668 SECTION V Pediatric Critical Care Pulmonary driving pressure for oxygen diffusion into the blood would be ap proximately 188 torr (228 torr 2 40 torr 5 188 torr), which is adequate to achieve 100%[.]
668 S E C T I O N V Pediatric Critical Care: Pulmonary driving pressure for oxygen diffusion into the blood would be approximately 188 torr (228 torr 40 torr 188 torr), which is adequate to achieve 100% saturation of hemoglobin Higher oxygen concentrations in the gas phase may be necessary to compensate for the loss of membrane surface area over time to maintain hemoglobin saturation Faster flows through the oxygenator may also decrease the time for gas exchange to occur At postoxygenator oxygen saturations greater than 95%, increasing the oxygen concentration of the sweep gas has little incremental effect on blood oxygen content (remember that the contribution of oxygen content by the Pao2 is small compared with the effect of hemoglobin and oxygen saturation) For this reason, oxygen concentration in sweep gas usually is adjusted to maintain an oxygen saturation of approximately 95% in postoxygenator blood While providing the most oxygen to the patient would seem to be beneficial, there are now several reports associating high levels of Pao2 returning to the patient with adverse events Whether these represent poor cardiac function so that the majority of Do2 is via the ECMO circuit without native venous admixture (and profound cardiac failure may have a higher risk of death), induction of oxygen radicals or other factors has not been proven Of interest, however, recent data have also identified higher levels of oxygenation in adult respiratory failure patients with decreased survival as compared with those with lower levels of measured Pao2.111–113 Similar to now resuscitating newborns with room air, ECMO initiation may be changing from high levels of Fio2 to the membrane lung to those that just maintain postmembrane saturations of 95% to 100% Carbon Dioxide Exchange Even though the pressure gradient for CO2 between venous blood and membrane gas is less than that for oxygen, CO2 removal is excellent across the membrane lung Despite the small pressure difference, the membrane’s high diffusion coefficient for CO2 allows excellent CO2 removal, even at low flow rates To eliminate more CO2, the gas flow in the membrane must be increased, much as alveolar ventilation must increase to eliminate CO2 from the body under physiologic conditions CO2 removal is also limited by the surface area across which gas exchange can occur Thus, increased CO2 clearance may be obtained by using larger oxygenators or using more than one oxygenator in parallel in the circuit Conversely, to prevent excessive CO2 removal and hypocapnia in small infants and neonates, the sweep of gas through the membrane lung can be reduced or low levels of CO2 may be blended into the gas mixture to further reduce the partial pressure difference between blood and gas and maintain normocarbia Oxygen Delivery During VA ECMO for respiratory failure, both increasing Do2 and increasing the patient’s Pao2 and arterial saturation can be accomplished by increasing the ECMO flow rate (“if the O’s are low, increase the flow”) This strategy diverts more of the systemic venous return into the ECMO circuit for oxygenation while at the same time proportionally decreasing the amount of venous blood that enters the diseased pulmonary circuit Studies have suggested that complete bypass of the pulmonary circuit may lead to pulmonary alkalosis or ischemia and cause direct damage to the pulmonary capillary bed Microsphere studies have shown that the majority of coronary artery perfusion during VA ECMO comes from native left heart ejection, which is another reason why ECMO is performed in a partial bypass state.114,115 The result of increasing ECMO flow will be an increase in Do2 provided by the circuit and an elevation in measured systemic arterial saturation and Pao2 Another means to change the proportion of native blood flow to that from the ECMO circuit is to decrease the overall blood volume in the patient (not usually done) During cardiopulmonary bypass, filling pressures and overall blood volume can be adjusted by removal of blood volume into the bypass circuit and venous reservoir During ECMO, these same principles can be followed: excessively high filling pressures can be lowered by simple removal of blood volume from the circuit (not usually done), and diuretics and renal replacement strategies can be used to control fluid balance However, care must be taken to avoid decreasing circulating volume excessively—this may, in turn, cause tissue hypoperfusion or an increase in oxygen extraction As blood returning from the ECMO circuit is already highly saturated with oxygen, oxygen content can also be augmented by increasing hemoglobin levels in the patient Do2 supplied by the ECMO circuit can be calculated by pump flow as the surrogate for cardiac output and oxygen content by hemoglobin and postmembrane lung oxygen saturation Determining the amount of Do2 supplied by the native heart is less clearly calculated Monitoring of adequate Do2 is aided by following venous saturation and other markers, such as lactate, perfusion, urine output, and mental status If ECMO flow cannot be increased enough to provide adequate support, an additional drainage cannula to provide more venous return and augment ECMO flow may be needed In centrifugal pump ECMO, reduction of mean arterial blood pressure in the patient may also allow easier forward flow from the centrifugal circuit and improve Do2 Physiologic equations applied to ECMO may help identify adequacy of support: DO Blood flow (L) (CaO ) 10 CaO (ECMO) Hb % sat (postoxygenator) 1.34 (PaO [postoxygenator] 0.003) Cv O (ECMO) Hb % sat (preoxygenator) 1.34 (Pv O [preoxygenator] 0.003) Oxygen consumption: V O Blood flow (CaO Cv O ) 10 Sample calculation: Assume Hb 10 g/dL, flow is L/min, Pao2 (postoxy) 300 mm Hg, sat 100% (or 1.00), Pvo2 (preoxy) 40 mm Hg, Svo2 75% (or 0.75): CaO (10 1.34) (300 0.003) 13.4 0.9 14.3 mL O2 /dL Cv O 10 0.75 1.34 0.003 40 10.05 0.12 10.17 DO L 14.3 mL O2 /dL 10 715 mL O2 /min V O Flow (CaO Cv O ) 10 L (14.3 10.17) 10 205 mL O2 /min Thus, Do2 is roughly 3.5 times that of oxygen consumption and should be sufficient to supply tissue needs In patients who undergo VV cannulation, understanding the relationship of Do2 to extraction becomes even more important, as systemic oxygenation will be lower The lower Pao2 observed in the patient during VV ECMO often causes concerns for CHAPTER 56 Extracorporeal Life Support clinicians However, as shown earlier, Pao2 is not nearly as important in terms of Do2 as flow and hemoglobin If the ECMO circuit is providing adequate Do2 and the balance between Do2:Vo2 is maintained within a to times ratio, then the patient is getting adequate Do2 even if measured Pao2 in the body is low This concept is the hardest to put into practice when VV ECMO is used If increased Do2 is desired, then increasing hemoglobin (associated risks of transfusion), Fio2 to the membrane if not fully saturated and increasing ECMO flow will help Conversely, a decrease in oxygen extraction can be obtained by lowering temperature, reducing metabolic work (sedation, treating infection, resolving problems such as pneumothorax or asynchrony with the ventilator, and so on), and even neuromuscular blockade The last resort should be to increase ventilator settings and Fio2, as these maneuvers may also increase the risk of ventilator-associated lung injury If gas exchange is poor, increasing Fio2 delivery via the ventilator is unlikely to help much Several other features unique to VV cannulation are important to understand First, because blood is both withdrawn and reinfused into the venous circulation, usually less of the total cardiac output is diverted to the ECMO system than with VA support Second, adequate native cardiac function must exist to provide the pumping of oxygenated ECMO return to the patient’s systemic circulation One factor that may beneficially influence cardiac function during VV ECMO is that well-oxygenated blood returning from the ECMO circuit will enter the right heart This highly oxygenated blood may reduce pulmonary artery pressure by reducing pulmonary vascular resistance, which, in turn, may improve right heart function Likewise, highly saturated blood returning to the left ventricle and pumped to the coronary arteries may improve myocardial blood flow and improve cardiac performance For these reasons, successful VV support can occur even in patients on vasoactive agents with cardiac dysfunction, with transition to VA support if needed Other clinicians prefer to use VA ECMO preferentially if cardiac dysfunction exists Of note, in one report, 30% of children with vasoactive requirements prior to ECMO tolerated VV ECMO well, and vasoactives were able to be weaned within the first 24 hours Recirculation Another feature of VV ECMO is that, because blood is withdrawn and reinfused into the venous side of the circulation, some portion of oxygenated blood is likely to be lost into the venous drainage cannula prior to entering the systemic arterial circulation.34 This phenomenon is known as recirculation; it can be a major limiting factor in providing adequate patient support with VV ECMO With newer double-lumen cannulas placed via the right IJ vein to the right atrium, careful orientation of the inflow lumen toward the tricuspid valve may limit recirculation The larger separation of drainage and inflow lumens with the Avalon or Crescent device seems to be associated with fewer recirculation difficulties than prior double-lumen cannulas whose inflow and outflow ports are both in the right atrium and fairly close together (see Fig 56.1C) With two-site venous cannulation, recirculation can be limited to some degree by ensuring that some distance separates the end tips of the drainage and infusion cannulas in the body One adult report noted that an increase in venous drainage of more than L by separation of femoral cannulas from cm to cm occurred Recirculation also can be reduced by draining from the femoral vein cannula and reinfusing into the right IJ vein cannula Following adequacy of Do2 in the patient by means of hemodynamic 669 stability, measures of acid-base balance (lactate) and clinical measures of adequate perfusion and oxygenation are required Whether VV cannulation will provide adequate capture of the patient’s cardiac output for ECMO support depends on how large the cannulas are, where they lie in the vessel, and how much overall ECMO support the patient requires New VV cannulas and placement strategies may limit recirculation, but it is unlikely that it can be prevented totally The extent of recirculation can be estimated by following the venous saturation in the ECLS circuit; high levels of recirculation will elevate the displayed venous saturation on the drainage line because some of the highly saturated return from the ECLS circuit is immediately drawn out by the drainage cannula Unlike VA ECMO, where increasing flow increases Do2 to the body, decreasing the flow rate of blood in VV support may decrease recirculation and improve Do2 to the patient Monitoring venous saturations from another site in the body where no recirculation of ECMO flow is occurring (i.e., usually outside the heart) is helpful to monitor if the balance of Do2 to extraction is adequate to meet tissue needs Persistent signs of inadequate Do2 or continued hemodynamic instability with VV ECMO may require conversion to VA ECMO A commonly quoted formula to follow recirculation is: R (Sat preoxy Sv O [pt])/(Sat postoxy Sv O [pt]) Example: Preox sat 80, Postox sat 100, Pt Sv O 60 R 80 60/100 60 20/40 0.5 (50% recirculati on) (This is bad!) Bifemoral cannulation often averages about 30% recirculation while newer double-lumen cannulas (Avalon, Crescent) may have 5% recirculation if placement is optimal Remember that the patient mixed venous oxygen saturation (Svo2) should be measured outside the heart to reduce the influence of oxygenated return from the circuit artificially increasing venous saturation One novel means of improving oxygenation to the head and upper body in patients who have undergone VV cannulation through the bilateral femoral veins is to add another venous cannula via the right IJ vein to the right atrium Connecting this cannula to the inflow return side of the ECMO circuit will increase the amount of oxygenated bypass directly returning to the right heart This procedure may improve overall Do2 to the patient while still avoiding the need for arterial vessel cannulation Other cannulation techniques may also limit differential hypoxemia.116 In roller pump systems, loose occlusion of the roller heads against the raceway tubing also can lead to less blood being propelled forward through the ECMO circuit and reduce systemic Do2 In centrifugal pumps, forward flow of blood is mandated by the pressure generated by the centrifugal heads being higher than that in the patient arterial system If the number of revolutions per minute of the pump head is too low, inadequate forward flow of blood to the patient may result If the patient’s arterial blood pressure is higher than that generated within the centrifugal circuit, arterial blood can flow from the patient into the centrifugal circuit Some circuits contain a one-way valve in the circuit that prevents backflow Increasing the revolutions per minute in the pump head will improve forward flow if the patient’s systemic vascular resistance is overcome Sudden increases in patient mean arterial pressure can reduce ECMO flow Persistent vasodilation, which occurs in patients with sepsis, may require the administration of low levels of vasoconstricting agents to maintain central venous pressures and allow for adequate flow However, it should be remembered that in 670 S E C T I O N V Pediatric Critical Care: Pulmonary some patients with severe vasoplegia, even high levels of ECMO support cannot overcome mitochondrial oxygen extraction dysfunction Such a circumstance is usually fatal Transport Interhospital transport of patients either for ECMO consideration or those for whom ECMO was initiated at a non-ECMO facility has become more available with the advent of smaller systems that are easier to transport Centers may maintain their own ECMO transport services or contract with specialized ECMO transport services.117 Whether increased use of ECLS will occur and the need for ECMO transport capabilities will increase is unknown at this time Maintaining a transport service requires meticulous planning and heavy resource use In addition, the services are expensive to maintain unless the transport volume is high This is one area in which regionalization or contracting with an experienced team of ECMO providers for this service might prove to be practical Patient Management on Extracorporeal Membrane Oxygenation Infants who are candidates for ECMO should undergo cranial ultrasonography, if time allows, to identify existing ICH or abnormalities prior to ECMO initiation Although ICH greater than that confined to the germinal matrix (grade I) has been a contraindication to ECMO in the past, concerns with the expansion of existing lesions due to anticoagulation have lessened and successful ECMO with good neurologic outcome has occurred even with infants with larger ICH Standard care is the performance of repetitive ultrasounds or computed tomography (CT) scans if concerns of intracranial pathology exist and to monitor the extension of known lesions In many patients, emergent initiation of ECMO precludes any imaging procedures and clinical neurologic evaluation may be hampered by ongoing sedation or neuromuscular blockade Use of CT prior to ECMO if time and patient status allow is also beneficial In one adult report, in patients who received ECMO and had CT imaging within hours, ICH (mainly subarachnoid) was found in 17% and care was altered by the withholding of anticoagulation for the first few days until repeat CT showed no increase in hemorrhage Neurologic outcome was good in these patients.118 Once hemodynamic and gas exchanges have been stabilized with ECMO, more informative neurologic testing or examination can be performed If the patient has evidence of neurologic devastation, the family should be informed and discussions as to whether support should be continued or withdrawn initiated.119 Echocardiography is usually performed prior to institution of ECMO in infants to determine whether hypoxia is a result of structural defects in the heart, which may be better served by surgical repair than by ECMO support Echocardiography also can identify ventricular dysfunction, pulmonary hypertension, and pericardial effusions These data are useful to manage the patient properly and to select the optimal form of ECMO or elect less invasive procedures if warranted Echocardiography also is used to detect the presence and direction of central shunts within the cardiac system In addition, it provides excellent information on cannula placement and cardiac function after ECMO is initiated Other helpful pre-ECMO considerations are to ensure that planned vascular access is not already in use with an indwelling venous or arterial line Movement of indwelling catheters to an alternative site in this circumstance should be carried out prior to ECMO or the site can be rewired to accommodate the ECMO cannula In patients with a history of repetitive surgical procedures or central-line insertions, evaluation of vessel patency by a diagram indicating open or thrombosed vessels or from review of the patient record can be very helpful Patients who are critically ill and in whom ECMO should not be considered should be identified by the clinical team; this information included in hand-offs Additionally, discussing cannulation techniques in patients with presumed difficult access prior to any ECMO need can speed cannulation and prevent confusion in an emergent situation Consider informing the family members if their child is determined to be unsuitable for ECMO and discuss rationale Recent laboratory measures of blood and platelet counts, electrolyte levels, and coagulation are included in data collection as ECMO is being planned Correction of existing coagulopathy by infusions of plasma, cryoprecipitate, or platelets may be helpful to prevent early bleeding and to correct baseline dysfunction Initiation of Extracorporeal Life Support In VA ECMO, the arterial waveform provides a rough estimation of the degree of bypass provided by the ECMO circuit ECMO is provided in partial bypass form as total bypass of the pulmonary circuit has been associated with pulmonary ischemia.115 Because ECMO flow is nonpulsatile, increasing flow and decreasing left ventricular output will result in flattening of the arterial wave contour and narrowing of the pulse pressure Severe myocardial dysfunction also may cause a flattened wave contour because left ventricular output may be minimal This effect must be kept in mind when waveform contour is used to monitor the extent of bypass Once goal oxygen saturations and blood pressure are achieved, reduction of ventilator settings and vasoactives can be accomplished In patients with severe left heart dysfunction, a pulse pressure of less than 10 mm Hg should prompt concern for left heart distension and recognition of the need for decompression Use of the femoral artery for access during VA ECMO requires careful monitoring of upper body oxygenation to avoid the red lower body, blue upper body syndrome, also known as the northsouth or harlequin syndrome If a long femoral artery cannula that reaches the high thoracic aorta or arch is used, good oxygenation to the upper body is ensured, but resistance to blood flow is high Aortic flow to renal vessels and others may also be obstructed by a large arterial ECMO cannula Most often, a short femoral artery cannula is used (18 cm), which normally sits in the iliac vessels (see Fig 56.1D) The amount of arterial return reaching the upper body, heart, and brain in this mode of ECMO is dependent on antegrade flow and pressure out of the native left heart and retrograde flow and pressure from the ECMO arterial return The point at which these two flows meet is often termed the mixing cloud and can be identified by ultrasound or echocardiography In patients with severe cardiac dysfunction, arterial return from the ECMO circuit flows further up the aorta and may even reach the aortic arch Thus, good oxygenation and blood flow are provided to the upper body, heart, and head In patients with good native cardiac output, however, the oxygenated return from the femoral ECMO flow may not reach the thoracic aorta Instead, it may be directed down the descending aorta where it will mix with venous return coming from the lower body back to the heart While this will raise the saturation of the venous return somewhat, it can create two problems (1) As optimal oxygenation across the CHAPTER 56 Extracorporeal Life Support membrane lung is best when the venous Po2 is low, this increase in Po2 in the venous drainage may somewhat decrease the amount of oxygen added by the membrane lung, as the partial pressure gradient between the venous blood and gas in the membrane lung will be less (2) If severe lung disease and poor gas exchange are present, then little additional oxygen will be added to blood flowing through the native cardiopulmonary circuit Thus, the oxygen content of blood perfusing the upper body (head and heart) may be quite low (and the same as that in the right atrium if pulmonary gas exchange is very poor) This may raise concern as to whether the head and heart are receiving adequate Do2 One study of various configurations of ECMO in an animal model of respiratory failure noted that venous saturations in the SVC during femoral venous and arterial cannulation reached only 40% Successful use of ECMO has been achieved, however, with femoral arterial cannulation, and it is extremely common in adults, especially those placed on ECMO during arrest Monitoring upper body oxygenation with a pulse oximeter (best on the right hand), cerebral near-infrared spectroscopy, or other measures are recommended to assess the amount of oxygenated flow getting to the upper body during this mode of ECMO While the exact level of Pao2 or saturation in ECMO that is too low is unknown, most clinicians become concerned if upper body saturation in femoral VA ECMO is less than 75% to 80% One method used to improve upper body oxygenation in the event of hypoxia or Do2 concerns with femoral arterial cannulation is to place an additional cannula in the right internal jugular vein and connect via a Y-adaptor into the arterial return portion coming from the ECMO circuit This will direct some oxygenated blood into the right heart, thus improving oxygen saturation and delivery to the upper body as this blood is ejected by the native left ventricle This hybrid model works well in many reports and often relieves fears of inadequate oxygenation to the heart and brain As the added IJ cannula is often larger (and shorter) than the femoral arterial one, blood may preferentially flow to this site Monitoring of blood flow through the femoral artery cannula should also be followed to avoid thrombosis from stagnant blood flow Such cannulation can also be performed in primary VV support.116 Patient Management During Extracorporeal Life Support 671 has not been observed with such care The clinical team assesses the balance struck between the needs of the patient and the risks of transfusion on an ongoing basis Whatever level of hemoglobin for routine patient management is chosen, intermittent administration of packed red blood cells to maintain adequate blood volume and hematocrit will likely be required Fresh frozen plasma also may be given intermittently to provide adequate clotting factors and help prevent excessive bleeding Platelet sequestration in the ECMO circuit is a constant problem Historically, platelet counts of 80,000 to 100,000/mm3 have been maintained routinely for patients undergoing ECMO to deter bleeding, but multiple examples now exist of patients undergoing ECMO with thrombocytopenia of 30,000/mm3 or lower and in whom significant bleeding was not a problem A recent evaluation of 514 infants and children found no increase in bleeding or clotting risk with platelet counts between 56 and 170/mm3.120 Little is known on platelet function during ECMO, which is likely more important than the specific count Another recently identified problem with ECMO, especially for prolonged runs, is heparin-induced thrombocytopenia (HIT) HIT should be suspected in any patient receiving heparin when a drop in platelet count occurs that is unresponsive to platelet transfusion, or when the platelet count continues to fall without an identified reason Although HIT usually develops to 15 days after the patient’s initial exposure to heparin, it can occur immediately in those who have been previously exposed to heparin, such as patients after cardiac surgery HIT can result in severe thrombocytopenia; the only primary treatment is to eliminate exposure to heparin During ECMO, stopping exposure to heparin necessitates the use of other anticoagulation methods Direct thrombin inhibitors (DTIs)—such as lepirudin, bivalirudin, and argatroban—are alternatives Transitioning from heparin to these agents is becoming increasingly common in pediatric sites In contrast to heparin, which requires a cofactor of antithrombin (AT) to exert anticoagulant effects, DTIs not The addition of aspirin to decrease platelet aggregation is practiced in some sites Inhaled nitric oxide through the membrane lung has also been used for similar purposes, but none of these adjuncts has been well studied or reported in the pediatric literature Excellent reviews on hemostasis and ECMO exist.121,122 General Principles Anticoagulation Monitoring When ECMO is initiated, alarm settings for negative and positive ECMO pressures and parameters for interventions such as blood or platelet transfusion, goal Pao2, and goal Paco2 are reviewed daily to assist bedside care Hypovolemia causes low central venous pressures, results in decreased venous return to the circuit, and increases negative pressure within the ECMO system This situation can be corrected with fluid administration Increased Do2 can also be accomplished by increasing the pump flow rate, which increases blood diverted into the ECMO circuit for oxygenation Anemia can be corrected with transfusion of blood products Maintenance of hemoglobin is needed to sustain adequate oxygen content Clinicians disagree about the level of hemoglobin needed during ECMO, but the current trend to accept lower levels of hemoglobin in critically ill patients is also followed in ECMO patients, with most centers delaying routine transfusion until the hemoglobin is 10 g/dL or even lower if the patient seems to be doing well Of interest, blood transfusion in adult ECMO and postcardiotomy patients is often not triggered until hemoglobin levels are less than g/dL, and increased mortality Despite advances in technology and our understanding of the coagulation cascade, the need for anticoagulation to prevent clotting of the extracorporeal circuit is still required Heparin remains the mainstay for anticoagulation, but the optimal management scheme to prevent thrombosis without causing bleeding remains elusive Newer methods of anticoagulation, such as DTIs, are also appearing Commonly used tests and variables that affect results are shown in Table 56.6 The activated clotting time (ACT) remains the most common method for monitoring heparin and anticoagulation Usually maintained at a level between 160 and 220 seconds, the ACT is a whole-blood test usually performed at the bedside It does not directly measure heparin but instead gives an overall picture of clotting within the body Results can be altered by platelet deficiency, platelet dysfunction, low fibrinogen levels, hemodilution, hemolysis, and clotting factor abnormalities As improved understanding of the coagulation cascade and means to measure factors within it have been obtained, other regimens now include the anti-Xa level, AT, specific factor analyses, and thromboelastography No monitoring strategy has proved 672 S E C T I O N V Pediatric Critical Care: Pulmonary TABLE 56.6 Common Anticoagulation Monitoring Tests Test Data Provided Variables Affecting Results How Results Are Affected aPTT Clotting via the intrinsic and common pathways High levels of factor VIII during acute phase reaction aPTT remains shorter than expected with heparin infusion More heparin is required to overcome heparin resistance Maturation status may affect results Elevated plasma-free hemoglobin Shortens aPTT Hyperbilirubinemia Prolongs aPTT DIC May prolong aPTT Thrombocytopenia or platelet dysfunction; DIC Prolongs ACT Thrombin formation with coagulation proteins may continue despite reassuring ACT Higher hematocrit Shortens ACT Hypothermia Prolongs ACT Elevated plasma-free hemoglobin (2 mg/mL) Not affected by DIC Decreases anti-Xa levels Hyperbilirubinemia (10–20 mg/dL) Decreases anti-Xa levels Hypertriglyceridemia (600–1250 mg/dL) Decreases anti-Xa levels Longer storage times, improper sample collection TEG appearance of hypercoagulable state Older equipment is very sensitive to operator error Inaccurate results possible Elevated plasma-free hemoglobin Increased R, MA, and K values ACT Anti-Xa TEG Entire clotting system in vitro Level of indirect and direct inhibition of factor Xa Activity of coagulation factors, platelets and fibrinogen; time to lysis of clot ACT, Activated clotting time; aPTT, activated partial thromboplastin time, DIC, disseminated intravascular coagulation; K, k-value; MA, maximum amplitude; r, reaction time; TEG, thromboelastography superior to another in terms of limiting complications or improving outcomes It is important to understand the pros and cons of each test in terms of blood volume required for testing, accuracy, and cost As one example, use of AT—a protease inhibitor that inactivates factor Xa and thrombin and that has markedly enhanced action in the presence of heparin—has increased 9.5-fold (used in over 52% of ECMO patients) despite no evidence that it is effective in decreasing complications and no identification of the correct dose in children In a similar fashion, anti-Xa measurement, which gives a more direct assessment of heparin level than the whole-blood ACT test, is also being used frequently While it is not shown to be superior to ACT, it has replaced the ACT in many sites Thromboelastography, a technique that produces a visual picture providing information on the degree of anticoagulation induced by heparin and other information regarding coagulation and platelet defects, is also being used more as new technology makes it easier to perform It is hoped that continued research in this area will yield an optimal anticoagulation regimen to reduce bleeding and thrombotic complications.123–125 It is also likely that individual response to anticoagulation will require investigation into genetic factors that may help define optimal therapy in the future Nutritional Support Adequate nutrition is essential for healing and is provided as total parenteral nutrition, enteral feeding, or a combination of both Enteral feeding has been shown to be safe and effective during ECMO in all groups of patients and may limit the need for parenteral nutrition with its associated complications.126,127 Fluid and Renal Replacement Therapy A conservative fluid management strategy currently is preferred in critically ill patients; those undergoing ECMO are no exception The use of diuretics, concentrated drug infusions, and hemofiltration in patients with renal insufficiency are other important aspects of patient care Renal failure, hypervolemia, and fluid overload are frequently seen in patients undergoing ECMO Use of continuous renal replacement therapies (CRRTs) has become commonplace during ECMO to maintain fluid balance, support failing kidneys, and potentially clear inflammatory mediators from the blood One of the proposed mechanisms for the development of acute renal failure (ARF) in patients undergoing ECMO is a reduction in the pulsatile character of renal perfusion Circuit-associated hemolysis can contribute to ARF CRRT can be accomplished by connecting a hemofiltration filter into the ECMO circuit while controlling the ultrafiltrate volume using an intravenous infusion pump or using a standard continuous renal replacement system Patients receiving CRRT during ECMO have decreased survival, but this is also true in CRRT recipients who not undergo ECMO Few survivors have long-term renal failure.128–132 Other adjunct extracorporeal therapies, such as plasmapheresis or liver support systems, also have been used successfully during ECMO Plasmapheresis for plasma exchange in the management of sepsis syndrome or immunologic disorders and extracorporeal liver support for hepatic failure can also be performed through the ECLS circuit without the need for additional vascular access ECMO also provides a stable hemodynamic platform for these adjuncts ... circuit This will direct some oxygenated blood into the right heart, thus improving oxygen saturation and delivery to the upper body as this blood is ejected by the native left ventricle This hybrid... right atrium Connecting this cannula to the inflow return side of the ECMO circuit will increase the amount of oxygenated bypass directly returning to the right heart This procedure may improve... unknown at this time Maintaining a transport service requires meticulous planning and heavy resource use In addition, the services are expensive to maintain unless the transport volume is high This