ropivacaine 0.2% at the end of surgery improves postoperative pain control in patients undergoing arthroscopic anterior cruciate ligament reconstruction (ACLR) under general anesthesia.MethodsIn a prospective, randomized, placebo-controlled, double-blind trial, we studied 44 patients scheduled for inpatient ACLR. Prior to incision, the treatment group (n = 22) received a femoral 3-in-1 block with 40 ml ropivacaine 0.2%, augmented by infiltrations of the lateral and anteromedial incisions with 20 ml ropivacaine 0.2% at the end of the procedure. The control group (n = 22) received saline 0.9% instead of ropivacaine. All patients received an intra-articular instillation with 30 ml ropivacaine 0.2% at the end of surgery. The primary efficacy variable was 24 hr morphine consumption postoperatively standardized by weight, administered intravenously via a patient-controlled analgesia (PCA) pump.ResultsThere was no difference between both groups in 24 hr PCA morphine consumption postoperatively (control, 0.45 ± 0.44 [mean ± SD] mg·kg−1; treatment, 0.37 ± 0.50 mg·kg−1; P = 0.55). No difference was found in postoperative visual analog scale pain scores, adverse events, or vital signs. In the treatment group, R = 10/22 patients did not require postoperative morphine compared with R = 6/22 in the control group (P = 0.35).ConclusionWe found no effect of a femoral 3-in-1 block with ropivacaine 0.2% on postoperative analgesic consumption, compared to intra-articular instillation with ropivacaine 0.2% alone, in patients undergoing ACLR under general anesthesia.RésuméObjectifVérifier l’hypothèse selon laquelle l’addition, avant l’incision, d’un blocage fémoral 3 en I à l’instillation intra- articulaire de ropivacaïne 0,2% de fin d’opération, améliore le soulagement de la douleur postopératoire chez les patients qui subissent une reconstruction arthroscopique du ligament croisé antéro-externe (RLCA) sous anesthésie générale.MéthodeIl s’agit d’un essai prospectif randomisé en double insu contre placebo concernant 44 patients qui subissent une RLCA élective en chirurgie ambulatoire. Avant l’incision, le groupe traité (n = 22) a reçu un bloc fémoral 3 en I de 40 ml de ropivacaïne 0,2%, augmenté par des infiltrations des incisions latérale et antéromédiane de 20 ml de ropivacaine 0,2% à la fin de l’intervention. Le groupe témoin (n = 22) a reçu une solution salée à 0,9%. Tous les patients ont reçu une instillation intra-articulaire de 30 ml de ropivacaine 0,2% à la fin de l’opération. La principale variable d’efficacité a été la demande de morphine postopératoire à 24 h, uniformisée selon le poids, dont l’administration intraveineuse s’est faite à l’aide d’une pompe d’analgésie contrôlée par le patient (ACP).RésultatsLa demande postopératoire de morphine ACP à 24 h n’a pas présenté de différence intergroupe (témoin, 0,45 ± 0,44 [moyenne ± écart type]mg·kg−1; traitement, 0,37 ± 0,50 mg·kg−1; P = 0,55), ni les seuils de douleur postopératoire, selon l’échelle visuelle analogue, les effets secondaires et les signes vitaux. Dans le groupe de traitement, 10/22 patients n’ont pas demandé de morphine postopératoire et 6/22 dans le groupe témoin (P = 0,35).ConclusionNous n’avons pas noté d’effet du blocage fémoral 3 en I de ropivacaïne 0,2% sur la demande postopératoire d’analgésique, comparé à l’instillation intra-articulaire de ropivacaïne 0,2% seule, chez des patients qui subissent une RLCA sous anesthésie générale.

Hemidiaphragmatic paralysis following ultrasound-guided supraclavicular versus infraclavicular brachial plexus blockade: a randomized clinical trial.

Background and Objectives The comparative incidences of hemidiaphragmatic paralysis associated with contemporary ultrasound-guided supraclavicular versus infraclavicular blockade have not received extensive study. We tested the hypothesis that the infraclavicular approach results in a lower incidence of hemidiaphragmatic paralysis compared with supraclavicular blockade when a standard local anesthetic volume and concentration are used. Methods With institutional human ethics board approval, we enrolled 64 patients undergoing right-sided upper extremity surgery in a randomized, blinded, parallel-group trial. Patients were assigned to ultrasound-guided supraclavicular or infraclavicular blockade with 30 mL of 0.5% ropivacaine. The primary end point was complete hemidiaphragmatic paralysis at 30 minutes, defined as a greater than 75% reduction in diaphragmatic excursion measured with the voluntary sniff test using M-mode ultrasonography. Partial paralysis was defined as a 25% to 75% reduction. Results Eleven (34%) of 32 patients in the supraclavicular group versus 1 (3%) of 32 in the infraclavicular group had complete hemidiaphragmatic paralysis (P = 0.001 [1-tailed]; relative risk, 11.0 [95% confidence interval, 1.5–80.3]); 44% versus 13% had any (complete or partial) paralysis (P = 0.006; relative risk, 3.5 [95% confidence interval, 1.3–9.5]). Eight (25%) of 32 patients in the supraclavicular group versus 5 (16%) of 32 in the infraclavicular group reported dyspnea (P = 0.54). Conclusions Ultrasound-guided supraclavicular blockade with 30 mL of 0.5% ropivacaine produced complete hemidiaphragmatic paralysis in approximately one-third of patients. The infraclavicular approach greatly reduced this risk but did not eliminate it. These data may aid in the selection of the approach to brachial plexus blockade, particularly in ambulatory patients and/or those with respiratory comorbidities.

Combined pre- and post-surgical bupivacaine would infiltrations decrease opioid requirements after knee ligament reconstruction

Purpose: To test the efficacy of a combination of selective pre- and post-surgical local anesthetic infiltrations of the knee, compared with standard intra-articular injection at the end of surgery alone, to reduce postoperative opioid requirements following arthroscopic cruciate ligament reconstruction (ACLR).Methods: In a double-blind, randomized, controlled trial, we studied 23 patients (ASA I or II) scheduled for elective ACLR under general anesthesia. The treatment group (n=12) received infiltrations with bupivacaine 0.25% with epinephrine 1:200 000 presurgically (10 ml into the portals, 10 ml at the medial tibial incision site, 10 ml at the lateral femoral incision site, and 10 ml intra-articularly) and postsurgically (5 ml at the medial tibial incision and 10 ml at the lateral femoral incision). The control group (n=11) received infiltrations with saline 0.9% in the same manner. All patients received a standard intra-articular local anesthetic instillation of the knee (25 ml of bupivacaine 0.25% with epinephrine 1:200 000) at the completion of surgery.Results: Postoperative opioid requirements were lower in the treatment group (5.8±2.9 mg morphine equivalent) than in the control group (13.7±5.8 mg;P=0.008). Treatment patients were ready for discharge approximately 30 min earlier than control patients (P=0.046). There were no adverse events in the treatment group. In the control group, 2/11 patients vomited and a third experienced transient postoperative diaphoresis, dizziness and pallor.Conclusion: We conclude that a combination of selective pre- and post-surgical would infiltration with bupivacaine 0.25% provides superior analgesia compared with a standard post-surgical intra-articular injection alone.RésuméObjectif: Tester l’efficacité d’une combinaison d’infiltrations sélectives du genou, préopératoires et postopératoires, avec un a nesthésique local, comparée à l’injection intra-articulaire régulière de fin d’intervention seulement, dans le but de réduire les besoins postopératoires d’opioïdes à la suite de la reconstruction arthroscopique du ligament croisé (RALC).Méthode: L’étude randomisée, contrôlée et à double insu a porté sur 23 patients (ASA I ou II) pour qui une RALC avait été prévue sous anesthésie générale. Les patients étudiés (n=12) ont reçu des infiltrations préchirurgicales de bupivacaïne à 0,25 % avec de l’épinéphrine à 1:200 000 (10 ml via le portail, 10 ml au site d’incision tibial médian, 10 ml dans l’incision fémorale latérale et 10 ml intra-articulaire) et postchirurgicales (5 ml dans l’incision tibiale médiane et 10 ml dans l’incision fémorale latérale). Les patients témoins (n=11) ont reçu des infiltrations de solution salée à 0,9 %, administrées de la même manière. Tous les patients ont reçu une instillation anesthésique standard locale dans l’articulation du genou (25 ml de bupivacaïne à 0,25 % avec de l’épinéphrine à 1:200 000) à la fin de l’opération.Résultats: Les patients testés ont demandé moins d’opioïdes postopératoires (5,8±2,9 mg d’équivalent de morphine) que les patients témoins (13,7±5,8 mg;P=0,008). Ils ont pu recveoir leur congé 30 min plus tôt que les patients témoins (P=0,046). On n’a pas noté d’effets indésirables chez les patients testés. Parmi les patients témoins, 2/11 ont eu des vomissements et un tiers a présenté une diaphorèse postopératoire transitoire, des étourdissements et de la pâleur.Conclusion: Une combinaison d’infiltrations préchirurgicales et postchirurgicales du site d’incision avec de la bupivacaïne à 0,25 % fournit une analgésie supérieure à la seule injection intra-articulaire postchirurgicale standard.

Analgesic Properties of the Novel Amino Acid, Isovaline

BACKGROUND:Isovaline, a nonproteinogenic &agr;-amino acid rarely found in the biosphere, is structurally similar to the inhibitory neurotransmitters glycine and &ggr;-aminobutyric acid. Because glycineA and &ggr;-aminobutyric acid receptor agonists are antiallodynic, we hypothesized that isovaline produces antinociception in mice. METHODS:All experiments were performed on female CD-1 mice using a blinded, randomized, and controlled design. The effects of RS-isovaline were studied on nociceptive responses to (1) formalin injection into the hindpaw; (2) glutamate injection into the hindpaw; and (3) strychnine injection either into the lumbar intrathecal space or cisterna magna. We determined the effects of IV RS-isovaline (50, 150, or 500 mg/kg; n = 10/dose) or intrathecal RS-, R-, and S-isovaline, glycine, and &bgr;-alanine into the lumbar intrathecal space (5-&mgr;L volumes of 60, 125, 250, and 500 mM; n = 9/dose/group) on the response to formalin in the paw. The response to 20 &mgr;L intraplantar glutamate (750 mM) was compared with glutamate (750 mM) coadministered with isovaline. We also determined the response to intraplantar strychnine. Lumbar intrathecal (100 &mgr;M) or intracisternal (200 &mgr;M) injections of strychnine into the lumbar intrathecal space or the cisterna magna were used to induce allodynia as a measure of glycine inhibitory dysfunction. The effects of intrathecal or intracisternal strychnine were compared with isovaline coapplied with the strychnine (n = 8/group). RESULTS:In the formalin paw test, IV isovaline did not change phase I but decreased phase II responses in a dose-dependent manner (50% effective dose = 66 mg/kg, n = 10, P < 0.01). There was no effect on rotarod performance, appearance, or behavior of the mouse, and no respiratory depression. Intrathecal isovaline, glycine, and &bgr;-alanine attenuated phase I and II responses (P < 0.01 for each drug). In contrast to &bgr;-alanine and glycine, isovaline at maximally effective doses did not produce scratching, biting, or agitation. Intrathecal RS- and S-isovaline attenuated phase I (P < 0.05 for each group) and RS-, R-, and S-isovaline attenuated phase II responses (P < 0.05 for each group), with no significant difference between the efficacies of R- and S-enantiomers. Localized strychnine-induced glycine inhibitory dysfunction was greatly reduced by intracisternal (P < 0.01) and intrathecal (P < 0.01) isovaline. Although intraplantar strychnine did not induce peripheral allodynia, high doses of isovaline did not block the peripheral allodynia induced by glutamate. CONCLUSIONS:Isovaline reduced responses in mouse pain models without producing acute toxicity, possibly by enhancing receptor modulation of nociceptive information.

Lumbar intrathecal administration of the quaternary lidocaine derivative, QX-314, produces irritation and death in mice.

Background:We recently found that peripheral administration of the quaternary lidocaine derivative, QX-314, produces long-lasting sensory and motor blockade in animals. The goal of this study was to test whether intrathecal QX-314 has similar properties. Methods:We conducted a randomized, double-controlled, blinded study with female CD-1 mice. Animals in the treatment group received lumbar intrathecal QX-314 (0.5–10 mm; volume, 2 &mgr;l; each concentration, n = 6). Normal saline and lidocaine (70 mm) served as negative and positive controls (each group, n = 12), respectively. Animals were tested for up to 3 h for lumbosacral neural blockade and observed for adverse effects. Results:No animal injected with saline and 11 of 12 (92%) animals injected with lidocaine displayed reversible lumbosacral motor blockade (P < 0.001). QX-314 (5 mm) produced motor blockade in four of the six (67%) and sensory blockade in five of the six animals (83%; P < 0.05 vs. saline). However, six of the six mice (100%) at 5 mm QX-314 and five of the six (83%) at 10 mm exhibited marked irritation; one of the six animals at 5 mm (17%) and two of the six at 10 mm (33%) died. We observed no neural blockade without adverse effects in any animal injected with QX-314. All animals injected with saline and 11 of the 12 (92%) animals injected with lidocaine demonstrated normal behavior. Conclusion:Lumbar intrathecal QX-314 concentration-dependently produced irritation and death in mice, at lower concentrations than those associated with robust motor blockade. Although QX-314 did produce long-lasting neural blockade, these findings indicate that QX-314 is unlikely to be a suitable candidate for spinal anesthesia in humans.

Optimizing the Tactile Display of Physiological Information: Vibro-Tactile vs. Electro-Tactile Stimulation, and Forearm or Wrist Location

Anesthesiologists use physiological data monitoring systems with visual and auditory displays of information to monitor patients in the operating room (OR). The efficacy of visual-audio systems may impose an increase in patient risk when the demand for constant switching of attention between the patient and the visual monitoring system is high. This is evidenced by auditory alarms frequently being neglected in a noisy OR environment. Hence, the use of a complementary patient data monitoring system, which utilizes other sensory modalities, could be of great value. In this paper, we describe a series of experiments designed to determine the performances of a tactile display that could be used to convey patients physiological information to the attending anesthesiologist. We tested both vibro-tactile and electro-tactile display prototypes in their ability to convey information using an alert scheme of four distinct tactile stimuli. Using pseudo-clinical data, the display was designed, for example, to provide an alert when a change in the monitored heart rate occurred. Based on previous research in human physiology and psychophysics, we selected the forearm and wrist of the users non-dominant hand as the stimulation site. In our study of 30 subjects, we evaluated the response time and accuracy of tactile pattern recognition to compare (1) the performance of a vibro-tactile display on the forearm (VF) and an electro- tactile display on the forearm (EF), and (2) the localization of stimulation between the forearm (VF) and a vibro-tactile display on the wrist (VW). A post-study questionnaire was completed by each subject to assess the comfort and usability of the three prototypes. We found that both VF and VW were superior to the EF in both accuracy and comfort and, that there were no differences between the wrist and the forearm. In conclusion, the tactile-display prototypes designed to alert the clinician of adverse changes in a patients physiological state efficaciously and unobtrusively delivered these data and warranted further investigation and development.