What is hypovolemic shock and how should it be monitored?

In life, we need to understand some common knowledge of pathology, which helps us detect diseases in their early stages and provide effective treatment, because the early stages of the disease are fragile. So what is hypovolemic shock?

Concept and etiology

Circulatory volume loss in hypovolemic shock includes exogenous and intrinsic losses.

1) Exogenous loss: refers to the loss of circulating volume outside the body. Blood loss is a typical exogenous loss. Exogenous loss can also be caused by vomiting, diarrhea, dehydration, diuresis, etc.

2) Endogenous volume loss: refers to the loss of circulating volume outside the circulatory system, but still in the body. The main reasons are increased vascular permeability, extravasation of circulating volume, or entry of circulating volume into the body cavity.

Key points for early recognition of traditional hypovolemic shock:

Traditional identification and diagnosis are mainly based on medical history, symptoms, and signs, including changes in mental status, cool and clammy skin, decreased systolic blood pressure (< 90 mmHg or 40 mmHg lower than baseline blood pressure) or decreased pulse pressure (< 20 mmHg), urine output < 0.5 ml/hr·kg, heart rate > 100 beats/min, CVP < 5 mmHg or PAWP < 8 mmHg.

In recent years, people have come to realize the important reference value of oxygen metabolism and tissue perfusion indicators for the early diagnosis of hypovolemic shock. Blood lactate (> 2 mmol/L) and alkali deficiency (< -5 mmol/L) are important indicators for the early diagnosis of hypovolemic shock. Indicators such as stroke volume (SV), cardiac output (CO), oxygen delivery (DO2), oxygen consumption (VO2), gastric mucosal CO2 tension (PgCO2), and mixed venous oxygen partial pressure (SVO2) also have a certain degree of clinical significance.

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General clinical monitoring

Including monitoring indicators such as skin temperature and color, heart rate, blood pressure, urine volume and mental state. However, it is often difficult to see obvious changes in these indicators in the early stages of shock.

The severity of the loss of skin temperature, pallor, and subcutaneous venous collapse depends on the severity of shock. However, these symptoms are not specific. An increased heart rate is usually one of the early diagnostic indicators of shock, but heart rate is not a reliable indicator of blood loss. Some patients can easily compensate for moderate blood loss through vasoconstriction, with only a mild increase in heart rate.

Changes in blood pressure require close dynamic monitoring. In the early stages of shock, blood pressure may remain at or near normal due to compensatory vasoconstriction. It is sometimes feasible to maintain "permissive hypotention" in hemorrhagic shock with uncontrolled bleeding. But what is the standard for permissible hypotension? Maintaining mean arterial pressure (MAP) at 60-80 mmHg is a common practice for some people.

Urine volume is a good indicator of renal perfusion and can indirectly reflect the circulatory status. When the hourly urine output is less than 0.5 ml/kg/h, fluid resuscitation should be continued. Attention should be paid to the osmotic diuresis caused by hyperglycemia and osmotic active substances such as contrast agents. Patients may experience shock without oliguria.

Body temperature monitoring is also very important. Some people believe that hypothermia is harmful and can cause myocardial dysfunction and arrhythmia. When the core body temperature is lower than 34°C, serious coagulation dysfunction may occur.