Lumbar disc herniation is a common disease, and the life and work of severe patients are affected, and some cases need surgical treatment . The conventional small incision discectomy is the gold standard for the treatment of this disease. The intervertebral foramen is exposed through the small posterior incision, and the nerve roots and protruding nucleus pulposus are removed, and the nucleus pulposus tissue is removed under direct vision. This operation requires high visual acuity of the operator, and the surgical field is small. Most of the nucleus pulposus is removed during the operation. Long-term follow-up shows intervertebral space stenosis and bone hyperplasia at the vertebral body's edge can quickly occur at the diseased segment after operation [9-11].
The development of endoscopy technology provides us with a new choice. The minimally invasive technique of transformational endoscopy has become the first choice to treat lumbar disc herniation. This technology has many advantages, such as small trauma, short recovery time, less pain, low cost, and highly praised by experts and professors [12-13]. Of course, there may be intraoperative hemorrhage, intraoperative intracranial pressure increase, nerve root injury, the dural sac injury, postoperative infection, postoperative hematoma formation, postoperative recurrence, and other complications [14-20]. The intraoperative bleeding is usually stopped by bipolar electrosurgical unit, increasing normal saline pressure, and pressing the working cannula. If there is severe bleeding, the operation should be suspended, and the gelatin sponge should stop bleeding. At present, the author usually uses the above three methods together. Improving the pressure of normal saline is the premise of keeping the operation vision clear, which provides the possibility of finding the bleeding point and using bipolar electrosurgical unit or working cannula to compress hemostasis.
Whether it is lateral or posterior laminectomy, endoscopic minimally invasive surgery needs flowing normal saline to maintain the visual field's pressure, reduce intraoperative bleeding, and keep the visual field clear. The standard method is to hang normal saline to a certain height to maintain water pressure. Too low water pressure cannot thoroughly wash out the blood in the operation field, cannot prevent the capillary blood leakage in the operation field, the operation vision is blurred, the operation difficulty is increased, and the operation time is the intraoperative and postoperative complications are increased. High water pressure can keep the vision of the operation clear. However, the pressure on the dural sac is increased, which may cause the symptoms of intracranial pressure increased during operation, such as neck pain, headache, dizziness, even nausea, and vomiting. Some patients need to suspend the operation and finish the operation as soon as possible after reducing the water pressure. Because the increase of intracranial pressure greatly influences patients, and it is impossible to measure the intracranial pressure during the operation accurately, five patients in the traditional water washing group had neck pain. The operator lowered the suspension height of normal saline, raised the head, suspended the operation, and operated again after the neck pain disappeared. The saline pressure is the most critical parameter, so try to control the minimum water flow speed to reduce saline consumption.
This study's key topic is to maintain a balance between the pressure and the water flow velocity, which can ensure the clear vision of surgery, reduce the consumption of normal saline, and reduce the occurrence of intraoperative and postoperative complications. The surgeon also found that the method could not maintain constant water pressure entirely and could not accurately adjust the flow rate. The reason is that normal saline is continuously decreasing. The liquid level is continually falling, and the relative height between the liquid and surgical fields is continuously decreasing. It is impossible to keep raising the physiological saline's height to maintain the water pressure during the operation. Therefore, most surgeons will try to hang the normal saline as high as possible to maintain a clear vision and reduce the operation time.
The author got a hint from the use of the hydraulic perfusion pump in urinary surgery in the cystoscope  and used the hydraulic perfusion pump to pump the normal saline into the surgical field of vision. The hydraulic perfusion pump consists of a perfusion pump and a perfusion rubber strip. The perfusion pump applies preset pressure and fluid velocity to the perfusion rubber strip to maintain constant water pressure and water flow velocity in the surgical field. One end of the perfusion rubber strip is connected with the saline bag, and the other end is connected with the inlet of the intervertebral foramen mirror. Under the continuous pressure of the perfusion pump, the normal saline with constant water pressure and water flow speed is provided for the surgical field. According to the normal saline hanging 1-1.5m from the patient's height, the author calculated that the effluent pressure was maintained at 74-110 mmHg, and the preliminary experiment was carried out. It was concluded that the scheme of maintaining the perfusion pressure at 60-80 mmHg and the water flow velocity at 80-100ml /min could maintain the clear vision of surgery and reduce the consumption of physiologic saline. During the operation, the water pressure and flow rate were set according to the patient's blood pressure and age. The water pressure and flow rate were appropriately increased according to the intraoperative visual field, starting from the lowest value. The conventional water pressure was maintained at 60-80 mmHg, and the water flow velocity was maintained at 80-100ml /min. In this study, there was no significant difference between the two groups. However, the operation time and intraoperative bleeding in the hydraulic perfusion pump group were significantly lower than those in the traditional water washing group. In the hydraulic perfusion pump group, there was no case occurring the symptoms of increased intracranial pressure, 1 case of nerve root adventitia injury, and 2 cases of postoperative recurrence. In the traditional water washing group, increased intracranial pressure symptoms caused operation time shortened in 5 cases. The adventitia of nerve root was damaged in 4 cases, and recurrence occurred in 4 cases. The incidence of intraoperative and postoperative complications in the hydraulic perfusion group was significantly lower than that in the traditional water flushing group.
To sum up the reasons, the hydraulic perfusion pump can accurately calculate the water pressure and water flow velocity when it is used in the intervertebral foramen endoscopic surgery. When it is used, it can start from the lower water pressure and water flow speed. According to the intraoperative visual field, the water pressure and flow velocity should be appropriately increased according to the intraoperative visual field situation. The pressure on the spinal dural sac caused by water pressure should be reduced as far as possible under maintaining a clear vision. The constant water pressure and water flow velocity should be maintained.
Reduce the effect of more considerable water pressure fluctuation on the spinal cord and reduce increased intracranial pressure symptoms. Constant water pressure and water flow velocity can better flush out the bleeding during the operation. The water pressure slightly higher than the capillary pressure is used to compress the ruptured capillaries. Without increasing the pressure of the spinal cord's dural sac, it can prevent capillary hemorrhage, keep the visual field clear, and reduce the operation time. When the nerve roots were decompressed, the direction of the nerve roots could be observed more clearly. The nucleus pulposus and other pressing materials could be removed, the probability of damage to the nerve root outer membrane would be reduced, the residual of the pressure substances could be reduced, and the postoperative recurrence could be reduced. The initial perfusion pressure should be appropriately increased in patients with hypertension before an operation, which may be associated with higher capillary pressure in the spinal canal of patients with hypertension. Elderly patients have immense vascular fragility, low spinal cord dural sac tolerance, intervertebral foramen stenosis, and superior adhesion. If the operation time is extended, the initial perfusion pressure should be reduced appropriately; the flow velocity should be increased appropriately, the spinal cord dural sac should be reduced.
Furthermore, the blood flow can be washed to remove the bleeding and keep the vision clear. After adequate decompression, the pressure and water flow velocity can be adjusted appropriately in a short time when the lateral recess is finally explored. Due to the abundant blood supply
of the lateral recess and the difficulty of hemostasis with bipolar electrosurgical unit during the operation, it is better to find the bleeding point of lateral recess and altogether stop bleeding by a short-term increase of water pressure and water flow velocity.
The limitations of this study are as follows:
① the perfusion pressure is maintained at 60-80 mmHg, and the water flow velocity is maintained at 80-100ml / min, and the initial water pressure and water flow velocity are estimated according to the patient's age, blood pressure, and other conditions, which is not accurate. Future clinical research should also consider other influencing factors, such as diabetes, rheumatoid arthritis, and other complications, through the development of a more accurate scoring table to set Initial data;
② There was no accurate instrument to measure intracranial pressure during the operation, and the data was not accurate enough to diagnose the increased intracranial pressure by the patients with neck pain;
③ The number of included samples is relatively small, and it is necessary to increase the number of cases in the future.