Undifferentiated shock

Undifferentiated Hypotension Algorithm

Check/manage the following in order:

• Pulse (assess based on pt's age)
  • Too slow or too fast (to the point where CO is affected)?
    • If so, HR is likely primary etiology of hypotension
    • Pace or cardiovert
• Volume Status
  • What is the LV end-diastolic volume?
    • Approximated by the IVC diameter or CVP
    • If low:
      • Assess for blood loss versus fluid loss
        • FAST for intra-abdominal bleed
        • US for ruptured AAA
        • Guaiac for GI bleed
        • CXR for hemothorax
      • Treat with IVF and/or pRBC depending on cause
• Contractility
  • Is the myocardium severely depressed in its contractile function (cardiogenic shock)?
    • Assess via ultrasound
    • Treat w/ inotrope
  • Is forward flow occurring?
    • Assess for valvular dysfunction (MR, AR)
    • Assess for obstruction (PE, tamponade)
• Systemic Vascular Resistance
  • Pathologic vasodilation (decreased SVR) suggested by:
    • Warm extremities
    • Bounding pulse
  • Treated based on likely etiology of distributive shock (see below)

Differential Diagnosis

Shock

• Cardiogenic
  • Acute valvular Regurgitation/VSD
  • CHF
  • Dysrhythmia
  • ACS
  • Myocardial Contusion
  • Myocarditis
  • Drug toxicity (e.g. beta blocker, CCB, or bupropion OD)
• Obstructive
  • Air embolism
  • Aortic Stenosis
  • Cardiac Tamponade
  • PE
  • Tension pneumothorax
• Distributive
  • Adrenal crisis
  • Anaphylaxis
  • Neurogenic shock
  • Sepsis
  • Toxicologic
• Hypovolemic
  • Severe dehydration
  • Hemorrhagic shock (traumatic and non-traumatic)

Management

• Treat underlying type

Vasopressors

Vasopressors may be initiated peripherally while central access is being obtained — do not delay for central line placement (SSC 2021).

Pressor	Initial Dose	Max Dose	Cardiac Effect	BP Effect	Arrhythmias	Special Notes
Dobutamine	2-5 mcg/kg/min	20 mcg/kg/min (up to 40 in refractory cases)	Strong β₁ agonist (+inotrope, +chronotrope); weak β₂ agonist (+vasodilation)	Minimal α effect; may decrease BP due to β₂ vasodilation	Variable HR effects; can cause tachycardia	Indicated in decompensated systolic CHF and cardiogenic shock with adequate BP. Not a vasopressor — it is an inotrope. Must be used with a vasopressor if hypotensive.
Dopamine	2-5 mcg/kg/min	20 mcg/kg/min	β₁ and endogenous norepinephrine release	Mixed α and β effects at all doses; α effects predominate at higher doses	Arrhythmogenic from β₁ effects	More adverse events (especially arrhythmia) when used in shock compared to norepinephrine. SSC 2021 suggests against dopamine as first-line except in select patients with bradycardia and low risk of tachyarrhythmia.
Epinephrine	1-10 mcg/min (0.01-0.1 mcg/kg/min)	0.5 mcg/kg/min	+Inotropy, +chronotropy (β₁)	Low dose: β₂ vasodilation may predominate; high dose: α₁ vasoconstriction predominates	Significant — tachycardia, SVT, VT. Increases myocardial O₂ demand.	2nd or 3rd line for septic shock (SSC 2021: add after norepinephrine ± vasopressin). 1st line for anaphylaxis (0.3-0.5 mg IM) and cardiac arrest. May cause splanchnic vasoconstriction, lactic acidosis, and hyperglycemia.
Norepinephrine	2-5 mcg/min (0.01-0.03 mcg/kg/min)	0.5-1 mcg/kg/min (some sources up to 3.3 mcg/kg/min)	Mild β₁ direct effect (+inotropy)	Strong α₁ and α₂ vasoconstriction; β₁ effect	Less arrhythmogenic than dopamine	1st line for septic shock (SSC 2021). Increases MAP primarily via vasoconstriction. Increases coronary perfusion pressure. Minimal β₂ effect.
Milrinone	50 mcg/kg IV over 10 min (loading dose often omitted in acute illness due to hypotension risk)	0.375-0.75 mcg/kg/min	PDE-3 inhibitor → ↑intracellular cAMP → ↑Ca²⁺ influx → +inotropy	Arteriolar and venous vasodilator (reduces preload AND afterload)	Less arrhythmogenic than dobutamine	Inodilator — useful in decompensated HF with elevated afterload, RV failure, or pulmonary hypertension. Causes hypotension — not a vasopressor; use with a vasopressor if MAP is low. Renally cleared — dose-reduce in CKD.
Phenylephrine	100-180 mcg/min, then 40-60 mcg/min	0.4-9.1 mcg/kg/min	No direct cardiac effect	Pure α₁ agonist → vasoconstriction	May cause reflex bradycardia	Short duration of action (5-20 min IV). Use in septic shock only if: NE causes arrhythmias, cardiac output is high with persistent hypotension, or as salvage when NE + vasopressin have failed.
Vasopressin	0.03 U/min (fixed dose)	0.04 U/min	No direct inotropic or chronotropic effect; possible reflex bradycardia	V₁ receptor agonist → vascular smooth muscle constriction	Minimal	2nd line in septic shock — add to NE rather than escalating NE (SSC 2021 suggests adding before epinephrine). Fixed dose — generally not titrated. May reduce the risk of atrial fibrillation vs. catecholamine-only regimens. Avoid dose >0.04 U/min → risk of cardiac and mesenteric ischemia.
Methylene blue	IV bolus 1-2 mg/kg over 15 min	1-2 mg/kg/hour (limited data on max duration)	Possible increased inotropy; improves cardiac ATP utilization	Inhibits NO-mediated peripheral vasodilation → increases SVR	Minimal reported	Salvage therapy for refractory vasodilatory shock unresponsive to catecholamines. Contraindicated in G6PD deficiency (hemolytic anemia), ARDS, severe pulmonary hypertension. Interferes with pulse oximetry readings (falsely low SpO₂). Avoid with serotonergic drugs (risk of serotonin syndrome).
Angiotensin II (Giapreza)	20 ng/kg/min	40-80 ng/kg/min (max 200 ng/kg/min per label)	No direct cardiac effect	AT₁ receptor agonist → potent arteriolar vasoconstriction; also stimulates aldosterone secretion	Minimal	Salvage therapy for refractory vasodilatory shock (ATHOS-3 trial). May be particularly useful in patients on ACEi/ARB or with high renin states. Monitor for thrombosis (increased risk reported).

Medication	IV Dose (mcg/kg/min)	Standard Concentration	Final Concentration
Norepinephrine (Levophed)	0.01-2 mcg/kg/min	8 mg in 500 mL D5W	16 mcg/mL
Dopamine	2-20 mcg/kg/min	400 mg in 250 mL D5W	1,600 mcg/mL
Dobutamine	2-20 mcg/kg/min	250 mg in 250 mL D5W	1,000 mcg/mL
Epinephrine	0.01-1 mcg/kg/min	1 mg in 250 mL D5W	4 mcg/mL

Norepinephrine 2-5 mcg/min (0.01-0.03 mcg/kg/min), max 0.5-1 mcg/kg/min IV drip — 1st line for septic shock (SSC 2021) Epinephrine 1-10 mcg/min (0.01-0.1 mcg/kg/min), max 0.5 mcg/kg/min IV drip — 1st line for anaphylaxis and cardiac arrest Vasopressin 0.03 U/min (fixed dose), max 0.04 U/min IV drip — Add to NE rather than escalating NE (SSC 2021) Dopamine 2-5 mcg/kg/min, max 20 mcg/kg/min IV drip — SSC 2021 suggests against as 1st line; more arrhythmogenic than NE Dobutamine 2-5 mcg/kg/min, max 20 mcg/kg/min IV drip — Inotrope, not a vasopressor; use with vasopressor if hypotensive Phenylephrine 100-180 mcg/min, then 40-60 mcg/min IV drip — Pure alpha-1 agonist; short duration 5-20 min Milrinone 0.375-0.75 mcg/kg/min (loading often omitted) IV drip — Inodilator; causes hypotension; useful in RV failure/pulmonary HTN Methylene blue 1-2 mg/kg IV bolus over 15 min IV — Salvage for refractory vasodilatory shock; contraindicated in G6PD deficiency Angiotensin II (Giapreza) 20 ng/kg/min, max 40-80 ng/kg/min IV drip — Salvage for refractory vasodilatory shock (ATHOS-3 trial)

See Also

• Ultrasound in Shock and Hypotension

Source

• Tintinalli
• Morchi, Undifferentiated Hypotension and Shock, All LA Conference, 05/06/2010