Acute blood loss leading to hemorrhagic shock is very common in acute trauma. The total blood volume of a healthy adult is about 4500ml (about 70-80ml/kg), and a blood loss of 30% (1350m1) may be life-threatening. The main cause of death in trauma patients is bleeding, and most patients will die if they are not actively treated within a short time after severe blood loss. Timely expansion of plasma volume and restoration of effective circulating blood volume is the first task of volume resuscitation.
I. Changes of organ blood flow
The rapid decrease of blood volume firstly stimulates the pressure receptors in the aortic arch and carotid sinus, and the nerve center and autonomic nerves stimulated by the above nerve impulses can lead to the release of various hormones, and the 5-HT, adrenocorticotropic hormone and pituitary hormone in the blood quickly and obviously increase, causing strong selective small artery contraction to maintain venous and arterial pressure, peripheral resistance obviously increases, and blood redistribution to ensure the important The blood is redistributed to ensure the perfusion of vital organs.
Changes in renal blood flow and glomerular filtration rate
When the blood pressure decreases moderately, the renal blood flow and glomerular filtration rate remain normal due to the inverse relaxation of the micro-artery; when the blood pressure decreases below 8 Kpa, the renal blood flow and glomerular filtration rate decrease due to the increase of renal vascular resistance due to the loss of compensation, and the retention of sodium and water increases significantly due to the effect of antidiuretic hormone and renin-vasopressin-aldosterone activity.
III. Compensatory condition of the organism
In the early stage of acute blood loss or when the blood loss is less than 20% of the normal blood volume, tissue fluid can enter the blood vessels from the tissue interstitium to supplement the blood volume deficit. When the blood loss exceeds 25% of the total blood volume, the total amount of extracellular fluid in the body cannot compensate for the amount of fluid lost due to blood loss. This is not only due to the very high concentration of intracellular ions, which prevents fluid from entering the interstitial space from the cells, but also reflects the direct damage to the permeability of the cell membrane, and the disturbance or damage to the internal and external cellular transport function and energy supply.
When the amount of blood loss exceeds what the body can compensate, the body shows a vicious cycle response. The persistent constriction of small arteries inevitably hinders the release of oxygen and the supply of nutrients, thus leading to ischemic damage and even organ insufficiency.
The traditional view is that hypotension in traumatic shock should be immediately resuscitated with fluid and vasoactive drugs to raise blood pressure as soon as possible. However, in recent years, with the in-depth understanding of the pathophysiological process of traumatic hemorrhagic shock, there is a new understanding of the timing and criteria of fluid resuscitation. The main point is to divide the course of severe traumatic shock into three stages, and adopt different resuscitation principles and programs according to the pathophysiological characteristics of each stage.
The first stage: the active bleeding period, from injury to surgical hemostasis about 8 hours. The main pathophysiological characteristics of this period are acute blood and fluid loss. Treatment principles are mainly resuscitation with balanced fluid and concentrated red blood cells in a ratio of 2.5:1, and hypertonic solutions (because hypertonic solutions increase the effective blood volume and raise blood pressure at the expense of intertissue and intracellular fluid reduction, which is detrimental to tissue cells), whole blood and excessive colloid solution resuscitation (is to prevent some small molecules of protein from entering the intertissue in the second phase and causing excessive extravascular fluid sequestration, which is detrimental to tissue cells. also detrimental to late recovery). If the patient bleeds heavily and has very low hematocrit, the amount of concentrated red blood cell transfusion can be increased. In addition, sympathetic nervous system excitement and high blood glucose level during this period may not be given glucose solution.
Phase II: A period of mandatory extravascular fluid sequestration lasting approximately 1-3 days. The main pathophysiological characteristics of this period are the increase of systemic capillary permeability, the entry of large amount of intravascular fluid into the intertissues, and the appearance of systemic edema and weight gain. The principle of treatment is active resuscitation with tolerated cardiac and pulmonary function to maintain adequate effective circulating blood volume in the organism. Similarly, the infusion of excessive colloidal solutions, especially albumin, is not advocated during this period. It is worth noting that during this period, due to the large amount of intravascular fluid entering the intertissues, the effective circulating blood volume is insufficient, and oliguria or even anuria may occur. At this time, it is not advocated to use a large amount of diuretics, and the key is to supplement the effective circulating blood volume.
Phase 3: A period of vascular refill. During this period, the function gradually recovers and a large amount of intertissue fluid flows back into the blood vessels. The treatment principle is to slow down the infusion rate and reduce the infusion volume, while diuretics can be used under the supervision of cardiac and pulmonary functions.
To sum up, for traumatic hemorrhagic shock, especially for shock patients with active bleeding, it is not advocated to give a large amount of fluid quickly for resuscitation, but to give a small amount of balanced salt solution to maintain the basic needs of the organism before arriving at the operating room to completely stop bleeding, and to resuscitate a large amount after the operation is completely processed, which is the concept of delayed resuscitation.
I. Restoration of effective circulating blood volume
The fluids for resuscitation are divided into two categories: crystalloid and colloid solutions. Crystal solutions are isotonic and hypertonic solutions, and colloidal solutions are artificial and natural.
Isotonic solutions are equivalent to extracellular fluids and are the basic solutions commonly used in resuscitating patients in hypovolemic shock. In other words, restoration of effective circulating blood volume is the main purpose of maintaining extracellular fluids. The commonly used isotonic solutions are 0.9% sodium chloride solution, lactic acid compounded sodium chloride solution, etc.
The hypertonic solution currently used is mainly 7.5% sodium chloride solution, which has the advantages of being suitable for emergency resuscitation, expanding plasma volume, increasing the amount of blood returned to the heart, raising blood pressure, dilating small arteries, increasing the contraction force of the heart and diuretic effects. The maintenance time is about 2 hours. Although it is cheap and easy to use, it should not be used in large quantities at one time, and a dosage of 4ml/kg is appropriate.
Natural colloid solution includes blood plasma, fresh frozen plasma, albumin, etc. Nowadays, there are less and less opportunities for blood transfusion because it is a backward method of wasting blood supply, and more and more component transfusion is used. The biggest problems for importing blood and blood products are infectious diseases and immune function suppression. The main infectious diseases are hepatitis, syphilis and AIDS disease, with hepatitis being the most common. Immune function suppression is only beneficial for organ transplantation and not for cancer spread and infection control. The functions of various components in blood are different and should be supplemented more reasonably according to the kind of components the organism lacks. The so-called view that blood transfusion can increase nutrition and strengthen body resistance is extremely unscientific. In hemorrhagic shock, blood transfusion can only play the role of replenishing red blood cells, some clotting factors and plasma proteins. Fresh frozen plasma contains clotting factors I, II, VII, VII, IX, X, XI, XII. Cold precipitation contains factor VIII, fibrin and fibrin-binding protein.
Artificial colloidal solutions include dextran, hydroxyethyl starch, urine-linked gelatin or succinyl gelatin, etc. These solutions can be classified as medium or low molecular weight solutions according to their molecular weight. The main purpose of correcting hypovolemic shock with colloidal solutions is to buy resuscitation time and maintain or expand blood volume. Practice has proved to be a very effective method.
Second, maintain the function of blood carrying oxygen
Both crystalloid solution and artificial colloid solution lack the function of carrying oxygen. Due to the expansion of volume, lowering blood viscosity and improving microcirculation after hemodilution, oxygen supply to tissues can be improved. However, the erythrocyte specific volume cannot be lower than 0.2, and up to this lower line should be supplemented with red blood cells or other solutions that can carry oxygen, such as fluorocarbon, matrix-free hemoglobin, artificial red blood cells, cross-linked hemoglobin and genetically engineered human hemoglobin. Perfluorocarbon emulsion is an oxygen-carrying human hematopoietic and has been used for casualty care with no complications noted. However, they are selectively taken up by the reticuloendothelial system and can sometimes cause hepatosplenomegaly, which limits their use in large quantities. It has been suggested that small doses of fluorocarbon solutions in combination with crystalloid volume expanders may be very useful. However, the prehospital application is still somewhat limited due to some problems in preparation technology and storage.
Substrate-free hemoglobin (SFHS) is a substance that carries oxygen by direct dissolution. Human SFHS is prepared from expired blood. Since this solution removes matrix phospholipids, it is a non-cellular oxygen-carrying substance. After decades of effort, purified and stabilized SFHS has been used in experimental animals. A polymerized SFHS has been used in patients with sickle cell anemia and has shown improvement in all signs of disease without side effects. Another SFHS with stability, double aspirin cross-linked hemoglobin (DCLHb), was used in a resuscitated murine model of lethal blood loss, and the results confirmed that DCLHb was as effective as whole blood in restoring hemodynamics and superior to lactated Ringer’s solution. This fluid may become an important adjunctive resuscitation fluid.
Since matrix-free hemoglobin in plasma has removed the 2,3-DPG-containing cell membrane, and oxygen carried by hemoglobin is not easily dissociated at low P50, efforts have been made to make artificial red blood cells, i.e., synthetic membranes instead of red blood cell membranes, with the aim of preserving 2,3-DPG. artificial red blood cells are non-toxic, and if successfully used in humans, it would be an effective pre-hospital resuscitation fluid.
The purpose of cross-linking hemoglobin is to cause the hemoglobin molecules to be cross-linked into polyhemoglobin aggregates, giving them a longer circulation time. In addition, the use of pyridoxal phosphate can replace 2,3-DPG to increase the oxygen release capacity. Cross-linked hemoglobin has little effect on coagulation and does not activate complement or platelets. The antigenicity of heterogeneous cross-linked hemoglobin currently requires further study.
Genetically engineered human hemoglobin is an artificial hemoglobin made by genetic engineering methods in recent years. E. coli can easily generate functional human hemoglobin, but a lot of work needs to be done before clinical application.
III. Maintaining normal hemostatic function
Crystal solutions and artificial colloid solutions do not contain platelets and clotting factors, and platelets and clotting factors of whole blood stocked in natural colloids are mostly destroyed. For the treatment of moderate (300m1) or less blood loss, blood transfusion and fluid transfusion are not clinically problematic, but for the treatment of severe blood loss (>3000m1), coagulation dysfunction will occur when a large amount of solutions without clotting factors and platelets are input. Therefore, blood and fluid transfusion in trauma emergency should consider three aspects of blood volume expansion, oxygen carrying and hemostatic function at the same time, so as to avoid the problem of losing one side and losing the other.
Section 4 Reasonable blood and fluid transfusion after trauma
Severe trauma, especially severe multiple injuries, about half of the patients combined with moderate or severe traumatic and hemorrhagic shock, which is characterized by severe trauma and microcirculatory stasis, so that the reduction of effective circulating blood volume greatly exceeds the blood loss, making the blood volume supplementation often reach three times of the blood loss.
I. Ratio of crystalloid
At present, the more consistent view is that transfusion of whole blood can only replenish the blood loss volume, but not the functional extracellular fluid, and the microcirculation will not be improved, thus the perfusion of cells cannot be improved rapidly; furthermore, severe trauma is mostly in young adults, whose internal environment is more stable, and there is no need to rely on transfusion of whole blood to resuscitate, and it can reduce the complications (circulatory overload, coagulation dysfunction, citric acidosis, etc.) caused by large amount of transfusion of depot blood . In severe shock, crystalloid and colloid fluids as well as appropriate transfusion of whole blood and blood components are advocated for resuscitation. The ratio of crystalloid fluid is generally 2:l or 3:l. Crystalloid fluid is preferable to balanced salt fluid because its electrolyte composition is similar to that of plasma, which is less likely to lead to electrolyte disorders, and it can replenish the extracellular fluid lost in the extravascular space, and moderate hemodilution can reduce the viscosity and peripheral resistance of blood, unblock the microcirculation and also shift the hemoglobin oxygen dissociation curve to the right, which is beneficial to the oxygen release of red blood cells. In addition, the balanced salt solution containing sodium bicarbonate is beneficial to the correction of acidosis.
Second, the infusion rate
Mild hemorrhagic shock is infused with 1200-2500mL of balanced fluid within one hour, and 3000mL within half an hour in severe cases, which is generally effective. This experimental treatment has a greater clinical guidance significance for monitoring blood loss. If the effect of the above measures is not obvious, the trauma cannot be stopped, and the blood pressure is still very low or at a level that cannot be measured, rapid surgical exploration should be performed to stop the bleeding at the same time as rapid fluid and blood transfusion, followed by targeted transfusion of whole blood or red blood cells to increase the red blood cell pressure product and input of albumin in plasma to maintain the colloid osmotic pressure of the patient according to the patient’s needs.
Application of hypertonic saline solution
In recent years, the use of hypertonic saline solution in the treatment of hemorrhagic shock has achieved more satisfactory results in clinical application. The input of 10-12% of the blood loss can receive a significant effect of blood pressure. Commonly used hypertonic salt solution has 7.5% NaCl, the infusion volume is 100-200ml (2-4ml/kg), rapid input within 3-5 minutes, after 15 minutes can be repeated infusion, the total amount generally does not exceed 400ml, generally 15 minutes after the obvious rise in blood pressure, and then can be quickly transfused.
The effect of small volume hypertonic salt solution on the immune system is mainly manifested in two aspects: changes in the function of T lymphocytes and neutrophils. In vivo and in vitro experiments have confirmed that hypertonic sodium chloride can enhance the immune function of normal T lymphocytes, restore the function of T lymphocytes that have been suppressed after traumatic blood loss, reduce immunosuppression and prevent secondary sepsis.
Different kinds of animal experiments and clinical studies have shown that early resuscitation with small volume hypertonic salt solution has good therapeutic effect on cerebral trauma combined with hemorrhagic shock, which can reduce cerebral vascular resistance, increase oxygen partial pressure and cerebral blood flow, reduce water content of brain tissue, and finally reduce intracranial pressure.
Hypertonic salt solutions have also shown good results for resuscitation of postoperative patients. Hypertonic salt solutions improve hemodynamic indices in patients undergoing elective and acute abdominal aortic aneurysm resection, reduce the volume of fluids and the possibility of edema, and offer new prospects for perioperative fluid resuscitation in such patients. In addition, hypertonic sodium chloride-hydroxyethyl starch can be used as a safe and effective solution to rapidly correct hypovolemia after cardiac bypass. However, it should not be considered sufficient to infuse only hypertonic saline solution during resuscitation, nor should it completely replace the infusion of balanced saline solution, and it has been suggested that it should be used with caution until bleeding is controlled to avoid aggravating bleeding.
There is also a kind of hypertonic sodium acetate solution, whose buffering base and vasodilating effect are beneficial to improve metabolic acidosis and tissue perfusion after traumatic hemorrhagic shock, and thus has received attention. However, its raw hypotensive effect is not obvious and aggravates hypokalemia. Compound medication may be more reasonable.
IV. Complications due to excessive transfusion of blood
(1) In the process of transfusion, we should prevent too much transfusion, excessive dilution of blood is easy to cause cerebral edema; if the rib is lower than 40 – 50g a few or so, and the red blood cell pressure product is lower than 20%, it will not only affect the healing of trauma, but also prone to infection. Therefore, blood pressure, pulse, erythrocyte pressure product, urine volume, capillary filling time, etc. should be monitored.
(2) Too much and too fast infusion can also cause circulatory overload. Central venous pressure, pulmonary artery wedge pressure, cardiac output, etc. should be monitored when available.
(3) When bleeding tendency occurs during massive transfusion of stock blood, the cause should be promptly identified, and fresh blood, frozen fresh plasma, platelet concentrate, fibrinogen or anti-fibrinogen lysozyme should be input respectively. 500ml of frozen fresh plasma can be transfused after 4-5L of blood transfusion if available to prevent bleeding tendency; or for every 3-5 units of stock blood transfusion, 1 unit of fresh blood should be transfused, and for primary fibrin For those with lysis, 6-aminocaproic acid or p-carboxybenzylamine can be used.
(4) Large amounts of blood transfusion are prone to citrate poisoning (citrate binding to blood calcium, resulting in hypocalcemia). Clinical manifestations are convulsions, convulsions, surgical wound bleeding, cardiac arrhythmia, decreased blood pressure, small pulse pressure, prolonged Q-T interval on ECG, and cardiac arrest in severe cases. Prevention: 2 to 3u of blood bank, 1g of calcium. Treatment: 10% calcium gluconate 10-20ml (moderate) or 10% calcium chloride lOml (shock, poor liver function is chosen).
V. Blood sources of transfusion for trauma patients
1.Autologous blood transfusion
Autologous blood transfusion refers to the collection of autologous blood for transfusion, including
① Pre-stored autologous blood transfusion;
②Hemodilution method of self-blood transfusion;
③Autologous blood loss transfusion during surgery.
Autologous blood transfusion is characterized by high oxygen-carrying capacity, which has saved the lives of many patients with acute blood loss in the case of difficult blood supply, without the concern of infectious diseases and complications of hemolytic reactions compared with stock allogeneic blood, and avoiding the potential danger of immunosuppression caused by immunosuppressive factors in the plasma of allogeneic blood transfusion.
Autologous blood transfusion in trauma patients mainly refers to intraoperative transfusion of autologous blood loss. This method can be used in any of the following cases.
(i) blunt abdominal or thoracic injury, such as splenic rupture;
(ii) ectopic pregnancy;
③Elective surgery with estimated massive bleeding (>1000m1), such as hepatic lobectomy, aortic aneurysm resection, etc;
(iv) Intracardiac direct surgery under extracorporeal circulation or deep hypothermia; (v) Drainage of blood for transfusion back (within 6 hours).
Any of the following conditions should be listed as contraindications to autologous blood transfusion.
①Blood contaminated by gastrointestinal tract;
②Blood may be contaminated by cancer cells;
③ Combined cardiac insufficiency and heart failure, obstructive lung disease, liver and kidney insufficiency or pre-existing anemia. There are still inconsistent views on whether contaminated blood can be used, but many studies and practical experiences point out that if the situation is urgent, it is not enough to transfuse this blood to save the patient’s life, and after the combination of a large number of broad-spectrum antibiotics and hormones, it can also be carefully transfused. The total amount of autologous blood loss transfusion should preferably be limited to 3500 ml.
The transfusion of autologous blood loss can save the blood in stock, without the need for cross-matching, and can buy time to facilitate emergency resuscitation. The disadvantage is that the content of platelets and fibrinogen in the blood is low, which can easily lead to hemostatic disorders after large amount of blood is imported, and the content of free Hb in the chest and abdomen is very high, which can be several times to hundreds of times higher than normal. If care is not taken to prevent this, diffuse intravascular coagulation (DIC) or acute renal failure is likely to occur (not reported so far). Therefore, when a large amount of autologous blood loss is transfused back, fresh frozen plasma or platelet-rich plasma should be supplemented appropriately.
2.Stock blood
There is a difference between fresh stock blood and general stock blood. Fresh stock blood refers to whole blood collected within 6-24 hours, the main advantage is the high platelet content. If the purpose is purely to replenish platelets, component transfusions can be used, i.e., platelet concentrate alone, without the application of fresh blood. The other components within the fresh blood are similar to the general stock blood and do not affect the physiological function. When a large amount of certain stock blood is rapidly imported, the problem of platelet reduction should be considered. Although platelets in the body should be redistributed at this time to replenish the deficiency of platelets in circulating blood, this substitution is limited and subject to time constraints.
Sixth, the application of plasma substitutes
Plasma substitute (Plasma substitute) is a colloidal solution with a molecular weight close to that of plasma albumin, which can be used to replace and expand blood volume after inputting into the blood vessels depending on its colloidal osmotic pressure, and can save some whole blood in the treatment of hemorrhagic shock.
When the blood loss is 50% of blood volume, then 1/3 of plasma substitute and 2/3 of whole blood is transfused.
1. The ideal plasma substitute crystal conditions
①No toxicity, no antigenicity, no pyrogen and no carcinogenic, teratogenic and mutagenic side effects;
②It can stay for a suitable time after inputting into blood vessels, so as to produce effective replacement effect on blood volume;
⑧Easy to excrete or metabolized by the body, but no lasting accumulation effect;
④No significant interference with the blood-forming component and coagulation system within the effective dose range, no significant damage to the important organs of the body, and no significant adverse effects on the balance of the body’s internal environment; ⑤Stable physical and chemical properties, and can be stored for a long time.
2.Commonly used plasma substitutes
(1) Dextran
Dextran is a kind of polysaccharide polymer formed by the polymerization of glucose Tsuen. There are three types clinically used: medium molecular weight (MW 70,000), low molecular weight (MW 40,000 or so), and small molecular weight (MW 20,000 or so). Medium-molecular dextran functions.
① Prevention and treatment of various types of shock, such as hemorrhage, trauma, burns, frostbite, poisoning and infection, or hypotension during surgical anesthesia, controlled hypotension.
② Hemorrhagic shock: Rescuing acute massive bleeding, rapid infusion of 500-1000m1 in the right to raise blood pressure to 10.7kPa, but should not be infused too much to avoid increasing bleeding tendency.
③Medical kidney disease; 500-1000ml daily, continuous titration for 7-10 days.
④Obstetrics and gynecology pregnancy toxemia.
⑤Extracorporeal circulation prefilling agent.
⑥Anesthetic filler: prolongs the nerve blocking effect.
Low molecular dextran action.
①Expands blood volume, causes hemodilution, reduces blood viscosity, and improves microcirculatory effects.
②Inhibit platelet function, prolong bleeding time, can inhibit the increase of platelet adhesion and aggregation force due to surgical trauma, also can reduce the release of platelet factor 3. If used properly and the dosage is controlled, it usually does not affect the coagulation function.
③Covers the surface of erythrocytes with a layer of dextrose, increasing the surface charge, causing erythrocytes to repel each other and avoid aggregation.
④Increases the deformability of red blood cells and makes it easy to pass through narrow capillaries.
⑤ Short residence time in the circulation and easy to discharge, so it is mostly used as an adjuvant therapy for microcirculatory perfusion.
(2) Hydroxyethyl starch
The electrolyte balance substitute plasma of 6% hydroxyethyl starch has been used more often in recent years. Its electrolytes are similar to plasma, containing sodium, potassium, chloride and magnesium ions, and can provide alkaline reserve, which is a better plasma bulking agent, and it not only has the function of replenishing blood volume and maintaining colloid osmotic pressure, but also can replenish the electrolyte components of functional extracellular fluid, prevent and correct acidosis that may arise after massive blood loss and hemodilution. .
The retention rate of hydroxyethyl starch in the blood is 80% for 4 hours and 60% for 24 hours after input into the body, and the concentration in the blood gradually decreases after 24 hours and is quickly excreted from the urine.
(3) Gelatin
Gelatin is a kind of protein, which can be extracted from collagen in animal skin, bones and tendons after hydrolysis, which contains a large amount of hydroxyproline. Gelatin-based plasma substitutes have been improved since the 1950s, and their colloid osmotic pressure is similar to that of human plasma albumin. However, its volume expansion effect is weaker than that of dextran and hydroxyethyl starch. In recent years, the clinical use of two solutions of urinary joint gelatin and succinyl gelatin.
3.Adverse reactions of plasma substitutes
Improper transfusion of plasma substitutes will have adverse effects on the body, such as coagulation dysfunction and renal impairment caused by excessive transfusion; allergic reactions. The incidence of dextran is about 0.07-0.1%, hydroxyethyl starch is about 0.1%, and gelatin is 0.05-1.0%. In case of severe allergic symptoms, appropriate treatment should be given promptly, with fluid replacement and treatment with adrenaline and corticosteroids.