Anesthesia and analgesia
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Anesthesia and analgesia · Feb 2002
Comparative StudyThe neurotoxicity of local anesthetics on growing neurons: a comparative study of lidocaine, bupivacaine, mepivacaine, and ropivacaine.
Local anesthetics can be neurotoxic. To test the hypothesis that exposure to local anesthetics produces morphological changes in growing neurons and to compare this neurotoxic potential between different local anesthetics, we performed in vitro cell biological experiments with isolated dorsal root ganglion neurons from chick embryos. The effects of lidocaine, bupivacaine, mepivacaine, and ropivacaine were examined microscopically and quantitatively assessed using the growth cone collapse assay. We observed that all local anesthetics produced growth cone collapse and neurite degeneration. However, they showed significant differences in the dose response. The IC(50) values were approximately, 10(-2.8) M for lidocaine, 10(-2.6) M for bupivacaine, 10(-1.6) M for mepivacaine, and 10(-2.5) M for ropivacaine at 15 min exposure. Some reversibility was observed after replacement of the media. At 20 h after washout, bupivacaine and ropivacaine showed insignificant percentage growth cone collapse in comparison to their control values whereas those for lidocaine and mepivacaine were significantly higher than the control values. Larger concentrations of the nerve growth factor (NGF) did not improve this reversibility. In conclusion, local anesthetics produced morphological changes in growing neurons with significantly different IC(50). The reversibility of these changes differed among the four drugs and was not influenced by the NGF concentration. ⋯ Local anesthetics induce growth cone collapse and neurite degeneration in the growing neurons. Mepivacaine was safer than lidocaine, bupivacaine, and ropivacaine for the primary cultured chick neurons.
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Anesthesia and analgesia · Feb 2002
Depression of diaphragm contractility by nitrous oxide in humans.
Nitrous oxide is widely used in anesthesia and critical care medicine. The effect of nitrous oxide on diaphragm contractility in humans is unknown. We evaluated the effect of a 50% nitrous oxide-50% oxygen mixture on diaphragm contractility in healthy adult volunteers. The sniff transdiaphragmatic pressure (Sn Pdi) and the twitch transdiaphragmatic pressure (Tw Pdi) elicited by bilateral supramaximal phrenic nerve stimulation were measured before during and after inhalation of a mixture of 50% nitrous oxide and 50% oxygen. Sn Pdi decreased by 15.4% during nitrous oxide inhalation, with a value of 136 +/- 21 cm H(2)O before nitrous oxide and a value of 115 +/- 27 cm H(2)O during nitrous oxide inhalation (P = 0.03). Similarly, Tw Pdi decreased from 21.2 +/- 1.8 cm H(2)O before nitrous oxide inhalation to 16.9 +/- 4.1 cm H(2)O during nitrous oxide inhalation (P = 0.03). The effect of nitrous oxide was totally abolished 20 min after its discontinuation. Nitrous oxide has a short-acting suppressant effect on the pressure generating capacity of the diaphragm in healthy humans. ⋯ We investigated whether nitrous oxide (a common component of gas anesthesia) reduces diaphragm strength in humans. Diaphragm strength is reduced by nitrous oxide but the effect wears off within 20 min of administration. Caution is advised when using nitrous oxide without anesthesiologist supervision in patients at risk of ventilatory failure
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Anesthesia and analgesia · Feb 2002
An evaluation of the cutaneous distribution after obturator nerve block.
In 1973, Winnie et al. introduced the inguinal paravascular three-in-one block, which allegedly provides anesthesia of three nerves--the femoral, lateral cutaneous femoral, and obturator nerves--with a single injection. This concept was undisputed until the success of the obturator nerve block was reassessed by using evidence of adductor weakness rather than cutaneous sensory blockade, the latter being variable in its distribution and often absent. We performed this study, therefore, to evaluate the area of sensory loss produced by direct injection of local anesthetic around the obturator nerve. A selective obturator nerve block with 7 mL of 0.75% ropivacaine was performed in 30 patients scheduled for knee surgery. Sensory deficit and adductor strength were evaluated for 30 min by using sensory tests (cold and light-touch perception) and the pressure generated by the patient's squeezing a blood pressure cuff placed between the knees. Subsequently, a three-in-one block was performed, and the sensory deficit was reassessed. The obturator nerve block was successful in 100% of cases. The strength of adductors decreased by 77% +/- 17% (mean +/- SD). In 17 patients (57%), there was no cutaneous contribution of the obturator nerve. The remaining 7 patients (23%) had an area of hypoesthesia (cold sensation was blunt but still present) on the superior part of the popliteal fossa, and the other 6 (20%) had sensory deficit located at the medial aspect of the thigh. The three-in-one block resulted in blockade of the lateral aspect of the thigh in 87% of cases, whereas the anteromedial aspect was always anesthetized. By use of magnetic resonance imaging in eight volunteers, we demonstrated that the obturator nerve has already divided into its two branches at the site of local anesthetic injection. However, the injection of blue dye after having simulated the technique in five cadavers showed that the fluid regularly spread to both branches. We conclude that after three-in-one block, a femoral nerve block may have been assessed as an obturator nerve block in 100% of cases when testing the cutaneous distribution of the obturator nerve on the medial aspect of the thigh. ⋯ Previous studies reporting an incidence of obturator nerve block after three-in-one block may have mistaken a femoral nerve block for an obturator nerve block in 100% of cases when the cutaneous distribution of the obturator nerve was assessed on the medial aspect of the thigh. The only way to effectively evaluate obturator nerve function is to assess adductor strength.
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Anesthesia and analgesia · Feb 2002
Case ReportsDifficult retrograde endotracheal intubation: the utility of a pharyngeal loop.
Direct laryngoscopy and tracheal intubation remains the technique of choice to achieve control of the airway. Alternative or additional techniques of airway control are required whenever an airway is deemed difficult because of anatomical and/or technical reasons. The retrograde intubation technique is an important option for gaining airway access from below the vocal cords in such situations (1). We report successful management and the problems encountered while gaining the upper airway by the retrograde catheter method in a patient having bilateral fibrous ankylosis of the temporomandibular joint (TMJ). ⋯ A 30-yr-old woman presented for redo-release of bilateral temporomandibular joint ankylosis under general anesthesia. During the previous anesthetic for primary release of ankylosis, tracheostomy was done, as conventional blind nasotracheal and retrograde intubation attempts failed several times. This case report describes the method for overcoming the difficulties of a retrograde intubation procedure in removing the guiding catheter nasally by using a pharyngeal loop assembly.
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Anesthesia and analgesia · Feb 2002
Case ReportsInterscalene and infraclavicular block for bilateral distal radius fracture.
Brachial plexus blockade is a suitable technique for surgery of the forearm, because it provides good intraoperative anesthesia as well as prolonged postoperative analgesia when long-acting local anesthetics are used. However, simultaneous blockade of both upper extremities has rarely been performed (1), because local anesthetic toxicity caused by the amount of drug needed to achieve an efficient block on both sides may be a problem. We report a case of successful bilateral brachial plexus block with ropivacaine in a patient with bilateral distal radius fracture, with each fracture requiring an open osteosynthesis. ⋯ This case report presents the performance of a simultaneous blockade of both upper extremities in a patient who sustained a bilateral distal radius fracture. The patient was known to be difficult to intubate and to have a severe hypersensitivity to opioids.