Nicholas West

Robust closed-loop control of induction and maintenance of propofol anesthesia in children

During closed‐loop control, a drug infusion is continually adjusted according to a measure of clinical effect (e.g., an electroencephalographic depth of hypnosis (DoH) index). Inconsistency in population‐derived pediatric pharmacokinetic/pharmacodynamic models and the large interpatient variability observed in children suggest a role for closed‐loop control in optimizing the administration of intravenous anesthesia.

Design and Clinical Evaluation of Robust PID Control of Propofol Anesthesia in Children

This paper describes the design of a robust proportional-integral derivative (PID) controller for propofol infusion in children and presents the results of clinical evaluation of this closed-loop system during endoscopic investigations in children age 6-17. The controller design is based on a set of models that describes the interpatient variability in the response to propofol infusion in the study population. The PID controller is tuned to achieve sufficient robustness margins for the identified uncertainty. 108 children were enrolled in this study, and anesthesia was closed-loop controlled in 102 of these cases. Clinical evaluation of the system shows that closed-loop control of both induction and maintenance of anesthesia in children based on the WAVCNS index as a measure of clinical effect is feasible. A robustly tuned PID controller can accommodate the interpatient variability in children and spontaneous breathing can be maintained in most subjects.

Quantification of the Variability in Response to Propofol Administration in Children

Closed-loop control of anesthesia is expected to decrease drug dosage and wake up time while increasing patient safety and decreasing the work load of the anesthesiologist. The potential of closed-loop control in anesthesia has been demonstrated in several clinical studies. One of the challenges in the development of a closed-loop system that can be widely accepted by clinicians and regulatory authorities is the effect of interpatient variability in drug sensitivity. This system uncertainty may lead to unacceptable performance, or even instability of the closed-loop system for some individuals. The development of reliable models of the effect of anesthetic drugs and characterization of the uncertainty is, therefore, an important step in the development of a closed-loop system. Model identification from clinical data is challenging due to limited excitation and the lack of validation data. In this paper, approximate models are validated for controller design by evaluating the predictive accuracy of the closed-loop behavior. A set of 47 validated models that describe the interpatient variability in the response to propofol in children is presented. This model set can be used for robust linear controller design provided that the experimental conditions are similar to the conditions during data collection.

Closed-Loop Anesthesia in Children using a PID Controller: A Pilot Study

8 Measuring adeQuacy of analgesia with cardiorespiratory coherence Chris Brouse, Walter Karlen, Guy Dumont, Dorothy Myers, Erin Cooke, Jonathan Stinson, Joanne Lim, J. Mark Ansermino The University of British Columbia, Vancouver, Canada Introduction: An automated nociception monitor would be very useful in general anesthesia, providing anesthesiologists with real-time feedback about the adequacy of analgesia. We have developed an algorithm to measure nociception using respiratory sinus arrhythmia (RSA) in heart rate variability (HRV). We have previously shown that this algorithm can detect patient movement (strongly nociceptive events) during general anesthesia 1. We will now attempt to determine if the algorithm responds to boluses of anesthetic drugs (strongly anti-nociceptive events). Method: Algorithm: The algorithm estimates cardiorespiratory coherence, which is the strength of linear coupling between HR and respiration (one measure of RSA). It measures and combines the spectral power in both signals using wavelet analysis. Coherence is dimensionless, and ranges from 0 (no coherence, strong nociception) to 1 (perfect coherence, no nociception). Data Analysis: Following ethics approval and informed consent, 60 drug bolus events (excluding induction of anesthesia) were recorded in 47 pediatric patients receiving general anesthesia during dental surgery. In post hoc analysis, coherence was averaged over the 60s immediately preceding the bolus dose of drug (nociceptive period). The bolus was given 30s to take effect, after which the coherence was averaged over the following 60s (anti-nociceptive period). The change in average coherence between the two periods was calculated. The change in average HR was also calculated, for comparison. Results: Coherence increased by an average of 0.14 (32%) in response to the bolus dose of anesthetic drug. HR decreased by an average of 4.1 beats/min (3.9%). Discussion: Cardiorespiratory coherence responded much more strongly to the anesthetic boluses than did HR alone. This result, combined with previous work showing that coherence is low during periods of nociception [1], demonstrates that cardiorespiratory coherence can be used to measure the adequacy of analgesia during general anesthesia. We are currently adapting the algorithm so that it can be used in real-time.

A smartphone version of the Faces Pain Scale-Revised and the Color Analog Scale for postoperative pain assessment in children.

Effective pain assessment is essential during postoperative recovery. Extensive validation data are published supporting the Faces Pain Scale‐Revised (FPS‐R) and the Color Analog Scale (CAS) in children. Panda is a smartphone‐based application containing electronic versions of these scales.

Safety, constraints and anti-windup in closed-loop anesthesia

Abstract Feasibility of closed-loop anesthesia has been shown in a number of clinical studies. Demonstration of patient safety will be essential to convince regulatory authorities of the benefits of such systems. This paper considers safety constraints for closed-loop propofol anesthesia based on its therapeutic range. Simulation scenarios are proposed for evaluation of control strategies in the presence of these constraints. The scenarios reproduce realistic situations encountered in clinical practice. Using the proposed scenarios, the performance of ℒ 2 anti-windup is compared to sliding mode reference conditioning and to back-calculation anti-windup. It is concluded that ℒ 2 anti-windup might not be appropriate for this problem. The sliding mode solution results in behaviour comparable to the Hanus conditioned controller and there seems to be no need for fast switching. The back-calculation anti-windup performs well in a variety of situations.

Preoperative warming and undesired surgical and anesthesia outcomes in pediatric spinal surgery—a retrospective cohort study

Underbody forced air warming is a method commonly used for intraoperative temperature maintenance in children. We previously reported that preoperative forced air warming of children undergoing spinal surgery substantially reduces the incidence and duration of intraoperative hypothermia (<36°C).

Dexmedetomidine and hydromorphone: A novel pain management strategy for the oncology ward setting during anti‐GD2 immunotherapy for high‐risk neuroblastoma in children

Treatment of neuroblastoma with targeted immunotherapy using chimeric anti‐GD2 monoclonal antibodies (ch14.18) is associated with significant pain requiring management with a high‐dose opioid infusion. We present a case series of six children, for whom dexmedetomidine and hydromorphone infusions safely and effectively reduced the pain of ch14.18 therapy in the oncology ward setting.

Developing an objective method for analyzing vital signs changes in neonates during general anesthesia.

Commonly used general anesthetics are considered to be neurotoxic to the developing rodent brain, leading to poor long‐term outcome. However, it is unclear whether these rodent studies can be extrapolated to the human neonate. Given that anesthesia for urgent neonatal surgery cannot be avoided, it is vitally important to assess other factors that may impact neurological outcome following anesthesia and surgery.

Integrating intraoperative physiology data into outcomes analysis for the ACS Pediatric National Surgical Quality Improvement Program

The Pediatric National Surgical Quality Improvement Program (P‐NSQIP) samples surgical procedures for benchmarking and quality improvement. While generally comprehensive, P‐NSQIP does not collect intraoperative physiologic data, despite potential impact on outcomes.