HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract 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): Kazumasa Orihashi Taijiro Sueda Kenji Okada Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Orihashi, K. Articles by Imai, K. Search for Related Content PubMed PubMed Citation Articles by Orihashi, K. Articles by Imai, K. Related Collections Cerebral protection Extracorporeal circulation Great vessels

Eur J Cardiothorac Surg 2004;26:907-911
© 2004 Elsevier Science NL

Near-infrared spectroscopy for monitoring cerebral ischemia during selective cerebral perfusion

Division of Cardiovascular Surgery, Hiroshima University Hospital, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551 Japan

Received 10 March 2004; received in revised form 17 June 2004; accepted 21 June 2004.

^* Corresponding author. Tel.: +81-82-257-5216; fax: +81-82-257-5219. (E-mail: orichan{at}hiroshima-u.ac.jp).

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
Objective: To minimize the neurological complications following cardiovascular surgery, it is essential to prevent an occurrence of cerebrovascular embolism and to detect and solve cerebral malperfusion without delay in the operating theater. Although we have introduced near-infrared spectroscopy (NIRS) monitoring for the purpose of detecting cerebral malperfusion, no criterion has been available. We searched for this criterion by examining the relationship of sustained drop in the regional oxygen saturation (rSO2) of the frontal lobes to the occurrence of neurological events. Methods: The 59 consecutive patients undergoing aortic surgery with selective cerebral perfusion (SCP) were examined. The rSO2 was monitored throughout the surgery and the durations of drops in rSO2 to below 55% and those below 60% were determined for each patient. The durations of rSO2 drop and other surgery-related parameters were compared between the patients in whom neurological events occurred and those without such events. Results: A total of 16 cases (27.1%) presented with neurological events. Newly developed cerebral infarction was documented in 6 of these 16 cases. Operation time and the durations for which rSO2 dropped were significantly longer for the 16 patients with neurological events than for the 43 patients without events (Op time: 546.8 versus 448.1min, P=0.0064; rSO2 below 60%: 141.2 versus 49.8min, P=0.0032; rSO2 below 55%: 66.6 versus 10.6min, P=0.0011), while there was no significant difference in age, bypass time, aortic clamping time, SCP time, and circulatory arrest time between the two groups. In the 3 patients with infarcts suggestive to hypoperfusion, sustained decrease in rSO2 was observed, while it was not significant in the remaining 3 patients with infarcts suggestive to embolism. Among the 53 patients without infarction, transient neurological events occurred more frequently in patients with sustained drop in rSO2 below 55% for over 5min (44.4% versus 5.7%, P=0.0014). Conclusions: A sustained drop in rSO2 during aortic surgery is closely related to the occurrence of neurological events following surgery. We recommend that recovery of drop in rSO2 below 55% should be addressed without delay. However, use of NIRS is limited for detecting embolic events or hypoperfusion in the basilar region.

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
Patients undergoing aortic surgery can be complicated by neurological events, including cerebral infarction and transient neurological disorders such as confusion or disorientation. While the former is permanent and leads to considerable deterioration in quality of life, the latter can lead to falls, violent behavior, and hemodynamic instability in the immediate postoperative period. Such neurological symptoms are likely to result from different degrees of brain ischemia during surgery, which is mainly caused either by arterial embolism or by diffuse malperfusion of the brain. Strategies for prevention differ between these two etiologies. To avoid arterial embolism, careful manipulation by the surgeon is essential, while diagnosis of the embolic event is of little value. In contrast, diffuse malperfusion can be avoided only by early detection of malperfusion, followed by immediate restoration of adequate perfusion before irreversible damage develops. Thus, for this purpose, sensitive, real-time monitoring of brain ischemia is needed.

A number of modalities have been introduced for detecting cerebral malperfusion during cardiovascular surgery or carotid artery surgery, including transcranial Doppler ultrasound [1–3] and near-infrared spectroscopy (NIRS) [1–9]. We have routinely used NIRS monitoring since 1998 and have recognized that the regional oxygen saturation (rSO2) promptly drops upon temporary circulatory arrest, and then recovers as systemic circulation resumes in patients undergoing aortic surgery with selective cerebral perfusion (SCP). However, we have also found that a steep but transient drop in rSO2 is not related to the occurrence of a neurological event, and this led to the conclusion that brain damage is related to both the extent and the duration of the drop in rSO2. In this study, we have examined the relationship of a ‘sustained’ drop in rSO2 with the occurrence of neurological events, by means of a retrospective analysis.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
We examined 59 consecutive cases of patients who underwent aortic surgery with SCP under moderately hypothermic circulatory arrest. The patients included 41 males and 18 females, with ages ranging from 24 to 84 years old (an average of 67.6 years old). The preoperative diagnosis was aortic arch aneurysm, aortic dissection, aortitis, adult patent ductus arteriosus, and left subclavian aneurysm in 33, 22, 2, 1 and 1 cases, respectively. The surgical procedures used were total arch replacement, transaortic stent graft implantation, ascending aorta replacement, aortic root replacement, aneurysm resection, and closure of the ductus arteriosus in 24, 20, 11, 2, 1 and 1 cases, respectively. This study was approved by the institutional ethics committee on human research in our institute and informed consent was obtained from each patient.

Surgery was performed by a single surgeon and the method of anesthesia and extracorporeal circulation, including SCP, was unchanged during the period over which the 59 procedures were performed. Alpha-stat protocol was used throughout this period. Circulatory arrest was started after the body temperature was reduced to 25°C and SCP was established with a basic perfusion rate of 250ml/min for each branch artery. Retrograde cerebral perfusion was not used in any case. During SCP, the perfusion pressure was monitored at the right radial artery and the tip of the perfusion cannula in the left common carotid artery. When the perfusion pressure was unusually low (<40mmHg), the total perfusion rate was increased to 1000ml/min and/or a vasoconstrictor was administered. Cerebral perfusion was regulated based on information from conventional monitoring of flow rate and perfusion pressure. Transfusion was initiated when the hemoglobin level fell below 7.0g/dl.

After induction of anesthesia, a dual sensor NIRS system, TOS-96 (TOSTEC Co., Tokyo, Japan), was attached to the patient's forehead for monitoring the rSO2 in the bilateral frontal lobes at a depth of approximately 3cm beneath the skin. Each sensor consists of one silicon diode which receives the signal and three LEDs which emit near-infrared light of wavelengths 750, 850 and 810nm, respectively, for measurement of deoxyhemoglobin (deoxy-Hb), oxyhemoglobin (oxy-Hb), and hemoglobin level (Hb Index), respectively. The rSO2 (%) was calculated from the NIRS data, using the following equation.

The Hb Index (proportional to the Hb concentration in brain tissue) was measured and expressed as a trend of relative values, starting from 1.0. The rSO2 was measured every 5s throughout the surgery. For subsequent analysis, all data were saved as text files on the hard disc of the NIRS system.

In examining the relationship of the rSO2 data to neurological symptoms, we focused only on clinically problematic events during and immediately following surgery. These included: (1) newly developed cerebral infarction; (2) transient neurological signs and symptoms, including anisocoria, mydriasis, or convulsion, which potentially suggest the occurrence of cerebral infarction; and (3) altered consciousness. Subtle cognitive disorders were excluded from analysis in the current study. Computed tomography (CT) and/or magnetic resonance imaging (MRI) was performed whenever brain injury was suspected, and data from these techniques was provided by radiologists who were blinded to the intraoperative rSO2 data. New cerebral infarction was diagnosed based on the CT/MRI findings, compared with preoperative findings whenever available. When the preoperative CT/MRI was not available, mainly due to unstable hemodynamics, the onset of infarction was determined as intraoperative based on the CT/MRI findings or longitudinal changes of the infarct. The size of the pupil was routinely checked by the anesthesiologists in the operating theater, and by the intensive care unit staff. Anisocoria was considered significant when the difference in pupil sizes was larger than 1mm, and mydriasis was considered significant when the pupil was larger than 7mm. Events of altered consciousness, such as restlessness, disorientation, or confusion, were picked up from the chart record and were considered significant when they required sedatives for safety reasons, as determined by the presiding doctor, who was also blinded to the intraoperative rSO2 data. Transient events which occurred later than the seventh postoperative day, and did not have a preceding neurological event, were excluded from the analysis.

The following parameters were examined for correlation with the occurrence of neurological events: (1) age, (2) type of operation, (3) operation time, (4) CPB time, (5) aortic cross-clamp (AOX) time, (6) SCP time, and (7) circulatory arrest time. From the rSO2 data, the durations of the drops in right and left rSO2 to below 60% were determined for each patient. The longer of the two rSO2 decreases (right and left) below 60% was used as the representative value for the individual patient. Similar data were also determined for the duration of a drop in rSO2 below 55%.

Statistical analysis was performed using a Mann–Whitney test for comparing the above parameters between two groups, and analysis of variance was used for comparing parameters among three or more groups. The data were expressed as mean±SE. Differences in the incidence of neurological events between categories was examined using the chi-square method, with Fisher's exact probability test used when the number was smaller than 5. A difference was considered to be statistically significant when the P value was less than 0.05.

	3. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
A total of 16 cases (27.1%) presented with neurological events: confusion, convulsion, anisocoria, mydriasis, and motor disturbance was observed in 5, 5, 4, 1 and 1 patients, respectively. Newly developed cerebral infarction was documented with postoperative CT and/or MRI in 6 of these 16 cases. The neurological symptoms alleviated within a few days and had completely disappeared within a few weeks.

NIRS data was obtained for every patient. The rSO2 mostly remained above 65% throughout the surgery, but occasionally dropped to below 60% at the onset of CPB; at the time of clamping and declamping of the aorta, during which the pressure dropped below 50mmHg for a few seconds; in the period from the onset of circulatory arrest to the start of SCP; and during anastomosis of branch arteries performed without selective perfusion. However, the rSO2 recovered to its previous level as soon as perfusion was resumed. However, in a subset of patients, the decrease in rSO2 was sustained for unusually long periods.

To examine the relevance of the sustained drop in rSO2, the total durations for which rSO2 dropped below 60 and 55% were compared between the 16 patients in whom neurological events occurred and the 43 patients without such events (Table 1). Surgery-related parameters were also compared between these two groups of patients (Table 1). The operation time was significantly longer for patients undergoing total arch replacement (548.9±32.8min), compared with the times for stent graft implantation (415.5±16.0min, P=0.0007) and ascending aorta replacement (435.5±26.5min, P=0.0070). Operation time and the durations for which rSO2 dropped below 60 and 55% were all significantly longer for patients with neurological events, while there was no significant difference in age, CPB time, AOX time, SCP time, and circulatory arrest time between the two groups. There was no significant difference in incidence of neurological events among the following three surgical procedures: total arch replacement, stent graft implantation, and others.

	4. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 
The results of this study show that the occurrence of a neurological event is significantly related to a sustained decrease in rSO2 during surgery. We have previously examined blood flow velocity in the central retinal artery (using orbital ultrasound monitoring) and demonstrated that the critical perfusion pressure for detectable blood flow varied significantly among individual cases (20–50mmHg), and that neurological events occurred more frequently in patients with higher critical pressure [10,11]. This result shows that tolerance of the brain to hypoperfusion varies among individuals, and that ischemic complications may be inevitable in a certain population of patients, if intraoperative management is uniform. Thus, tailor-made management based on real-time information of events in the skull is needed to prevent such neurological complications.

The most desirable intraoperative management in an individual case would be most accurately indicated by preoperative assessment of cerebral perfusion under hypotensive and non-pulsatile circulation. However, it is practically difficult to make this assessment in every patient, including in emergency cases. Thus, real-time monitoring available in the operating room is useful in the clinical setting. However, use of transcranial Doppler is limited during CPB or SCP with low perfusion pressure, and although orbital ultrasound monitoring might be an option, it is not suitable for continuous monitoring because of possible damage to the orbital tissue. In contrast, NIRS is advantageous since it automatically provides data both non-invasively and continuously.

To utilize NIRS effectively, development of criteria indicating cerebral malperfusion is necessary. In this study we adopted two cut-off values of rSO2 (60 and 55%), for the following reasons. First, the oxygen saturation of arterial blood is nearly 100% and that of venous blood is 50–60%. Assuming that the arterial blood occupies about one fourth of the tissue blood, the mean oxygen saturation in the tissue is estimated to be 60–70%. When the arterial blood supply is interrupted, oxygen is consumed and the rSO2 drops to that of venous blood, around 60%, and then anaerobic metabolism begins. The rSO2 actually shows a biphasic decline when arterial perfusion is interrupted: rSO2 initially drops rapidly, and then the slope becomes more gradual. Second, the lower normal limit of oxygen saturation that is commonly accepted in monitoring of jugular vein blood is 55%. Third, the lower limit of oxygen saturation of mixed venous blood is 60%. Consistent with this approach, Hirofumi et al. recently reported the criterion for neurological compromise as an rSO2 of less than 54–56.1% in cases of carotid endoarterectomy [12].

Our results indicate that occurrence of neurological events increases when a drop in rSO2 below 55% is sustained for longer than 5min. When the rSO2 drops, some measures to restore the oxygen saturation are needed to prevent development of brain damage. The drop in rSO2 is related to several factors: (1) reduced oxygen saturation in the arterial blood, (2) a low hemoglobin level, (3) reduced arterial blood flow, (4) increased oxygen consumption in the cerebral tissue, and (5) venous congestion. Whatever the cause, NIRS provides a measure of the ultimate oxygen balance in the brain. To clarify the reason for a drop in rSO2, analysis of oxy-Hb, deoxy-Hb, and Hb index is helpful.

This study also shows the limitations of NIRS monitoring for detection of cerebral ischemia. A drop in rSO2 was not apparent in cases of cerebral infarction caused by embolism, while patients with watershed infarction in the frontal lobe had a sustained rSO2 drop. Hence, rSO2 can remain unchanged when the emboli cause cerebral ischemia at a site other than the NIRS sampling site. In case #15, in which cerebral infarction in the basilar region occurred, the left subclavian artery was not perfused during SCP because it arose from the aneurysm. The surgeon expected that adequate collateral circulation would be present via the circle of Willis until the left subclavian artery could be reperfused. However, the rSO2 in the right frontal lobe remained low while the left rSO2 was mostly over 70%. If the basilar artery depended only on collateral perfusion from the right common carotid artery, hypoperfusion of the basilar artery region could be marked by insignificant ischemia in the right frontal lobe.

Electrocautery may also interfere with NIRS monitoring, leading to another limitation of NIRS. Fortunately, electrocautery is mostly used during sternotomy and chest closure, and interference is minimal during CPB, during which continuous rSO2 monitoring is important. It is also clear that use of NIRS monitoring alone cannot explain every neurological event. For example, NIRS is unlikely to be capable of differentiating the causes of the rSO2 drop: malperfusion, atheroma, or air. However, such monitoring can provide an alert that cerebral ischemia is likely to be present at a given moment. Once cerebral ischemia is suspected from the NIRS data, cerebral blood flow can be further examined to allow clarification of the problem.

In conclusion, a sustained drop in rSO2 drop during aortic arch surgery is closely related to the occurrence of neurological events. From our results, we recommend that recovery of a drop in rSO2 below 60% should be addressed without delay. One should be aware, however, that use of NIRS is limited for detecting embolic events or hypoperfusion in the basilar region.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion References

 

1. Edmonds Jr HL, Rodriguez RA, Audenaert SM, Austin III EH, Pollock Jr SB, Ganzel BL. The role of neuromonitoring in cardiovascular surgery. J Cardiothorac Vasc Anesth 1996;10:15-23.[CrossRef][Medline]
2. Mason PF, Dyson EH, Sellars V, Beard JD. The assessment of cerebral oxygenation during carotid endarterectomy utilising near infrared spectroscopy. Eur J Vasc Surg 1994;8:590-594.[CrossRef][Medline]
3. Kirkpatrick PJ, Lam J, Al Rawi P, Smielewski P, Czosnyka M. Defining thresholds for critical ischemia by using near-infrared spectroscopy in the adult brain. J Neurosurg 1998;89:389-394.[Medline]
4. Kurth CD, Steven JM, Nicolson SC. Cerebral oxygenation during pediatric cardiac surgery using deep hypothermic circulatory arrest. Anesthesiology 1995;82:74-82.[CrossRef][Medline]
5. Daubeney PE, Smith DC, Pilkington SN, Lamb RK, Monro JL, Tsang VT, Livesey SA, Webber SA. Cerebral oxygenation during paediatric cardiac surgery: identification of vulnerable periods using near infrared spectroscopy. Eur J Cardiothorac Surg 1998;13:370-377.
6. Baris RR, Israel AL, Amory DW, Benni P. Regional cerebral oxygenation during cardiopulmonary bypass. Perfusion 1995;10:245-248.[Abstract/Free Full Text]
7. Beese U, Langer H, Lang W, Dinkel M. Comparison of near-infrared spectroscopy and somatosensory evoked potentials for the detection of cerebral ischemia during carotid endarterectomy. Stroke 1998;29:2032-2037.[Abstract/Free Full Text]
8. de Letter JA, Sie HT, Thomas BM, Moll FL, Algra A, Eikelboom BC, Ackerstaff RG. Near-infrared reflected spectroscopy and electroencephalography during carotid endarterectomy—in search of a new shunt criterion. Neurol Res 1998;20(Suppl 1):S23-S27.
9. Samra SK, Dorje P, Zelenock GB, Stanley JC. Cerebral oximetry in patients undergoing carotid endarterectomy under regional anesthesia. Stroke 1996;27:49-55.[Abstract/Free Full Text]
10. Orihashi K, Matsuura Y, Sueda T, Shikata H, Morita S, Hirai S, Sueshiro M, Okada K. Flow velocity of central retinal artery and retrobulbar vessels during cardiovascular operations. J Thorac Cardiovasc Surg 1997;114:1081-1087.[Abstract/Free Full Text]
11. Orihashi K, Matsuura Y, Sueda T, Shikata H, Watari M, Okada K. Clinical implication of orbital ultrasound monitoring during selective cerebral perfusion. Ann Thorac Surg 2001;71:673-677.[Abstract/Free Full Text]
12. Hirofumi O, Otone E, Hiroshi I, Satosi I, Shigeo I, Yasuhiro N, Masato S. The effectiveness of regional cerebral oxygen saturation monitoring using near-infrared spectroscopy in carotid endarterectomy. J Clin Neurosci 2003;10:79-83.[CrossRef][Medline]

This article has been cited by other articles:

				K. C. Santo, A. Barrios, U. Dandekar, P. Riley, P. Guest, and R. S. Bonser Near-Infrared Spectroscopy: An Important Monitoring Tool During Hybrid Aortic Arch Replacement Anesth. Analg., September 1, 2008; 107(3): 793 - 796. [Abstract] [Full Text] [PDF]

				G. W. Fischer Recent Advances in Application of Cerebral Oximetry in Adult Cardiovascular Surgery Seminars in Cardiothoracic and Vascular Anesthesia, March 1, 2008; 12(1): 60 - 69. [Abstract] [PDF]

				D. Spielvogel, M. N. Mathur, and R. B. Griepp Aneurysms of the Aortic Arch Card. Surg. Adult, January 1, 2008; 3(2008): 1251 - 1276. [Full Text]

				D. Spielvogel, C. D. Etz, D. Silovitz, S. L. Lansman, and R. B. Griepp Aortic Arch Replacement With a Trifurcated Graft Ann. Thorac. Surg., February 1, 2007; 83(2): S791 - S795. [Abstract] [Full Text] [PDF]

				P. G. Al-Rawi and P. J. Kirkpatrick Tissue Oxygen Index: Thresholds for Cerebral Ischemia Using Near-Infrared Spectroscopy Stroke, November 1, 2006; 37(11): 2720 - 2725. [Abstract] [Full Text] [PDF]

				G. M. Hoffman Neurologic Monitoring on Cardiopulmonary Bypass: What Are We Obligated to Do? Ann. Thorac. Surg., June 1, 2006; 81(6): S2373 - S2380. [Abstract] [Full Text] [PDF]

				C. Olsson and S. Thelin Regional cerebral saturation monitoring with near-infrared spectroscopy during selective antegrade cerebral perfusion: Diagnostic performance and relationship to postoperative stroke J. Thorac. Cardiovasc. Surg., February 1, 2006; 131(2): 371 - 379. [Abstract] [Full Text] [PDF]

				F. L. Hanley Religion, politics...deep hypothermic circulatory arrest J. Thorac. Cardiovasc. Surg., November 1, 2005; 130(5): 1236 - 1236. [Full Text] [PDF]

This Article Abstract 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): Kazumasa Orihashi Taijiro Sueda Kenji Okada Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Orihashi, K. Articles by Imai, K. Search for Related Content PubMed PubMed Citation Articles by Orihashi, K. Articles by Imai, K. Related Collections Cerebral protection Extracorporeal circulation Great vessels