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Anaesthetic complications in pigs undergoing MRI guided convection enhanced drug delivery to the brain: a case series
Veterinary Anaesthesia and Analgesia, 2012
doi:10.1111/j.1467-2995.2012.00767.x
CASE REPORT
Anaesthetic complications in pigs undergoing MRI guided convection enhanced drug delivery to the brain: a case series Alan Jones*, Alison Bienemann , Neil Baruaà, Pamela J Murison* & Steven Gillà *School of Veterinary Sciences, University of Bristol, Bristol, UK Functional Neurosurgery Research Group, University of Bristol, Bristol, UK àDepartment of Neurosurgery, Frenchay Hospital, Bristol, UK
Correspondence: Pamela Murison, School of Clinical Veterinary Science, University of Bristol, BS8 1TH, Bristol, UK. E-mail: [email protected]
Abstract Observations A total of 13 intracerebral infusions were performed at approximately 1 month intervals in three NIH miniature pigs over the age range of 31–59 weeks. Pigs received azaperone and ketamine premedication to allow venous cannulation and propofol induction of anaesthesia. Anaesthesia was maintained with isoflurane throughout cranial surgery and MRI scanning. Physiological monitoring during surgery consisted of blood pressure, pulse, temperature and oxygen saturation monitoring, ECG and capnography. Analgesia consisted of meloxicam and morphine. However, during MRI scanning blood pressure and ECG monitoring had to be discontinued. Anaesthetized pigs underwent intermittent intraputamenal convection enhanced delivery (CED) of gadolinium with real-time magnetic resonance imaging. Progressive tachycardia was consistently observed in all pigs during CED with a mean ± SD maximum increase of 41 ± 22 beats minute)1 from a baseline heart rate of 96 ± 9 minute)1. The heart rate remained elevated until recovery. A mean reduction in body temperature of 2.8 ± 0.6 °C from the start of anaesthesia was also observed during the period of MRI scanning. All pigs recovered from anaesthesia smoothly and heart rates returned to normal during the recovery period.
Conclusions Hypothermia is common in pigs undergoing this sedation and anaesthesia protocol. Convection enhanced delivery of drugs in healthy anaesthetized pigs may result in tachycardia. Keywords adverse reactions, anaesthesia, heart rate, hypothermia, pig.
Introduction The pig increasingly is being used as a model for the study of neurological disorders including Parkinson’s Disease, Alzheimer’s Disease and neurotrauma. Our research group has recently described a technique guided by magnetic resonance imaging (MRI) for the study of convection-enhanced drug delivery in Large White/Landrace pigs (White et al. 2011). Convection-enhanced delivery (CED) describes a direct method of drug delivery to the brain through intraparenchymal microcatheters. By establishing a pressure gradient at the tip of the infusion catheter, CED confers several advantages over conventional intracerebral drug injection techniques (Bobo et al. 1994). Optimising the volume of distribution of an infusate delivered by CED is paramount to successful translation from pre-clinical to clinical trials. The non-human primate (NHP) is commonly used as a model for the study of CED. However, the larger 1
Complications associated with convection enhanced delivery A Jones et al.
volume of the pig brain compared to the NHP means that the pig also represents a clinicallyrelevant model for the study of CED. Whilst there are advantages in using pigs for the study of experimental neurological interventions, there are considerable anaesthetic and perioperative challenges, which must be addressed in order to facilitate safe and effective MRI-guided convectionenhanced delivery. This article describes complications observed during anaesthesia of pigs undergoing MRI-guided CED. Case descriptions All work was conducted in accordance with the Animals (Scientific Procedures) Act (1986) and with the authority of appropriate Home Office project and personal licences. Study protocols were pre-approved by the University of Bristol Ethical Review Board. Three miniature pigs (National Institute for Health, NIH) were studied. They were 31–59 weeks old and weighed 46–109 kg over the course of the study. An accurate pre-anaesthetic weight was measured and, whilst in the weigh crate, local anaesthetic cream EMLA (Astra Zeneca UK Ltd., UK) was applied to the pinna of one of the ears and covered with occlusive material. Pre-anaesthetic medication comprising of azaparone (2 mg kg)1, Janssen Ltd., UK) and ketamine (10 mg kg)1, Vetoquinol Ltd., UK) were mixed in the same syringe and administered by deep intramuscular injection into the dorso-lateral neck muscles. Profound sedation was achieved in all pigs. An intravenous (IV) catheter was placed into an ear vein, a T-port attached and secured with adhesive tape. Propofol (Abbot Laboratories, UK) was used IV to induce anaesthesia, and was titrated to effect (dose required mean 1.87 ± SD 0.6 mg kg)1). For endotracheal intubation, pigs were positioned in sternal recumbency as described by Theisen et al. (2009). Endotracheal tube sizes ranged from 10 to 12 mm internal diameter. Anaesthesia was maintained with isoflurane (Isoflo, Abbot Laboratories, UK) in oxygen delivered via a circle breathing system. Vaporiser setting was around 1.5%, altered as required to maintain a relaxed jaw tone and sluggish palpebral reflex. Morphine 0.1 mg kg)1 (Morphine sulphate, Martindale Pharmaceuticals Ltd., UK) by slow IV injection, and meloxicam 0.4 mg kg)1 slow IV, 2
(Metacam 20 mg mL)1 solution for injection, Boehringer Ingelheim Vet Medica GmbH., Germany) were administered as part of a multimodal analgesia component of the anaesthetic protocol. Analgesics were administered within the first 10 minutes of anaesthesia. During surgery physiological monitoring consisted of non-invasive oscillometric blood pressure measurement, pulse oximetry using an adhesive probe (LNOP Adt; Masimo Corp, CA, USA) on the ear contralateral to the IV access to measure haemoglobin oxygen saturation (SpO2), electrocardiography (ECG), rectal temperature and side stream capnography (Datascope Passport II with gas module; Datascope Corp, NJ, USA). The heart or pulse rate was taken from the ECG or the pulse oximeter as available; both values when available together agreed. The term heart rate (HR) is applied to both measurements throughout this report. The gas module of the Datascope also provided inspired and expired isoflurane concentration (not recorded). Monitoring during MRI was achieved using capnography and SpO2 measurement at the tail using a Nonin 8600FO pulse oximeter with fibreoptic cable sensor (Proact Medical Ltd., UK). Pigs were covered in bubble wrap and synthetic fleece bedding (Vetbed, Keith Rushfirth, UK) to reduce heat loss through convection. A heat mat (National Veterinary Services, UK) covered in fleece bedding was placed under the pigs to reduce conductive heat loss during surgical procedures. Rectal temperature was measured using a digital thermometer in the recovery period. Esmolol (Orpha – Devel Handels und Vertiebs GmbH., Austria) was available for managing tachycardia if required. Intravenous fluids (Hartmanns solution, Dechra Veterinary Products, UK) were administered at a rate of 10 mL kg)1 hour)1 throughout anaesthesia. Head immobilisation, MRI imaging, CED and catheter implantation into the putamen were performed as previously described (White et al. 2011), using a custom-made head frame, Pathfinder robotic arm (Prosurgics, UK) and surgical planning software (Mayfield ACCISS-II). Intracranial catheters were attached to subcutaneous septa to facilitate repeat infusion. All infusions were performed with real-time MR imaging. Imaging was performed with a 1.5T MRI scanner (Intera, Philips,UK). Following catheter implantation, infusions of GadoliniumDTPA were performed in order to allow verification of catheter tip position and MRI analysis of infusate distribution. Gadolinium-DTPA infusions were
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
Complications associated with convection enhanced delivery A Jones et al.
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commenced at a rate of 0.5 lL minute)1 and flow rates increased at 5 minute intervals to 1, 2.5 and 5 lL minute)1. The infusion then was continued at a maximum flow rate of 5 lL minute)1 in order to deliver a total volume of 120 lL into a single putamen. Gadolinium-DTPA infusions were repeated at 1 month intervals over a period of 5 months by percutaneous insertion of a needle into the subcutaneous septa or by elevation of a skin flap if septa were not easily palpated. One pig was euthanased after the third anaesthetic as it was apparent the catheter had failed, hence a total of 13 anaesthetics are included in analysis. During CED of 0.2% Gadolinium-DTPA into the putamen we observed a consistent pattern of tachycardia (Fig 1) with a mean ± SD increase in HR of 41 ± 22 (range 15–74) beats minute )1 from the HR before CED commenced. For each anaesthetic period, the heart rate readings were compared statistically before and after the CED. In order to do this, five HR readings were taken at 5 minute intervals before and after the CED and a mean calculated for each. ‘Before’ readings were taken from 20 to 40 minutes after anaesthetic induction to allow a period of stabilisation, ‘after’ readings were taken immediately after the CED was stopped. The means were compared using a paired t-test. The change in HR was statistically significant (p < 0.001). Respiratory rate, SpO2 and end tidal CO2 were stable over the study period (Fig. 1). During MRI scanning, ECG monitoring was not available, but no irregularity in pulse was observed. Sinus tachycardia was the only ECG abnormality seen during the periods where the ECG was observed. Duration of anaesthesia (from propofol injection to extubation) was a mean of 304 ± 55 minutes. A reduction in body temperature was seen in all animals during the period of MRI scanning until transfer to recovery pens. The mean fall in body temperature from the start of anaesthesia to the last recorded temperature on recovery was 2.8 ± 0.6 °C. Mean temperature before entering the MRI scanner was 36.1 ± 0.5 °C, and on return to theatre was 35.8 ± 0.8 °C. Pigs recovered from anaesthesia in a warmed, straw bedded pen and positioned on a soft material stretcher to reduce the potential for dust inhalation. The trachea was extubated when the palpebral reflex returned. Temperature measurement and active warming were continued until the pigs were able to stand. Neurological observations included response to finger clicks behind the ears, assessment
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Figure 1 Mean ± Standard Deviation of end tidal CO2 (a), respiratory rate (b), oxygen saturation (c) and heart rate (d) in pigs undergoing anaesthesia for Convection Enhanced Delivery (CED) of gadolinium. A total of 13 infusions were performed in 3 animals, however oxygen saturation data were not available for one anaesthetic due to technical difficulties. Mean duration of CED shown in figure d.
of visual function, pupillary responses and sense of smell. Locomotion scoring formed part of both pain assessment and neurological examination. Heart rate was monitored intermittently and returned to pre-anaesthetic values in approximately 30 minutes from extubation.
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
3
Complications associated with convection enhanced delivery A Jones et al.
Pain assessment was carried out, as described by Murison et al. (2009), after surgical procedures, by gentle palpation of the forehead moving closer to the wound margin with a gentle increase in pressure whilst observing for a response. Assessments using locomotor and behavioural factors (e.g. avoiding contact, reduced interaction with care staff) were used in the determination of analgesic requirements after all procedures. A single daily oral dose of meloxicam (Metacam 1.5 mg mL)1 Oral Suspension for Dogs, Boehringer Ingelheim Ltd, UK (0.4 mg kg)1) was administered via a syringe for 2 days following surgery. Pigs were regularly observed by animal care staff. All animals successfully recovered from anaesthesia following infusion, without evidence in the recovery period of adverse cardiovascular effect. and no pig required administration of esmolol to control HR. Pigs were stiff in gait after anaesthesia for a few hours, but showed no signs of continuing pain. One pig developed transient knuckling of the right rear foot following the procedure - this pig was referred for an orthopaedic opinion. No diagnosis was made and a full recovery was noted after 3 days. However, additional care was taken during positioning of the animals for surgery and MRI in subsequent procedures. Discussion The elevation in HR associated with CED was unexpected. Although no pigs suffered adverse consequences, tachycardia increases cardiac work and cardiac oxygen demand. The reason for this elevation is unclear. Tachycardia has been demonstrated in response to raised intracranial pressure in a number of neurosurgical procedures, and the bradycardia of Cushing’s triad is known to be a late-stage phenomenon (Kalmar et al. 2009). However, a tachycardic response and compensatory hypertension appears unlikely after such a localised infusion. Rodent studies have demonstrated tachycardia in response to dopamine release within the striatum, and also that striatal dopamine release is affected by information from arterial baroreceptors. Yang & Lin (1993) demonstrated that elevation of carotid blood pressure resulted in increased dopamine release within the striatum of rats. Whether an increase in arterial pressure as a result of raised ICP during intraputamenal CED contributed to the tachycardia seen in this study is difficult to ascertain in the 4
absence of ICP and arterial blood pressure monitoring during the infusions. Striatal dopamine release has also been demonstrated in response to ischaemia. Ahn et al. (1991) studied the effect of cerebral ischemia on dopamine release in gerbils and found that both early ischaemia and reperfusion resulted in biphasic dopamine release within the striatum. It could be postulated that the high volume CED infusions in this study resulted in a period of relative hypoxia within the putamen resulting in dopamine release. If dopamine release within the striatum is the cause of the cardiovascular effects seen in this study, tachycardia may be mediated by an increase in sympathetic efferent activity and reduced vagal efferent activity. The ultimate aim of the research of this current study is the translation of intraputamenal CED of therapeutics for Parkinson’s Disease, which is characterised by depletion of dopaminergic neurones within the nigrostriatal pathways. Consequently, it is unlikely that intraputamenal CED would cause a dopamine-mediated tachycardia in clinical trials. Drugs used in these pigs may affect HR. Azaperone causes vasodilation, which may affect blood pressure and induce a compensatory increase in heart rate. Morphine may reduce heart rate, in common with most opioids or if histamine is released after excessively rapid administration this could lower blood pressure and increase HR. However, the timings of the changes observed in this case report were such that it would appear the drug administration was not a cause (changes occurring approximately 1 hour after administration of azaperone and 30 minutes after IV administration of morphine). The loss of blood pressure measurement data during MRI is of concern and the search for suitable extension tubing that does not give a false low reading is on-going. Comparison of blood pressure and HR may have provided more data for proposing a mechanism for the observed tachycardia in this study. Blood pressure measurement and ECG monitoring were discontinued during scanning as MRI compatible cables were not available and comparison of the results of the oscillometric blood pressure measurement were inconsistent using extended tubing. Pulse rate and blood pressure are both used in the evaluation of nociception during anaesthesia in pigs as described by Henning et al. (2001). However, an unrelated tachycardia may confound such assessments. A nociceptive response could have caused the increase in heart rates, however alterations in
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
Complications associated with convection enhanced delivery A Jones et al.
vaporiser setting and additional opioid analgesic administration did not reduce the HR in pilot studies. Hypoventilation was common in these pigs. Retention of carbon dioxide tends to cause an increase in heart rate (related to epinephrine release) (Price 1960; Bille-Brahe et al. 1976). Hypoventilation tended to be consistent, with stable end-tidal CO2 values before the infusion of gadolinium. Furthermore there was no change in end-tidal CO2 during intracerebral infusion, so although hypoventilation could influence heart rate this appears unlikely to have been the cause of tachycardia in these pigs. Previous study cohorts undergoing CED of viral vectors have required slow injection of esmolol for the management of tachycardia (A Jones, A Bienemann, N Barua, PJ Murison and S Gill, unpublished data), suggesting that the nature of the infusate is not the cause of tachycardia. Intravenous use of gadolinium contrast during MRI rarely causes cardiovascular changes in dogs (Pollard et al. 2008; Mair et al. 2010). Anaphylactic type responses to gadolinium based contrast (including tachycardia) have been reported in dogs (Girard & Leece 2010). Blood pressure measurements would have been useful to detect hypotension, although other signs of anaphylaxis (e.g. facial oedema) were not observed in these pigs. The requirement for real-time MRI scanning during CED in this study protocol placed significant limitations on the strategies available for maintenance of normothermia, by preventing the use of active warming whilst in the scanner. Thermal maintenance was restricted to reducing heat loss by insulation alone. Radiant heat loss is proportional to the fourth power of the temperature difference between the patient and the ambient environment (Sessler 2001). To reduce radiant heat loss, multiple insulating layers were placed over the pigs. Mild core hypothermia has been associated with an increase in circulating catecholamine concentrations leading to tachycardia, systemic vascular constriction and hypertension (Frank et al. 1995). Therefore hypothermia may have been a contributory factor to the tachycardic responses seen during CED. Significant heat loss had occurred before moving pigs to the MRI scanner. The vasodilation produced by azaperone is likely to have contributed by promoting conductive and convective heat losses, and the ambient temperature after sedation and before insulation may also have contributed.
Although the room temperature was not recorded, subjectively the sedation area was colder than the operating theatre or MRI scanner. Warming the pigs during the recovery period appeared to improve the speed of recovery from the anaesthetic and the stability of initial gait. However, replacement of body temperature by externally applied thermal energy is of debatable benefit in hypothermic animals as peripheral vasoconstriction can reduce the efficacy of this strategy (Sessler 2001). During the latter part of the study, extension tubing was added to the bag mount of the circle breathing system to allow intermittent ‘sighs’ to be applied from outside the scanner room in order to facilitate CO2 elimination. Hypoventilation was common, and may have been related to the resistance of the breathing system, patient position in the MRI scanner and possibly the development of hypothermia. Conclusion Tachycardia and hypothermia are potential complications associated with MRI guided convection enhanced drug delivery trials in anaesthetized pigs. Acknowledgements The authors would like to thank Mr Lionel Wheeler and Mr Andy Downes for their skilled handling, husbandry and day to day care of these pigs during this study. References Ahn SS, Blaha CD, Alkire MT et al. (1991) Biphasic striatal dopamine release during transient ischemia and reperfusion in gerbils. Stroke 22, 674–679. Bille-Brahe NE, Sorensen MB, Rorth M et al. (1976) Cardiovascular effects of induced hypercarbia during halothane-nitrous oxide anaesthesia. Acta Chir Scand Suppl 472, 127–132. Bobo RH, Laske DW, Akbasak A et al. (1994) Convectionenhanced delivery of macromolecules in the brain. Proc Natl Acad Sci USA 91, 2076–2080. Frank SM, Higgins MS, Breslow MJ et al. (1995) The catecholamine, cortisol, and hemodynamic responses to mild perioperative hypothermia. A randomized clinical trial. Anesthesiology 82, 83–93. Girard NM, Leece EA (2010) Suspected anaphylactoid reaction following intravenous administration of gadolinium-based contrast agent in three dogs undergoing
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
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magnetic resonance imaging. Vet Anaesth Analg 37, 352–356. Henning AH, Asbjoern T, Henning M (2001) Electroencephalographic and cardiovascular indicators of nociception during isoflurane anaesthesia in pigs. Vet Anaesth Analg 28, 126–131. Kalmar AF, De Ley G, Van Den Broecke C et al. (2009) Influence of an increased intracranial pressure on cerebral and systemic haemodynamics during endoscopic neurosurgery: an animal model. Br J Anaesth 102, 361– 368. Mair AR, Woolley J, Martinez M (2010) Cardiovascular effects ofitnravenous gadolinium administration to anaesthetized dogs undergoing magnetic resonance imaging. Vet Anaesth Analg 37, 337–341. Murison PJ, Jones A, Mitchard L et al. (2009) Development of perioperative care for pigs undergoing laryngeal transplantation: a case series. Lab Anim 43, 338–343. Pollard RE, Puchalski SM, Pascoe PJ (2008) Hemodynamic and serum biochemical alterations associated with
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intravenous administration of three types of contrast media in anesthetized dogs. Am J Vet Res 69, 1268– 1273. Price HL (1960) Effects of carbon dioxide on the cardiovascular system. Anesthesiology 21, 652–663. Sessler DI (2001) Complications and treatment of mild hypothermia. Anesthesiology 95, 531–543. Theisen MM, Maas M, Hartlage MA et al. (2009) Ventral recumbency is crucial for fast and safe orotracheal intubation in laboratory swine. Lab Anim 43, 96–101. White E, Wooley M, Bienemann A et al. (2011) A robust MRI-compatible system to facilitate highly accurate stereotactic administration of therapeutic agents to targets within the brain of a large animal model. J Neurosci Methods 195, 78–87. Yang JJ, Lin MT (1993) Arterial baroreceptor information affects striatal dopamine release measured by voltammetry in rats. Neurosci Lett 157, 21–24. Received 17 June 2011; accepted 2 December 2011.
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
doi:10.1111/j.1467-2995.2012.00767.x
CASE REPORT
Anaesthetic complications in pigs undergoing MRI guided convection enhanced drug delivery to the brain: a case series Alan Jones*, Alison Bienemann , Neil Baruaà, Pamela J Murison* & Steven Gillà *School of Veterinary Sciences, University of Bristol, Bristol, UK Functional Neurosurgery Research Group, University of Bristol, Bristol, UK àDepartment of Neurosurgery, Frenchay Hospital, Bristol, UK
Correspondence: Pamela Murison, School of Clinical Veterinary Science, University of Bristol, BS8 1TH, Bristol, UK. E-mail: [email protected]
Abstract Observations A total of 13 intracerebral infusions were performed at approximately 1 month intervals in three NIH miniature pigs over the age range of 31–59 weeks. Pigs received azaperone and ketamine premedication to allow venous cannulation and propofol induction of anaesthesia. Anaesthesia was maintained with isoflurane throughout cranial surgery and MRI scanning. Physiological monitoring during surgery consisted of blood pressure, pulse, temperature and oxygen saturation monitoring, ECG and capnography. Analgesia consisted of meloxicam and morphine. However, during MRI scanning blood pressure and ECG monitoring had to be discontinued. Anaesthetized pigs underwent intermittent intraputamenal convection enhanced delivery (CED) of gadolinium with real-time magnetic resonance imaging. Progressive tachycardia was consistently observed in all pigs during CED with a mean ± SD maximum increase of 41 ± 22 beats minute)1 from a baseline heart rate of 96 ± 9 minute)1. The heart rate remained elevated until recovery. A mean reduction in body temperature of 2.8 ± 0.6 °C from the start of anaesthesia was also observed during the period of MRI scanning. All pigs recovered from anaesthesia smoothly and heart rates returned to normal during the recovery period.
Conclusions Hypothermia is common in pigs undergoing this sedation and anaesthesia protocol. Convection enhanced delivery of drugs in healthy anaesthetized pigs may result in tachycardia. Keywords adverse reactions, anaesthesia, heart rate, hypothermia, pig.
Introduction The pig increasingly is being used as a model for the study of neurological disorders including Parkinson’s Disease, Alzheimer’s Disease and neurotrauma. Our research group has recently described a technique guided by magnetic resonance imaging (MRI) for the study of convection-enhanced drug delivery in Large White/Landrace pigs (White et al. 2011). Convection-enhanced delivery (CED) describes a direct method of drug delivery to the brain through intraparenchymal microcatheters. By establishing a pressure gradient at the tip of the infusion catheter, CED confers several advantages over conventional intracerebral drug injection techniques (Bobo et al. 1994). Optimising the volume of distribution of an infusate delivered by CED is paramount to successful translation from pre-clinical to clinical trials. The non-human primate (NHP) is commonly used as a model for the study of CED. However, the larger 1
Complications associated with convection enhanced delivery A Jones et al.
volume of the pig brain compared to the NHP means that the pig also represents a clinicallyrelevant model for the study of CED. Whilst there are advantages in using pigs for the study of experimental neurological interventions, there are considerable anaesthetic and perioperative challenges, which must be addressed in order to facilitate safe and effective MRI-guided convectionenhanced delivery. This article describes complications observed during anaesthesia of pigs undergoing MRI-guided CED. Case descriptions All work was conducted in accordance with the Animals (Scientific Procedures) Act (1986) and with the authority of appropriate Home Office project and personal licences. Study protocols were pre-approved by the University of Bristol Ethical Review Board. Three miniature pigs (National Institute for Health, NIH) were studied. They were 31–59 weeks old and weighed 46–109 kg over the course of the study. An accurate pre-anaesthetic weight was measured and, whilst in the weigh crate, local anaesthetic cream EMLA (Astra Zeneca UK Ltd., UK) was applied to the pinna of one of the ears and covered with occlusive material. Pre-anaesthetic medication comprising of azaparone (2 mg kg)1, Janssen Ltd., UK) and ketamine (10 mg kg)1, Vetoquinol Ltd., UK) were mixed in the same syringe and administered by deep intramuscular injection into the dorso-lateral neck muscles. Profound sedation was achieved in all pigs. An intravenous (IV) catheter was placed into an ear vein, a T-port attached and secured with adhesive tape. Propofol (Abbot Laboratories, UK) was used IV to induce anaesthesia, and was titrated to effect (dose required mean 1.87 ± SD 0.6 mg kg)1). For endotracheal intubation, pigs were positioned in sternal recumbency as described by Theisen et al. (2009). Endotracheal tube sizes ranged from 10 to 12 mm internal diameter. Anaesthesia was maintained with isoflurane (Isoflo, Abbot Laboratories, UK) in oxygen delivered via a circle breathing system. Vaporiser setting was around 1.5%, altered as required to maintain a relaxed jaw tone and sluggish palpebral reflex. Morphine 0.1 mg kg)1 (Morphine sulphate, Martindale Pharmaceuticals Ltd., UK) by slow IV injection, and meloxicam 0.4 mg kg)1 slow IV, 2
(Metacam 20 mg mL)1 solution for injection, Boehringer Ingelheim Vet Medica GmbH., Germany) were administered as part of a multimodal analgesia component of the anaesthetic protocol. Analgesics were administered within the first 10 minutes of anaesthesia. During surgery physiological monitoring consisted of non-invasive oscillometric blood pressure measurement, pulse oximetry using an adhesive probe (LNOP Adt; Masimo Corp, CA, USA) on the ear contralateral to the IV access to measure haemoglobin oxygen saturation (SpO2), electrocardiography (ECG), rectal temperature and side stream capnography (Datascope Passport II with gas module; Datascope Corp, NJ, USA). The heart or pulse rate was taken from the ECG or the pulse oximeter as available; both values when available together agreed. The term heart rate (HR) is applied to both measurements throughout this report. The gas module of the Datascope also provided inspired and expired isoflurane concentration (not recorded). Monitoring during MRI was achieved using capnography and SpO2 measurement at the tail using a Nonin 8600FO pulse oximeter with fibreoptic cable sensor (Proact Medical Ltd., UK). Pigs were covered in bubble wrap and synthetic fleece bedding (Vetbed, Keith Rushfirth, UK) to reduce heat loss through convection. A heat mat (National Veterinary Services, UK) covered in fleece bedding was placed under the pigs to reduce conductive heat loss during surgical procedures. Rectal temperature was measured using a digital thermometer in the recovery period. Esmolol (Orpha – Devel Handels und Vertiebs GmbH., Austria) was available for managing tachycardia if required. Intravenous fluids (Hartmanns solution, Dechra Veterinary Products, UK) were administered at a rate of 10 mL kg)1 hour)1 throughout anaesthesia. Head immobilisation, MRI imaging, CED and catheter implantation into the putamen were performed as previously described (White et al. 2011), using a custom-made head frame, Pathfinder robotic arm (Prosurgics, UK) and surgical planning software (Mayfield ACCISS-II). Intracranial catheters were attached to subcutaneous septa to facilitate repeat infusion. All infusions were performed with real-time MR imaging. Imaging was performed with a 1.5T MRI scanner (Intera, Philips,UK). Following catheter implantation, infusions of GadoliniumDTPA were performed in order to allow verification of catheter tip position and MRI analysis of infusate distribution. Gadolinium-DTPA infusions were
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
Complications associated with convection enhanced delivery A Jones et al.
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commenced at a rate of 0.5 lL minute)1 and flow rates increased at 5 minute intervals to 1, 2.5 and 5 lL minute)1. The infusion then was continued at a maximum flow rate of 5 lL minute)1 in order to deliver a total volume of 120 lL into a single putamen. Gadolinium-DTPA infusions were repeated at 1 month intervals over a period of 5 months by percutaneous insertion of a needle into the subcutaneous septa or by elevation of a skin flap if septa were not easily palpated. One pig was euthanased after the third anaesthetic as it was apparent the catheter had failed, hence a total of 13 anaesthetics are included in analysis. During CED of 0.2% Gadolinium-DTPA into the putamen we observed a consistent pattern of tachycardia (Fig 1) with a mean ± SD increase in HR of 41 ± 22 (range 15–74) beats minute )1 from the HR before CED commenced. For each anaesthetic period, the heart rate readings were compared statistically before and after the CED. In order to do this, five HR readings were taken at 5 minute intervals before and after the CED and a mean calculated for each. ‘Before’ readings were taken from 20 to 40 minutes after anaesthetic induction to allow a period of stabilisation, ‘after’ readings were taken immediately after the CED was stopped. The means were compared using a paired t-test. The change in HR was statistically significant (p < 0.001). Respiratory rate, SpO2 and end tidal CO2 were stable over the study period (Fig. 1). During MRI scanning, ECG monitoring was not available, but no irregularity in pulse was observed. Sinus tachycardia was the only ECG abnormality seen during the periods where the ECG was observed. Duration of anaesthesia (from propofol injection to extubation) was a mean of 304 ± 55 minutes. A reduction in body temperature was seen in all animals during the period of MRI scanning until transfer to recovery pens. The mean fall in body temperature from the start of anaesthesia to the last recorded temperature on recovery was 2.8 ± 0.6 °C. Mean temperature before entering the MRI scanner was 36.1 ± 0.5 °C, and on return to theatre was 35.8 ± 0.8 °C. Pigs recovered from anaesthesia in a warmed, straw bedded pen and positioned on a soft material stretcher to reduce the potential for dust inhalation. The trachea was extubated when the palpebral reflex returned. Temperature measurement and active warming were continued until the pigs were able to stand. Neurological observations included response to finger clicks behind the ears, assessment
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Figure 1 Mean ± Standard Deviation of end tidal CO2 (a), respiratory rate (b), oxygen saturation (c) and heart rate (d) in pigs undergoing anaesthesia for Convection Enhanced Delivery (CED) of gadolinium. A total of 13 infusions were performed in 3 animals, however oxygen saturation data were not available for one anaesthetic due to technical difficulties. Mean duration of CED shown in figure d.
of visual function, pupillary responses and sense of smell. Locomotion scoring formed part of both pain assessment and neurological examination. Heart rate was monitored intermittently and returned to pre-anaesthetic values in approximately 30 minutes from extubation.
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
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Complications associated with convection enhanced delivery A Jones et al.
Pain assessment was carried out, as described by Murison et al. (2009), after surgical procedures, by gentle palpation of the forehead moving closer to the wound margin with a gentle increase in pressure whilst observing for a response. Assessments using locomotor and behavioural factors (e.g. avoiding contact, reduced interaction with care staff) were used in the determination of analgesic requirements after all procedures. A single daily oral dose of meloxicam (Metacam 1.5 mg mL)1 Oral Suspension for Dogs, Boehringer Ingelheim Ltd, UK (0.4 mg kg)1) was administered via a syringe for 2 days following surgery. Pigs were regularly observed by animal care staff. All animals successfully recovered from anaesthesia following infusion, without evidence in the recovery period of adverse cardiovascular effect. and no pig required administration of esmolol to control HR. Pigs were stiff in gait after anaesthesia for a few hours, but showed no signs of continuing pain. One pig developed transient knuckling of the right rear foot following the procedure - this pig was referred for an orthopaedic opinion. No diagnosis was made and a full recovery was noted after 3 days. However, additional care was taken during positioning of the animals for surgery and MRI in subsequent procedures. Discussion The elevation in HR associated with CED was unexpected. Although no pigs suffered adverse consequences, tachycardia increases cardiac work and cardiac oxygen demand. The reason for this elevation is unclear. Tachycardia has been demonstrated in response to raised intracranial pressure in a number of neurosurgical procedures, and the bradycardia of Cushing’s triad is known to be a late-stage phenomenon (Kalmar et al. 2009). However, a tachycardic response and compensatory hypertension appears unlikely after such a localised infusion. Rodent studies have demonstrated tachycardia in response to dopamine release within the striatum, and also that striatal dopamine release is affected by information from arterial baroreceptors. Yang & Lin (1993) demonstrated that elevation of carotid blood pressure resulted in increased dopamine release within the striatum of rats. Whether an increase in arterial pressure as a result of raised ICP during intraputamenal CED contributed to the tachycardia seen in this study is difficult to ascertain in the 4
absence of ICP and arterial blood pressure monitoring during the infusions. Striatal dopamine release has also been demonstrated in response to ischaemia. Ahn et al. (1991) studied the effect of cerebral ischemia on dopamine release in gerbils and found that both early ischaemia and reperfusion resulted in biphasic dopamine release within the striatum. It could be postulated that the high volume CED infusions in this study resulted in a period of relative hypoxia within the putamen resulting in dopamine release. If dopamine release within the striatum is the cause of the cardiovascular effects seen in this study, tachycardia may be mediated by an increase in sympathetic efferent activity and reduced vagal efferent activity. The ultimate aim of the research of this current study is the translation of intraputamenal CED of therapeutics for Parkinson’s Disease, which is characterised by depletion of dopaminergic neurones within the nigrostriatal pathways. Consequently, it is unlikely that intraputamenal CED would cause a dopamine-mediated tachycardia in clinical trials. Drugs used in these pigs may affect HR. Azaperone causes vasodilation, which may affect blood pressure and induce a compensatory increase in heart rate. Morphine may reduce heart rate, in common with most opioids or if histamine is released after excessively rapid administration this could lower blood pressure and increase HR. However, the timings of the changes observed in this case report were such that it would appear the drug administration was not a cause (changes occurring approximately 1 hour after administration of azaperone and 30 minutes after IV administration of morphine). The loss of blood pressure measurement data during MRI is of concern and the search for suitable extension tubing that does not give a false low reading is on-going. Comparison of blood pressure and HR may have provided more data for proposing a mechanism for the observed tachycardia in this study. Blood pressure measurement and ECG monitoring were discontinued during scanning as MRI compatible cables were not available and comparison of the results of the oscillometric blood pressure measurement were inconsistent using extended tubing. Pulse rate and blood pressure are both used in the evaluation of nociception during anaesthesia in pigs as described by Henning et al. (2001). However, an unrelated tachycardia may confound such assessments. A nociceptive response could have caused the increase in heart rates, however alterations in
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
Complications associated with convection enhanced delivery A Jones et al.
vaporiser setting and additional opioid analgesic administration did not reduce the HR in pilot studies. Hypoventilation was common in these pigs. Retention of carbon dioxide tends to cause an increase in heart rate (related to epinephrine release) (Price 1960; Bille-Brahe et al. 1976). Hypoventilation tended to be consistent, with stable end-tidal CO2 values before the infusion of gadolinium. Furthermore there was no change in end-tidal CO2 during intracerebral infusion, so although hypoventilation could influence heart rate this appears unlikely to have been the cause of tachycardia in these pigs. Previous study cohorts undergoing CED of viral vectors have required slow injection of esmolol for the management of tachycardia (A Jones, A Bienemann, N Barua, PJ Murison and S Gill, unpublished data), suggesting that the nature of the infusate is not the cause of tachycardia. Intravenous use of gadolinium contrast during MRI rarely causes cardiovascular changes in dogs (Pollard et al. 2008; Mair et al. 2010). Anaphylactic type responses to gadolinium based contrast (including tachycardia) have been reported in dogs (Girard & Leece 2010). Blood pressure measurements would have been useful to detect hypotension, although other signs of anaphylaxis (e.g. facial oedema) were not observed in these pigs. The requirement for real-time MRI scanning during CED in this study protocol placed significant limitations on the strategies available for maintenance of normothermia, by preventing the use of active warming whilst in the scanner. Thermal maintenance was restricted to reducing heat loss by insulation alone. Radiant heat loss is proportional to the fourth power of the temperature difference between the patient and the ambient environment (Sessler 2001). To reduce radiant heat loss, multiple insulating layers were placed over the pigs. Mild core hypothermia has been associated with an increase in circulating catecholamine concentrations leading to tachycardia, systemic vascular constriction and hypertension (Frank et al. 1995). Therefore hypothermia may have been a contributory factor to the tachycardic responses seen during CED. Significant heat loss had occurred before moving pigs to the MRI scanner. The vasodilation produced by azaperone is likely to have contributed by promoting conductive and convective heat losses, and the ambient temperature after sedation and before insulation may also have contributed.
Although the room temperature was not recorded, subjectively the sedation area was colder than the operating theatre or MRI scanner. Warming the pigs during the recovery period appeared to improve the speed of recovery from the anaesthetic and the stability of initial gait. However, replacement of body temperature by externally applied thermal energy is of debatable benefit in hypothermic animals as peripheral vasoconstriction can reduce the efficacy of this strategy (Sessler 2001). During the latter part of the study, extension tubing was added to the bag mount of the circle breathing system to allow intermittent ‘sighs’ to be applied from outside the scanner room in order to facilitate CO2 elimination. Hypoventilation was common, and may have been related to the resistance of the breathing system, patient position in the MRI scanner and possibly the development of hypothermia. Conclusion Tachycardia and hypothermia are potential complications associated with MRI guided convection enhanced drug delivery trials in anaesthetized pigs. Acknowledgements The authors would like to thank Mr Lionel Wheeler and Mr Andy Downes for their skilled handling, husbandry and day to day care of these pigs during this study. References Ahn SS, Blaha CD, Alkire MT et al. (1991) Biphasic striatal dopamine release during transient ischemia and reperfusion in gerbils. Stroke 22, 674–679. Bille-Brahe NE, Sorensen MB, Rorth M et al. (1976) Cardiovascular effects of induced hypercarbia during halothane-nitrous oxide anaesthesia. Acta Chir Scand Suppl 472, 127–132. Bobo RH, Laske DW, Akbasak A et al. (1994) Convectionenhanced delivery of macromolecules in the brain. Proc Natl Acad Sci USA 91, 2076–2080. Frank SM, Higgins MS, Breslow MJ et al. (1995) The catecholamine, cortisol, and hemodynamic responses to mild perioperative hypothermia. A randomized clinical trial. Anesthesiology 82, 83–93. Girard NM, Leece EA (2010) Suspected anaphylactoid reaction following intravenous administration of gadolinium-based contrast agent in three dogs undergoing
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
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magnetic resonance imaging. Vet Anaesth Analg 37, 352–356. Henning AH, Asbjoern T, Henning M (2001) Electroencephalographic and cardiovascular indicators of nociception during isoflurane anaesthesia in pigs. Vet Anaesth Analg 28, 126–131. Kalmar AF, De Ley G, Van Den Broecke C et al. (2009) Influence of an increased intracranial pressure on cerebral and systemic haemodynamics during endoscopic neurosurgery: an animal model. Br J Anaesth 102, 361– 368. Mair AR, Woolley J, Martinez M (2010) Cardiovascular effects ofitnravenous gadolinium administration to anaesthetized dogs undergoing magnetic resonance imaging. Vet Anaesth Analg 37, 337–341. Murison PJ, Jones A, Mitchard L et al. (2009) Development of perioperative care for pigs undergoing laryngeal transplantation: a case series. Lab Anim 43, 338–343. Pollard RE, Puchalski SM, Pascoe PJ (2008) Hemodynamic and serum biochemical alterations associated with
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intravenous administration of three types of contrast media in anesthetized dogs. Am J Vet Res 69, 1268– 1273. Price HL (1960) Effects of carbon dioxide on the cardiovascular system. Anesthesiology 21, 652–663. Sessler DI (2001) Complications and treatment of mild hypothermia. Anesthesiology 95, 531–543. Theisen MM, Maas M, Hartlage MA et al. (2009) Ventral recumbency is crucial for fast and safe orotracheal intubation in laboratory swine. Lab Anim 43, 96–101. White E, Wooley M, Bienemann A et al. (2011) A robust MRI-compatible system to facilitate highly accurate stereotactic administration of therapeutic agents to targets within the brain of a large animal model. J Neurosci Methods 195, 78–87. Yang JJ, Lin MT (1993) Arterial baroreceptor information affects striatal dopamine release measured by voltammetry in rats. Neurosci Lett 157, 21–24. Received 17 June 2011; accepted 2 December 2011.
Ó 2012 The Authors. Veterinary Anaesthesia and Analgesia Ó 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists