14.3 Lecture Circulatory Shock and Hypokalemia

• Circulatory shock is caused by conditions that reduce cardiac output.
• It is generally categorized into cardiogenic shock or factors decreasing venous return.
• Cardiogenic shock is caused by diminished cardiac pumping ability.
• Decreased blood volume is the most important factor decreasing venous return, but decreased vascular tone also plays a role.
• All forms of shock lead to inadequate nutrient delivery and waste removal at the tissue and organ level.
• Inadequate blood flow causes a positive feedback cycle, deteriorating the heart and circulatory system
• This deterioration further decreases cardiac output, leading to more deterioration.
• Compensated shock allows for recovery without therapy.
• Progressive shock worsens until death without intervention.
• Irreversible shock is when all known therapies are inadequate to save a person's life.

Hypokalemia and Blood Volume

• Hypokalemia decreases venous pressure, preload, and cardiac output.
• Removing 10% of total blood volume has almost no effect, but pressure and cardiac output fail at 40-45% removal.
• Ocular baroreceptors and vascular stretch receptors stimulate sympathetic reflexes.
• Sympathetic reflexes cause arterial constriction to increase peripheral resistance.
• Venous constriction increases venous return.
• Cardiac stimulation increases heart rate and contractility.
• Arterial pressure is maintained longer than cardiac output in a hemorrhaging person due to sympathetic stimulation causing arterial constriction.
• Arterial constriction maintains pressure, but has no direct effect on cardiac output
• Coronary and cerebral circulation are maintained as long as arterial pressure is above 70.
• Survival depends on strong sympathetic reflexes if blood loss is controlled
• Progressive shock occurs when a certain level of blood loss is reached and continues without intervention through positive feedback loops.
• Cardiac deterioration from hypoperfusion is one of the key features.
• Irreversible shock is when perfusion or any other type of therapy becomes incapable of saving a person

Plasma Loss and Types of Shock

• Hypovolemia can be caused by intestinal obstruction and severe burns, resulting in hypovolemic shock, same as hemorrhagic shock, except blood viscosity is also greatly increased
• Neurogenic shock is caused by increased faster capacity and decreased venous return.
• Anesthesia and brain damage can cause neurogenic shock.
• Anaphylactic shock is caused by basophils and mast cells releasing histamine or histamine-like substances, causing venous and arterial dilation.
• Septic shock is a frequent cause of shock-related deaths in hospitals.
• Septic shock is a widely disseminated bacterial infection causing high fever, marked vasodilation, high cardiac output, sludgy blood, and possibly disseminated intravascular coagulation.

Treatment

• The best treatment for hemorrhaging shock is whole blood
• Electrolyte solution or plasma substitutes can be used, but will not replace the oxygen carrying capacity of red blood cells.
• Plasma such as albumin or substitutes such as Dextran, can work by increasing the colloid osmotic pressure and causing fluid shifts.
• There's an immediate increase in intravascular volume, although the long term implications remain unclear.
• If you give more proteins, the liver decreases protein production.
• Sympathomimetic drugs such as norepinephrine and epinephrine work well in shock caused by decreased vasculature, such as neurogenic or anaphylactic shock.
• Sympathomimetic drugs do not work as well in hemorrhagic shock because the sympathetic system is already stimulated.