Bupivacaine is reported to have toxic effects on myocardial function (1,2). The QRS interval widens with increasing plasma bupivacaine concentrations, whereas systolic shortening and blood pressure decrease and left ventricular end diastolic pressure increases (3,4). Bupivacaine cardiotoxicity is attributed, in part, to its action on mitochondrial metabolism, where it inhibits fatty acid use and electron transport (5–7), uncouples oxygen consumption from adenosine diphosphate phosphorylation (8), and inhibits adenosine triphosphate (ATP) synthase (9). Simultaneously, bupivacaine causes detachment of glycolytic enzymes from the cytoskeleton, decreasing glycolysis. The net result of these effects is reduced ATP production and eventually cell death (10,11).
There may be an advantage in the metabolic-depressant effects of bupivacaine. Slowing of glycolysis, respiration, and cellular metabolism during cardiac arrest could, as with hypothermia, impede metabolic deterioration of myocardial tissue so that the point of irreversible ischemic injury is retarded. The development of myocardial tissue acidosis may be a critical factor in producing myocardial injury (12,13) and studies indicate that hypoxia and acidosis, but not hypoxia alone, will produce necrosis and apoptosis in isolated myocytes (14). Bupivacaine may attenuate acidosis during cardiac arrest and could be cardioprotective if the myocardial-depressant effects of the local anesthetic are reversible. We previously observed that asystole induced with bupivacaine is inhibited with lipid infusion (15), and return of cardiac function could be produced by lipid infusion after a period of circulatory collapse (16). The purpose of the present study was to determine whether bupivacaine changes the rate of myocardial tissue acidosis during ventricular fibrillation compared with a control saline treatment and if recovery of cardiac function can be obtained by lipid infusion and electrical defibrillation.
This study was approved by the Institutional Animal Care Committee and experiments were performed at the VA Chicago Healthcare System, West Side Division Animal Research Facility. Nonpurpose bred male hounds (22–26 kg) were used in this study. Dogs were fasted overnight. On the day of the study, the dog was anesthetized with 5 mg/kg propofol, intubated, and ventilated with 1.5% isoflurane and inspired oxygen concentration of 30%. Catheters were inserted into the femoral artery for blood pressure recording and blood gas sampling and into the femoral vein for fluid and drug administration. Sterile saline was infused IV (4 mL · kg−1 · h−1) for fluid maintenance.
An incision was made along the left fifth intercostal space and the left was ventricle exposed. A Paratrend tissue probe (Codman, Newark, NJ) was calibrated on the day of the study using precision gases. The probe is 0.5 mm in diameter, and 3 sensors measuring oxygen pressure (PmO2), carbon dioxide pressure (PmCO2), and pHm are contained in the final 2 cm (17). The probe was inserted into the myocardium in the region between the first and second diagonal branch of the left anterior descending coronary artery, parallel to the surface of the heart 6 mm below the surface using an 18-gauge angiocatheter as an introducer. Mechanical ventilation was adjusted to maintain arterial Pco2 at 35 ± 2 mm Hg and inspired oxygen concentration was maintained at 30%, with the balance nitrogen. Myocardial temperature was maintained at 38°C using a warming pad.
After equilibration of the myocardial tissue probe for 45 min, baseline measures of mean arterial blood pressure (MAP), heart rate, PmO2, PmCO2, and pHm were recorded and an arterial blood gas sample was taken. Eight dogs were randomly selected to receive an IV infusion of 10 mg/kg bupivacaine over 10 s. Three minutes later ventricular fibrillation was produced by touching a 9-volt battery to the ventricular epicardium. Eight other dogs received a similar volume of saline as a sham vehicle treatment and 3 min later ventricular fibrillation was produced. The treatments were not blinded to the investigators. Ventricular fibrillation was allowed to continue for up to 20 min or until pHm decreased to 7.0. When either of these criteria was achieved in each dog, cardiac massage was instituted to support MAP >35 mm Hg, combined with electrical defibrillation with the paddles applied directly to the heart. In saline-treated dogs, defibrillation was performed at a rate of one per minute with an energy of 15 joules until a supraventricular rhythm was produced. In bupivacaine-treated dogs, myocardial mechanical depression was reversed by IV infusion of a soy lipid emulsion (Intralipid 20%, Fresenius Kabi Clayton, Clayton, NC) administered as a 4 mL/kg bolus (over 2 min), followed by a continuous infusion of 0.5 mL · kg−1 · min−1 for 10 min during cardiac massage. Electrical defibrillation was then produced with a similar schedule as with saline-treated dogs. No vasopressors or inotropic drugs were given to either group during resuscitation but sodium bicarbonate (1 meq/kg) was given IV to correct systemic acidosis.
At the end of the study, when dogs had recovered to baseline levels of MAP, arterial blood gases, and tissue gases, a 15 min period of ventricular fibrillation was produced in 4 dogs from each group to evaluate pH trends over a similar period of time. In bupivacaine-treated dogs, a second 10 mg/kg dose of bupivacaine was given, followed 3 min later by ventricular fibrillation. At the end of the 15 min fibrillation period the dog was killed by anesthetic overdose.
Data are reported as mean ± sd. The maximum rate of decrease in PmO2 and pHm during ventricular fibrillation was determined by a line of best fit. Differences between groups for each treatment were compared by Tukey’s tests. PmO2, PmCO2, and pHm measured at 5, 10, and 15 min during ventricular fibrillation in 4 dogs per group were compared between baseline and subsequent treatments within each group using repeated measures analysis of variance with Tukey’s tests for post hoc comparisons. Significance was taken as P < 0.05.
There were no significant differences in MAP, heart rate, and arterial blood gases under baseline anesthetized conditions between groups (Table 1). Figure 1 shows PmO2, pHm, and PmCO2 traces in a dog after 10 mg/kg bupivacaine and ventricular fibrillation. PmO2 and pHm both changed biphasically, increasing initially after the bupivacaine, then gradually declining to lower levels during ventricular fibrillation. PmCO2 decreased after bupivacaine treatment and increased during fibrillation. Table 2 shows PmO2 and pHm under baseline conditions and during ventricular fibrillation in bupivacaine and saline-treated dogs. Baseline values were similar between the groups. During fibrillation, the rate of decrease in myocardial tissue pH was 4 times greater in sham-treated dogs than in dogs pretreated with bupivacaine. The decrease in PmO2 was not statistically different between the two groups. Ventricular fibrillation continued for the entire period in all dogs and defibrillation and resuscitation occurred when pHm decreased to 7.0.
Defibrillation was successfully performed in all 16 dogs. Saline-treated dogs reverted to normal sinus rhythm within 5 min. Electrical defibrillation was produced within 5 min after lipid infusion in bupivacaine-treated dogs. MAP and heart rate returned to within 10% of baseline levels in all dogs within 30 min.
After recovery of cardiac function and return of physiological variables to baseline levels, we repeated the sham and bupivacaine treatments, then reinstituted ventricular fibrillation for 15 min in 4 sham-treated dogs and 4 bupivacaine-treated dogs. The decrease in PmO2 and pHm and the increase in PmCO2 are shown in Figure 2. The rate of decrease in pHm and increase in PmCO2 were greater in sham-treated dogs.
These results show that bupivacaine, compared with saline, significantly attenuated myocardial tissue acidosis during ventricular fibrillation. Changes in myocardial tissue pH, PmO2, and PmCO2 after bupivacaine treatment but before ventricular fibrillation indicate an inhibition of cellular metabolism, which may explain the delayed progression of tissue acidosis. Our ability to revive all 8 dogs treated with bupivacaine using a lipid infusion and achieve a return of normal cardiac function confirms that bupivacaine could protect the heart from metabolic acidosis during prolonged periods of ventricular fibrillation and cardiac arrest (16).
These findings are consistent with a report that bupivacaine retarded the decrease in tissue pH during cardiac arrest (16). In that study, myocardial pH decreased from 7.36 to 7.16 after 10 minutes of hypotension and asystole produced by an IV bolus of 10 mg/kg bupivacaine. In addition, all 6 dogs treated with lipid infusion were successfully resuscitated, whereas no dogs treated with saline were revived. We concluded that lipid infusion could be used to reverse the cardiotoxic effects of bupivacaine and restore cardiac function to normal. The present study substantiates this observation and shows that bupivacaine inhibited acidosis during ventricular fibrillation compared with sham-treated control dogs. These studies also show that the toxic effects of bupivacaine can be reversed by lipid infusion.
We noted in this study that resuscitation of dogs required cardiac massage combined with electrical defibrillation and, for bupivacaine-treated dogs, lipid infusion. In other studies in rats, lipid pretreatment significantly increased the bupivacaine dose necessary to produce cardiac arrest and enhanced the survival of rats after resuscitation from bupivacaine-induced asystole (15). It is likely that the ameliorative effect of lipid infusion is attributable to its ability to sequester bupivacaine in plasma and decrease its myocardial depressant effects (16,18). It required less time for the sham-treated dogs to revert to normal sinus rhythm in comparison with the bupivacaine-treated dogs. This is likely attributable to myocardial metabolic inhibition by bupivacaine and the time required for lipid infusion to reverse this effect. This was observed as a delay in the return of myocardial muscle tone during cardiac massage in bupivacaine-treated dogs. We did not find a worsening of myocardial pH during the period of resuscitation and by the end of the recovery period the electrocardiogram, MAP, and heart rate had returned to baseline levels in both groups. This indicates the myocardial depressant effects of bupivacaine could be completely reversed by lipid infusion.
Bupivacaine has several effects on mitochondrial function and cellular metabolism. The local anesthetic uncouples oxidative phosphorylation in vitro at approximately 2 mM (8). Although uncoupling is expected to accelerate respiration, we found that declines in PmO2 were similar in control and bupivacaine-treated dogs. It is likely that the small amount of oxygen dissolved in the extracellular space after cardiac arrest was responsible for the rapid decrease in PmO2 in both groups. It is also possible that the concentration of bupivacaine in mitochondria was inadequate for collapsing the mitochondrial transmembrane potential and uncoupling oxidative phosphorylation.
PmO2 increased and PmCO2 decreased after bupivacaine treatment, suggesting that oxidative metabolism was decreased (Fig. 1). Bupivacaine inhibits carnitine acylcarnitine translocase (Ki∼220 μM), a key enzyme in mitochondrial fatty acid uptake (7). As fatty acids are the main energy source for the heart, inhibition of fatty acylcarnitine-dependent respiration could account for bupivacaine-induced changes in tissue PmO2 and PmCO2. It is likely that bupivacaine-induced suppression of metabolic function is responsible for the suppression in acidosis during ventricular fibrillation.
Bupivacaine could inhibit tissue acidosis by another mechanism. It causes glycolytic enzymes to detach from the cytoskeleton, inhibiting glycolysis and therefore lactate production (6). The net result of these effects is seen by the trend of pH (Fig. 1) to increase after bupivacaine, then decrease more slowly than controls during ventricular fibrillation (Fig. 2). Thus, although bupivacaine depresses myocardial function, it could potentially preserve organ viability during ischemia by inhibiting lactate and carbon dioxide formation and tissue acidosis. If the toxic effects of bupivacaine can be reversed, it may be possible to extend the time of ventricular fibrillation or cardiac arrest without ischemic myocardial damage and ultimately restore cardiac function to normal.
Anaerobic-induced myocardial acidosis alters the electrical activity of pacemaker cells in the sinoatrial node and worsens myocardial function, and washout of hydrogen ions may improve these functions (19–21). Although our data suggest that bupivacaine may limit ischemic acidosis by inhibiting glycolysis and carbon dioxide production in the heart, other mechanisms may explain this effect as well. If bupivacaine depresses myocardial contractility by limiting ATP production, this may inhibit tissue acidosis during ischemia by reducing cardiac work. It would be necessary to evaluate this question by treating dogs with a drug that inhibits myocardial contractility, such as a calcium channel blocker, without inhibiting cellular metabolic function and compare the acidosis produced by ventricular fibrillation with bupivacaine treatment. The second question of this study is whether subjects can survive a prolonged ischemic treatment and return of cardiac function without injury of other critical organs such as the brain. It is not known if bupivacaine would inhibit brain acidosis during prolonged ischemia in a manner similar to that seen with the heart.
It is acknowledged that the treatment of 4 dogs in each group with 2 bouts of ventricular fibrillation may have affected the myocardial response in the second challenge. The purpose in performing the second period of fibrillation was to compare not only the rate of decrease in pH and PmO2 in both groups but also the level of pH produced by 15 minutes of fibrillation. It is possible that the rate of decrease in PmO2 or pH may have been changed by repeating the bupivacaine treatment or ventricular fibrillation. However, the rate of decrease in PmO2 was similar in both groups in the first challenge (Table 1) and the second (Fig. 2). In addition, the rate of decrease in pH was consistently increased in saline-treated compared with bupivacaine-treated dogs. This suggests that the response to ventricular fibrillation was consistent between the first and second challenge in sham- and bupivacaine-treated dogs. It is important to note that because of the log function of pH, the decrease in pH units was 3 times more in sham- than in bupivacaine-treated dogs after 15 minutes of fibrillation, but the increase in hydrogen ion concentration was more than 4 times greater in the sham-treated group.
In conclusion, this study shows that bupivacaine inhibited acidosis during ventricular fibrillation compared with saline-treated controls. We hypothesize that bupivacaine reduced lactate and carbon dioxide production and that this led to an attenuation of ischemic acidosis in myocardial tissue. The ability of lipid infusion to reverse the myocardial depressant effects of bupivacaine and restore cardiac function to normal suggests that a combined, sequential treatment with bupivacaine and lipid may be cardioprotective for ventricular fibrillation or cardiac arrest.
1. Albright GA. Cardiac arrest following regional anesthesia with etidocaine or bupivacaine. Anesthesiology 1979; 51: 285–7.
2. Groban L, Deal DD, Vernon JC, et al. Cardiac resuscitation after incremental overdosage with lidocaine, bupivacaine, levobupivacaine, and ropivacaine in anesthetized dogs. Anesth Analg 2001; 92: 37–43.
3. Fujita Y. Comparative direct effects of lidocaine and bupivacaine on regional myocardial function in dogs at noncardiovascular toxic levels. Anesth Analg 1994; 78: 1158–63.
4. Lefrant JY, de La Coussaye JE, Ripart J, et al. The comparative electrophysiologic and hemodynamic effects of a large dose of ropivacaine and bupivacaine in anesthetized and ventilated piglets. Anesth Analg 2001; 93: 1598–605.
5. Terada H, Shima O, Yoshida K, Shinohara Y. Effects of the local anesthetic bupivacaine on oxidative phosphorylation in mitochondria: change from decoupling to uncoupling by formation of a leakage type ion pathway specific for H+ in cooperation with hydrophobic anions. J Biol Chem 1990; 265: 7837–42.
6. Sztark F, Malgat M, Dabadie P, Mazat JP. Comparison of the effects of bupivacaine and ropivacaine on heart cell mitochondrial bioenergetics. Anesthesiology 1998; 88: 1340–9.
7. Weinberg GL, Palmer JW, VadeBoncouer TR, et al. Bupivacaine inhibits acylcarnitine exchange in cardiac mitochondria. Anesthesiology 2000; 92: 523–8.
8. Dabadie P, Bendriss P, Erny P, Mazat JP. Uncoupling effects of local anesthetics on rat liver mitochondria. FEBS Lett 1987; 226: 77–82.
9. Sztark F, Ouhabi R, Dabadie P, Mazat JP. Effects of the local anesthetic bupivacaine on mitochondrial energy metabolism: change from uncoupling to decoupling depending on the respiration state. Biochem Mol Biol Int 1997; 43: 997–1003.
10. Schwartz D, Beitner R. Detachment of the glycolytic enzymes, phosphofructokinase and aldolase, from cytoskeleton of melanoma cells, induced by local anesthetics. Mol Genet Metab 2000; 69: 159–64.
11. Karniel M, Beitner R. Local anesthetics induce a decrease in the levels of glucose 1, 6-bisphosphate, fructose 1, 6-bisphosphate, and ATP, and in the viability of melanoma cells. Mol Genet Metab 2000; 69: 40–5.
12. Stanley WC, Marzilli M. Metabolic therapy in the treatment of ischaemic heart disease: the pharmacology of trimetazidine. Fundam Clin Pharmacol 2003; 17: 133–45.
13. Roewer N, Dziadzka A, Greim CA, et al. Cardiovascular and metabolic responses to anesthetic-induced malignant hyperthermia in swine. Anesthesiology 1995; 83: 141–59.
14. Kubasiak LA, Hernandez OM, Bishopric NH, Webster KA. Hypoxia and acidosis activate cardiac myocyte death through the Bcl-2 family protein BNIP3. Proc Natl Acad Sci U S A 2002; 99: 12825–30.
15. Weinberg GL, VadeBoncouer T, Ramaraju GA et al. Pretreatment or resuscitation with a lipid infusion shifts the dose-response to bupivacaine-induced asystole in rats. Anesthesiology 1998; 88: 1071–5.
16. Weinberg G, Ripper R, Feinstein DL, Hoffman W. Lipid emulsion infusion rescues dogs from bupivacaine induced cardiac toxicity. Reg Anesth Pain Med 2003; 28: 198–202.
17. Hoffman WE, Charbel FT, Edelman G. Brain tissue oxygen, carbon dioxide, and pH in neurosurgical patients at risk for ischemia. Anesth Analg 1996; 82: 582–6.
18. Mullick AE, Deckelbaum RJ, Goldberg IJ, et al. Apolipoprotein E and lipoprotein lipase increase triglyceride-rich particle binding but decrease particle penetration in arterial wall. Arterioscler Thromb Vasc Biol 2002; 22: 2080–5.
19. Gryshchenko O, Qu J, Nathan RD. Ischemia alters the electrical activity of pacemaker cells isolated from the rabbit sinoatrial node. Am J Physiol Heart Circ Physiol 2002; 282: H2284–95.
20. Khabbaz KR, Zankoul F, Warner KG. Intraoperative metabolic monitoring of the heart: II. Online measurement of myocardial tissue pH. Ann Thorac Surg 2001; 72: S2227–33.
21. Lazar HL, Rivers S, Cambrils M, et al. Continuous versus intermittent cardioplegia in the presence of a coronary occlusion. Ann Thorac Surg 1991; 52: 913–7.