A Comparison of Measurements of Change in Respiratory Status in Spontaneously Breathing Volunteers by the ExSpiron Noninvasive Respiratory Volume Monitor Versus the Capnostream Capnometer

Effects of asymmetric nasal high-flow cannula on carbon dioxide in hypercapnic patients: A randomised crossover physiological pilot study

Nasal high flow (NHF) therapy is an established form of non invasive respiratory support used in acute and chronic care. Recently, a new high flow nasal cannula with asymmetric prongs was approved for clinical use. The clinical benefits of the new cannula have not yet been defined and no evidence are available on the use of asymmetric NHF support in patient with Chronic Obstructive Pulmonary Disease (COPD). We conducted a single-centre, prospective, physiologic, crossover, randomised study to investigate the effects on partial pressure of carbon dioxide (PaCO2) levels of two different nasal cannula ("asymmetric" vs "standard" nasal interface) in 20 COPD hypercapnic patients. All patients were recovering from an acute exacerbation that required hospitalisation and had persistent hypercapnia, despite having attained a stable pH. After enrolment, two 90-min trials with the asymmetric nasal high flow interface (Optiflow + Duet, Fisher & Paykel Healthcare Ltd., New Zealand) or the standard interface (Optiflow, Fisher & Paykel Healthcare Ltd., New Zealand) were randomly applied and a washout period of 60 min between the two treatments was performed for minimising the carryover effect. Study results suggested that the asymmetrical cannula did not significantly decrease PaCO2 compared with the standard cannula. Similar performances were also observed in terms of diaphragm activity, dyspnoea and patient's comfort. Interestingly, asymmetric NHF cannula performed significantly better in reducing the dead space ventilation and increasing the ventilatory efficiency in more advanced COPD patients with more severe hypercapnia higher baseline PaCO2 values (PaCO2 ≥ 65 mmHg at baseline).   .

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.

A non-invasive continuous and real-time volumetric monitoring in spontaneous breathing subjects based on bioimpedance-ExSpiron®Xi: a validation study in healthy volunteers

Tidal volume (TV) monitoring breath-by-breath is not available at bedside in non-intubated patients. However, TV monitoring may be useful to evaluate the work of breathing. A non-invasive device based on bioimpedance provides continuous and real-time volumetric tidal estimation during spontaneous breathing. We performed a prospective study in healthy volunteers aimed at evaluating the accuracy, the precision and the trending ability of measurements of ExSpiron®Xi as compared with the gold standard (i.e. spirometry). Further, we explored whether the differences between the 2 devices would be improved by the calibration of ExSpiron®Xi with a pre-determined tidal volume. Analysis accounted for the repeated nature of measurements within each subject. We enrolled 13 healthy volunteers, including 5 men and 8 women. Tidal volume, TV/ideal body weight (IBW) and respiratory rate (RR) measured with spirometer (TVSpirometer) and with ExSpiron®Xi (TVExSpiron) showed a robust correlation, while minute ventilation (MV) showed a weak correlation, in both non/calibrated and calibrated steps. The analysis of the agreement showed that non-calibrated TVExSpiron underestimated TVspirometer, while in the calibrated steps, TVExSpiron overestimated TVspirometer. The calibration procedure did not reduce the average absolute difference (error) between TVSpirometer and TVExSpiron. This happened similarly for TV/IBW and MV, while RR showed high accuracy and precision. The trending ability was excellent for TV, TV/IBW and RR. The concordance rate (CR) was >95% in both calibrated and non-calibrated measurements. The trending ability of minute ventilation was limited. Absolute error for both calibrated and not calibrated values of TV, TV/IBW and MV accounting for repeated measurements was variably associated with BMI, height and smoking status. Conclusions: Non-invasive TV, TV/IBW and RR estimation by ExSpiron®Xi was strongly correlated with tidal ventilation according to the gold standard spirometer technique. This data was not confirmed for MV. The calibration of the device did not improve its performance. Although the accuracy of ExSpiron®Xi was mild and the precision was limited for TV, TV/IBW and MV, the trending ability of the device was strong specifically for TV, TV/IBW and RR. This makes ExSpiron®Xi a non-invasive monitoring system that may detect real-time tidal volume ventilation changes and then suggest the need to better optimize the patient ventilatory support.

Postoperative esketamine improves ventilation after video-assisted thoracoscopic lung resection: A double-blinded randomized controlled trial

Background

Pain management after lung resection plays a crucial role in reducing postoperative pulmonary complications (PPCs). This study aimed to examine the effect of postoperative esketamine infusion as an adjunct to opioid analgesia on ventilation and pulmonary complications in patients underwent lung resection.

Methods

Patients undergoing video-assisted thoracoscopic lung resection were randomly assigned to either the esketamine group or the control group. The esketamine group received a 24-h infusion of 1.5 mcg/ml sufentanil combined with 0.75 mcg/ml esketamine after surgery, while the control group received 1.5 mcg/ml sufentanil alone. The primary outcome measure was low minute ventilation, and the secondary outcome measures were hypoxemia, PaO2/FiO2 levels, postoperative pulmonary complications, hospital stay duration, ambulation time, Visual Analogue Scale (VAS) score, depression and anxiety levels, sleep quality, and analgesia satisfaction.

Results

80 patients were randomly divided into two groups: the esketamine group (n = 40) and the control group (n = 40). The esketamine group exhibited notably reduced incidence of low minute ventilation (P = 0.014), lower occurrence of postoperative pulmonary complications (PPCs) compared to the control group (P = 0.039), and decreased incidence of hypoxemia (P = 0.003). Furthermore, the esketamine group showed improved outcomes with lower VAS scores on the second postoperative day and enhanced sleep quality (P < 0.001) after the surgery.

Conclusions

Postoperative esketamine infusion with opioids improved ventilation and reduced PPCs after lung resection, warranting further clinical studies.

Trial registration

This study was registered on ClinicalTrials.gov (Trial ID: NCT05458453, https://clinicaltrials.gov/ct2/show/NCT05458453).

A technique to measure tidal volume during noninvasive respiratory support by continuous-flow helmet CPAP

PURPOSE

The coronavirus disease 2019 (COVID-19) pandemic has promoted the use of helmet continuous positive airway pressure (CPAP) for noninvasive respiratory support in hypoxic respiratory failure patients, despite the lack of tidal volume monitoring. We evaluated a novel technique designed to measure tidal volume during noninvasive continuous-flow helmet CPAP.

METHODS

A bench model of spontaneously breathing patients undergoing helmet CPAP therapy (three positive end-expiratory pressure [PEEP] levels) at different levels of respiratory distress was used to compare measured and reference tidal volumes. Tidal volume measurement by the novel technique was based on helmet outflow-trace analysis. Helmet inflow was increased from 60 to 75 and 90 L/min to match the patient's peak inspiratory flow; an additional subset of tests was conducted under the condition of purposely insufficient inflow (i.e., high respiratory distress and 60 L/min inflow).

RESULTS

The tidal volumes examined herein ranged from 250 to 910 mL. The Bland‒Altman analysis showed a bias of -3.2 ± 29.3 mL for measured tidal volumes compared to the reference, corresponding to an average relative error of -1 ± 4.4%. Tidal volume underestimation correlated with respiratory rate (rho = .411, p = .004) but not with peak inspiratory flow, distress, or PEEP. When the helmet inflow was maintained purposely low, tidal volume underestimation occurred (bias - 93.3 ± 83.9 mL), corresponding to an error of -14.8 ± 6.3%.

CONCLUSION

Tidal volume measurement is feasible and accurate during bench continuous-flow helmet CPAP therapy by the analysis of the outflow signal, provided that helmet inflow is adequate to match the patient's inspiratory efforts. Insufficient inflow resulted in tidal volume underestimation. In vivo data are needed to confirm these findings.

Non-Invasive Mapping of Cerebral Autoregulation Using Near-Infrared Spectroscopy: A Study Protocol

The ability of cerebral vessels to maintain a fairly constant cerebral blood flow is referred to as cerebral autoregulation (CA). Using near-infrared spectroscopy (NIRS) paired with arterial blood pressure (ABP) monitoring, continuous CA can be assessed non-invasively. Recent advances in NIRS technology can help improve the understanding of continuously assessed CA in humans with high spatial and temporal resolutions. We describe a study protocol for creating a new wearable and portable imaging system that derives CA maps of the entire brain with high sampling rates at each point. The first objective is to evaluate the CA mapping system's performance during various perturbations using a block-trial design in 50 healthy volunteers. The second objective is to explore the impact of age and sex on regional disparities in CA using static recording and perturbation testing in 200 healthy volunteers. Using entirely non-invasive NIRS and ABP systems, we hope to prove the feasibility of deriving CA maps of the entire brain with high spatial and temporal resolutions. The development of this imaging system could potentially revolutionize the way we monitor brain physiology in humans since it would allow for an entirely non-invasive continuous assessment of regional differences in CA and improve our understanding of the impact of the aging process on cerebral vessel function.

Real-Time Measurements of Relative Tidal Volume and Stroke Volume Using Electrical Impedance Tomography with Spatial Filters: A Feasibility Study in a Swine Model Under Normal and Reduced Ventilation

Continuous monitoring of both hemodynamic and respiratory parameters would be beneficial to patients, e.g., those in intensive care unit. The objective of this exploratory animal study was to test the feasibility of simultaneous measurements of relative tidal volume (rTV) and relative stroke volume (rSV) using an electrical impedance tomography (EIT) device equipped with a new real-time source separation algorithm implemented as two spatial filters. Five pigs were anesthetized and mechanically ventilated. The supplied tidal volume from a mechanical ventilator was reduced to 70, 50 and 30% from the 100% normal volume to simulate hypoventilation. The respiratory volume signal and cardiac volume signal were generated by applying the spatial filters to the acquired EIT data, from which values of rTV and rSV were extracted. The measured rTV values were compared with the TV values from the mechanical ventilator using the four-quadrant concordance analysis method. For changes in TV, the concordance rate in each animal ranged from 81.8% to 100%, while it was 92.5% when the data from all five animals were pooled together. When the measured rTV values for each animal were scaled to the absolute TV_EIT values in mL using the TV_Vent data from the mechanical ventilator, the smallest 95% limits of agreement (LoA) were - 6.04 and 7.44 mL for the 70% ventilation level, and the largest 95% LoA were - 18.1 and 19.4 mL for the 50% ventilation level. The percentage error between TV_EIT and TV_Vent was 10.3%. Although similar statistical analyses on rSV data could not be performed due to limited intra-animal variability, changes in rSV values measured by the EIT device were comparable to those measured by an invasive hemodynamic monitor. In this animal study, we were able to demonstrate the feasibility of an EIT device for noninvasive and simultaneous measurements of rTV and rSV in real time. However, the performance of the real-time source separation method needs to be further validated on animals and human subjects, particularly over a wide range of SV values. Future clinical studies are needed to assess the potential usefulness of the new method in dynamic cardiopulmonary monitoring and explore other clinical applications.

Phase II study comparing nasal pressure monitoring with capnography during invasive endoscopic procedures: a single-center, single-arm trial

Nasal pressure signal is commonly used to evaluate obstructive sleep apnea. This study aimed to assess its safety for respiratory monitoring during sedation. A total of 45 adult patients undergoing sedation with propofol and fentanyl for invasive endoscopic procedures were enrolled. While both nasal pressure and capnograph signals were continuously recorded, only the nasal pressure signal was displayed. The primary outcome was the incidence of oxygen desaturation below 90%. The secondary outcomes were the ability to predict the desaturation and incidence of harmful events and false alarms, defined as an apnea waveform lasting more than 3 min without desaturation. Of the 45 participants, 43 completed the study. At least one desaturation event occurred in 12 patients (27.9%; 95% confidence interval 15.3-43.7%). In these 12 patients, more than half of the desaturation events were predictable in 9 patients by capnography and 11 patients by nasal pressure monitoring (p = 0.59). In the 43 patients, false alarms were detected in 7 patients with capnography and 11 patients with nasal pressure monitoring (p = 0.427). Harmful events unrelated to nasal pressure monitoring occurred in 2 patients. Nasal pressure monitoring is safe and possibly useful for respiratory monitoring despite false alarms during sedation.

An Educational Intervention to Improve Comfort with Applying and Interpreting Transcutaneous CO2 and End-tidal CO2 Monitoring in the PACU

PURPOSE

The purpose of this study was to assess the effectiveness of an educational program about measuring ventilation using devices that assess carbon dioxide levels in patients recovering from a surgical procedure.

DESIGN

A pre-post survey of knowledge attainment from an educational intervention about measuring ventilation using end-tidal carbon dioxide (EtCO₂) and transcutaneous carbon dioxide (tcPCO₂) devices in the postanesthesia care unit (PACU) was distributed to current members of the American Society of PeriAnesthesia Nurses.

METHODS

Participants received a 12-question pre-intervention (five were related to demographics) and a five-question post-intervention survey. Non-demographic survey questions used a one to five Likert scale to assess comfortability or confidence. The intervention created was a voice-over presentation designed to improve PACU RN's comfort and confidence with using and interpreting tcPCO₂ or EtCO₂ in the PACU.

FINDINGS

PACU RNs (N = 108) reported they 'never' or 'rarely' used EtCO₂ (n = 57, 52.7%) monitoring or tcPCO₂ (n = 93, 86.1%) monitoring in the PACU. A paired t test revealed statistically significant differences in the PACU RN's pre-survey and posttest comfortability of applying and interpreting EtCO₂ or tcPCO₂ monitors (P < .05).

CONCLUSIONS

Capnography monitoring should be considered a standard of care for PACU patients. Education of registered nurses working in the PACU is critical before implementing EtCO₂ or tcPCO₂ monitoring.

Air Quality Monitoring During High-Level Biocontainment Ground Transport: Observations From Two Operational Exercises

OBJECTIVE

Stretcher transport isolators provide mobile, high-level biocontainment outside the hospital for patients with highly infectious diseases, such as Ebola virus disease. Air quality within this confined space may pose human health risks.

METHODS

Ambient air temperature, relative humidity, and CO₂ concentration were monitored within an isolator during 2 operational exercises with healthy volunteers, including a ground transport exercise of approximately 257 miles. In addition, failure of the blower unit providing ambient air to the isolator was simulated. A simple compartmental model was developed to predict CO₂ and H₂O concentrations within the isolator.

RESULTS

In both exercises, CO₂ and H₂O concentrations were elevated inside the isolator, reaching steady-state values of 4434 ± 1013 ppm CO₂ and 22 ± 2 mbar H₂O in the first exercise and 3038 ± 269 ppm CO₂ and 20 ± 1 mbar H₂O in the second exercise. When blower failure was simulated, CO₂ concentration exceeded 10 000 ppm within 8 minutes. A simple compartmental model predicted CO₂ and H₂O concentrations by accounting for human emissions and blower air exchange.

CONCLUSIONS

Attention to air quality within stretcher transport isolators (including adequate ventilation to prevent accumulation of CO₂ and other bioeffluents) is needed to optimize patient safety.

Effects of non-invasive respiratory supports on inspiratory effort in moderate-severe COVID-19 patients. A randomized physiological study

RATIONALE AND OBJECTIVE

Various forms of Non-invasive respiratory support (NRS) have been used during COVID-19, to treat Hypoxemic Acute Respiratory Failure (HARF), but it has been suggested that the occurrence of strenuous inspiratory efforts may cause Self Induced Lung Injury(P-SILI). The aim of this investigation was to record esophageal pressure, when starting NRS application, so as to better understand the potential risk of the patients in terms of P-SILI and ventilator induced lung injury (VILI).

METHODS AND MEASUREMENTS

21 patients with early de-novo respiratory failure due to COVID-19, underwent three 30 min trials applied in random order: high-flow nasal cannula (HFNC), continuous positive airway pressure (CPAP), and non-invasive ventilation (NIV). After each trial, standard oxygen therapy was reinstituted using a Venturi mask (VM). 15 patients accepted a nasogastric tube placement. Esophageal Pressure (ΔPes) and dynamic transpulmonary driving pressure (ΔPLDyn), together with the breathing pattern using a bioelectrical impedance monitor were recorded. Arterial blood gases were collected in all patients.

MAIN RESULTS

No statistically significant differences in breathing pattern and PaCO₂ were found. PaO₂/FiO₂ ratio improved significantly during NIV and CPAP vs VM. NIV was the only NRS to reduce significantly ΔPes vs. VM (-10,2 ±5 cmH20 vs -3,9 ±3,4). No differences were found in ΔPLDyn between NRS (10,2±5; 9,9±3,8; 7,6±4,3; 8,8±3,6 during VM, HFNC, CPAP and NIV respectively). Minute ventilation (Ve) was directly dependent on the patient's inspiratory effort, irrespective of the NRS applied. 14% of patients were intubated, none of them showing a reduction in ΔPes during NRS.

CONCLUSIONS

In the early phase of HARF due to COVID-19, the inspiratory effort may not be markedly elevated and the application of NIV and CPAP ameliorates oxygenation vs VM. NIV was superior in reducing ΔPes, maintaining ΔPLDyn within a range of potential safety.

Respiration monitoring in PACU using ventilation and gas exchange parameters

The importance of perioperative respiration monitoring is highlighted by high incidences of postoperative respiratory complications unrelated to the original disease. The objectives of this pilot study were to (1) simultaneously acquire respiration rate (RR), tidal volume (TV), minute ventilation (MV), SpO₂ and PetCO₂ from patients in post-anesthesia care unit (PACU) and (2) identify a practical continuous respiration monitoring method by analyzing the acquired data in terms of their ability and reliability in assessing a patient’s respiratory status. Thirteen non-intubated patients completed this observational study. A portable electrical impedance tomography (EIT) device was used to acquire RR_EIT, TV and MV, while PetCO₂, RR_Cap and SpO₂ were measured by a Capnostream35. Hypoventilation and respiratory events, e.g., apnea and hypopnea, could be detected reliably using RR_EIT, TV and MV. PetCO₂ and SpO₂ provided the gas exchange information, but were unable to detect hypoventilation in a timely fashion. Although SpO₂ was stable, the sidestream capnography using the oronasal cannula was often unstable and produced fluctuating PetCO₂ values. The coefficient of determination (R²) value between RR_EIT and RR_Cap was 0.65 with a percentage error of 52.5%. Based on our results, we identified RR, TV, MV and SpO₂ as a set of respiratory parameters for robust continuous respiration monitoring of non-intubated patients. Such a respiration monitor with both ventilation and gas exchange parameters would be reliable and could be useful not only for respiration monitoring, but in making PACU discharge decisions and adjusting opioid dosage on general hospital floor. Future studies are needed to evaluate the potential clinical utility of such an integrated respiration monitor.

Awake prone position reduces work of breathing in patients with COVID-19 ARDS supported by CPAP

BACKGROUND

The use of awake prone position concomitant to non-invasive mechanical ventilation in acute respiratory distress syndrome (ARDS) secondary to COVID-19 has shown to improve gas exchange, whereas its effect on the work of breathing remain unclear. The objective of this study was to evaluate the effects of awake prone position during helmet continuous positive airway pressure (CPAP) ventilation on inspiratory effort, gas exchange and comfort of breathing.

METHODS

Forty consecutive patients presenting with ARDS due to COVID-19 were prospectively enrolled. Gas exchange, esophageal pressure swing (ΔPes), dynamic transpulmonary pressure (dTPP), modified pressure time product (mPTP), work of breathing (WOB) and comfort of breathing, were recorded on supine position and after 3 h on prone position.

RESULTS

The median applied PEEP with helmet CPAP was 10 [8-10] cmH2O. The PaO2/FiO2 was higher in prone compared to supine position (Supine: 166 [136-224] mmHg, Prone: 314 [232-398] mmHg, p < 0.001). Respiratory rate and minute ventilation decreased from supine to prone position from 20 [17-24] to 17 [15-19] b/min (p < 0.001) and from 8.6 [7.3-10.6] to 7.7 [6.6-8.6] L/min (p < 0.001), respectively. Prone position did not reduce ΔPes (Supine: - 7 [- 9 to - 5] cmH2O, Prone: - 6 [- 9 to - 5] cmH2O, p = 0.31) and dTPP (Supine: 17 [14-19] cmH2O, Prone: 16 [14-18] cmH2O, p = 0.34). Conversely, mPTP and WOB decreased from 152 [104-197] to 118 [90-150] cmH2O/min (p < 0.001) and from 146 [120-185] to 114 [95-151] cmH2O L/min (p < 0.001), respectively. Twenty-six (65%) patients experienced a reduction in WOB of more than 10%. The overall sensation of dyspnea was lower in prone position (p = 0.005).

CONCLUSIONS

Awake prone position with helmet CPAP enables a reduction in the work of breathing and an improvement in oxygenation in COVID-19-associated ARDS.

Breathing variability-implications for anaesthesiology and intensive care

The respiratory system reacts instantaneously to intrinsic and extrinsic inputs. This adaptability results in significant fluctuations in breathing parameters, such as respiratory rate, tidal volume, and inspiratory flow profiles. Breathing variability is influenced by several conditions, including sleep, various pulmonary diseases, hypoxia, and anxiety disorders. Recent studies have suggested that weaning failure during mechanical ventilation may be predicted by low respiratory variability. This review describes methods for quantifying breathing variability, summarises the conditions and comorbidities that affect breathing variability, and discusses the potential implications of breathing variability for anaesthesia and intensive care.

Comparison of Respiratory Effects between Dexmedetomidine and Propofol Sedation for Ultrasound-Guided Radiofrequency Ablation of Hepatic Neoplasm: A Randomized Controlled Trial

Patient’s cooperation and respiration is necessary in percutaneous radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC). We compared the respiratory patterns of dexmedetomidine and propofol sedation during this procedure. Participants were randomly allocated into two groups: the continuous infusions of dexmedetomidine-remifentanil (DR group) or the propofol-remifentanil (PR group). We measured the tidal volume for each patient’s respiration during one-minute intervals at five points and compared the standard deviation of the tidal volumes (SDvt) between the groups. Sixty-two patients completed the study. SDvt at 10 min was not different between the groups (DR group, 108.58 vs. PR group, 149.06, p = 0.451). However, SDvt and end-tidal carbon dioxide (EtCO₂) level of PR group were significantly increased over time compared to DR group (p = 0.004, p = 0.021; ß = 0.14, ß = −0.91, respectively). Heart rate was significantly decreased during sedation in DR group (p < 0.001, ß = −2.32). Radiologist satisfaction was significantly higher, and the incidence of apnea was lower in DR group (p = 0.010, p = 0.009, respectively). Compared with propofol-remifentanil, sedation using dexmedetomidine-remifentanil provided a lower increase of the standard deviation of tidal volume and EtCO₂, and also showed less apnea during RFA of HCC.

Ventilation Monitoring

Ventilation or breathing is vital for life yet is not well monitored in hospital or at home. Respiratory rate is a neglected vital sign and tidal volumes together with breath sounds are checked infrequently in many patients. Medications with the potential to depress ventilation are frequently administered, and may be accentuated by obesity causing airway obstruction in the form of sleep apnea. Sepsis may adversely affect ventilation by causing an increase in respiratory rate, often a very early sign of infection. Changes in ventilation may be early signs of deterioration in the patient.

Ventilatory Effect of Midazolam in Propofol Deep Sedation for Hepatic Tumor Patients Undergoing Percutaneous Radiofrequency Ablation Procedure

Objective: The aim of the study was to compare the ventilatory effect between propofol deep sedation technique with and without midazolam in hepatic tumor patients undergoing radiofrequency ablation procedure. Methods: Three hundred and seventy-four patients who underwent radiofrequency ablation procedure in a single year were randomly assigned to the deep sedation without midazolam group (A, n = 187) and deep sedation with midazolam group (B, n = 187). Patients in group A received normal saline, and those in group B received 0.02 mg/kg of midazolam intravenously in equivalent volume. All patients were oxygenated with 100% O2 via nasal cannula and sedated with intravenous fentanyl and the titration of intravenous propofol. Ventilatory parameters, including oxygen saturation, end tidal carbon dioxide, and respiratory rate every five minutes, during and after the procedure, as well as the duration of sleep and sedation score in the recovery room, were recorded. Results: There were no significant differences in the patients’ characteristics, duration of procedure, total dose of propofol, ventilatory parameters including oxygen saturation, end tidal carbon dioxide, and respiratory rate, as well as sedation score at 20, 25, 30, 35, and 40 min after the procedure, between the two groups. However, mean sedation score at 5, 10, and 15 min after the procedure, in group B, was significantly lower than in group A. In addition, the duration of sleep after the procedure, in group B, was significantly greater than in group A. No serious ventilatory adverse effects were observed either group. Conclusion: Propofol deep sedation with and without midazolam for hepatic tumor patients who underwent radiofrequency ablation procedure was safe and effective. A low dose of midazolam in propofol deep-sedation technique did not create serious ventilatory effects.

Prospective Observational Investigation of Capnography and Pulse Oximetry Monitoring After Cesarean Delivery With Intrathecal Morphine

BACKGROUND

Intrathecal morphine provides excellent analgesia after cesarean delivery; however, respiratory events such as apnea, bradypnea, and hypoxemia have been reported. The primary study aim was to estimate the number of apneas per subject, termed "apnea alert events" (AAEs) defined by no breath for 30-120 seconds, using continuous capnography in women who underwent cesarean delivery.

METHODS

We performed a prospective, observational study with institutional review board approval of women who underwent cesarean delivery with spinal anesthesia containing 150-µg intrathecal morphine. A STOP-Bang obstructive sleep apnea assessment was administered to all women. Women were requested to use continuous capnography and pulse oximetry for 24 hours after cesarean delivery. Nasal sampling cannula measured end-tidal carbon dioxide (EtCO2) and respiratory rate (RR), and oxygen saturation (SpO2) as measured by pulse oximetry. Capnography data were defined as "valid" when EtCO2 >10 mm Hg, RR >5 breaths per minute (bpm), SpO2 >70%, or during apnea (AAE) defined as "no breath" (EtCO2, <5 mm Hg) for 30-120 seconds. Individual respiratory variable alerts were 10-second means of EtCO2 <10 mm Hg, RR <8 bpm, and SpO2 <94%. Nurse observations of RR (hourly and blinded to capnography) are reported.

RESULTS

We recruited 80 women, mean (standard deviation [SD]) 35 (5) years, 47% body mass index >30 kg/m2/weight >90 kg, and 11% with suspected obstructive sleep apnea (known or STOP-Bang score >3). The duration of normal capnography and pulse oximetry data was mean (SD) (range) 8:28 (7:51) (0:00-22:32) and 15:08 (6:42) (1:31-23:07) hours:minutes, respectively; 6 women did not use the capnography. There were 198 AAEs, mean (SD) duration 57 (27) seconds experienced by 39/74 (53%) women, median (95% confidence interval for median) (range) 1 (0-1) (0-29) per subject. Observation of RR by nurses was ≥14 bpm at all time-points for all women, r = 0.05 between capnography and nurse RR (95% confidence interval, -0.04 to 0.14). There were no clinically relevant adverse events for any woman. Sixty-five women (82%) had complaints with the capnography device, including itchy nose, nausea, interference with nursing baby, and overall inconvenience.

CONCLUSIONS

We report 198 AAEs detected by capnography among women who underwent cesarean delivery after receiving intrathecal morphine. These apneas were not confirmed by the intermittent hourly nursing observations. Absence of observer verification precludes distinction between real, albeit nonclinically significant alerts with capnography versus false apneas. Discomfort with the nasal sampling cannula and frequent alerts may impact capnography application after cesarean delivery. No clinically relevant adverse events occurred.

Tracking tidal volume noninvasively in volunteers using a tightly controlled temperature-based device: A proof of concept paper

INTRODUCTION

There is a paucity of noninvasive respiratory monitors for patients outside of critical care settings. The Linshom respiratory monitoring device is a novel temperature-based respiratory monitor that measures the respiratory rate as accurately as capnography.

OBJECTIVES

Determine whether the amplitude of the Linshom temperature profile was an accurate, surrogate and qualitative metric of the tidal volume (V_T ) that tracks V_T in healthy volunteers.

METHODS

Forty volunteers breathed room air spontaneously through a tight-fitting continuous positive airway pressure mask with a Linshom device mounted in the mask. V_T was measured contemporaneously using a standalone Maquet Servo-i ICU ventilator. The amplitudes of the Linshom temperature profiles were paired with the contemporaneous V_T measurements using least squares linear regression analysis and the coefficient of variation (R² ) was determined.

RESULTS

Forty volunteers completed the study. The data from 30 of the volunteers were analysed and are presented; data from 10 volunteers were not included due to protocol violations and/or technical issues unrelated to Linshom. The fluctuations in the amplitude of the Linshom temperature profiles mapped closely with the measured V_T using least squares linear regression analyses yielding a mean R² (95% CI) value of 0.87 (0.84-0.90).

CONCLUSION

These results support the notion that the Linshom temperature profile is an accurate and reliable surrogate that tracks changes in V_T in healthy volunteers. Further studies are warranted in patients in clinical settings to establish the effectiveness of this monitor.

Portable multi-parameter electrical impedance tomography for sleep apnea and hypoventilation monitoring: feasibility study

OBJECTIVE

Quantitative ventilation monitoring and respiratory event detection are needed for the diagnosis of sleep apnea and hypoventilation. We developed a portable device with a chest belt, nasal cannula and finger sensor to continuously acquire multi-channel signals including tidal volume, nasal pressure, respiratory effort, body position, snoring sound, ECG and SpO₂. The unique feature of the device is the continuous tidal volume signal obtained from real-time lung ventilation images produced by the electrical impedance tomography (EIT) technique.

APPROACH

The chest belt includes 16 electrodes for real-time time-difference EIT imaging and ECG data acquisitions. It also includes a microphone, accelerometer, gyroscope, magnetometer and pressure sensor to acquire, respectively, snoring sound, respiratory effort, body position and nasal pressure signals. A separate finger sensor is used to measure SpO₂. The minute ventilation signal is derived from the tidal volume signal and respiration rate.

MAIN RESULTS

The experimental results from a conductivity phantom, four swine subjects and one human volunteer show that the developed multi-parameter EIT device could supplement existing polysomnography (PSG) and home sleep test (HST) devices to improve the accuracy of sleep apnea diagnosis. The portable device could be also used as a new tool for continuous hypoventilation monitoring of non-intubated patients with respiratory depression.

SIGNIFICANCE

Following the feasibility study in this paper, future validation studies in comparison with in-lab PSG, HST and end-tidal CO₂ devices are suggested to find its clinical efficacy as a sleep apnea diagnosis and hypoventilation monitoring tool.

Improving patient safety during procedural sedation via respiratory volume monitoring: A randomized controlled trial

STUDY OBJECTIVE

Assess the utility of a respiratory volume monitor (RVM) to reduce the incidence of low minute ventilation events in procedural sedation.

DESIGN

Randomized control trial SETTING: Endoscopy suite PATIENTS: Seventy-three total patients (ASA Physical Status 1-3) undergoing upper endoscopies were analyzed.

INTERVENTION

Patients were randomized into two groups using a computer generated randomization table: Control (n=41): anesthesia provider was unable to see the screen of the RVM; RVM (n=32): anesthesia provider had access to RVM data to assist with management of the case.

MEASUREMENTS

Minute ventilation (MV), tidal volume, and respiratory rate were continuously recorded by the RVM. MV is presented as percent of Baseline MV (MV_Baseline), defined during a 30s period of quiet breathing prior to sedation. We defined Low MV as MV<40% MV_Baseline, and calculated the percentage of procedure spent with Low MV. Patients in the RVM group were stratified based on whether the anesthesiologist rated the RVM as "not useful", "somewhat useful", or "very useful" during the case.

MAIN RESULTS

Control patients experienced twice as much Low MV compared to RVM patients (15.3±2.8% vs. 7.1±1.4%, P=0.020). The "not useful" (13.7±3.8%) group showed no improvement over the Control group (p=0.81). However, both the "very useful" (4.7±1.4%) and "somewhat useful" (4.9±1.7%) groups showed significant improvement over the "not useful" group (p<0.05).

CONCLUSIONS

Patients in the Control group spent more than double the amount of time with Low MV compared to the RVM group. This difference became more pronounced when the anesthesiologist found the RVM useful for managing care, lending credibility to the usage of minute ventilation monitoring in procedural sedation.

Anesthesia in the Electrophysiology Laboratory

The electrophysiology suite is a foreign location to many anesthesiologists. The initial experience was with shorter procedures under conscious sedation, and the value of greater tailoring of the sedation/anesthesia by anesthesiologists was not perceived until practice patterns had already been established. Although better control of ventilation with general anesthesia may be expected, suppression of arrhythmias, blunting of the hemodynamic adaptation to induced arrhythmias, and interference by muscle relaxants with identification of the phrenic nerve may be seen. We review a range of electrophysiology procedures and discuss anesthetic approaches that balance patient safety and favorable outcomes.

The relationship between minute ventilation and end tidal CO2 in intubated and spontaneously breathing patients undergoing procedural sedation

BACKGROUND

Monitoring respiratory status using end tidal CO2 (EtCO2), which reliably reflects arterial PaCO2 in intubated patients under general anesthesia, has often proven both inaccurate and inadequate when monitoring non-intubated and spontaneously breathing patients. This is particularly important in patients undergoing procedural sedation (e.g., endoscopy, colonoscopy). This can be undertaken in the operating theater, but is also often delivered outside the operating room by non-anesthesia providers. In this study we evaluated the ability for conventional EtCO2 monitoring to reflect changes in ventilation in non-intubated surgical patients undergoing monitored anesthesia care and compared and contrasted these findings to both intubated patients under general anesthesia and spontaneously breathing volunteers.

METHODS

Minute Ventilation (MV), tidal volume (TV), and respiratory rate (RR) were continuously collected from an impedance-based Respiratory Volume Monitor (RVM) simultaneously with capnography data in 160 patients from three patient groups: non-intubated surgical patients managed using spinal anesthesia and Procedural Sedation (n = 58); intubated surgical patients under General Anesthesia (n = 54); and spontaneously breathing Awake Volunteers (n = 48). EtCO2 instrument sensitivity was calculated for each patient as the slope of a Deming regression between corresponding measurements of EtCO2 and MV and expressed as angle from the x-axis (θ). All data are presented as mean ± SD unless otherwise indicated.

RESULTS

While, as expected, EtCO2 and MV measurements were negatively correlated in most patients, we found gross systematic differences across the three cohorts. In the General Anesthesia patients, small changes in MV resulted in large changes in EtCO2 (high sensitivity, θ = -83.6 ± 9.9°). In contrast, in the Awake Volunteers patients, large changes in MV resulted in insignificant changes in EtCO2 (low sensitivity, θ = -24.7 ± 19.7°, p < 0.0001 vs General Anesthesia). In the Procedural Sedation patients, EtCO2 sensitivity showed a bimodal distribution, with an approximately even split between patients showing high EtCO2 instrument sensitivity, similar to those under General Anesthesia, and patients with low EtCO2 instrument sensitivity, similar to the Awake Volunteers.

CONCLUSIONS

When monitoring non-intubated patients undergoing procedural sedation, EtCO2 often provides inadequate instrument sensitivity when detecting changes in ventilation. This suggests that augmenting standard patient care with EtCO2 monitoring is a less than optimal solution for detecting changes in respiratory status in non-intubated patients. Instead, adding direct monitoring of MV with an RVM may be preferable for continuous assessment of adequacy of ventilation in non-intubated patients.

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

Background

Monitoring 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.

Methods

We 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 (MV_PRED) 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.

Results

Obese patients had higher MV than the non-obese patients before, during, and after surgery. Measured MV of obese patients was significantly higher than their MV_PRED from IBW formulas, with BSA-based MV_PRED being a closer estimate. Obese patients also had greater variability in MV post-operatively when treated with standard opioid dosing.

Conclusions

Our 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 MV_PRED 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.

A Brief Review of Non-invasive Monitoring of Respiratory Condition for Extubated Patients with or at Risk for Obstructive Sleep Apnea after Surgery

Obstructive sleep apnea (OSA) is one of the important risk factors contributing to postoperative airway complications. OSA alters the respiratory physiology and increases the sensitivity of muscle tone of the upper airway after surgery to residual anesthetic medication. In addition, the prevalence of OSA was reported to be much higher among surgical patients than the general population. Therefore, appropriate monitoring to detect early respiratory impairment in postoperative extubated patients with possible OSA is challenging. Based on the comprehensive clinical observation, several equipment have been used for monitoring the respiratory conditions of OSA patients after surgery, including the continuous pulse oximetry, capnography, photoplethysmography (PPG), and respiratory volume monitor (RVM). To date, there has been no consensus on the most suitable device as a recommended standard of care. In this review, we describe the advantages and disadvantages of some possible monitoring strategies under certain clinical conditions. According to the literature, the continuous pulse oximetry, with its high sensitivity, is still the most widely used device. It is also cost-effective and convenient to use but has low specificity and does not reflect ventilation. Capnography is the most widely used device for detection of hypoventilation, but it may not provide reliable data for extubated patients. Even normal capnography cannot exclude the existence of hypoxia. PPG shows the state of both ventilation and oxygenation, but its sensitivity needs further improvement. RVM provides real-time detection of hypoventilation, quantitative precise demonstration of respiratory rate, tidal volume, and MV for extubated patients, but no reflection of oxygenation. Altogether, the sole use of any of these devices is not ideal for monitoring of extubated patients with or at risk for OSA after surgery. However, we expect that the combined use of continuous pulse oximetry and RVM may be promising for these patients due to their complementary function, which need further study.

A Brief Review of Non-invasive Monitoring of Respiratory Condition for Extubated Patients with or at Risk for Obstructive Sleep Apnea after Surgery

Obstructive sleep apnea (OSA) is one of the important risk factors contributing to postoperative airway complications. OSA alters the respiratory physiology and increases the sensitivity of muscle tone of the upper airway after surgery to residual anesthetic medication. In addition, the prevalence of OSA was reported to be much higher among surgical patients than the general population. Therefore, appropriate monitoring to detect early respiratory impairment in postoperative extubated patients with possible OSA is challenging. Based on the comprehensive clinical observation, several equipment have been used for monitoring the respiratory conditions of OSA patients after surgery, including the continuous pulse oximetry, capnography, photoplethysmography (PPG), and respiratory volume monitor (RVM). To date, there has been no consensus on the most suitable device as a recommended standard of care. In this review, we describe the advantages and disadvantages of some possible monitoring strategies under certain clinical conditions. According to the literature, the continuous pulse oximetry, with its high sensitivity, is still the most widely used device. It is also cost-effective and convenient to use but has low specificity and does not reflect ventilation. Capnography is the most widely used device for detection of hypoventilation, but it may not provide reliable data for extubated patients. Even normal capnography cannot exclude the existence of hypoxia. PPG shows the state of both ventilation and oxygenation, but its sensitivity needs further improvement. RVM provides real-time detection of hypoventilation, quantitative precise demonstration of respiratory rate, tidal volume, and MV for extubated patients, but no reflection of oxygenation. Altogether, the sole use of any of these devices is not ideal for monitoring of extubated patients with or at risk for OSA after surgery. However, we expect that the combined use of continuous pulse oximetry and RVM may be promising for these patients due to their complementary function, which need further study.