An in vitro study of the effectiveness of carbon dioxide flushing of arterial line filters

Gaseous microemboli (GMEs) have been connected to neurologic impairment and other ischemic complications after surgery. The components of the extracorporeal circuit (ECC) have a large influence on GME production. This in vitro study investigates the use of carbon dioxide flushing of the 38-microm Medtronic Affinity CB351 and 38-microm Medtronic Affinity 351 arterial line filters (ALFs) to decrease GMEs and time for air to clear the ALE An adult circuit was implemented with a silicone oxygenator for vacuum-assisted gas removal and to reduce air before ALE The 48 filters were separated into four equal groups: flushed coated and non-coated and non-flushed coated and non-coated. Carbon dioxide flushing was performed at 6 L/min for 3 minutes. ALFs were retrograde primed at 200 mL/min. An Emboli Detection and Classification Quantifier (EDAC) was used to gather data. The average total emboli and time to clear (seconds) for flush coated were 20.25 +/- 16.78 and 142.17 +/- 174.80 seconds, respectively, flushed non-coated were 30.5 +/- 34.65 and 124.17 +/- 131.40 seconds, non-flushed coated were 162.08 +/- 79.90 and 390.42 +/- 84.36 seconds, and non-flushed non-coated were 163.67 +/- 212.67 and 305.92 +/- 179.36 seconds. Flushed filters had an average total emboli count of 25.375 +/- 27.14 and an average time to clear of 13.167 +/- 151.51 seconds. Non-flushed filters had an average total emboli count of 162.875 +/- 157.11 and an average time to clear of 348.167 +/- 143.70 seconds. Coated and non-coated filters for total emboli and time to clear had p values of .86 and .24, respectively. Flushed and non-flushed filters had total emboli and time to clear p values of < .001 and < .001, respectively. No significant difference was found between coated and non-coated filters involving total embolic count and time to clear. A significant difference was found in total embolic count and time to clear between flushed and non-flushed filters. This study shows that fewer emboli and faster embolic clearance time correlate with carbon dioxide flushing of the ALE.

Gaseous microemboli in a pediatric bypass circuit with an unprimed venous line: an in vitro study

Miniaturizing cardiopulmonary bypass (CPB) circuits to reduce hemodilution and allogenic blood product administration is common in cardiac surgery. One major concern associated with smaller CPB circuits is a possible increase in gaseous microemboli (GME) sent to the cerebral vasculature, which is exacerbated by vacuum-assisted venous drainage (VAVD). The use of VAVD has increased with smaller venous line diameter and venous cannulae. This study examines the effects of CPB initiation with an unprimed venous line and VAVD in a pediatric circuit. A CPB circuit was set up with reservoir, oxygenator, and arterial filter with a bag reservoir to simulate the patient. All trials were done in vitro, and GME were measured using the EDAC Quantifier by Luna Innovations. EDAC sensors were placed proximal and distal to the oxygenator and distal to the arterial filter. Group 1 was the control group with no VAVD and a primed venous line. Groups 2, 3, and 4 used an unprimed venous line and VAVD of -40, -20, and -10 mmHg, respectively. Total microemboli counts and total embolic load in micrometers were measured at each sensor. Groups 2 (12,379.00 +/- 3180.37) and 3 (8296.67 +/- 2818.76) had significantly more microemboli than group 1 (923.33 +/- 796.08, p < .05) at the pre-oxygenator sensor. Group 2 (57.33 +/- 25.01, p < .05) had significantly more microemboli than group 1 (5.33 +/- 3.21) at the post-oxygenator sensor. No other findings were statistically significant. The results suggest that, if an oxygenator and arterial filter with sufficient air handling capabilities are used, this method to reduce prime volume may not increase GME in the arterial line distal to the arterial filter.

Pediatric cardiopulmonary bypass circuits: a review of studies conducted at the Penn State Pediatric Cardiac Research Laboratories

Cardiopulmonary bypass (CPB) circuits are frequently necessary in the repair of congenital heart defects in infants and children. Although advances in technology and operative technique have decreased the mortality associated with cardiac procedures requiring CPB, post-operative neuro-cognitive outcome and the role of the CPB circuit in post-operative morbidity remains a significant concern. There are several factors that have been suggested to play a significant role in general post-operative outcome, including intraoperative inflammatory responses caused by the interaction of blood with circuit component surfaces, selection of appropriate perfusion mode to optimize organ function during CPB, and the introduction of gaseous microemboli into the patient's systemic circulation through circuit manipulations and modifications. These factors are the subject of continuing research at the Penn State Hershey Children's Hospital Pediatric Cardiac Research Laboratories, and this review will focus on the results of studies aimed at identifying circuit elements that affect the delivery of gaseous microemboli to the patient during CPB procedures, the role of anti-factor D monoclonal antibody in reducing systemic inflammation during CPB, and the results of preliminary plasma proteomics studies conducted on infants undergoing CPB.

A new method of measure of bubble gas volume shows that interleukin-6 injected into rats has no effect on gas embolism

The pleiotropic cytokine interleukin-6 increases in the plasma of rats after an air dive. Interleukin-6 shares both of inflammatory and anti-inflammatory properties and may condition the vascular system and gas embolism after an air dive. Up to now it is not known whether interleukin-6 has an effect on gas embolism. Aim of this work is to study the effect of interleukin-6 on gas embolism after a standard decompression protocol in a rat model. The volume of gas bubbles was measured in the heart cavities with a new method based on the buoyancy of the heart at different pressures which is physically sound, accurate and precise down to 10(-4) cm3. No effect was found after injecting physiological doses of interleukin-6 at different times before the air dive. The mortality of the rats in the first half hour after the decompression was associated with a substantial gas volume measured in the heart. Multi-variate logistic regression analysis showed that the female rats had a higher risk compared to male rats of developing a substantial bubble volume and of not surviving; the spring-summer season was a risk factor for the survival. Further studies are needed to see whether interleukin-6 in association with other cytokines has an effect on gas embolism.

Venous air embolism during surgery, especially cesarean delivery

Venous air embolism (VAE) is the entrapment of air or medical gases into the venous system causing symptoms and signs of pulmonary vessel obstruction. The incidence of VAE during cesarean delivery ranges from 10 to 97% depending on surgical position or diagnostic tools, with a potential for life-threatening events. We reviewed extensive literatures regarding VAE in detail and herein described VAE during surgery including cesarean delivery from background and history to treatment and prevention. It is intended that present work will improve the understanding of VAE during surgery.

Infusion therapy. Part two: Prevention and management of complications

In the second of two articles, the author identifies common complications associated with intravenous (i.v.) therapy and discusses preventive measures. Part one, published last week, provided an overview of i.v. therapy and the types of vascular access devices available.

Acoustical bubble trapper applied to hemodialysis

Gaseous microemboli can arise in extracorporeal lines and devices such as dialysis machines. They are associated with severe pulmonary side effects in patients undergoing chronic hemodialysis sessions. The goal of this study was to develop a gaseous emboli trapper using ultrasound waves to remove any air bubble from the tubing system before they reach the patient. A homemade bubble trapper, developed in the laboratory, consists of a Perspex block containing a main channel connected to the tubing of a hemodialysis machine and a second subchannel positioned perpendicularly to the main one, used to trap the air microemboli. The microemboli flowing in the main channel were insonified through an acoustic window with an ultrasound wave, at a frequency of 500 kHz and with a maximal acoustic pressure of 500 kPa, generated by a single-element transducer positioned 3 cm away from the main flow. The radiation force induced by the ultrasound beam acts directly on the flowing air emboli, by pushing them into the subchannel. Two Doppler probes operating both at 2 MHz, connected to a DWL Doppler machine were placed before and after the bubble trapper to count sequentially the number of embolic events. The flow of the machine was varied between 200 mL/min and 500 mL/min. Depending on the flow velocity, the number of microembolic signals (MES) detected by the Doppler probes before and after the trapping system was identical and ranged from 5 to 150 MES/min in absence of the ultrasound irradiation. When the air bubble trapper was activated, a reduction of the number of MES, up to 70%, was achieved. Doppler recordings suggest that the circulating bubbles were either fragmented into smaller bubble fragments or directly got pushed into the second subchannel where they were collected. This simple approach using an ultrasound-based trapping system was shown to operate adequately with the current settings and can be used to filter air microemboli.

Symptomatic cerebral air embolism during neuro-angiographic procedures: incidence and problem avoidance

BACKGROUND

While clinically symptomatic cerebral air embolism secondary to neuro-angiographic procedures is rare, the incidence in a large series of procedures is unknown. Understanding this complication's frequency and etiology is critical if systems are to be instituted to reduce its incidence.

METHODS

We prospectively reviewed 4,568 consecutive neuro-angiographic procedures performed between June 2000 and July 2005. The occurrence and etiology of a symptomatic air embolus was noted, and an incidence was calculated for all procedures and for diagnostic arteriograms and interventional procedures individually.

RESULTS

Four symptomatic cerebral arterial air emboli occurred in 4,568 neuro-angiographic procedures over the five-year period (0.08%). No events occurred in 3,150 diagnostic angiograms while four occurred during 1,418 interventional procedures (0.2%). Two cases occurred during aneurysm coiling embolization (2/548; 0.4%); one case occurred during a carotid stent placement (1/138; 0.7%); one occurred during an internal carotid artery balloon occlusion test (1/73; 1.3%). Three of these complications resulted in permanent neurologic deficits while one resulted in a transient neurologic change that cleared within 60 min of onset. Sources for the emboli included the pressurized arterial flush lines connected to internal carotid artery catheters (three cases) and sudden hypotension with air subsequently entering the internal carotid artery catheter (one case). Two patients were treated with hyperbaric oxygen therapy.

CONCLUSION

Symptomatic cerebral air embolism is a rare event during neuro-angiographic procedures. Analysis of the etiologies of this infrequent event may permit us to further reduce its incidence.

Arterial line filters ranked for gaseous micro-emboli separation performance: an in vitro study

Arterial line filters (ALFs) are arguably the most important component in the cardiopulmonary bypass circuit to protect the patient from gaseous macro- and micro-emboli (GME) originating in the perfusion circuit. The GME separating ability of 10 ALFs was ranked according to seven performance criteria. Ten ALFs rated between 20 and 43 microm were evaluated for flow resistance, the count, size, and volume of GME passed after a 10-mL room air bolus, and the ability to separate a high-count, 10- to 200-microm flowing distribution of GME. The Luna Innovations EDAC emboli detector was used to size, count, and sort GME. Three test trials were conducted for 3 each of the 10 filters. Performance criteria were correlated by regression analysis, statistically compared using analysis of variance, or ranked using non-parametric tests. Significance was set at 0.05. Weighting all seven test parameters equally, the most effective ALFs were the Cobe 21 and Gish 25-microm filters. The Pall LG-6 ranked more efficient than the Medtronic 20 and Dideco 27-microm filters. The Cobe 43, Terumo 40, Medtronic 38, Terumo 37, and Gish 40-microm filters were less effective as a group compared with the other filters. For the 10 filters, blood flow resistance was not correlated to rated pore size. Generally, the smaller the pore rating, the higher the GME separation ability rank, except for the leuko-reduction filter, which performed more effectively than other large pore filters.

KEYWORDS

arterial line filter, gaseous microemboli, in vitro test.

[A complementary clinical method to minimize air embolism during open-heart surgery]

Air from the left heart is ejected even up to several hours after cardiopulmonary bypass (CPB) despite the use of CO2. The following method is complementary in addition to surgical de-airing in order to further reduce the chance of air embolism, especially from the pulmonary veins. After re-expanding the lungs with standard bag inflation, the ventilation is restarted in consultation with the surgeon. The ventilator is set to the respiratory minute volume used before the CPB but at a respiratory frequency of 10/minutes whereas the regularly beating heart is filled from the heart lung machine. Transoesophageal echocardiography (TEE) reliably controls the effect.

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.

Factors influencing neurologic outcome after neonatal cardiopulmonary bypass: what we can and cannot control

Advances in cardiopulmonary bypass and surgical techniques have led to progress in the early repair of congenital heart defects in children. However, as increasing numbers survive their initial cardiac operation, an awareness is emerging that significant early and late neurologic morbidities continue to complicate otherwise successful operative repairs. Adverse neurologic outcomes after neonatal cardiac surgery are multifactorial and relate to both fixed and modifiable mechanisms. The purpose of this review is to (1) review mechanisms of brain injury after neonatal cardiopulmonary bypass, (2) examine risk factors, and (3) speculate on how investigations may improve our understanding of neurologic injury.

Role of the reverse-Trendelenberg patient position in maintaining low-CVP anaesthesia during liver resections

BACKGROUND AND AIMS

The Trendelenberg position is recommended during liver resection, to decrease the risk of venous air embolism. However, this position raises the central venous pressure and may increase blood loss. We propose that the reverse-Trendelenberg position can be safely and effectively used to maintain a low central venous pressure during liver surgery.

MATERIALS AND METHODS

Fifty consecutive patients underwent elective liver resection at a single centre during a 17-month period. Patients were positioned with a head-up tilt during division of the liver parenchyma.

RESULTS

Patients had a mean central venous pressure of 9.2 mmHg when supine, despite fluid restriction. The central venous pressure fell consistently and rapidly when they were tilted head-up, to a mean of 1.7 mmHg. The resections were completed with a median operative blood loss of 600 mL. No patient developed a clinically apparent venous air embolism. Postoperative renal dysfunction that could be attributed to low central venous pressure anaesthesia occurred in only one case.

CONCLUSION

The reverse-Trendelenberg position effectively lowers the CVP during liver surgery. It is easy to monitor, titrate and reverse, and avoids the need for complex pharmacological interventions. We recommend this position to liver surgeons and anaesthetists who have found it difficult to maintain a low CVP with the supine or Trendelenberg positions.

Risks and benefits of patient positioning during neurosurgical care

Positioning of the surgical patient is an important part of anesthesia care and attention to the physical and physiologic consequences of positioning can help prevent serious adverse events and complications. The general principles of patient positioning of the anesthetized and awake neurosurgical patient are discussed in this article.

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.

Elective removal of cuffed central venous catheters in children

BACKGROUND

Subcutaneously tunneled, cuffed central venous catheters (CVCs) are commonly used in children undergoing cytotoxic chemotherapy or hematopoietic stem-cell transplantation. When their use is no longer indicated or precluded by mechanical or infectious complications, CVCs have to be removed. General instructions on how cuffed CVC should be removed are available in the medical texts but none is adapted for use in children.

MATERIALS AND METHODS

A literature search from the MEDLINE and EMBASE to identify articles describing the procedure of removing CVC or complications arising from the procedure was carried out.

RESULTS

Specific guidance on the removal of CVC in children was not found. Venous air embolism appeared to be the most common complication associated with catheter removal but none involved pediatric patients. On the other hand, three out of the five incidents of catheter fracture with or without embolization happened in children.

CONCLUSION

Further studies are needed to define the optimal management of CVC removal in pediatric patients. A sequence of positioning the child, use of sedation, dissecting out the cuff, pulling off the catheter, closing the exit wound, and handling of the removed catheter is suggested.

Clinical advantages of using mini-bypass systems in terms of blood product use, postoperative bleeding and air entrainment: an in vivo clinical perspective☆

OBJECTIVE

In an effort to minimize the effect of extracorporeal circulation (ECC), mini-bypass is gaining clinical acceptance in routine coronary artery bypass grafting (CABG). These small circuits target combine the clinical advantages of reduced prime, 100% bio-coating and suction blood separation. We demonstrate that the use of mini-bypass in routine CABG reduces homologous blood product use and postoperative bleeding. Our goal was to also demonstrate that these small systems are effective in gaseous microemboli (GME) management as compared to a conventional extracorporeal system.

METHODS

Prospective, randomized study comparing 30 mini-bypass (Dideco ECC.O) to 30 conventional systems (n=30, Dideco 903 Avant). Study included CABG cases only, independent of preoperative coagulative status; clinic ethical committee approval and informed patient consent was obtained before initiating study.

RESULTS

There were no statistical differences in terms of patient demographics. Statistically significant differences were seen in transfusion frequency (27% of the study group vs 43% in the control group, p=0.05), transfused volume (133.3+/-244.5 ml vs 325+/-483.1 ml, p<0.05), fresh frozen plasma (0 unit vs 3 units, p<0.001), postoperative bleeding (301.8+/-531.9 ml vs 785.5+/-1000.4 ml, p<0.05) and GME activity post-arterial filter (0.14 microl vs 5.32 microl, p<0.05).

CONCLUSIONS

The adoption of mini-bypass significantly potentially reduces hemodilution, donor blood usage, postoperative bleeding and exposure to GME in routine CABG patients as compared to the use of conventional extracorporeal circulation circuits.

Development of Air Micro Bubbles in the Venous Outlet Line: An In Vitro Analysis of Various Air Traps Used for Hemodialysis

Venous air traps were tested in vitro with respect to presence of micro bubbles. Three types of venous air traps were measured (Bioline, Bioline GmbH, Luckenwalde, Germany; Gambro, Gambro AB, Lund, Sweden; Fresenius M.C., Fresenius Medical Care AG & Co. KGaA, Bad Homburg, Germany). Measurements (n = 10) were taken for each air trap, fluid flow (50-600 mL/min), and fluid level (high/low). A 1.5-MHz ultrasound probe was used with an analysis device. The probe was mounted on the outlet line downstream of the venous air trap. A semisynthetic fluid was used to resemble blood viscosity. Occurrences of micro bubbles, without inducing an alarm of the dialysis device, were detected in almost all measurements. The amount of bubbles increased with increasing flow. There were more bubbles with low fluid level compared with high level. The Bioline tubing released the least bubbles in high fluid level. At low level, the Gambro tubing showed the least bubbles at flows 50-400 mL/min, and the Fresenius M.C. tubing showed the least bubbles at flows 400-600 mL/min. High fluid level in the air trap reduced generation of micro bubbles compared to low level, as did lower fluid flow versus high flow. The design of the air trap was also of importance.

Recompression during decompression and effects on bubble formation in the pig

INTRODUCTION

There is a relationship between gas bubble formation in the vascular system and serious decompression sickness. Hence, control of the formation of vascular bubbles should allow safer decompression procedures.

METHODS

There were 12 pigs that were randomly divided into an experimental group (EXP) and a control group (CTR) of 6 animals each. The pigs were compressed to 500 kPa (5 ATA) in a dry hyperbaric chamber and held for 90 min bottom time breathing air. CTR animals were decompressed according to a modified USN dive profile requiring four stops. EXP followed the same profile except that a 5-min recompression of 50 kPa (0.5 ATA) was added at the end of each of the last three decompression stops before ascending to the next stop depth.

RESULTS

All CTR animals developed bubbles, compared with only one animal in EXP. The number of bubbles detected during and after the dive was 0.02 +/- 0.02 bubbles x cm(-2) in CTR, while the number of bubbles detected in EXP were 0.0009 +/- 0.005 bubbles x cm(-2); the difference was highly significant.

CONCLUSION

By brief recompression during late decompression stops, the amount of bubbles was reduced. Our findings give further support for a gas phase model of decompression.

Preventing iatrogenic air embolism in the intensive care unit

Air embolism is a potentially fatal consequence of incorrect connection of endotracheal tube cuff inflator devices. Currently, air lines from these devices can be connected to indwelling cannulae without impediment. This possibility can be eliminated with a simple modification of the air line, as described here.