Essay Example on Cardiothoracic surgeries which require use of a Heart Lung Machine









Cardiothoracic surgeries which require use of a Heart Lung machine HLM are considered the most common operation performed since 1953 all over the world but mainly in North America and Europe Notwithstanding that new technologies and techniques are being added in HLM also new guidelines are introduced to safety operate cardiopulmonary bypass CPB Nevertheless some things remains constant These things consider the achievement of the required optimal perfusion during HLM and relationship between the optimal blood flow and perfusion pressure during CPB Even though more research papers are in favour of a minor superiority of the optimal flow requirements compared to the corresponding optimal BP blood pressure needs their role is fairly dependant on each other The usage of the current Blood Parameter Monitoring System 500 Terumo CDI helped with evolution of the perfusion technique Optimal perfusion now can be delivered and assessed but its results in real time while information from CDI such as lactate LAC venous oxygen saturation Sv02 and levels of Hb haemoglobin or haematocrit Hct can be used as a marker of optimal perfusion and contribute to the development of new guidelines in the future Changing the BF and the BP to achieve a balance between two demands of optimal o2 delivery to the patient and surgical visualisation is important Andersson 1994 If the SvO2 is 80 or above it is believed that the patient is being given more 02 than his body demands is and the perfusion is adequate 

On the other hand if Sv02 is 70 or below it is believed that that the patient is not receiving enough 02 to supply his body demand and the perfusion is not optimal or Hct is too low and the patient should receive more red blood cells Other methods can be used to observe if the patient received optimal perfusion such as urine output or brain saturation however to asses other tissues it is more challenging Gravlee 2016 Blood Flow BF versus Blood Pressure BP The main function of HLM is to deliver O2 to tissues and organs that require it Fig 1 shows that the F is a function of ΔP and R from a purely teleological point of view it would be logical that maximizing blood F as opposed to maximizing ΔP which may or may not maximize F depending on R would be the most logical approach to HLM management during operation That stated notwithstanding over 65 years of study and experience the perfect BF or and perfusion BP is still not known Nor it is known whether BP or BF is more significant during CPB There are some issues with maximizing BF Firstly F rates are related with significant trauma of red blood cells and elevate the inflammatory response to HLM Secondly F carry an increased embolic burden Finally an increased in total F does not guarantee increased oxygen delivery DO2 to tissues and organs of interest this is because the HLM is not able to alter regional F Therefore if HLM F rates are raised by perfusing fairly unimportant tissues beds the increased in inflammation and or trauma cannot be accepted and might be harmful to the patient Slater 2001 in his study of regional F rate in Porcus on HLM discovered that regional F to the kidney pancreas and brain all when F were from 1 6 to 1 9L min m2 In fact at these increased levels kidney and brain F were 55 and 65 of pre HLM F rate respectively Slater s findings are similar to Rogers s 1992 human findings which proved that HLM flow from 1 75 to 2 25L min m2 has no effect on brain blood flow BBF or brain metabolic rate consumption in patients and was corresponding with Govier s 1984 findings which proved that changes in F rate from 1 01 to 2 01 L min m2 had no effect on BBF during hypothermic use of HLM in patients

Claims have been made in favour of optimizing BP at the expenses of BF firstly brain autoregulation maintains constant CBF Cerebral Blood Flow from mean arterial pressure MAP of 51 151mmHg probably decreased during hypothermic HLM Patients with BP are believed to have a right shifted autoregulation oxyhemoglobin dissociation curve and patients with Diabetes mellitus may have altered autoregulation thus BP or F can possibly be justified in these care receiver Moreover while HLM can change the total F it is not able to individually affect regional F this job is left to the organs themselves During HLM end organs have only one mechanism which they are able to change RF regional flow alterations in RVR regional vascular resistance Hasse 2012 The higher the BP the broader the range of RF available to each individual organ However this concept has not been proven Increased F rates are also unfavourable in that they raise brachial F to the Pulmonis increase suture line strain and increase collateral F to the Cor which accelerate washout of cardioplegia The other disadvantages of increased flow rates during CPB are red blood cells trauma less effective cardioplegia increased pulmonary shounting BBF velocities are associated with complement activation after HLM high microemboli loads and may not affect regional flow Slater 2001 Also BF velocities can lead to creation of turbulence flow increase in Reynolds number Fig 1a usually post stenotic when pulsatile F is used

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