Leanne Groban

Cardiac resuscitation after incremental overdosage with lidocaine, bupivacaine, levobupivacaine, and ropivacaine in anesthetized dogs

There is no information comparing the ability to reverse the cardiotoxic effects associated with incremental overdosage of bupivacaine (BUP) to levobupivacaine (LBUP), ropivacaine (ROP), or lidocaine (LIDO). Open-chest dogs were randomized to receive incremental escalating infusions of BUP, LBUP, ROP, and LIDO to the point of cardiovascular collapse (mean arterial pressure [MAP] ≤45 mm Hg). Hypotension and arrhythmias were treated with epinephrine, open-chest massage, and advanced cardiac life support protocols, respectively. Outcomes were defined as the following: successful (stable rhythm and MAP ≥55 mm Hg for 20 min), successful with continued therapy (stable rhythm and MAP <55 mm Hg after 20 min), or death. Continued therapy was required in 86% of LIDO dogs compared with only 10%–30% of the other dogs (P < 0.002). Mortality from BUP, LBUP, ROP, and LIDO was 50%, 30%, 10%, and 0%, respectively. Myocardial depression was primarily responsible for the profound hypotension, as the occurrence of lethal arrhythmias preceding resuscitation was not different among local anesthetics. Epinephrine-induced ventricular fibrillation occurred more frequently in BUP-intoxicated dogs than in dogs given LIDO or ROP (P < 0.05). The unbound plasma concentrations at collapse were larger for ROP, 19.8 &mgr;g/mL (10–39 &mgr;g/mL), compared with BUP, 5.7 &mgr;g/mL (3–11 &mgr;g/mL); whereas the concentrations of LBUP, 9.4 &mgr;g/mL (5–18 &mgr;g/mL) and BUP were not significantly different from each other. IMPLICATIONS There were consistent differences among the local anesthetics, the sum of which suggests that larger doses and blood concentrations of ropivacaine (ROP) and lidocaine will be tolerated as compared with bupivacaine (BUP) and levobupivacaine (LBUP). Lidocaine intoxication results in myocardial depression from which resuscitation is consistently successful but will require continuing drug support. After BUP, LBUP, or ROP, resuscitation is not always successful, and the administration of epinephrine may lead to severe arrhythmias. The unbound plasma concentrations at collapse were larger for ROP compared with BUP, whereas the concentrations of LBUP and BUP were not significantly different from each other. Furthermore, larger plasma concentrations of ROP than BUP are present after resuscitation, suggesting a wider margin of safety when large volumes and large concentrations are used to establish upper or lower extremity nerve blocks for surgical anesthesia and during long-term infusions for pain management.

Dexmedetomidine-Induced Sedation in Volunteers Decreases Regional and Global Cerebral Blood Flow

Dexmedetomidine is a selective &agr;2-agonist approved for sedation of critically ill patients. There is little information on the effects of dexmedetomidine on cerebral blood flow (CBF) or intracranial hemodynamics, despite considerable other pharmacodynamic data. We hypothesized that therapeutic doses of dexmedetomidine would decrease CBF. Therefore, nine supine volunteers, aged 24–48 yr, were infused with a 1 &mgr;g/kg IV loading dose of dexmedetomidine, followed by an infusion of 0.2 &mgr;g · kg−1 · h−1 (LOW DEX) and 0.6 &mgr;g · kg−1 · h−1 (HIGH DEX). Hemodynamic and CBF (via positron emission tomography) measurements were determined at each experimental time point. Dexmedetomidine decreased both cardiac output and heart rate during and 30 min after drug administration. Blood pressure decreased from 12% to 16% during and after the dexmedetomidine administration. Global CBF was decreased significantly from baseline (91 mL · 100 g−1 · min−1 [95% confidence interval, 72–114] to 64 mL · 100 g−1 · min−1 [51–81] LOW DEX and 61 mL · 100 g−1 · min−1 [48–76] HIGH DEX). This decrease in CBF remained constant for at least 30 min after the dexmedetomidine infusion was discontinued, despite the plasma dexmedetomidine concentration decreasing 40% during this same time period (628 pg/mL [524–732] to 380 pg/mL [253–507]).

Central nervous system and cardiac effects from long-acting amide local anesthetic toxicity in the intact animal model

With the development of the newer long-acting amide local anesthetics, ropivacaine and levobupivacaine, numerous animal studies of LA systemic toxicity have emerged. Because of the complex nature of the human response to LA intoxication, the task of designing and interpreting these animal studies of LA toxicity can be difficult. Accordingly, this report will review the selection of an animal model for the study of LA toxicity; examine the pertinent in vivo animal studies that compare the central nervous system toxicity, cardiovascular toxicity, and the ease of resuscitation of the single enantiomer local anesthetics to racemic bupivacaine; and extrapolate these findings to the clinical setting. Reg Anesth Pain Med 2003;28:3-11.

Local Anesthetic-Induced Cardiac Toxicity: A Survey of Contemporary Practice Strategies Among Academic Anesthesiology Departments

Though new local anesthetics (LA), effective test-dosing, and new regional anesthetic techniques may have improved the safety of regional anesthesia, the optimal management plan for LA-induced cardiac toxicity remains uncertain. Accordingly, we evaluated current approaches to LA cardiotoxicity among academic anesthesiology departments in the United States. A 19-question survey regarding regional anesthesia practices and approaches to LA cardiac toxicity was sent to the 135 academic anesthesiology departments listed by the Society of Academic Anesthesiology Chairs-Association of Anesthesiology Program Directors. Ninety-one anonymously completed questionnaires were returned, at a response rate of 67%. The respondents were categorized into groups according to the number of peripheral nerve blocks (PNBs) performed each month: >70 PNBs (38%), 51–70 PNBs (13%), 31–50 PNBs (20%), 11–30 PNBs (23%), and <10 PNBs (6%). Anesthesia practices administering >70 PNBs were 1.7-times more likely to use ropivacaine (NS), 3.9-times more likely to consider lipid emulsion infusions for resuscitation (P = 0.008), and equally as likely to have an established plan for use of invasive mechanical cardiopulmonary support in the event of LA cardiotoxicity (NS) than low-PNB volume centers. We conclude that there are differences in the management and preparedness for treatment of LA toxicity among institutions, but the safety implications of these differences are undetermined.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

Attenuation of Salt-Induced Cardiac Remodeling and Diastolic Dysfunction by the GPER Agonist G-1 in Female mRen2.Lewis Rats

Introduction The G protein-coupled estrogen receptor (GPER) is expressed in various tissues including the heart. Since the mRen2.Lewis strain exhibits salt-dependent hypertension and early diastolic dysfunction, we assessed the effects of the GPER agonist (G-1, 40 nmol/kg/hr for 14 days) or vehicle (VEH, DMSO/EtOH) on cardiac function and structure. Methods Intact female mRen2.Lewis rats were fed a normal salt (0.5% sodium; NS) diet or a high salt (4% sodium; HS) diet for 10 weeks beginning at 5 weeks of age. Results Prolonged intake of HS in mRen2.Lewis females resulted in significantly increased blood pressure, mildly reduced systolic function, and left ventricular (LV) diastolic compliance (as signified by a reduced E deceleration time and E deceleration slope), increased relative wall thickness, myocyte size, and mid-myocardial interstitial and perivascular fibrosis. G-1 administration attenuated wall thickness and myocyte hypertrophy, with nominal effects on blood pressure, LV systolic function, LV compliance and cardiac fibrosis in the HS group. G-1 treatment significantly increased LV lusitropy [early mitral annular descent (e′)] independent of prevailing salt, and improved the e′/a′ ratio in HS versus NS rats (P<0.05) as determined by tissue Doppler. Conclusion Activation of GPER improved myocardial relaxation in the hypertensive female mRen2.Lewis rat and reduced cardiac myocyte hypertrophy and wall thickness in those rats fed a high salt diet. Moreover, these advantageous effects of the GPER agonist on ventricular lusitropy and remodeling do not appear to be associated with overt changes in blood pressure.

Ventricular arrhythmias with or without programmed electrical stimulation after incremental overdosage with lidocaine, bupivacaine, levobupivacaine, and ropivacaine.

It is unclear whether the mechanism of death from local anesthetic (LA) intoxication is primarily a consequence of cardiac arrhythmias or myocardial contractile depression, and whether LAs might differ in this susceptibility to these two mechanisms. By using programmable electrical stimulation (PES) protocols in anesthetized, ventilated dogs, we compared the arrhythmogenic potential of bupivacaine (BUP), ropivacaine (ROP), levobupivacaine (LBUP), and lidocaine (LIDO). Open-chest dogs were randomized to receive escalating incremental infusions of the four local anesthetics until cardiovascular collapse. We assumed a concentration relationship of 4:1 for LIDO/BUP, LBUP, and ROP. The effective refractory period did not change significantly until the dose increment corresponding to target concentrations of 8 and 32 &mgr;g/mL for BUP, LBUP, ROP, and LIDO, respectively. Thirty percent to 50% increases in effective refractory period oc-curred in surviving dogs at this dose. The incidence ofspontaneous or PES-induced ventricular tachycardia and ventricular fibrillation did not differ among groups. Compared with LIDO, the incidence of PES-induced extrasystoles was more frequent for BUP- and LBUP-treated dogs (P < 0.05). ROP-treated dogs did not differ from LIDO-treated dogs with respect to PES-induced extrasystoles. At the dose increment preceding cardiovascular collapse, all LAs produced significant increases in heart rate and reductions in blood pressure compared with their respective baseline values. The incidence of programmable electrical stimulation-induced ventricular tachycardia and fibrillation with BUP does not differ from the incidence that occurs with the single S (−) enantiomers LBUP and ROP, providing further evidence against stereoselective arrhythmogenesis as a primary component of local anesthetic-induced cardiotoxicity. Implications Progressive bupivacaine intoxication in anesthetized, ventilated dogs does not produce early arrhythmogenic events. The incidence of programmable electrical stimulation-induced ventricular tachycardia and fibrillation with bupivacaine does not differ from the incidence that occurs with the single S (−) enantiomers levobupivacaine and ropivacaine, providing further evidence against stereoselective arrhythmogenesis as a primary component of local anesthetic-induced cardiotoxicity.

Activation of GPR30 attenuates diastolic dysfunction and left ventricle remodelling in oophorectomized mRen2.Lewis rats

AIMS GPR30 is a novel oestrogen receptor expressed in various tissues, including the heart. We determined the role of GPR30 in the maintenance of left ventricular (LV) structure and diastolic function after the surgical loss of ovarian hormones in the female mRen2.Lewis rat, a model emulating the cardiac phenotype of the post-menopausal woman. METHODS AND RESULTS Bilateral oophorectomy (OVX) or sham surgery was performed in study rats; the selective GPR30 agonist, G-1 (50 µg/kg/day), or vehicle was given subcutaneously to OVX rats from 13-15 weeks of age. Similar to the cardiac phenotype of sham rats, G-1 preserved diastolic function and structure relative to vehicle-treated OVX littermates independent of changes in blood pressure. G-1 limited the OVX-induced increase in LV filling pressure, LV mass, wall thickness, interstitial collagen deposition, atrial natriuretic factor and brain natriuretic peptide mRNA levels, and cardiac NAD(P)H oxidase 4 (NOX4) expression. In vitro studies showed that G-1 inhibited angiotensin II-induced hypertrophy in H9c2 cardiomyocytes, evidenced by reductions in cell size, protein content per cell, and atrial natriuretic factor mRNA levels. The GPR30 antagonist, G15, inhibited the protective effects of both oestradiol and G-1 on this hypertrophy. CONCLUSION These data show that the GPR30 agonist G-1 mitigates the adverse effects of oestrogen loss on LV remodelling and the development of diastolic dysfunction in the study rats. This expands our knowledge of the sex-specific mechanisms underlying diastolic dysfunction and provides a potential therapeutic target for reducing the progression of this cardiovascular disease process in post-menopausal women.

Lipid reversal of bupivacaine toxicity: has the silver bullet been identified?

S ince the first reports of unexpectedly difficult resuscitations after accidental intravenous administration of bupivacaine or other long-acting local anesthetics (LA), investigators have pursued 2 divergent lines of research.1 One line of investigation, attempting to define the mechanism for local anesthetic-induced cardiac arrest, has focused on differences between longer-acting (e.g., bupivacaine) and shorter-acting (e.g., lidocaine) LA.2-5 A variety of potential mechanisms have been considered. Many have concentrated on electrophysiologic actions of LA, and in particular, drug actions on cardiac sodium and calcium channels. Others have focused on the negative inotropic actions of LA emphasizing LA-mediated alterations in mitochondrial bioenergetics and intracellular calcium processing. LA are well recognized to produce toxic reactions in the central nervous system, and some investigators have even linked increased local anesthetic concentrations within the brain with dysrhythmias. Finally, investigators have noted that bupivacaine interferes with intracellular signaling and have questioned whether resuscitation difficulties might relate to local anesthetic interactions with the actions of resuscitation drugs. The other line of investigation generally has assumed either an electrophysiologic or contractile mechanism of cardiac toxicity, then has focused on identifying the best agent or technique by which to salvage the unfortunate patient or experimental animal subjected to local anesthetic intoxication.5 Thus, a long series of drugs that serve either as antiarrhythmics (phenytoin, bretylium, and many others), positive inotropics (isoproterenol, epinephrine, amrinone, insulin, and others), or vasopressors (epinephrine, vasopressin) and even extracorporeal circulation have been considered. In this cardiac-oriented mix we now find, to our surprise, an intravenous lipid emulsion.6,7 Yes, this is the same lipid that has been used for years as a part of parenteral nutrition and as a vehicle for the general anesthetic propofol. Weinberg et al. present in this issue of RAPM their provocative results that a bolus dose of lipid can reverse an animal model of bupivacaine cardiac toxicity after standard resuscitation has failed. Although this work cannot define a mechanism for these surprising findings, it seems likely that in some way the lipid is serving to more rapidly remove local anesthetic molecules from whatever binding site serves to produce the cardiovascular depression that has come to be known as bupivacaine toxicity. It may also be possible that the lipid is inducing some sort of metabolic change in the heart that serves to overcome bupivacaine intoxication. Three questions emerge from this work. First, should clinicians treat bupivacaine overdosage with lipid bolus emulsion? Second, given that lipid emulsion is likely not to be readily available at anesthetizing sites, should bupivacaine toxic side effects be treated with bolus propofol, which is formulated with lipid? Third, does the use of infused propofol (and the lipid with which it is formulated) result in protection from local anesthetic-induced toxicity? Our answer to the first question is an unqualified YES, but only after other, more conventional treatments have proven unsatisfactory. It clearly does not make sense at this time to treat local anesthetic-induced tremors or seizures with

Perioperative management of chronic heart failure

Heart failure (HF) is one of the few cardiac conditions that is increasing. Despite a better understanding of how hormones and other signaling systems underlie the pathophysiology, and despite improved outcomes from pharmacologic therapy, many HF patients receive no effective treatment. Patients with HF commonly require medical diagnosis and management in operating rooms and critical care units; thus anesthesiologists are obliged to remain up-to-date both with advances in outpatient (chronic) medical management and with inpatient treatments for acute exacerbations of HF. Accordingly, we reviewed angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-adrenergic receptor blockers, and aldosterone antagonists because these drugs prolong life and are included in current clinical practice guidelines for treating patients with chronic HF. We also reviewed the implications of chronic HF for patients undergoing surgery and anesthesia and discuss how best to provide intensive treatment for acute exacerbations of symptoms, such as might be caused by excessive intravascular volume, inappropriate drug “holidays,” or worsening of the underlying cardiac disease.