Rainer Nitzschke

Changes in sevoflurane plasma concentration with delivery through the oxygenator during on-pump cardiac surgery

BACKGROUND It is unclear what factors affect the uptake of sevoflurane administered through the membrane oxygenator during cardiopulmonary bypass (CPB) and whether this can be monitored via the oxygenator exhaust gas. METHODS Stable delivery of sevoflurane was administered to 30 elective cardiac surgery patients at 1.8 vol% (inspiratory) via the anaesthetic circuit and ventilator. During CPB, sevoflurane was administered in the oxygenator fresh gas supply (Compactflo Evolution™; Sorin Group, Milano, Italy). Sevoflurane plasma concentration (SPC) was measured using gas chromatography. Changes were correlated with bispectral index (BIS), patient temperature, haematocrit, plasma albumin concentration, oxygenator fresh gas flow, and the sevoflurane concentration in the oxygenator exhaust at predefined time points. RESULTS The mean SPC pre-bypass was 54.9 µg ml(-1) [95% confidence interval (CI): 50.6-59.1]. SPC decreased to 43.2 µg ml(-1) (95% CI: 40.3-46.1; P<0.001) after initiation of CPB, and was lower still during rewarming and weaning from bypass, 39.4 µg ml(-1) (95% CI: 36.6-42.3; P<0.001). BIS did not exceed a value of 55. SPCs were higher during hypothermia (P<0.001) and with an increase in oxygenator fresh gas flow (P=0.015), and lower with haemodilution (P=0.027). No correlation was found between SPC and the concentration of sevoflurane in the oxygenator exhaust gas (r=-0.04; 95% CI: -0.18 to 0.09; P=0.53). CONCLUSIONS The uptake of sevoflurane delivered via the membrane oxygenator during CPB seems to be affected by hypothermia, haemodilution, and changes in the oxygenator fresh gas supply flow. Measuring the concentration of sevoflurane in the exhaust from the oxygenator is not useful for monitoring sevoflurane administration during bypass.

Comparison of an automated respiratory systolic variation test with dynamic preload indicators to predict fluid responsiveness after major surgery

BACKGROUND Predicting the response of cardiac output to volume administration remains an ongoing clinical challenge. The objective of our study was to compare the ability to predict volume responsiveness of various functional measures of cardiac preload. These included pulse pressure variation (PPV), stroke volume variation (SVV), and the recently launched automated respiratory systolic variation test (RSVT) in patients after major surgery. METHODS In this prospective study, 24 mechanically ventilated patients after major surgery were enrolled. Three consecutive volume loading steps consisting of 300 ml 6% hydroxyethylstarch 130/0.4 were performed and cardiac index (CI) was assessed by transpulmonary thermodilution. Volume responsiveness was considered as positive if CI increased by >10%. RESULTS In total 72 volume loading steps were analysed, of which 41 showed a positive volume response. Receiver operating characteristic (ROC) curve analysis revealed an area under the curve (AUC) of 0.70 for PPV, 0.72 for SVV and 0.77 for RSVT. Areas under the curves of all variables did not differ significantly from each other (P>0.05). Suggested cut-off values were 9.9% for SVV, 10.1% for PPV, and 19.7° for RSVT as calculated by the Youden Index. CONCLUSION In predicting fluid responsiveness the new automated RSVT appears to be as accurate as established dynamic indicators of preload PPV and SVV in patients after major surgery. The automated RSVT is clinically easy to use and may be useful in guiding fluid therapy in ventilated patients.

Bispectral index guided titration of sevoflurane in on-pump cardiac surgery reduces plasma sevoflurane concentration and vasopressor requirements: a prospective, controlled, sequential two-arm clinical study.

BACKGROUND Electroencephalographic-based monitoring systems such as the bispectral index (BIS) may reduce anaesthetic overdose rates. OBJECTIVE We hypothesised that goal-directed sevoflurane administration (guided by BIS monitoring) could reduce the sevoflurane plasma concentration (SPC) and intraoperative vasopressor doses during on-pump cardiac surgery. DESIGN A prospective, controlled, sequential two-arm clinical study. SETTING German university medical centre with more than 2500 cardiac surgery interventions per year. PATIENTS Sixty elective on-pump cardiac surgery patients. INTERVENTION In group Sevo1.8% (n = 29), the sedation depth was maintained with a sustained inspired concentration of sevoflurane 1.8% before and during cardiopulmonary bypass (CPB). In group SevoBIS (n = 31), the inspired sevoflurane concentration was titrated to maintain a BIS target between 40 and 60. OUTCOME MEASURES SPC during CPB and the intraoperative administration of noradrenaline. Additional analyses were performed on intraoperative awareness, postoperative blood lactate concentration, duration of mechanical ventilation, intensive care unit length of stay and kidney injury. RESULTS Mean inspired sevoflurane concentration was 0.8% in group SevoBIS, representing a 57.1% reduction (P < 0.001) compared with group Sevo1.8%. The mean SPC was 42.3 &mgr;g ml−1 [95% confidence interval (CI) 40.0 to 44.6] in group Sevo1.8% and 21.0 &mgr;g ml−1 (95% CI 18.8 to 23.3) in group SevoBIS, representing a 50.2% reduction (P < 0.001). During CPB, the mean cumulative dose of noradrenaline administered was 13.48 &mgr;g kg−1 (95% CI 10.52 to 17.19) in group Sevo1.8% and 4.06 &mgr;g kg−1 (95% CI 2.67 to 5.97) in group SevoBIS (P < 0.001). Pearsons correlation coefficient (between the cumulative applied dosage of sevoflurane calculated from the area under the curve of the SPC over time and the administered cumulative noradrenaline dose) was 0.607 (P < 0.001). No intraoperative awareness signs were detected. CONCLUSION BIS-guided titration of sevoflurane reduces the SPC and decreases noradrenaline administration compared with routine care during on-pump cardiac surgery.

Prediction of volume-responsiveness during one-lung ventilation: a comparison of static, volumetric, and dynamic parameters of cardiac preload.

OBJECTIVES The aim of this study was to evaluate the ability of static, volumetric, and dynamic parameters of cardiac preload to predict volume responsiveness during one-lung ventilation (OLV). DESIGN Prospective experimental study. SETTING Laboratory of the animal facility of the University Medical Center Hamburg-Eppendorf. PARTICIPANTS Twenty-three German domestic pigs. INTERVENTIONS Hypovolemia was induced by withdrawing 20 mL/kg body weight (BW) of blood. OLV was established, and the volume withdrawn was re-transfused in 3 volume-loading steps, each consisting of 7 mL/kg BW. An ultrasonic flow probe around the pulmonary artery was used to measure the stroke-volume index (SVI) and to evaluate the volume response. An increase in the SVI of ≥ 15% was considered a positive response. For each measurement time point, central venous pressure (CVP), left atrial pressure (LAP), the global end-diastolic volume index (GEDI), stroke-volume variation (SVV), and pulse-pressure variation (PPV) were recorded. The ability to predict volume responsiveness was assessed using ROC analysis. MEASUREMENTS AND MAIN RESULTS A total of 69 volume loading steps were performed, 48 of which showed a positive volume response. ROC analysis revealed the following area under the curve (AUC) values: CVP, 0.88; LAP, 0.65; GEDI, 0.75; SVV, 0.78; and PPV, 0.83. A comparison of the areas under the ROC curves did not reveal any statistically significant differences (p>0.05), with the exception of LAP compared with CVP (p = 0.005). CONCLUSIONS Under these OLV experimental conditions, the volumetric and dynamic parameters of preload, as well as CVP, seemed to be of similar value in predicting volume responsiveness.

Validation of Innovative Techniques for Monitoring Nociception during General Anesthesia: A Clinical Study Using Tetanic and Intracutaneous Electrical Stimulation.

BACKGROUND This study compares the analgesic indices Analgesia Nociception Index (heart rate variability), Surgical Pleth Index (photoplethysmography), and pupillary dilatation, to heart rate, mean arterial pressure, and bispectral index, with regard to diagnostic accuracy and prediction probability for nociceptive response. The primary endpoint was the correlation between Δ values and the remifentanil dose administered. METHODS We anesthetized 38 patients with propofol and increasing doses of remifentanil and applied standardized tetanic and intracutaneous electrical painful stimulations on each analgesic level. Baseline and Δ values of the Analgesia Nociception Index, the Surgical Pleth Index, pupillary dilatation, heart rate, mean arterial pressure, and bispectral index and their relation to remifentanil doses were analyzed by receiver operating characteristic curves, prediction probability (PK), and mixed-model analysis. RESULTS Under propofol sedation, sensitivity and specificity of the Analgesia Nociception Index (PK = 0.98), the Surgical Pleth Index (PK = 0.87), and pupillary dilatation (PK = 0.98) for detecting both painful stimulations were high compared to heart rate (PK = 0.74), mean arterial pressure (PK = 0.75), and bispectral index (PK = 0.55). Baseline values had limited prediction probability toward the nociceptive response (Analgesia Nociception Index: PK = 0.7; Surgical Pleth Index: PK = 0.63; pupillary dilatation: PK = 0.67; and bispectral index: PK = 0.67). The remifentanil dose had an effect (P < 0.001) on all parameters except for bispectral index (P = 0.216). CONCLUSIONS The Analgesia Nociception Index, the Surgical Pleth Index, and pupillary dilatation are superior in detecting painful stimulations compared to heart rate and mean arterial pressure but had limited predictive value. These effects are attenuated by increasing dosages of remifentanil. Our data confirm that bispectral index is not a marker of analgesia.

Single-channel electroencephalography of epileptic seizures in the out-of-hospital setting: an observational study

Objectives To evaluate whether single-channel electroencephalography (EEG) recording can be conducted in the out-of-hospital setting and whether it can be used to record electrographic signs of convulsive epileptic seizures. Methods This prospective observational feasibility study included patients who presented with a recent or ongoing epileptic seizure during out-of-hospital emergency treatment. Bifrontal single-channel EEG recordings were conducted by ambulance physicians throughout the initial treatment. The data recorded were analysed for the quality of recording and the occurrence of ictal EEG patterns. Results There were 45 adult patients who had a recent or an ongoing epileptic seizure in the study group and 15 patients with no neurological disorders in the control group. The median percentage of time during which no artefacts were detected by the device was 88.0% in the study group and 96.0% in the control group. EEG recordings for 3 out of 45 (6.6%) patients were of poor quality and not evaluable. Spike/wave or polyspike patterns were found in 98% and 100% of patients in the study and control groups, respectively, whereas the occurrence of periodic epileptiform discharges and delta waves with spikes showed a sensitivity and specificity of 100% (10/10) for the presence of an ongoing epileptic seizure. Conclusions Single-channel EEG can be performed outside the hospital and yields useful recordings in most patients with acceptable rates of artefact. The diagnosis of generalised convulsive epileptic seizures by offline analysis of out-of-hospital EEG showed a high sensitivity and specificity when compared with the clinical diagnosis.

An assessment of global end-diastolic volume and extravascular lung water index during one-lung ventilation: is transpulmonary thermodilution usable?

BACKGROUND:The thermodilution curve assessed by transpulmonary thermodilution is the basis for calculation of global end-diastolic volume index (GEDI) and extravascular lung water index (EVLWI). Until now, it was unclear whether the method is affected by 1-lung ventilation. Therefore, aim of our study was to evaluate the impact of 1-lung ventilation on the thermodilution curve and assessment of GEDI and EVLWI. METHODS:In 23 pigs, mean transit time, down slope time, and difference in blood temperature (&Dgr;Tb) were assessed by transpulmonary thermodilution. “Gold standard” cardiac output was measured by pulmonary artery flowprobe (PAFP) and used for GEDIPAFP and EVLWIPAFP calculations. Measurements were performed during normovolemia during double-lung ventilation (M1), 15 minutes after 1-lung ventilation (M2) and during hypovolemia (blood withdrawal 20 mL/kg) during double-lung ventilation (M3) and again 15 minutes after 1-lung ventilation (M4). RESULTS:Configuration of the thermodilution curve was significantly affected by 1-lung ventilation demonstrated by an increase in &Dgr;Tb and a decrease in mean transit time and down slope time (all P < 0.04) during normovolemia and hypovolemia. GEDIPAFP was lower after 1-lung ventilation during normovolemia (M1: 459.9 ± 67.5 mL/m2; M2: 397.0 ± 54.8 mL/m2; P = 0.001) and hypovolemia (M3: 300.6 ± 40.9 mL/m2; M4: 275.2 ± 37.6 mL/m2; P = 0.03). EVLWIPAFP also decreased after 1-lung ventilation in normovolemia (M1: 9.0 [7.3, 10.1] mL/kg; M2: 7.4 [5.8, 8.3] mL/kg; P = 0.01) and hypovolemia (M3: 7.4 [6.3, 9.7] mL/kg; M4: 5.8 [5.2, 7.4]) mL/kg; P = 0.0009). CONCLUSION:Configuration of the thermodilution curve and therefore assessment of GEDI and EVLWI are significantly affected by 1-lung ventilation.

Relationship between Sevoflurane Plasma Concentration, Clinical Variables and Bispectral Index Values during Cardiopulmonary Bypass

Background Anesthetic administration is increasingly guided by electroencephalography (EEG)-based monitoring, such as the bispectral index (BIS). However, during cardiopulmonary bypass (CPB), factors other than the administered hypnotic agents may influence EEG signals, and their effects on BIS values are unknown. Methods This report is a secondary analysis of data from a prospective, controlled interventional study comparing the effect of sevoflurane administration guided by BIS monitoring (group SevoBIS) and constant administration of sevoflurane (group Sevo1.8Vol%) during CPB. Sevoflurane plasma concentration (SPC) was measured using gas chromatography. The relationships of BIS to SPC, CPB pump flow, arterial pressure, hematocrit, temperature, time on CPB, and patient characteristics were analysed. Results No association was observed between BIS values and SPC in group SevoBIS. In group Sevo1.8Vol%, a 40 μg ml-1 increase in SPC, which encompassed the entire range of observed values of the SPC in this analysis, was associated with a decrease of 3.6 (95% confidence interval (CI): 1.1–6.1) in BIS values (p = 0.005). Each increase in CPB time of 10 minutes was associated with an increase in BIS values of 0.25 (95%CI: 0.11–0.39, p<0.001). Path analysis revealed that the BIS values of SevoBIS patients were 5.3 (95%CI: 3.2–7.5) units higher than those of Sevo1.8Vol% patients (p<0.001), which was the strongest effect on BIS values. Path analysis revealed a slope of 0.5 (95%CI: 0.3–0.7) BIS units per 1°C body temperature (p<0.001). Conclusion BIS monitoring is insensitive to clinically relevant changes in SPC in individual patients during CPB.

Measuring Anesthetic Concentrations in the Exhaust Gas of the Oxygenator During Cardiopulmonary Bypass Can Be Unreliable.

580 www.anesthesia-analgesia.org anesthesia & anaLgesia sevoflurane in the exhaust port and the SPC was r = −0.044 (P = 0.530) in our study.2,6,7 Besides, if such a correlation existed, we would expect a reasonable correlation between sevoflurane concentration in the exhaust port and the parallel-derived bispectral index as well. However, we could not find any relevant correlation between the sevoflurane concentration measured in the exhaust port and the bispectral index values in our study sample (r = −0.13, P = 0.071).2 A possible explanation is that the gas exhaust of the oxygenator was connected to an anesthetic gas scavenging system with pressure-limited suction, which might have facilitated room-air admixture (Fig. 1). The results of other publications with good correlations might have been found without a scavenging system and a suction connected to the exhaust port. However, because of occupational medical reasons, we find a scavenging system necessary to minimize the workplace exposure to volatile anesthetics. This substantiates our conclusion that the concentration of volatile anesthetics measured in the exhaust port must be cautiously handled when dosing volatile anesthetics during CPB.

Electroencephalography during out-of-hospital cardiopulmonary resuscitation.

BACKGROUND At the present time there is no parameter that can estimate the quality of cerebral perfusion and possible success of cerebral resuscitation during advanced cardiac life support (ACLS) efforts. In recent years, various attempts have been made to use electroencephalography (EEG)-based cerebral neuromonitoring to assess the effectiveness of cardiopulmonary resuscitation (CPR). OBJECTIVES The Cerebral State Monitor M3 (Danmeter A/S, Odense, Denmark) is a portable, single-channel EEG monitor that provides the user with different EEG-based parameters and the raw waveform EEG to measure cerebral activity. CASE REPORT We report two cases of out-of-hospital CPR with single-channel EEG monitoring conducted parallel to ACLS with external chest compressions. We demonstrate an artifact in waveform EEG recordings that is caused by the external chest compressions, and that leads to a miscalculation of the Burst Suppression Ratio and Cerebral State Index. CONCLUSION These cases suggest that digitally processed EEG-monitoring is not a useful tool during CPR.