Relationship between A-line Autoregressive Index, Spectral Entropy and steady state predicted site-effect effective concentrations at 05-50-95 of propofol at different clinical endpoints.

AIM: Target controlled infusion intravenous anesthesia is a growing phenomenon. Nowadays, many anesthesiologists feel the need to monitor depth of anesthesia during total intravenous anesthesia, even though it is not a standard technique worldwide. Spectral Entropy (SE) is a relatively new depth of anesthesia index. The aim of this study was to investigate whether predicted site-effect propofol concentrations, A-line Autoregressive Index (AAI) and SE values are useful for predicting loss of verbal contact (LVC) and loss of consciousness (LOC) during steady-state conditions. METHODS: Forty-four patients scheduled for elective major abdominal surgery were recruited. All patients were unpremedicated. A target controlled infusion of propofol was administered using Schnider's pharmacokinetic model. The initial propofol infusion provided a site-effect concentration of 1.0 mcg mL-1, and was increased stepwise by 1.0 mcg mL-1 every 4 minutes until the concentration reached 6.0 mcg mL-1. A 4 minute interval was chosen to assure that steady state site-effect concentrations were obtained. AAI, SE and propofol site-effect concentrations were recorded when LVC occurred and also when LOC occurred. Population values for predicted site-effect concentrations at the clinical endpoints were estimated and correlated with AAI and SE values. RESULTS: In our study for LOC the effect-site concentration to include 90% of patients was 5.85 ?mcg mL-1 (5.70-5.90) and 3.4 mcg mL-1 (3.24-3.60) for LVC. In this study, 90% of patients lost verbal contact at an AAI value of 68 (64.6-71.4) and an SE value of 68.2 (66.2-70.2). LOC occurred in 90% of patients at an AAI value of 39.2 (37.2-41.1) and an SE value of 40.2 (38.1-41.3). CONCLUSIONS: LOC and LVC occur within a defined range of predicted site-effect concentrations. More emphasis should be given to site-effect concentrations. SE and AAI have similar values at different endpoints and similar correlation with Ceprop. AAI and SE are both useful tools in predicting both LVC and LOC.

BIS - AAI and clinical measures during propofol target controlled infusion with Schnider's pharmacokinetic model.

AIM: The A-line autoregressive index (AAI) and the Bispectral Index Score (BIS) are two commercially available indexes of anesthetic depth widely used in clinical practice. The aim of the current study was to compare the accuracy of AAI, BIS, Schnider's predicted effect-site concentration of propofol (Ce propofol) to assess depth of anesthesia. METHODS: Forty-four patients scheduled for major elective abdominal surgery received target effect-site controlled infusion of propofol. Target effect-site (Ce propofol) was started at 1.5 mug/mL and increased every 4 min by 1.0 microg/mL until 5.5 microg/mL were achieved. At every step sedation level was estimated, using AAI, BIS, Observer's Assessment of Alertness/Sedation scale (OAA/S), loss of eyelash reflex and Ce propofol. RESULTS: We enrolled 44 patients, 20 males and 24 females, ASA I/II 18/26, 48+/-10 years, 68.2+/-9 kg, 165+/-7.1 cm, body mass index (BMI) 25+/-3.5. At increasing Ce propofol BIS-AAI values decreased progressively (BIS range 97-38) (AAI range 97-17). Values of BIS < or = 50, of AAI < or = 48 and of Ce propofol > or = 5.1 resulted in OAA/S=0, while values of BIS < or = 62, AAI < or = 53 and Ce propofol < or = 3.5 resulted in OAA/S=2. Loss of eyelash reflex occurred when values were BIS < or = 64 and AAI < or 61. CONCLUSION: BIS, AAI, propofol site effect concentration revealed information on sedation level and consciousness but no gold standard yet exists because of consistent overlap between ''conscious'' and ''not conscious'' states.