Research progress of fluid management in posterior orthopedics of adolescent scoliosis

Fluid management in posterior orthopedics of adolescent scoliosis. Intraoperative fluid management is the key and difficult point in the perioperative management of posterior orthopedic surgery for adolescent scoliosis. It has a great impact on the physiological function of adolescent patients, and it is particularly necessary to evaluate cardiopulmonary function before surgery.

Summary

Scoliosis is defined as a three-dimensional structural rotation deformity with a Cobb angle ≥ 10° on the coronal plane of the spine. 2%~4% of adolescents worldwide suffer from scoliosis, and severe scoliosis (Cobb angle ≥45°) requires scoliosis correction.

The surgical process includes complicated operations such as osteotomy and bone grafting. The operation time is long, the trauma is large, and the large area of ​​soft tissue is exposed for a long time, which can cause blood loss and large fluid loss. In addition, the blood volume of adolescents in the developmental stage is limited, and they often have cardiopulmonary function. Insufficiency, the risk of severe hypotension, anemia, infection, nausea and vomiting during the perioperative period increases.

Intraoperative blood loss and fluid loss are supplemented by various crystal fluids, colloidal fluids and blood products. If the fluid overload during the operation may cause acute pulmonary edema, acute heart failure and gastrointestinal edema during the perioperative period; and insufficient fluid supplementation It can cause complications such as acute kidney injury and spinal cord hypoperfusion.

Therefore, optimizing intraoperative fluid management, maintaining stable perioperative hemodynamics, and ensuring good tissue perfusion and oxygen supply are essential to protect the function of important organs and reduce perioperative complications.

This article focuses on the special pathophysiology of adolescent scoliosis, special surgical methods for spinal correction, intraoperative fluid infusion and blood transfusion strategies, etc., to summarize the research progress of intraoperative fluid management in posterior scoliosis surgery in recent years. Intraoperative fluid management optimization provides new ideas and provides theoretical support for future research.

1 Special pathophysiology and posterior scoliosis correction

The common types of adolescent scoliosis are idiopathic, neuromuscular and congenital, of which about 85% are idiopathic scoliosis. Severe scoliosis of the spine and chest (upper back) causes chest wall deformity, which causes the lungs to fall into an abnormally restrictive shape, and can even change the position of the bronchus, resulting in failure to reach the maximum lung capacity, causing atelectasis, resulting in lung dysplasia. Impaired function.

At the same time, because the spine and the heart are in the same germ layer during growth and differentiation, adolescent scoliosis is often accompanied by congenital heart disease. Adolescents with severe thoracic scoliosis and congenital heart disease have unbalanced body posture, insufficient lung ventilation, and reduced oxygen entering the blood. At the same time, the restrictive shape of the lungs and other internal organs shift and squeeze the heart, making the heart more burdensome.

The posterior correction of scoliosis is divided into 6 stages: exposure, nail placement, loosening, correction, cortical removal, bone grafting and closure. Chiu et al. found that the highest intraoperative blood loss was in the decortical phase [(17.1±18.3) ml/min], followed by the loosening phase [(12.0±10.8) ml/min], and the highest total blood loss was in the screw placement Stage [(301.0±196.7) ml], followed by the correction stage [(226.8±171.2) ml], the patient’s hemodynamic status may change rapidly in the above stages, and we need to be vigilant.

Intraoperative blood loss is also different due to the type of scoliosis. In patients with idiopathic scoliosis, the intraoperative blood loss accounts for 16% to 44% of the blood volume, while the blood loss during neuromuscular scoliosis is more important. It accounts for 50% to 75% of blood volume. Possible reasons include fusion of more vertebral body segments, younger patients, lighter weight, longer operation time, excessive consumption or dilution of coagulation factors, and preoperative anemia.

In addition to the physiological changes caused by mechanical ventilation in the prone position during the operation, the cardiac index (CI) is reduced, the inferior vena cava is blocked, the functional residual volume is increased, the pulmonary blood flow and the redistribution of pulmonary ventilation are also caused by the traditional volume index monitoring. Interference, such as CVP, MAP, etc., in turn affects the accurate assessment of the state of the vascular volume.

2 Progress of intraoperative infusion strategy

2.1 　 Capacity monitoring-capacity responsiveness assessment

According to the Frank-Starling curve, only when the ventricular preload is in the ascending branch of the cardiac function curve, the increase in preload can significantly increase cardiac output (CO), and the purpose of volume response assessment is to guide fluid therapy to ensure tissue perfusion . In adolescents with posterior scoliosis correction surgery, blood loss and fluid loss are large, and hemodynamics are prone to rapid changes. Adolescent patients have limited blood volume and often have cardiopulmonary abnormalities, requiring timely and accurate indicators for guiding fluid therapy.

2.1.1　Static indicators

Traditional static indicators indirectly reflect cardiac preload by measuring intravascular pressure, and it is often impossible to accurately predict volume status in such operations. Although the invasive arterial blood pressure can intuitively and dynamically reflect the blood pressure changes of the patient in each cardiac cycle, arterial blood gas analysis can be performed at any time, combined with heart rate, pH, Hct, lactic acid, alkali residual and other indicators to roughly assess the patient’s volume status during surgery, but Only when the acute blood loss exceeds 20% of the total circulation will blood pressure drop significantly. Invasive arterial blood pressure is easily affected by many factors such as surgical stimulation, body position changes, chest pressure, ventricular compliance, and mechanical ventilation, and it is difficult to effectively guide intraoperative fluid management.

CVP is affected by mechanical ventilation and surgical operations in the prone position. It increases with the increase of intrathoracic pressure. It can also decrease due to improper positioning of abdominal pressure affecting venous blood return, especially in the nail placement stage, so CVP cannot accurately reflect blood volume. It can’t accurately predict the capacity responsiveness. MAP is an important monitoring index in spinal orthopedics, and the blood perfusion flow of organs (such as brain, spinal cord and kidney perfusion) is closely related to its level. A Chinese study based on 30 adolescents with posterior scoliosis surgery pointed out that maintaining MAP at (60±5) mmHg (1 mmHg=0.133 kPa) has less blood loss during the operation and does not affect the spinal cord, kidneys, etc. Important organ functions, the results have certain reference value for clinical practice.

2.1.2 　 dynamic indicators

The dynamic index is based on the principle that the intrathoracic pressure periodically changes during mechanical ventilation of the closed chest cavity to cause the cardiac ejection volume to change periodically, and the percentage of change increases with insufficient patient capacity. It reflects the dynamic change rate of the CO index within a certain respiratory cycle. This reflects the patient’s volume status and predicts the responsiveness of fluid therapy. At present, dynamic indicators using invasive arterial pulse waveform analysis technology are more commonly used, including stroke volume variation (SVV), pulse pressure variation (PPV) and pulse perfusion variability index (pleth variability index, PVI) and so on.

Biais et al. proposed for the first time that PPV and SVV can be used to predict responsiveness to fluid therapy in adult patients with scoliosis surgery. The study set that after intravenous supplementation of 500 ml of 6% hydroxyethyl starch solution (lasting> 10 min), if ΔCO ≥ 15%, it indicates volume responsiveness. It was found that PPV and SVV were significantly reduced after rehydration, and the cut-off value of PPV was 15% [sensitivity 100%, specificity 80%, area under curve (AUC) 0.959], the cut-off value of SVV is 14% (sensitivity 94%, specificity 80%, AUC 0.938), and PPV There was no statistically significant difference between AUC and SVV.

At the same time, the study also found that the prone position not only increased the basic values ​​of SVV and PVV, but also caused a significant decrease in CO, MAP, and respiratory system compliance. Yang et al. also confirmed that changes in PPV during prone spine surgery in adult patients can predict volume responsiveness, with a cut-off value of PPV of 14% (sensitivity 97%, specificity 90%, AUC 0.969).

Different from Biais et al., in this study, 6 ml/kg 6% hydroxyethyl starch solution was supplemented intravenously within 10 minutes. If the variability of stroke volume index measured by esophageal Doppler ultrasound is ≥10%, then Indicates a reaction to liquids.

Min et al. used the same liquid loading method as Yang et al. After setting ΔCIVigileo≥12%, it indicated that it was responsive to the liquid. They found that the non-invasive SVV monitoring based on the NICOM® system compared to the invasive monitoring based on FloTrac™/Vigileo™ is also predictable The volume responsiveness of adult patients in prone spinal surgery after fluid loading, and the cut-off values ​​of SVVNICOM and SVVVigileo for predicting volume responsiveness are both 12% (sensitivity 74%/68%, specificity 67%/81%, AUC 0.78 /0.79). Kim et al. also found that PVI maintained the ability to predict fluid reactivity during prone lumbar fusion in adult patients. The best cutoff value of PVI in the study was 8% (sensitivity 67%, specificity 69%, AUC 0.756).

Although various forms of research in recent years have confirmed that PPV, SVV, and PVI can successfully predict volume responsiveness during prone spine surgery in adult patients and can be used to guide fluid therapy, there is still a lack of research on the special group of adolescent scoliosis , Whether PPV, SVV, and PVI are applicable to adolescents who may have cardiopulmonary hypoplasia requires further research.

2.1.3　Non-invasive ultrasound technology

In recent years, with the popularization of visualization technology, ultrasound technology has also been used for the evaluation of intraoperative volume in posterior spinal orthopedics. Transesophageal echocardiography relies on the accurate positioning of the Doppler probe close to and perpendicular to the descending aorta, providing the anesthesiologist with visible ventricular cavity size and wall motion, thereby transforming traditional pressure measurement into volume measurement, which not only provides a basis Volume status and dynamic observation of volume responsiveness to achieve goal-oriented fluid therapy. As the advantages of transesophageal echocardiography become more prominent, its application in spinal orthopedics has become more and more widespread.

Recently, Hensley and Wang used the right long axis imaging technique of the inferior vena cava to evaluate the vascular volume of 10 patients undergoing lumbar surgery in the prone position and successfully obtained the right visual field of the inferior vena cava. Although the increase in the diameter of the inferior vena cava in some patients corresponds to the increase in the non-invasive measurement of CI, the number of study cases is too small to explain its effect, and more cases are needed for verification.

2.2　Rehydration method

2.2.1 　 Open rehydration/restrictive rehydration

Based on factors such as preoperative fasting for a long time, dehydration caused by abstinence, anesthesia-induced vasodilation, intraoperative non-dominant evaporation, and overestimation of intraoperative fluid loss caused by the hypothetical “third gap”, the anesthesiologist will Patients undergoing major surgery are supplemented with high-volume crystalloids to prevent inadequate fluid resuscitation in the case of low blood volume, resulting in a decrease in CO and tissue oxygen supply, resulting in organ dysfunction. However, for adolescent spinal orthopedics, the fluid overload caused by active supplementation of crystalloids will increase the burden of the heart and lungs, and is closely related to the increased risk of various postoperative complications and death.

A prospective study by Niescery et al. found that restrictive rehydration (23 cases, crystalloid fluid ≈5.5 ml·kg−1·h−1) during posterior orthopedic surgery for adolescent idiopathic scoliosis was better than open rehydration ( 22 cases, crystalloid fluid ≈ 11 ml·kg−1·h−1) Postoperative lung ventilation and oxygenation were better, and the incidence of postoperative pulmonary edema was also reduced. Recent studies have pointed out that the amount of intraoperative lens fluid supplementation is an important independent risk factor for early deep surgical site infection after pediatric spinal orthopedic surgery, and for every additional 1 L of lens fluid, the odds ratio increases by 1.547. However, over-restrictive fluid replacement, once the fluid is insufficient, the patient’s risk of acute kidney injury increases during the perioperative period, and it may also affect spinal cord perfusion, especially in adolescents in the developmental stage.

2.2.2　 SVV-based goal directed fluid therapy (GDFT)

GDFT monitors the dynamic parameter targets that reflect the patient’s blood volume (such as PPV, SVV, and PVI) to maintain it in the normal range, and performs personalized fluid replacement according to the continuously changing fluid requirements during the operation. In 2016, Bacchin et al. conducted a study on whether a SVV-based GDFT program can be applied to large-scale spine surgery in the prone position and whether it can effectively reduce allogeneic blood transfusion during perioperative period.

The study retrospectively analyzed 23 cases of using SVV-based GDFT program [ Set the background crystalloid infusion rate to 4 ml·kg−1·h−1. If ΔSVVp>20% of the normal base value of SVVp, increase the infusion rate (maximum 10 ml/kg), and repeat the assessment 5 minutes later. If SVVp does not fall to normal after 2 consecutive rehydrations, consider the use of vasoactive drugs (ephedrine)] and 23 cases at the same time use the intraoperative free rehydration regimen (experienced anesthesiologists should maintain MAP ≥ according to the general principles of good clinical practice The data of patients undergoing posterior spinal fusion (50-60 mmHg as the target for fluid replacement) found that the intraoperative lens fluid infusion in the GDFT group was 40% less than that in the free fluid replacement group, and the peak lactate was lower (1.0 mEq/L Compared with 1.8 mEq/L), there is less intraoperative bleeding, less red blood cell transfusion during the perioperative period, increased urine output after surgery, and earlier recovery of bowel function.

In terms of postoperative respiratory function, the GDFT group had no X-ray signs of pulmonary congestion, such as bilateral pleural effusion or peribronchial cuff, while 20% of the free fluid rehydration group had pulmonary complications. Although this study verifies the advantages of the SVV-based GDFT scheme for large-scale spine surgery for adults in the prone position, the number of cases is relatively small, and various complex factors including surgery, anesthesia, and drugs will affect the results of the study. For further analysis of a larger prospective study with a larger sample size, GDFT based on PPV, PVI, etc. can be considered, especially for the study of adolescents undergoing scoliosis orthopedics, and the data is relatively scarce.

2.3　 Choice of liquid type

Crystalline solution: In adolescent scoliosis surgery, if there is more blood loss during the operation, the patient may have pathophysiological changes of ischemic shock. At this time, excessive infusion of 0.9% sodium chloride or compound sodium chloride solution may Exacerbating the occurrence and development of metabolic acidosis, 0.9% sodium chloride is only used for a small amount of flushing after blood transfusion.

Sodium lactate Ringer’s solution contains dextro-lactate root, and its metabolism is strongly dependent on liver function. In the case of liver insufficiency and shock, the metabolism of lactate is weakened, and its buffering alkali capacity is also weakened accordingly, which can lead to the accumulation of lactic acid and even lactic acidosis.

Because sodium acetate Ringer’s solution does not contain lactic acid, it will not cause lactic acid accumulation, and the metabolism of acetic acid is less dependent on the liver. The domestic Sodium Acetate Ringer’s Solution (Lejia) contains 1% glucose. Appropriate infusion can supplement the energy required by the body and has a slight effect on blood sugar.

Colloidal fluid: 4%~5% of human albumin is the safest of all colloidal fluids, but its volume expansion effect and expensive price limit its application in scoliosis orthopedics. 6% hydroxyethyl starch (130/0.4) is a relatively new third-generation hydroxyethyl starch colloid, It is easier to be metabolized and eliminated by the kidneys while maintaining osmotic activity, which helps prevent the accumulation of hydroxyethyl starch in plasma after repeated doses, and also has a smaller impact on blood coagulation and renal function.

It shows faster recovery and better tissue perfusion than crystals, so 6% hydroxyethyl starch (130/0.4) is widely used in adolescent scoliosis correction surgery for volume expansion. Gelatin is a heterogeneous protein in the body. The most common side effect is allergic reactions, mainly urticaria or temporary fever. More serious reactions include varying degrees of hypotension and bronchospasm. Studies have retrospectively compared the effects of 6% hydroxyethyl starch (130/0.4) and 4% succinyl gelatin infusion during posterior spinal orthopedics on renal function in adolescent scoliosis patients.

The difference was not statistically significant. However, based on its volume expansion effect and various side effects, gelatin is not recommended to be widely used in such adolescent surgery, and it can be used as an alternative treatment for patients who are not suitable for 6% hydroxyethyl starch (130/0.4).

3 Progress of intraoperative blood transfusion strategy

3.1　 blood protection

3.1.1 　 Preoperative autologous blood pre-storage and intraoperative autologous blood transfusion

Although preoperative autologous blood storage technology can reduce allogeneic blood transfusion, it is expensive, time-consuming, and has the risk of bacterial contamination. Therefore, it is only suitable for special patients, such as patients with rare blood types and special religious beliefs who refuse to accept allogeneic blood. Because of the large amount of bleeding during posterior spinal orthopedics and easy recovery, intraoperative washing and recovery autotransfusion has made great progress in this type of surgery, which can greatly reduce or not transfuse foreign blood. A randomized controlled trial of 110 consecutive posterior spinal fusion surgery with cell salvage showed that compared with the control group, the intraoperative allogeneic blood transfusion rate (P=0.032) and the perioperative allogeneic blood transfusion rate ( P=0.025) were significantly reduced.

3.1.2 　 Antifibrinolytic drugs

Bosch et al. analyzed the coagulation function of adolescent patients with idiopathic scoliosis undergoing posterior spinal fusion and found that it has stable coagulation factors and platelets, and fibrinolysis is the main cause of intraoperative bleeding. Studies have shown that the preventive use of antifibrinolytic drugs during surgery can effectively reduce blood loss and the need for blood transfusion during adolescent idiopathic scoliosis surgery.

A meta-analysis on spinal surgery by Li et al. found that compared with aprotinin and aminocaproic acid, tranexamic acid (TXA) was more effective in reducing total blood loss, intraoperative blood loss, and blood transfusion. Similarly, Goobie et al.’s prospective study on the use of TXA in adolescent idiopathic scoliosis correction surgery also found that compared with the placebo group, TXA was administered after induction of anesthesia [loading dose 50 mg/kg (>15min), The maintenance dose is 10 mg·kg−1·h−1], the intraoperative blood loss is reduced by 27%, and its positive effect is most obvious in the operation of more than 4 hours, and its effect extends to the postoperatively, which can effectively reduce the postoperative drainage .

In addition, Johnson et al. retrospectively analyzed 116 cases of idiopathic scoliosis spinal fusion surgery and found that high-dose (loading dose 50 mg/kg, maintenance dose 5 mg·kg−1·h−1) TXA was higher than low dose (loading dose 10 mg/kg, maintenance dose 1 mg·kg−1·h−1) can more effectively reduce intraoperative blood loss and blood transfusion requirements. Hariharan et al. included 7 studies (2 RCTs and 5 cohort studies) to conduct a meta-analysis on the safety and effectiveness of TXA for this type of surgery, and found that TXA can reduce intraoperative blood loss and total blood transfusion while not increasing thrombosis. The risk of embolic events.

3.1.3 　 Controlled blood pressure reduction

Controlled blood pressure reduction can reduce blood oozing by reducing the pressure of the epidural venous plexus and the intraosseous pressure of the vertebrae, but hypotension may affect the perfusion of end organs (such as the spinal cord and optic nerve). Studies have found that a decrease in MAP of more than 50% from baseline in non-cardiac surgery for 5 minutes is related to the 30-day mortality rate after surgery. Intraoperative MAP <60 mmHg for more than 11 minutes can aggravate acute kidney injury.

O’Donnell et al. recommended maintaining MAP<70 mmHg during the period of heavy intraoperative bleeding (decortexing and internal fixation), and maintaining MAP>70 mmHg when correcting the spine curve, which can reduce the risk of hypoperfusion. There are also studies that combine controlled hypotension and acute high-volume hemodilution in scoliosis correction surgery to achieve the effect of effectively reducing the amount of bleeding while ensuring the perfusion and oxygen supply of the various organs of the body.

3.1.4　 Body temperature protection

Scoliosis patients have long surgical incisions (10-40 cm) and large areas of soft tissue that are continuously exposed to a low-temperature operating room environment for a long time, resulting in a large amount of body heat dissipation. These factors can easily lead to patients with low body temperature during the perioperative period happened. Hypothermia during general anesthesia has long been proven to reduce platelet function and damage the coagulation cascade during surgery. Avoiding hypothermia is an important factor in reducing central vasoconstriction and blood loss.

Therefore, real-time body temperature monitoring, raising the ambient temperature, and using active heating devices to prevent intraoperative hypothermia are indispensable for blood protection. Görges et al. advanced the pre-intervention of body temperature for children undergoing scoliosis correction surgery before entering the operating room. On the day of surgery, the children will be pre-heated on an insulation device (43 ℃) in the surgical daycare ward.

The air temperature in the operating room was adjusted to 43 ℃ to continue preheating until after induction of anesthesia. It was found that the incidence of intraoperative hypothermia was reduced by 16% in patients receiving preheating, and the amount of allogeneic blood transfusion was reduced.

3.2 Indications for allogeneic blood transfusion

The Hb content is an important factor in determining the time of blood transfusion. The Hb content is monitored by arterial blood gas analysis before, during and after the operation to choose the right time. A single-center retrospective study of posterior orthopedic surgery for adolescent idiopathic scoliosis found that patients with preoperative Hb <110 g/L have a 49.6 higher probability of postoperative blood transfusion than those with preoperative Hb>140 g/L Times.

Fontanals et al. also found in a large retrospective study that preoperative anemia was associated with a 50% increase in the risk of perioperative blood transfusion and a 30% increase in hospital stay (>7 days). Therefore, the treatment of preoperative anemia will greatly reduce allogeneic red blood cell transfusion and improve resource utilization. The blood transfusion guidelines approved by the American Association of Blood Banks recommend that the trigger window of intraoperative blood transfusion for orthopedic surgery patients is Hb ≤ 80 g/L (strong recommendation, moderate quality evidence).

Studies have also pointed out that reducing the trigger window to Hb ≤ 70 g/L can reduce blood usage by 32.5% and achieve similar or improved clinical results. Intraoperative thromboelastography is used to monitor blood coagulation function to guide the transfusion of blood components, and timely supplement of blood products such as platelets, fresh frozen plasma and cryoprecipitate as needed can help reduce the amount of red blood cell transfusion, which is more in line with the patient-centered blood transfusion plan.

4 Summary and outlook

Intraoperative fluid management is the key and difficult point in the perioperative management of posterior orthopedic surgery for adolescent scoliosis. It has a great impact on the physiological function of adolescent patients, and it is particularly necessary to evaluate cardiopulmonary function before surgery. Strengthening intraoperative hemodynamic monitoring, timely and accurate assessment of patient volume status, and maintaining circulatory stability are important guarantees for patient life safety.

However, effective volume monitoring indicators for adolescents in the prone position need to be further explored. The purpose of reasonable fluid replacement is to avoid fluid overload or insufficient fluid replacement, and to ensure intraoperative tissue perfusion and tissue oxygenation. Can the currently focused GDFT method based on SVV, PVV, and PVI effectively reduce blood loss and blood transfusion during such operations? The amount and the occurrence of perioperative complications still need to be verified by large-sample RCT studies.

In recent years, blood protection strategies such as intraoperative washing autologous blood transfusion, the use of TXA, controlled hypotension, and body temperature protection have been continuously developed and improved, which has significantly reduced intraoperative blood loss. At the same time, strict blood transfusion indications should be mastered to ensure volume safety while reducing allogeneic blood transfusion, reducing the potential risk of allogeneic blood transfusion for young people in the growth and development stage.

At present, there is a relatively lack of research on fluid treatment strategies during adolescent scoliosis correction surgery. In order to improve fluid management during surgery, it is necessary to further study the impact of different fluid rehydration methods combined with vasoactive drugs on the short-term and long-term prognosis of patients.

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