Doppler blood pressure measurement in pigs during anaesthesia

To determine the accuracy of Doppler blood pressure measurement in anaesthetised pigs eight large white pigs (Sus scrofa) were anaesthetised with zolazepam and tiletamine as Zoletil 100 (4 mg/kg) and xylazine (2 mg/kg) by intramuscular injection followed by isoflurane in 100% oxygen. Blood pressure measurements were recorded using a Doppler probe on the radial artery and a catheter in the femoral artery connected to a transducer. The sample mean of the Doppler measurements were compared with the sample mean of the invasive systolic arterial blood pressure while accounting for the heart rate, end-tidal CO₂ and temperature. The predicted error of the Doppler was greatest when pigs were hypotensive and normothermic: 11 mmHg (CI: 6–15). Doppler measurements should be interpreted with caution in anaesthetised pigs that are hypotensive and normothermic.     

Comparison of racemic ketamine and S-ketamine as agents for the induction of anaesthesia in goats

ObjectiveTo compare racemic ketamine and S-ketamine as induction agents prior to isoflurane anaesthesia.Study designProspective, blinded, randomized experimental study.AnimalsThirty-one healthy adult goats weighing 39-86 kg.MethodsGoats were premedicated with xylazine (0.1 mg kg^?1) intravenously (IV) given over 5 minutes. Each goat was assigned randomly to one of two treatments for IV anaesthetic induction: group RK (15 goats) racemic ketamine (3 mg kg^?1) and group SK (16 goats) S-ketamine (1.5 mg kg^?1). Time from end-injection to recumbency was measured and quality of anaesthetic induction and condition for endotracheal intubation were scored. Anaesthesia was maintained with isoflurane in oxygen for 90 minutes. Heart rate, invasive arterial blood pressure, oxygen saturation, temperature, end-tidal carbon dioxide and isoflurane were recorded every 5 minutes. Arterial blood samples were taken for analysis every 30 minutes. Recovery time to recurrence of swallowing reflex, to first head movement and to standing were recorded and recovery quality was scored. Two-way repeated measures anova, Mann-Whitney and a Mantel-Cox tests were used for statistical analysis as relevant with a significance level set at p < 0.05.ResultsInduction of anaesthesia was smooth and uneventful in all goats. There was no statistical difference between groups in any measured parameter. Side effects following anaesthetic induction included slight head or limb twitching, moving forward and backward, salivation and nystagmus but were minimal. Endotracheal intubation was achieved in all goats at first or second attempt. Recovery was uneventful on all occasions. All goats were quiet and needed only one or two attempts to stand.Conclusions and clinical relevanceS-ketamine at half the dose rate of racemic ketamine in goats sedated with xylazine and thereafter anaesthetised with isoflurane induces the same clinically measurable effects.     

Anaesthetic sparing effect of local anaesthesia of the ovarian pedicle during ovariohysterectomy in dogs

ObjectiveTo evaluate the effect of local anaesthesia of the mesovarium on end-tidal isoflurane (Fe′_iso) concentration and vital parameters during canine ovariohysterectomy.Study designProspective, randomized, blinded study.AnimalsTwenty client-owned dogs undergoing elective ovariohysterectomy. Mean age 1.7 (±0.53, SD) years and mean body weight 21 kg (±5.9, SD).MethodsPre-medication was with intravenous acepromazine (0.02 mg kg⁻¹) and methadone (0.1 mg kg⁻¹). Anaesthesia was induced with propofol and maintained with isoflurane in oxygen. One group (n = 10) received local infiltration of the mesovarium with 0.5 mL lidocaine 2% and one group (n = 10) with 0.5 mL NaCl 0.9%. Heart (HR) and respiratory rates (fr), invasive mean arterial blood pressure (MAP) and Fe′_isowere recorded. The Fe′_iso was adjusted according to changes in HR, RR and MAP. Time points used for comparison were T1 (after induction of anaesthesia before surgery), T2 (after lidocaine infiltration of the mesovarium) and T3 (surgical manipulation of the ovaries). Data were analysed using a mixed model for repeated measurement anova and the Tukey adjustment. Results are presented as mean ± SD; p < 0.05 was considered significant.ResultsIn both groups, HR and fr remained stable at the three time points. Mean values ranged from 84 to 94 beats minute⁻¹ and from 10 to 14 breaths minute⁻¹. The Fe′_iso was significantly lower at T3 compared to T1 and mean values ranged from 0.95% to 1.24%. The mean arterial blood pressure was significantly higher at T3 compared to T1 and mean values ranged from 58 to 96 mm Hg. At none of the time points were there significant differences between the two groups for HR, fr, MAP or Fe′_iso.ConclusionNeither an isoflurane sparing effect nor a difference in autonomic response to surgery was demonstrated following local anaesthesia of the mesovarium.Clinical relevanceThere appeared to be minimal benefit from local anaesthesia of the mesovarium during this study.     

ANGIOGRAPHIC APPEARANCE OF COMMON CAROTID COLLATERAL CIRCULATION IN THE GOAT RESULTING FROM PROSTHETIC GRAFT IMPLANTATION

Carotid arteriography was performed in six normal goats. The same procedure was performed on these six and 112 other goats at various time intervals after placement of an arterial graft in one or both carotid arteries. An arterial catheter was introduced into the femoral artery and advanced to the origin of the brachiocephalic trunk with the aid of image-intensified fluoroscopy. Hand-injection of the contrast medium resulted in complete opacification of both common carotid arteries in normal animals. Opacification of one or both of the vertebral arteries was usually seen in the goats with prosthetic grafts. The left vertebral artery was seen more often than the right, and when both vertebral arteries were seen together, the left was often larger. This angiographic method proved to be reliable for opacifying both common carotid arteries from their origin on the brachiocephalic trunk to the cranial cervical region. No clinical problems were associated with either the catheterization procedure or with the permanent ligation of the catheterized femoral artery.     

Agreement between arterial and central venous blood pH and its contributing variables in anaesthetized dogs with respiratory acidosis

ObjectiveTo determine the accuracy of variables that influence blood pH, obtained from central venous (jugular vein) blood samples compared with arterial (dorsal pedal artery) samples in anaesthetized dogs with respiratory acidosis.Study designProspective, comparative, observational study.AnimalsA group of 15 adult male dogs of various breeds weighing 17 (11-42) kg [median (range)].MethodsDogs were premedicated with buprenorphine (0.03 mg kg^–1) and medetomidine (0.01 mg kg^–1) administered intramuscularly by separate injections, anaesthetized with propofol intravenously to effect and maintained with isoflurane in 50% air-oxygen. Arterial and central venous catheters were placed. After 15 minutes of spontaneous breathing, arterial and central venous blood samples were obtained and analysed within 5 minutes, using a bench-top gas analyser. Differences between arterial and central venous pH and measured variables were assessed using Wilcoxon rank sum test and effect size (r: matched-pairs rank-biserial correlation) was calculated for each comparison. The agreement (bias and limits of agreement: LoAs) between arterial and central venous pH and measured variables were assessed using Bland-Altman; p < 0.05. Data are reported as median and 95% confidence interval.ResultsArterial blood pH was 7.23 (7.19-7.25), and it was significantly greater than central venous samples 7.21 (7.18-7.22; r = 0.41). Agreement between arterial and venous pH was acceptable with a bias of 0.01 (0.002-0.02) and narrow LoAs. PCO₂ [arterial 54 (53-58) mmHg, 7.2 (7.1-7.7) kPa; venous 57 (54-62) mmHg, 7.6 (7.2-8.3) kPa], bicarbonate ion concentration and base excess did not differ between samples; however, agreement between arterial and venous PCO₂ was not acceptable with a bias of –2 (–5 to 0) mmHg and wide LoAs.Conclusions and clinical relevanceBlood pH measured from central venous (jugular vein) blood is an acceptable clinical alternative to arterial blood (dorsal pedal artery) in normovolaemic anaesthetized dogs with respiratory acidosis.     

Effects of isoflurane upon minimum alveolar concentration and cerebral cortex depression in pigs and goats: An interspecies comparison

This study compared the effects of isoflurane in pigs (n = 10 Yorkshire–Landrace cross) and dairy goats (n = 10) by evaluation of electroencephalographic (EEG) burst suppression thresholds (BST) in the cerebral cortex and minimum alveolar concentration (MAC) values in the spinal cord. The study also investigated whether individual MAC values can predict the effects of isoflurane on the cerebral cortex. MAC values and BST/MAC ratios were significantly different between species. Inhibition of movement by isoflurane may be less effective in pigs than in goats. No significant correlation was found between individual MAC and BST values, indicating that in single animals the individual MAC poorly reflects the cerebrocortical depressant effect of isoflurane in pigs and goats.     

A comparison of the haemodynamic effects of isoflurane and halothane anaesthesia in horses

The purpose of this study was to compare the haemodynamic effects of equipotent isoflurane and halothane anaesthesia. Six adult horses were investigated on two separate occasions at least 4 weeks apart. On both occasions anaesthesia was induced by ketamine 2.2 mg/kg bwt given 5 min after i.v. administration 100 microg/kg bwt romifidine. Anaesthesia was maintained either by halothane or isoflurane (end-tidal concentrations 0.9-1.0% and 1.3-1.4%, respectively). Horses were ventilated by intermittent positive pressure to maintain PaCO2 between 40-50 mmHg. Haemodynamic variables were measured using catheter-mounted strain gauge transducers in the left and right ventricle, aorta, and right atrium. Cardiac output (CO), velocity time integral (VTI), maximal aortic blood flow velocity (Vmax) and acceleration (dv/dt(max)), left ventricular pre-ejection period (PEP) and ejection time (ET) were measured from aortic blood flow velocity waveforms obtained by transoesophageal Doppler echocardiography. Flow velocity waveforms were recorded from the femoral arteries and veins using low pulse repetition frequency Doppler ultrasound. Time-averaged mean velocity (TAV), velocity of component a (TaVa), velocity of component b (TaVb) and early diastolic deceleration slope (EDDS) were measured. Pulsatility index (PI) and volumetric flow were calculated. Microvascular blood flow was measured in the left and right semimembranosus muscles by laser Doppler flowmetry. Maximal rate of rise of LV pressure (LVdp/dt(max)), CO, Vmax, dv/dt(max), ET, VTI were significantly higher at all time points during isoflurane anaesthesia compared to halothane anaesthesia. Pre-ejection period and diastolic aortic blood pressure were significantly less throughout isoflurane anaesthesia compared to halothane. Isoflurane anaesthesia was associated with significantly lower systemic vascular resistance than halothane anaesthesia. Femoral arterial and venous blood flow were significantly higher and EDDS and PI were significantly lower during isoflurane anaesthesia compared to halothane anaesthesia. In addition during both halothane and isoflurane anaesthesia, femoral arterial flow was higher and EDDS and PI lower in the left (dependent) artery compared to the right (nondependent) artery. This study supports previous work demonstrating improved left ventricular systolic function during isoflurane compared to halothane anaesthesia. This improvement was still evident after premedication with a potent-long acting alpha2-adrenoreceptor agonist, romifidine, and induction of anaesthesia with ketamine. There was also evidence of increased hindlimb blood flow during isoflurane anaesthesia. However, there were differences observed in flow between the left and right hindlimb during maintenance of anaesthesia with each agent, suggesting that there were differences in regional perfusion in anaesthetised horses caused by factors unrelated to agents administered.     

Effects of isoflurane on somatosensory-evoked potentials in calves: A pilot study

Somatosensory evoked potentials (SSEP) are used to monitor sensory function and are often recorded under general anesthesia. The objective of the study was to evaluate the effects of isoflurane on SSEPs in calves as it has not been reported. Eight calves (mean age: 40 days), were included in the study. Calves were anesthetized with a randomized sequence of four different isoflurane partial pressures. Blood gas analysis was performed before each measurement. SSEP were induced by repeated stimulation of the common dorsal digital nerve III. SSEPs were recorded from the lumbo-sacral junction (s-SSEP) and the head (c-SSEP). Latency and inter-amplitude of each peak were measured. For s-SSEP: One negative (N_sp1) and two positive (P_sp1 and P_sp2) peaks were identified in all tracings except for two calves. There was a significant effect of isoflurane on the latency of P_sp2 (P = 0.01). Inter-amplitude decreased significantly with PaO₂, PaCO₂ and temperature (P < 0.05). P_sp2 latency decreased with PaO₂ (P = 0.01). For c-SSEP: two positive (P_c1 and P_c2) and two negative (N_c1 and N_c2) peaks were identified. There were identifiable peaks for the analysis of P_c1 latencies only. There was a significant positive linear relation between end-tidal isoflurane partial pressure (ET_iso) and P_c1 latency (P = 0.04). None of the co-variables had a significant effect on the latency of P_c1 (P > 0.1). Isoflurane has a major impact on the recording of c-SSEP. Recording should be done at the lowest ET_iso as possible, and anesthesia parameters should be kept constant.     

Detomidine and the combination of detomidine and MK‐467, a peripheral alpha‐2 adrenoceptor antagonist,as premedication in horses anaesthetized with isoflurane

ObjectiveTo investigate MK-467 as part of premedication in horses anaesthetized with isoflurane.Study designExperimental, crossover study with a 14 day wash-out period.AnimalsSeven healthy horses.MethodsThe horses received either detomidine (20 μg kg⁻¹ IV) and butorphanol (20 μg kg⁻¹ IV) alone (DET) or with MK-467 (200 μg kg⁻¹ IV; DET + MK) as premedication. Anaesthesia was induced with ketamine (2.2 mg kg⁻¹) and midazolam (0.06 mg kg⁻¹) IV and maintained with isoflurane. Heart rate (HR), mean arterial pressure (MAP), end-tidal isoflurane concentration, end-tidal carbon dioxide tension, central venous pressure, fraction of inspired oxygen (FiO₂) and cardiac output were recorded. Blood samples were taken for blood gas analysis and to determine plasma drug concentrations. The cardiac index (CI), systemic vascular resistance (SVR), ratio of arterial oxygen tension to inspired oxygen (P_aO₂/FiO₂) and tissue oxygen delivery (DO₂) were calculated. Repeated measures anova was applied for HR, CI, MAP, SVR, lactate and blood gas variables. The Student's t-test was used for pairwise comparisons of drug concentrations, induction times and the amount of dobutamine administered. Significance was set at p < 0.05.ResultsThe induction time was shorter, reduction in MAP was detected, more dobutamine was given and HR and CI were higher after DET+MK, while SVR was higher with DET. Arterial oxygen tension and P_aO₂/FiO₂ (40 minutes after induction), DO₂ and venous partial pressure of oxygen (40 and 60 minutes after induction) were higher with DET+MK. Plasma detomidine concentrations were reduced in the group receiving MK-467. After DET+MK, the area under the plasma concentration time curve of butorphanol was smaller.Conclusions and clinical relevanceMK-467 enhances cardiac function and tissue oxygen delivery in horses sedated with detomidine before isoflurane anaesthesia. This finding could improve patient safety in the perioperative period. The dosage of MK-467 needs to be investigated to minimise the effect of MK-467 on MAP.     

The effects of halothane and isoflurane on cardiovascular function in dorsally recumbent horses undergoing surgery

ObjectiveTo determine the haemodynamic effects of halothane and isoflurane with spontaneous and controlled ventilation in dorsally recumbent horses undergoing elective surgery.Study designProspective randomized clinical trial.AnimalsTwenty-five adult horses, body mass 487 kg (range: 267–690).MethodsHorses undergoing elective surgery in dorsal recumbency were randomly assigned to one of four treatment groups, isoflurane (I) or halothane (H) anaesthesia, each with spontaneous (SB) or controlled ventilation (IPPV). Indices of cardiac function and femoral arterial blood flow (ABF) and resistance were measured using transoesophageal and transcutaneous Doppler echocardiography, respectively. Arterial blood pressure was measured directly.ResultsFour horses assigned to receive isoflurane and spontaneous ventilation (SBI) required IPPV, leaving only three groups for analysis: SBH, IPPVH and IPPVI. Two horses were excluded from the halothane groups because dobutamine was infused to maintain arterial blood pressure. Cardiac index (CI) was significantly greater, and pre-ejection period (PEP) shorter, during isoflurane compared with halothane anaesthesia with both spontaneous (p = 0.04, p = 0.0006, respectively) or controlled ventilation (p = 0.04, p = 0.008, respectively). There was an association between CI and PaCO₂ (p = 0.04) such that CI increased by 0.45 L minute⁻¹m⁻² for every kPa increase in PaCO₂. Femoral ABF was only significantly higher during isoflurane compared with halothane anaesthesia during IPPV (p = 0.0006). There was a significant temporal decrease in CI, but not femoral arterial flow.ConclusionThe previously reported superior cardiovascular function during isoflurane compared with halothane anaesthesia was maintained in horses undergoing surgery. However, in these clinical subjects, a progressive decrease in CI, which was independent of ventilatory mode, was observed with both anaesthetic agents.Clinical relevanceCardiovascular function may deteriorate progressively in horses anaesthetized for brief (<2 hours) surgical procedures in dorsal recumbency. Although cardiovascular function is superior with isoflurane in dorsally recumbent horses, the need for IPPV may be greater.     

Cardiovascular effects of epidural administration of methadone, ropivacaine 0.75% and their combination in isoflurane anaesthetized dogs

ObjectiveTo compare the cardiovascular effects of four epidural treatments in isoflurane anaesthetised dogs.Study designProspective, randomized. experimental study.AnimalsSix female, neutered Beagle dogs (13.3 ± 1.0 kg), aged 3.6 ± 0.1 years.MethodsAnaesthesia was induced with propofol (8.3 ± 1.1 mg kg^?1) and maintained with isoflurane in a mixture of oxygen and air [inspiratory fraction of oxygen (FiO₂) = 40%], using intermittent positive pressure ventilation. Using a cross-over model, NaCl 0.9% (P); methadone 1% 0.1 mg kg^?1 (M); ropivacaine 0.75% 1.65 mg kg^?1 (R) or methadone 1% 0.1 mg kg^?1 + ropivacaine 0.75% 1.65 mg kg^?1 (RM) in equal volumes (0.23 mL kg^?1) using NaCl 0.9%, was administered epidurally at the level of the lumbosacral space. Treatment P was administered to five dogs only. Cardiovascular and respiratory variables, blood gases, and oesophageal temperature were recorded at T-15 and for 60 minutes after epidural injection (T0).ResultsMean overall heart rate (HR in beats minute^?1) was significantly lower after treatment M (119 ± 16) (p = 0.0019), R (110 ± 18) (p < 0.0001) and RM (109 ± 13) (p < 0.0001), compared to treatment P (135 ± 21). Additionally, a significant difference in HR between treatments RM and M was found (p = 0.04). After both ropivacaine treatments, systemic arterial pressures (sAP) were significantly lower compared to other treatments. No significant overall differences between treatments were present for central venous pressure, cardiac output, stroke volume, systemic vascular resistance, oxygen delivery and arterial oxygen content (CaO₂). Heart rate and sAP significantly increased after treatment P and M compared to baseline (T-15). With all treatments significant reductions from baseline were observed in oesophageal temperature, packed cell volume and CaO₂. A transient unilateral Horner’s syndrome occurred in one dog after treatment R.Conclusions and clinical relevanceClinically important low sAPs were observed after the ropivacaine epidural treatments in isoflurane anaesthetised dogs. Systemic arterial pressures were clinically acceptable when using epidural methadone.     

Hemodynamic effects of dexmedetomidine in isoflurane-anesthetized cats

ObjectiveTo characterize the hemodynamic effects of dexmedetomidine in isoflurane-anesthetized cats.Study designProspective experimental study.AnimalsSix healthy adult female cats weighing 4.6 ± 0.8 kg.MethodsDexmedetomidine was administered intravenously using target-controlled infusions to maintain nine plasma concentrations between 0 and 20 ng mL^?1 in isoflurane-anesthetized cats. The isoflurane concentration was adjusted for each dexmedetomidine concentration to maintain the equivalent of 1.25 times the minimum alveolar concentration, based on a previous study. Heart rate, systemic and pulmonary arterial pressures, central venous pressure, pulmonary artery occlusion pressure, body temperature, and cardiac output were measured at each target plasma dexmedetomidine concentration. Additional variables were calculated. Arterial and mixed-venous blood samples were collected for blood gas, pH, and (on arterial blood only) electrolyte, glucose and lactate analysis. Plasma dexmedetomidine concentration was determined for each target. Pharmacodynamic models were fitted to the data.ResultsHeart rate, arterial pH, arterial bicarbonate concentration, mixed-venous PO₂, mixed-venous pH, mixed-venous hemoglobin oxygen saturation, cardiac index, stroke index, and venous admixture decreased following dexmedetomidine administration. Arterial blood pressure, central venous pressure, pulmonary arterial pressure, pulmonary arterial occlusion pressure, packed cell volume, PaO₂, PaCO₂, arterial hemoglobin concentration, mixed-venous PCO₂, mixed-venous hemoglobin concentration, ionized calcium concentration, glucose concentration, rate-pressure product, systemic and pulmonary vascular resistance indices, left ventricular stroke work index, arterial oxygen concentration, and oxygen extraction increased following dexmedetomidine administration. Most variables changed in a dexmedetomidine concentration-dependent manner.Conclusion and clinical relevanceThe use of dexmedetomidine as an anesthetic adjunct is expected to produce greater negative hemodynamic effects than a higher, equipotent concentration of isoflurane alone.     

A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics

ObjectiveTo test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine–isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.Study designProspective blinded randomised clinical trial.Animals61 horses undergoing elective surgery.MethodsHorses were sedated with intravenous (IV) medetomidine (7 μg kg^?1); anaesthesia was induced with IV ketamine (2.2 mg kg^?1) and diazepam (0.02 mg kg^?1) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg^?1 hour^?1). Group MB (n = 31) received butorphanol CRI (25 μg kg^?1 IV bolus then 25 μg kg^?1 hour^?1); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO₂ in the normal range. Horses received lactated Ringer’s solution 5 mL kg^?1 hour^?1, dobutamine <1.25 μg kg^?1 minute^?1 and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann–Whitney Rank Sum test (p < 0.05).ResultsThere was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute^?1), pH, PaO₂ (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO_2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).Conclusion and clinical relevanceButorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine–isoflurane and has no influence on cardiopulmonary function or recovery.     

Anatomical location of arterial and venous lines significantly affects motor performance in rats

Several motor‐function scales have been developed to assess neurological function in animal models of stroke, subarachnoid hemorrhage and closed head injury. We hypothesize that the location of arterial and venous catheters, even in the absence of brain injury, may impact rats' motor performance. Our study examined the effect of catheter location, rate of infection and the time required for catheter placement. We further describe an original technique of tail artery cannulation without exposure of the artery. Sixty‐one rats were anesthetized and randomly assigned to one of seven groups, including no catheter, tail artery or artery + vein catheters, or femoral artery or artery + vein catheters. A neurological severity score (NSS) was determined at 1 h, 24 h and 48 h after surgical preparation or catheter placement. NSS at 1 h after placement of unilateral and bilateral femoral catheters was higher than the NSS observed at 1 h after placement of tail arterial and venous catheters (P < 0.01). The NSS also was higher at 24 h in the bilateral femoral catheter groups as compared with the tail catheter groups (P < 0.05). There were no differences in the NSS observed between the groups that had tail catheters and the sham group at 1 h, 24 h or 48 h. Infection rate at the site of catheter placement and the time required for catheter placement was also higher in the femoral catheter groups (P < 0.001). Thus, we propose that the line location may bias a study's results and lead to deceptive interpretations of neurological assessment following rat head injury. Compared to femoral vessels, tail blood vessels are preferable locations for lines placement.     

The use of lingual venous blood to determine the acid‐base and blood‐gas status of dogs under anesthesia

ObjectiveTo assess the suitability of lingual venous blood (LBG) as an alternative to arterial blood (ABG) samples in determining acid–base balance and blood–gas status in dogs anesthetized for elective procedures and with medetomidine and isoflurane administration under experimental conditions.Study designProspective, randomized clinical and experimental study.AnimalsClinical population of 18 ASA I/II dogs for elective surgery and five healthy Beagles (3 females and 2 males) for the experimental study.MethodsBlood sampling was simultaneously performed at dorsal pedal arterial and lingual venous sites, generating paired data. Two paired samples were collected from each dog in the clinical part and four from each dog in the experimental part (two during isoflurane anesthesia and two during isoflurane plus medetomidine). A modified Bland and Altman method was used to examine data from the clinical part and the experimental data were subjected to a paired sign's test following transformation where appropriate.ResultsThe pH of LBG overestimated ABG, with limits of agreement of (?0.01, 0.02). The partial pressure of carbon dioxide (PCO₂) of LBG overestimated ABG by 0.6 mmHg [0.1 kPa], with limits of agreement of (?3.5, 4.6) mmHg [?0.5, 0.6 kPa]. The partial pressure of oxygen (PO₂) of LBG underestimated ABG by 86.3 mmHg [?11.5 kPa], with limits of agreement of (?199.8, 27.3) mmHg [?26.6, 3.6 kPa]. During medetomidine administration values for PO₂ (p = 0.03) and lactate (p = 0.03) were lower for LBG when compared with ABG. The LBG value of PO₂ was lower (p = 0.03) during medetomidine and isoflurane administration versus isoflurane alone.Conclusions and clinical relevanceThe pH and PCO₂ of LBG samples provide clinically acceptable substitutes of ABG samples in the dog population studied. The wider limits of agreement for PO₂ render it less reliable as a substitute for ABG. The difference in PO₂ identified between LBG and ABG during medetomidine administration may not preclude the use of LBG as substitutes for ABG samples.     

Comparison of femoral and auricular arterial blood pressure monitoring in pigs

Objective To compare arterial blood pressure measurements obtained from the femoral and auricular arteries in anaesthetized pigs. Study design Prospective experimental study. Animals Fifteen female Large White pigs were used weighing 21.3 ± 2.3 kg. Methods The pigs were anaesthetized with tiletamine/zolazepam and xylazine administered intramuscularly, and anaesthesia maintained with isoflurane delivered in oxygen/nitrogen. Arterial oxygen partial pressures were maintained between 11.3 and 13.3 kPa and PaCO₂ between 4.6 and 6.0 kPa. Monitoring included electrocardiogram, capnography and invasive blood pressure. The auricular and femoral arteries were catheterized for continuous systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP) measurements. Measurements were recorded every 15 minutes. Statistical analysis involved a Bland–Altman plot analysis. Results The mean difference ± confidence intervals between the femoral and the auricular arterial diastolic, systolic and mean blood pressure measurements during hypotension were 2 ± 7, 2 ± 5 and 2 ± 5 mmHg respectively. In conditions of normotension mean difference ± confidence intervals, of femoral and auricular arterial blood pressure measurements of diastolic, systolic and mean blood pressure were 4 ± 5, 3 ± 7 and 4 ± 4 mmHg respectively. In conditions of increased arterial blood pressure, mean difference ± confidence intervals, of femoral and auricular arterial blood pressure measurements of diastolic, systolic and mean blood pressure were 4 ± 5, 3 ± 8 and 4 ± 4 mmHg respectively. Conclusion Auricular artery catheterization is easier and quicker to perform. Pressure measurements from the auricular artery compared well with the femoral artery. Clinical relevance We found that auricular arterial blood pressures were similar to femoral arterial values under the conditions of this experiment. We did not test extremes of blood pressure or significant alterations in body temperature.     

Effects of 8 hemodynamic conditions on direct blood pressure values obtained simultaneously from the carotid,femoral and dorsal pedal arteries in dogs

ObjectivesThis study aimed to evaluate the effect of 8 hemodynamic conditions on blood pressure measurements taken from the carotid, femoral and dorsal pedal arteries of dogs.AnimalsSix healthy dogs.MethodsDuring isoflurane anesthesia, catheters were introduced into the carotid, femoral and dorsal pedal arteries of dogs to allow simultaneous monitoring of direct blood pressure in each artery. The dogs were submitted to 8 hemodynamic conditions induced by combining changes in heart rate (bradycardia, normocardia, tachycardia) with changes in blood pressure (hypotension, normotension, hypertension). Values obtained from each arterial catheter were compared and agreement between central (carotid) and peripheral (femoral and dorsal pedal) values were analyzed by the Bland–Altman method.ResultsDuring hypotensive conditions, systolic arterial pressure (SAP) was lower in the femoral and dorsal pedal arteries compared to the carotid artery whereas during normotensive and hypertensive conditions, SAP was higher in peripheral arteries. During hypotensive states, increases in heart rate resulted in greater bias between central and peripheral SAP whereas during normotensive states, the bias decreased as heart rate increased. Mean and diastolic arterial pressures were lower in the femoral and dorsal pedal arteries than in the carotid artery during most hemodynamic conditions.ConclusionsIn healthy anesthetized dogs, invasive blood pressure measurements in peripheral arteries may differ significantly from measurements in a central artery. The greatest differences were observed in SAP and the magnitude of differences between central and peripheral blood pressure measurements varied according to the dog's hemodynamic condition.     

Hemodynamic effects of intravenous lidocaine in isoflurane anesthetized cats

Lidocaine dose‐dependently decreases the minimum alveolar concentration (MAC) of isoflurane in cats. The purpose of this study was to determine the hemodynamic effects of six lidocaine plasma concentrations in isoflurane anesthetized cats. Six cats were studied. After instrumentation, end‐tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration (MAC), which was determined in a previous study. Lidocaine was administered intravenously to target pseudo‐steady state plasma concentrations of 0, 3, 5, 7, 9, and 11 μg ml^–1, and isoflurane concentration was reduced to an equipotent concentration, determined in a previous study. Cardiovascular variables; blood gases; PCV; total protein and lactate concentrations; and lidocaine and monoethylglycinexylidide concentrations were measured at each lidocaine target concentration, before and during noxious stimulation. Derived variables were calculated. Data were analyzed using a repeated measures anova , followed by a Tukey test for pairwise comparisons where appropriate. One cat was excluded from analysis because the study was aborted at 7 μg ml^–1 due to severe cardiorespiratory depression. Heart rate, cardiac index, stroke index, right ventricular stroke work index, total protein concentration, mixed‐venous PO₂ and hemoglobin oxygen saturation, arterial and mixed‐venous bicarbonate concentrations, and oxygen delivery were significantly lower during lidocaine administration than when no lidocaine was administered. Mean arterial pressure, central venous pressure, pulmonary artery pressure, systemic and pulmonary vascular resistance indices, PCV, arterial and mixed‐venous hemoglobin concentrations, lactate concentration, arterial oxygen concentration, and oxygen extraction ratio were significantly higher during administration of lidocaine than when no lidocaine was administered. Most changes were significant at lidocaine target plasma concentrations of 7 μg ml^–1 and above. Noxious stimulation did not significantly affect most variables. Despite significantly decreasing in inhalant requirements, when combined with isoflurane, lidocaine produces greater cardiovascular depression than an equipotent dose of isoflurane alone. The use of lidocaine to reduce isoflurane requirements is not recommended in cats.     

The cardiovascular dose-response effects of isoflurane alone and combined with butorphanol in the green iguana (Iguana iguana)

Objective To assess the cardiovascular effects (arterial blood pressure, heart rate, and metabolic acid–base status) of three doses (MAC multiples) of isoflurane alone and combined with butorphanol in the green iguana (Iguana iguana). Study design Prospective randomized double‐blind, two‐period cross‐over trial. Animals Six mature healthy green iguanas (Iguana iguana). Methods The iguanas received each of two treatments, saline 0.1 mL kg^?1 (SAL) and butorphanol 1.0 mg kg^?1 (BUT) during isoflurane anesthesia. Treatments were separated by at least 1 week. The iguanas were exposed to each of the three minimum alveolar concentration (MAC) multiples (1.0, 1.5, and 2.0) in random order. Anesthesia was induced with isoflurane and maintained using controlled ventilation. Instrumentation included use of an ECG, airway gas monitor, cloacal thermometer, esophageal pulse oximeter, and the placement of a femoral arterial catheter. Body temperature was stabilized and maintained at 32 °C. The treatment was administered, and the animals were equilibrated for 20 minutes at each MAC multiple. At each concentration, the heart rate, blood pressure (systolic, mean, diastolic), end‐tidal CO₂, and SpO₂ were measured. At 1.0 and 2.0 MAC, simultaneous blood samples were drawn from the tail vein/artery complex and femoral catheter for blood gas analysis. Data were analyzed using a two‐way analysis of variance for repeated measures looking for differences between treatments and among MAC multiples. Results There were no significant differences in any of the cardiovascular variables between the treatments. Significant differences among isoflurane MAC multiples were observed for HR, mean, diastolic, and systolic blood pressures. Blood pressure and heart rate decreased with an increasing dose of anesthetic. There were no significant differences between treatments or MAC multiples for any of the blood gas variables. The blood pH, PCO₂, HCO₃^?, and hemoglobin saturation differed significantly between sites. Pulse oximetry values measured from the carotid complex did not correlate with and were significantly different from the calculated hemoglobin saturation values determined using the gas analyzer. Conclusion and clinical relevance Cardiovascular depression associated with isoflurane anesthesia in the green iguana is dose dependent. The degree of cardiovascular depression was not significantly different when isoflurane was combined with butorphanol. This finding suggests that the pre‐emptive or intraoperative use of butorphanol is unlikely to be detrimental to cardiovascular function. Butorphanol may be a useful anesthetic adjunct to isoflurane anesthesia in the green iguana.     

Cardiovascular Effects After Epidural Injection of Xylazine in Isoflurane-Anesthetized Dogs

The cardiovascular effects following epidural injection of xylazine or isotonic saline during isoflurane anesthesia were assessed in six healthy dogs. Dogs were anesthetized with isoflurane in O₂ and maintained at 2.0% end-tidal concentration. Ventilation was controlled to maintain PaCO₂ at 35 to 45 mm Hg. The dorsal pedal artery was cannulated for measurement of arterial blood pressure (AP)(systolic AP, mean AP, diastolic AP) and for blood sample collection. Arterial pH and blood gas tensions (PaO₂ and PaCO₂) were determined. Cardiac output was measured by thermodilution. The electrocardiogram (ECG), heart rate (HR), core body temperature, central venous pressure (CVP), mean pulmonary AP, and end-tidal isoflurane concentration (ETISO) and CO₂ tension (ETCO₂) were monitored. Systemic vascular resistance (SVR), arterial HCO₂ concentration, base balance, and cardiac index (CI) were calculated. After baseline measurements were taken, either xylazine (0.2 mg/kg) in 5 mL isotonic saline or 5 mL of isotonic saline was injected into the lumbosacral epidural space. Data were then recorded at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after epidural injection. Data were analyzed by two-way analysis of variance (ANOVA) for repeated measures. When significant differences were encountered, mean values were compared using Bonferroni's test. The level of significance was set at P <.05. Mean values for diastolic AP decreased at 90 and 120 minutes compared with the mean value at 15 minutes after epidural injection of xylazine. No differences were detected at any time or between treatments for HR, systolic AP, mean AP, CVP, CI, SVR, mean pulmonary AP, temperature, ETCO₂, ETISO, arterial pH, PaCO₂, PaO₂, plasma bicarbonate concentration, or base balance. Results of this study indicate that epidural injection of xylazine (0.2 mg/kg) is associated with minimal cardiovascular side effects during isoflurane anesthesia in mechanically ventilated dogs.