J Thorac Cardiovasc Surg 1998;116:531
© 1998 Mosby, Inc.
The relation between pump flow rate and pulsatility on cerebral hemodynamics during pediatric cardiopulmonary bypass
Gabriel Chow, MRCIP,
Idris G. Roberts, BSc,
A. A. David Edwards, FRCP,
Adrian Lloyd-Thomas, FRCA,
Martin J. Elliott, FRCS
Reply to the Editor
We thank Ündar and Fraser for their interest in our work. We agree that there are significant difficulties in defining pulsatility; indeed modified roller pumps may produce relatively little pulsatile power, particularly when used with membrane oxygenators. Nevertheless, since they are commercially available and their proponents consider them to have significant advantages for their patients in terms of neurologic outcome, as well as cardiac function, it is not unreasonable to assess their effects onthe cerebral circulation. We used the hollow-fiber membrane oxygenators, chosen for our neonatal and paediatric patients (M. Davis, personal communication), because they have the lowest transmembrane pressure gradient both before and after the oxygenator. It is difficult in a clinical situation to produce data on all the aspects of pulsatility that might be examined on a research basis, but we provided evidence that our modified roller pump did produce a pulsatile waveform in the middle cerebral artery. Since the aim in patients must be to minimize the need for invasive hardware, the transcranial Doppler ultrasound technique and the Gosling pulsatility index
1 might be useful tools in future studies of pulsatile pumps in clinical cardiopulmonary bypass.
It may well be that any benefit of pulsatile pumps will be seen at low cerebral perfusion pressures. Our study was designed to look at this question, but could not demonstrate a higher total hemoglobin value at low perfusion pressures using the Stöckert pump (Stöckert, Munich, Germany) in the pulsatile compared with the nonpulsatile mode. The short time periods were chosen to ensure that six different situations (pulsatile vs nonpulsatile flow at each of three pump flows) could be examined in each patient. We were interested to hear of the development of a pulsatile pump designed for use in infants; clinical studies specifically targeted at examining their performance at the low pump flows commonly used during cardiopulmonary bypass in very young children might look at total hemoglobin over longer time periods. However, inasmuch as Lodge and associates 2 also found no difference in cerebral blood flow between pulsatile and nonpulsatile flow in their animal model, there are no data available to support the use of pulsatile flow in children as a means of improving cerebral hemodynamics.
Departments of Neurosciences, Cardiothoracic Surgery, and AnaestheticsInstitute of Child Health/Great Ormond Street Hospital for ChildrenDepartments of Paediatrics and Neonatal MedicineRoyal Postgraduate Medical School,
London, United Kingdom
References
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Grossi EA, Connolly MW, Krieger KH, Nathan IM, Hunter CE, Colvin SB, et al. Quantification of pulsatile flow during cardiopulmonary bypass to permit direct comparison of the effectiveness of various types of pulsatile and nonpulsatile flow. Surgery 1985;98:547-53.[Medline]
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Lodge AJ, Ündar A, Daggett W, Runge TM, Calhoon JH, Ungerleider RM. Regional blood flow during pulsatile cardiopulmonary bypass and after circulatory arrest in an infant model. Ann Thorac Surg 1997;63:1243-50.[Abstract/Free Full Text]
