Preoperative hemoglobin thresholds for survival equity in women and men.

Anemia affects humans throughout life, and is linked to higher morbidity and mortality. Unclear is whether hemoglobin values are equivalent between women and men. This study evaluates the association of preoperative hemoglobin levels with in-hospital mortality and estimates thresholds for survival equity between men and women. All adult patients undergoing surgery between 2010 and 2019 from 14 German hospitals were included in the study. Thresholds for survival equity were determined with generalized additive models. In total, 842,130 patients with a median in-hospital follow-up time of 7 days were analyzed. During follow-up 20,370 deaths occurred. Preoperative hemoglobin stratified in-hospital mortality (log-rank test p < 0.001) and was associated with mortality independently of demographic risk, surgical risk and health status. For each 1 g/dL reduction in preoperative hemoglobin, the odds of mortality increased by a factor of 1.22 (95% CI 1.21-1.23, p < 0.001). A preoperative hemoglobin threshold of 10.5 g/dL reflected equivalent risk for both male and female patients. Hemoglobin levels below 10.5 g/dL had higher risk of mortality for women than for men. The findings from this study aid evidence-based thresholds, inform anemia management and promote equitable care, thus enhancing patient outcomes.

German Patient Blood Management Network: effectiveness and safety analysis in 1.2 million patients.

BACKGROUND: Patient Blood Management (PBM) is a patient-centred, systematic, evidence-based approach to improve patient outcomes by managing and preserving a patient's own blood whilst promoting patient safety and empowerment. The effectiveness and safety of PBM over a longer period have not yet been investigated. METHODS: We performed a prospectively designed, multicentre follow-up study with non-inferiority design. Data were retrospectively extracted case-based from electronic hospital information systems. All in-hospital patients (≥18 yr) undergoing surgery and discharged between January 1, 2010 and December 31, 2019 were included in the analysis. The PBM programme focused on three domains: preoperative optimisation of haemoglobin concentrations, blood-sparing techniques, and guideline adherence/standardisation of allogeneic blood product transfusions. The outcomes were utilisation of blood products, composite endpoint of in-hospital mortality and postoperative complications (myocardial infarction/ischaemic stroke/acute renal failure with renal replacement therapy/sepsis/pneumonia), anaemia rate at admission and discharge, and hospital length of stay. RESULTS: A total of 1 201 817 (pre-PBM: n=441 082 vs PBM: n=760 735) patients from 14 (five university/nine non-university) hospitals were analysed. Implementation of PBM resulted in a substantial reduction of red blood cell utilisation. The mean number of red blood cell units transfused per 1000 patients was 547 in the PBM cohort vs 635 in the pre-PBM cohort (relative reduction of 13.9%). The red blood cell transfusion rate was significantly lower (P<0.001) with odds ratio 0.86 (0.85-0.87). The composite endpoint was 5.8% in the PBM vs 5.6% in the pre-PBM cohort. The non-inferiority aim (safety of PBM) was achieved (P<0.001). CONCLUSIONS: Analysis of >1 million surgical patients showed that the non-inferiority condition (safety of Patient Blood Management) was fulfilled, and PBM was superior with respect to red blood cell transfusion. CLINICAL TRIAL REGISTRATION: NCT02147795.

Association of anaemia, co-morbidities and red blood cell transfusion according to age groups: multicentre sub-analysis of the German Patient Blood Management Network Registry.

BACKGROUND: Blood transfusions are common medical procedures and every age group requires detailed insights and treatment bundles. The aim of this study was to examine the association of anaemia, co-morbidities, complications, in-hospital mortality, and transfusion according to age groups to identify patient groups who are particularly at risk when undergoing surgery. METHODS: Data from 21 Hospitals of the Patient Blood Management Network Registry were analysed. Patients were divided into age subgroups. The incidence of preoperative anaemia, co-morbidities, surgical disciplines, hospital length of stay, complications, in-hospital mortality rate, and transfusions were analysed by descriptive and multivariate regression analysis. RESULTS: A total of 1 117 919 patients aged 18-108 years were included. With increasing age, the number of co-morbidities and incidence of preoperative anaemia increased. Complications, hospital length of stay, and in-hospital mortality increased with age and were higher in patients with preoperative anaemia. The mean number of transfused red blood cells (RBCs) peaked, whereas the transfusion rate increased continuously. Multivariate regression analysis showed that increasing age, co-morbidities, and preoperative anaemia were independent risk factors for complications, longer hospital length of stay, in-hospital mortality, and the need for RBC transfusion. CONCLUSION: Increasing age, co-morbidities, and preoperative anaemia are independent risk factors for complications, longer hospital length of stay, in-hospital mortality, and the need for RBC transfusion. Anaemia diagnosis and treatment should be established in all patients.

Preoperative anaemia and red blood cell transfusion in patients with aneurysmal subarachnoid and intracerebral haemorrhage - a multicentre subanalysis of the German PBM Network Registry.

PURPOSE: Anaemia is common in patients presenting with aneurysmal subarachnoid (aSAH) and intracerebral haemorrhage (ICH). In surgical patients, anaemia was identified as an idenpendent risk factor for postoperative mortality, prolonged hospital length of stay (LOS) and increased risk of red blood cell (RBC) transfusion. This multicentre cohort observation study describes the incidence and effects of preoperative anaemia in this critical patient collective for a 10-year period. METHODS: This multicentre observational study included adult in-hospital surgical patients diagnosed with aSAH or ICH of 21 German hospitals (discharged from 1 January 2010 to 30 September 2020). Descriptive, univariate and multivariate analyses were performed to investigate the incidence and association of preoperative anaemia with RBC transfusion, in-hospital mortality and postoperative complications in patients with aSAH and ICH. RESULTS: A total of n = 9081 patients were analysed (aSAH n = 5008; ICH n = 4073). Preoperative anaemia was present at 28.3% in aSAH and 40.9% in ICH. RBC transfusion rates were 29.9% in aSAH and 29.3% in ICH. Multivariate analysis revealed that preoperative anaemia is associated with a higher risk for RBC transfusion (OR = 3.25 in aSAH, OR = 4.16 in ICH, p < 0.001), for in-hospital mortality (OR = 1.48 in aSAH, OR = 1.53 in ICH, p < 0.001) and for several postoperative complications. CONCLUSIONS: Preoperative anaemia is associated with increased RBC transfusion rates, in-hospital mortality and postoperative complications in patients with aSAH and ICH. TRIAL REGISTRATION: ClinicalTrials.gov , NCT02147795, https://clinicaltrials.gov/ct2/show/NCT02147795.

Critical Care Providers' Moral Distress: Frequency, Burden, and Potential Resources.

BACKGROUND: Critical Care Providers (CCPs) experience situations that challenge their ethics and professional standards and may entail moral distress (MD). AIM: To analyze MD perceived by CCPs in intensive care units (ICUs) or emergency departments (EDs) and further clarify whether CCPs who rely on spiritual resources differ in their perception of MD from those who do not utilize these resources. METHODS: A cross-sectional anonymous survey was administered using a modified version of the German language version of the Moral Distress Scale (MDS) with 2 × 12 items to assess the frequency and the respective perceived burden of specific situations by applying a 5-point Likert scale. Explorative factor analysis was performed and the sub-constructs of the respective items regarding MD frequency and burden were identified. Job burden and professional satisfaction were measured using visual analogue scales (VAS) and a four-point Likert scale, respectively. The 15-item SpREUK questionnaire was applied to measure spiritual attitudes and behaviours and to differentiate between religious and spiritual persons. Data from 385 German-speaking CCPs were included (55% physicians, 45% nurses). RESULTS: Conflict situations are similar for physicians and nurses although they are perceived as more burdensome by nurses. Among physicians, the MDS factor Looking away/Resignation scores highest for assistant physician residents, whereas distress caused by looking away is more often perceived by specialist physicians without a managerial position. Work satisfaction is inversely associated with MD and emotional exhaustion is positively associated with it. Participants' spirituality is marginally associated with MD. The best predictors of both MD frequency and burden are emotional exhaustion with further influences of work satisfaction, being a nurse, and being a non-believer on the frequency of MD perception. Being a nurse, participants' experience in ICU/ED, and being of the male gender are further predictors of MD burden. CONCLUSIONS: MD is experienced differently by different groups of CCPs depending on their place in the hierarchy of responsibility. As MD perception is best predicted by emotional exhaustion, these situations should be avoided. Although some CCPs may rely on spiritual resources, all need individual and team support to cope with MD.

[Significance of patient-specific risk factors for regional cerebral oxygen saturation in beach chair position]. / Bedeutung patientenspezifischer Risikofaktoren für die regionale zerebrale Sauerstoffsättigung in "Beach-chair"-Position.

BACKGROUND: Despite numerous studies on the regional cerebral oxygen saturation (rSO2) measured by near infrared spectroscopy (NIRS) in orthopedic patients in the beach chair position, it is still unclear whether patient-specific factors, such as concomitant cardiovascular diseases, are more frequently associated with the occurrence of cerebral desaturation events (CDE). OBJECTIVE: The aim of the present study was therefore to identify possible patient-specific risk factors that enable prediction of CDE. METHODS: Data were collected on 397 orthopedic patients undergoing shoulder surgery in the beach chair position. Routine anesthesia management and standard monitoring was used in all patients. Target value for the inspiratory oxygen concentration (FIO2) was set to 50% and for the end-tidal carbon dioxide partial pressure to 35-45 mm Hg. RSO2 was quantified using NIRS. The responsible anesthesiologist was blinded to the rSO2 data. A decrease in rSO2 > 20% or a value < 50% in the beach chair position was defined as CDE. Patients with and without CDE were analyzed with respect to different classifications, American Society of Anesthesiologists (ASA) and Revised Cardiac Risk Index (RCRI) as well as existing arterial hypertension and age. A value of p <0.05 was considered statistically significant. RESULTS: Patients with CDE (n = 238) were significantly more often classified as ASA > 2 (p = 0.01) and RCRI > 1 (p = 0.01), suffered more often from arterial hypertension (p = 0.01) and were older (median: 60 years compared to 55 years; p = 0.01) than patients without CDE (n = 159) in the beach chair position (Wilcoxon rank sum test). Arterial hypertension remained significant after removing the effect of age (p = 0.03) and RCRI classification (p = 0.04; two-way ANOVA multivariate analysis). CONCLUSION: On the basis of our study, patient-specific prognosis and risk factors for the occurrence of CDE, such as higher age, ASA > 2 and RCRI > 1 classification as well as pre-existing arterial hypertension could be determined. Arterial hypertension represents the main risk factor for the occurrence of CDE in the beach chair position. RCRI > 1 classification or age, however, only has an effect on the occurrence of pathological rSO2 values due to the greater probability of simultaneous arterial hypertension.

Preoperative Anaemia in Primary Hip and Knee Arthroplasty. / Präoperative Anämie in der Hüft- und Kniegelenkendoprothetik.

INTRODUCTION: Approximately one in three patients has untreated preoperative anaemia, which in turn is associated with an increased need for transfusion of allogenic red blood cell concentrates (RBC) and complications in the context of a surgical intervention. Here, the prevalence of preoperative and postoperative anaemia as well as their effects on transfusion rate, hospital length of stay and hospital mortality in primary hip and knee arthroplasty has been analysed. METHODS: From January 2012 to September 2018, 378,069 adult inpatients from 13 German hospitals were analysed on the basis of an anonymized registry. Of these, n = 10,017 patients had a hip and knee joint primary arthroplasty. The primary endpoint was the incidence of preoperative anaemia, which was analysed by the first available preoperative haemoglobin value according to the WHO definition. Secondary endpoints included in-hospital length of stay, number of patients with red blood cell concentrate transfusion, incidence of hospital-acquired anaemia, number of deceased patients, and postoperative complications. RESULTS: The preoperative anaemia rate was 14.8% for elective knee joint arthroplasty, 22.9% for elective hip joint arthroplasty and 45.0% for duo-prosthesis implantation. Preoperative anaemia led to a significantly higher transfusion rate (knee: 8.3 vs. 1.8%; hip: 34.5 vs. 8.1%; duo-prosthesis: 42.3 vs. 17.4%), an increased red blood cell concentrate consumption (knee: 256 ± 107 vs. 29 ± 5 RBC/1000 patients; hip: 929 ± 60 vs. 190 ± 16 RBC/1000 patients; duo-prosthesis: 1411 ± 98 vs. 453 ± 42 RBC/1000 patients). Pre-operative anaemia was associated with prolonged hospital stay (12.0 [10.0; 17.0] d vs. 11.0 [9.0; 13.0] d; p < 0.001) and increased mortality (5.5% [4.6 - 6.5%] vs. 0.9% [0.7 - 1.2%]; Fisher p < 0.001) compared to non-anaemic patients. In patients aged 80 years and older, the incidence of preoperative anaemia and thus the transfusion rate was almost twice as high as in patients under 80 years of age. SUMMARY: Preoperative anaemia is common in knee and hip primary arthroplasty and was associated with a relevant increase in red blood cell concentrate consumption. In the context of patient blood management, a relevant potential arises, especially in elective orthopaedic surgery, to better prepare elective patients, to avoid unnecessary transfusions and thus to conserve the valuable resource blood.

A Comparative Analysis of Bupivacaine and Ropivacaine Effects on Human Cardiac SCN5A Channels.

BACKGROUND: Intoxication with local anesthetics may induce cardiac arrhythmias by interaction with ion channels. Ropivacaine has been introduced into clinical anesthesia as a safer alternative to bupivacaine, which is associated with a relatively high risk of cardiac arrhythmias. Diverging safety profiles may result from differences in the mode of interaction with cardiac Na(+) channels. We conducted this study to test this hypothesis and to provide experimental basis for the ongoing discussion regarding the cardiotoxic profiles of these local anesthetics. METHODS: The influence of bupivacaine and ropivacaine on the electrophysiological properties of Na(+) channels was investigated in human embryonic kidney-293 cells stably transfected with SCN5A channels cloned from the human heart using the patch-clamp technique in the outside-out configuration. RESULTS: Open-channel block of SCN5A channels was concentration dependent, with bupivacaine being approximately 4.5-fold more potent than ropivacaine (IC50 = 69.5 ± 8.2 µM vs IC50 = 322.2 ± 29.9 µM). Both drugs influenced the voltage dependency of channel activation and steady-state inactivation by shifting the membrane potential of half-maximal activation/inactivation toward somewhat more negative membrane potentials. In their inactivated state, SCN5A channels were slightly more sensitive toward bupivacaine than toward ropivacaine (IC50 = 2.18 ± 0.16 µM vs IC50 = 2.73 ± 0.27 µM). Blockade of inactivated channels developed in a concentration-dependent manner, with comparable time constants for both drugs, whereas recovery from block was approximately 2-fold faster for ropivacaine than for bupivacaine. CONCLUSIONS: Human cardiac Na(+) channels show state-dependent inhibition by ropivacaine, and the mode of interaction is comparable to that of bupivacaine. Therefore, modest differences in cardiotoxicity between these local anesthetic drugs are compatible with subtle differences in their interaction with human cardiac Na(+) channels.

How to perform indexing of extravascular lung water: a validation study.

BACKGROUND: Extravascular lung water is a quantitative marker of the amount of fluid in the thoracic cavity besides the vasculature. Indexing to both predicted and actual body weight have been proposed to compare different individuals and provide a uniform range of normal. OBJECTIVE: We explored extravascular lung water measured by single-indicator transpulmonary thermodilution in a large cohort of patients without cardiopulmonary instability, in order to evaluate current and alternative indexing methods. DESIGN: Prospective, observational. SETTING: Neurosurgical ICU in a tertiary referral academic teaching hospital. PATIENTS: One hundred and one consecutive patients requiring elective brain tumor surgery and postoperative ICU surveillance. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Indexed to predicted body weight, females had a mean extravascular lung water of 9.1 (SD=3.1, range: 5-23) mL/kg and males of 8.0 (SD=2.0, range: 4-19) mL/kg (p<0.001). Values indexed to predicted body weight were inversely correlated with the patient's height (p<0.001). Indexed to the traditionally used actual body weight, data showed a significant relationship to weight (p<0.001) and gender (p<0.05). In contrast, indexing to body height presented a method without dependencies on height, weight, or gender, yielding a uniform 95% confidence interval of 218-430 mL/m. Extravascular lung water increased with positive perioperative fluid balance (p=0.04). CONCLUSIONS: Using either predicted or actual body weight for indexing extravascular lung water does not lead to independence of height, weight, and gender of the patient. Specifying a fixed range of normal or a uniform upper threshold for all patients is misleading for either method, despite widespread use. Our data suggest that indexing extravascular lung water to height is superior to weight-based methods. As we are not aware of any abnormal hemodynamic profile for brain tumor patients, we propose our findings to be a close approximation to normal values.

Brief report: identification of the great auricular nerve by ultrasound imaging and transcutaneous nerve stimulation.

Superficial cervical plexus neuropathy after interscalene brachial plexus block affects about 8% of patients postoperatively. One of the nerves involved in superficial cervical plexus neuropathy is the great auricular nerve. We report success in identification of the great auricular nerve with ultrasound and transcutaneous nerve stimulation in a clinical setting in the majority of cases (95% lower confidence limit 63%). Identification of the nerve is significantly more difficult in female and in obese patients. Further studies will allow determination of whether this information will help to reduce the incidence of superficial cervical plexus neuropathy.

Bupivacaine destabilizes action potential duration in cellular and computational models of long QT syndrome 1.

BACKGROUND: The effects of the local anesthetic bupivacaine on cardiac action potentials (APs) are mainly attributed to inhibition of cardiac Na(+) channels. The relevance of its ability to also induce high-affinity blockade of human ether-à-gogo-related gene (hERG) channels is unclear. We investigated whether this interaction may functionally become more significant in cellular and computational models of long (L)QT syndromes. METHODS: Left ventricular cardiomyocytes were isolated from adult guinea pig hearts, and bupivacaine-induced effects on APs were investigated using the patch-clamp technique. LQT-like states were pharmacologically induced by either blocking I(Ks) (LQT1-like, 10 µmol/L chromanol 293B), or I(Kr) (LQT2-like, 10 µmol/L E4031). Computational analysis of bupivacaine's effects was based on the Luo-Rudy dynamic model. RESULTS: Bupivacaine induced dose-dependent AP shortening in control myocytes. However, in the presence of 1 to 30 µmol/L bupivacaine, a high variability in AP duration with AP prolongations of up to 40% was observed. This destabilizing effect on AP duration was significantly increased in LQT1-like but not in LQT2-like myocytes. Similarly, the incidence of AP prolongations in the presence of 3 µmol/L bupivacaine was significantly increased from 6% in control myocytes to 24% in LQT1-like but not in LQT2-like myocytes. Computational modeling supported the concept that this bupivacaine-induced AP instability and the AP prolongations in the control and LQT1-like myocytes were caused by inhibition of hERG channels. CONCLUSIONS: This study provides evidence that bupivacaine induces inhibition of hERG channels, which is functionally silent under normal conditions but will become more relevant in LQT1-like states in which repolarization relies to a larger degree on hERG channels. Interactions with ion channels other than cardiac Na(+) channels may, therefore, determine the net cardiac effects of bupivacaine when the normal balance of ionic currents is altered.

The subtype-specific effects of droperidol on action potential duration in cellular and computational models of long QT syndrome.

BACKGROUND: Droperidol is a highly potent butyrophenone used for the therapy of postoperative nausea and vomiting. Its cardiac safety in cardiovascular-healthy patients and those with long QT (LQT) syndrome is a matter of debate. In this study, we investigated whether droperidol has subtype-specific effects in cellular and computational models of LQT syndrome. METHODS: Left ventricular cardiac myocytes were isolated from adult guinea pig hearts. LQT1-like behavior was pharmacologically induced by chromanol 293B (10 micromol/L) and LQT2-like states by E4031 (10 micromol/L). Computational analysis was performed using the Luo-Rudy dynamic model. Data are given as mean + or - SEM. RESULTS: In control myocytes, droperidol lengthened action potentials in a concentration-dependent manner with a maximal prolongation of 37% + or - 13% (n = 4) at a concentration of 0.6 micromol/L. In LQT1-like myocytes, droperidol (0.6 micromol/L) further prolonged action potentials by 31% + or - 6% (n = 6) but shortened action potentials of LQT2-like myocytes by 11% + or - 2% (n = 8). Computational modeling supported the concept that droperidol, in addition to the rapid component of the delayed K(+) current, blocks depolarizing targets, such as the L-type Ca(2+) current, the Na(+)-Ca(2+) exchanger, and the Na(+)-K(+) adenosine triphosphatase. CONCLUSIONS: Droperidol has more detrimental effects on cardiac repolarization of LQT1-like than of LQT2-like myocytes suggesting subtype-specific cardiotoxic effects in patients with LQT syndrome. The subtype specificity of droperidol seems to be caused by a complex interaction of droperidol with several different molecular targets. This interaction deserves further investigation to establish the feasibility of a subtype-directed approach in the perioperative management of patients with LQT syndrome.

Global end-diastolic volume acquired by transpulmonary thermodilution depends on age and gender in awake and spontaneously breathing patients.

INTRODUCTION: Volumetric parameters acquired by transpulmonary thermodilution had been repeatedly proven superior to filling pressures for estimation of cardiac preload. Up to now, the proposed normal ranges were never studied in detail. We investigated the relationship of the global end-diastolic volume (GEDV) acquired by transpulmonary thermodilution with age and gender in awake and spontaneously breathing patients. METHODS: Patients requiring brain tumor surgery were equipped prospectively with a transpulmonary thermodilution device. On postoperative day one, thermodilution measurements were performed in 101 patients ready for discharge from the ICU. All subjects were awake, spontaneously breathing, hemodynamically stable and free of catecholamines. RESULTS: Main finding was a dependence of GEDV on age and gender, height and weight of the patient. Age was a highly significant non-linear coefficient for GEDV with large inter-individual variance (p < 0.001). On average, GEDV was 131.1 ml higher in males (p = 0.027). Each cm body height accounted for 13.0 ml additional GEDV (p < 0.001). GEDV increased by 2.90 ml per kg actual body weight (p = 0.043). Each cofactor, including height and weight, remained significant after indexing GEDV to body surface area using predicted body weight. CONCLUSIONS: The volumetric parameter GEDV shows a large inter-individual variance and is dependent on age and gender. These dependencies persist after indexing GEDV to body surface area calculated with predicted body weight. Targeting resuscitation using fixed ranges of preload volumes acquired by transpulmonary thermodilution without concern to an individual patient's age and gender seems not to be appropriate.

Superficial cervical plexus neuropathy after single-injection interscalene brachial plexus block.

BACKGROUND: Interscalene brachial plexus block (ISB) using the modified lateral approach provides a well-established method of anesthesia and analgesia for patients undergoing shoulder surgery. Considering the neural anatomy at the site of injection, the superficial cervical plexus may be at risk of injury. We evaluated the incidence and characteristics of superficial cervical plexus neuropathy. METHODS: During a 1-yr period, 273 consecutive patients requiring single-injection ISB for shoulder or proximal arm surgery were studied. Patients were examined for symptoms compatible with superficial cervical plexus injury before surgery, 24 h postoperatively, and contacted by telephone 31 days after surgery. Symptomatic patients received an additional phone call 6 mo after surgery. RESULTS: Twenty-four hours after shoulder surgery, 21 patients (7.7%) showed symptoms consistent with superficial cervical plexus neuropathy. Symptoms consisted of hypesthesia in 1-4 cutaneous branches of the cervical plexus. Five patients (1.8%) reported symptoms that lasted for >31 days. All symptoms had entirely resolved after 6 mo. CONCLUSIONS: Superficial cervical plexus neuropathy is not uncommon after ISB using the modified lateral approach and the possibility should be discussed with patients preprocedurally.

Lipophilic and stereospecific interactions of amino-amide local anesthetics with human Kv1.1 channels.

BACKGROUND: This study's aim was to investigate the interaction of amino-amide local anesthetics with human Kv1.1 potassium channels. These channels were chosen because of their proven physiologic role. By using a homolog series of local anesthetics with different lengths of the N-substituent, it was intended to elucidate the role of lipophilic interactions with Kv1.1. The use of stereoisomers allowed testing of the role of polar drug actions. METHODS: Human Kv1.1 channels were measured with the patch clamp technique. Concentration-response data were described by Hill functions. Gating changes were described by Boltzmann functions. RESULTS: Inhibition of Kv1.1 channels by dextrobupivacaine, bupivacaine, levobupivacaine, dextroropivacaine, levoropivacaine, and mepivacaine was concentration dependent, reversible, stereoselective, voltage dependent, and frequency independent. The IC(50) values were (mean +/- SEM) 41 +/- 3 microm (n = 20), 56 +/- 3 microm (n = 26), 76 +/- 8 microm (n = 24), 135 +/- 29 microm (n = 23), 313 +/- 32 microm (n = 25), and 1,451 +/- 351 microm (n = 23), respectively. The midpoint of current activation was shifted into the hyperpolarizing direction. The inhibitory potency as well as the potency to induce gating changes correlated with the number of CH(2) groups in the side chain of the drugs (r > 0.9, P < 0.05). CONCLUSIONS: Kv1.1 channels constitute an important biophysical model for elucidating molecular mechanisms underlying local anesthetic drug effects. Inhibition likely results from an open state-dependent blocking mechanism. Interaction of local anesthetics with the ion channel protein is determined by lipophilic drug properties.

Amitriptyline is a potent blocker of human Kv1.1 and Kv7.2/7.3 channels.

BACKGROUND: Kv1.1 and Kv7.2/7.3 channels control excitability of neuronal cells. As hyperexcitability is a sign of neuropathic pain, epilepsy, and anxiety disorders, these channels may be important molecular targets of amitriptyline that cause pharmacological as well as toxicological effects by altering neuronal excitability. Since the molecular mechanisms underlying these effects of amitriptyline have not been fully elucidated, we aimed to characterize the interaction of amitriptyline with human Kv1.1 and Kv7.2/7.3 channels. We also intended to establish the interaction of amitriptyline with the Kv7.2/7.3 channel opener, retigabine. METHODS: Kv1.1 and Kv7.2/7.3 channels were expressed in human embryonic kidney cells and in Chinese hamster ovary cells. The effects of amitriptyline and retigabine were studied with the patch-clamp technique. RESULTS: Amitriptyline inhibited Kv1.1 and Kv7.2/7.3 channels in a concentration-dependent and reversible manner. The IC50-value was 22 +/- 3 microM (n = 33) and 10 +/- 1 microM (n = 40), respectively. Deactivating inward currents of Kv7.2/7.3 channels were inhibited with an IC50-value of 4.2 +/- 0.6 microM (n = 32). Inhibition of Kv7.2/7.3 channels by amitriptyline reversibly depolarized the resting membrane potential. Retigabine reversed both the inhibitory action of amitriptyline on Kv7.2/7.3 channels as well as the depolarization of the membrane potential. CONCLUSIONS: Since amitriptyline inhibited Kv1.1 and Kv7.2/7.3 channels only at toxicologically relevant plasma concentrations, our results suggest a role for these channels in the neuroexcitatory side effects of amitriptyline. As the inhibitory effects of amitriptyline were reversed by retigabine, a combination of amitriptyline and retigabine could be of additional benefit in the therapy of neuropathic pain.

Molecular interaction of droperidol with human ether-a-go-go-related gene channels: prolongation of action potential duration without inducing early afterdepolarization.

BACKGROUND: The cardiac safety of droperidol given at antiemetic doses is a matter of debate. Although droperidol potently inhibits human ether-a-go-go-related gene (HERG) channels, the molecular mode of this interaction is unknown. The role of amino acid residues typically mediating high-affinity block of HERG channels is unclear. It is furthermore unresolved whether droperidol at antiemetic concentrations induces action potential prolongation and arrhythmogenic early afterdepolarizations in cardiac myocytes. METHODS: Molecular mechanisms of HERG current inhibition by droperidol were established using two-electrode voltage clamp recordings of Xenopus laevis oocytes expressing wild-type and mutant channels. The mutants T623A, S624A, V625A, Y652A, and F656A were generated by site-directed mutagenesis. The effect of droperidol on action potentials was investigated in cardiac myocytes isolated from guinea pig hearts using the patch clamp technique. RESULTS: Droperidol inhibited currents through HERG wild-type channels with a concentration of half-maximal inhibition of 0.6-0.9 microM. Droperidol shifted the channel activation and the steady state inactivation toward negative potentials while channel deactivation was not affected. Current inhibition increased with membrane potential and with increasing duration of current activation. Inhibition of HERG channels was similarly reduced by all mutations. Droperidol at concentrations between 5 and 100 nM prolonged whereas concentrations greater than 300 nm shortened action potentials. Early afterdepolarizations were not observed. CONCLUSIONS: Droperidol is a high-affinity blocker of HERG channels. Amino acid residues typically involved in high-affinity block mediate droperidol effects. Patch clamp results and computational modeling allow the hypothesis that interaction with calcium currents may explain why droperidol at antiemetic concentrations prolongs the action potential without inducing early afterdepolarizations.

Structural requirements of human ether-a-go-go-related gene channels for block by bupivacaine.

BACKGROUND: Local anesthetics interact with human ether-a-go-go-related gene (HERG) channels via the aromatic amino acids Y652 and F656 in the S6 region. This study aimed to establish whether the residues T623, S624, and V625 residing deeper within the pore are also involved in HERG channel block by bupivacaine. In addition, the study aimed to further define the role of the aromatic residues Y652 and F656 in bupivacaine inhibition by mutating these residues to threonine. METHODS: Alanine and threonine mutants were generated by site-directed mutagenesis. Electrophysiologic and pharmacologic properties of wild-type and mutant HERG channels were established using two-electrode voltage-clamp recordings of Xenopus laevis oocytes expressing HERG channels. RESULTS: Tail currents at -120 mV through HERG wild-type channels were inhibited with an IC50 value of 132 +/- 22 microm (n = 33). Bupivacaine (300 microm) inhibited wild-type tail currents by 62 +/- 12% (n = 7). Inhibition of HERG tail currents by bupivacaine (300 microm) was reduced by all mutations (P < 0.001). The effect was largest for F656A (inhibition 5 +/- 2%, n = 6) in the lower S6 region and for T623A (inhibition 13 +/- 4%, n = 9) near the selectivity filter. Introducing threonine at positions 656 and 652 significantly reduced inhibition by bupivacaine compared with HERG wild type (P < 0.001). CONCLUSIONS: The authors' results indicate that not only the aromatic residues Y652 and F656 but also residues residing deeper within the pore and close to the selectivity filter of HERG channels are involved in inhibition of HERG channels by the low-affinity blocker bupivacaine.

Long QT 1 mutation KCNQ1A344V increases local anesthetic sensitivity of the slowly activating delayed rectifier potassium current.

BACKGROUND: Anesthesia in patients with long QT syndrome (LQTS) is a matter of concern. Congenital LQTS is most frequently caused by mutations in KCNQ1 (Kv7.1), whereas drug-induced LQTS is a consequence of HERG (human ether-a-go-go-related gene) channel inhibition. The aim of this study was to investigate whether the LQT1 mutation A344V in the S6 region of KCNQ1, at a position corresponding to the local anesthetic binding site in HERG, may render drug insensitive KCNQ1 channels into a toxicologically relevant target of these pharmacologic agents. This may suggest that LQTS constitutes not only a nonspecific but also a specific pharmacogenetic risk factor for anesthesia. METHODS: The authors examined electrophysiologic and pharmacologic properties of wild-type and mutant KCNQ1 channels. The effects of bupivacaine, ropivacaine, and mepivacaine were investigated using two-electrode voltage clamp and whole cell patch clamp recordings. RESULTS: The mutation A344V induced voltage-dependent inactivation in homomeric KCNQ1 channels and shifted the voltage dependence of KCNQ1/KCNE1 channel activation by +30 mV. The mutation furthermore increased the sensitivity of KCNQ1/KCNE1 channels for bupivacaine 22-fold (KCNQ1wt/KCNE1: IC50 = 2,431 +/- 582 microM, n = 20; KCNQ1A344V/KCNE1: IC50 = 110 +/- 9 microM, n = 24). Pharmacologic effects of the mutant channels were dominant when mutant and wild-type channels were coexpressed. Simulation of cardiac action potentials with the Luo-Rudy model yielded a prolongation of the cardiac action potential duration and induction of early afterdepolarizations by the mutation A344V that were aggravated by local anesthetic intoxication. CONCLUSIONS: The results indicate that certain forms of the LQTS may constitute a specific pharmacogenetic risk factor for regional anesthesia.