Management of geriatric patients. A common occurrence.

The anesthetic and perioperative care of geriatric animals requires increased vigilance and support. The margin of acceptable physiological variation is probably more narrow than in younger patients. Underlying disease, which is often subclinical, influences metabolism and recovery from anesthetics and also predisposes the patients to adverse outcome. Limited respiratory and cardiovascular reserve diminishes the ability of many older patients to meet the challenges of anesthesia and surgery or other stressful medical procedures. The psychological, as well as physiological, stress of hospitalization is increased in many geriatric patients.

Alpha 2 agonists and antagonists.

The alpha 2 agonists can produce reliable dose-dependent sedation and analgesia in most species. Nevertheless, they can also produce significant physiological adverse side effects depending on dose, rate, route of administration, and the concurrent use of other CNS depressants. For this reason, it may be best to use a low dose of an alpha 2 agonist as a preanesthetic agent. The alpha 2 agonists are best suited for young, healthy, exercise-tolerant patients. The combining of low doses of alpha 2, opioid, and benzodiazepine agonists results in a synergistic CNS depressant response while minimizing the undesirable side effects of these three classes of drugs. Each group of drugs has specific antagonists available for their reversal, thus allowing veterinarians to reverse one or more of the agonists depending on the desired response. This may represent a significant advantage to the use of low-dose alpha 2 agonists in combination with opioids and benzodiazepines.

Butorphanol tartrate for partial reversal of oxymorphone-induced postoperative respiratory depression in the dog.

A randomized, blinded, crossover study was designed to evaluate the respiratory, cardiovascular, and behavioral effects of butorphanol given postoperatively to oxymorphone-premedicated and surgically stimulated dogs. Nine healthy adult dogs were premedicated intramuscularly with atropine (0.04 mg/kg), acepromazine (0.10 mg/kg), and oxymorphone (0.2 mg/kg). Anesthesia was induced with thiamylal (12 mg/kg) and maintained with halothane in oxygen. According to the protocol of a concurrent study, all dogs had percutaneous endoscopic gastrostomy (PEG) feeding tubes placed during the first anesthetic episode and removed during the second anesthetic episode. All dogs received postoperatively either butorphanol tartrate (0.2 mg/kg) or an isovolumetric dose of saline placebo, both given intravenously. Respiratory rate (RR), tidal volume (TV), minute ventilation (MV), end-tidal CO2 concentration (ETCO2), heart rate (HR), and indirect diastolic (DP), systolic (SP) and mean arterial (MAP) blood pressures were measured at times 0, 2, 5, 10, 20, 40, 80, and 120 minutes after injection. The time from injection of the test drug until extubation was recorded. RR, MV, HR, and DP were significantly (P < .05) increased, while ETCO2 was significantly decreased, for a minimum of 30 minutes in butorphanol-treated dogs compared with saline controls. TV, SP, and MAP were transiently (< or = 15 minutes) increased in butorphanol-treated dogs compared with saline controls. There was no significant difference between the times to extubation in the butorphanol-treated dogs versus the saline control dogs.

Anesthesia for cesarean section in the dog.

At the time of cesarean section, the mother may suffer respiratory depression, hypotension, increased gastric acidity, and increased predisposition to regurgitation, and the newborn may suffer anesthetic-induced respiratory depression. Preanesthetic metaclopramide, cimetidine, and anticholinergic agent are recommended. Sedatives can be administered if necessary. Neuroleptanalgesic and low-dose general anesthetic, with local anesthetic line-blocks, are preferred techniques. Supportive care of the newborn is mandatory.

Advantages and guidelines for mask induction.

Inhalational agents with low blood/gas solubilities (halothane, isoflurane, and nitrous oxide) are preferred for mask induction. A gradual step up in the vaporizer concentration is the recommended induction method because it is generally smoother and safer than the crash induction technique.

Critical care surgical techniques.

A veterinarian dealing with critical and trauma patients must be proficient with techniques for tracheostomy, thoracostomy tube placement for chest drainage, diagnostic peritoneal lavage, and autotransfusion. The utilization of these techniques may be life-saving in the critical patient. A tracheostomy is indicated in any patient with upper airway obstruction that cannot be managed with supplemental oxygen and/or orotracheal intubation. A tracheostomy tube with an inner cannula is preferred. Tracheostomy tubes should be cleaned at 3- to 4-h intervals, and methods should be employed to decrease thick tracheal secretions and to remove them from the trachea. A patient with a tracheostomy tube should be monitored continuously. A thoracostomy tube is indicated in any patient with large and/or continuous accumulation of air, blood, fluid, or chyle in the pleural space. The thoracostomy tube should be at least the same size as the patient's main stem bronchus. The thoracostomy tube is placed aseptically at the seventh intercostal space at the junction of the upper one third and lower two thirds of the lateral chest wall. Fluid or air may be removed from the chest intermittently with a three-way stopcock attached to the thoracostomy tube and a 60-ml syringe. If continuous drainage is needed, a continuous underwater seal and suction system should be used. Diagnostic abdominal paracentesis and peritoneal lavage are useful techniques in the determination of abdominal trauma, hollow viscus rupture, peritonitis, hepatic trauma, and urinary system trauma. When a multiholed catheter and lavage are used, the accuracy of detecting abdominal trauma is 95 per cent. When only needle paracentesis is used, the accuracy drops to 47 per cent. Abdominal lavage fluid can be analyzed for bacteria, whole blood, white blood cells, free bilirubin, creatinine, blood urea nitrogen, amylase, alkaline phosphatase, and alanine aminotransferase. Large volumes of whole blood recovered from abdominal or thoracic paracentesis can be reinfused into the patient if needed, providing it is not contaminated or markedly hemolyzed. The blood should be collected aseptically into blood bottles or bags. If the bleeding is ongoing or the blood only a few hours old, anticoagulants should be used. If the hemorrhage is several hours old, then clotting and defibrination has already occurred and the blood can be collected into "dry" bags or bottles. Before use, abdominal blood should be analyzed for urine, bile or fecal contamination. Blood collected from the thoracic cavity is much less likely to be contaminated. Autotransfused blood is administered through a standard blood administration set.

Anesthetic considerations for the geriatric patient.

The geriatric patient presents an anesthetic challenge due to the physiologic alterations that occur during aging. The geriatric patient usually has an increased number of disease processes and does not possess the functional organ reserve capabilities compared to a younger patient. The geriatric patient seems more susceptible to the cardiopulmonary depressant effects of the preanesthetic and anesthetic agents in common use and, due to decreased hepatic function and other factors, may have a delayed recovery from these drugs. The preanesthetic and anesthetic drugs chosen for a geriatric patient will depend on that particular patient's physiologic status, the procedure to be done, and the experience of the veterinarian. Adequate fluid and monitoring support should always be provided for the geriatric patient.

Prevention of postmetrizamide myelographic seizures in dogs, using 5% dextrose solution.

Diuresis by IV administration of 5% dextrose in a balanced electrolyte solution (BES) reduced the frequency of occurrence of postmyelographic seizures in dogs. In the first study, a single myelogram was obtained in 8 dogs without dextrose diuresis. Two of these dogs weighed greater than 15 kg and both had seizures after metrizamide myelography. The remaining 6 dogs weighed less than 15 kg and only 2 had seizures. Greater body weight may have increased the risk of postmyelographic convulsions. In a crossover study, myelograms were obtained in 12 dogs weighing 20 to 31 kg. Six dogs were given 5% dextrose in BES (20 ml/kg of body weight/hr [diuresed]) and 6 were given BES alone (10 ml/kg/hr [not diuresed]). When myelography was repeated 10 days later, the 6 dogs that had been given 5% dextrose in BES were given BES only and the 6 dogs that had been given BES alone were given 5% dextrose in BES. The frequency of convulsions after metrizamide myelography was lower when dogs were given dextrose (33%) than when they were not (100%).

Twelfth rib resection as an approach for portal vein cannulation in sheep.

A surgical technique involving resection of the twelfth rib was used to insert silastic cannulas into the portal veins of three sheep to study amino acid metabolism. Good exposure to the vein was achieved by this method although it required positive ventilation due to the penetration of the thoracic cavity. All cannulas were buried subcutaneously and exteriorized near the dorsal midline. This facilitated continuous infusion into the portal cannula without disturbing cannula placement.

Preanesthetic evaluation and management of malignant hyperthermia in the pig experimental model.

Fifty-three swine from the University of Missouri Sinclair Medical Research Farm were used in experimentation to determine their susceptibility to malignant hyperthermia, to determine appropriate anesthetic agents for susceptible swine and to investigate appropriate pharmaceutical agents which could protect against the development of malignant hyperthermia. The screening technics used were successful in determining susceptible animals to MH and the anesthesia studies indicated that dissociative anesthetics had less tendency to trigger MH than did halothane and pancuronium was shown to have greater safety as a muscle relaxant than succinylcholine in this group of pigs. Pigs pretreated with reserpine had less tendency to develop symptoms of MH and some were completely protected. The principle undesirable effect was the development of hypotension if sufficient reserpine was used to provide total protection.