Biomedical subjects

William W Muir

Publications and source records attributed to William W Muir.

26 records · Page 2Linked to original sources

PubMed2003

Minimum alveolar concentration measures of central nervous system activation in cats anesthetized with isoflurane.

OBJECTIVE: To compare the minimum alveolar concentration (MAC) of isoflurane required to prevent corticocerebral activation, autonomic responses, and purposeful movements after somatic or visceral stimulation in cats anesthetized with isoflurane. ANIMALS: 17 healthy spayed female cats. PROCEDURE: Bispectral index (BIS), autonomic parameters, and purposeful movements were monitored before and after somatic or visceral stimuli in cats anesthetized with isoflurane. End-tidal (ET) isoflurane concentration was varied to determine MAC values for cortical arousal (MAC(BIS)), autonomic responsiveness (MAC(BAR)), and purposeful movement (MAC). Bispectral index values > or = 60 were considered to represent corticocerebral activation. RESULTS: Minimum alveolar concentration for purposeful movement was significantly less than MAC(BIS) and MAC(BAR) for both somatic and visceral stimulation. Individual MAC values for somatic stimulation were not significantly different from respective MAC values for visceral stimulation. The percentage of cats that had a BIS response > or = 60 was inversely related to the end-tidal isoflurane concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Corticocerebral arousal and subcortical autonomic reflexes occured at isoflurane anesthetic concentrations at which reflexive or purposeful movements were absent. These results suggested that isoflurane had a preferential effect on voluntary motor output at low end-tidal isoflurane concentrations, and that sensory pathways, subcortical sympathetic output, and cortical responsiveness are less susceptible to the anesthetic effects of isoflurane. Bispectral index values obtained after somatic or visceral stimulation were sensitive for the detection of early changes in cortical excitability.

Analysis of Variance↗

PubMed2003

Use of the bispectral index as a monitor of anesthetic depth in cats anesthetized with isoflurane.

OBJECTIVE: To determine whether the prestimulation bispectral index (BIS) value or relative change in BIS after noxious stimulation can be used to assess the depth of isoflurane anesthesia in cats. ANIMALS: 17 healthy female cats. PROCEDURE: Electroencephalogram (EEG) patterns and BIS values were examined in cats that received increasing end-tidal (ET) isoflurane concentrations. Subsequently, BIS values were determined before and after either a noxious somatic or visceral stimulus in cats that received ET isoflurane concentrations ranging from 1.8% to 2.4%. Electrical stimuli of the tail base and bladder distension to 50 cm of water were the somatic and visceral stimuli, respectively. RESULTS: The resting BIS at ET isoflurane concentrations from 1.4% to 1.9% steadily decreased concurrently with increasing degrees of EEG suppression. Prestimulation BIS values, however, were not related to 1.8% to 2.4% ET isoflurane concentrations and not useful for prediction of BIS values or hemodynamic and movement responses after a noxious stimulus. The poststimulation BIS value and the difference between mean BIS values before and after stimulation were inversely correlated with increasing ET isoflurane concentrations. Poststimulation BIS values > 60 were observed at ET isoflurane concentrations greater than those associated with a movement response after a stimulus. CONCLUSIONS AND CLINICAL RELEVANCE: The prestimulation BIS value has limited use in assessing anesthetic depth in cats during isoflurane anesthesia. The change in BIS values after a noxious somatic or visceral stimulus was a reliable measure of anesthetic depth and may be a useful measure of early arousal from the hypnotic state.

Analysis of Variance↗

PubMed2002

Clinical comparison of xylazine and medetomidine for premedication of horses.

OBJECTIVE: To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia. DESIGN: Randomized clinical trial. ANIMALS: 40 horses. PROCEDURE: Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at the time of anesthetic induction. After induction of anesthesia, sodium pentothal was administered as necessary to prevent limb movements. Hypotension was treated with dobutamine; hypoventilation and hypoxemia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored. RESULTS: Scores for the quality of the transition to inhalation anesthesia were significantly higher for horses premedicated with medetomidine than for horses premedicated with xylazine. However, other scores, recovery times, and numbers of attempts needed to achieve sternal recumbency and to stand were not significantly different between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that medetomidine is suitable for premedication of horses undergoing general anesthesia. Analgesic and cardiopulmonary effects of medetomidine were similar to those of xylazine, except that the transition to inhalation anesthesia was smoother when horses were premedicated with medetomidine, rather than xylazine.

Adrenergic alpha-Agonists↗

PubMed2002

Infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses.

OBJECTIVE: To evaluate effects of infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses. DESIGN: Randomized clinical trial. ANIMALS: 40 horses. PROCEDURE: Horses were premedicated with xylazine and anesthetized with diazepam and ketamine. Anesthesia was maintained by infusion of guaifenesin, ketamine, and medetomidine and inhalation of sevoflurane (20 horses) or by inhalation of sevoflurane (20 horses). A surgical plane of anesthesia was maintained by controlling the inhaled concentration of sevoflurane. Sodium pentothal was administered as necessary to prevent movement in response to surgical stimulation. Hypotension was treated with dobutamine; hypoxemia and hypercarbia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored. RESULTS: The delivered concentration of sevoflurane (ie, the vaporizer dial setting) was significantly lower and the quality of transition to inhalation anesthesia and of anesthetic maintenance were significantly better in horses that received the guaifenesin-ketamine-medetomidine infusion than in horses that did not. Five horses, all of which received sevoflurane alone, required administration of pentothal. Recovery time and quality of recovery were not significantly different between groups, but horses that received the guaifenesin-ketamine-medetomidine infusion required fewer attempts to stand. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in horses, the combination of a guaifenesin-ketamine-medetomidine infusion and inhalation of sevoflurane resulted in better transition and maintenance phases while improving cardiovascular function and reducing the number of attempts needed to stand after the completion of anesthesia, compared with inhalation of sevoflurane.

Anesthesia↗

PubMed2002

Cardiovascular effects of a high dose of romifidine in propofol-anesthetized cats.

OBJECTIVE: To determine the hemodynamic effects of IM administration of romifidine hydrochloride in propofol-anesthetized cats. ANIMALS: 15 adult domestic shorthair cats. PROCEDURE: Cats were randomly assigned to receive romifidine (0, 400, or 2,000 microg/kg, IM). Cats were anesthetized with propofol and mechanically ventilated with oxygen. The right jugular vein, left carotid artery, and right femoral artery and vein were surgically isolated and catheterized. Heart rate; duration of the PR, QRS, and QT intervals; mean pulmonary artery pressure; mean right atrial pressure; systolic, diastolic, and mean arterial pressures; left ventricular systolic pressure; left ventricular end-diastolic pressure; and cardiac output were monitored. Systemic vascular resistance, rate of change of left ventricular pressure, and rate pressure product were calculated. Arterial and venous blood samples were collected anaerobically for determination of pH and blood gas tensions (Po2 and Pco2). RESULTS: Administration of romifidine at 400 and 2,000 microg/kg, IM, decreased heart rate, cardiac output, rate of change of left ventricular pressure, rate pressure product, and pH. Arterial and pulmonary artery pressures, left ventricular pressure, left ventricular end-diastolic pressure, and right atrial pressure increased and then gradually returned to baseline values. Arterial blood gas values did not change, whereas venous Pco2 increased and venous Po2 decreased. Significant differences between low and high dosages were rare, suggesting that the dosages investigated produced maximal hemodynamic effects. CONCLUSIONS AND CLINICAL RELEVANCE: Romifidine produces cardiovascular effects that are similar to those of other alpha2-agonists. High dosages of romifidine should be used with caution in cats with cardiovascular compromise.

Anesthesia↗

PubMed2002

Cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture.

OBJECTIVE: To determine cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture (EA). ANIMALS: 8 healthy 10- to 20-year-old mares that weighed between 470 and 600 kg. PROCEDURE: Each horse received 2 hours of acupuncture and 2 hours of PAES at acupoints Bladder 18, 23, 25, and 28 on both sides of the vertebral column as well as sham needle placement (control treatment). Each treatment was administered in a random order. At least 7 days elapsed between treatments. Nociceptive cutaneous pain threshold was measured by use of skin twitch reflex latency (STRL) and avoidance to radiant heat (< or = 50 degrees C) in the lumbar area. Skin temperature, cardiovascular and respiratory variables, and beta-endorphin concentration in spinal fluid (CSF-EN) and plasma (plasma-EN) were measured. RESULTS: Acupuncture and PAES significantly increased STRL and skin temperature. The CSF-EN was significantly increased from baseline values 30 to 120 minutes after onset of PAES, but it did not change after acupuncture and control treatments. Heart and respiratory rates, rectal temperature, arterial blood pressure, Hct, total solids and bicarbonate concentrations, base excess, plasma-EN, and results of blood gas analyses were not significantly different from baseline values after acupuncture, PAES, and control treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of PAES was more effective than acupuncture for activating the spinal cord to release beta-endorphins into the CSF of horses. Acupuncture and PAES provided cutaneous analgesia in horses without adverse cardiovascular and respiratory effects.

Acupuncture Analgesia↗

PubMedDate not supplied

Sodium nitroprusside-induced deliberate hypotension to facilitate patent ductus arteriosus ligation in dogs.

OBJECTIVE: To report the use of sodium nitroprusside to induce deliberate hypotension to reduce hemorrhage and facilitate surgical ligation of complicated patent ductus arteriosus (PDA) in dogs. STUDY DESIGN: Retrospective study. ANIMALS: Six dogs. METHODS: Hemorrhage occurred during surgical ligation of PDA in 5 dogs. Surgical dissection and isolation of the PDA were very difficult in a sixth dog that was considered to be at increased risk for ductus rupture. Sodium nitroprusside (5 to 25 microg/kg/min intravenously) was administered to these 6 dogs to induce hypotension to reduce blood loss and facilitate surgical ligation of the PDA. RESULTS: Sodium nitroprusside infusion reduced blood pressure (mean arterial pressure, 45 to 60 mm Hg) within 5 to 10 minutes and hemorrhage from the PDA, facilitating its surgical ligation. Recovery from surgery and anesthesia was uneventful in all 6 dogs. CONCLUSIONS: Sodium nitroprusside infusion can be used to induce deliberate hypotension in dogs to facilitate surgical ligation of PDA. CLINICAL RELEVANCE: Sodium nitroprusside infusion produces hypotension within 5 to 10 minutes and is easy to control, rapidly abates, and should help to facilitate surgical ligation of PDA.

Animals↗

PubMedDate not supplied

Hemoglobin solutions and tissue oxygenation.

Oxygen (O2) delivery to tissues plays an important role in determining microcirulatory autoregulatory responses. The balance between O2 delivery by whole blood and tissue O2 consumption likely has evolved based on regulatory processes designed to accommodate the encapsulation of hemoglobin (Hb) within red blood cells (RBCs). The hemodynamic, rheologic, and physical properties of blood, or an alternate O2-carrying solution, can have important consequences for O2 delivery to tissue. The development of acellular hemoglobin-based oxygen carriers (HBOC) requires reassessment of the O2 loading and unloading charactistics of Hb. the effects of altering the rheologic properties of blood, and the impact of these changes on microcirculatory autoregulation and tissue oxygenation. A variety of experimental and clinical studies have demonstrated beneficial effects of HBOCs. However, mechanisms responsible for HBOC-facilitated, O2-dependent autoregulatory changes in the microcirculation have not been completely elucidated.

Animals↗