HYPOVOLEMIA LÀ GÌ

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StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.


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Continuing Education Activity

Patients with hypovolemic shock have severe hypovolemia with decreased peripheral perfusion. If left untreated, these patients can develop ischemic injury of vital organs, leading khổng lồ multi-system organ failure. The first factor to lớn be considered is whether the hypovolemic shock has resulted from hemorrhage or fluid losses, as this will dictate treatment. When etiology of hypovolemic shock has been determined, replacement of blood or fluid loss should be carried out as soon as possible to minimize tissue ischemia. Factors lớn consider when replacing fluid loss include the rate of fluid replacement và type of fluid khổng lồ be used. This activity reviews the causes, pathophysiology and presentation of shock và highlights the role of the interprofessional team in its management.Bạn đang xem: Hypovolemia là gì

Objectives:Identify the etiology of hypovolemic shock.Recall the presentation of hypovolemic shock.List the treatment và management options available for hypovolemic shock.Discuss interprofessional team strategies for improving care coordination & communication lớn advance the treatment of hypovolemic shock & improve outcomes.

Bạn đang xem: Hypovolemia là gì

Introduction

Patients with hypovolemic shock have severe hypovolemia with decreased peripheral perfusion. If left untreated, these patients can develop ischemic injury of vital organs, leading to multi-system organ failure. The first factor to lớn be considered is whether the hypovolemic shock has resulted from hemorrhage or fluid losses, as this will dictate treatment. When etiology of hypovolemic shock has been determined, replacement of blood or fluid loss should be carried out as soon as possible lớn minimize tissue ischemia. Factors to consider when replacing fluid loss include the rate of fluid replacement và type of fluid to lớn be used. 

Etiology

The annual incidence of shock of any etiology is 0.3 khổng lồ 0.7 per 1000, with hemorrhagic shock being most common in the intensive care unit. Hypovolemic shock is the most common type of shock in children, most commonly due lớn diarrheal illness in the developing world. Hypovolemic shock occurs as a result of either blood loss or extracellular fluid loss. Hemorrhagic shock is hypovolemic shock from blood loss. Traumatic injury is by far the most common cause of hemorrhagic shock. Other causes of hemorrhagic shock include gastrointestinal (GI) bleed, bleed from an ectopic pregnancy, bleeding from surgical intervention, or vaginal bleeding. 

Hypovolemic shock as a result of extracellular fluid loss can be of the following etiologies: 

Gastrointestinal Losses

GI losses can occur via many different etiologies. The gastrointestinal tract usually secretes between 3 to lớn 6 liters of fluid per day. However, most of this fluid is reabsorbed as only 100 lớn 200 mL are lost in the stool. Volume depletion occurs when the fluid ordinarily secreted by the GI tract cannot be reabsorbed. This occurs when there is retractable vomiting, diarrhea, or external drainage via stoma or fistulas.

Renal Losses

Renal losses of salt và fluid can lead lớn hypovolemic shock. The kidneys usually excrete sodium và water in a manner that matches intake. Diuretic therapy and osmotic diuresis from hyperglycemia can lead to lớn excessive renal sodium & volume loss. In addition, there are several tubular and interstitial diseases beyond the scope of this article that cause severe salt-wasting nephropathy.

Skin Losses

Fluid loss also can occur from the skin. In a hot and dry climate, skin fluid losses can be as high as 1 khổng lồ 2 liters/hour. Patients with a skin barrier interrupted by burns or other skin lesions also can experience large fluid losses that lead khổng lồ hypovolemic shock.

Third-Space Sequestration

Sequestration of fluid into a third-space also can lead lớn volume loss and hypovolemic shock. Third-spacing of fluid can occur in intestinal obstruction, pancreatitis, obstruction of a major venous system, or any other pathological condition that results in a massive inflammatory response. 

Epidemiology

While the incidence of hypovolemic shock from extracellular fluid loss is difficult to quantify, it is known that hemorrhagic shock is most commonly due to trauma. In one study, 62.2% of massive transfusions at a cấp độ 1 trauma center were due to lớn traumatic injury. In this study, 75% of blood products used were related to lớn traumatic injury. Elderly patients are more likely to lớn experience hypovolemic shock due khổng lồ fluid losses as they have a less physiologic reserve.

Pathophysiology

Hypovolemic shock results from depletion of intravascular volume, whether by extracellular fluid loss or blood loss. The body toàn thân compensates with increased sympathetic tone resulting in increased heart rate, increased cardiac contractility, and peripheral vasoconstriction. The first changes in vital signs seen in hypovolemic shock include an increase in diastolic blood pressure with narrowed pulse pressure. As volume status continues lớn decrease, systolic blood pressure drops. As a result, oxygen delivery khổng lồ vital organs is unable lớn meet oxygen demand. Cells switch from aerobic metabolism to anaerobic metabolism, resulting in lactic acidosis. As sympathetic drive increases, blood flow is diverted from other organs lớn preserve blood flow to lớn the heart và brain. This propagates tissue ischemia & worsens lactic acidosis. If not corrected, there will be worsening hemodynamic compromise and, eventually, death. 

History và Physical

Patients with volume depletion may complain of thirst, muscle cramps, and/or orthostatic hypotension. Severe hypovolemic shock can result in mesenteric and coronary ischemia that can cause abdominal or chest pain. Agitation, lethargy, or confusion may result from brain malperfusion. 

Although relatively nonsensitive và nonspecific, physical exam can be helpful in determining the presence of hypovolemic shock. Physical findings suggestive of volume depletion include dry mucous membranes, decreased skin turgor, & low jugular venous distention. Tachycardia & hypotension can be seen along with decreased urinary output. Patients in shock can appear cold, clammy, và cyanotic.

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Evaluation

Various laboratory values can be abnormal in hypovolemic shock. Patients can have increased BUN và serum creatinine as a result of prerenal kidney failure. Hypernatremia or hyponatremia can result, as can hyperkalemia or hypokalemia. Lactic acidosis can result from increased anaerobic metabolism. However, the effect of acid-base balance can be variable as patients with large GI losses can become alkalotic. In cases of hemorrhagic shock, hematocrit and hemoglobin can be severely decreased. However, with a reduction in plasma volume, hematocrit & hemoglobin can be increased due to lớn hemoconcentration.

Low urinary sodium is commonly found in hypovolemic patients as the kidneys attempt lớn conserve sodium and water to lớn expand the extracellular volume. However, sodium urine can be low in a euvolemic patient with heart failure, cirrhosis, or nephrotic syndrome. A fractional excretion of sodium under 1% is also suggestive of volume depletion. Elevated urine osmolality can also suggest hypovolemia. However, this number also can be elevated in the setting of impaired concentrating ability by the kidneys.

Central venous pressure (CVP) is often used to assess volume status. However, its usefulness in determining volume responsiveness has recently come into question. Ventilator settings, chest wall compliance, and right-sided heart failure can compromise CVPs accuracy as a measure of volume status. Measurements of pulse pressure variation via various commercial devices has also been postulated as a measure of volume responsiveness. However, pulse pressure variation as a measure of fluid responsiveness is only valid in patients without spontaneous breaths or arrhythmias. The accuracy of pulse pressure variation also can be compromised in right heart failure, decreased lung or chest wall compliance, & high respiratory rates.

Similar lớn examining pulse pressure variation, measuring respiratory variation in inferior vena cava diameter as a measure of volume responsiveness has only been validated in patients without spontaneous breaths or arrhythmias. Measuring the effect of passive leg raises on cardiac contractility by echo appears lớn be the most accurate measurement of volume responsiveness, although it is also subject lớn limitations.

Treatment / Management

For patients in hemorrhagic shock, early use of blood products over crystalloid resuscitation results in better outcomes. Balanced transfusion using 1:1:1 or 1:1:2 of plasma to lớn platelets lớn packed red blood cells results in better hemostasis. Anti-fibrinolytic administration to lớn patients with severe bleed within 3 hours of traumatic injury appears khổng lồ decrease death from major bleed as shown in the CRASH-2 trial. Research on oxygen-carrying substitutes as an alternative khổng lồ packed red blood cells is ongoing, although no blood substitutes have been approved for use in the United States.

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Crystalloid fluid resuscitation is preferred over colloid solutions for severe volume depletion not due lớn bleeding. The type of crystalloid used to resuscitate the patient can be individualized based on the patients’ chemistries, estimated volume of resuscitation, acid/base status, & physician or institutional preferences. Isotonic saline is hyperchloremic relative khổng lồ blood plasma, & resuscitation with large amounts can lead to lớn a hyperchloremic metabolic acidosis. Several other isotonic fluids with lower chloride concentrations exist, such as lactated Ringer”s solution or PlasmaLyte. These solutions are often referred to as buffered or balanced crystalloids. Some evidence suggests that patients who need large volume resuscitation may have a less renal injury with restrictive chloride strategies and use of balanced crystalloids. Crystalloid solutions are equally as effective and much less expensive than colloid. Commonly used colloid solutions include those containing albumin or hyperoncotic starch. Studies examining albumin solutions for resuscitation have not shown improved outcomes, while other studies have shown resuscitation with hyperoncotic starch leads to lớn increased mortality và renal failure.