Protocol for the "Michigan Awareness Control Study": A prospective, randomized, controlled trial comparing electronic alerts based on bispectral index monitoring or minimum alveolar concentration for the prevention of intraoperative awareness

Background

The incidence of intraoperative awareness with explicit recall is 1-2/1000 cases in the United States. The Bispectral Index monitor is an electroencephalographic method of assessing anesthetic depth that has been shown in one prospective study to reduce the incidence of awareness in the high-risk population. In the B-Aware trial, the number needed to treat in order to prevent one case of awareness in the high-risk population was 138. Since the number needed to treat and the associated cost of treatment would be much higher in the general population, the efficacy of the Bispectral Index monitor in preventing awareness in all anesthetized patients needs to be clearly established. This is especially true given the findings of the B-Unaware trial, which demonstrated no significant difference between protocols based on the Bispectral Index monitor or minimum alveolar concentration for the reduction of awareness in high risk patients.

Methods/Design

To evaluate efficacy in the general population, we are conducting a prospective, randomized, controlled trial comparing the Bispectral Index monitor to a non-electroencephalographic gauge of anesthetic depth. The total recruitment for the study is targeted for 30,000 patients at both low and high risk for awareness. We have developed a novel algorithm that is capable of real-time analysis of our electronic perioperative information system. In one arm of the study, anesthesia providers will receive an electronic page if the Bispectral Index value is >60. In the other arm of the study, anesthesia providers will receive a page if the age-adjusted minimum alveolar concentration is <0.5. Our minimum alveolar concentration algorithm is sensitive to both inhalational anesthetics and intravenous sedative-hypnotic agents.

Discussion

Awareness during general anesthesia is a persistent problem and the role of the Bispectral Index monitor in its prevention is still unclear. The Michigan Awareness Control Study is the largest prospective trial of awareness prevention ever conducted.

Trial Registration

Clinical Trial NCT00689091

A novel classification instrument for intraoperative awareness events

BACKGROUND

Intraoperative awareness with explicit recall occurs in approximately 1-2 cases per 1000. Given the rarity of the event, a better understanding of awareness and its sequelae will likely require the compilation of data from numerous studies. As such, a standard description and expression of awareness events would be of value.

METHODS

We developed a novel classification instrument for intraoperative awareness events: Class 0: no awareness; Class 1: isolated auditory perceptions; Class 2: tactile perceptions (e.g., surgical manipulation or endotracheal tube); Class 3: pain; Class 4: paralysis (e.g., feeling one cannot move, speak, or breathe); and Class 5: paralysis and pain. An additional designation of "D" for distress was also included for patient reports of fear, anxiety, suffocation, sense of doom, sense of impending death, or other explicit descriptions. We reviewed 15 studies of the incidence of awareness that provided specific information about awareness reports. Five anesthesiologists at three institutions who developed the categories independently classified the events. An additional 20 individuals (attending anesthesiologists, anesthesiology residents, nurse anesthetists, medical students, and ancillary staff) not involved in the development of the categories also independently classified the events. Fleiss's kappa statistic was used to evaluate inter-observer agreement.

RESULTS

One hundred fifty-one cases of intraoperative awareness in adults were identified as valid for analysis. The overall kappa value was 0.851 (0.847-0.856, 95% confidence interval) for the basic Classes 1-5. Including additional designations of emotional distress, the overall kappa value was 0.779 (0.776-0.783, 95% confidence interval).

CONCLUSION

We report a novel classification instrument for intraoperative awareness events that has excellent inter-observer agreement and that may facilitate the study of intraoperative awareness.

Impact of gender on the myocardial metabolic response to obesity

OBJECTIVES

We sought to determine the gender-specific effects of obesity on myocardial metabolism, work, and efficiency.

BACKGROUND

Myocardial metabolism abnormalities may contribute to the development of obesity-related heart failure. Increased myocardial oxygen consumption (MVO(2)) and fatty acid (FA) metabolism and decreased efficiency occur with obesity in women. It is unknown whether similar changes occur with obesity in men.

METHODS

We quantified cardiac work, efficiency, myocardial blood flow (MBF), MVO(2), glucose, and FA metabolism with echocardiography and positron emission tomography in nonobese and obese men and women (N = 86).

RESULTS

There were significant differences between the obese (n = 35) and nonobese (n = 51) subjects in age, body composition, plasma lipids, and insulin resistance in addition to differences between the men (n = 30) and women (n = 56) in body composition and plasma lipids. Female gender independently predicted increased cardiac work (p < 0.001). Female gender also related to lower efficiency (p < 0.05). Obesity and female gender independently predicted greater MBF (p < 0.01, p < 0.0005, respectively) and MVO(2) (p < 0.0005, p < 0.0001). Myocardial glucose uptake was not different among the 4 subject groups, but obesity and gender interacted in predicting glucose uptake (p < 0.05). Lower myocardial glucose utilization was independently predicted by female gender (p < 0.05), and it independently predicted lower myocardial glucose utilization/plasma insulin (p < 0.05). Obesity and gender significantly interacted in the determination of glucose utilization/plasma insulin (p = 0.01). There were no differences in FA uptake among the 4 groups, and although increasing obesity correlated with greater myocardial FA utilization and oxidation; female gender (p < 0.005, p < 0.01) and plasma triglycerides (p < 0.05, p < 0.005) were their independent predictors.

CONCLUSIONS

Women's and men's myocardial metabolic responses to obesity are not exactly the same. Obesity and gender modulate MBF and MVO(2), are related to myocardial substrate metabolism, and sometimes interact in its prediction. Gender modifies efficiency. Gender-related differences in myocardial metabolism may affect the development of/adaptation to obesity-related cardiac disease.

Performance of certified registered nurse anesthetists and anesthesiologists in a simulation-based skills assessment

BACKGROUND

Anesthesiologists and certified registered nurse anesthetists (CRNAs) must acquire the skills to recognize and manage a variety of acute intraoperative emergencies. A simulation-based assessment provides a useful and efficient means to evaluate these skills. In this study, we evaluated and compared the performance of board-certified anesthesiologists and CRNAs managing a set of simulated intraoperative emergencies.

METHODS

We enrolled 26 CRNAs and 35 board-certified anesthesiologists in a prospective, randomized, single-blinded study. These 61 specialists each managed 8 of 12 randomly selected, scripted, intraoperative simulation exercises. Participants were expected to recognize and initiate appropriate therapy for intraoperative events during a 5-min period. Two primary raters scored 488 simulation exercises (61 participants x 8 encounters).

RESULTS

Anesthesiologists achieved a modestly higher mean overall score than CRNAs (66.6% +/- 11.7 [range = 41.7%-86.7%] vs 59.9% +/- 10.2 [range = 38.3%-80.4%] P < 0.01). There were no significant differences in performance between groups on individual encounters. The raters were consistent in their identification of key actions. The reliability of the eight-scenario assessment, with two raters for each scenario, was 0.80.

CONCLUSION

Although anesthesiologists, on average, achieved a modestly higher overall score, there was marked and similar variability in both groups. This wide range suggests that certification in either discipline may not yield uniform acumen in management of simulated intraoperative emergencies. In both groups, there were practitioners who failed to diagnose and treat simulated emergencies. If this is reflective of clinical practice, it represents a patient safety concern. Simulation-based assessment provides a tool to determine the ability of practitioners to respond appropriately to clinical emergencies. If all practitioners could effectively manage these critical events, the standard of patient care and ultimately patient safety could be improved.

Prevention of awareness during general anesthesia

Awareness during general anesthesia with subsequent explicit recall is a serious and frequently preventable problem that is gaining attention from clinicians and patients alike. Cost-effective interventions that increase vigilance should be implemented to decrease the likelihood of this complication.

Anesthesia awareness and the bispectral index

BACKGROUND

Awareness during anesthesia is a serious complication with potential long-term psychological consequences. Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below 60. In this trial, we sought to determine whether a BIS-based protocol is better than a protocol based on a measurement of end-tidal anesthetic gas (ETAG) for decreasing anesthesia awareness in patients at high risk for this complication.

METHODS

We randomly assigned 2000 patients to BIS-guided anesthesia (target BIS range, 40 to 60) or ETAG-guided anesthesia (target ETAG range, 0.7 to 1.3 minimum alveolar concentration [MAC]). Postoperatively, patients were assessed for anesthesia awareness at three intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation).

RESULTS

We assessed 967 and 974 patients from the BIS and ETAG groups, respectively. Two cases of definite anesthesia awareness occurred in each group (absolute difference, 0%; 95% confidence interval [CI], -0.56 to 0.57%). The BIS value was greater than 60 in one case of definite anesthesia awareness, and the ETAG concentrations were less than 0.7 MAC in three cases. For all patients, the mean (+/-SD) time-averaged ETAG concentration was 0.81+/-0.25 MAC in the BIS group and 0.82+/-0.23 MAC in the ETAG group (P=0.10; 95% CI for the difference between the BIS and ETAG groups, -0.04 to 0.01 MAC).

CONCLUSIONS

We did not reproduce the results of previous studies that reported a lower incidence of anesthesia awareness with BIS monitoring, and the use of the BIS protocol was not associated with reduced administration of volatile anesthetic gases. Anesthesia awareness occurred even when BIS values and ETAG concentrations were within the target ranges. Our findings do not support routine BIS monitoring as part of standard practice. (ClinicalTrials.gov number, NCT00281489 [ClinicalTrials.gov].).

Mild Hypercapnia After Uncomplicated Heart Surgery Is Not Associated With Hemodynamic Compromise

OBJECTIVE

The aim of this study was to examine the effects of small changes in PaCO(2) on hemodynamic parameters after uncomplicated heart surgery with cardiopulmonary bypass.

DESIGN

This was a prospective, randomized crossover study.

SETTING

A large academic medical center.

PARTICIPANTS

Twenty-four subjects who were scheduled for elective cardiac surgery were enrolled in this study.

INTERVENTIONS

Each subject underwent the normal procedures that are associated with cardiac surgery. General anesthesia, including muscle relaxation, were continued in the immediate postoperative period. Measured tidal volumes and minute ventilation were kept constant for the duration of the study. Target PaCO(2) concentrations of 30, 40, and 50 mmHg were achieved by adding varying amounts of exogenous CO(2) gas to the inhaled oxygen. Various measurements were made at each target PaCO(2), including cardiac index, mixed venous oxygen saturation, blood pressure, heart rate, and pulmonary artery pressure.

MEASUREMENTS AND MAIN RESULTS

Twenty-four patients were enrolled. Seven were withdrawn before commencement of the study. The cardiac index increased when the PaCO(2) was increased from 30 to 40 mmHg (p < 0.001) and remained unchanged between 40 and 50 mmHg. Mixed venous oxygen saturation increased (p < 0.001) with elevations in PaCO(2) up to 50 mmHg and decreased again when the PaCO(2) was returned to 30 mmHg. The blood pressure decreased (p < 0.001) with increasing PaCO(2). The pulmonary pressure increased (p < 0.001) with elevations in PaCO(2). No patient became hemodynamically unstable or had any arrhythmias.

CONCLUSION

The findings of this study suggest that unless there is a specific contraindication to mild hypercapnia, such as pulmonary hypertension or hemodynamic instability, concerns about mild respiratory acidosis should not prevent weaning of sedation and mechanical ventilation after uncomplicated heart surgery.

Case report: Inferior vena-cava right atrial anastomotic stenosis after bicaval orthotopic heart transplantation

PURPOSE

This case report describes the occurrence of acute postoperative liver and renal failure after bicaval orthotopic heart transplantation (OHT) due to stenosis of the inferior vena cava (IVC)-right atrial (RA) anastomosis. We also discuss the role of measuring femoral venous pressure and transesophageal echocardiography (TEE) in establishing the diagnosis.

CLINICAL FEATURES

A 42-yr-old female patient with idiopathic dilated cardiomyopathy underwent an OHT, using the bicaval anastomotic technique. During the first 12 hr postoperatively she developed unexplained kidney and liver failure. Her left and right ventricular functions were excellent and the right and left sided filling pressures were normal. The femoral pressure was elevated while the RA pressure was normal. An emergent TEE showed colour-flow and Doppler characteristics consistent with IVC-RA anastomotic stenosis. Emergent surgical re-exploration was undertaken; a hemostatic suture was found at the RA cannulation site that had caused the constriction of the IVC-RA anastomosis.

CONCLUSIONS

Acute liver and renal failure after OHT can have multiple causes including ischemia due to a low flow state. This case demonstrates the importance of doing a detailed intraoperative TEE after OHT, and the importance of repeating the intraoperative examination after any hemostatic sutures are placed. Femoral venous pressure monitoring can be a useful diagnostic tool in detecting IVC-RA stenosis.

Intrapatient Reproducibility of the BISxp® Monitor

Background

The Bispectral Index (BIS) reportedly reflects anesthetic depth. It is recommended that anesthetic agents should be titrated to maintain the BIS between 40 and 60 arbitrary BIS units during anesthesia. For anesthesia providers to follow this recommendation, the monitor should be predictably affected by different anesthetic agents and have good interpatient and intrapatient reproducibility. The authors hypothesized that when two BISxp devices (Aspect Medical Systems, Newton, MA) are placed concurrently on the same patient, their readings are concordant throughout the anesthetic period.

Methods

Simultaneous BIS recordings from two BISxp monitors were obtained during anesthesia at 5-s intervals from 12 participants.

Results

In total 22,860 concurrent paired BIS readings were obtained. For 10.7% of the time, there were sustained periods of 30 s or greater where the readings suggested a different depth of anesthesia. For 6% of the time, there were sustained periods of 30 s or greater where the readings differed by 10 or more arbitrary BIS units. The regression coefficient (R) for the two devices was 0.65 (range, 0.35-0.92). There was zero bias between the devices, and the 95% limits of agreement ranged between -18 and +17.

Conclusion

A conflicting anesthetic management was suggested by the simultaneous BIS readings 10.7% of the time. These results suggest that BISxp does not always provide a reproducible single number. Anesthesia providers should not rely exclusively on the BIS reading when assessing depth of anesthesia.

Recombinant human antithrombin III restores heparin responsiveness and decreases activation of coagulation in heparin-resistant patients during cardiopulmonary bypass

OBJECTIVES

We sought to evaluate the efficacy of recombinant human antithrombin III for restoration of heparin responsiveness in heparin-resistant patients scheduled for cardiac surgery.

METHODS

This was a multicenter, randomized, double-blind, placebo-controlled study in heparin-resistant patients undergoing elective cardiac surgery. Patients were considered heparin resistant if the activated clotting time was less than 480 seconds after 400 U/kg heparin. Fifty-two heparin-resistant patients were randomized into 2 cohorts. One cohort received a single bolus (75 U/kg) of recombinant human antithrombin III (n = 28), and the other, the placebo group (n = 24), received a normal saline bolus. If the activated clotting time remained less than 480 seconds, this was defined as treatment failure, and 2 units of fresh frozen plasma were transfused. Patients were monitored for adverse events during hospitalization.

RESULTS

Six (21%) of the patients in the recombinant human antithrombin III group received fresh frozen plasma transfusions compared with 22 (92%) of the placebo-treated patients ( P < .001). Two units of fresh frozen plasma did not restore heparin responsiveness. There was no increased incidence of adverse events associated with recombinant human antithrombin III administration. Postoperative 24-hour chest tube bleeding was not different in the 2 groups. Surrogate measures of hemostatic activation suggested that there was less activation of the hemostatic system during cardiopulmonary bypass in the recombinant human antithrombin III group.

CONCLUSION

Treatment with recombinant human antithrombin III in a dose of 75 U/kg is effective in restoring heparin responsiveness and promoting therapeutic anticoagulation for cardiopulmonary bypass in the majority of heparin-resistant patients. Two units of fresh frozen plasma were insufficient to restore heparin responsiveness. There was no apparent increase in bleeding associated with recombinant human antithrombin III.

A Phase III, Double-blind, Placebo-controlled, Multicenter Study on the Efficacy of Recombinant Human Antithrombin in Heparin-resistant Patients Scheduled to Undergo Cardiac Surgery Necessitating Cardiopulmonary Bypass

Background

The study evaluated the efficacy of recombinant human antithrombin (rhAT) for restoring heparin responsiveness in heparin resistant patients undergoing cardiac surgery.

Methods

This was a multicenter, randomized, double-blind, placebo-controlled study in heparin-resistant patients undergoing cardiac surgery with cardiopulmonary bypass. Heparin resistance was diagnosed when the activated clotting time was less than 480 s after 400 U/kg heparin. Fifty-four heparin-resistant patients were randomized. One cohort received 75 U/kg rhAT, and the other received normal saline. If the activated clotting time remained less than 480 s, this was considered treatment failure, and 2 units fresh frozen plasma was transfused. Patients were monitored for adverse events.

Results

Only 19% of patients in the rhAT group received fresh frozen plasma, compared with 81% of patients in the placebo group (P &lt; 0.001). During their hospitalization, 48% of patients in the rhAT group received fresh frozen plasma, compared with 85% of patients in the placebo group (P = 0.009). Patients in the placebo group required higher heparin doses (P &lt; 0.005) for anticoagulation. There was no increase in serious adverse events associated with rhAT. There was increased blood loss 12 h postoperatively (P = 0.05) with a trend toward increased 24-h bleeding in the rhAT group (P = 0.06). There was no difference between the groups in blood and platelet transfusions.

Conclusion

Treatment with 75 U/kg rhAT is effective in restoring heparin responsiveness and promoting therapeutic anticoagulation in the majority of heparin-resistant patients. Treating heparin-resistant patients with rhAT may decrease the requirement for heparin and fresh frozen plasma.

Inhaled prostacyclin is safe, effective, and affordable in patients with pulmonary hypertension, right heart dysfunction, and refractory hypoxemia after cardiothoracic surgery

BACKGROUND

The purpose of this study was to describe our institutional experience in using inhaled prostacyclin as a selective pulmonary vasodilator in patients with pulmonary hypertension, refractory hypoxemia, and right heart dysfunction after cardiothoracic surgery.

METHODS

Between February 2001 and March 2003, cardiothoracic surgical patients with pulmonary hypertension (mean pulmonary artery pressure >30 mm Hg or systolic pulmonary artery pressure >40 mm Hg), hypoxemia (PaO(2)/fraction of inspired oxygen <150 mm Hg), or right heart dysfunction (central venous pressure >16 mm Hg and cardiac index <2.2 L.min(-1).m(-2)) were prospectively administered inhaled prostacyclin at an initial concentration of 20,000 ng/mL and then weaned per protocol. Hemodynamic variables were measured before the initiation of inhaled prostacyclin, 30 to 60 minutes after initiation, and again 4 to 6 hours later.

RESULTS

One hundred twenty-six patients were enrolled during the study period. At both time points, inhaled prostacyclin significantly decreased the mean pulmonary artery pressure without altering the mean arterial pressure. The average length of time on inhaled prostacyclin was 45.6 hours. There were no adverse events attributable to inhaled prostacyclin. The average cost for inhaled prostacyclin was 150 US dollars per day. Compared with nitric oxide, which costs 3000 US dollars per day, the potential cost savings over this period were 681,686 US dollars.

CONCLUSIONS

Inhaled prostacyclin seems to be a safe and effective pulmonary vasodilator for cardiothoracic surgical patients with pulmonary hypertension, refractory hypoxemia, or right heart dysfunction. Overall, inhaled prostacyclin significantly decreases mean pulmonary artery pressures without altering the mean arterial pressure. Compared with nitric oxide, there is no special equipment required for administration or toxicity monitoring, and the cost savings are substantial.

Comparison of structured use of routine laboratory tests or near-patient assessment with clinical judgement in the management of bleeding after cardiac surgery

BACKGROUND

Using algorithms based on point of care coagulation tests can decrease blood loss and blood component transfusion after cardiac surgery. We wished to test the hypothesis that a management algorithm based on near-patient tests would reduce blood loss and blood component use after routine coronary artery surgery with cardiopulmonary bypass when compared with an algorithm based on routine laboratory assays or with clinical judgement.

METHODS

Patients (n=102) undergoing elective coronary artery surgery with cardiac bypass were randomized into two groups. In the point of care group, the management algorithm was based on information provided by three devices, the Hepcon, thromboelastography and the PFA-100 platelet function analyser. Management in the laboratory test group depended on rapidly available laboratory clotting tests and transfusion of haemostatic blood components only if specific criteria were met. Blood loss and transfusion was compared between these two groups and with a retrospective case-control group (n=108), in which management of bleeding had been according to the clinician's discretion.

RESULTS

All three groups had similar median blood losses. The transfusion of packed red blood cells (PRBCs) and blood components was greater in the clinician discretion group (P<0.05) but there was no difference in the transfusion of PRBCs and blood components between the two algorithm-guided groups.

CONCLUSION

Following algorithms based on point of care tests or on structured clinical practice with standard laboratory tests does not decrease blood loss, but reduces the transfusion of PRBCs and blood components after routine cardiac surgery, when compared with clinician discretion. Cardiac surgery services should use transfusion guidelines based on laboratory-guided algorithms, and the possible benefits of point of care testing should be tested against this standard.

Low complication rate associated with cesarean section under spinal anesthesia for HIV-1-infected women on antiretroviral therapy

BACKGROUND

Elective cesarean section decreases the likelihood of vertical human immunodeficiency virus (HIV) transmission from mother to infant. This study aimed to determine whether cesarean section done with spinal anesthesia on HIV-1-infected pregnant women taking antiretroviral therapy is associated with intraoperative hemodynamic instability, postoperative complications, or changes in immune function or HIV-1 viral load.

METHODS

A case-controlled study was conducted over a 3-year period in a London academic hospital. Forty-four women infected with HIV-1 and a control group of 45 HIV-negative women undergoing cesarean sections were included. The main outcome measures included intraoperative blood pressure, heart rate, blood loss, and ephedrine requirements, and postoperative infective complications, blood transfusion, changes in blood HIV-1 viral load and lymphocyte subsets, and time to hospital discharge.

RESULTS

There were no differences in hemodynamic stability and postoperative complications between the HIV-infected group and the controls. There was an acute postoperative increase in the CD4T lymphocyte count (P = 0.01), but the CD4T:CD8T ratio and viral load did not change.

CONCLUSIONS

Elective cesarean section under spinal anesthesia for women infected with HIV-1 taking antiretroviral therapy was not associated with intraoperative or postoperative complications.

Regulation of hypoxic death in C. elegans by the insulin/IGF receptor homolog DAF-2

To identify genetic determinants of hypoxic cell death, we screened for hypoxia-resistant (Hyp) mutants in Caenorhabditis elegans and found that specific reduction-of-function (rf) mutants of daf-2, an insulin/insulinlike growth factor (IGF) receptor (INR) homolog gene, were profoundly Hyp. The hypoxia resistance was acutely inducible just before hypoxic exposure and was mediated through an AKT-1/PDK-1/forkhead transcription factor pathway overlapping with but distinct from signaling pathways regulating life-span and stress resistance. Selective neuronal and muscle expression of daf-2(+) restored hypoxic death, and daf-2(rf) prevented hypoxia-induced muscle and neuronal cell death, which demonstrates a potential for INR modulation in prophylaxis against hypoxic injury of neurons and myocytes.

Glucose, insulin and potassium for heart protection during cardiac surgery

BACKGROUND

Coronary artery bypass grafting with hypothermic cardiac arrest and cardiopulmonary bypass (CPB) is associated with myocardial injury. Our study investigated whether an infusion of glucose, insulin and potassium (GIK) during elective coronary artery bypass surgery decreases myocardial cell death.

METHODS

We measured cardiac troponin I (cTnI), a myofibrillar structural protein, which is a sensitive and specific indicator of myocytic injury. With ethics committee approval, 42 patients were enrolled into a randomized, prospective, double-blinded study. In the GIK group, 500 ml of 50% dextrose solution containing 100 IU insulin and potassium 80 mmol was infused at the rate of 0.75 ml kg(-1) h(-1). Patients in the non-GIK group received 5% dextrose solution at the same rate. Arterial blood samples were taken before induction of anaesthesia, after removal of the aortic clamp and 6 and 12 h after CPB.

RESULTS

In both groups there was an increase in cTnI concentration (P<0.05), which was greatest about 6 h after CPB. At no time did the cTnI concentration differ between the two groups.

CONCLUSION

The results suggest that GIK does not decrease the irreversible myocardial damage associated with routine coronary artery bypass surgery.

The cardiovascular response to insertion of the intubating laryngeal mask airway

Sixty-one patients received a standardised anaesthetic and were randomly assigned to three groups: tracheal intubation via direct laryngoscopy, tracheal intubation via an intubating laryngeal mask airway with immediate removal of the device, and tracheal intubation via an intubating laryngeal mask airway with delayed removal. The cardiovascular response to intubation was of a similar magnitude in all groups, although delayed removal of the intubating laryngeal mask airway was associated with a second pressor response. Norepinephrine changed significantly over time following direct laryngoscopy and following immediate removal of the intubating laryngeal mask airway, but not after delayed removal. The findings of this study do not support using the intubating laryngeal mask instead of direct laryngoscopy purely to decrease the response to intubation.

The effects of aprotinin on thromboelastography with three different activators

BACKGROUND

Thromboelastography is used for assessment of hemostasis. Adherence to thromboelastography-guided algorithms and aprotinin administration each decrease bleeding and blood product usage after cardiac surgery. Aprotinin, through inhibition of kallikrein, causes prolongation of the celite-activated clotting time and the activated partial thromboplastin ratio. The aim of this study was to assess the effects of aprotinin on the thromboelastography trace.

METHODS

Three activators were used in the thromboelastography: celite (which is widely established), kaolin, and tissue factor. Assessment was performed on blood from volunteers and from patients before and after cardiac surgery.

RESULTS

The tissue factor-activated thromboelastography trace was unaffected by the addition of aprotinin. When celite and kaolin were used as activators in the presence of aprotinin, the reaction time (time to clot formation) of the thromboelastography trace was prolonged (P < 0.0001) and the maximum amplitude (clot strength) was decreased (P < 0.05). With celite as an activator, the addition of aprotinin decreased (P < 0.05) the thromboelastography alpha angle (rate of clot extension). The reaction time of the celite-activated trace correlated with the activated partial thromboplastin ratio (P < 0.01). The reaction time of the tissue factor-activated trace correlated with the international normalized ratio (P < 0.01).

CONCLUSION

The thromboelastography trace is altered in the presence of aprotinin when celite and kaolin are used as activators but not when tissue factor is the activator.

Mechanisms and attenuation of hemostatic activation during extracorporeal circulation

Patients undergoing cardiac surgery with cardiopulmonary bypass are at risk for excessive microvascular bleeding, which often leads to transfusion of allogeneic blood and blood components as well as reexploration in a smaller subset of patients. Excessive bleeding after cardiac surgery is generally related to a combination of several alterations in the hemostatic system pertaining to hemodilution, excessive activation of the hemostatic system, and potentially the use of newer, longer-acting antiplatelet or antithrombotic agents. Although several nonpharmacologic strategies have been proposed, this review summarizes the role of pharmacologic interventions as means to attenuate the alterations in the hemostatic system during CPB in an attempt to reduce excessive bleeding, transfusion, and reexploration. Specifically, agents that inhibit platelets, fibrinolysis, factor Xa and thrombin, as well as broad-spectrum agents, have been investigated with respect to their role in reducing consumption of clotting factors and better preservation of platelet function. Prophylactic administration of agents with antifibrinolytic, anticoagulant, and possibly antiinflammatory properties can decrease blood loss and transfusion. Although aprotinin seems to be the most effective blood conservation agent (which is most likely related to its broad-spectrum nature), agents with isolated antifibrinolytic properties may be as effective in low-risk patients. The ability to reduce blood product transfusions and to decrease operative times and reexploration rates favorably affects patient outcomes, availability of blood products, and overall health care costs.

Fibreoptic views through the laryngeal mask and the intubating laryngeal mask

BACKGROUND AND OBJECTIVE

The intubating laryngeal mask (intubating laryngeal mask airway) was designed to facilitate blind intubation. Its value as an adjunct to fibreoptic laryngoscopy has not been evaluated. This study compares the intubating laryngeal mask airway with the standard laryngeal mask airway as conduits for fibreoptic laryngoscopy.

METHODS

The fibreoptic view of the laryngeal inlet was graded via both devices in 60 anaesthetized patients. The fibreoptic view through the intubating laryngeal mask airway was assessed after the central epiglottic elevator bar had been lifted out of the field of vision by an 8-mm Euromedical tracheal tube, which was inserted to a depth of 18 cm. The fibreoptic view from the aperture bars of the laryngeal mask was recorded.

RESULTS

The vocal cords were viewed less frequently through the intubating laryngeal mask airway (52%) than through the laryngeal mask airway (92%) [difference = 40% (95% CI = 26% to 54%), P < 0.0001].

CONCLUSION

The view of the laryngeal inlet is better through the laryngeal mask airway than through a tracheal tube inserted to 18 cm in the intubating laryngeal mask.

A comparison of the intubating and standard laryngeal mask airways for airway management by inexperienced personnel

Twenty-four inexperienced participants were timed inserting the intubating laryngeal mask airway and the laryngeal mask airway in 75 anaesthetised subjects. Adequacy of ventilation was assessed on a three-point scale. The pressure at which a leak first developed around the device's cuff was also measured. There was no significant difference in insertion time or the likelihood of achieving adequate ventilation between devices. However, the intubating laryngeal mask airway was better at providing adequate ventilation without audible leak (58/75 (77%) vs. 42/75 (56%); p = 0.009). The median (range [IQR]) pressure at which an audible leak developed was higher for the intubating laryngeal mask airway, 34.5 (14-40 [29-40]) cmH2O, than for the laryngeal mask airway, 27.5 (14-40 [22-33]) cmH2O (p < 0.001). The intubating laryngeal mask airway is worthy of further consideration as a tool for emergency airway management for inexperienced personnel.