The potential of quantified lower cranial nerve EMG for monitoring of anesthetic depth.

BACKGROUND: During surgery, lower cranial nerve (CN) electromyography (EMG) may show spontaneous activity without surgical correlate. These episodes have been observed in association with sudden patient movement. In the study presented, this activity was quantified and correlated to the Bispectral Index (BIS) to evaluate the potential of lower CN-EMG for monitoring the depth of anesthesia. METHODS: Spontaneous EMG activity in muscles targeted by the CNs IX, X, and XII was quantified and correlated with the BIS measured in 23 patients operated on for posterior fossa pathology. In a blinded retrospective analysis, the time interval from beginning of build-up of the respective parameter (EMG activity and BIS) until extubation was marked. The resulting time intervals were then compared between BIS and EMG. RESULTS: EMG and BIS build-up was seen 12.3 and 5.9 minutes, respectively, before extubation in median. Thus, EMG provided a longer "warning time" (P=0.026). Isolated lower CN EMG channels preceded BIS in 53%, 62%, and 70% (CN IX, X, and XII). The earliest available EMG channel preceded BIS in 67% of the patients by a median time of 4.3 minutes. The beginning of EMG build-up in the earliest channel was found to be significantly earlier than BIS (P<0.001). CONCLUSIONS: Spontaneous EMG of muscles targeted by lower CNs seems to correlate well with arousal reactions at the end of anesthesia. In many cases, this effect preceded BIS changes. Thus, lower CN EMG monitoring may be a valuable tool in monitoring adequate depth of anesthesia.

Methemoglobinemia in critically ill patients during extended hemodialysis and simultaneous disinfection of the hospital water supply.

INTRODUCTION: To evaluate the cause of methemoglobinemia in patients undergoing extended daily hemodialysis/hemodiafiltration we analyzed the relationship between methemoglobinemia and the water disinfection schedule of the hospital. METHODS: We reviewed all arterial blood gas analyses, obtained over a one-year period, in patients undergoing extended hemodialysis/hemodiafiltration, and compared the methemoglobin concentrations obtained on the days when the water supply was disinfected, using a hydrogen peroxide/silver ion preparation, with data measured on disinfection-free days. RESULTS: The evaluation of 706 measurements revealed a maximum methemoglobin fraction of 1.0 (0.8; 1.2) % (median and 25th; 75th percentiles) during hemodialysis/hemodiafiltration on the disinfection-free days. The methemoglobin fraction increased to 5.9 (1.3; 8.4) % with a maximal value of 12.2% on the days of water disinfection (P < 0.001 compared to disinfection-free days). Spot checks on hydrogen peroxide concentrations in the water supply, the permeate, and the dialysate, using a semi-quantitative test, demonstrated levels between 10 and 25 mg/l during water disinfection. CONCLUSIONS: Our results demonstrate that even a regular hospital water disinfection technique can be associated with significant methemoglobinemia during extended hemodialysis. Clinicians should be aware of this potential hazard.

Predicted and measured plasma propofol concentration and bispectral index during deep sedation in patients with impaired left ventricular function.

OBJECTIVE: To evaluate the ability of the Schnider pharmacokinetic model to predict plasma propofol concentration during target-controlled propofol infusion in patients with impaired left ventricular function and to investigate the predictive value of the bispectral index (BIS) to indicate deep sedation in this patient group. DESIGN: Prospective, observational study. PARTICIPANTS: Thirty-four patients (mean left ventricular ejection fraction 31% +/- 9%) undergoing the implantation of a cardioverter-defibrillator during deep sedation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Predicted and measured propofol plasma concentrations and BIS were assessed during steady-state conditions with the propofol infusion rate constant for at least 20 minutes. The plasma propofol concentration was significantly underestimated by the pharmacokinetic model used (mean percentage prediction error 37% +/- 49%). The 50% probability of deep sedation was calculated at a predicted propofol concentration of 2.09 (95% confidence interval [CI], 2.04-2.14) mug/mL and at a measured propofol concentration of 2.70 (95% CI, 2.62-2.78) mug/mL. BIS values showed a marked variability among individuals during deep sedation (5th-95th percentiles: 25-81). CONCLUSIONS: The pharmacokinetic model used markedly underestimated propofol plasma levels in the patient group studied. The large variability among patients suggests that BIS monitoring is not suitable for indicating an exact endpoint corresponding to deep sedation.

Changes in pulse pressure variability during cardiac resynchronization therapy in mechanically ventilated patients.

INTRODUCTION: The respiratory variation in pulse pressure (PP) has been established as a dynamic variable of cardiac preload which indicates fluid responsiveness in mechanically ventilated patients. The impact of acute changes in cardiac performance on respiratory fluctuations in PP has not been evaluated until now. We used cardiac resynchronization therapy as a model to assess the acute effects of changes in left ventricular performance on respiratory PP variability without the need of pharmacological intervention. METHODS: In 19 patients undergoing the implantation of a biventricular pacing/defibrillator device under general anesthesia, dynamic blood pressure regulation was assessed during right ventricular and biventricular pacing in the frequency domain (power spectral analysis) and in the time domain (PP variation: difference between the maximal and minimal PP values, normalized by the mean value). RESULTS: PP increased slightly during biventricular pacing but without statistical significance (right ventricular pacing, 33 +/- 10 mm Hg; biventricular pacing, 35 +/- 11 mm Hg). Respiratory PP fluctuations increased significantly (logarithmically transformed PP variability -1.27 +/- 1.74 ln mm Hg2 versus -0.66 +/- 1.48 ln mm Hg2; p < 0.01); the geometric mean of respiratory PP variability increased 1.8-fold during cardiac resynchronization. PP variation, assessed in the time domain and expressed as a percentage, showed comparable changes, increasing from 5.3% (3.1%; 12.3%) during right ventricular pacing to 6.9% (4.7%; 16.4%) during biventricular pacing (median [25th percentile; 75th percentile]; p < 0.01). CONCLUSION: Changes in cardiac performance have a significant impact on respiratory hemodynamic fluctuations in ventilated patients. This influence should be taken into consideration when interpreting PP variation.

Continuously assessed right ventricular end-diastolic volume as a marker of cardiac preload and fluid responsiveness in mechanically ventilated cardiac surgical patients.

INTRODUCTION: Assessing cardiac preload and fluid responsiveness accurately is important when attempting to avoid unnecessary volume replacement in the critically ill patient, which is associated with increased morbidity and mortality. The present clinical trial was designed to compare the reliability of continuous right ventricular end-diastolic volume (CEDV) index assessment based on rapid response thermistor technique, cardiac filling pressures (central venous pressure [CVP] and pulmonary capillary wedge pressure [PCWP]), and transesophageal echocardiographically derived evaluation of left ventricular end-diastolic area (LVEDA) index in predicting the hemodynamic response to volume replacement. METHODS: We studied 21 patients undergoing elective coronary artery bypass grafting. After induction of anesthesia, hemodynamic parameters were measured simultaneously before (T1) and 12 min after volume replacement (T2) by infusion of 6% hydroxyethyl starch 200/0.5 (7 ml/kg) at a rate of 1 ml/kg per min. RESULTS: The volume-induced increase in thermodilution-derived stroke volume index (SVITD) was 10% or greater in 19 patients and under 10% in two. There was a significant correlation between changes in CEDV index and changes in SVITD (r2 = 0.55; P < 0.01), but there were no significant correlations between changes in CVP, PCWP and LVEDA index, and changes in SVITD. The only variable apparently indicating fluid responsiveness was LVEDA index, the baseline value of which was weakly correlated with percentage change in SVITD (r2 = 0.38; P < 0.01). CONCLUSION: An increased cardiac preload is more reliably reflected by CEDV index than by CVP, PCWP, or LVEDA index in this setting of preoperative cardiac surgery, but CEDV index did not reflect fluid responsiveness. The response of SVITD following fluid administration was better predicted by LVEDA index than by CEDV index, CVP, or PCWP.