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.     

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.

Neuromuscular blocking properties of atracurium during sevoflurane or propofol anaesthesia in dogs

OBJECTIVE: To quantify the neuromuscular blockade (NMB) produced by atracurium in either sevoflurane or propofol-anaesthetized dogs. ANIMALS: Twelve healthy, female adult mixed-breed dogs weighing 13 +/- 3 kg (range 10-22 kg). MATERIALS AND METHODS: Three doses of atracurium (0.1, 0.2 and 0.3 mg kg(-1)) were tested at 1-week intervals. Anaesthesia was induced with inhaled sevoflurane or intravenous propofol and maintained with end-tidal sevoflurane concentrations of 1.95% (1.25 x MAC) or propofol 0.6 mg kg(-1) minute(-1) respectively. Acceleromyography and train-of-four stimulation of the fibular nerve were used for the assessment of NMB. The percentage depression of the first twitch (T1) and the fourth to the first twitch ratio (T4/T1), the maximum degree of neuromuscular block achieved and surgical muscle relaxation were recorded. Before and during neuro muscular blockade (at 10 minute intervals) body temperature, ECG, arterial blood pressure, inspired and expired CO2 concentrations and SpO2 were recorded. RESULTS: Atracurium produced a dose-dependent duration of NMB in both propofol and sevoflurane-anaesthetized dogs. Duration of block was longer in dogs anaesthetized with sevoflurane. All studied doses of atracurium caused twitch depression > or =95% with little or no cardiovascular changes. CONCLUSIONS: Sevoflurane produces a clinically relevant potentiation of atracurium-induced NMB in dogs compared with propofol. CLINICAL RELEVANCE: Significant differences in the potentiation of NMB drugs are encountered with commonly used anaesthetics in the dog.     

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.

Diabetes mellitus does not affect the neuromuscular blocking action of atracurium in dogs

Objective

To compare the duration of action of atracurium in diabetic and nondiabetic dogs.

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.     

Clinical use of the neuromuscular blocking agents atracurium and pancuronium for equine anesthesia

Neuromuscular blocking agents (muscle relaxants) are useful and common adjuncts to general anesthesia for human beings, but have not been used extensively during anesthesia of large animal species. Over a 3-year period, atracurium or pancuronium were used as adjuncts to general anesthesia for 89 anesthetic procedures in 88 equids (of 18 breeds and age ranging in age from 5 weeks to 25 years) at the teaching hospital. Forty-one of the anesthetic procedures were for abdominal surgery, and orthopedic (n = 19), ophthalmologic (n = 17), thoracotomy (n = 1), and soft tissue (n = 14) procedures composed the rest. Most equids were given atracurium because it was less expensive than pancuronium. Initial dosage of either relaxant ranged from 0.12 to 0.2 mg/kg of body weight IV, and repeat doses ranged from 10 to 30 mg. Relaxants were used for as long as 205 minutes. Muscles of the face or hind limb digital extensor muscles were used to monitor relaxation. Muscles of the hind limb were more sensitive to the effects of relaxants than were muscles of the face. At the end of a surgical procedure, just prior to being taken to the recovery stall, a relaxant antagonist, edrophonium (0.5 to 1 mg/kg), was administered IV to each equid. Edrophonium caused blood pressure to increase in most of the equids. Heart rate change was variable, with approximately half the equids having no change or increased heart rate and the remainder having decreased heart rate. Recovery to standing after anesthesia was rated excellent or good for 72 equids, fair for 11, and poor for 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of neostigmine antagonism at different levels of vecuronium-induced neuromuscular blockade in isoflurane anesthetized dogs

Residual neuromuscular block (NMB) during recovery from general anesthesia may be minimized by antagonizing NMB with neostigmine. We examined neostigmine for restoring neuromuscular function when administered at 2 levels of vecuronium-induced NMB in dogs. Eight healthy adult dogs received vecuronium 0.1 mg/kg body weight (BW), IV, during isoflurane anesthesia. Recovery from vecuronium occurred spontaneously (control group; C), or was enhanced with neostigmine, 0.04 mg/kg BW, IV, administered when 2 (N2) or 4 (N4) responses to train-of-four (TOF) stimulation were first observed. Duration of NMB was significantly shorter for N2 and N4 than for C. The period of complete NMB was equal for all groups; differences were observed during the recovery phase of NMB. Time of neostigmine-enhanced recovery was significantly shorter for N4 than N2, but overall duration of NMB was not reduced. Recovery from NMB was faster with neostigmine. There is no clinical advantage in delaying neostigmine administration once 2 responses to TOF are present.     

Continuous infusion of ketamine in hypovolemic dogs anesthetized with desflurane

Objective: To evaluate the cardiorespiratory effects of continuous infusion of ketamine in hypovolemic dogs anesthetized with desflurane. Design: A prospective experimental study. Animals: Twelve mixed breed dogs allocated into 2 groups: saline (n=6) and ketamine (n=6). Interventions: After obtaining baseline measurements (time [T] 0) in awake dogs, hypovolemia was induced by the removal of 40 mL of blood/kg over 30 minutes. Anesthesia was induced and maintained with desflurane (1.5 minimal alveolar concentration) and 30 minutes later (T75) a continuous intravenous (IV) infusion of saline or ketamine (100 μg/kg/min) was initiated. Cardiorespiratory evaluations were obtained 15 minutes after hemorrhage (T45), 30 minutes after desflurane anesthesia, and immediately before initiating the infusion (T75), and 5 (T80), 15 (T90), 30 (T105) and 45 (T120) minutes after beginning the infusion. Measurements and main results: Hypovolemia (T45) reduced the arterial blood pressures (systolic arterial pressure, diastolic arterial pressure [DAP] and mean arterial pressure [MAP]), cardiac (CI) and systolic (SI) indexes, and mean pulmonary arterial pressure (PAP) in both groups. After 30 minutes of desflurane anesthesia (T75), an additional decrease of MAP in both groups was observed, heart rate was higher than T0 at T75, T80, T90 and T105 in saline‐treated dogs only, and the CI was higher in the ketamine group than in the saline group at T75. Five minutes after starting the infusion (T80), respiratory rate (RR) was lower and the end‐tidal CO₂ (ETCO₂) was higher compared with values at T45 in ketamine‐treated dogs. Mean values of ETCO₂ were higher in ketamine than in saline dogs between T75 and T120. The systemic vascular resistance index (SVRI) was decreased between T80 and T120 in ketamine when compared with T45. Conclusions: Continuous IV infusion of ketamine in hypovolemic dogs anesthetized with desflurane induced an increase in ETCO₂, but other cardiorespiratory alterations did not differ from those observed when the same concentration of desflurane was used as the sole anesthetic agent. However, this study did not evaluate the effectiveness of ketamine infusion in reducing desflurane dose requirements in hypovolemic dogs or the cardiorespiratory effects of ketamine–desflurane balanced anesthesia.     

Cardiopulmonary effects of a new inspiratory impedance threshold device in anesthetized hypotensive dogs

ObjectiveTo compare the hemodynamic and respiratory effects of an inspiratory impedance threshold device (ITD) in anesthetized normotensive and hypotensive dogs.Study designProspective randomized study.AnimalsTen adult dogs.MethodsDogs were anesthetized with propofol followed by isoflurane. During spontaneous ventilation, tidal volume ( $\dot{\mathrm{V}}$), systolic (SAP), mean (MAP) and diastolic arterial blood pressure, central venous pressure, gastric PCO₂ as an indicator of gastric perfusion, subcutaneous oxygen tension, subcutaneous blood flow, cardiac index (CI), systemic vascular resistance and blood lactate were monitored. To monitor respiratory compliance (RC) and resistance (ResR), animals were briefly placed on mechanical ventilation. Dogs were studied under four different conditions: 1) normotension (MAP > 60 mmHg) with and without the ITD and 2) hypotension (target MAP = 40 mmHg) with and without ITD. These four conditions were performed during one anesthetic period, allowing for stabilization of parameters for each condition. Data were analyzed by anova repeated measure mixed models.ResultsNo cardiovascular changes were detected between no ITD and ITD in the normotensive state. During hypotension, CI was higher with the ITD (5 ± 1.0 L minute^?1 m^?2) compared with no ITD (4 ± 1.3 L minute^?1 m^?2). During hypotension, SAP was increased with ITD (80 ± 14 mmHg) versus without ITD (67 ± 13 mmHg). There was an increase in ResR and decreased RC with the ITD in both normotensive and hypotensive state.Conclusion and clinical relevanceImpedance threshold device in dogs during isoflurane-induced hypotension improved CI and SAP but had negative effects on RC and ResR.     

Indirect measurement of blood pressure using a pulse oximeter in isoflurane anesthetized dogs

Objective: To determine the accuracy of indirect blood pressure (BP) measurements obtained with a pulse oximeter as compared with direct measurements in dogs under isoflurane anesthesia. The Doppler and oscillometric BP monitors were included for comparison. Design: Prospective, experimental study. Animals: Twenty healthy dogs (23 ± 8 kg) anesthetized for research or teaching. Interventions: Dogs were anesthetized with propofol or thiopental and maintained using positive pressure ventilation with isoflurane in 100% O₂. Random adjustment of BP was achieved by inhalant adjustment or dopamine infusion to achieve low (≤85 mmHg), normal (90–120 mmHg), or high systolic BP (≥125 mmHg). Triplicate measurements for BP were taken with direct (dorsal pedal artery), Doppler (forelimb), oscillometric (same forelimb), and plethysmographic (pulse oximeter on tongue) methods. Measurements and main results: Using regression analysis and a modified Bland–Altman's technique, the lowest bias was achieved with the Doppler. Systolic BP readings at low, normal, and high BP were within 10 mmHg of direct recordings 95%, 70%, and 30% of the time for pulse oximetry; 95%, 85%, and 55% of the time for Doppler; 42%, 65%, and 30% of the time for oscillometric determination, respectively. Oscillometric mean BP readings were within 10 mmHg of direct measurements 53%, 60%, and 45% of the time, respectively. Conclusions: The pulse oximeter is an acceptable method for measuring BP in anesthetized dogs if assessment of trends is sufficient. All indirect methods showed greater bias and poorer precision at high BP. The Doppler may be the preferred indirect method.     

Investigation into the use of the laryngeal mask airway in pentobarbital anesthetized dogs

OBJECTIVE: To investigate the use of the laryngeal mask airway (LMA) in dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Eight healthy adult mixed breed dogs weighing from 15 to 20 kg. METHODS: The dogs were anesthetized with intravenous pentobarbital. An LMA was introduced after the induction of anesthesia and 1 L/min O2 plus 1 L/min air was delivered using a circle anesthetic system. Respiratory rate, tidal volume, arterial O2 saturation (pulse oximetry), end tidal CO2, inspired fraction of O2, pulse rate, and mean arterial blood pressure were measured after the insertion of the LMA and 30, 60, 90, and 120 minutes afterwards. RESULTS: There were no changes in respiratory rate, tidal volume, arterial O2 saturation, and pulse rate during anesthesia. End tidal CO2 decreased significantly by the end of anesthesia and ventilation appeared satisfactory. CONCLUSIONS: An LMA appeared to be an alternative option to maintain the patency of the airway in dogs. CLINICAL RELEVANCE: This device may allow safe maintenance of an airway in dogs when intubation is difficult or when it interferes with the procedure (eg, cervical myelography).     

Definition and clinical evaluation of a recruiting airway pressure based on the specific lung elastance in anesthetized dogs

ObjectiveTo determine the specific lung elastance (SE_L) in anesthetized dogs and to evaluate the efficacy of a SE_L-based recruiting airway pressure (RP_aw) at improving global and regional lung aeration.Study designRetrospective and prospective clinical study.AnimalsA total of 28 adult dogs were included in the retrospective study and six adult dogs in the prospective study.MethodsRetrospective study: SE_L and SE_L-based RP_aw were determined using previously published data. In mechanically ventilated dogs undergoing thoracic computed tomography (CT), SE_L was calculated as ΔP_L/(V_T/EELV), where ΔP_L is the driving transpulmonary pressure, V_T is the tidal volume and EELV is the end-expiratory lung volume. The ratio of lung to respiratory system elastance (E_L/E_rs) was determined. SE_L and E_L/E_rs were used to calculate the SE_L-based RP_aw. Prospective study: dogs underwent thoracic CT at end-expiration and at end-inspiration using the SE_L-based RP_aw, and global and regional aeration was determined. For analysis of regional aeration, lungs were divided into cranial, intermediate and caudal regions. Regional compliance was also calculated. A p value <0.05 was considered significant.ResultsThe SE_L and E_L/E_rs were 12.7 ± 3.1 cmH₂O and 0.54 ± 0.07, respectively. The SE_L-based RP_aw was 29.1 ± 7.6 cmH₂O. In the prospective study, the RP_aw was 28.2 ± 1.3 cmH₂O. During RP_aw, hyperinflation increased (p = 0.0003) whereas poorly aerated (p < 0.0001) and nonaerated (p = 0.01) tissue decreased. Normally aerated tissue did not change (p = 0.265). Regional compliance was higher in the intermediate (p = 0.0003) and caudal (p = 0.034) regions compared with the cranial region. Aeration did not differ between regions (p > 0.05).Conclusions and clinical relevanceAn SE_L-based RP_aw reduces poorly and nonaerated lung tissue in anesthetized dogs. In nonsurgical anesthetized dogs, an RP_aw near 30 cmH₂O is effective at improving lung aeration.     

Effects of nitrous oxide on IOP and pupillary diameter in dogs anesthetized with varying concentrations of desflurane

Objective The aim of the present study was to evaluate the effects of nitrous oxide on IOP and pupillary diameter (PD) of dogs anesthetized with varying desflurane concentrations. Animals studied Twenty adult Mongrel dogs were used. Methods They were anesthetized with propofol (10 mg/kg, IV) and maintained with varying concentrations of desflurane (1.6, 1.4, and 1.2 MAC) diluted in 100% oxygen (G1) or in 70% nitrous oxide and 30% oxygen (G2) (30 mL/kg/min). IOP was measured by applanation tonometry and horizontal PD was taken with a caliper adjacent to the cornea. Mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), and end‐tidal CO₂ (etCO₂) were also measured. All parameters were measured at T0, T30, T45, and T60 time points. One‐way repeated measures anova and the t‐test were used to assess statistical differences (P < 0.05). Results T30, T45, and T60 IOP measures were within normal limits for both groups and IOP did not differ between groups at any time. There was a significant decrease in PD in G1 between T0 and T30, T45 and T60, and also between T30 and T60. PD did not differ between groups. All vital parameters were within normal limits throughout anesthesia. Conclusions Administration of nitrous oxide with desflurane results in maintenance of normal IOP and prevents a decrease in horizontal PD during anesthesia. Therefore, this may be a suitable protocol in dogs undergoing intraocular surgeries that require mydriasis and maintenance of normal IOP.     

Contrast enhanced ultrasonography of kidney in conscious and anesthetized beagle dogs

Contrast enhanced ultrasound (CEUS) is useful to evaluate tissue perfusion in the kidney. In veterinarymedicine, sedation or anesthesia may be required in uncooperative or panting patients. The aim of this studywas to evaluate and compare the normal kidney perfusion patterns in conscious and anesthetized dogs usingCEUS. Eight healthy beagles were used in this study. Scanning was performed in conscious dogs using manualrestraint (conscious group), or under general anesthesia using tiletamine-zolazepam and medetomidine (TZMgroup) or medetomidine (M group). The contrast agent (Sonovue^®) was administered as an IV bolus.The peak intensity (PI), time to peak enhancement from injection (TTP₀) and the time to peakenhancement from the initial rise (TTP_up), upslope, downslope and area under the curve (AUC) wereanalyzed. Compared to the cortical values in the conscious group, TTP₀ was significantly delayed inthe TZM group, and upslope, TTP₀ and TTP_up were significantly different in the M group.The AUCs in the TZM and M groups were not different from those in the conscious group. The upslope of renalmedullary perfusion was significantly decreased in the TZM and M groups. TTP₀ and TTP_upwere also significantly delayed in these groups. The AUC of the medulla was significantly decreased in the Mgroup. Therefore, TZM is useful as an anesthetic protocol when performing CEUS, and the obtained data mayserve as reference values in the evaluation of renal perfusion using CEUS in dogs under anesthesia.     

Observations on the use of tetracycline and niacinamide as antipruritic agents in atopic dogs

Tetracycline and niacinamide were administered in combination to 19 atopic dogs to determine their effectiveness in controlling pruritus. The pruritus was controlled successfully in only one dog. One dog experienced diarrhea that was severe enough to warrant stopping the medication.     

Correlation between clinical signs of depth of anaesthesia and cerebral state index responses in dogs with different target-controlled infusions of propofol

ObjectiveTo evaluate if the cerebral state index (CSI), measured by a Cerebral State Monitor (CSM), can predict depth of anaesthesia as assessed clinically or by estimated propofol plasma concentrations.Study designProspective clinical study.AnimalsFourteen mixed breed dogs, weighing 24.5 ± 4.7 kg, scheduled to undergo neutering procedures.MethodsDogs were premedicated with 0.05 mg kg^?1 acepromazine intramuscularly. The CSM and cardiovascular monitoring equipment were attached. Anaesthesia was induced with propofol using a target controlled infusion (TCI) to varying plasma propofol targets (PropCp). Following endotracheal intubation the dogs were ventilated with oxygen. Anaesthetic maintenance was with propofol by TCI. A PropCp of 3 μg dL^?1 was set initially, then PropCps were increased in 1 μg dL^?1 steps to 7, 9 and then 11 μg dL^?1. Each PropCp was held constant for a 5 minute period, at the end of which depth of anaesthesia was classified using a previously evaluated scale of ‘planes’ based on palpebral and corneal reflexes and eye position. Cerebral state index (CSI), burst suppression (BSR) and electromyogram were measured at these time points. The prediction probability (PK) of these variables, or of the PropCp in predicting depth of anaesthesia was calculated.ResultsThe PKs for predicting anaesthetic planes were 0.74, 0.91, 0.76 and 0.78 for CSI, BSR, EMG and PropCp, respectively. The PKs for PropCp to predict CSI, BSR and EMG were 0.65, 0.71 and 0.65 respectively.Conclusion and clinical relevance The Cerebral State Monitor was able to detect very deep planes of anaesthesia when BSR occurs, but was not able to distinguish between the intermediate anaesthetic planes likely to be used in clinical anaesthesia.     

Ultrasonographical identification of the superficial circumflex iliac artery as a landmark for location of the femoral nerve in dogs

Objective

To investigate the utility of identifying the superficial circumflex iliac artery (SCIA) via ultrasound as an anatomical landmark for ultrasound-guided femoral nerve block.

贵州黑山羊胚胎移植手术不同麻醉方法比较

为了筛选适合于贵州黑山羊胚胎移植手术的麻醉方法,试验以贵州黑山羊为试验动物,比较了速眠新Ⅱ注射液2种麻醉方法（肌肉麻醉和静脉麻醉）对山羊生理指标,麻醉山羊的诱导期、麻醉期、苏醒期,麻醉苏醒后山羊的采食、反刍及精神状况的影响。结果表明：2种麻醉方法下,麻醉效果优、良的山羊数量和生理指标无明显差异;速眠新Ⅱ注射液静脉注射麻醉时,山羊的诱导期、麻醉期和苏醒期均较短,在苏醒后0.5 h,90.0%的山羊可以采食,83.3%的山羊可以反刍,93.3%的山羊精神状况良好;苏醒后1 h基本上全部可以恢复正常;采用静脉注射麻醉山羊进行胚胎移植手术,速眠新Ⅱ注射液用药剂量小,且安全、有效,明显优于肌肉注射。