Cardiopulmonary effects of halothane anesthesia in cats

The cardiopulmonary effects of 2 planes of halothane anesthesia (halothane end-tidal concentrations of 1.78% [light anesthesia] and 2.75% [deep anesthesia]) and 2 ventilatory modes (spontaneous ventilation [SV] or mechanically controlled ventilation [CV]) were studied in 8 cats. Anesthesia was induced and maintained with halothane in O2 only, and each cat was administered each treatment according to a Latin square design. Cardiac output, arterial blood pressure, pulmonary arterial pressure, heart rate, respiratory frequency, and PaO2, PaCO2, and pH were measured during each treatment. Stroke volume, cardiac index, and total peripheral resistance were calculated. A probability value of less than 5% was accepted as significant. In the cats, cardiac output, cardiac index, and stroke volume were reduced by deep anesthesia and CV, although only the reduction attributable to CV was significant. Systemic arterial pressure was significantly reduced by use of deep anesthesia and CV. Respiratory frequency was significantly lower during CV than during SV. Arterial PO2 was significantly decreased at the deeper plan of anesthesia, compared with the lighter plane. At the deeper plane of anesthesia, arterial PCO2 and pulmonary arterial pressure were significantly lower during CV than during SV. The deeper plane of halothane anesthesia depressed cardiopulmonary function in these cats, resulting in hypotension and considerable hypercapnia. Compared with SV, CV significantly reduced circulatory variables and should be used with care in cats. Arterial blood pressure was judged to be more useful for assessing anesthetic depth than was heart rate or respiratory frequency.     

Effect of yohimbine on xylazine-ketamine anesthesia in cats

Xylazine and ketamine are an anesthetic combination used in feline practice for routine surgical procedures. In a controlled study, we evaluated the effects of yohimbine, an antagonist of xylazine, on the anesthesia induced by this anesthetic combination in cats. Two intramuscular doses of xylazine and ketamine (2.2 mg of xylazine/kg plus 6.6 mg of ketamine/kg and 4.4 mg of xylazine/kg plus 6.6 mg of ketamine/kg) caused approximately 60 and 100 minutes of anesthesia, respectively, in control cats. When yohimbine (0.1 mg/kg) was given intravenously 45 minutes after ketamine administration, the cats regained consciousness within 3 minutes. They were ambulatory 1 to 2 minutes after regaining consciousness. Yohimbine also reversed the bradycardia and respiratory depression elicited by xylazine-ketamine. The results indicated that yohimbine may be useful for controlling the duration of xylazine-ketamine anesthesia in cats.     

AAHA anesthesia guidelines for dogs and cats

Safe and effective anesthesia of dogs and cats rely on preanesthetic patient assessment and preparation. Patients should be premedicated with drugs that provide sedation and analgesia prior to anesthetic induction with drugs that allow endotracheal intubation. Maintenance is typically with a volatile anesthetic such as isoflurane or sevoflurane delivered via an endotracheal tube. In addition, local anesthetic nerve blocks; epidural administration of opioids; and constant rate infusions of lidocaine, ketamine, and opioids are useful to enhance analgesia. Cardiovascular, respiratory, and central nervous system functions are continuously monitored so that anesthetic depth can be modified as needed. Emergency drugs and equipment, as well as an action plan for their use, should be available throughout the perianesthetic period. Additionally, intravenous access and crystalloid or colloids are administered to maintain circulating blood volume. Someone trained in the detection of recovery abnormalities should monitor patients throughout recovery. Postoperatively attention is given to body temperature, level of sedation, and appropriate analgesia.     

Blood pressure assessment in healthy cats and cats with hypertensive retinopathy

OBJECTIVE: To determine whether there was an association between hypertensive retinopathy and high systolic, diastolic, and mean arterial blood pressures in cats. ANIMALS: 181 cats. PROCEDURE: Systolic, diastolic, and mean arterial blood pressures were measured by use of a noninvasive oscillometric technique. The range of blood pressure measurements in healthy cats from various age groups was determined. Associations among systolic, diastolic, and mean arterial blood pressure; hypertensive retinopathy; hyperthyroidism; left ventricular cardiac hypertrophy; chronic renal failure; and serum biochemical abnormalities were determined. RESULTS: All blood pressure measurements increased with age in healthy cats. The frequency of hypertensive retinopathy also increased with age and with blood pressure, and hypertensive retinopathy was particularly found in cats with systolic blood pressures > 168 mm Hg. There was an increased risk for hypertensive retinopathy in cats that were female, > 10 years old, and neutered. The risk of chronic renal failure also increased as blood pressure, particularly systolic blood pressure, increased. CONCLUSIONS AND CLINICAL RELEVANCE: Hypertensive retinopathy was common in cats > or = 10 years of age and was associated with systolic blood pressures > 168 mm Hg when measured by the noninvasive oscillometric technique.     

Evaluation of tumescent local anesthesia in cats undergoing unilateral mastectomy

ObjectiveTo evaluate the analgesic efficacy and safety of tumescent local anesthesia (TLA) in cats undergoing unilateral mastectomy.Study designProspective clinical trial.AnimalsA total of 12 ovariohysterectomized female cats.MethodsAll animals were premedicated with pethidine (4 mg kg^–1) intramuscularly (IM), followed by induction of anesthesia with propofol (5 mg kg^–1) intravenously and maintenance with isoflurane in oxygen. A refrigerated TLA solution (15 mL kg^–1, 8 °C) was injected using a Klein cannula. The solution was composed of 0.5 mL of epinephrine (1 mg mL^–1) and 40 mL of 2% lidocaine added to 210 mL lactated Ringer’s solution (final lidocaine concentration 0.32%). Heart and respiratory rates, systolic arterial blood pressure, temperature and oxygen saturation were measured during anesthesia. Blood samples were collected from the jugular vein for measurement of plasma lidocaine concentration using high performance liquid chromatography. Postoperative pain scores were evaluated hourly for 6 hours. Analgesic rescue was performed with tramadol (2 mg kg^–1) IM and meloxicam (0.15 mg kg^–1) subcutaneously.ResultsPlasma lidocaine concentration peaked at 90 minutes after injection of TLA, but no concentration considered toxic for the species was measured. The median postoperative analgesia time was 6 hours after injection of TLA.ConclusionsThis study found that TLA prevented sympathetic response to noxious stimuli during anesthesia and provided satisfactory postoperative analgesia in cats submitted to total unilateral mastectomy, with no apparent signs of toxicity.Clinical relevanceTLA can prevent sympathetic stimulation resulting from noxious stimuli during anesthesia, promoting good intraoperative conditions, proving to be a viable addition to analgesia in cats submitted to a total unilateral mastectomy.     

Plasma fentanyl concentrations in awake cats and cats undergoing anesthesia and ovariohysterectomy using transdermal administration

Objective To measure the plasma fentanyl concentrations achieved over time with transdermal fentanyl patches in awake cats and cats undergoing anesthesia and ovariohysterectomy. Study design Randomized prospective experimental study. Animals Twenty‐four purpose‐bred cats. Methods Cats were randomly assigned to three groups for Part I of a larger concurrent study. Group P received only a 25 μg hour^?1 transdermal fentanyl patch. Group P/A received the patch and anesthesia. Group A received only anesthesia. After a minimum 1‐week washout period, the cats were randomly reassigned to two groups for Part II of the larger study. Group P/A/O received the patch, anesthesia and ovariohysterectomy. Group A/O received anesthesia and ovariohysterectomy. Patches were left in place for 72 hours and plasma samples were obtained for fentanyl analysis while the patches were in place, and for 8 hours after patch removal for cats in Group P, P/A, and P/A/O. Results The 25 μg hour^?1 transdermal fentanyl patches were well tolerated by the cats in this study (mean body weight of 3.0 kg) and no overt adverse effects were noted. Mean plasma fentanyl concentrations over time, mean plasma fentanyl concentrations at specific times (8, 25, 49, and 73 hours after patch placement), time to first detectable plasma fentanyl concentration, time to reach maximum plasma fentanyl concentration, maximum plasma fentanyl concentration, mean plasma fentanyl concentration from 8 to 73 hours, elimination half‐life, and total area under concentration (AUC) were not statistically different among the groups. Conclusions Halothane anesthesia and anesthesia/ovariohysterectomy did not significantly alter the plasma fentanyl concentrations achieved or pharmacokinetic parameters measured, when compared with awake cats. There was a high degree of individual variability observed both within and between groups of cats in parameters measured. Clinical significance The high degree of variability observed suggests that careful observation of cats with fentanyl patches in place is required to assess efficacy and any potential adverse effects. Anesthesia and anesthesia/ovariohysterectomy do not appear to alter plasma fentanyl concentrations achieved by placement of a 25 μg hour^?1 transdermal fentanyl patch when compared to cats not undergoing these procedures.     

Electrocardiographic assessment of hyperkalemia in dogs and cats

Objective: To determine if electrocardiogram (ECG) changes induced by hyperkalemia in clinical patients correspond with previously reported changes in experimental animals. Design: Prospective clinical study. Setting: Two private practice 24‐hour emergency and critical care facilities. Animals: Fifteen dogs and 22 cats with serum potassium levels >5.5 mEq/L. Interventions: None. Measurements: The following data were collected when hyperkalemia was documented: ECG (n=37), sodium and chloride (mEq/L) (n=35), total magnesium (mg/dL) (n=18), total calcium (mg/dL) (n=30), and venous pH (n=18). Animals were divided into five groups based on severity of hyperkalemia and ECG interpretation included rate, rhythm and P‐QRS‐T evaluation. Main Results: Twenty‐two of 37 (59%) of the ECGs were normal or revealed abnormalities that have not been previously described in conjunction with hyperkalemia. In dogs, there was no correlation (r=0) between potassium blood levels and heart rate (n=15). There was weak correlation (r=0.40; P=0.06) between potassium blood levels and heart rate in cats (n=22). The correlation was stronger (r=0.64; P<0.05) when data were compared in cats with serum potassium level >8.5 mEq/L (Groups 4 and Group 5; n=11). Conclusions: ECGs obtained from ill dogs and cats with hyperkalemia are inconsistent with ECGs from experimentally induced hyperkalemia. It is difficult to determine the clinical relevance of heart rate differences between cats with serum potassium levels >8.5 mEq/L and animals with experimentally induced hyperkalemia; this may be due to the presence of other biochemical abnormalities in diseased animals.