Normal Cardiac Output Values and Management of Output States
Normal cardiac index (CI) in adults ranges from 1.9-4.3 L/min/m² by Doppler echocardiography, with low output defined as CI <2.2 L/min/m² and high output as CI >4.0 L/min/m² 1, 2.
Normal Values
Cardiac Index (CI):
- Standard range: 1.9-4.3 L/min/m² for both men and women 1
- CI remains stable across age groups and is not significantly affected by gender or obesity 1
- In older adults (>60 years), mean CI ranges from 2.1-3.2 L/min/m² 3
Cardiac Output (CO):
- Men: 3.5-8.2 L/min
- Women: 3.3-7.3 L/min 1
- CO is influenced by gender, with men having higher absolute values, but this difference disappears when indexed to body surface area 1, 4
Important caveat: Measurement technique matters significantly—2D echocardiography yields lower values than Doppler or 3D methods, and these techniques are not interchangeable 4.
Low Cardiac Output State
Definition and Recognition
Low output is defined hemodynamically as CI <2.2 L/min/m² 2. In cardiogenic shock, this must be accompanied by:
- Systolic blood pressure <90 mmHg or mean arterial pressure <60 mmHg
- Evidence of end-organ hypoperfusion (decreased mentation, cold extremities, urine output <30 mL/h, lactate >2 mmol/L) 2
- Pulmonary capillary wedge pressure >15 mmHg 2
Management Algorithm for Low Output
Step 1: Initial Assessment and Monitoring
- Invasive hemodynamic monitoring with arterial line ± pulmonary artery catheter is recommended when clinical assessment cannot determine filling pressures or when very low cardiac output with poor tissue perfusion is present 5.
Step 2: Pharmacologic Support Based on Blood Pressure
If systolic BP <90 mmHg with low output 5:
- Start dobutamine 2-5 μg/kg/min OR milrinone 0.275 μg/kg/min immediately
- Combine with IV diuretics if volume overload present
- Once BP improves, add vasodilator therapy (IV nitroglycerin 5-10 μg/min) to reduce filling pressures
If adequate BP but persistent hypoperfusion 6:
- Trial of dobutamine up to 20 μg/kg/min
- Monitor for arrhythmias and titrate to perfusion endpoints
Critical point: The 2012 Surviving Sepsis guidelines explicitly recommend against targeting supranormal cardiac index levels (Grade 1B) 6, as large trials showed no mortality benefit and potential harm.
Step 3: Escalation for Refractory Shock
- If pharmacologic therapy fails to restore end-organ perfusion, temporary mechanical circulatory support should be considered before end-organ dysfunction becomes irreversible 7, 2
- Triage to centers capable of providing advanced MCS 2
High Cardiac Output State
Definition and Recognition
High output is defined as CI >4.0 L/min/m² 8, 1. A "pre-high output" state exists at CI 3.8-4.0 L/min/m² 8.
Common Etiologies to Identify
The most frequent causes include 9, 8:
- Anemia (36% of cases)
- Obesity (34%)
- Cirrhosis/liver failure (17%)
- Chronic lung disease (32%)
- Thyrotoxicosis
- Sepsis
- Arteriovenous shunts
- Paget's disease
Critical distinction: High output states mimic heart failure symptoms but the primary abnormality is not cardiac disease—these conditions cause abnormally low systemic vascular resistance driving compensatory high cardiac output 9.
Management Approach
The fundamental principle: Treat the underlying cause, NOT with standard heart failure therapies 9.
Why this matters: Standard guideline-directed heart failure medications (ACE inhibitors, ARBs, vasodilators) reduce systemic vascular resistance further and will worsen the hemodynamic state 8.
Specific management:
- Identify and treat the primary pathology (correct anemia, treat thyrotoxicosis, manage cirrhosis, etc.)
- Avoid routine heart failure medications that reduce afterload
- Monitor closely—high output states carry 25-39% mortality at median follow-up of 17-31 months 8
- Consider rate-limiting calcium channel blockers in select cases with preserved systolic function 5
Prognostic Considerations
High output cardiac state is not benign—it represents a serious condition with high hospitalization rates and significant mortality 8. The ESC guidelines note that these conditions are "treatable and should be excluded when diagnosing HF" 9, emphasizing the importance of correct diagnosis to avoid inappropriate therapy.
Measurement considerations: When using pure vasopressors in any hemodynamic state, cardiac output measurement targeting maintenance of normal or elevated flow is desirable 6.