A New Minimized Perfusion Circuit Provides Highly Effective Ultrasound Controlled Deairing

Minimized perfusion circuits (MPCs) have been criticized for insufficient air elimination. The deairing capabilities of a new MPC, including an ultrasound controlled deairing unit, were compared to a standard extracorporeal circuit (ECC) in a laboratory setup. During blood flow of 4.0l/min, we injected 30-cc air over a period of 30 s into the venous line of both systems (n = 10 measurements/15-min intervals). Air was detected during the first 2 min post injection using a dual-channel ultrasound bubble counter. Venous air bubble measurements were made after the MPC bubble trap and the ECC hard-shell reservoir, respectively. Arterial air bubble data were obtained after the arterial filters (40 microm). Venous bubble count was significantly (P < 0.01) reduced in the MPC group (5-250 microm, 681 +/- 177; >40 microm, 288 +/- 92) compared with the ECC group (5-250 microm, 19 272 +/- 682; >40 microm, 7642 +/- 520). After the arterial filter, minimal numbers of air bubbles (5-250 microm, 172 +/- 59; >40 microm, 0) could be detected in the MPC group, but large amounts of air (5-250 microm, 16 194 +/- 1072; >40 microm, 3732 +/- 997) were measured in the ECC group. The air elimination of the modern MPC is superior to conventional ECC, which may result in a reduction of neurological complications.

Gaseous and solid cerebral microembolization during proximal aortic anastomoses in off-pump coronary surgery: the effect of an aortic side-biting clamp and two clampless devices

OBJECTIVES

Intraoperative cerebral microembolism is a cause of cerebral dysfunction after cardiac surgery, and particulate microemboli are the most damaging. Using a new-generation transcranial Doppler ultrasound, we compared the number and nature of microemboli in patients undergoing off-pump coronary artery bypass grafting during performance of proximal anastomoses with three techniques: an aortic side-biting clamp and two clampless devices (the Enclose II device [Novare Surgical Systems, Inc, Cupertino, Calif] and the Heartstring II device [Guidant Corporation, Santa Clara, Calif]) developed to obviate the need for an aortic side-biting clamp, thereby reducing the number of cerebral microemboli.

METHODS

Bilateral continuous monitoring of the middle cerebral arteries was performed with a multirange, multifrequency transcranial Doppler device that both automatically rejects artifacts online and discriminates between solid and gaseous microemboli. Recordings were continuously undertaken during performance of 66 proximal aortic anastomoses in 42 patients. Thirty-five anastomoses were performed with an aortic side-biting clamp, 20 with the Enclose device, and 11 the Hearstring device.

RESULTS

Most microemboli occurred during application/insertion and removal of each device from the ascending aorta. The median number (interquartile range) of total microemboli was 11 (6-32) during side clamping, 11 (6-15) with the Enclose device, 40 (31-48) with the Heartstring device (P < .01). The proportion of solid microemboli was significantly higher in the side-clamp group (23%) compared with 6% and 1% in the Enclose and Heartstring groups, respectively (P < .01).

CONCLUSIONS

Avoidance of aortic side clamping results in a significant reduction in the proportion of solid microemboli detected with transcranial Doppler. As solid microemboli are probably the most damaging, use of the Enclose and Heartstring devices may represent an important strategy for minimizing cerebral injury during proximal aortic anastomoses.

Diagnosis and treatment of vascular air embolism

Vascular air embolism is a potentially life-threatening event that is now encountered routinely in the operating room and other patient care areas. The circumstances under which physicians and nurses may encounter air embolism are no longer limited to neurosurgical procedures conducted in the "sitting position" and occur in such diverse areas as the interventional radiology suite or laparoscopic surgical center. Advances in monitoring devices coupled with an understanding of the pathophysiology of vascular air embolism will enable the physician to successfully manage these potentially challenging clinical scenarios. A comprehensive review of the etiology and diagnosis of vascular air embolism, including approaches to prevention and management based on experimental and clinical data, is presented. This compendium of information will permit the healthcare professional to rapidly assess the relative risk of vascular air embolism and implement monitoring and treatment strategies appropriate for the planned invasive procedure.

Gas embolism and surfactant-based intervention: implications for long-duration space-based activity

Intravascular gas embolism can occur with decompression in space flight, and it commonly occurs during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. Surfactant-based intervention is a novel treatment for gas embolism. Intravascular surfactant can adsorb onto the gas-liquid interface and compete with blood-borne macromolecules for interfacial occupancy. Surfactants can retard the progress of pathophysiological molecular and cellular events stimulated by the bubble surface, including endothelial cell injury and initiation of blood clotting. Bulk and surface transport of a surfactant to provide competition for interfacial occupancy is a therapeutic strategy because surfactant adsorption can dominate protein (or other macromolecule) adsorption. The presence of surfactant along the gas-liquid interface also induces variation in the interfacial tension, which in turn affects the blood flow and the bubble motion. We describe the interplay between biological transport processes and physiological events occurring and the cellular and molecular level in vascular gas embolization. Special consideration is given to modeling the transport and hydrodynamic interactions associated with surfactant-based intervention.

Air Bubbles Pass the Security System of the Dialysis Device Without Alarming

During hemodialysis microembolic findings have been noted after the venous chamber (subclavian vein). The aim of this study was to evaluate if air could pass the venous chamber and, if so, if it passes the safety-system detector for air-infusion without triggering an alarm. Various in vitro dialysis settings were performed using regular dialysis devices. A dextran fluid was used instead of blood to avoid the risk of development of emboli. Optical visualization as well as recirculation and collection of eventual air into an intermediate bag were investigated. In addition, a specifically designed ultrasound monitor was placed after the venous air trap to measure the presence of eventual microbubbles. Speed of dialysis fluid was changed, as was the level of the fluid in the air trap. Thereby a fluid level was considered "high" if it was close to the top of the air trap and "low" if it was around the mid part of the air trap. By optical vision microbubbles were seen at the bottom of the air trap and could pass the air trap towards the venous line without alarming. During recirculation several mL of air were collected in an intermediate bag after the venous line. Ultrasound monitoring exhibited the presence of microbubbles of the size of approximately 5 microm upwards passing to the venous line in all runs performed. Amount of bubbles differed between devices and in general an increased fluid speed correlated significantly with the increased counts of microbubbles/min. No alarming of the detector occurred. A more concentrated fluid allowed higher counts/min when flow was increased to 600 mL/min. Data revealed that air passes the safety-sensor in the air trap without alarming. The presence of air increased in general with fluid speed and a lower fluid level in the air trap. Differences were present between devices. If this affects the patients has to be elucidated.

The Sensor in the Venous Chamber Does Not Prevent Passage of Air Bubbles During Hemodialysis

We previously showed, in vitro, that micro bubbles pass the air trap without inducing an alarm. The aim was to investigate if micro bubbles bypass the detector during hemodialysis (HD). During HD (40 patients, 47 HD sessions, 231 measurements), an ultrasound detector was fixed just after the venous air trap. Micro bubble size was measured in the range from 5 microm up to >42.5 microm. Blood flow was at a mean 346 mL/min (SD +/- 57). The mean of all micro bubbles per minute, without inducing an alarm, was at start 128 (range 0-769). Measurements revealed the presence of micro bubbles in all of the series and in 90% of the measurements. There was no difference between start and end of the same dialyses. There was a correlation between blood flow and extent of micro bubbles for the smaller sizes and the sum of all bubbles (r > or = 0.29, P < or = 0.026). Micro bubbles passed the air trap without alarming. Most bubbles were approximately 5 microm.

Laparoscopic parenchymal division of the liver in a porcine model: comparison of the efficacy and safety of three different techniques

BACKGROUND

Bleeding is a known and CO2 embolization a suggested risk factor for increased morbidity after laparoscopic liver resection. Devices for laparoscopic liver parenchymal transection must be evaluated for safety in this context.

METHOD

Twelve piglets underwent laparoscopic surgery during CO2 pneumoperitoneum, each animal receiving three 6 cm long transections into the liver parenchyma made with ultrasonic dissector, ultrasonic shears and vessel sealing system, respectively. Endpoints were bleeding, operation time and gas embolization. The transections and embolization events, evaluated with transesophageal echocardiography, were video recorded. Bleeding and embolization were also assessed on video tapes and operating time measured. Arterial blood gases were recorded on line.

RESULTS

The ultrasonic dissector was least advantageous in terms of bleeding and operation time. Gas embolization was more frequent with the vessel sealing system than with the ultrasonic dissector and ultrasonic shears. During two episodes of gas embolization, pCO2 increased and pO2 and pH decreased.

CONCLUSIONS

Use of all three devices is feasible. Bleeding and operation time are greatest with the ultrasonic dissector. Gas embolization occurs during transection, though in most instances it is completely harmless. Laparoscopic liver surgery with these techniques used may pose a risk of gas embolization with clinical implications. Monitoring for such events is probably to be recommended.

Dynamic bubble trap can replace an arterial filter during cardiopulmonary bypass surgery

Objective: The arterial filter (AF) and the dynamic bubble trap (DBT) reduce the number of air microbubbles passing through these devices. The aim of the study was to confirm that the DBT diminishes microbubbles in the arterial line similar to, or better than, the AF, and can replace it.

Methods: In a clinical study, we evaluated 60 patients undergoing cardiopulmonary bypass surgery, divided into two groups (30 patients each). In the first group, we used an open extracorporeal system, and in the second group, a closed system. For 15 patients in each group, the AF was incorporated, the other 15 patients received the DBT. The microbubbles were counted before and after the AF or DBT, using two-channel-ultrasonic Doppler devices.

Results: The exposure of patients to small bubbles (<45μm) is significantly higher in the AF than in the DBT group. The DBT reduces large bubbles (<45μm) better than the AF, with a rate exceeding 16%.

Conclusion: The use of the DBT instead of the AF yields higher air micro-bubble removal efficacy, allowing replacement of the AF, assuming the AF is used for air removal purpose only.

[Cerebral gas embolism secondary to withdrawal of a central venous line]

AIM

To report a case of cerebral gas embolism secondary to the withdrawal of a central venous line in a patient who had recently undergone abdominal surgery.

CASE REPORT

An 82-year-old male who suddenly presented myoclonias in the right upper extremity and a sharp drop in the level of consciousness. A computerised tomography (CT) scan revealed air bubbles in the intracranial circulatory system and associated infarction in the right hemisphere. The patient's clinical progression was poor and he died some days later.

CONCLUSIONS

Cerebral gas embolism can be diagnosed using a CT scan of the head if it is performed immediately after the entrance of air into the bloodstream inside the brain. In later phases, findings are unspecific and difficult to distinguish from ischaemic infarction or from diffuse leukoencephalopathy. Treatment is based on supportive measures and, in some cases, hyperbaric oxygen, although their true effectiveness is a controversial issue. Cerebral gas embolism is a potentially fatal and avoidable complication in patients with a central venous line or other iatrogenic procedures that can allow air to enter the arterial or venous circulatory systems.

Reduction in Air Bubble Size Using Perfluorocarbons During Cardiopulmonary Bypass in the Rat

BACKGROUND

Perfluorocarbon (PFC) emulsions are artificial oxygen-carrying compounds with a high solubility for gases that have experimentally been shown to ameliorate cerebral air embolism. Cerebral air embolism has been associated with adverse cerebral outcomes after cardiac surgery using cardiopulmonary bypass (CPB). We designed this study to test whether PFC emulsions could reduce the volume of bubbles within the CPB circuit.

METHODS

Male Sprague-Dawley rats undergoing 60 min of normothermic nonpulsatile CPB were randomized to one of the three groups. The PFC group (n = 10) received 60% O(2)/36% N(2)/4% CO(2) via the membrane oxygenator and 2.7 g/kg (4.5 mL/kg) of PFC into the venous reservoir; the control group (n = 10) received the same gas mixture and 4.5 mL/kg of saline; the N(2)O group (n = 6) was exposed to 36% N(2)O/60% O(2)/4% CO(2) and received 4.5 mL/kg of saline. After 10 min and 35 min of CPB, 400 microL of air was injected into a bubble chamber in the CPB circuit. After 20 min, the bubble was removed for volumetric analysis.

RESULTS

Compared with baseline, the bubble decreased 13% +/- 5% in size in the PFC group and increased 46% +/- 9% in the nitrous oxide group, both of these changes significantly different from the control group (P < 0.0001).

CONCLUSION

The results suggest that PFC administration may be useful in reducing the volume of gaseous bubbles present during CPB.

The Jena universal perfusion system: a universal cardiopulmonary bypass circuit for cardiac surgery

Cardiopulmonary bypass (CPB) is a standard technique in cardiac surgery, which itself contributes to postoperative morbidity. Neurologic sequelae after CPB is caused by air embolism or systemic inflammatory response due to artificial surface and is closely related to the characteristics of the extracorporeal circuit. Minimized systems without a venous reservoir take these factors into account. They require a differentiated volume management to avoid excessive negative pressure in the venous line, which may lead to spontaneous formation of microbubbles and are said to cause air embolism. Perfusion technology also offers systems with closed soft-bag and open hard-shell reservoirs, that require individual setups with little flexibility. We developed an all-purpose perfusion system for application as cardiopulmonary bypass. The central part is a compound reservoir, consisting of a lower hard shell and an upper self-expanding shell, which is capable of actively increasing volume. It allows application of the circuit as closed or open system. Crossclamping the inflow turns the system into a minimized circuit, in which the reservoir compensates volume when backflow is low and safeguards against excessive subzero pressure. The system has been applied in pilot experiments. In cardiac surgery today patients present at higher ages and with complex comorbidities. Not all of them are suitable candidates for off-pump procedures and might profit from perfusion technology with reduced adverse effects. The Jena Universal Perfusion System (JUPS) may be applied as a minimized system with the option to compensate low venous backflow and allows flexible extension to a closed or open circuit anytime during the procedure.

First Clinical Experience With the Air Purge Control and Electrical Remote-controlled Tubing Clamp in Mini Bypass

Most mini bypass systems do not contain a venous and cardiotomy reservoir in the cardiopulmonary bypass (CPB) circuit and lack the capability to remove venous air. In conjunction with the manufacturer the air purge control system, a system which automatically removes air that is captured in a venous bubble trap, has been developed. This system is combined with an electrical remote clamp, which automatically clamps the arterial line in case air leaves the bubble trap. Twenty consecutive patients undergoing surgery with CPB were included in this clinical validation. Venous air was removed by the air purge control during bypass. The electrical remote clamp was never activated by the system, confirming that the air purge control adequately removed venous air during these cases. The air purge control, in conjunction with the electrical remote clamp, is a valuable safety feature in mini bypass, enhancing patient safety and user friendliness while providing a level of safety equivalent to those of conventional bypass systems.

The safe removal of central venous catheters

Many nurses working in general wards and departments are caring for patients with central venous catheters and are increasingly responsible for their removal. This article outlines the basis of good practice and the possible complications, focusing on air embolism.

Using HFMEA to Assess Potential for Patient Harm from Tubing Misconnections

BACKGROUND

Reported cases of tubing misconnections and other tubing errors prompted Columbus Children's Hospital to study their potential for harm in its patient population. A Health Failure Mode and Effects Analysis (HFMEA) was conducted in October 2004 to determine the risks inherent in the use and labeling of various enteral, parenteral, and other tubing types in patient care and the potential for patient harm.

METHODS

An assessment of the practice culture revealed considerable variability among nurses and respiratory therapists within and between units. Work on an HFMEA culminated in recommendations of risk reduction strategies. These included standardizing the process of labeling of tubing throughout the organization, developing an online pictorial catalog to list available tubing supplies with all aliases used by staff, and conducting an inventory of all supplies to identify products that need to be purchased or discontinued. Three groups are working on implementing each of the recommendations.

RESULTS

Most of the results already realized occurred in labeling of tubing. The pediatric intensive care unit labels all tubing with infused medications 85% of the time; tubings inserted during surgery or in interventional radiology are labeled 53% and 93% of the time. Pocket-size cards with printed labels were tested in three units.

DISCUSSION

This proactive risk assessment project has identified failure modes and possible causes and solutions; several recommendations have been implemented. No tubing misconnections have been reported.

Aerostasis during Central Venous Access: Updates in Protective Sheaths

PURPOSE

Air emboli (AE) complicating central venous catheter (CVC) placement are rare but potentially fatal events. Building on earlier experience, the authors conducted in vitro testing of the aerostatic properties of newly designed protective sheaths.

MATERIALS AND METHODS

The standard peel-away sheath, the previously studied sliding-valve sheath, and newer fixed-valve and double-valved sheaths were evaluated. Aerostatic stability of the sheaths was evaluated by measuring air flow into the model under standard and stressed conditions. In addition, volumes of AE created during simulated CVC insertion through the sheaths were determined.

RESULTS

Under physiologic conditions, significantly smaller volumes of AE occurred with a pinch 2 inches from the sheath hub relative to a pinch at 1 inch. Sliding-, fixed-, and double-valve sheaths yielded leak rates of 0.05 +/- 0.05 mL/sec, 0.06 +/- 0.05 mL/sec, and 0.08 +/- 0.07 mL/sec, respectively. Under stress, protective sheath leak rates increased to 1.8 +/- 0.4 mL/sec, 1.6 +/- 0.5 mL/sec, and 1.8 +/- 0.4 mL/sec, respectively. Use of a double-valved sheath demonstrated no significant difference in leak rates under standard and stressed conditions. In most cases, protective sheaths yielded significantly smaller AE than control sheaths. In comparison of protective sheaths, AE volumes during CVC insertion for sliding-, fixed-, and double-valved sheaths were 22.8 +/- 4.5 mL, 16.6 +/- 7.3 mL, and 10.8 +/- 4.5 mL, respectively. Double-valved sheaths yielded significantly smaller AE volumes than did sliding-valve sheaths (P < .01).

CONCLUSIONS

In most standard situations, AE volumes and aerostatic stability of protective sheaths tested favorably in comparison with control sheaths. When some sheaths were stressed, their aerostatic properties failed. In a comparison of the three protective sheaths in standard and stressed conditions, the double-valved sheath fared better than the sliding and fixed-valve sheaths.

Flooding the surgical field with carbon dioxide during open heart surgery improves segmental wall motion

Air embolization to the coronary arteries is a common cause of myocardial ischemia during open heart surgery. Carbon dioxide emboli may be absorbed faster than air emboli. In this randomized, double blind, placebo-controlled trial, we determined that flooding the surgical field with carbon dioxide is associated with improved myocardial function assessed by transesophageal echocardiography. Forty-three valve surgeries were randomized to insufflation of 6 L/min of carbon dioxide or placebo through a Jackson Pratt drain into the pericardium during cardiopulmonary bypass. During rewarming, as pulse pressure rose above 10 mmHg, two observers graded severity of bubbles in the left heart. Two other observers evaluated wall motion in the transgastric midpapillary short axis view of the left ventricle using transesophageal echocardiography. Compared with baseline average scores among all walls (carbon dioxide, 1.42 +/- 0.46; placebo, 1.39 +/- 0.45), worsening of wall motion was less at 1 minute in the carbon dioxide (1.60 +/- 0.62) than in the placebo group (1.95 +/- 0.54; p = 0.0266). Better wall motion tended to persist in the carbon dioxide group at 10 (1.58 +/- 0.59 vs. 1.77 +/- 0.6) and 60 minutes (1.61 +/- 0.45 vs. 1.66 +/- 0.58). Particularly, the inferior wall tended toward transiently better function in the carbon dioxide group (at baseline and 1, 10, and 60 minutes: placebo, 1.62 +/- 0.72, 2.68 +/- 0.79, 2.48 +/- 0.95, 2.10 +/- 0.9 vs. 1.88 +/- 0.97, 2.33 +/- 1.1, 2.18 +/- 0.96, 2.20 +/- 0.94). Preoperative characteristics, length of bypass, anesthesia time, hospitalization, and intensive care unit stay were not different. We recommend administration of carbon dioxide because it may improve myocardial function. We describe how to avoid adverse effects of giving carbon dioxide by filtering the supply, continuously managing its level during bypass, increasing sweep speeds, continuously analyzing the in-line blood gas, and avoiding suctioning gases in the field into the cardiotomy reservoir.

Reduction of carbon dioxide embolism for endoscopic saphenous vein harvesting

BACKGROUND

The endoscopic saphenous vein harvesting (EVH) introduced in coronary artery bypass surgery (CABG) is associated with less wound complication and postoperative pain. Carbon dioxide (CO2) insufflation is used during EVH to facilitate the procedure. The purpose of this study was to determine whether the incidence of CO2 embolism during EVH with CO2 insufflation could be reduced with lower CO2 insufflation pressure.

METHODS

Four hundred and ninety-eight consecutive patients scheduled for elective off-pump CABG were prospectively studied. These patients were randomly assigned into high and low groups in which 15 and 12 mm Hg CO2 insufflation pressures were used during EVH, respectively. Multiplane transesophageal echocardiography (TEE) with transgastric inferior vena cava view was used to monitor the appearances of CO2 bubbles. If a burst of many CO2 bubbles were found by TEE, the CO2 insufflation would be stopped until detailed examination of the operative field.

RESULTS

The incidence of CO2 embolisms in the high group of patients (13.3%) was significantly higher than that in the low group (6.5%, p < 0.05). Two episodes of emergent cessation of CO2 insufflation occurred in the high group of patients. No massive CO2 embolism with significant hemodynamic alterations occurred in either group.

CONCLUSIONS

The incidence of CO2 embolisms during EVH could be reduced with lower CO2 insufflation pressure, which, in combination with increased surgical experience and continuous TEE monitoring of the inferior vena cava, helps to reduce the risks of massive CO2 embolism.

Precordial Doppler Probe Placement for Optimal Detection of Venous Air Embolism During Craniotomy

Verification of appropriate precordial Doppler probe position over the anterior chest wall is crucial for early detection of venous air embolism. We studied responses to normal saline (NS) and carbon dioxide (CO2) test injections at various probe locations during elective craniotomy. All patients received four IV injections (10 mL of NS and 1 mL of CO2 via central and peripheral venous catheters). Doppler sounds were simultaneously recorded with two separate probes. In Group A, probes were placed in left and right parasternal positions. In Group B, the left probe was intentionally malpositioned as far laterally over the left precordium as was compatible with an audible signal. In Group A (n = 23), a left parasternal Doppler signal was easily obtainable in 23 of 23 patients, versus 18 of 23 patients for the right parasternal probe (P < 0.05). In Group B (n = 17), central CO2 injection yielded a positive right parasternal response rate of 88% compared with 29% over the far left precordium (P < 0.015), where central NS injections yielded a 76% response rate (P < 0.015 versus central CO2 injection). Left parasternal placement is at least as sensitive to clinical venous air embolism events as right parasternal placement. Peripheral saline injection represents a viable alternative (83% response rate). Vigorous central injection of 10 mL of NS however, risks false positive verification of left lateral precordial probe placement.

Deairing of the venous drainage in standard extracorporeal circulation results in a profound reduction of arterial micro bubbles

OBJECTIVE

Standard extracorporeal circulation (ECC) remains the staple procedure for cardiac surgeons. Despite modern membrane oxygenators and arterial filters micro bubbles are regularly detected in the arterial line. We investigated whether initial deairing of the venous drainage during connection can reduce the quantity and size of micro bubbles on the arterial side.

METHODS

12 patients underwent isolated coronary artery revascularization with conventional ECC using a two-stage venous catheter and an open, passive venous return into a reservoir. In 6 patients (Control) the venous catheter was routinely connected to the venous line, thereby accepting moderate incorporation of air. In another 6 patients (deaired) the catheter was connected avoiding any visible air entrapment. A bubble counter was used to detect the number and size of any micro bubbles in the arterial line of the ECC. The total number of bubbles as well as the number of bubbles of different sizes was assessed directly after initiation of ECC and during the first 60 sec.

RESULTS

All patients had an uneventful surgery with a normal postoperative course. In the Control group a considerable number of bubbles of all sizes occurred initially and after 60 sec. In contrast, very few bubbles were detected in the deaired group.

CONCLUSION

Incorporated venous air inevitably reaches the arterial side of the ECC. As deairing of the venous line is a simple and effective manoeuvre to significantly reduce the amount of micro bubbles on the arterial side, we recommend and perform routine deairing in all our patients.

[The use of tissue glue and its effect on hospital cost in patients undergoing pulmonary surgery]

Prolonged air leak following pulmonary resections is an important cause of morbidity and increased hospital costs. We compared 19 homologous/autologous tissue glue (fibrin glue) applied patients (FG group), 12 beriplast-P applied patients (beriplast group) and 27 control patients with respect to prolonged air leak, chest tube removal time and hospital costs. The mean ages for FG group (19 patients), beriplast group (12 patients) and control group (27 patients) were 48.5 +/- 14, 50.5 +/- 6.8 and 55 +/- 12.9 respectively. The groups were comparable with respect to age (p= 0.210), sex (p= 0.287) and the surgical procedure performed (p= 0.289). The incidence of prolonged air leak in FG group, beriplast group and the control group was 48%, 50% and 63%, respectively (p= 0.533). The mean chest tube removal time in FG group, beriplast group and the control group was 10.7 +/- 8.7, 9 +/- 4.1 and 8 +/- 3.1 days, respectively (p= 0.282). Mean hospital costs in FG group, beriplast group and the control group were 4633 +/- 3272 YTL, 4611 +/- 1583 YTL and 4015 +/- 911 YTL, respectively (p= 0.547). Fibrin glue had no effect on the incidence of prolonged air leak, chest tube removal time and hospital costs.

Air Detection Performance of the Level 1 H-1200 Fluid and Blood Warmer

We evaluated the Level 1 H-1200 fluid warmer during simulated conditions of minor to massive air embolism. The fluids we tested were crystalloid and diluted red cells (estimated hematocrit 50%) during gravity and pressure driven flow. The air volumes tested ranged from 1-60 mL for crystalloid and 30-150 mL for red cells. No air was observed distal to the air detector and clamp during all test conditions. The device consistently alarmed and automatically shut off flow. Air was easily purged through the gas vent-filter assembly during simulated air embolism with crystalloid but not with red cell infusion. The use of ultrasonic air detection coupled with automatic shutoff is a significant safety improvement of the Level 1 H-1200 fluid and blood warmer.

Bench-Top Evaluation of Air Flow through a Valved Peelable Introducer Sheath

PURPOSE

Air embolism is a rare but potentially fatal complication that may occur during the insertion of a central venous catheter. A valved peelable introducer sheath was developed to reduce the likelihood of an air embolus. This study was performed to determine the rate of air flow through this valved introducer sheath under different conditions that may be encountered in a clinical setting.

MATERIALS AND METHODS

A 16-F-diameter valved peelable introducer sheath was used for all experiments. A bench-top testing system was constructed that consisted of a vacuum source, a mass flow meter, and a digital vacuum gauge. A coupling device with a pneumatic O-ring was used to seal and connect the distal end of the introducer sheath to the testing system. A vacuum of -5 mm Hg was applied to the sealed distal end of the sheath to simulate physiologic conditions. The rate of air flow through the valved sheath was measured under three different conditions; (i) valve open, (ii) valve closed, and (iii) valve open but with the sheath manually pinched. Thirty air flow measurements were performed for each of the three test conditions.

RESULTS

When the valve was in the open position, the mean rate of air flow through the introducer sheath was 417.2 mL/sec (range, 415.5-419.7 mL/sec). When the valve was in the closed position, the mean rate of air flow was 0.004 mL/sec (range, 0.000-0.067 mL/sec). When the valve was open but the sheath was manually pinched, the mean rate of air flow through the sheath was 31.7 mL/sec (range, 23.0-38.8 mL/sec). During the 90 testing procedures, the mean vacuum was -5.10 mm Hg (range, -5.00 to -5.45 mm Hg).

CONCLUSIONS

This bench-top study revealed that a massive amount of air flowed through the open 16-F introducer sheath when it was subjected to a vacuum of -5 mm Hg, a situation that may occur under normal physiologic conditions. The rate of air flow could be decreased by aggressively pinching the sheath but the rate of air flow was still substantial. This study demonstrated that the addition of a sophisticated valve mechanism can essentially eliminate air flow through a peelable introducer sheath.

Measurement of Air Emboli during Central Venous Access: Do “Protective” Sheaths or Insertion Techniques Matter?

PURPOSE

Clinically significant air emboli during placement of central venous catheters are rare yet potentially fatal events. An in vitro model was developed to measure the volume of air emboli during catheter placement under a variety of experimental conditions.

MATERIALS AND METHODS

The volume of air emboli during catheter insertion with use of a standard sheath was measured using "open," "finger-pinch," and "hemostat" techniques. Corresponding experiments were performed with newly designed protective sheaths. Additional experiments evaluated the air emboli related to specific steps of catheter insertion, a sheathless insertion technique, and two commonly used dialysis catheters.

RESULTS

Under physiologic conditions, the volumes of air emboli were 9.1 mL +/- 3.6, 8.6 mL +/- 3.9, and 10.0 mL +/- 4.1 for dialysis catheter insertions with open, finger-pinch, and hemostat techniques, respectively. In the open and closed positions, the sliding-valve protective sheath yielded 5.8 mL +/- 2.3 and 4.4 mL +/- 2.3 of air emboli, respectively, and the slide-clamp protective sheath yielded 5.6 mL +/- 2.0 and 5.4 mL +/- 2.1 of air emboli, respectively. The standard sheath demonstrated air emboli volumes of 14.4 mL +/- 12.8, 17.3 mL +/- 3.9, and 32.3 mL +/- 10.9 during cumulative steps of catheter insertion. The sliding-valve and slide-clamp protective sheaths yielded air emboli measuring 4.4 mL +/- 2.0, 10.9 mL +/- 5.2, and 8.6 mL +/- 1.5, and 4.4 mL +/- 1.8, 10.9 mL +/- 1.4, and 9.4 mL +/- 4.0, respectively. The sheathless insertion technique resulted in air emboli measuring 12.2 mL +/- 5.4. Split-tip and step-tip catheters resulted in air emboli volumes of 16.1 mL +/- 4.5 and 15.3 mL +/- 7.6, respectively, in the open position and 11.3 mL +/- 3.1 and 12.9 mL +/- 5.0, respectively, in the closed position.

CONCLUSIONS

The newly designed protective sheaths result in smaller volumes of air emboli compared with standard sheaths in most situations evaluated. There was no significant difference in the volume of air emboli with use of protective clinical maneuvers. In some cases, the volume of the air emboli continued to increase during catheter insertion and sheath removal. There was no statistically significant difference between the use of protective sheaths and the use of the sheathless insertion technique.

[Application of dynamic bubble trap in coronary artery bypass with cardiopulmonary bypass: an initial study]

OBJECTIVE

To investigate the effectiveness of dynamic bubble trap (DBT) on air microbubble elimination from both the cardiopulmonary bypass (CPB) circuit and middle cerebral arteries, and evaluate its possible impact on blood cells and coagulatory function.

METHODS

Twenty patients undergoing coronary artery bypass graft (CABG), 12 males and 8 females, with similar perioperative data were assigned randomly to DBT group and control group. Each CABG was finished with identical circuit sets except the integration of a DBT between the arterial filtrator and the aortic cannula in the DBT group. Air microbubbles were detected before and after the integration of DBT with ultrasonographic detector and microembolism signals (MES) in middle cerebral arteries were counted by transcranial Doppler (TCD). Plasma free hemoglobin (PFH), lactate dehydrogenase (LDH), fibrinogen, platelet count, coagulation factor II and anti-thrombin III (ATIII) were also assayed respectively before the operation, at the termination of CPB, and 6 hours after the operation.

RESULTS

In the DBT group the microbubbles of different size could be expelled significantly with the clearance rates between 68% - 74% (10 - 120 microm bubbles), 79% - 81% (20 - 120 microm bubbles), and 88% - 96% (40 - 120 microm bubbles). During the total CPB phase, the mean number of MES reached 197 +/- 137 in the control group and 158 +/- 178 in the DBT group, without a significant difference between these 2 groups. The PFH and LDH levels raised while the platelet count, fibrinogen level, and coagulation factor II and AT III activities decreased sharply after CPB in these 2 groups, however without significant differences in these parameters between the two groups.

CONCLUSION

DBT integration into the CPB circuit enhances neither blood cell damage nor coagulation disturbance. DBT effectively eliminates air microbubbles in arterial conduit; however, its microembolus elimination function is prone to die down during the total period of CPB.

The effectiveness of low-prime cardiopulmonary bypass circuits at removing gaseous emboli

During extracorporeal circulation, the patient's blood is siphoned into the extracorporeal circuit (ECC) by gravity or may be assisted kinetically or by vacuum. In all instances, negative pressure is generated in the venous line, which can cause entrainment of air into the ECC at the cannulation site. The typical ECC uses a venous reservoir, membrane oxygenator, and arterial line filter, which together aid in removal of air that has entered the venous line and minimize the transmission of gaseous microemboli to the patient. Recently, several manufacturers have introduced low prime ECCs with component configurations that differ from conventional ECCs, including the omission of a venous reservoir. These configuration changes may change the ability of the circuit to handle air and therefore their ability to minimize gaseous microemboli. The purpose of this study was to test the ability of new low prime ECCs to remove air introduced into the venous line and minimize gaseous microemboli from entering the patient's circulation. Using a model of CPB, air was introduced into the venous line of a low prime ECC and a conventional CPB circuit. The detection of the gaseous microemboli produced was monitored distal to the oxygenator by an ultrasonic emboli detector to determine if venous air was able to traverse the ECC at varying rates of air introduction and blood flow. Data was collected using data acquisition software loaded on a personal computer. Gaseous microemboli levels detected in the arterial line of the low prime ECC were 8 to 10 times higher than the microemboli levels detected in the conventional ECC at all blood flow rates. Every effort should be made to minimize and prevent air from being entrained in the venous line of a low prime CPB circuit to minimize the risk of arterial gaseous microemboli generation.

Treatment of Severe Pulmonary Hemorrhage After Cardiopulmonary Bypass by Selective, Temporary Balloon Occlusion

Severe pulmonary bleeding causes frequent mortality, particularly if this event occurs during separation from extracorporeal circulation during cardiac surgery. We present a new approach to treat this life-threatening complication: temporary balloon occlusion of the pulmonary artery feeding the involved lobe. On attempting to wean a 71-yr-old female patient from cardiopulmonary bypass after aortic valve replacement, she lost more than 2 L of blood through her trachea over approximately 15 min and severe gas embolism into the left atrium was visualized on transesophageal echocardiography. As the bleeding was too vigorous to be localized by fiberoptic bronchoscopy, an interventional cardiologist was consulted. After localizing the affected lobe using fluoroscopy, he inflated a balloon dilating catheter in the lower lobe artery. This effectively stopped the bleeding. Separation from extracorporeal circulation was uneventful using one-lung ventilation to prevent further gas embolism. Sixteen hours after the end of surgery the catheter could be deflated and removed without any further intervention. The patient made an excellent recovery.

Management of continuous venous gas emboli during extracorporeal life support utilizing the Kolobow gas trap

Extracorporeal life support (ECLS) with a roller pump system uses a closed cardiopulmonary bypass (CPB) circuit not equipped with a venous reservoir. Hence, gas emboli cannot escape the ECLS circuit, predisposing to clot formation, membrane failure and potential gas embolism. Rarely, some patients may develop a continuous release of gas into the venous circulation from multiple sources. Two pediatric ECLS cases are presented with continuous venous gas embolism. A 'gas trap' was devised by creating a column of fluid erected vertically on the venous line. This allowed gas to rise within the column, separating it from the ECLS circuit, thus, preventing gas from lodging in the membrane.

Heparin and air filters reduce embolic events caused by intra-arterial cerebral angiography: a prospective, randomized trial

BACKGROUND

Intra-arterial cerebral angiography is associated with a low risk for neurological complications, but clinically silent ischemic events after angiography have been seen in a substantial number of patients.

METHODS AND RESULTS

In a prospective study, diffusion-weighted magnetic resonance imaging (DW-MRI) before and after intra-arterial cerebral angiography and transcranial Doppler sonography during angiography were used to evaluate the frequency of cerebral embolism. One hundred fifty diagnostic cerebral angiographies were randomized into 50 procedures, each using conventional angiographic technique, or systemic heparin treatment throughout the procedure, or air filters between the catheter and both the contrast medium syringe and the catheter flushing. There was no neurological complication during or after angiography. Overall, DW-MRI revealed 26 new ischemic lesions in 17 patients (11%). In the control group, 11 patients showed a total of 18 lesions. In the heparin group, 3 patients showed a total of 4 lesions. In the air filter group, 3 patients exhibited a total of 4 lesions. The reduced incidence of ischemic events in the heparin and air filter groups compared with the control group was significantly different (P=0.002). Transcranial Doppler sonography demonstrated a large number of microembolic signals that was significantly lower in the air filter group compared with the heparin and control groups (P<0.01), which did not differ from each other.

CONCLUSIONS

Air filters and heparin both reduce the incidence of silent ischemic events detected by DW-MRI after intra-arterial cerebral angiography and can potentially lower clinically overt ischemic complications. This may apply to any intra-arterial angiographic procedure.

Transesophageal Echocardiography as a Guide for Patient Positioning Before Neurosurgical Procedures in Semi-sitting Position

With an incidence of a patent foramen ovale in nearly one fourth of the normal population, neurosurgical procedures in the semi-sitting position are associated with the risk of paradoxical air embolism. The present study was undertaken to evaluate an anesthetic concept to detect a patent foramen ovale with the help of transesophageal echocardiography in anesthetized patients before neurosurgical procedures in the semi-sitting position. Transesophageal echocardiography was performed after induction of anesthesia before surgery to avoid additional physical and psychologic stress for the patients. Thirty-five neurosurgical patients scheduled for elective surgery in the semi-sitting position were examined with help of contrast transesophageal echocardiography. The data of the examined patients were analyzed with respect to efficiency, logistic efforts, and adverse events. Contrast transesophageal echocardiography was combined with a ventilation maneuver to increase right atrial pressure. A patent foramen ovale was detected in 3 of 35 patients. These patients were operated on in a supine position. Oral insertion of the echoprobe was possible in all patients without difficulties. A short-lasting hypertension was observed in 5 patients despite adequate analgesia and sedation. The average time of examination was 25 minutes. None of the patients showed paradoxical air embolism as judged by postoperative neurologic assessment. Contrast transesophageal echocardiography combined with a ventilation maneuver is an effective method in detecting a patent foramen ovale. Moreover, transesophageal echocardiography is a clinical guide to patient positioning. The method of anesthetic management presented to examine anesthetized patients immediately before surgery means less physical and psychologic stress for the patients and causes approximately a 30-minute delay of surgery.

The air elimination capabilities of pressure infusion devices and fluid-warmers

Pressurised infusion devices may have only limited capability to detect and remove air during pressurised infusions. In order to assess pressure infusion systems with regard to their actual air elimination capabilities four disposable pressure infusion systems and fluid warmers were investigated: The Level 1 (L-1), Ranger (RA), Gymar (GY), and the Warmflo (WF). Different volumes of air were injected proximal to the heat exchanger and the remaining amount of air that was delivered at the end of the tubing was measured during pressurised infusions. Elimination of the injected air (100-200 ml) was superior by the RA system when compared to L-1 (p < 0.01). The GY and WF systems failed to eliminate the injected air. In conclusion, air elimination was best performed by the RA system. In terms of the risk of air embolism during pressurised infusions, improvements in air elimination of the investigated devices are still necessary.

Acute decompensation after removing a central line: practical approaches to increasing safety in the intensive care unit

Intensive care is one of the largest, most expensive, and complex components of U.S. health care. Errors and the resulting adverse events are, however, common in intensive care units (ICUs). Theories about errors in high-risk environments, developed by aviation and other industries, provide insight into why ICUs are prone to errors. Complex systems--of which ICUs are certainly an example--are breeding grounds for errors because interdependent components interact in unexpected ways. To achieve favorable outcomes, ICUs require that many processes occur in sequence. For example, patients are cared for by many providers with varying levels of expertise across several disciplines, and these providers use highly sensitive and potentially dangerous technologies and medications. Such complex systems require careful planning, excellent teamwork and communication, and designed redundancies to recheck for proper care processes. This paper provides a practical framework for improving patient safety.

[The ventrolateral position]

AIM

To propose an alternative to the sitting position and the other horizontal positions while maintaining the advantages of the sitting position and assuring maximum safety for the patient particularly with respect to the risk of air embolism. POSITION: The patient is positioned as for the sitting position with the median axis of the posterior cranial fossa prolonging the spinal axis. The head is maintained by a Mayfield head holder and is inclined without force. The patient rests laterally on the apron, the thorax and the lower limbs resting on cushions. The upper limbs rest on the arm rests interdependent with the table facilitating surgical access and rolling movements.

DATA

Since 1993, this position was used for 556 patients. For 81.3% of the patients lesions were located in the posterior cranial fossa and for 12.75% in the supratentorial region. Access to the cervical area was achieved for 4.7% of the patients.

RESULTS

This position gave us access to the lesions without specific difficulties, irrespective of the patient's morphology. There were no air embolism events and no capnographic anomaly was reported.

CONCLUSION

Since discontinuing use of the sitting position in our institution, we have found that the ventrolateral position can replace the sitting position advantageously. It allowed us to approach lesions located in a large area, from the cervical spine to the supratentorial area located behind external auditory meatus, and was compatible with anesthetic and surgical requirements.

Exercise effects during diving and decompression on postdive venous gas emboli

BACKGROUND

Exercise and diving have generally been associated with an increased risk of decompression sickness (DCS), thus accounting for the lack of studies involving exercise during decompression. However, theoretical and observational evidence contrary to this association motivated the present investigation on the effects of moderate, intermittent exercise during diving and/or during decompression on venous gas emboli (VGE) activity following a dive.

HYPOTHESIS

VGE observed at both the precordium and subclavian vein sites after diving should be reduced if moderate exercise is performed during decompression vs. remaining inactive.

METHODS

In a water-filled hyperbaric chamber, 39 healthy male subjects were compressed to a pressure of 450 kPa (45 msw) for 30 min followed by 55 min of staged decompression. Subjects were either active or inactive at the bottom phase (450 kPa) and/or during the decompression. Activity comprised three 5-min intervals of moderate arm or leg exercise at the bottom and five such intervals during decompression. After decompression, VGE were monitored at the precordium and subclavian vein sites using Doppler detection. Bubble activity scores were converted to various indices and analyzed using non-parametric statistics.

RESULTS

VGE activity was invariant as to whether subjects were active or sedentary during the bottom phase of the dive. However, it was significantly lower for all indices examined (p < 0.05) after dives in which exercise was performed during decompression vs. inactive decompression.

CONCLUSION

Moderate, intermittent physical activity during decompression decreases VGE activity after diving.

What is the optimal device for carbon dioxide deairing of the cardiothoracic wound and how should it be positioned?

OBJECTIVES

To compare recently described insufflation devices for efficient carbon dioxide (CO(2)) deairing of the cardiothoracic wound and to determine the importance of their position.

DESIGN

Experimental and clinical.

SETTING

A cardiothoracic operating room at a university hospital.

PARTICIPANTS

A full-size torso with a cardiothoracic wound and 10 patients undergoing cardiac surgery.

INTERVENTIONS

Insufflation of CO(2) into the wound cavity at 2.5, 5, 7.5, and 10 L/min with a multiperforated catheter and a 2.5-mm tube with either a gauze sponge or a gas-diffuser of polyurethane foam at its end. The devices were tested when positioned at the level of the wound opening and 5 cm below and after exposure to fluid.

MEASUREMENTS AND MAIN RESULTS

Deairing was assessed by measuring the remaining air content at the right atrium. With the multiperforated catheter, the gauze sponge, and the gas-diffuser, the lowest median air content in the torso was 8.4%, 2.5%, and 0.3%, respectively (p < 0.001), when positioned inside the wound cavity. When exposed to fluid, the gauze sponge and the multiperforated catheter immediately became inefficient (70% and 96% air, respectively), whereas the gas-diffuser remained efficient (0.4% air). During surgery, the gas-diffuser provided a median air content of 1.0% at 5 L/min, and 0.7% at 10 L/min.

CONCLUSIONS

For efficient deairing, CO(2) has to be delivered from within the wound cavity. The gas-diffuser was the most efficient device. In contrast to a gas-diffuser, a multiperforated catheter or a gauze sponge is unsuitable for CO(2) deairing because they will stop functioning when they get wet in the wound.