Assisted venous drainage presents the risk of undetected air microembolism

Clinical relevance of transcranial Doppler in a cardiac surgery setting: embolic load predicts difficult separation from cardiopulmonary bypass

BACKGROUND

During cardiac surgery, transcranial Doppler (TCD) represents a non-invasive modality that allows measurement of red blood cell flow velocities in the cerebral arteries. TCD can also be used to detect and monitor embolic material in the cerebral circulation. Detection of microemboli is reported as a high intensity transient signal (HITS). The importance of cerebral microemboli during cardiac surgery has been linked to the increased incidence of postoperative renal failure, right ventricular dysfunction, and hemodynamic instability. The objective of this study is to determine whether the embolic load is associated with hemodynamic instability during cardiopulmonary bypass (CPB) separation and postoperative complications.

METHODS

A retrospective single-centre cohort study of 354 patients undergoing cardiac surgery between December 2015 and March 2020 was conducted. Patients were divided in tertiles, where 117 patients had a low quantity of embolic material (LEM), 119 patients have a medium quantity of microemboli (MEM) and 118 patients who have a high quantity of embolic material (HEM). The primary endpoint was a difficult CPB separation. Multivariate logistic regression was used to determine the potential association between a difficult CPB separation and the number of embolic materials.

RESULTS

Patients who had a difficult CPB separation had more HITS compared to patients who had a successful CPB separation (p < 0.001). In the multivariate analysis, patients with MEM decreased their odds of having a difficult CPB weaning compared to patients in the HEM group (OR = 0.253, CI 0.111-0.593; p = 0.001). In the postoperative period patients in the HEM group have a higher Time of Persistent Organ Dysfunction (TPOD), a longer stay in the ICU, a longer duration under vasopressor drugs and a higher mortality rate compared to those in the MEM and LEM groups.

CONCLUSION

The result of this study suggests that a high quantity of cerebral embolic material increases the odds of having a difficult CPB separation. Also, it seems to be associated to more complex surgery, a longer CPB time, a higher TPOD and a longer stay in the ICU. Six out of eight patients who died in this cohort were in the HEM group.

Virtually Wall-Less versus Standard Thin-Wall Venous Cannula in the Minimally Invasive Mitral Valve Surgery: Single-Center Experience

Background and Objectives: Minimally invasive cardiac surgery (MICS) has been developing since 1996. Peripheral cannulation is required to perform MICS, and good venous drainage and a bloodless field are crucial for the success of this procedure. We assessed the benefits of using a virtually wall-less cannula in comparison with the standard thin-wall cannula in clinical practice. Materials and Methods: Between January 2021 and December 2022, we evaluated 65 elective patients, who underwent isolated minimally invasive mitral valve surgery. Both the virtually wall-less and the thin-wall cannulas were placed through a surgical cut-down. Patients' characteristics at baseline were similar in the two groups, except for the body surface area (BSA), which was greater in the virtually wall-less group compared to the thin-wall one. In the standard group, the size of the cannula was chosen depending on the patient's BSA, and the choice of the Smartcannula was based on their height. Results: There were no significant differences between the two groups in terms of negative pressure applied, target flow achieved, hemolysis, the need for blood transfusion, and the post-operative increases in liver and renal enzymes. However, in all the patients, the estimated target flow was achieved, thereby showing the better hemodynamic performance of the virtually wall-less cannula, since, in this group, the patients' BSA was significantly greater compared to the thin-wall group. Ultimately, the mean cross-clamp time, as an indirect index of the effectiveness of the venous drainage, is shorter in the virtually wall-less group compared with the thin-wall group. Conclusions: The virtually wall-less cannula should be preferred in minimally invasive mitral valve surgery due to its superior performance in terms of venous drainage compared with the standard thin-wall cannula.

Development of a cannula device for gas fraction removal in surgical drains

The development of low-traumatic surgical drains aimed at maximum possible separation of blood and air, is an important trend in modern medicine. The objective of this work is to create an inexpensive, user-friendly and low-traumatic dynamic blood aspiration system (DBAS). The system allows effective separation of blood and air when drawing blood from a wound under vacuum conditions required for blood aspiration. The operating principle of the system is to separate liquid and gas fractions of the blood-air mixture by modifying the blood intake cannula. The effect is achieved by applying the principles of centrifugal forces of a rotating blood-air flow combined with Archimedes lift forces.

Vacuum-assisted venous drainage in adult cardiac surgery: a propensity-matched study

OBJECTIVES

Conventional cardiopulmonary bypass with gravity drainage leads inevitably to haemodilution. Vacuum-assisted venous drainage (VAVD) utilizes negative pressure in the venous reservoir, allowing active drainage with a shortened venous line to reduce the priming volume. The goal of this study was to analyse the efficacy and safety of VAVD.

METHODS

Data on 19 687 patients (18 681 with gravity drainage and 1006 with VAVD) who underwent cardiac operations between 1 January 2015 and 31 January 2018 were retrospectively collected from a single centre. Propensity matching identified 1002 matched patient pairs with VAVD and gravity drainage for comparison of blood product transfusion rate, major morbidities and in-hospital mortality rates.

RESULTS

The blood transfusion rate of the VAVD group was lower than that of the gravity drainage group (28.1% vs 35% for red blood cells, 13% vs 18% for fresh frozen plasma and 0.1% vs 1.8% for platelets; P = 0.0009, 0.0020 and <0.0001, respectively). The mean difference (95% confidence interval) between the groups for red blood cells, fresh frozen plasma and platelets was -6.9% (-11.0% to -2.8%), -5.0% (-8.1% to -1.8%) and -1.7% (-2.5% to -0.9%), respectively. No difference was observed regarding the major morbidities of cerebrovascular accidents, acute kidney injury, hepatic failure and perioperative myocardial infarction and the in-hospital deaths between the 2 groups.

CONCLUSIONS

VAVD was associated with a reduction in blood product transfusions, and an increase in the risk of major morbidities and in-hospital deaths of the VAVD group was not observed.

Impact of Vacuum-Assisted Venous Drainage on Forward Flow in Simulated Pediatric Cardiopulmonary Bypass Circuits Utilizing a Centrifugal Arterial Pump Head

Objective

To analyze the impact of vacuum-assisted venous drainage (VAVD) on arterial pump flow in a simulated pediatric cardiopulmonary bypass circuit utilizing a centrifugal pump (CP) with an external arterial filter.

Methods

The simulation circuit consisted of a Quadrox-I Pediatric oxygenator, a Rotaflow CP (Maquet Cardiopulmonary AG, Rastatt, Germany), and a custom pediatric tubing set primed with Lactated Ringer's solution and packed red blood cells. Venous line pressure, reservoir pressure, and arterial flow were measured with VAVD turned off to record baseline values. Four other conditions were tested with progressively higher vacuum pressures (-20, -40, -60, and -80 mmHg) applied to the baseline cardiotomy pressure. An arterial filter was placed into the circuit and arterial flow was measured with the purge line in both open and closed positions. These trials were repeated at set arterial flow rates of 1500, 2000, and 2500 mL/min.

Results

The use of progressively higher vacuum caused a reduction in effective arterial flow from 1490±0.00 to 590±0.00, from 2020±0.01 to 1220±0.00, and from 2490±0.0 to 1830±0.01 mL/min. Effective forward flow decreased with increased levels of VAVD.

Conclusion

The use of VAVD reduces arterial flow when a CP is used as the main arterial pump. The reduction in the forward arterial flow increases as the vacuum level increases. The loss of forward flow is further reduced when the arterial filter purge line is kept in the recommended open position.

An independent flow probe is essential to monitor pump flow during cardiopulmonary bypass.

Clinical Experience in Minimally Invasive Cardiac Surgery With Virtually Wall-Less Venous Cannulas

OBJECTIVE

Inadequate peripheral venous drainage during minimally invasive cardiac surgery (MICS) is a challenge and cannot always be solved with increased vacuum or increased centrifugal pump speed. The present study was designed to assess the benefit of virtually wall-less transfemoral venous cannulas during MICS.

METHODS

Transfemoral venous cannulation with virtually wall-less cannulas (3/8″ 24F 530-630-mm ST) was performed in 10 consecutive patients (59 ± 10 years, 8 males, 2 females) undergoing MICS for mitral (6), aortic (3), and other (4) procedures (combinations possible). Before transfemoral insertion of wall-less cannulas, a guidewire was positioned in the superior vena cava under echocardiographic control. The wall-less cannula was then fed over the wire and connected to a minimal extracorporeal system. Vacuum assist was used to reach a target flow of 2.4 l/min per m with augmented venous drainage at less than -80 mm Hg.

RESULTS

Wall-less venous cannulas measuring either 630 mm (n = 8) in length or 530 mm (n = 2) were successfully implanted in all patients. For a body size of 173 ± 11 cm and a body weight of 78 ± 26 kg, the calculated body surface area was 1.94 ± 0.32 m. As a result, the estimated target flow was 4.66 ± 0.78 l/min, whereas the achieved flow accounted for 4.98 ± 0.69 l/min (107% of target) at a vacuum level of 21.3 ± 16.4 mm Hg. Excellent exposure and "dry" intracardiac surgical field resulted.

CONCLUSIONS

The performance of virtually wall-less venous cannulas designed for augmented peripheral venous drainage was tested in MICS and provided excellent flows at minimal vacuum levels, confirming an increased performance over traditional thin wall cannulas. Superior results can be expected for routine use.

A novel augmented venous-drainage model of cardiopulmonary bypass for deep hypothermic circulatory arrest without blood priming

Objective:

Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) are commonly used in cardiac surgery. However, the mortality and morbidity are still high in practice. Developing novel protective stategies and elucidating the underlying mechanisms for the pathophysiological consequences of DHCA have been hampered because of the absence of a satisfactory recovery animal model. The aim of this study was to establish a novel and safe DHCA model without blood priming in rats to study the pathophysiology of potential complications.

Methods:

Ten adult male Sprague-Dawley rats (age, 14-16 weeks; weight, 200-300g) were used. The entire CPB circuit consisted of a modified reservoir, a custom-designed small-volume membrane oxygenator, a roller pump and a home-made heat exchanger, all of which were connected via silicon tubing. The volume of the priming solution was less than 10 ml. The right jugular vein, right carotid artery and left femoral artery were cannulated. The blood was drained from the right atrium through the right jugular vein and fed back to the rat via the left femoral artery. CPB was commenced at a full flow rate. The animals were cooled to a pericranial temperature of 18°C and then subjected to 45 minutes of DHCA with global ischemia. Circulatory arrest was followed by rewarming and over 60 minutes of reperfusion. CPB was terminated carefully. Blood in the circuit was centrifuged and slowly transfused to achieve optimal hematocrit. Blood gas and hemodynamic parameters were recorded at each time point before CPB, during CPB and after CPB.

Results:

All CPB and DHCA processes were achieved successfully. No rat died in our research. Blood gas analyses at different times were normal. Cardiac function and blood pressure were stable after the operation. The vital signs of all the rats were stable.

Conclusion:

The novel augmented venous-drainage CPB and DHCA model in rats could be established successfully without blood priming.

Hemolysis During Open-Heart Surgery With Vacuum-Assisted Venous Drainage at Different Negative Pressures in Pediatric Patients Weighing Less Than 10 kilograms

BACKGROUND

This study examined the degree of hemolysis during vacuum-assisted venous drainage at different negative pressures to identify an adequate negative pressure that provides effective venous drainage without significant hemolysis in open-heart surgery in children weighing less than 10 kg.

METHODS

Patients weighing less than 10 kg who underwent surgery for ventricular septal defect or atrial septal defect from 2011 to 2014 were enrolled. We used one of four negative pressures (20, 30, 40, or 60 mm Hg) for each patient. We measured haptoglobin, plasma hemoglobin, aspartate aminotransferase, and lactate dehydrogenase levels in the patients' blood three times perioperatively and determined the potential correlation between the change in each parameter with the level of negative pressure.

RESULTS

Forty-six patients were enrolled in this study (mean age: 7.1 ± 7.0 months, mean body weight: 6.1 ± 1.8 kg). There were no significant differences according to the degree of negative pressure with respect to patient age, body weight, cardiopulmonary bypass (CPB) time, aorta cross-clamping time, blood flow during CPB, or lowest body temperature. All parameters that we measured reflected progression of hemolysis during CPB; however, the degree of change in the parameters did not correlate with negative pressure.

CONCLUSION

In pediatric patients weighing less than 10 kg, the change in the degree of hemolysis did not differ with the amount of negative pressure. We may apply negative pressures up to 60 mm Hg without increasing the risk of hemolysis, with almost same the level of hemolysis using negative pressures of 20, 30, and 40 mm Hg for effective venous drainage and an ideal operative field during open-heart surgery.

Bubbles and bypass: an update

Bubbles in the bloodstream are not a normal condition -yet they remain a fact of cardiopulmonary bypass (CPB), having been extensively studied and documented since its inception some 50 years ago. While detectable levels of gaseous microemboli (GME) have decreased significantly in recent years and gross air embolism has been nearly eliminated due to increased awareness of etiologies and technological advances, methods of use of current perfusion systems continue to elicit concerns over how best to totally eliminate GME during open-heart procedures. A few studies have correlated adverse neurocognitive manifestations associated with excessive quantities of GME.

Newer techniques currently in vogue, such as vacuum-assisted venous drainage, low-prime perfusion circuits, and carbon dioxide flooding of the operative field, have, in some instances, exacerbated the problem of gas embolism or engendered secondary complications in the safe conduct of CPB. Doppler monitoring (circuit or transcranial) primarily remains a research tool to detect GME emanating from the circuit or passing into the patients’ cerebral vasculature. Newer developments not yet widely available, such as multiple-frequency harmonics, may finally provide a tool to distinguish particulate microemboli from GME and further delineate the clinical significance of GME.

New, Virtually Wall-Less Cannulas Designed for Augmented Venous Drainage in Minimally Invasive Cardiac Surgery

Objective

Inadequate venous drainage during minimally invasive cardiac surgery becomes most evident when the blood trapped in the pulmonary circulation floods the surgical field. The present study was designed to assess the in vivo performance of new, thinner, virtually wall-less, venous cannulas designed for augmented venous drainage in comparison to traditional thin-wall cannulas.

Methods

Remote cannulation was realized in 5 bovine experiments (74.0 ± 2.4 kg) with percutaneous venous access over the wire, serial dilation up to 18 F and insertion of either traditional 19 F thin wall, wire-wound cannulas, or through the same access channel, new, thinner, virtually wall-less, braided cannulas designed for augmented venous drainage. A standard minimal extracorporeal circuit set with a centrifugal pump and a hollow fiber membrane oxygenator, but no inline reservoir was used. One hundred fifty pairs of pump-flow and required pump inlet pressure values were recorded with calibrated pressure transducers and a flowmeter calibrated by a volumetric tank and timer at increasing pump speed from 1500 RPM to 3500 RPM (500-RPM increments).

Results

Pump flow accounted for 1.73 ± 0.85 l/min for wall-less versus 1.17 ± 0.45 l/min for thin wall at 1500 RPM, 3.91 ± 0.86 versus 3.23 ± 0.66 at 2500 RPM, 5.82 ± 1.05 versus 4.96 ± 0.81 at 3500 RPM. Pump inlet pressure accounted for 9.6 ± 9.7 mm Hg versus 4.2 ± 18.8 mm Hg for 1500 RPM, −42.4 ± 26.7 versus −123 ± 51.1 at 2500 RPM, and −126.7 ± 55.3 versus −313 ±116.7 for 3500 RPM.

Conclusions

At the well-accepted pump inlet pressure of −80 mm Hg, the new, thinner, virtually wall-less, braided cannulas provide unmatched venous drainage in vivo. Early clinical analyses have confirmed these findings.

Perfusion techniques for minimally invasive valve procedures

In this paper, we present, in detail, the simplified perfusion technique that we have adopted since January 2009 and that we have utilized in 200 cases for cardiac minimally invasive valvular procedures that were performed through a right lateral mini-thoracotomy in the 3(rd)-4(th) intercostal space. Cardiopulmonary bypass was achieved by means of the direct cannulation of the ascending aorta and the insertion of a percutaneous venous cannula in the femoral vein. A flexible aortic cross-clamp was applied through the skin incision and cardioplegic arrest was obtained with the antegrade delivery of a crystalloid solution. Gravity drainage was enhanced by vacuum-assisted aspiration. There were no technical complications related to this perfusion technique that we have adopted in minimally invasive surgical procedures.

Superior vena cava drainage during thoracoscopic cardiac surgery: bilateral internal jugular vein sheaths versus one percutaneous superior vena cava cannula

OBJECTIVE

To evaluate bilateral internal jugular vein sheaths as a replacement of one percutaneous superior vena cava cannula for superior vena cava drainage during thoracoscopic cardiac surgery.

DESIGN

A prospective and randomized study.

SETTING

Single cardiovascular institute.

PARTICIPANTS

Adults undergoing thoracoscopic cardiac surgery.

INTERVENTIONS

Patients were randomized into a percutaneous superior vena cava cannula group and a bilateral internal jugular vein sheaths group. The superior vena cava drainage for cardiopulmonary bypass was performed with one percutaneous superior vena cava cannula (14-18 Fr) or the bilateral internal jugular vein sheaths (8 Fr).

MEASUREMENTS AND MAIN RESULTS

Both interventions reached theoretic flow rate in all patients. In patients weighing<50 kg (n=38) and 50-70 kg (n=64), the average central venous pressure values during cardiopulmonary bypass of both groups showed no significant differences. The patients weighing>70 kg (n=15) in the bilateral internal jugular vein sheaths group had a normal average central venous pressure value, but it was significantly higher than that of percutaneous superior vena cava cannula group ([10.5±3.1] mmHg vs. [4.5±4.4] mmHg, p=0.013). The patient satisfaction scale scores for the cervical incisions were significantly higher in the bilateral internal jugular vein sheaths group than in the percutaneous superior vena cava cannula group ([2.6±0.9] vs. [2.1±0.8], p=0.002).

CONCLUSIONS

The bilateral internal jugular vein sheaths were a feasible and effective option to replace one percutaneous superior vena cava cannula during thoracoscopic cardiac surgery, with better patient satisfaction.

Brain emboli distribution and differentiation during cardiopulmonary bypass

OBJECTIVE

Cardiopulmonary bypass (CPB) is a lifesaving practice in cardiac surgery, but its use frequently is associated with cerebral injury and neurocognitive dysfunctions. Despite the involvement of numerous factors, microembolism occurring during CPB seems to be one of the main mechanisms leading to such alterations. The aim of the present study was to characterize the occurrence of cerebral microembolism with reference to microembolic amount, nature, and distribution in different combinations of cardiac procedures and CPB on the microembolic load.

DESIGN

A retrospective observational clinical study.

SETTING

A single-center regional hospital.

PARTICIPANTS

Fifty-five patients undergoing elective cardiac surgery with CPB.

INTERVENTIONS

Bilateral detection of the patients' middle cerebral arteries using a multifrequency transcranial Doppler.

MEASUREMENTS AND MAIN RESULTS

Patients were divided into 3 groups depending on the CPB circuit used (open, open with vacuum, or closed). There was a significant difference between the number of solid and gaseous microemboli (p<0.001), with the solid lower than the gaseous ones. The number of solid microemboli was affected by group (p< 0.05), CPB phase (p<0.001), and laterality (p<0.01). The number of gaseous microemboli was affected only by group (p<0.05) and CPB phase (p<0.001). Generally, the length of CPB phase did not affect the number of microemboli.

CONCLUSIONS

Surgical procedures combined with CPB circuits, but not the CPB phase length, affected the occurrence, nature, and laterality of microemboli.

Excessive negative venous line pressures and increased arterial air bubble counts during miniaturized cardiopulmonary bypass: an experimental study comparing miniaturized with conventional perfusion systems

OBJECTIVES

Miniaturized cardiopulmonary bypass (MCPB) is increasingly used in cardiac surgery, because it can lower clinically significant complications such as systemic inflammatory response, haemolysis and high transfusion requirements. A limitation of MCPB is the risk of excessive negative pressure in the venous line during volume depletion, probably leading to gaseous microembolism.

METHODS

In an experimental study with 24 pigs, we compared conventional open cardiopulmonary bypass (CCPB group, n = 11) with MCPB (n = 13). The same pump and identical tubing materials were used in both groups. Primary endpoints were pressure values in the venous line and the right atrium as well as the amount of air bubbles >500 µm. Secondary endpoints were biochemical parameters of systemic inflammatory response, ischaemia, haemodilution and haemolysis.

RESULTS

Nearly 20% of venous pressure values were below -150 mmHg and approximately 10% of the right atrial pressure values were below -100 mmHg in the MCPB group, during the experiment. No such low values were observed in the CCPB group. In addition, the number of large arterial air bubbles was higher in the MCPB group compared with the CCPB group (mean ± standard deviation [SD]: 13 444 ± 5709 vs 0.9 ± 0.6, respectively; P < 0.001). Bubble volume was also significantly larger during MCPB compared with CCPB (mean ± SD: 1522 ± 654 vs 4.1 ± 2.5 µl, respectively; P < 0.001). Blood levels of interleukin-6, free haemoglobin and creatine kinase were significantly higher in the CCPB group compared with the MCPB group.

CONCLUSIONS

Despite the benefits of MCPB regarding systemic inflammatory response and haemolysis, this technique is associated with excessive negative venous line pressures and a significant increase in the number and volume of arterial air bubbles compared with CCPB. Mini-perfusion systems and the management of MCPB require further refinements to avoid such adverse effects.

Spontaneous ear hemorrhage during cardiac surgery

A 79-year-old patient who underwent mitral valve replacement experienced prolonged elevated central venous pressure associated with poor venous return during a cardiopulmonary bypass. After the procedure, the patient was noted to have spontaneous bleeding from the left ear. Otolaryngologic examination in the operating room showed no trauma in the exterior auditory canal and suggested that the hemorrhage was related to a superior vena cava syndrome and anticoagulation during the cardiopulmonary bypass. Determinants and management considerations of poor venous return, including maintenance of cerebral perfusion pressure, are discussed.

Can minimized cardiopulmonary bypass systems be safer?

Although a growing body of evidence indicates superiority of minimized cardiopulmonary bypass (mCPB) systems over conventional CPB systems, limited venous return can result in severe fluctuations of venous line pressure which can result in gaseous emboli. In this study, we investigated the influence of sub-atmospheric pressures and volume buffer capacity added to the venous line on the generation of gaseous emboli in the mCPB circuit.

Two different mCPB systems (MEC - Maquet, n=7 and ECC.O - Sorin, n=8) and a conventional closed cardiopulmonary bypass (cCPB) system (n=12) were clinically evaluated. In the search for a way to increase volume buffer capacity of mCPB systems, we additionally evaluated the ‘Better Bladder’ (BB) in a mock circulation by simulating, repeatedly, decreased venous return while measuring pressure and gaseous embolic activity.

Arterial gaseous emboli activity during clinical perfusion with a cCPB system was the lowest in comparison to the mCPB systems (312±465 versus 311±421 with MEC and 1,966±1,782 with ECC.O, counts per 10 minute time interval, respectively; p=0.03). The average volume per bubble in the arterial line was the highest in cases with cCPB (12.5±8.3 nL versus 8.0±4.2 nL with MEC and 4.6±4.8 nL with ECC.O; p=0.04 for both). Significant cross-correlation was obtained at various time offsets from 0 to +35 s between sub-atmospheric pressure in the venous line and gaseous emboli activity in both the venous and arterial lines. The in vitro data showed that incorporation of the BB dampens fluctuations of venous line pressure by approximately 30% and decreases gaseous emboli by up to 85%.

In conclusion, fluctuations of sub-atmospheric venous line pressure during kinetic-assisted drainage are related to gaseous emboli. Volume buffer capacity added to the venous line can effectively dampen pressure fluctuations resulting from abrupt changes in venous return and, therefore, can help to increase the safety of minimized cardiopulmonary bypass by reducing gaseous microemboli formation resulting from degassing.

Venous drainage--gravity or assisted?

Since the early start of cardiopulmonary bypass, vascular access has been recognized as a main variable for obtaining optimal blood flow during cardiopulmonary bypass. In particular, venous drainage can limit the maximum flow as the wide, low-resistance, collapsible veins are connected with smaller stiff cannulas and tubing. Due to the introduction of long venous cannulas for minimally invasive cardiac surgery and the desire to limit hemodilution during cardiopulmonary bypass, more and more centers have started using assisted venous drainage techniques. This article gives an overview of these techniques, with their respective advantages and disadvantages.

Beneficial effects of modern perfusion concepts in aortic valve and aortic root surgery

Minimized perfusion circuits (MPC) were found to reduce side effects of standard extracorporeal circulation (ECC). We evaluated the safety and efficacy of the ROCsafe™ MPC for aortic valve and aortic root surgery. One hundred and seventy patients were randomized for surgery using either MPC [n = 85, 30 female/55 male, mean age: 69.8 ± 11.8 years; aortic valve replacement (AVR): n = 40; AVR + coronary artery bypass graft (CABG): n = 31; David operation: n = 3; aortic root replacement (ARR): n = 11] or ECC [n = 85, 29 female/56 male, mean age: 67.7 ± 9.5 years; AVR: n = 39; AVR+CABG: n = 35, David operation: n = 2; ARR: n = 9]. Neurological status, length of ICU stay, C-reactive protein (CRP), blood count, transfusion requirements and bleeding volume were analyzed. The MPC system provided ultrasound-controlled de-airing. A small roller pump and a flexible reservoir were used for left ventricular venting. As a control, we used a standard ECC with cardiotomy suction and hard-shell reservoir. Cross-clamp time (MPC: 76.5 ± 29.5; ECC: 79.0 ± 34.0 min) and bypass time (MPC: 103.0 ± 37.9; ECC: 106.9 ± 44.9 min) were comparable between groups. Transfusion requirements (red blood cells: MPC: 1.5 ± 1.5 vs. ECC: 2.2 ± 2.1 units [p = 0.05], frozen plasma: MPC: 1.2 ± 1.8 vs. ECC: 1.9 ± 2.4 units [p = 0.03]), postoperative bleeding (MPC: 521 ± 283 vs. ECC: 615 ± 326 ml/24 h, p = 0.09) were lower using MPC. ICU stay was shorter with MPC (1.6 ± 1.6 days) compared to ECC (2.4 ± 2.8 days, p = 0.001). One stroke occurred in each group. The ROCsafe™ MPC provides safe circulatory support for a wide range of aortic valve surgeries. Transfusion requirements, postoperative bleeding and length of ICU stay were markedly reduced compared to standard extracorporeal perfusion.

Surgical, anesthetic, perfusion-related advances in minimal access surgery

As we enter the fifth decade in cardiac surgery, traditionally cardiac surgery has been performed using a median sternotomy with cardiopulmonary bypass providing great access to the heart and all the surrounding structures. During the last decade, there has been a paradigm shift in the methods by which surgery has been performed. The invasiveness of many procedures has been dramatically reduced, with significantly superior outcomes, as evidenced by improved survival, fewer complications, and quicker return to functional health and productive life. This resulted in significant interest and excitement in adopting less invasive techniques in cardiac surgery. Unfortunately, this was an unrealistic expectation due to the limitations that existed in cardiac surgical techniques and conventional endoscopic instruments, cardiac anesthesia, and cardiopulmonary bypass techniques. In this article, the advances in minimally invasive surgical, cardiac anesthesia, and cardiopulmonary bypass techniques in the evolution of minimal access cardiac surgery are summarized.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

Microemboli detection on extracorporeal bypass circuitsa

Numerous authors have associated gaseous microembolization with adverse cerebral outcomes during cardiopulmonary bypass (CPB). The introduction to this review provides background on the connection between microemboli and adverse cerebral outcomes. This connection is often difficult to quantify, as outcomes depend on a number of factors, including the size of the bubble, where it passes through the patient, patient co-morbidities and other factors. Nonetheless, numerous studies have shown statistically significant differences in the mean number of cerebral emboli detected in patients that stroked and those that did not, as well as for patients with major cardiac complications and patients with a longer length of hospital stay. Our introduction is followed by case reports and laboratory studies showing how monitoring for gaseous microemboli (GME) can be used to reduce the embolic load delivered to the patient through the bypass circuit. These methods include improved qualification of bypass circuit design prior to surgery, modification of priming procedures to reduce air in the circuit at the start of surgery, new methods for injecting drugs into the circuit during surgery, and better detection of removal of sources of air during surgery. The review concludes with background on the ultrasonic detection of GME, comparing through-transmission gross air detectors and Doppler ultrasound technology with fixed-beam ultrasonic imaging of emboli, a new ultrasonic technique that images moving emboli in the blood using a single ultrasound transducer element in a fixed position. This overview is meant to shed light on why different ultrasonic detection technologies report widely varying counts and emboli loads, and why fixed-beam ultrasonic imaging represents an improvement in the ability to monitor, measure and quantitate embolic load during CPB.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

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.

An In Vitro and In Vivo Study of the Detection and Reversal of Venous Collapse During Extracorporeal Life Support

The objective of this study was to investigate venous collapse (VC) related to venous drainage during the use of an extracorporeal life support circuit. A mock circulation was built containing a centrifugal pump and a collapsible vena cava model to simulate VC under controlled conditions. Animal experiments were performed for in vivo verification. Changing pump speed had a different impact on flow during a collapsed and a distended caval vein in both models. Flow measurement in combination with pump speed interventions allows for the detection and quantitative assessment of the degree of VC. Additionally, it was verified that a quick reversal of a VC situation could be achieved by a two-step pump speed intervention, which also proved to be more effective than a straightforward decrease in pump speed.

Vacuum-assisted venous drainage in extrathoracic cardiopulmonary bypass management during minimally invasive cardiac surgery

The diffusion of minimally invasive cardiac surgery (MICS) during open-heart surgery has increased the use of assisted venous drainage support for cardiopulmonary bypass (CPB). Peripheral cannulation with small cannulae and vacuum-assisted venous drainage (VAVD) during MICS has been adopted in our institution since 1998.

After the Heartport technique (HP) experience, the trans-thoracic clamp technique is now currently used. The aim of this study is to report our experience with extrathoracic CPB with VAVD application (on CPB) during open-heart MICS.

From October 1999 to June 2006, 193 patients underwent MICS. Thirty-seven (19.2%) patients were treated with the HP - 13 (35%) with robotic technology and 156 (80.8%) with trans-thoracic aortic clamping (TTAC). Mean age was 39 years (range: 12-77), and 114 patients (59.1%) were female. A total of 128 patients (66.3%) underwent mitral valve surgery, 57 (29.6%) atrial septal defect closure, five (2.6%) cardiac mass removal, and three (1.5%) tricuspid valve repair. Four patients (2.0%) had a previous cardiac procedure.

Peripheral CPB was established with a standard coated circuit. A 14 Fr arterial cannula was inserted into the right jugular vein and positioned at the atrial/superior vena cava junction. A 21 or 28 percutaneous femoral cannula, depending on body surface area, was inserted in the femoral vein and an arterial cannula in the right femoral artery. Gravitational drainage was combined with VAVD. To improve the safety and effectiveness of this technique, we monitored the pressure on each venous cannula and in the reservoir. The mean CPB time was 74.8∓30 min (TTAC) and 119∓48 min (HP); mean aortic clamping time was 51∓19 min (TTAC) and 73∓29 min (HP).

We did not record any neurological complication. Two patients (1.0%), one from each group, were converted to sternotomy. Three patients (1.5%) underwent re-exploration for bleeding. In-hospital mortality was 0.5% (N = 1) (HP). Mechanical ventilation time and intensive care unit stay were comparable to those recorded with conventional sternotomy.

In conclusion, we found that extrathoracic CPB and VAVD during trans-thoracic clamping is a safe, simple, and effective technique for MICS. However, there is a potential risk of haemolysis and air embolism, which can be prevented with vacuum monitoring, and with the addition of gravitational drainage to reduce vacuum pressure.

Open and closed chest extrathoracic cannulation for cardiopulmonary bypass and extracorporeal life support: methods, indications, and outcomes

Extrathoracic cannulation to establish cardiopulmonary bypass has been widely applied in recent years and includes: (a) repeat surgery, (b) minimally invasive surgery, and (c) cases with diseased vessels such as porcelain, aneurysmal, and dissecting aorta. In addition, the success and relative ease of peripheral cannulation, among other technological advances, has permitted the development of closed chest extracorporeal life support, in the form of cardiopulmonary support and extracorporeal membrane oxygenation. With this development have come applications for cardiopulmonary bypass based support outside the traditional cardiac theatre setting, including emergency circulatory support for patients in cardiogenic shock and respiratory support for patients with severely impaired gas exchange. This review summarises the approach to extrathoracic cannulation for the generalist.

Vacuum-Assisted Venous Drainage during Fetal Cardiopulmonary Bypass

We investigated a miniature magnetically levitated centrifugal blood pump intended to deliver 0.3-1.5 l/min of support to neonates and infants. The back clearance gap between the housing and large volume of the rotor, where the suspension and motor bearings are located, forms a continuous leakage flow path. Within the gap, flow demonstrates a very complex three-dimensional structure: the fluid adjacent to the rotating disk tends to accelerate by centrifugal force to flow radially outwards toward the outlet of the impeller against an unfavorable pressure gradient, which in turn forces blood to return along the stationary housing surfaces. Consequently, one or multiple vortices may be generated in the gap to block blood flow and cause the formation of a retrograde and antegrade leakage flow phenomenon at the gap outlet using an optimization process including extensive computational fluid dynamics (CFD) analysis of impeller refinements, we found that secondary blades located along the back or extended to the side surfaces of the rotor have the capacity to reduce and eliminate the retrograde flow in the back clearance gap. Flow visualization confirmed the CFD-predicted flow patterns. This work demonstrates the utility of CFD-based design optimization to optimize the fluid path of a miniature centrifugal pump.

Venous drainage method for cardiopulmonary bypass in single-access minimally invasive cardiac surgery: siphon and vacuum-assisted drainage

Vacuum-assisted venous drainage (VAVD) can facilitate venous drainage in single-access minimally invasive cardiac surgery (SAMICS). We retrospectively examined the use of VAVD in SAMICS in our hospital for this report. VAVD has been performed according to a VAVD protocol since 2000. Data from the 110 patients who underwent SAMICS in our institute from January 2000 to June 2002 were reviewed retrospectively. The total negative pressure was maintained at no greater than -90 mmHg. Indications for use of VAVD (protocol) were: insufficient venous return by siphon drainage alone, persistent elevation of the central venous pressure (CVP), and, insufficient venous drainage in the operative field. Of 110 patients, 97 (88.2%) underwent VAVD. The body surface area was significantly smaller in the group that did not require VAVD (the non-VAVD group) than in the group that did (VAVD group) (VAVD group versus non-VAVD group: 1.586 +/- 0.175 versus 1.408 +/- 0.153 m(2), P < 0.001). Other factors such as cardiopulmonary bypass time, aortic cross-clamp time, postoperative maximum lactate dehydrogenase, postoperative maximum creatinine, postoperative maximum blood urea nitrogen were similar in the two groups. VAVD is necessary in SAMICS except for small patients. A VAVD total negative pressure of -90 mmHg did not hinder operative procedures or cause clinical problems.

Minimally invasive technology for mitral valve surgery via left thoracotomy: experience with forty cases

BACKGROUND

Recent evolution of minimally invasive technology has expanded the application of the right thoracotomy approach for mitral valve surgery. These same technological advances have also made the left posterior minithoracotomy approach attractive in complex mitral procedures.

METHODS

From 1996 to 2003, 921 isolated mitral valve procedures were performed without sternotomy; 40 (4.3%) of these were performed via left posterior minithoracotomy. In the left posterior minithoracotomy group, ages ranged from 18 to 84 years; 36 patients had had previous cardiac surgery (9 on > or =2 occasions). Other factors precluding right thoracotomy included mastectomy/radiation and pectus excavatum.

RESULTS

Arterial perfusion was via femoral artery (n = 26) or descending aorta (n = 14); long femoral venous cannulas with vacuum-assisted drainage were used in 39 procedures. Two patients had direct aortic crossclamping, 18 had hypothermic fibrillation, and 20 had balloon endoaortic occlusion. The mean crossclamp and bypass times were 81.9 and 117.2 minutes, respectively. Hospital mortality was 5.0% (2/40); both deaths occurred in octogenarians. There were no injuries to bypass grafts or conversions to sternotomy. Complications included perioperative stroke (2/40; 5.0%), bleeding (2/40; 5.0%), and respiratory failure (1/40; 2.5%); 28 patients (70%) had no postoperative complications. There was no incidence of perioperative myocardial infarction, renal failure, sepsis, or wound infection. The median length of stay was 7 days.

CONCLUSIONS

Advances in minimally invasive cardiac surgery technology are readily adaptable to a left-sided minithoracotomy approach to the mitral valve. The left posterior minithoracotomy approach is a valuable option in complicated reoperative mitral procedures with acceptable perioperative morbidity and mortality.

Vacuum-assisted venous return reduces blood usage

OBJECTIVE

To determine whether vacuum-assisted venous return has clinical advantages over conventional gravity drainage apart from allowing the use of smaller cannulas and shorter tubing.

METHODS

A total of 150 valve operations were performed at our institution between February and July 1999 using vacuum-assisted venous return with small venous cannulas connected to short tubing. These were compared with (1) 83 valve operations performed between April 1997 and January 1998 using the initial version of vacuum-assisted venous return, and (2) 124 valve operations performed between January and April of 1997 using conventional gravity drainage. Priming volume, hematocrit value, red blood cell usage, and total blood product usage were compared multivariably. These comparisons were covariate and propensity adjusted for dissimilarities between the groups and confirmed by propensity-matched pairs analysis.

RESULTS

Priming volume was 1.4 +/- 0.4 L for small-cannula vacuum-assisted venous return, 1.7 +/- 0.4 L for initial vacuum-assisted venous return, and 2.0 +/- 0.4 L for gravity drainage (P <.0001). Smaller priming resulted in higher hematocrit values both at the beginning of cardiopulmonary bypass (27% +/- 5% compared with 26% +/- 4% and 25% +/- 4%, respectively, P <.0001) and at the end (30% +/- 4% compared with 28% +/- 4% and 27% +/- 4%, respectively, P <.0001). Red cell transfusions were used in 17% of the patients having small-cannula vacuum-assisted venous return, 27% of the initial patients having vacuum-assisted venous return, and 37% of the patients having gravity drainage (P =.001); total blood product usage was 19%, 27%, and 39%, respectively (P =.002). Although ministernotomy also was associated with reduced blood product usage (P <.004), propensity matching on type of sternotomy confirmed the association of vacuum-assisted venous return with lowered blood product usage.

CONCLUSIONS

Vacuum-assisted venous return results in (1) higher hematocrit values during cardiopulmonary bypass and (2) decreased red cell and total blood product usage.

Neuroprotection in cardiac surgery

This article reviews past and present neuroprotective efforts and outlines a framework for the future development of techniques for neuroprotection during cardiac surgery.

Centrifugal versus roller head pumps for cardiopulmonary bypass: effect on early neuropsychologic outcomes after coronary artery surgery

OBJECTIVE

To test the hypothesis that routine use of a centrifugal pump in the cardiopulmonary bypass circuit would result in a lower incidence of early neuropsychologic deficit when compared with conventional roller pumps.

DESIGN

Prospective, randomized, double-blind.

SETTING

University teaching hospital.

PARTICIPANTS

Patients (n = 103) scheduled for elective coronary artery surgery.

INTERVENTIONS

Patients were randomized into group C (centrifugal pump for cardiopulmonary bypass; n = 54) and group R (roller pump for cardiopulmonary bypass; n = 49).

MEASUREMENTS AND MAIN RESULTS

A neuropsychologic test battery of 6 standard tests was administered before surgery and 5 days after surgery. An abnormal test result was defined as deterioration by >1 group SD from an individual's preoperative test performance. There were no significant differences between groups in preoperative or surgical parameters, intensive care unit stay, or hospital stay. There were no significant differences in the incidence of neuropsychologic deficit for patients with a deficit in at least 1 test (group C, 33%; group R, 51%; odds ratio, 0.48; 95% confidence interval, 0.22 to 1.06) or patients with a deficit in >/=2 tests (group C, 6%; group R, 18%; odds ratio, 0.26; 95% confidence interval, 0.07 to 1.03). In group R, there were more individual test deficits per patient than in group C (p = 0.04).

CONCLUSION

There was no significant difference in the incidence of neuropsychologic deficit postoperatively with routine use of centrifugal pumps. The larger number of individual test deficits in the roller pump group suggest that further studies to assess the potential neuropsychologic benefits of the use of centrifugal pumps are warranted.

Does vacuum-assisted venous drainage increase gaseous microemboli during cardiopulmonary bypass?

BACKGROUND

Vacuum-assisted venous drainage enables adequate drainage through small-diameter cannulas but concerns are that it results in more gaseous microemboli delivered to the patient.

METHODS

Five identical embolus detectors monitored the propagation of entrained air through a cardiopulmonary bypass (CPB) model. The ability of the CPB circuit to remove gaseous microemboli was studied with vacuum-assisted venous drainage and gravity siphon venous drainage using different pump speeds and rates of gaseous microemboli delivery.

RESULTS

Under all conditions entrained venous air resulted in the detection of gaseous microemboli in the perfusate after the arterial filter. In blood-primed circuits, increased flow rates and higher levels of vacuum-assisted venous drainage were independently associated with increased gaseous microemboli counts in the arterial line. Vacuum-assisted venous drainage at -40 mm Hg did not significantly increase gaseous microemboli activity when compared with gravity siphon venous drainage at 4 L/min flow rate.

CONCLUSIONS

Vacuum-assisted venous drainage at -40 mm Hg does not statistically reduce the ability of the CPB circuit to remove gaseous microemboli at lower pump rates. High levels of vacuum and increased pump flow rates should be avoided. Air should not be introduced into the venous line.