a 38-year - old male was admitted to the local hospital with pneumonia . despite medical treatment
, his symptoms did not show any signs of improvement , and he was therefore referred to our hospital .
when he arrived at the emergency department , initial arterial blood gas analysis ( abga ) showed a ph of 7.451 , a pco2 of 29.3 , a po2 of 43.6 , an hco3 level of 20.6 mmol / l , and an o2 saturation value of 82.3% , and bilateral lung infiltration was noted on a simple chest x - ray .
his heart rate was 12l beats per minute , his respiratory rate was 40 breaths per minute , his blood pressure was 162/94 mmhg , and his body temperature was 37.7c .
he was diagnosed with acute respiratory failure and therefore , after endotracheal intubation , he was supported with mechanical ventilation . on the day that the patient was admitted , despite the 100% oxygen supplied by the ventilator , his abga results were as follows : a ph of 7.295 , a pco2 of 54.6 , a po2 of 69.7 , a hco3 value of 26.8 mmol / l , and an o2 saturation value of 91.3% . therefore , we decided to initiate venovenous extracorporeal membrane oxygenation ( vv ecmo ) for systemic oxygenation and pulmonary support .
vv ecmo ( pls ; maquet , rastatt , germany ) was established via bilateral femoral cannulation under local anesthesia ( biomedicus 21 fr venous cannula ; medtronic biomedicus inc . , anaheim , ca , usa ) .
a right cannula was inserted into the superior vena cava - right atrium junction and a left cannula was inserted at the diaphragm level ( fig .
ecmo flow was initially started with a flow rate of 5.0 l / min , considering the patient s body weight of 103 kg .
after the ecmo insertion , the following abga results were obtained : a ph of 7.429 , a pco2 of 29.5 , a po2 of 82.9 , an hco3 value of 19.4 mmol / l , and a saturated o2 value of 96.6% .
the patient was finally diagnosed with influenza ( h1n1)-induced acute respiratory distress syndrome ( ards ) and was treated with intravenous antiviral drugs .
however , 20 days after admission , despite treatment with intravenous inotropics and high - fractionated oxygen ( 100% ) using ecmo and a mechanical ventilator , his blood pressure decreased to < 90 mmhg and his o2 saturation value fluctuated between 80%85% . on follow - up
echocardiography , a severely dilated right ventricle ( rv ) with diminished systolic function was noted .
a flattened interventricular septum was noted during systole , which suggested pressure overloading in the rv .
additionally , pulmonary hypertension with an estimated pulmonary arterial pressure of 40 mmhg ( fig .
2a ) and a central venous pressure of 21.5 mmhg were noted , which indicated the existence of right ventricular dysfunction .
laboratory findings showed worsening of end organ function : the ratio of aspartate transanimase to alanine transaminase was 151:96 , his bilirubin level ( total / direct ) was 14.8/8.4 mg / dl , his d - dimer level was 3.34 g / ml , and his fibrinogen level was 468 mg / dl .
we decided to add adjunctive cardiac support and changed the ecmo mode from vv mode to venoarteriovenous ( vav ) mode .
we inserted an additional 15 fr biomedicus arterial cannula into the right femoral artery ( fig .
1b ) , changed the oxygenator , and created a y - shaped inflow line . in order to unload the rv pressure
, we partially clamped the venous input cannula at approximately 90% of its diameter and maintained an ecmo flow rate of 5.56.0 l / min .
approximately 5 l of blood flow was infused into the femoral artery through the new arterial cannula , and the remnants were infused into the right atrium through the venous input cannula . after changing the ecmo mode , the rv size decreased to close to normal , and the interventricular septal flattening disappeared . improved rv systolic function
we changed the degree of clamping of the venous input cannula according to the changing conditions of the patient .
the patient s condition gradually improved as his pneumonia resolved , and we eventually decided to wean him from ecmo based on his lung function status .
after 37 days of hospitalization , we removed the right femoral venous inflow line , and on the next day we successfully weaned the patient from ecmo .
on day 42 , the patient was weaned from the mechanical ventilator , and on day 54 , he was transferred from the intensive care unit to the general ward . after a long period of rehabilitation therapy , his tracheostomy cannula
when avian flu was widespread worldwide in the early 2000s , cases of ards due to influenza also increased abruptly . when severe respiratory failure is refractory to medical and conventional mechanical ventilator therapy , vv ecmo is the last line of treatment .
vv ecmo can supply oxygenated blood to the right atrium and reduce the burden of the mechanical ventilator .
thus , it provides time for the patient s lungs to rest and recover from respiratory failure and shock .
hill et al .   reported the first case of a patient who recovered from trauma - induced adult respiratory failure through the application of vv ecmo treatment .
he and his colleagues showed the possibilities of ecmo to be an effective treatment for respiratory failure and cardiogenic shock . in the cesar ( conventional ventilation or ecmo for severe adult respiratory failure ) trial , which was a multicenter randomized controlled trial comparing conventional ventilation to ecmo for severe respiratory failure , ecmo showed a survival benefit of six months .
the results of ecmo in that group were excellent , with reported survival rates of 68%77% .
reported a survival rate of 50% in adults with severe respiratory failure who were treated with ecmo support .
the main reason for the development of rvf in ards is the increase in the pulmonary vascular resistance ( pvr ) . during the treatment of ards patients with a mechanical ventilator ,
the elevation of pvr is caused by hypoxic pulmonary vascular constriction , endothelial hyperplasia , and myointimal proliferation .
mechanical ventilation with positive end - expiratory pressure itself is also a cause of pvr elevation [ 710 ] .
the incidence of rvf related to ards has been reported to be 9.6%25% [ 1012 ] .
rvf is known to develop from rv pressure overload , reduced rv contractility , and volume overload .
rvf with pulmonary hypertension has poor outcomes in the intensive care unit . in studies addressing hemodynamic variables and survival with pulmonary arterial hypertension , a low cardiac index and high mean right atrial pressure
reported a mode change from vv to venoarterial ( va ) in 3.3% of ards cases in the extracorporeal life support organization registry between 1986 and 2006 .
they hypothesized that right heart failure could be one of the causes of mode change . in our case ,
the patient s cardiac function was found to be good on the echocardiography imaging that was performed on admission .
however , with continuing hypoxia and bilateral lung infiltration that lasted for longer than 20 days despite vv ecmo , his rv function probably decreased due to the increase in pvr caused by the abovementioned factors .
this situation was verified by the high central venous pressure , pulmonary arterial pressure , and d - shaped left ventricle found on echocardiography ( fig .
another reason that vv ecmo may have led to rvf was the long duration of high flow from ecmo .
non - pulsatile flow has been reported to show disadvantages in tissue perfusion and ventricular recoil function when compared to physiological pulsatile flow .
non - pulsatile ecmo flow may sustain rv overloading despite normal rv contraction , which can induce a decrease in rv recoil function . with this hypothesis in mind
, we are planning to carry out additional research on this topic in the near future .
ecmo consists of long tubing systems , a membrane oxygenator , and a high - speed rotating centrifugal pump .
it can infuse highly oxygenated blood into the venous or arterial circulation , but can also induce a systemic inflammatory reaction , hemolysis , bleeding , or thromboembolism .
as occurred in this case our patient , when rv failure develops , vv - mode ecmo can be changed to va or vav mode for unloading the rv volume and rv shear stress .
va or vav mode infuses the oxygenated blood into the left heart in order to elevate the cardiac output .
however , in cases where pulmonary function has decreased significantly , va mode alone may not deliver enough oxygen to the tissues .
if the cardiac function of an ards patient is good , va ecmo flow may not reach the aortic root , because the retrograde ecmo outflow may collide with the strong outflow from the patient s heart .
in such cases , when unsaturated blood is supplied to the proximal aorta ( coronary arteries or brachiocephalic arteries ) , which is a well - known complication of femoral va ecmo , vav ecmo can be utilized to overcome the upper body hypoxemia .
if rvf occurs in a patient with severe ards who is being treated with peripheral vv ecmo , adding an arterial cannula to the femoral artery and partially clamping the inflow venous cannula may be an easy solution for overcoming rvf . in this case ,
rvf during vv ecmo support was successfully treated by changing the mode to vav ecmo .
 a 38-year - old male was admitted with symptoms of upper respiratory infection . despite medical treatment , 
 his symptoms of dyspnea and anxiety became aggravated , and bilateral lung infiltration was noted on radiological imaging studies . 
 his hypoxemia failed to improve even after the application of endotracheal intubation with mechanical ventilator care , and we therefore decided to initiate venovenous extracorporeal membrane oxygenation ( vv ecmo ) for additional pulmonary support . on his twentieth day of hospitalization , hypotension and desaturation ( arterial saturated oxygen < 85% ) developed , and right ventricular failure was confirmed by two - dimensional echocardiography . 
 therefore , we changed from vv ecmo to venoarteriovenous ( vav ) ecmo , and the patient ultimately recovered . in this case , right ventricular dysfunction and volume overloading were induced by long - term vv ecmo therapy , and we successfully treated these conditions by changing to vav ecmo . 
CASE REPORT
DISCUSSION