When patient is connected lo cardio pulmonary bypass for an operative procedure, it is considered to be open-heart operation. In a routine coronw-y artery bypass, no cardiac chamber is opened. Yet, as the patient is connecled to heart lung machine and heart is stopped, it is considered as open-heart surgery.
Hypothermia
Hypothermia reduces the metabolic requirements of the body thereby reducing oxygen consumption. It also preserves high-energy phosphate stores of the body. At normal temperature, if there is circulatory arrest for three minutes,brain suffers hypoxic damage. At 30°C, this period extends up lo 10 minutes.If the temperature is brought down to lS°C, this period extends up to 45 minutes. .In 1953, John Lewis used surface hypothermia up to 28OC and by inflow occlusion method closed atrial septa1 de'fect while the heart was arrested for 5.5 minutes. Japanese surgeons started surface cooling followed by short period of core cooling to achieve deep hypothermia (lS°C) to have circulato~y arrest to correct complicated intra cardiac lesions in babies. Surface cooling being a cumbersome procedure, these days both cooling and re warming are done on tile pump. In this technique of deep hypothermia and circulatory ai'rest (DHCA), it is safe if the period of arrest is 30 minutes or less. Between 30 minutes and 45 minutes, it is relatively safe. Above one hour, brain danlage is likely lo occur. In adults, the same technique is used for aortic arch aneurysms and pullnonay tlrombo-endarterectomy. At the time of circulatory arresl,retrograde cerebral perrusion with cold pei-fusate through superior vena cava (cerebroplegia) is practised.
Myocardial Protection
To a great extent, the result of cardiac surgery depends on how well the myocardium is protected during cardio pulmonary bypass. Temporary depression 01 myocardium (stunning) or myocardial necrosis resulting in low cardiac output may occur after bypass. Sub endocardial layer is particularly vulnerable to injury. A still heart, free of blood is essential for accurate intra cardiac repair. In the earlier era, fibrillatoiy arrest or ischaemic arrest by cross clamping the aorta was used to facilitate open-heart surgery. These days,diastolic arrest of the heart is achieved by administration of cold cardioplegic solution, proximal to aortic clamp. When there is aortic regurgitation, aoi-ta is opened and direct coronary ostial cani~ulation is required for giving cardioplegia. When there are multiple blocks in coronary arteries, ante grade cardioplegia will not ensure uniform distribution of the solution. Such cases will need retrograde cardioplegia administered through a coronary sinus cannula. Special retrograde cardioplegia cannulae are available with balloons,which will fill up at the time of cardioplegia. The coronaiy sinus can be cannulated blindly through a purse string on the right atrium. The coronary sinus pressure should be kept below 30 rnm of Hg at the time of cardioplegia.
The cardioplegic solution could be cold asanguinous (clear) or with blood. The comrnomlly used one is St. Thomas solution that essentially contains 20 .meq of potassium cooled down to 4°C. Cardioplegia is usually suppleinenled with topical cold saline or ice slush.
Cardioplegia may be cold or warm. At times patients are operated at normothermia with warm blood cardioplegia. If the patient has recent myocardial infarction or when the ejection fraction is low, it is good to give warm blood (hotshot) just before releasing aortic clamp, to reduce reperfusion injury. The cardioplegic solution is slightly hyper osmolar and buffered with sodium bicarbonate or THAM. Amino acids like Glutamate and Aspartate added to the solution reduces reperfusion injury. Adenosine adds to further
protection. To reduce the injuiy due to oxygen free radicals, super oxide dismutase (SOD) and dimethyl sulphoxide (DMSO) can be added to the cardioplegic solution.Venting of the Heart
It is important that heart does not distend during cardio pulmonary bypass. This is prevented by venting of the left side of the heart by inserting a caiinula into the left atrium, left ventricle, pullnonary artery or aortic root below the cross clamp. The cannula is connected to low suction and the saine ca~lnula is used for &airing of the chambers of the left heart at the end of the intracardinc procedure.
Blood Salvage and Bloodless Open-heart Surgery
At the tiiiie of cardio pulmonary bypass, cardioto~ny suckers suck blood from the chanibers or the heart and pericardium back into the reservoir. In operations like repair of alleurysln of aorta, an equipment called cell saves can be used. This sucks all the spilled blood, wilslies, centrifuges ancl packs into red cell concentrate ready to be administered to the patient. is not without harni: ( I ) It may lend to transfer of infections
Blood transfusion like HIV. Hepatitis B or C, cytomegalovirus, malaria etc., (2) Fcbrilc reaction,(3) Incompatibility, and (4) Limited supply. Conservation ol' blood could be achicved by autologus blootl donation. I11 n Sit patient, blood could I,e collected pre-operatively, up to tcn days before surgery. Intra operatively one or two ini its can be collectetl, just bcfo1.e bypass.
With these methods, it is now possiblc to do blootlless open-heart surgcsy.
Haemo Filtration
Ultra filt~.ution during open heart surgery helps in removing excess l'luicl,especially in rcnal failure patients. Patients are 11:temo diluted (haematocrit 18-20) during bypass. Haemo I'iltration hclps in hlood preservation, cspcci;llly platelets and coagulation hctors. It 1-educes post operative complemenl ;~ctiva[ion and cardio pulmonary bypass induced inllnmrnatory response. There is also improvement in pul~~ioanry and neurologic:~l function. Ultra i'iltration cquipmcnt is connected to the circuit. In childrcn and bal~ies, it is carricd out j u s ~ hcfi~rc coming off bypass. This is called ~nodificd ultra Siltratio~i (MUF).
Circulatory Assist Devices
Intra aortic balloon pump (IAUP) was introduced by Kantrowitz (19hX). It is also known as Counter pulsation or Diastolic augmentation.Indication IABP is comnloiily uscd to s~ipport failing left veiltricle after open-I1ca1-t sui.gery or in cardiogenic shock after myocardial infarction. It is at times used i n unstable angina and as a supportive measure for urgent PTCA or revasc~llarizarion. In patients with post infarction ventriculiu. seplal defect and haemo dynamic instability, IABP is indicated before surgery.
Contra Indication
It is absolutely contra indicated if tl~ere is more than trivial aorlic regurgitation.Aortic aneurysm and severe aorto iliac disease are also contra indications for use of IABP.
Equipment
Basically, it has an intra aortic balloon pump. A balloon with a capacity of 40 ml is passed percutaneously through the femoral artery up to the upper end of descending thoracic aorta. The tip of the balloon has radio opaque marker and should be placed below the left subclavian artery. An inert gas like helium is pumped into the balloon, lo synchronise with diastole. The balloon is deflated
during systole. Synchronisation is achieved by ECG trigger or aortic pressure wave. This will cause diastolic augmentation of blood pressure (counter pulsation) causing augmentation of coronary and cerebral blood flow. When the pump deflates during systole, there is reduction in the after load and of inyocardial oxygen consumption. This improves cardiac output by 10 per cent and helps recovely of myocardium.
Complications
IABP can compromise blood flow to the leg at the time of insertion, pumping or after removal of balloon. It may also cause perforation, bleeding, thrombosis,embolism or dissection of the artery. It is importanl to check the vasculLvity of the leg frequently, both clinically and by Doppler.
Ventricular Assist Devices
These come handy when IABP has failed or when prolonged circulatory supporl is needed. Now Ieft ventricula- (LVAD), right ventricular (RVAD) and bivenlricular assisl devices are available. Implantable assist devices can be fitted in when patient is awaiting h e m transplailtation (biidge to transplantation).
Total Artificial Heart
Jarvik seven was the first successful total artificial heart supporting the patient for 112 days. The disadvantage is that the patient has to be connected to a power source outside and the patienl's heart has to be removed. Totally implantable heart is still a distant dream.
Hypothermia
Hypothermia reduces the metabolic requirements of the body thereby reducing oxygen consumption. It also preserves high-energy phosphate stores of the body. At normal temperature, if there is circulatory arrest for three minutes,brain suffers hypoxic damage. At 30°C, this period extends up lo 10 minutes.If the temperature is brought down to lS°C, this period extends up to 45 minutes. .In 1953, John Lewis used surface hypothermia up to 28OC and by inflow occlusion method closed atrial septa1 de'fect while the heart was arrested for 5.5 minutes. Japanese surgeons started surface cooling followed by short period of core cooling to achieve deep hypothermia (lS°C) to have circulato~y arrest to correct complicated intra cardiac lesions in babies. Surface cooling being a cumbersome procedure, these days both cooling and re warming are done on tile pump. In this technique of deep hypothermia and circulatory ai'rest (DHCA), it is safe if the period of arrest is 30 minutes or less. Between 30 minutes and 45 minutes, it is relatively safe. Above one hour, brain danlage is likely lo occur. In adults, the same technique is used for aortic arch aneurysms and pullnonay tlrombo-endarterectomy. At the time of circulatory arresl,retrograde cerebral perrusion with cold pei-fusate through superior vena cava (cerebroplegia) is practised.
Myocardial Protection
To a great extent, the result of cardiac surgery depends on how well the myocardium is protected during cardio pulmonary bypass. Temporary depression 01 myocardium (stunning) or myocardial necrosis resulting in low cardiac output may occur after bypass. Sub endocardial layer is particularly vulnerable to injury. A still heart, free of blood is essential for accurate intra cardiac repair. In the earlier era, fibrillatoiy arrest or ischaemic arrest by cross clamping the aorta was used to facilitate open-heart surgery. These days,diastolic arrest of the heart is achieved by administration of cold cardioplegic solution, proximal to aortic clamp. When there is aortic regurgitation, aoi-ta is opened and direct coronary ostial cani~ulation is required for giving cardioplegia. When there are multiple blocks in coronary arteries, ante grade cardioplegia will not ensure uniform distribution of the solution. Such cases will need retrograde cardioplegia administered through a coronary sinus cannula. Special retrograde cardioplegia cannulae are available with balloons,which will fill up at the time of cardioplegia. The coronaiy sinus can be cannulated blindly through a purse string on the right atrium. The coronary sinus pressure should be kept below 30 rnm of Hg at the time of cardioplegia.
The cardioplegic solution could be cold asanguinous (clear) or with blood. The comrnomlly used one is St. Thomas solution that essentially contains 20 .meq of potassium cooled down to 4°C. Cardioplegia is usually suppleinenled with topical cold saline or ice slush.
Cardioplegia may be cold or warm. At times patients are operated at normothermia with warm blood cardioplegia. If the patient has recent myocardial infarction or when the ejection fraction is low, it is good to give warm blood (hotshot) just before releasing aortic clamp, to reduce reperfusion injury. The cardioplegic solution is slightly hyper osmolar and buffered with sodium bicarbonate or THAM. Amino acids like Glutamate and Aspartate added to the solution reduces reperfusion injury. Adenosine adds to further
protection. To reduce the injuiy due to oxygen free radicals, super oxide dismutase (SOD) and dimethyl sulphoxide (DMSO) can be added to the cardioplegic solution.Venting of the Heart
It is important that heart does not distend during cardio pulmonary bypass. This is prevented by venting of the left side of the heart by inserting a caiinula into the left atrium, left ventricle, pullnonary artery or aortic root below the cross clamp. The cannula is connected to low suction and the saine ca~lnula is used for &airing of the chambers of the left heart at the end of the intracardinc procedure.
Blood Salvage and Bloodless Open-heart Surgery
At the tiiiie of cardio pulmonary bypass, cardioto~ny suckers suck blood from the chanibers or the heart and pericardium back into the reservoir. In operations like repair of alleurysln of aorta, an equipment called cell saves can be used. This sucks all the spilled blood, wilslies, centrifuges ancl packs into red cell concentrate ready to be administered to the patient. is not without harni: ( I ) It may lend to transfer of infections
Blood transfusion like HIV. Hepatitis B or C, cytomegalovirus, malaria etc., (2) Fcbrilc reaction,(3) Incompatibility, and (4) Limited supply. Conservation ol' blood could be achicved by autologus blootl donation. I11 n Sit patient, blood could I,e collected pre-operatively, up to tcn days before surgery. Intra operatively one or two ini its can be collectetl, just bcfo1.e bypass.
With these methods, it is now possiblc to do blootlless open-heart surgcsy.
Haemo Filtration
Ultra filt~.ution during open heart surgery helps in removing excess l'luicl,especially in rcnal failure patients. Patients are 11:temo diluted (haematocrit 18-20) during bypass. Haemo I'iltration hclps in hlood preservation, cspcci;llly platelets and coagulation hctors. It 1-educes post operative complemenl ;~ctiva[ion and cardio pulmonary bypass induced inllnmrnatory response. There is also improvement in pul~~ioanry and neurologic:~l function. Ultra i'iltration cquipmcnt is connected to the circuit. In childrcn and bal~ies, it is carricd out j u s ~ hcfi~rc coming off bypass. This is called ~nodificd ultra Siltratio~i (MUF).
Circulatory Assist Devices
Intra aortic balloon pump (IAUP) was introduced by Kantrowitz (19hX). It is also known as Counter pulsation or Diastolic augmentation.Indication IABP is comnloiily uscd to s~ipport failing left veiltricle after open-I1ca1-t sui.gery or in cardiogenic shock after myocardial infarction. It is at times used i n unstable angina and as a supportive measure for urgent PTCA or revasc~llarizarion. In patients with post infarction ventriculiu. seplal defect and haemo dynamic instability, IABP is indicated before surgery.
Contra Indication
It is absolutely contra indicated if tl~ere is more than trivial aorlic regurgitation.Aortic aneurysm and severe aorto iliac disease are also contra indications for use of IABP.
Equipment
Basically, it has an intra aortic balloon pump. A balloon with a capacity of 40 ml is passed percutaneously through the femoral artery up to the upper end of descending thoracic aorta. The tip of the balloon has radio opaque marker and should be placed below the left subclavian artery. An inert gas like helium is pumped into the balloon, lo synchronise with diastole. The balloon is deflated
during systole. Synchronisation is achieved by ECG trigger or aortic pressure wave. This will cause diastolic augmentation of blood pressure (counter pulsation) causing augmentation of coronary and cerebral blood flow. When the pump deflates during systole, there is reduction in the after load and of inyocardial oxygen consumption. This improves cardiac output by 10 per cent and helps recovely of myocardium.
Complications
IABP can compromise blood flow to the leg at the time of insertion, pumping or after removal of balloon. It may also cause perforation, bleeding, thrombosis,embolism or dissection of the artery. It is importanl to check the vasculLvity of the leg frequently, both clinically and by Doppler.
Ventricular Assist Devices
These come handy when IABP has failed or when prolonged circulatory supporl is needed. Now Ieft ventricula- (LVAD), right ventricular (RVAD) and bivenlricular assisl devices are available. Implantable assist devices can be fitted in when patient is awaiting h e m transplailtation (biidge to transplantation).
Total Artificial Heart
Jarvik seven was the first successful total artificial heart supporting the patient for 112 days. The disadvantage is that the patient has to be connected to a power source outside and the patienl's heart has to be removed. Totally implantable heart is still a distant dream.
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