Objective—To compare the effects of a nonrebreathing circuit versus a reduced volume circle anesthetic breathing circuit on body temperature change in cats during inhalation anesthesia for ovariohysterectomy.
Design—Randomized, controlled clinical trial.
Animals—141 female domestic cats hospitalized for routine ovariohysterectomy.
Procedures—Cats were randomly assigned to receive inhalation anesthetics from either a nonrebreathing circuit or a reduced volume circle system with oxygen flow rates of 200 and 30 mL/kg/min (90.9 and 13.6 mL/lb/min), respectively. Body temperatures were monitored throughout the anesthetic period via an intrathoracic esophageal probe placed orally into the esophagus to the level of the heart base.
Results—No difference in body temperature was found between the 2 treatment groups at any measurement time. The duration of procedure had a significant effect on body temperature regardless of the type of anesthetic circuit used.
Conclusions and Clinical Relevance—Duration of the procedure rather than the type of anesthetic circuit used for inhalation anesthesia was more influential on thermal loss in cats undergoing ovariohysterectomy.
Objective—To compare 2 techniques for induction of cats by use of isoflurane in an anesthetic chamber.
Design—Prospective, randomized study.
Animals—51 healthy cats.
Procedures—Cats were randomly allocated to 2 induction techniques. Cats were premedicated with acepromazine (0.1 mg/kg [0.045 mg/lb], SC) and buprenorphine (0.01 mg/kg [0.0045 mg/lb], SC) 30 minutes before induction. Cats were then placed into an induction chamber, and anesthetic induction was initiated. One technique involved a conventional flow-through system that used an oxygen flowmeter and an isoflurane vaporizer to flow vapors into the induction chamber. Alternatively, liquid isoflurane was injected into a vaporization tray that was mounted to the interior surface of the chamber lid. Inductions were videotaped for analysis. Five variables (head bobbing, head swinging side to side, paddling, rotating 180° to 360°, and rolling over or flipping) were scored to assess induction quality. Time variables recorded during induction corresponded to the interval until onset of excitatory motion, duration of excitatory motion, interval until recumbency, and interval until complete induction.
Results—Compared with cats anesthetized by use of a conventional vapor chamber technique, cats anesthetized by use of the liquid injection technique had a significantly shorter interval until recumbency and interval until complete induction and lower scores for quality of induction, indicating a smoother induction.
Conclusions and Clinical Relevance—Anesthetic induction in cats by use of a liquid injection technique was more rapid and provided a better quality of induction, compared with results for cats induced by use of a conventional vapor technique.
Objective—To measure the effects of tidal volume, ventilatory frequency, and oxygen insufflation flow on the fraction of inspired oxygen in cadaveric horse heads attached to a lung model.
Sample—8 heads of equine cadavers.
Procedures—Each cadaveric horse head was intubated with a nasotracheal tube that extended into the proximal portion of the trachea. Oxygen was delivered through an oxygen catheter contained within and extending to the tip of the nasotracheal tube. The trachea was connected to the lung model by use of a spiral-wound hose with a sampling adaptor. Eight treatment combinations involving 2 tidal volumes (5 and 8 L), 2 ventilatory frequencies (6 and 12 mechanical breathes/min), and 2 insufflation rates (10 and 15 L/min) were applied to each head. Hand-drawn inspired gas samples were collected and analyzed for oxygen concentrations.
Results—The fraction of inspired oxygen (measured at mid trachea) ranged from 26.8% to 39.4%. Fraction of inspired oxygen was significantly higher with a smaller tidal volume, lower ventilatory frequency, and higher insufflation rate.
Conclusions and Clinical Relevance—In the study model, measured fraction of inspired oxygen varied with ventilatory pattern as well as oxygen insufflation rate. Clinically, this information could be beneficial for interpretation of data regarding arterial blood gases and hemoglobin saturation and in making appropriate oxygen insufflation decisions for anesthetized horses that are breathing room air.
Objective—To compare the effects of 2 fractions of inspired oxygen, 50% and > 95%, on ventilation, ventilatory rhythm, and gas exchange in isoflurane-anesthetized horses.
Animals—8 healthy adult horses.
Procedures—In a crossover study design, horses were assigned to undergo each of 2 anesthetic sessions in random order, with 1 week separating the sessions. In each session, horses were sedated with xylazine hydrochloride (1.0 mg/kg, IV) and anesthesia was induced via IV administration of diazepam (0.05 mg/kg) and ketamine (2.2 mg/kg) Anesthesia was subsequently maintained with isoflurane in 50% or > 95% oxygen for 90 minutes. Measurements obtained during anesthesia included inspiratory and expiratory peak flow and duration, tidal volume, respiratory frequency, end-tidal CO2 concentration, mixed expired partial pressures of CO2 and O2, Pao2, Paco2, blood pH, arterial O2 saturation, heart rate, and arterial blood pressure. Calculated values included the alveolar partial pressure of oxygen, alveolar-to-arterial oxygen tension gradient (Pao2 − Pco2), rate of change of Pao2 − Pao2, and physiologic dead space ratio. Ventilatory rhythm, based on respiratory rate and duration of apnea, was continuously observed and recorded.
Results—Use of the lower inspired oxygen fraction of 50% resulted in a lower arterial oxygen saturation and Pao2 than did use of the higher fraction. No significant difference in Paco2, rate of change of Pao2 − Pao2, ventilatory rhythm, or other measured variables was observed between the 2 sessions.
Conclusion and Clinical Relevance—Use of 50% inspired oxygen did not improve the ventilatory rhythm or gas exchange and increased the risk of hypoxemia in spontaneously breathing horses during isoflurane anesthesia. Use of both inspired oxygen fractions requires adequate monitoring and the capacity for mechanical ventilation.
Objective—To assess the effects of oxygen insufflation rate, respiratory rate, and tidal volume on fraction of inspired oxygen (Fio2) in cadaveric canine heads attached to a lung model.
Sample—16 heads of canine cadavers.
Procedures—Each cadaver head was instrumented with a nasal insufflation catheter through which oxygen was delivered. The trachea was attached to a sample collection port connected by means of corrugated tubing to a lung model. Eight treatment combinations that varied in respiratory rate (10 or 20 breaths/min), tidal volume (10 or 15 mL/kg), and oxygen insufflation rate (50 or 100 mL/kg/min) were applied to each head in a replicated Latin square design. Gas samples were manually collected, and inspired oxygen concentrations were analyzed. The Fio2 and end-tidal CO2 concentration were determined and compared among sample groups.
Results—Estimated least squares mean Fio2 for various treatment combinations ranged from 32.2% to 60.6%. The Fio2 was significantly increased at the higher insufflation rate (estimated marginal least squares mean, 48.7% vs 38.6% for 100 and 50 mL/kg/min, respectively), lower respiratory rate (48.9% vs 38.3% for 10 and 20 breaths/min, respectively), and smaller tidal volume (46.8% vs 40.0% for 10 and 15 mL/kg, respectively).
Conclusions and Clinical Relevance—Fio2 in the model was affected by oxygen insufflation rate, respiratory rate, and tidal volume. This information may potentially help clinicians interpret results of blood gas analysis and manage canine patients receiving oxygen insufflation via a nasal catheter.
Objective—To determine effects of sedation
achieved by xylazine (XYL) or acepromazine (ACE) on
cardiopulmonary function and uterine blood flow in
cows in late gestation.
Animals—8 cows between 219 and 241 days of gestation.
Procedure—Doses of ACE (0.02 mg/kg) or XYL (0.04
mg/kg) were administered IV. Measurements were
obtained to determine cardiopulmonary effects and
oxygen delivery to the uterus.
Results—Heart rate was not significantly affected by
administration of ACE, but it decreased markedly after
administration of XYL. Uterine artery flow was
decreased at all times by XYL and was always less
than for ACE. Xylazine increased uterine vascular
resistance through 30 minutes and caused reduced
PaO2 and increased PaCO2 at all time periods.
Acepromazine caused a 5% decrease in PaO2 only at
5 minutes. Xylazine reduced oxygen delivery by 59%
at 5 minutes and 32% at 45 minutes. In contrast, ACE
caused a nonsignificant reduction of oxygen delivery
by 16% at 15 minutes and a return to baseline values
by 45 minutes
Conclusions and Clinical Relevance—Xylazine
markedly reduces flow and availability of oxygenated
blood to the uterus, which may critically impair delivery
of oxygen to the fetus at a stressful and important time
of development or delivery. Acepromazine was associated
with slight reductions of much shorter duration.
When XYL is used to sedate pregnant cows, it could
impose physiologic distress on the fetus and potentially
increase fetal morbidity and mortality. When sedation
of the dam is desirable, ACE could be an alternative
to XYL. (Am J Vet Res 2002;63:1695–1699)
Objective—To determine effects of atracurium on
intraocular pressure (IOP), eye position, and arterial
blood pressure in eucapnic and hypocapnic dogs
anesthetized with isoflurane.
Procedure—Ventilation during anesthesia was controlled
to maintain PaCO2 at 38 to 44 mm Hg in group-I dogs (n = 8) and 26 to 32 mm Hg in group-II dogs
(8). Baseline measurements for IOP, systolic, diastolic,
and mean arterial blood pressure, central venous
pressure (CVP), and heart rate (HR) were recorded.
Responses to peroneal nerve stimulation were monitored
by use of a force-displacement transducer.
Atracurium (0.2 mg/kg) was administered IV and measurements
were repeated at 1, 2, 3, and 5 minutes
and at 5-minute intervals thereafter for 60 minutes.
Results—Atracurium did not affect IOP, HR, or CVP.
Group II had higher CVP than group I, but IOP was not
different. There was no immediate effect of atracurium
on arterial blood pressure. Arterial blood pressure
increased gradually over time in both groups. Thirty
seconds after administration of atracurium, the eye
rotated from a ventromedial position to a central position
and remained centrally positioned until 100%
recovery of a train-of-four twitch response. The time
to 100% recovery was 53.1 ± 5.3 minutes for group I
and 46.3 ± 9.2 minutes for group II.
Conclusions and Clinical Relevance—Atracurium
did not affect IOP or arterial blood pressure in isoflurane-
anesthetized dogs. Hyperventilation did not
affect IOP or the duration of effect of atracurium. (Am
J Vet Res 2004;65:179–182)
Objective—To compare recoveries from anesthesia of horses placed on a conventional padded stall floor or on a specially designed air pillow.
Animals—409 horses (> 1 year old) that were anesthetized for surgical procedures during a 37-month period.
Procedures—By random allocation, horses were allowed to recover from anesthesia in either a foammat–padded recovery stall or an identical recovery stall equipped with a rapidly inflating-deflating air pillow. All recoveries were videotaped for subsequent analysis by an independent evaluator. Times to first movement, first attempt to attain sternal recumbency, attainment of sternal recumbency, first attempt to stand, and successful standing were recorded. The numbers of attempts before achieving sternal recumbency and standing were counted, and scores for quality of standing and overall recovery were assigned. Recovery-related variables were compared between groups.
Results—Compared with horses allowed to recover in a conventional manner, horses that recovered from anesthesia on the air pillow had a significantly longer rest period before attempting to attain sternal recumbency and rise to standing. Once the pillow was deflated, horses were able to stand after significantly fewer attempts and the quality of their standing was significantly better. Between the 2 groups of horses, there was no significant difference in overall recovery quality scores. The air pillow and padded floor systems were equally safe.
Conclusions and Clinical Relevance—Results suggested that use of a rapidly inflating-deflating air pillow promotes a longer period of recumbency and a better quality of standing after anesthesia in horses.