A surgical technique for a terminal intracranial hypertension model in pigs.

The life-threatening effects of intracranial hypertension on brain perfusion and cerebral metabolism are the subject of current research in different animal models. The purpose of this study was to describe an efficient, reliable and inexpensive surgical method for temporary elevation of intracranial pressure (ICP) in acutely instrumented pigs in a research setting. Therefore, a balloon catheter was inserted into the left lateral ventricle and an ICP sensor was placed in the parenchyma of the right cerebral hemisphere. Ten acutely instrumented pigs were studied while under deep terminal general anaesthesia. The step-by-step inflation of the intraventricular balloon allows one to achieve the desired ICP up to 46 mmHg and maintain it at this level. ICP values ranged from a median of 2 (1-2) mmHg to 43 (29-45) mmHg. To the authors' knowledge, this is the first detailed description of a minimally invasive surgical technique for temporary ICP elevation in pigs via stepwise inflation of an intraventricular balloon.

Clinical evaluation of a simultaneous closed-loop anaesthesia control system for depth of anaesthesia and neuromuscular blockade*.

We developed a closed-loop system to control the depth of anaesthesia and neuromuscular blockade using the bispectral index and the electromyogram simultaneously and evaluated the clinical performance of this combined system for general anaesthesia. Twenty-two adult patients were included in this study. Anaesthesia was induced by a continuous infusion of remifentanil at 0.4 µg.kg(-1) .min(-1) (induction dose) and then 0.25 µg.kg(-1) .min(-1) (maintenance dose) and propofol at 2 mg.kg(-1) 3 min later. The combined automatic control was started 2 min after tracheal intubation. The depth of anaesthesia was recorded using bispectral index monitoring using a target value of 40. The target value of neuromuscular blockade, using mivacurium, was a T1/T1(0) twitch height of 10%. The precision of the system was calculated using internationally defined performance parameters. Twenty patients were included in the data analysis. The mean (SD) duration of simultaneous control was 129 (69) min. No human intervention was necessary during the computer-controlled administration of propofol and mivacurium. All patients assessed the quality of anaesthesia as 'good' to 'very good'; there were no episodes of awareness. The mean (SD) median performance error, median absolute performance error and wobble for the control of depth of anaesthesia and for neuromuscular blockade were -0.31 (1.78), 6.76 (3.45), 6.32 (2.93) and -0.38 (1.68), 3.75 (4.83), 3.63 (4.69), respectively. The simultaneous closed-loop system using propofol and mivacurium was able to maintain the target values with a high level of precision in a clinical setting.

[Feedback control of depth of anesthesia during propofol administration. Bispectral index as the controlled variable]. / Regelkreisgesteuerte Narkosetiefe bei Propofolapplikation. Verwendung des Bispektralindex als Regelungsgrösse.

BACKGROUND: The objective of this study was to evaluate the performance of a new system for closed-loop control of propofol administration using the bispectral index (BIS) under total intravenous anesthesia in the index values of middle-to-deep depth of anaesthesia. METHODS: In this study 20 adult patients anesthetized with propofol and remifentanil were investigated. The propofol infusion was carried out using a fuzzy-PD+I controller with a target BIS value of 40. RESULTS: Closed-loop control was able to provide maintenance of anesthesia and adequate operating conditions for all patients. The following quality control criteria were calculated: median performance error (MDPE; 0.16%, SD +/-1.4%), median absolute performance error (MDAPE; 6.9%, SD +/-2.8%) and wobble (6.8%, SD +/-2.5%). CONCLUSION: The present study showed the clinical feasibility of the controller compared to existing devices regarding a high level of quality criteria of a model with an implemented fuzzy-PD+I structure controlling depth of hypnosis.

[Feedback control of muscle relaxation with a varying on-off controller using cisatracurium]. / Regelkreisgesteuerte Muskelrelaxation mit einem modifizierten Zweipunktregler mit Cisatracurium.

BACKGROUND: Under clinical conditions constant neuromuscular blockade can also be maintained by a simple closed-loop system. However, delayed onset time, non-linearity of the dose-response curve and different sensitivity to muscle relaxants for each patient are limiting factors. METHODS: In 20 patients who underwent elective surgical procedures under continuous propofol/alfentanil anaesthesia and relaxation with cisatracurium, the maintenance of an electromyographically controlled cisatracurium block of 90% was achieved by a varying on-off control system. Using an own computer-aided measuring device, the course of the neuromuscular blockade and deviations from the desired neuromuscular block were registered. RESULTS: Over a period of 64.2+/-14.0 min, neuromuscular block could be controlled on average at a T(1)-level of 10% (90% block). The mean error of the deviation of the obtained neuromuscular blockade from the set-point was -1.6+/-0.9% on average. To maintain this neuromuscular blockade, a dose rate of 1.4+/-0.9 micro g x kg(-1) x min(-1) cisatracurium was necessary. CONCLUSIONS: It can be concluded that a simple closed-loop system allows the safe use of the intermediate term muscle relaxant cisatracurium for the performance of surgical procedures.

[The syringe pump as actuator--a practical application problem of feedback control systems]. / Die Spritzenpumpe als Stellglied--Ein Problem im praktischen Einsatz regelkreisgesteuerter Systeme.

Based on a computer simulation programme, the accuracy of the Graseby 3400 syringe pump was tested for its use in a feedback control system of the neuromuscular block. Firstly, a calculation of errors to determine the difference between the target and actual flow rates was carried out. Next, the characteristic curves of the syringe pump were determined under different flow and sampling rates to correct the application software of the feedback controller with a view to obtaining the correct flow rates online. It was discovered that, particularly with short 12 s sampling rates, dose-dependent errors of almost 100% were provable. Therefore, the application of a robust controller and integration of the characteristic curves at the outlet of the controller software are required. For the adoption of syringe pumps in medical feedback control systems, definite determination of the actual infusion quantity using an exact calculation of errors is required. Especially in cases of short sampling rates in combination with low infusion quantities, the syringe pump comes almost to a standstill, which results in extreme differences between target and actual flow rates.