Anesthesia and analgesia
-
Anesthesia and analgesia · Oct 1998
The analgesic potency of dexmedetomidine is enhanced after nerve injury: a possible role for peripheral alpha2-adrenoceptors.
This study investigated the analgesic potency and site of action of systemic dexmedetomidine, a selective alpha2-adrenoceptor (alpha2AR) agonist, in normal and neuropathic rats. Ligation of the L5-6 spinal nerves produced a chronic mechanical and thermal neuropathic hyperalgesia in rats. von Frey fibers and a thermoelectric Peltier device were used to measure mechanical and heat withdrawal thresholds over the hindpaw. Systemic dexmedetomidine dose-dependently increased the mechanical and thermal thresholds in the control animals (50% effective dose [ED50] 144 and 180 microg/kg intraperitoneally [i.p.], respectively). Neuropathic animals responded to much smaller doses of dexmedetomidine with mechanical and thermal ED50 values of 52 and 29 microg/kg i.p., respectively. There was no difference between the control and neuropathic animals with respect to dexmedetomidine-evoked sedation, as determined by decreased grid crossings in an open-field activity chamber (ED50 12 and 9 microg/kg i.p., respectively). Atipamezole, a selective alpha2AR antagonist, blocked the analgesic and sedative actions of dexmedetomidine inboth the neuropathic and control animals. However, L-659,066, a peripherally restricted alpha2AR antagonist, could only block the analgesic actions of dexmedetomidine in the neuropathic rats, with no effect in control animals. In conclusion, nerve injury enhanced the analgesic but not the sedative potency of systemic dexmedetomidine and may have shifted the site of alpha2 analgesic action to outside the blood-brain barrier. ⋯ We tested the analgesic efficacy of the alpha2 agonist dexmedetomidine in normal and nerve-injured rats. The analgesic potency of dexmedetomidine was enhanced after nerve injury with a site of action outside the central nervous system. Peripherally restricted alpha2 agonists may be useful in the management of neuropathic pain.
-
Anesthesia and analgesia · Oct 1998
Infraclavicular brachial plexus block: parasagittal anatomy important to the coracoid technique.
Infraclavicular brachial plexus block is a technique well suited to prolonged continuous catheter use. We used a coracoid approach to this block to create an easily understood technique. We reviewed the magnetic resonance images of the brachial plexus from 20 male and 20 female patients. Using scout films, the parasagittal section 2 cm medial to the coracoid process was identified. Along this oblique section, we located a point approximately 2 cm caudad to the coracoid process on the skin of the anterior chest wall. From this point, we determined simulated needle direction to contact the neurovascular bundle and measured depth. At the skin entry site, the direct posterior insertion of a needle will make contact with the cords of the brachial plexus where they surround the second part of the axillary artery in all images. The mean (range) distance (depth along the needle shaft) from the skin to the anterior wall of the axillary artery was 4.24 +/- 1.49 cm (2.25-7.75 cm) in men and 4.01 +/- 1.29 cm (2.25-6.5 cm) in women. Hopefully, this study will facilitate the use of this block. ⋯ We sought a consistent, palpable landmark for facilitation of the infraclavicular brachial plexus block. We used magnetic resonance images of the brachial plexus to determine the depth and needle orientation needed to contact the brachial plexus. Hopefully, this study will facilitate the use of this block.
-
Anesthesia and analgesia · Oct 1998
Randomized Controlled Trial Clinical TrialDecreased mivacurium requirements and delayed neuromuscular recovery during sevoflurane anesthesia in children and adults.
The purpose of this study was to compare the mivacurium infusion requirements and neuromuscular recovery in adults and children during propofol/opioid and sevoflurane anesthesia. Seventy-five adult and 75 pediatric patients were randomized to receive propofol/opioid 0.5 or 1.0 minimum alveolar anesthetic concentration (MAC) (age-related) sevoflurane anesthesia. Plasma cholinesterase (PChE) activity was measured. Neuromuscular blockade was monitored by train-of-four (TOF) stimulation every 10 s and adductor pollicis electromyography. A bolus of 2 x the 95% effective dose of mivacurium (0.25 mg/kg) was followed by an infusion titrated to maintain 90%-95% blockade. Mivacurium doses were recorded every 5 min. At the end of surgery, the infusion was stopped, and recovery from mivacurium was monitored until TOF > or =0.7. PChE concentrations were within the normal range (adults 4-12 KU/L, children 6-16 KU/L) and correlated with mivacurium dose. Mivacurium infusion rates were higher in children than in adults: at 30 min, the rates in children were 13.1 +/- 6.4, 8.1 +/- 4.7, and 5.2 +/- 2.9 microg x kg(-1) x min(-1) at 0, 0.5, and 1.0 MAC sevoflurane, respectively; the corresponding rates in adults were 5.9 +/- 3.1, 4.3 +/- 1.7, and 2.9 +/- 0.7 microg x kg(-1) x min(-1) (P < 0.01). Sevoflurane decreased mivacurium requirements, maximal decreases at 45 min in children and 10 min in adults, and delayed neuromuscular function recovery. Children recovered twice as quickly as adults, achieving TOF > or =0.7 at 9.8 +/- 2.5, 11.4 +/- 2.8, and 19.6 +/- 6.3 min compared with 19.9 +/- 5.4, 26.4 +/- 8.3, and 32.9 +/- 9.8 min in adults (P < 0.0001). In conclusion, mivacurium requirements were correlated with PChE, were greater in children than in adults, and were reduced by sevoflurane. Neuromuscular recovery occurred more rapidly in children and was delayed by sevoflurane. ⋯ The mivacurium infusion requirement to maintain constant 90%-95% neuromuscular block during anesthesia is correlated with plasma cholinesterase activity. It is increased in children and reduced by the inhaled anesthetic sevoflurane. Despite the larger dose administered to children, recovery from block occurred more rapidly in children than in adults and was delayed by sevoflurane.
-
Anesthesia and analgesia · Oct 1998
Comparative StudyA comparison of three modes of ventilation with the use of an adult circle system in an infant lung model.
We examined the efficiency of an adult circle system with adult bellows to deliver minute ventilation (VE) to an infant test lung model. A Narkomed 2B system (North American Drager, Telford, PA) using three modes of ventilator setup were used: A = time-cycled, volume-controlled using bellows excursion to control delivered volume; B = time-cycled, pressure-controlled using inspiratory pressure limit adjustment to control delivered volume; C = time-cycled, pressure-controlled using the inspiratory flow adjustment to control delivered volume. VE was measured with two compliances (normal and low) and four endotracheal tube (ETT) sizes (2.5-, 3.0-, 3.5-, and 4.0-mm inner diameter). VE was measured at peak inspiratory pressures (PIP) of 20, 30, 40 or 50 cm H2O while respiratory rate (RR) was held constant at 20 breaths/min. VE was measured as RR was set at 20, 30, 40, or 50 breaths/min while target PIP was held constant at 20 cm H2O. Data were analyzed using the multiple regression technique. With the low compliance model, VE was nearly identical regardless of the ventilator setup. With the normal compliance model, minor differences in VE were observed, especially at the highest RR and PIP. VE was dependent on RR, PIP, and lung compliance. Overall, the ventilator setup resulted in minor changes in VE. Very high PIPs were required to deliver VE to the low compliance model. ETT size did not affect VE when lung compliance was low; however, smaller ETT size was a factor when test lung compliance was normal, decreasing delivered VE at higher PIP and RR. We conclude that with a Narkomed 2B adult circle system VE is dependent on PIP, RR, and lung compliance, but not on mode of ventilator setup. ⋯ The results of this laboratory investigation indicate that when an adult circle system is used during infant anesthesia, the ventilation delivered depends primarily on the respiratory rate, peak inspiratory pressure, and the compliance of the lung being ventilated, rather than on the specific mode of ventilator setup.
-
Anesthesia and analgesia · Oct 1998
A survey on the intended purposes and perceived utility of preoperative cardiology consultations.
Cardiology consultations are often requested by surgeons and anesthesiologists for patients with cardiovascular disease. There can be confusion, however, regarding both the reasons for a consultation and their effect on patient management. This study was designed to determine the attitudes of physicians toward preoperative cardiology consultations and to assess the effect of such consultations on perioperative management. A multiple-choice survey regarding the purposes and utility of cardiology consultations was sent to randomly selected New York metropolitan area anesthesiologists, surgeons, and cardiologists. In addition, the charts of 55 consecutive patients aged >50 yr who received preoperative cardiology consultations were examined to determine the stated purpose of the consult, recommendations made, and concordance by surgeons and anesthesiologists with cardiologists' recommendations. Of the 400 surveys sent to each specialty, 192 were returned from anesthesiologists, 113 were returned from surgeons, and 129 were returned from cardiologists. There was substantial disagreement on the importance and purposes of a cardiology consult: intraoperative monitoring, "clearing the patient for surgery," and advising as to the safest type of anesthesia were regarded as important by most cardiologists and surgeons but as unimportant by anesthesiologists (all P < 0.05). Most surgeons (80.2%) felt obligated to follow a cardiologist's recommendations, whereas few anesthesiologists (16.6%) felt so obligated (P < 0.05). The most commonly stated purpose of the 55 cardiology consultations examined was "preoperative evaluation." Only 5 of these (9%) were obtained for patients in whom there was a new finding. Of the cardiology consultations, 40% contained no recommendations other than "proceed with case," "cleared for surgery," or "continue current medications." Recommendations regarding intraoperative monitoring or cardiac medications were largely ignored. ⋯ We conclude that there seems to be considerable disagreement among anesthesiologists, cardiologists, and surgeons as to the purposes and utility of cardiology consultations. A review of 55 consecutive cardiology consultations suggests that most of them give little advice that truly affects management.