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1.  Block-Dependent Sedation during Epidural Anaesthesia is Associated with Delayed Brainstem Conduction 
British journal of anaesthesia  2004;93(2):228-234.
Neuraxial anaesthesia produces a sedative and anesthetic-sparing effect. Recent evidence suggests that spinal cord anaesthesia modifies reticulo-thalamo-cortical arousal by decreasing afferent sensory transmission. We hypothesized that epidural anaesthesia produces sensory deafferentation-dependent sedation that is associated with impairment of brainstem transmission. We used brainstem auditory evoked potentials (BAEP) to evaluate reticular function in 11 volunteers. Epidural anaesthesia was induced with 2% 2-chloroprocaine. Hemodynamic and respiratory responses, sensory block level, sedation depth and BAEP were assessed throughout induction and resolution of epidural anaesthesia. Sedation was evaluated using verbal rating score (VRS), observer's assessment alertness/sedation (OAA/S) score, and bispectral index (BIS). Prediction probability (PK) was used to associate sensory block with sedation, as well as BIS with other sedation measures. Spearman rank order correlation was used to associate block level and sedation with the absolute and interpeak BAEP latencies. Sensory block level significantly predicted VRS (PK = 0.747), OAA/S score (PK = 0.748) and BIS. Bispectral index predicted VRS and OAA/S score (PK = 0.728). The latency of wave III of BAEP significantly correlated with sedation level (rho = 0.335, P < 0.01) and sensory block (rho = 0.394, P < 0.01). The other BAEP parameters did not change during epidural anaesthesia. Hemodynamic and respiratory responses remained stable throughout the study. Sedation during epidural anaesthesia depends on sensory block level and is associated with detectable block-dependent alterations in the brainstem auditory evoked responses. Sensory deafferentation may reduce CNS alertness through mechanisms related to brainstem neural activity.
PMCID: PMC1361808  PMID: 15220178
Afferentation theory; Brainstem auditory evoked potentials; Chloroprocaine; Deafferentation; Epidural anaesthesia; Sedation; Sensory block
2.  Magnesium Sulfate Only Slightly Reduces the Shivering Threshold in Humans 
British journal of anaesthesia  2005;94(6):756-762.
Background: Hypothermia may be an effective treatment for stroke or acute myocardial infarction; however, it provokes vigorous shivering, which causes potentially dangerous hemodynamic responses and prevents further hypothermia. Magnesium is an attractive antishivering agent because it is used for treatment of postoperative shivering and provides protection against ischemic injury in animal models. We tested the hypothesis that magnesium reduces the threshold (triggering core temperature) and gain of shivering without substantial sedation or muscle weakness.
Methods: We studied nine healthy male volunteers (18-40 yr) on two randomly assigned treatment days: 1) Control and 2) Magnesium (80 mg·kg-1 followed by infusion at 2 g·h-1). Lactated Ringer's solution (4°C) was infused via a central venous catheter over a period of approximately 2 hours to decrease tympanic membrane temperature ≈1.5°C·h-1. A significant and persistent increase in oxygen consumption identified the threshold. The gain of shivering was determined by the slope of oxygen consumption vs. core temperature regression. Sedation was evaluated using verbal rating score (VRS, 0-10) and bispectral index of the EEG (BIS). Peripheral muscle strength was evaluated using dynamometry and spirometry. Data were analyzed using repeated-measures ANOVA; P<0.05 was statistically significant.
Results: Magnesium reduced the shivering threshold (36.3±0.4 [mean±SD] vs. 36.6±0.3°C, P=0.040). It did not affect the gain of shivering (Control: 437±289, Magnesium: 573±370 ml·min-1·°C-1, P=0.344). The magnesium bolus did not produce significant sedation or appreciably reduce muscle strength.
Conclusions: Magnesium significantly reduced the shivering threshold; however, due to the modest absolute reduction, this finding is considered to be clinically unimportant for induction of therapeutic hypothermia.
PMCID: PMC1361806  PMID: 15749735
Magnesium; Temperature; Thermoregulation; Therapeutic hypothermia; Brain protection; Cardiac protection; Shivering
3.  Supplemental Oxygen Does Not Reduce Postoperative Nausea and Vomiting after Thyroidectomy 
British journal of anaesthesia  2003;91(6):857-861.
Supplemental intra-operative oxygen (80%) halves the incidence of nausea and vomiting after open and laparoscopic abdominal surgery, perhaps by ameliorating the subtle intestinal ischemia associated with abdominal surgery. It is unlikely that thyroid surgery compromises intestinal perfusion. We therefore tested the hypothesis that supplemental perioperative oxygen does not reduce the risk of postoperative nausea and vomiting (PONV) after thyroidectomy. As a positive control, we simultaneously evaluated the anti-nausea efficacy of droperidol. One hundred and fifty patients undergoing thyroidectomy were given sevoflurane anaesthesia. After induction, patients were randomly assigned to the following treatments: 1) 30% oxygen, balance nitrogen; 2) 80% oxygen, balance nitrogen; or 3) 30% oxygen with droperidol 0.625 mg. The overall incidence of nausea during the first 24 postoperative hours was 48% in the patients given 30% oxygen, 46% in those given 80% oxygen, and 22% in those given droperidol (P = 0.004). There were no significant differences between the 30% and 80% oxygen groups in incidence or severity of PONV, the need for rescue anti-emetics, or patient satisfaction. Droperidol significantly shortened the time to first meal. Supplemental oxygen was ineffective in preventing nausea and vomiting after thyroidectomy, but droperidol halved the incidence.
PMCID: PMC1343506  PMID: 14633758
Anaesthesia; droperidol; oxygen; postoperative complications: nausea and vomiting; surgery: thyroidectomy
4.  The Intubating Laryngeal Mask Airway Allows Tracheal Intubation When the Cervical Spine Is Immobilized by a Rigid Collar 
British journal of anaesthesia  2004;93(5):655-659.
An intubating laryngeal mask airway (ILMA) facilitates tracheal intubation with the neck in neutral position, which is similar to the neck position maintained by a rigid cervical collar. However, a cervical collar virtually obliterates neck movement, even the small movements that normally facilitate airway insertion. We therefore tested the hypothesis that the ILMA facilitates tracheal intubation even in patients wearing a rigid cervical collar. In 50 cervical spine surgery patients with a rigid Philadelphia collar in place and 50 general surgery patients under general anaesthesia, we performed blind tracheal intubation via an ILMA. The time required for intubation, intubation success rate, and numbers and type of adjusting manoeuvres employed were recorded. Inter-incisor distance was significantly smaller (4.1 [0.8] cm vs. 4.6 [0.7] cm, mean [SD], P<0.01) and Mallampati scores were significantly greater (P<0.001) in the collared patients. ILMA insertion took longer (30 [25] vs. 22 [6] seconds), more patients required 2 insertion attempts (15 vs. 3; P<0.005), and ventilation adequacy with ILMA was worse (P<0.05) in collared patients. However, there were no significant differences between the collared and control patients in terms of total time required for intubation (60 [41] vs. 50 [30] seconds), number of intubation attempts, overall intubation success rate (96 vs. 98%), or the incidence of intubation complications. Blind intubation through an ILMA is thus a reasonable strategy for controlling the airway in patients who are immobilized with a rigid cervical collar, especially when urgency precludes a fiberoptic approach.
PMCID: PMC1283102  PMID: 15321932
anaesthesia; intubation; tracheal; laryngeal mask; cervical collar

Results 1-4 (4)