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EFFECT OF DILTIAZEM ON PORCINE MALIGNANT HYPERPYREXIA INDUCED BY SUXAMETHONIUM AND HALOTHANE
Br. J. Anaesth. (1989), 62, 560-565
EFFECT OF DILTIAZEM ON PORCINE MALIGNANT HYPERPYREXIA INDUCED BY SUXAMETHONIUM AND HALOTHANE P. S. FOSTER, K. C. HOPKINSON AND M. A. DENBOROUGH
P. S. FOSTER, PH.D.; K. C. HOPKINSON, DIP.APP.SCI.; M. A. DENBOROUGH, M.D., D.PHIL., D.SO, F.R.C.P., F.R.A.C.P.;
Department of Medicine and Clinical Science, The John Curtin School of Medical Research, The Australian National University, GPO Box 334, Canberra, ACT 2601, Australia. Accepted for Publication: December 19, 1988. Correspondence to M.A.D.
SUMMARY We have studied the ability of the calcium channel antagonist diltiazem to inhibit and reverse the porcine malignant hyperpyrexia (MH) syndrome. Pretreatment with diltiazem modified an MH response. Treatment with diltiazem was partially effective against a mild (or early) MH response. Diltiazem should not be considered to be an effective therapeutic agent for MH and should not displace the use of dantrolene.
seems that diltiazem acts to inhibit Ca-+ fluxes associated with the transverse tubular membrane in skeletal muscle [8,9]. This study has investigated the therapeutic value of diltiazem in inhibiting and antagonizing the porcine MH syndrome. MATERIALS AND METHODS
Six MH-susceptible (MHS) and four control pigs (body weights 25-47 kg, both sexes) were selected from mixed litters. All were premedicated by i.m. injection of stresnil (4-fluor4(4-(2-pyridyl)-l-piperazinyl)-butyrophenone) 1.5-2 mg kg"1. Tracheal intubation was performed after anaesthesia was induced with thiopentone 3—4mgkg~'. Anaesthesia was maintained with nitrous oxide in oxygen supplemented with thiopentone. Muscle tissue for the diagnosis of susceptibility was removed and anaesthesia maintained subsequently with 66 "„ nitrous oxide in oxygen. Susceptibility to MH was identified by using the established isolated contracture test [10]. Physiological variables were recorded every 1 min for approximately 15 min and venous blood was taken for biochemical analysis. Suxa-
Downloaded from http://bja.oxfordjournals.org/ at University of Western Ontario on June 8, 2015
Porcine MH may be induced by suxamethonium and halothane [1,2]. In the presence of a precipitating agent, the clinical features of the porcine MH syndrome are similar to those described in man. Essentially, MH in swine is characterized by a rapid and sustained increase in core body temperature and muscle rigidity. Biochemical changes such as metabolic acidosis and increased arterial carbon dioxide tensions precede the development of these features [1]. Increases in serum electrolytes and creatine phosphokinase (CPK) concentrations are detected also during and after the syndrome [1,3]. An increased concentration of Ca-+ in the myoplasm of skeletal muscle is considered to be the major factor in the development of MH [3,4]. Successful management requires early diagnosis, immediate cessation of anaesthesia, correction of metabolic acidosis by i.v. administration of sodium bicarbonate and prompt i.v. administration of the drug dantrolene sodium [3]. Dantrolene acts to decrease myoplasmic concentrations of Ca-+ by suppressing excitationcontraction coupling. One of the rationales for the original use of dantrolene in the treatment of MH was based on the demonstration that the skeletal myoneural blocking drug could prevent and antagonize the contracture responses to the diagnostic agents halothane and caffeine in isolated muscle fibres [5]. The calcium channel antagonist diltiazem also has been shown to inhibit and antagonize the drug-induced hypercontractility of isolated MHS human and porcine muscle preparations [6-8]. It
DILTIAZEM AND THE PORCINE MH SYNDROME methonium and halothane were administered in the presence (inhibition experiment) or absence (antagonism experiment) of diltiazem.
pigs, blood being taken for biochemical analysis under nitrous oxide-oxygen anaesthesia and at two periods during halothane anaesthesia. Halothane anaesthesia was maintained for 90 min.
Criteria for establishing the initiation of an MH episode In this study, an MH episode was considered to have occurred when body temperature increased by at least 1 °C, a clinical score of at least 3 was obtained for extensor rigidity, and tachycardia and a decreasing arterial pressure were observed. Often, abnormal patterns also were observed on Inhibition experiments the electrocardiogram (ECG). While metabolic Increasing doses of diltiazem were administered changes such as increased Pa,-,,, and lactate i.v. to a total dose of 2, 5 or 10 mg kg"1 (one, one precede the development of muscular rigidity and and four pigs, respectively). After physiological hyperpyrexia during an MH crisis, it was not variables had stabilized, suxamethonium was possible to monitor these continuously throughadministered i.v. (ear vein) in four doses (to out the duration of the challenge. The syndrome reduce fasciculations) to a total dose of 2 mg kg"1. was therefore characterized primarily by muscular If required, the lungs were ventilated manually at rigidity and increased body temperature. The a constant rate until ventilatory function returned. development of these later features of MH was After the administration of the neuromuscular considered sufficient to render any observed blocker, nitrous oxide was discontinued and response to diltiazem unequivocal. anaesthesia with 1 "„ halothane in oxygen initiAn increase in rectal temperature of 1 °C was ated. Halothane anaesthesia was maintained for considered sufficient to indicate an MH reaction, approximately 90 min. Physiological variables as increased body temperature is not only a late were monitored every 1 min for the duration of feature of an MH episode, but occurs also against the challenge. Blood for biochemical analyses was a tendency to hypothermia under halothane taken and anaesthesia ceased. anaesthesia. Furthermore, death has occurred at rectal temperatures as low as 40 °C in MH Antagonism experiments pigs [11]. In two pigs which had been used for inhibition MHS pigs were allowed to recover for no less than 2 weeks before being challenged again in the and antagonism experiments, MH was induced absence of diltiazem. After vital signs had again under identical conditions. Halothane anstabilized under nitrous oxide-oxygen anaes- aesthesia was discontinued and sodium bicarthesia, suxamethonium was administered in four bonate administered at stages in the reaction doses to a total concentration of 2 mg kg"1 and which were similar to those of previous an1 ",, halothane administered. After the initiation tagonism experiments. These experiments were of an MH syndrome, halothane was discontinued conducted with a view to establishing that withand increasing doses of diltiazem were admini- drawal of the triggering agent would not prevent stered i.v. to a total concentration of 7-10 mg kg"1 the development of the hyperpyrexic response. in five pigs and 2 mg kg"1 in one other. Sodium bicarbonate was also administered i.v. Physiological measurements and anaesthesia was maintained with 66 "„ nitrous Arterial pressure was monitored via a femoral oxide in oxygen. Blood samples for biochemical arterial catheter connected to a pressure transanalysis were taken: (1) immediately before the ducer (Bentley) coupled to a cardiac monitor administration of suxamethonium and halothane, (Telectronics HSG). Patency of the catheter was (2) when the MH syndrome was established and maintained by a1 constant infusion of (approxi(3) after administration of diltiazem. Vital signs mately 10 ml h"1 ) heparinized saline solution were monitored every 1 min throughout the 1000 units litre" . Electrodes were also placed for the monitoring of heart rate and ECG. Rectal challenge. The same procedure was followed with control temperature was measured using a mercury-in-
Downloaded from http://bja.oxfordjournals.org/ at University of Western Ontario on June 8, 2015
Administration of diltiazem Diltiazem (Marion Laboratories) was dissolved in sterile water (Abbot Laboratories) to a final concentration of 1 mg ml"1 and administered i.v. through a catheter placed in the ear. The rate of administration varied but did not exceed 1 mg kg"1 min"1. This prevented dramatic and sustained decreases in arterial pressure.
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TABLE I. Effect of dilliazem in malignant hyperpyrexia pigs in the presence of suxameihonium and halothane : physiological variables (mean or mean (SEM)) from six MH-susceplible sviine. Swine were premedicaled with dilliazem before administration of suxameihonium and halothane. After recovery of at least 2 weeks, MH episodes were precipitated by suxameihonium and halothane and the effect of dilliazem observed
Anaesthetic conditions
36.0 35.0
0 0
37.2 38.3
0 3-4
77 (1.94) 163 (21.52)
105/54 (2.6/2.5) 74/42 (5.9/3.7)
37.2
0
114 (11.97)
86/46 (3.4/2.2)
glass thermometer. Muscular rigidity of the front extensor was estimated and given a clinical score: 0 = flaccid extensor; 1 = initiation of rigidity; 2 = mild rigidity; 3 = pronounced rigidity of extensor; 4 = severe rigidity, difficulty in bending extensor; 5 = rigor, unable to bend extensor.
Heart rate (beat min ') 80.3 (2.8) 97 (5.6)
Arterial pressure (SAP/DAP) (mm Hg) 99/58 (2.5/2.3) 93/48 (2.9/2.6)
diltiazem and recovered within 5-10 min (results not shown). Heart rate did not exceed 100 beat min"1. Blood pH and base excess values decreased slightly, but not to the same degree as observed during an MH episode (table II). Similar observations were made during anaesthesia in control swine (table III). Furthermore, in MHS pigs Biochemical measurements treated with diltiazem, plasma lactate concenArterial blood samples were taken and analysed tration did not increase, and blood-gas analysis for pH, Pa,,,,, Pa,,,, potassium, inorganic phos- indicated that Pa,,,, and Pa,,, did not change phate, calcium, lactate and CPK. Blood-gas analy- markedly. Plasma concentrations of calcium, sis was conducted within 30 min of sampling. All potassium and inorganic phosphate also remained biochemical measurements were conducted by the essentially unchanged. CPK concentration did animals during anaesthesia, Department of Clinical Biochemistry at Royal increase in pretreated by 638 u. litre"1 (table II). However, this increase Canberra Hospital. was substantially less than that in untreated pigs (2112u. litre"1) (table II) and was probably a RESULTS result of muscular fasciculations induced by Inhibition experiments suxamethonium. Pretreatment of MHS pigs with diltiazem modified the induction of the MH syndrome by Antagonism e.xperintents suxamethonium 2 mg kg"1 and 1 "„ halothane Treatment with diltiazem was partially effective (tables I, II) over a 90-min period. In the absence against a mild (or early) MH response. Exposure of diltiazem, all reactor pigs developed the of MHS pigs to suxamethonium 2 mg kg ' and syndrome within 15-30 min (see antagonism 1 "„ halothane in the absence of diltiazem resulted experiments). In the presence of diltiazem, ex- in the development of the MH syndrome (tables I tensor muscles remained flaccid and body tempera- and II). Pigs developed pronounced muscular ture decreased by approximately 1 °C. Arterial rigidity (clinical score of 3-4), followed by an pressure decreased following administration of increase in rectal temperature. Heart rate doubled
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Inhibition of MH Nitrous oxide-oxygen Diltiazem 2-10 mg kg ', suxamethonium 2 mg kg ' and halothane Antagonism of MH Nitrous oxide—oxygen Suxamethonium 2 mg kg ' and 1 ",, halothane (precipitation of MH) After diltiazem 2-10 mg kg ', halothane off, N.O/O., on, NaHCO., i.v"
Temperature (°C)
Extensor rigidity (Clinical score)
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DILTIAZEM AND THE PORCINE MH SYNDROME
TABLE 11. Effect of diltiazem in malignant hyperpyrexia pigs in the presence of suxamethonium and halothane: biochemical variables {mean (SEM)) from six MH-susceptible swine. Swine were premedicated with diltiazem before administration of suxamethonium and halothane. After recovery of at least 2 weeks, MH episodes were precipitated by suxamethomum and halothane and the effect of diltiazem observed
Anaesthetic conditions Inhibition of MH Nitrous oxide-oxygen
Antagonism of MH Nitrous oxide-oxygen Suxamethonium 2 mg kg"1, 1 "„ halothane (precipitation of MH) After diltiazem 2-10 mg kg"', halothane off, N.O/Oj on, NaHCO;1 i.v!
Pa,,. (kPa)
1410 (250) 2048 (287)
7.41 5.8 (0.01) (0.3) 7.36 6.0 (0.03) (0.3)
40.7 (2.9) 33.5 (4.0)
3.12 (0.34) 1.9 (0.44)
2.8 (0.51) 1.9 (0.63)
3.1 (0.21) 3.7 (0.31)
2.3 (0.51) 2.4 (0.21)
2.3 (0.25) 2.4 (0.32)
1670 (299) 3515 (186)
7.42 6.1 (0.01) (0.3) 7.26 8.5 (0.01) (0.4)
45.6 (3.5) 28.5 (2.5)
5.03 (1.24) 0.62 (0.59)
3.8 (0.51) 6.9 (0.41)
3.3 (0.12) 4.5 (0.55)
2.5 (0.11) 3.0 (0.16)
2.4 (0.06) 2.3 (0.04)
3782 (577)
7.44 5.4 (0.02) (0.4)
34.0 (5.3)
6.3 (0.46)
4.8 (0.46)
3.1 (0.23)
2.3 (0.09)
CPK (u. litre"')
pH
and blood-gas analysis showed an increase in Pa,.()i tensions of 2.31 kPa and a decrease in Pa,,,. Plasma lactate concentration increased from 3.8 to 6.9 mmol litre"1 while blood pH and base excess decreased by 0.16 units and 4.4 mmol litre"1, respectively, consistent with
Lactate (mmol litre"')
K (mmol litre"1)
PO4 (mmol litre ')
Ca (mmol litre ')
—
metabolic acidosis (table II). Plasma potassium and inorganic phosphate concentrations were increased during and after the challenge, while calcium concentration remained virtually unchanged. CPK concentration also increased, approximately two-fold (table II). In three of the
TABLE III. Effect of suxamethomum and halothane on the physiological and biochemical variables offour control swine {mean or mean (SEM)) Anaesthetic conditions
N2O/O.2 Temp. (°C) Rigidity (clinical score) CPK (u. litre"1) Heart rate (beat min"') Arterial pressure (SAP/DAP) (mm Hg) pH Pa,,,. (kPa) Pa,,/(kPa) BE "(mmol litre"') Lactate (mmol litre"') K (mmol litre"1) PO, (mmol litre"1) Ca (mmol litre"')
36.3 0 953.5 (64.76) 86(3.17) 112/65 (5.7/5.7) 7.37 (0.03) 6.5 (0.5) 39.8 (7.7) 2.02 (0.42) 3.50 (0.2) 3.1 (0.11) 2.0(0.19) 2.3 (0.02)
Suxamethonium + halothane (after 30 min anaesthesia)
Suxamethonium + halothane (after 90 min anaesthesia)
35.7 0
35.6 0
1059 (20) 90 (4.4)
1119 (27) 95 (6.25)
105/65 (5.2/5.7) 7.4 6.3 55.5 3.38 2.67 3.6 1.9 2.1
(0.03) (0.6) (5.7) (0.83) (0.21) (0.24) (0.17) (0.08)
103/61 (4.7/5.0) 7.35 7.1 55.6 2.84 2.84 3.4 2.1 2.1
(0.02) (0.4) (7.5) (0.85) (0.33) (0.12) (0.09) (0.05)
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Diltiazem 2-10 mg kg"', suxamethonium 2 mg kg"1, halothane
Pa, „. (kPaj
Base excess (mmol litre"1)
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MH response. In the absence of diltiazem, MHsusceptible pigs developed the characteristic clinical features of MH. These included hyperpyrexia, muscular rigidity, metabolic acidosis, increased plasma potassium, inorganic phosphate and CPK concentrations and increased Pa,,,.,. Tachycardia, arrhythmias (results not shown) and hypotension were also observed. Blood-gas analysis in unpretreated swine was consistent with the early expression of the MH syndrome. In this study, all pigs underwent continuous or intermittent ventilation at a constant rate. Alterations in blood-gas values occurred in the absence of any obvious respiratory cause (eg. underventilation) and reflected metabolic acidosis and increased carbon dioxide production. A rapid decrease in base excess corresponding to the increase in Pa,-,,, was also observed. Furthermore, despite relatively high arterial Pa,,., (>27kPa) at all times, lactate production reflecting anaerobic glycolysis was always observed during halothane anaesthesia in the absence of diltiazem in MH pigs. By comparison, Pa,-,,,, Pa,,,, pH and base excess measurements remained essentially constant during halothane anaesthesia in control and diltiazem-pretreated MH pigs. When MHS pigs were pretreated with diltiazem, suxamethonium and halothane did not trigger the MH syndrome. Skeletal muscle metabolism was not accelerated, and plasma lactate and arterial pH and blood-gas values remained essentially unchanged. Subsequently, extensors remained flaccid and cardiac dysfunction and increased plasma concentrations of inorganic phosphate and potassium were not observed. Also, rectal temperature decreased over the duration of the challenge. Plasma CPK concentrations increased, but not to the same degree as observed in unpretreated MHS pigs. Suxamethonium and halothane anaesthesia in This increase probably reflected increased muscontrol pigs cular activity, observed as fasciculation after the Temperature decreased by approximately 1 °C administration of suxamethonium, as CPK conand extensors remained flaccid during suxa- centrations increased also in control swine after methonium 2 mg kg"1 and 1 "„ halothane-induced the administration of suxamethonium. The clinianaesthesia in control swine (table III). Physio- cal features of halothane anaesthesia in pretreated logical and biochemical features remained es- MHS pigs were essentially the same as those observed in control swine. sentially constant. Furthermore, two MHS pigs in which MH was initiated by halothane (but which did not receive DISCUSSION diltiazem), developed fulminant MH and died. The calcium channel antagonist diltiazem modi- This suggests that metabolism had been stimufied and partially antagonized a mild (or early) lated sufficiently and withdrawal of halothane six challenged pigs, blotchy cyanosis of the skin was also observed. When the clinical features of MH had been identified, with muscular rigidity and an increase in body temperature of at least 1 °C, diltiazem 2-10 mg kg"1 was administered i.v. Diltiazem caused a rapid decrease in both systolic and diastolic arterial pressures (results not shown). However, administration of small doses of diltiazem with careful monitoring of arterial pressure prevented sustained hypotension. Arterial pressure recovered to pre-administration values within 5-10 min (allowing further administration if required). The administration of diltiazem caused a rapid loss of extensor rigidity, followed by a progressive decrease in rectal temperature. Heart rate decreased, while arterial pressure remained low in the presence of diltiazem. Blood pH, base excess and Pa,,,, returned to values approaching those before the challenge. Pa,,, also increased (table II). A total concentration of diltiazem 7lOmgkg"1 was required to antagonize the MH syndrome in five pigs and 2 mg kg"1 was needed in another. The only ancillary treatment pigs received was the administration of sodium bicarbonate; active cooling of one pig was required after body temperature had increased above 40 °C. All pigs survived. In two MHS swine which had previously been included in inhibition and antagonism experiments, MH was induced under identical conditions. Halothane anaesthesia was discontinued and sodium bicarbonate administered at stages in the reaction which were similar to previous antagonism experiments. Both pigs developed fulminant MH and died. This suggests that metabolism had been stimulated sufficiently and withdrawal of the triggering agent did not prevent the development of the hyperpyrexic response.
DILTIAZEM AND THE PORCINE MH SYNDROME
REFERENCES 1. Bcrman MC, Harrison GG, Bull AB, Kench JE. Changes underlying halothane-induced malignant hyperpyrexia in Landrace pigs. Nalure {London) 1970; 255: 653-655. 2. Gronert GA, Milde JH, Theye RA. Porcine malignant hyperthermia induced by halothane and succinylcholine.
Failure of treatment with procaine or procainamide. Anesthesiology 1976; 44: 124-131. 3. Denborough MA. The pathopharmacology of malignant hyperpyrexia. Pharmacology and Therapeutics 1980; 9: 357-365. 4. Kalow W, Britt BA, Terreau ME, Haist C. Metabolic error of muscle metabolism after recovery from malignant hyperthermia. Lancet 1970; 2: 895-898. 5. Okumura F, Crocker BD, Denborough MA. Site of the muscle cell abnormality in swine susceptible to malignant hyperpyrexia. British Journal of Anaesthesia 1980; 52: 377-383. 6. Ilias WK, Williams CH, Fulfer RT, Dozier SE. Diltiazem inhibits halothane-induced contractions in malignant hyperthermia-susceptible muscle in vitro. British Journal of Anaesthesia 1985; 57: 994-996. 7. Iwatsuki N, Koga Y, Amaha K. Calcium channel blocker for the treatment of malignant hyperthermia. Anesthesia and Analgesia 1983; 62 : 861. 8. Foster PS, Denborough MA. Proceedings of Australian Society of Experimental Biology 1988; 414. 9. Fosset M, Jaimovich E, Delpont E, Lazdunski M. f'H] Nitrendipine receptors in skeletal muscle. Properties and preferential localization in transverse tubules. Journal 'of Biological Chemistry 1983; 258: 6089-6092. 10. Okumura F, Crocker BD, Denborough MA. Identification of susceptibility to malignant hyperpyrexia in swine. British Journal of Anaesthesia 1979; 51: 171-176. 11. Hall GM, Lucke JN, Lister D. Treatment of porcine malignant hyperthermia. Anesthesiology 1975; 30: 308317. 12. Lucke JN, Hall GM, Lister D. Porcine malignant hyperthermia. I: Metabolic and physiological change. British Journal of Anaesthesia 1976; 48: 297-306. 13. Harrison GG. Control of the malignant hyperpyrexic syndrome in MHS swine by dantrolene sodium. British Journal of Anaesthesia 1975; 47: 62-65. 14. Godfraind T, Miller R, Wibo W. Calcium antagonism and calcium entry blockade. Pharmacological Reviews 1986; 38: 321^117. 15. Douglas WW, Rubin RP. The mechanism of catecholamine release from the adrenal medulla and the role of calcium stimulus secretion coupling. Journal of Physiology 1963; 167: 288-310. 16. Yamaguchi I, Akimoto Y, Nishiyama S, Sato M, Nakashima H, Kiyomoto A. Effects of diltiazem on catecholamine release from cat adrenal glands. Folia Phannacologica Japonica 1987; 78: 501-509.
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did not prevent the development of the MH response. Similar observations have been made by other investigators who have shown that, when metabolism has been stimulated sufficiently, the MH syndrome can continue unabated with further increases in temperature in the absence of the triggering agent [1,12,13]. Pharmacological experiments indicate that diltiazem may modify CaJ+ fluxes at the level of the T-tubule membrane [8]. Ca-+ entering the muscle via T-tubules may therefore be important in the aetiology of the MH syndrome. Diltiazem not only acts on skeletal muscle, but also has well known cardiovascular effects [14]. Diltiazem prevents arrhythmias and protects the heart from ischaemia, effects which would be beneficial during an MH episode. Although diltiazem causes hypotension, this was not an adverse effect in this study during MH. The release of catecholamines from the adrenal medulla is a Ca-+-dependent process [15]. The increased concentration of circulating catecholamines observed during an MH episode [12] may also be mediated by Ca~+ [3]. Diltiazem may also inhibit this Ca-+-dependent process and attenuate cardiovascular changes [16]. In common with dantrolene, diltiazem modifies the onset of MH and the further expression of an initiated MH syndrome. However, diltiazem is not as effective as dantrolene, and should not displace this drug in the treatment of MH.
565
EFFECT OF DILTIAZEM ON PORCINE MALIGNANT HYPERPYREXIA INDUCED BY SUXAMETHONIUM AND HALOTHANE P. S. FOSTER, K. C. HOPKINSON AND M. A. DENBOROUGH
P. S. FOSTER, PH.D.; K. C. HOPKINSON, DIP.APP.SCI.; M. A. DENBOROUGH, M.D., D.PHIL., D.SO, F.R.C.P., F.R.A.C.P.;
Department of Medicine and Clinical Science, The John Curtin School of Medical Research, The Australian National University, GPO Box 334, Canberra, ACT 2601, Australia. Accepted for Publication: December 19, 1988. Correspondence to M.A.D.
SUMMARY We have studied the ability of the calcium channel antagonist diltiazem to inhibit and reverse the porcine malignant hyperpyrexia (MH) syndrome. Pretreatment with diltiazem modified an MH response. Treatment with diltiazem was partially effective against a mild (or early) MH response. Diltiazem should not be considered to be an effective therapeutic agent for MH and should not displace the use of dantrolene.
seems that diltiazem acts to inhibit Ca-+ fluxes associated with the transverse tubular membrane in skeletal muscle [8,9]. This study has investigated the therapeutic value of diltiazem in inhibiting and antagonizing the porcine MH syndrome. MATERIALS AND METHODS
Six MH-susceptible (MHS) and four control pigs (body weights 25-47 kg, both sexes) were selected from mixed litters. All were premedicated by i.m. injection of stresnil (4-fluor4(4-(2-pyridyl)-l-piperazinyl)-butyrophenone) 1.5-2 mg kg"1. Tracheal intubation was performed after anaesthesia was induced with thiopentone 3—4mgkg~'. Anaesthesia was maintained with nitrous oxide in oxygen supplemented with thiopentone. Muscle tissue for the diagnosis of susceptibility was removed and anaesthesia maintained subsequently with 66 "„ nitrous oxide in oxygen. Susceptibility to MH was identified by using the established isolated contracture test [10]. Physiological variables were recorded every 1 min for approximately 15 min and venous blood was taken for biochemical analysis. Suxa-
Downloaded from http://bja.oxfordjournals.org/ at University of Western Ontario on June 8, 2015
Porcine MH may be induced by suxamethonium and halothane [1,2]. In the presence of a precipitating agent, the clinical features of the porcine MH syndrome are similar to those described in man. Essentially, MH in swine is characterized by a rapid and sustained increase in core body temperature and muscle rigidity. Biochemical changes such as metabolic acidosis and increased arterial carbon dioxide tensions precede the development of these features [1]. Increases in serum electrolytes and creatine phosphokinase (CPK) concentrations are detected also during and after the syndrome [1,3]. An increased concentration of Ca-+ in the myoplasm of skeletal muscle is considered to be the major factor in the development of MH [3,4]. Successful management requires early diagnosis, immediate cessation of anaesthesia, correction of metabolic acidosis by i.v. administration of sodium bicarbonate and prompt i.v. administration of the drug dantrolene sodium [3]. Dantrolene acts to decrease myoplasmic concentrations of Ca-+ by suppressing excitationcontraction coupling. One of the rationales for the original use of dantrolene in the treatment of MH was based on the demonstration that the skeletal myoneural blocking drug could prevent and antagonize the contracture responses to the diagnostic agents halothane and caffeine in isolated muscle fibres [5]. The calcium channel antagonist diltiazem also has been shown to inhibit and antagonize the drug-induced hypercontractility of isolated MHS human and porcine muscle preparations [6-8]. It
DILTIAZEM AND THE PORCINE MH SYNDROME methonium and halothane were administered in the presence (inhibition experiment) or absence (antagonism experiment) of diltiazem.
pigs, blood being taken for biochemical analysis under nitrous oxide-oxygen anaesthesia and at two periods during halothane anaesthesia. Halothane anaesthesia was maintained for 90 min.
Criteria for establishing the initiation of an MH episode In this study, an MH episode was considered to have occurred when body temperature increased by at least 1 °C, a clinical score of at least 3 was obtained for extensor rigidity, and tachycardia and a decreasing arterial pressure were observed. Often, abnormal patterns also were observed on Inhibition experiments the electrocardiogram (ECG). While metabolic Increasing doses of diltiazem were administered changes such as increased Pa,-,,, and lactate i.v. to a total dose of 2, 5 or 10 mg kg"1 (one, one precede the development of muscular rigidity and and four pigs, respectively). After physiological hyperpyrexia during an MH crisis, it was not variables had stabilized, suxamethonium was possible to monitor these continuously throughadministered i.v. (ear vein) in four doses (to out the duration of the challenge. The syndrome reduce fasciculations) to a total dose of 2 mg kg"1. was therefore characterized primarily by muscular If required, the lungs were ventilated manually at rigidity and increased body temperature. The a constant rate until ventilatory function returned. development of these later features of MH was After the administration of the neuromuscular considered sufficient to render any observed blocker, nitrous oxide was discontinued and response to diltiazem unequivocal. anaesthesia with 1 "„ halothane in oxygen initiAn increase in rectal temperature of 1 °C was ated. Halothane anaesthesia was maintained for considered sufficient to indicate an MH reaction, approximately 90 min. Physiological variables as increased body temperature is not only a late were monitored every 1 min for the duration of feature of an MH episode, but occurs also against the challenge. Blood for biochemical analyses was a tendency to hypothermia under halothane taken and anaesthesia ceased. anaesthesia. Furthermore, death has occurred at rectal temperatures as low as 40 °C in MH Antagonism experiments pigs [11]. In two pigs which had been used for inhibition MHS pigs were allowed to recover for no less than 2 weeks before being challenged again in the and antagonism experiments, MH was induced absence of diltiazem. After vital signs had again under identical conditions. Halothane anstabilized under nitrous oxide-oxygen anaes- aesthesia was discontinued and sodium bicarthesia, suxamethonium was administered in four bonate administered at stages in the reaction doses to a total concentration of 2 mg kg"1 and which were similar to those of previous an1 ",, halothane administered. After the initiation tagonism experiments. These experiments were of an MH syndrome, halothane was discontinued conducted with a view to establishing that withand increasing doses of diltiazem were admini- drawal of the triggering agent would not prevent stered i.v. to a total concentration of 7-10 mg kg"1 the development of the hyperpyrexic response. in five pigs and 2 mg kg"1 in one other. Sodium bicarbonate was also administered i.v. Physiological measurements and anaesthesia was maintained with 66 "„ nitrous Arterial pressure was monitored via a femoral oxide in oxygen. Blood samples for biochemical arterial catheter connected to a pressure transanalysis were taken: (1) immediately before the ducer (Bentley) coupled to a cardiac monitor administration of suxamethonium and halothane, (Telectronics HSG). Patency of the catheter was (2) when the MH syndrome was established and maintained by a1 constant infusion of (approxi(3) after administration of diltiazem. Vital signs mately 10 ml h"1 ) heparinized saline solution were monitored every 1 min throughout the 1000 units litre" . Electrodes were also placed for the monitoring of heart rate and ECG. Rectal challenge. The same procedure was followed with control temperature was measured using a mercury-in-
Downloaded from http://bja.oxfordjournals.org/ at University of Western Ontario on June 8, 2015
Administration of diltiazem Diltiazem (Marion Laboratories) was dissolved in sterile water (Abbot Laboratories) to a final concentration of 1 mg ml"1 and administered i.v. through a catheter placed in the ear. The rate of administration varied but did not exceed 1 mg kg"1 min"1. This prevented dramatic and sustained decreases in arterial pressure.
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TABLE I. Effect of dilliazem in malignant hyperpyrexia pigs in the presence of suxameihonium and halothane : physiological variables (mean or mean (SEM)) from six MH-susceplible sviine. Swine were premedicaled with dilliazem before administration of suxameihonium and halothane. After recovery of at least 2 weeks, MH episodes were precipitated by suxameihonium and halothane and the effect of dilliazem observed
Anaesthetic conditions
36.0 35.0
0 0
37.2 38.3
0 3-4
77 (1.94) 163 (21.52)
105/54 (2.6/2.5) 74/42 (5.9/3.7)
37.2
0
114 (11.97)
86/46 (3.4/2.2)
glass thermometer. Muscular rigidity of the front extensor was estimated and given a clinical score: 0 = flaccid extensor; 1 = initiation of rigidity; 2 = mild rigidity; 3 = pronounced rigidity of extensor; 4 = severe rigidity, difficulty in bending extensor; 5 = rigor, unable to bend extensor.
Heart rate (beat min ') 80.3 (2.8) 97 (5.6)
Arterial pressure (SAP/DAP) (mm Hg) 99/58 (2.5/2.3) 93/48 (2.9/2.6)
diltiazem and recovered within 5-10 min (results not shown). Heart rate did not exceed 100 beat min"1. Blood pH and base excess values decreased slightly, but not to the same degree as observed during an MH episode (table II). Similar observations were made during anaesthesia in control swine (table III). Furthermore, in MHS pigs Biochemical measurements treated with diltiazem, plasma lactate concenArterial blood samples were taken and analysed tration did not increase, and blood-gas analysis for pH, Pa,,,,, Pa,,,, potassium, inorganic phos- indicated that Pa,,,, and Pa,,, did not change phate, calcium, lactate and CPK. Blood-gas analy- markedly. Plasma concentrations of calcium, sis was conducted within 30 min of sampling. All potassium and inorganic phosphate also remained biochemical measurements were conducted by the essentially unchanged. CPK concentration did animals during anaesthesia, Department of Clinical Biochemistry at Royal increase in pretreated by 638 u. litre"1 (table II). However, this increase Canberra Hospital. was substantially less than that in untreated pigs (2112u. litre"1) (table II) and was probably a RESULTS result of muscular fasciculations induced by Inhibition experiments suxamethonium. Pretreatment of MHS pigs with diltiazem modified the induction of the MH syndrome by Antagonism e.xperintents suxamethonium 2 mg kg"1 and 1 "„ halothane Treatment with diltiazem was partially effective (tables I, II) over a 90-min period. In the absence against a mild (or early) MH response. Exposure of diltiazem, all reactor pigs developed the of MHS pigs to suxamethonium 2 mg kg ' and syndrome within 15-30 min (see antagonism 1 "„ halothane in the absence of diltiazem resulted experiments). In the presence of diltiazem, ex- in the development of the MH syndrome (tables I tensor muscles remained flaccid and body tempera- and II). Pigs developed pronounced muscular ture decreased by approximately 1 °C. Arterial rigidity (clinical score of 3-4), followed by an pressure decreased following administration of increase in rectal temperature. Heart rate doubled
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Inhibition of MH Nitrous oxide-oxygen Diltiazem 2-10 mg kg ', suxamethonium 2 mg kg ' and halothane Antagonism of MH Nitrous oxide—oxygen Suxamethonium 2 mg kg ' and 1 ",, halothane (precipitation of MH) After diltiazem 2-10 mg kg ', halothane off, N.O/O., on, NaHCO., i.v"
Temperature (°C)
Extensor rigidity (Clinical score)
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DILTIAZEM AND THE PORCINE MH SYNDROME
TABLE 11. Effect of diltiazem in malignant hyperpyrexia pigs in the presence of suxamethonium and halothane: biochemical variables {mean (SEM)) from six MH-susceptible swine. Swine were premedicated with diltiazem before administration of suxamethonium and halothane. After recovery of at least 2 weeks, MH episodes were precipitated by suxamethomum and halothane and the effect of diltiazem observed
Anaesthetic conditions Inhibition of MH Nitrous oxide-oxygen
Antagonism of MH Nitrous oxide-oxygen Suxamethonium 2 mg kg"1, 1 "„ halothane (precipitation of MH) After diltiazem 2-10 mg kg"', halothane off, N.O/Oj on, NaHCO;1 i.v!
Pa,,. (kPa)
1410 (250) 2048 (287)
7.41 5.8 (0.01) (0.3) 7.36 6.0 (0.03) (0.3)
40.7 (2.9) 33.5 (4.0)
3.12 (0.34) 1.9 (0.44)
2.8 (0.51) 1.9 (0.63)
3.1 (0.21) 3.7 (0.31)
2.3 (0.51) 2.4 (0.21)
2.3 (0.25) 2.4 (0.32)
1670 (299) 3515 (186)
7.42 6.1 (0.01) (0.3) 7.26 8.5 (0.01) (0.4)
45.6 (3.5) 28.5 (2.5)
5.03 (1.24) 0.62 (0.59)
3.8 (0.51) 6.9 (0.41)
3.3 (0.12) 4.5 (0.55)
2.5 (0.11) 3.0 (0.16)
2.4 (0.06) 2.3 (0.04)
3782 (577)
7.44 5.4 (0.02) (0.4)
34.0 (5.3)
6.3 (0.46)
4.8 (0.46)
3.1 (0.23)
2.3 (0.09)
CPK (u. litre"')
pH
and blood-gas analysis showed an increase in Pa,.()i tensions of 2.31 kPa and a decrease in Pa,,,. Plasma lactate concentration increased from 3.8 to 6.9 mmol litre"1 while blood pH and base excess decreased by 0.16 units and 4.4 mmol litre"1, respectively, consistent with
Lactate (mmol litre"')
K (mmol litre"1)
PO4 (mmol litre ')
Ca (mmol litre ')
—
metabolic acidosis (table II). Plasma potassium and inorganic phosphate concentrations were increased during and after the challenge, while calcium concentration remained virtually unchanged. CPK concentration also increased, approximately two-fold (table II). In three of the
TABLE III. Effect of suxamethomum and halothane on the physiological and biochemical variables offour control swine {mean or mean (SEM)) Anaesthetic conditions
N2O/O.2 Temp. (°C) Rigidity (clinical score) CPK (u. litre"1) Heart rate (beat min"') Arterial pressure (SAP/DAP) (mm Hg) pH Pa,,,. (kPa) Pa,,/(kPa) BE "(mmol litre"') Lactate (mmol litre"') K (mmol litre"1) PO, (mmol litre"1) Ca (mmol litre"')
36.3 0 953.5 (64.76) 86(3.17) 112/65 (5.7/5.7) 7.37 (0.03) 6.5 (0.5) 39.8 (7.7) 2.02 (0.42) 3.50 (0.2) 3.1 (0.11) 2.0(0.19) 2.3 (0.02)
Suxamethonium + halothane (after 30 min anaesthesia)
Suxamethonium + halothane (after 90 min anaesthesia)
35.7 0
35.6 0
1059 (20) 90 (4.4)
1119 (27) 95 (6.25)
105/65 (5.2/5.7) 7.4 6.3 55.5 3.38 2.67 3.6 1.9 2.1
(0.03) (0.6) (5.7) (0.83) (0.21) (0.24) (0.17) (0.08)
103/61 (4.7/5.0) 7.35 7.1 55.6 2.84 2.84 3.4 2.1 2.1
(0.02) (0.4) (7.5) (0.85) (0.33) (0.12) (0.09) (0.05)
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Diltiazem 2-10 mg kg"', suxamethonium 2 mg kg"1, halothane
Pa, „. (kPaj
Base excess (mmol litre"1)
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MH response. In the absence of diltiazem, MHsusceptible pigs developed the characteristic clinical features of MH. These included hyperpyrexia, muscular rigidity, metabolic acidosis, increased plasma potassium, inorganic phosphate and CPK concentrations and increased Pa,,,.,. Tachycardia, arrhythmias (results not shown) and hypotension were also observed. Blood-gas analysis in unpretreated swine was consistent with the early expression of the MH syndrome. In this study, all pigs underwent continuous or intermittent ventilation at a constant rate. Alterations in blood-gas values occurred in the absence of any obvious respiratory cause (eg. underventilation) and reflected metabolic acidosis and increased carbon dioxide production. A rapid decrease in base excess corresponding to the increase in Pa,-,,, was also observed. Furthermore, despite relatively high arterial Pa,,., (>27kPa) at all times, lactate production reflecting anaerobic glycolysis was always observed during halothane anaesthesia in the absence of diltiazem in MH pigs. By comparison, Pa,-,,,, Pa,,,, pH and base excess measurements remained essentially constant during halothane anaesthesia in control and diltiazem-pretreated MH pigs. When MHS pigs were pretreated with diltiazem, suxamethonium and halothane did not trigger the MH syndrome. Skeletal muscle metabolism was not accelerated, and plasma lactate and arterial pH and blood-gas values remained essentially unchanged. Subsequently, extensors remained flaccid and cardiac dysfunction and increased plasma concentrations of inorganic phosphate and potassium were not observed. Also, rectal temperature decreased over the duration of the challenge. Plasma CPK concentrations increased, but not to the same degree as observed in unpretreated MHS pigs. Suxamethonium and halothane anaesthesia in This increase probably reflected increased muscontrol pigs cular activity, observed as fasciculation after the Temperature decreased by approximately 1 °C administration of suxamethonium, as CPK conand extensors remained flaccid during suxa- centrations increased also in control swine after methonium 2 mg kg"1 and 1 "„ halothane-induced the administration of suxamethonium. The clinianaesthesia in control swine (table III). Physio- cal features of halothane anaesthesia in pretreated logical and biochemical features remained es- MHS pigs were essentially the same as those observed in control swine. sentially constant. Furthermore, two MHS pigs in which MH was initiated by halothane (but which did not receive DISCUSSION diltiazem), developed fulminant MH and died. The calcium channel antagonist diltiazem modi- This suggests that metabolism had been stimufied and partially antagonized a mild (or early) lated sufficiently and withdrawal of halothane six challenged pigs, blotchy cyanosis of the skin was also observed. When the clinical features of MH had been identified, with muscular rigidity and an increase in body temperature of at least 1 °C, diltiazem 2-10 mg kg"1 was administered i.v. Diltiazem caused a rapid decrease in both systolic and diastolic arterial pressures (results not shown). However, administration of small doses of diltiazem with careful monitoring of arterial pressure prevented sustained hypotension. Arterial pressure recovered to pre-administration values within 5-10 min (allowing further administration if required). The administration of diltiazem caused a rapid loss of extensor rigidity, followed by a progressive decrease in rectal temperature. Heart rate decreased, while arterial pressure remained low in the presence of diltiazem. Blood pH, base excess and Pa,,,, returned to values approaching those before the challenge. Pa,,, also increased (table II). A total concentration of diltiazem 7lOmgkg"1 was required to antagonize the MH syndrome in five pigs and 2 mg kg"1 was needed in another. The only ancillary treatment pigs received was the administration of sodium bicarbonate; active cooling of one pig was required after body temperature had increased above 40 °C. All pigs survived. In two MHS swine which had previously been included in inhibition and antagonism experiments, MH was induced under identical conditions. Halothane anaesthesia was discontinued and sodium bicarbonate administered at stages in the reaction which were similar to previous antagonism experiments. Both pigs developed fulminant MH and died. This suggests that metabolism had been stimulated sufficiently and withdrawal of the triggering agent did not prevent the development of the hyperpyrexic response.
DILTIAZEM AND THE PORCINE MH SYNDROME
REFERENCES 1. Bcrman MC, Harrison GG, Bull AB, Kench JE. Changes underlying halothane-induced malignant hyperpyrexia in Landrace pigs. Nalure {London) 1970; 255: 653-655. 2. Gronert GA, Milde JH, Theye RA. Porcine malignant hyperthermia induced by halothane and succinylcholine.
Failure of treatment with procaine or procainamide. Anesthesiology 1976; 44: 124-131. 3. Denborough MA. The pathopharmacology of malignant hyperpyrexia. Pharmacology and Therapeutics 1980; 9: 357-365. 4. Kalow W, Britt BA, Terreau ME, Haist C. Metabolic error of muscle metabolism after recovery from malignant hyperthermia. Lancet 1970; 2: 895-898. 5. Okumura F, Crocker BD, Denborough MA. Site of the muscle cell abnormality in swine susceptible to malignant hyperpyrexia. British Journal of Anaesthesia 1980; 52: 377-383. 6. Ilias WK, Williams CH, Fulfer RT, Dozier SE. Diltiazem inhibits halothane-induced contractions in malignant hyperthermia-susceptible muscle in vitro. British Journal of Anaesthesia 1985; 57: 994-996. 7. Iwatsuki N, Koga Y, Amaha K. Calcium channel blocker for the treatment of malignant hyperthermia. Anesthesia and Analgesia 1983; 62 : 861. 8. Foster PS, Denborough MA. Proceedings of Australian Society of Experimental Biology 1988; 414. 9. Fosset M, Jaimovich E, Delpont E, Lazdunski M. f'H] Nitrendipine receptors in skeletal muscle. Properties and preferential localization in transverse tubules. Journal 'of Biological Chemistry 1983; 258: 6089-6092. 10. Okumura F, Crocker BD, Denborough MA. Identification of susceptibility to malignant hyperpyrexia in swine. British Journal of Anaesthesia 1979; 51: 171-176. 11. Hall GM, Lucke JN, Lister D. Treatment of porcine malignant hyperthermia. Anesthesiology 1975; 30: 308317. 12. Lucke JN, Hall GM, Lister D. Porcine malignant hyperthermia. I: Metabolic and physiological change. British Journal of Anaesthesia 1976; 48: 297-306. 13. Harrison GG. Control of the malignant hyperpyrexic syndrome in MHS swine by dantrolene sodium. British Journal of Anaesthesia 1975; 47: 62-65. 14. Godfraind T, Miller R, Wibo W. Calcium antagonism and calcium entry blockade. Pharmacological Reviews 1986; 38: 321^117. 15. Douglas WW, Rubin RP. The mechanism of catecholamine release from the adrenal medulla and the role of calcium stimulus secretion coupling. Journal of Physiology 1963; 167: 288-310. 16. Yamaguchi I, Akimoto Y, Nishiyama S, Sato M, Nakashima H, Kiyomoto A. Effects of diltiazem on catecholamine release from cat adrenal glands. Folia Phannacologica Japonica 1987; 78: 501-509.
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did not prevent the development of the MH response. Similar observations have been made by other investigators who have shown that, when metabolism has been stimulated sufficiently, the MH syndrome can continue unabated with further increases in temperature in the absence of the triggering agent [1,12,13]. Pharmacological experiments indicate that diltiazem may modify CaJ+ fluxes at the level of the T-tubule membrane [8]. Ca-+ entering the muscle via T-tubules may therefore be important in the aetiology of the MH syndrome. Diltiazem not only acts on skeletal muscle, but also has well known cardiovascular effects [14]. Diltiazem prevents arrhythmias and protects the heart from ischaemia, effects which would be beneficial during an MH episode. Although diltiazem causes hypotension, this was not an adverse effect in this study during MH. The release of catecholamines from the adrenal medulla is a Ca-+-dependent process [15]. The increased concentration of circulating catecholamines observed during an MH episode [12] may also be mediated by Ca~+ [3]. Diltiazem may also inhibit this Ca-+-dependent process and attenuate cardiovascular changes [16]. In common with dantrolene, diltiazem modifies the onset of MH and the further expression of an initiated MH syndrome. However, diltiazem is not as effective as dantrolene, and should not displace this drug in the treatment of MH.
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