シャドーイング練習: Introduction to ECMO Part 3 - V-A ECMO - 動画で英語スピーキングを学ぶ
レッスンを作成中...
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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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このレッスンについて
このレッスンでは、Veno-arterial ECMO（VA ECMO）についての理解を深め、英語でのスピーキング練習を行います。トランスクリプトを通じて、医療分野における専門用語やコンセプトを学び、実際の会話で使えるフレーズを習得することが目的です。この知識は、特にIELTS スピーキング対策に役立つでしょう。また、shadow speak や shadowspeak の手法を使用して、英語のプレゼンテーション技術を向上させることができます。
重要な語彙とフレーズ
- Veno-arterial ECMO (VA ECMO) - 静脈動脈ECMO
- complications - 合併症
- hypoxia - 低酸素症
- cardiac output - 心拍出量
- membrane oxygenator - 膜酸素化装置
- thrombosis - 血栓症
- ischemia - 虚血
- arterial circulation - 動脈循環
練習のコツ
このトランスクリプトの音声はやや速めですが、練習を通じてしっかりと理解していきましょう。まずは、shadowingの手法を使って、話し手の発音やリズムを真似することから始めてください。特に、重要な専門用語やフレーズを繰り返し発音することで、医療用語の習熟度を高めることができます。
具体的には、1文ずつ聞いては止め、発音を確認しながらゆっくりと口に出すことをおすすめします。この時、声のトーンや抑揚にも注意を払い、実際の会話の中で自然に聞こえるようにすることが大切です。また、自分の流れに合わせて少しスピードを調整しても構いません。適宜、英語スピーキング練習を行いながら、IELTS スピーキング対策としても活用してください。
このようにして英語の表現力を高めていくことで、医療現場での会話能力も向上します。興味深い内容を学びながら、実践的なスピーキングスキルの向上を目指しましょう。
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。