SVV guided GDFT strategies
GDFT refers to an individualized rehydration regimen based on the patient's gender, age, body weight, disease type, preoperative systemic condition, and volume status. Traditional indicators such as central venous pressure and pulmonary wedge pressure (PAWP) are static indicators that are susceptible to anesthesia, stress and circulatory functions, and they are imperfect and lagging. Functional hemodynamic parameters (FHP) monitoring including systolic blood pressure variability (SPV), SVV, pulse pressure variability (PPV), etc., this is a new hemodynamic monitoring method, SPV and PPV also has its limitations. It is required to be applied in a regular heart rhythm, standard ventilation mode, and also affected by factors such as intrathoracic pressure, intra-abdominal pressure or heart failure.9 The FloTrac/Vigileo Monitoring System is a new tool for calculating SVV and cardiac output (CO). Studies have shown that SVV has a good correlation with volume changes in major surgery patients undergoing mechanical ventilation, and confirmed its effectiveness and accuracy.10,11 It is also sensitive and reliable for neurosurgery to predict the fluid reactivity of patients.12,13 This study was based on the literature [6] and numerical value of the SVV is set to 13%, it as a target-directed liquid therapy.
Controversy over the choice of resuscitation fluid.14 Isotonic crystal solutions can be used for fluid management in patients with craniocerebral injury, and saline is the recommended solution. Lactic acid Ringer's solution is slightly hypotonic, which may reduce serum osmotic pressure and aggravate brain edema during large infusions.15 Persistent hyperglycemia is an independent risk factor for poor prognosis in patients with severe head injury. In addition, acidosis and free brain water produced by the anaerobic hydrolysis of glucose can make brain edema worse. Therefore, if the patient is not accompanied by hypoglycemia due to lack of nutritional support, the glucose solution should be avoided during anesthesia.16 Studies have shown that the ability of artificial colloids such as 6% hydroxyethyl starch (HES) 130 / 0.4 and succinyl gelatin to restore and stabilize circulation is better than that of crystal fluids. At the same time, it is beneficial to maintain cerebral oxygen supply and demand balance and reduce inflammation.17,18 Maintaining the circulation stability of TBI patients during the perioperative period is the cornerstone of fluid therapy. When the patient's circulation cannot be maintained by using the crystal fluid alone, the anesthesiologist should use the colloid fluid reasonably according to the specific circumstances of the patient.Studies have shown that compared with the traditional fluid replacement methods, the FloTrac/Vigileo system provides SVV and SVV guided GDFT fluid management strategies to optimize perioperative volume status, further reducing postoperative complications and facilitating patient surgery and facilitating postoperative recovery.19 In this study, GDFT strategies decreased intraoperative total transfusion volume, crystalloid solution volume and colloidal solution volume in TBI patients. It indicates that SVV guides the liquid management strategy of GDFT can accurately and reliably reflect the human body's responsiveness to liquid therapy. Individualized infusion according to different or fluctuating fluid needs of patients, and correction of patients with occult circulating blood volume deficiency or excess in advance, so that both vascular tone and cardiac load are in an optimal state.
DEX as a commonly used anesthesia adjuvant and its brain protection research
DEX is a new type of highly selective α2 - adrenergic receptor agonist. It is a commonly used anesthesia adjuvant in clinical practice. Wang suggested that DEX exerts neuroprotective effects on rats with subarachnoid hemorrhage by activating the EPK pathway.20 DEX has been widely used in neurology.21, 22 Our study found that patients with traumatic brain injury were given DEX (1µg/kg) intravenously before anesthesia induction, followed by 0.5µg·kg− 1·h− 1 infusion, and the results showed DEX can reduce the serum S100β protein concentration of patients and DEX has brain protection. This study was based on the literature [8], prior to induction of anesthesia, DEX was injected intravenously 1µg/kg for 10 min and then 0.5µg·kg− 1·h− 1 to the end of the surgery.
One of the purposes of the GDFT combined with DEX is to optimize capacity management and stabilize hemodynamics.
In this study, after applying DEX, the patient's heart rate has a slowing trend. The reason may be the following two points. DEX has an inhibitory effect on stress and anti - sympathetic nerves. Its main mechanism of action against sympathetic nerves is to activate the α2A/D receptor on the postsynaptic membrane of the solitary tract nucleus, reducing sympathetic tone, then lowering blood pressure and heart rate; DEX stimulates the α2A/D receptor on the presynaptic membrane of the sympathetic nerve, inhibits the release of norepinephrine, reduces the concentration of plasma catecholamine, and thus plays a cyclically stable role.23, 24 Compared with the traditional fluid replacement methods, the other three groups of patients have a more stable blood pressure at the surgeon to open the dura mater. And compared with DEX alone, the MAP is more stable when GDFT combined with DEX. It indicates that the GDFT can accurately and reliably reflect the human body's responsiveness to liquid therapy. Individualized infusion according to different or fluctuating fluid needs of patients, and correction of patients with occult circulating blood volume deficiency or excess in advance, so that both vascular tone and cardiac load are in an optimal state. So the GDFT combined with DEX is to optimize capacity management and stabilize hemodynamics.
The second purpose of the GDFT combined with DEX is to play a role in brain protection and improve the neurological outcome
Improve cerebral oxygen metabolism
The blood in the internal jugular vein is returned from the venous sinus to the venous ball, and there is generally no mixed extracranial venous blood. Therefore, this study collected blood samples from this site for blood gas analysis and observation indicators. SjvO2 is the first clinically used indicator to evaluate the oxygen metabolism of brain tissue, reflecting the changes in oxygen supply and oxygen consumption throughout the brain. According to Fick theory, SjvO2 and Da-jvO2 may reflect the relationship between cerebral blood flow and cerebral oxygen consumption- that is oxygen balance. Therefore, collect blood from jugular bulb to detect SjvO2 and calculate Da-jvO2 is very important to accurately assess the whole-brain blood flow and metabolism.25 CERO2 can reflect organic respiratory situation and organic perfusion, which is tightly relative to microcirculation perfusion. Thus, oxygen supply and consumption in brain tissue can be reflected by CERO2 respectively. Therefore, the combination of SjvO2, Da-jvO2 and CERO2 in this study can more accurately and reliably assess the oxygen supply and demand of the brain. And study has shown that DEX-induced sedation reduces cerebral blood flow (CBF), which may be due to direct alpha(2) - receptor cerebral smooth muscle vasoconstriction or DEX-induced reduction in brain metabolic rate the CBF changes, thus maintaining the balance of cerebral oxygen supply and demand.26 In this study, the lactic acid value was directly measured by collecting the blood of the internal jugular vein, and the brain tissue perfusion was understood from the aspect of energy metabolism. Blood lactic acid and urine volume were important indicators for evaluating microcirculation perfusion.27 And the study has confirmed that the amount of lactic acid in the blood is directly related to the prognosis and mortality of patients, which is helpful to evaluate the prognosis of patients with major surgery.28 In this study, patients in the DEX group or the GDFT group had higher SjvO2, lower Da-jvO2 and CERO2 than the traditional fluid replacement method, this is suggested that the use of DEX or GDFT can improve the patient's cerebral oxygen metabolism. Patients in the GDFT combined with DEX group had higher SjvO2, lower Da-jvO2 and CERO2 than the other three groups, and the group had blood lactate concentrations decreased in the surgery and surgery after 12 hours. It is indicated that the GDFT combined with DEX further improves cerebral oxygen metabolism and brain tissue perfusion.
Decrease the S100β protein and NSE concentration
S100β is a calcium-binding protein that is secreted mainly by glial cells in the brain.The study has shown that S100β protein is a sensitive neurobiochemical marker of brain tissue damage.29, 30 NSE is a key protease, it involved in the cytoplasmic glycolytic pathway of neuroendocrine cells and brain neurons. It is mainly found in neuroendocrine cells and neuronal cytoplasm. The glial cells and related nervous tissues in the brain do not contain this. Enzymes, body fluids are also less abundant, so NSE has neurological specificity. The study has shown that NSE concentration is significantly elevated in patients with acute traumatic brain injury, and can be used as a biomarker to reflect damage to nerve tissue.31, 32 In this study, the professional enzymes used the classical enzyme-linked immunosorbent assay (ELISA) to determine the concentration of S100β protein and NSE in serum, which ensured the objectivity and reliability of the collected data. In this study, compared with the traditional fluid replacement method, S100β protein concentration and NSE decreased in patients treated with DEX or goal-directed therapy at certain time points, whereas application of GDFT combined with DEX decreased at each time point, and the GDFT combined with the DEX group was further reduced at some time points than the S100β protein concentration and NSE. It is suggested that the application of DEX or GDFT can reduce craniocerebral injury, and GDFT combined with DEX further reduces the extent of craniocerebral injury.
Improve clinical outcome
The Glasgow Coma Scale (GCS) is a method for determining the severity of craniocerebral injury based on the patient's condition of consciousness disorder. It is a well-established method for determining the severity of craniocerebral injury, and a simple and practical scale.33 It performs 15 tests in three different reactions of blinking, speech and exercise. A total of 15 points, 15 points indicating waking, and 8 points and below indicating conscious coma. The GOS score scored the patient's language, recovery of limb motor function, and assessed the quality of life 1 week after surgery. The enduring appeal of the GOS is linked to its simplicity, short administration time, reliability and validity, stability, flexibility of administration cost-free availability and ease of access.34 The Glasgow Outcome Scale (GOS) is the most widely cited assessment of outcome in the community after brain injury.35 In this study, compared with the traditional fluid replacement methods, the days of postoperative length of hospital stay (LOS) and the GOS was higher in the GDFT combined with DEX. It is suggested that GDFT combined with DEX can reduce the postoperative length of hospital stay and improve their prognosis.
The limitations of this study are as follows. First, this study is a single-center study with a limited number of cases included, therefore, this study may have a bias in patient selection, and the results may not be universally applicable. Second, long-term outcome of patients was not observed and followed up.
In summary, GDFT combined with DEX can better optimize fluid therapy strategy and improve neurological outcomes in patients undergoing surgery for TBI.