Block-dependent sedation during epidural anaesthesia is associated with delayed brainstem conduction.

BACKGROUND: Neuraxial anaesthesia produces a sedative and anaesthetic-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. METHODS: Epidural anaesthesia was induced with 2-chloroprocaine 2%. Haemodynamic 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 score (BIS). Prediction probability (PK) was used to associate sensory block with sedation, as well as BIS with other sedation measures. Spearman's rank order correlation was used to associate block level and sedation with the absolute and interpeak BAEP latencies. RESULTS: Sensory block level significantly predicted VRS (PK=0.747), OAA/S score (PK=0.748) and BIS. BIS 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. Haemodynamic and respiratory responses remained stable throughout the study. CONCLUSIONS: 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.

Automated responsiveness test and bispectral index monitoring during propofol and propofol/N2O sedation.

BACKGROUND: Sedation practice, especially when non-anaesthesia personnel are involved, requires efficient anaesthetic depth monitoring. Therefore, we used prediction probability (PK) to evaluate the performance of the bispectral index (BIS) of the EEG and automated responsiveness test (ART) to predict sedation depth and loss of subject's responsiveness during propofol sedation, with and without N2O. METHODS: Twenty volunteers were studied during propofol administration with (N2O) and without (Air) N2O. The protocol consisted of sequential 15-min cycles. After a control period, propofol was infused to a target effect-site concentration of 0.25 microg/ml (N2O) or 1.5 microg/ml (Air), which was subsequently increased by 0.25 or 0.5 microg/ml, respectively, until loss of responsiveness was detected by loss of response to command [observer's assessment of alertness/sedation (OAA/S) score

Frequency and type of injuries in responders of hazardous substances emergency events, 1996 to 1998.

This analysis describes the frequency and type of injuries among responders to hazardous materials releases. Data were analyzed from states that participated in the Hazardous Substances Emergency Events Surveillance system maintained by the Agency for Toxic Substances and Disease Registry from 1996 through 1998. A total of 348 responders were injured in 126 (0.7%) of 16,986 reported events. Firefighters and police officers were most often injured. Respiratory irritation and nausea were the most commonly reported injuries, and no injuries resulted in death. Almost half of the responder victims wore firefighter turn-out gear, and about a third had received hazardous materials training. Chemicals frequently released during these events were in the category "other substances not otherwise specified" and "acids." Training, education, planning, and coordination are needed to effectively respond to hazardous substances emergency events.

Risk factors for hazardous substance releases that result in injuries and evacuations: data from 9 states.

This study was undertaken to determine risk factors associated with hazardous substance releases (at fixed facilities or during transport) that have public health consequences. Data from nine states with surveillance systems for such releases and their consequences were analyzed. Risk factors were determined for releases resulting in (1) injuries or (2) evacuations. Both outcomes were more likely to occur as a result of facility releases (odds ratio [OR] = 1.89, 95% confidence interval [CI] = 1.44, 2.47, for injuries; OR = 3.29, 95% CI = 2.28, 4.74, for evacuations). Releases of ammonia, chlorine, and acids resulted in injuries and evacuations more frequently than releases of other substances.