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Pathophysiology of shock

Dr Mostafavi SNDepartement of Pediatric Infectious Disease

Isfahan University of Medical Science

Shock Acute dramatic syndrome due to

inadequate circulation to vital organs2% of hospital admissions20-50% mortality, most due to

complicationsThe most common cause in children is

hypovolemia then sepsis

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Factors that influence adequate circulation to organs

• Cardiac output–Stroke volume• End diastolic volume: Preload• Contractility: Inotropy• Vascular tone : Afterload–Heart rate: Chronotropy

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Types of shockHypovolemic: ↓ preload Distributive: ↓ afterload Cardiogenic: ↓ inotropy, ↓

chronotropyObstructive: ↑ afterloadSeptic : ↓ preload, ↓

afterload, ↓ inotropy

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Hypovolemic shockCauses: ◦excessive loss GI: Vomiting, diarrhea Kidney: DM, DI, renal failure Vascular: bleeding◦Inadequate intake

Course: ↓blood volume→ ↓ preload→ ↓ stroke volume→ shock+ ↓preload

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Distributive shockTypes◦Anaphylactic◦Brainstem/ spinal injury

Course: loss of vasomotor tone → ↑venous and arterioles pool → ↓preload & afterload→ ↓↓cardiac output → shock+ ↓preload

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Cardiogenic shockCauses: myocardiotis, cardiomyopathy,

dysrhythmia, congenital heart diseaseDecreased myocardial contractility

&/or HR → shock & heart failure+ ↑preload

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Obstructive shockCauses: tamponad, pneumothorax,

tumor, pulmonary emboli, critical CoA, severe AS

Blood flow obstruction→ ↑afterload → shock & heart failure+ ↑preload

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Septic shockCourse: exaggerated immune response

due to infection & toxic metabolites:◦Vasodilatation and increased permeability

→ ↓afterload → ↓cardiac output◦Extravasation of fluids →↓ venous return →

↓preload → ↓cardiac output◦Depression of myocardial function →

↓cardiac output

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Steps of shock 1. Insufficient delivery of blood, oxygen

and nutrients to the cells2. Anaerobic metabolism3. Lactic acidosis4. Sympathoadrenal and respiratory

responses( Compensated shock)5. ( no intervention) Decompensated

shock6. Multisystem organ dysfunction 7. Death

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Decompensated shockProgress of insult→ inadequate compensatory

mechanisms → ↓BP↑HR→ ↓coronary flow & ventricular filling→ ↓

myocardial function → ↓BP↑ Vascular resistance+ ↑contractility → ↑

myocardial oxygen need+ ↓ O2→ ↓ myocardial function → ↓BP

Vasoconstriction → tissue ischemia → ↑vasoactive peptides → ↓ myocardial function & ↑ capillary permeability → ↓BP

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Multisystem organ dysfunction Brain: cytotoxic edema, ischemia→

decreased level of consciousness, convulsion, focal signs

Kidneys: prerenal renal failure, Acute tubular necrosis

Coagulation: Disseminated intravascular coagulopathy, thrombosis

Lungs: Acute respiratory distress syndrom

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Multisystem organ dysfunction Blood: anemia, thrombocytopenia,

leukopenia, leukocytosisLiver: ↑bilirubine, ↑ transaminase,

↓coagulation factors, ↑ amoniaEndocrine: ↑ or ↓insulin, ↑ counter

regulatory hormones, ↓ parathyroid→ hypo or hyperglycemia, hypocalcemia

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Stages of shockStages of shockStage Pathogenesis Signs

1. Warm Hypoxia, sympathetic release

Tachypnea, hyperpnea, tachycardia, bounding pulses, NL BP, capillary refill time, urine output, alertness

2. Cold Above+ adrenal release

Tachypnea, tachycardia, weak pulse, cool and mottled extremities, delay capillary refill time, ↓U/O, drowsiness

3.Decompensated

↓ myocardial function, ↑ capillary permeability

Tachypnea, tachycardia, No palpable pulse, hypotension, progression of drowsiness and decreased renal function

4. MODS Ischemia, vasoactive peptides, cytokines

Hypotension, coma, renal failure, coagulopathy, DIC, hypoglycemia, hyperglycemia, hypocalcemia, electrolyte imbalance, liver failure, cytopenia, …

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↑↑HRHR< 2 mo → 1802-12 mo → 1601-2 yr → 1202-8 yr → 110

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↑↑RRRR< 2 mo → 602- 12 mo → 501-5 yr → 405-8 yr → 30>8 yr → 25

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Normal valuesNormal valuesSystolic Blood Pressure: > [70+ 2

age(yr)] or > 80 mmHgCapilary Refill Time: 2-3 secUrine Output: > 1 cc/kg/hLevel Of Counsciousness: Alert,

Drowsiness, Confused, Stupor, Light coma, Deep coma

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Suggestive signs in shockSuggestive signs in shockType of shock Symptom and signsHypovolemic

History of vomiting, diarrhea, low intake, polyuria,Signs of severe dehydration(Dry mouth, sunken eye, depressed fontanel)

Anaphylactic Immediately after injection of a drug, generalized urticaria, stridor, wheezing

Traumatic After major trauma to brainstem/spinal cord

Cardiogenic Congenital or acquired heart diseaseHeart failure signs: (cardiomegaly, hepatomegaly, ↑JVP, edema), rales, murmur

Obstructive Heart failure signs: (cardiomegaly, hepatomegaly, ↑JVP), rales, murmur

Septic Fever, infection, leukocytosis, ↑ESR, ↑CRP

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Treatment of shockTreatment of shockMechanism Drug Type of shock

↑ O2 delivery O2, ventilation All

↑ preload Fluid( crystalloid, colloid)

All, aggressive in hypovolemic, distributive, septic

↑ afterload Norepinephrine, Dopamine( high dose), epinephrine, phenylephrine

All, especially in anaphylactic, septic, hypovolemic

↓ afterload Dobutamine,nitroglycerine, milrinon

All, in cold shock

↑ contractility Dopamine, epinephrine, dobutamine, milrinon

All, cautiously in cardiogenic and obstructive

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