Evaluation of neonatal membrane oxygenators with respect to gaseous microemboli capture and transmembrane pressure gradients

A series of studies performed at our center demonstrates that gaseous microemboli (GME) remain a challenge in cardiac surgical procedures. Evaluation of novel oxygenators must address hemodynamic parameters and microemboli capture capability. The objective of this study is to compare two neonatal membrane oxygenators, the Quadrox‐i (MAQUET Cardiopulmonary AG, Hirrlingen, Germany) and the Capiox RX05 (Terumo Corporation, Tokyo, Japan), with respect to GME capture and hemodynamic energy delivery. The experimental circuit included a Maquet HL‐20 heart‐lung machine, a Heater‐Cooler Unit HCU 30 (MAQUET Cardiopulmonary AG), a membrane oxygenator (Quadrox‐i Neonatal or Capiox RX05), and ¼‐inch tubing from the COBE Heart/Lung Perfusion Pack (COBE Cardiovascular, Inc., Arvada, CO, USA). A Capiox cardiotomy reservoir CX*CR10NX (Terumo Corporation) acted as a pseudopatient. The circuit was primed with human packed red blood cells and lactated Ringer's solution and de‐aired according to clinical priming procedure. Heparin (5000 IU) was added into the circuit. The total volume was 400 mL and hematocrit was 30%. Pump flow rate was maintained at 500 or 1000 mL/min under both pulsatile and nonpulsatile modes. All trials were conducted under 100 mm Hg of circuit pressure at normothermia (35°C). In each trial, bolus air (0.5 mL) was injected into the circuit at the prepump site over 5 s. Total emboli counts and total emboli volume were significantly reduced by the Quadrox‐i Neonatal membrane oxygenator compared to the Capiox RX05 membrane oxygenator. Classification and quantification of GME detected at the postoxygenator site at two different flow rates indicated that the Quadrox‐i Neonatal captures the majority of microemboli larger than 40 µm in diameter. The Quadrox‐i Neonatal membrane oxygenator had a higher transmembrane pressure drop at 500 mL/min, whereas it had a lower pressure drop at 1000 mL/min compared to the Capiox Baby RX05 oxygenator. Additionally, the Quadrox‐i Neonatal oxygenator preserved more pulsatile energy than the Baby RX05 oxygenator at both flow rates. Compared to the Capiox RX05 membrane oxygenator, the Quadrox‐i Neonatal membrane oxygenator has significantly improved GME handling capacity and had better hemodynamic energy preservation. Further research encompassing in vivo and clinical studies is needed to investigate the magnitude and mechanisms of these benefits.     

Preventing gaseous microemboli during blood sampling and drug administration: an in vitro investigation

The detection and prevention of gaseous microemboli (GMEs) during cardiopulmonary bypass has generated considerable interest within the cardiac surgical community. There have been several landmark papers that have used transcranial Doppler devices during cardiopulmonary bypass to detect gaseous microemboli activity in the patients' middle cerebral artery during perfusionist interventions. To determine if this source of emboli could be prevented, a shunt was developed between the oxygenator's sampling manifold and the oxygenator's venous line. This shunt bypassed the venous line and emptied into the oxygenator's integral cardiotomy. An in vitro experiment was performed using three open system oxygenators (Sorin Synthesis, Sorin PrimeOx2, and Terumo Capiox SX25) to compare post-arterial filter emboli detection using the Hatteland CMD20 Microbubble Detector under tightly controlled conditions. After injection of air through the sampling manifold, the PrimeOx2 and the Synthesis oxygenators had statistically significant fewer GMEs with the shunt used than when the shunt was not used. Using a shunt in the sampling manifold during perfusionist interventions will dramatically reduce or eliminate gaseous microemboli transmission to the patient during bypass with both the PrimeOx2 and Synthesis oxygenators. However, results indicate that further study of GME handling with all oxygenator's integral cardiotomies is warranted.     

In vitro evaluation of gaseous microemboli handling of cardiopulmonary bypass circuits with and without integrated arterial line filters

The delivery of gaseous microemboli (GME) by the cardiopulmonary bypass circuit should be minimized whenever possible. Innovations in components, such as the integration of arterial line filter (ALF) and ALFs with reduced priming volumes, have provided clinicians with circuit design options. However, before adopting these components clinically, their GME handling ability should be assessed. This study aims to compare the GME handling ability of different oxygenator/ALF combinations with our currently utilized combination. Five commercially available oxygenator/ALF combinations were evaluated in vitro: Terumo Capiox SX25RX and Dideco D734 (SX/D734),Terumo Capiox RX25R and AF125 (RX/AF125), Terumo FX25R (FX), Sorin Synthesis with 102 microm reservoir filter (SYN102), and Sorin Synthesis with 40 microm reservoir filter (SYN40). GME handling was studied by introducing air into the venous return at 100 mL/min for 60 seconds under two flow/ pressure combinations: 3.5 L/min, 150 mmHg and 5 L/min, 200 mmHg. Emboli were measured at three positions in the circuit using the Emboli Detection and Classification (EDAC) Quantifier and analyzed with the General Linear Model. All circuits significantly reduced GME. The SX/D734 and SYN40 circuits were most efficient in GME removal whilst the SYN102 handled embolic load (count and volume) least efficiently (p < .001). A greater number of emboli <70 microm were observed for the SYN102, FX and RX/AF125 circuits (p < .001). An increase in embolic load occurred with higher flow/pressure in all circuits (p < .001). The venous reservoir significantly influences embolic load delivered to the oxygenator (p < .001). The majority of introduced venous air was removed; however, significant variation existed in the ability of the different circuits to handle GME. Venous reservoir design influenced the overall GME handling ability. GME removal was less efficient at higher flow and pressure, and for smaller sized emboli. The clinical significance of reducing GME requires further investigation.     

Evaluation of Capiox RX25 and Quadrox‐i Adult Hollow Fiber Membrane Oxygenators in a Simulated Cardiopulmonary Bypass Circuit

The Capiox RX25 and Quadrox‐i Adult oxygenators are commonly used in clinical adult cardiopulmonary bypass circuits. This study was designed to test the effectiveness of two adult oxygenators in order to evaluate gaseous microemboli (GME) trapping capability and hemodynamic performance. A simulated adult CPB circuit was used and primed with Ringer's lactate and packed red blood cells (hematocrit 25%). All trials were conducted at flow rates of 2–5 L/min (1 L/min increments) with a closed and open arterial filter purge line at 35°C. The postcannula pressure was maintained at 100 mm Hg. After a 5 cc of bolus air was introduced into the venous line, an Emboli Detection and Classification system was used to detect and classify GME at the preoxygenator, postoxygenator, and precannula sites. At the same time, real‐time pressure and flow data were recorded, and hemodynamic energy was calculated using a custom‐made data acquisition system and Labview software. Our results showed that the oxygenator pressure drops of Quadrox‐i Adult oxygenator were lower than Capiox RX25 at all flow rates. The Quadrox‐i Adult oxygenator retained more hemodynamic energy across the oxygenator. Both oxygenators could trap the majority of GME, but Capiox RX25 did better than the Quadrox‐i Adult oxygenator. No GME was delivered to the pseudo patient at all flow rates in the Capiox group. The Capiox RX25 venous reservoir could capture more GME at lower flow rates, while the Quadrox‐i Adult venous reservoir performed better at higher flow rates. An open arterial filter purge line reduced GME slightly in the Capiox group, but GME increased in the Quadrox group. The Quadrox‐i Adult oxygenator is a low‐resistance, high‐compliance oxygenator. The GME handling ability of Capiox RX25 performed well under our clinical setting. Further optimized design for the venous/cardiotomy reservoir is needed.     

Evaluation of Capiox FX05 oxygenator with an integrated arterial filter on trapping gaseous microemboli and pressure drop with open and closed purge line

Gaseous microemboli (GME) remain a challenge for cardiopulmonary bypass (CPB) because there is a positive correlation between microemboli exposure during CPB and postoperative neurological injury. Thus, minimizing the number of GME delivered to pediatric patients undergoing CPB procedures would lead to better clinical outcomes. In this study, we used a simulated CPB model to evaluate the effectiveness of capturing GME and the degree of membrane pressure drop for a new membrane oxygenator, Capiox Baby FX05 (Terumo Corporation,Tokyo, Japan), which has an integrated arterial filter with open and closed purge line.We used identical components in this study as our clinical CPB circuit. Three emboli detection and classification quantifier transducers were placed at prepump, preoxygenator, and postoxygenator sites in the circuit.Two flow probes as well as three pressure transducers were placed upstream and downstream of the oxygenator. The system was primed with human blood titrated to 30% hematocrit with Lactated Ringer’s solution.A bolus of air (1 mL) was injected in the prepump site under nonpulsatile perfusion mode at three flow rates (500,750, and 1000 mL/min) and with the purge line either open or closed. Six trials were performed for each unique set-up for a total of 36 trials.All trials were conducted at 35°C. The circuit pressure was kept constant at 100 mm Hg. Both the size and quantity of microemboli detected at postoxygenator site were recorded for 5 min postair injection. It was found that total counts of GME were significantly reduced with the purge line open when compared to keeping the purge line closed (P < 0.0001 at 1000 mL/min). At all flow rates, most of the GME were under 20 microns in size. In terms of microemboli greater than 40 microns, the counts were significantly higher with the purge line closed compared to keeping the purge line open at flow rates of 750 mL/min and 1000 mL/min (P < 0.01). At all flow rates,there is a tiny difference of less than 1 mmHg in membrane pressure drop between keeping the purge line open and closed, which is due to the small arteriovenous (A-V) shunt(P < 0.001). These results suggest that the integrated arterial filter of the Capiox FX05 oxygenator significantly improves the capturing of GME but has little impact on membrane pressure drop.     

A clinical evaluation of the Terumo Capiox SX18R hollow fiber oxygenator

The Terumo Capiox SX18R is a commercially available, low prime, reverse phase, hollow fiber membrane oxygenator. The oxygenator consists of a 1.8 m2 microporous polypropylene hollow fiber bundle, a 2200 cm2 tubular stainless steel heat exchanger, and an open hard shell venous reservoir with integral cardiotomy filter. The Terumo Capiox SX18R oxygenator was evaluated to determine its clinical oxygenating performance. Blood samples were drawn from 25 patients yielding 114 data points. The following parameters were recorded: blood flow, cardiac index, gas flow, gas to blood flow ratio, and oxygen fraction. Samples were assayed for hematocrit, hemoglobin, arterial and venous blood gas values, and venous oxygen saturation. The data and assay results were used to calculate arterial, venous, and membrane gas oxygen content, oxygen transfer, shunt fraction, and oxygen diffusion capacity. The Terumo Capiox SX18R oxygenator performed adequately with sufficient oxygen transfer reserve and carbon dioxide clearance under a variety of clinical conditions for the tested population.     

Blood temperature management and gaseous microemboli creation: an in-vitro analysis

Gaseous microemboli have been associated with post operative neurological deficits in patients undergoing cardiopulmonary bypass. Creating an optimal perfusion system that minimizes microemboli production and has enhanced abilities to sequester entrained air during the bypass procedure has been an important focus. This study examines the air-handling capabilities of a cardiopulmonary bypass circuit and correlates blood temperatures with microemboli loads proximal and distal to the arterial line filter within the circuit. Utilizing a Capiox RX25R oxygenator, Capiox 37 micron arterial filter, vacuum assisted venous return, and emboli detectors, 30 mL of air were injected into the venous line of a bypass circuit at eight different temperatures. Emboli were counted distal to the arterial line filter by the EDAQ Quantifier (Emboli Detection and Classification). The average number of emboli detected distal to the arterial filter progressively increased as the perfusate temperature was dropped. At 37.0 degrees C an average of 1.4 emboli was observed distal to the arterial filter within 90 seconds of the air injection. At 23.0 degrees C an average of 49.8 emboli was detected. Air introduced into the venous side of the bypass circuit resulted in showers of microemboli being sent past the arterial line filter. In addition, as the bovine blood was cooled, the air handling capability of the circuit was diminished.     

Pulse Conductance and Flow‐induced Hemolysis During Pulsatile Cardiopulmonary Bypass

In this study, the hypothesis was tested that a low‐resistant, high‐compliant oxygenator provides better pulse conductance and less hemolysis than a high‐resistant, low‐compliant oxygenator during pulsatile cardiopulmonary bypass. Forty adults undergoing coronary artery bypass surgery were randomly divided into two groups using either an oxygenator with a relatively low hydraulic resistance (Quadrox BE‐HMO 2000, Maquet Cardiopulmonary AG, Hirrlingen, Germany) or with a relatively high hydraulic resistance (Capiox SX18, Terumo Cardiovascular Systems, Tokyo, Japan). The phase shift between the flow signals measured at the inlet and outlet of the oxygenator was used to assess compliance. Pulse conductance in terms of pressure attenuation was calculated by dividing the outlet pulse pressure of the oxygenator by the inlet pulse pressure. A normalized index was used to assess hemolysis. The phase shifts in time of the flow pulses were 36 ± 6 ms in the low‐resistant (high‐compliant) oxygenator, and 14 ± 2 ms in the high‐resistant (low‐compliant) oxygenator group (P < 0.001). The low‐resistant, high‐compliant oxygenator provided 27% better pulse conductance compared with the high‐resistant, low‐compliant oxygenator (0.84 ± 0.02 and 0.66 ± 0.01, respectively, P < 0.001). Inlet pulse pressures were significantly higher (29%) in the high‐resistant, low‐compliant (Capiox) group than in the low‐resistant, high‐compliant (Quadrox) group (838 ± 38 mm Hg and 648 ± 25 mm Hg respectively, P < 0.001), but no significant difference in hemolysis was found. A low‐resistant, high‐compliant oxygenator provides better pulse conduction than a high‐resistant, low‐compliant oxygenator. However, the study data could not confirm the association of high pressures with increased hemolysis.     

Impact of oxygenator selection on hemodynamic energy indicators under pulsatile and nonpulsatile flow in a neonatal extracorporeal life support model

This study compared the quality of perfusion delivered by two oxygenators--the hollow-fiber membrane Capiox Baby RX05 and silicone membrane Medtronic 0800--using hemodynamic energy indicators. The oxygenators were tested across varying flow rates and perfusion modes in a neonatal extracorporeal life support (ECLS) model. The experimental ECLS circuit included a Jostra HL-20 heart/lung machine with Jostra Roller pump, oxygenators with associated tubing and components, and a neonatal pseudo-patient. We used a 40/60 glycerin/water solution in the circuit as a blood analog. Testing occurred at flow rates of 250, 500, and 750 mL/min at 37°C under both pulsatile and nonpulsatile flow conditions. Hemodynamic data points consisted of recording 20-s intervals of data, and a total of 96 experimental repetitions were conducted. The pressure drop across the Capiox Baby RX05 oxygenator was significantly lower than the pressure drop across the Medtronic 0800 at all flow rates and perfusion modes. Furthermore, the Medtronic 0800 oxygenator showed significantly lower post-oxygenator energy equivalent pressures, total hemodynamic energy values, and surplus hemodynamic energy retention values compared to those of the Capiox Baby RX05. These results indicate the Medtronic 0800 oxygenator significantly dampens the hemodynamic energy compared to the Capiox Baby RX05. Consequently, clinical use of the Medtronic 0800 in a pulsatile ECLS setting is likely to mitigate the benefits provided by pulsatile flow. In contrast, the Capiox Baby RX05 better transmits hemodynamic energy to the patient with much lower pressure drop.     

Oxygenator safety evaluation: a focus on connection grip strength and arterial temperature measurement accuracy

This report describes the assessment of three specific safety-related specifications in the consideration of an alternate oxygenator; first the grip strength relationship between various oxygenator connectors and SMARxT tubing, second, the grip strength of various biopassive tubings and an isolated SMARxT connector, and finally, the accuracy of the arterial outlet temperature measurement. Grip strength experiments for the connections between the SMARxT tubing and the venous reservoir outlet and the oxygenator venous inlet and oxygenator arterial outlet of the Medtronic Affinity, Sorin Synthesis, Sorin Primox, and Terumo Capiox RX25 oxygenators were performed. In addition we compared the grip strength of polyvinyl chloride, Physio, Trillium, Carmeda, X-Coating, and SMARxT tubing. The accuracy of the integrated arterial outlet temperature probes was determined by comparing the temperatures measured by the integrated probe with a precision reference thermometer. Connector grip strength comparisons for the evaluation oxygenators with SMARxT tubing showed significant variation between oxygenators and connections (p = .02). Evaluation of the arterial outlet showed significant variation between evaluation oxygenators, while at the venous reservoir outlet and oxygenator inlet, there were no significant differences. Grip strength comparison data for the various tubing types demonstrated a main effect for tubing type F(5, 18) = 8.01, p = .002, eta(p)(2) = .77. Temperature accuracy measurements demonstrated that all oxygenators overread the arterial outlet temperature at 15 degrees C, whilst at temperatures > or = 25 degrees C, all oxygenators underread the arterial outlet temperature. The integrity of SMARxT tubing connection is influenced by the connector type, and may decline over time, highlighting the importance to not consider interchanging components of the bypass circuit as inconsequential.     

In vitro evaluation of Capiox FX05 and RX05 oxygenators in neonatal cardiopulmonary bypass circuits with varying venous reservoir and vacuum-assisted venous drainage levels

The purpose of this study was to evaluate the hemodynamic properties and microemboli capture associated with different vacuum-assisted venous drainage (VAVD) vacuum levels and venous reservoir levels in a neonatal cardiopulmonary bypass circuit. Trials were conducted in 2 parallel circuits to compare the performance of Capiox Baby RX05 oxygenator with separate AF02 arterial filter to Capiox FX05 oxygenator with integrated arterial filter. Arterial cannula flow rate to the patient was held at 500 mL/min and temperature maintained at 32°C, while VAVD vacuum levels (0 mm Hg, −15 mm Hg, −30 mm Hg, −45 mm Hg, −60 mm Hg) and venous reservoir levels (50 mL, 200 mL) were evaluated in both oxygenators. Hemodynamic parameters measuring flow, pressure, and total hemodynamic energy were made in real time using a custom-made data acquisition system and Labview software. Nearly 10 cc bolus of air was injected into the venous line and gaseous microemboli detected using an Emboli Detection and Classification Quantifier. Diverted blood flow via the arterial filter’s purge line and mean pressures increased with increasing VAVD levels (P < 0.01). Mean pressures were lower with lower venous reservoir levels and were greater in RX05 groups compared to FX05 (P < 0.01). Microemboli detected at the preoxygenator site increased with higher VAVD vacuum levels and lower venous reservoir levels (P < 0.01). The amount of microemboli captured by the FX05 oxygenator with integrated arterial filter was greater than by the RX05 oxygenator alone, although both oxygenators were able to clear microemboli before reaching the pseudo-patient.     

Ultrasonic identification of sources of gaseous microemboli during open heart surgery

An ultrasonic transducer was used to detect gaseous microemboli during open heart surgery. When placed over the carotid artery of patients during surgery it was recognized that gaseous emboli were released into the systemic circulation following recognizable surgical procedures and from the oxygenator during bypass. Fixation of the transducer on the arterial return from the oxygenator demonstrated that the two types of disposable bubble oxygenators and disc oxygenators tested delivered microbubbles in the arterial blood. Some factors affecting the number of bubbles released were recognized and are discussed. Case reports of two patients who received large volumes of gaseous microemboli from different sources are presented.     

In Vitro Hemodynamic Evaluation of Five 6 Fr and 8 Fr Arterial Cannulae in Simulated Neonatal Cardiopulmonary Bypass Circuits

The objective of this study was to evaluate five small‐bore arterial cannulae (6Fr and 8Fr) in terms of pressure drop and hemodynamic performance in simulated neonatal cardiopulmonary bypass (CPB) circuits. The experimental circuits consisted of a Jostra HL‐20 roller pump, a Terumo Capiox Baby FX05 oxygenator with integrated arterial filter, an arterial and a venous tubing (1/4, 3/16, or 1/8 in × 150 cm), and an arterial cannula (Medtronic Bio‐Medicus 6Fr and 8Fr, Maquet 6Fr and 8Fr, or RMI Edwards 8Fr). The circuit was primed using lactated Ringer's solution and heparinized packed human red blood cells (hematocrit 30%). Trials were conducted at different flow rates (6Fr: 200–400 mL/min; 8Fr: 200–600 mL/min) and temperatures (35 and 28°C). Flow and pressure data were collected using a custom‐based data acquisition system. Higher circuit pressure, circuit pressure drop, and hemodynamic energy loss across the circuit were recorded when using small‐bore arterial cannula and small inner diameter arterial tubing in a neonatal CPB circuit. The maximum preoxygenator pressures reached 449.7 ± 1.0 mm Hg (Maquet 6Fr at 400 mL/min), and 395.7 ± 0.4 mm Hg (DLP 8Fr at 600 mL/min) when using 1/8 in ID arterial tubing at 28°C. Hypothermia further increased circuit pressure drop and hemodynamic energy loss. Compared with the others, the RMI 8Fr arterial cannula had significantly lower pressure drop and energy loss. Maquet 6Fr arterial cannula had a greater pressure drop than the DLP 6Fr. A small‐bore arterial cannula and arterial tubing created high circuit pressure drop and hemodynamic energy loss. Appropriate arterial cannula and arterial tubing should be considered to match the expected flow rate. Larger cannula and tubing are recommended for neonatal CPB. Low‐resistance neonatal arterial cannulae need to be developed.     

Evaluation of HL-20 roller pump and Rotaflow centrifugal pump on perfusion quality and gaseous microemboli delivery

The purpose of this study was to compare the HL‐20 roller pump (Jostra USA, Austin, TX, USA) and Rotaflow centrifugal pump (Jostra USA) on hemodynamic energy production and gaseous microemboli (GME) delivery in a simulated neonatal cardiopulmonary bypass (CPB) circuit under nonpulsatile perfusion. This study employed a simulated model of the pediatric CPB including a Jostra HL‐20 heart‐lung machine (or a Rotaflow centrifugal pump), a Capiox BabyRX05 oxygenator (Terumo Corporation, Tokyo, Japan), a Capiox pediatric arterial filter (Terumo Corporation), and ¼‐inch tubing. The total volume of the experimental system was 700 mL (500 mL for the circuit and 200 mL for the pseudo neonatal patient). The hematocrit was maintained at 30% using human blood. At the beginning of each trial, a 5 mL bolus of air was injected into the venous line. Both GME data and pressure values were recorded at postpump and postoxygenator sites. All the experiments were conducted under nonpulsatile perfusion at three flow rates (500, 750, and 1000 mL/min) and three blood temperatures (35, 30, and 25°C). As n = 6 for each setup, a total of 108 trials were done. The total number of GME increased as temperature decreased from 35°C to 25°C in the trials using the HL‐20 roller pump while the opposite effect occurred when using the Rotaflow centrifugal pump. At a given temperature, total GME counts increased with increasing flow rates for both pumps. Results indicated the Rotaflow centrifugal pump delivered significantly fewer microemboli compared to the HL‐20 roller pump, especially under high flow rates. Less than 10% of total microemboli were larger than 40 µm in size and the majority of GME were in the 0–20 µm class in all trials. Postpump total hemodynamic energy (THE) increased with increasing flow rates and decreasing temperatures in both circuits using these two pumps. The HL‐20 roller pump delivered more THE than the Rotaflow centrifugal pump at all tested flow rates and temperature conditions. Results suggest the HL‐20 roller pump delivers more GME than the Rotaflow centrifugal pump but produces more hemodynamic energy under nonpulsatile perfusion mode.     

Building a Better Neonatal Extracorporeal Life Support Circuit: Comparison of Hemodynamic Performance and Gaseous Microemboli Handling in Different Pump and Oxygenator Technologies

Neurologic complications during neonatal extracorporeal life support (ECLS) are associated with significant morbidity and mortality. Gaseous microemboli (GME) in the ECLS circuit may be a possible cause. Advances in neonatal circuitry may improve hemodynamic performance and GME handling leading to reduction in patient complications. This study compared hemodynamic performance and GME handling using two centrifugal pumps (Maquet RotaFlow and Medos Deltastream DP3) and polymethylpentene oxygenators (Maquet Quadrox‐iD and Medos Hilite 800LT) in a neonatal ECLS circuit model. The experimental circuit was primed with Lactated Ringer's solution and packed human red blood cells (hematocrit 40%) and arranged in parallel with the RotaFlow and DP3 pump, Quadrox‐iD and Hilite oxygenator, and Better‐Bladder. Hemodynamic trials evaluating pressure drops and total hemodynamic energy (THE) were conducted at 300 and 500 mL/min at 36°C. GME handling was measured after 0.5 mL of air was injected into the venous line using the Emboli Detection and Classification Quantifier System with unique pump, oxygenator, and Better‐Bladder combinations. The RotaFlow pump and Quadrox oxygenator arrangement had lower pressure drops and THE loss at both flow rates compared to the DP3 pump and Hilite oxygenator (P < 0.01). Total GME volume and counts decreased with Better‐Bladder at both flow rates with all combinations (P < 0.01). Hemodynamic performance and energy loss were similar in all of the circuit combinations. The Better‐Bladder significantly decreased GME. All four combinations of pumps and oxygenators also performed similarly in terms of GME handling.     

Comparison of gaseous microemboli counts in arterial, simultaneous and venous heat exchange with a hollow fiber membrane oxygenator

Potential sources of gaseous microemboli during cardiopulmonary bypass are varied. However, it is known that membrane oxygenators generate fewer gaseous microemboli than bubble oxygenators and that bubblers cannot utilize arterial heat exchange without generating significant gaseous microemboli during rewarming. A membrane oxygenator utilizing simultaneous gas and heat exchange raises the concern that concurrent gas and heat exchange would result in a higher production of gaseous microemboli compared to conventional venous heat exchange devices. This in vitro study compared venous, simultaneous, arterial and control (venous) heat exchanger gaseous microemboli counts during rewarming. No significant difference was found between the four heat exchangers when comparing inlet and outlet gaseous microemboli counts. This in vitro study suggests that there is no difference in gaseous microemboli generation when varying the position of the heat exchanger in the extracorporeal circuit incorporating a microporous membrane oxygenator.     

The detection of microemboli in the middle cerebral artery during cardiopulmonary bypass: a transcranial Doppler ultrasound investigation using membrane and bubble oxygenators

Twenty-seven patients were examined who were undergoing cardiopulmonary bypass (CPB) surgery with either a bubble oxygenator or a capillary membrane oxygenator. The latter incorporated an arterial filter and bubble trap. A noninvasive Doppler ultrasound technique is described for monitoring irregularities in the Doppler flow signals attributable to gaseous microemboli detected in the middle cerebral artery during CPB. The ultrasound index for detecting gaseous microemboli (MEI) indicated the presence of such microemboli in 22 of the 27 patients during insertion of the aortic cannula. Measurements during CPB showed the MEI ranged from 4 to 39 in the 17 patients with a bubble oxygenator. However, all 10 patients with a membrane oxygenator had an MEI of 0. Varying the gas flow rates in 3 patients with bubble oxygenators showed a change in MEI from 4 +/- 4 (SD) at a flow rate of 2 L/min to 17 +/- 9 at a flow rate of 5 L/min. This observation supports the assumption that the MEI is providing quantitative information regarding the presence of gaseous emboli in the middle cerebral artery.     

Impact of oxygenator characteristics on its capability to remove gaseous microemboli

Since the advent of cardiopulmonary bypass, the generation and elimination of gaseous and solid (micro) emboli have been a concern. Major improvements with respect to gaseous microemboli have been made by the introduction of arterial line filtration and membrane oxygenators. Animal experiments have shown a clear correlation between massive air embolism and outcome. However, limited knowledge is available regarding the cut-off point between the occurrence of negative outcome and the number and size of gaseous microemboli. Generation of gaseous microemboli can occur when using cardiopulmonary bypass. However, no consensus exists on when a given diameter or number of emboli becomes injurious to the patient. An important variable is the gas mixture inside the bubble. Nitrogen has a very long dissolution time that results in a prolonged ischemia for tissue behind the occlusion. The pathophysiologic reaction of the body when exposed to gaseous microemboli is most likely based on ischemia caused by partial occlusion of blood vessels and by endothelial damage. Gaseous microemboli can be cleared mechanically by using filters, by reduction of blood velocity, and by rapid reduction of the nitrogen content. Elimination of gaseous microemboli is dependent on the design of the cardiopulmonary bypass circuit. A membrane oxygenator, although not designed for it, can remove gaseous microemboli. Arterial line filtration is not the best solution for removal of gaseous microemboli, because larger emboli have been fractionated before reaching the arterial filter. Venous line filtration is a more efficient way for clearing gaseous microemboli.     

Is the Air Handling Capability of the Quadrox D Pump Dependent within an ECMO Circuit? An In Vitro Study

The occurrence of gaseous microemboli (GME) within the extracorporeal membrane oxygenation circuit is largely overlooked, as are methods to ameliorate this occurrence. We aimed to determine if the air handling capability of the Quadrox D oxygenator was dependent upon whether it was used in conjunction with a centrifugal or roller pump; and if application of a Pall air eliminating filter (AEF) would prevent circuit air introduction from intravenous infusions. Using a blood primed circuit 1 mL of air was infused pre pump. GME were quantified post pump and post oxygenator using the EDAC Quantifier. Trials were conducted at 1 and 2 L/min flow. To prevent GME recirculation a Capiox SX18 was used in circuit with negative pressure applied to its oxygenator; an EDAC cuvette distal to this device quantified GME recirculation. Following air infusion, 3-5 minute data recordings were carried out for each trial. Separate trials were carried out for centrifugal and roller pumps, and for each flow rate. The process was then repeated following the application of the AEF to the air infusion line. More GME were detected post Quadrox D when the centrifugal pump was used in comparison to the roller pump at 1 L/min (p < .05), and 2 L/min (p = .05). A greater volume of air was detected post Quadrox D when used in conjunction with the centrifugal device at 1 L/min (p < or = .05), and 2 L/min (p < or = .05). Application of the AEF resulted in zero GME detected at any circuit location. The results of this study confirm that a greater total count and volume of GME are detected distal to the Quadrox D when used in conjunction with a Rotaflow centrifugal pump. Application of a Pall AEF to infusion and drug lines can prevent air introduction from this source.     

The relationship between oxygenator exhaust P(CO2) and arterial P(CO2) during hypothermic cardiopulmonary bypass

During cardiopulmonary bypass the partial pressure of carbon dioxide in oxygenator arterial blood (P(a)CO2) can be estimated from the partial pressure of gas exhausting from the oxygenator (P(E)CO2). Our hypothesis is that P(E)CO2 may be used to estimate P(a)CO2 with limits of agreement within 7 mmHg above and below the bias. (This is the reported relationship between arterial and end-tidal carbon dioxide during positive pressure ventilation in supine patients.) During hypothermic (28-32 degrees C) cardiopulmonary bypass using a Terumo Capiox SX membrane oxygenator, 80 oxygenator arterial blood samples were collected from 32 patients during cooling, stable hypothermia, and rewarming as per our usual clinical care. The P(a)CO2 of oxygenator arterial blood at actual patient blood temperature was estimated by temperature correction of the oxygenator arterial blood sample measured in the laboratory at 37 degrees C. P(E)CO2 was measured by connecting a capnograph end-to-side to the oxygenator exhaust outlet. We used an alpha-stat approach to cardiopulmonary bypass management. The mean difference between P(E)CO2 and P(a)CO2 was 0.6 mmHg, with limits of agreement (+/-2 SD) between -5 to +6 mmHg. P(E)CO2 tended to underestimate P(a)CO2 at low arterial temperatures, and overestimate at high arterial temperatures. We have demonstrated that P(E)CO2 can be used to estimate P(a)CO2 during hypothermic cardiopulmonary bypass using a Terumo Capiox SX oxygenator with a degree of accuracy similar to that associated with the use of end-tidal carbon dioxide measurement during positive pressure ventilation in anaesthetized, supine patients.