Overview of hypovolemic shock
Hypovolemic shock is a pathophysiologic process in which the loss of circulating volume from various causes results in a decrease in effective circulating blood volume and cardiac output, inadequate tissue perfusion, and disturbances in cellular metabolism and impaired function.
Causes
1. Exogenous loss
Circulating volume is directly lost to the outside of the body, such as trauma, burns, blood loss in major surgery, peptic ulcer, rupture of esophageal varices and rupture of ectopic pregnancy, etc. It can also be caused by vomiting, diarrhea, dehydration, polyuria and other reasons.
2. Endogenous volume loss
Circulating volume is lost outside the circulatory system, which is mainly caused by allergy, hypoproteinemia and endocrine dysfunction, resulting in increased vascular permeability, leading to extravasation of circulating volume into the tissue interstitial space or thoracic and abdominal cavities to form the “third interstitial fluid”.
Symptoms
Patients with hypovolemic shock may have clinical symptoms such as palpitations, dizziness, fatigue, sweating, fainting, low urine output, rapid respiration, cold, clammy and pale skin, and altered mental status (indifference, lethargy or agitation). One should be particularly alert to early symptoms of internal bleeding such as sweating, palpitations, weakness, and a feeling of light-headedness. Patients may also present with etiology-related symptoms such as black stools, blood in the stool, blood in the urine, diarrhea, vomiting, polyuria, bleeding from the skin and mucous membranes, and other symptoms of blood volume loss. Trauma patients should be asked about chest pain, abdominal pain, low back and limb pain, and about the mechanism of injury, such as a fall, being thrown out of a car in traffic, or being run over. Early blood pressure may not fall or mildly increase, and later show a fall in blood pressure.
Examination
1. Oxygen saturation in central venous blood gas
Oxygen saturation in central venous blood gas can be completely normal in the compensatory period of hypovolemic shock or show a decrease in oxygen saturation in central venous blood gas.
2. Metabolic acidosis
Metabolic acidosis may be manifested during the compensatory phase of hypovolemic shock.
3. Hemoglobin
If blood loss is the main cause, the hemoglobin will decrease progressively; if fluid loss is the main cause, the hemoglobin may not decrease or even increase due to the influence of concentration.
4. Others
Decrease in blood pH, decrease in base excess (BE), increase in lactate.
Diagnosis
Hypovolemic shock should be considered if one or more of the following conditions are present.
1. a history of trauma, burns, gastrointestinal bleeding, diarrhea, enterocutaneous fistulae, or other etiologies that result in decreased blood volume, i.e., secondary to acute massive blood loss or loss of body fluids both internally and externally, or a history of severely inadequate fluid (water) intake.
2. Systolic blood pressure is less than 90-80 mmHg, or in hypertensive persons, blood pressure falls by more than 20%, and capillary filling time is prolonged and cannot be corrected by initial fluid resuscitation.
3. The patient has thirst, excitement, irritability, and then apathy, confusion or even coma, cold and clammy skin, decreased urine output (urine output <30 ml/h), increased heart rate and other low perfusion, as well as superficial venous atrophy, pale to cyanotic skin color, shallow and rapid respiration, rapid rapid pulse, and decreasing body temperature as clinical signs.
4. Increased plasma lactate concentration, decreased hemoglobin or hematocrit, increased urine specific gravity or urine osmolality, central venous pressure (CVP) <5 mmHg and pulmonary capillary wedge pressure (PCWP) <8 mmHg, and decreased cardiac output.
Treatment
1. Actively correcting the cause of hypovolemic shock is the basic measure of treatment. For shock patients with clear bleeding site and active blood loss, surgery or intervention should be performed as soon as possible to stop bleeding. For patients with unclear bleeding site and active blood loss, all necessary means including ultrasound and CT should be utilized rapidly to find the cause of the disease.
2. In order to ensure the supply of tissue oxygen, blood transfusion should be considered when the hemoglobin drops to 70 g/L.
3. Patients with hypovolemic shock are generally not the first to use vasoconstrictive drugs. Studies have confirmed that these drugs can further exacerbate organ underperfusion and hypoxia.