Progress in the application of microdialysis technology in neurosurgery
Microdialysis (MD) technology was originally conceived by Delgado and Ungerstedt, who broke the traditional biosensor thinking and moved biochemical analysis from the body to the body. In 1966, Bito inserted a dialysis membrane bag containing 6% dextran into the cerebral hemisphere of the dog, and then removed the amino acid content of the analysis bag. In the 1970s, this technique was shaped into a modern MD, and the perfusate penetrated into the semi-permeable membrane catheter placed in the brain tissue and interbedded with the interstitial fluid (ECF) to achieve continuity of interstitial fluid. sampling. In the 1990s, the successful production of MD bed catheters and the introduction of bedside dialysate analyzers (CMA MicrodialysiS, Solna, Sweden) enabled it to be used clinically.
1 MD technology
1.1 MD principle
The MD catheter includes a dual lumen probe with a semi-dialysis membrane at the tip. After the probe is placed on the biological tissue, the isotonic solution is perfused through the lumen. When the perfusate passes through the dialysis membrane, the substances on both sides of the membrane diffuse and the dialysate flows from the outer tube to the collection container. The MD catheter is more like an artificial capillaries. The concentration of the substance in the dialysate depends partly on the diffusion balance of the substances on both sides of the membrane, and also depends on the uptake and supply of the substance in the tissue fluid. For example, a decrease in capillary blood flow and/or an increase in cellular sugar uptake results in a decrease in the concentration of sugar in the assay fluid. The ratio of the concentration of the substance in the dialysate to the actual concentration in the interstitial fluid is referred to as the relative recovery, and the recovery depends on the pore size of the membrane, the membrane area, the perfusion flow rate, and the diffusion rate of the substance. If the dialysis membrane is large enough and the flow rate is low enough, the recovery will reach 100%. The brain MD catheter used clinically, such as a flow rate of 0.3 ul / min, dialysis membrane length of 10 mm, the recovery rate of about 70%.
1.2 MD placement, positioning
MD can only monitor the biochemical changes of brain tissue around the diameter of the dialysis membrane and the diameter of the membrane, so the positioning of the catheter is very important. The MD catheter can be placed through the cranial plug and can be completed without going to the operating room. In the craniotomy, the catheter can also be placed under the vision to the peripheral area of â€‹â€‹the injury (1 cm from the boundary of the injury) or the blood supply area of â€‹â€‹the tumor-bearing artery. As for white matter or gray matter, there seems to be no difference, but there may be differences in neurotransmitters. Regardless of how the catheter is placed, it is important to determine the position of the metal tip on the CT. Its positioning will determine how we interpret the pathological changes in the brain.
1.3 MD perfusion flow selection criteria
The MD pump flow rate is 0.3 gl / min, at which time the 10 mm dialysis membrane recovery rate is 70%, and the 20 or 3 omm dialysis membrane can reach 100%. However, high perfusion flow is sometimes necessary. For example, during the temporary clamping of the artery, high frequency sampling is needed to monitor the ischemic state. At this time, the flow rate of 0.3t11/min will not be able to collect sufficient samples. The recovery rate of the 10 mm dialysis membrane was reduced to 30% at a flow rate of 1 ul/min. Another reason for using high perfusion flow is to reduce the time delay (the time from dialysate to brain analysis). The delay time is 20 min when the flow rate is 0.3 ul/min, and can be reduced to 1 min when the flow rate is 5 ul/min. In the neurological ward, the biochemical changes in the brain are slow, and the time delay has little effect on the prognosis. Therefore, it is recommended to use standard flow and standard catheters, which can facilitate the comparison of data from different patients at different times.
2 clinical research
MD is mainly used for early monitoring of secondary brain injury, to prevent or minimize secondary injury, to evaluate and guide treatment in perioperative and critical care, and to facilitate individualized treatment.
2.1 Subarachnoid hemorrhage (SAH) MD has been widely used for cerebral ischemia monitoring in SAH patients. Neurology organizations recommend that patients with SAH who are monitored for intracranial pressure and cerebral perfusion pressure can routinely use MD monitoring. Glutamate and LPR are sensitive indicators of cerebral ischemic deterioration. Combined with other monitoring, it can be used to guide treatment and prevent secondary deficiency. Blood damage. Vasospasm is preceded by an increase in glutamate followed by a change in lactic acid, LPR, and glycerol 181. Elevated levels of glutamate are closely related to clinical outcomes and symptoms. The concentration of glutamate and glycerol monitored by MD after SAH is closely related to regional cerebral blood flow. LPR has high sensitivity and specificity for cerebral ischemic symptoms. LPR and glycerol increase 11 to 23 hours before the onset of clinical symptoms, which may indicate delayed ischemic injury caused by vasospasm. Sakowitz et al suggest that MD can be routinely monitored as a critically ill patient in neurology, and that it is more specific than TCD to monitor delayed ischemic changes after aneurysmal hemorrhage. VID can not only help diagnose vasospasm, but also be used to guide 3H treatment; especially for comatose patients who are difficult to monitor clinically, MD monitoring will be helpful for diagnosis and treatment.
2.2 Traumatic Brain Injury (TBI) Neurology Organizational Recommendations: In patients with diffuse TBI, MD catheters can be placed in the right frontal area; in patients with focal TBI, two MD catheters can be used, respectively. Into the vulnerable area and normal brain tissue area; LPR can reflect the redox state of the brain tissue and the severity of ischemia, and is more reliable than other monitoring indicators; the degree of LPR increase and the severity and prognosis of clinical symptoms after severe TBI related. Bullock et al. inserted the MD catheter near the contused brain tissue and found that sustained cerebral blood flow reduced the release of a large amount of excitatory amino acids, whereas in patients without secondary ischemic or local contusion, glutamate release was only temporary. of. Brain MD monitors changes in cell levels that can be monitored for hypoxia or ischemia prior to the onset of neurological symptoms or prior to routine monitoring (eg, ICP, etc.). In patients with severe TBI, an increase in LPR and glycerol may indicate a cranial hypertension within 3 hours. Nordstrom et al. It is suggested that the management of cerebral perfusion pressure (CPP) should be individualized. MD can be used to determine the safety threshold of CPP, and uniform management standards should not be implemented mechanically. The poor prognosis in the acute phase after severe TBI is associated with an increase in systemic blood glucose concentration and is also associated with a decrease in MD blood glucose concentration. A recent study has shown that TBI can not routinely control blood glucose, MD glucose concentration monitoring can guide individualized treatment of blood glucose.
2.3 intraoperative sputum monitoring Mendelowitsch [131 first introduced MD monitoring technology in the surgery, they inserted the catheter into the brain tissue 1.5 cm away from the bypass area in the intracranial and extracranial artery bypass surgery, 3 patients found brain tissue The concentration of glutamate in the interstitial fluid was significantly increased during surgery, and 2 of them had hemiparesis after surgery. In the resection of the pituitary adenoma, xu et al found that although the sugar in the cortex of the stretched brain tissue did not change, LPR, glutamic acid and glycerol increased significantly; the increase of LPR suggested that the brain tissue was incomplete. Ischemia, while the increase in glutamate and glycerol suggests secondary brain injury. Li Jian et al. placed the MD catheter into the cerebral cortex of the corresponding donor artery in the intracranial aneurysm clipping process, and found that the excitatory amino acid increased significantly with the prolongation of the temporary blocking time. According to Bhatia et al., although microdialysis technology is delayed by 9 minutes due to the length of the dialysis catheter to the analyzer and the flow rate of the dialysate, it can provide reliable information for surgeons and anesthesiologists; especially when it is necessary to quickly and quickly understand brain tissue. Monitoring of sugar and lactic acid by MD is a very effective method when the interstitial changes.
2.4 Intracerebral pharmacokinetics VID can monitor the concentration of endogenous and exogenous substances in brain tissue fluid, and solves the problem of brain pharmacokinetic research in the past with the whole brain homogenization method. For critically ill patients in neurology, it is very useful to monitor the penetration of anti-infective drugs into the blood-brain barrier. Bouw et al found that the concentration of morphine in the interstitial fluid of the contusion area was significantly higher than that of the uninjured area, which may be due to the impaired permeability of the blood-brain barrier in the brain tissue of the wound and stroke. This means that brain cells prone to secondary damage are not known at the time of drug treatment. On the one hand, it may provide a better therapeutic concentration for vulnerable cells, or it may be more likely to occur due to environmental changes due to vulnerable cells. Secondary damage.
(Source: Wenzhou Medical College Vol. 37, No. 6 of Renqiu Sheng, etc.)
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