Christopher Voscopoulos

Evaluation of a Novel Noninvasive Respiration Monitor Providing Continuous Measurement of Minute Ventilation in Ambulatory Subjects in a Variety of Clinical Scenarios

BACKGROUND:Currently there is no technology that noninvasively measures the adequacy of ventilation in nonintubated patients. A novel, noninvasive Respiratory Volume Monitor (RVM) has been developed to continuously measure and display minute ventilation (MV), tidal volume (TV), and respiratory rate (RR) in a variety of clinical settings. We demonstrate the RVM’s accuracy and precision as compared with a standard spirometer under a variety of clinically relevant breathing patterns in nonintubated subjects. METHODS:Thirty-one voluntary subjects completed the primary study. MV, TV, and RR measurements were collected from the RVM and spirometer simultaneously for each participant on day 1 and day 2 and analyzed to determine accuracy, precision, and bias for normal, fast, slow, irregular, and closed-glottis breathing. RESULTS:Data demonstrated that RVM and spirometer measurements of MV and TV are equivalent in a wide range of ambulatory subjects with an average error <10% (95% confidence interval for accuracy <16%, precision <12%, and bias <11%). Repeated measures analysis of variance found no significant difference between spirometry and RVM individual measurements of MV, TV, and RR (P > 0.7), whereas a paired-difference equivalent test demonstrated, with 99% power, that both MV and TV measurements from the 2 devices are equivalent within ±15%. CONCLUSIONS:This study demonstrates RVM’s clinically relevant accuracy and precision in measuring MV, TV, and RR over a 24-hour period and during various breathing patterns.

Continuous noninvasive respiratory volume monitoring for the identification of patients at risk for opioid-induced respiratory depression and obstructive breathing patterns.

BACKGROUND Opioid-induced respiratory depression (OIRD) and postoperative apnea (POA) can lead to complications after surgery or traumatic injury. Previously, real-time monitoring of respiratory insufficiency and identification of apneic events have been difficult. A noninvasive respiratory volume monitor (RVM) that reports minute ventilation (MV), tidal volume, and respiratory rate is now available. The RVM was used to report the effect of opioids on respiratory status as well as demonstrate apneic breathing patterns in a hospital postanesthesia care unit. METHODS RVM traces were collected from 132 patients. Predicted MV (MVPRED) for each patient was used to calculate and the “percent predicted” MV (MVMEASURED / MVPRED × 100%) before opioid administration. Patients were stratified patients into two categories: “at risk,” MV of less than 80% MVPRED, and “not at risk,” MV of 80% MVPRED or greater. After opioid dosing, patients with MV of less than 40% MVPRED were categorized as “unsafe.” POA was defined as more than five apneic or hypopneic events per hour. RESULTS Of the 132 patients, 50 received opioids. Baseline MV was 7.2 ± 0.5 L/min. The MV-based protocol classified 18 of 50 patients as at risk before opioid administration. After the first opioid dose administration, at-risk patients experienced an average MV decrease (36.7% ± 8.5% MVPRED) and 13 of 18 decreased into unsafe; the 32 not at-risk patients experienced a lesser average MV decrease (76.9% ± 6.3% MVPRED). Only 1 of 32 not at-risk patients had a decrease in MV to unsafe. The proposed protocol had a sensitivity of 93% and a specificity of 86%. Of the 132 patients, 26 displayed POA. Of the 26 patients, 12 experienced POA without receiving opioids. Of the 26 patients with POA, 14 also received opioids, and of those, 6 were classified as unsafe. CONCLUSION This investigation indicates that at risk and unsafe respiratory patterns occur frequently after procedure. RVM provides continuous noninvasive objective measurements of OIRD and POA. The RVM may prove a useful tool in opioid dosing and in recognition and management of POA and strong potential value in the rapid detection of OIRD and apnea in the contemporary combat casualty environment. LEVEL OF EVIDENCE Care management study, level V.

Non-Invasive Respiratory Volume Monitoring to Detect Apnea in Post-Operative Patients: Case Series

Obstructive sleep apnea (OSA) is a potential independent risk factor for postoperative complications, adverse surgical outcomes, and longer hospital stays. Obese patients with OSA have increased post-operative complications. An estimated 25-30% of pre-operative patients are at a high risk for OSA. A novel, non-invasive respiratory volume monitor (RVM) has been developed to provide a real time respiratory curve demonstrating lung volumes as well as a continuous, display of minute ventilation, tidal volume and respiratory rate. Clinical application of this device in the post-anesthesia care unit (PACU) can “unmask” post-operative apneic events resulting from partial or complete airway collapse due to the residual effects of narcotic administration and volatile and/or intravenous anesthetics. Clinical examples from two patients, one with known OSA and one without a previous diagnosis of OSA, monitored in the PACU with RVM are presented here. Post-operatively both patients had an increase in apneic episodes with significant decreases in their MV during apneic episodes after opioid administration as compared to pre-op baseline. In addition, oxygen saturation, for both patients, which is an essential component of current respiratory monitoring remained normal in the cases presented, despite the significant decreases in MV. Continuous RVM monitoring demonstrates both changes in respiratory patterns and overall adequacy of ventilation, and allows practitioners to quantify the increase in the number and duration apneic episodes as a response to narcotic administration. These case studies demonstrate that a non-invasive respiratory volume monitoring system can detect and quantify respiratory disturbances that currently go undetected.

Non-invasive respiratory volume monitoring identifies opioid-induced respiratory depression in an orthopedic surgery patient with diagnosed obstructive sleep apnea: a case report

IntroductionObstructive sleep apnea and opioid-induced respiratory depression can unpredictably threaten respiratory competence in the post-anesthesia care unit. Current respiratory monitoring relies heavily on respiratory rate and oxygen saturation, as well as subjective clinical assessment. These assessments have distinct limitations, and none provide a real-time, objective, quantitative direct measurement of respiratory status. A novel, non-invasive respiratory volume monitor uses bioimpedance to provide accurate, quantitative measurements of minute ventilation, tidal volume and respiratory rate continuously in real time, providing a direct measurement of ventilation.Case presentationThe case describes an orthopedic surgery patient (54-year-old Caucasian man, body mass index 33.7kg/m2) with diagnosed obstructive sleep apnea in whom the respiratory volume monitor data depicted persistent apneic behavior undetected by other monitoring. The monitor was able to detect a sudden reduction in minute ventilation after initial opioid administration in the post-anesthesia care unit. The patient had sustained low minute ventilation until discharge. Neither respiratory rate data from the hospital monitor nor oxygen saturation readings reflected the respiratory decompensation, remaining within normal limits even during sustained low minute ventilation.ConclusionsThe events of this case illustrate the limitations of current respiratory rate monitoring and pulse oximetry in the evaluation of post-surgical respiratory status. Our patient displayed stable respiratory rate and no evidence of desaturation, despite sustained low minute ventilation, and he received opioids in the post-anesthesia care unit despite already compromised ventilation. Because the available monitoring did not indicate the patient’s true respiratory status, he was treated with additional opioids, markedly increasing his risk for further respiratory decline.

A Comparison of the Speed, Success Rate, and Retention of Rescue Airway Devices Placed by First-responder Emergency Medical Technicians: A High-fidelity Human Patient Simulation Study

BACKGROUND Current airway management for most first-responder basic emergency medical technicians (EMT-Bs) does not include the use of blind-advanced-airway devices. OBJECTIVE To compare the speed, success rates, and skill retention with which EMT-Bs providers can place three blind-advanced-airway devices. METHODS Prospective study of 43 EMT-Bs trained in the use of the Esophageal-Tracheal-Combitube(®) (ETC), King LT(®) (KLT), and Laryngeal Mask Airway(™) (LMA). The time it took each participant to place each device correctly and ventilate a human patient simulator was assessed. Primary outcome measures were the success rate of proper insertion for each device and time interval from initiation of mouth insertion to initiation of chest rise. To assess skill retention, at 3 months the providers were reassessed under exact conditions. RESULTS At Day 1, time required to place an ETC, LMA, and KLT were 32.7 ± 12.3, 19.2 ± 6.2, and 20.1 ± 6.6 s, respectively. Using paired t-tests, LMA and KLT were faster than ETC, p < 0.0001. At 3 months, pair-wise comparisons showed the ETC took longer to place than the KLT and LMA, p < 0.0001; and the LMA took longer to place than the KLT, p = 0.0034 (36.4 ± 13.1 ETC, 24.8 ± 12.4 LMA, 19.0 ± 6.9 KLT). There was no statistical difference of failures in placing any device. CONCLUSIONS Comparison of three rescue airway devices placed by EMT-Bs providers showed that it takes significantly longer to place an ETC compared to an LMA and KLT both on Day 1 and 3 months later. Three-month retention studies revealed that it took significantly longer to place an LMA compared to the KLT.