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LETTER TO EDITOR |
Department of Cardiovascular and Thoracic Surgery, Postgraduate Institute of Medical Education & Research, Chandigarh 160012, India, Email: drjaswindersingh{at}yahoo.co.in, Telephone: 91 172 2226 2741, Fax: 91 172 274 4401
This is in reference to the article ‘Cardiopulmonary Bypass without preoperative exchange transfusion in sicklers’ by Madan M Maddali, et al1.We would like to congratulate the authors for the excellent article by bringing out important issues and like to emphasise a few points in management of patients with sickle cell disorder.
In patients with sickle cell disease some sickling begins to appear at 85% hemoglobin oxygen saturation and sickling of red blood cells is complete at 38% hemoglobin oxygen saturation, whereas in patients with sickle cell trait sickling begins at hemoglobin oxygen saturation of approximately 40%.Since sickling results from decreased hemoglobin oxygen saturation, maintaining adequate arterial oxygen tension assumes paramount importance. Adequate capillary perfusion with short transit time and avoidance of low output states (to prevent low mixed venous hemoglobin oxygen saturation) are also important 2. Thus continuous or frequent measurements of arterial and mixed venous hemoglobin oxygen saturation help to maintain adequate saturation.
The aim of preoperative exchange transfusion is to achieve hemoglobin A fraction of 60%–70%, which is also the level sought when treating a major sickle cell crisis 2. It not only increases the hemoglobin A but also suppresses the production of hemoglobin S. In non anemic patients exchange transfusion can be accomplished intra operatively, by sequestrating the initial cardiopulmonary bypass venous return from patient after priming the circuit with whole blood containing hemoglobin A 3. As done for 9 of 29 CABG patients, 3 of 8 patients undergoing valve replacement and all 8 patients of intracardiac repair1.
It is well known that acidosis shifts the oxyhemoglobin dissociation curve to right, which increases tendency towards sickling .Thus arterial and mixed venous blood gases should be done frequently and any developing acidosis should be aggressively treated with sodium bicarbonate.2,3 It is rightly pointed out in the article that hypoperfusion resulting from hypothermia, diminished intravascular volume, poor patient positioning, tourniquets, low cardiopulmonary bypass systemic flows or low cardiac output states should be avoided.
Authors have not mentioned which types of valve prosthesis were used in 8 patients undergoing valve replacement. Mechanical prosthetic valves may predispose the patient to increased hemolysis thus such valves are not recommended in these patients 4. Other means of avoiding mechanical blood trauma include minimizing the use of cardiotomy suction and venting.
Successful cases have been reported even using hypothermic circulatory arrest 4. But it appears advisable to minimize or avoid hypothermia during CPB, thus noromothermic beating heart surgery may be a good option for these patients if it is feasible.
REFERENCES
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