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Biomedical subjects

David B Macleod

Publications and source records attributed to David B Macleod.

5 recordsLinked to original sources
PubMed2004

Dexmedetomidine pharmacodynamics: part I: crossover comparison of the respiratory effects of dexmedetomidine and remifentanil in healthy volunteers.

BACKGROUND: Dexmedetomidine, a highly selective alpha2-adrenoceptor agonist used for short-term sedation of mechanically ventilated patients, has minimal effect on ventilation. METHODS: This study compared the respiratory effect of dexmedetomidine to that of remifentanil. The authors measured and compared respiratory responses of six healthy male volunteers during (1) a stepwise target-controlled infusion of remifentanil, (2) a stepwise target-controlled infusion of dexmedetomidine, and (3) a pseudonatural sleep session. RESULTS: Compared with baseline, remifentanil infusions resulted in respiratory depression as evidenced by a decrease in respiratory rate and minute ventilation, respiratory acidosis, and apnea episodes resulting in desaturations. Remifentanil disturbed the natural pattern of breathing and flattened the distribution of ventilatory timing (inspiratory time/ventilatory cycle time). The respiratory effects of dexmedetomidine markedly contrasted with those of remifentanil. When compared with baseline, during dexmedetomidine infusions, the respiratory rate significantly increased, and the overall apnea/hypopnea index significantly decreased. The distribution of inspiratory time/ventilatory cycle time showed an increased peak. In addition, dexmedetomidine seemed to mimic some aspect of natural sleep. While the subjects were breathing a 5% CO2 mixture, hypercapnic arousal phenomena (documented by the Bispectral Index, the electroencephalogram, and sudden increase in the minute ventilation) were observed during dexmedetomidine infusions. Similar phenomena during natural sleep have been reported in the literature. CONCLUSIONS: In comparison with remifentanil, dexmedetomidine infusions (1) did not result in clinically significant respiratory depression, (2) decreased rather than increased the apnea/hypopnea index, and (3) exhibited some similarity with natural sleep.

Adult↗
PubMedDate not supplied

Severe phantom leg pain in an amputee after lumbar plexus block.

OBJECTIVES: To describe the onset of phantom leg pain in an amputee with the performance of a lumbar plexus block and the subsequent alleviation after the performance of a sciatic nerve block. CASE REPORT: A 72-year-old American Society of Anesthesiologists physical status III woman presented for left total hip arthroplasty. Her history was significant for a left below the knee amputation. Since the amputation she had suffered from intermittent phantom leg pain. A lumbar plexus block was performed for postoperative pain management. After the lumbar plexus block, the patient experienced severe pain radiating to the left phantom foot. Because of the severity of the phantom pain, a sciatic nerve block was performed. The phantom leg pain resolved within 5 minutes. The intraoperative care under general anesthesia was uneventful. After surgery the patient had continued blockade in both nerve distributions with excellent analgesia. Full recovery of the lumbar plexus and sciatic nerve function was present on the first postoperative day. CONCLUSION: The temporal relationship between the onset of the phantom leg pain and the lumbar plexus block suggests a causal relationship. In this case, it appears that ongoing peripheral input from the lumbar plexus may have been sufficient for the tonic inhibition of phantom pain in the sciatic distribution. The immediate reactivation of the phantom pain and its subsequent relief suggests dynamic processing of peripheral inputs by central neurons, which apparently is rapid and reversible in some cases of phantom pain.

Adrenergic Agonists↗
PubMedDate not supplied

Central nervous system toxicity following the administration of levobupivacaine for lumbar plexus block: A report of two cases.

BACKGROUND AND OBJECTIVES: Central nervous system and cardiac toxicity following the administration of local anesthetics is a recognized complication of regional anesthesia. Levobupivacaine, the pure S(-) enantiomer of bupivacaine, was developed to improve the cardiac safety profile of bupivacaine. We describe 2 cases of grand mal seizures following accidental intravascular injection of levobupivacaine. CASE REPORT: Two patients presenting for elective orthopedic surgery of the lower limb underwent blockade of the lumbar plexus via the posterior approach. Immediately after the administration of levobupivacaine 0.5% with epinephrine 2.5 microgram/mL, the patients developed grand mal seizures, despite negative aspiration for blood and no clinical signs of intravenous epinephrine administration. The seizures were successfully treated with sodium thiopental in addition to succinylcholine in 1 patient. Neither patient developed signs of cardiovascular toxicity. Both patients were treated preoperatively with beta-adrenergic antagonist medications, which may have masked the cardiovascular signs of the unintentional intravascular administration of levobupivacaine with epinephrine. CONCLUSIONS: Although levobupivacaine may have a safer cardiac toxicity profile than racemic bupivacaine, if adequate amounts of levobupivacaine reach the circulation, it will result in convulsions. Plasma concentrations sufficient to result in central nervous system toxicity did not produce manifestations of cardiac toxicity in these 2 patients.

Aged↗