Regional Cerebral Oxygen Saturation Monitoring during Spinal Surgery in Order to Identify Patients at Risk for Cerebral Desaturation

Round 1

Reviewer 1 Report

The authors propose near infrared spectroscopy (NIRS) for cerebral oximetry monitoring. The paper writing is almost generally correct, some typos and repeated words were detected though.

The handicap of this paper is mainly related to the very low number of patients considered in the study. Only three out of 44 triggered the proposed commercial NIR system. I’m afraid that this cannot lead to unquestionable conclusions in such kind of study. To warrant significance, this study needs to be extensively extended to larger populations, otherwise this will be a so what? paper reporting on preliminary results only. I strongly encourage the authors to continue gathering more data and proposing rigorous statistical analysis of it.

In the introduction lines 44 to 46 the authors mention optodes and electrodes consecutively, which confuses the reader a lot. Of course, of a light source is incorporated there, as mentioned by the authors, then the electrodes must be present to power on the led, lasers, lamps …. whatever light source they emit through the patient’s head. This description must be enriched to avoid misunderstanding of such a simple setup.

The paragraph on lines 48-53 is written without a proper use of technical English.

The authors justify that NIRS is widely used in other operations, mainly in cardiac bypass implants, but fail to provide a path towards proposing an implementation of their technical approach in common medicine practice. This must also be expanded with in-depth scientific arguments, given that utmost relevance they acknowledge this may have.

Lines 65-71 are to be improved and better connected to the vertical idea of the paper.

In my view, their Introduction is too vague and does not hold enough significance to the paper.

Section 2 explains the methods used for controlling the parameters of interest to stabilize the patience; many ranges of values are presented in lines 84 to 89 without citing any previous article/book that explains why these are considered. This needs more scientific background to be accepted by the reader.

Correct the word 'values' in line 93.

The authors explain the protocol to follow should the patients’ level of rScO2 fall below 50 %, whereas many steps are described. However, it is then acknowledged on the results/discussion sections that it was unnecessary to proceed with the third step described.

No real images or signals recorded in this study are present in the manuscript, I

As mentioned above, the results only account for 3 patients that entered in the NIR study. No description is provided on the age of the patient that fell below the 20% threshold or whether there might be a connection with age at all.

The word 'and' is repeated twice in Table 2 caption. Please correct this.

I fully agree with the scientific argument of the authors in line 153, without NIR, the symptoms described would have been undetected. This mainly sends a message: this study is to be substantially expanded before concluding on it. This is my recommendation to the authors.

Author Response

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Reviewer 2 Report

Using intra-operative NIRS monitoring, authors evaluated the usefulness of cerebral oxygenation during spinal surgery.

 

Please see my comments below:

• Line 21, Page 1: at line 21 and several other lines you used the term “NIRS algorithm” to explain about the interventional protocol you followed to return the rScO2 level back to normal. The term “algorithm” does not relay the clear meaning. I would suggest replacing it with “NIRS interventional-protocol” everywhere in the text.

 

• Line 23, page 1: “increased above the threshold”. Please clarify if the threshold is the same as the avg. personal baseline value.

 

• After the first paragraph in the introduction section, please explain the importance of keeping brain blood flow intact during the surgery and the dangerous inter and intra operative effects that long periods of brain desaturation could cause.

 

• Line 38, Page 1: “The brain is one of the least monitored organs during anaesthesia, as the majority of available methods are invasive [1].”

Please add a few instances.

 

• In the second paragraph of the Introduction, my understanding is that the authors explained about the NIRS technology and how it works in general. However, it seems to me that it is a combination of specifics about INVOS 4100 and general NIRS technology. These should get separated to reduce confusion.

For example:

Line 41, Page 1: “near – infrared light in the spectrum of 700 – 1100 nm wave length”

These wavelengths are not the same for all the NIRS systems and the authors should correct that in the paper.

 

 

• Line 44,page 1:

“A cerebral oximeter consists of a monitor and two adhesive optodes, that are attached to the patients’ forehead – one above the left and one above the right cerebral haemisphere overlying the frontal lobe. In each electrode there is an incorporated light source – emitting near infrared light – and one or two light detectors – collecting the scattered light returning  to the surface”

Please clearly mention how many sources of light and how many detectors you have in your system. In addition, you need to mention how many light channels you have in your system.

A schematic needs to be added showing the relative position of the sources, detectors, and channels.

 

 

• Does your system have a short-distance separation technology and does the NIRS mathematical algorithm uses mathematical models to remove the superficial changes in the Oxy and de-oxy hemoglobin or not?

 

• I believe you should have AT LEAST two NIRS channels (if not more). Could you please clarify if you see the rScO2 level for each channel on the NIRS monitor or if just one how it was calculated?

 

• What is the duration of baseline recording for each patient?

 

• Line 91, page 2: the monitoring rate for the rScO2 is very slow (every 5 minutes). With this, it would be very probable that you have missed a lot of desaturations during the operation.

 

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

It is important to monitor the patient in deep anesthesia during major surgery. Near-infrared spectroscopy is widely used in many surgeries to help in making the right decisions. With this method, cerebral oxygen saturation was monitored to estimate the level of oxygenation in the blood flow of the cerebrum. 3 patients with low blood oxygenation were screened out and helped in time through this method. Based on these cases, it was suggested that blood loss and operative duration are negatively relevant to the cerebral oxygen level. 

Author Response

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