Monitoring Respiratory Rate Continuously Without Attaching a Sensor During a Challenging Ramped Protocol.

INTRODUCTION: Respiratory rate (RR) is a crucial vital sign in patient monitoring and is often the best marker of the deterioration of a sick patient. It can be used to help diagnose numerous medical conditions and has been demonstrated to be an independent predictor of patient outcomes in various critical care settings and is incorporated in many clinical early warning scores. Here, we report on the performance of depth-camera-based system for the noncontact monitoring of RR during a ramped RR protocol. The ramped breathing protocol was developed specifically to test the relatively rapid changes in rates, which include clinically important low and high ranges of RRs. MATERIALS AND METHODS: We performed a series of experimental runs with healthy volunteers who were instructed to breathe over a wide range of RRs, where the rates were ramped up from 4 breaths/min to 50 breaths/min then back down to 4 breaths/min in a series of ramped steps. Depth information was acquired from the scene and used to determine a respiratory rate (RRdepth), and this was compared to capnograph or spirometer respiratory rate reference (RRref). A total of 9,482 contemporaneous data pairs (RRdepth, RRref) were collected during the study for comparison. RESULTS: A Pearson correlation coefficient of 0.995 was achieved and a line of best fit given by RRdepth = 0.99 × RRref + 0.36 breaths/min. The overall root mean squared difference (RMSD) across the runs was 1.29 breaths/min with a corresponding bias of 0.16 breaths/min, respectively. The associated Bland-Altman analysis found limits of agreement of -2.45 and 2.75 breaths/min. When the data were subdivided according to low, medium, and high RRs, corresponding to ≤10, >10 to 20, and >20 breaths/min, the RMSD accuracies were found to be 0.94, 1.34, and 1.55 breaths/min, respectively. CONCLUSIONS: The technology performed well, exhibiting an RMSD accuracy well within our target of 3 breaths/min, both across the whole range and across each individual subrange. In summary, our results indicate the potential viability of continuous noncontact monitoring for the determination of RR over a clinically relevant range.

Does Cuff Design Impact Insertion and Removal Force of Tracheostomy Tubes? A Bench Model.

INTRODUCTION: Percutaneous dilatational tracheostomy is a commonly performed procedure in intensive care units. Unrecognized tracheal ring fracture has been suggested as a possible factor for tracheal stenosis. The degree of tracheal compression relates to the amount of force required to cannulate the trachea. The objective of this study was to determine the force required to insert two types of tracheostomy tubes with different cuff designs. MATERIALS AND METHODS: This bench model measured the insertion and removal force of two tracheostomy tubes; one with a barrel-shaped, high-volume, low-pressure cuff (traditional Shiley tracheostomy tube) and another with a taper-shaped, low-volume, low-pressure cuff (Shiley flexible tracheostomy tube). Three sizes of tracheostomy tubes either with a barrel- or taper-shaped cuff were tested (Jackson sizes 4, 6, and 10, corresponding to 6.5-, 7.5-, and 10-mm ISO sizes, respectively). A model representing the tissue that the tube traverses to enter the tracheal lumen was designed, and the tracheostomy tube was mounted on a universal testing machine to measure the force necessary to insert and remove the tube. RESULTS: Across all tracheostomy tubes' sizes tested, significantly less force was required to insert the Shiley flexible tracheostomy tube compared to the traditional Shiley tracheostomy tube. Significantly less force was also required to remove the flexible tracheostomy tube compared to the traditional tracheostomy tube. CONCLUSIONS: This model suggests that less force is required to insert the Shiley flexible tracheostomy tube, which could result in less tracheal compression. This may be because of the smaller taper-shaped cuff that, when deflated, occupies less volume compared to the barrel-shaped cuff. As a result, less tracheal injury may occur when using the Shiley flexible tracheostomy tube during percutaneous tracheostomy procedures.

Near-Infrared Spectroscopy Monitoring to Detect Changes in Cerebral and Renal Perfusion During Hypovolemic Shock, Volume Resuscitation, and Vasoconstriction.

INTRODUCTION: Rapidly changing hemodynamic conditions, such as uncontrolled hemorrhage and the resulting hypovolemic shock, are a common contributor to active duty military deaths. These conditions can cause cerebral desaturation, and outcomes may improve when regional cerebral oxygen saturation (CrSO2) is monitored using near-infrared spectroscopy (NIRS) and desaturation episodes are recognized and reversed. The purpose of this porcine study was to investigate the ability of NIRS monitoring to detect changes in regional cerebral and regional renal perfusion during hypovolemia, resuscitation by volume infusion, and vasoconstriction. MATERIALS AND METHODS: Hemorrhagic shock was induced by removing blood through a central venous catheter until mean arterial pressure (MAP) was <40 mmHg. Each blood removal step was followed by a 10-minute stabilization period, during which cardiac output, blood pressure, central venous pressure, blood oxygen saturation, and CrSO2 and regional renal oxygen saturation (RrSO2) were measured. Shock was reversed using blood infusion and vasoconstriction separately until MAP returned to normal. Statistical comparisons between groups were performed using the paired t-test or the Wilcoxon signed-rank test. RESULTS: Using volume resuscitation, both CrSO2 and RrSO2 returned to normal levels after hypovolemia. Blood pressure management with phenylephrine returned CrSO2 levels to normal, but RrSO2 levels remained significantly lower compared to the pre-hemorrhage values (P < .0001). Comparison of the percent CrSO2 as a function of MAP showed that CrSO2 levels approach baseline when a normal MAP is reached during volume resuscitation. In contrast, a significantly higher MAP was required to return to baseline CrSO2 during blood pressure management with phenylephrine (P < .0001). Evaluation of carotid blood flow and CrSO2 indicated that during induction of hypovolemia, the two measures are strongly correlated. In contrast, there was limited correlation between carotid blood flow and CrSO2 during blood infusion. CONCLUSIONS: This study demonstrated that it is possible to restore CrSO2 by manipulating MAP with vasoconstriction, even in profound hypotension. However, MAP manipulation may result in unintended consequences for other organs, such as the kidney, if the tissue is not reoxygenated sufficiently. The clinical implications of these results and how best to respond to hypovolemia in the pre-hospital and hospital settings should be elucidated by additional studies.

Accurate and continuous respiratory rate using touchless monitoring technology.

PURPOSE: Respiratory rate is a commonly used vital sign with various clinical applications. It serves as a crucial marker of acute health issues and any significant alteration in respiratory rate may be an early warning sign of major issues such as infections in the respiratory tract, respiratory failure, or cardiac arrest. Timely recognition of changes in respiratory rate enables prompt medical action, while neglecting to detect a change may lead to adverse patient outcomes. Here, we report on the performance of respiratory rate determined using a depth sensing camera system (RRdepth) which allows for continuous, non-contact 'touchless' monitoring of this important vital sign. METHODS: Thirty adult volunteers undertook a range of set breathing rates to cover a target breathing range of 4-40 breaths/min. Depth information was acquired from the torso region of the subjects using an Intel D415 RealSense camera positioned above the bed. The depth information was processed to generate a respiratory signal from which RRdepth was calculated. This was compared to a manually scored capnograph reference (RRcap). RESULTS: An overall RMSD accuracy of 0.77 breaths/min was achieved across the target respiratory rate range with a corresponding bias of 0.05 breaths/min. This corresponded to a line of best fit given by RRdepth = 1.01 x RRcap - 0.22 breaths/min with an associated high degree of correlation (R = 0.997). A breakdown of the performance with respect to sub-ranges corresponding to respiratory rates or ≤7, >7-10, >10-20, >20-30, >30 breaths/min all exhibited RMSD accuracies of less than 1.00 breaths/min. We also had the opportunity to test the performance of spontaneous breathing of the subjects which occurred during the study and found an overall RMSD accuracy of 1.20 breaths/min with corresponding accuracies ≤1.30 breaths/min across each of the individual sub-ranges. CONCLUSIONS: We have conducted an investigative study of a prototype depth sensing camera system for the non-contact monitoring of respiratory rate. The system achieved good performance with high accuracy across a wide range of rates including both clinically important high and low rates.

Robust Non-Contact Monitoring of Respiratory Rate using a Depth Camera.

PURPOSE: Respiratory rate (RR) is one of the most common vital signs with numerous clinical uses. It is an important indicator of acute illness and a significant change in RR is often an early indication of a potentially serious complication or clinical event such as respiratory tract infection, respiratory failure and cardiac arrest. Early identification of changes in RR allows for prompt intervention, whereas failing to detect a change may result in poor patient outcomes. Here, we report on the performance of a depth-sensing camera system for the continuous non-contact 'touchless' monitoring of Respiratory Rate. METHODS: Seven healthy subjects undertook a range of breathing rates from 4 to 40 breaths-per-minute (breaths/min). These were set rates of 4, 5, 6, 8, 10, 15, 20, 25, 30, 35 and 40 breaths/min. In total, 553 separate respiratory rate recordings were captured across a range of conditions including body posture, position within the bed, lighting levels and bed coverings. Depth information was acquired from the scene using an Intel D415 RealSenseTM camera. This data was processed in real-time to extract depth changes within the subject's torso region corresponding to respiratory activity. A respiratory rate RRdepth was calculated using our latest algorithm and output once-per-second from the device and compared to a reference. RESULTS: An overall RMSD accuracy of 0.69 breaths/min with a corresponding bias of -0.034 was achieved across the target RR range of 4-40 breaths/min. Bland-Altman analysis revealed limits of agreement of -1.42 to 1.36 breaths/min. Three separate sub-ranges of low, normal and high rates, corresponding to < 12, 12-20, > 20 breaths/min, were also examined separately and each found to demonstrate RMSD accuracies of less than one breath-per-minute. CONCLUSIONS: We have demonstrated high accuracy in performance for respiratory rate based on a depth camera system. We have shown the ability to perform well at both high and low rates which are clinically important.

Evaluation of Common Nasal Cannulas in Neonatal Noninvasive Ventilation (NIV) Using a Novel Neonatal Nasal Model.

Purpose: Non-invasive ventilation (NIV) may reduce intubation rates and be especially beneficial in the care of preterm infants, in addition to other care modalities. Currently, ventilators do not display the pressure at the nares but the pressure in the ventilator tubing system. There are several nasal cannulas available for use to deliver NIV. The purpose of this study was to compare the inspiratory pressure on the ventilator to the measured pressure delivered at the nares using three cannula brands (Manufacturer A, Fisher & Paykel; Manufacturer B, Neotech RAM; and Manufacturer C, Hudson RCI). Patients and Methods: This bench study utilized a 3D printed nasal model, including nares in multiple sizes to accommodate all nasal prongs studied. The nasal adaptors were connected to neonatal test lungs, to simulate patient breathing. Multiple sizes of nasal cannulas from the three manufacturers were tested for inspiratory vs delivered pressure at the patient side of the cannula, using eight combinations of ventilator settings. Each nasal cannula was tested on six Puritan Bennett™ 980 ventilators. Results: The measured delivered pressure at the nares was consistently lower than the clinician-set inspiratory pressure. Across all ventilator settings, 7 of the 11 cannulas delivered significantly less pressure at the nares compared to the inspiratory ventilator pressure (p < 0.01). For each cannula, as inspiratory pressure increased, the difference between delivered and inspiratory pressures also increased. The cannula from Manufacturer B consistently demonstrated the greatest differences between set inspiratory and delivered pressures for each ventilator setting. Conclusion: This study demonstrated substantial differences between ventilator inspiratory pressure and measured delivered pressure, which may have clinical significance. Being unaware of the actual airway pressure delivered to the patient may lead to erroneous adjustments to the level of ventilator pressure, which may be especially consequential to those with delicate and developing respiratory systems.

Do tapered tracheostomy cuffs improve translaryngeal gas flow when compared to barrel cuffed fenestrated tubes: A laboratory study.

Objective: The benefits of tracheostomy are well documented and include improved comfort and a reduction in sedative requirements that may facilitate more rapid ventilation weaning. A stable airway established with tracheostomy allows pulmonary toilet that may help in addressing aspiration. It is postulated that it may also increase translargyngeal airflow and allow phonation. We hypothesized that taper-shaped cuffed tracheostomy tubes have less bulk upon cuff deflation, and on this basis, gas flow past the deflated tapered cuff is better than non-tapered barrel cuffs and equal to gas flow in equivalent-sized fenestrated versions. Methods: This comparative bench study measured exhaled gas flow of Shiley™ Flexible taper-cuffed tracheostomy and Fenestrated Shiley™ FEN tubes of equivalent sizes. Three sizes of Shiley™ tracheostomy tubes were used in printed 3D model tracheas, Jackson sizes 4, 6, and 10 (6.5, 7.5, and 10 mm ISO sizes). A standard ventilator provided tidal volumes to mechanical lungs. Because expiratory volume was the focus, the mechanical lungs exhaled through the model trachea and only the air exiting the model trachea, representing exhalation, was measured. Results: Across three sizes, the Shiley™ Flexible tracheostomy tube allowed significantly more translaryngeal airflow compared to the tracheostomy tube with fenestrations. Conclusion: This bench study showed significantly improved air flow past the cuff compared to fenestrated tubes. Improved airflow may help the phonation ability of patients. Clinical studies are required to elucidate use of this cuff design to allow phonation in patients with a tracheostomy.Level of evidence: NA.

Noncontact Respiratory Monitoring Using Depth Sensing Cameras: A Review of Current Literature.

There is considerable interest in the noncontact monitoring of patients as it allows for reduced restriction of patients, the avoidance of single-use consumables and less patient-clinician contact and hence the reduction of the spread of disease. A technology that has come to the fore for noncontact respiratory monitoring is that based on depth sensing camera systems. This has great potential for the monitoring of a range of respiratory information including the provision of a respiratory waveform, the calculation of respiratory rate and tidal volume (and hence minute volume). Respiratory patterns and apneas can also be observed in the signal. Here we review the ability of this method to provide accurate and clinically useful respiratory information.

Continuous respiratory rate monitoring during an acute hypoxic challenge using a depth sensing camera.

Respiratory rate is a well-known to be a clinically important parameter with numerous clinical uses including the assessment of disease state and the prediction of deterioration. It is frequently monitored using simple spot checks where reporting is intermittent and often prone to error. We report here on an algorithm to determine respiratory rate continuously and robustly using a non-contact method based on depth sensing camera technology. The respiratory rate of 14 healthy volunteers was studied during an acute hypoxic challenge where blood oxygen saturation was reduced in steps to a target 70% oxygen saturation and which elicited a wide range of respiratory rates. Depth sensing data streams were acquired and processed to generate a respiratory rate (RRdepth). This was compared to a reference respiratory rate determined from a capnograph (RRcap). The bias and root mean squared difference (RMSD) accuracy between RRdepth and the reference RRcap was found to be 0.04 bpm and 0.66 bpm respectively. The least squares fit regression equation was determined to be: RRdepth = 0.99 × RRcap + 0.13 and the resulting Pearson correlation coefficient, R, was 0.99 (p < 0.001). These results were achieved with a 100% reporting uptime. In conclusion, excellent agreement was found between RRdepth and RRcap. Further work should include a larger cohort combined with a protocol to further test algorithmic performance in the face of motion and interference typical of that experienced in the clinical setting.

Video-based heart rate monitoring across a range of skin pigmentations during an acute hypoxic challenge.

The robust monitoring of heart rate from the video-photoplethysmogram (video-PPG) during challenging conditions requires new analysis techniques. The work reported here extends current research in this area by applying a motion tolerant algorithm to extract high quality video-PPGs from a cohort of subjects undergoing marked heart rate changes during a hypoxic challenge, and exhibiting a full range of skin pigmentation types. High uptimes in reported video-based heart rate (HRvid) were targeted, while retaining high accuracy in the results. Ten healthy volunteers were studied during a double desaturation hypoxic challenge. Video-PPGs were generated from the acquired video image stream and processed to generate heart rate. HRvid was compared to the pulse rate posted by a reference pulse oximeter device (HRp). Agreement between video-based heart rate and that provided by the pulse oximeter was as follows: Bias = - 0.21 bpm, RMSD = 2.15 bpm, least squares fit gradient = 1.00 (Pearson R = 0.99, p < 0.0001), with a 98.78% reporting uptime. The difference between the HRvid and HRp exceeded 5 and 10 bpm, for 3.59 and 0.35% of the reporting time respectively, and at no point did these differences exceed 25 bpm. Excellent agreement was found between the HRvid and HRp in a study covering the whole range of skin pigmentation types (Fitzpatrick scales I-VI), using standard room lighting and with moderate subject motion. Although promising, further work should include a larger cohort with multiple subjects per Fitzpatrick class combined with a more rigorous motion and lighting protocol.

Correction of tissue oxygen saturations using arterial oxygen levels for cerebrovascular autoregulation analysis.

Adequate perfusion of blood is fundamental to brain tissue viability, and failure to appropriately regulate cerebral blood flow is related to neurological damage. Cerebral tissue oxygenation is commonly used as a surrogate of cerebral blood flow for non-invasive measures of autoregulation, but may only be valid during periods of constant oxygen delivery. We present a new algorithm to correct for supply oxygen-induced variations in cerebral tissue oxygenation, and we validate it by measuring the improved correlation of the corrected tissue oxygenation with blood flow. The algorithm corrects tissue oxygenation by calculating its linear dependence with arterial oxygen saturation below a baseline level. A porcine model (N=8) of hypoxia is used to test the algorithm and compare the tissue oxygen correction with a blood flow reference signal. The correction provides significant improvement in the correlation between flow and tissue oxygenation (Wilcoxon signed rank, p<;0.01), and for the root mean square distance between the corrected hypoxic periods and the rSO2-flow regression line (Wilcoxon signed rank, p<;0.01). This method allows the correction of tissue oxygenation levels used in the non-invasive monitoring of autoregulation.

Video-Based Physiologic Monitoring During an Acute Hypoxic Challenge: Heart Rate, Respiratory Rate, and Oxygen Saturation.

BACKGROUND: The physiologic information contained in the video photoplethysmogram is well documented. However, extracting this information during challenging conditions requires new analysis techniques to capture and process the video image streams to extract clinically useful physiologic parameters. We hypothesized that heart rate, respiratory rate, and oxygen saturation trending can be evaluated accurately from video information during acute hypoxia. METHODS: Video footage was acquired from multiple desaturation episodes during a porcine model of acute hypoxia using a standard visible light camera. A novel in-house algorithm was used to extract photoplethysmographic cardiac pulse and respiratory information from the video image streams and process it to extract a continuously reported video-based heart rate (HRvid), respiratory rate (RRvid), and oxygen saturation (SvidO2). This information was then compared with HR and oxygen saturation references from commercial pulse oximetry and the known rate of respiration from the ventilator. RESULTS: Eighty-eight minutes of data were acquired during 16 hypoxic episodes in 8 animals. A linear mixed-effects regression showed excellent responses relative to a nonhypoxic reference signal with slopes of 0.976 (95% confidence interval [CI], 0.973-0.979) for HRvid; 1.135 (95% CI, 1.101-1.168) for RRvid, and 0.913 (95% CI, 0.905-0.920) for video-based oxygen saturation. These results were obtained while maintaining continuous uninterrupted vital sign monitoring for the entire study period. CONCLUSIONS: Video-based monitoring of HR, RR, and oxygen saturation may be performed with reasonable accuracy during acute hypoxic conditions in an anesthetized porcine hypoxia model using standard visible light camera equipment. However, the study was conducted during relatively low motion. A better understanding of the effect of motion and the effect of ambient light on the video photoplethysmogram may help refine this monitoring technology for use in the clinical environment.

Detection of critical cerebral desaturation thresholds by three regional oximeters during hypoxia: a pilot study in healthy volunteers.

BACKGROUND: Regional oximetry is increasingly used to monitor post-extraction oxygen status of the brain during surgical procedures where hemodynamic fluctuations are expected. Particularly in cardiac surgery, clinicians employ an interventional algorithm to restore baseline regional oxygen saturation (rSO2) when a patient reaches a critical desaturation threshold. Evidence suggests that monitoring cardiac surgery patients and intervening to maintain rSO2 can improve postoperative outcomes; however, evidence generated with one manufacturer's device may not be applicable to others. We hypothesized that regional oximeters from different manufacturers respond uniquely to changes in oxygen saturation in healthy volunteers. METHODS: Three devices were tested: INVOS™ 5100C (Medtronic), EQUANOX™ 7600 (Nonin), and FORE-SIGHT™ (CASMED) monitors. We divided ten healthy subjects into two cohorts wearing a single sensor each from INVOS and EQUANOX (n = 6), or INVOS and FORE-SIGHT (n = 4). We induced and reversed hypoxia by adjusting the fraction of inspired oxygen. We calculated the magnitude of absolute rSO2 change and rate of rSO2 change during desaturation and resaturation, and determined if and when each device reached a critical interventional rSO2 threshold during hypoxia. RESULTS: All devices responded to changes in oxygen directionally as expected. The median absolute rSO2 change and the rate of rSO2 change was significantly greater during desaturation and resaturation for INVOS compared with EQUANOX (P = 0.04). A similar but nonsignificant trend was observed for INVOS compared with FORE-SIGHT; our study was underpowered to definitively conclude there was no difference. A 10% relative decrease in rSO2 during desaturation was detected by all three devices across the ten subjects. INVOS met a 20% relative decrease threshold in all subjects of both cohorts, compared to 1 with EQUANOX and 2 with FORE-SIGHT. Neither EQUANOX nor FORE-SIGHT reached a 50% absolute rSO2 threshold compared with 4 and 3 subjects in each cohort with INVOS, respectively. CONCLUSIONS: Significant differences exist between the devices in how they respond to changes in oxygen saturation in healthy volunteers. We suggest caution when applying evidence generated with one manufacturer's device to all devices.

Gradient adjustment method for better discriminating correlating and non-correlating regions of physiological signals: application to the partitioning of impaired and intact zones of cerebral autoregulation.

Cerebral blood flow (CBF) is regulated over a range of systemic blood pressures by the cerebral autoregulation (CA) control mechanism. This range lies within the lower and upper limits of autoregulation (LLA, ULA), beyond which blood pressure drives CBF, and CA function is considered impaired. A standard method to determine autoregulation limits noninvasively using NIRS technology is via the COx measure: a moving correlation index between mean arterial pressure and regional oxygen saturation. In the intact region, there should be no correlation between these variables whereas in the impaired region, the correlation index should approximate unity. In practice, however, the data may be noisy and/or the intact region may often exhibit a slightly positive relationship. This positive relationship may render traditional autoregulation limit calculations difficult to perform, resulting in the need for manual interpretation of the data using arbitrary thresholds. Further, the underlying mathematics of the technique are asymmetric in terms of the results produced for impaired and intact regions and are, in fact, not computable for the ideal case within the intact region. In this work, we propose a novel gradient adjustment method (GACOx) to enhance the differences in COx values observed in the intact and impaired regions. Results from a porcine model (N = 8) are used to demonstrate that GACOx is successful in determining LLA values where traditional methods fail. It is shown that the derived GACOx indices exhibit a mean difference between the intact/impaired regions of 1.54 ± 0.26 (mean ± SD), compared to 0.14 ± 0.10 for the traditional COx method. The GACOx effectively polarizes the COx data in order to better differentiate the intact and impaired zones and, in doing so, makes the determination of the LLA and ULA points a simpler and more consistent task. The method lends itself to the automation of the robust determination of autoregulation zone limits.

Data clustering methods for the determination of cerebral autoregulation functionality.

Cerebral blood flow is regulated over a range of systemic blood pressures through the cerebral autoregulation (CA) control mechanism. The COx measure based on near infrared spectroscopy (NIRS) has been proposed as a suitable technique for the analysis of CA as it is non-invasive and provides a simpler acquisition methodology than other methods. The COx method relies on data binning and thresholding to determine the change between intact and impaired autoregulation zones. In the work reported here we have developed a novel method of differentiating the intact and impaired CA blood pressure regimes using clustering methods on unbinned data. K-means and Gaussian mixture model algorithms were used to analyse a porcine data set. The determination of the lower limit of autoregulation (LLA) was compared to a traditional binned data approach. Good agreement was found between the methods. The work highlights the potential application of using data clustering tools in the monitoring of CA function.

Video monitoring of oxygen saturation during controlled episodes of acute hypoxia.

A method for extracting video photoplethysmographic information from an RGB video stream is tested on data acquired during a porcine model of acute hypoxia. Cardiac pulsatile information was extracted from the acquired signals and processed to determine a continuously reported oxygen saturation (SvidO2). A high degree of correlation was found to exist between the video and a reference from a pulse oximeter. The calculated mean bias and accuracy across all eight desaturation episodes were -0.03% (range: -0.21% to 0.24%) and accuracy 4.90% (range: 3.80% to 6.19%) respectively. The results support the hypothesis that oxygen saturation trending can be evaluated accurately from a video system during acute hypoxia.