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EDITORIAL Table of Contents   
Year : 2009  |  Volume : 12  |  Issue : 2  |  Page : 104-106
Brain, cardiopulmonary bypass and temperature: What should we be doing?


Department of Cardiac Anaesthesia, All India Institute of Medical Sciences, New Delhi, India

Click here for correspondence address and email

Date of Web Publication21-Jul-2009
 

How to cite this article:
Chauhan S. Brain, cardiopulmonary bypass and temperature: What should we be doing?. Ann Card Anaesth 2009;12:104-6

How to cite this URL:
Chauhan S. Brain, cardiopulmonary bypass and temperature: What should we be doing?. Ann Card Anaesth [serial online] 2009 [cited 2022 Jan 27];12:104-6. Available from: https://www.annals.in/text.asp?2009/12/2/104/53427


Neurological complications after cardiopulmonary bypass (CPB) can render an otherwise perfect surgery less meaningful. Neurological dysfunction after cardiac surgery increases the duration of hospitalization, costs, morbidity and mortality and decreases the postoperative quality of life. Various causative mechanisms have been postulated for neurological injury after CPB including, embolization of gaseous and particulate matter, cerebral hypoperfusion, and inflammatory response to CPB. [1]

Although a major neurological event such as stroke after cardiac surgery is not very common (1.5% to 7.5%), occurrence of neurocognitive dysfunction after CPB is. Incidence varies from 30 to 80%. Such dysfunction may persist for up to five years after surgery. [2]

Various techniques have been described to reduce or prevent the occurrence of stroke and encephalopathy. They include epiaortic scanning (to avoid aortic cannulation at atheromatous sites), avoidance of repeated side clamping and unclamping and use of a single aortic cross clamp for performing both proximal and distal coronary anastamosis. Use of arterial line filters to trap microemboli, both gaseous and particulate, maintenance of high perfusion pressure during CPB, and segregation and fat filtration of cardiotomy suction have also been shown to benefit the patients. [3]

The management of temperature during CPB is one of the simplest interventions that could affect neurological outcome after CPB. Traditionally, hypothermia has been the mainstay of management during CPB allowing reduction of regional blood flows, lowering of hematocrit, and decreased use of blood for the priming of the bypass circuit. [4] Hypothermia reduces the size of experimental brain infarction and leads to improved neurological outcome and survival. [5] In victims of out-of-hospital cardiac arrest, cerebral benefits occurred with modest temperature reductions of 2 to 5 o C. [6] Therapeutic hypothermia has been used to improve neurological outcomes in patients with severe head injury [7] and resuscitation from cardio-respiratory arrest with mild hypothermia improving both survival and neurological outcome. [8] However, after providing hypothermia during CPB, rewarming is necessary, and rewarming has come to be recognized as yet another cause of neurological dysfunction after CPB. Unrecognized cerebral hyperthermia could worsen ischemic brain injury after CPB. [9] Cerebral hyperthermia could occur due to the selective hyperperfusion of the brain because of proximity of the carotid arteries to the aortic cannula, and the actual brain temperature may be underestimated by standard temperature monitoring. There are many strategies proposed to avoid hyperthermia during rewarming, the most notable being the avoidance of full rewarming to 37 o C. Nathan and colleagues [10] reported that rewarming from hypothermic (32 o C) bypass to a nasopharyngeal temperature of 34 o C was associated with fewer neurocognitive deficits at one week and three months after cardiac surgery compared to rewarming to 37 o C. In this study on 223 patients undergoing CABG, there was no difference in the duration of postoperative mechanical ventilation, blood loss, transfusion requirements, and reoperation rates irrespective of whether rewarmed to 34 or 37 o C.

Hyperthermia delays neuronal metabolic recovery and increases excitotoxic neurotransmitter release, which are as glutamate, oxygen free radical production, intra- cellular acidosis, and blood brain barrier permeability. Hyperthermia also affects protein kinase activity and destabilizes the cytoskeleton. [11] Hyperthermia worsens the prognosis of patients with acute stroke by increasing the infarct size and mortality. The site of temperature monitoring is also important. [12] If rectal or bladder temperatures are brought to 37 o C, brain temperature is likely to be 2 to 4 o C higher than that. Nasopharyngeal temperature monitoring is the closest to brain, and although it equilibrates with jugular bulb blood temperature during cooling, by 1-2 o C during rewarming, at which time thermal injury can occur. As majority of strokes and embolic episodes occur during surgery; cerebral hyperthermia may aggravate such neurological injury. Aggressive rewarming in an attempt to avoid the after drop of temperature may worsen cerebral injury that may result from embolism or infarction.

Clinicians are concerned about the risks posed by postoperative hypothermia as a consequence of inadequate rewarming, which include coagulopathy, shivering, arrhythmias, possibility of wound infection, and increased hospital stay. [13] However, the studies by Nathan [10] and Sahu [14] show that these occur. [15] Sahu and colleagues studied neurocognitive dysfunction in 80 adults undergoing CABG with the use of hypothermic CPB. They observed that patients rewarmed to 33 o C had less neurocognitive dysfunction, and less release of S - 100 b at 24 hours compared to the group rewarmed to 37 o C. They also studied 80 children with tetralogy of Fallot undergoing intra- cardiac repair with hypothermic CPB at 28 o C. The group of children rewarmed to 33 o C had less neurocognitive dysfunction, less release of s - 100 b at 24 hours, and there was no difference in post operative bleeding, inotrope requirement, or need for pacing. Based on their results, it was recommended that rewarming should be slow with a gradient between patient blood, water bath temperature maintained at not more than 2 o C and water bath temperatures more than 37 o C. Grigore [16] studied the rewarming rate and found that patients rewarmed from hypothermia (32 to 34 o C) in a conventional manner with nasopharyngeal and CPB perfusate gradient of 4 to 6 o C, had worse neurocognitive outcome compared to the study group where the temperature gradient was 2 o C. These measurements were made after admitting credence to aortic cross clamp time, presence of diabetes, and baseline congnitive function.

As the cardiac surgical population presenting for CABG and valve surgery gets older and that presenting for congenital cardiac surgery gets younger, the risk of neurological injury gets higher. Rapid rewarming may result in an overshoot of targeted temperature and the resultant hyperthermia may increase the incidence of neurocognitive dysfunction. Some studies [17] have reported significant reduction in the jugular vein oxygen saturation (SjvO 2 ) during rewarming from hypothermic CPB was associated with a poor neurological outcome. Diabetic patients have an altered autoregulation during rewarming and may specially benefit from slower rewarming.

The Cordeon Cobra catheter [18] (Cordeon Corp, Cupertino, Clarify Calif) allows independent control of aortic arch and descending aortic temperatures, and profoundly reduces incidence of cerebral complications, maintains cerebral hypothermia and systemic normothermia due to dual perfusion. Investigators at Emory [19] studied 1001 patients and observed a stroke rate of 3.1% in a warm cohort and a 1.0% in a cold cohort; higher incidence in the warm group, probably due to active rewarming to 37 o C, while the Warm Heart Investigators, [20] group from Toronto cited a stroke rate of 1.6%, in the warm and 1.5% in the cold group out of a total of 1732 patients. This difference in contrast to the emory study [19] was seen because patients in the warm group in this study were not warmed actively to 37 o C compared to the Emory study but temperatures in the warm group were allowed to drift.

It is difficult to study the incidence of stroke as an outcome indicator during cardiac surgery in relation to hypothermia. Because of its low incidence, the researchers use the incidence of neurocognitive dysfunction as a surrogate of neurological injury. Postoperative neurocognitive dysfunction results from diffuse brain injury which might be caused by microemboli during CPB.

Regragui [21] randomized 93 patients to three groups perfused at 37 or 32 or 28 o C. They found the least postoperative dysfunction in the 28 o C group. Rubensss [22] studied 900 patients undergoing CABG in two parts. In the first part, patients randomized to hypothermia with passive postoperative rewarming had less neurocognitive dysfunction compared to patients actively rewarmed to 37 o C. In order to clarify the role of hypothermia compared to active rewarming in part II of the study, the patients in the hypothermic group were cooled and maintained at 34 o C with no active rewarming, while in the normothermic group the patients were kept at 37 o C throughout the operative period. No difference in neurocognitive dysfunction in the two groups was seen, implying that the benefit in part I of the study was due to lack of active rewarming, and not hypothermia alone.

All these and other similar studies on CPB and temperature related neurological dysfunction allow us to make the following observations related to temperature management on CPB. Use adequate hypothermic CPB as dictated by the requirements of the surgery and the patient. Start rewarming early; avoid gradients of more than 2 o C between the water bath and the patient's blood. Avoid water bath temperatures above 37 o C. In patients who are at high risk for development of neurological injury (such as diabetics, elderly, presence of occlusive carotid artery disease, previous neurological injury), it may be wise to allow rewarming up to 33 o C. If an intra-operative event that is likely to have an adverse neurological outcome such as prolonged hypotension, bradycardia or cardiorespiratory arrest occurs, it may be wise to electively render the patient hypothermic (33 o C) for at least 24-48 hours.

 
   References Top

1.Arrowsmith JE, Grocot HP, Reves JG, Newman MF. Central nervous system complications of cardiac surgery. Br J Anaesth 2000;84:378-93.  Back to cited text no. 1    
2.Neuman MF, Grocot HP, Mathew JP, White WD, Landolfo K, Reves JG, et al . Report of the substudy assessing impact of neurocognitive function on quality of life 5 years after cardiac surgery. Stroke 2001;32:2874-81.   Back to cited text no. 2    
3.Hogue CW, Gottesman RF, Stearn J. Mechanisms of neurological injury from cardiac surgery. Crit Care Clin 2008;24:83-98.  Back to cited text no. 3    
4.Bigelow WG, Lindsey WK, Greenwood WF. Hypothermia: It's possible role in cardiac surgery: An investigation of factors governing survival of dogs at low body temperatures. Ann Surg 1950;132:849-66.  Back to cited text no. 4    
5.Busto R, Dietrich WD, Globus MY, Valdιs I, Scheinberg P, Ginsberg MD. Small differences in brain temperature critically determine the extent of neurological injury. J Cereb Blood Flow Metab 1987;7:729-38.  Back to cited text no. 5    
6.Schneider A, Bottinger BW, Popp E. Cerebral resuscitation after cardiocirculatory arrest. Anesth Analg 2009;108:971-9.  Back to cited text no. 6    
7.Marion DW, Penrod LE, Kelsey SF, Orbist WD, Kochanek PM, Palmer AM, et al . Treatment of traumatic brain injury with moderate hypothermia. J Neurosurg 1997;336:540-6.  Back to cited text no. 7    
8.The Hypothermia After Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve neurological outcome after cardiac arrest. N Engl J Med 2002;346:549-56.   Back to cited text no. 8    
9.Cook DJ, Orszulak TA, Daly RC, Buda DA. Cerebral hyperthermia during cardiopulmonary bypass in adults. J Thorac Cardiovasc Surg 1996;111:268-9.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]
10.Nathan HJ, Rodriguez R, Wozny D, Dupuis JY, Rubens FD, Bryson GL, et al . Neuroprotective effect of mild hypothermia in patients undergoing coronary artery bypass surgery with cardiopulmonary bypass: 5 years follow up of a randomized trial. J Thorac Cardiovasc Surg 2007;133:1206-11.   Back to cited text no. 10  [PUBMED]  [FULLTEXT]
11.Chopp M, Welch KM, Tidwell CD, Knight R, Helpern JA. Effect of mild hyperthermia on recovery of metabolic function after global cerebral ischemia in cats. Stroke 1988;19:1521-5.   Back to cited text no. 11  [PUBMED]  [FULLTEXT]
12.Nussmier MA, Chang W, Marino M, Spata T, Li S, Daniels G, et al . Temperature during cardiopulmonary bypass: The discrepancy between monitored sites. Anesth Analg 2006;103:1373-9.   Back to cited text no. 12    
13.Cook DJ. Changing temperature management for cardiopulmonary bypass. Anesth Analg 1999;88:1254-71.  Back to cited text no. 13  [PUBMED]  [FULLTEXT]
14.Sahu B, Chauhan S, Kiran U, Bisoi A, Lakshmy R, Selvaraj T, et al . Neurocognitive function in patients undergoing coronary artery bypass surgery with cardiopulmonary bypass: the effect of two different rewarming strategies. J Cardiothor Vasc Anaesth.2009;23:8-13.   Back to cited text no. 14    
15.Sahu B, Chauhan S, Kiran U, Bisoi AK, Ramakrishnan L, Nehra A. Neuropsychological function in children with cyanotic congenital heart disease undergoing corrective cardiac surgery: effect of 2 different rewarming strategies. Eur J Cardiother Surg 2009;35:505-10.   Back to cited text no. 15    
16.Grigore AM, Grocot HP, Matthew JP, Phillips-Bute B, Stanley TO, Butler A, et al , The rewarming rate and increased peak temperature alter neurocognitive outcome after cardiac surgery. Anesth Analg 2002;94:4-10.   Back to cited text no. 16    
17.Kiziltan HT, Baltali M, Koca D, Oner S, Sener M, Tasdelen A. Reduced Jugular venous oxygen saturation during rewarming from deep hypothermic circulatory arrest: Cerebral over extraction? Cardiovasc Surg 2002;11:213-7.   Back to cited text no. 17    
18.Cook DJ, Orszulak TA, Zehr KJ, Nussmeier NA, Livesay JJ, Hammon JW, et al . Effectiveness of the Cobra aortic catheter for dual temperature management during adult cardiac surgery. J Thorac Cardiovasc Surg 2003;125:378-84.   Back to cited text no. 18  [PUBMED]  [FULLTEXT]
19.Martin TJ, Craven JM, Gott JP, Weintraub WS, Ramsay J, Mora CT, et al . Prospective randomized trial of retrograde warm blood cardioplegia: myocardial benefit and neurological threat. Ann Thorac Surg 1994;57:298-304.   Back to cited text no. 19    
20.The warm heart investigators. Randomized trial of normothermic vs hypothermic coronary artery bypass surgery. Lancet 1994;343:559-63.   Back to cited text no. 20  [PUBMED]  
21.Regragui IA, Izzat MB, Birdi I,Lapsley M, Bryan AJ, Angelini GD. Cardiopulmonary bypass perfusion temperature does not influence renal function. Ann Thorac Surg 1995;60:160-4.   Back to cited text no. 21  [PUBMED]  [FULLTEXT]
22.Rubens FD, Nathan H. Lessons learnt in the path to a healthier brain: Dispelling the myth and challenging the hypothesis. Perfusion 2007;22:153-60.  Back to cited text no. 22    

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Correspondence Address:
Sandeep Chauhan
E-6 Ansari Nagar, AIIMS Campus, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-9784.53427

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