Hypovolemic shock

Hypovolemic shock is a medical emergency and an advanced form of hypovolemia due to insufficient amounts of blood and/or fluid inside human body to let heart pump enough blood to the body. More specifically, hypovolemic shock occurs when there is decreased intravascular volume to the point of cardiovascular compromise. The hypovolemic shock could be due to severe dehydration through a variety of mechanisms or from blood loss.

Early signs and symptoms comprise tachycardia given rise to by catecholamine release, skin pallor due to vasoconstriction triggered by catecholamine release, hypotension followed by hypovolaemia and perhaps come after myocardial insufficiency, confusion, aggression, drowsiness and coma either caused by cerebral hypoxia or acidosis. Tachypnoea owing to hypoxia and acidosis, general weakness caused by hypoxia and acidosis, thirst induced by hypovolaemia and oliguria caused by reduced perfusion.

Except for the two most common causes, the less common causes are intra-operative and post-operative bleeding, abdominal aortic rupture or left ventricle aneurysm rupture, aortic–enteric fistula, hemorrhagic pancreatitis, iatrogenic eg, inadvertent biopsy of arteriovenous malformation, severed artery., tumors or abscess erosion into major vessels, post-partum hemorrhage, uterine or vaginal hemorrhage owing to infection, tumors, lacerations, spontaneous peritoneal hemorrhage caused by bleeding diathesis, and ruptured hematoma.

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

The body compensates for volume loss by increasing heart rate and contractility, followed by baroreceptor activation resulting in sympathetic nervous system activation and peripheral vasoconstriction. Typically, there is a slight increase in the diastolic blood pressure with narrowing of the pulse pressure. As diastolic ventricular filling continues to decline and cardiac output decreases, systolic blood pressure drops.

Low urinary sodium is commonly found in hypovolemic patients as the kidneys attempt to conserve sodium and water to expand the extracellular volume. However, sodium urine can be low in a euvolemic patient with heart failure, cirrhosis, or nephrotic syndrome. 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.

History and physical can often make the diagnosis of hypovolemic shock. For patients with hemorrhagic shock, a history of trauma or recent surgery is present[4]. For hypovolemic shock due to fluid losses, history and physical should attempt to identify possible GI, renal, skin, or third-spacing as a cause of extracellular fluid loss.

The quantity, type of fluids to be used, and endpoints of resuscitation remain topics of much study and debate. For crystalloid resuscitation, normal saline and lactated ringers are the most commonly used fluids. Normal saline has the drawback of causing a non-anion gap hyperchloremic metabolic acidosis due to the high chloride content, while lactated ringers can cause a metabolic alkalosis as lactate metabolism regenerates into bicarbonate.

Isotonic saline is hyperchloremic relative to blood plasma, and resuscitation with large amounts can lead to 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 hyper-oncotic starch leads to increased mortality rate and renal failure. Patients in shock can appear cold, clammy, and cyanotic.