An assessment of the validity of spectral entropy as a measure of sedation state in mechanically ventilated critically ill patients.

OBJECTIVE: To assess whether the Entropy Module (GE Healthcare, Helsinki, Finland), a device to measure hypnosis in anesthesia, is a valid measure of sedation state in critically ill patients by comparing clinically assessed sedation state with Spectral Entropy DESIGN: Prospective observational study. SETTING: Teaching hospital general ICU. PATIENTS AND PARTICIPANTS: 30 intubated, mechanically ventilated patients without primary neurological diagnoses or drug overdose receiving continuous sedation. INTERVENTIONS: Monitoring of EEG and fEMG activity via forehead electrodes for up to 72h and assessments of conscious level using a modified Ramsay Sedation Scale. MEASUREMENTS AND RESULTS: 475 trained observer assessments were made and compared with concurrent Entropy numbers. Median State (SE) and Response (RE) Entropy values decreased as Ramsay score increased, but wide variation occurred, especially in Ramsay 4-6 categories. Discrimination between different sedation scores [mean (SEM) P(K) value: RE 0.713 (0.019); SE 0.710 (0.019)] and between lighter (Ramsay 1-3) vs.deeper (Ramsay 4-6) sedation ranges was inadequate [P(K): RE 0.750 (0.025); SE 0.748 (0.025)]. fEMG power decreased with increasing Ramsay score but was often significant even at Ramsay 4-6 states. Frequent "on-off" effects occurred for both RE and SE, which were associated with fEMG activity. Values switched from low to high values even in deeply sedated patients. High Entropy values during deeper sedation were strongly associated with simultaneous high relative fEMG powers. CONCLUSIONS: Entropy of the frontal EEG does not discriminate sedation state adequately for clinical use in ICU patients. Facial EMG is a major confounder in clinical sedation ranges.

Indirect calorimetry in patients with active respiratory infection--prevention of cross-infection.

BACKGROUND: Measurement of resting energy expenditure in patients with active respiratory infection is hampered by the risk of contamination of indirect calorimeters and connecting tubes that cannot be sterilized. This validation study tested whether the use of disposable standard-bore air tubes and an antibacterial filter, by reducing air flow, introduces an error due to recirculation of expired air in the canopy. METHODS: Eleven healthy volunteers underwent indirect calorimetry twice in random order, using a Deltatrac calorimeter either with standard wide-bore tubing or with a disposable standard-bore air tube and filter. Methods were compared by Bland-Altman plots and by calculating trends over time. RESULTS: The new tube and filter reduced air flow by 40%. Measured resting energy expenditure did not differ significantly between methods, with limits of agreement -135 to +188 kcal/d. Carbon dioxide flow (VCO(2)) and respiratory quotient (RQ), but not oxygen flow decreased slowly over time with both methods. CONCLUSIONS: The use of an air filter and standard-bore tubes do not introduce a systematic error into indirect calorimetry. Although trends in VCO(2) and RQ are consistent with minor recirculation of exhaled air, this modified Deltatrac system can be safely and reliably used to measure resting energy expenditures in patients with active tuberculosis and other airborne infection.