How to use mixed venous gas for congestive heart failure (CHF), vasopressor management, and cardiomyopathy?

From the Guidelines

To effectively use mixed venous gas for managing patients with congestive heart failure (CHF), cardiomyopathy, and those requiring vasopressors, place a pulmonary artery catheter to sample blood from the pulmonary artery and monitor SvO2 values, which should range from 60-80%, with values below 60% indicating inadequate oxygen delivery or increased oxygen consumption. For CHF and cardiomyopathy management, use SvO2 to guide therapy by titrating inotropes like dobutamine (starting at 2.5 mcg/kg/min, increasing as needed up to 20 mcg/kg/min) or milrinone (0.375-0.75 mcg/kg/min) to improve cardiac output when SvO2 is low 1. When using vasopressors such as norepinephrine (starting at 0.01-0.03 mcg/kg/min) or vasopressin (0.01-0.04 units/min), monitor SvO2 to ensure tissue perfusion remains adequate despite increased afterload 1.

Key Considerations

• Trending SvO2 values over time is more valuable than single measurements, as it reflects the balance between oxygen delivery and consumption.
• Low SvO2 can result from decreased cardiac output, anemia, hypoxemia, or increased metabolic demand, so interpret values in the context of other clinical parameters like lactate levels, urine output, and mental status.
• In patients with cardiogenic shock, norepinephrine is the recommended vasopressor when mean arterial pressure needs pharmacologic support 1.
• Dobutamine might be used in patients with no beta-blockers, while levosimendan may be used as an alternative, especially in patients on beta-blockers on admission.

Management Strategies

• Use diuretics to improve symptoms and reduce congestion in patients with acute heart failure, with initial recommended doses of 20-40 mg i.v. furosemide (or equivalent) 1.
• Consider combination of loop diuretic with either thiazide-type diuretic or spironolactone in patients with resistant congestion.
• Use vasodilators, such as i.v. vasodilators, for symptomatic relief in acute heart failure with systolic blood pressure >90 mmHg (and without symptomatic hypotension) 1.

From the FDA Drug Label

Milrinone lactate is a positive inotrope and vasodilator, with little chronotropic activity different in structure and mode of action from either the digitalis glycosides or catecholamines Clinical studies in patients with congestive heart failure have shown that milrinone lactate produces dose-related and plasma drug concentration-related increases in the maximum rate of increase of left ventricular pressure Milrinone lactate also produces dose-related and plasma concentration-related increases in forearm blood flow in patients with congestive heart failure, indicating a direct arterial vasodilator activity of the drug.

The use of mixed venous gas for CHF, vasopressors, and cardiomyopathy is not directly addressed in the provided drug label. However, milrinone lactate is used to treat congestive heart failure and has been shown to improve myocardial contractility and diastolic function.

• The drug label does mention the use of milrinone lactate in patients with chronic heart failure, heart failure associated with cardiac surgery, and heart failure associated with myocardial infarction 2.
• It is essential to note that milrinone lactate is a positive inotrope and vasodilator, which can be beneficial in treating heart failure.
• However, without direct information on the use of mixed venous gas, it is impossible to provide a specific answer to the question.

From the Research

Mixed Venous Gas in CHF, Vasopressors, and Cardiomyopathy

• Mixed venous oxygen saturation (SvO2) can be used as a therapeutic indicator in the treatment of advanced congestive heart failure (CHF) 3.
• The correlation between cardiac output (CO) and SvO2 may not occur in seriously ill CHF patients, possibly due to a changing oxygen consumption rate 3.
• SvO2 may be a more useful parameter than thermodilution cardiac output (COtd) for evaluating hemodynamic status and monitoring therapy in patients with severe congestive heart failure 4.
• In patients receiving milrinone, the increase in dose correlates better with SvO2 than with COtd, and repeated SvO2 measurements are more reproducible than COtd 4.

Relationship between Mixed Venous Oxygen Saturation and Cardiac Index

• There is no correlation between cardiac index (CI) and SvO2 in every patient with CHF, and the lack of correlation may be due to an associated increase in oxygen consumption (VO2) 5.
• SvO2 cannot be used instead of CI to determine the hemodynamic consequences of the use of cardiovascular drugs 5.

Vasopressors and Cardiomyopathy

• Elevated levels of arginine vasopressin (AVP) play a role in the development of hyponatremia in heart failure (HF) patients, and AVP antagonists may be beneficial in treating HF 6.
• Vasopressin receptor antagonists (VRAs) can inhibit vasoconstriction and cardiac remodeling, and increase urine osmolality and decrease water excretion, but their optimal use is yet to be determined 6.

Using Mixed Venous Gas

• Mixed venous gas can be used to monitor the effectiveness of dobutamine administration in patients with advanced CHF 3.
• SvO2 can be used to evaluate the hemodynamic status and monitor therapy in patients with severe CHF, especially when using milrinone 4.
• The relationship between CI and SvO2 should be individualized, as it may vary between patients 5.