Shock Classification
| Type | CO/CI | SVR | PCWP | ScvOβ | Common Causes |
|---|---|---|---|---|---|
| Distributive | ββ | ββ | Normal/β | β (maldistribution) | Sepsis, anaphylaxis, neurogenic, adrenal crisis, SIRS |
| Cardiogenic | ββ | ββ | ββ | ββ | STEMI, acute cardiomyopathy, myocarditis, severe valvular disease |
| Hypovolaemic | β | ββ | ββ | β | Haemorrhage, GI losses, burns, third-spacing |
| Obstructive | β | β | β (tamponade) / β (PE) | β | Massive PE, cardiac tamponade, tension pneumothorax |
Always Exclude Obstructive Causes First
Tension pneumothorax and cardiac tamponade are immediately reversible if treated early. FAST echo and clinical examination are essential before starting vasopressors in undifferentiated shock.
Adrenoreceptor Pharmacology
| Receptor | Location | Effect on Activation | Haemodynamic Result |
|---|---|---|---|
| Ξ±β | Vascular smooth muscle, skin, splanchnic | Vasoconstriction | β SVR, β MAP, β tissue perfusion at high doses |
| Ξ²β | Heart (SA node, AV node, myocardium) | β Heart rate, β contractility, β conduction | β CO, β HR, β myocardial Oβ demand |
| Ξ²β | Vascular smooth muscle, bronchi | Vasodilation, bronchodilation | β SVR, bronchodilation, β CO (mild) |
| DAβ / DAβ | Renal, splanchnic, coronary | Vasodilation (dose-dependent) | β renal/splanchnic blood flow at low doses (controversial) |
| Vβ (AVP) | Vascular smooth muscle | Vasoconstriction (non-catecholamine) | β SVR without direct cardiac effect; useful in catecholamine-resistant vasoplegia |
Drug Reference β Doses & Effects
| Drug | Dose Range | Main Receptors | Primary Effect | Key Side Effects | Indication |
|---|---|---|---|---|---|
| Noradrenaline (NE) | 0.01β3 mcg/kg/min | Ξ±β+++ Ξ²β+ | ββ SVR, mild β HR | Peripheral ischaemia (high doses), reflex bradycardia | First-line: septic/distributive shock |
| Vasopressin | 0.01β0.04 U/min (fixed) | Vβ+++ | ββ SVR, no cardiac effect | Mesenteric ischaemia, hyponatraemia, skin necrosis | Add-on to NE in refractory septic shock; catecholamine-sparing |
| Adrenaline (Epinephrine) | 0.01β1 mcg/kg/min | Ξ±β++ Ξ²β+++ Ξ²β++ | ββ CO + β SVR | Tachyarrhythmia, β lactate (Ξ²β mediated), splanchnic vasoconstriction | Anaphylaxis (IM/IV); refractory cardiogenic/septic shock |
| Dobutamine | 2.5β20 mcg/kg/min | Ξ²β+++ Ξ²β++ | ββ CO, β SVR (inotropy) | Tachyarrhythmia, hypotension, NOT for isolated vasoplegia | Cardiogenic shock; septic cardiomyopathy (low CO, β PCWP) |
| Phenylephrine | 0.5β5 mcg/kg/min | Ξ±β++++ | βββ SVR, reflex bradycardia (no β HR) | Reflex bradycardia, β CO if ventricular dysfunction | Distributive shock with tachycardia; avoid in cardiogenic |
| Dopamine | 1β20 mcg/kg/min | DA, Ξ²β, Ξ±β (dose-dependent) | Dose-dependent (inotropy at 5β10; pressor at >10) | Tachyarrhythmia more than NE; arrhythmias common | NOT recommended as first-line (SOAP II trial) |
| Levosimendan | 0.05β0.2 mcg/kg/min (no loading in ICU) | CaΒ²βΊ sensitiser + K_ATP opener | β contractility WITHOUT β Oβ demand; vasodilation | Hypotension, tachycardia; long half-life (active metabolite 80h) | Acute decompensated HF; post-cardiac surgery LV failure |
| Methylene Blue | 1β2 mg/kg IV over 20β60 min; repeat at 1 mg/kg | Inhibits NO synthase & guanylate cyclase | β SVR in vasoplegic syndrome | Haemolysis in G6PD deficiency; serotonin syndrome (with serotoninergic drugs) | Refractory vasoplegic shock (post-cardiac surgery, anaphylaxis, sepsis) |
| Angiotensin II | 20β200 ng/kg/min | ATβ receptor | β SVR via ATβ receptor; catecholamine-sparing | Thromboembolism; ventricular hypertrophy | Catecholamine-resistant vasodilatory shock (ATHOS-3 trial) |
Septic Shock β Vasopressor Algorithm
Step-up approach β SSC 2021 / ISCCM 2020
- Step 1: Noradrenaline β first-line; titrate to MAP β₯65 mmHg (Strong recommendation, 1B)
- Step 2: NE dose >0.25 mcg/kg/min β add Vasopressin 0.03 U/min (fixed rate); reduces NE requirement and may reduce arrhythmias
- Step 3: Still refractory β add Adrenaline (0.1β0.5 mcg/kg/min) OR consider Hydrocortisone 200 mg/day
- Step 4: Evidence of low CO (cold peripheries, ScvOβ <65%, elevated lactate despite adequate MAP) β add Dobutamine 5β10 mcg/kg/min
- Step 5 (Rescue): Consider Methylene Blue 1β2 mg/kg or Angiotensin II for catecholamine-refractory vasoplegia
MAP target: 65β70 mmHg for most patients. Target MAP 80β85 mmHg only in hypertensives with early AKI (SEPSISPAM trial) β no overall mortality benefit but reduced RRT requirement.
Cardiogenic Shock
Cardiogenic shock: βCO, βSVR, βPCWP, βScvOβ. Primary goal is to restore CO and coronary perfusion.
| Scenario | First Choice | Second Choice | Avoid |
|---|---|---|---|
| Pure LV failure + hypotension | Noradrenaline (maintain MAP) + Dobutamine (βCO) | Levosimendan if on beta-blockers | Phenylephrine alone (βafterload) |
| RV failure (massive PE, PHT) | Vasopressin (systemic pressor without βPVR) + inhaled NO/prostacyclin | Noradrenaline (cautious) | Dobutamine alone (βSVR β hypotension) |
| Cardiogenic + distributive | Noradrenaline + Dobutamine | Adrenaline (combined vasopressor + inotrope) | Dopamine (more arrhythmias) |
Mechanical Circulatory Support
- IABP (Intra-aortic Balloon Pump): IABP-SHOCK II (2012) β no survival benefit in cardiogenic shock complicating MI. Still widely used for haemodynamic support pre-PCI.
- Impella: Provides up to 3.5β5.5 L/min support; superior haemodynamic support to IABP. Benefit on mortality inconclusive.
- VA-ECMO: For refractory cardiogenic shock β provides full cardiopulmonary support. Refer early to ECMO-capable centre.
Anaphylaxis
Adrenaline β the Only First-Line Drug in Anaphylaxis
- Adrenaline 0.5 mg IM (1:1000 = 1 mg/ml) into anterolateral thigh β give IMMEDIATELY
- Repeat every 5β15 min if no response (no ceiling)
- IV adrenaline ONLY in ICU with monitoring: 50β100 mcg boluses IV or 0.05β0.5 mcg/kg/min infusion
- Adjuncts (secondary β after adrenaline):
- Hydrocortisone 200 mg IV (reduces biphasic reactions)
- Chlorpheniramine 10 mg IV slow (antihistamine)
- Salbutamol nebuliser 5 mg for bronchospasm
- IV Fluids 1β2L crystalloid rapidly
- Position: supine + legs elevated (unless respiratory distress)
Observe for minimum 6h after adrenaline for biphasic anaphylaxis. Discharge with adrenaline auto-injector (EpiPen) prescription and allergy referral.
Haemodynamic Monitoring in Shock
| Tool | What it Measures | When to Use | Limitations |
|---|---|---|---|
| Arterial Line | Beat-to-beat MAP, PPV, waveform | All vasopressor-requiring patients | Damping; need regular zeroing |
| Central Venous Catheter | CVP (unreliable), drug delivery, ScvOβ | Vasopressor delivery, ScvOβ monitoring | CVP unreliable for preload assessment |
| Point-of-care Echo (POCUS) | Cardiac function, volume status, IVC, pericardial effusion | Undifferentiated shock, all ICU patients | Operator-dependent |
| PiCCO / LIDCO | Cardiac output, SVR, EVLWI, GEDVI | Complex haemodynamic instability, mixed shock | Invasive, calibration required |
| Pulmonary Artery Catheter (PAC) | PCWP, PA pressures, CO, SvOβ | Refractory mixed shock, severe PHT | Invasive; no mortality benefit (PACMAN trial) |
Clinical Pearls
- Arterial line is mandatory once vasopressors are started β NIBP is unreliable in shock
- Lactate, not MAP is the best marker of tissue perfusion β target lactate clearance
- ScvOβ <65% suggests mixed problem (inadequate CO) β add dobutamine or inotrope
- Peripheral vasopressors: Acceptable for 6β12h in emergency situations (use antecubital or wrist with 2-cm catheter); inspect site every 30 min for extravasation; noradrenaline 4β8 mg in 50 ml (concentration 80β160 mcg/ml)
- Vasopressor weaning: Wean noradrenaline last; taper gradually (10β20% per hour)
- Monitor peripheries: Mottling score, cap refill, extremity temperature at high vasopressor doses
- Serotonin syndrome + Methylene Blue: Never give methylene blue to patients on SSRIs, SNRIs, MAOIs, fentanyl, tramadol β risk of fatal serotonin syndrome
References
- De Backer D, Biston P, Devriendt J, et al. Comparison of Dopamine and Norepinephrine in the Treatment of Shock (SOAP II). N Engl J Med. 2010;362(9):779β789.
- Russell JA, Walley KR, Singer J, et al. Vasopressin versus Norepinephrine Infusion in Patients with Septic Shock (VASST). N Engl J Med. 2008;358(9):877β887.
- Asfar P, Meziani F, Hamel JF, et al. High versus Low Blood-Pressure Target in Patients with Septic Shock (SEPSISPAM). N Engl J Med. 2014;370(17):1583β1593.
- Khanna A, English SW, Wang XS, et al. Angiotensin II for the Treatment of Vasodilatory Shock (ATHOS-3). N Engl J Med. 2017;377(5):419β430.
- Thiele H, Zeymer U, Neumann FJ, et al. Intraaortic Balloon Support for Myocardial Infarction with Cardiogenic Shock (IABP-SHOCK II). N Engl J Med. 2012;367(14):1287β1296.
- Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49(11):e1063βe1143.
- Hollenberg SM. Vasoactive Drugs in Circulatory Shock. Am J Respir Crit Care Med. 2011;183(7):847β855.
- Panchal AR, Bartos JA, CabaΓ±as JG, et al. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(16_suppl_2):S366βS468.