SHOCK

1. SHOCK

2. Life is provided through a variety of mechanisms, however all of them depend on proper circulation. Circulation itself consists of 2 parts: work of heart (pump of the body) and vessels, through which blood is pumped to the most remote organs and tissues. During every systolic contraction heart pump 70-80 ml of blood 9so called stroke volume). Thus in case of heart rate 70 beats per minute heart pumps nearly 5 liters of blood, what makes more than 7 tones per day. • From the left ventricle blood gets to the arterial system of the systemic circuit. Arteries contain 15% of the whole circulating blood volume; they carry blood from the heart to their distal departments – arterioles (vessels of resistance). Arterioles themselves are defining blood distribution: in condition of constriction (spasm) they make blood supply of the capillaries impossible (ischemia appears). On the contrary, in condition of dilatation they provide maximal oxygenation. When arterioles are blocked due to the spasm blood is flowing through the arterio-venous anastomosis directly to the venous system.

3. Distribution of blood in the vascular bed (% of CBV). • heart cavity 3% • arteries 15% • capillaries 12% • venous system 70% • Among the natural vasoconstrictors (agents, which cause constriction of the blood vessel) are epinephrine, norepinephrine, serotonin, angiotensin II. Stress enhances the secretion of cathecholamines, their blood concentration increases and arterioles constrict. Spasm of the arterioles is the basis of blood flow centralization: peripheral flow is disregarded in order to provide brain with the oxygenated blood as long as possible.

4. To the group of vasodilatators (agents, which provide dilatation of the vessels) belong “acid” metabolites (lactate, pyruvate, adenylic acid, inosinic acid), bradykinin, acetylcholine, different medicines (neuroleptics, α-adrenergic antagonists, peripheral vasodilatators, ganglionic blocking agents, etc.), some exogenous poisons. All of them cause blood flow decentralization: opening of arterioles and distribution of the blood from central vessels to the capillary bed. • Capillaries are the interweaving network of the smallest body vessels with the general length of 90-100 thousands of kilometers. However simultaneously work only 20-25% of them. They provide metabolic exchange bringing oxygen and nutrients to the tissues and take back wastes of metabolism.

5. Periodically, every 30-40 seconds one of them get closed and others open (vasomotion effect). Capillaries contain 12% of the whole circulating blood volume, but different pathological conditions can increase this amount even 3 and more times. • “Used” blood from the capillaries flows to the venous system. Veins are the blood reservoir, which contains 70% of the total circulating blood volume. Unlike arteries they are capable of volume control and thus they influence the amount of blood, which returns to the heart. • The most important haemodynamic index of venous system is central venous pressure. CVP represents the pressure which blood causes to the walls of cava veins and right atrium. This parameter is an integral index of circulating blood volume, systemic vascular resistance and pump function of the heart. It can be measure with a special device called “phlebotonometer” (pic. 4.9) or with a usual infusion set and a ruler. Normally CVP measured from the sternum point is 0-14 cm H2O and from midaxillary line is 8-15 cm H2O.

6. Central venous pressure decreases (sometimes even to negative) in case of: • - blood loss • - excessive water loss (dehydration) • - distributive shock (decrease of peripheral resistance due to venous and arterial dilatation) • In those conditions decreases volume of blood returning to the heart and thus suffers cardiac output. In case of negative CVP cardiac arrest is highly probable. • Central venous pressure increases in case of: • - heart failure (insufficiency of left or right ventricle) •  - hypervolemia (excessive blood infusion, improper infusion therapy) •  - obstructions to blood flow (pulmonary embolism, cardiac tamponade, etc.) • When CVP over 15-16 cm H2O is combined with left ventricle insufficiency the risk of pulmonary edema is very high.

7. Blood pressure is an integral index of arterial part of systemic haemodynamics. Talking about blood pressure we may refer to systolic, diastolic, pulse and mean arterial pressure. Systolic (Psyst) and diastolic (P diast) pressures are measured with the manometer (method with the usage of phonendoscope was invented by M. Korotkoff). Pulse pressure (PP) is a difference between systolic and diastolic blood pressure. • Mean arterial pressure (MAP) is calculated according to the formula: • MAP= P dias + 1/3 PP                            mm Hg

9. MAP defines the level of pressure necessary for the metabolic exchange in the tissues. Its measurement allows the evaluation of tissue perfusion level. • Blood pressure depends on different factors, but the most important are cardiac output and vascular resistance (mostly arterioles). This dependence is direct, thus you can increase blood pressure using: • -         infusion of vasoconstrictors - solutions of epinephrine, phenylephrine (mesaton), etc. (they will increase the vascular resistance); • -         infusion of hydroxyethyl starch solutions or saline (they will increase circulating blood volume) • -         infusion of cardiac glycosides or other medicine which stimulate myocardium

10. General volume of blood in the body of a healthy adult is nearly 7% from the body weight: 70 ml per kilogram for male and 65 mil per kilogram of body weight for female. Of course circulating blood volume is lower, because part of blood is out of metabolic processes as a reserve. CBV can be measured with the infusion of coloring substance to the blood flow (Evans blue, polyglucin) and later evaluation of its dissolution degree. • Therefore measurement of CVP, BP, cardiac output and circulating blood volume allow to evaluate condition of circulation system of the patients and to provide adequate correction.

11. Shock is a pathological state which can be described as a tissue hypoxia caused by hypoperfusion. Pathogenetic basis of shock depends on its reason (trauma, toxins, thermal injury) and at the same time on reactivity of the organism (level of defense mechanisms mobilization).

12. Stimulation of sympathetic nervous system - production of catecholamines and other vasoactive substances by hypothalamus and adrenal glands are the universal response of the body to the stress. Those mediators interact with the receptors of peripheral vessels causing their constriction and at the same time they dilatate the vascular bed of life-important organs. This is so called “centralization of the flow”: rational decrease of blood flow in less important tissues (skin, organs of abdominal cavity, kidneys) in case of aggressive external influence for protecting life itself (brain, heart, lungs).

13. However influence of shock agents (pain, hypovolemia, destroyed cells, toxic metabolites), extended microcirculation violations (vascular spasm, microthrombosis and sludge) and caused by them tissue ischemia lead to hypoxic affection and cellular death of the internal organs. Further it can bring multiple organ dysfunction syndrome.

14. Collapse is a vascular failure. It occurs when body is not able to provide blood flow according to the new level of its needs (either because reaction is not fast enough or because sympathetic activation fails).Vascular bed volume and circulating blood volume are disproportional: too much blood gets to the microcirculation vascular reserve and the amount, which returns to the heart is not enough for the systemic needs (so called “decentralization” of the blood flow). Cardiac output and blood pressure decrease, that causes hypoperfusion of the central nervous system and thus unconsciousness and life-threatening complications.

15. Pathogenetic classification of shock (according to P. Marino, 1998): • -         hypovolemic • -         cardiogenic • -         distributive • -         mixed (two and more factors). • Clinical classification of shock: • -         traumatic shock; • -         haemorrhagic shock; • -         dehydration shock; • -         burn shock; • -         septic shock; • -         anaphylactic shock; • -         cardiogenic shock; • -         exotoxic shock.

17. Outline • Definition • Epidemiology • Physiology • Classes of Shock • Clinical Presentation • Management • Controversies

40. Definition • A physiologic state characterized by • Inadequate tissue perfusion • Clinically manifested by • Hemodynamic disturbances • Organ dysfunction