Non-invasive Respiratory Volume Monitor Research Articles

Pediatric obstructive sleep apnea: a prospective observational study of respiratory events in the immediate recovery period after adenotonsillectomy

BackgroundAdenotonsillectomy is often curative for pediatric obstructive sleep apnea, yet children remain at high risk of respiratory complications in the postoperative period. We sought to determine the incidence and risk factors for respiratory depression and airway obstruction, as well as clinically apparent respiratory events in the post-anesthesia care unit (PACU) in high-risk children after adenotonsillectomy. MethodsIn this prospective cohort study, we enrolled 60 high-risk children having adenotonsillectomy. Our primary outcome was respiratory depression and airway obstruction in the PACU measured using a noninvasive respiratory volume monitor (RVM) and defined by episodes of predicted minute ventilation less than 40% for at least 2 min. We measured clinically apparent respiratory events using continuous observation by trained study staff. ResultsThe median (range) age of our sample was 4 years (1, 16) and 27 (45%) were female. Black and Hispanic race children comprised 80% (n = 48) of our cohort. Thirty-nine (65%) had at least one episode of PACU respiratory depression or airway obstruction measured using the RVM, while only 21 (35%) had clinically apparent respiratory events. Poisson regression demonstrated the following associations with an increase in episodes of respiratory depression and airway obstruction: BMI Z-score less than −1 (estimate 3.91; [95%CI 1.49–10.23]), BMI Z-score 1–2 (estimate 2.04; [1.20–3.48]), and two or more comorbidities (estimate 1.96; [1.11–3.46]). ConclusionsRespiratory volume monitoring in the immediate postoperative period after pediatric high-risk adenotonsillectomy identifies impaired ventilation more frequently than is clinically apparent.

The evaluation of a non-invasive respiratory monitor in ards patients in supine and prone position

Purpose: The Prone positioning in addition to non invasive respiratory support is commonly used in patients with acute respiratory failure. The aim of this study was to assess the accuracy of an impedance-based non-invasive respiratory volume monitor (RVM) in supine and in prone position. Methods: In sedated, paralyzed and mechanically ventilated patients in volume-controlled mode with acute respiratory distress syndrome scheduled for prone positioning it was measured and compared non-invasively tidal volume and respiratory rate provided by the RVM in supine and, subsequently, in prone position, by maintaining unchanged the ventilatory setting. Results: Forty patients were enrolled. No significant difference was found between measurements in supine and in prone position either for tidal volume (p = 0.795; p = 0.302) nor for respiratory rate (p = 0.181; p = 0.604). Comparing supine vs. prone position, the bias and limits of agreements for respiratory rate were 0.12 bpm (-1.4 to 1.6) and 20 mL (-80 to 120) for tidal volume. Conclusions: The RVM is accurate in assessing tidal volume and respiratory rate in prone compared to supine position. Therefore, the RVM could be applied in non-intubated patients with acute respiratory failure receiving prone positioning to monitor respiratory function.

The Evaluation of a Noninvasive Respiratory Volume Monitor in Mechanically Ventilated Neonates and Infants

(Anesth Analg. 2022;134:141–148) Monitoring respiratory function is an essential part of caring for children in ambulatory and hospital settings. Yet, assessing ventilation in children by physical examination is difficult due to fast respiratory rates (RRs) and small tidal volumes (TV). In addition, pulse oximeters, capnometers, and other noninvasive respiratory monitors may not reliably assess minute ventilation (MV). While pulse oximeters detect oxygen desaturation, they do not directly monitor ventilation. Capnometers have also been found unreliable in intubated children. Recently a respiratory volume monitor (RVM) (ExSpiron, Watertown, MA) has been developed to measure TV, RRs, and MV noninvasively. It has been found to be accurate in adults and children above 1 year of age. The aim of this study is to evaluate the accuracy of the RVM on RRs, TV, and MV in neonates and infants below 1 year.

Breathing variability during propofol/remifentanil procedural sedation with a single additional dose of midazolam or s-ketamine: a prospective observational study

PurposeRegulation of spontaneous breathing is highly complex and may be influenced by drugs administered during the perioperative period. Because of their different pharmacological properties we hypothesized that midazolam and s-ketamine exert different effects on the variability of minute ventilation (MV), tidal volume (TV) and respiratory rate (RR).MethodsPatients undergoing procedural sedation (PSA) with propofol and remifentanil received a single dose of midazolam (1–3 mg, n = 10) or s-ketamine (10–25 mg, n = 10). We used non-invasive impedance-based respiratory volume monitoring to record RR as well as changes in TV and MV. Variability of these three parameters was calculated as coefficients of variation.ResultsTV and MV decreased during PSA to a comparable extent in both groups, whereas there was no significant change in RR. In line with our hypothesis we observed marked differences in breathing variability. The variability of MV (– 47.5% ± 24.8%, p = 0.011), TV (– 42.1% ± 30.2%, p = 0.003), and RR (– 28.5% ± 29.3%, p = 0.011) was significantly reduced in patients receiving midazolam. In contrast, variability remained unchanged in patients receiving s-ketamine (MV + 16% ± 45.2%, p = 0.182; TV +12% ± 47.7%, p = 0.390; RR +39% ± 65.2%, p = 0.129). After termination of PSA breathing variables returned to baseline values.ConclusionsWhile midazolam reduces respiratory variability in spontaneously breathing patients undergoing procedural sedation, s-ketamine preserves variability suggesting different effects on the regulation of spontaneous breathing.

Variations in respiratory rate do not reflect changes in tidal volume or minute ventilation after major abdominal surgery

Monitoring of postoperative pulmonary function usually includes respiratory rate and oxygen saturation measurements. We hypothesized that changes in postoperative respiratory rate do not correlate with changes in tidal volume or minute ventilation. In addition, we hypothesized that variability of minute ventilation and tidal volume is larger than variability of respiratory rate. Respiratory rate and changes in tidal volume and in minute ventilation were continuously measured in 27 patients during 24 h following elective abdominal surgery, using an impedance-based non-invasive respiratory volume monitor (ExSpiron, Respiratory Motion, Waltham, MA, US). Coefficients of variation were used as a measure for variability of respiratory rate, tidal volume and minute ventilation. Data of 38,149 measurements were analyzed. We found no correlation between respiratory rate and tidal volume or minute ventilation (r2 = 0.02 and 0.01). Mean respiratory rate increased within the first 24 h after abdominal surgery from 13.9 ± 2.5 to 16.2 ± 2.4 breaths/min (p = 0.008), while tidal volume and minute ventilation remained unchanged (p = 0.90 and p = 0.18). Of interest, variability of respiratory rate (0.21 ± 0.06) was significantly smaller than variability of tidal volume (0.37 ± 0.12, p < 0.001) and minute ventilation (0.41 ± 0.12, p < 0.001). Changes in postoperative respiratory rate do not allow conclusions about changes in tidal volume or minute ventilation. We suggest that postoperative alveolar hypoventilation may not be recognized by monitoring respiratory rate alone. Variability of respiratory rate is smaller than variability in tidal volume and minute ventilation, suggesting that adaptations of alveolar ventilation to metabolic needs may be predominately achieved by variations in tidal volume.

Evaluation of Noninvasive Respiratory Volume Monitoring in the PACU of a Low Resource Kenyan Hospital

This research aims to evaluate the use of the noninvasive respiratory volume monitor (RVM) compared to the standard of care (SOC) in the Post-Anesthesia Care Unit (PACU) of Kijabe Hospital, Kenya. The RVM provides real-time measurements for quantitative monitoring of non-intubated patients. Our evaluation was focused on the incidence of postoperative opioid-induced respiratory depression (OIRD). The RVM cohort (N = 50) received quantitative OIRD assessment via the RVM, which included respiratory rate, minute ventilation, and tidal volume. The SOC cohort (N = 46) received qualitative OIRD assessment via patient monitoring with oxygenation measurements (SpO2) and physical examination. All diagnosed cases of OIRD were in the RVM cohort (9/50). In the RVM cohort, participants stayed longer in the PACU and required more frequent airway maneuvers and supplemental oxygen, compared to SOC (all p < 0.05). The SOC cohort may have had fewer diagnoses of OIRD due to the challenging task of distinguishing hypoventilation versus OIRD in the absence of quantitative data. To account for the higher OIRD risk with general anesthesia (GA), a subgroup analysis was performed for only participants who underwent GA, which showed similar results. The use of RVM for respiratory monitoring of OIRD may allow for more proactive care.

Respiratory Volume Monitoring in the Perioperative Setting Across Multiple Centers.

The prevalence of nuisance (technical) alarms is the leading cause of alarm fatigue resulting in decreased awareness and a reduction in effective care. The Joint Commission identified in their National Patient Safety goals alarm fatigue as a major safety issue. The introduction of noninvasive respiratory volume monitoring (RVM) has implications for effective perioperative respiratory status management. We evaluated this within the Kaiser Permanente health system. This observational study was conducted at 4 hospitals in the Kaiser Permanente system. Standard data from RVM, pulse oximetry, and capnography were collected postoperatively in the post-anesthesia care unit (PACU) and/or on the general hospital floor. Device-specific alarm types, rates, and respective actions were recorded and analyzed by non-study staff. RVM was applied to 247 subjects (143 females, body mass index 32.3 ± 8.7 kg/m2, age 60.9 ± 13.9 y) providing 2,321 h. RVM alarms occurred 605 times (0.25 alarms/h); 64% were actionable and addressed, 17% were not addressed, 13% were self-resolved, and only 6% were nuisance. In a subgroup, RVM completed all 127 h of monitoring, whereas oximetry with capnography only completed 51 h with 12.9 alarms/h (73% nuisance). The overall RVM alarm rate was significantly lower than with either pulse oximeters or capnography monitors. We saw a nearly 1,000-fold reduction in nuisance alarms compared to capnography and a 20-50-fold reduction in nuisance alarms compared to pulse oximetry. Our study indicates that alarm fatigue due to nuisance alarms continues to be a clinical challenge in perioperative settings. Among the 3 common technologies for respiratory function monitoring, RVM had the lowest rate of overall technical alarms and the highest rate of compliance. Furthermore, with early interventions, none of the subjects monitored with RVM suffered any negative outcomes.

Minute ventilation assessment in the PACU is useful to predict postoperative respiratory depression following discharge to the floor: A prospective cohort study

Study Objective.Reliably identifying patients at risk for postoperative respiratory depression (RD) remains an unmet need. We hypothesized that defined low minute ventilation events (LMVe) near the end of the post-anesthesia care unit (PACU) stay identifies patients at RD risk on the general hospital floor (GHF). DesignProspective observational study. SettingTertiary care, urban academic medical center. PACU and GHF during the first postoperative night. PatientsOne hundred-and-nineteen adult, ASA I – III patients undergoing elective surgery under general anesthesia completed the study. InterventionsData collection from a non-invasive respiratory volume monitor and the patients' medical record perioperatively through the first postoperative night. MeasurementsMinute ventilation (MV), tidal volume (TV) and respiratory rate (RR) were measured continuously in the PACU and on the GHF. MV was counted as the percent of individual predicted MV (MVPRED), and RD was defined as ≥1 LMVe/h on the GHF. Based on the number of LMVes within 30 min before PACU discharge, patients were grouped into A, ‘Not-At-Risk’: 0 LMVe and B, ‘At-Risk’: ≥1 LMVes. Unpaired t-test, Mann-Whitney U test, ANOVA, Kruskal-Wallis test, Fisher's exact test, sensitivity and specificity and ROC curve analyses were applied as appropriate. Main resultsOne hundred-and-six (89%) and 13 (11%) patients met Group A and B criteria respectively. The latter had more LMVe/h on the GHF (median 0.81 vs 0, p ≤ 0.001), and their MVPRED was significantly less. Following opioid administration, the LMVe likelihood was 43% in Group B and 5.6% in Group A. As a predictor for RD on the GHF, the number of LMVe in the last 30 min of PACU, had positive and negative predictive values of 61.5% and 90.6%, respectively. ConclusionMinute ventilation assessment in the PACU as described in this study can be useful to identify patients at risk for postoperative respiratory depression.

Low minute ventilation episodes during anesthesia recovery following intraperitoneal surgery as detected by a non-invasive respiratory volume monitor.

An electrical impedance-based noninvasive respiratory volume monitor (RVM) accurately reports minute volume, tidal volume and respiratory rate. Here we used the RVM to quantify the occurrence of and evaluate the ability of clinical factors to predict respiratory depression in the post-anesthesia care unit (PACU). RVM generated respiratory data were collected from spontaneously breathing patients following intraperitoneal surgeries under general anesthesia admitted to the PACU. Respiratory depression was defined as low minute ventilation episode (LMVe, < 40% predicted minute ventilation for at least 2min). We evaluated for associations between clinical variables including minute ventilation prior to opioid administration and LMVe following the first PACU administration of opioid. Also assessed was a low respiratory rate (< 8 breaths per minute) as a proxy for LMVe. Of 107 patients, 38 (36%) had LMVe. Affected patients had greater intraoperative opioid dose, P = 0.05. PACU opioids were administered to 45 (42.1%) subjects, of which 27 (25.2%) had LMVe (P = 0.42) within 30min following opioid. Pre-opioid minute ventilation < 70% of predicted normal value was associated with LMVe, P < 0.01, (sensitivity = 100%, specificity = 81%).Low respiratory rate was a poor predictor of LMVe (sensitivity = 11.8%). Other clinical variables (e.g., obstructive sleep apnea) were not found to be predictors of LMVe. Using RVM we identified that mild, clinically nondetectable, respiratory depression prior to opioid administration in the PACU was associated with the development of substantial subsequent respiratory depression during the PACU stay.

Assessment of perioperative minute ventilation in obese versus non-obese patients with a non-invasive respiratory volume monitor

BackgroundMonitoring the adequacy of spontaneous breathing is a major patient safety concern in the post-operative setting. Monitoring is particularly important for obese patients, who are at a higher risk for post-surgical respiratory complications and often have increased metabolic demand due to excess weight. Here we used a novel, noninvasive Respiratory Volume Monitor (RVM) to monitor ventilation in both obese and non-obese orthopedic patients throughout their perioperative course, in order to develop better monitoring strategies.MethodsWe collected respiratory data from 62 orthopedic patients undergoing elective joint replacement surgery under general anesthesia using a bio-impedance based RVM with an electrode PadSet placed on the thorax. Patients were stratified into obese (BMI ≥ 30) and non-obese cohorts and minute ventilation (MV) at various perioperative time points was compared against each patient’s predicted minute ventilation (MVPRED) based on ideal body weight (IBW) and body surface area (BSA). The distributions of MV measurements were also compared across obese and non-obese cohorts.ResultsObese patients had higher MV than the non-obese patients before, during, and after surgery. Measured MV of obese patients was significantly higher than their MVPRED from IBW formulas, with BSA-based MVPRED being a closer estimate. Obese patients also had greater variability in MV post-operatively when treated with standard opioid dosing.ConclusionsOur study demonstrated that obese patients have greater variability in ventilation post-operatively when treated with standard opioid doses, and despite overall higher ventilation, many of them are still at risk for hypoventilation. BSA-based MVPRED formulas may be more appropriate than IBW-based ones when estimating the respiratory demand of obese patients. The RVM allows for the continuous and non-invasive assessment of respiratory function in both obese and non-obese patients.

Quantification of respiratory depression during pre-operative administration of midazolam using a non-invasive respiratory volume monitor.

BackgroundPre-operative administration of benzodiazepines can cause hypoventilation—a decrease in minute ventilation (MV)—commonly referred to as “respiratory compromise or respiratory depression.” Respiratory depression can lead to hypercarbia and / or hypoxemia, and may heighten the risk of other respiratory complications. Current anesthesia practice often places patients at risk for respiratory complications even before surgery, as respiratory monitoring is generally postponed until the patient is in the operating room. In the present study we examined and quantified the onset of respiratory depression following the administration of a single dose of midazolam in pre-operative patients, using a non-invasive respiratory volume monitor that reports MV, tidal volume (TV), and respiratory rate (RR).MethodsImpedance-based Respiratory Volume Monitor (RVM) data were collected and analyzed from 30 patients prior to undergoing orthopedic or general surgical procedures. All patients received 2.0 mg of midazolam intravenously at least 20 minutes prior to the induction of anesthesia and the effects of midazolam on the patient's respiratory function were analyzed.ResultsWithin 15 minutes of midazolam administration, we noted a significant decrease in both MV (average decrease of 14.3% ± 5.9%, p<0.05) and TV (22.3% ± 4.5%, p<0.001). Interestingly, the corresponding RR increased significantly by an average of 10.3% ± 4.7% (p<0.05). Further analysis revealed an age-dependent response, in which elderly patients (age≥65 years, n = 6) demonstrated greater reductions in MV and TV and a lack of compensatory RR increase. In fact, elderly patients experienced an average decrease in MV of 34% ± 6% (p<0.05) compared to an average decrease of 9% ± 6% (p<0.05) in younger patients.ConclusionsWe were able to quantify the effects of pre-operative midazolam administration on clinically significant respiratory parameters (MV, TV and RR) using a non-invasive RVM, uncovering that the respiratory depressive effect of benzodiazepines affect primarily TV rather than RR. Such respiratory monitoring data provide the opportunity for individualizing dosing and adjustment of clinical interventions, especially important in elderly patients. With additional respiratory data, clinicians may be able to better identify and quantify respiratory depression, reduce adverse effects, and improve overall patient safety.

The Evaluation of a Noninvasive Respiratory Volume Monitor in Pediatric Patients Undergoing General Anesthesia

Pediatric patients following surgery are at risk for respiratory compromise such as hypoventilation and hypoxemia depending on their age, comorbidities, and type of surgery. Quantitative measurement of ventilation in nonintubated infants/children is a difficult and inexact undertaking. Current respiratory assessment in nonintubated patients relies on oximetry data, respiratory rate (RR) monitors, and subjective clinical assessment, but there is no objective measure of respiratory parameters that could be utilized to predict early respiratory compromise. New advances in technology and digital signal processing have led to the development of an impedance-based respiratory volume monitor (RVM, ExSpiron, Respiratory Motion, Inc, Waltham, MA). The RVM has been shown to provide accurate real-time, continuous, noninvasive measurements of tidal volume (TV), minute ventilation (MV), and RR in adult patients.In this prospective observational study, our primary aim was to determine whether the RVM accurately measures TV, RR, and MV in pediatric patients. A total of 72 pediatric patients (27 females, 45 males), ASA I to III, undergoing general anesthesia with endotracheal intubation were enrolled. After endotracheal intubation, continuous data of MV, TV, and RR were recorded from the RVM and an in-line monitoring spirometer (NM3 monitor, Phillips Healthcare). RVM and NM3 measurements of MV, TV, and RR were compared during a 10-minute period prior to the incision ("Presurgery") and a 10-minute period after the end of surgery ("Postsurgery"). Relative errors were calculated over 1-minute segment within each 10-minute period. Bias, precision, and accuracy were calculated using Bland-Altman analyses and paired-difference equivalence tests were performed. Combined across the Presurgery and Postsurgery periods, the RVM's mean measurement bias (RVM - NM3 measurement) for MV was -3.8% (95% limits of agreement) (±1.96 SD): (-19.9% to 12.2%), for TV it was -4.9 (-21.0% to 11.3%), and for RR it was 1.1% (-4.1% to 6.2%). The mean measurement accuracies for MV, TV, and RR were 11.9%, 12.0%, and 4.2% (0.6 breaths/min), respectively. Note that lower accuracy numbers correspond to more accurate RVM measurements. The equivalence tests rejected the null hypothesis that the RVM and NM3 have different mean values and conclude with 90% power that the measurements of MV, TV, and RR from the RVM and NM3 are equivalent within ±10%. Our data indicate acceptable agreement between RVM and NM3 measurements in pediatric mechanically-ventilated patients. Future studies assessing the capability of the RVM to detect respiratory compromise in other clinical settings are needed.

A risk stratification algorithm using non-invasive respiratory volume monitoring to improve safety when using post-operative opioids in the PACU.

Late detection of respiratory depression in non-intubated patients compromises patient safety. SpO2 is a lagging indicator of respiratory depression and EtCO2 has proven to be unreliable in non-intubated patients. A decline in minute ventilation (MV) is the earliest sign of respiratory depression. A non-invasive respiratory volume monitor (RVM) that provides accurate, continuous MV measurements enables clinicians to predict and quantify respiratory compromise. For this observational study, practitioners were blinded to the RVM measurements and pain management followed the usual routine. Patients were stratified by their MV on PACU admission and classified as "At-Risk" or "Not-At-Risk," with progression to "Low MV" status following opioids assessed for each category. The purpose was to determine if stratifying based on MV on PACU arrival could identify patients at higher risk for respiratory depression. Ability to identify in advance patients at higher risk for respiratory depression following standard opioid dosing would drive changes in pain management and improve patient care. RVM and opioid administration data from 150 PACU patients following elective joint-replacement surgery were collected in an observational study. "Predicted" MV (MVPRED) and "Percent Predicted" (MVMEASURED/MVPRED×100%) were calculated for each patient using standard formulas. Prior to opioid administration, patients were classified as either "Not-At-Risk" (MV≥80% MVPRED) or "At-Risk" (MV<80% MVPRED). "Low MV" was defined as MV<40% MVPRED. Post-operative apnea (POA) was defined as ≥5 ten-second apneas per hour of PACU stay. We compared the incidences of Low MV following a single opioid dose, POA, and Low MV at discharge for both groups. In the PACU, 74/150 patients received opioids. Within 15min of opioid administration, 32% (24/74) developed Low MV. The risk-stratification algorithm identified 22/24 patients (92% sensitivity). Only 46% of them had POA, and the majority had Low MV without POA. At discharge, 29/150 patients had Low MV and those receiving opioids were 50% more likely to display Low MV (23 vs. 16%). The RVM can identify patients at-risk for opioid-induced respiratory depression and/or experiencing POA. Monitoring of MV can guide opioid-dosing regimens and may increase patient safety across the continuum of care.

The Incidence of Postoperative Respiratory Compromise May Not Be Reduced by Spinal Anesthesia

The Incidence of Postoperative Respiratory Compromise May Not Be Reduced by Spinal Anesthesia

(129) The use of a non-invasive respiratory volume monitor to identify patients at high-risk for opioid-induced respiratory depression for a low-dose opioid regimen in the PACU

(129) The use of a non-invasive respiratory volume monitor to identify patients at high-risk for opioid-induced respiratory depression for a low-dose opioid regimen in the PACU

Non-invasive respiratory volume monitoring for quantification of respiratory depression after benzodiazepine administration

Benzodiazepines are used in many of settings to induce sedation, but can cause a reduction in respiratory drive. Objective monitoring of the effect of benzodiazepines on respiratory status in non-intubated patients has been difficult, putting patient safety at risk. A non-invasive respiratory volume monitor (RVM) that provides continuous measurement of minute ventilation (MV), tidal volume (TV) and respiratory rate (RR) was used to quantify the effects of midazolam on respiratory status in spontaneously breathing patients.

Abstract 19116: Assessment of Perioperative Minute Ventilation in Obese versus Non-Obese Patient Using a Non-Invasive Respiratory Volume Monitor

Introduction: Adequate respiration is critical to survival and can be influenced by opioids, sedatives and apnea. Direct monitoring of ventilation has previously not been available for non-intubated patients. Reliance on indirect measures (SpO2, RR) may delay needed interventions and obese patients may be at further risk. A non-invasive respiratory volume monitor (RVM) providing real-time direct measures of MV, TV &amp; RR in non-intubated patients is used to assess respiratory status in obese and non-obese patients. Methods: Data collected from an impedance-based RVM (ExSpiron-1Xi, Respiratory Motion, Waltham, MA) in 62 orthopedic patients (65.4 ±12.0 yrs, BMI: 30.8 ±6.0 kg/m 2 ) before, during &amp; after surgery (PACU arrival &amp; discharge) were compared to predicted MV (MV PRED ) based on IBW. Ventilator MV (Apollo, Draeger, Telford, PA) during GA was assumed to be adjusted to maintain appropriate end-tidalCO 2 . Patients were stratified based on obesity status (cutoff BMI=30). The distributions of MV at various times were compared (non-obese vs obese) using an un-paired 1-sided t-test &amp; a 2-sample F-test. Results: Despite similar MV PRED in both groups (6.2±0.2; 6.1±0.2 L/min, p&gt;0.3) obese patients were managed at a higher MV during surgery (6.1±0.2; 5.3±0.2 L/min, p&lt;0.01). MV differences were far greater preoperatively (9.7±0.4 vs. 6.7±0.3 L/min), at PACU arrival (11.4 ±1.2; 6.8±0.7 L/min) &amp; discharge (7.7±0.5; 5.0±0.6 L/min, p&lt;0.01 all, Fig 1). Patient-to-patient variability in MV was similar in both groups pre-op, but larger in obese patients. Even with the large average MV in obese patients, 6% of them left the PACU with MV&lt;40% MV PRED . Conclusions: On average, obese patients have greater MV than predicted by IBW formula, likely due to greater metabolic demand. Post-op, obese patients have greater variability in ventilation when treated with standard opioid doses &amp; may be at greater risk for hypoventilation. RVM can provide data for individualized treatment plans.

Abstract 16248: Comparison of a Non-Invasive Respiratory Volume Monitor to End-Tidal CO2 in Measuring Changes in Minute Ventilation

Introduction: Monitoring respiratory performance is a challenge. Use of secondary indicators like oxygen saturation (SpO 2 ) and capnography (EtCO 2 ) have introduced delay in diagnosis and can produce false alarms. EtCO 2 in non-intubated patients has been problematic. We compared performance of an EtCO 2 monitor to a respiratory volume monitor (RVM), which provides accurate (error &lt;10%) measurements of minute ventilation (MV), tidal volume &amp; respiratory rate, to assess changes in respiratory status in non-intubated subjects. Methods: Continuous RVM (ExSpiron, Respiratory Motion, Waltham, MA) and capnography data (Capnostream 20, SmartCapnoLine Plus &amp; Filterline Set, Covidien, Mansfield, MA) were collected from 39 subjects. The relationship between EtCO 2 &amp; MV for each patient was quantified &amp; EtCO 2 sensitivity to MV changes and mean EtCO 2 values were compared across the two EtCO 2 sampling techniques (paired t-test). Results: A strong negative correlation between MV changes and EtCO 2 changes was found (similar between nasal sampling (NS) and in-line sampling (IS) ( -0.6 ±0.1 v -0.7±0.1 mmHg/(L/min), p&gt;0.1, Fig 1A)). IS readings were higher than NS for each patient. In the same patients (normal breathing) the average IS EtCO 2 was 36.7 ±0.7 vs 33.7±0.6 mmHg for NS (p&lt;0.01) despite larger MV (8.74 ±0.5 vs 7.0±0.5 L/min). Similar disparity was present during hypo &amp; hyperventilation (Fig 1B&amp;C). Regardless of sampling methodology, EtCO 2 displayed poor resolution in response to large swings in MV (13 &amp; 14 mmHg in response to 17 &amp; 21 fold increase in MV; IS &amp; NS, respectively). Conclusions: Under controlled experimental conditions &amp; with an in-line sensor capable of capturing 100% of exhaled air, EtCO 2 did not report large swings in MV with fidelity. Commonly used nasal sampling introduced a systematic bias that could further delay informing clinicians of dangerously low MV. RVM provides a direct measure of MV, eliminating the lag between a change in MV and secondary measurements.

Non-invasive respiratory volume monitoring in patients with traumatic thoracic injuries

Background Respiratory decompensation is common after traumatic thoracic injuries such as multiple rib fractures and pulmonary contusions. A continuous, non-invasive, impedance-based respiratory volume monitor generates right and left tidal volume measurements, reflecting air exchange in the lungs and derives an instantaneous respiratory rate. The feasibility of using unilateral respiratory volume monitor–based tidal impedance measurements to monitor respiratory status in trauma patients is evaluated. Methods Three intensive care unit patients with three or more rib fractures following blunt trauma had continuous respiratory volume monitor measurements with a novel non-invasive impedance-based device (ExSpiron, Respiratory Motion Inc., Waltham, MA) and corresponding clinical data to permit analysis. Tidal impedance measurements were collected from both the injured and non-injured sides and converted into bilateral respiratory volume monitor measurements using advanced algorithms. Results In Patient 1, following evacuation of a pneumothorax, the respiratory volume monitor showed a significant increase in tidal measurements coupled with a compensatory decrease in tidal measurements on the uninjured side and a decrease in respiratory rate. In Patient 2, tidal measurements were only slightly decreased on both the injured side and uninjured side; respiratory rate remained unchanged. This patient remained stable and required no intervention. Patient 3 demonstrated a sustained decrease in tidal measurements on the injured side that corresponded with radiograph findings and clinical deterioration leading to the need for endotracheal intubation. Conclusions The results from these cases demonstrate that respiratory volume monitor can generate unilateral respiratory tidal measurements and respiratory rate in patients with traumatic thoracic injuries. Continuous respiratory volume monitor in patients with thoracic trauma has strong potential for application in the military, aeromedical, and other austere environments where respiratory monitoring is problematic. Future studies to investigate the utility of this technology are warranted.

Incidence of Postoperative Respiratory Depression and Postoperative Apnea in the Obese General Surgical Population

Figure 1: A non-invasive Respiratory Volume Monitor (RVM, ExSpiron, Respiratory Motion, Inc.) that provides continuous, real-time, non-invasive measurements of MV, TV and RR. Figure shows standard electrode placement. One electrode is placed at the sternal notch, another is placed on the xiphoid and the third is placed in the right mid-axillary line at the level of the xiphoid. Post-operative respiratory depression (PORD) and sleep disordered breathing, including obstructive sleep apnea (OSA) are well-established risk factors for post-operative respiratory complications, with increased prevalence in the obese population. Current post-operative monitoring does not provide quantitative measurements of ventilation, and the true incidences of PORD and post-operative apnea (POA) remain unknown. Because these incidences often increase with opioid use, accurately determining the risk associated with both PORD and POA is especially important given the prevalent use of opioids and other respiratory depressants in post-operative analgesia.