Tracheal sound-based apnea detection using hidden Markov model in sedated volunteers and post anesthesia care unit patients.

The current method of apnea detection based on tracheal sounds is limited in certain situations. In this work, the Hidden Markov Model (HMM) algorithm based on segmentation is used to classify the respiratory and non-respiratory states of tracheal sounds, to achieve the purpose of apnea detection. Three groups of tracheal sounds were used, including two groups of data collected in the laboratory and a group of patient data in the post anesthesia care unit (PACU). One was used for model training, and the others (laboratory test group and clinical test group) were used for testing and apnea detection. The trained HMMs were used to segment the tracheal sounds in laboratory test data and clinical test data. Apnea was detected according to the segmentation results and respiratory flow rate/pressure which was the reference signal in two test groups. The sensitivity, specificity, and accuracy were calculated. For the laboratory test data, apnea detection sensitivity, specificity, and accuracy were 96.9%, 95.5%, and 95.7%, respectively. For the clinical test data, apnea detection sensitivity, specificity, and accuracy were 83.1%, 99.0% and 98.6%. Apnea detection based on tracheal sound using HMM is accurate and reliable for sedated volunteers and patients in PACU.

Response surface model comparison and combinations for remifentanil and propofol in describing response to esophageal instrumentation and adverse respiratory events.

BACKGROUND: The primary aim of this essay was to explore the best fitting model in remifentanil-propofol combined administrations during esophageal instrumentation (EI) from five distinct response surface models. The secondary aim was to combine the models to give appropriate effect-site drug concentrations (Ces) range with maximal comfort and safety. METHODS: The Greco, reduced Greco, Minto, Scaled C50 Hierarchy and Fixed C50 Hierarchy models were constructed to fit four drug effects: loss of response to esophageal instrumentation (LREI), loss of response to esophageal instrumentation revised (LREIR), intolerable ventilatory depression (IVD) and respiratory compromise (RC). Models were tested by chi-square statistical test and evaluated with Akaike Information Criterion (AIC). Model prediction performance were measured by successful prediction rate (SPR) and three prediction errors. RESULTS: The reduced Greco model was the best fitting model for LREI and RC, and the Minto model was the best fitting model for LREIR and IVD. The SPRs of reduced Greco model for LREI and RC were 81.76% and 79.81%. The SPRs of Minto model for LREIR and IVD were 80.32% and 80.12%. Overlay of the reduced Greco model for LREI and Minto model for IVD offered visual aid for guidance in drug administration. CONCLUSION: Using proper response surface model to fit different drug effects will describe the interactions between anesthetic drugs better. Combining response surface models to select the more reliable effect-site drug concentrations range can be used to guide clinical drug administration with greater safety and provide an improvement of anesthesia precision.

Structural inequities in seasonal influenza vaccination rates.

BACKGROUND: Influenza immunization is a highly effective method of reducing illness, hospitalization and mortality from this disease. However, influenza vaccination rates in the U.S. remain below public health targets and persistent structural inequities reduce the likelihood that Black, American Indian and Alaska Native, Latina/o, Asian groups, and populations of low socioeconomic status will receive the influenza vaccine. METHODS: We analyzed correlates of influenza vaccination rates using the 2019 Behavioral Risk Factor Surveillance System (BRFSS) in the year 2020. Our analysis compared influenza vaccination as the outcome of interest with the variables age, sex, race, education, income, geographic location, health insurance status, access to primary care, history of delaying care due to cost, and comorbidities such as: asthma, cardiovascular disease, hypertension, body mass index, cancer and diabetes. RESULTS: Non-Hispanic White (46.5%) and Asian (44.1%) participants are more likely to receive the influenza vaccine compared to Non-Hispanic Black (36.7%), Hispanic (33.9%), American Indian/Alaskan Native (36.6%), and Native Hawaiian/Other Pacific Islander (37.9%) participants. We found persistent structural inequities that predict influenza vaccination, within and across racial and ethnic groups, including not having health insurance [OR: 0.51 (0.47-0.55)], not having regular access to primary care [OR: 0.50 (0.48-0.52)], and the need to delay medical care due to cost [OR: 0.75 (0.71-0.79)]. CONCLUSION: As COVID-19 vaccination efforts evolve, it is important for physicians and policymakers to identify the structural impediments to equitable U.S. influenza vaccination so that future vaccination campaigns are not impeded by these barriers to immunization.

An Automated Algorithm Incorporating Poincaré Analysis Can Quantify the Severity of Opioid-Induced Ataxic Breathing.

BACKGROUND: Opioid-induced respiratory depression (OIRD) is traditionally recognized by assessment of respiratory rate, arterial oxygen saturation, end-tidal CO2, and mental status. Although an irregular or ataxic breathing pattern is widely recognized as a manifestation of opioid effects, there is no standardized method for assessing ataxic breathing severity. The purpose of this study was to explore using a machine-learning algorithm for quantifying the severity of opioid-induced ataxic breathing. We hypothesized that domain experts would have high interrater agreement with each other and that a machine-learning algorithm would have high interrater agreement with the domain experts for ataxic breathing severity assessment. METHODS: We administered target-controlled infusions of propofol and remifentanil to 26 healthy volunteers to simulate light sleep and OIRD. Respiration data were collected from respiratory inductance plethysmography (RIP) bands and an intranasal pressure transducer. Three domain experts quantified the severity of ataxic breathing in accordance with a visual scoring template. The Krippendorff alpha, which reports the extent of interrater agreement among N raters, was used to assess agreement among the 3 domain experts. A multiclass support vector machine (SVM) was trained on a subset of the domain expert-labeled data and then used to quantify ataxic breathing severity on the remaining data. The Vanbelle kappa was used to assess the interrater agreement of the machine-learning algorithm with the grouped domain experts. The Vanbelle kappa expands on the Krippendorff alpha by isolating a single rater-in this case, the machine-learning algorithm-and comparing it to a group of raters. Acceptance criteria for both statistical measures were set at >0.8. The SVM was trained and tested using 2 sensor inputs for the breath marks: RIP and intranasal pressure. RESULTS: Krippendorff alpha was 0.93 (95% confidence interval [CI], 0.91-0.95) for the 3 domain experts. Vanbelle kappa was 0.98 (95% CI, 0.96-0.99) for the RIP SVM and 0.96 (0.92-0.98) for the intranasal pressure SVM compared to the domain experts. CONCLUSIONS: We concluded it may be feasible for a machine-learning algorithm to quantify ataxic breathing severity in a manner consistent with a panel of domain experts. This methodology may be helpful in conjunction with traditional measures to identify patients experiencing OIRD.

A comparison of ventilation with a non-invasive ventilator versus standard O2 with a nasal cannula for colonoscopy with moderate sedation using propofol.

The aim of this study was to test the effects of CPAP on moderately sedated patients undergoing colonoscopy. Our hypothesis was that CPAP can reduce the incidence and duration of obstructive apnea and hemoglobin oxygen desaturation in patients undergoing procedural sedation for colonoscopy. Two groups of consenting adult patients scheduled to undergo routine colonoscopy procedures and sedated with propofol and fentanyl were monitored in this study: control and intervention. Patients in the intervention group were connected via a facemask to a ventilator that delivered supplemental oxygen (100%) through a standard air-cushion mask. The mask had a built-in leak to facilitate CO2 clearance during CPAP. Patients in the control group received 2-10 L/min of oxygen via nasal cannula or non-rebreather mask. Subjects in the control group were collected in a prior study and used as historical controls. The primary outcome measures were the number of apneic events and the cumulative duration of apneic events. An apneic event was defined as a period longer than 10 s without respiration. The secondary outcome was the area under the curve (AUC) for the arterial oxygen saturation less than 90% versus time during sedative and analgesic administration (time (s) below threshold multiplied by percent below threshold). A desaturation event was defined as a period of time during which arterial oxygen saturation was less than 90%. 29 patients were enrolled in the intervention group and 156 patients were previously enrolled in the control group as part of an earlier study. The median number of apneic events in the control group was 7 compared to 0 in the intervention group. The intervention group experienced apnea less than 1% of the total procedure time compared to 17% in the control group (p < 0.001). There were no desaturation events observed in the 29 patients in the intervention group. In contrast, 27 out of 156 patients in the control group experienced a desaturation event. Average AUC of patients in the control group was 70%-s (time (s) * oxygen saturation below < 90%) (95% CI 32.34-108.60%) whereas the average AUC in intervention group patients was 0%-s (% time (s) * oxygen saturation < 90%) (95% CI 0-0%), p = 0.01. This preliminary study found that CPAP via a tight-fitting mask may be an effective tool to reduce the incidence and duration of obstructive apneic events as well as hemoglobin oxygen desaturation during lower endoscopy procedures that use propofol and fentanyl for sedation.Clinical Trial Registration ClinicalTrials.gov ID: NCT02623270. https://clinicaltrials.gov/ct2/show/NCT02623270 .

Comparison of 7 Different Sensors for Detecting Low Respiratory Rates Using a Single Breath Detection Algorithm in Nonintubated, Sedated Volunteers.

BACKGROUND: Numerous technologies are used to monitor respiratory rates in nonintubated patients. No technology has emerged as the standard. The primary aim of this study was to assess the limits of agreement between a reference sensor signal (respiratory inductance plethysmography bands) and 7 alternative sensor signals (nasal capnometer, nasal pressure transducer, oronasal thermistor, abdominal accelerometer, transpulmonary electrical impedance, peritracheal microphone, and photoplethysmography) for measuring low respiratory rates in sedated, nonintubated, supine volunteers. A unified approach based on a single breath detection algorithm was applied to each sensor to facilitate comparison. We hypothesized that all of the sensor signals would allow detection of low (<10 breaths per minute) respiratory rates to within ±2 breaths per minute of the reference sensor signal. METHODS: Volunteers received remifentanil and propofol infusions at selected target concentration pairs to induce depression of ventilation. Signals from each sensor were analyzed by an identical threshold-based detection algorithm to compute the breathing rate. Bland-Altman limits of agreement and error rate analyses were used to characterize the performance of each sensor compared to the reference sensor. RESULTS: The analysis of the accelerometer and capnometer signals, using Bland-Altman and error rate analyses, showed the highest breath rate agreement (1.96 × standard deviation) of the 7 sensors with -2.1 to 2.2 and -2.5 to 2.7 breaths per minute, respectively. All other signals exhibited wider limits of agreement, with impedance being the widest at -7.8 to 7.4 breaths per minute. For the abdomen accelerometer, 95% of Bland-Altman data points were within ±2 breaths per minute. For the capnometer, 96% of data points were within ±2 breaths per minute. Nasal pressure, thermistor, and microphone all had >80% of data points within ±2 breaths per minute. Impedance and photoplethysmograph signals had 58% and 64%, respectively. CONCLUSIONS: A unified approach can be applied to a variety of sensor signals to estimate respiratory rates in spontaneously breathing, nonintubated, sedated volunteers. However, detecting clinically relevant low respiratory rates (<6 breaths per minute) is a technical challenge. By our analysis, no single sensor was able to detect slow respiratory rates with adequate precision (<±2 breaths per minute of the reference signal). Of the sensors evaluated, capnometers and abdominal accelerometers may be the most reliable sensors for identifying hypopnea and central apnea.

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 55.5 ± 13.2 years (mean ± SD) with a body mass index of 24.6 ± 3.7 kg/m2 were included in data analysis. The total monitoring time was 52.6 h. Thirty-four patients experienced 236 events of apnea lasting for a total of 122.2 min. 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.

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.

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.

Using a novel in-mask non-invasive ventilator microphone to improve talker intelligibility in healthy and hospitalised adults.

Purpose: Non-invasive ventilation (NIV) provides respiratory support without invasive endotracheal intubation but can hinder patients' ability to communicate effectively. The current study presents preliminary results using a novel in-mask ventilator microphone to enhance talker intelligibility while receiving NIV.Method: A proof-of-concept study assessed sentence intelligibility of five healthy adult talkers using a prototype model of the microphone under continuous positive airway pressure (CPAP; 5/5 cm H2O) and bilevel positive airway pressure (BiPAP; 8/4 cm H2O) ventilator conditions. A pilot study then assessed intelligibility, subjective comprehensibility and naturalness, and patient- and conversation partner-reported communication outcomes for eight patients undergoing therapeutic NIV while being treated in an intensive care unit (ICU).Result: Intelligibility increased significantly with the microphone on in the BiPAP condition for healthy volunteers. For patients undergoing NIV in an ICU, intelligibility, comprehensibility, and patient and conversation partner ratings of conversation satisfaction significantly improved with the microphone on. Patients with lower baselines without the microphone in certain measures (intelligibility, comprehensibility) generally showed a greater microphone benefit than patients with higher baselines.Conclusion: Use of a novel microphone integrated into NIV improved intelligibility during ventilation for both healthy volunteers and patients undergoing therapeutic NIV. Additional clinical studies will define precise benefits and implications of such improved intelligibility.

Contributors to Early Mortality in African Americans, the Jackson Heart Study.

Introduction: In recent years, premature "deaths of despair" (ie, due to alcohol, drug use, and suicide) among middle-aged White Americans have received increased attention in the popular press, yet there has been less discussion on what explains premature deaths among young African Americans. In this study, we examined factors related to deaths of despair (alcohol use, drug use, smoking) and contextual factors (perceived discrimination, socioeconomic status, neighborhood conditions) as predictors of premature deaths before the age of 65 years among African Americans. Methods: The Jackson Heart Study (JHS) is a longitudinal cohort study of African Americans in the Jackson, Mississippi, metropolitan statistical area. We included participants younger than 65 years at baseline (n=4000). Participant enrollment began in 2000 and data for these analyses were collected through 2019. To examine predictors of mortality, we calculated multivariable adjusted hazard ratios (HRs; 95% CI), using Cox proportional hazard models adjusted for age, sex, ideal cardiovascular health metrics, drug use, alcohol intake, functional status, cancer, chronic kidney disease, asthma, waist circumference, depression, income, education, health insurance status, perceived neighborhood safety, and exposure to lifetime discrimination. Results: There were 230 deaths in our cohort, which spanned from 2001-2019. After adjusting for all covariates, males (HR, 1.50; 95% CI, 1.11-2.03), participants who used drugs (HR, 1.53; 95% CI, 1.13-2.08), had a heavy alcohol drinking episode (HR, 1.71; 95% CI, 1.22-2.41), reported 0-1 ideal cardiovascular health metrics (HR, 1.78; 95% CI, 1.06-3.02), had cancer (HR, 2.38; 95% CI, 1.41-4.01), had poor functional status (HR, 1.68; 95% CI, 1.19-2.37), or with annual family income less than $25,000 (HR, 1.63; 95% CI, 1.02-2.62) were more likely to die before 65 years of age. Conclusions: In our large cohort of African American men and women, clinical predictors of premature death included poor cardiovascular health and cancer, and social predictors included low income, drug use, heavy alcohol use, and being a current smoker. Clinical and social interventions are warranted to prevent premature mortality in African Americans.

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

OBJECTIVE: There 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 CO(2) rebreathing method for FRC measurement that is based on the change in partial pressure of end-tidal carbon dioxide and volume of CO(2) 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. METHODS: Accuracy and precision of measurements were assessed by comparing the CO(2) rebreathing FRC values to the gold standard, body plethysmography FRC, in twenty spontaneously breathing volunteers. The CO(2) 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 CO(2) 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. RESULTS: Compared to body plethysmography, the accuracy (average error) for the CO(2) rebreathing method during stable ventilation (n = 8) was 0.03 L and precision (1 standard deviation of the error) was 0.29 L (0.8 ± 7.6% of body plethysmography). During stable mechanical ventilation (n = 9), the accuracy was -0.02 L and precision was 0.26 L (-1.1 ± 12.6% of nitrogen washout). CONCLUSIONS: The CO(2) 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 CO(2) 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.

Pregnancy Intention: Associations with Maternal Behaviors and Experiences During and After Pregnancy.

Background: The associations between levels of pregnancy intention and adverse behaviors or experiences during pregnancy and postpartum have not been well described. Materials and Methods: We used 2018 Pregnancy Risk Assessment Monitoring System data from 31 jurisdictions in the United States (n = 32,777) to estimate prevalence of inadequate prenatal care (PNC), inappropriate gestational weight gain, depression during pregnancy, intimate partner violence (IPV) during pregnancy, third trimester smoking, no breastfeeding, no postpartum visit, postpartum depressive symptoms, and postpartum smoking by categories of pregnancy intention: unwanted, ambivalent (i.e., unsure), mistimed (i.e., wanted later), or wanted (i.e., wanted then/sooner). Regression models estimated adjusted prevalence ratios (aPR) and 95% confidence intervals (CIs) of associations between pregnancy intention and maternal behaviors or experiences. Results: Approximately 16% of women reported pregnancy ambivalence. Women with pregnancy ambivalence (versus wanted pregnancies) had higher prevalence of all adverse maternal behaviors and experiences. Separate models found women with unwanted pregnancy (vs. ambivalent) had higher prevalence for depression during pregnancy (aPR: 1.40, 95% CI: 1.21-1.63), IPV (aPR: 1.75, 95% CI: 1.11-2.77), no breastfeeding (aPR: 1.22, 95% CI: 1.04-1.44), no postpartum visit (aPR: 1.28, 95% CI: 1.06-1.55), and postpartum depressive symptoms (aPR: 1.19, 95% CI: 1.00-1.42); Women with mistimed pregnancy (vs. ambivalent) had lower prevalence for inadequate PNC (aPR: 0.89, 95% CI: 0.81-0.98), third trimester smoking (aPR: 0.68, 95% CI: 0.57-0.80), no breastfeeding (aPR: 0.85, 95% CI: 0.74-0.98), and postpartum smoking (aPR: 0.83, 95% CI: 0.73-0.95). Discussion: The results emphasize the importance of recommended screening and care during the preconception, prenatal, and postpartum periods.

The Analysis of How Apnea Influences the Autonomic Nervous System Using Short-Term Heart Rate Variability Indices.

Objective: Frequent cessations of respiration can greatly increase the prevalence rate of arrhythmia. It has been confirmed that cardiac modulation is regulated by the autonomic nervous system (ANS). And heart rate variability (HRV) is widely used as a method to evaluate the function of the ANS. Therefore, we analyzed whether apnea can affect the balance and normal function of the ANS using short-term HRV indices. Methods: Forty-five healthy subjects were asked to breathe normally and hold their breathing to simulate 10 times apnea. Thirty-six patients from the dataset of a sleep laboratory for the diagnosis of sleep disorders with 10 times apnea were included in analysis. We calculated short-term HRV indices of subjects in normal respiratory and apneic states, respectively. Results: Compared with the normal respiratory state, respiration cease would lead to the values of Mean-RR, nLF, LF/HF, and α1 which significantly increased, whereas the values of rMSSD and nHF significantly decreased. Conclusions: Cessations of respiration would lead to an imbalance in the function of the ANS, as well as an increase in fractal characteristics of the heart. These changes in the physiological state are likely to induce and cause the occurrence of arrhythmia, which is regulated by the ANS.

Anatomic dead space cannot be predicted by body weight.

BACKGROUND: Anatomic dead space (also called airway or tracheal dead space) is the part of the tidal volume that does not participate in gas exchange. Some contemporary ventilation protocols, such as the Acute Respiratory Distress Syndrome Network protocol, call for smaller tidal volumes than were traditionally delivered. With smaller tidal volumes, the percentage of each delivered breath that is wasted in the anatomic dead space is greater than it is with larger tidal volumes. Many respiratory and medical textbooks state that anatomic dead space can be estimated from the patient's weight by assuming there is approximately 1 mL of dead space for every pound of body weight. With a volumetric capnography monitor that measures on-airway flow and CO2, the anatomic dead space can be automatically and directly measured with the Fowler method, in which dead space equals the exhaled volume up to the point when CO2 rises above a threshold. METHODS: We analyzed data from 58 patients (43 male, 15 female) to assess the accuracy of 5 anatomic dead space estimation methods. Anatomic dead space was measured during the first 10 min of monitoring and compared to the estimates. RESULTS: The coefficient of determination (r2) between the anatomic dead space estimate based on body weight and the measured anatomic dead space was r2 = 0.0002. The mean +/- SD error between the body weight estimate and the measured dead space was 60 +/- 54 mL. CONCLUSIONS: It appears that the anatomic dead space estimate methods were sufficient when used (as originally intended) together with other assumptions to identify a starting point in a ventilation algorithm, but the poor agreement between an individual patient's measured and estimated anatomic dead space contradicts the assumption that dead space can be predicted from actual or ideal weight alone.

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.

Measurement of functional residual capacity of the lung by partial CO2 rebreathing method during acute lung injury in animals.

BACKGROUND: Several techniques for measuring the functional residual capacity (FRC) of the lungs in mechanically ventilated patients have been proposed, each of which is based on either nitrogen wash-out or dilution of tracer gases. These methods are expensive, difficult, time-consuming, impractical, or require an intolerably large change in the fraction of inspired oxygen. We propose a CO(2) wash-in method that allows automatic and continual FRC measurement in mechanically ventilated patients. METHODS: We measured FRC with a CO(2) partial rebreathing technique, first in a mechanical lung analog, and then in mechanically ventilated animals, before, during, and subsequent to an acute lung injury induced with oleic acid. We compared FRC measurements from partial CO(2) rebreathing to measurements from a nitrogen wash-out reference method. Using an approved animal protocol, general anesthesia was induced and maintained with propofol in 6 swine (38.8-50.8 kg). A partial CO(2) rebreathing monitor was placed in the breathing circuit between the endotracheal tube and the Y-piece. The partial CO(2) rebreathing signal obtained from the monitor was used to calculate FRC. FRC was also measured with a nitrogen wash-out measurement technique. In the animal studies we collected data from healthy lungs, and then subsequent to a lung injury that simulated the conditions of acute lung injury/acute respiratory distress syndrome. The injury was created by intravenously infusing 0.09 mL/kg of oleic acid over a 15-min period. At each stage of the experiment, the positive end-expiratory pressure (PEEP) was set to 0, 5, 10, or 15 cm H(2)O. At each PEEP level we compared the average of 3 CO(2) rebreathing FRC measurements to the average of 3 nitrogen wash-out reference measurements. We also tested the FRC measurement system with a mechanical test lung in which the true FRC could be directly measured. RESULTS: The squared correlation for the linear regression between CO(2) rebreathing and nitrogen wash-out measurements in the animals was r(2) = 0.89 (n = 50). The average error of the CO(2) wash-out system was -87 mL and the limits of agreement were+/- 263 mL. In the mechanical test lung, the average error of the FRC measured via the CO(2) wash-in system was 37 mL, and the limits of agreement were +/- 103 mL, which was equivalent to 1.7% of the true FRC. The squared correlation was r(2) = 0.96. CONCLUSION: These results indicate that FRC measurement via CO(2) rebreathing can reliably detect an FRC decrease during lung injury and can reflect the response of the FRC to treatment with PEEP.

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.).