Thesis proposal
ABSTRACT
NIRS is the continuous real- time monitoring of the efficiency of human brain perfusion. It can provide important information that belongs to the variety of clinical situations. Typical technologies can include pharmaceutical, food and agrochemical quality control, medical diagnostics that include blood sugar and pulse oximetry and combo-tion reach. The current availability of near- infrared spectroscopy can detect the cerebral ischemia. Moreover, NIRS can be also used in monitoring of other tissue beds. These are splanchnic, renal and spinal cord. Near- infrared spectroscopy is based on molecular overtone and combination vibrations. As a result, in the near- IR region the molar absorbtivity is quite small. One positive fact is that NIR can penetrate deeper into a sample than mid- infrared radiation. This type of spectroscopy is not a sensitive one technique, but it can be very useful in little or no ample preparation. My review will include the short overview of operation method, current limitations and confounders, clinical applications and potential future of NIRS technics.
INTRODUCTION
In 1977 it was first reported that it is available to detect the oxygen saturation of brain tissues in real- time because of its transparency by the transillumination spectroscopy method. The first mention about usage of NIRS was done in 1985. It was approved by the United States Food and Drug Administration.
After that, in May 1993, was started to sell the first commercial cerebral oximetry device. It was named INVOS 3100w. As a result, CAS Medical Systems and Nonin Medical Inc. started marketing NIRS cerebral oximetry devices. It can be used in measuring the oxygen saturation of cerebral tissue.
The very main problems in using the NIRS technology include the great knowledge of the photon pathlenght, the presence of non- scheme chromophores and variable light absorption by overlying of extracerebral tissue.[2]
NIRS LIMITATIONS AND CONFOUNDS
Extracerebral plexus
Through skin technic of NIRS is repulse of tissue that contain blood networks and other tissue. In contrast, for cerebral tissue, exact photons must go through different tissue layers. These are scalp, skull and the dura. It can contain different concentrations of chromophores and blood.
The experimental and computer tissue models of NIR light transmission have demonstrated a distribution with the elliptical type of photon, that is centered near the transmitter. It means that the proportion of average depth of the division of optodes is 1/3. So, if transmitter/ receptor length of penetration increases, the effect of extracerebral plexus minimizes. In addition, the power should be controlled to prevent in case of thermal damage to tissue.
Spatial resolution
As I said, average length of photon infiltration is 1/3 (that is meant - the transmitter/ receiver) type of separation, there are two different forms of receiving optodes: one is spaced very close and another is on the other way from the transmitter. Thus, the closer one detects superficial tissue and the farther one detects deeper tissue. Taking into account this information were created the algorithm that calculates the difference between two signals or cortical plexus saturation. As a result, the differential spacing can provide distinguishing of the signs from cerebral virus extracerebral tissue. Due to this, was estimated that 85% of brain regional O2 saturation is clipped from cortical plexus. The 15% that remains are derived from over-laying extracerebral plexus.
Human mind blood partitioning
Human brain NIRS devices can measure average oxygenation of tissue and detect hemoglobin aeration in arterial, venous and capillary blood that comprise the sampling capacity. The proportion of average tissue hemoglobin is 70/30 (venous/arterial). Indeed, clinical researches demonstrated that there could be some variations in individual human mind A/V correlation among patients.
The very next confound can introduce significant change in hemoglobin concentration due to haemodilution. It is not steel unclear if this fact represents zonal ischemia, variations in pathlenght of photon or alterations in human mind arterial/venous partitioning. As a good fact, I can name the especially lower situations of clinical cases in patients that are undergoing the surgery of the artery.
Extracerebral tissue
You should not forget, that factors such as subdural or/and extracerebral hematoma can vary the difference of cerebral/ extracerebral hemoglobin and as a result offset plexus O2 saturation can vary. Usage of computed protection of skull fatness and con-centration of hemoglobin, were compared NIRO-100w and INVOS-4100w taking into account 103 cardiac surgical and neurosurgial patients. INVOS had more accurate results in rSO2 values. It is because INVOS software uses a special algorithm as equalization. While hemoglobin shows the elementary Chromophore, the subdural hemorrhage may artificially change on cerebral saturation results.
As was already said, NIRS devices show venous/arterial comparison as 70/30%. Thus, changes in rSO2 largely reflect changes in cerebral venous saturation and can vary between patients. However, there wasn’t correlation among cerebral rSO2 and brain vein oxidation in the non - tourniquet study of blood oxygenation. In contrast, a significant difference among jugular venous jar and regional cerebral oxygenations took place. Also, extracranial tissue oxygenation did not have a big influence on NIRS re-corder results.[3]
CLINICAL APPLICATIONS
PAEDIATRICS
Taking into account difficult settings, for example, pediatric surgery or pediatric neurosurgery, NIRS is often used to monitor and detect cases of cerebral ischemia when combined with bispectral monitoring and after the operation where cerebral SO2 decreased, within 48 hours of surgery were associated with an unsuccessful outcome after the Norwood procedures. Big amount of cerebral ischemia happens when the child is premature or have low birth weight. During apnetic cases took place, standard monitoring included heart rate, SO2, ventilatory frequency and arterial pressure.
In recent studies, cerebral oximetry were used in documentation of changes in cerebral perfusion while the mild system were sold. Were identified a reduction in cerebral blood volume during hypothermia, while brain oxygenation remained stable. So, the NIRS monitoring can be useful in prediction of cerebral insults during hypothermia treatment is going.
Taking into account bigger studies, 155 critically ill neonates, index of cerebral tissue oxygenation correlated with arterial and central venous oxygen saturation. A significant correlation of cerebral SO2 during inhalation of patients with oxygen was 100% undergoing myocardial biopsy. Also, rSO2 was the best predictor of pulmonary artery saturations. Moreover, monitoring of systemic perfusion using cerebral oximetry is a good alternative for patients whose haemodynamic monitoring is necessarily limited.[4]
DISCUSSIONS
As cerebral dysautoregulation can occur like head injury, the potential of cerebral NIRS is growing while providing a reliable bedside assessment is being actively re-searched in different clinical situations and can provide a further prediction of cerebral ischemia risk. Moreover, cerebral oximetry sensors can provide detection of progressive spinal cordischaema too.
Finally, all these studies make real an increasing of NIRS usage not taking into account all limitations and provide an indication of compromised brain and tissue perfusion in different clinical cases. NIRS monitoring must be considered the relative sensitivity compared with other monitoring methods.
CONCLUSION
BIBLIOGRAPHY
Naulaers, G. (2016). Non-Invasive Measurement of the Neonatal Cerebral and Splanchnic Circulation by Near-Infrared Spectroscopy. Google Books. Retrieved 15 March 2016, from https://books.google.fi/books?id=93peCLr62kYC&printsec=frontcover&dq=Near-infrared+spectroscopy+cerebral&hl=fi&sa=X&redir_esc=y#v=onepage&q=Near-infrared%20spectroscopy%20cerebral&f=false
Near-Infrared Spectroscopy. (2016). Google Books. Retrieved 15 March 2016, from https://books.google.fi/books?id=U7vqrf2YqmcC&printsec=frontcover&dq=Near-infrared+spectroscopy&hl=fi&sa=X&redir_esc=y#v=onepage&q=Near-infrared%20spectroscopy&f=false
Practical Guide to Interpretive Near-Infrared Spectroscopy. (2016). Google Books. Retrieved 15 March 2016, from https://books.google.fi/books?id=TJZYWo7gUN8C&pg=PA107&dq=Near-infrared+spectroscopy+history&hl=fi&sa=X&redir_esc=y#v=onepage&q=Near-infrared%20spectroscopy%20history&f=false
The Role of Regional Oxygen Saturation. Using Near Infrared Spectroscopy During Low Output Syndrome in Pediatric Heart Surgery. (2016). Google Books. Retrieved 15 March 2016, from https://books.google.fi/books?id=lFNB4BLGpYsC&pg=PA21&dq=Near-infrared+spectroscopy+limitations&hl=fi&sa=X&redir_esc=y#v=onepage&q=Near-infrared%20spectroscopy%20limitations&f=false
