Advantages and guidelines for using methoxyflurane.

Methoxyflurane anesthesia is particularly useful for orthopedic surgery (muscle relaxation, analgesia, and slow recovery), ophthalmic surgery (central eye position), and small laboratory animals (high therapeutic index and slow induction).     

Advantages and guidelines for using isoflurane.

Isoflurane offers many advantages over other inhalational anesthetics. Its faster induction and recovery, relative sparing effect on cardiovascular function and cerebral blood flow autoregulation, and negligible metabolism make this drug particularly useful in the anesthetic management of the debilitated, aged, or unusual veterinary patient.     

Advantages and guidelines for using halothane.

Halothane is a frequently used agent. Its cost is inexpensive. Halothane is a safe and effective anesthetic agent if used properly. Proper usage includes adjusting the concentration administered to produce adequate anesthesia for the procedure without excess depression of cardiac, respiratory, and neurologic function. Proper monitoring of the patient indicates the adjustments needed in concentration or needed medications or procedures to increase safe usage. Potent tranquilizers, sedatives, and analgesics used as preanesthetics during halothane anesthesia or the early postanesthetic period may produce profound changes in anesthetic concentrations required or physiologic responses to the combined medications.     

Advantages and guidelines for using opioid agonist-antagonist analgesics.

The opioid agonist-antagonists are not controlled substances requiring strict record keeping and security because of their low abuse potential. They are effective analgesics in their own right and can be used to antagonize opioid agonist-induced depression while retaining a degree of analgesia. Respiratory depression is less than that induced by opioid agonists, but degree of analgesia is somewhat limited also owing to the ceiling effect.     

Advantages and guidelines for using epidural drugs for analgesia.

The administration of drugs by the epidural route is a safe and effective method for providing analgesia before, during, and after a surgical procedure. Local anesthetics administered by this route block nociceptive input as well as providing excellent muscle relaxation for surgery. The use of local anesthetics may be associated with short-term motor dysfunction and hypotension as a result of sympathetic blockade. Morphine given by the epidural route also provides effective analgesia and has the advantages of giving more prolonged analgesia with no effect on either motor or sympathetic pathways.     

Advantages of and guidelines for using neuromuscular blocking agents.

Neuromuscular blocking agents, although not commonly used in veterinary practice, should be considered when muscle relaxation is needed to facilitate surgical exposure and minimize tissue trauma. These drugs should be administered only once respiration has been controlled and anesthetic agents have been administered to induce unconsciousness and analgesia. Following administration of neuromuscular blocking drugs, neuromuscular and cardiovascular function must be monitored.     

Advantages and guidelines for using ketamine for induction of anesthesia.

Ketamine in combination with a sedative or tranquilizer is a relatively safe and effective drug for intravenous induction of anesthesia in dogs and cats. If properly dosed, the combination can be used to induce anesthesia with minimal adverse cardiovascular effects, and it is a reasonable method for induction of anesthesia in patients with cardiac disease. If dosage is kept low, the rate of recovery is acceptable, and some of the drugs commonly used in the regimen with ketamine are reversible with appropriate antagonists.     

Advantages and guidelines for using opioid agonists for induction of anesthesia.

Opioids have a central role in the anesthetic management of small animals, as premedicants, as part of a balanced anesthetic technique, or for the provision of postoperative analgesia. These drugs are safe to use, provide excellent analgesia, and are easily reversible. They cause minimal cardiovascular depression and induce no deleterious renal or hepatic changes. These agents, combined with a sedative, generally provide an ideal anesthetic state.     

Advantages and guidelines for using ultrashort barbiturates for induction of anesthesia.

Despite the introduction of a number of new injectable agents, ultrashort barbiturates continue to be popular. Some of the reasons include rapid, smooth onset of action; predictable hypnotic effects; relatively rapid, smooth recovery; and inexpensiveness. Ultrashort barbiturates also possess some pharmacodynamic properties that make them ideal agents for use in patients with certain diseases or undergoing certain procedures. These include patients with raised intracranial pressure, patients with a history of seizures, patients with corneal lacerations or glaucoma, patients for examination of vocal cord and arytenoid cartilage function, patients with hyperthyroidism, and patients thought to be susceptible to malignant hyperthermia.     

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.     

Advantages and guidelines for using alpha-2 agonists as anesthetic adjuvants.

Xylazine and medetomidine produce reliable sedation, muscle relaxation, and analgesia in dogs and cats. In addition, alpha-2 agonists have proved very effective as sedative-analgesic adjuncts when coadministered with benzodiazepine or opioid agonists. Alpha-2 agonists should not be classified as monoanesthetics. They are excellent anesthetic adjuncts when combined with dissociatives and opioids. Because of the acute alterations in cardiopulmonary function commonly induced by alpha-2 agonists, it is suggested that their use be restricted to the young healthy patient undergoing routine surgical or diagnostic procedure. The development of more specific and selective alpha-2 agonists will continue to enhance the safety and reliability of this novel class of compounds. The unique spectrum of anesthetic properties induced by alpha-2 agonists has assured them of an increasingly prominent role in the development of new and sophisticated ways of achieving anesthesia.     

Hemodynamic effects of nitrous oxide in isoflurane-anesthetized cats

OBJECTIVE: To determine the hemodynamic effects of nitrous oxide in isoflurane-anesthetized cats. ANIMALS: 12 healthy adult domestic shorthair cats. PROCEDURE: Cats were anesthetized by administration of isoflurane in oxygen. After instruments were inserted, end-tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration, and nitrous oxide was administered in a Latin-square design at 0, 30, 50, and 70%. Each concentration was administered for 25 minutes before measurements were obtained to allow for stabilization. Heart rate; systemic and pulmonary arterial pressures; central venous pressure; pulmonary artery occlusion pressure; cardiac output; body temperature; arterial and mixed-venous pH, PCO2, PO2, and hemoglobin concentrations; PCV; and total protein and lactate concentrations were measured before and during noxious stimulation for each nitrous oxide concentration. Arterial and mixed-venous bicarbonate concentrations and oxygen saturation, cardiac index, stroke index, rate-pressure product, systemic and pulmonary vascular resistance indices, left and right ventricular stroke work indices, arterial and mixed-venous oxygen contents, oxygen delivery, oxygen consumption, oxygen extraction ratio, alveolar-to-arterial oxygen difference, and venous admixture were calculated. RESULTS: Arterial pressure, central venous pressure, pulmonary arterial pressure, rate-pressure product, systemic and pulmonary vascular resistance indices, arterial PCO2, and PCV increased during administration of 70% nitrous oxide. Arterial and mixed-venous pH, mixed-venous PO2, and alveolar-to-arterial oxygen difference decreased during administration of 70% nitrous oxide. Results before and during noxious stimulation were similar. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of 70% nitrous oxide to isoflurane-anesthetized cats resulted in improved arterial pressure, which was related to a vasoconstrictive effect.     

冻融交替对高寒草甸N_2O排放速率的影响

采用室内培养方法,分析了高寒矮嵩草草甸土壤N_2O排放速率对土壤冻融交替作用的响应特征。结果表明:随着冻结时间增加,-10℃和-5℃冻结土壤N_2O排放速率均明显降低,且前者的降低速率显著高于后者、均低于对照土壤N_2O排放速率;随着冻结土壤的融化,-10℃和-5℃培养土壤N_2O排放速率急剧增加,融化2h出现排放峰值,而后逐渐降低,但均高于对照样地,在冻结21d时,各处理高寒草甸土壤N_2O排放速率达到最低值。随着冻融交替循环次数从1次增加到12次,高寒草甸土壤N_2O排放速率明显增加,从最初的1.23±0.05g/(kg·h)增加到3.34±0.59g/(kg·h)。从第12次到第24次冻融循环时,高寒草甸土壤N_2O排放速率显著下降(P0.05),降低幅度达到31.7%。土壤冻融过程会显著激发高寒草甸N_2O排放速率,有助于科学估算高寒草甸N_2O排放量。     

Anesthetic potency of sevoflurane with and without nitrous oxide in mechanically ventilated Dumeril monitors

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of sevoflurane and assess the sevoflurane-sparing effect of coadministration of nitrous oxide in mechanically ventilated Dumeril monitors (Varanus dumerili). DESIGN: Prospective crossover study. ANIMALS: 10 healthy adult Dumeril monitors. PROCEDURE: Anesthesia was induced with sevoflurane in 100% oxygen or sevoflurane in 66% nitrous oxide (N2O) with 34% oxygen, delivered through a face mask. Monitors were endotracheally intubated, and end-tidal and inspired isoflurane concentrations were measured continuously; MAC was determined by use of a standard bracketing technique. An electrical stimulus (50 Hz, 50 V) was delivered to the ventral aspect of the tail as the supramaximal stimulus. A blood sample for blood gas analyses was collected from the ventral coccygeal vessels at the beginning and end of the anesthetic period. An interval of at least 7 days was allowed to elapse between treatments. RESULTS: The MAC +/- SDs of sevoflurane in oxygen and with N2O were 2.51 +/- 0.46% and 1.83 +/- 0.33%, respectively. There was a significant difference between the 2 treatments, and the mean MAC-reducing effect of N2O was 26.4 +/- 11.4%. Assuming simple linear additivity of sevoflurane and N2O, the MAC for N2O was estimated to be 244%. No significant differences in blood gas values--with the predictable exception of oxygen pressure--were detected between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of sevoflurane in Dumeril monitors is similar to that reported for other species. The addition of N2O significantly decreased the MAC of sevoflurane in this species.     

The effects of nitrous oxide on recovery from isoflurane anaesthesia in dogs

O bjectives : To assess rate and quality of recovery from anaesthesia where isoflurane was delivered in oxygen or oxygen/nitrous oxide.
M ethods : Dogs anaesthetised with propofol were randomly allocated to receive isoflurane maintenance in either 100 per cent oxygen (group 1) or 66 per cent nitrous oxide (N₂O)/34 per cent oxygen (group 2). Time from end of anaesthesia to achieving sternal recumbency was recorded. Incidence of adverse behaviours (vocalisation, uncontrolled head movement and restlessness) were assessed. Recovery quality was recorded on a visual analogue scale (VAS) (anchored at 0 with "best possible" recovery and "did not recover" at 100 mm). Age, weight, gender, anaesthetic duration, mean vaporiser setting, VAS scores, recovery times, postoperative temperature and behavioural scores were compared (chi-squared test, Mann-Whitney U test or t -test as appropriate, significance P≤0·05).
R esults : Objective data from 54 dogs were analysed, only VAS data where the observer was unaware of treatment group were used (n=33). Recovery was faster in group 2 dogs (median 10 min [range 4 to 31] compared with 14 minutes [3 to 43] in group 1, P=0·049) with less restlessness (0 [0 to 4] compared with 2 [0 to 4] in group 1, P=0·013) and uncontrolled head movement (0 [0 to 4] compared with 1 [0 to 3] in group 1, P<0·001). However, VAS scores were not statistically different between groups (group 1: mean 39·4 mm [s.d. 24·0)]; group 2: 30·1 mm [25·9]; P=0·303).
C linical S ignificance : Addition of N₂O to isoflurane anaesthesia results in a lower incidence of adverse behaviour (for example restlessness) and marginally faster recovery.     

The effects of halothane and nitrous oxide on the pharmacokinetics of propofol in dogs

The pharmacokinetics of propofol, 6.5 mg/kg, administered as a bolus dose intravenously (i.v.) were studied in six dogs (group 1). The effect of maintaining anaesthesia with halothane and nitrous oxide in oxygen on propofol pharmacokinetics was also investigated in six dogs undergoing routine anaesthesia (group 2). Induction of anaesthesia was rapid in all animals. Post-induction apnoea was a feature in three of the 12 dogs. The blood propofol concentration-time profile was best described by a bi-exponential decline in two dogs in group 1 and in 3 dogs in group 2, and by a tri-exponential decline in four dogs in group 1 and 3 dogs in group 2. The elimination half-life was long in both groups (90.9 min and 75.2 min, respectively), the volume of distribution at steady state large (4889 and 4863 ml/kg) and the clearance rapid (58.6 and 56.3 ml/kg.min). There were no significant differences between the groups, thus indicating that maintenance of anaesthesia with halothane and nitrous oxide had no effect on the pharmacokinetics of propofol in the dog.     

Anesthetic potency of nitrous oxide in young swine (Sus scrofa)

Determination of nitrous oxide (N2O) potency was accomplished by extrapolation using the concepts of minimum alveolar concentration (MAC) and additivity among inhalation anesthetics. Halothane and isoflurane anesthetic requirement (alveolar concentration) necessary to achieve MAC in 9 pigs decreased with each successive increase in the percentage of inspired N2O (25%, 50%, 75%). Halothane and isoflurane MAC was determined to be 0.94 +/- 0.03 and 1.75 +/- 0.01 volumes percent, respectively. Halothane and isoflurane requirements decreased to 0.74 +/- 0.02, 0.66 +/- 0.02, and 0.58 +/- 0.02; and to 1.56 +/- 0.02, 1.38 +/- 0.02, and 1.08 +/- 0.03 volumes percent with 25%, 50%, and 75% N2O, respectively. The line of best fit derived from regression analysis of the combined data (isoflurane and halothane MAC values) had a correlation coefficient of 0.987 and an X intercept equivalent to 195% N2O. The potency of N2O in pigs was similar to that of other domesticated mammals and reduced halothane and isoflurane anesthetic requirements by approximately 50% of the reduction observed in human beings.     

Comparison of two combinations of sedatives before anaesthetising pigs with halothane and nitrous oxide

Two groups of 21 three-month-old Landrace x Large White pigs were sedated with either azaperone (2 mg/kg), butorphanol (0.2 mg/kg) and ketamine (5 mg/kg) (group A), or detomidine (100 microg/kg), butorphanol (0.2 mg/kg) and ketamine (5 mg/kg) (group D) administered intramuscularly, before being anaesthetised with halothane, oxygen and nitrous oxide for a bilateral stifle arthrotomy. The pigs' heart rate, respiratory rate, mean arterial blood pressure, electrocardiogram, arterial oxygen saturation, arterial blood gases, and oesophageal and rectal temperature were measured while they were anaesthetised and five minutes after they were disconnected, and their recovery times and any complications were recorded. Both groups were well sedated. Their heart rate was unchanged during the period of anaesthesia but increased when they recovered. The respiratory rate, mean arterial blood pressure and rectal temperature were lower in group A than in group D (P<0.05). Mild respiratory acidosis developed during anaesthesia in both groups. Both groups recovered equally rapidly and complications were generally minor, though two pigs in group D appeared to develop malignant hyperthermia.