SAMAY S24: a novel wireless 'online' device for real-time monitoring and analysis of volumetric capnography.

Volumetric capnography (VCap) provides information about CO2 exhaled per breath (VCO2br) and physiologic dead space (VDphys). A novel wireless device with a high response time CO2 mainstream sensor coupled with a digital flowmeter was designed to monitor all VCap parameters online in rabbits (SAMAY S24).Ten New Zealand rabbits were anesthetized and mechanically ventilated. VCO2br corresponds to the area under the VCap curve. We used the modified Langley method to assess the airway VD (VDaw) and the alveolar CO2 pressure. VDphys was estimated using Bohr's formula, and the alveolar VD was calculated by subtracting VDaw from VDphys. We compared (Bland-Altman) the critical VCap parameters obtained by SAMAY S24 (Langley) with the Functional Approximation based on the Levenberg-Marquardt Algorithm (FA-LMA) approach during closed and opened chest conditions.SAMAY S24 could assess dead space volumes and VCap shape in real time with similar accuracy and precision compared to the 'offline' FA-LMA approach. The opened chest condition impaired CO2 kinetics, decreasing the phase II slope, which was correlated with the volume of CO2 exhaled per minute.

Inferior vena cava ultrasonography before general anesthesia cannot predict arterial hypotension in patients undergoing vascular surgery.

INTRODUCTION: Intraoperative hypotension (IH) is an independent predictor of mortality. Some experts have suggested that ultrasound measurement of the inferior vena cava (IVC) in spontaneous ventilation can predict IH. OBJECTIVE: To evaluate the capacity of ultrasound measures of IVC in spontaneous ventilation to predict episodes of IH after anaesthesia induction. PATIENTS AND METHODS: We studied 55 high-risk cardiac patients undergoing vascular surgery. The maximum (dIVCmax) and minimum (dIVCmin) diameter of the IVC were measured and the collapsibility index CI = (dIVCmax-dIVCmin)/dIVCmax was calculated prior to anaesthesia induction. Three definitions of IH were used: systolic blood pressure (SBP) less than 100 mmHg, mean arterial pressure (MAP) less than 60 mmHg, and a decrease in MAP greater than or equal to 30% compared to baseline. RESULTS: There were no significant differences in dIVCmax or in CI between patients presenting IH after anaesthesia induction and those who did not. ROC curves for dIVCmax showed an area under the curve of 0.55 (0.39-0.70), 0.69 (0.48-0.90), and 0.57 (0.42-0.73) and ROC curves for the CI were 0.62 (0.47-0.78), 0.60 (0.41-0.78) and 0.62 (0.47-0.78) for the 3 definitions of IH (<100 mmHg, MAP < 60 mmHg, and MAP ≥30% baseline), respectively. CONCLUSIONS: Ultrasound measurements of IVC in spontaneous ventilation are not good predictors of IH after anaesthesia induction in these patients. The optimal cut-off points show low specificity and moderate sensitivity for predicting IH.

Microcirculatory changes during cardiac surgery with cardiopulmonary bypass. / Alteraciones microcirculatorias en cirugía cardíaca con circulación extracorpórea.

OBJECTIVE: To evaluate microcirculation in intermediate and high mortality risk patients undergoing cardiac surgery (CS) with cardiopulmonary bypass (CPB). PATIENTS AND METHODS: The study included 22 patients with a Euroscore >3. Using the Videomicroscopy Side Stream Dark Field system, and evaluation was made of, capillary density, proportion of perfused capillaries, density of perfused capillaries, microcirculatory flow index (MFI), and heterogeneity flow index. Three to five video sequences were recorded: after induction of anaesthesia (T1), at the beginning of the CPB (T2), before finalising CPB (T3), at the end of the surgery, and before the patient was transferred to Intensive Care Unit (T4). Mean arterial pressure decreased, while the blood lactate increased significantly, when comparing the initial and final values (P<.05). MFI increased significantly in T3 and T4 (P<.05) with regards to the initial values. When the patients with and without postoperative complications were compared, significant differences were found in, Euroscore, left ventricular ejection fraction, and MFI in T3. CONCLUSIONS: in patients with intermediate/high preoperative risk, CS and CBP can involve an increase in MFI and blood lactate at the end of the study. These alterations suggest the possibility of a functional microcirculatory shunt at tissue perfusion level, secondary to the surgical injury and the CPB. Further investigation is needed to have a better understanding of the mechanisms involved.

[The changes in the oxygen saturations in the superior vena cava and the pulmonary artery are not the same during cardiac surgery]. / Las tendencias en el tiempo de las saturaciones de oxígeno en la vena cava superior y la arteria pulmonar no son equivalentes en cirugía cardiaca.

OBJECTIVE: To evaluate the changes over time (trend) in sign and magnitude for SSVO2 and SVO2 during and after cardiac surgery. PATIENTS AND METHODS: A prospective and observational study was conducted on 34 cardiac surgery patients. Venous blood samples were taken simultaneously from the introductor (SVCO2) and distal (SVO2) port of the pulmonary artery catheter at predefined intervals. Systemic and pulmonary hemodynamic variables were measured at the same time. The trend was calculated as the difference between 2 consecutive measurements (tSO2). Data were processed with ANOVA for multiple comparisons, Pearson correlation coefficient and Bland-Altman analysis. RESULTS: There was a significant correlation between SVCO2 and tSVO2 (R(2)=0.55), the mean of the differences was 0.36±7.75%, and the limits of agreement ranged from -15.1 to 15.9%. The sign of the trend was similar in 85.1% of the paired data. However, the magnitude of the changes in tSVCO2 and tSVO2 were not always equivalent. Between 0 and 5% of the change in the tSVCO2 was coincident with only 44.7% of the tSVO2. A wide variation was found between both trends when the signs and magnitudes of the changes were taken into account. CONCLUSIONS: When considering the sign and magnitude, the change over time of central venous O2 saturations were not interchangeable in cardiac surgery patients. Clinical decisions based exclusively on tSVCO2 monitoring should be taken with caution.

Contribution of the coronary sinus blood to the pulmonary artery oxygen saturation gradient in cardiac surgery patients.

BACKGROUND: The coronary sinus oxygen saturation (SO2) can affect the oxygen saturation of the superior vena cava (superior cava SO2) and the pulmonary artery (pulmonary artery SO2), causing a gradient between the latter two (ΔSO2), as has been observed in different physiological and pathological conditions. The objective of the study was to evaluate the different determinants of ΔSO2 in cardiac surgery patients. METHODS: An observational, prospective study was carried out on 18 patients undergoing elective cardiac surgery. Blood samples were obtained from the superior vena cava, the pulmonary artery, the inferior vena cava, and the coronary sinus before extracorporeal circulation. RESULTS: The following measurements were made: superior cava SO2, pulmonary artery SO2, coronary sinus SO2, and inferior cava SO2. The mean values (± SD) were as follows: superior cava SO2=76.4±12.6%; inferior cava SO2=72.7±15.8%; coronary sinus SO2=46.6±17.0%; and pulmonary artery SO2=71.9±12.9%. The ΔSO2 was 4.5±5.5%. The average oxygen saturation (SO2avg=[Superior cava SO2 + inferior cava SO2]/2) was 74.6±13.7%. The superior cava SO2 was significantly higher than the pulmonary artery SO2, and the ΔSO2 was significantly different from zero (P≤0.05). No significant differences were found between the superior cava SO2 and the inferior cava SO2, and both were significantly different from the coronary sinus SO2. The difference between SO2avg and the pulmonary artery SO2 was 2.74±4.4%. CONCLUSION: The observed ΔSO2 could only be explained by dilution of the superior cava SO2 with blood with a lower SO2. The coronary sinus blood contributed to generate this gradient.

[Orotracheal intubation training: assessment with the cumulative sum method]. / Evaluación del aprendizaje de la Intubación Orotraqueal mediante el método de la suma acumulativa (CuSum).

OBJECTIVES: Orotracheal intubation is one of the first techniques a new resident learns. The cumulative sum (cusum) method has been shown to be a useful tool for the assessment of learning, as it provides qualitative and quantitative information that allows technical competence to be certified. The aim of this study was to use the cusum method to assess the learning of orotracheal intubation by a group of first year residents. METHODS: The residents were evaluated at 2 stages. In the first, the acceptable failure rate was set at 10% and in the second it was reduced to 5%. Learning curves were constructed for each resident for both stages. RESULTS: Eight residents were evaluated. They performed 868 intubations, 330 at the first stage and 538 at the second. Forty (4.6%) of the intubations failed: 26 (7.9%) in the first stage and 14 (2.6%) in the second. All residents achieved the acceptable failure rate of 10% in the first 3 months with a mean (SD) number of intubations of 41.3 (6). All achieved the 5% acceptable failure rate within the 11 months of study, after a mean of 67.3 (28) intubations. CONCLUSIONS: The cusum method proved a useful tool for training residents to perform tracheal intubation. It afforded objective information on performance and facilitated evaluation while learning was taking place.