What is the definition of shock?
- State of cellular and tissue hypoxia
- Acute circulatory failure
- Initially reversible (but must be treated to prevent irreversible organ dysfunction)
- “Undifferentiated shock” refers to the situation where shock is recognized but the cause is
unclear
What does cellular hypoxia cause?
1) Cell membrane ion pump dysfunction -> intracellular edema -> leakage of intracellular
contents into extracellular space -> inadequate regulation of intracellular pH similar PP to cerebellar hypoxia)
2) Ultimately results in acidosis, endothelial dysfunction, stimulation of inflammatory and
anti-inflammatory cascades
Components of the shock graph (oxygen consumption vs oxygen delivery) and physiology
Supply independent phase:
- Tissue oxygen consumption (VO₂) is maintained at a constant level despite decreasing oxygen delivery (DO₂)
- Body compensates by ^ oxygen extraction from the blood
Supply dependent phase:
- Once oxygen delivery (DO₂) falls below a critical threshold, tissue oxygen consumption (VO₂) becomes dependent on oxygen delivery
- The reduced oxygen delivery leads directly to reduced oxygen consumption -> causing cellular dysfunction and energy failure.
Formulas in oxygen delivery and extraction ratio
DO2 (oxygen delivery) =
CO (cardiac output) x
CaO2 (arterial O2 content)
ER (Extraction ratio) = VO2 (oxygen consumption)
/ DO2
Note: tf lower ER is better as it means tissues are able to meet its metabolic needs within having to extract more o2 from the blood
What are the causes of High ER?
OH CRAP, Shock!
Oxygen (hypoxia, high altitude, lung disease)
Hemoglobin (anemia)
Contractility
Rhythm
Afterload
Preload
Shock
What are the causes of very low ER?
Hyperoxia
What are the causes of high VO2?
- Fever and inflammatory states
- Increased metabolic rate
~ Hyperthyroidism, adrenergic drugs, hyperthermia - Increased muscular activity
What are the causes of decreased VO2?
- Decreased muscular activity
~ Analgesia/sedation, muscle paralysis, ventilator support - Decreased metabolic rate
~ Hypothyroidism, hypothermia - Antipyretics
- Hyponutrition
- Sepsis
What are the stages of shock?
[Pre-shock]
- Not many changes yet
- Compensatory mechanisms to dec tissue perfusion
~ Tachycardia, mild ^ in SBP and hyperlactatemia
- Body goes into supply-dependent phase
[Shock]
- Compensatory mechanisms become overwhelmed
- Organ dysfunction begins
- Compensatory -> Progressive -> Refractory (irreversible)
~ a. Sympathetic nervous system is stimulated, vasocontriction, occurs, aldosterone released
~ b. electrolyte imbalance, m/a acidosis, peripheral edema, tacchyarrhythmias, hypotension, pallor, cool and clammy skin, altered consciousness
[End-organ dysfunction]
- Anuria (no urine) and acute renal failure develops
- Acidemia further depresses CO
- Hypotension becomes severe, often resistant to ionotropes
- Multi organ failure (MOF) and death follows
What are the s/s of organ dysfunction?
- Symptomatic tachycardia
- Dyspnea
- Restlessness
- Diaphoresis (^ sweat)
- Metabolic acidosis
- Hypotension
- Oliguria
- Cool + clammy skin
What are the compensatory mechanisms (through sympathetic nervous system) to maintain BP when a px is in shock?
1) ^ CO
- ^ HR + SV
- ^ sympathetic tone
~ Causes constriction of venous circulation (^ in preload inc CO)
2) Maintain normovolemia
- ^ sympathetic tone
~ Causes constriction of arterial circulation (redistributes blood to vital organs)
3) Stimulate adrenal gland
- ^ secretion of adrenaline, noradrenaline and cortisol
~ ^ arterial and venous tone
What are the compensatory mechanisms (through RAAS) to maintain BP when a px is in shock?
1) Maintaining normovolemia
- Aldosterone ^ sodium reabsorption in the kidneys
~ ^ CO
- Angiotensin II causes vasoconstriction
2) Renal protective actions
- Angiotensin II preferentially constricts the efferent arteriole to maintain GFR and prevent pre-renal AKI
What are the s/s differences in compensated and uncompensated shock?
Comp vs Uncomp
Alert w some irritability VS Altered mental state
Tachycardia + hypotension in uncomp
Tachypnea + ARDS in uncomp
Decreased urine output VS prerenal azotemia, metabolic acidosis, anuria
Nausea, anorexia VS Hypoactive bowel sounds
Hyperglycemia vs hypoglycemia
Warm extremities VS Cold extremities w slowed capillary refill
Decreased venous PO2 VS elevated lactate
What is Systemic Inflammatory Response Syndrome (SIRS) and how is it related to shock?
- Exaggerated defense response to a noxious stressor
- Mostly found in septic shock cases
Diagnostic criteria (at least 2)
- <36deg C or >38deg C
- RR >20 (or PaCO2 <32mmHg)
- HR > 90
- WBC is <4000m^3 or >12000m^3 or >10%
What is the sepsis continuum/progression?
1) Infection
- Invasion of normally sterile tissue
2) SIRS
- Infection
overcomes the body’s
local defense mechanism
- Induces a body-wide
response
3) Sepsis
- Infection ± SIRS + Organ
dysfunction
- Dysregulated immune response occurs due to intensity of infection
- Injury to tissues and
organs
4) Septic Shock
- Sepsis + refractory
hypotension
- Profound circulatory,
cellular, and metabolic
abnormalities
5) Death
How to diagnose shock?
1) Lab studies
- To determine the degree of end-organ perfusion
- Lactate > 2 mmol/L
- Renal panel – AKI as evidenced by creatinine
- Liver function tests(LFT) – transaminitis suggestive of ischemic hepatitis
- Troponin – raised with MI
- ABG/VBG
2) Point-of-care Ultrasound Studies (POCUS)
- Usually for px with undifferentiated shock
- Do Focused Assessment with Sonography for Trauma (FAST) +
Echocardiography
- Perihepatic, perisplenic, pelvic, pericardial, pneumothorax, pleural effusion
- Or Rapid Ultrasound in Shock (RUSH)
What is the general management of shock? (Airway and breathing)
- Supplemental o2
- Advanced airway maneuvers if:
~ Severe hemodynamic compromise
~ Hypercapnic respiratory failure
~ Hypoxemic respiratory failure
What is the general management of shock? (Circulation)
- Establish vascular access and obtain blood samples for testing
- Begin hemodynamic monitoring
~ Telemetry, SpO2, BP
~ May or may not do an arterial line - Provide hemodynamic support
~ Fluid resus (colloids or crystalloids)
~ Do passive leg raise test if fluid responsiveness is in doubt
~ Determine need for vasopressors, inotropes or blood transfusions
~ Fluids, crystalloids and colloids first then more aggressive inotropes and vasopressors at progressive stage - Insert urine catheter for renal perfusion monitoring
What are colloids and crystalloids in IV solutions for fluid resuscitation?
Colloids vs crystalloids
Large insoluble molecules (eg starch, protein) VS Electrolytes
Small volumes given VS Large volumes
Lower risk of edema VS Higher
Slower perfusion VS Faster
Albumin, Dextran VS NaCl, Lactated Ringers, D5W
Inotropes vs vasopressors
Inotropes:
- Increases CO, which may indirectly improve BP
- Increase myocardial contractility (stroke volume)
- Targets heart
Vasopressors:
- Directly increases blood pressure by vasoconstriction
- Increase vascular tone (blood pressure)
- Targets BV
When are certain inotropes and vasopressors given?
- Vasopressors when the problem is low BP
- Inotropes when the problem is low CO
- After px is adequately hydrated
Vaso:
- Norepinephrine (1st choice for septic, cardiogenic and hypovolemic shock)
- Epinephrine (1st choice for anaphylatic shock)
- Dopamine (alternative for septic shock in some px)
Ino:
- Dobutamine (1st choice for cardiogenic shock w low CO and normal BP)
What is the general management of shock? (Disability and Exposure)
- POCUS
- CXR (to rule out pneumothorax)
- ECG
- ABG
- Labs
- Adrenaline and antihistamines for anaphylaxis
- Needle thoracostomy for tension pneumothorax
- Corticosteroids for adrenal crisis
What are the types of shock?
1) Distributive (severe peripheral BV dilation -> inadequate perfusion / dec SVR)
- Septic
- Non-septic
2) Cardiogenic (failure of heart to pump effectively despite normal blood volume)
- Cardiomyopathic
- Arrhythmogenic
- Mechanical
3) Hypovolemic
- Hemorrhagic
- Non-hemorrhagic
4) Obstructive (Obstruction to blood flow -> dec CO)
- Pulmonary vascular
- Mechanical
5) Mixed/unknown
What are the most common causes of septic shock (Distributive)?
- Gram negative bacteria
- Fungi
- Viruses
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