Observation of microbubbles during standard dialysis treatments

Hemodialysis patients have signs of a chronic thrombotic burden

BACKGROUND

Cardiovascular diseases are the dominant cause of morbidity in hemodialysis (HD) patients. Unless sufficient anticoagulation is used during HD, clotting may appear. The objective was to investigate if levels of fibrin degradation products (D-dimer) were increased before and during HD.

METHODS

The combined observational study included 20 patients performing a total of 60 hemodialysis divided into three sessions of low-flux dialysis. None of the patients suffered from any clinically evident thromboembolic event before or during the study. Median bolus anticoagulation (mainly tinzaparin) doses were 84 Units/kg bow. Blood samples were drawn before HD (predialysis), and at 30min and 180min during HD with focus on analyzing D-dimer levels and its relation to interdialytic weight gain (IDWG) and speed of fluid elimination by HD (UF-rate).

RESULTS

Predialysis, D-dimer levels (mean 0.767 ±0.821, min 0.136mg/L) were above the upper reference value in 95% of the sessions. D-dimer levels were lowered at 30min (p<0.001) and returned to predialysis levels at 180min. Predialysis D-dimer correlated with NT-pro-BNP, Troponin T, IDWG and UF-rate. Multiple regression analysis revealed that the D-dimer levels were significantly related to IDWG and the UF-rate.

CONCLUSIONS

D-dimer levels were elevated in a high proportion predialysis and during HD and related to the IDWG and the UF-rate. Awareness of D-dimer levels and future studies will help clarify if optimization of those variables, besides anticoagulation and biocompatibility measures, will eradicate the repeated subclinical thromboembolic events related to each HD; one reason that may explain organ damage and shortened life span of these patients.

The Number of Microbubbles Generated During Cardiopulmonary Bypass Can Be Estimated Using Machine Learning From Suction Flow Rate, Venous Reservoir Level, Perfusion Flow Rate, Hematocrit Level, and Blood Temperature

GOAL

Microbubbles (MBs) are known to occur within the circuits of cardiopulmonary bypass (CPB) systems, and higher-order dysfunction after cardiac surgery may be caused by MBs as well as atheroma dispersal associated with cannula insertion. As complete MB elimination is not possible, monitoring MB count rates is critical. We propose an online detection system with a neural network-based model to estimate MB count rate using five parameters: suction flow rate, venous reservoir level, perfusion flow rate, hematocrit level, and blood temperature.

METHODS

Perfusion experiments were performed using an actual CPB circuit, and MB count rates were measured using the five varying parameters.

RESULTS

Bland-Altman analysis indicated a high estimation accuracy (R2 > 0.95, p < 0.001) with no significant systematic error. In clinical practice, although the inclusion of clinical procedures slightly decreased the estimation accuracy, a high coefficient of determination for 30 clinical cases (R2 = 0.8576) was achieved between measured and estimated MB count rates.

CONCLUSIONS

Our results highlight the potential of this system to improve patient outcomes and reduce MB-associated complication risk.

Ultrasonic Traveling Waves for Near-Wall Positioning of Single Microbubbles in a Flowing Channel

Although microbubbles are used primarily in the medical industry as ultrasonic contrast agents, they can also be manipulated by acoustic waves for targeted drug delivery, sonothrombolysis and sonoporation. Acoustic waves can also potentially remove microbubbles from tubing systems (e.g., in hemodialysis) to prevent the negative effects associated with circulating microbubbles. A deeper understanding of the interactions between the acoustic radiation force, the microbubble and the channel wall could greatly benefit these applications. In this study, single air-filled microbubbles were injected into a flowing (polydimethylsiloxane) channel and monitored by a high-speed camera while passing through a pulsed ultrasonic wave zone (0.5 MHz). This study compared various bubble sizes, flow rates and acoustic pressure amplitudes to better understand the three physical regimes observed: free bubble translation (away from the wall); on-wall translation; and bubble-wall attachment. Comparison with a theoretical model revealed that the acoustic radiation force needs to exceed the combined repulsive forces (shear lift, wall lubrication and repulsive Van der Waal forces) for the dead state of bubble-wall attachment. The bubble dynamics revealed through this investigation provide an opportunity for efficient positioning of microbubbles in a channel flow, for either in vivo manipulation or removal in biological applications.

Parametric study of a bubble removing device for hemodialysis

BACKGROUND

This paper sets out to design a device for removing bubbles during the process of hemodialysis. The concept is to guide the bubbles while traveling through the device and eventually the bubbles can be collected. The design focuses on the analysis of various parameters i.e. inlet diameter, inlet velocity and size of the pitch. The initial diameters of Models 1 and 2 have thread regions of 6 and 10 mm, respectively.

PARAMETERS

Swirl number, Taylor number, Lift coefficient along with pressure field are also implemented.

RESULTS

Based on computational fluid dynamics analysis, the bubbles' average maximum equilibrium position for Model 1 reached 1.995 mm, being greater than that of Model 2, which attained 1.833 mm. Then, 16,000 bubbles were released into Model 1 to validate the performance of the model. This number of bubbles is typically found in the dialysis. Thus, it was found that 81.53% of bubbles passed through the radial region of 2.20 ± 0.30 mm. The appropriate collecting plane was at 100 mm, as measured from the inlet position along the axial axis. The Taylor number, Lift coefficient, and Swirl number proved to be significant parameters for describing the movement of the bubbles. Results were based on multiple inlet velocities. It is seen that Model 3, the improved model with unequal pitch, reached a maximum equilibrium position of 2.24 mm.

CONCLUSION

Overall, results demonstrated that Model 1 was the best design compared to Models 2 and 3. Model 1 was found capable of guiding the bubbles to the edge location and did not generate extra bubbles. Thus, the parametric study, herein, can be used as a prototype for removing bubbles during the process of hemodialysis.

Venous chambers in clinical use for hemodialysis have limited capacity to eliminate microbubbles from entering the return bloodline: An in vitro study

BACKGROUND

During hemodialysis (HD), blood passes through an extracorporeal circuit (ECC). To prevent air administration to the patient, a venous chamber (chamber) is located before the blood return. Microbubbles (MBs) may pass through the chamber and end up as microemboli in organs such as the brain and heart. This in vitro study investigated the efficacy of various chambers in MB removal.

MATERIALS AND METHODS

The in vitro recirculated setting of an ECC included an FX10 dialyzer, a dextran-albumin solution to mimic blood viscosity and chambers with different flow characteristics in clinical use (Baxter: AK98 and Artis, Fresenius: 5008 and 6008) and preclinical test (Embody: Emboless®). A Gampt BCC200 device measured the presence and size of MBs (20-500 μm). Percentage change of MBs was calculated: ΔMB% = 100*(outlet-inlet)/inlet for each size of MB. Blood pump speed (Qb) was 200 (Qb200) or 300 (Qb300) ml/minute. Wilcoxon paired test determined differences.

RESULTS

With Qb200 median ΔMB% reduction was: Emboless -58%, AK98 -24%, Fresenius 5008 -23%, Artis -8%, and Fresenius 6008 ± 0%. With Qb300 ΔMB% was: Emboless -36%, AK98 ± 0%, Fresenius 5008 ± 0%, Artis +25%, and Fresenius 6008 + 21%. The Emboless was superior to all other chambers with Qb200 and Qb300 (p < 0.001). Further, the Emboless with Qb300 still eliminated more MBs than all other chambers with Qb200 (p ≤ 0.003).

CONCLUSION

The results from the present study indicate that flow characteristics of the chamber and the Qb are important factors to limiting exposure of MB to the return bloodline. The Emboless chamber reduced MBs more effective than those chambers in clinical use investigated.

Novel Capped-Needle Device: A Novel Safety Feature to Eliminate Air Bubbles in Hemodialysis

INTRODUCTION

Air bubbles in the dialysis circuit are rarely visible after automatic priming; however, they are often visible after the needles are manually connected to the circuit. To prevent this issue, we thought to prime needles with a circuit at automatic priming by the hemodialysis machine. In order to achieve this idea, we designed and manufactured a novel capped needle to connect the needles to the extracorporeal circuit before the automatic priming of the hemodialysis machine. This study investigated the effectiveness of this novel capped needle and compared it with the conventional method for preventing air bubble contamination.

METHODS

We tested novel capped needles ten times to evaluate whether the dialysis machine works appropriately and removes air bubbles even with the attached capped needle. Next, we performed 25 trials using the conventional method, in which skilled nurses manually connect the needle. In both methods, we thoroughly counted the air bubbles with our naked eyes. We predicted that the capped needle would leave few bubbles in the circuit. In order to evaluate fewer bubbles, we conducted an additional experiment using a microparticle counter to measure the size and number of the bubbles.

RESULTS

We thoroughly searched for air bubbles during each of the ten tests but could not find any bubbles visible to the naked eye. In the conventional method, bubbles were visible in 29 out of 50 cases. The bubble count was significantly lower in the capped-needle method than in the conventional method (p < 0.0001, Pearson's χ2 test). In the additional experiments using the microparticle counter, the average remaining air volume in the extracorporeal circuit was 0.0999 ± 0.2438 nL when the priming was performed using the novel capped needles.

CONCLUSION

The novel capped needle eliminated all visible bubbles efficiently and effectively; therefore, it could be a valuable device for hemodialysis treatment. The reduction of air from the dialysis circuit may improve patient prognosis.

Microemboli induced by air bubbles may be deposited in organs as a consequence of contamination during medical care

Background

Larger volumes of accidental air infused during medical care may end up as emboli while microbubbles of air are supposed to be absorbed and cause no harm. The aim of this autopsy study was to investigate if microbubbles of air accidently entering the bloodline may be detected as microemboli (ME) in tissue such as lungs, brain and heart. If so, do differences in prevalence exist between haemodialysis (HD) and amyotrophic lateral sclerosis (ALS) patients.

Methods

Included were data from 44 patients treated by medical healthcare before death. Twenty-five cases had been treated with chronic HD and 19 cases died from ALS. Since air in the bloodline activates coagulation, ME could appear. To discriminate between microbubbles caused by artificial contamination during autopsy versus microbubbles deposited in vivo, tissues were stained with a polyclonal fluorescent antibody against fibrinogen, fibrin and fragments E and D. Fluorescence staining was used to visualize ME counted within 25 microscopic fields (600×) of a tissue preparation. One tissue preparation was used if available from the lung, heart and frontal lobe of the brain and in five cases also the cerebellum.

Results

Microbubbles can be verified at autopsy as ME in the lung, heart and brain in tissue from patients exposed to more extensive medical care. There were significantly more ME in the lungs versus the heart or brain. Women had fewer ME than men. The HD group had a higher median of ME per section than the ALS group (lung: 6 versus 3, P = .007; heart: 2.5 versus 1, P = .013; brain: 7.5 versus 2, P = .001) and had more sections with ME findings than the ALS group (P = .002). A correlation existed between the time on HD (months) and ME in the lungs.

Conclusions

More ME were present in HD patients compared with those who suffered from ALS. Minimizing air contamination from syringes, infusions and bloodlines will decrease ME and subsequent tissue injury.

Dialysis-Induced Cardiovascular and Multiorgan Morbidity

Hemodialysis has saved many lives, albeit with significant residual mortality. Although poor outcomes may reflect advanced age and comorbid conditions, hemodialysis per se may harm patients, contributing to morbidity and perhaps mortality. Systemic circulatory "stress" resulting from hemodialysis treatment schedule may act as a disease modifier, resulting in a multiorgan injury superimposed on preexistent comorbidities. New functional intradialytic imaging (i.e., echocardiography, cardiac magnetic resonance imaging [MRI]) and kinetic of specific cardiac biomarkers (i.e., Troponin I) have clearly documented this additional source of end-organ damage. In this context, several factors resulting from patient-hemodialysis interaction and/or patient management have been identified. Intradialytic hypovolemia, hypotensive episodes, hypoxemia, solutes, and electrolyte fluxes as well as cardiac arrhythmias are among the contributing factors to systemic circulatory stress that are induced by hemodialysis. Additionally, these factors contribute to patients' symptom burden, impair cognitive function, and finally have a negative impact on patients' perception and quality of life. In this review, we summarize the adverse systemic effects of current intermittent hemodialysis therapy, their pathophysiologic consequences, review the evidence for interventions that are cardioprotective, and explore new approaches that may further reduce the systemic burden of hemodialysis. These include improved biocompatible materials, smart dialysis machines that automatically may control the fluxes of solutes and electrolytes, volume and hemodynamic control, health trackers, and potentially disruptive technologies facilitating a more personalized medicine approach.

Air contamination during medical treatment results in deposits of microemboli in the lungs: An autopsy study

INTRODUCTION

Microbubbles of air may enter into patients during conventional hemodialysis, infusions of fluids, or by injections. The aim of this study was to investigate whether the air that enters the patient during hemodialysis can be detected in the lungs after death, and if so, whether this may be related to tissue damage.

METHODS

The material consisted of lung tissue from five chronic hemodialysis patients who died either during (two) or after hemodialysis (range 10 min from start until 3333 min after the last hemodialysis session); as reference group tissue was taken from seven patients who died due to amyotrophic lateral sclerosis. The lung tissue was investigated by microscopy after autopsy using a fluorescein-marked polyclonal antibody against fibrinogen as a marker for clots preformed before death.

RESULTS

All five hemodialysis patients had microbubbles of air in the lung tissue, whereas two of seven amyotrophic lateral sclerosis patients had such findings (Fisher's test p = 0.0278, relative risk = 3.5, confidence interval: 1.08-11.3). There were more microbubbles of air/10 randomly investigated microscopic fields of tissue in the hemodialysis patients than the amyotrophic lateral sclerosis patients (Student's test, p < 0.05). All hemodialysis patients had a medium graded extent of pulmonary fibrosis that was not found in any of the ALS patients. The microbubbles of air were surrounded by fibrin as a sign of development of clots around the air bubbles while the patients were still alive.

CONCLUSION

Exposure to microbubbles of air during various treatments such as hemodialysis may result in microemboli. Future studies should clarify whether microbubbles of air contribute to tissue scarring. We suggest preventive measures against the exposure to microbubbles of air during especially repeated exposures such as hemodialysis.

Formation of Blood Foam in the Air Trap During Hemodialysis Due to Insufficient Automatic Priming of Dialyzers

We were encouraged to investigate the reasons for large amounts of foam observed in bloodlines during hemodialysis (HD). Foam was visible in the venous air trap within the Artis Gambro dialysis device. Estimates of the extent of foam were graded (0-no foam, 10-extensive foam) by two persons that were blind to the type of dialyzer used. Thirty-seven patients were involved in the dialysis procedures. Consecutive dialyses were graded using dialyzers from Fresenius Medical Care (CorDiax dialyzers that were used for high flux HD-FX80 and FX100, and for hemodiafiltration-FX1000). The extracorporeal circuit was primed automatically by dialysate using Gambro Artis software 8.15 006 (Gambro, Dasco, Medolla Italy, Baxter, Chicago, IL, USA). The priming volume recommended by the manufacturer was 1100 mL, whereas our center uses 1500 mL. Extensive amounts of blood foam were visual in the air traps. Although the manufacturer recommended extension of priming volume up to 3000 mL, this did not eliminate the foam. Microbubble measurement during HD revealed the air to derive from the dialyzers. When changing to PF210H dialyzers (Baxter) and using a priming volume of 1500 mL, the foam was significantly less (P < 0.01). The extent of foam correlated with the size of the FX-dialyzer surface (P = 0.002). The auto-priming program was updated to version 8.21 by the manufacturer and the extent of foam in the air trap using FX dialyzers was now reduced and there was no longer a difference between FX and PF dialyzers, although less foam was still visible in the venous air trap during several dialyses. In conclusion, this study urgently calls attention to blood foam development in the venous air trap when using Artis devices and priming software 8.15 in combination with Fresenius dialyzers. Updated auto-priming software (version 8.21) of Artis should be requested to reduce the extent of foam for the Fresenius dialyzers. Other interactions may also be present. We recommend further studies to clarify these problems. Meanwhile caution is warranted for the combined use of dialysis devices and dialyzers with incompatible automatic priming.

Diagnosis, Treatment, and Prevention of Hemodialysis Emergencies

Given the high comorbidity in patients on hemodialysis and the complexity of the dialysis treatment, it is remarkable how rarely a life-threatening complication occurs during dialysis. The low rate of dialysis emergencies can be attributed to numerous safety features in modern dialysis machines; meticulous treatment and testing of the dialysate solution to prevent exposure to trace elements, toxins, and pathogens; adherence to detailed treatment protocols; and extensive training of dialysis staff to handle medical emergencies. Most hemodialysis emergencies can be attributed to human error. A smaller number are due to rare idiosyncratic reactions. In this review, we highlight major emergencies that may occur during hemodialysis treatments, describe their pathogenesis, offer measures to minimize them, and provide specific interventions to prevent catastrophic consequences on the rare occasions when such emergencies arise. These emergencies include dialysis disequilibrium syndrome, venous air embolism, hemolysis, venous needle dislodgement, vascular access hemorrhage, major allergic reactions to the dialyzer or treatment medications, and disruption or contamination of the dialysis water system. Finally, we describe root cause analysis after a dialysis emergency has occurred to prevent a future recurrence.

Hemodialysis Treatment Time: As Important as it Seems?

Hemodialysis treatment time and Kt/V can both be considered to be primary measures of hemodialysis adequacy, because when either goes to zero, mortality is certain in patients without residual kidney function. Treatment time is important, but it needs to be adjusted based on surface-area-normalized Kt/V, residual kidney function, and expected ultrafiltration rate. Rescaling dose of dialysis measured as Kt/V to body surface area prevents ultrashort dialysis in small patients, women, and children with minimal residual kidney function. Most if not all of the observational studies of associations between outcome and dialysis session length are probably confounded by dose targeting bias. Once adequate Kt/V (taking into account body surface area) has been provided, adequate dialysis time probably is most relevant in terms of limiting the need for a high fluid removal rate. The latter may adversely impact survival by causing recurrent ischemia to cardiovascular and other tissues. There is little high-quality evidence at this time to support a minimum 4-hour treatment time for all patients, regardless of body size, solute removal, or residual kidney function. On the other hand, there is little evidence that prolonging weekly treatment time up to 24 hours per week is harmful. The final decision regarding treatment time is best individualized, based on patient acceptability and experience, residual kidney function, body surface-area-normalized Kt/V, and expected ultrafiltration rate.

Why Is Your Patient Still Short of Breath? Understanding the Complex Pathophysiology of Dyspnea in Chronic Kidney Disease

Dyspnea is one of the most common symptoms associated with CKD. It has a profound influence on the quality of life of CKD patients, and its underlying causes are often associated with a negative prognosis. However, its pathophysiology is poorly understood. While hemodialysis may address fluid overload, it often does not significantly improve breathlessness, suggesting multiple and co-existing alternative issues exist. The aim of this article is to discuss the main pathophysiologic mechanisms and the most important putative etiologies underlying dyspnea in CKD patients. Congestive heart failure, unrecognized chronic lung disease, pulmonary hypertension, lung fibrosis, air microembolism, dialyzer bio-incompatibility, anemia, sodium, and fluid overload are potential frequent causes of breathing disorders in this population. However, the relative contributions in any one given patient are poorly understood. Systemic inflammation is a common theme and contributes to the development of endothelial dysfunction, lung fibrosis, anemia, malnutrition, and muscle wasting. The introduction of novel multimodal imaging techniques, including pulmonary functional magnetic resonance imaging with inhaled contrast agents, could provide new insights into the pathophysiology of dyspnea in CKD patients and ultimately contribute to improving our clinical management of this symptom.

Fatal Cerebral Air Embolism: A Case Series and Literature Review

Cerebral air embolism (CAE) is an infrequently reported complication of routine medical procedures. We present two cases of CAE. The first patient was a 55-year-old male presenting with vomiting and loss of consciousness one day after his hemodialysis session. Physical exam was significant for hypotension and hypoxia with no focal neurologic deficits. Computed tomography (CT) scan of head showed gas in cerebral venous circulation. The patient did not undergo any procedures prior to presentation, and his last hemodialysis session was uneventful. Retrograde rise of venous air to the cerebral circulation was the likely mechanism for venous CAE. The second patient was a 46-year-old female presenting with fever, shortness of breath, and hematemesis. She was febrile, tachypneic, and tachycardic and required intubation and mechanical ventilation. An orogastric tube inserted drained 2500 mL of bright red blood. Flexible laryngoscopy and esophagogastroduodenoscopy were performed. She also underwent central venous catheter placement. CT scan of head performed the next day due to absent brain stem reflexes revealed intravascular air within cerebral arteries. A transthoracic echocardiogram with bubble study ruled out patent foramen ovale. The patient had a paradoxical CAE in the absence of a patent foramen ovale.