Lara Brewer

Breathfinding: A Wireless Network That Monitors and Locates Breathing in a Home

This paper explores using RSS measurements on the links between commercial wireless devices to locate where a breathing person is located and to estimate their breathing rate, in a home, while the person is sitting, lying down, standing, or sleeping. Prior RSS-based device-free localization methods required calibration measurements to be able to locate stationary people, or did not require calibration but only located people who moved. We collect RSS measurements multiple short (3-7 minute) tests and during a longer 66 minute test, and show the location of the breathing person can be estimated, to within about 2 m average error. We describe a detector that distinguishes between sample times during which a person is moving and sample times during which a person is breathing but otherwise motionless. This detector enables removal of motion interference, i.e., RSS changes due to movements other than a persons breathing, and more accurately estimate a persons breathing rate. Being able to locate and monitor a breathing person, without calibration, is important for applications in search and rescue, health care, and security.

The Myth of Rescue Reversal in "Can't Intubate, Can't Ventilate" Scenarios.

BACKGROUND:An unanticipated difficult airway during induction of anesthesia can be a vexing problem. In the setting of can’t intubate, can’t ventilate (CICV), rapid recovery of spontaneous ventilation is a reasonable goal. The urgency of restoring ventilation is a function of how quickly a patient’s hemoglobin oxygen saturation decreases versus how much time is required for the effects of induction drugs to dissipate, namely the duration of unresponsiveness, ventilatory depression, and neuromuscular blockade. It has been suggested that prompt reversal of rocuronium-induced neuromuscular blockade with sugammadex will allow respiratory activity to recover before significant arterial desaturation. Using pharmacologic simulation, we compared the duration of unresponsiveness, ventilatory depression, and neuromuscular blockade in normal, obese, and morbidly obese body sizes in this life-threatening CICV scenario. We hypothesized that although neuromuscular function could be rapidly restored with sugammadex, significant arterial desaturation will occur before the recovery from unresponsiveness and/or central ventilatory depression in obese and morbidly obese body sizes. METHODS:We used published models to simulate the duration of unresponsiveness and ventilatory depression using a common induction technique with predicted rates of oxygen desaturation in various size patients and explored to what degree rapid reversal of rocuronium-induced neuromuscular blockade with sugammadex might improve the return of spontaneous ventilation in CICV situations. RESULTS:Our simulations showed that the duration of neuromuscular blockade was longer with 1.0 mg/kg succinylcholine than with 1.2 mg/kg rocuronium followed 3 minutes later by 16 mg/kg sugammadex (10.0 vs 4.5 minutes). Once rocuronium neuromuscular blockade was completely reversed with sugammadex, the duration of hemoglobin oxygen saturation >90%, loss of responsiveness, and intolerable ventilatory depression (a respiratory rate of ⩽4 breaths/min) were dependent on the body habitus and duration of oxygen administration. There is a high probability of intolerable ventilatory depression that extends well beyond the time when oxygen saturation decreases <90%, especially in obese and morbidly obese patients. If ventilatory rescue is inadequate, oxygen desaturation will persist in the latter groups, despite full reversal of neuromuscular blockade. Depending on body habitus, the duration of intolerable ventilatory depression after sugammadex reversal may be as long as 15 minutes in 5% of individuals. CONCLUSIONS:The clinical management of CICV should focus primarily on restoration of airway patency, oxygenation, and ventilation consistent with the American Society of Anesthesiologist’s practice guidelines for management of the difficult airway. Pharmacologic intervention cannot be relied upon to rescue patients in a CICV crisis.

Measurement of functional residual capacity by modified multiple breath nitrogen washout for spontaneously breathing and mechanically ventilated patients

BACKGROUNDnThere is a need for a bedside functional residual capacity (FRC) measurement method that performs well in intensive care patients during many modes of ventilation including controlled, assisted, spontaneous, and mixed. We developed a modified multiple breath nitrogen washout method for FRC measurement that relies on end-tidal gas fractions and alveolar tidal volume measurements as inputs but does not require the traditional measurements of volume of nitrogen or oxygen. Using end-tidal measurements, not volume, reduces errors from signal synchronization. This study was designed to assess the accuracy, precision, and repeatability of the proposed FRC system in subjects with variable ventilation patterns including some spontaneous effort.nnnMETHODSnThe accuracy and precision of measurements were assessed by comparing the novel N₂ washout FRC values to the gold standard, body plethysmography, in 20 spontaneously breathing volunteers. Repeatability was assessed by comparing subsequent measurements in 20 intensive care patients whose lungs were under controlled and assisted mechanical ventilation.nnnRESULTSnCompared with body plethysmography, the accuracy (mean bias) of the novel method was -0.004 litre and precision [1 standard deviation (sd)] was 0.209 litre [mean (sd)] [-0.1 (5.9)% of body plethysmography]. The difference between repeated measurements was 0.009 (0.15) litre [mean (sd)] [0.4 (6.4)%]. The coefficient of repeatability was 0.31 litre (12.7%).nnnCONCLUSIONSnThe modified multiple breath nitrogen washout method for FRC measurement provides improved precision and equivalent accuracy and repeatability compared with existing methods during ventilation with variable ventilation patterns. Further study of the novel N₂ washout method is needed.

Using the Entropy of Tracheal Sounds to Detect Apnea during Sedation in Healthy Nonobese Volunteers

Background:Undetected apnea can lead to severe hypoxia, bradycardia, and cardiac arrest. Tracheal sounds entropy has been proved to be a robust method for estimating respiratory flow, thus maybe a more reliable way to detect obstructive and central apnea during sedation. Methods:A secondary analysis of a previous pharmacodynamics study was conducted. Twenty volunteers received propofol and remifentinal until they became unresponsive to the insertion of a bougie into the esophagus. Respiratory flow rate and tracheal sounds were recorded using a pneumotachometer and a microphone. The logarithm of the tracheal sound Shannon entropy (Log-E) was calculated to estimate flow rate. An adaptive Log-E threshold was used to distinguish between the presence of normal breath and apnea. Apnea detected from tracheal sounds was compared to the apnea detected from respiratory flow rate. Results:The volunteers stopped breathing for 15 s or longer (apnea) 322 times during the 12.9-h study. Apnea was correctly detected 310 times from both the tracheal sounds and the respiratory flow. Periods of apnea were not detected by the tracheal sounds 12 times. The absence of tracheal sounds was falsely detected as apnea 89 times. Normal breathing was detected correctly 1,196 times. The acoustic method detected obstructive and central apnea in sedated volunteers with 95% sensitivity and 92% specificity. Conclusions:We found that the entropy of the acoustic signal from a microphone placed over the trachea may reliably provide an early warning of the onset of obstructive and central apnea in volunteers under sedation.

Evaluation of a CO2 partial rebreathing functional residual capacity measurement method for use during mechanical ventilation

ObjectiveThere is a need for an automated bedside functional residual capacity (FRC) measurement method that does not require a step change in inspired oxygen fraction. Such a method can be used for patients who require a high inspired oxygen fraction to maintain arterial oxygenation and for patients ventilated using a circle breathing system commonly found in operating rooms, which is not capable of step changes in oxygen. We developed a CO2 rebreathing method for FRC measurement that is based on the change in partial pressure of end-tidal carbon dioxide and volume of CO2 eliminated at the end of a partial rebreathing period. This study was designed to assess the accuracy and precision of the proposed FRC measurement system compared to body plethysmography and nitrogen washout FRC.MethodsAccuracy and precision of measurements were assessed by comparing the CO2 rebreathing FRC values to the gold standard, body plethysmography FRC, in twenty spontaneously breathing volunteers. The CO2 rebreathing FRC measurements were then compared to nitrogen washout FRC in twenty intensive care patients whose lungs were mechanically ventilated. For each subject, an average value of CO2 rebreathing FRC was compared to the average gold standard method. Measurements were accepted for statistical analysis if they had been recorded from periods of stable tidal ventilation, defined as a coefficient of variation of tidal volume of <0.13. ResultsCompared to body plethysmography, the accuracy (average error) for the CO2 rebreathing method during stable ventilation (nxa0=xa08) was 0.03xa0L and precision (1 standard deviation of the error) was 0.29xa0L (0.8 ± 7.6% of body plethysmography). During stable mechanical ventilation (nxa0=xa09), the accuracy was −0.02xa0L and precision was 0.26xa0L (−1.1 ± 12.6% of nitrogen washout).ConclusionsThe CO2 rebreathing method for FRC measurement provides acceptable accuracy and precision during stable ventilation compared to the gold standards of body plethysmography and nitrogen washout. The results based on periods of stable ventilation best approximate the performance of the system in the likely areas of application during controlled mechanical ventilation. Further study of the CO2 rebreathing method is needed to evaluate accuracy in a larger group of controlled mechanical ventilation patients, including patients with respiratory insufficiency and significant lung injury.

Noninvasive cardiac output monitor algorithms are more sophisticated and perform better than indicated in modeling paper

To the Editor:—A 77-yr-old man undergoing insertion of a J-splint for renal obstruction received general anesthesia delivered with an ADU anesthesia machine (Anesthesia Delivery Unit; Datex-Ohmeda, Stockholm, Sweden). A 5% desflurane vaporizer concentration setting with an O2/N2O mixture (2 and 3 l/min, respectively) resulted in stable inspired and expired desflurane concentrations (fig. 1). Immediately after lowering the fresh gas flow (FGF) to 0.35 l/min O2 and 0.35 l/min N2O, and while maintaining the same vaporizer concentration setting, a dramatic increase in inspired and expired desflurane concentrations to about 14% (15:45) was noticed, as shown in figure 1. The duration of this high concentration was short-lived ( 2 min) and did not trigger an alarm; the vaporizer concentration setting was decreased to 4.5% and was left unchanged throughout the remainder of the procedure (until 16:13). After a rapid decrease of the inspiratory and end-expiratory desflurane concentrations to about 7–8.5%, the concentrations started to increase again, leading to a gradual decrease in blood pressure. Because vaporizer malfunction was suspected, the FGF was increased to 5 l/min O2/N2O and was decreased again (to the previous settings) within a period of 1 min (15:56). Inspired and expired concentrations were noticed to decrease and increase again. This maneuver was repeated at 16:03, confirming that indeed something was wrong with the vaporizer output with the use of lower FGF (0.7 l/min). At 16:05, the FGF was therefore increased to 5 l/min. Vaporizer output itself was then checked at low FGF (0.7 l/min) by interrupting ventilation and having the sampling line of the multigas analyzer (Compact Airway Module M-CAiOV, Datex-Ohmeda, Helsinki, Finland) sample gases leaving the common gas outlet (16:10). Desflurane output read 14.5% (at 16:10) during the use of low flows, but matched the dialed 4.5% (16:12) when the FGF was increased again to its previous settings (O2/N2O mixture, 2 and 3 l/min, respectively). An alarm message appeared (“Service fresh gas unit.”). Anesthesia was continued for a few more minutes for the remainder of the surgical procedure with desflurane and high FGF (5 l/min), and the patient was allowed to awaken without further incident. On the same day of our observation, a similar case was reported by the Anesthesiology Discussion Group on GASNet.† With FGF of 0.6 l/min O2 and 0.6 l/min air and a desflurane dial setting at 8%, the desflurane concentration on the agent analyzer display slowly approached 4.5–5.5%. Then, without warning, the desflurane concentration suddenly increased to 15%. It is unclear whether the events were the same as in our case. The ADU vaporizing unit is an electronically controlled, flow-over, variable bypass, and measured flow vaporizer, and its mechanism of action and performance have been described recently. Vaporizer output increased with lower FGF, with the largest error with FGF of 0.2 l/min (4.3 and 7.3% absolute output measured with 3% and 6% dialed, respectively, in a single instance). In the current case, however, substantially higher total FGFs (0.7 l/min) were used. Very preliminary testing by Datex-Ohmeda indicates that the one-way valve that prevents backflow of saturated vapor from the cassette via inspiratory channel toward the bypass channel may have failed to close after lowering the FGF (fig. 2). This problem may be more significant when desflurane is used because the pressure in the desflurane Aladin cassette (Datex-Ohmeda, Stockholm, Sweden) may exceed 1 atm because of its high vapor pressure when the temperature is greater than 22.8°C (boiling point of desflurane at 1 atm pressure). A similar problem in 1999 prompted a redesign of this one-way valve and an upgrading of all ADU anesthesia machines in service worldwide (Mr. Ola Lassborn, Quality Manager, Datex-Ohmeda, Stockholm, Sweden, verbal personal communication, March 2003). Despite the new design, this report suggests a continued problem with this valve with the possible delivery of unintended high concentrations of inhaled anesthetics. It is unclear whether the valve still has a design problem or whether only a few defective valves exist (a manufacturing issue). This safety issue is being addressed by Datex-Ohmeda. For now, it is advisable to monitor carefully for excessive agent concentrations when using the ADU Datex-Ohmeda anesthesia machines, especially if desflurane is administered.

Defeating information overload in health surveillance using a metacognitive aid innovation from military combat systems

Modern sensors for health surveillance generate high volumes and rates of data that currently overwhelm operational decision-makers. These data are collected with the intention of enabling front-line clinicians to make effective clinical judgments. Ironically, prior human–systems integration (HSI) studies show that the flood of data degrades rather than aids decision-making performance. Health surveillance operations can focus on aggregate changes to population health or on the status of individual people. In the case of clinical monitoring, medical device alarms currently create an information overload situation for front-line clinical workers, such as hospital nurses. Consequently, alarms are often missed or ignored, and an impending patient adverse event may not be recognized in time to prevent crisis. One innovation used to improve decision making in areas of data-rich environments is the Human Alerting and Interruption Logistics (HAIL) technology, which was originally sponsored by the US Office of Naval Research. HAIL delivers metacognitive HSI services that empower end-users to quickly triage interruptions and dynamically manage their multitasking. HAIL informed our development of an experimental prototype that provides a set of context-enabled alarm notification services (without automated alarm filtering) to support users’ metacognition for information triage. This application is called HAIL Clinical Alarm Triage (HAIL-CAT) and was designed and implemented on a smartwatch to support the mobile multitasking of hospital nurses. An empirical study was conducted in a 20-bed virtual hospital with high-fidelity patient simulators. Four teams of four registered nurses (16 in total) participated in a 180-minute simulated patient care scenario. Each nurse was assigned responsibility to care for five simulated patients and high rates of simulated health surveillance data were available from patient monitors, infusion pumps, and a call light system. Thirty alarms per nurse were generated in each 90-minute segment of the data collection sessions, only three of which were clinically important alarms. The within-subjects experimental design included a treatment condition where the nurses used HAIL-CAT on a smartwatch to triage and manage alarms and a control condition without the smartwatch. The results show that, when using the smartwatch, nurses responded three times faster to clinically important and actionable alarms. An analysis of nurse performance also shows no negative effects on their other duties. Subjective results show favorable opinions about utility, usability, training requirement, and adoptability. These positive findings suggest the potential for the HAIL HSI system to be transferrable to the domain of health surveillance to achieve the currently unrealized potential utility of high-volume data.

Faster clinical response to the onset of adverse events: A wearable metacognitive attention aid for nurse triage of clinical alarms

Objective This study evaluates the potential for improving patient safety by introducing a metacognitive attention aid that enables clinicians to more easily access and use existing alarm/alert information. It is hypothesized that this introduction will enable clinicians to easily triage alarm/alert events and quickly recognize emergent opportunities to adapt care delivery. The resulting faster response to clinically important alarms/alerts has the potential to prevent adverse events and reduce healthcare costs. Materials and methods A randomized within-subjects single-factor clinical experiment was conducted in a high-fidelity 20-bed simulated acute care hospital unit. Sixteen registered nurses, four at a time, cared for five simulated patients each. A two-part highly realistic clinical scenario was used that included representative: tasking; information; and alarms/alerts. The treatment condition introduced an integrated wearable attention aid that leveraged metacognition methods from proven military systems. The primary metric was time for nurses to respond to important alarms/alerts. Results Use of the wearable attention aid resulted in a median relative within-subject improvement for individual nurses of 118% (W = 183, p = 0.006). The top quarter of relative improvement was 3,303% faster (mean; 17.76 minutes reduced to 1.33). For all unit sessions, there was an overall 148% median faster response time to important alarms (8.12 minutes reduced to 3.27; U = 2.401, p = 0.016), with 153% median improvement in consistency across nurses (F = 11.670, p = 0.001). Discussion and conclusion Existing device-centric alarm/alert notification solutions can require too much time and effort for nurses to access and understand. As a result, nurses may ignore alarms/alerts as they focus on other important work. There has been extensive research on reducing alarm frequency in healthcare. However, alarm safety remains a top problem. Empirical observations reported here highlight the potential of improving patient safety by supporting the meta-work of checking alarms.

Tracheal sounds accurately detect apnea in patients recovering from anesthesia

Apnea should be monitored continuously in the post anesthesia care unit (PACU) to avoid serious complications. It has been confirmed that tracheal sounds can be used to detect apnea during sedation in healthy subjects, but the performance of this acoustic method has not been evaluated in patients with frequent apnea events in the PACU. Tracheal sounds were acquired from the patients in the PACU using a microphone encased in a plastic bell. Concurrently, a processed nasal pressure signal was used as a reference standard to identify real respiratory events. The logarithm of the tracheal sound variance (log-var) was used to detect apnea, and the results were compared to the reference method. Sensitivity, specificity, positive likelihood ratios (PLR), and negative likelihood ratios (NLR) were calculated. One hundred and twenty-one patients aged 55.5u2009±u200913.2xa0years (meanu2009±u2009SD) with a body mass index of 24.6u2009±u20093.7xa0kg/m2 were included in data analysis. The total monitoring time was 52.6xa0h. Thirty-four patients experienced 236 events of apnea lasting for a total of 122.2xa0min. The log-var apnea detection algorithm detected apnea with 92% sensitivity, 98% specificity, 46 PLR and 0.08 NLR. The performance of apnea detection in the PACU using the log-var tracheal sounds method proved to be reliable and accurate. Tracheal sounds could be used to minimize the potential risks from apnea in PACU patients.

A Turbine-Driven Ventilator Improves Adherence to Advanced Cardiac Life Support Guidelines During a Cardiopulmonary Resuscitation Simulation

BACKGROUND: Research has shown that increased breathing frequency during cardiopulmonary resuscitation is inversely correlated with systolic blood pressure. Rescuers often hyperventilate during cardiopulmonary resuscitation (CPR). Current American Heart Association advanced cardiac life support recommends a ventilation rate of 8–10 breaths/min. We hypothesized that a small, turbine-driven ventilator would allow rescuers to adhere more closely to advanced cardiac life support (ACLS) guidelines. METHODS: Twenty-four ACLS-certified health-care professionals were paired into groups of 2. Each team performed 4 randomized rounds of 2-min cycles of CPR on an intubated mannikin, with individuals altering between compressions and breaths. Two rounds of CPR were performed with a self-inflating bag, and 2 rounds were with the ventilator. The ventilator was set to deliver 8 breaths/min, pressure limit 22 cm H2O. Frequency, tidal volume (VT), peak inspiratory pressure, and compression interruptions (hands-off time) were recorded. Data were analyzed with a linear mixed model and Welch 2-sample t test. RESULTS: The median (interquartile range [IQR]) frequency with the ventilator was 7.98 (7.98–7.99) breaths/min. Median (IQR) frequency with the self-inflating bag was 9.5 (8.2–10.7) breaths/min. Median (IQR) ventilator VT was 0.5 (0.5–0.5) L. Median (IQR) self-inflating bag VT was 0.6 (0.5–0.7) L. Median (IQR) ventilator peak inspiratory pressure was 22 (22–22) cm H2O. Median (IQR) self-inflating bag peak inspiratory pressure was 30 (27–35) cm H2O. Mean ± SD hands-off times for ventilator and self-inflating bag were 5.25 ± 2.11 and 6.41 ± 1.45 s, respectively. CONCLUSIONS: When compared with a ventilator, volunteers ventilated with a self-inflating bag within ACLS guidelines. However, volunteers ventilated with increased variation, at higher VT levels, and at higher peak pressures with the self-inflating bag. Hands-off time was also significantly lower with the ventilator. (ClinicalTrials.gov registration NCT02743299.)