Determination of the minimum alveolar concentration (MAC) and cardiopulmonary effects of sevoflurane in sheep

Accepted Manuscript Determination of the minimum alveolar concentration (MAC) and cardiopulmonary effects of sevoflurane in sheep Nicolò Columbano, DMV, PhD, Antonio Scanu, DMV, PhD, Lauren Duffee, VMD, Valentino Melosu, DMV, Giovanni Sotgiu, MD, PhD, Bernd Driessen, DVM, PhD, Dipl. ACVAA, Dipl. ECVPT PII:

S1467-2987(18)30018-7

DOI:

10.1016/j.vaa.2018.01.007

Reference:

VAA 236

To appear in:

Veterinary Anaesthesia and Analgesia

Received Date: 30 June 2017 Revised Date:

12 December 2017

Accepted Date: 14 January 2018

Please cite this article as: Columbano N, Scanu A, Duffee L, Melosu V, Sotgiu G, Driessen B, Determination of the minimum alveolar concentration (MAC) and cardiopulmonary effects of sevoflurane in sheep, Veterinary Anaesthesia and Analgesia (2018), doi: 10.1016/j.vaa.2018.01.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Original Article

2 3

Determination of the minimum alveolar concentration (MAC) and cardiopulmonary effects of sevoflurane in sheep

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Nicolò Columbano, DMV, PhDa,d, Antonio Scanu, DMV, PhDa, Lauren Duffee, VMDc, Valentino Melosu, DMVa, Giovanni Sotgiu, MD, PhDb, Bernd Driessen, DVM, PhD, Dipl. ACVAA, Dipl. ECVPTc

RI PT

1

a

M AN U

SC

Dipartimento di Medicina Veterinaria, Università degli Studi di Sassari, Via Vienna, 2 07100 Sassari, Italy b Dipartimento di Scienze Biomediche, Università degli Studi di Sassari, Piazza Università 21, Sassari, Italy c Department of Clinical Studies-New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, 382 West Street Rd, Kennett Square, PA 19348, USA d Centro di Ricerca di Chirurgia Comparata (CRCC), Università degli Studi di Sassari Piazza Università 21, Sassari, Italy Correspondence: Bernd Driessen, Department of Clinical Studies-New Bolton Center, University of Pennsylvania, School of Veterinary Medicine, 382 West Street Rd, Kennett Square, PA, USA 19348

TE D

E-mail: [email protected] Tel: +1 (610) 925-6130

Acknowledgements

26

We thank Dräger, Italy for having provided us with technical support throughout the study

27

period.

28

Conflict of interest statement

29

None to report.

33 34

AC C

30 31 32

EP

25

Running title: Sevoflurane anaesthesia in sheep

ACCEPTED MANUSCRIPT Abstract

2

Objective To determine sevoflurane’s minimum alveolar concentration (MACSEVO) and its

3

cardiopulmonary effects in sheep.

4

Study design Prospective experimental study

5

Animals Ten female non-pregnant Sardinian milk sheep

6

Methods Anesthesia was induced in each sheep twice with sevoflurane in oxygen. After a 30-

7

minute equilibration at end-tidal sevoflurane concentration (FEʹSevo) of 2.8 %, an electrical

8

stimulus (5 Hz/1 ms/50 mA) was applied to the right forelimb for one minute or until gross

9

purposeful movement occurred. The FEʹSevo was then changed using a 0.2 % up-and-down

M AN U

SC

RI PT

1

protocol, dependent on whether the response was positive or not, and then noxious stimulation

11

was repeated. The MACSEVO was defined as the mean FEʹSevo between that allowing

12

purposeful movement and that not. Ten sheep were re-anesthetized and MACSEVO was re-

13

determined. Thereafter, FEʹSevo was maintained for 15 minutes each at concentrations

14

corresponding to 1.0, 1.3, 1.6, 1.9, and 0.75 MACSEVO-multiples, and cardiopulmonary, blood

15

gas, acid-base variables, and plasma electrolytes were determined. Also, time to induction of

16

anesthesia, extubation, and recovery were recorded.

17

Results The mean ± SD of the MACSEVO was 2.74 ± 0.38 %. Median (IQR) time to intubation

18

was 3.13 (2.98-3.33) minutes, time to extubation was 6.85 ± 2.65 minutes and time to

19

recovery was 13.4 ± 5.2 minutes. With increasing FEʹSevo arterial blood pressures

20

progressively decreased as did minute ventilation, which in turn caused end-tidal carbon

21

dioxide, arterial partial pressure of carbon dioxide, and bicarbonate values to steadily increase

22

without significantly affecting arterial partial pressure of oxygen.

23

Conclusions and clinical relevance The reported MACSEVO agrees with published data in

24

this and other species. Administration of sevoflurane in sheep caused marked hemodynamic

AC C

EP

TE D

10

ACCEPTED MANUSCRIPT and respiratory depression but soon after turning off the vaporizer sheep could be extubated

26

and recovered rapidly and event-free.

27

Keywords Sevoflurane; Minimum alveolar concentration (MAC); Cardiopulmonary effects;

28

Sheep

RI PT

25

AC C

EP

TE D

M AN U

SC

29

ACCEPTED MANUSCRIPT Introduction

31

Sevoflurane (SEVO) is a halogenated inhalational anesthetic with favourable pharmacokinetic

32

and pharmacodynamic properties that is increasingly utilized in veterinary anesthesia and

33

biomedical research. Its low blood solubility facilitates rapid induction of anesthesia and

34

faster adjustment of anesthetic depth during maintenance than with isoflurane (Patel et al.

35

1996; Steffey et al. 2015). Recent studies in animals revealed pharmacodynamic effects

36

comparable with those obtained with isoflurane or SEVO in humans (Eger, 1994; Steffey et

37

al. 2015).

SC

RI PT

30

The minimum alveolar concentration (MAC) of a volatile anesthetic prevents gross

39

purposeful movement in response to a supramaximal noxious stimulus in 50 % of subjects

40

studied and determines an inhalational anesthetic’s potency (Merkel and Eger 1963; Eger et

41

al. 1965). Recent data indicate that volatile anesthetics target the spinal cord to suppress

42

motor responses to noxious stimuli (Haseneder et al. 2004).

TE D

M AN U

38

The MACSEVO has been determined in many species including human, goats, horses,

44

llamas, and alpacas (Steffey et al. 2015). However, MACSEVO and SEVO’s cardiopulmonary

45

effects in adult sheep have not been established. The purpose of this study was to determine

46

MACSEVO in sheep and to describe the cardiopulmonary effects of SEVO. We hypothesized

47

that SEVO exhibits an anesthetic potency similar to that in other species and causes

48

depression of cardio-respiratory function of similar magnitude as in other species.

AC C

49

EP

43

50

Materials and Methods

51

This prospective experimental study was approved by the Institutional Animal Care and Use

52

Committee at the at the University of Sassari (CIBASA; protocol number 23/052) according

53

to Italian legislation. The scientific idea behind this study was original and no similar studies

ACCEPTED MANUSCRIPT have been carried out in the past in this species. On this basis, we did not have any

55

possibilities to prepare a list of feasible statistical assumptions based on previous scientific

56

evidence. Our scientific hypothesis could not rely on specific statistical assumptions and,

57

therefore, the computation of an appropriate sample size could not be performed.

58

Consequently, the epidemiological design of the present study could be defined “pilot”. After

59

the enrolment of the ten animals and at the end of the experimental MACSEVO determination, a

60

post-hoc power calculation was informally carried out to verify inclusion of ten sheep for the

61

second part of the study (Determination of dose-dependent effects of SEVO), in which a two-

62

tailed t test with power of 0.98, and an alpha error of 0.05 was applied.

63

Animals

64

Ten female Sardinian milk sheep that were judged healthy based on physical examination,

65

hematology, and serum chemistry results (American Society of Anesthesiologists status I)

66

were enrolled and anesthetized twice, 12 weeks apart.

67

Preanesthetic instrumentation and anesthesia

68

Food was withheld for 12 hours prior to anesthesia, with maintained access to water. Body

69

weight (kg), heart rate (HR, beats minute-1), respiratory rate (fR, breaths minute-1), and rectal

70

temperature (°C) were recorded prior to experimentation. Sheep were positioned in lateral

71

recumbency for catheterization of the auricular artery with a 20 gauge, 2.5-cm catheter (Delta

72

Ven 1; Delta Med, Italy) using aseptic technique and peri-arterial infiltration with

73

subcutaneous lidocaine 2 % to obtain access for invasive arterial pressure readings and arterial

74

blood collection. The saphenous vein was similarly catheterized with an 18-gauge catheter

75

(Delta Ven 1; Delta Med) for infusion of lactated Ringer’s solution at 5 mL kg-1 hour-1. No

76

premedication was administered. With gentle physical restraint, the sheep were

77

preoxygenated for three minutes with oxygen (O2) at 3 L minute-1 via a tight-fitting face mask

AC C

EP

TE D

M AN U

SC

RI PT

54

ACCEPTED MANUSCRIPT connected to a standard rebreathing system (Dräger, Germany), which was attached to a

79

workstation (Fabius GS; Dräger) that operates with a rebreathing/circle system with an

80

integrated mechanical ventilator (E-vent; Dräger) and sodalime (Drägersorb 800 Plus; Dräger)

81

as carbon dioxide absorbent. During this time, baseline measurements were performed,

82

including HR, invasive systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood

83

pressures (mmHg), arterial oxygenation (SpO2, %) and the electrocardiogram (ECG).

Anesthesia was induced with SEVO (Sevoflo; Zoetis, MI, USA) delivered from a

SC

84

RI PT

78

calibrated, agent-specific, out-of-circuit vaporizer (Blease Sevo “L series”; Blease Datum,

86

UK) by setting the SEVO vaporizer dial to 8 %. Once the depth of anesthesia was judged

87

adequate, a cuffed 8.5-mm (internal diameter) endotracheal tube (Safety-Flex; Mallinckrodt

88

Medical, Ireland) was placed and connected to the anesthetic circuit. Thereafter, sheep were

89

mechanically ventilated to maintain a partial pressure of end-tidal carbon dioxide (PEʹCO2) of

90

40-50 mmHg (5.3-6.7 kPa). The HR, ECG, invasive arterial blood pressures, SpO2, and

91

oesophageal body temperature (T, °C) were continuously monitored using a multiparameter

92

monitor (Infinity Delta; Dräger, Germany). The fraction of inspired oxygen concentration

93

(FIO2), tidal volume, (VT), end-tidal SEVO concentration (FEʹSevo, %), and PEʹCO2 (mmHg,

94

kPa) were continuously monitored in side stream (250 mL minute-1, Fabius GS and its Scio

95

four Oxi Plus gas module, Dräger). The gas module was calibrated daily using gas standards

96

(1 % SEVO, 5 % CO2 calibration Gas; Air Liquide Healthcare America, PA, USA). The O2

97

flow rate was maintained at 3 L minute-1 throughout all experiments. Arterial blood was

98

collected in heparin coated syringes and immediately analysed using a blood gas analyser

99

(ABL 80 CO-OX flex; Radiometer, Denmark).

AC C

EP

TE D

M AN U

85

100 101

Supramaximal noxious stimulation

ACCEPTED MANUSCRIPT Pilot experiments conducted in six sheep revealed that repeated brief stimulations of the

103

lateral palmar nerves with 60 second trains of constant current electrical impulses produced

104

motor responses of similar magnitude. Unlike repeated clamping of the tail using a rubber-

105

covered hemostat applied at full ratchet for 60 seconds, a technique commonly applied in

106

MAC studies (Valverde et al. 2003), repetitive electrical stimulation does not cause noticeable

107

tissue damage. Therefore, we chose this method of noxious stimulation.

Disposable low-resistance silver/silver chloride electrodes (Norotrode 20 Bipolar

SC

108

RI PT

102

SEMG Electrodes; Myotronics-Noromed, Inc., WA, USA) with an inter-electrode distance of

110

1 cm were applied on the lateral metacarpal surface midway between the carpus and

111

metacarpophalangeal joints and secured in place. Stimuli were delivered by a 220 Volt

112

powered constant current stimulator, model DS7A (Digitimer Ltd, UK) triggered by a 9-Volt

113

battery-powered Train/Delay Generator, model DG2A (Digitimer Ltd). Supramaximal

114

noxious stimulation consisted of trains of square-wave impulses (5 Hz/1 ms/50 mA) delivered

115

for 60 seconds or until a gross purposeful motor response was noted. As the maximum

116

voltage delivered by the stimulator was 200 V, the electrical resistance between electrodes

117

was measured using an ohmmeter (Personal 20; Mega Elettronica, Italy) prior to each

118

stimulation, in order to ensure resistance remained at <3 kΩ necessary to discharge a current

119

of 50 mA. In case resistance increased to >3 kΩ, electrodes were exchanged.

TE D

EP

AC C

120

M AN U

109

121

Determination of MACSEVO

122

A modified Dixon up-and-down method was employed (Dixon & Massey 1983). After 30

123

minutes of equilibration at FEʹSevo of 2.8 %, noxious stimulation was applied. Electrical

124

stimulation was discontinued immediately upon observation of gross purposeful movement or

125

completion of the 60 second stimulation cycle. A response was considered positive when

ACCEPTED MANUSCRIPT major motor responses were observed in non-stimulated body areas, such as flexion or

127

extension of the contralateral hind limb or gross neck movements. Muscle tremors, occasional

128

swallowing, nystagmus, and changes in cardio-respiratory parameters were not considered a

129

positive response. Depending on the presence or lack of a positive response, the vaporizer dial

130

setting was increased or decreased, respectively, to arrive at an FEʹSevo 0.2 % higher or lower

131

than previously recorded. The new FEʹSevo concentration was maintained for 15 minutes

132

before the electrical stimulation was repeated. Each determination of MACSEVO was

133

performed in duplicate.

SC

RI PT

126

M AN U

134

Experimental data collection during MACSEVO determination

136

The rectal temperature, fR, HR, SAP, DAP and MAP were recorded at baseline prior to

137

induction of anesthesia. The T, fR, PEʹCO2, FEʹSevo, HR, SAP, DAP and MAP, and SpO2

138

were continuously monitored and recorded at the following time points: 5 minutes after the

139

induction of anesthesia (Time1), at the end of the 30-minute equilibration period (Time2);

140

during the first MACSEVO determination (Time3, Time4), during the second MACSEVO

141

determination (Time5, Time6) and at the end of the experimental procedure (Time7). Arterial

142

blood gas and acid-base parameters [pH, arterial partial pressure of carbon dioxide (PaCO2),

143

arterial partial pressure of oxygen (PaO2), base excess (BE), bicarbonate (HCO3-), arterial

144

saturation of oxygen (SaO2)] were measured at Time0, Time2 and Time7. The following time

145

intervals were recorded: time of induction, defined as the time between start of SEVO

146

administration and successful intubation; time of anesthesia, defined as the time between

147

intubation and extubation; time of extubation, defined as the time between turning off the

148

SEVO vaporizer to extubation; time to sternal, defined as the time between turning off the

149

SEVO vaporizer to the time when the sheep could maintain sternal recumbency; and time to

AC C

EP

TE D

135

ACCEPTED MANUSCRIPT 150

standing, defined as the time between turning off the SEVO vaporizer to the point when the

151

sheep could remain standing.

152 Determination of dose-dependent effects of SEVO on cardiopulmonary, blood gas, acid-base

154

variables and electrolyte homeostasis.

155

Ten sheep were anesthetized a second time and MACSEVO was re-determined as described

156

above, except that animals were allowed to breathe spontaneously. The SEVO vaporizer dial

157

setting was adjusted to an FEʹSevo that corresponded to the individual’s previously

158

determined MACSEVO value. The FEʹSevo was then maintained for 15 minutes before

159

recording of T, fR, VT, O2 flow rate, FIO2, PEʹCO2, FEʹSevo, HR, SAP, DAP and MAP, SpO2,

160

arterial blood gas and acid-base parameters (pH, PaCO2, PaO2, BE, HCO3-, SaO2), blood

161

electrolyte concentrations (Na+, K+, Cl-) and total haemoglobin (Hb). Blood gas and pH data

162

were corrected for body temperature using a standard nomogram based on human blood.

163

Thereafter, the SEVO dial setting was increased until an FEʹSevo corresponding to 1.3 times

164

the previously determined individual MACSEVO was obtained. This FEʹSevo was again

165

maintained for 15 minutes before recording of the previously listed parameters. This

166

procedure was repeated for FEʹSevo concentrations corresponding to 1.6 and 1.9 MACSEVO

167

multiples. Then the SEVO dial setting was reduced until an FEʹSevo corresponding to 0.75

168

MACSEVO was obtained, and again all parameters were recorded. Thereafter, the SEVO

169

vaporizer was turned off, the animal allowed to recover from anesthesia and the time period to

170

extubation, sternal recumbency and standing were recorded.

SC

M AN U

TE D

EP

AC C

171 172

RI PT

153

Statistical analysis

ACCEPTED MANUSCRIPT All continuous data (Temp, fR, HR, SAP, DAP and MAP, O2 flow rate, FIO2, minute

174

ventilation (Vሶ E ), PEʹCO2, FEʹSevo, SpO2, pH, PCO2, PO2, BE, HCO3-, SaO2, Na+, K+, Cl-,

175

total Hb; time periods measured) and MAC values were tested for normal distribution via a

176

Shapiro-Wilk test. Normally distributed variables are reported as means ± standard deviations

177

(SD). Non-parametric data are reported as median (IQR). All individual MACSEVO

178

determinations listed in Table 1 were averaged and then reported as one mean ± SD value. For

179

the time points Time0-Time7 mentioned above all numeric data were pooled and group means

180

determined. Data obtained for time points Time1-Time7 were then compared to baseline

181

(Time0) and amongst each other using analysis of variance (ANOVA). Data in the dose-

182

response investigation were grouped by dose (MACSEVO multiple) and group means were then

183

compared to baseline (FEʹSevo = 0) and amongst each other using analysis of variance

184

(ANOVA). All analyses were two-sided. Analyses were performed using the Stata Statistical

185

Software, version 13.0 (Stata Corp, Texas, USA). P < 0.05 was considered significant.

TE D

M AN U

SC

RI PT

173

186

The MACSEVO was individually calculated as the average of two successive FEʹSevo

188

concentrations, one allowing and one preventing gross purposeful movement in response to

189

the supramaximal electrical stimulation. The population MACSEVO was calculated as the

190

arithmetic mean (± SD) of the 10 individual animals’ MACs. Linear regression was used to

191

determine any relationship between MAC values determined and age of the individual

192

animals. Sassari, Italy is located at 225 meters (738 ft) above sea level.

AC C

EP

187

193 194

Results

195

Animals

ACCEPTED MANUSCRIPT 196

The mean ± standard deviation (SD) age of the sheep studied was 6 ± 2 years and their weight

197

was 35.6 ± 4.8 kg.

198 Determination of MACSEVO

200

In the present population of 2 to 10-year-old Sardinian sheep, the mean ± SD MACSEVO was

201

2.74 ± 0.38 % based on MAC determinations during the first and second anesthetic episodes

202

(Table 1). For each MACSEVO determination (i.e. 1st, 2nd, and 3rd MACSEVO) variability

203

amongst animals ranged from 10-16 % (see Table 1). Mask induction of anesthesia with

204

SEVO was achieved within 3.13 (2.98-3.33) minutes and required one attempt for successful

205

orotracheal intubation in all but one sheep. One sheep required three attempts to place the

206

endotracheal tube and time to induction was about twice as long. Body temperature,

207

cardiovascular, respiratory and acid-base parameters recorded between time points Time0 and

208

Time7 are listed in Table 2. The total anesthesia time was 117 ± 35 minutes and extubation

209

was achieved within 6.85 ± 2.62 minutes following turning off the vaporizer. Sheep were

210

standing within 13.4 ± 5.2 minutes.

TE D

M AN U

SC

RI PT

199

EP

211

Dose-dependent effects of SEVO on cardiopulmonary, blood-gas, acid-base variables, and

213

electrolyte homeostasis

214

Body temperature, cardiovascular, respiratory and acid-base parameters measured in the

215

awake and anesthetized sheep at different FEʹSevo concentrations are listed in Table 3.

216

Increasing FEʹSevo concentrations were associated with significant changes: systolic,

217

diastolic, and mean arterial blood pressures progressively decreased; minute ventilation also

218

decreased, which caused PEʹCO2, PaCO2, and HCO3- values to increase without significantly

219

affecting PaO2 values (Table 3). Plasma electrolyte concentrations were not affected by

220

SEVO. Total Hb concentration stayed decreased by 30 %, even after SEVO exposure had

AC C

212

ACCEPTED MANUSCRIPT been decreased at the end of these experiments to a low FEʹSevo concentration (0.75

222

MACSEVO). Arterial blood pressures recovered to almost preanesthetic values. Extubation of

223

the animals was successful within 2.9 ± 0.9 minutes of turning off the SEVO vaporizer. The

224

sheep resumed sternal recumbency and were standing at 6.8 ± 4.9 minutes and 15.3 ± 5.6

225

minutes, respectively following turning off the SEVO vaporizer.

226

RI PT

221

Discussion

228

The purpose of the current study was to examine the anesthetic potency and

229

pharmacodynamic effects of SEVO in sheep. Eger et al. (1965) established MAC as an

230

appropriate methodology for measuring and comparing potency of volatile anesthetics among

231

different species and across different conditions (Quasha et al. 1980). One may interpret MAC

232

also as a measure of anesthetic-induced unresponsiveness towards noxious stimulation,

233

because the spinal cord is an important site of action of volatile anesthetics. In the spinal cord

234

they inhibit transmission of nociceptive signals to ascending pathways and suppress synaptic

235

transmission in motor neurones, thereby producing immobility (Haseneder et al. 2004; Sonner

236

et al. 2003).

EP

TE D

M AN U

SC

227

We determined in adult, female sheep of the Sardinian breed a MACSEVO of 2.74 ±

238

0.38 %, which is approximately midway between values in non-pregnant sheep previously

239

reported by Okutomi et al. (2009) (1.92 ± 0.17 %) and by Lukasik et al. (3.3 %)1. This

240

finding is not surprising, as we determined for two sheep in our study group average

241

MACSEVO values between 2.23 and 2.28 % and for two other animals between 3.07 and

242

3.35 %. The overall inter-animal variability of MACSEVO determinations in the present study

243

did not exceed 16 %. Valverde et al. (2003) described that MAC values reported in the

AC C

237

1

Lukasik VM, Nogami WM, Morgan SE (1997) Minimum alveolar concentration and cardiovascular effects of sevoflurane in sheep. Proceedings of the Annual Meeting of the Am Col Vet Anesth, San Diego CA, p. 168.

ACCEPTED MANUSCRIPT 244

literature for a single inhalation anesthetic can differ substantially amongst animals of the

245

same species with variability at times exceeding 40 %, when data from different experimental

246

sources are compared (Steffey et al. 2015). Differences in barometric pressures alone can also account for some of the variability

248

in results (Mama et al. 1999). In case of the present study, atmospheric pressure was between

249

1011 and 1028 mbar (101-103 kPa) during the time period of the initial MACSEVO

250

determinations, while between 740 und 746 mbar (74-75 kPa) during the SEVO dose-

251

response experiments. This may explain the on average 12 % variability in MACSEVO values

252

we noticed in the same animals between the first and the second anesthetic period (Table 1).

M AN U

SC

RI PT

247

Furthermore, differences in pharmacogenetic characteristics among individual animal

254

groups of the same species may be responsible for variability in MAC values reported. In

255

humans, a gene association seems to exist between the MAC value for desflurane and carriers

256

of different variants of the MC1R gene, with red-haired subjects requiring exposure to a 19 %

257

higher desflurane concentration than dark-haired individuals (Liem et al. 2004). Also, an

258

association between ethnicity and sevoflurane requirements has been described (Ezri et al.

259

2007). To what extent this applies to domestic animals remains uncertain. Also differences in

260

animal age, body temperature, and circadian rhythm could contribute to the variation in

261

reported MAC data (Quasha et al. 1980).

EP

AC C

262

TE D

253

Certainly, inconsistencies in experimental methodologies among different studies

263

(type of noxious stimulus applied, assessment of gross purposeful movement, calculation of

264

MAC values, and length of equilibration period after each step-up/step-down in end-tidal

265

inhalational anesthetic concentration) account for much of the variability in results (Valverde

266

et al. 2003). Unlike other investigators who employed a mechanical stimulus, who either

267

clamped the earlobe of the sheep (Okutomi et al. 2009) or applied a haemostat to the coronary

ACCEPTED MANUSCRIPT band of the right, rear, lateral claw (Lukasik et al. 1997) for at least 60 seconds, we chose an

269

electrical stimulus as supramaximal noxious stimulation because this technique is not

270

associated with sustained tissue injury upon repeated application. Isoflurane MAC studies in

271

dogs and rabbits revealed that experiments with current intensities of 30 mA and 50 mA

272

provided consistent results independent of the electrode placement to the oral mucosa, tail,

273

thoracic limbs, or pelvic limbs, and that MAC data minimally differed from those obtained

274

using mechanical stimulation such as tail or paw clamping; in contrast, skin incision in either

275

of these species lead to determination of significantly lower MAC values (Valverde et al.

276

2003; Figueiró et al. 2016). This finding in dogs and rabbits is contrary to observations in

277

humans, in which skin incision and electrical stimulation result in similar MAC values

278

(Quasha et al. 1980). While comparisons of MAC values obtained with different noxious

279

stimuli are not available for sheep, we had confirmed in pilot experiments that stimulation

280

with 60 seconds trains of electrical impulses delivered at a constant current of 50 mA to the

281

skin over the lateral palmar nerves represented a supramaximal noxious stimulus that reliably

282

elicited gross purposeful motor activity.

SC

M AN U

TE D

The authors of the previous MACSEVO studies in sheep incompletely described what

EP

283

RI PT

268

they considered a purposeful movement. Additionally, they determined MAC differently.

285

Okutomi et al. (2009) defined MACSEVO as the SEVO concentration which ‘prevented

286

movement in 50 % of the tests’, a somewhat equivocal approach given the small number of

287

non-pregnant animals tested (n=3). In contrast, Lukasik et al. (1997) calculated the MACSEVO

288

for each of six ewes as arithmetic mean between the FEʹSevo concentration that allowed

289

purposeful movement and that which did not, as performed in the present study. However, our

290

electrical noxious stimulus allowed repeated MACSEVO determinations, avoiding the risk of

291

producing confounding peripheral and/or central hyperalgesia caused by severe tissue injury

292

as a result of repetitive clamping of peripheral body parts.

AC C

284

ACCEPTED MANUSCRIPT 293

It is well accepted that following 15-minute equilibration periods, when differences between inspired and expired end-tidal concentrations of inhalational anesthetics have largely

295

diminished, the end-tidal inhalational concentration or partial pressure of an inhalational

296

anesthetic adequately reflects arterial inhalational anesthetic partial pressure and therefore

297

correlates well with the partial pressure of the agent at its target sites in the central nervous

298

system (Quasha et al. 1980). This holds true for agents like SEVO, which is characterized by

299

a relatively low blood-gas partition coefficient of 0.56 ± 0.03 in sheep (Soares 2012).

300

The MACSEVO value we report for sheep is somewhat higher but still close to

301

MACSEVO values reported for other species (Steffey et al. 2015). This applies in particular to

302

other farm animal species such as goats (MAC SEVO = 2.33 %) (Hikasa et al. 2003), horses

303

(MAC SEVO = 2.31 %) (Aida et al. 1994), and llamas and alpacas (MAC SEVO = 2.29 and

304

2.33 %, respectively) (Grubb et al. 2003).

M AN U

SC

RI PT

294

The dose-dependent decrease in arterial blood pressures and minute ventilation that

306

also affects arterial acid-base status becomes rapidly apparent when FEʹSevo rises from 0.75

307

to 1.9 times MACSEVO as our data revealed (Table 3). Those findings were expected and

308

corresponded well with data reported for SEVO in this (Lukasik et al. 1997) and other species

309

such as goats (Hikasa et al. 2003), dogs (Polis et al. 2001), and horses (Aida et al. 1994).

EP

TE D

305

The methodology of the second part of the study had a limitation. When sheep were

311

anesthetized the second time and MACSEVO was re-determined, the FEʹSevo concentration

312

was not reduced to 0.75 x MACSEVO but instead was first successively increased from 1.0 to

313

1.9 x MACSEVO before it was allowed to drift down to 0.75 x MACSEVO just prior to the end of

314

the experiment. While we considered this approach necessary to protect animals from

315

prematurely waking up, we cannot rule out the possibility that some residual drug effects from

316

prior SEVO exposure had an influence on measured hemodynamic and respiratory

317

parameters. However, due SEVO’s low blood-gas coefficient and hence relatively rapid

AC C

310

ACCEPTED MANUSCRIPT 318

elimination from the body of the animals, we considered any residual drug effect to be rather

319

small.

320 Conclusions

322

The MACSEVO in Sardinian sheep is somewhat higher than in other farm animal species but is

323

within the range reported in the veterinary literature. Administration of SEVO in sheep, as in

324

other species, caused a concentration-dependent depression of cardiopulmonary function

325

calling for vigilant monitoring of vital parameters. Soon after turning off the vaporizer

326

animals could be extubated and recovered rapidly and event-free.

M AN U

SC

RI PT

321

327 References

329

Aida H, Mizuno Y, Hobo S, et al. (1994) Determination of the minimum alveolar

330

concentration (MAC) and physical response to sevoflurane inhalation in the horse. J Vet Med

331

Sci 56, 1161-1165.

332

Dixon WJ, Massey FJ (1983) The “up-and-down” method. In: Introduction to Statistical

333

Analysis (4th edn). Dixon WJ, Massey FJ (eds). McGraw-Hill, New York, NY, USA, pp. 428-

334

39.

335

Eger EI II, Saidman LJ, Brandstater B (1965) Minimum alveolar anesthetic concentration: a

336

standard of anesthetic potency. Anesthesiology 26, 756–763.

337

Eger EI II (1994) New inhaled anesthetics. Anesthesiology 80, 906-922.

338

Ezri T, Sessler D, Weisenberg M, et al. (2007) Association of ethnicity with the minimum

339

alveolar concentration of sevoflurane, Anesthesiology 107, 9-14.

340

Figueiró MR, Soares JH, Ascoli FO, et al. (2016) Isoflurane MAC determination in dogs

341

using three intensities of constant-current electrical stimulation. Vet Anesth Analg 43, 464-

342

471.

AC C

EP

TE D

328

ACCEPTED MANUSCRIPT Grubb TL, Schlipf JW, Riebold TW, et al. (2003) Minimum alveolar concentration of

344

sevoflurane in spontaneously breathing llamas and alpacas. J Am Vet Med Assoc 223, 1167–

345

1169.

346

Haseneder R, Kurz J, Dodt HU, et al. (2004) Isoflurane reduces glutamatergic transmission in

347

neurons in the spinal cord superficial dorsal horn: Evidence for a presynaptic site of an

348

analgesic action. Anesth Analg 98, 1718-1723.

349

Hikasa Y, Okuyama K, Kakuta T, et al. (2003) Anesthetic potency and cardiopulmonary

350

effects of sevoflurane in goats: comparison with isoflurane and halothane. Can J vet Res 62,

351

299-306.

352

Liem EB, Lin CM, Suleman MI, et al. (2004) Anesthetic requirement is increased in redheads,

353

Anesthesiology 101, 279-283.

354

Mama KR, Wagner AE, Parker DE, et al. (1999) Determination of the minimum alveolar

355

concentration of isoflurane in llamas. Vet Surg 28, 121-125.

356

Merkel G, Eger EI II (1963) A comparative study of halothane and halopropane anesthesia

357

including method for determining equipotency. Anesthesiology 24, 346-357.

358

Okutomi T, Whittington RA, Stein DJ, et al. (2009). Comparison of the effects of sevoflurane

359

and isoflurane anesthesia on the maternal-fetal unit in sheep. J Anesth 23, 392–398.

360

Patel SS, Goa KL (1996) Sevoflurane – A review of its pharmacodynamic and

361

pharmacokinetic properties and its clinical use in general anesthesia. Drugs 51, 658-700.

362

Polis I, Gasthuys F, Van Ham L, et al. (2001) Recovery times and evaluation of clinical

363

hemodynamic parameters of sevofurane, isoflurane and halothane anesthesia in mongrel dogs.

364

J Vet Med A Physiol Pathol Clin Med 48, 401-411.

365

Quasha AL, Eger EI II, Tinker JH (1980) Determinations and application of MAC.

366

Anesthesiology 53, 315–334.

AC C

EP

TE D

M AN U

SC

RI PT

343

ACCEPTED MANUSCRIPT Soares JH, Brosnan RJ, Fukushima FB, et al. (2012) Solubility of Haloether Anesthetics in

368

Human and Animal Blood. Anesthesiology 117, 48 –55.

369

Sonner JM, Antognini JF, Dutton RC, et al. (2003) Inhaled anesthetics and immobility:

370

mechanisms, mysteries, and minimum alveolar anesthetic concentration. Anesth Analg 97,

371

718-740.

372

Steffey EP, Mama KR, Brosnan RJ (2015) Inhalation anesthetics. In: Veterinary Anesthesia

373

and Analgesia (5th edn). Grimm, K.A., Lamont, L.A., Tranquilli, W.J., Greene, S.A.,

374

Robertson, S.A. (eds). Wiley-Blackwell, Ames, IA, USA, pp. 297-331.

375

Valverde A, Morey TE, Hernández J (2003) Validation of several types of noxious stimuli for

376

use in determining the minimum alveolar concentration for inhalation anesthetics in dogs and

377

rabbits. Am J Vet Res 64, 957–962.

AC C

EP

TE D

M AN U

SC

RI PT

367

ACCEPTED MANUSCRIPT

Table 1

379

Displayed are the recorded minimum alveolar concentrations of sevoflurane (MACSEVO) for each of the 10 sheep. The MACSEVO was

380

determined in duplicate in mechanically ventilated sheep during for the first series of experiments (first and second MACSEVO) and again as

381

a single determination at the beginning of the second series of experiments 12 weeks later, in which the dose-dependent effects of

382

sevoflurane on cardio-pulmonary and other variables were studied (third MACSEVO).

383 384

386

First MACSEVO

Second MACSEVO

Sheep 1

2.80

2.80

Sheep 2

2.80

3.00

Sheep 3

2.80

2.60

2.80 ± 0.00

3.00

2.93 ± 0.12

2.80

2.73 ± 0.12

Sheep 4

2.35

2.20

2.30

2.28 ± 0.08

Sheep 5

2.20

2.20

2.30

2.23 ± 0.06

391

Sheep 6

2.60

3.40

3.20

3.07 ± 0.42

2.80

Sheep 8

2.60

393

Sheep 9

3.15

394

Sheep 10

2.30

395 396

.

AC C

Sheep 7

392

2.40

2.70

2.63 ± 0.21

3.20

3.00

2.93 ± 0.31

3.50

3.40

3.35 ± 0.18

2.50

2.50

2.43 ± 0.12

TE D

390

EP

389

Mean ± SD

2.80

387 388

Third MACSEVO

M AN U

Animal

385

SC

RI PT

378

ACCEPTED MANUSCRIPT

397

Table 2 Selected cardiovascular, respiratory, and acid-base parameters determined in 10 mechanically ventilated sheep during minimum

398

alveolar concentration of sevoflurane (MACSEVO) determinations.

SpO2 FIO2 pH

mmHg kPa %

Time1 38.7 ± 0.5 110 ± 15* 92 ± 14* 71 ± 13* 80 ± 14* 14 ± 2

Time2 37.8 ± 0.6 90 ± 11 92 ± 12* 66 ± 12* 77 ± 11* 14 ± 3

Time3 37.6 ± 0.5 103 ± 21 109 ± 13 82 ± 11 94 ± 12 17 ± 5

Time4 37.5 ± 0.6 98 ± 17 115 ± 11 90 ± 8 100 ± 9 17 ± 4

-

2.8 ± 0.4 41 ± 5

2.8 ± 0.3 43 ± 2

2.6 ± 0.3 42 ± 3

2.9 ± 0.4 42 ± 2

-

5.5 ± 0.7 100 ± 1

5.7 ± 0.3 100 ± 0

5.6 ± 0.4 100 ± 0

5.6 ± 0.3 100 ± 1

0.90 ± 0.16 -

0.93 ± 0.12 7.37 ± 0.02 55 ± 2 7.3 ± 0.3

0.93 ± 0.16 -

0.92 ± 0.10 -

-

421 ± 104

-

-

SC

Time0 38.3 ± 0.6 91 ± 18 108 ± 9 84 ± 5 94 ± 8 29 ± 2

M AN U

Unit °C minute-1 mmHg mmHg mmHg minute-1 %

TE D

Variable T HR SAP DAP MAP fR FEʹSevo PEʹCO2

RI PT

399

mmHg kPa

PaO2

mmHg

84 ± 6

11.2 ± 0.8

HCO3-

kPa mmol L-1

28.6 ± 2.0

-

30.4 ± 2.1

-

-

BE

mmol L-1

5.3 ± 2.0

-

5.5 ± 2.1

-

-

AC C

EP

PaCO2

0.21 7.48 ± 0.03 40 ± 3 5.3 ± 0.4

Time5 37.2 ± 0.7 96 ± 15 111 ± 13 85 ± 8 96 ± 9 17 ± 4 2.6 ± 0.5

Time6 37.1 ± 0.7 95 ± 15 110 ± 12 84 ± 10 94 ± 10 17 ± 4 2.8 ± 0.5

Time7 37.1 ± 0.7 95 ± 14 113 ± 14 86 ± 12 98 ± 12 17 ± 4 2.5 ± 0.6

43 ± 2 5.7 ± 0.3 100 ± 0 0.92 ± 0.01

43 ± 2 5.7 ± 0.3 100 ± 0 0.92 ± 0.02

42 ± 2 5.6 ± 0.3 100 ± 0 0.92 ± 0.01

-

-

7.37 ± 0.03 54 ± 3 7.2 ± 0.4

-

-

437 ± 130 58.3 ± 17.3

56.1 ± 13.9 -

-

31.1 ± 1.7 6.0 ± 1.8

ACCEPTED MANUSCRIPT

Parameters displayed are oesophageal body temperature (T, °C), heart rate (HR), systolic (SAP), diastolic (DAP) and mean (MAP) arterial blood

401

pressures (mmHg), respiratory rate (fR, minute-1), expired sevoflurane concentration (FEʹSevo, %), partial pressure of end-tidal CO2 (PEʹCO2, mmHg,

402

kPa), arterial oxygen saturation (SpO2, %), fraction of inspired oxygen concentration (FIO2), arterial pH, partial pressure of arterial CO2 (PaCO2,

403

mmHg), partial pressure of arterial O2 (PaO2, mmHg), arterial bicarbonate (HCO3-, mmol L-1), and arterial base excess (BE, mmol L-1). Data were

404

recorded prior to induction of anesthesia (Time0), 5 min after the induction of anesthesia (Time1), at the end of the 30-min equilibration period

405

(Time2); during the first MACSEVO determination (Time3, Time4), during the second MACSEVO determination and (Time5, Time6) and at the end of

406

experimental procedure (Time7). Values are means ± SD of 10 sheep. Significant differences from values recorded at Time0: *P < 0.05.

SC

RI PT

400

AC C

EP

TE D

M AN U

407

ACCEPTED MANUSCRIPT

Table 3 Dose-dependent effects of sevoflurane on selected parameters in 10 spontaneously breathing sheep when not exposed to any

409

noxious stimulation. Awake

Anesthetized with an FEʹSevo concentration of

(0 MACSEVO)

0.75 MACSEVO

1.0 MACSEVO 38.4 (38.138.7)* 60 ± 6* 101 ± 7*

°C

39.2 (38.8-39.2)

HR SAP

minute-1

101 ± 17

37.0 (36.237.1)* 65 ± 16*

mmHg

114 ± 7

101 ± 10*

DAP

mmHg

MAP fR Vሶ E FIO2

mmHg min-1 mL kg-1 minute-1

88 ± 8 98 ± 7 29 ± 8 -

76 ± 11* 87 ± 9* 27 ± 7 195 ± 65

0.21

0.89 ± 24*

mmHg kPa

pH

1.9 MACSEVO

38.1 (37.638.3)* 67 ± 9*

37.9 (37.138.0)* 78 ± 11 *a b

37.4 (36.737.7)* 84 ± 14* a b c

94 ± 9*

83 ± 13* a b

73 ± 12* a b c

78 ± 10* 88 ± 7* 35 ± 6* a 204 ± 58

70 ± 9* a 78 ± 10* 30 ± 6* a 173 ± 35a

57 ± 13* a b 67 ± 12*b 26 ± 9 143 ± 25a b

42 ± 15* a b c 54 ± 14*b c 23 ± 9 b 138 ± 55a b

0.90 ± 18*

0.90 ± 19*

0.90 ± 15*

0.89 ± 24*

-

65 ± 16 8.7 ± 2.1

60 ± 6 8.0 ± 0.8

67 ± 9 8.9 ± 1.2

78 ± 11 10.4 ± 1.5a

84 ± 14 a 11.2 ± 1.9a b

7.61 ± 0.07

7.29 ± 0.09*

7.37 ± 0.05*

7.30 ± 0.09*

7.20 ± 0.07* a b

7.17 ± 0.05* a b c

81 ± 10* 10.8 ± 1.3*

97 ± 15* 12.9 ± 2.0*

120 ± 25* a b 16.0 ± 3.3* a b

138 ± 22* a b c 18.4 ± 2.9* a b

EP

PEʹCO2

1.6 MACSEVO

TE D

T

1.3 MACSEVO

SC

Unit

M AN U

Variable

RI PT

408

ab

PaCO2

mmHg kPa

40 ± 7 5.3 ± 0.9

PaO2

mmHg

94 ± 2.2

285 ± 117*

279 ± 104*

287 ± 98*

282 ± 98*

264 ± 109*

kPa

12.5 ± 0.3

38.0 ± 15.6*

37.2 ± 13.9*

39.6 ± 13.1*

37.6 ± 13.1*

35.2 ± 14.5*

% mmol L-1

94.2 ± 2.2

99.5 ± 0.5

99.7 ± 0.5

99.2 ± 1.9

99.4 ± 0.7

98.6 ± 1.3

36.5 ± 6.2 14.8 ± 6.5

42.5 ± 5.4* 11.5 ± 6.3

39.8 ± 5.4* 16.2 ± 7.5a

42.1 ± 7.0* 13.5 ± 7.9

42.7 ± 4.7* 10.0 ± 4.5

47.7 ± 7.8* 12.9 ± 7.0

BE

-1

mmol L

AC C

SaO2 HCO3-

92 ± 16* 12.3 ± 2.1*

ACCEPTED MANUSCRIPT

+

K

Cl Hb

mEq L-1 -1

mEq L mEq L-1 g dL-1

150 ± 5

152 ± 5

154 ± 5

154 ± 7

153 ± 7

156 ± 9

4.0 ± 0.2 118 ± 4 9.0 ± 0.8

3.9 ± 0.5 117 ± 3 6.3 ± 1.0*

3.9 ± 0.4 118 ± 3 6.4 ± 0.8*

4.1 ± 0.5 118 ± 5 6.6 ± 1.2*

4.2 ± 0.3 117 ± 4 6.3 ± 1.0*

4.3 ± 0.3 117 ± 5 6.6 ± 1.2*

410

RI PT

Na+

Displayed are the effects of increasing expired sevoflurane concentrations (FEʹSevo in MACSEVO multiples) on oesophageal body temperature (T, °C),

412

heart rate (HR), systolic (SAP), diastolic (DAP) and mean (MAP) arterial blood pressures (mmHg), respiratory rate (fR, minute-1), minute ventilation

413

(Vሶ E , in mL·kg-1·minute-1), partial pressure of end-tidal CO2 (PEʹCO2, mmHg, kPa), arterial pH, partial pressure of arterial CO2 (PaCO2, mmHg, kPa),

414

partial pressure of arterial O2 (PaO2, mmHg), arterial oxygen saturation (SaO2, %), arterial bicarbonate (HCO3-, mmol L-1), and arterial base excess

415

(BE, mmol L-1) as well as the plasma electrolyte concentrations for Na+, K+, and Cl- (in mEq L-1) and total hemoglobin (Hb, in g dL-1). Data were

416

recorded prior to induction of anesthesia in awake animals and then after exposure of the animals to increasing doses of sevoflurane. Values are means

417

± SD of 10 sheep. Significant differences from values recorded in awake animals: *P < 0.05. Significant differences from values recorded in animals

418

exposed to an ETSEVO concentration of 0.75 MACSEVO: aP < 0.05. Significant differences from values recorded in animals exposed to an FEʹSevo

419

concentration of 1.0 MACSEVO: bP < 0.05. Significant differences from values recorded in animals exposed to an FEʹSevo concentration of 1.3

420

FEʹSevo: cP < 0.05. Significant differences from values recorded in animals exposed to FEʹSevo concentration of 1.6 MACSEVO: dP < 0.05.

M AN U

TE D

EP AC C

421 422

SC

411