Robert D. Keegan

Effects of a polymerized ultrapurified bovine hemoglobin blood substitute administered to ponies with normovolemic anemia.

The development of ultrapurified hemoglobin-based oxygen carriers has eliminated many problems associated with whole-blood transfusions in other species. We hypothesized that the administration of polymerized ultrapurified bovine hemoglobin (PUBH) would result in improved hemodynamic parameters in ponies with normovolemic anemia without adverse effects on renal function or coagulation times. Normovolemic anemia was induced in 6 healthy adult ponies. Over a 3-day period, at least 45 mL/kg of whole blood was withdrawn from each pony until a target PCV of <12% was attained. Plasma was separated from the red blood cells via centrifugation and readministered to the ponies on each day. After the final plasma transfusion, 15 mL/kg of hetastarch (control, n = 6) or 15 mL/kg of PUBH (treatment, n = 6) was administered at 10 mL/kg/h IV. Administration of PUBH at a rate of 10 mL/kg/h was not associated with any adverse effects in 5 of the 6 ponies. One pony experienced an anaphylactoid reaction during infusion of PUBH. The reaction, characterized by intense pruritus, tachycardia, and tachypnea resolved shortly after stopping the infusion. Ponies receiving PUBH had significantly lower cardiac indices (P = .03) and heart rates (P = .002) than control animals. A significantly greater increase in central venous pressure was observed in the PUBH group compared to the hetastarch group (P = .02). No adverse renal or coagulation effects were observed with PUBH infusion. These results suggest that PUBH improves hemodynamics and oxygen transport parameters in horses experiencing normovolemic anemia. Patients should be monitored closely during infusion for any adverse reactions.

Effects of 6% hetastarch (600/0.75) or lactated Ringer’s solution on hemostatic variables and clinical bleeding in healthy dogs anesthetized for orthopedic surgery

OBJECTIVE To evaluate and compare hemostatic variables and clinical bleeding following the administration of 6% hetastarch (600/0.75) or lactated Ringers solution (LRS) to dogs anesthetized for orthopedic surgery. STUDY DESIGN Randomized blinded prospective study. ANIMALS Fourteen, healthy adult mixed-breed hound dogs of either sex, aged 11-13 months, and weighing 20.8±1.2 kg. METHODS The dogs were randomly assigned to receive a 10 mL kg(-1) intravenous (i.v.) bolus of either 6% hetastarch (600/0.75) or LRS over 20 minutes followed by a maintenance infusion of LRS (10 mL kg(-1)  hour(-1)) during anesthesia. Before (Baseline) and at 1 and 24 hours after bolus administration, packed cell volume (PCV), total protein concentration (TP), prothrombin time (PT), activated partial thromboplastin time (APTT), von Willebrands factor antigen concentration (vWF:Ag), factor VIII coagulant activity (F VIII:C), platelet count, platelet aggregation, colloid osmotic pressure (COP) and buccal mucosal bleeding time (BMBT) were measured. In addition a surgeon who was blinded to the treatments assessed bleeding from the incision site during the procedure and at 1 and 24 hours after the bolus administration. RESULTS Following hetastarch or LRS administration, the PCV and TP decreased significantly 1-hour post-infusion. APTT did not change significantly compared to baseline in either treatment group, but the PT was significantly longer at 1-hour post-infusion than at 24 hours in both groups. No significant change was detected for vWF:Ag, FVIII:C, platelet aggregation or clinical bleeding in either group. The BMBT increased while platelet count decreased significantly at 1-hour post-infusion in both groups. The COP decreased significantly in both treatment groups 1-hour post-infusion but was significantly higher 1-hour post-infusion in the hetastarch group compared to the LRS group. CONCLUSIONS AND CLINICAL RELEVANCE At the doses administered, both hetastarch and LRS can alter hemostatic variables in healthy dogs. However, in these dogs undergoing orthopedic surgery, neither fluid was associated with increased clinical bleeding.

Cardiovascular effects of sevoflurane in Holstein calves

OBJECTIVE The purpose of this study was to determine the cardiovascular effects of sevoflurane in calves. STUDY DESIGN Prospective experimental study. ANIMALS Six, healthy, 8-12-week-old Holstein calves weighing 80 ± 4.5 (mean ± SEM) kg were studied. METHODS Anesthesia was induced by face-mask administration of 7% sevoflurane in O2. Calves tracheae were intubated, placed in right lateral recumbency, and maintained with 3.7% end-tidal concentration sevoflurane for 30 minutes to allow catheterization of the auricular artery and placement of a Swan-Ganz thermodilution catheter into the pulmonary artery. After instrumentation, administration of sevoflurane was temporarily discontinued until mean arterial pressure was > 100 mm Hg. Baseline values were recorded and the vaporizer output increased to administer 3.7% end-tidal sevoflurane concentration. Ventilation was controlled to maintain normocapnia. The following were recorded at 5, 10, 15, 30 and 45 minutes after collection of baseline data and expressed as the mean value (± SEM): direct systolic, diastolic, and mean arterial blood pressures; cardiac output; mean pulmonary arterial pressure; pulmonary arterial occlusion pressure, heart rate; and pulmonary arterial temperature. Cardiac index and systemic and pulmonary vascular resistance values were calculated using standard formulae. Arterial blood gases were analyzed at baseline, and at 15 and 45 minutes. Differences from baseline values were determined using one-way analysis of variance for repeated measures with post-hoc differences between mean values identified using Dunnets test (p < 0.05). RESULTS Mean time from beginning sevoflurane administration to intubation of the trachea was 224 ± 9 seconds. The mean end-tidal sevoflurane concentration at baseline was 0.7 (± 0.11)%. Sevoflurane anesthesia was associated with decreased arterial blood pressure at all sampling times. Mean arterial blood pressure decreased from a baseline value of 112 ± 7 mm Hg to a minimum value of 88 ± 4 mm Hg at 5 minutes. Compared with baseline, arterial pH was decreased at 15 minutes. Pulmonary arterial blood temperature was decreased at 15, 30 and 45 minutes. Arterial CO2 tension increased from a baseline value of 43 ± 3 to 54 ± 4 mm Hg (5.7 ± 0.4 to 7.2 ± 0.3 kPa) at 15 minutes. Mean pulmonary arterial pressure was increased at 30 and 45 minutes. Pulmonary arterial occlusion pressure increased from a baseline value of 18 ± 2 to 23 ± 2 mm Hg at 45 minutes. There were no significant changes in other measured variables. All calves recovered from anesthesia uneventfully. CONCLUSION We conclude that sevoflurane for induction and maintenance of anesthesia was effective and reliable in these calves and that neither hypotension nor decreased cardiac output was a clinical concern. CLINICAL RELEVANCE Use of sevoflurane for mask induction and maintenance of anesthesia in young calves is a suitable alternative to injectable and other inhalant anesthetics.

Hemodynamic Changes During Laparoscopic Radiofrequency Ablation of Normal Adrenal Tissue in Dogs

OBJECTIVE To determine the hemodynamic response to radiofrequency ablation (RFA) of normal adrenal tissue in dogs. STUDY DESIGN Experimental study. ANIMALS Healthy adult mixed-breed dogs (n=6). METHODS During general anesthesia a Swan-Ganz thermodilution catheter was flow directed into the pulmonary artery and used to quantify cardiac output. An arterial catheter was used for direct blood pressure measurements. An RFA device was introduced into the left adrenal gland under observation through laparoscopic instrumentation. Blood samples were collected and hemodynamic variables studied after a stable surgical anesthetic depth was achieved (time 1), during CO(2) insufflation of the abdomen (time 2), during adrenal RFA (time 3), and after completed RFA (time 4). Catecholamine determinations were performed with a human enzyme immunoassay. Histopathology was performed to verify medullary necrosis. RESULTS Arterial, pulmonary arterial and central venous pressure, and plasma norepinephrine increased more during RFA than during abdominal insufflation. Heart rate and cardiac index did not differ between time points. High baseline epinephrine was present and significant differences between time points were not detected. Systemic vascular resistance had very high individual variation and differences were not detected. CONCLUSIONS RFA of normal adrenal tissues is associated with severe hemodynamic alterations. Further studies of the optimal blockage of catecholamine-induced hypertension in dogs are warranted. CLINICAL RELEVANCE Clinicians should prepare for potential hypertensive crisis during RFA of adrenal masses, especially if treating a margin of normal tissue.

Intracranial pressure and cardiopulmonary variables during isoflurane or sevoflurane anesthesia at various minimum alveolar concentration multiples in normocapnic dogs

OBJECTIVE To compare effects of isoflurane and sevoflurane on intracranial pressure and cardiovascular variables at 1.0, 1.5, and 2.0 times the minimum alveolar concentration (MAC) in mechanically ventilated normocapnic dogs. ANIMALS 6 healthy male Beagles. PROCEDURES The individual MAC was determined for each agent with an electrical stimulus. After a minimum of 1 week, anesthetic induction by use of a mask with one of the inhalation anesthetics selected randomly was followed by mechanical ventilation and instrumentation for measurement of intracranial pressure and cardiovascular variables. Heart rate; systolic, mean, and diastolic arterial blood pressures; central venous pressure; mean pulmonary arterial pressure; pulmonary artery occlusion pressure; cardiac output; intracranial pressure (ICP); core body temperature; end-tidal inhalation anesthetic and carbon dioxide concentration; and arterial blood gas values were measured after attaining equilibrium at 1.0, 1.5, and 2.0 MAC of each inhalation anesthetic. Cardiac index, systemic vascular resistance, pulmonary vascular resistance, and cerebral perfusion pressure (CPP) were calculated. RESULTS Mean ICP did not differ within and between anesthetics at any MAC. Compared with equipotent concentrations of isoflurane, the CPP and mean values for systolic, mean, and diastolic arterial blood pressures were increased at 2.0 MAC for sevoflurane, whereas mean values for mean and diastolic arterial blood pressures and systemic vascular resistance were increased at 1.5 MAC for sevoflurane. CONCLUSIONS AND CLINICAL RELEVANCE Although ICP was similar in healthy normocapnic dogs, CPP was better maintained during 2.0 MAC for sevoflurane, compared with isoflurane.

Virtual Ventilator: a Win32 application to teach the principles of mechanical ventilation

Instruction within the veterinary curriculum in many disciplines has traditionally relied upon use of animal intensive laboratories to teach the effects of a technique, procedure or treatment on a living patient. Due to concerns raised about live animal usage in teaching, many veterinary training programs have introduced static models or mannequins into their curricula to facilitate teaching the mechanics of a task such as suturing a wound. Such models, while valuable, provide little feedback to the student as to how poorly the wound will heal if sutured improperly. The practice of clinical anesthesia is in large part concerned with feed back. The response of the patient to anesthetic drugs and techniques dictates how the drugs and techniques will be applied to the individual patient. A static model may suffice when teaching the technique of endotracheal intubation, but clearly ‘patient’ response is invaluable when teaching how one should respond to inadequate ventilation. The Virtual Ventilator (RD Keegan, Moscow, ID, USA) application attempts to combine the simplicity of a static model with user feed back to provide the student a realistic model/simulation of connecting patient to a mechanical ventilator. Virtual Ventilator is a 32-bit application designed for a PC running either Windows 95, 98 or NT (Microsoft Corporation, Redmond, WA, USA). The Virtual Ventilator main screen depicts a ventilator bellows, several ventilator controls that are manipulated using the mouse and several digital/analog displays. The student adjusts ventilator settings using the controls while the displays and the position and movement of the bellows provide feedback as to the effects the chosen ventilator settings are having on the patient and on the ventilator itself. A split window permits viewing the patients capnograph concurrently with the ventilator settings. Student evaluations have indicated that the application has been useful as a training tool to facilitate subsequent live animal anesthesia laboratories using mechanical ventilation.