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Ritu Airan, Dr.Ujjwal Chowdhury, Dr.Balram Airan, Dr. Poonam Malhotra Which is the most appropriate criterion for size selection of membrane oxygenator for patients with cyanotic congenital heart diseases: Body weight or high hematocrit? Ritu Airan, Dr.Ujjwal Chowdhury, Dr.Balram Airan, Dr. Poonam Malhotra

AIM The primary purpose of the cardiovascular system is to ensure effective perfusion through the capillaries, with the majority of the vessels dealing with blood distribution belonging to the microvasculature

The principal haemodynamic parameters in some polycythaemias have been significantly correlated with increased : haematocrit blood viscosity blood volume Cardiac output diminishes and peripheral vascular resistance increases thereby reducing organ blood flow.

The sustained increase in red cell production in primary polycythaemia is known to elevate both haematocrit and blood viscosity levels. When haematocrit exceeds 50%, blood viscosity increases steeply blood volume also increases in polycythaemia. These increases are responsible for the principal manifestations of polycythaemic patients

Risk factors of high hematocrit Hypoxia: Hypoperfusion Hemolysis

Indications Assesment for hypoxia an assessment of tissue oxygenation PaO2O2 dissolved in arterial bloodTissue Oxygenation PaO2 LowHypoxia Even if PaO2 Normal, Low TissueOxygenationHypoperfusionHyperviscosity

Background Polycythemia (cyanotics)- decreased microcirculatory blood flow (hypoperfusion and hypoxia) Determinants of blood viscosity Aggregation and dispersion of cellular elements Flow velocity (shear rate) Temperature Endothelial integrity Plasma viscosity

Background (contd…) Cyanotics- RBC (Biconcave microspherocytes) rigid, resist deformation in the microcirculation that has high shear stress Cyanotics- increased viscosity, iron deficiency, polycythemia- decreased tissue perfusion reduced cerebral blood flow (hyperviscosity)

Background (contd…) Surface area of gas exchange in oxygenator is (<10m2) which is considerably less than that in the lung (70m2) Thicker blood films- longer exposure to oxygenating membrane Thinner blood films- high flow rates per units area of membrane

Background (contd…) Oxygen transfer in the membrane oxygenator obeys “Ficks Law Of Diffusion” Oxygen transfer vary directly : With total surface area of the membrane Oxygen gradient developed across the membrane Permeability of membrane material to oxygen

Background (contd…) As the driving force for oxygen across the membrane is very high, the oxygenating capacity of a particular membrane is only dependent on the thickness of the blood film

References Annals of Internal Medicine 1988; 109. Anesthesiology 2000; 92. Journal of Cardiothoracic and Vascular Anesthesia 2002 Annals of Medicine 1993; 25.

Factors affecting oxygenation FiO2 / sweep gas Hematocrit Flows Hypothermia

Standardized protocol in AIIMS Body weight Oxygenator Priming volume 8-12kg Medtronic – minimax 800ml 12-30 kg Terumo Sx-10 1000ml >30 kg Terumo SX-18 1800 ml

Patients and methods Number of patients : 132 Tetralogy of Fallot : n=104 Bi-directional Glenn: n=20 Total cavopulmonary connection: n=8 Age: 3 years – 50 years (mean±SD 102.27±80.1)

Patients and methods (contd…) Group I (n=62) Cyanotic patients with preoperative hematocrit > 60% Group II (n=70) Cyanotic patients preoperative hematocrit <60%

Patients and methods (contd…) In group I Large surface oxygenator used Hemodilution done Withdrawal of perfusate In group II Regular oxygenator used

Patients and methods (contd…) Blood samples monitored for PO2 PCO2 Hemoglobin Saturation Acidosis Observation for intraoperative hematuria

Results Body weight (kg) Oxygenators Priming volume (ml) Flow range (LPM) No. of patients Group I (n=62) Group II (n=70) 8-12 Medtronic-Minimax 800 0.5-2.3 5+15* 20 12-30 Terumo SX-10 1000 0.5-4.0 20+8+2** 40 >30 Terumo SX-18 1800 0.5-7.0 12 10 *Used Terumo SX-10 ** Terumo Sx-18 During CPB, group II patients demonstrated normal PaO2 (223.8±20.3). Despite recommended perfusion flow and gas-to-blood flow ratio, 32 patients of group I weighing between 20-30kg and >30kg with Terumo SX-10 and SX-18 oxygenators respectively demonstrated systemic arterial desaturation (91-98%) with intraoperative hematocrit ranging >35% and intraoperative hematuria (n=20).

Results (contd…) Optimal intraoperative SaO2 >99% and oxygenation was achieved by further hemodilution in patients weighing >30kg and by withdrawal of prime to promote additional hemodilution in patients weighing between 12-30kg. With this background, Terumo SX-10 was successfully used instead of Minimax in 15 of 20 patients weighing between 8kg-12kg Terumo SX-18 was used instead of Terumo SX-10 in patients weighing between 20kg-30kg to achieve SaO2 between 99-100% with mean PaO2 234.8±20.30

Group comparison for PaO2 Variables Group I Group II P value PO2 162.16±50.86 234.8±20.30 0.001

Results (contd…) Variables Pre Post P value Group I 162.16±50.86 220.05±37.95 0.001 Group II 234.8±20.3 249.55±18.36 0.002

Trend SX-10 was used instead of minimax in patients weighing 8-12 kg SX-18 was used instead of SX-10 in patients weighing 18-30kg Withdrawal of perfusate to promote additional hemodilution was done to achieve improved gas efficiency and decrease hemolysis and hypoperfusion

ADVANTAGE OF HEMODILUTION Lowers Blood Viscosity⇒decrease in Hematocrit. Improves Microcirculation. Counteracts the increased Viscosity by Hypothermia

Conclusions Hemoconcentration causes marked reduction in blood flow through microcirculation Greater risk of arterial desaturation in cyanotic patients with high hematocrit Hence larger membrane surface oxygenator and hemodilution may be done for cyanotic patients with high hematocrit to ensure effective perfusion and oxygenation during Cardiopulmonary Bypass

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