Anaesthesia is a multivariable problem where a combination of drugs are used to induce desired hypnotic, analgesia and immobility states. The automation of anaesthesia may improve the safety and cost-effectiveness of anaesthesia. However, the realization of a safe and reliable multivariable closed-loop control of anaesthesia is yet to be achieved due to a manifold of challenges. In this paper, several significant challenges in automation of anaesthesia are discussed, namely model uncertainty, controlled variables, closed-loop application and dependability. The increasingly reliable measurement device, robust and adaptive controller, and better fault tolerance strategy are paving the way for automation of anaesthesia.
The primary objective of this study is to compare the effectiveness of cricoid pressure (CP) and paralaryngeal pressure (PLP) on occlusion of eccentric esophagus in patients under general anesthesia (GA). Secondary objectives include the prevalence of patients with central or eccentric esophagus both before and after GA, and the success rate of CP in occluding centrally located esophagus in patients post GA. Fifty-one ASA physical status I and II patients, undergoing GA for elective surgery were enrolled in this study. Ultrasonography imaging were performed to determine the position of the esophagus relative to the trachea: (i) before induction of GA, (ii) after GA before external CP maneuver, (iii) after GA with CP, and (iv) after GA with PLP. CP was applied to all patients whilst PLP via fingertip technique was only applied to patients with an eccentric esophagus. Among a total of 51 patients, 28 of them (55%) had eccentric esophagus pre GA, while this number increase to 33 (65%) after induction of GA. CP success rate was 100% in 18 patients with central esophagus post GA versus 27% in 33 patients with eccentric esophagus post GA (P<0.00001). Overall success rate for CP was 53%. In 33 patients with eccentric esophagus anatomy post GA, PLP success rate was 30% compared with 27% with CP (P=1.000). Ultrasound guided PLP fingertips technique was not effective in patients with an eccentrically located esophagus post GA. Ultrasound guided CP achieved 100% success rate in patients with a centrally located esophagus post GA.
The displayed readings of Masimo pulse oximeters used in the Benefits Of Oxygen Saturation Targeting (BOOST) II and related trials in very preterm babies were influenced by trial-imposed offsets and an artefact in the calibration software. A study was undertaken to implement new algorithms that eliminate the effects of offsets and artefact. In the BOOST-New Zealand trial, oxygen saturations were averaged and stored every 10 s up to 36 weeks' post-menstrual age. Two-hundred and fifty-seven of 340 babies enrolled in the trial had at least two weeks of stored data. Oxygen saturation distribution patterns corresponding with a +3 % or -3 % offset in the 85-95 % range were identified together with that due to the calibration artefact. Algorithms involving linear and quadratic interpolations were developed, implemented on each baby of the dataset and validated using the data of a UK preterm baby, as recorded from Masimo oximeters with the original software and a non-offset Siemens oximeter. Saturation distributions obtained were compared for both groups. There were a flat region at saturations 85-87 % and a peak at 96 % from the lower saturation target oximeters, and at 93-95 and 84 % respectively from the higher saturation target oximeters. The algorithms lowered the peaks and redistributed the accumulated frequencies to the flat regions and artefact at 87-90 %. The resulting distributions were very close to those obtained from the Siemens oximeter. The artefact and offsets of the Masimo oximeter's software had been addressed to determine the true saturation readings through the use of novel algorithms. The implementation would enable New Zealand data be included in the meta-analysis of BOOST II trials, and be used in neonatal oxygen studies.
Thermal imbalances are very common during surgery. Hypothermia exposes the patient to post-operative shivering, cardiac dysfunction, coagulopathy, bleeding, wound infection, delayed anesthesia recovery, prolonged hospital stay and increased hospitalization cost. There are many factors contributing to intraoperative hypothermia. This is a prospective cohort study conducted through observation and measurement of pediatric surgical patients' temperature. Convenience sampling methods were used in this study. Initial skin temperature and core temperature at 10 min, 30 min,1 h, 2 h, 3 h, 4 h, 5 h, 6 h and at the end of surgery were recorded. Body temperature was monitored from time of transfer to the operating table until recovery and discharge to the respective pediatric ward. The overall incidence of intraoperative hypothermia was still very high at about 46.6% even though active and passive temperature management were carried out during surgery. Patient's age, body weight, duration of surgery, type of surgery, intraoperative blood loss, type of anesthesia and operating room temperature were factors that contributed to intraoperative hypothermia. Hypothermia is common in surgery, especially in major and long duration surgery. Intraoperative hypothermia can be life threatening if it is not handled carefully. Various methods are used before, during and after surgery to maintain a patient's body temperature within the normothermia range. The use of an active warming device like the Bair Hugger® air-forced warming system seems to be a good method for reducing the risk of intraoperative hypothermia and effectively maintaining body temperature for all major and minor surgeries.
Inter-individual variability possesses a major challenge in the regulation of hypnosis in anesthesia. Understanding the variability towards anesthesia effect is expected to assist the design of controller for anesthesia regulation. However, such studies are still very scarce in the literature. This study aims to analyze the inter-individual variability in propofol pharmacokinetics/pharmacodynamics (PK/PD) model and proposed a suitable controller to tackle the variability. This study employed Sobol' sensitivity analysis to identify significance parameters in propofol PK/PD model that affects the model output Bispectral Index (BIS). Parameters' range is obtained from reported clinical data. Based on the finding, a multi-model generalized predictive controller was proposed to regulate propofol in tackling patient variability. [Formula: see text] (concentration that produces 50% of the maximum effect) was found to have a highly-determining role on the uncertainty of BIS. In addition, the Hill coefficient, [Formula: see text], was found to be significant when there is a drastic input, especially during the induction phase. Both of these parameters only affect the process gain upon model linearization. Therefore, a predictive controller based on switching of model with different process gain is proposed. Simulation result shows that it is able to give a satisfactory performance across a wide population. Both the parameters [Formula: see text] and [Formula: see text], which are unknown before anesthesia procedure, were found to be highly significant in contributing the uncertainty of BIS. Their range of variability must be considered during the design and evaluation of controller. A linear controller may be sufficient to tackle most of the variability since both [Formula: see text] and [Formula: see text] would be translated into process gain upon linearization.
To date, most of the studies on safety and efficacy of supraglottic airway devices were done in Caucasian patients, and the results may not be extrapolated to Asian patients due to the different airway anatomy. We conducted this study to compare Supreme™ LMA (SLMA) and Proseal™ LMA (PLMA) size 1.5 in anaesthetized children among an Asian population. This prospective randomized clinical trial was conducted in a tertiary teaching hospital from September 2013 until May 2016. Sixty children, weighing 5-10 kg, who were scheduled for elective surgery under general anaesthesia were recruited and completed the study. Patients were randomly assigned to have either SLMA or PLMA as the airway device for general anaesthesia, and standard anaesthesia protocol was followed. The primary outcome measured was the oropharyngeal leak pressure (OLP). The rate of successful insertion, insertion time, fibreoptic view of larynx and airway complications for each device were also assessed. There were no statistically significant differences between SLMA and PLMA size 1.5 in oropharyngeal leak pressure [19.1 (± 5.5) cmH2O vs. 19.8 (± 4.5) cmH2O, p = 0.68]. Secondary outcomes including time to insertion [20.8 (± 8.3) vs. 22.1 (± 8.3) s, p = 0.57], first attempt success rate for device insertion, fibreoptic view of larynx, and airway complications were also comparable between the two devices. We found that all the patients who had a failed device insertion (either PLMA or SLMA) were of a smaller size (5-6.2 kg). The oropharyngeal leak pressure of the SLMA 1.5 was comparable with the PLMA 1.5, and both devices were able to maintain an airway effectively without significant clinical complications in anaesthetized children from an Asian population.
Since the recent editorial 2, we were approached to evaluate another video laryngeal mask airway - the Besdata Video Laryngeal Mask (BD-VLM) TM, which has a different design concept, specifications and characteristics (Figure 1) compared to the other two.