Anesthesia Patient Monitoring 2050.

The monitoring of vital signs in patients undergoing anesthesia began with the very first case of anesthesia and has evolved alongside the development of anesthesiology ever since. Patient monitoring started out as a manually performed, intermittent, and qualitative assessment of the patient's general well-being in the operating room. In its evolution, patient monitoring development has responded to the clinical need, for example, when critical incident studies in the 1980s found that many anesthesia adverse events could be prevented by improved monitoring, especially respiratory monitoring. It also facilitated and perhaps even enabled increasingly complex surgeries in increasingly higher-risk patients. For example, it would be very challenging to perform and provide anesthesia care during some of the very complex cardiovascular surgeries that are almost routine today without being able to simultaneously and reliably monitor multiple pressures in a variety of places in the circulatory system. Of course, anesthesia patient monitoring itself is enabled by technological developments in the world outside of the operating room. Throughout its history, anesthesia patient monitoring has taken advantage of advancements in material science (when nonthrombogenic polymers allowed the design of intravascular catheters, for example), in electronics and transducers, in computers, in displays, in information technology, and so forth. Slower product life cycles in medical devices mean that by carefully observing technologies such as consumer electronics, including user interfaces, it is possible to peek ahead and estimate with confidence the foundational technologies that will be used by patient monitors in the near future. Just as the discipline of anesthesiology has, the patient monitoring that accompanies it has come a long way from its beginnings in the mid-19th century. Extrapolating from careful observations of the prevailing trends that have shaped anesthesia patient monitoring historically, patient monitoring in the future will use noncontact technologies, will predict the trajectory of a patient's vital signs, will add regional vital signs to the current systemic ones, and will facilitate directed and supervised anesthesia care over the broader scope that anesthesia will be responsible for.

Prolonged Opioid Use and Pain Outcome and Associated Factors after Surgery under General Anesthesia: A Prospective Cohort Association Multicenter Study.

BACKGROUND: There is insufficient prospective evidence regarding the relationship between surgical experience and prolonged opioid use and pain. The authors investigated the association of patient characteristics, surgical procedure, and perioperative anesthetic course with postoperative opioid consumption and pain 3 months postsurgery. The authors hypothesized that patient characteristics and intraoperative factors predict opioid consumption and pain 3 months postsurgery. METHODS: Eleven U.S. and one European institution enrolled patients scheduled for spine, open thoracic, knee, hip, or abdominal surgery, or mastectomy, in this multicenter, prospective observational study. Preoperative and postoperative data were collected using patient surveys and electronic medical records. Intraoperative data were collected from the Multicenter Perioperative Outcomes Group database. The association between postoperative opioid consumption and surgical site pain at 3 months, elicited from a telephone survey conducted at 3 months postoperatively, and demographics, psychosocial scores, pain scores, pain management, and case characteristics, was analyzed. RESULTS: Between September and October 2017, 3,505 surgical procedures met inclusion criteria. A total of 1,093 cases were included; 413 patients were lost to follow-up, leaving 680 (64%) for outcome analysis. Preoperatively, 135 (20%) patients were taking opioids. Three months postsurgery, 96 (14%) patients were taking opioids, including 23 patients (4%) who had not taken opioids preoperatively. A total of 177 patients (27%) reported surgical site pain, including 45 (13%) patients who had not reported pain preoperatively. The adjusted odds ratio for 3-month opioid use was 18.6 (credible interval, 10.3 to 34.5) for patients who had taken opioids preoperatively. The adjusted odds ratio for 3-month surgical site pain was 2.58 (1.45 to 4.4), 4.1 (1.73 to 8.9), and 2.75 (1.39 to 5.0) for patients who had site pain preoperatively, knee replacement, or spine surgery, respectively. CONCLUSIONS: Preoperative opioid use was the strongest predictor of opioid use 3 months postsurgery. None of the other variables showed clinically significant association with opioid use at 3 months after surgery.

The impact of urine flow on urine oxygen partial pressure monitoring during cardiac surgery.

PURPOSE: Urine oxygen partial pressure (PuO2) may be useful for assessing acute kidney injury (AKI) risk. The primary purpose of this study was to quantify the ability of a novel urinary oxygen monitoring system to make real-time PuO2 measurements intraoperatively which depends on adequate urine flow. We hypothesized that PuO2 data could be acquired with enough temporal resolution to provide real-time information in both AKI and non-AKI patients. METHODS: PuO2 and urine flow were analyzed in 86 cardiac surgery patients. PuO2 data associated with low (< 0.5 ml/kg/hr) or retrograde urine flow were discarded. Patients were excluded if > 70% of their data were discarded during the respective periods, i.e., during cardiopulmonary bypass (CPB), before CPB (pre-CPB), and after CPB (post-CPB). The length of intervals of discarded data were recorded for each patient. The median length of intervals of discarded data were compared between AKI and non-AKI patients and between surgical periods. RESULTS: There were more valid PuO2 data in CPB and post-CPB periods compared to the pre-CPB period (81% and 90% vs. 31% of patients included, respectively; p < 0.001 and p < 0.001). Most intervals of discarded data were < 3 minutes during CPB (96%) and post-CPB (98%). The median length was < 25 s during all periods and there was no significant difference in the group median length of discarded data intervals for AKI and non-AKI patients. CONCLUSIONS: PuO2 measurements were acquired with enough temporal resolution to demonstrate real-time PuO2 monitoring during CPB and the post-CPB period. GOV IDENTIFIER: NCT03335865, First Posted Date: Nov. 8th, 2017.

Practice Patterns and Variability in Intraoperative Opioid Utilization: A Report From the Multicenter Perioperative Outcomes Group.

BACKGROUND: Opioids remain the primary mode of analgesia intraoperatively. There are limited data on how patient, procedural, and institutional characteristics influence intraoperative opioid administration. The aim of this retrospective, longitudinal study from 2012 to 2016 was to assess how intraoperative opioid dosing varies by patient and clinical care factors and across multiple institutions over time. METHODS: Demographic, surgical procedural, anesthetic technique, and intraoperative analgesia data as putative variables of intraoperative opioid utilization were collected from 10 institutions. Log parenteral morphine equivalents (PME) was modeled in a multivariable linear regression model as a function of 15 covariates: 3 continuous covariates (age, anesthesia duration, year) and 12 factor covariates (peripheral block, neuraxial block, general anesthesia, emergency status, race, sex, remifentanil infusion, major surgery, American Society of Anesthesiologists [ASA] physical status, non-opioid analgesic count, Multicenter Perioperative Outcomes Group [MPOG] institution, surgery category). One interaction (year by MPOG institution) was included in the model. The regression model adjusted simultaneously for all included variables. Comparison of levels within a factor were reported as a ratio of medians with 95% credible intervals (CrI). RESULTS: A total of 1,104,324 cases between January 2012 and December 2016 were analyzed. The median (interquartile range) PME and standardized by weight PME per case for the study period were 15 (10-28) mg and 200 (111-347) µg/kg, respectively. As estimated in the multivariable model, there was a sustained decrease in opioid use (mean, 95% CrI) dropping from 152 (151-153) µg/kg in 2012 to 129 (129-130) µg/kg in 2016. The percent of variability in PME due to institution was 25.6% (24.8%-26.5%). Less opioids were prescribed in men (130 [129-130] µg/kg) than women (144 [143-145] µg/kg). The men to women PME ratio was 0.90 (0.89-0.90). There was substantial variability in PME administration among institutions, with the lowest being 80 (79-81) µg/kg and the highest being 186 (184-187) µg/kg; this is a PME ratio of 0.43 (0.42-0.43). CONCLUSIONS: We observed a reduction in intraoperative opioid administration over time, with variability in dose ranging between sexes and by procedure type. Furthermore, there was substantial variability in opioid use between institutions even when adjusting for multiple variables.

Volatile anesthetic gas concentration sensing using flow sensor fusion for use in Austere settings.

Flow sensors are often sensitive to the presence of volatile anesthetics. However, this sensitivity provides a unique opportunity to combine flow sensors of differing technological principles as an alternative to measuring volatile anesthetic gas concentration, particularly for austere settings. To determine the feasibility of flow sensor fusion for volatile anesthetic concentrations monitoring, eight flow sensors were tested with isoflurane, sevoflurane, and desflurane, ranging in concentrations from 0-4.5%, 0-3.5%, and 0-18%, respectively. Pairs of flow sensors were fit to the volatile anesthetic gas concentration with a leave-one-out cross-validation method to reduce the likelihood of overfitting. Bland-Altman was used for the final evaluation of sensor pair performance. Several sensor pairs yielded limits of agreement comparable to the rated accuracy of a commercial infrared spectrometer. The ultrasonic and orifice-plate flowmeters yielded the most combinations of viable sensor pairs for all three volatile anesthetic gases. Conclusion: Measuring volatile anesthetic gases using flow sensor fusion is a feasible low-cost, low-maintenance alternative to infrared spectroscopy. In this study, testing was done under steady-state conditions in 100% oxygen. Further testing is necessary to ensure sensor fusion performance under conditions that are more reflective of the clinical use case.

Noninvasive Urine Oxygen Monitoring and the Risk of Acute Kidney Injury in Cardiac Surgery.

BACKGROUND: Acute kidney injury (AKI) is a common complication of cardiac surgery. An intraoperative monitor of kidney perfusion is needed to identify patients at risk for AKI. The authors created a noninvasive urinary oximeter that provides continuous measurements of urinary oxygen partial pressure and instantaneous urine flow. They hypothesized that intraoperative urinary oxygen partial pressure measurements are feasible with this prototype device and that low urinary oxygen partial pressure during cardiac surgery is associated with the subsequent development of AKI. METHODS: This was a prospective observational pilot study. Continuous urinary oxygen partial pressure and instantaneous urine flow were measured in 91 patients undergoing cardiac surgery using a novel device placed between the urinary catheter and collecting bag. Data were collected throughout the surgery and for 24 h postoperatively. Clinicians were blinded to the intraoperative urinary oxygen partial pressure and instantaneous flow data. Patients were then followed postoperatively, and the incidence of AKI was compared to urinary oxygen partial pressure measurements. RESULTS: Intraoperative urinary oxygen partial pressure measurements were feasible in 86/91 (95%) of patients. When urinary oxygen partial pressure data were filtered for valid urine flows greater than 0.5 ml · kg-1 · h-1, then 70/86 (81%) and 77/86 (90%) of patients in the cardiopulmonary bypass (CPB) and post-CPB periods, respectively, were included in the analysis. Mean urinary oxygen partial pressure in the post-CPB period was significantly lower in patients who subsequently developed AKI than in those who did not (mean difference, 6 mmHg; 95% CI, 0 to 11; P = 0.038). In a multivariable analysis, mean urinary oxygen partial pressure during the post-CPB period remained an independent risk factor for AKI (relative risk, 0.82; 95% CI, 0.71 to 0.95; P = 0.009 for every 10-mmHg increase in mean urinary oxygen partial pressure). CONCLUSIONS: Low urinary oxygen partial pressures after CPB may be associated with the subsequent development of AKI after cardiac surgery.

Intraoperative Urinary Biomarkers and Acute Kidney Injury After Cardiac Surgery.

OBJECTIVES: To evaluate the association of intraoperative urinary biomarker excretion during cardiac surgery and the subsequent development of acute kidney injury (AKI). DESIGN: Prospective, nonrandomized, observational study. SETTING: Single tertiary-level, university-affiliated hospital. PARTICIPANTS: Ninety patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Urinary samples were collected every 30 minutes intraoperatively and then at four, 12, and 24 hours after CPB. Samples were measured for interleukin 18 (IL-18), kidney injury molecule-1 (KIM1), and creatinine concentrations. Urinary biomarker excretion (raw and indexed to creatinine) for four intraoperative and three postoperative points were compared between patients with and those without subsequent AKI defined by increased serum creatinine concentration ≥0.3 mg/dL within the first 48 hours or ≥1.5 times baseline within seven days. Raw and indexed median IL-18 values were similar between AKI groups at all intraoperative points, but became significantly different at 12 hours after CPB. Raw and indexed median KIM1 values were significantly different between AKI groups at multiple intraoperative points and at four and 12 hours after CPB. During intraoperative and postoperative points, patients in the fourth quartile of KIM1 excretion had greater AKI incidence and longer intensive care and hospital lengths of stay than those in the first quartile. Only postoperatively did the differences in these outcomes between the fourth and first quartile of IL-18 excretion occur. CONCLUSIONS: Intraoperative KIM1 but not IL-18 excretion was associated with postoperative development of AKI.

Comparing Nasal End-Tidal Carbon Dioxide Measurement Variation and Agreement While Delivering Pulsed and Continuous Flow Oxygen in Volunteers and Patients.

BACKGROUND: Supplemental oxygen is administered during procedural sedation to prevent hypoxemia. Continuous flow oxygen, the most widespread method, is generally adequate but distorts capnography. Pulsed flow oxygen is novel and ideally will not distort capnography. We have developed a prototype oxygen administration system designed to try to facilitate end-tidal carbon dioxide (ETCO2) measurement. We conducted a volunteer study (ClinicalTrials.gov, NCT02886312) to determine how much nasal ETCO2 measurements vary with oxygen flow rate. We also conducted a clinical study (NCT02962570) to determine the median difference and limits of agreement between ETCO2 measurements made with and without administering oxygen. METHODS: Both studies were conducted at the University of Utah and participants acted as their own control. Inclusion criteria were age 18 years and older with an American Society of Anesthesiologists physical status of I-III. Exclusion criteria included acute respiratory distress syndrome, pneumonia, lung or cardiovascular disease, nasal/bronchial congestion, pregnancy, oxygen saturation measured by pulse oximetry <93%, and a procedure scheduled for <20 minutes. For the volunteer study, pulsed and continuous flow was administered at rates from 2 to 10 L/min using a single sequence of technique and flow. The median absolute deviation from the median value was analyzed for the primary outcome of ETCO2. For the clinical study, ETCO2 measurements (the primary outcome) were collected while administering pulsed and continuous flow at rates between 1 and 5 L/min and were compared to measurements without oxygen flow. Due to institutional review board requirements for patient safety, this study was not randomized. After completing the study, measurements with and without administering oxygen were analyzed to determine median differences and 95% limits of agreement for each administration technique. RESULTS: Thirty volunteers and 60 patients participated in these studies which ended after enrolling the predetermined number of participants. In volunteers, the median absolute deviation for ETCO2 measurements made while administering pulsed flow oxygen (0.89; 25%-75% quantiles: 0.3-1.2) was smaller than while administering continuous flow oxygen (3.93; 25%-75% quantiles: 2.2-6.2). In sedated patients, the median difference was larger during continuous flow oxygen (-6.8 mm Hg; 25%-75% quantiles: -12.5 to -2.1) than during pulsed flow oxygen (0.1 mm Hg; 25%-75% quantiles: -0.5 to 1.5). The 95% limits of agreement were also narrower during pulsed flow oxygen (-2.4 to 4.5 vs -30.5 to 2.4 mm Hg). CONCLUSIONS: We have shown that nasal ETCO2 measurements while administering pulsed flow have little deviation and agree well with measurements made without administering oxygen. We have also demonstrated that ETCO2 measurements during continuous flow oxygen have large deviation and wide limits of agreement when compared with measurements made without administering oxygen.

Technologies to Optimize the Care of Severe COVID-19 Patients for Health Care Providers Challenged by Limited Resources.

Health care systems are belligerently responding to the new coronavirus disease 2019 (COVID-19). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a specific condition, whose distinctive features are severe hypoxemia associated with (>50% of cases) normal respiratory system compliance. When a patient requires intubation and invasive ventilation, the outcome is poor, and the length of stay in the intensive care unit (ICU) is usually 2 or 3 weeks. In this article, the authors review several technological devices, which could support health care providers at the bedside to optimize the care for COVID-19 patients who are sedated, paralyzed, and ventilated. Particular attention is provided to the use of videolaryngoscopes (VL) because these can assist anesthetists to perform a successful intubation outside the ICU while protecting health care providers from this viral infection. Authors will also review processed electroencephalographic (EEG) monitors which are used to better titrate sedation and the train-of-four monitors which are utilized to better administer neuromuscular blocking agents in the view of sparing limited pharmacological resources. COVID-19 can rapidly exhaust human and technological resources too within the ICU. This review features a series of technological advancements that can significantly improve the care of patients requiring isolation. The working conditions in isolation could cause gaps or barriers in communication, fatigue, and poor documentation of provided care. The available technology has several advantages including (a) facilitating appropriate paperless documentation and communication between all health care givers working in isolation rooms or large isolation areas; (b) testing patients and staff at the bedside using smart point-of-care diagnostics (SPOCD) to confirm COVID-19 infection; (c) allowing diagnostics and treatment at the bedside through point-of-care ultrasound (POCUS) and thromboelastography (TEG); (d) adapting the use of anesthetic machines and the use of volatile anesthetics. Implementing technologies for safeguarding health care providers as well as monitoring the limited pharmacological resources are paramount. Only by leveraging new technologies, it will be possible to sustain and support health care systems during the expected long course of this pandemic.

Multicenter Perioperative Outcomes Group Enhanced Observation Study Postoperative Pain Profiles, Analgesic Use, and Transition to Chronic Pain and Excessive and Prolonged Opioid Use Patterns Methodology.

To study the impact of anesthesia opioid-related outcomes and acute and chronic postsurgical pain, we organized a multicenter study that comprehensively combined detailed perioperative data elements from multiple institutions. By combining pre- and postoperative patient-reported outcomes with automatically extracted high-resolution intraoperative data obtained through the Multicenter Perioperative Outcomes Group (MPOG), the authors sought to describe the impact of patient characteristics, preoperative psychological factors, surgical procedure, anesthetic course, postoperative pain management, and postdischarge pain management on postdischarge pain profiles and opioid consumption patterns. This study is unique in that it utilized multicenter prospective data collection using a digital case report form integrated with the MPOG framework and database. Therefore, the study serves as a model for future studies using this innovative method. Full results will be reported in future articles; the purpose of this article is to describe the methods of this study.

A comparison of controlled ventilation with a noninvasive ventilator versus traditional mask ventilation.

After induction, but before intubation, many general anesthesia patients are manually bag-mask ventilated. The objective of this study was to determine the efficacy of bag-mask ventilation (MkV) of an anesthetized patient versus mask ventilation using a noninvasive ventilator (NIV). We hypothesized that feedback-controlled, mask ventilation via NIV is more efficacious and safer. This critical short period of time in the operating room was chosen to compare MkV versus NIV. 30 ASA I-III patients, aged 18-74, presenting for elective surgery under general anesthesia were enrolled in the study. Patients were ventilated first with MkV and then with NIV. One minute of ventilation data was collected for each method. Respiratory inductance plethysmography (RIP) bands around the chest and abdomen were used to measure tidal volumes and breath rates for each method of ventilation. The NIV was set to deliver 10 breaths per minute with 12 cmH2O of pressure support. A non-inferiority test was used to compare MkV and NIV. MkV breaths had an average of 13 breaths and tidal volume of 364 mL (SD 145 mL). NIV resulted in an average of 10 breaths and tidal volume of 552 mL, i.e., 188 mL more than MkV (lower bound of the 95% confidence interval equal to 120 mL). The hypothesis of non-inferiority at the - 100 mL level and the superiority hypothesis at the + 100 mL level was accepted. NIV also resulted in much more consistent ventilation rates (zero variation since it is controlled by the ventilator) when compared to manual ventilation while maintaining safe airway pressures (8 cmH2O EPAP and 20 cmH2O IPAP). Feedback controlled mask ventilation via a NIV is a viable alternative to MkV. It can deliver more optimal tidal volumes with the operator utilizing only one hand. The airway pressures are fixed at safe limits during a period where the goal is to reach a maximal level of oxygenation prior to intubation. Over-ventilation or over-pressurization of the airway is not a concern with NIV since the pressures are maintained well within safe thresholds to avoid injury.

A comparison of ventilation with a non-invasive ventilator versus standard O2 with a nasal cannula for colonoscopy with moderate sedation using propofol.

The aim of this study was to test the effects of CPAP on moderately sedated patients undergoing colonoscopy. Our hypothesis was that CPAP can reduce the incidence and duration of obstructive apnea and hemoglobin oxygen desaturation in patients undergoing procedural sedation for colonoscopy. Two groups of consenting adult patients scheduled to undergo routine colonoscopy procedures and sedated with propofol and fentanyl were monitored in this study: control and intervention. Patients in the intervention group were connected via a facemask to a ventilator that delivered supplemental oxygen (100%) through a standard air-cushion mask. The mask had a built-in leak to facilitate CO2 clearance during CPAP. Patients in the control group received 2-10 L/min of oxygen via nasal cannula or non-rebreather mask. Subjects in the control group were collected in a prior study and used as historical controls. The primary outcome measures were the number of apneic events and the cumulative duration of apneic events. An apneic event was defined as a period longer than 10 s without respiration. The secondary outcome was the area under the curve (AUC) for the arterial oxygen saturation less than 90% versus time during sedative and analgesic administration (time (s) below threshold multiplied by percent below threshold). A desaturation event was defined as a period of time during which arterial oxygen saturation was less than 90%. 29 patients were enrolled in the intervention group and 156 patients were previously enrolled in the control group as part of an earlier study. The median number of apneic events in the control group was 7 compared to 0 in the intervention group. The intervention group experienced apnea less than 1% of the total procedure time compared to 17% in the control group (p < 0.001). There were no desaturation events observed in the 29 patients in the intervention group. In contrast, 27 out of 156 patients in the control group experienced a desaturation event. Average AUC of patients in the control group was 70%-s (time (s) * oxygen saturation below < 90%) (95% CI 32.34-108.60%) whereas the average AUC in intervention group patients was 0%-s (% time (s) * oxygen saturation < 90%) (95% CI 0-0%), p = 0.01. This preliminary study found that CPAP via a tight-fitting mask may be an effective tool to reduce the incidence and duration of obstructive apneic events as well as hemoglobin oxygen desaturation during lower endoscopy procedures that use propofol and fentanyl for sedation.Clinical Trial Registration ClinicalTrials.gov ID: NCT02623270. https://clinicaltrials.gov/ct2/show/NCT02623270 .

Evaluation and application of a method for estimating nasal end-tidal O2 fraction while administering supplemental O2.

This paper describes a method for estimating the oxygen enhanced end-tidal fraction of oxygen (FetOe), the end-tidal fraction of oxygen (FetO2) that is raised by administering supplemental oxygen. The paper has two purposes: the first is to evaluate the method's accuracy on the bench and in volunteers; the second purpose is to demonstrate how to apply the method to compare two techniques of oxygen administration. The method estimates FetOe by analyzing expired oxygen as oxygen washes out of the lung. The method for estimating FetOe was first validated using a bench simulation in which tracheal oxygen was measured directly. Then it was evaluated in 30 healthy volunteers and compared to the bench simulation. Bland-Altman analysis compared calculated and observed FetOe/FetO2 measurements. After the method was evaluated, it was implemented to compare the FetOe obtained when administering oxygen using two different techniques (pulsed and continuous flow). A total of eighteen breath washout conditions were evaluated on the bench. FetOe estimates and tracheal FetO2 had a mean difference of - 0.016 FO2 with 95% limits of agreement from - 0.048 to 0.016 FO2. Thirteen breath washouts per volunteer were analyzed. Extrapolated and observed FetO2 had a mean difference of - 0.001 FO2 with 95% limits of agreement from - 0.006 to 0.004 FO2. Pulsed flow oxygen (PFO) achieved the same FetOe values as continuous flow oxygen (CFO) using 32.1% ± 2.27% (mean ± SD) of the CFO rate. This paper has demonstrated that the method estimates FetO2 enhanced by administering supplemental oxygen with clinically insignificant differences. This paper has also shown that PFO can obtain FetO2 similar to CFO using approximately one-third of the oxygen volume. After evaluating this method, we conclude that the method provides useful estimates of nasal FetO2 enhanced by supplemental oxygen administration.

Investigating Capnography Innovation for Better Patient Monitoring in the Resource Limited Surgical Setting.

BACKGROUND: Access to basic anesthetic monitoring in the developing world is lacking, which contributes to the 100 times greater anesthesia-related mortality in low- and middle-income countries. We hypothesize that an environmental sensor with a lower sampling rate could provide some clinical utility by providing CO2 levels, respiratory rate, and support in detection of clinical abnormalities. MATERIALS AND METHODS: A bench-top lung simulation was created to replicate CO2 waveforms, and an environmental sensor was compared with industry-available technology. Sensor response time and respiratory rates were compared between devices. Additionally, an in silico model was created to replicate capnography pathology as waveforms would appear using the environmental sensor. RESULTS AND CONCLUSION: Breath simulations using the bench-top lung simulation produced similar results to industry standards with a degree of variability. Respiratory rates did not differ between the environmental sensor and all other devices tested. Finally, pathological waveforms created in silico carried a certain level of detail regarding ventilatory pathology, which could provide some clinical insight to an anesthesiologist. We believe our prototype is the first step toward making low-cost and portable capnography available in the resource-limited setting, and future efforts should focus on bridging the gap to safer anesthesia and surgery globally.

Perioperative Noninvasive Blood Pressure Monitoring.

The most commonly monitored variable for perioperative hemodynamic management is blood pressure. Several indirect noninvasive blood pressure monitoring techniques have been developed over the last century, including intermittent techniques such as auscultation (Riva-Rocci and Korotkoff) and oscillometry (Marey) and continuous techniques. With the introduction of automated noninvasive blood pressure devices in the 1970s, the oscillometric technique quickly became and remains the standard for automated, intermittent blood pressure measurement. It tends to estimate more extreme high and low blood pressures closer to normal than what invasive measurements indicate. The accuracy of the oscillometric maximum amplitude algorithm for estimating mean arterial pressure is affected by multiple factors, including the cuff size and shape, the shape of the arterial compliance curve and arterial pressure pulse, and pulse pressure itself. Additionally, the technique typically assumes a consistent arterial compliance and arterial pressure pulse, thus changes in arterial compliance and arrhythmias that lead to variation in the pressure pulse can affect accuracy. Volume clamping, based on the Penaz principle, and arterial tonometry provide continuous tracking of the arterial pressure pulse. The ubiquitous use of blood pressure monitoring is in contrast with the lack of evidence for optimal perioperative blood pressure targets.

Near-infrared spectroscopy for kidney oxygen monitoring in a porcine model of hemorrhagic shock, hemodilution, and REBOA.

Acute kidney injury is a common complication of trauma and hemorrhagic shock. In a porcine model of hemorrhagic shock, resuscitative endovascular balloon aortic occlusion (REBOA) and hemodilution, we hypothesized that invasive kidney oxygen concentration measurements would correlate more strongly with noninvasive near infra-red spectroscopy (NIRS) oxygen saturation measurements when cutaneous sensors were placed over the kidney under ultrasound guidance compared to placement over the thigh muscle and subcutaneous tissue. Eight anesthetized swine underwent hemorrhagic shock 4 of which were resuscitated with intravenous fluids prior to the return of shed blood (Hemodilution protocol) and 4 of which underwent REBOA prior to resuscitation and return of shed blood (REBOA protocol). There was a moderate correlation between the NIRS and kidney tissue oxygen measurements (r = 0.61 p < 0.001; r = 0.67 p < 0.001; r = 0.66 p < 0.001for left kidney, right kidney, and thigh NIRS respectively). When the animals were separated by protocol, the Hemodilution group showed a weak or nonsignificant correlation between NIRS and kidney tissue oxygen measurements (r = 0.10 p < 0.001; r = 0.01 p = 0.1007; r = 0.28 p < 0.001 for left kidney, right kidney, and thigh NIRS respectively). This contrasts with the REBOA group, where left and right kidney as well as thigh NIRS were moderately correlated with kidney tissue oxygen (r = 0.71 p < 0.001; r = 0.74 p < 0.001; r = 0.70 p < 0.001; for left kidney, right kidney, and thigh NIRS respectively). There was a strong correlation between both kidney NIRS signals and thigh NIRS measurements (r = 0.85 p < 0.001; r = 0.88 p < 0.001;for left kidney vs thigh and right kidney vs thigh respectively). There was also a strong correlation between left and right kidney NIRS (r = 0.90 p < 0.001). These relationships were maintained regardless of the resuscitation protocol. These results suggest that kidney NIRS measurements were more closely related to thigh NIRS measurements than invasive kidney tissue oxygen concentration.