This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Alston, R. P. Articles by Kurumatani, N. Search for Related Content PubMed PubMed Citation Articles by Alston, R. P. Articles by Kurumatani, N.

---

LETTERS TO THE EDITOR

Cerebral Oxygenation and Cognitive Decline

Department of Anesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, Edinburgh, Scotland, UK

To the Editor:

The article of Yoshitani et al. (1) regarding cerebral hypoperfusion and cognitive outcome after cardiac surgery has some limitations (1). The arterial carbon dioxide tension (PaCO₂) values reveal a large degree of variance. As PaCO₂ is a fundamental determinant of SjvO₂, it should have been entered as varying covariate into the analysis of variance model. As a result, most of the between-group and within-group differences would likely have been eliminated (2,3).

A statistical tenet is that variables should be orthogonal, i.e., independent of each other. All the predictor variables in Table 4 are nonorthogonal, being related by being either mathematically coupled, highly intercorrelated, or repeated measures (3–5). Being robust and independent estimates, either jugular venous oxygen saturation or tension (SjvO₂, PjvO₂) should have been used, and given the orthogonal nature of repeated measures, a summary should have been generated for all the time points (5,6).

Although some advocate the use of categorical definitions of cognitive decline (7), they are arbitrary (5). As SjvO₂, PjvO₂, and cognitive decrement are continua, linear (not logistic) regression should have been used (5). In taking this approach, we have been unable to relate any level of SjvO₂, high or low, to either cognitive or neurological outcome 3 mo after coronary artery bypass grafting surgery (5,6).

References

1. Yoshitani K, Kawaguchi M, Sugiyama N, et al. The association of high jugular bulb venous oxygen saturation with cognitive decline after hypothermic cardiopulmonary bypass. Anesth Analg 2001; 92: 1370–6.[Abstract/Free Full Text]
2. Millar SA, Alston RP, Souter MJ, Andrews PJD. Aerobic, anaerobic and combination estimates of cerebral hypoperfusion during and after cardiac surgery. Br J Anaesth 1999; 81: 936–9.
3. Millar SM, Alston RP, Andrews PJ, Souter MJ. Cerebral hypoperfusion in the immediate postoperative period following coronary artery bypass grafting, heart valve and abdominal aortic surgery. Br J Anaesth 2001; 87: 229–36.[Abstract/Free Full Text]
4. Walsh TS, Le A. Mathematical coupling in medical research: lessons from studies of oxygen kinetics. Br J Anaesth 1998; 81: 118–20.[Free Full Text]
5. Robson MJ, Alston RP, Deary IJ, et al. Cognition after coronary artery surgery is not related to postoperative jugular bulb desaturation. Anesth Analg 2000; 91: 1317–26.[Abstract/Free Full Text]
6. Robson MJA, Alston RP, Deary IJ, et al. Jugular bulb oxyhaemoglobin desaturation, S100ß and neurological and cognitive outcome after coronary artery surgery. Anesth Analg, In Press.
7. Murkin JM, Newman SP, Stump DA, Blumenthal JA. Statement of consensus on assessment of neurobehavioral outcomes after cardiac-surgery. Ann Thorac Surg 1995; 59: 1289–95.[Free Full Text]

Department of Anesthesiology, Nara Medical University, Nara, Japan Department of Hygiene, Nara Medical University, Nara, Japan

In Response:

Our study (1) aimed to clarify the role of SjO₂ for cognitive decline after hypothermic cardiopulmonary bypass. We used the logistic regression model for this purpose. Dr. Alston, however, states that the linear (not logistic) regression model should be used because SjO₂ and other parameters involved are continuous variables. We do not agree with this opinion. Logistic regression model can accept continuous variables as explanatory variables in nature, and examples using continuous variables are shown in the standard textbook of logistic regression analysis (2). Our outcome is dichotomous: either "decline" or "not decline" of cognitive function. Such outcomes agree with the logistic model better than with the linear model. A more important issue is whether the model suits the data when adopting a statistical model. In our case, Hosmer-Lemeshow goodness-of-fit test revealed that the logistic regression model fit to the observed data shown in Tables 4 and 5. We therefore conclude that our analysis did not have any statistical problems.

In our article (1), Table 4 showed significant predictors of postoperative cognitive decline. Although large correlations among the predictors were recognized, we presented the basic information for the multivariate logistic regression analysis. Although variables should be independent of each other, highly intercorrelated variables are generally eliminated in multivariate regression analysis. As a result, multivariate logistic regression analysis in our study indicated SjO₂ and PjvCO₂, which are reciprocally independent, as significant predictors.

We recognized that PaCO₂ is a fundamental determinant of SjO₂. PaCO₂ was entered as varying covariate into the univariate logistic regression analysis in our study. PaCO₂ was not a significant predictor, although we did not show the result in Table 4.

To compare the cognitive decline of two divided groups, such as cardiopulmonary bypass (CPB) group and non-CPB group, noncategorical definition may be used. However, most previous studies (3–10) advocated the use of categorical definitions of cognitive decline. It is controversial whether linear regression is better than logistic regression analysis as a statistical method for investigating the associated factors of cognitive decline. We should complete an even more detailed examination on cognitive decline.

References

1. Yoshitani K, Kawaguchi M, Sugiyama N, et al. The association of high jugular bulb venous oxygen saturation with cognitive decline after hypothermic cardiopulmonary bypass. Anesth Analg 2001; 92: 1370–6.
2. Hosmer DW, Lemshow SL. Applied logistic regression. New York: John Wiley & Sons, 1989.
3. Robson MJ, Alston RP, Deary IJ, et al. Cognition after coronary artery surgery is not related to postoperative jugular bulb desaturation. Anesth Analg 2000; 91: 1317–26.
4. Shaw PJ, Bates D, Cartlidge NEF, et al. Neurologic and neuropsychologic morbidity following major surgery: comparison of coronary artery bypass and peripheral vascular surgery. Stroke 1987; 18: 700–7.[Abstract/Free Full Text]
5. Thomas AH, James EH. Neuropsychological alterations after cardiac surgery. J Thorac Cardiovasc Surg 1988; 96: 326–31.[Abstract]
6. Bruggemans EF, Van Dijk JG, Huysmans HA, et al. Residual cognitive dysfunction at 6 months following coronary artery bypass graft surgery. Eur J Cadiothorac Surg 1995; 9: 636–43.[Abstract]
7. Murkin JM, Martzke JS, Buchan AM, et al. A randomized study of the influence of perfusion technique and pH management strategy in 316 patients undergoing coronary artery bypass surgery. J Thorac Cardiovasc Surg 1995; 110: 349–62.[Abstract/Free Full Text]
8. Venn GE, Patel RL, Chambers DJ. Cardiopulmonary bypass: perioperative cerebral blood flow and postoperative cognitive deficit. Ann Thorac Surg 1995; 59: 1331–5.[Abstract/Free Full Text]
9. Vingerhoets G, Van Nooten G, Vermassen F, et al. Short-term and long-term neuropsychological consequences of cardiac surgery with extracorporeal circulation. Eur J Cadiothorac Surg 1997; 11: 424–31.[Abstract]
10. Toner I, Taylor KM, Newman S, et al. Cerebral functional changes following cardiac surgery: Neuropsychological and EEG assessment. Eur J Cadiothorac Surg 1998; 13: 13–20.[Abstract/Free Full Text]

This article has been cited by other articles:

				R. P. Alston and Y. Kadoi Rewarming Rate, Diabetes, Jugular Bulb Saturation, and Cognitive Outcome from CABG Surgery * Response Anesth. Analg., March 1, 2003; 96(3): 914 - 915. [Full Text] [PDF]

				Y. Kadoi, S. Saito, F. Goto, and N. Fujita Slow Rewarming Has No Effects on the Decrease in Jugular Venous Oxygen Hemoglobin Saturation and Long-Term Cognitive Outcome in Diabetic Patients Anesth. Analg., June 1, 2002; 94(6): 1395 - 1401. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Alston, R. P. Articles by Kurumatani, N. Search for Related Content PubMed PubMed Citation Articles by Alston, R. P. Articles by Kurumatani, N.