Shock

Shock is a life threatening clinical syndrome of cardiovascular collapse characterised by

Hypotension: acute reduction in circulating blood volume

Hypoperfusion: inadequate perfusion of cells & tissues

Shock is a life-threatening medical

emergency and one of the most

common causes of death for critically ill

people.

One of the key dangers of shock is that it

progresses by a positive feedback

mechanism. Once shock begins, it tends

to make itself worse. This is why

immediate treatment of shock is critical.

◊ Pallor- paleness

◊ Sweating

◊ Clammy limbs-Cold extremities

◊ Tachycardia

◊ Low blood pressure (sometimes not seen)

◊ Decreased urine output

◊ Weak & rapid pulse

◊ Unconsciousness

◊ Sighing & shallow breath

Reduced effective circulating blood volume

Reduced venous return to heart

Reduced cardiac output

Reduced blood flow

Reduced supply of oxygen

Anoxia

Inflammatory mediators

SHOCK

Compensated/Initial/Reversible shock

Progressive decompensated shock

Irreversible shock

STAGE PATHOGENESIS EFFECTS

INITIAL / COMPENSATED

SHOCK

i. Widespread

vasoconstriction

ii. Fluid conservation by

kidney

iii. Stimulation of adrenal

medulla

Tachycardia

Cool clammy skin

PROGRESSIVE

DECOMPENSATED SHOCK

i. Pulmonary

hypoperfusion

ii. Tissue ischaemia

Decreased cardiac

output

Mental confusion

Decreased urine output

IRREVERSIBLE

DECOMPENSATED SHOCK

i. Progressive

vasodilatation

ii. Increased vascular

permeability

iii. Pulmonary

hypoperfusion

iv. Anoxic damage

v. Hypercoagulability

Hypoxic

encephalopathy

Focal myocardial

necrosis

Acute respiratory distress

syndrome

Acute tubular necrosis

Adrenal & Liver necrosis

DIC (disseminated

intravascular coagulation)

Haemorrhagic

gastroenteropathy

Hypovolaemic shock

Cardiogenic shock

Septic shock

Anaphylactic shock

Neurogenic shock Hypoadrenal shock

Traumatic shock

Shock of any type requires immediate treatment

Form of shock resulting from inadequate

blood volume

Either the RBCs along with plasma are

reduced or plasma volume alone

Causes: Acute haemorrhage

Dehydration (vomitings, diarrhoea)

Burns

Excessive use of diuretics

Depending upon the degree of blood

volume lost, hypovoleamic shock is

divided into four types:

i. </= 1000 ml : Compensated

ii. 1000-1500 : Mild

iii. 1500-2000 : Moderate

iv. > 2000 : Severe

Resulting from sudden fall in cardiac

output due to severe left ventricular

dysfunction

Normovoleamic shock

Causes : Myocardial infarction

Cardiomyopathies

Cardiac arrhythmias

Pulmonary embolism

Precipitated by severe bacterial infection

May be due to release of bacterial toxins

There is immune system activation &

severe systemic inflammatory response

Causes : Gram negative septicaemia (endotoxic shock) eg.E.coli,

Klebsiella, Pseudomonas

Gram positive septiceamia(exotoxic shock) eg.Streptococci,

Pneumococci

Due to inflammation, there is : Vasodilatation - profound vasodilatation causes

peripheral pooling of blood & hyperdynamic

circulation,

Increased vascular permeability - causes inflammatory

oedema

Disseminated Intravascular Coagulation

is prone to develop due to endothelial

cell injury by toxins

Type I hypersensitivity reaction

Caused by a severe anaphylactic

reaction to an allergen, antigen, drug or

foreign protein

Causes release of histamine which

causes widespread vasodilatation,

hypotension, & increased capillary

permeability

results from Slow heart rate due to

interruption of sympathetic vasomotor

supply

Causes :

High cervical spinal cord injury

Accidental high spinal anaesthesia

Severe head injury Should not be confused with SPINAL SHOCK which is a

recoverable loss of function of the spinal cord after injury and does not refer to the haemodynamic instability

Occurs from unknown adrenal

insufficiency

Patient fails to respond normally to stress

of trauma, surgery or illness

Causes : Administration of high doses of glucocorticoids

Secondary adrenal insufficiency eg . tuberculosis, idiopathic

adrenal trauma

Initially hypovoleamic shock

Even after hemorrhage control, patient

continues to suffer plasma loss into

interstitium of injured tissue

Causes : Severe injuries

Surgeries with marked blood loss

Obstetrical trauma

Cause should be identified & treated

Foot end of the bed should be elevated to increase venous return, this raises the BP to some extent

BP & plasma should be maintained with appropriate intra venous fluids

Vasopressors like Dopamine may be given intravenously when BP cannot be maintained by IV fluids.

Plasma expanders may help in cases of severe hypovleamia

Acid base & electrolyte disturbances should be corrected

Adequate urine output should be ensured

To restore the intravascular volume, the component that is lost should be ideally replaced-like plasma in burns, blood in haemorrhage. But in emergency, immediate volume replacement is important. In such cases, plasma expanders and IV fluids are used

Apart from restoration of intravascular volume, the specific cause of shock should be identified, and treated

Adrenaline

Morphine

Drotrecogin alpha (Activated

Protein C)

Vasopressors & inotropes

Plasma expanders

Adrenaline is the drug of choice in anaphylactic shock

0.3 – 0.5 ml of 1:1000 solution is used

Promptly reverses hypotension, laryngeal edema & bronchospasm and is life saving in presence of anaphylactic shock

Absorption by SC route is not reliable in presence of shock, hence IM route is preferred

Anaphylaxis can occur following the use of any drug, even in dental practice

IV morphine is the drug if choice in cardiogenic shock

Dose : 10-20 mg IM

Morphine affords symptomatic relief of pain without affecting the underlying disease

In MI morphine relieves pain & apprehension. As a result reflex sympathetic stimulation is reduced & shock is minimised

Drotrecogin alpha (Activated human protein C) is a drug recently introduced found to be useful in the treatment of septic shock

In septic shock, bacterial toxins evoke inflammatory response associated with impairment of coagulation & fibrinolysis

Protein C inhibits coagulation & improves fibrinolysis

May also inhibit TNF synthesis

Obtained by recombinant DNA technology

Very expensive

High molecular weight substances,

which when infused intravenously, exert

osmotic pressure and remain in the body

for long time

Colloids

•Dextrans

•Gelation polymer

•Polyvinyl pyrrolidine

•Hydroxyethyl starches

Crystalloids

•Normal saline

•dextrose

Substances causing vasoconstriction are called vasopressors

Vasopressors are used when BP cannot maintained by IV fluids

Vasopressors are administered only when the patient is normovoleamic

Norepinephrine is considered first line vasopressor, dobutamine first line inotrope

Epinephrine is second line catecholamine in shock that is unresponsive to other catecholamines

Itntravenous fluids are sterile solutions

meant for intravenous administration

IV fluids are used for the replacement of

fluid, electrolytes, & nutrition

IV fluids are given in almost all types of

shock. Therefore, a knowledge of

different IV fluids available is important

Intravenous fluids are devided into 3 types depending

on osmolality compared with that of the ECF.

Osmolality of plasma is nearly equal to 300 mmol/L

Type of IV Electrolyte content

(in mEq/L)

Isotonic = 310

Hypotonic < 250

Hypertonic >375

Electrolyte content of ECF nearly equal to 310

mEq/L

Osmolality is almost equal to that of ECF, hence does not alter the of shape of RBCs.

One liter of this solution expands ECF by one liter

But, quickly diffuses into ECF, & therefore three liters of isotonic fluid is required to replenish one liter of lost blood

Patients with hypertension & cardiac failure should be carefully monitered to avoid fluid overload

Isotonic solutions include normal saline & lactated ringer solution

Normal saline solution :

0.9% sodium chloride. It is used in

hyponatraemia . It should be avoided in

heart failure, pulmonary edema and

renal impairment.

Lactated ringer solution :

Contains potassium, calcuim, and sodium

chloride. It is used to correct

dehydration, hyponatraemia and to

replace gastrointestinal fluids.

Replace cellular fluids as they are

hypotonic to plasma

Half normal saline (0.45 % NaCl sol.) is the

one normally used

Used in hypeynatraemia and other

hyperosmolar conditions

Over dosage can result in intravascular

fluid depletion, hypotension, cellular

edema, and later cell damage

5% dextrose in normal saline or lactated ringer solution or in hypotonic solution has osmolality more than ECF

45 – 50% dextrose solution may be administered in hypoglyceamia or to supplement calories

Being strongly hypertonic, these fluids should be injected into central veins foe rapid dilution

They are injected slowly and carefully to avoid cell shrinkage and ECF volume overload