Clinical comparison of the effects of isoflurane or propofol anaesthesia on mean arterial blood pressure and ventilation in dogs undergoing orthopaedic surgery receiving epidural anaesthesia.

The aim of this study was to compare the effects on mean arterial pressure (MAP) and ventilation of propofol total IV anaesthesia (TIVA) and isoflurane as anaesthetic maintenance in healthy dogs undergoing orthopaedic surgery, with epidural anaesthesia. Dogs were premedicated IM with dexmedetomidine (4µg/kg) and methadone (0.3mg/kg), induced with IV propofol (0.65-5mg/kg) and randomly assigned to be maintained with isoflurane (group I) or propofol (group P). Isoflurane end-tidal concentration (EtISO) and propofol infusion rate were adjusted during the surgery to maintain a suitable anaesthetic depth. All dogs received bupivacaine (1mg/kg) and morphine (0.1mg/kg) in the lumbosacral epidural space (total volume 0.2mL/kg). MAP was recorded every 5min during the procedure. Statistical analysis was performed using parametric (Student's t test) and nonparametric (Mann-Whitney U-test, chi-square) tests, as appropriate. Anaesthetic maintenance in groups I and P was accomplished by providing a mean EtISO of 1.12±0.15% and a mean propofol infusion rate of 15.0±4.7mg/kg/h, respectively. MAP was significantly higher in group P than in group I (92±17mmHg versus 78±10mmHg; P=0.021). Eleven dogs in group P and two dogs in group I reached an EtCO2>7.3kPa, requiring mechanical ventilation (P=0.001). In combination with epidural anaesthesia, propofol TIVA improved MAP and is a suitable alternative to isoflurane in orthopaedic surgery of the hind limb in healthy dogs. Nevertheless, since it was associated with increased respiratory depression, mechanical ventilation should be available.

Comparison of sedation scores and propofol induction doses in dogs after intramuscular administration of dexmedetomidine alone or in combination with methadone, midazolam, or methadone plus midazolam.

The objectives of this study were to determine: (1) the sedative effects of dexmedetomidine in combination with methadone, midazolam, or both, and (2) the propofol dose required to achieve endotracheal intubation in healthy dogs. Seven healthy Beagle dogs were included in a prospective experimental, crossover, randomised and masked design. All dogs received four treatments IM, with at least 1 week between sessions, as follows: dexmedetomidine 5 µg/kg (D) alone, or combined with methadone 0.3 mg/kg (DMe), midazolam 0.3 mg/kg (DMi), or both (DMeMi). The degree of sedation was evaluated using a numerical scale (maximum 15 points). The dose of propofol required for intubation was also calculated for each group. Recovery time and quality were determined. Statistical analysis was performed using parametric (ANOVA) and nonparametric tests (Friedman, Cochran Q), as appropriate. The degree of sedation obtained with DMe and DMeMi (13, [7-14]; 13, [6-14], respectively) was significantly higher than in the control group (2, [1-4]; P = 0.023, P = 0.006, respectively). The required dose of propofol was lower in all groups (DMi, 1.5 ± 0.5 mg/kg, P = 0.002; DMe, 1.2 ± 0.5 mg/kg, P <0.001; DMeMi, 0.9 ± 0.3 mg/kg) than in the control group (2.9 ± 0.9 mg/kg; P <0.001). Recovery quality was not different between groups (P = 0.137). In healthy dogs, the addition of midazolam did not enhance the sedative effects of dexmedetomidine or a dexmedetomidine-methadone combination at the doses studied, and propofol requirements were reduced. The sedative effect of dexmedetomidine was enhanced with methadone, and the required dose of propofol was reduced.

Evaluation of an oesophageal Doppler device for monitoring cardiac output in anaesthetised healthy normotensive dogs.

OBJECTIVES: To compare cardiac output measured by oesophageal Doppler and by thermodilution monitoring and to correlate the Doppler cardiac output-generated minute distance with thermodilution cardiac output in healthy anaesthetised beagle dogs. MATERIALS AND METHODS: Prospective experimental study. Six healthy adult beagle dogs were pre-medicated with intramuscular acepromazine (0 · 05 mg/kg) and methadone (0 · 3 mg/kg). Anaesthesia was induced with intravenous propofol (dose-effect) and maintained with isoflurane in oxygen. Simultaneously, a constant rate infusion of dopamine (3 µg/kg/minute) was administered to the dogs to prevent hypotension. The minute distance, Doppler and thermodilution cardiac outputs were assessed at three different end-tidal concentrations of isoflurane (1 · 0, 1 · 3 and 2 · 0%). RESULTS: Correlation between Doppler and thermodilution cardiac output (r(2) = 0 · 582) and between minute distance and thermodilution cardiac output (r(2) = 0 · 658) were moderately good, but the limits of agreement between Doppler and thermodilution cardiac outputs were above the recommended values (±39%, for a recommended value up to 30%). CLINICAL SIGNIFICANCE: Doppler and minute distance cannot be considered as an alternative method to thermodilution to monitor cardiac output in the healthy anaesthetised dog.

Effects of fluid load on cardiovascular function during stepwise lung recruitment manoeuvre in healthy dogs.

The aim of this study was to evaluate the effects of a stepwise lung recruitment manoeuvre (RM) on cardiac output (CO) in mechanically ventilated dogs, with or without a previous fluid load. Eight healthy adult Beagle dogs were enrolled in a prospective crossover study. Following sedation with dexmedetomidine and methadone, anaesthesia was induced with propofol and maintained with isoflurane. CO (thermodilution method) and direct arterial blood pressure were monitored. The dogs were mechanically ventilated in a volume-controlled mode (tidal volume, VT = 10 mL/kg; positive end-expiratory pressure [PEEP] = 0 cm H2O) until normocapnia was achieved (end tidal CO2 35-45 mmHg). The RM was then performed in a pressure-controlled mode, with progressive increases of the PEEP and end-inspiratory pressure of 5 cm H2O, until 15 cm H2O and 30 cm H2O were reached, respectively. After the RM, the ventilatory mode was returned to volume-control, and the PEEP was sequentially decreased to 10, 5 and 0 cm H2O. Baseline ventilation was maintained for 30 min. Next, 10 mL/kg of lactated Ringer's solution was administered within 10 min, prior to a second RM. The CO was determined before each RM (baseline) and at each pressure step. A repeated measures ANOVA test was used to compare data. Compared to baseline, CO decreased during the RM in both groups. However, there was a significantly higher CO during the second RM at the highest pressure step (P<0.05) and during all decreasing pressure steps (P<0.05). In conclusion, a previous crystalloid fluid load could reduce the impact of a RM on CO in healthy dogs.

Effects of a stepwise lung recruitment manoeuvre and positive end-expiratory pressure on lung compliance and arterial blood oxygenation in healthy dogs.

This study was performed to evaluate the effects of a stepwise lung recruitment manoeuvre (RM) on dynamic lung compliance (Cdyn) and gas exchange in mechanically ventilated healthy dogs. Fourteen healthy adult dogs, scheduled for elective surgery in dorsal recumbency were employed. After anaesthetic induction, dogs were mechanically ventilated in a volume-controlled mode (tidal volume, VT=10 mL/kg); positive end-expiratory pressure (PEEP)=0 cm H(2)O; oxygen inspired fraction (FiO(2))=0.4 for 30 min (baseline). The dogs were then randomly allocated into two groups, control and RM. The ventilatory mode was maintained during the whole surgical procedure in the control group without any intervention, as in general practice. The RM was performed in a pressure-controlled mode, with progressive increases of PEEP and end-inspiratory pressure of 5 cm H(2)O until 15 cm H(2)O and 30 cm H(2)O, respectively. After RM, PEEP was decreased to 4 cm H(2)O, and the ventilatory mode was returned to volume-control. Arterial blood gases and Cdyn were determined at baseline, 20 and 60 min afterwards. Student's t test and the one-way ANOVA test were employed to compare data. Cdyn increased in the RM group (183 ± 30% and 165 ± 24% at 20 and 60 min, respectively; P=0.000). The baseline partial pressure of arterial oxygen to FiO(2) ratio (PaO(2)/FiO(2) ratio) did not change in the control group, but was higher in the RM group (527 ± 41 mm Hg and 511 ± 46 mm Hg at 20 and 60 min, respectively; baseline 371 ± 34 mm Hg, P<0.001). In conclusion, a stepwise RM followed by the use of PEEP improves Cdyn and oxygenation in mechanically ventilated healthy dogs.

Comparison of different aminoglycoside antibiotic treatments to refine ototoxicity studies in adult mice.

Hearing and balance receptors in the inner ear are highly susceptible to damage caused by a wide variety of toxic substances, including aminoglycosides. This class of antibiotics is commonly used in medicine, even though they may produce irreversible bilateral neurosensorial deafness. To identify potential ototoxic agents and novel therapeutic targets, it is necessary to generate standardized animal models of aminoglycoside ototoxicity, which will also serve to explore otic cell repair and regeneration. Although the mouse is the species most often used in biomedical research, due to the genetic information and genetically-modified strains available, there are few standard models of aminoglycoside ototoxicity in adult mice. Most protocols to produce ototoxicity in adult mice employ high doses of aminoglycosides for long periods of time, which causes systemic toxicity, side-effects and high mortality rates. Here, we compare the effects of systemic treatment with four different, yet common, aminoglycoside antibiotics in two mouse strains, evaluating their effects on mortality, cochlear morphology and auditory brainstem responses. Our data indicate that gentamicin and neomycin caused high mortality in the adult mouse without significantly changing the auditory threshold. Amikacin produced a tolerable rate of mortality but at doses that did not exhibit ototoxicity. Finally, intramuscular injection of kanamycin in C57BL/6JOlaHsd mice induced significant dose-dependent bilateral hearing loss with a moderate rate of mortality and less discomfort than following subcutaneous administration.

Impairment of the reproductive potential of male fathead minnows by environmentally relevant exposures to 4-nonylphenolf.

The synthetic organic compound 4-nonylphenol (NP) has been detected in many human-impacted surface waters in North America. In this study, we examined the ability of NP to alter reproductive competence in male fathead minnows after a 28 day flow-through exposure in a range of environmentally relevant concentrations bracketing the U.S. Environmental Protection Agency toxicity-based NP chronic exposure criterion of 6.1 microg NP/L. Exposure to NP at and above the EPA chronic exposure criterion resulted in an induction of plasma vitellogenin (VTG) within 14 days. However, 7 days after the cessation of exposure, VTG concentrations had dropped more than 50% and few males expressed VTG above the detection threshold. All of the morphological endpoints, including gonadosomatic index, hepatosomatic index, secondary sexual characters, and histopathology, were unaltered by all NP treatments. However, when NP-exposed male fish were allowed to compete with control males for access to nest sites and females, most treatments altered the reproductive competence of exposed males. At lower NP concentrations, exposed males out-competed control males, possibly by being primed through the estrogenic NP exposure in a fashion similar to priming by pheromones released from female fathead minnows. At higher NP exposure concentrations, this priming effect was negated by the adverse effects of the exposure and control males out-competed treated males. Results of this study indicate the complexity of endocrine disrupting effects and the need for multiple analysis levels to assess the effects of these compounds on aquatic organisms.

Sensorineural hearing loss in insulin-like growth factor I-null mice: a new model of human deafness.

It has been reported that mutations in the gene encoding human insulin-like growth factor-I (IGF-I) cause syndromic hearing loss. To study the precise role of IGF-I in auditory function and to hypothesize the possible morphological and electrophysiological changes that may occur in the human inner ear, we have analysed the auditory brainstem response in a mouse model of IGF-I deficiency. We show here that homozygous Igf-1(-/-) mice present an all-frequency involved bilateral sensorineural hearing loss. Igf-1(-/-) mice also present a delayed response to acoustic stimuli; this increases along the auditory pathway, indicating a contribution of the central nervous system to the hearing loss in Igf-1(-/-) mice. These results support the use of the Igf-1(-/-) mouse as a new model for the study of human syndromic deafness.

Clinical actions of subarachnoid sevoflurane administration in vivo: a study in dogs.

BACKGROUND: Halogenated ethers produce clinical effects at spinal sites. Nevertheless, in vitro and in vivo studies have not determined whether the immobilizing effect in the spinal cord is due to inhibition of nociceptive or motor transmission or both. Our goal was to characterize the clinical effects of direct spinal sevoflurane administration. METHODS: Five adult beagle dogs completed the study. In a randomized and blinded manner each animal received placebo (saline 0.1 ml kg(-1)) and three concentrations of pure sevoflurane administered intrathecally (0.05, 0.075 and 0.1 ml kg(-1)) by means of a permanent spinal catheter. Sensory and motor block and state of consciousness were determined at baseline and at predetermined regular intervals until at least 2 h after total recovery. RESULTS: None of the dogs presented a decrease in consciousness with either 0.05 or 0.075 ml kg(-1) of sevoflurane. Administration of 0.1 ml kg(-1) produced light sedation (2 on a four-point sedation scale) in three of the five dogs. A comparison of the duration of the sensory and motor blocks among the three sevoflurane dosages shows a significant dose-dependent increase that is greater in all cases than that for the saline solution. CONCLUSIONS: Spinal administration of pure sevoflurane resulted in a dose-related and totally reversible motor and sensory regional block without any signs of clinical neurotoxicity or significant decrease in consciousness. Therefore the model allows us to comment on the analgesic effects at the spinal level in addition to the direct immobilizing effects of sevoflurane.

Anestesia regional en pediatría: bloqueos periféricos / Paediatric regional anaesthesia: peripheral blocks

Los bloqueos periféricos son una herramienta muy útil para el tratamiento del dolor postoperatorio y reducción de las necesidades de opiáceos intraoperatorios en los pacientes pediátricos. Algunos bloqueos periféricos como el bloqueo de nervios peneanos o el bloqueo ilioinguinal e iliohipogástrico están totalmente aceptados y son bloqueos realizados por la mayoría de los anestesiólogos pediátricos de forma rutinaria. sin embargo, otros bloqueos como el amigdalar o el paraumbilical tienen menos difusión, probablemente porque son menos efectivos y presenta un índice superior de fracasos de la técnica. El bloqueo auricular, sin embargo, es uno de los bloqueos más eficaces y fáciles de realizar que también colabora en la disminución del empleo de opiáceos intraoperatorios y mejora la calidad de la analgesia postoperatoria muy especialmente en el paciente pediátrico (AU)