Key Facts

Shock is a life-threatening condition requiring rapid identification and targeted treatment. Haemodynamic monitoring guides resuscitation to achieve adequate tissue perfusion while avoiding fluid overload.

Epidemiology

Shock affects approximately 30-40% of ICU patients. Septic shock is the most common form in ICU (62%), followed by cardiogenic (16%), hypovolaemic (16%), and obstructive (2%). In-hospital mortality for septic shock is approximately 30-40%.

Aetiology

• Hypovolaemic: Haemorrhage, burns, dehydration, third-space losses
• Cardiogenic: MI, arrhythmia, valvular disease, cardiomyopathy
• Distributive: Sepsis (most common), anaphylaxis, neurogenic
• Obstructive: PE, cardiac tamponade, tension pneumothorax

Pathophysiology

Tissue hypoxia is the final common pathway in all forms of shock. Compensatory mechanisms (tachycardia, vasoconstriction, ADH/aldosterone release) initially maintain vital organ perfusion. Decompensation leads to lactic acidosis, cellular dysfunction, and multi-organ failure. The type of shock determines the primary circulatory abnormality: reduced preload (hypovolaemic), reduced contractility (cardiogenic), reduced SVR (distributive), or mechanical obstruction to flow (obstructive).

General Features of Shock

• Tachycardia, hypotension (MAP <65 mmHg)
• Tachypnoea, altered mental status
• Oliguria (<0.5 mL/kg/hr)
• Cool, clammy peripheries (except distributive — warm peripheries early)
• Raised lactate (>2 mmol/L)

Differentiating Features

• Hypovolaemic: Dry mucous membranes, flat neck veins, clear lungs
• Cardiogenic: Raised JVP, pulmonary crackles, S3 gallop
• Septic: Fever/hypothermia, warm peripheries, suspected source of infection
• Obstructive: Distended neck veins, muffled heart sounds (tamponade), absent breath sounds (tension pneumothorax)

Red Flags

• MAP <65 mmHg despite fluid resuscitation — start vasopressors
• Lactate >4 mmol/L — high mortality, aggressive resuscitation needed
• Rising lactate despite treatment — reassess diagnosis and adequacy of resuscitation
• New onset AF with hypotension — consider cardioversion if haemodynamically unstable

Bedside

• ABG with lactate: Immediate — assess oxygenation, ventilation, acid-base, tissue perfusion
• ECG: Arrhythmia, MI, PE (right heart strain)
• POCUS/echocardiography: Cardiac function, fluid status, pericardial effusion, RV dilatation
• Urine output: Catheterise — target >0.5 mL/kg/hr
• CVP monitoring: Useful trend; absolute value less informative

Bloods

• FBC, U&Es, LFTs: Organ function
• Lactate (serial): Guide resuscitation; clearance rate is prognostic
• Troponin: If cardiogenic shock suspected
• Blood cultures (×2): Before antibiotics in sepsis
• Coagulation, fibrinogen: DIC screening
• Procalcitonin: Differentiate septic from non-septic causes

Imaging

• CXR: Pulmonary oedema, pneumothorax, mediastinal widening
• CTPA: If PE suspected
• CT abdomen: If intra-abdominal source of sepsis suspected
• Focused echocardiography: Rapid assessment (FATE/FICE protocol)

Special Tests

• Cardiac output monitoring: PiCCO (transpulmonary thermodilution), LiDCO, oesophageal Doppler, PA catheter (now rarely used)
• Fluid responsiveness assessment: PLR test, SVV/PPV on arterial waveform, IVC variability on USS
• Mixed/central venous oxygen saturation (ScvO2): <70% suggests inadequate oxygen delivery

Non-pharmacological

• ABCDE assessment: Simultaneous assessment and resuscitation
• IV access: Two large-bore cannulae; central venous access for vasopressors
• Position: Supine with legs raised (if hypovolaemic); sit up (if cardiogenic pulmonary oedema)

Pharmacological

Fluid resuscitation:

• Crystalloid (Hartmann's or 0.9% NaCl) 250-500mL boluses, reassess after each
• Blood products for haemorrhagic shock (O-neg → crossmatched; 1:1:1 ratio in massive haemorrhage)

Vasopressors and inotropes:

• Noradrenaline: First-line vasopressor for septic/distributive shock — 0.05-1mcg/kg/min
• Vasopressin: 0.03 units/min — adjunct to noradrenaline in septic shock
• Dobutamine: 2.5-20mcg/kg/min — inotrope for cardiogenic shock with low CO
• Adrenaline: 0.05-0.5mcg/kg/min — combined inotrope/vasopressor; anaphylactic shock first-line (500mcg IM)
• Milrinone: PDE3 inhibitor — inodilator for acute heart failure (not first-line)

Sepsis-specific:

• IV antibiotics within 1 hour (Surviving Sepsis Campaign hour-1 bundle)
• Hydrocortisone 200mg/day if vasopressor-dependent >4 hours despite adequate fluid resuscitation

Surgical/Interventional

• Chest drain: Tension pneumothorax
• Pericardiocentesis: Cardiac tamponade
• Thrombolysis/embolectomy: Massive PE
• Source control: Drainage of abscess, debridement, laparotomy for peritonitis
• IABP/Impella/ECMO: Cardiogenic shock refractory to medical therapy

Referral Criteria

• Any shock not responding to initial resuscitation — ICU referral
• Cardiogenic shock — cardiology/cardiac surgery
• Massive PE — interventional radiology or cardiothoracic surgery
• Septic shock — ICU admission

• Septic shock: 30-40% mortality despite best care; early antibiotics and fluids improve outcomes
• Cardiogenic shock (MI-related): ~50% mortality; PCI/CABG improve outcomes
• Haemorrhagic shock: Outcome depends on rapidity of haemorrhage control and transfusion
• Lactate clearance: >10% decrease in lactate at 6 hours is associated with improved survival
• Obstructive shock: Rapidly fatal if cause not identified and treated; excellent recovery if treated promptly

Haemodynamic Monitoring Devices

Classification of Haemorrhagic Shock (ATLS)