Assessing the incremental value of blood oxygen saturation (SpO(2)) in the miniPIERS (Pre-eclampsia Integrated Estimate of RiSk) Risk Prediction Model

OBJECTIVE

To assess the incremental value of blood oxygen saturation (SpO(2)) as a predictor in the miniPIERS model, a risk prediction model for adverse outcomes among women with a diagnosis of hypertensive disorder of pregnancy (HDP) in low-resourced settings.

METHODS

Using data from a prospective cohort including 852 women admitted to hospital for a HDP, the association between SpO(2) and adverse maternal outcome was assessed using logistic regression. The miniPIERS model was recalibrated and extended to include SpO(2). The incremental value of adding SpO(2) to the model was measured using a net reclassification index (NRI), sensitivity, specificity, positive and negative predictive values, and likelihood ratios.

RESULTS

SpO(2) of < 93% was associated with a 30-fold increase in risk (95% CI 14 to 68) of adverse maternal outcome compared to women with SpO(2) > 97%. After recalibration and extension, the miniPIERS model including SpO(2) (vs. not including SpO(2)) had improved sensitivity (32.8% vs. 49.6%) at the cost of minimally decreased specificity (91.5% vs. 96.2%) with a NRI of 0.122.

CONCLUSION

SpO(2) is a significant independent predictor of risk in women with a HDP. Adding SpO(2) to the miniPIERS model improved the model's ability to correctly identify high-risk patients who would benefit most from interventions.

The nicotinergic receptor as a target for cognitive enhancement in schizophrenia: barking up the wrong tree?

RATIONALE

Cognitive symptoms have increasingly been recognized as an important target in the development of future treatment strategies in schizophrenia. The nicotinergic neurotransmission system has been suggested as a potentially interesting treatment target for these cognitive deficits. However, previous research yielded conflicting results, which may be explained by several methodological limitations, such as the failure to include both a group of smoking and non-smoking schizophrenic patients, the use of only a single nicotine dose, and the inclusion of a very limited cognitive battery.

OBJECTIVES

The present study aims at investigating the cognitive effects of nicotine in schizophrenia while addressing these methodological issues.

METHODS

In a double-blind placebo-controlled randomized crossover design, cognitive effects are assessed in smoking (n =16) and non-smoking (n =16) schizophrenic patients after receiving active (1 or 2 mg) or placebo oromucosal nicotine spray.

RESULTS

A modest improving effect of nicotine on attention in the smoking but not the non-smoking group was found. No enhancing effects were found on measures of visual memory, working memory, processing speed, psychomotor speed, or social cognitive functioning in either patient group.

CONCLUSIONS

These findings suggest that the nicotinic receptor only has limited value as a cognitive treatment target in schizophrenia.

Closed-loop fluid resuscitation: robustness against weight and cardiac contractility variations

BACKGROUND

Surgical patients present with a wide variety of body sizes and blood volumes, have large differences in baseline volume status, and may exhibit significant differences in cardiac function. Any closed-loop fluid administration system must be robust against these differences. In the current study, we tested the stability and robustness of the closed-loop fluid administration system against the confounders of body size, starting volume status, and cardiac contractility using control engineering methodology.

METHODS

Using an independently developed previously published hemodynamic simulation model that includes blood volumes and cardiac contractility, we ran a Monte-Carlo simulation series with variation in starting blood volume and body weight (phase 1, weight 35-100 kg), and starting blood volume and cardiac contractility (phase 2, contractility from 1500 [severe heart failure] to 6000 [hyperdynamic]). The performance of the controller in resuscitating to the target set point was evaluated in terms of milliliters of blood volume error from optimal, with <250 mL of error defined as "successful."

RESULTS

One thousand simulations were run for each of the 2 phases of the study. The phase 1 mean blood volume error ± SD from optimal was 25 ± 59 mL. The phase 2 mean blood volume error from optimal was -60 ± 89 mL. The lower 95% Clopper-Pearson binomial confidence interval for resuscitation to within 250 mL of optimal blood volume for phase 1 and 2 was 99.6% and 97.1%, respectively.

CONCLUSION

The results indicate that the controller is highly effective in targeting optimal blood and stroke volumes, regardless of weight, contractility or starting blood volume.

Design challenges for camera oximetry on a mobile phone

The use of mobile consumer devices as medical diagnostic tools allows standard medical tests to be performed anywhere. Cameras embedded in consumer devices have previously been used as pulse oximetry sensors. However, technical limitations and implementation challenges have not been described. This manuscript provides a critical analysis of pulse oximeter technology and technical limitations of cameras that can potentially impact implementation of pulse oximetry in mobile phones. Theoretical and practical examples illustrate difficulties and recommendations to overcome these challenges.

Correlation of heart rate variability and circadian markers in humans

The frequency of adverse cardiovascular events is greater in the morning compared to its 24-hour average. A circadian variation in the regulation of the cardiovascular system could contribute to this increased cardiovascular risk in the morning. Indeed, circadian rhythms have been shown for a wide array of physiological processes. Using an ultradian sleep-wake cycle (USW) procedure, we sought to determine how heart rate (HR) and heart rate variability (HRV) correlate with the well-characterized circadian rhythms of cortisol and melatonin secretion. Specific HRV components, namely the low frequency (LF) power, high frequency (HF) power, and the LF:HF ratio can be used as markers of the autonomic modulation of the heart. Cross-correlation between HRV parameters and hormonal rhythms demonstrated that mean RR interval is significantly phase-advanced relative to salivary cortisol and urinary 6-sulfatoxy-melatonin (UaMt6s). Parasympathetic modulation of the heart (HF power) was phase-advanced relative to cortisol, but was in-phase with UaMt6s levels. Maximal correlation of the sympathovagal balance (the LF:HF ratio) had no significant lag compared to cortisol secretion and UaMt6s excretion. The protective effect of the parasympathetic nervous system at night, combined with the putative risk associated with the sympathetic nervous system peaking in the morning, could be associated with the increased cardiovascular risk observed in the morning hours.

Adaptive pulse segmentation and artifact detection in photoplethysmography for mobile applications

Pulse oximeters non-invasively measure heart rate and oxygen saturation and have great potential for predicting critical illness. The photoplethysmogram (PPG) recorded from pulse oximetry is often corrupted with artifacts. These artifacts render the derived vital signs inaccurate.

Model-based human circadian phase estimation using a particle filter

We present a method for tracking an individual's circadian phase that integrates dynamic models of circadian physiology with physiological measurements in a Bayesian statistical framework. A model of the circadian pacemaker's response to light exposure is transformed into a nonlinear state-space model with a circadian phase state. The probability distribution of the circadian phase is estimated by a particle filter that predicts changes over time based on the model, and performs updates with information gained from physiological measurements. Simulations demonstrate how probability distributions allow flexible initialization of model states and enable statistical quantification of entrainment and divergence properties of the circadian pacemaker. The combined use of sleep-wake scheduling data and physiological measurements is demonstrated in a case study highlighting advantages for addressing the challenge of noninvasive ambulatory monitoring of circadian physiology.

Slower administration of propofol preserves adequate respiration in children

BACKGROUND

Propofol is a versatile anesthetic agent used in pediatric practice to facilitate investigational and interventional procedures. Propofol can cause significant respiratory depression, the management of which may require advanced airway management skills. This investigation aimed to increase the safety of propofol administration by developing a dosing schedule that would preserve spontaneous respiration in at least 95% of subjects.

METHODS

With Research Ethics Board approval and informed consent, American Society of Anesthesiologists' Status I and II children aged 6-15 years presenting for upper or lower gastrointestinal endoscopy were enrolled. An intravenous loading dose of propofol (4 mg·kg(-1) ) was administered at a rate determined by a randomization schedule in a two-phased study. Following the loading dose, additional propofol was infused at 200 mcg·kg(-1) ·min(-1) for 5 min or until respiratory insufficiency was observed. In Phase I, the infusion rate was modified by 100 mcg·kg(-1) ·min(-1) increments depending upon the respiratory response of the previous subject. In Phase II, the duration of infusion was randomized according to a Biased Coin Design principle to determine the 95% threshold for respiratory insufficiency.

RESULTS

Fifty subjects were included in the analysis. Infusion rates ranged from 1000 to 2300 mcg·kg(-1) ·min(-1) . Seven subjects experienced respiratory insufficiency. The mean (sd) time to respiratory insufficiency was 104 (36) s and duration was 93 (51) s. A propofol loading dose administered over 3.0 min (CI = 1.9-3.4 min) maintained spontaneous respiration in 95% of subjects.

CONCLUSIONS

The respiratory response to propofol is highly variable in children. Slower infusion of propofol will result in a lower risk of respiratory depression.

The effect of a target controlled infusion of propofol on predictability of recovery from anesthesia in children

BACKGROUND

Emergence following termination of a general anesthetic depends on the effect site concentration (C(e)) of the drug declining to an awakening value (C(e)-awake). C(e)-awake has been described in adults, but is unknown in children.

OBJECTIVES

To determine C(e)-awake in children following a target-controlled infusion (TCI) of propofol and to assess a C(e)-driven TCI system's ability to predict times to emergence from anesthesia.

METHODS

Subjects undergoing elective surgery, aged 3 months to <10 years were recruited into three age-stratified groups. A target C(e) of 3-4 microg x ml(-1) was selected for induction and subsequently titrated to patient response and surgical stimulus. Preoperative acetaminophen, a remifentanil infusion and regional anesthesia were permitted for supplemental analgesia. State Entropy (SE) was monitored from induction to emergence. Emergence was defined as the time of first purposeful spontaneous movement (PSM). Time zero was defined as the end of propofol infusion. Based on a pilot study, a C(e)-awake of 1.9 microg x ml(-1) was chosen as the wake-up threshold used by the software to predict emergence times.

RESULTS

Data was collected for 90 of 104 recruited patients. PSM occurred at a mean (sd) C(e) of 2.0 (0.5) microg x ml(-1) and an SE of 79 (11). There were no differences between age groups. A wide variation in emergence time was observed, with a mean (sd) of 16.9 (7) min, and a trend to more rapid emergence in older subjects.

CONCLUSION

A predicted C(e)-awake of 2.0 microg x ml(-1) in children aged 3 months to <10 years was identified with the selected model. For expert users of propofol in children, during shorter surgical procedures, TCI predicted emergence times do not offer significant clinical advantages.

Evaluation of a tactile display around the waist for physiological monitoring under different clinical workload conditions

In this study, we have assessed the usability of a tactile belt prototype for clinical monitoring of physiologic patient data in the operating room under low workload (LW) and high workload (HW) conditions. In previous investigations, we have evaluated tactile technology in clinical settings and demonstrated that anesthesiologists have enhanced situational awareness towards adverse clinical events when a tactile display prototype is used as a supplemental monitoring device. To further evaluate the effectiveness of our tactile belt prototype, we compared the effects of workload on the performance of anesthesiologists in terms of accuracy and response time in tactile alert identification. We also administered a post-study questionnaire to evaluate the usability of the tactile belt as well as users' opinions about the device. We found that the response time to tactile alert identification to be faster under LW than under HW, however the accuracy of identification was not statistically different. Participants rated the tactile belt prototype as comfortable to use and the tactile alert scheme as easy to learn. Our findings further support the feasibility and efficacy of vibrotactile devices for enhancing physiological monitoring of patients in clinical environments.

Clinical evaluation of algorithms for context-sensitive physiological monitoring in children

BACKGROUND

Subtle changes in monitored physiological signals might be used to guide clinical actions and give early warning of potential adverse events. Automated early warning systems could enhance the clinician's interpretation of data by instantaneously processing new information and presenting it within the context of previous observations. In this study, we tested algorithms for tracking the behaviour of dynamic physiological systems and automatically detecting key events over time.

METHODS

Algorithms were activated in real-time during anaesthesia to run context-sensitive monitoring of six variables (end-tidal PCO(2), heart rate, exhaled minute ventilation, non-invasive arterial pressure, respiratory rate, and oxygen saturation), alongside standard physiological monitors. The clinical evaluation included real-time feedback on each change point (change in the physiological trend) detected by the algorithms and the completion of a usability questionnaire.

RESULTS

Fifteen anaesthetists completed the evaluation during paediatric surgical cases. A total of 38 cases were evaluated, with a mean duration of 103 (102) min. The mean number of change points per case was 22.8 (23.4). Sixty-one per cent of all rated change points were considered clinically significant, and <7% were due to artifacts.

CONCLUSIONS

The algorithms were able to detect a range of clinically significant physiological changes during paediatric anaesthesia, and were considered useful by participating anaesthetists. These findings indicate that automated detection of context-sensitive changes is possible and could be used by early warning systems during physiological monitoring. Further investigations are required to assess how this information can best be communicated to the anaesthetist.

Cerebral temperature varies across circadian phases in humans

The 24-hour rhythm of core body temperature (CBT) is commonly used in humans as a tool to assess the oscillation of the central endogenous circadian pacemaker. The invasive nature of the rectal sensor used to collect CBT makes it difficult to use in ambulatory conditions. Here we validate the use of a newly developed brain temperature (BT) sensor against that of a standard rectal temperature sensor using a 72-hour ultra-rapid sleep-wake (URSW) cycle procedure. A significant circadian variation of both body temperature recordings was observed from which a phase and amplitude was reliably determined. These results indicate that BT can be refined as a non-invasive alternative to CBT measurements in the evaluation of circadian phase in field conditions.

iAssist: a software framework for intelligent patient monitoring

A software framework (iAssist) has been developed for intelligent patient monitoring, and forms the foundation of a clinical monitoring expert system. The framework is extensible, flexible, and interoperable. It supports plugins to perform data acquisition, signal processing, graphical display, data storage, and output to external devices. iAssist currently incorporates two plugins to detect change point events in physiological trends. In 38 surgical cases, iAssist detected 868 events, of which clinicians rated more than 50% as clinically significant and less than 7% as artifacts. Clinicians found iAssist intuitive and easy to use.

Multivariate analysis in clinical monitoring: detection of intraoperative hemorrhage and light anesthesia

The number of vital sign variables measured during a typical surgery is beyond the simultaneous surveillance capabilities of most experienced clinicians. Most intraoperative events cause trend changes in multiple variables, and many clinical events can only be detected by investigating the inter-relationship between the direction and amplitude of these trend changes in the whole measurement array. We have compared the techniques of principal component analysis (PCA) and factor analysis (FA) in extracting latent variables to represent the underlying physiological mechanism. The detection performance of each method was tested on three simulated cases of intraoperative hemorrhage and a case of variation in depth of anesthesia. The results show that although the detection schemes based on PCA and FA both reduce dimensionality and detect changes in the variance, the FA-based method performs better in detecting subtle changes in the correlation structure.