Veterinary Anaesthesia and Analgesia, 2015, 42, 242–249
doi:10.1111/vaa.12198
RESEARCH PAPER
Haemodynamic differences between pancuronium and vecuronium in an experimental pig model Kristoffer Grong*, Pirjo-Riitta Salminen*,†, Lodve Stangeland* & Geir O. Dahle*,† *Department of Clinical Science, University of Bergen, Bergen, Norway †Section of Cardiothoracic Surgery, Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
Correspondence: Kristoffer Grong, Department of Clinical Science, Faculty of Medicine and Dentistry, University of Bergen, Haukeland University Hospital, NO-5020 Bergen, Norway. E-mail: [email protected]
Abstract Objective To compare baseline cardiovascular function in anesthetised pigs using either pancuronium or vecuronium as a neuromuscular blocker. Study design Retrospective, non-randomized comparison. Animals Norwegian Land Race pigs (Sus scrofa domesticus) weighing mean 42 SD 3 kg. Methods One hundred and sixteen animals from four different research protocols premedicated with identical doses of ketamine, diazepam, atropine and isoflurane, and anaesthetised with pentobarbital, fentanyl, midazolam and N2O were arranged into three uniform groups with respect to neuromuscular blocking agent: pancuronium bolus of 0.063 mg kg 1 followed by 0.14 mg kg 1 hour 1 (n = 54), low-dose vecuronium 0.4 mg kg 1/0.2 mg kg 1 hour 1 (n = 29) and high-dose vecuronium 0.6 mg kg 1/0.3 mg kg 1 hour 1 (n = 33). Results The majority of cardiovascular parameters demonstrated no significant differences between groups. For heart rate, there was an overall group difference, p = 0.036. Dromotropy was low in the pancuronium group, with an increased normalised PR-interval compared to the high-dose vecuronium group, median 0.200 interquartile range (0.190, 0.215) versus 0.182 (0.166, 0.199), p < 0.05. Left ventricular compliance was increased in pancuro242
nium-treated animals, demonstrated as a reduction in the nonlinear end-diastolic pressure volume relationship b compared to both vecuronium groups, 0.021 (0.016, 0.025) versus 0.031 (0.025, 0.046) and 0.031 (0.022, 0.048), p < 0.05. The linear enddiastolic pressure volume relationship EDPVRlin was reduced as well in the pancuronium group, compared to the low-dose vecuronium group, 0.131 (0.116, 0.169) versus 0.181 (0.148, 0.247), p < 0.05. Conclusions There are only minor haemodynamic differences when using pancuronium compared to vecuronium in the fentanyl-pentobarbital-midazolam-N2O anesthetised domestic pigs. Furthermore, increasing doses of vecuronium have minimal haemodynamic effects. Clinical relevance Experimental studies in pigs using either pancuronium or vecuronium as a neuromuscular blocking agent are comparable with regard to cardiac and haemodynamic performance. Keywords cardiovascular, haemodynamic effects, neuromuscular blockers, pancuronium, pigs, vecuronium.
Introduction In cardiac research, the in vivo large animal model is an important tool for translating knowledge from basic research into clinical trials and practise. Together with the possibility of using more invasive
Neuromuscular blockade in pig models K Grong et al. techniques and methods developed for experimental research, one of the key points in such models is the standardization of the study population, allowing statistically powerful studies on relatively few subjects. Experimental cardiac research inevitably involves monitoring haemodynamic parameters as a way to evaluate cardiovascular performance. As anaesthetic agents have a particularly significant impact on the cardiovascular system, a strict standardised anaesthetic regime is essential for the predictability and stability of such research protocols. In addition to analgesic and hypnotic agents, general anaesthetic protocols may also include neuromuscular blocking agents. These are used to facilitate endotracheal intubation, prevent involuntary muscular contraction and disturbance of surgical procedures, as well as to minimise shivering during tepid/hypothermic cardiopulmonary bypass. The two muscle relaxants studied, pancuronium (Pavulon; Organon, Norway) and vecuronium (Norcuron; Organon, Norway), are both nondepolarising neuromuscular blocking agents. Pancuronium has been previously demonstrated to possess stimulatory haemodynamic effects in man (Ferres et al. 1987; Sethna et al. 1987; Virmani et al. 2006) and animals (Domenech et al. 1976). In cardiac surgery and experimental settings, these effects are beneficial, and thus pancuronium has been used widely (Murphy et al. 2002). Vecuronium seems to have only minor cardiovascular implications across species (Booij et al. 1980; Chen et al. 1991; Husby et al. 1996), as well as in increasing doses in man (Chen et al. 1991; Husby et al. 1996), although parasympatholytic effects have been reported in dogs (Narita et al. 1992). The use of muscle relaxants in experimental animal models is restricted, and should not be used unless the anaesthetic protocol has been meticulously evaluated without neuromuscular blocking agents in the species studied. This would ensure that sedation and analgesia is sufficient, thus preventing paralysis of the animal in a conscious/semiconscious state (Institute for Laboratory Animal Research 2010). An anaesthetic protocol allowing the use of muscular relaxation was documented prior to the introduction of muscle relaxants in our studies (Fannelop et al. 2004). Our research group has used pancuronium as a neuromuscular blocking agent in a porcine model related to tepid cardiopulmonary bypass, cardioplegic arrest and reperfusion, primarily to counteract the effects of shivering
during controlled hypothermia. The instrumentation was identical in all included animals, intended for extensive evaluation of haemodynamic and cardiac function, together with load-independent variables describing systolic and diastolic function before and after cardiac arrest. As a result of pancuronium’s deregistration in Norway in 2010, costs and supply has forced the use of vecuronium instead. In this retrospective non-randomised study, we hypothesised that using vecuronium instead of pancuronium in pigs has only minor or no cardiac and haemodynamic influences on this experimental pig model, making such studies comparable. Material and methods Animals From four experimental animal protocols with Norwegian Land Race pigs (Sus scrofa domesticus), the baseline cardiac and haemodynamic variables from a total of 116 pigs were compared. By combining baseline values from these studies, the large number of animals allows valid statistical evaluations without the need for separate animal experiments. The Norwegian State Commission has approved all experimental protocols (project No. 2004220, 20092088 and 20113923) that have been conducted in accordance with regulations of the European Communities Council Directives of 1986 and 2010. Animals were acclimatised for at least seven days in our animal facility under controlled lighting, humidity and temperature, and cared for under veterinary surveillance. The pigs were fed with a standard commercial young pig diet twice daily. Before the surgical procedure, animals were fasted overnight, but given free access to water. Anaesthesia All pigs were premedicated with ketamine (20 mg kg 1), diazepam (10 mg) and atropine (1 mg) by intramuscular injection in the dorsal region of the neck and then weighed. Body surface areas (BSA) were calculated by the formula BSA = k BW2/3/100, where BW is bodyweight in kilogrammes, and k for pigs is 9 m2 kg 2. The pigs weighed (mean SD) 42 3 kg with a calculated body surface area of 1.09 0.06 m2. During a short period of ventilation with oxygen and 3% isoflurane by mask, two ear veins were cannulated for administration of
© 2014 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia, 42, 242–249
243
Neuromuscular blockade in pig models K Grong et al.
fluids and anaesthesia. Intravenous (IV) loading doses of fentanyl (0.02 mg kg 1), midazolam (0.3 mg kg 1) and pentobarbital (15 mg kg 1) were administered. In addition, either pancuronium or vecuronium was added (Table 1). The animals either underwent endotracheal intubation or were tracheotomized and were then mechanically ventilated (Dr€ ager, L€ ubeck, Germany) with 57–58% endtidal N2O and oxygen. A tidal volume of 11 mL kg 1 was used, with frequency adjustments aiming to obtain an end-tidal partial pressure of carbon dioxide of 5.3–5.5 kPa (40–41 mmHg). Animals were placed on a warm water blanket, and anaesthesia was sustained with N2O and continuous infusion of sodium pentobarbital (4 mg kg 1 hour 1), fentanyl (0.02 mg kg 1 hour 1), midazolam (0.3 mg kg 1 hour 1) and the neuromuscular blocker (Table 1). Fluid loss was substituted with a continuous infusion of Ringer acetate (15 mL kg 1 hour 1) with 10 mmol KCl added. Instrumentation External ECG, rectal temperature and pulse oximetry were monitored continuously. The right femoral artery and vein were exposed surgically in the right inguinal region and cannulated. A bladder catheter was inserted through a suprapubic incision. A midline sternotomy and longitudinal pericardiotomy gave access to the heart. The pulmonary artery was cannulated with a 7.5F balloon floating continuous cardiac output catheter (139H-7.5F, Edward Lifesciences Inc, CA, USA) with injection/pressure ports advanced through the right atrium and ventricle, via the left Table 1 Overview of bolus and continuous infusion doses of neuromuscular blocking agents in the present study
Bolus
Pancuronium (Fannelop et al. 2009; Salminen et al. 2011) n = 54 Vecuronium low-dose (L.D) (Unpublished results) n = 29 Vecuronium high-dose (H.D) (Unpublished results) n = 33
0.063 mg kg
244
Experimental groups
Continuous infusion
Study
1
1
0.14 mg kg
internal thoracic vein. The catheter was connected to a continuous cardiac output computer (Vigilance or Vigilance II, Edward Lifesciences Inc, CA, USA). Cardiac output, central venous pressure and pulmonary artery pressure were obtained with this catheter, pressures zeroed at heart level. Central aortic pressure was obtained using a microtip pressure transducer catheter (MPC-500, Millar Corp, TX, USA). Left ventricular variables were assessed by a pressure-conductance catheter (SPR 788, Millar Corp, TX, USA) inserted through the apex, secured with a tourniquet and connected to a Sigma 5 signal conditioner (CD Leycom, The Netherlands). The left atrium was cannulated for later infusion of coloured or fluorescent microspheres for tissue blood flow measurements used in the original studies. Cannulation sutures were prepared in advance. A snare was placed loosely around the inferior caval vein to allow transient preload reductions. Finally, protocols employed full heparinisation (500 IU kg 1). In all experiments, the surgery and instrumentation procedures were performed by two experienced cardio-thoracic surgeons. After instrumentation was finished, a ten minute stabilisation period was allowed. Variables in the baseline situation were registered during respiratory shut-off in the end-expirium. Six to ten cardiac cycles were recorded during a stable haemodynamic condition without intervention, followed by recordings during the subsequent inferior caval occlusion, resulting in a dynamic preload reduction. After registration of baseline variables, the animals were entered into the original research protocols studying cardiac function after different routines for cardioplegic arrest. Animals were finally euthanazed, still in the same narcosis, with intra-cardiac saturated KCl after completing the research protocols.
1
hour
0.4 mg kg
1
0.2 mg kg
1
hour
1
0.6 mg kg
1
0.3 mg kg
1
hour
1
According to the anaesthetic protocols, the baseline results could be arranged into the following three comparable study-groups with identical instrumentation: pancuronium (n = 54), low-dose (L.D.) vecuronium (n = 29) and high-dose (H.D.) vecuronium (n = 33) (Table 1). Data analysis Haemodynamic variables were digitised and recorded with Gould ES2000 (Gould Instruments Systems, OH, USA) or ACQ-7700 Acquisition Interface Unit (Data
© 2014 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia, 42, 242–249
Neuromuscular blockade in pig models K Grong et al. Sciences International, MN, USA), and were analysed by internally developed software or Ponemah 5.0 (Data Science International). Variables from the conductance catheter were recorded by a Sigma-5 or Sigma-M unit (CD Leycom, The Netherlands) and calculated with Conduct 2000 (CD Leycom) or internally developed software. Statistical analysis Statistical analysis was performed with commercial software SigmaStat 3.5 (Systat Software, Inc., IL, USA). All variables were investigated for normality and equal distribution by Kolmogorov-Smirnov and the Levene’s median tests, respectively. If both tests were passed (p ≥ 0.05), groups were compared with one-way analysis of variance (ANOVA). If not (p < 0.05), Kruskal-Wallis ANOVA was used. Following a significant ANOVA, Student-Newman-Keul’s or
Dunn’s multiple contrast tests were used to compare individual means and medians whenever appropriate. Retrospective analysis of minimal detectable difference between means was performed using the non-centrality parameter and variance within groups from the original ANOVA, with level of significance and power set to 0.05 and 0.80, respectively (Cohen 1988; Zar 2010). Values are presented as mean SD or median (interquartile range). p-value < 0.05 are considered significant. Results Bodyweight and calculated body surface area did not differ between experimental groups. At the time of haemodynamic evaluation, the core temperature averaged 38.6 1.1, 38.7 0.8 and 38.6 0.7 °C in the pancuronium, L.D. and H.D. vecuronium groups, respectively (ANOVA p = 0.87).
Table 2 Cardiac and load-independent variables in three groups of domestic pigs anaesthetized in combination with neuromuscular blockade. Variables are mean SD or median (interquartile range)
Cardiac variables HR (beats minute 1) LV-ESP (mmHg) LV-ESVi (mL m 2) LV-EDP (mmHg) LV-EDVi (mL m 2) EF LV-dP/dtmax (mmHg second 1) LV-dP/dtmin (mmHg second 1) Ea (mmHg mL 1) s SVi (mL m 2) SWi (mmHg mL m 2) CI (L minute 1 m 2) PR-interval (s) PR-intervalRR (fraction) Load-independent variables ESPVRslope (mmHg mL 1) PRSW (mmHg) EDPVRlin (mmHg mL 1) b
Pancuronium (n = 54) A
Vecuronium L.D. (n = 29) B
Vecuronium H.D. (n = 33) C
ANOVA
MDD
92 (85, 97) 114 15 32 (22, 43) 10.9 2.7 78 18 0.59 0.10 1492 (1325, 1643) 2069 312 2.45 (2.10, 2.78) 31.4 (30.3, 34.4) 44 7 4407 (3769, 4950) 4.0 0.5 0.133 0.014 0.200 (0.190, 0.215)
84 (73, 95) 112 20 34 (25, 41) 9.5 2.8 79 15 0.57 0.09 1527 (1281, 1889) 1939 224 2.28 (1.98, 2.66) 30.0 (27.3, 34.7) 44 5 4154 (3489, 4471) 3.7 0.7 0.136 0.016 0.196 (0.162, 0.219)
87 (76, 93) 105 19 34 (25, 48) 9.8 3.2 80 16 0.57 0.10 1547 (1339, 1896) 1979 351 2.10 (1.81, 2.75) 30.4 (29.1, 33.8) 45 8 3864 (3332, 4644) 3.8 0.6 0.127 0.015b 0.182 (0.166, 0.199)a
p p p p p p p p p p p p p p p
= = = = = = = = = = = = = = =
0.036 0.10 0.60 0.07 0.80 0.60 0.39 0.145 0.093 0.13 0.92 0.12 0.065 0.037 0.017
– 12 10 2.0 12 0.07 246 218 0.39 3.0 5 726 0.4 – –
1.36 (1.08, 1.73) 61.2 10.4 0.131 (0.116, 0.169) 0.021 (0.016, 0.025)
1.44 (1.24, 2.48) 64.8 12.6 0.181 (0.148, 0.247)a 0.031 (0.025, 0.046)a
1.52 (1.14, 1.97) 64.2 12.9 0.163 (0.124, 0.219) 0.031 (0.022, 0.048)a
p p p p
= = =
doi:10.1111/vaa.12198
RESEARCH PAPER
Haemodynamic differences between pancuronium and vecuronium in an experimental pig model Kristoffer Grong*, Pirjo-Riitta Salminen*,†, Lodve Stangeland* & Geir O. Dahle*,† *Department of Clinical Science, University of Bergen, Bergen, Norway †Section of Cardiothoracic Surgery, Department of Heart Disease, Haukeland University Hospital, Bergen, Norway
Correspondence: Kristoffer Grong, Department of Clinical Science, Faculty of Medicine and Dentistry, University of Bergen, Haukeland University Hospital, NO-5020 Bergen, Norway. E-mail: [email protected]
Abstract Objective To compare baseline cardiovascular function in anesthetised pigs using either pancuronium or vecuronium as a neuromuscular blocker. Study design Retrospective, non-randomized comparison. Animals Norwegian Land Race pigs (Sus scrofa domesticus) weighing mean 42 SD 3 kg. Methods One hundred and sixteen animals from four different research protocols premedicated with identical doses of ketamine, diazepam, atropine and isoflurane, and anaesthetised with pentobarbital, fentanyl, midazolam and N2O were arranged into three uniform groups with respect to neuromuscular blocking agent: pancuronium bolus of 0.063 mg kg 1 followed by 0.14 mg kg 1 hour 1 (n = 54), low-dose vecuronium 0.4 mg kg 1/0.2 mg kg 1 hour 1 (n = 29) and high-dose vecuronium 0.6 mg kg 1/0.3 mg kg 1 hour 1 (n = 33). Results The majority of cardiovascular parameters demonstrated no significant differences between groups. For heart rate, there was an overall group difference, p = 0.036. Dromotropy was low in the pancuronium group, with an increased normalised PR-interval compared to the high-dose vecuronium group, median 0.200 interquartile range (0.190, 0.215) versus 0.182 (0.166, 0.199), p < 0.05. Left ventricular compliance was increased in pancuro242
nium-treated animals, demonstrated as a reduction in the nonlinear end-diastolic pressure volume relationship b compared to both vecuronium groups, 0.021 (0.016, 0.025) versus 0.031 (0.025, 0.046) and 0.031 (0.022, 0.048), p < 0.05. The linear enddiastolic pressure volume relationship EDPVRlin was reduced as well in the pancuronium group, compared to the low-dose vecuronium group, 0.131 (0.116, 0.169) versus 0.181 (0.148, 0.247), p < 0.05. Conclusions There are only minor haemodynamic differences when using pancuronium compared to vecuronium in the fentanyl-pentobarbital-midazolam-N2O anesthetised domestic pigs. Furthermore, increasing doses of vecuronium have minimal haemodynamic effects. Clinical relevance Experimental studies in pigs using either pancuronium or vecuronium as a neuromuscular blocking agent are comparable with regard to cardiac and haemodynamic performance. Keywords cardiovascular, haemodynamic effects, neuromuscular blockers, pancuronium, pigs, vecuronium.
Introduction In cardiac research, the in vivo large animal model is an important tool for translating knowledge from basic research into clinical trials and practise. Together with the possibility of using more invasive
Neuromuscular blockade in pig models K Grong et al. techniques and methods developed for experimental research, one of the key points in such models is the standardization of the study population, allowing statistically powerful studies on relatively few subjects. Experimental cardiac research inevitably involves monitoring haemodynamic parameters as a way to evaluate cardiovascular performance. As anaesthetic agents have a particularly significant impact on the cardiovascular system, a strict standardised anaesthetic regime is essential for the predictability and stability of such research protocols. In addition to analgesic and hypnotic agents, general anaesthetic protocols may also include neuromuscular blocking agents. These are used to facilitate endotracheal intubation, prevent involuntary muscular contraction and disturbance of surgical procedures, as well as to minimise shivering during tepid/hypothermic cardiopulmonary bypass. The two muscle relaxants studied, pancuronium (Pavulon; Organon, Norway) and vecuronium (Norcuron; Organon, Norway), are both nondepolarising neuromuscular blocking agents. Pancuronium has been previously demonstrated to possess stimulatory haemodynamic effects in man (Ferres et al. 1987; Sethna et al. 1987; Virmani et al. 2006) and animals (Domenech et al. 1976). In cardiac surgery and experimental settings, these effects are beneficial, and thus pancuronium has been used widely (Murphy et al. 2002). Vecuronium seems to have only minor cardiovascular implications across species (Booij et al. 1980; Chen et al. 1991; Husby et al. 1996), as well as in increasing doses in man (Chen et al. 1991; Husby et al. 1996), although parasympatholytic effects have been reported in dogs (Narita et al. 1992). The use of muscle relaxants in experimental animal models is restricted, and should not be used unless the anaesthetic protocol has been meticulously evaluated without neuromuscular blocking agents in the species studied. This would ensure that sedation and analgesia is sufficient, thus preventing paralysis of the animal in a conscious/semiconscious state (Institute for Laboratory Animal Research 2010). An anaesthetic protocol allowing the use of muscular relaxation was documented prior to the introduction of muscle relaxants in our studies (Fannelop et al. 2004). Our research group has used pancuronium as a neuromuscular blocking agent in a porcine model related to tepid cardiopulmonary bypass, cardioplegic arrest and reperfusion, primarily to counteract the effects of shivering
during controlled hypothermia. The instrumentation was identical in all included animals, intended for extensive evaluation of haemodynamic and cardiac function, together with load-independent variables describing systolic and diastolic function before and after cardiac arrest. As a result of pancuronium’s deregistration in Norway in 2010, costs and supply has forced the use of vecuronium instead. In this retrospective non-randomised study, we hypothesised that using vecuronium instead of pancuronium in pigs has only minor or no cardiac and haemodynamic influences on this experimental pig model, making such studies comparable. Material and methods Animals From four experimental animal protocols with Norwegian Land Race pigs (Sus scrofa domesticus), the baseline cardiac and haemodynamic variables from a total of 116 pigs were compared. By combining baseline values from these studies, the large number of animals allows valid statistical evaluations without the need for separate animal experiments. The Norwegian State Commission has approved all experimental protocols (project No. 2004220, 20092088 and 20113923) that have been conducted in accordance with regulations of the European Communities Council Directives of 1986 and 2010. Animals were acclimatised for at least seven days in our animal facility under controlled lighting, humidity and temperature, and cared for under veterinary surveillance. The pigs were fed with a standard commercial young pig diet twice daily. Before the surgical procedure, animals were fasted overnight, but given free access to water. Anaesthesia All pigs were premedicated with ketamine (20 mg kg 1), diazepam (10 mg) and atropine (1 mg) by intramuscular injection in the dorsal region of the neck and then weighed. Body surface areas (BSA) were calculated by the formula BSA = k BW2/3/100, where BW is bodyweight in kilogrammes, and k for pigs is 9 m2 kg 2. The pigs weighed (mean SD) 42 3 kg with a calculated body surface area of 1.09 0.06 m2. During a short period of ventilation with oxygen and 3% isoflurane by mask, two ear veins were cannulated for administration of
© 2014 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia, 42, 242–249
243
Neuromuscular blockade in pig models K Grong et al.
fluids and anaesthesia. Intravenous (IV) loading doses of fentanyl (0.02 mg kg 1), midazolam (0.3 mg kg 1) and pentobarbital (15 mg kg 1) were administered. In addition, either pancuronium or vecuronium was added (Table 1). The animals either underwent endotracheal intubation or were tracheotomized and were then mechanically ventilated (Dr€ ager, L€ ubeck, Germany) with 57–58% endtidal N2O and oxygen. A tidal volume of 11 mL kg 1 was used, with frequency adjustments aiming to obtain an end-tidal partial pressure of carbon dioxide of 5.3–5.5 kPa (40–41 mmHg). Animals were placed on a warm water blanket, and anaesthesia was sustained with N2O and continuous infusion of sodium pentobarbital (4 mg kg 1 hour 1), fentanyl (0.02 mg kg 1 hour 1), midazolam (0.3 mg kg 1 hour 1) and the neuromuscular blocker (Table 1). Fluid loss was substituted with a continuous infusion of Ringer acetate (15 mL kg 1 hour 1) with 10 mmol KCl added. Instrumentation External ECG, rectal temperature and pulse oximetry were monitored continuously. The right femoral artery and vein were exposed surgically in the right inguinal region and cannulated. A bladder catheter was inserted through a suprapubic incision. A midline sternotomy and longitudinal pericardiotomy gave access to the heart. The pulmonary artery was cannulated with a 7.5F balloon floating continuous cardiac output catheter (139H-7.5F, Edward Lifesciences Inc, CA, USA) with injection/pressure ports advanced through the right atrium and ventricle, via the left Table 1 Overview of bolus and continuous infusion doses of neuromuscular blocking agents in the present study
Bolus
Pancuronium (Fannelop et al. 2009; Salminen et al. 2011) n = 54 Vecuronium low-dose (L.D) (Unpublished results) n = 29 Vecuronium high-dose (H.D) (Unpublished results) n = 33
0.063 mg kg
244
Experimental groups
Continuous infusion
Study
1
1
0.14 mg kg
internal thoracic vein. The catheter was connected to a continuous cardiac output computer (Vigilance or Vigilance II, Edward Lifesciences Inc, CA, USA). Cardiac output, central venous pressure and pulmonary artery pressure were obtained with this catheter, pressures zeroed at heart level. Central aortic pressure was obtained using a microtip pressure transducer catheter (MPC-500, Millar Corp, TX, USA). Left ventricular variables were assessed by a pressure-conductance catheter (SPR 788, Millar Corp, TX, USA) inserted through the apex, secured with a tourniquet and connected to a Sigma 5 signal conditioner (CD Leycom, The Netherlands). The left atrium was cannulated for later infusion of coloured or fluorescent microspheres for tissue blood flow measurements used in the original studies. Cannulation sutures were prepared in advance. A snare was placed loosely around the inferior caval vein to allow transient preload reductions. Finally, protocols employed full heparinisation (500 IU kg 1). In all experiments, the surgery and instrumentation procedures were performed by two experienced cardio-thoracic surgeons. After instrumentation was finished, a ten minute stabilisation period was allowed. Variables in the baseline situation were registered during respiratory shut-off in the end-expirium. Six to ten cardiac cycles were recorded during a stable haemodynamic condition without intervention, followed by recordings during the subsequent inferior caval occlusion, resulting in a dynamic preload reduction. After registration of baseline variables, the animals were entered into the original research protocols studying cardiac function after different routines for cardioplegic arrest. Animals were finally euthanazed, still in the same narcosis, with intra-cardiac saturated KCl after completing the research protocols.
1
hour
0.4 mg kg
1
0.2 mg kg
1
hour
1
0.6 mg kg
1
0.3 mg kg
1
hour
1
According to the anaesthetic protocols, the baseline results could be arranged into the following three comparable study-groups with identical instrumentation: pancuronium (n = 54), low-dose (L.D.) vecuronium (n = 29) and high-dose (H.D.) vecuronium (n = 33) (Table 1). Data analysis Haemodynamic variables were digitised and recorded with Gould ES2000 (Gould Instruments Systems, OH, USA) or ACQ-7700 Acquisition Interface Unit (Data
© 2014 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia, 42, 242–249
Neuromuscular blockade in pig models K Grong et al. Sciences International, MN, USA), and were analysed by internally developed software or Ponemah 5.0 (Data Science International). Variables from the conductance catheter were recorded by a Sigma-5 or Sigma-M unit (CD Leycom, The Netherlands) and calculated with Conduct 2000 (CD Leycom) or internally developed software. Statistical analysis Statistical analysis was performed with commercial software SigmaStat 3.5 (Systat Software, Inc., IL, USA). All variables were investigated for normality and equal distribution by Kolmogorov-Smirnov and the Levene’s median tests, respectively. If both tests were passed (p ≥ 0.05), groups were compared with one-way analysis of variance (ANOVA). If not (p < 0.05), Kruskal-Wallis ANOVA was used. Following a significant ANOVA, Student-Newman-Keul’s or
Dunn’s multiple contrast tests were used to compare individual means and medians whenever appropriate. Retrospective analysis of minimal detectable difference between means was performed using the non-centrality parameter and variance within groups from the original ANOVA, with level of significance and power set to 0.05 and 0.80, respectively (Cohen 1988; Zar 2010). Values are presented as mean SD or median (interquartile range). p-value < 0.05 are considered significant. Results Bodyweight and calculated body surface area did not differ between experimental groups. At the time of haemodynamic evaluation, the core temperature averaged 38.6 1.1, 38.7 0.8 and 38.6 0.7 °C in the pancuronium, L.D. and H.D. vecuronium groups, respectively (ANOVA p = 0.87).
Table 2 Cardiac and load-independent variables in three groups of domestic pigs anaesthetized in combination with neuromuscular blockade. Variables are mean SD or median (interquartile range)
Cardiac variables HR (beats minute 1) LV-ESP (mmHg) LV-ESVi (mL m 2) LV-EDP (mmHg) LV-EDVi (mL m 2) EF LV-dP/dtmax (mmHg second 1) LV-dP/dtmin (mmHg second 1) Ea (mmHg mL 1) s SVi (mL m 2) SWi (mmHg mL m 2) CI (L minute 1 m 2) PR-interval (s) PR-intervalRR (fraction) Load-independent variables ESPVRslope (mmHg mL 1) PRSW (mmHg) EDPVRlin (mmHg mL 1) b
Pancuronium (n = 54) A
Vecuronium L.D. (n = 29) B
Vecuronium H.D. (n = 33) C
ANOVA
MDD
92 (85, 97) 114 15 32 (22, 43) 10.9 2.7 78 18 0.59 0.10 1492 (1325, 1643) 2069 312 2.45 (2.10, 2.78) 31.4 (30.3, 34.4) 44 7 4407 (3769, 4950) 4.0 0.5 0.133 0.014 0.200 (0.190, 0.215)
84 (73, 95) 112 20 34 (25, 41) 9.5 2.8 79 15 0.57 0.09 1527 (1281, 1889) 1939 224 2.28 (1.98, 2.66) 30.0 (27.3, 34.7) 44 5 4154 (3489, 4471) 3.7 0.7 0.136 0.016 0.196 (0.162, 0.219)
87 (76, 93) 105 19 34 (25, 48) 9.8 3.2 80 16 0.57 0.10 1547 (1339, 1896) 1979 351 2.10 (1.81, 2.75) 30.4 (29.1, 33.8) 45 8 3864 (3332, 4644) 3.8 0.6 0.127 0.015b 0.182 (0.166, 0.199)a
p p p p p p p p p p p p p p p
= = = = = = = = = = = = = = =
0.036 0.10 0.60 0.07 0.80 0.60 0.39 0.145 0.093 0.13 0.92 0.12 0.065 0.037 0.017
– 12 10 2.0 12 0.07 246 218 0.39 3.0 5 726 0.4 – –
1.36 (1.08, 1.73) 61.2 10.4 0.131 (0.116, 0.169) 0.021 (0.016, 0.025)
1.44 (1.24, 2.48) 64.8 12.6 0.181 (0.148, 0.247)a 0.031 (0.025, 0.046)a
1.52 (1.14, 1.97) 64.2 12.9 0.163 (0.124, 0.219) 0.031 (0.022, 0.048)a
p p p p
= = =
