Anaesthesia Of Short Duration Research Articles

Effects of a medetomidine-midazolam-butorphanol combination on renal cortical, intestinal and muscle microvascular blood flow in isoflurane anaesthetized dogs: a laser Doppler study

To obtain renal cortical, ileal, colonic and skeletal muscle microvascular blood flow measurements in dogs using the laser Doppler technique and to characterize the effects of medetomidine-midazolam-butorphanol combination on these flows. Prospective randomized experimental study. Fourteen clinically normal beagles (two groups of seven), aged 1-4 years and weighing 13.2 ± 1.8 kg. All dogs were anaesthetized with 1.7% end-tidal isoflurane in oxygen. In the treatment group, after instrumentation and when anaesthesia was considered stable, medetomidine (1 mg m-2 body surface area (BSA)) was administered intramuscularly (time 0). Midazolam (1 mg kg-1) and butorphanol (0.1 mg kg-1) were administered intravenously 20 minutes later. Atipamezole (2.5 mg m-2 BSA) was administered intramuscularly 60 minutes after medetomidine. In the control group, saline (0.5, 2.5 and 0.25 mL) was administered at the corresponding times. Heart rate, systolic, diastolic and mean arterial pressures, body temperature, renal cortical, ileal, colonic and skeletal muscle microvascular blood flows were measured before time 0, and 5, 15, 25, 40, 60, 65, 70 and 90 minutes thereafter. Heart rate, ileal and skeletal muscle blood flows decreased in the treatment group, while no changes were observed in the control group. Laser Doppler flowmetry allowed the measurement of microvascular blood flow in different organs. The medetomidine-midazolam-butorphanol combination decreases intestinal and skeletal muscle microvascular blood flows, while renal cortical blood flow is maintained. Medetomidine-midazolam-butorphanol combination can be used to induce a short duration anaesthesia in dogs, but it will induce cardiovascular depression. This depression appears to be accompanied by a redistribution of blood flow.

Extradural anaesthesia using lidocaine, ropivacaine, hyperbaric lidocaine and a combination of lidocaine and ropivacaine in mares

Gynaecological surgery and obstetric manipulations in horses are usually performed under extradural anaesthesia. Lidocaine provides effective short duration anaesthesia, but may produce ataxia or recumbency. Ropivacaine has a longer duration of action and produces less motor block, in humans and dogs, when compared to lidocaine. This study investigated the speed of onset and duration of anaesthesia, and the degree of muscle relaxation, produced by various local anaesthetics used for extradural anaesthesia in mares.

Predictors of arterial oxygen tension in anesthetized horses: 1,610 cases (1992–1994)

Objective To identify factors associated with various arterial partial pressures of oxygen (PaO2) in anesthetized horses. Design Retrospective study. Animals 1,450 horses anesthetized a total of 1,610 times with isoflurane or halothane. Procedure Anesthesia records, particularly results of blood gas analyses, were reviewed, and horses were grouped on the basis of lowest Pao2. Results For horses with lowest Pao2 < 120 mm Hg, those with low pulse pressure, that underwent anesthesia on an emergency basis, or that were males were more likely to have Pao2 < 80 mm Hg. For horses with lowest Pao22 < 250 mm Hg, those that were positioned in dorsal recumbency, that underwent anesthesia on an emergency basis, or that had a shorter duration of anesthesia were more likely to have lowest Pao2 < 120 mm Hg. For horses with lowest PaO2 < 400 mm Hg, those that were positioned in dorsal recumbency, that underwent anesthesia on an emergency basis, that had a shorter duration of anesthesia, that were older, that were heavier, or that were being ventilated mechanically were more likely to have lowest Pao2 < 250 mm Hg. Conclusions and Clinical Relevance Low pulse pressure, emergency case status, dorsal recumbency, and short duration of anesthesia were significantly related with lower Pao2 in anesthetized horses. (J Am Vet Med Assoc 1999;215:978–981)

Suprascapular palsy: a complication of surgical positioning?

We report a case of persisting suprascapular nerve palsy after surgery under general anaesthesia of short duration in a conventional position. Surgical exploration, eight months later, showed a suprascapular notch narrowed by a hypertrophied and calcified superior transverse ligament. Such a lesion and the practice of volley-ball by the patient are in favour of a pre-existing infraclinical neuropathy.

Short duration anaesthesia with medetomidine and ketamine in cynomolgus monkeys.

Cynomolgus monkeys were anaesthetized with either intramuscular ketamine (10 mg/kg or intramuscular ketamine 2 mg/kg and medetomidine 50 microg/kg. Various physiological measurements were made once the animals were safe to handle and again 10 min later. Cardiovascular and respiratory function were well maintained with both regimens but the heart rate was lower and arterial-alveolar carbon dioxide gradient was higher in the animals that received medetomidine. In those animals that received medetomidine, atipamezole was given to reverse the medetomidine but there was no difference in recovery times between the two regimens. Anaesthesia was not entirely reliable with medetomidine/ketamine and we recommend caution when using this mixture.

Intracameral anesthesia: in vitro iris and corneal uptake and washout of 1% lidocaine hydrochloride.

To characterize the uptake, washout, and metabolism of lidocaine hydrochloride in the iris/ciliary body and cornea. Iris/ciliary body uptake of lidocaine hydrochloride was measured by incubating human and rabbit irides in radiolabeled carbon 14-1% lidocaine hydrochloride for 2 to 60 minutes. Washout was determined by incubating the iris in 14C-1% lidocaine hydrochloride for 5 minutes and transferring the iris to a series of wells. The wells contained a common intraocular irrigating solution of essential ions, glucose, and glutathione buffered with bicarbonate (an enriched balanced salt solution [BSS PLUS]), which is similar to aqueous humor. Corneal uptake was measured by exposing the endothelial surface to 14C-1% lidocaine hydrochloride for 5 or 15 minutes. Corneal washout was performed after 5-minute exposure to 14C-1% lidocaine hydrochloride using a 2-chambered diffusion apparatus. Samples of the iris, cornea, and BSS PLUS washout solution were analyzed by high-performance liquid chromatography and liquid scintillation spectrometry. In vitro iris/ciliary body uptake of 14C-1% lidocaine hydrochloride follows a logarithmic curve, with 50% to 60% of maximum lidocaine hydrochloride uptake present at 5 minutes. There was no difference in uptake between human, albino rabbit, and pigmented rabbit irides. Washout of lidocaine from the iris occurs with a halflife of 8 to 9 minutes. Corneal uptake of lidocaine was greater after incubation for 15 vs. 5 minutes. The washout of lidocaine from the cornea had a half-life of 5 minutes. Results of high-performance liquid chromatography confirmed that there were no metabolites or breakdown products in the iris, cornea, or washout solution. Lidocaine is taken up quickly by the iris/ ciliary body and cornea and rapidly removed from these tissues after BSS PLUS washout. Irrigation during phacoemulsification seems to limit lidocaine exposure to the ocular tissues, resulting in a short duration of anesthesia. Lidocaine is not metabolized or broken down by the iris or cornea during this short period.

Spinal anesthesia for pediatrics

Spinal anesthesia for pediatrics first appeared at the beginning of 20th century. After an initial period of disuse, it has now gained popularity due to its favorable characteristics such as cardiovascular stability in children less than 5 years of age; satisfactory analgesia and muscle relaxation; the possibility of performing surgical procedures in patients at risk for general anesthesia (ie, formerly preterm infants at risk for postoperative apnea); and the ability to administer small doses of local anesthetic (preferably hyperbaric tetracaine or bupivacaine) with consequent reduced toxic effects. This technique is limited mainly by a relatively short duration of anesthesia (surgical procedures generally cannot last more than 90 min), by the absence of satisfactory postoperative pain control, and obviously by the lack of experience of anesthetist. Postdural puncture headache is rare. Although this technique could appear to be less invasive, we recommend an accurate, postoperative control for at least 12 hours.

LOW FLOW ANESTHESIA FOR AMBULATORY SURGERY

S10 For low flow anesthesia (LFA) techniques an initial high flow phase of 15-20 min is required, thus limiting the effectiveness in saving anesthetic vapors in short duration anesthesia. Anesthetic gas monitoring offers the opportunity to reduce the duration of the inital wash-in phase down to 1-2 min. This renders LFA practicable for brief surgical procedures. The aim of the study was to evaluate LFA for brief surgical procedures. METHODS: After IRB approval and written informed consent the anesthetic procedure shown in Figure 1 was employed in an ambulatory surgery unit. After premedication with nordiazepam, anesthesia was induced with propofol (1-2mg/kg body weight) and alfentanil (1mg) and maintained with nitrous oxide in oxygen and isoflurane or enflurane. The patient's age, surgical procedure, duration of anesthesia and post-anesthetic care unit time spent were recorded. The consumption of anesthetic vapors per patient was calculated from the overall consumption.Figure 1: Course of modified low flow anesthesia: T0: preoxygenation, intravenous induction, endotracheal intubation, controlled ventilation: T1: wash in phase - fresh gas flow at 9 L/min for 1-2 min, vaporizer setting 5Vol% isoflurane (Iso) or enflurane (Enf) until the desired endtidal anesthetic gas concentration is reached: T2: low-flow phase - fresh gas flow reduction to 1 L/min, adaptation of the vaporizer setting: T3: discontinuation of Isoflurane/N2 O, patient breathing spontaneously, O2 flow at 9 Lmin: T4: extubationRESULTS: 3185 consecutive patients were included in the study. The age of the patients ranged from 5 months to 94 years with a median of 31 years, duration of anesthesia from 15 min to 4 h with a median of 46 min. 29% of the patients were discharged from the post-anesthetic care unit within 2 h, 56% after 2-4 h and 15% after more than 4 h. On the average 24 l N2 O, 7.1 ml enflurane or 3.7 ml isoflurane (liquid) per patient were needed. CONCLUSION: LFA proved to be a useful, practicable and cost-effective anesthetic technique for brief surgical procedures in ambulatory patients. The extremely short wash-in phase as compared to previously described LFA techniques can be achieved by using anesthetic gas monitoring.

Short duration anaesthesia for minor procedures in dogs

SUMMARY Anaesthesia was maintained with 4 different techniques in each of 12 dogs of ASA grades I or 11 undergoing 4 treatment sessions of mega-voltage x-ray therapy at weekly intervals. After induction of anaesthesia with propofol, these dogs received either: i) continiious pi-opofol iv infusion together with nitrous oxide/oxygen by inhalation: ii) halothane in nitrous oxiddoxygen; iii) entluraiie in nitrous oxide/oxygen; or iv) isollurane in nitrous oxide/oxygen. Anaesthesia dways enabled irradiation to be performed but stable anaesthesia was achieved more easily when enflurnne was used. The incidence of undesirable effects during anaesthesia wiis low. Recovery from the end of anaesthesia to swallowing was fastest Lifter enfluraiie (2.2 min median) but the recovery times to walking were similar (medians: halothane 12.5 min; entlurane 12.0 min; isoflurane 12.5 min; propofol I3 min). Personal preferences. local facilities and cost are likely to be the deciding factors in choice of any one of these techniques for dogs undergoing short procedures unussociatcd with surgical stimulation.

Pre-emptive use of the space blanket reduces shivering after general anaesthesia

We have investigated the role of aluminized metal foil (space blanket, UN 320), used pre-emptively, in post-anaesthetic shivering and patients' subjective perception of cold after general anaesthesia of short duration. Sixty-eight ASA I and II patients undergoing orthopaedic and plastic surgery on the peripheries were allocated randomly to two groups: those in group 1 were wrapped (not less than 60% of body surface area) in the space blanket before induction of anaesthesia. In group 2 patients had standard surgical draping. In all subjects, anaesthesia was induced with fentanyl and propofol, and maintained with nitrous oxide and enflurane in oxygen, after a laryngeal mask airway was positioned. Patients were asked to grade their perception of cold on a visual analogue scale, before induction and on recovery. Skin (dorsum of hand) and core (nasopharyngeal) temperatures were recorded at 15-min intervals. Occurrence of shivering and cold scores were recorded by blinded observers. Groups were similar in age and gender; duration of anaesthesia was also similar (mean 41.6 (SEM 4.8) vs 47.5 (3.3) min, respectively). The incidences of shivering were 15% and 63% in groups 1 and 2, respectively (P < 0.001). Cold scores were 2.4 (0.4) and 5.7 (0.5), respectively (P < 0.001). Skin temperatures increased with increasing duration of anaesthesia in both groups but were greater at 15, 30 and 45 min in group 1 (33.38 (0.25) vs 31.56 (0.31), 34.46 (0.25) vs 32.45 (0.31) and 35.22 (0.36) vs 33.13 (0.34), respectively; P < 0.001 each comparison). Core temperature increased slightly in group 1 and decreased in group 2 (P = 0.11).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo fluorine‐19 magnetic resonance spectroscopy of cerebral halothane in postoperative patients: Preliminary results

This study reports the use of 19F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal-to-noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (+/- SD) chemical shift of +43.3 (+/- 1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited a T1 value of between 0.5 and 1 s, and a T2* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility of in vivo 19F MRS studies of fluorinated volatile agents in humans. The potential for clinical 19F MRS of fluorinated anesthetics is discussed.

Anxiety levels following anaesthesia for day‐case surgery

The effect of different induction agents on postoperative state anxiety levels was investigated. Propofol produces statistically significant lower levels when compared with thiopentone. This finding suggests that propofol should remain the drug of choice for short duration anaesthesia.

Factors influencing the outcome of equine anaesthesia: a review of 1,314 cases.

Patient data, physiological variables and recovery quality were extracted from 1,314 records of equine anaesthetics covering a 7-year period and analysed retrospectively. Better recovery quality was significantly associated with shorter duration of anaesthesia, longer recovery times, less invasive surgery, a lower pulse rate at induction and higher pulse and respiratory rates during anaesthesia. Nineteen animals suffered serious anaesthetic-related problems (1.4% incidence) and 9 died (0.68% incidence). Clinical treatment of hypotension during anaesthesia significantly reduced the hypotensive index but did not significantly alter the recovery quality or incidence of post-anaesthetic myopathy. The severity of the myopathy was, however, markedly reduced in the animals treated for hypotension.

Effects of anaesthetics, anticonvulsants and glutamate antagonists on kainic acid-induced local and distal neuronal loss

A semi-quantitative estimation has been made of the effect of anaesthetics, anticonvulsants and glutamate antagonists on the extent of neuronal loss in the hippocampus caused by the local injection of the excitotoxin kainic acid, and on the vulnerability of neurons in various extrahippocampal regions due to the resulting seizure activity. Following the intrahippocampal injection of 0.47 nmol kainic acid (a submaximal dose), the amount of neuronal loss in the dorsal hippocampus was greater when given under the short-acting anaesthetics halothane and ketamine (a non-competitive glutamate antagonist), than when given under pentobarbital anaesthesia (with or without co-administration of ketamine (30 mg/kg)). When kainic acid was injected under halothane or ketamine anaesthesia a greater number of extrahippocampal limbic regions (distal toxicity) were also affected, usually on the ipsilateral side, and the extent of damage in each of these regions was generally more extensive. The anticonvulsants MK 801 and diazepam, or multiple injections of ketamine over a period of 5 h, decreased both the local and distal toxicity of kainic acid injected under short duration anaesthesia, to levels similar to those found under pentobarbital anaesthesia. However, these compounds, even at high doses, could not reliably prevent all seizure-related damage in extrahippocampal areas.

The Case for Maintenance of General Anesthesia with an Injectable Agent

The maintenance of anesthesia with injectable drugs provides a safe alternative to inhalant techniques, provided that the basic needs of the patient are met. The standard drugs (e.g., thiobarbiturates, methohexital, ketamine) can be used, economically and safely, to provide a short duration of anesthesia, but the best drugs for more prolonged procedures are more expensive (e.g., alfentanil, fentanyl, propofol) and require more sophisticated equipment to provide optimal conditions.

Effects of Anesthesia and Stimulus Intensity on Posterior Tibial Nerve Somatosensory Evoked Potentials

Under anesthesia peak latencies occurring up to 75 milliseconds after stimulus onset upon somatosensory evoked potential testing of the somatosensory evoked potential testing of the posterior tibial nerve were not affected by stimulus intensity (between 5 and 19 ma) or by length of time under isoflurane and nitrous oxide up to over 2 hours. When pre- and postoperative tests on patients who were not under anesthesia were compared with results under anesthesia, no significant latency differences were found in relation to stimulus intensity for peaks N30, P40 and N50. For peaks P60 and N75, however, significantly increased latencies were seen during anesthesia, more pronounced and consistent for N75. Amplitudes, however, were affected by both stimulus intensity and anesthesia duration. A curvilinear relationship was found during early anesthesia. Maximum amplitudes were found at 7 or 11 ma stimulus intensity levels, depending upon which peak was analyzed, with lesser amplitudes occurring at both lower and higher stimulus intensity levels. Stimulus intensity and anesthesia interacted such that maximum amplitude occurred, in general, at 11 ma after short duration anesthesia (6') and at 7 ma after long duration anesthesia (125'). Under long duration anesthesia amplitudes were significantly diminished, mostly at the 11 ma intensity level. At 15 and 19 ma intensity levels peak amplitudes remained relatively constant regardless of anesthesia duration and therefore are the intensities to use to monitor changes during prolonged surgeries. When preoperative during prolonged surgeries. When preoperative and postoperative tests were compared to tests under anesthesia, there was a decrease in amplitude under anesthesia, greater for long than short duration anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic Drug Interactions in Anaesthetic Practice

Patients receive on average 10 different drugs while in hospital; when fewer than 6 are administered the probability of an adverse drug interaction is about 5%, but when more than 15 are given the probability increases to over 40%. Patients presenting for anaesthesia and surgery are likely to receive multiple preoperative drug therapy and also many perioperative medications as part of their anaesthetic regimen. Thus, there is a considerable potential for interactions to occur in anaesthetic practice. Pharmacokinetic interactions occur when the administration of 1 drug alters the disposition of another, and hence alters the concentration of drug at the receptor site, leading to altered drug response. These changes in drug concentration at the receptor site may be produced by alteration of (a) drug absorption and uptake into the body, (b) drug distribution, (c) drug metabolism and (d) drug elimination or excretion by nonmetabolic routes. Interactions affecting the absorption of orally administered medications are often due to the indirect effect of 1 drug on gastric motility and emptying, which leads to reduced, delayed or variable systemic drug availability. Gastric emptying time before elective surgery is normal, but premedication with morphine, pethidine (meperidine) and anticholinergics all delay gastric emptying and hence drug absorption. Inhalational anaesthesia of short duration does not appear to affect drug absorption, although halothane anaesthetic used for longer periods produces a slight delay in gastric emptying. Volatile anaesthetics have been shown to delay the intramuscular absorption of ketamine. Anaesthetic agents may affect drug distribution, and peak concentrations of propranolol, for example, are 4 times higher during halothane anaesthesia in dogs, accompanied by a marked decrease in volume of distribution. This effect has been noted for other drugs, including thiopental and verapamil. Volatile anaesthetics also affect plasma protein binding, leading to displacement interactions in some cases. Volatile anaesthetics affect the metabolism of concomitantly administered drug (a) by altering the rate of delivery to the organ of clearance (e.g. decreasing hepatic blood flow) and (b) by altering the activity of drug metabolising enzymes. It is now well recognised that all the volatile anaesthetics currently in use inhibit the metabolism of a large variety of drugs, e.g. propranolol, lidocaine (lignocaine), fentanyl and pethidine. Other examples of interactions of clinical importance to anaesthesiologists include those between cimetidine and the local anaesthetics and benzodiazepines; inhibition of plasma cholinesterase by drugs such as ecothiopate; interactions between monoamine oxidase inhibitors and sympathomimetics or pethidine and between monoamine oxidase inhibitors and sympathomimetics or pethidine and between isoniazid and enflurane.(ABSTRACT TRUNCATED AT 400 WORDS)

Pregnanolone emulsion A preliminary pharmacokinetic and pharmacodynamic study of a new intravenous anaesthetic agent

Pregnanolone emulsion, a new steroid anaesthetic agent, was administered intravenously as bolus doses to six young healthy male volunteers in a preliminary pharmacokinetic and pharmacodynamic study. The plasma concentration-time curves fitted a two-compartment model. The elimination half-life was between 0.9 and 1.4 hours, volume of central compartment between 0.95 and 2.10 litres/kg, volume of distribution between 3.75 and 5.58 litres/kg and total body clearance between 1.80 and 3.07 (litres/hour)/kg. The excretion in urine of unchanged pregnanolone was less than 0.1%. The pharmacodynamic properties were found to be similar to those of Althesin, with immediate induction of anaesthesia of short duration. The anaesthetic affected haemodynamics only slightly; minor depression of ventilation, with an increase in PaCO2, occurred in several of the subjects. Excitation of short duration occurred in one subject during induction of sleep and slight involuntary muscle movements in another subject during sleep. It is impossible to draw any clear conclusions of the clinical efficacy and tolerance from this limited normal subject trial, but pregnanolone emulsion seems worthy of further clinical trial.

Long-Term Results of Sacculotomy in Older Patients

In patients with Meniere's disease with incapacitating vertiginous complaints in whom medical treatment has failed, sacculotomies by both the Fick and tack operations are relatively simple surgical procedures, whose short duration of anesthesia and hospitalization of patients minimizes the risks of morbidity in older patients appropriately to their general health, with good results in controlling vertigo. With respect to preservation of hearing, the tack operation is superior to the Fick operation.

Spinal anesthetic agents.

Lidocaine, tetracaine, and bupivacaine are the local anesthetic agents most commonly employed for spinal anesthesia in the U.S. Lidocaine provides a short duration of anesthesia and is primarily useful for surgical and obstetrical procedures lasting less than one hour. Tetracaine and bupivacaine are used for procedures lasting 2 to 5 hours. Tetracaine appears to provide a somewhat longer duration of anesthesia and a more profound degree of motor block than does bupivacaine. On the other hand, compared with tetracaine, bupivacaine has been demonstrated to be associated with a decreased incidence of hypotension. In addition, bupivacaine may be better than tetracaine for use in orthopedic surgical procedures since it appears to be associated with a lower incidence of tourniquet pain. Vasoconstrictors can prolong the duration of spinal anesthesia of all three agents. However, the greatest duration is seen when vasoconstrictors are added to tetracaine solutions. Lidocaine and bupivacaine do not appear to benefit as much from the addition of vasoconstrictors. In general, the local anesthetic agents that are currently available for spinal anesthesia provide significant versatility. By carefully considering the planned surgical procedure, the surgeon's requirements, and the patient's characteristics (e.g., age, height, gravidity), and by understanding the factors that influence spinal anesthesia, the anesthesiologist can select a local anesthetic agent that will assure adequate and satisfying spinal anesthesia.