The discriminatory value of cardiorespiratory interactions in distinguishing awake from anaesthetised states: a randomised observational study.

Depth of anaesthesia monitors usually analyse cerebral function with or without other physiological signals; non-invasive monitoring of the measured cardiorespiratory signals alone would offer a simple, practical alternative. We aimed to investigate whether such signals, analysed with novel, non-linear dynamic methods, would distinguish between the awake and anaesthetised states. We recorded ECG, respiration, skin temperature, pulse and skin conductivity before and during general anaesthesia in 27 subjects in good cardiovascular health, randomly allocated to receive propofol or sevoflurane. Mean values, variability and dynamic interactions were determined. Respiratory rate (p = 0.0002), skin conductivity (p = 0.03) and skin temperature (p = 0.00006) changed with sevoflurane, and skin temperature (p = 0.0005) with propofol. Pulse transit time increased by 17% with sevoflurane (p = 0.02) and 11% with propofol (p = 0.007). Sevoflurane reduced the wavelet energy of heart (p = 0.0004) and respiratory (p = 0.02) rate variability at all frequencies, whereas propofol decreased only the heart rate variability below 0.021 Hz (p < 0.05). The phase coherence was reduced by both agents at frequencies below 0.145 Hz (p < 0.05), whereas the cardiorespiratory synchronisation time was increased (p < 0.05). A classification analysis based on an optimal set of discriminatory parameters distinguished with 95% success between the awake and anaesthetised states. We suggest that these results can contribute to the design of new monitors of anaesthetic depth based on cardiovascular signals alone.

Dynamic variables and fluid responsiveness in patients for aortic stenosis surgery.

BACKGROUND: Aortic stenosis is the most common valvular disease in developed countries, but it carries an increased mortality during non-cardiac surgery underscoring the importance of adequate hemodynamic management. Further, haemodynamic management of patients immediately after surgery for aortic stenosis can be challenging. Prediction of fluid responsiveness using dynamic variables has not been sufficiently studied in patients for aortic stenosis surgery. METHODS: Observational study evaluating fluid responsiveness on 32 (31 analysed) patients scheduled for aortic valve replacement due to aortic stenosis on mechanical ventilation before and after valve replacement. Increase in stroke volume (oesophagus Doppler) ≥ 15% to a fluid challenge defined fluid responders. RESULTS: Before surgery (31 fluid loads performed in 31 patients), areas under receiver operating characteristics curves (95% confidence intervals) were stroke volume variation (from arterial pulse contour analysis) 0.77 (0.58-0.90), pulse pressure variation 0.75 (0.54-0.90) and Pleth variability index 0.51 (0.31-0.69). After aortic valve replacement (31 fluid loads performed in 23 patients) the values were stroke volume variation 0.90 (0.74-0.98), pulse pressure variation 0.95 (0.80-1.0) and Pleth variability index 0.72 (0.52-0.87). CONCLUSIONS: The arterial pressure-based variables had moderate predictive values before valve replacement, but it predicted fluid responsiveness well postoperatively. Pleth variability index did not predict fluid responsiveness preoperatively, and it had a moderate predictive value postoperatively. These results indicate that arterial pressure-based dynamic variables have limited potential to guide fluid therapy in patients with aortic stenosis. Their ability to guide fluid therapy after aortic valve replacement seems better.

Impact of enzymatic degradation of the endothelial glycocalyx on vascular permeability in an awake hamster model.

Background. The inside of the endothelium is covered by a glycocalyx layer, and enzymatic degradation of this layer induces vascular leakage ex vivo. We hypothesized that enzymatic degrading of the glycocalyx in an in vivo, whole body model, would induce plasma leakage and affect the microcirculation. Methods. Golden Syrian hamsters were divided into an enzyme (hyaluronidase) and a control group. Mean arterial pressure (MAP), heart rate (HR), hematocrit (Hct), base excess (BE), and plasma volume were obtained before, 45 and 120 min after enzyme/saline treatment. Plasma volume was evaluated by the distribution volume of indocyanine green and the microcirculation by functional capillary density (FCD). The enzymatic effect was determined by measuring plasma levels of hyaluronan (HA). Results. There were no differences in MAP, HR, Hct, and BE between the two groups. Enzyme treatment did not induce changes in plasma volume but reduced FCD. There was a 50-100-fold increase in plasma HA, but no relationship was found between HA levels and plasma volume or FCD. Conclusion. Vascular leakage was not confirmed in an in vivo, whole body model after degradation of the endothelial glycocalyx. The microcirculation was affected, but no relationship between plasma levels of HA and FCD was seen.

Dynamic variables of fluid responsiveness during pneumoperitoneum and laparoscopic surgery.

BACKGROUND: Few data exist on dynamic variables predicting fluid responsiveness during laparoscopic surgery. The aim of this study was to explore the effects of laparoscopy on four dynamic variables: respiratory variations in pulse pressure (ΔPP), stroke volume variation by Vigileo/FloTrac (SVV (Vigileo) ), pleth variability index (PVI) and respiratory variations in pulse oximetry plethysmography waveform amplitude (ΔPOP), and their relation to fluid challenges during laparoscopic surgery. METHODS: ΔPP, SVV (Vigileo) , PVI and ΔPOP were studied in 20 adult patients before and during pneumoperitoneum (10-12 mmHg). During ongoing laparoscopic surgery, relations between the dynamic variables and changes in stroke volume oesophageal Doppler, (SV(OD) ) after fluid challenges (250 ml colloid) were evaluated. RESULTS: Pneumoperitoneum changed the dynamic variables as follows {mean [95% confidence interval (CI)]}: ΔPP 0.5 (-1.3, 2.3)%, P = 0.53; SVV (Vigileo) 0.6 (-1.3, 2.5)%, P = 0.52; PVI 2.9 (0.4, 5.3)%, P = 0.025. For ΔPOP, median difference (95% CI) was 2.5 (-0.15, 6.7)%, P = 0.058. During laparoscopic surgery, areas under receiver operating characteristics curves (95% CI) were ΔPP 0.53 (0.31-0.75), SVV (Vigileo) 0.74 (0.51-0.90), PVI 0.61 (0.38-0.81), ΔPOP 0.63 (0.40-0.82). Correlation coefficients (P-values) between changes in dynamic variables and changes in SV(OD) were ΔPP r = -0.65, P = 0.009; SVV (Vigileo) r = -0.73, P = 0.002; PVI r = -0.22, P = 0.44; ΔPOP r = -0.32, P = 0.24. CONCLUSION: ΔPP and SVV (Vigileo) did not change as pneumoperitoneum was established, whereas PVI increased and ΔPOP tended to increase. All four dynamic variables predicted fluid responsiveness relatively poor during ongoing laparoscopic surgery. ΔPP and SVV (Vigileo) tracked changes in stroke volume induced by fluid challenges during ongoing laparascopic surgery, whereas ΔPOP and PVI did not.

Photoplethysmographic and pulse pressure variations during abdominal surgery.

BACKGROUND: Respiratory variations in pulse pressure (ΔPP) predict fluid responsiveness during mechanical ventilation. Variations in pulse oximetry plethysmography amplitude (ΔPOP) are proposed as a non-invasive alternative. Large variations in ΔPOP and poor agreement between ΔPP and ΔPOP are found in intensive care unit patients. General anaesthesia is suggested to reduce variability of ΔPOP and improve agreement between the variables. We evaluated the variability of the agreement between and the diagnostic values of ΔPP and ΔPOP during ongoing open abdominal surgery. The variability of diagnostic methods in specific clinical conditions is important, as this reflects the stability over time during which clinical decisions are made. METHODS: Observational study during open abdominal surgery in general anaesthesia. ΔPP and ΔPOP were calculated semi-automatically from recording periods of approximately 5 min both before and after fluid challenges. Fluid responsiveness was evaluated by changes in stroke volume (oesophageal Doppler) after 250 ml colloid. RESULTS: Thirty-four fluid challenges were performed in 25 patients. Variance both within registration periods and between patients were significantly larger for ΔPOP than for ΔPP (54.1% vs. 22.1% and 69.6% vs. 22.6%, respectively, both P < 0.001). Limits of agreement with a regression-based correction were ± 13.9%. Areas under receiver operating characteristics curves for fluid responsiveness were 0.67 for ΔPP and 0.72 for ΔPOP. CONCLUSIONS: Analysis of raw signals during open abdominal surgery documents that the variance of ΔPOP is larger than of ΔPP, with wide limits of agreement between ΔPP and ΔPOP. The diagnostic values of ΔPP and ΔPOP are relatively poor.