Annette P N Kutter

Changes in subchondral bone in cartilage resurfacing—an experimental study in sheep using different types of osteochondral grafts

OBJECTIVE This article addresses the subchondral bone integrity in cartilage resurfacing by comparing fresh, untreated auto-, xeno-, and photooxidized osteochondral allo- and xenografts. Photooxidation was expected to improve mechanical stability of the osteochondral grafts through an improved linkage of the collagen fibers within the bone matrix. DESIGN Untreated auto- and xenografts and with photooxidation pretreated allo- and xenografts were surgically implanted in femoral condyles of sheep (n=40). After 2, 6, 12 and 18 months results were evaluated histologically using non-decalcified bone embedded in acrylic resin. Qualitative evaluation was performed with emphasis on bone matrix, biomechanical stability of graft anchorage, formation of cystic lesions, and bone resorption and formation. Quantitative evaluation of the total subchondral bone area was conducted histomorphometrically. Statistical analysis (factorial ANOVA test) was used to compare differences between groups with respect to the percentage of bone matrix and fibrous tissue per section. RESULTS Subchondral bone resorption was fastest in untreated, fresh autografts, followed by photooxidized allografts, untreated, fresh xenografts and last pretreated photooxidized xenografts. Cystic lesions were seen in all types of grafts, but were most pronounced at 6 months in autografts and least in photooxidized grafts. Cyst-like lesions had subsided substantially in the untreated auto- and photooxidized xenografts, if no graft dislocation occurred during the healing period. Mononuclear cell infiltration and an increase in the presence of multinuclear cells were observed at 2 months, mostly in untreated autografts, followed by photooxidized allo- and untreated xenografts. They were much higher in numbers compared to photooxidized grafts, at least in the early specimens at 2 months. Graft stability was linked to the rate of bone resorption. CONCLUSION Substantial resorption of the subchondral bone, involving the development of cyst-like lesions, lead to dislocation and finally to cartilage matrix degradation of the grafts. The process of photooxidation decreased the speed of bone resorption in osteochondral grafts and, thus, improved graft stability and cartilage survival. These results suggest that the remodeling of the subchondral bone of the host and the graft within the first 6 months is an important factor in graft stability and overall results of cartilage resurfacing.

Catheter closure of patent ductus arteriosus in dogs: variation in ductal size requires different techniques.

BACKGROUND : Catheter closure of patent ductus arteriosus Botalli (PDA) is increasingly replacing traditional surgical ligation via thoracotomy. A variety of techniques have been described in dogs, although the technique and implant chosen may depend on the minimum ductus diameter. OBJECTIVES : To evaluate the feasibility and treatment of choice of catheter closure of large and small PDAs in dogs. METHODS : In 16 dogs with a PDA, catheter closure was performed using transarterial embolisation using detachable or free coils, or transvenously using an Amplatzer, duct occluder (ADO). RESULTS : In 8 dogs, closure of PDA with a minimum diameter of < 4 mm was achieved using detachable coils; 2 or more coils were required in 3 dogs. In 5 dogs with minimum ductus diameters of > 4 mm, detachable coils were not applicable. In one of these dogs, (incomplete) surgical ligation was performed and later a free coil placed for complete closure. In 2 dogs with moderately large PDA (5 mm), several free coils were implanted. Complete closure was not achieved in either dog and transient haemolysis occurred as a complication. In 2 dogs with a very large PDA (6 mm), implanted free coils embolised to pulmonary arteries and closure was then achieved using an ADO. In 3 dogs with an excessively large PDA (7.5-10 mm) closure was successfully achieved using an ADO with no complications. CONCLUSIONS : Coil embolisation is readily feasible for closure of PDA < 4 mm, less feasible for PDA < 5 mm and unlikely to be feasible to close PDA > 5 mm. Detachable coils are safe for PDA < 4 mm, and the ADO is an excellent device for PDA > 5 mm.

Evaluation of anesthesia recovery quality after low-dose racemic or S-ketamine infusions during anesthesia with isoflurane in horses

OBJECTIVE To compare anesthesia recovery quality after racemic (R-/S-) or S-ketamine infusions during isoflurane anesthesia in horses. ANIMALS 10 horses undergoing arthroscopy. PROCEDURES After administration of xylazine for sedation, horses (n = 5/group) received R-/S-ketamine (2.2 mg/kg) or S-ketamine (1.1 mg/kg), IV, for anesthesia induction. Anesthesia was maintained with isoflurane in oxygen and R-/S-ketamine (1 mg/kg/h) or S-ketamine (0.5 mg/kg/h). Heart rate, invasive mean arterial pressure, and end-tidal isoflurane concentration were recorded before and during surgical stimulation. Arterial blood gases were evaluated every 30 minutes. Arterial ketamine and norketamine enantiomer plasma concentrations were quantified at 60 and 120 minutes. After surgery, horses were kept in a padded recovery box, sedated with xylazine, and video-recorded for evaluation of recovery quality by use of a visual analogue scale (VAS) and a numeric rating scale. RESULTS Horses in the S-ketamine group had better numeric rating scale and VAS values than those in the R-/S-ketamine group. In the R-/S-ketamine group, duration of infusion was positively correlated with VAS value. Both groups had significant increases in heart rate and mean arterial pressure during surgical stimulation; values in the R-/S-ketamine group were significantly higher than those of the S-ketamine group. Horses in the R-/S-ketamine group required slightly higher end-tidal isoflurane concentration to maintain a surgical plane of anesthesia. Moderate respiratory acidosis and reduced oxygenation were evident. The R-norketamine concentrations were significantly lower than S-norketamine concentrations in the R-/S-ketamine group. CONCLUSIONS AND CLINICAL RELEVANCE Compared with R-/S-ketamine, anesthesia recovery was better with S-ketamine infusions in horses.

Effect of inhalation of isoflurane at end-tidal concentrations greater than, equal to, and less than the minimum anesthetic concentration on bispectral index in chickens

OBJECTIVE To determine the effect of inhalation of isoflurane at end-tidal concentrations greater than, equal to, and less than the minimum anesthetic concentration (MAC) on bispectral index (BIS) in chickens. Animals-10 chickens. PROCEDURES For each chicken, the individual MAC of isoflurane was determined by use of the toe-pinch method. After a 1-week interval, chickens were anesthetized with isoflurane at concentrations 1.75, 1.50, 1.25, 1.00, and 0.75 times their individual MAC (administered from higher to lower concentrations). At each MAC multiple, a toe pinch was performed and BIS was assessed and correlated with heart rate, blood pressure, and an awareness score (derived by use of a visual analogue scale). RESULTS Among the chickens, mean +/- SD MAC of isoflurane was 1.15 +/- 0.20%. Burst suppression was detected at every MAC multiple. The BIS and awareness score were correlated directly with each other and changed inversely with increasing isoflurane concentration. Median (range) BIS values during anesthesia at 1.75, 1.50, 1.25, 1.00, and 0.75 MAC of isoflurane were 25 (15 to 35), 35 (25 to 45), 35 (20 to 50), 40 (25 to 55), and 50 (35 to 65), respectively. Median BIS value at extubation was 70 +/- 9. Values of BIS correlated with blood pressure, but not with heart rate. Blood pressure changed with end-tidal isoflurane concentrations, whereas heart rate did not. CONCLUSIONS AND CLINICAL RELEVANCE Assessment of BIS can be used to monitor the electrical activity of the brain and the degree of unconsciousness in chickens during isoflurane anesthesia.

Electrocardiographic alterations during intravascular application of three different test doses of bupivacaine and epinephrine: experimental study in neonatal pigs

BACKGROUND Origin of electrocardiographic (ECG) alterations during intravascular injection of local anaesthetic solutions is controversial. The aim of this study was to elucidate whether epinephrine, bupivacaine or their combination is responsible for ECG alteration. METHODS Forty-five piglets were randomized into three groups. After induction of general anaesthesia using sevoflurane and peripheral venous cannulation, the trachea was intubated, the lungs were artificially ventilated, and anaesthesia was maintained by sevoflurane. Under steady state 0.2 ml kg(-1) and after 10 min 0.4 ml kg(-1) of one of the following three test solutions was administered i.v.: bupivacaine 0.125% (Group 1), bupivacaine 0.125%+epinephrine 1:200 000 (Group 2), and plain epinephrine 1:200,000 (Group 3). The ECG was analysed for alterations in heart rate and T-elevation. RESULTS After injection of 0.2 or 0.4 ml kg(-1) test solution, an increase in heart rate of at least 10% was found in none of Group 1 and in all of Groups 2 and 3. After application of 0.2 ml kg(-1) test solution, T-elevation was found in 7% of Group 1 and in 93% of Groups 2 and 3. The injection of 0.4 ml kg(-1) revealed a T-elevation in 27%, 100%, and 100%, respectively, in Groups 1, 2, and 3. CONCLUSIONS This animal model demonstrated that increases in heart rate and T-elevation in the ECG during i.v. application of a common test dose (0.2 ml kg(-1)) of bupivacaine are caused by epinephrine addition. Whether higher doses of bupivacaine alone can cause similar ECG changes or not requires further studies.

Electrocardiographic changes during continuous intravenous application of bupivacaine in neonatal pigs

BACKGROUND It is controversial as to whether T-wave elevation is caused by local anaesthetics, epinephrine, or their combination. It has been shown that T-elevation after intravascular injection of a small bupivacaine test dose is caused by epinephrine and not by bupivacaine. The aim of this study was to investigate ECG changes with higher doses of i.v. bupivacaine. METHODS Thirty neonatal pigs were anaesthetized with sevoflurane and their tracheas intubated and artificially ventilated. Under steady-state conditions, bupivacaine was continuously infused (flow rate 3.2 ml kg(-1) min(-1)) by a syringe infusion pump through a central venous catheter. Group 1 received bupivacaine 0.125%, Group 2 bupivacaine 0.5%. The ECG was continuously printed and subsequently analysed for alterations in heart rate, ventricular de- and repolarization, and arrhythmias at 1.25, 2.5, and 5 mg kg(-1) bupivacaine infused. RESULTS Sinus rhythm persisted in all pigs. Heart rate decreased progressively in both groups, but this was significantly more pronounced in Group 1. T-wave elevation occurred in 40% and 0% (Groups 1 and 2) at 1.25 mg kg(-1), in 80% and 0% at 2.5 mg kg(-1), and in 93% and 80% at 5 mg kg(-1) bupivacaine infused. There were significant differences between the two groups at 1.25 and 2.5 mg kg(-1) infused. CONCLUSIONS Higher doses of i.v. infused bupivacaine can cause T-elevation. With slower injection technique, T-elevation can already be detected at lower bupivacaine doses administered.

Cardiopulmonary effects of dexmedetomidine in goats and sheep anaesthetised with sevoflurane

In sheep, α2-agonists can induce severe hypoxaemia. In goats, reports on changes in oxygenation are inconsistent. The aim of this study was to compare the cardiopulmonary effects of dexmedetomidine in six goats and four sheep anaesthetised with sevoflurane and maintained at approximately 1 minimal alveolar concentration. The animals were ventilated mechanically and held in an upright position to minimise the influence of positioning on pulmonary function. After baseline cardiopulmonary measures, 2 μg/kg dexmedetomidine was injected intravenously over one minute, and measurements were made for 120 minutes. In both species, respiratory resistance, alveolar dead space and shunt fraction increased and thoracic compliance decreased significantly; arterial, pulmonary arterial, pulmonary capillary wedge and central venous pressures increased and heart rate and cardiac output decreased significantly. Arterial oxygen tension decreased significantly, with no significant difference between the goats and sheep. Wide interindividual differences were observed in both the goats (mean [sd] 144 [149·1] mmHg, range 54·8 to 443·7 mmHg) and sheep (mean [sd] 129·8 [132·1] mmHg, range 33·7 to 352·8 mmHg), but the cardiovascular and respiratory changes were similar in the two species.

Effect of rapid fluid resuscitation using crystalloids or colloids on hemostasis in piglets

Impairment of blood coagulation is one of the main side effects of volume replacement, particularly if artificial colloids such as hydroxyethyl starch (HES) and gelatine preparations are used. This animal study aimed to evaluate the effect of a single fast intravenous crystalloid or colloid fluid bolus on blood coagulation as measured by rotation thromboelastometry (ROTEM®).

Intrarater and interrater variability of point of care coagulation testing using the ROTEM delta

This study aimed to assess intrarater and interrater variability of coagulation point-of-care testing (POCT) using ROTEM delta operated by trained staff. Arterial blood samples were taken from 43 anesthetized piglets aged up to 6 weeks and weighing 4–6 kg. The following clotting measurements were recorded: clotting time, clot formation time (CFT), maximum clot firmness (MCF) and alpha angle using ROTEM delta assays ExTEM, InTEM, FibTEM and ApTEM. Intrarater variability was assessed when a single operator performed the same assay simultaneously in all four channels of the ROTEM device. Interrater variability was assessed by two different operators simultaneously performing the same assay. Variance components of the data were analyzed using linear mixed modeling. Three hundred and forty-three tests from 86 samples were loaded and analyzed. The intraclass correlation coefficient (ICC) was more than 0.7 for clotting measurements except for CFT and alpha in InTEM. For intrarater and interrater assessment, different relative variability for the ROTEM measurements were found with consistently higher variability for clotting time and CFT and lower variability of MCF and alpha angle. Interrater variability was not statistically significant as supported using Akaikes information criterion. Piglet coagulation testing using ROTEM delta showed a high ICC. Variability was significantly lower in MCF and angle alpha compared with clotting time and CFT. No further variability was added by a second user. Based on these data, ROTEM delta appears to be suitable as POCT.

Evaluation of a minimally invasive non–calibrated pulse contour cardiac output monitor (FloTrac/Vigileo) in anaesthetized dogs

OBJECTIVE To evaluate the accuracy of a new cardiac output monitor (FloTrac/Vigileo), originally designed for humans, in dogs. This pulse contour cardiac output monitoring system cannot be calibrated and measures cardiac output (Q̇t) from a standard arterial catheter. STUDY DESIGN Prospective experimental trial. ANIMALS Eight adult Beagle dogs weighing 13.1 (9.8-17.1) kg [median (range)]. METHODS Anaesthesia in the dogs was maintained using isoflurane. A pulmonary artery catheter and a metatarsal arterial catheter (22 gauge) were placed. Cardiac output was measured simultaneously 331 times by thermodilution and FloTrac technique. A broad spectrum of Q̇t measurements was achieved through alterations of isoflurane concentration, administration of propofol boluses and dobutamine infusions. Agreement between the methods was quantified with Bland Altman analysis and disagreement was assessed with linear mixed models. Results  Median (10th and 90th percentile) cardiac output as measured with thermodilution was 2.54 (1.47 and 5.15) L minute(-1) and as measured with FloTrac 8.6 (3.9 and 17.3) L minute(-1) . FloTrac measurements were consistently higher with a mean bias of 7 L minute(-1) and limits of agreement of -3.15 to 17.17 L minute(-1) . Difference between the methods was most pronounced in high Q̇t measurements. Linear mixed models showed an estimated difference between the two methods of 8.05 (standard error 1.18) L minute(-1) and a significant interaction between mean arterial pressure and method. Standard deviation (4.45 higher) with the FloTrac method compared to thermodilution was increased. CONCLUSION Compared to thermodilution measurements, the FloTrac system was influenced to a higher degree by arterial blood pressure, resulting in consistent overestimation of cardiac output. CLINICAL RELEVANCE The FloTrac monitor, whose algorithms were developed based on human data, cannot be used as an alternative for thermodilution in dogs.