The effect of passive leg-raising maneuver on hemodynamic stability during anesthesia induction for adult cardiac surgery

Blood pressure response to clonidine in children with short stature is correlated with postural characteristics: a retrospective cross-sectional study

BACKGROUND

Clonidine stimulation test has been widely used in the diagnosis of growth hormone deficiency in children with short stature with a high level of reliability. However, it may cause hypotension, which usually appears as headache, dizziness, bradycardia, and even syncope. It is well known that elevating the beds to make patients' feet above their cardiac level might relieve this discomfort. However, the real efficiency of this method remains to be proved while the best angle for the elevated bed is still unclear.

METHODS

A total of 1200 children with short stature were enrolled in this retrospective cross-sectional study. Age, gender, weight, and basic systolic and diastolic blood pressure were collected. Blood pressure at 1, 2, 3, and 4 h after stimulation tests were recorded. The participants were divided into 3 groups based on the angles of the elevated foot of their beds named 0°, 20°, and 40° groups.

RESULTS

At one hour after the commencement of the tests, participants lying on the elevated beds showed a higher mean increase on the change of pulse pressure. The difference in the angles of the elevated beds did not show statistical significance compared with those who did not elevate their beds (0.13 vs. 2.83, P = 0.001; 0.13 vs. 2.18, P = 0.005; 2.83 vs. 2.18, P = 0.369). When it came to 4 h after the tests began, participants whose beds were elevated at an angle around 20° had a significantly higher mean increase in the change of pulse pressure values compared with those whose beds were elevated at an angle around 40° (1.46 vs. -0.05, P = 0.042).

CONCLUSION

Elevating the foot of the beds of the patients who are undergoing clonidine stimulation tests at an angle of 20°might be a good choice to alleviate the hypotension caused by the tests.

Prediction of post-induction hypotension by point-of-care echocardiography: A prospective observational study

BACKGROUND

Post-induction hypotension (PIH) is a common side effect of general anaesthesia and is associated with poor perioperative outcomes. We assessed the ability of two point-of-care echocardiographic variables to predict the occurrence of PIH: the passive leg raising-induced changes in the velocity-time integral of the left ventricular outflow tract (ΔVTI-PLR) and the inferior vena cava collapsibility index (IVC-CI).

METHODS

We studied 64 patients > 50 years scheduled for elective abdominal surgery. ΔVTI-PLR and IVC-CI were prospectively obtained before general anaesthesia induction. PIH was defined by a systolic arterial pressure < 90 mmHg or a mean arterial pressure < 65 mmHg or by a decrease in systolic or mean arterial pressure > 30% from pre-induction level. Intraclass correlation coefficients (ICCs) were calculated to assess the reproducibility of echocardiographic measurements. Receiver operating characteristic (ROC) curves with 95% confidence intervals (CIs) were generated to test the ability of ΔVTI-PLR and IVC-CI to predict the occurrence of PIH.

RESULTS

PIH occurred in 33 (51%) patients. The ICCs for VTI and IVC measurements showed excellent reproducibility. The occurrence of PIH was accurately predicted by ΔVTI-PLR with an area under the ROC curve (AUROC) of 0.89 (95% CI: 0.80-0.97), a threshold value of 18% with a sensitivity of 88% (95% CI: 71-97%) and a specificity of 84% (95% CI: 66-94%). The occurrence of PIH was poorly predicted by IVC-CI with an AUROC of 0.68 (95% CI: 0.54-0.80) and a threshold value of 42%.

CONCLUSIONS

ΔVTI-PLR, unlike IVC-CI, could reliably predict the occurrence of PIH. The use of ΔVTI-PLR could help individualise anaesthesia management to prevent PIH.

Assessing rheoencephalography dynamics through analysis of the interactions among brain and cardiac networks during general anesthesia

Cerebral blood flow (CBF) reflects the rate of delivery of arterial blood to the brain. Since no nutrients, oxygen or water can be stored in the cranial cavity due to space and pressure restrictions, a continuous perfusion of the brain is critical for survival. Anesthetic procedures are known to affect cerebral hemodynamics, but CBF is only monitored in critical patients due, among others, to the lack of a continuous and affordable bedside monitor for this purpose. A potential solution through bioelectrical impedance technology, also known as rheoencephalography (REG), is proposed, that could fill the existing gap for a low-cost and effective CBF monitoring tool. The underlying hypothesis is that REG signals carry information on CBF that might be recovered by means of the application of advanced signal processing techniques, allowing to track CBF alterations during anesthetic procedures. The analysis of REG signals was based on geometric features extracted from the time domain in the first place, since this is the standard processing strategy for this type of physiological data. Geometric features were tested to distinguish between different anesthetic depths, and they proved to be capable of tracking cerebral hemodynamic changes during anesthesia. Furthermore, an approach based on Poincaré plot features was proposed, where the reconstructed attractors form REG signals showed significant differences between different anesthetic states. This was a key finding, providing an alternative to standard processing of REG signals and supporting the hypothesis that REG signals do carry CBF information. Furthermore, the analysis of cerebral hemodynamics during anesthetic procedures was performed by means of studying causal relationships between global hemodynamics, cerebral hemodynamics and electroencephalogram (EEG) based-parameters. Interactions were detected during anesthetic drug infusion and patient positioning (Trendelenburg positioning and passive leg raise), providing evidence of the causal coupling between hemodynamics and brain activity. The provided alternative of REG signal processing confirmed the hypothesis that REG signals carry information on CBF. The simplicity of the technology, together with its low cost and easily interpretable outcomes, should provide a new opportunity for REG to reach standard clinical practice. Moreover, causal relationships among the hemodynamic physiological signals and brain activity were assessed, suggesting that the inclusion of REG information in depth of anesthesia monitors could be of valuable use to prevent unwanted CBF alterations during anesthetic procedures.