Physiology of Circulatory shocks and therapeutical approach

PHYSIOLOGY OF CIRCULATORY SHOCKS AND A THERAPEUTICAL APPROACH. By LawFirm, University of Ibadan.

Hi everyone! And good day. Today we’re going to be looking at the physiology of circulatory shocks that occur in the body of the Cardiovascular system.

"PHYSIOLOGY

Circulatory Shocks

Generally speaking means inadequate blood flow in the body, to an extent to which the body tissues are affected due to inadequate Oxygen and other nutrients got from the blood.
Circulatory shocks tend to become progressively worse once it starts because the cardiovascular system {heart muscles, smooth muscles in blood vessels, vasomotor etc} starts deteriorating once the shock starts.

PHYSIOLOGIC CAUSES OF SHOCKS.

Since shocks are inadequate blood flows, then it means Cardiac output must be small or inadequate. So the major causes of shocks are causes of low cardiac output.
*Two Category of Factors* severely lower the cardiac output. Viz :
*1* Cardiac Anomalies that decrease Heart pumping Ability. These factors include mainly Myocardial Infarction, and some other conditions like severe heart valve dysfunction, heart arrhythmias(heartbeat rhythm alterations.) etc. Circulatory shocks resulting from low heart pumping ability are generally known as *Cardiogenic Shocks.*

*2* Factors that decrease venous return to the Heart. These reduce the cardiac output because the heart cannot pump blood that doesn’t flow into it. Common causes are diminished blood volume, decreased vascular tone, obstruction of blood flow.etc.

However, some shocks can occur without diminished cardiac output. This may be as a result of excessive metabolism, that normal cardiac output cannot suffice, or blood passes through vessels other than those supplying the tissues.

It is of importance to note that *Arterial Pressure level normally drops* during circulatory shocks and therefore is used as a measure of circulatory normalcy. This might be wrong at times, because of some sympathetic reflexes that stabilize arterial pressure and cardiac output till about 40-45% of the blood is removed.

"PHYSIOLOGY

STAGES OF CIRCULATORY SHOCKS
Shocks occur basically in three stages:
1. Compensated {non progressive} Stage
2. Progressive stage.
3. Irreversible Stage.

COMPENSATED OR NON PROGRESSIVE CIRCULATORY SHOCKS.
Normally, once a shock gets initiated, regardless of its initiating factor, _the shock leads to more shocks_ .
But if a shock isn’t severe enough to cause more shocks and it is compensated for successfully by mechanisms of sympathetic responses, it is non progressive.

Recovery from shocks happen as a result of a lot of mechanisms of circulation that tends to return arterial pressure and cardiac output back to normal levels. Some of the mechanisms include:
— Baroreceptor reflexes
— the Ischemic response of the CNS.
— Reversal of stress relaxation of the circulatory system.
— Increased Renin secretion in the kidneys, Angiotensin II formation.
— Increased secretion of Vasopressin, Epinephrine and Norepinephrine.

PROGRESSIVE SHOCKS
They are shocks that are beyond recovery by the normal negative feedbacks of the sympathetic reflexes alone. The intensive positive feedbacks enable the shock to cause more shocks, thereby worsening the condition.
Some of the positive feedbacks that ensures the progression of shocks are as follows:
–*Cardiac Depression:* when arterial pressure falls to a certain level, the coronary blood supply is impaired, leading to low nutrients supply to the myocardial cells and thereby diminishing cardiac output. This causes more shocks.
Moreover, cardiac depression could be caused by *Endotoxins* released by dead gram negative bacteria in the intestines, due to ischemia. This is particularly notable in Septic shocks.
–*Capillary Permeability:* when hypoxia occurs in the capillary cells for some times, permeability gradually increases, making the capillaries lose more fluid thus diminishing cardiac output more… This causes more shocks.
–*Vasomotor failure:* When the cells of the brain are ischemic, especially the vasomotor centers in the brain, the sympathetic responses becomes progressively less active and eventually inactive, leading to dilation of all vessels constricted before, thus worsening the shocks.
–*Blockage of Blood vessels:* metabolic wastes from cells continue to empty into the minute blood vessels and slows blood flow, also deteriorating products from ischemic tissues cause some agglutinations, reducing blood flow, known as *Sludged Blood*

SHOCK ACIDOSIS: during shocks, hypoxia occurs in cells of tissues concerned, thereby hampering the oxidative metabolism in the cells. The cells thus opt for anaerobic glycolytic processes, which produces lactic acid. Moreover, since Carbon dioxide normally produced isn’t efficiently removed by the blood, it accumulates, reacting with water in the cells to produce high concentrations of Carbonic acid, acidosis of tissues therefore occur, producing more shocks.

However, it should be noted that progressive shocks can still be salvaged by therapeutic procedures. Only that the body’s response alone cannot cause recovery, external therapies could.

"PHYSIOLOGY
IRREVERSIBLE SHOCKS
When shocks has attained a threshold beyond which any therapy known could not reverse it or cause recovery of tissues, they become Irreversible.
Ironically, in irreversible shocks, transfusion could stabilize cardiac output and arterial pressure for some minutes, but the circulatory system continues to deteriorate till death in few minutes to hours.

 

ENERGY DEPLETION IN SHOCKS.
During shocks, all high energy reserves in the body gets used up as a result of increased metabolism, especially by the liver and heart. All Creatine phosphate used up, then ATP reduced to ADP reduced to AMP and eventually to adenosine, which just diffuses out of the cell and converted to uric acid.
HYPOVOLEMIC HEMORRHAGIC SHOCKS
Shocks occur most times by *Hypovolemia* {low blood volume.}. Of these shocks, hemorrhage is the most common cause. Hemorrhage reduces both cardiac output and arterial pressure and thus leads to shocks. Quick transfusion salvage this shocks.
*Hypovolemic shocks* can also be caused by plasma loss or trauma.
Severe plasma loss can occur due to intestinal obstructions or severe burns and skin stripping hazards. Plasma loss alone, even if RBCs are not lost can remarkably reduce the blood volume, causing Hypovolemic shocks.

NEUROGENIC SHOCKS
These occur when the normal blood volume is not enough to circulate around the body. It’s caused by the *increase in vascular capacity*. This means the normal blood volume cannot sufficiently reach all part of the body. One major cause is Vasomotor damage, when the normal tone of the muscles in the vessels is lost, thereby causing massive dilation of veins, preventing blood flow back to the heart. This results to _VENOUS POOLING OF BLOOD_ causing neurogenic shocks.
Vasomotor damage however could be caused by Spinal anaesthesia, deep general anaesthesia or brain damage.

ANAPHYLACTIC AND HISTAMINE SHOCKS.
This shock results from antigen-antibody reactions in incompatible transfusions. Basophils in the blood and Mast cells are stimulated to release Histamine and histamine-like substances. This leads to anaphylaxis, increasing arterial and venous dilation, vascular capacity, and increased capillary permeability. All working together to cause a shock. This type of shock can also be caused by large amounts of histamine injections.

SEPTIC SHOCKS
Previously known as *blood poisoning*, occurs when a bacterial infection is being spread round the body, being mediated by the blood, and transferred to all tissues, causing severe damages.
Septic shocks can be caused by peritonitis, unsterile instrumental abortion, streptococcal or staphylococcal infections, gangrenous infections, colon bacilli infections etc.

PHYSIOLOGY OF SHOCK THERAPIES

*–Replacement therapies*
Blood and plasma transfusion.
Dextran Solution for plasma substitute

*– the use of Sympathomimetic drugs*
*–Head-down position therapy*
*–Oxygen therapy*
*–Glucocorticoids therapy*

Post Author: Dr Dee

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