Shock

PEARLS

DEFINITION

Shock is a life-threatening state where there is globally insufficient delivery and/or utilisation of oxygen at the cellular level⁽¹⁾. It is characteristically (but not always) associated with low blood pressure and impaired tissue perfusion. The consequence of shock is cellular and tissue hypoxia and ultimately cellular death and organ dysfunction.

Early effects of shock can be reversible, however, a delay in diagnosis or without appropriate and timely treatment can lead to irreversible damage including multiorgan dysfunction syndrome (MODS) and death.

PATHOPHYSIOLOGY

• Oxygen delivery (DO₂) is the product of cardiac output (CO) and the oxcygen content of arterial blood, where:
  • DO₂ (mL/min) = CO x ([1.39 x Hb x SaO₂] + [PaO₂ x 0.003])
    • Hb (g/L), SaO2 %, PaO2 O2 pressure in mmHg, 1.39 is the theoretical O₂ carrying capacity of Hb (also 1.34mL directly measured), 0.003mL = capacity of O₂ in plasma
• If there is adequate arterial O₂ concentration, the CO is the main determinant of (DO₂) where:
  • CO = HR x Stroke volume (SV)
    • Stroke volume determinants include: Preload, afterload, contractility
• Normal VO₂ (Oxygen uptake) is about 250mL/min at rest, compared with normal global DO₂ which is about 1000mL/min
• When DO₂ becomes critical, inadequate supply results in a transition to anaerobic cellular metabolism and results in impaired end-organ function with the characteristic clinical signs of drowsiness, reduced capillary refill, oliguria and hyperlactataemia
• In septic shock, there is a massive proinflammatory response involving: cytokines, the complement cascade, activation of coagulation and platelet aggregation, increased arachidonic acid metabolites, reactive oxygen species and nitric oxide.
  • The result is: Vasodilation, increased CO (despite impaired contractility) and reduced intravascular volume secondary to increased permeability
• DO₂ in septic shock is increased, however, VO₂ is also increased due to increased metabolic activity.
  • Abnormalities in the microcirculation (e.g. shunting, microvascular thrombosis), as well as induced mitochondrial dysfunction drive the altered cellular metabolism and the resulting damage

CLASSIFICATION

CHOD (Classic four main types, further elaborated below)

• Cardiogenic
• Hypovolaemic
• Obstructive
• Distributive

PROVED?

• cardiogenic (Pump)
• Rhythm abnormalities (some purists exclude dysrhythmia as a cause of cardiogenic shock)
• Obstructive
• hypovolemia (Volume)
• Endocrine causes (often mixed classification, but a useful subheading to make sure endocrine causes aren’t missed!)
• Distributive (due to vasodilation)
• ? = is it real? (check the BP measurement, is the arterial line in an artery, is the transducer at the correct height?)

Remember that drugs and toxic exposures can contribute to cardiogenic, rhythm, or distributive causes of shock.

CARDIOGENIC SHOCK

Impaired contractility

• Myocardial ischemia and compliations
  • Infarction — anterior MI, reinfarction, right ventricular infarction, myocardial stunning
  • Acute mitral regurgitation due to papillary muscle rupture
  • Ventricular septal rupture
  • Left ventricular free wall rupture and tamponade
• Myocarditis
• Myocardial contusion
• Takotsubo Cardiomyopathy
• Septic shock
• Poisoning or toxic exposure including calcium channel blockers, beta-blockers and digoxin
• End stage cardiomyopathy

Dysrhythmia

• Tachycardias
• Bradycardias

Valvular dysfunction

• Severe aortic regurgitation
• Severe aortic or mitral stenosis

Left ventricular outflow tract obstruction

• Hypertrophic cardiomyopathy
• Left atrial myxoma

OBSTRUCTIVE SHOCK

Within the circulatory system

• Massive pulmonary embolus
• atrial thrombus or myxoma
• occulsive valvular lesion
• other emboli (e.g. air, amniotic fluid)

External to the circulatory system

• Cardiac tamponade
• abdominal compartment syndrome
• Tension pneumothorax
• Dynamic hyperinflation (e.g. severe asthma)
• Tension pneumomedistinum
• caval compression (e.g. supine hypotension syndrome in the pregnant female)

HYPOVOLAEMIC SHOCK

Hemorrhage

• Traumatic
  • Major vessel injury
  • Pelvic vessel disruption
  • Massive hemothorax
  • Intra-abdominal hemorrhage
  • Retroperitoneal hemorrhage
  • Long bone fracture
  • External blood loss
• Non-traumatic
  • Gastrointestinal bleeding
  • Epistaxis
  • Hemorrhagic pancreatitis
  • Aneurysm rupture
  • Ectopic pregnancy
  • Postpartum
  • Coagulopathy

Fluid loss

• GI losses (vomiting, diarrhoea, short gut, etc)
• Excessive diuresis (diabetes insipidus, diuretics)
• Excessive diaphoresis (heat-related illness)
• Diabetic ketoacidosis
• Burns
• “Third spacing” (pancreatitis, severe sepsis, anaphylaxis)
• Iatrogenic (post-dialysis)

DISTRIBUTIVE SHOCK

• neurogenic shock
• liver failure
• adrenal insufficiency
• anaphylaxis
• septic shock
• post-bypass vasoplegia
• drugs and toxic exposures, e.g. calcium channel blockers, epidural anaesthesia

ENDOCRINE AND METABOLIC CAUSES OF SHOCK

• Adrenal insufficiency
• Hypothyroidism
• Hyperthyroidism
• Diabetic ketoacidosis
• Severe acidosis/ alkalosis and electrolyte disturbances (e.g. hypocalcemia)

? (ERRORS AND ARTEFACTS)

• non-invasive blood pressure measurement error
• arterial line inadvertently sited in a vein
• arterial line transducer position higher than the right atrium

HAEMODYNAMIC VALUES IN DIFFERENT TYPES OF SHOCK

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References and Links

LITFL

• Shock Hot Case
• Multiple Organ Dysfunction Syndrome

Books and Journal Articles

• (1) Haseer Koya H, Paul M. Shock. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531492/
• Marshall, S., Cadogan, M., Celenza, A., Ruedy, J. and Brown, A., 2011. Marshall & Ruedy’s On Call: Principles & Protocols: Australian Version. Elsevier Australia.
• Bersten, A. and Soni, N., 2014. Oh’s Intensive Care Manual. 7th ed. Elsevier.

CCC Differential Diagnosis Series
NEURO	Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT	Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
LABS	LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,  HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,  ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes