Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study.

BACKGROUND: Expiratory time constant (τ) objectively assesses the speed of exhalation and can guide adjustments of the respiratory rate and the I:E ratio with the goal of achieving complete exhalation. Multiple methods of obtaining τ are available, but they have not been compared. The purpose of this study was to compare six different methods to obtain τ and to test if the exponentially decaying flow corresponds to the measured time constants. METHODS: In this prospective study, pressure, flow, and volume waveforms of 30 postoperative patients undergoing volume (VCV) and pressure-controlled ventilation (PCV) were obtained using a data acquisition device and analyzed. τ was measured as the first 63% of the exhaled tidal volume (VT) and compared to the calculated τ as the product of expiratory resistance (RE) and respiratory system compliance (CRS), or τ derived from passive flow/volume waveforms using previously published equations as proposed by Aerts, Brunner, Guttmann, and Lourens. We tested if the duration of exponentially decaying flow during exhalation corresponded to the duration of the predicted second and third τ, based on multiples of the first measured τ. RESULTS: Mean (95% CI) measured τ was 0.59 (0.57-0.62) s and 0.60 (0.58-0.63) s for PCV and VCV (p = 0.45), respectively. Aerts method showed the shortest values of all methods for both modes: 0.57 (0.54-0.59) s for PCV and 0.58 (0.55-0.61) s for VCV. Calculated (CRS * RE) and Brunner's τ were identical with mean τ of 0.64 (0.61-0.67) s for PCV and 0.66 (0.63-069) s for VCV. Mean Guttmann's τ was 0.64 (0.61-0.68) in PCV and 0.65 (0.62-0.69) in VCV. Comparison of each τ method between PCV and VCV was not significant. Predicted time to exhale 95% of the VT (i.e., 3*τ) was 1.77 (1.70-1.84) s for PCV and 1.80 (1.73-1.88) s for VCV, which was significantly longer than measured values: 1.27 (1.22-1.32) for PCV and 1.30 (1.25-1.35) s for VCV (p < 0.0001). The first, the second and the third measured τ were progressively shorter: 0.6, 0.4 and 0.3 s, in both ventilation modes (p < 0.0001). CONCLUSION: All six methods to determine τ show similar values and are feasible in postoperative mechanically ventilated patients in both PCV and VCV modes.

Development and evaluation of a mechanical ventilator-sharing system.

Background: During the COVID-19 pandemic surge in the hospitalization of critically ill patients and the global demand for mechanical ventilators, alternative strategies for device sharing were explored. We developed and assessed the performance of a system for shared ventilation that uses clinically available components to individualize tidal volumes under a variety of clinically relevant conditions. The feasibility of remote monitoring of ventilators was also assessed. Methods: By using existing resources and off-the-shelf components, a ventilator-sharing system (VSS) that ventilates 2 patients simultaneously with a single device, and a ventilator monitoring system (VMS) that remotely monitors pulmonary mechanics were developed. The feasibility and effectiveness of VSS and VMS were evaluated in benchtop testing using 2 test lungs on a single ventilator, and then performance was assessed in translational swine models of normal and impaired lung function. Results: In benchtop testing, VSS and VMS delivered the set individualized parameters with minimal % errors in test lungs under pressure- and volume-regulated ventilation modes, suggesting the highest precision and accuracy. In animal studies, the VSS and VMS successfully delivered the individualized mechanical ventilation parameters within clinically acceptable limits. Further, we found no statistically significant difference between the target and measured values. Conclusion: The VSS adequately ventilated 2 test lungs or animals with variable lung conditions. The VMS accurately displayed mechanical ventilation settings, parameters, and alarms. Both of these systems could be rapidly assembled for scaling up to ventilate several critically ill patients in a pandemic or mass casualty disaster situations by leveraging off-the-shelf and custom 3D printed components.

Effect of transcutaneous cervical vagus nerve stimulation on declarative and working memory in patients with Posttraumatic Stress Disorder (PTSD): A pilot study.

BACKGROUND: Posttraumatic stress disorder (PTSD) is associated with changes in multiple neurophysiological systems, including verbal declarative memory deficits. Vagus Nerve Stimulation (VNS) has been shown in preliminary studies to enhance function when paired with cognitive and motor tasks. The purpose of this study was to analyze the effect of transcutaneous cervical VNS (tcVNS) on attention, declarative and working memory in PTSD patients. METHODS: Fifteen PTSD patients were randomly assigned to active tcVNS (N = 8) or sham (N = 7) stimulation in a double-blinded fashion. Memory assessment tests including paragraph recall and N-back tests were performed to assess declarative and working memory function when paired with active/sham tcVNS once per month in a longitudinal study during which patients self-administered tcVNS/sham twice daily. RESULTS: Active tcVNS stimulation resulted in a significant improvement in paragraph recall performance following pairing with paragraph encoding for PTSD patients at two months (p < 0.05). It resulted in a 91 % increase in paragraph recall performance within group (p = 0.03), while sham tcVNS exhibited no such trend in performance improvement. In the N-back study, positive deviations in accuracy, precision and recall measures on different day visits (7,34,64,94) of patients with respect to day 1 revealed a pattern of better performance of the active tcVNS population compared to sham VNS which did not reach statistical significance. LIMITATIONS: Our sample size was small. CONCLUSIONS: These preliminary results suggest that tcVNS improves attention, declarative and working memory, which may improve quality of life and productivity for patients with PTSD. Future studies are required to confirm these results.

Time constant to determine PEEP levels in mechanically ventilated COVID-19 ARDS: a feasibility study.

BACKGROUND: We hypothesized that the measured expiratory time constant (TauE) could be a bedside parameter for the evaluation of positive end-expiratory pressure (PEEP) settings in mechanically ventilated COVID-19 patients during pressure-controlled ventilation (PCV). METHODS: A prospective study was conducted including consecutively admitted adults (n = 16) with COVID-19-related ARDS requiring mechanical ventilation. A PEEP titration using PCV with a fixed driving pressure of 14 cmH2O was performed and TauE recorded at each PEEP level (0 to 18 cmH2O) in prone (n = 29) or supine (n = 24) positions. The PEEP setting with the highest TauE (TauEMAX) was considered to represent the best tradeoff between recruitment and overdistention. RESULTS: Two groups of patterns were observed in the TauE plots: recruitable (R) (75%) and nonrecruitable (NR) (25%). In the R group, the optimal PEEP and PEEP ranges were 8 ± 3 cmH2O and 6-10 cmH2O for the prone position and 9 ± 3 cmH2O and 7-12 cmH2O for the supine position. In the NR group, the optimal PEEP and PEEP ranges were 4 ± 4 cmH2O and 1-8 cmH2O for the prone position and 5 ± 3 cmH2O and 1-7 cmH2O for the supine position, respectively. The R group showed significantly higher optimal PEEP (p < 0.004) and PEEP ranges (p < 0.001) than the NR group. Forty-five percent of measurements resulted in the most optimal PEEP being significantly different between the positions (p < 0.01). Moderate positive correlation has been found between TauE vs CRS at all PEEP levels (r2 = 0.43, p < 0.001). CONCLUSIONS: TauE may be a novel method to assess PEEP levels. There was wide variation in patient responses to PEEP, which indicates the need for personalized evaluation.

Use of a Portable Electronic Interface Improves Clinical Handoffs and Adherence to Lung Protective Ventilation.

Background: Mechanical ventilation (MV) is used to support patients with respiratory impairment. Evidence supports the use of lung-protective ventilation (LPV) during MV to improve outcomes. However, studies have demonstrated poor adherence to LPV guidelines. We hypothesized that an electronic platform adapted to a hand-held tablet receiving real-time ventilatory parameters could increase clinician awareness of key LPV parameters. Furthermore, we speculated that an electronic shift-change tool could improve the quality of clinician handoffs. Methods: Using a specially designed Wi-Fi dongle to transmit data from three ventilators and a respiratory monitor, we implemented a system that displays data from all ventilators under the care of a Respiratory Care Practitioner (RCP) on an electronic tablet. In addition, the tablet created a handoff checklist to improve shift-change communication. In a simulated ICU environment, we monitored the performance of eight RCPs at baseline and while using the system. Results: Using the system, the time above guideline Pplat decreased by 74% from control, and the time outside the VT range decreased by 60% from control, p = 0.007 and 0.015, respectively. The handoff scores improved quality significantly from 2.8 to 1.6 on a scale of 1 to 5 (1 being best), p = 0.03. Conclusion: In a simulated environment, an electronic RT tool can significantly improve shift-change communication and increase the RCP's level of LPV adherence.

Patients alter power of breathing as the primary response to changes in pressure support ventilation.

INTRODUCTION: The patient-ventilator relationship is dynamic as the patient's health fluctuates and the ventilator settings are modified. Spontaneously breathing patients respond to mechanical ventilation by changing their patterns of breathing. This study measured the physiologic response when pressure support (PS) settings were modified during mechanical ventilation. METHODS: Subjects were instrumented with a non-invasive pressure, flow, and carbon dioxide airway sensor to estimate tidal volume, respiratory rate, minute ventilation, and end-tidal CO2. Additionally, a catheter was used to measure esophageal pressure and estimate effort exerted during breathing. Respiratory function measurements were obtained while PS settings were adjusted 569 times between 5 and 25 cmH2O. RESULTS: Data was collected on 248 patients. The primary patient response to changes in PS was to adjusting effort (power of breathing) followed by adjusting tidal volume. Changes in respiratory rate were less definite while changes in minute ventilation and end-tidal CO2 appeared unrelated to the change in PS. CONCLUSION: The data indicates that patients maintain a set minute ventilation by adjusting their breathing rate, volume, and power. The data indicates that the subjects regulate their Ve and PetCO2 by adjusting power of breathing and breathing pattern.

Breathing variability predicts the suggested need for corrective intervention due to the perceived severity of patient-ventilator asynchrony during NIV.

Patient-ventilator asynchrony is associated with intolerance to noninvasive ventilation (NIV) and worsened outcomes. Our goal was to develop a tool to determine a patient needs for  intervention by a practitioner due to the presence of patient-ventilator asynchrony. We postulated that a clinician can determine when a patient needs corrective intervention due to the perceived severity of patient-ventilator asynchrony. We hypothesized a new measure, patient breathing variability, would indicate when corrective intervention is suggested by a bedside practitioner due to the perceived severity of patient-ventilator asynchrony. With IRB approval data was collected on 78 NIV patients. A panel of experts reviewed retrospective data from a development set of 10 NIV patients to categorize them into one of the three categories. The three categories were; "No to mild asynchrony-no intervention needed", "moderate asynchrony-non-emergent corrective intervention required", and "severe asynchrony-immediate intervention required". A stepwise regression with a F-test forward selection criterion was used to develop a positive linear logic model predicting the expert panel's categorizations of the need for corrective intervention. The model was incorporated into a software tool for clinical implementation. The tool was implemented prospectively on 68 NIV patients simultaneous to a bedside practitioner scoring the need for corrective intervention due to the perceived severity of patient-ventilator asynchrony. The categories from the tool and the practitioner were compared with the rate of agreement, sensitivity, specificity, and receiver operator characteristic analyses. The rate of agreement in categorizing the suggested need for clinical intervention due to the perceived presence of patient-ventilator asynchrony between the tool and experienced bedside practitioners was 95% with a Kappa score of 0.85 (p < 0.001). Further analysis found a specificity of 84% and sensitivity of 99%. The tool appears to accurately match the suggested need for corrective intervention by a bedside practitioner. Application of the tool allows for continuous, real time, and non-invasive monitoring of patients receiving NIV, and may enable early corrective interventions to ameliorate potential patient-ventilator asynchrony.

Clinical decision support recommending ventilator settings during noninvasive ventilation.

NIV therapy is used to provide positive pressure ventilation for patients. There are protocols describing what ventilator settings to use to initialize NIV; however, the guidelines for titrating ventilator settings are less specific. We developed an advisory system to recommend NIV ventilator setting titration and recorded respiratory therapist agreement rates at the bedside. We developed an algorithm (NIV advisor) to recommend when to change the non-invasive ventilator settings of IPAP, EPAP, and FiO2 based on patient respiratory parameters. The algorithm utilized a multi-target approach; oxygenation, ventilation, and patient effort. The NIV advisor recommended ventilator settings to move the patient's respiratory parameters in a preferred target range. We implemented a pilot study evaluating the usability of the NIV advisor on 10 patients receiving critical care with non-invasive ventilation (NIV). Respiratory therapists were asked their agreement on recommendations from the NIV advisor at the patient's bedside. Bedside respiratory therapists agreed with 91% of the ventilator setting recommendations from the NIV advisor. The POB and VT values were the respiratory parameters that were most often out of the preferred target range. The IPAP ventilator setting was the setting most often considered in need of changing by the NIV advisor. The respiratory therapists agreed with the majority of the recommendations from the NIV advisor. We consider the IPAP recommendations informative in providing the respiratory therapist assistance in targeting preferred POB and Vt values, as these values were frequently out of the target ranges. This pilot implementation was unable to produce the results required to determine the value of the EPAP recommendations. The FiO2 recommendations from the NIV advisor were treated as ancillary information behind the IPAP recommendations.

Evaluating Fundal Dominant Contractions on Spatiotemporal Electrohysterography as a Marker for Effective Labor Contractions.

OBJECTIVE: To evaluate if fundal (F) dominance of the electrohysterogram is associated with vaginal delivery and lack of F dominance is associated with cesarean for labor dystocia. STUDY DESIGN: We conducted a prospective cohort study of nulliparous women in spontaneous labor at ≥36 weeks. Clinicians were blinded to electrohysterography data which were in addition to standard cardiotocography. All contractions in the hour preceding diagnosis of complete cervical dilation (for women delivering vaginally) or the hour preceding the decision for cesarean were analyzed. RESULTS: Of 224 patients, 167 had evaluable data. The proportion of F dominant contractions was not different for women undergoing cesarean for labor dystocia (n = 11) compared with all others (n = 156)-88.7 ± 10.2 versus 86.0 ± 11.4%; p = 0.44. Results were similar when comparing the cesarean for labor dystocia group to those undergoing cesarean for other indications (n = 10) and vaginal deliveries (n = 146)-88.7 ± 10.2 versus 86.5 ± 10.0 versus 85.9 ± 11.5%; p = 0.74. CONCLUSION: We were unable to confirm our earlier finding that F dominance of the electrohysterogram is associated with vaginal delivery and lack of F dominance is associated with cesarean for dystocia.

Photoplethysmography and Heart Rate Variability for the Diagnosis of Preeclampsia.

BACKGROUND: The goal of this study was to determine a set of timing, shape, and statistical features available through noninvasive monitoring of maternal electrocardiogram and photoplethysmography that identifies preeclamptic patients. METHODS: Pregnant women admitted to Labor and Delivery were monitored with pulse oximetry and electrocardiogram for 30 minutes. Photoplethysmogram features and heart rate variability were extracted from each data set and applied to a sequential feature selection algorithm to discriminate women with preeclampsia with severe features, from normotensive and hypertensive controls. The classification boundary was chosen to minimize the expected misclassification cost. The prior probabilities of the misclassification costs were assumed to be equal. RESULTS: Thirty-seven patients with clinically diagnosed preeclampsia with severe features were compared with 43 normotensive controls; all were in early labor or beginning induction. Six variables were used in the final model. The area under the receiver operating characteristic curve was 0.907 (standard error [SE] = 0.004) (sensitivity 78.2% [SE = 0.3%], specificity 89.9% [SE = 0.1%]) with a positive predictive value of 0.883 (SE = 0.001). Twenty-eight subjects with chronic or gestational hypertension were compared with the same preeclampsia group, generating a model with 5 features with an area under the curve of 0.795 (SE = 0.007; sensitivity 79.0% [SE = 0.2%], specificity 68.7% [SE = 0.4%]), and a positive predictive value of 0.799 (SE = 0.002). CONCLUSIONS: Vascular parameters, as assessed noninvasively by photoplethysmography and heart rate variability, may have a role in screening women suspected of having preeclampsia, particularly in areas with limited resources.

Decision support system facilitates rapid decreases in pressure support and appropriate inspiratory muscle workloads in adults with respiratory failure.

PURPOSE: A commercially available decision support system (DSS) provides guidance for setting inspiratory pressure support (PS) to maintain work of breathing (WOB/min), breathing frequency (f), and tidal volume (VT) in proper clinical ranges (VentAssist™). If these values are outside the proper clinical range patients may suffer fatigue, atrophy, hypoventilation, hyperventilation, volutrauma, or VT deficiency. The purpose of our study was to evaluate the increase of the percentage of breaths in the targeted clinical ranges when the DSS guidance for setting the PS was followed. MATERIALS AND METHODS: The study included 43 intubated adults with respiratory failure in an academic medical intensive care unit. Each of the patients had received ventilatory support for >24h with no weaning trials attempted. Clinicians switched the ventilator to PS then proceeded to utilize the guidance recommended by the DSS for setting PS for 21 patients (intervention group); while the clinicians caring for the remaining 23 patients did not have access to the DSS (control group). RESULTS: The use of a DSS to set PS level increased the percentage of breaths in the targeted clinical range [28% to 48%, p value<0.0001]. An unexpected result was that while following the DSS 18 of the 21 patients were rapidly weaned to minimal ventilator settings within 46±38min; however, when the DSS was not available weaning to minimal ventilator settings lasted 21±12h [p value<0.0001]. CONCLUSIONS: The DSS is successful at assisting clinicians on how to set PS specific to a patient's individual demands (VT and f) while accounting for their breathing effort (WOB/min). The DSS appears to promote rapid weaning of PS to minimal ventilator settings when appropriate.

Monitoring Fetal Heart Rate during Labor: A Comparison of Three Methods.

The purpose of the study was to compare the accuracy of a noninvasive fetal heart rate monitor with that of ultrasound, using a fetal scalp electrode as the gold standard, in laboring women of varying body habitus, throughout labor and delivery. Laboring women requiring fetal scalp electrode were monitored simultaneously with the investigational device (noninvasive fetal ECG), ultrasound, and fetal scalp electrode. An algorithm extracted the fetal heart rate from the noninvasive fetal ECG signal. Each noninvasive device recording was compared with fetal scalp electrode with regard to reliability by positive percent agreement and accuracy by root mean squared error. Seventy-one women were included in this analysis. Positive percent agreement was 83.4 ± 15.4% for noninvasive fetal ECG and 62.4 ± 26.7% for ultrasound. The root mean squared error compared with fetal scalp electrode-derived fetal heart rate was 4.8 ± 2.0 bpm for noninvasive fetal ECG and 14.3 ± 8.2 bpm for ultrasound. The superiority of noninvasive fetal ECG was maintained for stages 1 and 2 of labor and increases in body mass index. Compared with fetal scalp electrode-derived fetal heart rate, noninvasive fetal ECG is more accurate and reliable than ultrasound for intrapartum monitoring for stages 1 and 2 of labor and is less affected by increasing maternal body mass index. This confirms the results of other workers in this field.

Performance, Reliability, Usability, and Safety of the ID-Cap System for Ingestion Event Monitoring in Healthy Volunteers: A Pilot Study.

Background: Nonadherence to prescribed medications is an important consideration in the clinical management of patients and in clinical research and drug development. The ID-Cap System is a novel technology that provides an objective measure of medication ingestion and enables real-time reporting of verified medication adherence data at the dose level. The ID-Cap System consists of an ingestible microsensor that is embedded in an oral dosage form and, once activated by stomach fluid, communicates digital messages to an external wearable reader to confirm ingestion. Objective: The objective of this exploratory study was to evaluate the performance, reliability, usability, and safety of the ID-Cap System for remote monitoring of 20 ingestion events over four weeks in 20 healthy volunteers. Design: This study was an open-label, single-arm, exploratory study of the ID-Cap System. The study design included the following three phases: 1) screening phase, 2) treatment phase consisting of 20 daily capsule ingestion events over a four-week period, and 3) follow-up phase consisting of a follow-up study visit that included an abdominal X-ray and a follow-up phone call. The initial use of the ID-Cap Reader and ingestion of the first study capsule were directly observed by the investigator during the first study visit. Subsequent study capsule ingestions were completed outside the research facility at the study participant's home or other location of his or her choice with ingestion assessed using the ID-Cap System. Setting: The study was conducted at a single clinical research site in Gainesville, Florida. Participants: Twenty healthy volunteers were enrolled in this four-week pilot study that was conducted between September and November 2014. Measurements: Study measurements included ID-Tag detection indicating capsule ingestion, utilization of the ID-Cap System consistent with instructions for use, adverse event reports, discontinuations of the System during the study, and safety assessments related to excretion of the ID-Tags through abdominal X-ray evaluations. Results: Positive detection accuracy was 100 percent for the 20 directly observed ingestions of study capsules that occurred during the initial study visits. Of the 384 ingestion events that were self-administered by the study participants without direct observation, 371 were accurately detected using the ID-Cap System. Overall adherence to the prescribed study capsules as measured by the ID-Cap System was 97.75 percent (391 detections/400 expected ingestion events). Significant intra-individual and inter-individual variability in the timing of self-administered doses was observed in this study. No adverse events were reported, and no study participants discontinued use of the ID-Cap System for any reason during the study. There was no evidence indicating retention of ID-Tags based on abdominal X-ray evaluations. Conclusion: The ID-Cap System enables accurate measurement of medication adherence for oral drug therapy at the dose level. This study supports the clinical validation of the technology and feasibility in using the system for the collection and real-time reporting of medication adherence in the clinical management of patients and in clinical research and drug development.

Monitoring Uterine Activity during Labor: Clinician Interpretation of Electrohysterography versus Intrauterine Pressure Catheter and Tocodynamometry.

Objective The aim of this article was to compare clinical interpretation of uterine activity tracings acquired by tocodynamometry and electrohysterography with the gold standard, intrauterine pressure. Study Design Using data from a previous study, subjects who had simultaneous monitoring with all three uterine activity devices were included in this study. These were parturients who required intrauterine pressure catheter (IUPC) placement for obstetric indication. A Web-based application displayed scrolling 30-minute segments of uterine activity. Two blinded obstetricians and two blinded obstetric nurses independently reviewed the segments, marking uninterpretable segments and the peak of each contraction. Interpretability was compared using positive percent agreement. False positives are contractions marked in the noninvasive strip that have no corresponding contraction in the IUPC strip. False negatives are the reverse. Results A total of 135 segments, acquired during either Stage 1 (active labor) or Stage 2 (pushing), from 105 women, were included in this analysis. For all four observers, both interpretability and sensitivity of electrohysterography exceeded that of tocodynamometry (p < 0.0001). This remained true for the obese population (96 segments). Conclusion Compared with the IUPC, electrohysterography is more sensitive and provides tracings that are more often interpretable than tocodynamometry for intrapartum monitoring; electrohysterography is also less affected by increasing maternal body mass index.

Real time noninvasive estimation of work of breathing using facemask leak-corrected tidal volume during noninvasive pressure support: validation study.

We describe a real time, noninvasive method of estimating work of breathing (esophageal balloon not required) during noninvasive pressure support (PS) that uses an artificial neural network (ANN) combined with a leak correction (LC) algorithm, programmed to ignore asynchronous breaths, that corrects for differences in inhaled and exhaled tidal volume (VT) from facemask leaks (WOBANN,LC/min). Validation studies of WOBANN,LC/min were performed. Using a dedicated and popular noninvasive ventilation ventilator (V60, Philips), in vitro studies using PS (5 and 10 cm H2O) at various inspiratory flow rate demands were simulated with a lung model. WOBANN,LC/min was compared with the actual work of breathing, determined under conditions of no facemask leaks and estimated using an ANN (WOBANN/min). Using the same ventilator, an in vivo study of healthy adults (n = 8) receiving combinations of PS (3-10 cm H2O) and expiratory positive airway pressure was done. WOBANN,LC/min was compared with physiologic work of breathing/min (WOBPHYS/min), determined from changes in esophageal pressure and VT applied to a Campbell diagram. For the in vitro studies, WOBANN,LC/min and WOBANN/min ranged from 2.4 to 11.9 J/min and there was an excellent relationship between WOBANN,LC/breath and WOBANN/breath, r = 0.99, r(2) = 0.98 (p < 0.01). There were essentially no differences between WOBANN,LC/min and WOBANN/min. For the in vivo study, WOBANN,LC/min and WOBPHYS/min ranged from 3 to 12 J/min and there was an excellent relationship between WOBANN,LC/breath and WOBPHYS/breath, r = 0.93, r(2) = 0.86 (p < 0.01). An ANN combined with a facemask LC algorithm provides noninvasive and valid estimates of work of breathing during noninvasive PS. WOBANN,LC/min, automatically and continuously estimated, may be useful for assessing inspiratory muscle loads and guiding noninvasive PS settings as in a decision support system to appropriately unload inspiratory muscles.

Creating clinical decision support systems for respiratory medicine.

Clinical decision support systems are vital for advances in improving patient therapeutic care. We share lessons learned from creating two respiratory clinical decisions support systems for ventilating patients in a critical care setting.

Oxygenation advisor recommends appropriate positive end expiratory pressure and FIO2 settings: retrospective validation study.

A decision support, rule-based oxygenation advisor that provides guidance for setting positive end expiratory pressure (PEEP) and fractional inhaled oxygen concentration (FIO2) for patients with respiratory failure is described. The target oxygenation goal is to achieve and maintain pulse oximeter oxygen saturation (SpO2) ≥ 88 and ≤ 95%, as posited by the Acute Respiratory Distress Syndrome Network, by recommending appropriate combinations of PEEP and FIO2. For patient safety, the oxygenation advisor monitors mean arterial blood pressure (MAP) to ensure it is ≥ 65 mmHg for hemodynamic stability and inspiratory plateau pressure (Pplt) so it is ≤ 30 cm H2O for lung protection. The purpose of this validation study was to compare attending physicians' recommendations to those recommendations of the oxygenation advisor for setting PEEP and FIO2. Adults with respiratory failure (n = 117) receiving ventilatory support were studied. PEEP, FIO2, SpO2, MAP, and Pplt are input variables into the advisor. Recommendations to increase, maintain, or decrease PEEP and FIO2 are the oxygenation advisor's output variables. Physicians' recommendations for setting PEEP and FIO2 were recorded; the oxygenation advisor's recommendations were also recorded for comparison. At all times, ventilator settings were based on recommendations from attending physicians. PEEP ranged from 2 to 22 cm H2O and FIO2 ranged from 0.30 to 0.65. A total of 326 recommendations by the oxygenation advisor and attending physicians were made to increase, maintain, or decrease PEEP and FIO2. There was a very significant relationship (p < 0.0001) between recommendations of the oxygenation advisor and attending physicians for setting PEEP and FIO2. The agreement rate for recommendations by the oxygenation advisor and attending physicians was 92%. The K statistic, a test of the strength of agreement of recommendations between the oxygenation advisor and attending physicians, was 0.82 (p < 0.0001), indicating "almost perfect agreement". Relationships for recommendations made by the oxygenation advisor and attending physicians for setting PEEP and FIO2 were excellent, PEEP: r = 0.98 (p < 0.01), r(2) = 0.96; FIO2: r = 0.91 (p < 0.01), r(2) = 0.83, bias and precision values were negligible. A novel oxygenation advisor provided continuous and automatic recommendations for setting PEEP and FIO2 that were shown to be as good as the clinical judgment of experienced attending physicians. For all patients, the target oxygenation goal was achieved. Concerning patient safety, the oxygenation advisor detected those occasions when MAP and Pplt were in potentially unsafe ranges.

Expiratory time constant for determinations of plateau pressure, respiratory system compliance, and total resistance.

INTRODUCTION: We hypothesized the expiratory time constant (ƬE) may be used to provide real time determinations of inspiratory plateau pressure (Pplt), respiratory system compliance (Crs), and total resistance (respiratory system resistance plus series resistance of endotracheal tube) (Rtot) of patients with respiratory failure using various modes of ventilatory support. METHODS: Adults (n = 92) with acute respiratory failure were categorized into four groups depending on the mode of ventilatory support ordered by attending physicians, i.e., volume controlled-continuous mandatory ventilation (VC-CMV), volume controlled-synchronized intermittent mandatory ventilation (VC-SIMV), volume control plus (VC+), and pressure support ventilation (PSV). Positive end expiratory pressure as ordered was combined with all aforementioned modes. Pplt, determined by the traditional end inspiratory pause (EIP) method, was combined in equations to determine Crs and Rtot. Following that, the ƬE method was employed, ƬE was estimated from point-by-point measurements of exhaled tidal volume and flow rate, it was then combined in equations to determine Pplt, Crs, and Rtot. Both methods were compared using regression analysis. RESULTS: ƬE, ranging from mean values of 0.54 sec to 0.66 sec, was not significantly different among ventilatory modes. The ƬE method was an excellent predictor of Pplt, Crs, and Rtot for various ventilatory modes; r2 values for the relationships of ƬE and EIP methods ranged from 0.94 to 0.99 for Pplt, 0.90 to 0.99 for Crs, and 0.88 to 0.94 for Rtot (P <0.001). Bias and precision values were negligible. CONCLUSIONS: We found the ƬE method was just as good as the EIP method for determining Pplt, Crs, and Rtot for various modes of ventilatory support for patients with acute respiratory failure. It is unclear if the ƬE method can be generalized to patients with chronic obstructive lung disease. ƬE is determined during passive deflation of the lungs without the need for changing the ventilatory mode and disrupting a patient's breathing. The ƬE method obviates the need to apply an EIP, allows for continuous and automatic surveillance of inspiratory Pplt so it can be maintained ≤ 30 cm H2O for lung protection and patient safety, and permits real time assessments of pulmonary mechanics.

Monitoring uterine activity during labor: a comparison of 3 methods.

OBJECTIVE: Tocodynamometry (Toco; strain gauge technology) provides contraction frequency and approximate duration of labor contractions but suffers frequent signal dropout, necessitating repositioning by a nurse, and may fail in obese patients. The alternative invasive intrauterine pressure catheter (IUPC) is more reliable and adds contraction pressure information but requires ruptured membranes and introduces small risks of infection and abruption. Electrohysterography (EHG) reports the electrical activity of the uterus through electrodes placed on the maternal abdomen. This study compared all 3 methods of contraction detection simultaneously in laboring women. STUDY DESIGN: Upon consent, laboring women were monitored simultaneously with Toco, EHG, and IUPC. Contraction curves were generated in real-time for the EHG, and all 3 curves were stored electronically. A contraction detection algorithm was used to compare frequency and timing between methods. Seventy-three subjects were enrolled in the study; 14 were excluded due to hardware failure of 1 or more of the devices (n = 12) or inadequate data collection duration (n = 2). RESULTS: In comparison with the gold-standard IUPC, EHG performed significantly better than Toco with regard to the Contractions Consistency Index (CCI). The mean CCI for EHG was 0.88 ± 0.17 compared with 0.69 ± 0.27 for Toco (P < .0001). In contrast to Toco, EHG was not significantly affected by obesity. CONCLUSION: Toco does not correlate well with the gold-standard IUPC and fails more frequently in obese patients. EHG provides a reliable noninvasive alternative, regardless of body habitus.