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Eur J Cardiothorac Surg 2001;19:732-733
© 2001 Elsevier Science NL

Letter to the Editor

Normothermic cardiopulmonary bypass is beneficial for cognitive brain function after coronary artery bypass grafting – a prospective randomized trial

^a Department of Anaesthesia, Papworth Hospital, Cambridge, UK
^b Department of Surgery, Papworth Hospital, Cambridge, UK

Received 12 October 2000; accepted 23 February 2001.

Corresponding author.

We read with interest the article by Grimm and colleagues [1] comparing cognitive brain function after normothermic and mild hypothermic cardiopulmonary bypass (CPB). At first glance, the observation that patients subjected to mildly hypothermic CPB have significantly prolonged postoperative P300 auditory evoked potentials (AEPs) lends support to the suggestion that this strategy causes more subclinical neurological impairment than normothermic CPB. We would, however, like to make a number of comments:

In this study, 144 consecutive patients were randomized to either hypothermic or normothermic CPB. Details of the randomization process are not, however, provided. We assume that the statement "We performed normothermic CPB in all patients" (page 272) is a typographical error.

It is now established that rapid and excessive rewarming during CPB is associated with jugular bulb desaturation [2] and adverse neuropsychological outcome [3]. Moreover, nasopharyngeal temperature monitoring during rewarming has been shown to underestimate jugular venous temperature by as much as 3.4°C [4]. As the authors allude to this in their discussion, it is curious that they omit a description of how core body temperature was maintained at 37°C before and after CPB in their normothermic group. Furthermore, there is no description of the management of patients in the hypothermic group – specifically inflow temperature and the rate and extent of rewarming. We cannot be sure that patients in the hypothermic CPB group were not subjected to significant cerebral hyperthermia during rewarming.

The significantly greater postoperative blood loss observed in the hypothermic group, while probably not of clinical significance, may indicate differences in intraoperative bleeding. If cardiotomy suction was used in all cases and bleeding was greater in the hypothermic group it could be expected that patients in this group were subjected to a greater cerebral microembolic load during CPB [5]. In addition, it could be anticipated that prolonged CPB would have increased cerebral microembolic load [6]. No data concerning the duration of CPB in the two study groups are presented.

The significantly greater mean duration of postoperative tracheal intubation (21.2 vs. 13.4 h; P=0.005) observed in the hypothermic group is rather puzzling. Our own experience, and indeed that reported by others [7], is that any trend toward prolonged intubation in patients subjected to hypothermic CPB is neither clinically nor statistically significant. It is interesting to note that, in a prospective randomized study of the influence of CPB temperature on neuropsychologic outcome, the Bristol group [8] reported a decreased mean duration of intubation in their hypothermic and tepid CPB groups (10.7 and 8.3 h, respectively, vs. 12.8 h, P>0.05).

We were not surprised to read that mini mental state examination (MMSE) scores remained normal in both groups. Although the MMSE is a reliable screening tool it is relatively insensitive to post cardiac surgery changes. The finding that a single psychometric test failed to detect any difference between the patient groups is not unexpected for two reasons. Firstly the study was probably insufficiently powered to detect a significant difference, and secondly, it is recognized that the use of a battery of psychometric tests, which permits assessment of several cognitive domains, increases the likelihood of detecting change in cognitive function.

In conclusion, therefore, we suggest that it is not possible to conclude from the data presented, that hypothermia per se is responsible for prolonged postoperative P300 AEPs.

References

1. Grimm M., Czerny M., Baumer H., Kilo J., Madl C., Kramer L., Rajek A., Wolner E. Normothermic cardiopulmonary bypass is beneficial for cognitive brain function after coronary artery bypass grafting – a prospective randomized trial. Eur J Cardio-thorac Surg 2000;18:270-275.[Abstract/Free Full Text]
2. Croughwell N.D., Frasco P., Blumenthal J.A., Leone B.J., White W.D., Reves J.G. Warming during cardiopulmonary bypass is associated with jugular bulb desaturation. Ann Thorac Surg 1992;53:827-832.[Abstract]
3. Croughwell N.D., Newman M.F., Blumenthal J.A., White W.D., Lewis J.B., Frasco P.E., Smith L.R., Thyrum E.A., Hurwitz B.J., Leone B.J. Jugular bulb saturation and cognitive dysfunction after cardiopulmonary bypass. Ann Thorac Surg 1994;58:1702-1708.[Abstract]
4. Grocott H.P., Newman M.F., Croughwell N.D., White W.D., Lowry E., Reves J.G. Continuous jugular venous versus nasopharyngeal temperature monitoring during hypothermic cardiopulmonary bypass for cardiac surgery. J Clin Anesth 1997;9:312-316.[Medline]
5. Brooker R.F., Brown W.R., Moody D.M., Hammon J.W., Reboussin D.M., Deal D.D., Ghazi-Birry H.S., Stump D.A. Cardiotomy suction: a major source of brain lipid emboli during cardiopulmonary bypass. Ann Thorac Surg 1998;65:1651-1655.[Abstract/Free Full Text]
6. Brown W.R., Moody D.M., Challa V.R., Stump D.A., Hammon J.W. Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli. Stroke 2000;31:707-713.[Abstract/Free Full Text]
7. Engelman R.M., Pleet A.B., Rousou J.A., Flack J.E., Deaton D.W., Pekow P.S., Gregory C.A. Influence of cardiopulmonary bypass perfusion temperature on neurologic and hematologic function after coronary artery bypass grafting. Ann Thorac Surg 1999;67:1547-1555.[Abstract/Free Full Text]
8. Regragui I., Birdi I., Izzat M.B., Black A.M., Lopatatzidis A., Day C.J., Gardner F., Bryan A.J., Angelini G.D. The effects of cardiopulmonary bypass temperature on neuropsychologic outcome after coronary artery operations: a prospective randomized trial. J Thorac Cardiovasc Surg 1996;112:1036-1045.[Abstract/Free Full Text]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): John J. Dunning Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Arrowsmith, J. E. Articles by Dunning, J. J. Search for Related Content PubMed PubMed Citation Articles by Arrowsmith, J. E. Articles by Dunning, J. J. Related Collections Cerebral protection Coronary disease