Determination of the minimum alveolar concentration of sevoflurane in Holstein steers

OBJECTIVE

To determine the minimum alveolar concentration (MAC) of sevoflurane in Holstein steers using electric stimulation.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 15 Holstein steers aged 7.3 ± 1.2 months and weighing 121 ± 25 kg.

METHODS

Animals were anesthetized with sevoflurane at 8% in oxygen at 5 L minute-1 via facemask and were intubated with an orotracheal tube of a compatible size. After 15 minutes of stabilization of the initial expired concentration of sevoflurane (Fe'Sevo) at 2.6%, electrical stimulation on the thoracic limb was initiated with a sequence of 2 × 10 ms followed by 2 × 3 second electrical currents of 50 V and 50 Hz, 5 seconds apart. Following each stimulus with a negative response, the Fe'Sevo was decreased by 0.2% and a 15 minute interval was awaited before the next stimulus. The procedure was repeated until the first Fe'Sevo value with a positive motor response was obtained. The Fe'Sevo was then increased by 0.1%, followed by a new stimulus, until a negative response was obtained. The value of MAC was calculated as the arithmetic mean between the lowest Fe'Sevo associated with a negative motor response and the highest Fe'Sevo associated with a positive response.

RESULTS

The mean MAC for the 15 steers was 2.0 ± 0.3%, which corresponds to 2.1 ± 0.3% at sea level.

CONCLUSIONS

Based on the proposed methodology, the MAC of sevoflurane for healthy Holstein steers is 2.1 ± 0.3% at sea level.

CLINICAL RELEVANCE

This Fe'Sevo value can be used to guide depth of anesthesia in steers weighing approximately 120 kg in clinical practice.

Comparison of lidocaine, levobupivacaine or ropivacaine for distal paravertebral thoracolumbar anesthesia in ewes

OBJECTIVE

To compare the effects of lidocaine, levobupivacaine, or ropivacaine on the onset time and duration of anesthesia of the flank of ewes, using the distal paravertebral thoracolumbar approach.

STUDY DESIGN

Randomized experimental study.

ANIMALS

Twenty-six healthy mixed-breed ewes (46 ± 3.1 kg).

METHODS

Thoracolumbar paravertebral nerve blocks were performed using the distal approach in sheep for ruminal fistulation. The 13th thoracic (T13), first lumbar (L1) and second lumbar (L2) nerves were infiltrated with 2% lidocaine (group GLI, n = 9), 0.5% levobupivacaine (group GLE, n = 8) or 0.5% ropivacaine (group GRO, n = 9); 1.5 mL on the dorsal branch and 2.5 mL on the ventral branch, total volume of 12 mL per ewe. Anesthesia onset time and duration were assessed by application of superficial and deep pin pricks, and skin clamping with a hemostat. Heart rate, respiratory rate, rectal temperature and systemic arterial pressures were recorded prior to nerve block (T0), after the anesthetic agent injection and onset time (T1) and predetermined time points during the surgical procedure (T2-T6).

RESULTS

Incomplete nerve blocks were present in five of the 26 ewes enrolled in the study and they were not included in the statistical analyzes. Onset times in GLI, GLE and GRO were 1.5 ± 0.5, 3.1 ± 1.5 and 2.1 ± 0.8 minutes, respectively, with GLE significantly longer than GLI. The durations of anesthesia for GLI, GLE and GRO were 80 ± 27, 649 ± 68 and 590 ± 40 minutes, respectively, with the duration of GLI significantly shorter than GLE and GRO. There were no clinically important changes in cardiopulmonary variables.

CONCLUSION AND CLINICAL RELEVANCE

Administration of levobupivacaine and ropivacaine at the distal paravertebral site to block nerves T13, L1 and L2 produced a longer duration of anesthesia of the ewe's flanks compared with lidocaine.

Continuous infusion of propofol in calves: bispectral index and hemodynamic effects

OBJECTIVE

To assess the bispectral index (BIS) and the hemodynamic effects of propofol administered by continuous infusion at different rates in calves.

STUDY DESIGN

Experimental crossover study.

ANIMALS

Eight intact male Dutch calves, aged 6-12 months and weighing 84-124 kg.

METHODS

The calves were anesthetized with propofol (5 mg kg(-1) ) intravenously (IV), and after endotracheal intubation, positioned in right lateral recumbency and allowed to breathe ambient air. Anesthesia was maintained by continuous infusion of propofol, administered IV with an infusion pump at 0.6 mg kg(-1)  minute(-1) (treatment G6) or 0.8 mg kg(-1)  minute(-1) IV (treatment G8), for 60 minutes. The eight animals were anesthetized twice, 1 week apart. The following hemodynamic variables and BIS were assessed before the induction of anesthesia (baseline) and 15, 30, 45, and 60 minutes after beginning the infusion of propofol: heart rate, systolic, diastolic and mean arterial pressures, cardiac output, mean pulmonary artery pressure, cardiac index, stroke index, pulmonary vascular resistance index, and systemic vascular resistance index, BIS, electromyography, and signal quality index.

RESULTS

The continuous infusions of propofol at different rates did not alter BIS variables during the infusion time between dose rates, and no clinically significant hemodynamic changes were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

A continuous infusion of propofol at 0.6 or 0.8 mg kg(-1)  minute(-1) caused minimal hemodynamic changes without clinical relevance in calves. BIS could not be reliably used to discriminate the anesthetic depth during the two propofol infusion rates.

Fear and/or anxiety of children and parents associated with the dental environment

AIM

To assess levels of anxiety in children concerning different dental instruments and equipment and to relate them with parents' anxiety levels moments before the appointment.

MATERIALS AND METHODS

Fifty children from 4 to 12 years of age (average of 10±3.07) and their respective parents were evaluated. A facial scale was used to assess children's anxiety levels, while the Dental Anxiety Scale (DAS) was used to assess parents. Friedman test was applied to check any differences in children's anxiety levels relative to the equipment/instruments, and this was complemented by the use of the Wilcoxon test for two-by-two comparison. In order to assess correlation between parents' and their children's anxiety levels, the study used Spearman correlation coefficient.

RESULTS

With regard to parents' anxiety levels, 4% resulted as null, 18% were low, 56% were moderate, and 22% were exacerbated; children's anxiety level results were: 52% light, 44% intermediate, and 4% intense. Anxiety levels related to instruments/equipment were, in descending order: carpule syringe > paediatric forceps > dental explorer > x-ray machine > rubber dam punch > high speed handpiece > rubber dam forceps > mouth mirror > clinical tweezers > dental chair. No correlation was found between parents' anxiety levels and those of their children (p=0.546).

CONCLUSION

The instruments/equipment used in the assessment generated different anxiety levels in the children. No correlation was found between parents' anxiety levels and those of their children.

Effect of whitening agents on dentin bonding

BACKGROUND

Several studies have shown a reduction in enamel bond strengths when the bonding procedure is carried out immediately after vital bleaching with peroxides. This reduction in bond strengths has become a concern in cosmetic dentistry with the introduction of new "in-office" and "waiting-room" bleaching techniques. The aim of this in vitro study was to evaluate the effect of three bleaching regimens: 35% hydrogen peroxide (HP), 35% carbamide peroxide (CP), and 10% CP, on dentin bond strengths.

MATERIALS AND METHODS

One hundred and twenty fresh bovine incisors were used in this study. The labial surface of each tooth was ground flat to expose dentin and was subsequently polished with 600-grit wet silicon carbide paper. The remaining dentin thickness was monitored and kept at an average of 2 mm. The teeth were randomly assigned to four bleaching regimens (n = 30): (A) control, no bleaching treatment; (B) 35% HP for 30 minutes; (C) 35% CP for 30 minutes; and (D) 10% CP for 6 hours. For each group, half of the specimens (n = 15) were bonded with Single Bond/Z100 immediately after the bleaching treatment, whereas the other half was bonded after the specimens were stored for 1 week in artificial saliva at 37 degrees C. The specimens were fractured in shear using an Instron machine.

RESULTS

For the groups bonded immediately after bleaching, one-way analysis of variance (ANOVA) followed by the Duncan's post hoc test revealed a statistically significant reduction in bond strengths in a range from 71% to 76%. For the groups bonded at 1 week, one-way ANOVA showed that group B (35% HP for 30 min) resulted in the highest bond strengths, whereas 10% CP resulted in the lowest bond strengths. Student's t-test showed that delayed bonding resulted in a significant increase in bond strengths for groups B (35% HP) and C (35% CP); whereas the group bleached with 10% CP (group D) remained in the same range obtained for immediate bonding. Storage in artificial saliva also affected the control group, reducing its bond strengths to 53% of the original.