Differences between acceleromyography and electromyography during neuromuscular function monitoring in anesthetized Beagle dogs

ObjectiveQuantitative neuromuscular monitoring is essential for studies of potency and duration of neuromuscular blocking agents, and for detecting residual paralysis in anesthetized patients. This investigation evaluates whether there are systematic differences between acceleromyography (AMG) and electromyography (EMG); two quantitative methods for monitoring neuromuscular block.Study designProspective.AnimalsTen healthy Beagle dogs.MethodsDogs were anesthetized with isoflurane and dexmedetomidine. Both ulnar nerves were stimulated with a train-of-four (TOF) pattern every 15 seconds. The magnitude of the first twitch (T1) and the TOF ratio (magnitude of T4/T1; TOFR) were quantified simultaneously with AMG and EMG, applied randomly to each extremity. The extent of maximal block (T1 depression) and onset time were measured by AMG and EMG during TOF monitoring after the administration of cisatracurium (0.05 mg kg⁻¹). In addition, recovery of T1 to 25% and 75%, the recovery index (time between T1 of 25% and 75%), and recovery of the TOFR to 0.9 were used to characterize recovery from cisatracurium and were compared between monitors. Regression and Bland-Altman plots for T1 and TOFR were also created.ResultsMaximal block and onset time were not different between monitors. Time to recovery of T1 to 25% and 75%, and time to TOF ratio 0.9 was significantly shorter with AMG. The recovery index was not different between monitors. When the TOFR returned to 0.9 with AMG, EMG still measured considerable residual block (TOFR 0.47).Conclusions and clinical relevanceElectromyography consistently detected residual NMB when recovery from NMB was complete as assessed by AMG.     

Recovery from neuromuscular block in dogs: restoration of spontaneous ventilation does not exclude residual blockade

ObjectiveTo evaluate if return of spontaneous ventilation to pre-relaxation values indicates complete recovery from neuromuscular blockade.Study designProspective, with each individual acting as its own control.AnimalsTen healthy adult female Beagle dogs weighing 6.2–9.4 kg.MethodsDogs were anesthetized with propofol, dexemedetomidine and isoflurane. Spontaneous ventilation was assessed by measuring end-tidal CO₂, expired tidal volume, peak inspiratory flow, respiratory rate and minute ventilation. Vecuronium 25 μg kg^?1 IV was administered and neuromuscular block was evaluated by measuring the train-of-four (TOF) ratio with acceleromyography in the hind limb. During spontaneous recovery from neuromuscular block, the TOF ratio when each ventilatory variable returned to baseline was recorded.ResultsThis dose of vecuronium produced moderate neuromuscular block in all dogs, with TOF ratio values of 0–18% at maximal block. Expired tidal volume, peak inspiratory flow and minute ventilation returned to pre-relaxation values when the median TOF ratio was ≤ 20%. The median TOF ratio was 42% when the end-tidal CO₂ returned to pre-relaxation values.Conclusions and clinical relevanceSignificant residual neuromuscular block could be measured at the hind limb with acceleromyography when ventilation had spontaneously returned to pre-vecuronium values. Monitoring spontaneous ventilation, including end-tidal CO₂, expired tidal volume, peak inspiratory flow or minute ventilation cannot be used as a surrogate for objective neuromuscular monitoring, and this practice may increase the risk of postoperative residual paralysis.     

Comparison between acceleromyography and visual assessment of train-of-four for monitoring neuromuscular blockade in horses undergoing surgery

ObjectiveTo compare acceleromyography (AMG) with visual assessment of train-of-four (TOF) for monitoring neuromuscular blockade and detecting residual muscle paralysis in horses receiving atracurium.Study designProspective, controlled clinical study.AnimalsNine adult, client-owned horses weighing 577 (436, 727) kg (median, minimum, maximum) and ASA physical status I–II, admitted for surgery.MethodsAn electrical nerve stimulator was used to stimulate the peroneal nerve with TOFs at 1 minute intervals. Before and after atracurium administration (0.15 mg kg⁻¹, IV), the number of twitches observed (TOF count, or TOFc) was assessed visually. When four twitches were seen (i.e., TOFc = 4) presence or absence of fade by visual assessment was recorded. Simultaneously, the response to each TOF was assessed by AMG; this measured TOFc, and twitch fade using TOF ratio (TOFR; ratio of fourth to first twitch). The anesthetist performing the visual evaluation was blinded to the AMG readings. Recovery from neuromuscular blockade was defined as the absence of fade by visual inspection or a TOFR ≥90% by AMG.ResultsDuring onset of action of the drug, fade was first detected 4 (1, 8) minutes earlier by AMG (p = 0.008). Maximal blockade started at 6 (3, 17) minutes by visual assessment and 9 (3, 25) minutes by AMG (not significantly different). Only four horses achieved complete neuromuscular blockade (TOFc of zero by both methods); in those four horses AMG did not detect the start of the return of neuromuscular transmission before visual assessment. Visual assessment indicated the return of four twitches with no fade 12 (8, 42) minutes before AMG gave a TOFR of ≥90% (p = 0.004).Conclusion and clinical relevance There was no substantial advantage for AMG in detecting the onset of atracurium-induced neuromuscular blockade. However, AMG detected residual blockade when visual assessment of TOF did not. Application of AMG is likely to reduce the incidence of residual blockade.     

Twitch potentiation: a potential source of error during neuromuscular monitoring with acceleromyography in anesthetized dogs

ObjectiveTo measure twitch potentiation (the staircase phenomenon) in anesthetized dogs, and assess its relevance during neuromuscular monitoring with acceleromyography (AMG).Study designRandomized, prospective clinical trial.AnimalsSixteen dogs undergoing ovariohysterectomy.MethodsUnder isoflurane anesthesia, neuromuscular function was monitored with train-of-four (TOF) stimuli every 15 seconds and quantified by AMG. Neuromuscular blockade (NMB) was produced with 0.15 mg kg^?1 atracurium IV. Dogs were randomly divided into two groups; a potentiation group (PG) in which TOF stimulation was applied for 20 minutes before atracurium was administered; and a control group (CG) where no such time was allowed. In both groups, the AMG was calibrated (at tCAL) just before atracurium was administered. TOF stimulation continued throughout the experiment in all dogs. The height of the first twitch (T₁) (expressed as a fraction of T₁ at tCAL) and train-of-four ratio (TOFR) were recorded until TOFR returned to ≥90%.ResultsIn PG, T₁ increased significantly (p = 0.0078) from a median of 102% (range, 95, 109) at baseline to 118% (100, 142) at 20 minutes. In PG, no difference was found between T₁ at tCAL (immediately before atracurium administration) and T₁ when neuromuscular transmission returned (p = 0.42). In the CG, T₁ increased significantly between tCAL and the time neuromuscular transmission returned (p = 0.027). TOFR did not increase during twitch potentiation (all p = 0.32).Conclusions and clinical relevanceT₁ increased significantly during 20 minutes of uninterrupted TOF stimulation in the absence of NMB, establishing that twitch potentiation occurs in anesthetized dogs. With no time for potentiation, T₁ increased during the course of recovery from NMB; this phenomenon introduces a bias in T₁ measurements and could affect studies reporting potency and duration of NMB based on T₁ or single twitches. TOFR was unaltered by potentiation emphasizing its clinical usefulness for excluding post-operative residual NMB.     

Effects of sevoflurane,propofol or alfaxalone on neuromuscular blockade produced by a single intravenous bolus of rocuronium in dogs

ObjectiveTo compare the effects of sevoflurane, propofol and alfaxalone on the neuromuscular blockade induced by a single intravenous bolus of rocuronium in dogs.Study designA randomized, prospective, crossover experimental study.AnimalsA total of eight adult Beagle dogs (four female, four male), weighing 8.9–15.3 kg and aged 5–7 years.MethodsThe dogs were anesthetized three times with 1.25× minimum alveolar concentration of sevoflurane (SEVO treatment) and 1.25× minimum infusion rate of propofol (PROP treatment) or alfaxalone (ALFX treatment) at intervals of ≥14 days. Neuromuscular function was monitored with train-of-four (TOF) stimulation of the peroneal nerve by acceleromyography. After recording the control TOF ratio (TOFRC), a single bolus dose of rocuronium (1 mg kg^–1) was administered intravenously. The times from rocuronium administration to achieving TOF count 0 (onset time), from achieving TOF count 0 to the reappearance of TOF count 4 (clinical blockade period), from 25% to 75% of TOFRC (recovery index) and from achieving TOF count 0 to TOF ratio/TOFRC >0.9 (total neuromuscular blockade duration) were recorded.ResultsThe onset time and recovery index did not differ among the treatments. The median clinical blockade period was longer in the SEVO treatment [27.3 (26.0–30.3) minutes] than in PROP [16.6 (15.4–18.0) minutes; p = 0.002] and ALFX [22.4 (18.6–23.1) minutes; p = 0.017] treatments; and longer in the ALFX treatment than in the PROP treatment (p = 0.020). The mean total neuromuscular blockade duration was longer in the SEVO treatment (43.7 ± 9.9 minutes) than in PROP (25.1 ± 2.7 minutes; p < 0.001) and ALFX (32.5 ± 8.4 minutes; p = 0.036) treatments.Conclusions and clinical relevanceCompared with alfaxalone and propofol, sevoflurane prolonged rocuronium-induced neuromuscular blockade by a significantly greater extent in dogs.     

Can we see fade? A survey of anesthesia providers and our ability to detect partial neuromuscular block in dogs

Objective

To assess the ability to visually detect fade during train-of-four (TOF) or double burst stimulation (DBS) in anesthetized dogs recovering from nondepolarizing neuromuscular block.

Observations of the potency and duration of vecuronium in isoflurane-anesthetized horses

ObjectiveTo evaluate the potency and duration of three subparalyzing doses of vecuronium (VEC) in isoflurane-anesthetized horses.Study designProspective experimental study.AnimalsThirteen healthy adult horses undergoing arthroscopic surgery.MethodsDuring isoflurane anesthesia, horses received one of three doses of vecuronium (25, 50, or 100 μg kg^?1). Neuromuscular transmission was monitored with acceleromyography (AMG) with train-of-four (TOF) stimulation of the radial nerve. Maximal depression of the first twitch (T1), and onset time were recorded for each dose. Recovery time to a TOF ratio >90% was also evaluated.ResultsVecuronium 25 μg kg^?1 produced no observable T1 depression in four horses. VEC 50 μg kg^?1 (n = 5) produced a maximal T1 depression of [median (min, max)] 41 (20, 71) % in four horses, and no neuromuscular block was seen in the fifth. VEC 100 μg kg^?1 was given to four horses and produced a T1 depression of 73 (64, 78) %. Of the four horses in which VEC 50 μg kg^?1 produced a measurable neuromuscular block, three recovered spontaneously 43 (40, 52) minutes after VEC administration; a fourth subject received edrophonium to reverse residual block at the end of the surgery. Spontaneous recovery after VEC 100 μg kg^?1 occurred by 112 minutes in one horse, and had to be facilitated by edrophonium in the remaining three horses, more than 2 hours after VEC had been given.Conclusions and clinical relevanceA dose of 100 μg kg^?1 VEC in isoflurane anesthetized horses failed to produce complete paralysis. The partial neuromuscular block lasted at least 2 hours after this dose had been administered. Edrophonium was required to reverse the neuromuscular block in three of four horses. It is likely that more than 100 μg kg^?1 VEC would be necessary for complete neuromuscular blockade in horses, and that this dose will last >2 hours.     

Partial neuromuscular block impairs arytenoid abduction during hypercarbic challenge in anesthetized dogs

Objective

To evaluate the effect of two levels of partial neuromuscular block (NMB) on arytenoid abduction, tidal volume (V_T) and peak inspiratory flow (PIF) in response to a hypercarbic challenge in anesthetized dogs.

Speed of reversal of vecuronium neuromuscular block with different doses of neostigmine in anesthetized dogs

Objectives

Neostigmine is routinely used to reverse non-depolarizing neuromuscular block. Given its indirect mechanism, a plateau may exist whereby increasing doses of neostigmine do not result in clinical benefit. This study was designed to measure the speed of reversal of vecuronium-induced neuromuscular block in isoflurane-anesthetized dogs after the administration of three doses of neostigmine as used in clinical practice.

ED50 and ED95 of rocuronium during alfaxalone anesthesia in dogs

ObjectiveTo determine the median effective dose (ED₅₀) and effective dose required to depress the twitch value by 95% (ED₉₅) of rocuronium during alfaxalone anesthesia in dogs.Study designA randomized, prospective, crossover experimental study.AnimalsA total of eight adult Beagle dogs (four female, four male), weighing 10.3–14.6 kg and aged 6–8 years.MethodsThe dogs were anesthetized three times with 1.25-fold the individual minimum infusion rate of alfaxalone at intervals of ≥ 14 days. Neuromuscular function was monitored with train-of-four (TOF) stimulation of the peroneal nerve by acceleromyography. After recording the control TOF ratio (TOFRC) and first twitch of TOF (T1C), a single bolus dose of rocuronium 100, 175 or 250 μg kg^–1 (treatments R100, R175 or R250) was administered intravenously. The maximum suppression of the first twitch of TOF (T1) was recorded and calibrated with T1C to construct the dose–response curve, from which ED₅₀ and ED₉₅ were calculated. Time from rocuronium administration to TOF ratio/TOFRC > 0.9 (duration TOFR0.9) was recorded.ResultsED₅₀ and ED₉₅ of rocuronium during alfaxalone anesthesia were 175 and 232 μg kg^–1, respectively. The median (range) duration TOFR0.9 was longer in treatment R250 [10.1 (9.2–10.9) minutes] than in treatments R100 [3.1 (2.9–4.4) minutes; p < 0.0001] and R175 [7.7 (6.9–8.1) minutes; p < 0.0001]; and longer in treatment R175 than in treatment R100 (p < 0.0001).Conclusions and clinical relevanceThe duration of TOFR0.9 correlated positively with the dosage of rocuronium, indicating that recovery time of rocuronium was also dose-dependent in dogs anesthetized with alfaxalone. The duration TOFR0.9 of rocuronium 250 μg kg^–1 was 10 minutes during alfaxalone anesthesia in dogs.     

Comparison of the neuromuscular blocking effects of cisatracurium during isoflurane or propofol anesthesia in dogs

ObjectiveTo compare the neuromuscular blocking effects of cisatracurium during isoflurane versus propofol anesthesia in dogs.Study designProspective, randomized study.AnimalsA total of 20 healthy, client-owned dogs (16 females, four males) weighing 12.5–22 kg and aged 1–8 years.MethodsDogs undergoing elective surgery were randomized in equal numbers to an isoflurane (ISO) or propofol (PPF) group. Other drugs used during anesthesia were equal between groups. Single-twitch (ST) stimulation was used to monitor neuromuscular response. After recording the baseline ST (T0), cumulative doses of cisatracurium (0.05 mg kg^–1) were administered intravenously until ST/T0 ≤5%. Effective doses 50 (ED₅₀) and 95 (ED₉₅) of cisatracurium in each group were calculated from group dose-response curves. Recovery of ST (TR) was defined as spontaneous recovery of ST to 80–120% of T0 remaining stable for 2 minutes. The ST after each dose of cisatracurium, duration 25% (time after the last dose until 25% recovery of TR), recovery index (time to recovery from 25% to 75% of TR) and duration to TR (time after the last dose until recovery of TR) were recorded.ResultsIncremental doses of cisatracurium, median (range), were 2 (1–3) in ISO and 4 (2–5) in PPF to achieve ≥95% depression of ST/T0 (p < 0.01). ED₅₀ and ED₉₅ were 20 μg kg^–1 and 117 μg kg^–1 in ISO and 128 μg kg^–1 and 167 μg kg^–1 in PPF, respectively. The duration 25%, recovery index and duration to TR, median (range), were longer in ISO [22.6 (10.3–24.3), 5.3 (3.0–7.8) and 36.1 (20.1–49.7) minutes, respectively] than in PPF [10.2 (6.8–16.5), 3.0 (2.0–3.8) and 17.7 (14.2–28.7) minutes, respectively] (p < 0.01).Conclusions and clinical relevanceCisatracurium-induced neuromuscular blockade was significantly enhanced and prolonged by isoflurane compared with propofol.     

The clinical use of the neuromuscular blocking agent rocuronium in dogs

Objective The aim of this study was to characterize the onset and duration of action of the aminosteroid muscle relaxant rocuronium in dogs under clinical conditions. Study design Prospective single dose trial. Animals Twenty‐three dogs aged between 6 months and 12 years, weighing between 5.5 and 61.5 kg admitted to the University of Liverpool Small Animal Hospital between January and March 2000, and undergoing elective surgical procedures under general anaesthesia. Materials and methods Following induction of general anaesthesia, neuromuscular function was evaluated using train‐of‐four (TOF) stimulation. An initial dose of 0.4 mg kg^?1 rocuronium was administered intravenously (IV) and neuromuscular blockade was monitored by visually assessing the number of responses (twitches) to TOF stimulation (train‐of‐four count: TOFC). Incremental doses of 0.16 mg kg^?1 rocuronium were administered as indicated, when at least two twitches of the TOFC had returned. Results Rocuronium (0.4 mg kg^?1) abolished all responses to TOF stimulation in all dogs. The mean time to onset of neuromuscular blockade (complete abolition of all twitches) was 98 ± 52 seconds. Neuromuscular blockade (absence of all twitches to return of all four) lasted 32.3 ± 8.2 minutes. Incremental doses of 0.16 mg kg^?1 had a mean duration of action of 20.8 ± 4.9 minutes and up to seven increments were shown to be noncumulative. The effects of rocuronium were readily antagonized with neostigmine and atropine. Small transient increases in arterial blood pressure, which occurred in three dogs after the administration of rocuronium, were the only cardiovascular side‐effects observed. Conclusions Rocuronium is an effective nondepolarizing neuromuscular blocking agent in the dog, with a rapid onset of neuromuscular block after intravenous administration and an intermediate duration of action. Clinical relevance Rocuronium produced a neuromuscular block with similar characteristics to those obtained with vecuronium, thus apparently offering little advantage over vecuronium. However, its availability in aqueous solution and a longer shelf‐life increases convenience.     

Rocuronium infusion: A higher rate is needed in diabetic than nondiabetic dogs

Objective

To determine the infusion rates that maintain the train-of-four (TOF) ratio within 20–70% in dogs and compare the infusion rates between diabetic and nondiabetic dogs.

Cardiovascular and autonomic nervous effects of edrophonium and atropine combinations during neuromuscular blockade antagonism in sheep

ObjectiveTo study heart rate (HR), arterial blood pressure (BP) and autonomic nervous (AN) effects of edrophonium–atropine combinations during neuromuscular blockade (NMB) antagonism in sheep.Experimental design Randomized, prospective and experimental study.AnimalsSeventy-eight Scottish blackface ewes; mean age: 4.5 years; mean body mass: 54 kg.MethodsAfter induction with IV etomidate (0.5 mg kg⁻¹) and midazolam (0.5 mg kg⁻¹), anaesthesia was maintained with halothane and NMB produced with atracurium or mivacurium. In the first study (n = 53), the electrocardiographic (ECG), HR, BP and AN effects of low (40 μg kg⁻¹) and high (80 μg kg⁻¹) atropine doses combined with either of two edrophonium doses (0.5 or 1.0 mg kg⁻¹) were investigated. These variables were also measured in a second study when edrophonium (1.0 mg kg⁻¹) was administered 5 minutes before atropine (80 μg kg⁻¹) and vice versa. Data were analysed using one-way within-subjects and repeated measures anova.ResultsIn the first study, all combinations reversed NMB but significantly (p < 0.001) increased HR and BP within 2 minutes without arrhythmias. In the second study, edrophonium (1.0 mg kg⁻¹) significantly increased HR and BP, saliva flow (n = 1) and lung sounds (n = 3) and caused ECG changes (n = 1). Cardiovascular changes were partially reversed by atropine (80 μg kg⁻¹) administered 5 minutes later. Administered first, atropine (80 μg kg⁻¹) significantly decreased HR and BP effects which were fully (HR) and partially (BP) reversed by edrophonium (1 mg kg⁻¹) administered 5 minutes later.Conclusion and clinical relevance The cardiovascular effects of edrophonium and atropine were opposite to those reported in humans and dogs. Edrophonium (0.5 mg kg⁻¹) and atropine (80 μg kg⁻¹) caused the mildest HR changes without ECG and noncardiac AN disturbances, and is recommended for the antagonism of NMB in sheep.     

Neuromuscular blockade with rocuronium bromide for ophthalmic surgery in horses

Purpose The production of a central eye to ease surgical access for intraocular surgery is generally dependent on the depth of anesthesia. The aim of this study was to evaluate the eyeball position under muscle relaxation with rocuronium during general anesthesia. Material and methods Twenty horses, body weight 480 ± 62 kg; age 12.6 ± 6.2 years (mean ± SD) were anesthetised for various ophthalmic surgeries. Horses were premedicated with acepromazine, xylazine, and butorphanol intravenously and anesthesia induced with ketamine and diazepam. Anesthesia was maintained with isoflurane in 100% oxygen and 0.6 mL/kg/h of an infusion containing midazolam, ketamine, and xylazine diluted in 500 mL 0.9% NaCl. Horses were mechanically ventilated. Neuromuscular function was assessed with an acceleromyograph (TOF‐Guard^®) and the N. peroneus superficialis was stimulated every 15 s with a train‐of‐four stimulation pattern. A dose of 0.3 mg/kg rocuronium was administered intravenously. The changes in the eyeball position were recorded. Results The dose of 0.3 mg/kg rocuronium produced a 100% neuromuscular block in all horses. Onset time and clinical duration of block was 2.38 ± 2.02 min (range 0.5–8) and 32 ± 18.6 min (range 7.7–76.2), respectively. The globe rotated to central position within 31 ± 2.8 s. The whole iris was visible after 42 ± 7.7 s in all horses. No additional bolus of rocuronium was necessary for any surgery. Conclusion Neuromuscular blockade with rocuronium bromide can be used safely to facilitate ophthalmic surgery in equines.     

The effects of medetomidine on the action of vecuronium in dogs anaesthetized with halothane and nitrous oxide

ObjectiveTo quantify the effects of medetomidine on the onset and duration of vecuronium-induced neuromuscular blockade in dogs.Study designRandomized, prospective clinical study.AnimalsTwenty-four, healthy, client-owned dogs of different breeds, aged between 6 months and 10 years and weighing between 5.0 and 40.0 kg undergoing elective surgery.MethodsDogs were randomly allocated to two groups. Pre-anaesthetic medication in group M+ was intramuscular acepromazine (ACP) 25 μg kg⁻¹, morphine 0.5 mg kg⁻¹ and medetomidine 5 μg kg⁻¹. Group M− received ACP and morphine only, at the same dose rate. After induction with thiopental, anaesthesia was maintained with halothane in oxygen and nitrous oxide. End-tidal halothane concentration was maintained at 1.1%. Neuromuscular blockade was produced with intravenous vecuronium (50 μg kg⁻¹) and monitored using a train of four stimulus applied at the ulnar nerve. The times taken for loss and reappearance of the four evoked responses (twitches [T]) were recorded. Normal and nonparametric data were analysed with an independent t-test and Mann-Whitney's U-test, respectively.ResultsThe fourth twitch (T4) disappeared at similar times in each group: 107 ± 19; [72–132] (mean ± SD; [range]) seconds in M+ and 98 ± 17 [72–120] seconds in M− dogs. The first twitch (T1) was lost at 116 ± 15; [96–132] seconds in group M+ and 109 ± 19; [72–132] seconds in M−. The fourth twitch returned significantly earlier in M+ dogs: 20.8 ± 3.8 [14–28] minutes compared with 23.8 ± 2.7 [20–27] minutes (p = 0.032). The duration of drug effect (T4 absent) was significantly shorter (p = 0.027) in M+ (18.9 ± 3.7 minutes) compared with M− dogs (22.2 ± 2.9 minutes). The recovery rate (interval between reappearance of T1 and T4) was significantly more rapid (p = 0.0003) in medetomidine recipients (3.0 ± 1.2 versus 5.2 ± 1.3 minutes).Conclusion and clinical relevance Medetomidine 5 μg kg⁻¹ as pre-anaesthetic medication shortened the duration of effect of vecuronium in halothane-anaesthetized dogs and accelerated recovery, but did not affect the onset time. These changes are of limited clinical significance.     

Mandibular nerve block in juvenile Nile crocodile: a cadaveric study

ObjectiveTo develop a technique for performing the mandibular nerve block in Nile crocodiles.Study designExperimental cadaveric study.AnimalsA total of 16 juvenile Nile crocodile heads.MethodsTo study the course of the mandibular nerve, one head was dissected. Computed tomography (CT) examination was performed in two heads to identify useful landmarks. Thereafter, a hypodermic needle was inserted through the external mandibular fenestra of 17 hemimandibles (13 heads), and a mixture of methylene blue and iohexol was injected. Injection volumes were 0.5 (n = 7) and 1.0 mL (n = 10) for hemimandibles < 15 and ≥ 15 cm long, respectively. Iohexol spread and nerve staining with methylene blue were assessed with CT and anatomical dissection, respectively. Data were analysed with one-sample t test or Mann–Whitney U test. Significance was set at p < 0.05.ResultsBoth anatomical dissection and imaging confirmed the external mandibular fenestra as a useful anatomical landmark for needle insertion. The CT images acquired after needle positioning confirmed that its tip was located on the medial bony mandibular surface formed by the fusion of the angular and coronoid bones in 100% cases. In all the hemimandibles, the rostrocaudal spread of contrast was > 23 mm. The length of the stained mandibular nerve in the temporal region and of the stained medial branch of the mandibular nerve, as well as the dorsoventral and mediolateral spread of iohexol, was greater in group 1.0 than in group 0.5 (p < 0.001). The caudal spread of iohexol was greater in group 1.0 than in group 0.5 (p = 0.01).Conclusions and clinical relevanceThe technique developed in this study is feasible. Both injection volumes resulted in staining of the mandibular nerve. The spread of contrast in the anatomical region of interest may result in successful sensory block.     

Diabetes mellitus affects the duration of action of vecuronium in dogs

ObjectiveTo compare the duration of action of vecuronium in diabetic dogs with a control group.Study designProspective clinical study.AnimalsForty client-owned diabetic (n = 20) and non-diabetic dogs.MethodsDogs were considered free from other concurrent disease based on clinical examination and laboratory data. After pre-anaesthetic medication with acepromazine and methadone, anaesthesia was induced with intravenous (IV) propofol and maintained with isoflurane-nitrous oxide in oxygen. Neuromuscular blockade (NMB) was achieved with vecuronium, 0.1 mg kg^?1 IV and its effects recorded by palpation (pelvic limb digital extension) and electromyography (m. tibialis cranialis) of responses (twitches; T) to repeated train-of-four (TOF) nerve stimulation. Time to onset of NMB was the period between vecuronium injection and loss of fourth twitch (T4) in the TOF pattern recorded by EMG and palpation. Duration of NMB was defined as the time from drug administration to return of T1 by palpation (T1_tactile) and EMG (T1_EMG). Times to return of T2-4 were also recorded. Time from induction of anaesthesia to vecuronium injection was recorded. Heart rate, non-invasive mean arterial pressure, body temperature, end-tidal isoflurane and end-tidal CO₂ concentrations were recorded at onset of NMB and when T1_EMG returned. Loss and return of palpable and EMG responses for diabetic and non-diabetic dogs were compared using t-tests and Mann Whitney U-tests.ResultsThere were significant (p < 0.05) differences between diabetic and non-diabetic dogs for the return of all four palpable and EMG responses. Times (mean ± SD) for return of T1_tactile were 13.2 ± 3.5 and 16.9 ± 4.2 minutes in diabetic and non-diabetic dogs respectively. There were no differences between diabetic and non-diabetic dogs in the time to onset of vecuronium with EMG or tactile monitoring.Conclusions and clinical relevanceThe duration of action of vecuronium was shorter in diabetic dogs as indicated by both tactile and EMG monitoring.     

Haemodynamic differences between pancuronium and vecuronium in an experimental pig model

ObjectiveTo compare baseline cardiovascular function in anesthetised pigs using either pancuronium or vecuronium as a neuromuscular blocker.Study designRetrospective, non-randomized comparison.AnimalsNorwegian Land Race pigs (Sus scrofa domesticus) weighing mean 42 ± SD 3 kg.MethodsOne 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).ResultsThe 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 pancuronium-treated animals, demonstrated as a reduction in the nonlinear end-diastolic pressure volume relationship β 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 end-diastolic pressure volume relationship EDPVR_lin 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.ConclusionsThere 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 relevanceExperimental studies in pigs using either pancuronium or vecuronium as a neuromuscular blocking agent are comparable with regard to cardiac and haemodynamic performance.