Repost from Operational Medicine on Facebook:
Hypovolemic Shock. Shock is defined as the inability to perfuse the tissues. This is often (but not always) a result of dropping cardiac output. Cardiac output is the volume of the left ventricle (stroke volume) multiplied by the number of times the ventricle pushes blood out each minute (heart rate) [CO = SV x HR] ๐ Failure to maintain a normal CO of 4-8L/min will result in lower blood pressure, impaired cellular metabolism, organ failure, and death. ๐
Hypovolemic shock is caused by a significant loss of circulating blood volume. This can be caused by bleeding, fluid shifts from burns, sweating, excessive urination caused by disease or medication, or persistent diarrhea. ๐ฉ You generally need to lose about 15% of your intravascular volume to start your compensatory mechanism. ๐ท
Your body has two means of bringing CO back up: 1. increase heart rate and forcefulness of heart contractions, and 2. increase circulating volume. 1. As CO decreases your adrenal glands release a surge of catecholamines, hormones such as dopamine, epinephrine, and norepinephrine (sympathoadrenal activation). ๐ These hormones not only cause the heart to beat faster and harder, but they constrict peripheral blood vessels increasing systemic vascular resistance (SVR). ๐ช 2. Fluid shifts from the interstitial space into the vascular space. The liver and spleen disgorge plasma and young red blood cells. The kidneys release aldosterone which causes retention of sodium (and thus water). ๐ง The pituitary gland releases Vasopressin, also called antidiuretic hormone or ADH, which causes water to be reabsorbed into the blood from the kidneys. Vasopressin also helps increase SVR by constricting blood vessels.
However, if fluid loss continues the bodyโs compensatory mechanism will be overwhelmed resulting in CO continuing to drop. Systemic pressures continue to decline which impairs the delivery of oxygen and nutrients to the tissues of the body. Without oxygen and nutrients, cellular metabolism becomes anaerobic resulting in lactic acidosis and electrolyte abnormalities.
Treatment involves stopping the source of volume loss. Repletion of the fluids lost with attention paid to the type of fluid. If shock resulted from hemorrhage, whole blood should be used for volume replacement. Hypothermia and coagulopathies commonly complicate the treatment of hypovolemic shock. If tissue perfusion isnโt restored quickly, systemic inflammation and multiple organ failure are likely. Even if the patient survives, they may experience a life of immunocompromise and low-level organ dysfunction.
(H/T to Ethan and Frances)
