Практика Shadowing: Introduction to ECMO Part 3 - V-A ECMO - Изучайте разговорный английский по видео
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Veno-arterial ECMO is a bit like Veno-Venous ECMO, except you return the non-pulsatile blood flow into a high pressure system.
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Oh, and the blood is travelling in the wrong direction.
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My name is Ken Hoffman.
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I'm an intensivist at the Alfred Hospital in Melbourne.
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This is the third video in our introduction to ECMO series, aimed at new staff joining our team.
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It will cover the principles of Veno-arterial or VA ECMO,
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the indications, complications and considerations for liberation from VA ECMO support.
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To start with, the circuit itself for VA ECMO is very similar to VV ECMO.
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The major difference is that blood is returned to an artery under high pressure.
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In this way, we can consider the ECMO pump being an artificial heart pumping non-pulsatile blood in parallel around the body.
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The circuit starts with an access cannula in the right atrium or vena cava which removes venous blood from the body.
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As this blood will return to the arterial circulation without going through the lungs, it must pass through a membrane oxygenator for gas exchange.
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It will then be returned back under high pressure to the arterial circulation, usually via the common femoral artery.
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The returning blood travels in the opposite direction through the arterial system, back towards the heart.
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If the heart is still able to contract and eject some blood, this blood will mix with the ECMO blood somewhere in the proximal aorta.
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This combination of a native pulsatile circulation and an artificial retrograde non-pulsatile circulation will be important when considering some specific complications later.
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One specific difference with a VA ECMO circuit is the requirement for a backflow cannula.
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As the large return cannula will sit in the common femoral artery, this can occlude blood flow to the leg.
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To prevent leg ischemia, a smaller cannula is placed in the superficial femoral artery
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which is connected into the ECMO circuit and allows downstream perfusion of the leg with oxygenated ECMO blood.
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To titrate the amount of VA ECMO flow, we rely on clinical parameters such as mean arterial pressure,
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lactate, urine output and peripheral perfusion.
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Turning up the fresh gas flow doesn't really change the oxygen delivery.
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So if the patient needs more support, the ECMO circuit flow should be increased.
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It is important to remember that with VA ECMO, the fresh gas flow should never be turned to zero,
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as this would result in deoxygenated blood being returned into the arterial circulation.
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To summarise, VA ECMO can provide cardiac support by pumping oxygenated blood into the arterial circulation.
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It can also be used for respiratory support as the returned blood is fully oxygenated.
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In terms of the indications for VA ECMO, it is used as support for severe heart failure.
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It is important to remember that VA ECMO doesn't actually fix anything.
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Instead, it provides time so the patient can be bridged to recovery, bridged to a durable left ventricular assist device, or transplantation.
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This is why VA ECMO is still a niche support modality.
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A lot of the complexity comes from decision-making about how and when to liberate the patient from VA ECMO support.
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The next thing to talk about are complications.
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These can be divided into the common ECMO complications of bleeding,
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thrombosis, infection and hemolysis and specific VA ECMO complications.
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The specific VA ECMO complications to discuss are differential hypoxia,
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left ventricular distension, leg ischemia and cardiac arrest on VA ECMO support.
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Differential hypoxia occurs as a result of mixing between the forward flowing native cardiac output and retrograde flow from the ECMO circuit.
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If the native lungs are poorly oxygenating the native cardiac output, then hypoxic blood will be pumped into the aorta.
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The relative proportions of native cardiac output to ECMO flow will determine where the mixing point will be in the aortic arch.
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If native heart function improves but the lungs still have respiratory failure, increasing amounts of hypoxic blood will enter the arterial circulation,
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which will disproportionately affect the upper parts of the body.
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In order to detect this, the arterial line is routinely inserted in the right radial artery
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and the pulse oximeter should be placed on the right hand or right ear lobe.
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This will confirm if the blood in the first branch of the aortic root, which is the brachiocephalic trunk,
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is delivering adequately oxygenated blood to the right subclavian artery and more importantly, the right common carotid artery.
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When differential hypoxia occurs the focus should be on trying to
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improve the native lung function to increase oxygenation of the native cardiac output.
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Other options include reducing inotropy to decrease the native cardiac output,
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increasing ECMO flow to move the mixing point proximally or reconfiguring to return sites other than the femoral vessels.
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Rarely fancy ECMO modes are required such as VAV or even separate VA and VV ECMO circuits.
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Next complication to talk about is left ventricular distension.
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This occurs
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when the left ventricle is unable to generate enough tension for
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the aortic valve to open during systole due to the pathology affecting the ventricle plus the increased afterload from retrograde ecmine flow.
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This is exacerbated by any aortic valve regurgitation.
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When left ventricular distension occurs,
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the forward flow through the lungs is impaired and can result in pulmonary edema and pulmonary hemorrhage.
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Rarely, stagnant blood in the left ventricle can clot.
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Signs of left ventricular distension include a loss of arterial line pulsatility, a chest x-ray with pulmonary edema
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or an echo with a dilated poorly functioning left ventricle with an aortic valve that is not opening.
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Management of left ventricular distension involves increasing left ventricular ejection with inotropes,
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reducing peripheral resistance and lowering mean arterial pressure targets and fluid removal to reduce the main systemic filling pressure.
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If these interventions don't work, the left ventricle needs to be decompressed.
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Usually, this is with a left ventricular vent cannula, which is joined into the access part of the ECMO circuit and drains the left ventricle with negative pressure.
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The complication of leg ischemia has already been discussed.
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It is prevented with insertion of a backflow cannula in the superficial femoral artery.
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The leg still requires regular vascular observation by monitoring non-pulsatile Doppler flow as the backflow cannula can develop thrombosis.
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The last complication to discuss is cardiac arrest on VA ECMO.
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This is detected by a loss of pulsatility on the arterial line and an ECG that is not in a perfusing rhythm.
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When this occurs, chest compressions are not required.
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Instead, attempt to increase the VA ECMO flow to provide support whilst trying to restore a perfusing rhythm.
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The reason restoring a perfusing rhythm is important is that stagnant blood in the left ventricle may clot.
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Large clots in the left ventricle are unsurvivable.
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and even small clots may result in embolic complications with restoration of cardiac output.
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The final thing to discuss is liberation from VA ECMO support.
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As already mentioned, if there is no cardiac recovery, then ECMO is a bridge to another treatment,
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such as a durable left ventricular assist device or transplantation.
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If there is cardiac recovery, then an echo-guided weaning study is performed.
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This examines cardiac function with progressively reducing VA ECMO flow to determine
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if the heart is able to cope without VA ECMO support.
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If the weaning study is passed,
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the VA ECMO is removed in the operating theatre as the large arterial cannulation site requires some stitches to control bleeding.
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In summary, VA ECMO is used for cardiac support when the heart is unable to pump sufficient blood to maintain organ function.
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Complications occur related to the ECMO circuit including the VA specific complications of differential hypoxia and left ventricular distension.
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Liberation from VA ECMO is complicated as it is used either
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as a bridge to recovery guided by an echo weaning study
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or as a bridge to a durable left ventricular assist device or transplantation.
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If you would like to read more about our ECMO protocols, they are freely available at ecmo.icu.
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Thank you for listening.
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If you enjoyed this video, please hit the like button.
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Почему стоит практиковать речь с этим видео?
В видео "Введение в ЭКМО Часть 3 - V-A ЭКМО" представлена уникальная возможность улучшить свои навыки устной речи на английском языке в контексте сложной медицинской темы. Понимание таких концепций, как венозно-артериальное ЭКМО, не только повышает вашу медицинскую грамотность, но и помогает развить уверенность в разговорной практике. Слушая и повторяя, вы можете практиковать медицину на английском, углубляя знания терминологии и улучшаюест свои навыки общения.
Грамматика и выражения в контексте
- Фраза: "The circuit itself for VA ECMO is very similar to VV ECMO." Эта структура позволяет вам говорить о сравнительных характеристиках, что полезно в любых дискуссиях.
- Использование пассивного залога: "is returned to an artery under high pressure." Это основной прием в научной и медицинской речи, который можно использовать для описания процессов.
- Выражение: "It must pass through a membrane oxygenator for gas exchange." Это пример бессоюзного предложения, указывающего на необходимость выполнения действия, что полезно в объяснении сложных понятий.
Изучая такие структуры, вы можете улучшить свои навыки коммуникации на английском, используя подход "shadow speaks" для повторения и закрепления новых знаний.
Распространенные трудности произношения
Некоторые слова в видео могут оказаться сложными для произнесения, например, “hemolysis” и “thrombosis”. Эти термины часто вызывают затруднения из-за их длинной длины и сложной фонетики. Практикуя их с помощью методов 'shadow speech', вы сможете улучшить свое произношение и уверенность при использовании медицинской лексики.
Кроме того, обратите внимание на акцент и интонацию произнесения ключевых слов, таких как “ECMO” и “oxygenator”. Регулярные занятия на платформе shadowing site помогут вам услышать и воспроизвести правильное произношение, что будет полезно для вашего общего уровня владения языком.
Что такое техника Shadowing?
Shadowing — это научно обоснованная техника изучения языка, изначально разработанная для подготовки профессиональных переводчиков и популяризированная полиглотом доктором Александром Аргуэльесом. Метод прост, но эффективен: вы слушаете аудио на английском от носителей языка и немедленно повторяете вслух — как тень, следующая за говорящим с задержкой в 1–2 секунды. В отличие от пассивного прослушивания или грамматических упражнений, Shadowing заставляет мозг и мышцы рта одновременно обрабатывать и воспроизводить реальные речевые паттерны. Исследования показывают, что это значительно улучшает точность произношения, интонацию, ритм, связную речь, понимание на слух и беглость речи — что делает его одним из самых эффективных методов для подготовки к IELTS Speaking и реального общения на английском.