Comparison of heart rate variability response in children undergoing elective endotracheal intubation with and without neuromuscular blockade: a randomized controlled trial.

BACKGROUND: The routine use of neuromuscular blocking drugs (NMBD) for endotracheal intubation in children is the subject of much controversy. The analysis of heart rate variability (HRV) can reveal information about the functional state of the autonomic nervous system (ANS). AIM: The purpose of this study was to determine if HRV elucidates differences in the sympathovagal balance of children undergoing elective endo-tracheal intubation with and without neuromuscular blockade (NMB). METHODS: In this prospective study, 38 children (2-6 years) scheduled for adenotonsillectomy were randomized into two groups to receive fentanyl 2 µg·kg(-1) and propofol 4 mg·kg(-1) , with either mivacurium 0.25 mg·kg(-1) (NMB group) or saline solution (NoNMB group) for anesthesia induction. The same experienced, blinded anesthesiologist performed endotracheal intubation. Heart rate variability, RR intervals, ECG as well as an electroencephalogram were recorded with HRV and BIS XP monitors, respectively. Heart rate variability was analyzed in the frequency domain. RESULTS: There was no significant difference in HRV changes immediately after mivacurium administration compared with an administration of saline. The groups were comparable for the bispectral index value (NMB 35 [33-41] vs NoNMB 34 [32-42]) during endotracheal intubation. Changes in both the low-frequency power and the low-/high-frequency ratio immediately after endotracheal intubation compared with the unstimulated state before laryngoscopy were significantly higher without NMB (P = 0.015 and P = 0.006, respectively), whereas there was no significant difference with respect to the high-frequency power. CONCLUSIONS: The stress response during endotracheal intubation in pediatric patients represented by the frequency domain analysis of HRV was found to be higher without NMB. When mivacurium was added to a propofol-fentanyl induction regimen, the ANS alterations during endotracheal intubation decreased significantly.

[Blood pressure control in the area of surgical interventions]. / Blutdruckregelung im Umfeld chirurgischer Interventionen.

For specific surgical interventions, such as aortic stent implantation, it might be temporarily necessary to decrease mean arterial pressure to rather low levels (around 40 mm Hg). Such hypotensive pressure levels are necessary to avoid intra- and postoperative intricacies. Traditionally, the drug Nitroprussidnatrium is used for this task. To adjust the correct amount of drug to reach the target pressure as fast as possible and without overshoot, the anaesthetists typically use empirical knowledge and might need several minutes until the target point is reached. In our research group, an adaptive control system was developed for this task which is able to compute and set the transient drug release automatically. For the design and testing of the adaptive control strategy, the well known Guyton model was implemented into the MATLAB/Simulink development environment. This paper describes the implementation and adaption of the Guyton model to hypotensive pressure control and provides some algorithmic details of the adaptive control strategy for automatic drug delivery in deep hypotension. The designed control system was successfully validated in animal trials (25 trials on 7 pigs). Following this, an additional controller component for increase of blood pressure with the help of the drug Noradrenalin was implemented. It is now possible to increase blood pressure to a specific value to save defined cerebral perfusion pressure for patients with craniocerebral injury. In a second pilot trial, this controller extension was tested in 10 pigs.

The benefits of using Guyton's model in a hypotensive control system.

In order to improve the intraoperative applications, this paper presents the advantages of using Guyton's model in hypotensive control system development. In this system, the mean arterial pressure is decreased and maintained at a low level during anaesthesia by controlling sodium nitroprusside infusion rate. The key of the study is to develop a physiological model of cardiovascular dynamics to present the mean arterial pressure response to sodium nitroprusside, which was considered as a linear model in most of known blood pressure control systems. Being linear, the previous models cannot accurately mimic a physiological system of human circulation, especially at deep hypotensive control with strong reaction of the body. The enhanced model in this study was modified based on Guyton's model of human circulation. It is useful to design a PID controller, which allows studying and handling the wide range of the body sensitivities. This model is also helpful for studying the behaviors of patients under anaesthesia conditions, such as the perfusion of organs and the reaction of the body at hypotensive state. A fuzzy gain scheduler and a supervising algorithm were also developed for online tuning the controller to handle the behavior of the body. The control system was tested on 25 experiments on seven pigs in the animal laboratory. Simulation and experiment results proved the usefulness of Guyton's model in control system design which can present the dynamical response of blood pressure in the circulation under and after hypotensive control. The results also indicated the safety and stability of the controller.

A surgical technique for catheterization of the sagittal sinus in pigs.

The purpose of our study was to describe an efficient, reliable and inexpensive surgical method for cerebral venous blood gas sampling in acutely instrumented pigs in a research setting. Parameters from the blood samples are used to monitor brain perfusion and oxygenation in different animal models. To the authors' knowledge, this is the first detailed description of an accurate surgical technique for catheterization of the sagittal sinus in pigs.

Design and implementation of a control system reflecting the level of analgesia during general anesthesia.

INTRODUCTION: Measuring and ensuring an adequate level of analgesia in patients are of increasing interest in the area of automated drug delivery during general anesthesia. Therefore, the aim of this investigation was to develop a control system that may reflect the intraoperative analgesia value. Our hypothesis was that a feedback controller could be applied in clinical practice safely and at an adequate quality of analgesia. The purpose of this study was to evaluate the practical feasibility of such a system in a clinical setting. METHODS: The control system for the level of analgesia described in this paper relies on a parameter combination of heart rate variability (HRV), heart rate (HR), and blood pressure (mean arterial pressure, MAP), which serve as input variables for an expert system. For this fuzzy system, the experience of the participating anesthesiologists was translated into a set of fuzzy rules. In a pilot trial, the control system for automated titration of remifentanil, a short-acting opioid, was tested combined with a closed-loop propofol infusion system for hypnosis. Ten adult patients (4 women, 6 men), aged 22-52 years (median, 45 years; range, 29-49 years), with an American Society of Anesthesiologists physical status class I or II and who were scheduled for elective trauma surgery in a supine position were enrolled in this prospective trial. The precision of the system was calculated using internationally defined performance parameters. RESULTS: There was no human intervention necessary during the computer-controlled administration of propofol and remifentanil, and operating conditions were satisfactory in all patients. All patients assessed the quality of anesthesia as "good" to "very good". Median performance error, median absolute performance error, and wobble for HR and MAP during maintenance of anesthesia were -8.98 (5.32), 10.08 (4.17), and 2.68 (1.29) and -4.51 (12.73), 13.63 (2.27), and 3.90 (2.08) [mean (SD)], respectively. CONCLUSION: The control system, reflecting the level of analgesia during general anesthesia designed and evaluated in this study, allows for a clinically practical, nearly fully automated infusion of an opioid during medium-length surgical procedures with acceptable technical requirements and an adequate precision.

The impact of intra-aortic balloon pumping on cardiac output determination by pulmonary arterial and transpulmonary thermodilution in pigs.

OBJECTIVE: The aim of this study was to evaluate the impact of intra-aortic balloon pumping (IABP) on the comparison of simultaneous measurements of cardiac output via pulmonary arterial and transpulmonary thermodilution (PiCCO; Pulsion Medical Systems, Munich, Germany). DESIGN: Prospective. SETTINGS: University research laboratory. PARTICIPANTS: The data were derived from 9 anesthetized (fentanyl, propofol, flunitrazepam, rocuronium) and ventilated pigs. INTERVENTIONS: A thermodilution catheter was inserted into the pulmonary artery, a PiCCO catheter into the abdominal aorta through the right femoral artery, epicardial atrial pacing wires through a thoracotomy, and a balloon catheter for counterpulsation into the descending thoracic aorta through the left femoral artery. Cardiac output was varied over a wide range by cardiac pacing between 80 and 150/min in steps of 10/min and was measured without and during IABP at an assist frequency of 1:1. MEASUREMENTS AND MAIN RESULTS: A total of 236 paired cardiac output measurements were carried out in a range of cardiac output between 1.4 to 4.9 L/min. A close correlation was found between transpulmonary and pulmonary arterial thermodilution both without and during IABP (r = 0.94 and 0.93, respectively) and a good agreement of both methods (bias of 0.30 and 0.26 L/min, respectively; precision 0.47 and 0.52 L/min, respectively). CONCLUSIONS: Transpulmonary thermodilution is suitable for cardiac output measurement during IABP. Hence, in critically ill patients with cardiac pump failure, blood flow may be determined as accurately with the less-invasive transpulmonary method as with the traditional pulmonary arterial thermodilution one.