Morphine (1.0 mg/kg) and butorphanol (0.08 and 0.8 mg/kg) induced significant reductions in MAC of isoflurane that were considered clinically important. Although significant, reductions in MAC of isoflurane induced by morphine (0.1 mg/kg), buprenorphine (0.005 and 0.05 mg/kg), and U50488H (0.02 and 0.2 mg/kg) were not considered clinically relevant because they fell within the error of the measurement technique. Administration of morphine or butorphanol decreases the need for potent inhalant anesthetics in cats and could potentially be beneficial in combination with inhalants.

Propofol alone or combined with ketamine may be used for total IV anesthesia in healthy cats at the infusion rates determined in this study for attenuation of specific reflex activity.

Objective To determine the e¡ect of two doses of fentanyl, administered transdermally, on the minimum alveolar concentration (MAC) of iso£urane in cats.Study design Prospective, randomized study.Animals Five healthy, spayed, female cats.Methods Each cat was studied thrice with at least 2 weeks between each study. In study 1, the baseline iso£urane MAC was determined in triplicate for each cat. In studies 2 and 3, iso£urane MAC was determined 24 hours after placement of either a 25-or 50-mg hour À1 fentanyl patch. In each MAC study, cats were instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Twenty-four hours prior to studies 2 and 3, a catheter was placed and secured in the jugular vein and either a 25 or 50-mg hour À1 fentanyl patch was placed in random order on the left thorax. Blood samples for plasma fentanyl determination were collected prior to patch placement and at regular intervals up to 144 hours. After determination of MAC in studies 2 and 3, naloxone was administered as a bolus dose (0.1 mg kg À1) followed by an infusion (1 mg kg) and MAC redetermined.Results The baseline iso£urane MAC was 1.51 AE 0.21% (mean AE SD). Fentanyl (25 and 50 mg hour À1 ) administered transdermally signi¢cantly reduced MAC to 1.25 AE 0.26 and 1.22 AE 0.16%, respectively. These MAC reductions were not signi¢cantly di¡er-ent from each other. Iso£urane MAC determined during administration of fentanyl 25 mg hour À1 and naloxone (1.44 AE 0.16%) and fentanyl 50 mg hour À1and naloxone (1.51 AE0.19%) was not signi¢cantly di¡erent from baseline MAC (1.51 AE0.21%).Conclusions and clinical relevance Fentanyl patches are placed to provide long-lasting analgesia. In order to be e¡ective postoperatively, fentanyl patches must be placed prior to surgery. Plasma fentanyl concentrations achieved intraoperatively decrease the need for potent inhalant anesthetics in cats.

Background Monitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs. Hypothesis/Objective Assessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects. Animals Seven adult, bred‐for‐research dogs. Methods In a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia. Results Baseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement. Conclusions and Clinical Importance Use of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension.

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