Long-term surgical anaesthesia with isoflurane in human habituated Nile Crocodiles

Sedation and general anaesthesia of crocodilians: a systematic review

Sedation and general anaesthesia of crocodilians pose unique challenges due to their aggressive nature, poikilothermic physiology, and specific anatomical and physiological characteristics, all factors that complicate crocodilian anaesthesia. This review aimed to systematically review the literature regarding sedation and general anaesthesia of crocodilians with focus on efficacy and impact on vital parameters. A systematic literature search was performed according to PRISMA guidelines on May 2, 2023 in the databases Embase, PubMed, Scopus and Web of Science. Publications were excluded based on predefined exclusion criteria, which encompassed non-standard publications and publications unrelated to crocodilians, with fewer than five animals and/or with insufficient data on sedation and general anaesthesia. Five key factors were used to evaluate the strength of evidence: number of included animals, study design, definition of recovery time, blinded assessment of recovery and conflict of interest. Ten publications were included in this systematic review. Drugs used included alpha-2-adrenoceptor agonists, dissociative anaesthetics, benzodiazepines, neuromuscular blocking agents, propofol, alfaxalone, and inhalant gasses. The studies included in total 55 Alligator mississippiensis, 110 Crocodylus porosus, 15 Crocodylus johnstoni, and 15 Crocodylus niloticus. Factors such as temperature, administration route, dose, species, and age influenced protocols for sedation and general anaesthesia of crocodilians. The studies included used five different study designs. Only one study included a control group, done on retrospectively collected data. Blinded recovery assessments and declarations of no conflict of interest were noted in some studies. The use of four distinct recovery definitions posed challenges to comparability in this systematic review. The studies reported that medetomidine provided stable and reversible sedation, although it depressed heart rate. Alfaxalone was less stable outside the optimal temperature range. Intubation and inhalation anaesthesia were effective, and adrenaline reduced the length of the recovery period. Overall, the review provides valuable insights for veterinarians, researchers, and wildlife professionals involved in sedation and general anaesthesia of the crocodilian species, however, the literature is limited, and further research is needed to improve evidence-based medical management.

Evaluating the Physiologic Effects of Alfaxalone, Dexmedetomidine, and Midazolam Combinations in Common Blue-Tongued Skinks (Tiliqua scincoides)

Common blue-tongued skinks (Tiliqua scincoides) are popular pet reptiles; however, there has been limited research to investigate sedatives for this species. The purpose of this study was to measure the physiologic effects of four combinations of alfaxalone, dexmedetomidine, and midazolam for minor procedures such as intubation and blood collection. Eleven common blue-tongued skinks (Tiliqua scincoides) were used for this prospective, randomized cross-over study. The subcutaneous combinations were used as follows: 20 mg/kg alfaxalone (A); 10 mg/kg alfaxalone and 1 mg/kg midazolam (AM); 0.1 mg/kg dexmedetomidine and 1 mg/kg midazolam (DM); and 5 mg/kg alfaxalone, 0.05 mg/kg dexmedetomidine, and 0.5 mg/kg midazolam (ADM). Heart rate, respiratory rate, palpebral reflex, righting reflex, escape reflex, toe pinch withdrawal reflex, tongue flicking, and the possibility of intubation were recorded at baseline and every 5 min for 60 min. Venous blood gases were measured at baseline, full sedation, and recovery. Heart and respiratory rates decreased significantly in all groups, but the reductions were most prominent in DM and ADM. Analgesic effects, as measured by the toe pinch withdrawal reflex, were only observed in DM and ADM. Intubation was possible in all four protocols; however, it was not possible in two DM skinks. Based on these trials, ADM and AM are recommended for minor procedures in blue-tongue skinks.

Pharmacokinetics and pharmacodynamics of dextroketamine alone or combined with midazolam in Caiman crocodilus

Pharmacokinetics studies of anesthetic agents are important for understanding of the pharmacology and metabolism of anesthetic agents in reptilians. This study was designed to examine the pharmacokinetic and pharmacodynamic properties of intravenous dextroketamine alone or combined with midazolam in Caiman crocodilus. Eight caimans were anesthetized with dextroketamine (10 mg/kg; group D) or dextroketamine and midazolam (10 and 0.5 mg/kg respectively; group DM) into the occipital venous sinus. The pharmacokinetic parameters were calculated by HPLC using a non-compartmental modeling. Serial blood samples were collected at baseline and within 15 and 30 min, and 11.5, 2, 4, 8, 12, 24 and 48 h of drug administration. Sedation status over time differed between groups. All animals in group D (8/8; 100%) showed signs of light sedation at t10. Half (4/8; 50%) of these caimans did not progress to deeper levels of sedation. In spite of light sedation at t10, animals in group DM were deeply sedated within 13.13 ± 7.04 min of anesthetic agent injection. The area under the plasma concentration-time curve (AUC0-48) and half-life of dextroketamine changed significantly after combination with midazolam. Even without significant changes in clearance, the almost two-fold increase in the half-life of dextroketamine suggests a slower rate of elimination.

Transesophageal echocardiography of cardiac function in Nile crocodiles - A novel tool for assessing complex hemodynamic patterns

BACKGROUND

The crocodilian heart is unique among reptiles with its four-chambered structure and complete intracardiac separation of pulmonary and systemic blood flows and pressures. Crocodiles have retained two aortic arches; one from each ventricle, that communicate via Foramen of Panizza, immediately distally from the aortic valves. Moreover, crocodiles can regulate vascular resistance in the pulmonary portion of the right ventricular outflow tract (RVOT). These unique features allow for a complex regulation of shunting between the pulmonary and systemic circulations. Studies on crocodile shunting have predominantly been based on invasive measurements, but here we report on the use of echocardiography.

METHODS

Experiments were performed on seven pentobarbital anaesthetized juvenile Nile crocodiles (length and mass of 192 ± 13 cm and 26 ± 5 kg, respectively). Echocardiographic imaging was performed using a transesophageal (TEE) approach. All images were EKG-gated.

RESULTS

We obtain excellent views of cardiac structures and central vasculature through the esophagus. Standard imaging planes were defined for both long- and short axis views of the left ventricle and truncus arteriosus. For the RV, only a short axis view could be obtained. Color Doppler was used to visualize flow. Pulsed waved Doppler for measuring flow profiles across the atrioventricular valves, in the two RVOTs and the left ventricular outflow tract. Shunting across the Foramen of Panizza could be visualized and gated to the EKG.

CONCLUSION

TEE can be used to image the unique features of the crocodile heart and allow for in-vivo imaging of the complex shunting hemodynamics, including timing of cardiac shunts.

Effect of atropine and propofol on the minimum anaesthetic concentration of isoflurane in the freshwater turtle Trachemys scripta (yellow-bellied slider)

OBJECTIVE

To determine if the administration of atropine would reduce the measured minimum anaesthetic concentration of isoflurane (MAC_isoflurane) in freshwater turtles - the yellow-bellied slider (Trachemys scripta scripta).

STUDY DESIGN

Paired, blinded, randomized, prospective studies of 1) the effect of atropine in isoflurane anaesthetized freshwater turtles (T. scripta scripta) and 2) the effect of atropine in yellow-bellied sliders in which anaesthesia was induced with propofol and maintained with isoflurane.

ANIMALS

T. scripta scripta (n = 8), female, adult.

METHODS

Atropine (2 mg kg^-1) or an isovolumetric control injection of saline was administered intraperitoneally 15 minutes prior to induction of anaesthesia with isoflurane. Individual MAC_isoflurane was then determined by end-tidal gas analysis in a bracketing design by an experimenter blinded to the administered drug, with a 2 week washout period. The experiment was repeated, with atropine (2 mg kg^-1) or saline administered intravascularly in combination with propofol for anaesthetic induction. Linear mixed modelling was used to determine the effects of atropine and propofol on the individual MAC_isoflurane. Data are presented as mean ± standard deviation.

RESULTS

Premedication with atropine significantly reduced MAC_isoflurane (p = 0.0039). In isoflurane-induced T. scripta scripta, MAC_isoflurane decreased from 4.2 ± 0.4% to 3.3 ± 0.8% when atropine had been administered. Propofol as an induction agent had a MAC-sparing effect (p < 0.001) such that MAC_isoflurane following propofol and a control injection of saline was 2.3 ± 1.0%, which decreased further to 1.5 ± 0.8% when propofol was combined with atropine.

CONCLUSIONS AND CLINICAL RELEVANCE

Atropine, presumably by inhibiting parasympathetically mediated pulmonary artery constriction, decreases right-to-left cardiac shunting and the MAC_isoflurane in yellow-bellied sliders, and thereby may facilitate control of inhalant anaesthesia. Propofol can be used for induction of anaesthesia and reduces the required concentration of inhaled anaesthesia assessed 1.5 hours following induction.

Tulathromycin – a semi-synthetic macrolidе antibiotic. II. Usage in veterinary medicine

This article presents the results of studies on the use of the new macrolide antibiotic tulathromycin in veterinary medicine. The information is presented according to the species of domestic animals, diseases, doses and shemes for therapy and metaphylaxis. The first section includes data for cattle and calves affected by respiratory diseases, caused by M. haemolytica, M. bovis, H. somni and P. multocida, and keratoconjunctivitis caused by M. bovis. The second one shows data for swine and pigs affected by the respiratory pathogens A. pleuropneumoniae, P. multocida, H. parasuis, B. bronhiseptica and M. hyopneumoniae. A third group presents information about small ruminants with manifested respiratory diseases caused by M. haemolytica, P. multocida, Mycoplasma spp., Pseudomonas spp. and hoof diseases from Dehelobacter nodosus. Fourth group includes the first test results of Rhodococcus equi, Streptococcus zooepidemicus, Theileria equi, Babesia bovis and Babesia bigemina, causing diseases in horses. The fifth section includes reports of treated rabbits most commonly suffering from P. multocida respiratory infections. Finally, data from new studies on the use of tulathromycin in exotic animals and cases of some tropical diseases are listed. The provided information gives proof for the high sensitivity of the tested pathogens to tulathromycin and high clinical and economical effect that is efficient in single dose of 2.5 mg/kg. Compared to other antibacterial agents there is no resistance according to data available so far. Local accumulation and prolonged persistence of the drug in lung tissues, that result in a treatment regime with a single low-volume dose (2.5 mg/kg), are associated with positive clinical outcome in domestic animals: large ruminants, pigs, small ruminants and rabbits with respiratory diseases caused by M. haemolytica, H. somni, P. multocida and M. bovis; A. pleuropneumoniae, B. bronchiseptica, P. multocida, H. parasuis and M. hyopneumoniae; S.aureus, C. pseudotuberculosis and Streptococcus spp. and P.multocida

Ectothermy and cardiac shunts profoundly slow the equilibration of inhaled anaesthetics in a multi-compartment model

The use of inhalational anaesthesia is ubiquitous in terrestrial vertebrates. Given the dependence of these agents on delivery by the cardiorespiratory system, we developed a new computational model predicting equilibration of inhaled anaesthetics in mammalian and ectotherm conditions including the ability of reptiles to maintain vascular shunts. A multi-compartment model was constructed from simultaneously-solved equations, verified by comparison to the literature for endo and ectotherm physiology. The time to 90% equilibration of anaesthetic in arterial blood (t₉₀) is predicted and used to compare anaesthetics and physiologies. The five to tenfold lower cardiac output and minute ventilation of ectothermic vertebrates is predicted to slow equilibration times by five to ten times leading to 90% equilibration in ectotherm arterial blood of over 200 min, compounded by reduction in body temperature, and the extent of right-to-left vascular shunts. The impact of these findings is also influenced by the solubility coefficient of the anaesthetic, such that at net right-to-left shunt fractions of over 0.8, sevoflurane loses the advantage of faster equilibration, in comparison with isoflurane. We explore clinical strategies to regulate anaesthetic uptake in ectotherms by managing convectional flow especially by supportive ventilation and reduction of the right-to-left shunt.