Evaluation of indirect blood pressure monitoring in awake and anesthetized red-tailed hawks (Buteo jamaicensis): effects of cuff size, cuff placement, and monitoring equipment

The heart, a secondary organ in the control of blood circulation

Circulation of the blood is a fundamental physiological function traditionally ascribed to the pressure-generating function of the heart. However, over the past century the 'cardiocentric' view has been challenged by August Krogh, Ernst Starling, Arthur Guyton and others, based on haemodynamic data obtained from isolated heart preparations and organ perfusion. Their research brought forth experimental evidence and phenomenological observations supporting the concept that cardiac output occurs primarily in response to the metabolic demands of the tissues. The basic tenets of Guyton's venous return model are presented and juxtaposed with their critiques. Developmental biology of the cardiovascular system shows that the blood circulates before the heart has achieved functional integrity and that its movement is intricately connected with the metabolic demands of the tissues. Long discovered, but as yet overlooked, negative interstitial pressure may play a role in assisting the flow returning to the heart. Based on these phenomena, an alternative circulation model has been proposed in which the heart functions like a hydraulic ram and maintains a dynamic equilibrium between the arterial (centrifugal) and venous (centripetal) forces which define the blood's circular movement. In this focused review we introduce some of the salient arguments in support of the proposed circulation model. Finally, we present evidence that exercising muscle blood flow is subject to local metabolic control which upholds optimal perfusion in the face of a substantive rise in muscle vascular conductance, thus lending further support to the permissive role of the heart in the overall control of blood circulation.

Anaesthetic management and complications of a Humboldt penguin (Spheniscus humboldti) undergoing diagnostic imaging

BACKGROUND

The presence of a tracheal septum dividing the trachea into two makes intubation one of the main challenges of penguin anaesthesia. Differences in the length and location of the aforementioned tracheal septum have been described in some penguin species. However, to the best of the authors' knowledge, it has not been reported in Humboldt penguins (Spheniscus humboldti). Therefore, one of the aims of this publication is to report the septal position in this Humboldt penguin. Furthermore, this publication describes the anaesthetic protocol and complications encountered and discusses some of the more important features of penguin anaesthesia. It is anticipated that this case report will aid in future procedures requiring anaesthesia of this penguin species.

CASE PRESENTATION

A 25-year-old female Humboldt penguin was anaesthetized at the University College Dublin Veterinary Hospital for radiographs and computed tomography (CT) following three weeks of inappetence. After assessing the health status of the penguin from the clinical history and performing a physical examination, an American Society of Anesthesiologists physical status score of II was assigned and a combination of butorphanol 1 mg/kg and midazolam 1 mg/kg was administered intramuscularly to sedate the penguin. Induction of anaesthesia was performed via a face mask using sevoflurane in oxygen. The airway was intubated with a 4.0 mm Cole tube and anaesthesia was maintained with sevoflurane in oxygen during the entire procedure. Anaesthetic monitoring consisted of an electrocardiogram, pulse oximetry, non-invasive blood pressure, capnography, and body temperature.

CONCLUSIONS

Tracheal bifurcation was identified as the start of the tracheal septum 4.67 cm from the glottis using CT. Most of the anticipated complications of penguin anaesthesia, such as hyperthermia, hypothermia, regurgitation, hypoventilation, and difficulties in intubation were present in this case. However, no major sequalae occurred following the anaesthetic protocol described.

Cardiovascular Diseases in Pet Birds: Therapeutic Options and Challenges

Cardiovascular disease, including congestive heart failure, pericardial disease, and atherosclerosis, is becoming increasingly better recognized in companion birds. A wide range of medications is available to treat these conditions, including diuretics, vasodilators, positive and negative inotropes, antiarrhythmic agents, and pentoxifylline. This review systematically discusses each of these drug classes and their potential applications in avian species. Although treatment approaches remain largely empirical and extrapolated from small animal and human medicine, the management strategies presented here have the potential to both maintain quality of life and extend survival time for the avian cardiac patient.

Heart Disease in Pet Birds - Diagnostic Options

Cardiovascular diseases are common in pet birds. Diagnosis is often made postmortem only. In any case, suspicious for cardiac disease, a full diagnostic work up should be applied. First indications are given by the anamnestic data. Relative predisposition to cardiovascular diseases is associated with the species, breed, age, gender, lifestyle, and diet. Clinical signs and examination can reveal further indications of cardiovascular diseases, but may be unspecific or even without any pathologic finding. Diagnostic imaging, at least radiography, and echocardiography are always recommended. Advanced imaging methods, especially angiocardiography, can be valuable but is also more invasive and expensive.

Backyard Poultry and Waterfowl Sedation and Anesthesia

The popularity of backyard poultry (chickens, turkey, guinea fowl) and waterfowl (ducks and geese) is increasing in the United States, and these animals frequently present for veterinary care. Like other birds, these species have unique anatomy that should be clinically considered before anesthesia. A balanced approach to an injectable, inhalational, or combination anesthesia protocol must be taken to ensure a safe outcome for the patient and to achieve the procedural needs. A well-informed clinician may use both sedation and general anesthesia to care for backyard bird patients in practice.

Use of Amlodipine in Psittacine Birds: 5 Cases (2010-2018)

Amlodipine is a calcium channel blocker shown to be effective in lowering blood pressure with minimal adverse effects in mammals. To provide a retrospective evaluation of amlodipine use in psittacine birds, medical records were reviewed for all avian patients prescribed amlodipine for treatment for the presumptive diagnosis of hypertension, based on clinical signs and indirect blood pressure measurements. Five birds were treated with amlodipine between 2010 and 2018. The median age was 33 years (range, 22-37 years) and 3/5 birds presented for ataxia or seizures. The median indirect systolic blood pressure at diagnosis was 243 mm Hg (range, 200-275 mm Hg). In 3/5 birds, amlodipine was the only drug prescribed, whereas, in 2/5 birds, enalapril was also prescribed in addition to amlodipine. In addition to the prescription of enalapril, blood pressure measurements were obtained indirectly, which are variables to be considered in this report. The initial median dose of amlodipine prescribed was 0.4 mg/kg (range, 0.1-0.4 mg/kg) PO q24h. In 3/5 birds, amlodipine administration was increased either in dose or frequency. Median follow-up time was 25 months (range, 2-55 months) after the initiation of amlodipine treatment. Owners in all 5 cases reported improvement of clinical signs by a median time of 2 months (range, 1-15 months). Three of 5 birds (60%) demonstrated a decreasing trend in blood pressure during the first 6 months after treatment with amlodipine was started (average, ≥20% decrease). Prospective, controlled studies are needed to investigate the efficacy of amlodipine in psittacine birds.

Effects of isoflurane and sevoflurane alone and in combination with butorphanol or medetomidine on the bispectral index in chickens

BACKGROUND

The bispectral index (BIS) is an anaesthesia monitoring technique able to assess the level of central nervous system depression in humans and various animal species. In birds, it has been validated in chickens undergoing isoflurane anaesthesia. The aim of this study was to evaluate in an avian species the influence of isoflurane and sevoflurane on BIS, each at different minimum anaesthetic concentrations (MAC) multiples, alone or combined with butorphanol or medetomidine. Ten chickens (5 males and 5 females) underwent general anaesthesia with isoflurane or sevoflurane alone, and combined with either intramuscular administration of butorphanol (1 mg/kg) or medetomidine (0.1 mg/kg), in a prospective and cross-over study (i.e., 6 treatments per animal). BIS measurements were compared to heart rate (HR), non-invasive blood pressure (NIBP) and to a visual analogue scale (VAS) of anaesthesia depth.

RESULTS

HR was significantly increased, and both NIBP and VAS were significantly reduced, with higher gas concentrations. NIBP (but not HR or VAS) was additionally affected by the type of gas, being lower at higher concentrations of sevoflurane. Butorphanol had no additional effect, but medetomidine led to differences in HR, NIBP, and in particular a reduction in VAS. With respect to deeper level of hypnosis at higher concentrations and the absence of difference between gases, BIS measurements correlated with all other measures (except with HR, where no significant relationship was found) The difference in BIS before (BISpre) and after stimulation (BISpost) did not remain constant, but increased with increasing MAC multiples, indicating that the BISpost is not suppressed proportionately to the suppression of the BISpre values due to gas concentration. Furthermore, neither butorphanol nor medetomidine affected the BIS.

CONCLUSIONS

The difference of degree of central nervous system depression monitored by BIS compared with neuromuscular reflexes monitored by VAS, indicate that BIS records a level of anaesthetic depth different from the one deducted from VAS monitoring alone. BIS provided complementary information such as that medetomidine suppressed spinal reflexes without deepening the hypnotic state. As a consequence, it is concluded that BIS improves the assessment of the level of hypnosis in chickens, improving anaesthesia monitoring and anaesthesia quality in this species.

ISOFLURANE RESPIRATORY ANESTHETIC INDEX IN CHICKENS (GALLUS GALLUS DOMESTICUS)

Respiratory depression from isoflurane seems to be greater in birds than in mammals. Isoflurane respiratory anesthetic index (AI) has only been evaluated in ducks (Anas platyrhynchos), which indeed showed a lower AI compared to mammals, but the isoflurane AI for other avian species is not known. The aim of this study was to evaluate the isoflurane AI in chickens (Gallus gallus domesticus). Six adult hens were anesthetized with isoflurane for determination of the minimum anesthetic concentration (MAC) using the bracketing method. During a second anesthetic event, the isoflurane AI was determined by progressively increasing the expired fraction of isoflurane by 0.5 times MAC until apnea was achieved (ET_iso-apnea). The isoflurane AI was considered the ratio between the ET_iso-apnea and the MAC. Heart rate, systolic arterial pressure, respiratory rate, and end-tidal carbon dioxide were continuously monitored throughout both anesthetic events. Data were analyzed using a mixed-effect model with Greenhouse-Geisser correction, followed by Tukey's test. The MAC for isoflurane was 1.18% ± 0.09% (mean ± SD). The ET_iso-apnea was 3.31% ± 0.34% and the isoflurane AI was 2.80 ± 0.26. In chickens, isoflurane AI is similar to that measured in mammals, which is in contrast with published data in other avian species.

A DESCRIPTION OF ARTERIAL BLOOD PRESSURE MEASUREMENT IN TWO SPECIES OF FLYING FOXES (PTEROPUS VAMPYRUS AND PTEROPUS HYPOMELANUS)

Blood pressure assessment is valuable during management of chronic conditions with increased risk of developing hypertension and as a standard practice for anesthetic monitoring. Normal arterial blood pressure values have not been well described in megachiropteran species. Following anesthetic induction and maintenance with isoflurane in oxygen, arterial blood pressure was obtained from the posterior tibial artery of eight large flying foxes (Pteropus vampyrus) and six variable flying foxes (Pteropus hypomelanus), two with structural cardiac disease and four in good clinically health. Normal values reported as a median with interquartile range for systolic, diastolic, and mean (MAP) arterial pressures for P. vampyrus were 101 (94, 107), 69 (57, 80), and 86 (75, 93), respectively. Normal MAP for clinically healthy P. hypomelanus was 86 (67, 93). Placement of P. hypomelanus in a vertical head-down position did not alter blood pressure in clinically healthy bats, but significantly increased MAP in two bats with structural cardiac disease. Arterial catheterization of both the posterior tibial and median arteries in these species was easily performed without major complication.

Pharmacokinetics and pharmacodynamics of methadone administered intravenously and intramuscularly to isoflurane-anesthetized chickens

OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of methadone after IV or IM administration to isoflurane-anesthetized chickens.

ANIMALS

6 healthy adult Hy-Line hens.

PROCEDURES

In a randomized crossover-design study, methadone (6 mg/kg) was administered IV and IM to isoflurane-anesthetized chickens with a 1-week washout period between experiments. Blood samples were collected immediately before and at predetermined time points up to 480 minutes after methadone administration. Plasma concentrations were determined by liquid chromatography-mass spectrometry, and appropriate compartmental models were fit to the plasma concentration-versus-time data. Cardiorespiratory variables were compared between treatments and over time with mixed-effect repeated-measures analysis.

RESULTS

A 3-compartment model best described the changes in plasma methadone concentration after IV or IM administration. Estimated typical values for volumes of distribution were 692 mL/kg for the central compartment and 2,439 and 2,293 mL/kg for the first and second peripheral compartments, respectively, with metabolic clearance of 23.3 mL/kg/min and first and second distributional clearances of 556.4 and 51.8 mL/kg/min, respectively. Typical bioavailability after IM administration was 79%. Elimination half-life was 177 minutes, and maximum plasma concentration after IM administration was 950 ng/mL. Heart rate was mildly decreased at most time points beginning 5 minutes after IV or IM drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Disposition of methadone in isoflurane-anesthetized chickens was characterized by a large volume of distribution and moderate clearance, with high bioavailability after IM administration. Additional studies are warranted to assess pharmacokinetics and pharmacodynamics of methadone in awake chickens.

Impact of heat stress on broilers with varying body weights: Elucidating their interactive role through physiological signatures

Physiological determinants of different body weight (BW) broiler chickens under heat stressed conditions were investigated to compare the performance at market age considering medium body weight group as standard. At 5 weeks, broilers were categorized randomly into 3 treatments (N = 24 per group) as high (HBW) (>1050 g), medium (MBW) (900-1050 g) and low (LBW) (<900 g) followed by simultaneous exposure to normal and heat stress (HS) conditions at 40 ± 1 °C and 45 ± 5% RH for 4 h/day for a period of 7 days (D) and sample collection was employed at D0, D3 and D7. Physiological and stress responses, haematological and biochemical profile, intestinal gross and histological aspects were estimated using standard protocols. Heart rate and mean arterial blood pressure were significantly (P = 0.000) higher in HBW broilers followed by low and medium ones. Heat stress exposure indicated significant (P = 0.000) increase in heart rate, arterial blood pressure, respiration rate and comb temperature while cloacal temperature remained unaffected. Lymphocytes, eosinophils, total red blood cell count, haemoglobin, and haematocrit were reduced (P = 0.000) whereas mean corpuscular volume and mean corpuscular hemoglobin, heterophil count and heterophil to lymphocyte ratio were increased (P = 0.000) in response to HS. Circulating corticosterone and tri-iodothyronine concentrations showed inverse relationship with respect to BW variation and HS duration respectively with significant interaction (P = 0.000). Higher protein in LBW was observed on D3. Serum triglycerides remained unaffected till D3 exposure but significantly (P = 0.017) reduced on D7 with lowest content in HBW group. Serum alkaline phosphatase increased in LBW group with significant heat stress interaction (P = 0.000) on D3. HS reduced villi length and crypt depth; but their corresponding ratio increased. In conclusion, HBW broilers are more affected than MBW or LBW groups. This study established interactive roles of BW and HS on physiological responses in broilers.

Effects of Isoflurane Anesthesia on the Hematologic Values of Rehabilitated Wild Owls

Isoflurane anesthesia is commonly used for owls when they are being rehabilitated to minimize stress during treatments and procedures, as well as to ensure caretaker safety. However, the effects of isoflurane anesthesia on the hematologic response of owls are not known. To investigate the effects of isoflurane anesthesia on the hematology of owls, 3 phases of investigation were performed on the subject animals: 1) single, short manual- versus single, short isoflurane-restraint episodes (n = 12; 38%); 2) a single, prolonged isoflurane episode (n = 10; 31%); and 3) serial, short isoflurane episodes (n = 10; 31%). All owls were classified as adult, and the sex for most individuals was unknown. Twelve owls (38%) were included in phase 1: 5 great horned owls (Bubo virginianus; 42%), 2 eastern screech owls (Megascops asio; 17%), and 5 barred owls (Strix varia; 42%). A separate cohort of 10 novel owls (31%) were selected for inclusion in both phases 2 and 3: 4 great horned owls (40%), 2 eastern screech owls (20%), 2 barred owls (20%), 1 barn owl (Tyto alba; 10%), and 1 snowy owl (Bubo scandiacus; 10%). For each anesthetic episode, blood was collected within 3 minutes of capture and in 15-minute intervals according to the duration of the procedure. Phase 2 had additional blood collections with the patient awake at 2 and 24 hours after time 0 blood collection, whereas phase 3 had an additional blood collection at 24 hours after time 0 blood collection. Hematologic analyses included packed cell volume, total solids, total white blood cell count, heterophil to lymphocyte ratio, and absolute heterophil, lymphocyte, monocyte, eosinophil, and basophil counts. Total white blood cell count decreased significantly during phase 1; packed cell volume decreased significantly during phases 2 and 3; total solids decreased significantly in phase 2; phase 2 demonstrated a lymphopenia with a concurrent decrease in the heterophil to lymphocyte ratio; and phase 3 demonstrated a heteropenia and significant changes in the eosinophil count. All hematologic changes noted in the study were within appropriate reference intervals for the owls but do suggest that there are physiologic consequences of restraining and anesthetizing these avian patients.

Sympathomimetics in veterinary species under anesthesia

Sympathomimetic drugs mimic the physiological action of the sympathetic nervous system through interaction with adrenergic receptors. These drugs are commonly used to provide cardiovascular support in many veterinary species. Despite their common use, the literature evaluating their effectiveness can be somewhat limited depending on the species. This review details the mechanism of action of various sympathomimetic drugs and summarizes the literature that is available describing the efficacy of these drugs and their use in anesthetized veterinary species.

Technological Advances in Exotic Pet Anesthesia and Analgesia

Even when performed by skilled operators, locating the nerves can be challenging in small exotic pets; in such cases, the use of an electrical nerve stimulator may be useful to confirm the correct identification of the target nerve. Exotic animal anesthesia and analgesia have dramatically progressed over the past decade and continue to do so as more research and technologies develop. Technological advancements such as airway devices, endoscopic intubation techniques, positive intermittent pressure ventilators, and invasive and noninvasive blood pressure monitors have played a significant role in improving patient safety and the anesthetic outcomes of exotic animals.

Cardiovascular Drugs in Avian, Small Mammal, and Reptile Medicine

Cardiovascular disease, including congestive heart failure, pericardial disease, and atherosclerosis, is becoming increasingly better recognized in companion birds, small mammals, and reptiles. A wide range of medications is available to treat these conditions, including diuretics, vasodilators, positive and negative inotropes, antiarrhythmic agents, and pentoxifylline. This review systematically discusses each of these drug classes and their potential applications in exotic species. Although treatment approaches remain largely empirical and extrapolated from small animal and human medicine, the management strategies presented here have the potential to both maintain quality of life and extend survival time for the exotic cardiac patient.

Advancements in Evidence-Based Anesthesia of Exotic Animals

Anesthesia and sedation of pet nondomestic species are often necessary for both invasive and noninvasive procedures. Even minimally invasive procedures can be stressful for small prey species that are not domesticated or acclimated to human contact and restraint. Recent advancements in evidence-based practice will continue to improve the field based on scientifically sound best practices and rely less on anecdotal recommendations. This article focuses on new scientific literature that has been published in the past 5 years. For ease of reading, the authors divide the article to highlight advances in anesthetic pharmacology and discoveries in anesthetic physiology and monitoring.