Blood Pressure Monitoring for the Anesthesiologist

Transfer Learning Enhanced Blood Pressure Monitoring Based on Flexible Optical Pulse Sensing Patch

Blood pressure (BP), a crucial health biomarker, is essential for detecting early indications of cardiovascular disease in routine monitoring and clinical surveillance of inpatients. However, conventional cuff-based BP measurements are limited in providing continuous comfort monitoring. Here, we present an optical pulse sensing patch for BP monitoring, which integrates three units of Gallium Nitride (GaN) optopairs with micronanostructured polydimethylsiloxane films to capture pulse waves. Multipoint pulse signals are transformed into BP and other cardiovascular indicators through machine learning. The transfer learning method is developed to calibrate the machine learning model with few training sets, simplifying the practical implementation. The developed sensing patch holds great potential for long-term, precise BP monitoring, enhancing clinical diagnosis, and management of cardiovascular diseases.

Factors Influencing Preoperative Blood Pressure Fluctuations in Patients Undergoing Elective Surgery: A Retrospective Observational Study

Purpose

To investigate the factors influencing preoperative blood pressure fluctuations in patients undergoing elective surgery.

Patients and Methods

This retrospective observational study included 776 patients who underwent elective surgery between January and October 2021. Preoperative blood pressure fluctuations were defined las a systolic or diastolic change exceeding 20% compared to baseline measurements taken one day prior to surgery. Patients were divided into two groups: the elevated blood pressure group (n=328) and the non-fluctuating group (n=448). Multivariate logistic regression analysis was employed to identify independent risk factors associated with blood pressure fluctuations.

Results

Among the 776 patients (335 males and 441 females), the average systolic blood pressure increased by 12.98 ± 19.33 mmHg, and diastolic blood pressure increased by 6.67 ± 13.20 mmHg on the day of surgery compared to the previous day. Preoperative blood pressure fluctuations exceeding 20% were observed in 42.27% of patients. Multivariate logistic regression revealed that older age (OR = 1.021; 95% CI: 1.007-1.035; P = 0.003), preoperative hypertension (OR = 1.785; 95% CI: 1.142-2.807; P = 0.011), and shorter sleep duration the night before surgery (OR = 0.835; 95% CI: 0.747-0.932; P = 0.001) were independent risk factors for blood pressure fluctuations.

Conclusion

Significant increases in preoperative blood pressure were observed upon patient entry into the operating room. Older age, preoperative hypertension, and inadequate sleep duration were identified as independent risk factors for blood pressure fluctuations. These findings underscore the need for targeted preoperative interventions to minimize blood pressure variability, particularly in elderly and hypertensive patients with inadequate sleep duration.

Silk Fibroin Hydrogel for Pulse Waveform Precise and Continuous Perception

Precise and continuous monitoring of blood pressure and cardiac function is of great importance for early diagnosis and timely treatment of cardiovascular diseases. The common tests rely on on-site diagnosis and bulky equipments, hindering early diagnosis. The emerging hydrogels have gained considerable attention in skin bioelectronics by virtue of the similarities to biological tissues and versatility in mechanical, electrical, and biofunctional engineering. However, hydrogels should overcome intrinsic issues such as poor mechanical strength, easy dehydration and freezing, weak adhesiveness and self-recovery, severely limiting their precision and reliability in practical applications. Here, silk fibroin hydrogels are developed as resistive sensors for pulse waveform monitoring. The silk fibroin hydrogel is simultaneously transparent, extremely stretchable, extra tough, adhesive, printable, and environmentally endurable. The silk fibroin hydrogel is also conductive with high sensitivity, short self-healing time, highly repeatable and reliable response, meeting the requirements for wearable sensors for continuous monitoring. The sensors with silk fibroin hydrogel present high-quality and stable waveforms of radical and brachial pulses with high precision and rich features, providing physiological signals of blood pressure and cardiac function. The sensors are promising for personalized health management, daily monitoring and timely diagnosis.

Ultrasound-guided short-axis out-of-plane versus long-axis in-plane technique of Posterior Tibial Artery Cannulation in adult patients: The POTACUT (POsterior Tibial Artery Access with Ultrasound Trial) Randomized Trial

BACKGROUND

No research has been conducted to compare long-axis in-plane and short-axis out-of-plane techniques for ultrasound-guided posterior tibial artery cannulation in adults. This study compared these two procedures for cannulating the posterior tibial artery.

METHODS

This prospective randomized trial included 236 adult patients undergoing general anesthesia who required arterial cannulation. The posterior tibial artery was cannulated using either the long-axis in-plane technique (group LAIP) or the short-axis out-of-plane method (group SAOP) with an ultrasound machine. First-attempt cannulation success, the number of cannulation attempts required to achieve successful cannulation, ultrasound localization time, cannulation time, and perioperative complications in these two groups were analyzed.

RESULTS

The LAIP group demonstrated a significantly higher first-attempt success rate (40.7% vs 18.6%, p < 0.001), shorter ultrasound localization time (36.5 [30, 60] s vs 50 [35, 80] s, p < 0.001), and faster cannulation time (80 [55, 100] s vs 110 [70, 180] s, p < 0.001). LAIP group showed a significantly higher overall success rate (92.4% vs 81.4%, p = 0.012). The median number of cannulation attempts in the LAIP and SAOP groups were 2 [1, 2] and 2 [2, 3], respectively (p < 0.001). Complications were comparable between groups (p = 0.248).

CONCLUSIONS

The LAIP group demonstrated higher first-attempt and overall success rates compared to the SAOP group for ultrasound-guided posterior tibial artery (PTA) cannulation in adult patients.

PeriOperative Quality Initiative (POQI) international consensus statement on perioperative arterial pressure management

Arterial pressure monitoring and management are mainstays of haemodynamic therapy in patients having surgery. This article presents updated consensus statements and recommendations on perioperative arterial pressure management developed during the 11th POQI PeriOperative Quality Initiative (POQI) consensus conference held in London, UK, on June 4-6, 2023, which included a diverse group of international experts. Based on a modified Delphi approach, we recommend keeping intraoperative mean arterial pressure ≥60 mm Hg in at-risk patients. We further recommend increasing mean arterial pressure targets when venous or compartment pressures are elevated and treating hypotension based on presumed underlying causes. When intraoperative hypertension is treated, we recommend doing so carefully to avoid hypotension. Clinicians should consider continuous intraoperative arterial pressure monitoring as it can help reduce the severity and duration of hypotension compared to intermittent arterial pressure monitoring. Postoperative hypotension is often unrecognised and might be more important than intraoperative hypotension because it is often prolonged and untreated. Future research should focus on identifying patient-specific and organ-specific hypotension harm thresholds and optimal treatment strategies for intraoperative hypotension including choice of vasopressors. Research is also needed to guide monitoring and management strategies for recognising, preventing, and treating postoperative hypotension.

The NARCOguide index - a novel parameter for monitoring depth of hypnosis during anaesthesia/sedation with propofol: A comparison study with the Narcotrend index

BACKGROUND

The NARCOguide algorithm calculates an EEG-derived index to monitor the hypnotic component of anaesthesia.

OBJECTIVE

This study evaluates the accuracy of the index calculated by NARCOguide against the Narcotrend index as a reference. Secondly, the automatic detection of burst-suppression patterns as represented by the burst suppression ratio was compared.

DESIGN

Comparative study to assess the agreement between two medical devices.

SETTING

At two study centres, patient data were collected from a total of 40 adults receiving general anaesthesia or sedation with propofol.

INTERVENTIONS

Patients underwent either general anaesthesia for oral surgery with propofol/remifentanil/rocuronium (study centre 1) or light general anaesthesia/deep sedation with propofol alone for laryngoscopic upper airway exploration (study centre 2).

MAIN OUTCOME MEASURES

In a posthoc analysis, the NARCOguide index was compared with the Narcotrend index. Comparison was made after averaging over 1 min at defined clinical markers using classic linear least squares regression and Bland-Altman plots. Precision and recall for the detection of burst suppression were determined using human scoring as a reference.

RESULTS

Data analysis showed good agreement [Bland-Altman mean difference (MD) = -2.3; limits of agreement = -27.1, to +22.4; n = 1209] and high correlation (r 2 = 0.76) between the depth of anaesthesia index calculated by NARCOguide and Narcotrend. The precision and recall of NARCOguide and Narcotrend for the detection of burst suppression were in a similar range. Over the entire dataset, the NARCOguide algorithm showed higher precision and recall than the Narcotrend algorithm (56% vs. 36% and 68% vs. 58%, respectively).

CONCLUSION

The NARCOguide index can be used to monitor the hypnotic component of anaesthesia in patients undergoing general anaesthesia or sedation with propofol, with a performance similar to that of the Narcotrend index.

TRIAL REGISTRATION

Trial registration number: 18020, regulatory authority: Ethikkommission der bayerischen Landesärztekammer, chairman: Dr med. Gerald Quitterer, applicant: Dr Gert Küchler, date of approval: 12. Jun 2018, completion of data collection: 12 December 2018, study completion: 31 March 2022.

SQI-DOANet: electroencephalogram-based deep neural network for estimating signal quality index and depth of anaesthesia

Objective. Monitoring the depth of anaesthesia (DOA) during surgery is of critical importance. However, during surgery electroencephalography (EEG) is usually subject to various disturbances that affect the accuracy of DOA. Therefore, accurately estimating noise in EEG and reliably assessing DOA remains an important challenge. In this paper, we proposed a signal quality index (SQI) network (SQINet) for assessing the EEG signal quality and a DOA network (DOANet) for analyzing EEG signals to precisely estimate DOA. The two networks are termed SQI-DOANet.Approach. The SQINet contained a shallow convolutional neural network to quickly determine the quality of the EEG signal. The DOANet comprised a feature extraction module for extracting features, a dual attention module for fusing multi-channel and multi-scale information, and a gated multilayer perceptron module for extracting temporal information. The performance of the SQI-DOANet model was validated by training and testing the model on the large VitalDB database, with the bispectral index (BIS) as the reference standard.Main results. The proposed DOANet yielded a Pearson correlation coefficient with the BIS score of 0.88 in the five-fold cross-validation, with a mean absolute error (MAE) of 4.81. The mean Pearson correlation coefficient of SQI-DOANet with the BIS score in the five-fold cross-validation was 0.82, with an MAE of 5.66.Significance. The SQI-DOANet model outperformed three compared methods. The proposed SQI-DOANet may be used as a new deep learning method for DOA estimation. The code of the SQI-DOANet will be made available publicly athttps://github.com/YuRui8879/SQI-DOANet.

Reproduction of central-brachial-radial arterial blood pressure wave propagation using a cardiovascular hardware simulator

This study reproduced changes according to the central-brachial-radial blood pressure wave propagation using a cardiovascular hardware simulator. Blood pressure is a key indicator of cardiovascular health, and its importance has recently emerged, and research into the correlation between the two is in progress. This requires a large amount of clinical data, but the amount and distribution are limited. The hardware simulator in this study mimics the structure and properties of the human cardiovascular system. This reproduces the pulse wave velocity and the generation of a blood pressure wave. The reproduced central-brachial-radial blood pressure waves are similar to those of humans in magnitude, waveform, and changes due to propagation. Blood pressure waves propagate from the central aorta to the radial artery, showing waveform changes due to systolic amplification and reduced overlap area. Reproducing these blood pressure waveforms can compensate for the lack of quantity and quality in clinical data. In the future, it can be expanded to a testbed for health sensors and research on the origin of bio-signals through the addition of upper arm and wrist phantoms.

Haemodynamic monitoring during noncardiac surgery: past, present, and future

During surgery, various haemodynamic variables are monitored and optimised to maintain organ perfusion pressure and oxygen delivery - and to eventually improve outcomes. Important haemodynamic variables that provide an understanding of most pathophysiologic haemodynamic conditions during surgery include heart rate, arterial pressure, central venous pressure, pulse pressure variation/stroke volume variation, stroke volume, and cardiac output. A basic physiologic and pathophysiologic understanding of these haemodynamic variables and the corresponding monitoring methods is essential. We therefore revisit the pathophysiologic rationale for intraoperative monitoring of haemodynamic variables, describe the history, current use, and future technological developments of monitoring methods, and finally briefly summarise the evidence that haemodynamic management can improve patient-centred outcomes.

Continuous Noninvasive Blood Pressure Measurement With "ClearSight" Compared to Standard Intermittent Blood Pressure Measurement in Patients With Peripheral Arterial Disease. Are Potential Differences Influenced by Phenylephrine or Dobutamine?

OBJECTIVES

To investigate the agreement between continuous noninvasive blood pressure measurement with the ClearSight system (cNIBP-CS) and standard intermittent noninvasive blood pressure measurement (iNIBP) in patients with peripheral arterial disease (PAD). Additionally, the influence of vasoactive medication on potential measurement differences was assessed.

DESIGN

A secondary analysis of a randomized controlled trial.

SETTING

At a university hospital.

PARTICIPANTS

Thirty-four patients with PAD undergoing percutaneous transluminal angioplasty of the lower limbs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Continuous noninvasive blood pressures were measured with the "ClearSight" system and compared to standard iNIBPs. Bland-Altman analysis revealed a mean bias of 13 mmHg (±15) between cNIBP-CS and iNIBP, with 95% limits of agreement (LOA) ranging from -17 to 42 mmHg. When comparing both medication groups, a similar mean bias was found for phenylephrine and dobutamine (12 mmHg [±13] and 13 mmHg [±13], respectively).

CONCLUSION

In this study, in patients with PAD, cNIBP-CS showed an underestimation of blood pressure compared to iNIBP in phenylephrine- and dobutamine-treated patients. Compared to previous studies, a larger bias and wider 95% LOA were found.

Surgical Emergencies in Patients with Significant Comorbid Diseases

Emergency surgery in patients with significant comorbidities benefits from a structured approach to preoperative evaluation, intra-operative intervention, and postoperative management. Providing goal concordant care is ideal using shared decision-making. When operation cannot achieve the patient's goal, non-operative therapy including Comfort Care is appropriate. When surgical therapy is offered, preoperative physiology-improving interventions are far fewer than in other phases. Reevaluation of clinical care progress helps define trajectory and inform goals of care. Palliative Care Medicine may be critical in supporting loved ones during a patient's critical illness. Outcome evaluation defines successful strategies and outline opportunities for improvement.

A prospective comparison of invasive and non-invasive blood pressure in children undergoing cardiac catheterization

BACKGROUND

Blood pressure measurement is a standard of monitoring during general anesthesia. Invasive measurement is considered the gold standard but is less commonly used than non-invasive. Automated oscillometric blood pressure devices measure the mean arterial pressure (MAP) and use an algorithm to determine the systolic and diastolic pressures. Few devices have been validated in children, particularly during anesthesia. Few studies have assessed the agreement between invasive and non-invasive blood pressure measurements in children.

METHODS

This was a multi-center prospective observational study of children under 16 years undergoing cardiac catheterization with general anesthesia. Paired invasive and non-invasive blood pressure measurements were recorded for each patient during stable periods of the procedure. Correlation within and between sites was assessed with Pearson's correlation coefficient, and agreement was examined using Bland-Altman methodology to determine bias. Agreement during episodes of hypotension and for age and weight was also determined. Bias greater than 5 mmHg and standard deviation greater than 8 mmHg was considered clinically significant. The primary end point was agreement of MAP measurements.

RESULTS

A total of 683 paired blood pressure values were collected from 254 children in three pediatric hospitals. Median [IQR] age and weight were 3 [1-7] years and 13.9 [8-23] Kg. The overall bias (SD) for mean arterial pressure values was 7.2 (11.4) mmHg. During hypotension (190 readings), the bias (SD) was 15 (11.0) mmHg. The non-invasive MAP was frequently higher than invasive MAP during infancy, and lower in older children.

CONCLUSION

Automated oscillometric blood pressure measurement is unreliable in anesthetized children during cardiac catheterization. Invasive pressure measurement should be considered for high-risk cases.

Hypotension and cognitive impairment among the elderly: Evidence from the CLHLS

BACKGROUND

While high blood pressure has been linked to cognitive impairment, the relationship between low blood pressure, especially hypotension, and cognitive impairment has not been well studied. Therefore, this study aimed to assess the prevalence of hypotension and cognitive impairment in the seniors of China, and the association between hypotension and cognitive function impairment.

METHODS

The data was derived from the 2018 wave of the Chinese Longitudinal Healthy Longevity Survey (CLHLS). Systolic blood pressures (SBP) and diastolic blood pressures (DBP) were measured by objective examination. The Chinese version of the Mini-Mental State Examination (CMMSE) was used to evaluate the cognitive impairment of the elderly. Generalized linear models were conducted to evaluate the association of hypotension with cognitive impairment.

RESULTS

The prevalence of hypotension and cognitive impairment in the Chinese elderly were 0.76% and 22.06%, respectively. Participants with hypotension, lower SBP, and lower DBP, had odds ratios of 1.62, 1.38, and 1.48 for cognitive impairment, respectively. Besides, the CMMSE scores decreased by 2.08, 0.86, and 1.08 in the elderly with hypotension, lower SBP, and DBP, compared with those with non-hypotension, higher SBP, and DBP, respectively. Subgroup analyses showed that the association of cognitive impairment with hypotension was stronger in Chinese elderly who had decreased activity of daily living. Moreover, there was statistical evidence of a nonlinear dose-response relationship of SBP and DBP with cognitive impairment (Pnonlinear < 0.05).

CONCLUSION

Hypotension was a potential risk factor for cognitive impairment of the Chinese elderly, especially for those having decreased activity of daily living. Blood pressure management should be conducted to prevent them from cognitive impairment.

Monitoring blood pressure and cardiac function without positioning via a deep learning-assisted strain sensor array

Continuous and reliable monitoring of blood pressure and cardiac function is of great importance for diagnosing and preventing cardiovascular diseases. However, existing cardiovascular monitoring approaches are bulky and costly, limiting their wide applications for early diagnosis. Here, we developed an intelligent blood pressure and cardiac function monitoring system based on a conformal and flexible strain sensor array and deep learning neural networks. The sensor has a variety of advantages, including high sensitivity, high linearity, fast response and recovery, and high isotropy. Experiments and simulation synergistically verified that the sensor array can acquire high-precise and feature-rich pulse waves from the wrist without precise positioning. By combining high-quality pulse waves with a well-trained deep learning model, we can monitor blood pressure and cardiac function parameters. As a proof of concept, we further constructed an intelligent wearable system for real-time and long-term monitoring of blood pressure and cardiac function, which may contribute to personalized health management, precise and early diagnosis, and remote treatment.

Agreement between distal and forearm radial arterial pressures in patients undergoing prone spinal surgery: a prospective, self-controlled, observational study

OBJECTIVE

To test agreement and interchangeability between distal (dRA) and forearm radial arterial (RA) pressures (AP) during general anesthesia (GA) for prone spinal surgery.

METHODS

This prospective observational study involved 40 patients scheduled for GA spinal surgery. The right dRA and left forearm RA were cannulated in all patients to continuously measure invasive blood pressures (IBP). We compared the agreement and trending ability of systolic AP (SAP), diastolic AP (DAP), and mean AP (MAP) at each site 15 minutes after tracheal intubation, start of surgery, 30 and 60 minutes after the start of surgery, and after skin suturing.

RESULTS

Paired BP values (n = 184) (37 cases) were analyzed. The bias (standard deviation), limits of agreement, and percentage error were: SAP: 0.19 (3.03), -5.75 to 6.12, and 5.04%; DAP: -0.06 (1.75), -3.50 to 3.38, and 5.10%; and MAP: 0.08 (1.52), -2.90 to 3.05, and 3.54%, respectively. The linear regression coefficients of determination were 0.981, 0.982, and 0.988 for SAPs, DAPs, and MAPs, respectively; four-quadrant plot concordance rates were 95.11%, 92.03%, and 92.66%, respectively.

CONCLUSION

All arterial BPs showed good agreement and trending capabilities for both the dRA and RA. The dRA may be substituted for the RA in IBP monitoring.

Patent landscape review of non-invasive medical sensors for continuous monitoring of blood pressure and their validation in critical care practice

Objectives

Continuous non-invasive monitoring of blood pressure is one of the main factors in ensuring the safety of the patient's condition in anesthesiology, intensive care, surgery, and other areas of medicine. The purpose of this work was to analyze the current patent situation and identify directions and trends in the application of non-invasive medical sensors for continuous blood pressure monitoring, with a focus on clinical experience in critical care and validation thereof.

Materials and methods

The research results reflect data collected up to September 30, 2022. Patent databases, Google Scholar, the Lens database, Pubmed, Scopus databases were used to search for patent and clinical information.

Results

An analysis of the patent landscape indicates a significant increase in interest in the development of non-invasive devices for continuous blood pressure monitoring and their implementation in medical practice, especially in the last 10 years. The key players in the intellectual property market are the following companies: Cnsystems Medizintechnik; Sotera Wireless INC; Tensys Medical INC; Healthstats Int Pte LTD; Edwards Lifesciences Corp, among others. Systematization of data from validation and clinical studies in critical care practice on patients with various pathological conditions and ages, including children and newborns, revealed that a number of non-invasive medical sensor technologies are quite accurate and comparable to the "gold standard" continuous invasive blood pressure monitoring. They are approved by the FDA for medical applications and certified according to ISO 81060-2, ISO 81060-3, and ISO/TS 81060-5. Unregistered and uncertified medical sensors require further clinical trials.

Conclusion

Non-invasive medical sensors for continuous blood pressure monitoring do not replace, but complement, existing methods of regular blood pressure measurement, and it is expected to see more of these technologies broadly implemented in the practice in the near future.

Post-induction hypotension with remimazolam versus propofol in patients routinely administered angiotensin axis blockades: a randomized control trial

BACKGROUND

Certain routine medication could result in post-induction hypotension (PIH), such as angiotensin axis blockades, which are frequently administered as a first-line therapy against hypertension. Remimazolam is reportedly associated with lesser intraoperative hypotension than propofol. This study compared the overall incidence of PIH following remimazolam or propofol administration in patients managed by angiotensin axis blockades.

METHODS

This single-blind, parallel-group, randomized control trial was conducted in a tertiary university hospital in South Korea. Patients undergoing surgery with general anesthesia were considered for enrollment if the inclusion criteria were met: administration of an angiotensin converting enzyme inhibitor or angiotensin receptor blocker, 19 to 65 years old, American Society of Anesthesiologists physical status classification ≤ III, and no involvement in other clinical trials. The primary outcome was the overall incidence of PIH, defined as a mean blood pressure (MBP) < 65 mmHg or decrease by ≥ 30% of the baseline MBP. The time points of measurement were baseline, just before the initial intubation attempt, and 1, 5, 10, and 15 min following intubation. The heart rate, systolic and diastolic blood pressures, and bispectral index were also recorded. Groups P and R included patients administered propofol and remimazolam, respectively, as an induction agent.

RESULTS

A total of 81 patients were analyzed, of the 82 randomized patients. PIH was less frequent in group R than group P (62.5% versus 82.9%; t value 4.27, P = 0.04, adjusted odds ratio = 0.32 [95% confidence interval 0.10-0.99]). The decrease in the MBP from baseline was 9.6 mmHg lesser in group R than in group P before the initial intubation attempt (95% confidence interval 3.3-15.9). A similar trend was observed for systolic and diastolic blood pressures. No severe adverse events were observed in either group.

CONCLUSION

Remimazolam results in less frequent PIH than propofol in patients undergoing routine administration of angiotensin axis blockades.

TRIAL REGISTRATION

This trial was retrospectively registered on Clinical Research Information Service (CRIS), Republic of Korea (KCT0007488). Registration date: 30/06/2022.

Continuous cuffless blood pressure monitoring with a wearable ring bioimpedance device

Smart rings provide unique opportunities for continuous physiological measurement. They are easy to wear, provide little burden in comparison to other smart wearables, are suitable for nocturnal settings, and can be sized to provide ideal contact between the sensors and the skin at all times. Continuous measuring of blood pressure (BP) provides essential diagnostic and prognostic value for cardiovascular health management. However, conventional ambulatory BP measurement devices operate using an inflating cuff that is bulky, intrusive, and impractical for frequent or continuous measurements. We introduce ring-shaped bioimpedance sensors leveraging the deep tissue sensing ability of bioimpedance while introducing no sensitivity to skin tones, unlike optical modalities. We integrate unique human finger finite element model with exhaustive experimental data from participants and derive optimum design parameters for electrode placement and sizes that yields highest sensitivity to arterial volumetric changes, with no discrimination against varying skin tones. BP is constructed using machine learning algorithms. The ring sensors are used to estimate arterial BP showing peak correlations of 0.81, and low error (systolic BP: 0.11 ± 5.27 mmHg, diastolic BP: 0.11 ± 3.87 mmHg) for >2000 data points and wide BP ranges (systolic: 89-213 mmHg and diastolic: 42-122 mmHg), highlighting the significant potential use of bioimpedance ring for accurate and continuous estimation of BP.

Bridging vascular physiology to vascular medicine: an integrative laboratory class

Vascular diseases of the legs are highly prevalent and constitute an important part of medical curricula. The understanding of these diseases relies on strongly interwoven aspects of vascular physiology and vascular medicine. We aimed to connect these within a horizontally integrated laboratory class on vascular physiology of the leg that was designed in cooperation between the departments of physiology and vascular surgery. Conceptually, we applied examination techniques of vascular medicine to visualize physiological parameters that are altered by the most frequent diseases. This facilitates integrative discussions on malfunctions, trains diagnostic skills, and bridges to vascular medicine. In four experiments, we use oscillometry and impedance venous occlusion plethysmography to address key aspects of the arterial and venous system of the legs: 1) arterial pulse wave, 2) arterial systolic blood pressure, 3) venous capacitance and venous outflow, and 4) reactive hyperemia. After the experiments, physiological vascular function, the associated diseases, their impact on the recorded parameters, and diagnostic options are discussed. To allow reproduction, we describe the course structure and the experimental setup in detail. We present the experimental data of a cohort of medical students and document learning success and student satisfaction. All experiments were feasible and provided robust data on physiologically and clinically relevant vascular functions. The activity was perceived positively by the students and led to a substantial improvement of knowledge. With this work, we offer a template for reproduction or variation of a proven concept of horizontally integrated teaching of vascular physiology of the leg.NEW & NOTEWORTHY This article presents an integrative laboratory class on vascular physiology bridging to vascular medicine. The four experiments rely on oscillometry and venous occlusion plethysmography. We describe in detail this new class regarding structure, experimental setup, and experimental procedure, and we give insight into the applied materials. Moreover, we present the experimental data of 74 students and a quantitative evaluation of the students' learning success and acceptance.

Photoplethysmography waveform analysis for classification of vascular tone and arterial blood pressure: Study based on neural networks

BACKGROUND

To test whether a Shallow Neural Network (S-NN) can detect and classify vascular tone dependent changes in arterial blood pressure (ABP) by advanced photopletysmographic (PPG) waveform analysis.

METHODS

PPG and invasive ABP signals were recorded in 26 patients undergoing scheduled general surgery. We studied the occurrence of episodes of hypertension (systolic arterial pressure (SAP) >140 mmHg), normotension and hypotension (SAP < 90 mmHg). Vascular tone according to PPG was classified in two ways: 1) By visual inspection of changes in PPG waveform amplitude and dichrotic notch position; where Classes I-II represent vasoconstriction (notch placed >50% of PPG amplitude in small amplitude waves), Class III normal vascular tone (notch placed between 20-50% of PPG amplitude in normal waves) and Classes IV-V-VI vasodilation (notch <20% of PPG amplitude in large waves). 2) By an automated analysis, using S-NN trained and validated system that combines seven PPG derived parameters.

RESULTS

The visual assessment was precise in detecting hypotension (sensitivity 91%, specificity 86% and accuracy 88%) and hypertension (sensitivity 93%, specificity 88% and accuracy 90%). Normotension presented as a visual Class III (III-III) (median and 1st-3rd quartiles), hypotension as a Class V (IV-VI) and hypertension as a Class II (I-III); all p < .0001. The automated S-NN performed well in classifying ABP conditions. The percentage of data with correct classification by S-ANN was 83% for normotension, 94% for hypotension, and 90% for hypertension.

CONCLUSIONS

Changes in ABP were correctly classified automatically by S-NN analysis of the PPG waveform contour.

EVALUATION OF AGREEMENT BETWEEN OSCILLOMETRIC AND DIRECT BLOOD PRESSURE MEASUREMENTS IN ANESTHETIZED TIGERS (PANTHERA TIGRIS)

Noninvasive blood pressure measurement is commonly performed with oscillometry; however, this technique provides clinically helpful information only if it is representative of the gold standard. Agreement between direct and oscillometric blood pressure measurements were performed in 14 anesthetized, captive tigers (Panthera tigris). A cuff, placed around the tail base and connected to a multiparameter monitor, was used to measure arterial blood pressure oscillometrically and provided systolic, mean, and diastolic pressures. At the same time, direct blood pressures were obtained from a dorsal pedal arterial catheter, and the oscillometric and direct readings were considered paired data points. Agreement between the two methods was evaluated by Bland-Altman plots. All animals completed the study and provided 196 paired data points. The bias (mm Hg) for systolic, mean, and diastolic arterial pressures was -3.7, -0.8, and -1.6, respectively. Limits of agreement (mm Hg) for systolic, mean, and diastolic arterial pressures were -31 to 24, -29 to 27, and -29 to 26, respectively. Oscillometry provided an acceptable amount of readings within 10 and 20 mm Hg of the gold standard. The oscillometric technique provided reasonable agreement with direct measurements. Therefore, in the conditions used in this study, oscillometric blood pressure measured via the ventral coccygeal artery provided reasonable estimates of invasive blood pressure in anesthetized tigers.

A new noninvasive finger sensor (NICCI system) for continuous blood pressure and pulse pressure variation monitoring: A method comparison study in patients having neurosurgery

BACKGROUND

The NICCI system (Getinge, Gothenburg, Sweden) is a new noninvasive haemodynamic monitoring system using a finger sensor.

OBJECTIVES

We aimed to investigate the performance of the NICCI system to measure blood pressure and pulse pressure variation compared with intra-arterial measurements.

DESIGN

A prospective method comparison study.

SETTING

University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

PATIENTS

Forty-seven neurosurgery patients.

MAIN OUTCOME MEASURES

We performed a method comparison study in 47 neurosurgery patients to compare NICCI blood pressure measurements (BP NICCI ) with intra-arterial blood pressure measurements (BP ART ) (Bland-Altman analysis, four-quadrant plot, error grid analysis) and NICCI pulse pressure variation measurements (PPV NICCI ) with pulse pressure variation calculated manually from the intra-arterial blood pressure waveform (PPV ART ) (Bland-Altman analysis, predictive agreement, Cohen's kappa).

RESULTS

The mean of the differences ± standard deviation (95% limits of agreement) between BP NICCI and BP ART was 11 ± 10 mmHg (-8 to 30 mmHg) for mean blood pressure (MBP), 3 ± 12 mmHg (-21 to 26 mmHg) for systolic blood pressure (SBP) and 12 ± 10 mmHg (-8 to 31 mmHg) for diastolic blood pressure (DBP). In error grid analysis, 54% of BP NICCI and BP ART MBP measurement pairs were classified as 'no risk', 43% as 'low risk', 3% as 'moderate risk' and 0% as 'significant risk' or 'dangerous risk'. The mean of the differences between PPV NICCI and PPV ART was 1 ± 3% (-4 to 6%). The predictive agreement between PPV NICCI and PPV ART was 80% and Cohen's kappa was 0.55.

CONCLUSIONS

The absolute agreement between BP NICCI and BP ART was not clinically acceptable. We recommend not using the current version of the NICCI system for blood pressure monitoring during surgery. The absolute agreement between PPV NICCI and PPV ART was clinically acceptable with moderate predictive agreement regarding pulse pressure variation categories. The NICCI system needs to be further developed and re-evaluated when an improved version is available.

TRIAL REGISTRATION

The study was registered in the German Clinical Trials Register (DRKS00023188) on 2 October 2020.

Extradural anaesthesia-analgesia in dogs undergoing cholecystectomy: A single centre retrospective study

Objectives

To assess the effects of extradural anaesthesia-analgesia (EAA) in dogs undergoing cholecystectomy.

Materials and methods

Medical records of dogs undergoing cholecystectomy between 2011 and 2019 were retrieved and allocated to two groups depending if analgesia was provided systemically (group SA) or extradurally (EAA). Preoperative data, intraoperative antinociceptive medications, postoperative analgesia, perioperative complications, and food intake were compared.

Results

Overall 41 medical records were included in the study: 19 and 22 dogs were allocated to groups SA and EAA, respectively. In group EAA, an extradural catheter was placed preoperatively in 8 dogs; in the remaining, it was placed postoperatively but an extradural injection was performed preoperatively. The extradural catheter tip was between the 4th lumbar and the 10th thoracic vertebrae. Intraoperatively, nociception was more likely to occur in group SA [OR 55.42 (2.97–1,035.06)]. During the first 24 and 48 h postoperatively, more dogs in group SA required methadone [OR 24 (2.81–268.4) and OR 11.56 (2.37–45.06), respectively] and additional analgesic drugs [OR 25 (3.47–281.9) and OR 35.29 (1.86–668.2), respectively] compared to group EAA. Voluntary postoperative food intake was also significantly higher in group EAA.

Clinical significance

Compared to systemic analgesia, the use of extradural anaesthesia-analgesia reduced perioperative analgesic requirement and promoted postoperative food intake in dogs undergoing cholecystectomy.

Continuous cuffless monitoring of arterial blood pressure via graphene bioimpedance tattoos

Continuous monitoring of arterial blood pressure (BP) in non-clinical (ambulatory) settings is essential for understanding numerous health conditions, including cardiovascular diseases. Besides their importance in medical diagnosis, ambulatory BP monitoring platforms can advance disease correlation with individual behaviour, daily habits and lifestyle, potentially enabling analysis of root causes, prognosis and disease prevention. Although conventional ambulatory BP devices exist, they are uncomfortable, bulky and intrusive. Here we introduce a wearable continuous BP monitoring platform that is based on electrical bioimpedance and leverages atomically thin, self-adhesive, lightweight and unobtrusive graphene electronic tattoos as human bioelectronic interfaces. The graphene electronic tattoos are used to monitor arterial BP for >300 min, a period tenfold longer than reported in previous studies. The BP is recorded continuously and non-invasively, with an accuracy of 0.2 ± 4.5 mm Hg for diastolic pressures and 0.2 ± 5.8 mm Hg for systolic pressures, a performance equivalent to Grade A classification.

Provisional Decision-Making for Perioperative Blood Pressure Management: A Narrative Review

Blood pressure (BP) is a basic determinant for organ blood flow supply. Insufficient blood supply will cause tissue hypoxia, provoke cellular oxidative stress, and to some extent lead to organ injury. Perioperative BP is labile and dynamic, and intraoperative hypotension is common. It is unclear whether there is a causal relationship between intraoperative hypotension and organ injury. However, hypotension surely compromises perfusion and causes harm to some extent. Because the harm threshold remains unknown, various guidelines for intraoperative BP management have been proposed. With the pending definitions from robust randomized trials, it is reasonable to consider observational analyses suggesting that mean arterial pressures below 65 mmHg sustained for more than 15 minutes are associated with myocardial and renal injury. Advances in machine learning and artificial intelligence may facilitate the management of hemodynamics globally, including fluid administration, rather than BP alone. The previous mounting studies concentrated on associations between BP targets and adverse complications, whereas few studies were concerned about how to treat and multiple factors for decision-making. Hence, in this narrative review, we discussed the way of BP measurement and current knowledge about baseline BP extracting for surgical patients, highlighted the decision-making process for BP management with a view to providing pragmatic guidance for BP treatment in the clinical settings, and evaluated the merits of an automated blood control system in predicting hypotension.

Waveform Morphology Comparison in Wearable Blood Pressure Sensors

Wearable devices for continuous non-invasive blood pressure monitoring must be capable of providing a continuous waveform representative of arterial blood pressure. This paper establishes the distinctions in waveform morphology between wearable sensor modalities, specifically millimeter-wave radar and photoplethysmography, when compared to a reference continuous non-invasive blood pressure monitor. An analysis of a 115-subject dataset was conducted to assess waveform suitability. Millimeter-wave radar waveform morphology was found to more closely resemble continuous non-invasive blood pressure than photoplethysmography. Clinical Relevance- This paper compares the waveform morphology and content of signals from wearable sensors in the context of continuous non-invasive blood pressure monitoring.

Role of Chrononutrition in the Antihypertensive Effects of Natural Bioactive Compounds

Hypertension (HTN) is one of the main cardiovascular risk factors and is considered a major public health problem. Numerous approaches have been developed to lower blood pressure (BP) in hypertensive patients, most of them involving pharmacological treatments. Within this context, natural bioactive compounds have emerged as a promising alternative to drugs in HTN prevention. This work reviews not only the mechanisms of BP regulation by these antihypertensive compounds, but also their efficacy depending on consumption time. Although a plethora of studies has investigated food-derived compounds, such as phenolic compounds or peptides and their impact on BP, only a few addressed the relevance of time consumption. However, it is known that BP and its main regulatory mechanisms show a 24-h oscillation. Moreover, evidence shows that phenolic compounds can interact with clock genes, which regulate the biological rhythm followed by many physiological processes. Therefore, further research might be carried out to completely elucidate the interactions along the time–nutrition–hypertension axis within the framework of chrononutrition.

MAP 65-is it enough?

PURPOSE OF REVIEW

The purpose of this review is to look at the current evidence on the consequences of intraoperative hypotension and discuss improvements that can be implemented for its prevention.

RECENT FINDINGS

Literature continues to supply convincing evidence that even brief periods of intraoperative hypotension are associated with increased perioperative morbidity and mortality. Recent randomized controlled trial showed intraoperative early use of vasopressor and maintaining blood pressure within tight ranges improves outcomes.

SUMMARY

There should be a shift in paradigm in focusing on the prevention of intraoperative hypotension instead treatment. The suggested goals to help maintaining hemodynamic stability during anesthesia include ensure adequate blood pressure and flow; hypotension prevention; and ensure adequate anesthetic depth without overdose.

Comparison of invasive blood pressure monitoring versus normal non-invasive blood pressure monitoring in ST-elevation myocardial infarction patients with percutaneous coronary intervention

BACKGROUND

Hypotension post percutaneous coronary intervention (PCI) causes stent thrombosis and reduced coronary perfusion, which aggravate myocardial ischemia and lead to patient death. Therefore, the accuracy and timeliness of blood pressure monitoring (BPM) are crucial for the nursing of patients post PCI. However, it is still controversial whether invasive blood pressure monitoring (IBPM) or non-invasive blood pressure monitoring (NIBPM) should be used for patients post PCI, and the magnitude of their assistance for patients' recovery remains unclear.

METHODS

A randomized controlled trial was performed in this study. 126 ST-segment elevation myocardial infarction (STEMI) patients post PCI were recruited and randomly divided into two groups (NIBPM group n = 63; IBPM group n = 63).

RESULTS

Clinical characteristics and physiological outcomes of participants received different BPM methods were collected and analyzed to compare the effects of these two methods on the nursing of PCI patients. Compared to NIBPM group, IBPM assisted to shorten the time of myocardial ischemia, promote coronary reperfusion, reduce the occurrence of cardiovascular disease and other complications, and ultimately reduce the mortality of patients post PCI.

CONCLUSION

The application of IBPM contributed to reduce the occurrence of complications, shorten the time of vascular reperfusion, and guide treatment of clinicians in time.

A single nucleotide polymorphism-based formula to predict the risk of propofol TCI concentration being over 4 µg mL-1 at the time of loss of consciousness

We aim to develop a formula based on single nucleotide polymorphisms (SNPs) to predict whether the propofol target-controlled infusion (TCI) concentration would be over 4 μg mL^-1 at the time of loss of consciousness (LOC). We recruited 184 patients undergoing thyroid or breast surgeries with propofol anaesthesia. A total of 48 SNPs of CYP2B6, CYP2C9, UGT1A9, HNF4A, ABCB1, ABCC4, ABCG2, GABRA2, GABRA4, GABRB1, GABRB3, GABRG2, GABBR2, GAD1, SLC1A3, BDNF, and NRXN1, previously associated with propofol metabolic and pharmacology pathway, were genotyped. The formula was developed in the training cohort using the least absolute shrinkage and selection operator logistic regression model, and then validated in the testing cohort. The SNPs, GABBR2 rs1167768, GABBR2 rs1571927, NRXN1 rs601010, BDNF rs2049046, GABRA4 rs1512135, UGT1A9 rs11692021, GABBR2 rs2808536, HNF4A rs1884613, GABRB3 rs2017247, and CYP2B6 rs3181842 were selected to construct the SNP-based formula, which was used to calculate the risk score for over 4 μg mL^-1 TCI concentration of propofol at the time of LOC. Patients in the high-risk group were more likely to require a propofol concentration higher than 4 μg mL^-1 and presented a longer LOC latency. The SNP-based formula may significantly improve the safety and effectiveness of propofol-induced anaesthesia.

Comparison of noninvasive continuous arterial blood pressure measured by NICAP with arterial line in elderly patients

BACKGROUND

Non-Invasive Continuous Arterial Pressure system (NICAP) allows continuous monitoring, timely detection of hypotension, and avoiding risks from invasive procedures. A previous study showed good comparability of NICAP with arterial line in people with no evidence of cardiovascular disease. Therefore, the goal of this study was to investigate whether NICAP could be accurately applied to elderly patients.

METHODS

In this single-centered observational study, forty-one patients above 65 undergoing elective surgeries requiring artery catheterizations were enrolled from July 17, 2020, to June 25, 2021. Radial artery cannulation and NICAP monitoring were started before anesthesia. Blood pressure during the anesthesia induction and the whole surgery, trend of blood pressure changes, time needed for establishing continuous monitoring, and complications were recorded.

RESULTS

A total of 6751 valid pairs of blood pressure measurements were analyzed. In the Bland-Altman analysis, the arithmetic means for systolic, diastolic, and mean arterial pressure were 2.2, 3.3, and 2.8 mmHg, respectively. NICAP and arterial line correlation coefficients for systolic, diastolic, and mean arterial pressure were 0.49, 0.33, and 0.45, respectively. In the trending analysis, the polar concordance rates at 30 degrees were 70.9% for systolic, 67.7% for diastolic, and 69.3% for mean arterial blood pressure. During the anesthesia induction, the arithmetic means for systolic, diastolic, and mean arterial pressure in the Bland-Altman analysis were 1.7, -0.2, and 0.5 mmHg, respectively. NICAP and arterial line correlation coefficients for systolic, diastolic, and mean arterial pressure were 0.78, 0.61 and 0.75, respectively. No severe complications occurred.

CONCLUSIONS

NICAP has a poor correlation with the arterial line in elderly patients for the whole surgery or during anesthesia induction. Moreover, it showed poor comparability in the detection of blood pressure change trends with arterial lines. Our findings suggest that NICAP might not be sufficiently accurate to be applied clinically in elderly patients with comorbidities. More accurate calibration and iteration are needed.

Validation of Continuous Noninvasive Blood Pressure Monitoring Using Error Grid Analysis

BACKGROUND

Error grid analysis was recently proposed to compare blood pressure obtained by 2 measurement methods. This study aimed to compare continuous noninvasive blood pressure (CNBP) with invasive blood pressure (IBP) using the error grid analysis and investigate the confounding risk factors attributable to the differences between CNBP and IBP.

METHODS

Sixty adult patients undergoing general anesthesia were prospectively enrolled. Simultaneous comparative data regarding CNBP and IBP were collected. The Bland-Altman analysis was conducted to compare CNBP and IBP for systolic blood pressure (SBP) and mean blood pressure (MBP; acceptable accuracy: mean bias <5 mm Hg; standard deviation <8 mm Hg). The clinical relevance of the discrepancies between CNBP and IBP was evaluated by the error grid analysis, which classifies the differences into 5 zones from "no risk" (A) to "dangerous risk" (E). Additionally, an ordinal logistic regression analysis was performed to evaluate the relationship between the risk zones for MBP, classified by the error grid analysis and covariates of interest.

RESULTS

A total of 10,663 pairs of CNBP/IBP were finally analyzed. The Bland-Altman analysis showed an acceptable accuracy with a bias of -3.3 ± 5.6 mm Hg for MBP but a poor accuracy with a bias of 5.4 ± 10.5 mm Hg for SBP. The error grid analysis showed the proportions of zones A to E as 96.7%, 3.2%, 0.1%, 0%, and 0% for SBP, respectively, and 72.0%, 27.9%, 0.1%, 0%, and 0% for MBP, respectively. The finger cuff missed 23.9% of epochs when SBP <90 mm Hg and 55.3% of epochs when MBP <65 mm Hg. The ordinal logistic regression analysis revealed that older age (adjusted odds ratio for decade: 1.54, 95% confidence interval [CI], 1.15-2.08; P = .004) and length of time from the initiation of finger cuff inflation (adjusted odds ratio for 60 minutes: 1.40, 95% CI, 1.13-1.73; P = .002) were significant factors of being in a more dangerous zone of the error grid.

CONCLUSIONS

The error grid analysis revealed the larger clinical discrepancy between CNBP and IBP in MBP compared with that in SBP. Old age and longer finger cuff inflation time were significant factors of being in a more dangerous zone of the error grid, which could affect the hemodynamic management during surgery.

End-tidal Carbon Dioxide for Diagnosing Anaphylaxis in Patients with Severe Postinduction Hypotension

BACKGROUND

Perioperative hypersensitivity reactions may be difficult to diagnose during general anesthesia. Postinduction hypotension is the most common sign but is not specific. It was recently suggested that low end-tidal carbon dioxide (ETco2) might be a marker of anaphylaxis (Ring and Messmer grades III to IV immediate hypersensitivity reactions) in hypotensive patients under mechanical ventilation. To test this hypothesis, the authors compared ETco2 in patients with a diagnosis of anaphylaxis and in patients with severe hypotension from any other cause after the induction of anesthesia.

METHODS

This was a retrospective single-center case-control study in which two groups were formed from an anesthesia data warehouse. The anaphylaxis group was formed on the basis of tryptase/histamine assay data and allergy workup data recorded over the period 2010 to 2018. The control (hypotension) group consisted of all patients having experienced severe hypotension (mean arterial pressure less than 50 mmHg for 5 min or longer) with a cause other than anaphylaxis after anesthesia induction in 2017.

RESULTS

The anaphylaxis and hypotension groups comprised 49 patients (grade III: n = 38; grade IV: n = 11) and 555 patients, respectively. The minimum ETco2 value was significantly lower in the anaphylaxis group (median [interquartile range]: 17 [12 to 23] mmHg) than in the hypotension group (32 [29 to 34] mmHg; P < 0.001). The area under the receiver operating characteristic curve (95% CI) for ETco2 was 0.95 (0.91 to 0.99). The sensitivity and specificity (95% CI) for the optimal cutoff value were 0.92 (0.82 to 0.98) and 0.94 (0.92 to 0.99), respectively. In multivariable analysis, minimum ETco2 was associated with anaphylaxis after adjusting for confounders and competing predictors, including arterial pressure, heart rate, and peak airway pressure (odds ratio [95% CI] for ETco2: 0.51 [0.38 to 0.68]; P < 0.001).

CONCLUSIONS

In case of severe hypotension after anesthesia induction, a low ETco2 contributes to the diagnosis of anaphylaxis, in addition to the classical signs of perioperative immediate hypersensitivity.

EDITOR’S PERSPECTIVE

Central Hypovolemia Detection During Environmental Stress-A Role for Artificial Intelligence?

The first step to exercise is preceded by the required assumption of the upright body position, which itself involves physical activity. The gravitational displacement of blood from the chest to the lower parts of the body elicits a fall in central blood volume (CBV), which corresponds to the fraction of thoracic blood volume directly available to the left ventricle. The reduction in CBV and stroke volume (SV) in response to postural stress, post-exercise, or to blood loss results in reduced left ventricular filling, which may manifest as orthostatic intolerance. When termination of exercise removes the leg muscle pump function, CBV is no longer maintained. The resulting imbalance between a reduced cardiac output (CO) and a still enhanced peripheral vascular conductance may provoke post-exercise hypotension (PEH). Instruments that quantify CBV are not readily available and to express which magnitude of the CBV in a healthy subject should remains difficult. In the physiological laboratory, the CBV can be modified by making use of postural stressors, such as lower body "negative" or sub-atmospheric pressure (LBNP) or passive head-up tilt (HUT), while quantifying relevant biomedical parameters of blood flow and oxygenation. Several approaches, such as wearable sensors and advanced machine-learning techniques, have been followed in an attempt to improve methodologies for better prediction of outcomes and to guide treatment in civil patients and on the battlefield. In the recent decade, efforts have been made to develop algorithms and apply artificial intelligence (AI) in the field of hemodynamic monitoring. Advances in quantifying and monitoring CBV during environmental stress from exercise to hemorrhage and understanding the analogy between postural stress and central hypovolemia during anesthesia offer great relevance for healthy subjects and clinical populations.

Agreement between oscillometric and direct blood pressure measurements in anesthetized captive chimpanzees (Pan troglodytes)

OBJECTIVE

To evaluate the level of agreement (LOA) between direct and oscillometric blood pressure (BP) measurements and the ability of oscillometric measurements to accurately detect hypotension in anesthetized chimpanzees (Pan troglodytes).

ANIMALS

8 captive, adult chimpanzees.

PROCEDURES

During prescheduled annual examinations, each chimpanzee underwent general anesthesia and patient monitoring for their examination, echocardiography for a concurrent study, and measurement of direct BP with the use of tibial artery catheterization and oscillometry with the use of a cuff placed around a brachium and a cuff placed around the second digit of the contralateral forelimb for the present study. Bland-Altman plots were generated to compare results for direct and oscillometric BP measurements. Mean bias and 95% LOAs were calculated for oscillometric measurements of systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP) for each cuff site. Sensitivity and specificity in detecting hypotension were also determined for each cuff site.

RESULTS

There were 74 paired direct and brachial oscillometric measurements of each, SAP, MAP, and DAP and 66 paired direct and digit oscillometric measurements of each, SAP, MAP, and DAP. Only brachial oscillometric measurements of MAP had adequate sensitivity (78%) and specificity (95%) to accurately detect hypotension, and this technique also had the least mean bias (0.8 mm Hg; 95% LOA, -29 to 31 mm Hg).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that brachial oscillometric measurement of MAP provided reasonable agreement with tibial arterial direct MAP measurement and performed well in diagnosing hypotension in anesthetized chimpanzees.

Clinical Validation of a Soft Wireless Continuous Blood Pressure Sensor During Surgery

We test a new wireless soft capacitance sensor (CAP) based on applanation tonometry at the radial and dorsalis pedis arteries against the gold standard, invasive arterial line (A-Line), for continuous beat to beat blood pressure (BP) measurements in the Operating Room during surgical procedures under anesthesia in 17 subjects with the mean age and body mass index (BMI) of 57. 35 ± 18.72 years and 27.36 ± 4.20 kg/m², respectively. We have identified several parameters to monitor in order to compare how well the CAP sensor tracks the entire hemodynamic waveform as compared to the A-Line. This includes waveform similarity, heart rate (HR), absolute systolic BP (SBP), diastolic BP (DBP), and temporal response to a vasopressor. Overall, the CAP sensor shows good correlations with A-Line with respect to hemodynamic shape (r > 0.89), HR (mean bias = 0.0006; SD = 0.17), absolute SBP, and DBP in a line of best fit (slope = 0.98 in SBP; 1.08 in DBP) and the mean bias derived from Bland-Altman method to be 1.92 (SD = 12.55) in SBP and 2.38 (SD = 12.19) in DBP across body habitus and age in OR patients under general anesthesia. While we do observe drifts in the system, we still obtain decent correlations with respect to the A-Line as evidenced by excellent linear fit and low mean bias across patients. When we post-process using a different calibration method to account for the drift, the mean bias and SD improve dramatically to −1.85 and 7.19 DBP as well as 1.43 and 7.43 SBP, respectively, indicating a promising potential for improvement when we integrate strategies to account for movement identified by our integrated accelerometer data.

Intraoperative Invasive Blood Pressure Monitoring and the Potential Pitfalls of Invasively Measured Systolic Blood Pressure

Invasive intraarterial blood pressure measurement is currently the gold standard for intraoperative hemodynamic monitoring but accurate systolic blood pressure (SBP) measurement is difficult in everyday clinical practice, mostly because of problems with hyper-resonance or damping within the measurement system, which can lead to erroneous treatment decisions if these phenomena are not recognized. A hyper-resonant blood pressure trace significantly overestimates true systolic blood pressure while underestimating the diastolic pressure. Invasively measured systolic blood pressure is also significantly more affected than mean blood pressure by the site of measurement within the arterial system. Patients in the intraoperative period should be treated based on the invasively measured mean blood pressure rather than the systolic blood pressure. In this review, we discuss the pros/cons, mechanisms of invasive blood pressure measurements, and the interpretation of the invasively measured systolic blood pressure value.

Branham sign in dogs undergoing interventional patent ductus arteriosus occlusion or surgical ligation: A retrospective study

Background:

The Branham sign is a baroreceptor response that follows patent ductus arteriosus (PDA) closure. Although described in dogs following both interventional and surgical ductal closure, a direct comparison of the Branham sign elicited by these two techniques has not been made.

Aim:

Since closure with an Amplatz canine ductal occluder (ACDO) occurs over 10 minutes and surgical ligation (SL) is more rapid, we hypothesized that the Branham sign following occlusion of a PDA with an ACDO would be less severe than following SL.

Methods:

Clinical records of dogs diagnosed with left-to-right shunting PDA between 2008 and 2018 were retrospectively reviewed. Of 139 dogs undergoing PDA occlusion, only 41 dogs (ACDO n = 32, SL n = 9) were included after applying exclusion criteria. Heart rate (HR) and blood pressure (BP) from occlusion time (T₀) until 30 minutes post occlusion (T₃₀) were recorded. Signalment and anesthetic protocol were also recorded. The influence of age and weight on the hemodynamic variations was assessed. Hemodynamic variables and calculations were compared between and within groups using a repeated measures general linear model, and post hoc tests were applied if significance was identified.

Results:

A mild Branham sign was present in both groups, and hemodynamic changes were not significantly different between groups. In both groups, there was a significant decrease in HR (11 bpm, 5.3–16.3; p < 0.001) (10.4%, 5.4–15.5; p < 0.001) and increase in diastolic BP (9.5 mmHg, 3–16; p = 0.002) (23.5%, 7.1–39.9; p = 0.002), but systolic BP did not change significantly (p = 0.824). Age and weight did not influence Branham sign.

Conclusion:

The Branham sign in dogs is mild in both groups, lasts for at least 30 minutes, and is independent of the method of PDA closure.

Performance of the Hypotension Prediction Index With Noninvasive Arterial Pressure Waveforms in Awake Cesarean Delivery Patients Under Spinal Anesthesia

BACKGROUND

Arterial hypotension is common after spinal anesthesia (SA) for cesarean delivery (CD), and to date, there is no definitive method to predict it. The hypotension prediction index (HPI) is an algorithm that uses the arterial waveform to predict early phases of intraoperative hypotension. The aims of this study were to assess the diagnostic ability of HPI working with arterial waveforms detected by ClearSight system in predicting impending hypotension in awake patients, and the agreement of pressure values recorded by ClearSight with conventional noninvasive blood pressure (NIBP) monitoring in patients undergoing CD under SA.

METHODS

In this retrospective analysis of pregnant patients scheduled for elective CD under SA, continuous hemodynamic data measured with the ClearSight monitor until delivery were downloaded from an Edwards Lifesciences HemoSphere platform and analyzed. Receiver operating characteristic (ROC) curves were constructed to evaluate the performance of HPI algorithm working on the ClearSight pressure waveform in predicting hypotensive events, defined as mean arterial pressure (MAP) <65 mm Hg for >1 minute. The sensitivity, specificity, positive predictive value, and negative predictive value were computed at the optimal cutpoint, selected as the value that minimizes the difference between sensitivity and specificity. ClearSight MAP values were compared to NIBP MAP values by linear regression and Bland-Altman analysis corrected for repeated measurements.

RESULTS

Fifty patients undergoing CD were included in the analysis. Hypotension occurred in 23 patients (48%). Among patients experiencing hypotension, the HPI disclosed 71 alerts. The HPI predicted hypotensive events with a sensitivity of 83% (95% confidence interval [CI], 69-97) and specificity of 83% (95% CI, 70-95) at 3 minutes before the event (area under the curve [AUC] 0.913 [95% CI, 0.837-0.99]); with a sensitivity of 97% (95% CI, 92-100) and specificity of 97% (95% CI, 92-100) at 2 minutes before the event (AUC 0.995 [95% CI, 0.979-1.0]); and with a sensitivity of 100% (95% CI, 100-100) and specificity 100% (95% CI, 100-100) 1 minute before the event (AUC 1.0 [95% CI, 1.0-1.0]). A total of 2280 paired NIBP MAP and ClearSight MAP values were assessed. The mean of the differences between the ClearSight and NIBP assessed using Bland-Altman analysis (±standard deviation [SD]; 95% limits of agreement with respective 95% CI) was -0.97 mm Hg (±4.8; -10.5 [-10.8 to -10.1] to 8.5 [8.1-8.8]).

CONCLUSIONS

HPI provides an accurate real time and continuous prediction of impending intraoperative hypotension before its occurrence in awake patients under SA. We found acceptable agreement between ClearSight MAP and NIBP MAP.

Goal-directed fluid therapy in autologous breast reconstruction results in less fluid and more vasopressor administration without outcome compromise

OBJECTIVE

Aggressive or restricted perioperative fluid management has been shown to increase complications in patients undergoing microsurgery. Goal-directed fluid therapy (GDFT) aims to administer fluid, vasoactive agents, and inotropes according to each patient's hemodynamic indices. This study assesses GDFT impact on perioperative outcomes of autologous breast reconstruction (ABR) patients, as there remains a gap in management understanding. We hypothesize that GDFT will have lower fluid administration and equivocal outcomes compared to patients not on GDFT.

METHODS

A single-center retrospective review was conducted on ABR patients from January 2010-April 2017. An enhanced recovery after surgery (ERAS) using GDFT was implemented in April 2015. With GDFT, patients were administered intraoperative fluids and vasoactive agents according to hemodynamic indices. Patients prior to April 2015 were included in the pre-ERAS cohort. Primary outcomes included the amount and rate of fluid delivery, urine output (UOP), vasopressor administration, major (i.e., flap failure) and minor (i.e., seroma) complications, and length of stay (LOS).

RESULTS

Overall, 777 patients underwent ABR (ERAS: 312 and pre-ERAS: 465). ERAS patients received significantly less total fluid volume (ERAS median: 3750 mL [IQR: 3000-4500 mL]; pre-ERAS median: 5000 mL [IQR 4000-6400 mL]; and p<0.001), had lower UOP, were more likely to receive vasopressor agents (47% vs 35% and p<0.001), and had lower LOS (ERAS: 4 days [4-5]; pre-ERAS: 5 [4-6]; and p<0.001) as compared to pre-ERAS patients. Complications did not differ between cohorts.

CONCLUSIONS

GDFT, as part of ERAS, and the prudent use of vasopressors were found to be safe and did not increase morbidity in ABR patients. GDFT provides individualized perioperative care to the ABR patient.

Transesophageal echocardiography for perioperative management in thoracic surgery

PURPOSE OF REVIEW

Perioperative transesophageal echocardiography (TEE) is most often employed during cardiac surgery. This review will summarize some of the recent findings relevant to TEE utilization during thoracic surgical procedures.

RECENT FINDINGS

Hemodynamic monitoring is a key component of goal-directed fluid therapy, which is also becoming more common for management of thoracic surgical procedures. Although usually not required for the anesthetic management of common thoracic surgeries, TEE is frequently used during lung transplantation and pulmonary thromboendarterectomy. Few clinical studies support current practice patterns, and most recommendations are based on expert opinion.

SUMMARY

Currently, routine use of TEE in thoracic surgery is often limited to specific high-risk patients and/or procedures. As in other perioperative settings, TEE may be utilized to elucidate the reasons for acute hemodynamic instability without apparent cause. Contraindications to TEE apply and have to be taken into consideration before performing a TEE on a thoracic surgical patient.

Error grid analysis for risk management in the difference between invasive and noninvasive blood pressure measurements

PURPOSE

Invasive arterial blood pressure (IAP) and noninvasive blood pressure (NIBP) measurements are both common methods. Recently, a new method of error grid analysis was proposed to compare blood pressure obtained using two measurement methods. This study aimed to compare IAP and NIBP measurements using the error grid analysis and investigate potential confounding factors affecting the discrepancies between IAP and NIBP.

METHODS

Adult patients who underwent general anesthesia in the supine position with both IAP and NIBP measurements were retrospectively investigated. The error grid analyses were performed to compare IAP and NIBP. In the error grid analysis, the clinical relevance of the discrepancies between IAP and NIBP was evaluated and classified into five zones from no risk (A) to dangerous risk (E).

RESULTS

Overall, data of 1934 IAP/NIBP measurement pairs from 100 patients were collected. The error grid analysis revealed that the proportions of zones A-E for systolic blood pressure were 96.4%, 3.5%, 0.05%, 0%, and 0%, respectively. In contrast, the proportions for mean blood pressure were 82.5%, 16.7%, 0.8%, 0%, and 0%, respectively. The multiple regression analysis revealed that continuous phenylephrine administration (p = 0.016) and age (p = 0.044) were the significant factors of an increased clinical risk of the differences in mean blood pressure.

CONCLUSIONS

The error grid analysis indicated that the differences between IAP and NIBP for mean blood pressure were not clinically acceptable and had the risk of leading to unnecessary treatments. Continuous phenylephrine administration and age were the significant factors of an increased clinical risk of the discrepancies between IAP and NIBP.

Clinical Evaluation of a High-fidelity Upper Arm Cuff to Measure Arterial Blood Pressure during Noncardiac Surgery

BACKGROUND

In most patients having noncardiac surgery, blood pressure is measured with the oscillometric upper arm cuff method. Although the method is noninvasive and practical, it is known to overestimate intraarterial pressure in hypotension and to underestimate it in hypertension. A high-fidelity upper arm cuff incorporating a hydraulic sensor pad was recently developed. The aim of the present study was to investigate whether noninvasive blood pressure measurements with the new high-fidelity cuff correspond to invasive measurements with a femoral artery catheter, especially at low blood pressure.

METHODS

Simultaneous measurements of blood pressure recorded from a femoral arterial catheter and from the high-fidelity upper arm cuff were compared in 110 patients having major abdominal surgery or neurosurgery.

RESULTS

550 pairs of blood pressure measurements (5 pairs per patient) were considered for analysis. For mean arterial pressure measurements, the average bias was 0 mmHg, and the precision was 3 mmHg. The Pearson correlation coefficient was 0.96 (P < 0.0001; 95% CI, 0.96 to 0.97), and the percentage error was 9%. Error grid analysis showed that the proportions of mean arterial pressure measurements done with the high-fidelity cuff method were 98.4% in zone A (no risk), 1.6% in zone B (low risk) and 0% in zones C, D, and E (moderate, significant, and dangerous risk, respectively). The high-fidelity cuff method detected mean arterial pressure values less than 65 mmHg with a sensitivity of 84% (95% CI, 74 to 92%) and a specificity of 97% (95% CI, 95% to 98%). To detect changes in mean arterial pressure of more than 5 mmHg, the concordance rate between the two methods was 99.7%. Comparable accuracy and precision were observed for systolic and diastolic blood pressure measurements.

CONCLUSIONS

The new high-fidelity upper arm cuff method met the current international standards in terms of accuracy and precision. It was also very accurate to track changes in blood pressure and reliably detect severe hypotension during noncardiac surgery.

EDITOR’S PERSPECTIVE

Effect of Systemic Vascular Resistance on the Reliability of Noninvasive Hemodynamic Monitoring in Cardiac Surgery

OBJECTIVE

To assess the effect of systemic vascular resistance (SVR) on the reliability of the ClearSight system (Edwards Lifesciences, Irvine, CA) for measuring blood pressure (BP) and cardiac output (CO).

DESIGN

Observational study.

SETTING

University hospital.

PARTICIPANTS

Twenty-five patients undergoing cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

BP, measured using ClearSight and an arterial line, and CO, measured using ClearSight and a pulmonary artery catheter, were recorded before (T1) and two minutes after phenylephrine or ephedrine administration. Bland-Altman analysis was used to compare BP and CO measurements at T1. A polar plot was used to assess trending abilities. Patients were divided into the following three groups according to the SVR index (SVRI) at T1: low (<1,200 dyne s/cm⁵/m²), normal (1,200-25,00 dyne s/cm⁵/m²), and high (>2,500 dyne s/cm⁵/m²). The bias in BP and CO was -4.8 ± 8.9 mmHg and 0.10 ± 0.81 L/min, respectively, which was correlated significantly with SVRI (p < 0.05). The percentage error in CO was 40.6%, which was lower in the normal SVRI group (33.3%) than the low and high groups (46.3% and 47.7%, respectively). The angular concordance rate was 96.3% and 95.4% for BP and 87.0% and 92.5% for CO after phenylephrine and ephedrine administration, respectively. There was a low tracking ability for CO changes after phenylephrine administration in the low-SVRI group (angular concordance rate 33.3%).

CONCLUSION

The ClearSight system showed an acceptable accuracy in measuring BP and tracking BP changes in various SVR states; however, the accuracy of CO measurement and its trending ability in various SVR states was poor.

Non-invasive haemodynamic monitoring with Clearsight in patients undergoing spinal anaesthesia for total hip replacement. A prospective observational cohort study

BACKGROUND

Patients undergoing elective primary total hip replacement and spinal anesthesia may encounter significant hemodynamic instability Objective: The study is aimed at observing the haemodynamic modifications after spinal anaesthesia during total hip replacement in patients managed to "preload independence" with goal directed fluid therapy (GDFT) and monitored non-invasively with Clearsight.

METHODS

Thirty patients, aged 50-80 years, with an American Society of Anaesthesiologists' (ASA) score II-III, undergoing elective primary total hip replacement and spinal anaesthesia were enrolled. Patients were monitored with the EV1000 platform and the Clearsight finger-cuff and managed with a goal directed fluid therapy.

RESULTS

The 79% of the population showed preload independence at baseline. After spinal, the 93% did not show a significant mean arterial pressure reduction. In our population, 79% reported a decrease >10% of the stroke volume during surgery, while 66% in the Recovery Room. Patients showed an improvement in mean arterial pressure, systemic vascular resistances indexed (SVRI), stroke volume (SV) and stroke volume indexed (SVI) at spinal resolution compared to baseline.

CONCLUSIONS

Our cohort population showed hemodynamic stability throughout the study period, with increased SV and decreased SVRI at spinal resolution compared to basal values. Further randomized prospective studies are advocated in the same setting.