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LETTERS TO EDITOR
Year : 2018  |  Volume : 62  |  Issue : 8  |  Page : 643-645  

Persistent cerebral desaturation on near-infrared spectroscopy without neurological insult


1 Department of Cardiac Anesthesiology, NH Rabindranath Tagore International Institute of Cardiac Sciences, Kolkata, West Bengal, India
2 Department of Cardiac Surgery, NH Rabindranath Tagore International Institute of Cardiac Sciences, Kolkata, West Bengal, India

Date of Web Publication13-Aug-2018

Correspondence Address:
Dr. Pradeep Narayan
Department of Cardiac Surgery, NH Rabindranath Tagore International Institute of Cardiac Sciences, 124, EM Bypass, Mukundapur, Kolkata - 700 099, West Bengal
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ija.IJA_277_18

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How to cite this article:
Natarajan P, GuhaBiswas R, Saha A, Narayan P. Persistent cerebral desaturation on near-infrared spectroscopy without neurological insult. Indian J Anaesth 2018;62:643-5

How to cite this URL:
Natarajan P, GuhaBiswas R, Saha A, Narayan P. Persistent cerebral desaturation on near-infrared spectroscopy without neurological insult. Indian J Anaesth [serial online] 2018 [cited 2020 Nov 26];62:643-5. Available from: https://www.ijaweb.org/text.asp?2018/62/8/643/238908



Sir,

Near-infrared spectroscopy (NIRS), a noninvasive technique to monitor cerebral oxygenation, provides rapid evaluation of cerebral oxygenation, leading to its popularity in procedures requiring cerebral oxygenation monitoring. However, NIRS may be associated with poor specificity in certain situations. We describe one such case where NIRS monitoring using cerebral INVOS (Somanetics Corp. Troy, MI) revealed persistent cerebral oxygen desaturation but was not associated with any postoperative neurological deficit in an elderly gentleman undergoing repair for type B aortic dissection.

An elderly gentleman, with no history of neurological disorder, presented with type B aortic dissection and underwent a hybrid procedure with a carotid-carotid bypass and an endovascular stent to treat the condition. Neurological monitoring was performed with INVOS (Somanetics Corp. Troy, MI) cerebral oximeter. Fresh sensors were applied and reliable recording quality was confirmed by signal strength index. Baseline bilateral cerebral oxygen saturation (rSO2) was low (Channel 1: 47%; Channel 2: 41%) [Figure 1]. The rSO2 did not reach 50% at any point during the procedure. A systematic approach to this unexplained cerebral desaturation was performed based on the algorithm proposed by Denault et al.[1] The rSO2 remained persistently and critically low with a mean of 38% in Channel 1and35% in Channel 2 during entire procedure. The patient did not have any major or minor neurological event during the hospital stay or at 6months follow-up.
Figure 1: Baseline bilateral cerebral oxygen saturation (rSo2)

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NIRS with the INVOS monitoring system has become increasingly popular for cerebral oxygen monitoring. It is based on the fact that oxygenated and deoxygenated haemoglobin have characteristic absorption spectra and light in the range of 650–1100 nm and has an absorbance that is proportional to the relative concentrations of these two chromophores.[2] The INVOS monitor is a saturation monitor that measures the ratio of haemoglobin and oxyhaemoglobin by using a single light-emitting diode and displays a single unitless value defined as “regional haemoglobin oxygen saturation (rSO2).”[3] The typical acceptable range of rSO2 is 55–80%. It has been reported that rSO2 values below 59 provide 100% sensitivity and 47% specificity.[4] As seen in our case where the mean values were significantly lower with no postoperative neurological impairment, it is the specificity that is of major concern. Interestingly, in our case the rSO2 remained low throughout, and no considerable drop was seen during the procedure phase compared to the preprocedure evaluation. To address similar situation, it has been proposed that along with absolute numbers, perhaps a percentage decrease from baseline might be a useful criterion for cerebral ischaemia. A proposed cutoff value of 20% was reported to have 83% sensitivity and 83% specificity for cerebral ischaemia.[4]

Artifactually low rSO2 values may be attributable to cranial bone anomaly or frontal sinus inflammation, presence of infrared-absorbing intracranial or intravascular pigments or dyes, optode positioning over an intracranial photon sink (i.e., intracranial venous sinus or haematoma), excessive photon scattering (i.e., hair or hair follicles), or dyshaemoglobinemias.[5] In this particular patient, despite critical evaluation, we were unable to find a definite cause for the low rSO2 values. However, it has been shown that during hypothermic cardiopulmonary bypass, as needed in this case, the rSO2 values can be paradoxically low and may have been the cause for the persistent low rSO2 value seen.[6]

NIRS may produce not only artifactually low rSO2 values but can also fail to detect cerebral ischaemia in certain cases. It is possible that the placement of sensors on the forehead may not be able to detect ischaemia of parietal or deeper lobes without reflecting any changes in the monitored frontal lobe. Infarct of the middle cerebral artery with an entirely satisfactory rSO2 values have been reported in the literature. Moreover, as NIRS reflects the balance between regional oxygen supply and demand, saturation may be near-normal in infarcted nonmetabolizing brain.

The problem with NIRS or any other monitoring system for cerebral ischaemia is absence of an objective gold standard with no single monitoring method providing perfect sensitivity and specificity.

Transcranial Doppler sonography and carotid artery stump pressure are the other monitoring techniques currently available; however, no single method has been proved to be superior to others. Considering that NIRS is easy to carry out and provides comparable accuracy, this should perhaps continue to be the technique of choice. However, rather than relying only on absolute rSO2values of 50%, a 20% drop from baseline rSO2 values should also be incorporated in order to increase the specificity of this diagnostic tool for cerebral ischaemia.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Denault A, Deschamps A, Murkin JM. A proposed algorithm for the intraoperative use of cerebral near-infrared spectroscopy. Semin Cardiothoracic Vasc Anesth 2007;11:274-81.  Back to cited text no. 1
    
2.
Owen-Reece H, Smith M, Elwell CE, Goldstone JC. Near infrared spectroscopy. Br J Anaesth 1999;82:418-26.  Back to cited text no. 2
    
3.
Davies LK, Janelle GM. Con: all cardiac surgical patients should not have intraoperative cerebral oxygenation monitoring. J Cardiothorac Vasc Anesth 2006;20:450-5.  Back to cited text no. 3
    
4.
Moritz S, Kasprzak P, Arlt M, Taeger K, Metz C. Accuracy of cerebral monitoring in detecting cerebral ischaemia during carotid endarterectomy: A comparison of transcranial Doppler sonography, near-infrared spectroscopy, stump pressure, and somatosensory evoked potentials. Anesthesiology 2007;107:563-9.  Back to cited text no. 4
    
5.
Yoshitani K, Kawaguchi M, Miura N, Okuno T, Kanoda T, Ohnishi Y, et al. Effects of hemoglobin concentration, skull thickness, and the area of the cerebrospinal fluid layer on near-infrared spectroscopy measurements. Anesthesiology 2007;106:458-62.  Back to cited text no. 5
    
6.
Baraka A, Naufal M, El-Khatib M. Correlation between cerebral and mixed venous oxygen saturation during moderate versus tepid hypothermic hemodiluted cardiopulmonary bypass. J Cardiothorac Vasc Anesth 2006;20:819-25.  Back to cited text no. 6
    


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