Using Digital Biomarkers for Objective Assessment of Perfusionists' Workload and Acute Stress During Cardiac Surgery.

The cardiac operating room (OR) is a high-risk, high-stakes environment inserted into a complex socio-technical healthcare system. During cardiopulmonary bypass (CPB), the most critical phase of cardiac surgery, the perfusionist has a crucial role within the interprofessional OR team, being responsible for optimizing patient perfusion while coordinating other tasks with the surgeon, anesthesiologist, and nurses. The aim of this study was to investigate objective digital biomarkers of perfusionists' workload and stress derived from heart rate variability (HRV) metrics captured via a wearable physiological sensor in a real cardiac OR. We explored the relationships between several HRV parameters and validated self-report measures of surgical task workload (SURG-TLX) and acute stress (STAI-SF), as well as surgical processes and outcome measures. We found that the frequency-domain HRV parameter HF relative power - FFT (%) presented the strongest association with task workload (correlation coefficient: -0.491, p-value: 0.003). We also found that the time-domain HRV parameter RMSSD (ms) presented the strongest correlation with perfusionists' acute stress (correlation coefficient: -0.489, p-value: 0.005). A few workload and stress biomarkers were also associated with bypass time and patient length of stay in the hospital. The findings from this study will inform future research regarding which HRV-based biomarkers are best suited for the development of cognitive support systems capable of monitoring surgical workload and stress in real time.

Using machine learning to predict perfusionists' critical decision-making during cardiac surgery.

The cardiac surgery operating room is a high-risk and complex environment in which multiple experts work as a team to provide safe and excellent care to patients. During the cardiopulmonary bypass phase of cardiac surgery, critical decisions need to be made and the perfusionists play a crucial role in assessing available information and taking a certain course of action. In this paper, we report the findings of a simulation-based study using machine learning to build predictive models of perfusionists' decision-making during critical situations in the operating room (OR). Performing 30-fold cross-validation across 30 random seeds, our machine learning approach was able to achieve an accuracy of 78.2% (95% confidence interval: 77.8% to 78.6%) in predicting perfusionists' actions, having access to only 148 simulations. The findings from this study may inform future development of computerised clinical decision support tools to be embedded into the OR, improving patient safety and surgical outcomes.

Fraction of expired oxygen: an additional safety approach to monitor oxygen delivery to the heart lung machine oxygenator.

BACKGROUND: Monitoring oxygen delivery to the oxygenator of a heart lung machine (HLM) is typically accomplished with an O2 analyzer connected to the gas inflow line. It is assumed when the FiO2 is greater than 21% that oxygen is being delivered to the oxygenator. However, this assumption is imperfect because the connection of the inflow line to the oxygenator is downstream from the O2 analyzer. FiO2 monitoring will not alert the perfusionist if the inflow line is not actually connected to the oxygenator. Measuring the fraction of expired oxygen (FEO2) is a more reliable way of monitoring O2 delivery. METHODS: An O2 analyzer was placed on the scavenging line that is attached to the exhaust port of oxygenator (FEO2). RESULTS: Whenever the FiO2 is greater than 21%, and the inflow line is properly connected, the FEO2 exiting the oxygenator is greater than 21%. The FEO2 falls to 21% when the inflow line is not functioning. CONCLUSION: Monitoring the FEO2 is a more reliable way to verify O2 delivery to an oxygenator. An alarm can be set on the FEO2 monitor to alert the perfusionist if the FEO2 falls below a predetermined threshold so any issue with O2 delivery will always be recognized.

Analysis of Dynamic Changes in Cognitive Workload During Cardiac Surgery Perfusionists' Interactions With the Cardiopulmonary Bypass Pump.

OBJECTIVE: This novel preliminary study sought to capture dynamic changes in heart rate variability (HRV) as a proxy for cognitive workload among perfusionists while operating the cardiopulmonary bypass (CPB) pump during real-life cardiac surgery. BACKGROUND: Estimations of operators' cognitive workload states in naturalistic settings have been derived using noninvasive psychophysiological measures. Effective CPB pump operation by perfusionists is critical in maintaining the patient's homeostasis during open-heart surgery. Investigation into dynamic cognitive workload fluctuations, and their relationship with performance, is lacking in the literature. METHOD: HRV and self-reported cognitive workload were collected from three Board-certified cardiac perfusionists (N = 23 cases). Five HRV components were analyzed in consecutive nonoverlapping 1-min windows from skin incision through sternal closure. Cases were annotated according to predetermined phases: prebypass, three phases during bypass, and postbypass. Values from all 1min time windows within each phase were averaged. RESULTS: Cognitive workload was at its highest during the time between initiating bypass and clamping the aorta (preclamp phase during bypass), and decreased over the course of the bypass period. CONCLUSION: We identified dynamic, temporal fluctuations in HRV among perfusionists during cardiac surgery corresponding to subjective reports of cognitive workload. Not only does cognitive workload differ for perfusionists during bypass compared with pre- and postbypass phases, but differences in HRV were also detected within the three bypass phases. APPLICATION: These preliminary findings suggest the preclamp phase of CPB pump interaction corresponds to higher cognitive workload, which may point to an area warranting further exploration using passive measurement.

Sensors for Continuous Monitoring of Surgeon's Cognitive Workload in the Cardiac Operating Room.

Monitoring healthcare providers' cognitive workload during surgical procedures can provide insight into the dynamic changes of mental states that may affect patient clinical outcomes. The role of cognitive factors influencing both technical and non-technical skill are increasingly being recognized, especially as the opportunities to unobtrusively collect accurate and sensitive data are improving. Applying sensors to capture these data in a complex real-world setting such as the cardiac surgery operating room, however, is accompanied by myriad social, physical, and procedural constraints. The goal of this study was to investigate the feasibility of overcoming logistical barriers in order to effectively collect multi-modal psychophysiological inputs via heart rate (HR) and near-infrared spectroscopy (NIRS) acquisition in the real-world setting of the operating room. The surgeon was outfitted with HR and NIRS sensors during aortic valve surgery, and validation analysis was performed to detect the influence of intra-operative events on cardiovascular and prefrontal cortex changes. Signals collected were significantly correlated and noted intra-operative events and subjective self-reports coincided with observable correlations among cardiovascular and cerebral activity across surgical phases. The primary novelty and contribution of this work is in demonstrating the feasibility of collecting continuous sensor data from a surgical team member in a real-world setting.

A Quick Reference Tool for Goal-Directed Perfusion in Cardiac Surgery.

Traditionally, blood flow rates on cardiopulmonary bypass are based primarily on a formula that matches cardiac index to the patient's body surface area (BSA). However, Ranucci and associates in the Goal-Directed Perfusion Trial (GIFT) trial have shown that coupling the BSA with delivery of oxygen (DO2), known as goal-directed perfusion (GDP), may be a safer approach to determine appropriate blood flows. The objective of this study was to create a GDP reference tool that would allow perfusionists to quickly determine the lowest acceptable blood flow needed to provide a patient of any BSA with a satisfactory DO2 without the need for additional dedicated technology. We approached this problem by deriving a formula for flow (L/min), based on BSA, oxygen content of the blood, and a minimum DO2 of 280 mL·min-1m-2. A quick reference GDP chart was created based on the derived formula, requiring only the patient's BSA and hemoglobin level to determine a safe minimum flow rate. The proposed tool allows any cardiac surgery center to adopt the GDP technique, even in the absence of instantaneous DO2 monitoring equipment.

Establishing a Ventilator-Heart Lung Machine Communication Bridge to Mitigate Errors when Weaning from Bypass.

If a perfusionist weans a patient off the heart lung machine (HLM) and the anesthesiologist has not re-started the ventilator, the patient will become hypoxic. The objective of this project was to create a redundant safety system of verbal and electronic communication to prevent failure to ventilate errors after cardiopulmonary bypass. This objective could be realized by building an electronic communication bridge directly between the HLM and ventilator. A software application was created to retrieve and interpret data from the pump and ventilator and trigger a programmed smart alarm. The software is able to interpret data from the pump and ventilator. When both are off simultaneously (defined as a pump flow of 0 L/min with a respiratory rate of 0 breaths/min), the application will raies an alarm. Communication between a pump and ventilator is possible, enabling the deployment of a safety system that could exist in the operating room (OR) as a standalone alarm. A device dataset can be used to optimize clinical performance of the alarm. The application could also be integrated into smart checklists and computer-assisted OR process models that are currently in development.

Evaluation of blood components exposed to coated arterial filters in extracorporeal circuits.

BACKGROUND: Biocompatible surfaces play an important role in the inflammatory response during cardiopulmonary bypass (CBP), with the arterial filter contributing a large surface area of the circuit. Different filter-coating materials designed to improve blood-filter biocompatibility are currently used in CPB circuits. This study evaluates eight biocompatible coatings used for arterial filters and their effects on blood components during circulation. METHODS: Arterial filters were randomly assigned in eight independent heparin-bonded tubing loops and perfused by a single swine (n=8). Arterial blood was routed simultaneously, but separately, into each circuit and circulated for 30 minutes at 37 degrees C. Blood samples were drawn for CBC, ACT, and TAT III measurements at baseline, post-heparinization and post-circulation. At study completion, filters were imaged using multiphoton microscopy. RESULTS: RBC, platelet, and WBC counts, and TAT III complex were all decreased after 30 minutes of circulation; however, WBC count was the only parameter that showed statistically significant differences between the filters. Circulating WBC reduction ranged from 6% (Carmeda and Trillium) to 41% (Terumo-X-coating) with corresponding microscopic confirmation of increased WBC entrapment. CONCLUSION: All eight filter coatings altered the blood components to varying degrees. Selection of the most effective filter, in conjunction with a heparin-bonded circuit for CPB, may decrease the intraoperative foreign-surface activation of blood cells.

Expired liquid preserved platelet releasates retain proliferative activity.

BACKGROUND: Donated platelets for clinical use currently have a shelf life of 5 days as the result of possible bacterial contamination and loss of hemostatic function. Platelet releasates contain multiple growth factors that have been shown to accelerate wound healing. We sought to demonstrate that although expired platelets can no longer sustain hemostasis, they serve a longer term role as a reservoir of growth factors that could be harnessed in wound healing applications. MATERIALS AND METHODS: Liquid preserved human platelets were activated from 1 to 21 days after collection using zeolite and were then analyzed for their ability to stimulate human fibroblast proliferation, which is an in vitro serogate of growth factor activity and wound healing potential. Total protein content, the concentration of platelet-derived growth factor (PDGF) and transforming growth factor-beta were also measured. RESULTS: Activated liquid preserved platelet releasates significantly stimulated fibroblast proliferation. Twenty-one-day-old platelets were as stimulatory as 2-day-old platelets. Total protein concentration, PDGF, and transforming growth factor-beta concentrations remained constant throughout the 21-day course. Western blot analysis using an antibody against human PDGF revealed minimal protein degradation over time. CONCLUSIONS: These data demonstrate that although the role of platelets as hemostatic agents degrades rapidly with time, platelets' ability to serve as a reservoir for growth factors remains intact for at least 3 weeks. These growth factors could be collected, stored, and used as a topical agent to promote healing of chronic and recalcitrant wounds.

In vitro effects of poly-N-acetyl glucosamine on the activation of platelets in platelet-rich plasma with and without red blood cells.

BACKGROUND: This study was performed to assess the effect of poly-N-acetyl glucosamine fiber slurry on plasma clotting proteins, platelets, and red blood cells in the clotting of the blood. METHODS: Citrate phosphate dextrose whole blood was stored at 22degreesC for 48 hours to prepare platelet-poor plasma, platelet-rich plasma (PRP), and PRP plus red blood cells with hematocrit values of 20%, 35%, and 45% with and without an equal volume of poly-N-acetyl glucosamine fibers (1 mg/mL 0.9% NaCl). RESULTS: Thromboelastogram data show that poly-N-acetyl glucosamine fibers (p-GlcNAc) significantly reduced the R time in platelet-poor plasma, PRP, and PRP supplemented with red blood cells. Poly-N-acetyl glucosamine fibers increased, but not significantly, Annexin V and factor X binding to platelets, platelet microparticles, and red blood cell Annexin V binding. Poly-N-acetyl glucosamine fibers increased the production of thromboxane B2 by PRP. CONCLUSION: Poly-N-acetyl glucosamine slurry activates platelets.

The in vitro quality of red blood cells frozen with 40 percent (wt/vol) glycerol at -80 degrees C for 14 years, deglycerolized with the Haemonetics ACP 215, and stored at 4 degrees C in additive solution-1 or additive solution-3 for up to 3 weeks.

BACKGROUND: Red blood cells (RBCs) frozen with 40 percent (wt/vol) glycerol, stored at -80 degrees C (mean temperature; range, -65 to -90 degrees C) for 14 years, deglycerolized in the Haemonetics automated cell processor (ACP) 215 with the 325-mL disposable bowl, and stored at 4 degrees C in additive solution (AS)-1 or AS-3 for 21 days were evaluated. STUDY DESIGN AND METHODS: A total of 106 units of citrate phosphate dextrose adenine-1 RBCs were frozen with 40 percent (wt/vol) glycerol in the original 800-mL polyvinylchloride plastic bag and stored in corrugated cardboard boxes at -80 degrees C for 14 years. The thawed units were deglycerolized with the ACP 215 with a 325-mL disposable bowl and stored in AS-1 or AS-3 at 4 degrees C for 21 days. RESULTS: The freeze-thaw recovery value was 94 +/- 4 percent (mean +/- SD), the freeze-thaw-wash recovery value was 80 +/- 7 percent, and there was no breakage. Thirty-eight units were processed as 19 pairs. Two units of ABO-matched units were thawed, pooled, divided equally into two units, and deglycerolized. One unit was stored in AS-1 and the other in AS-3 at 4 degrees C for 21 days. Units stored in AS-1 exhibited significantly greater hemolysis than those stored in AS-3. CONCLUSIONS: Acceptable results were achieved when RBCs frozen at -80 degrees C for 14 years were deglycerolized in the ACP 215. Deglycerolized RBCs in AS-1 exhibited significantly higher hemolysis than those in AS-3 after storage at 4 degrees C for 7 to 21 days.

Comparison of radioisotope methods and a nonradioisotope method to measure the RBC volume and RBC survival in the baboon.

BACKGROUND: RBC volume, 24-hour posttransfusion survival, and life span can be measured with radio-isotopes and nonradioactive procedures. STUDY DESIGN AND METHODS: RBC volume was measured directly with autologous baboon RBCs labeled with biotin-X-N-hydroxysuccinimide (NHS), 51Cr, 99mTc, and 111In-oxine and indirectly from the 125I plasma volume and the total body Hct. Twenty-four-hour posttransfusion survival and life span were measured in autologous fresh baboon RBCs labeled with 51Cr, 111In-oxine, 99mTc, and biotin-X-NHS. RESULTS: Significantly larger RBC volumes were observed when the fresh autologous RBCs were labeled with 51Cr, 111In-oxine, or 99mTc than when they were labeled with the nonradioactive biotin-X-NHS. Twenty-four-hour posttransfusion survival values were significantly lower in the RBCs labeled with 111In-oxine or 99mTc than in the RBCs labeled with 51Cr. CONCLUSIONS: The greater in vivo elution of 51Cr, 111In-oxine, and 99mTc than that of biotin-X-NHS influenced the measurements of RBC volume, 24-hour posttransfusion survival, and life span of the fresh baboon RBCs.

Effect of WBC reduction and storage temperature on PLTs frozen with 6 percent DMSO for as long as 3 years.

BACKGROUND: PLTs frozen with 6 percent DMSO can be stored at -80 degrees C for 2 years, while those frozen with 5 percent DMSO at -150 degrees C can be stored for at least 3 years. The more rapid deterioration seen in PLTs frozen at -80 degrees C may be due to the presence of granulocytes. The effects of storage temperature and WBC reduction on PLTs frozen with DMSO and the breakage of the PVC plastic bags stored at -80 and -135 degrees C were assessed. STUDY DESIGN AND METHODS: Apheresed PLT-rich plasma (PRP) was either divided into two equal volumes where one volume was WBC-reduced and the other volume was not or filtered or not and then divided into two equal volumes. PLTs frozen with 6 percent DMSO were stored in PVC plastic bags at either -80 or -135 degrees C for as long as 3 years. RESULTS: After 2 years of storage at -80 degrees C, the PLTs exhibited satisfactory freeze-thaw-wash values regardless of whether or not they were WBC-reduced, but after 2 to 3 years of storage at -80 degrees C, the PLTs had significantly reduced freeze-thaw-wash values. Freeze-thaw-wash values were not reduced in PLTs stored at -135 degrees C for up to 3 years. CONCLUSIONS: WBC reduction did not improve freeze-thaw-wash recovery values in PLTs stored at -80 or -135 degrees C for up to 3 years, but reducing the storage temperature from -80 to -135 degrees C did. Breakage of PVC plastic bags stored at -135 degrees C was excessive.

Incidence of breakage of human RBCs frozen with 40-percent wt/vol glycerol using two different methods for storage at -80 degrees C.

BACKGROUND: We reported previously that the incidence of breakage was 34.2 percent when human RBCs were frozen with 40-percent wt/vol glycerol in polyolefin plastic bags stored in aluminum containers at -80 degrees C and subjected to transportation. When human RBCs were frozen with 40-percent wt/vol glycerol at -80 degrees C in PVC plastic bags placed in polyester plastic bags and stored in rigid corrugated cardboard boxes, transportation resulted in a 2.4-percent incidence of breakage. The present study was done to confirm this incidence of breakage. STUDY DESIGN AND METHODS: The Meryman- Hornblower freezing method was compared to the Naval Blood Research Laboratory (NBRL) method of freezing for incidence of bag breakage. Human RBCs frozen by the Meryman-Hornblower method with 40-percent wt/vol glycerol with supernatant glycerol and stored in polyolefin plastic bags in aluminum containers at -80 degrees C were stored at the NBRL from 1974 to 2002. With the NBRL method, human RBCs frozen at -80 degrees C without supernatant glycerol in the 800-mL PVC plastic primary bag inside a polyester plastic bag in a rigid corrugated cardboard box were stored at the NBRL from 1984 to 2002. RESULTS: The incidence of breakage for 532 units of RBCs that had been frozen by the Meryman- Hornblower method and stored in aluminum containers was 47.3 percent for nontransported units. RBCs that had been frozen by the NBRL method and stored in rigid corrugated cardboard boxes exhibited breakage of 2.4 percent for 2424 nontransported units and 6.7 percent for 633 transported units. DISCUSSION: The incidence of breakage was significantly lower for RBCs frozen by the NBRL method than for the RBCs frozen by the Meryman-Hornblower method.