Fluid restriction, particularly a 1500 ml daily limit, has been a long-standing recommendation for patients with heart failure (HF), rooted in the belief that it counteracts the overactivation of the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS). However, the effectiveness and necessity of such strict fluid restriction remain controversial. This article aims to summarize current recommendations, review the scientific evidence surrounding fluid restriction in both acute decompensated heart failure (ADHF) and chronic compensated HF, and provide practical guidelines for patients who require it.
The Evolving Landscape of Heart Failure Management
The number of patients with HF is increasing globally due to the aging population and advancements in medical treatment. HF is associated with high mortality rates, frequent hospitalizations, decline in physical ability, and increased healthcare costs. Self-care, including adherence to medications, physical activity, symptom monitoring, and fluid management, is strongly recommended in HF guidelines.
Traditionally, fluid restriction was a cornerstone of non-pharmacological management, based on the idea that reducing body fluids could decrease congestion episodes. Excessive fluid intake was presumed to contribute to decompensation. However, this recommendation was largely based on expert opinion, and the evidence supporting it is not definitive.
Historical Context and the Role of Diuretics
Fluid retention, historically known as “dropsy,” has been recognized for centuries. Early treatments were primitive, such as bloodletting. The advent of diuretics, particularly loop diuretics in the 1950s, revolutionized fluid management. Loop diuretics increase urine output, promoting water excretion, primarily through the excretion of sodium (Na). Managing sodium is closely linked to fluid management, making dietary sodium restriction an important strategy in HF treatment and prevention.
In acute HF, congestion and respiratory distress can occur even without increased body weight. Water retention can easily facilitate lung congestion due to increased venous return. Therefore, managing fluids, weight, and sodium is crucial for preventing HF onset and recurrence, leading to recommendations for restricting water and sodium intake.
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The Physiological Basis of Fluid Restriction in Heart Failure
In HF, the initial heart function decline triggers compensatory mechanisms, including activation of the SNS and RAAS. These systems maintain cardiac output through increased salt and water retention, peripheral arterial vasoconstriction, increased contractility, and inflammatory mediators. While beneficial in the short term, sustained activation can lead to worsened left ventricular (LV) remodeling and cardiac decompensation.
Sodium and water restriction have been believed to prevent this pathophysiology, as ingested sodium and water are completely absorbed through the intestine, regardless of the presence of HF. In untreated pre-clinical HF patients, volume overload by acute saline load showed impaired natriuretic response, which was partially restored by exogenous natriuretic peptide administration.
However, studies suggest that fluid or sodium restriction can further promote the activation of the RAAS and the SNS, creating a vicious cycle. In stable HF patients treated with guideline-directed medical therapy (GDMT) such as renin-angiotensin system inhibitors (RASis), beta-blockers, and mineralocorticoid receptor antagonists (MRAs), the renal, hemodynamic, and neuroendocrine responses to alterations in sodium intake did not differ from those observed in healthy individuals. This suggests that the neuroendocrine mechanism responsible for sensing intravascular volume expansion might be preserved in stable HF patients treated with GDMT. Strict dietary salt or water restriction is often associated with persistent thirst and reduced food intake, making the effects of water restriction controversial in HF.
Current Guidelines and Recommendations
According to Braunwald's textbook, fluid restriction is generally unnecessary unless the patient is hyponatremic (<130 mEq/L), which may develop due to activation of the renin-angiotensin system, excessive secretion of arginine vasopressin, or loss of salt in excess of water from prior diuretic use. Fluid restriction (<2 L/day) is considered in hyponatremic patients (<130 mEq/L) or for those whose fluid retention is difficult to control despite high doses of diuretics and sodium restriction.
Recent HF guidelines from Japan and the United States do not address fluid intake recommendations. The European Society of Cardiology (ESC) guidelines advocate avoiding excessive fluid intake in all HF patients. Generally, normal fluid intake falls within the range of 1.5-2.5 L/day, corresponding to 15-30 mL/kg/day. In hot and humid weather or with gastrointestinal fluid loss, increased fluid intake is recommended. In severe HF or hyponatremia, a fluid restriction of 1-1.5 L/day may be considered. Fluid restriction may assist in managing sodium levels in acute decompensated HF (ADHF) patients with dilutional hyponatremia. However, a registry study of acute decompensated HF patients with hyponatremia (the HN Registry) indicates that fluid restriction was the least effective approach for correcting hyponatremia. In Japan, Tolvaptan, a vasopressin type 2 receptor antagonist, has been approved since 2010 for HF patients with volume overload and who are refractory to other conventional diuretic therapies, regardless of the presence of hyponatremia.
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Challenges in Monitoring and Implementation
While compensatory mechanisms alter fluid metabolism in HF patients, accurately monitoring intravascular volume in clinical practice is challenging. Methods like chest X-ray, echocardiographic volume measurements, IVC ultrasound, lung ultrasound, and bioimpedance analysis are used, but there is no single most-reliable indicator. Self-care monitoring often relies on body weight as a surrogate marker. Total fluid volume is often specified for water restriction, but how these fluids are absorbed and distributed is unknown.
Fluid restriction can also impact a patient’s quality of life, increasing thirst distress. It is challenging for HF patients to follow fluid restrictions due to a lack of knowledge about the liquid content of different foods and the management of co-morbidities such as kidney diseases. Maintaining fluid restriction can be difficult due to habitual behavior of consuming water with meals. HF patients sometimes have difficulty monitoring daily fluid intake and adjusting fluid intake based on climatic conditions or fluid loss. Some patients may adhere to fluid restriction even in very hot conditions, leading to dehydration, especially among the elderly. Excessive fluid restriction, combined with diuretic use, can result in dehydration, heightened thirst sensation, and impaired quality of life. Thus, education, support, and planned evaluation are essential for implementation of fluid restriction. To ensure successful fluid management in patients with HF, it is crucial not only to address the quantity of fluid intake but also to discuss dietary habits, climatic conditions, and diuretic treatment.
Evidence from Clinical Trials
Acute Decompensated Heart Failure (ADHF)
In ADHF, fluid restriction may seem logical for achieving hemodynamic stability and symptomatic improvement. It was traditionally believed to be beneficial in expediting recovery. However, it could also predispose patients to adverse outcomes due to the resultant activation of the renin-angiotensin-aldosterone system.
Aliti et al. randomized 75 patients to either restricted fluid (<800 mL/day) and sodium (<800 mg/day) intake or liberal fluid and sodium intake (>2.5 L/day and 3-5 g/day, respectively). Weight loss and change in clinical congestion score were similar between both groups. Thirst was significantly worse in the fluid and Na restriction group. Readmission rates at 30 days were also similar.
Travers et al. randomized 67 patients with ADHF to either fluid restriction (<1 L/day) or free fluid intake. They observed no significant difference in the time to clinical stabilization between the two groups. Changes in serum urea, serum creatinine, B-type natriuretic peptides (BNPs), and sodium did not differ between the two groups.
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Albert et al. randomized 46 patients with ADHF and hyponatremia (<135 mmol/L) to 1000 mL/day fluid restriction and usual care at discharge. There were no significant differences in clinical endpoints such as all-cause death, emergency care visits due to HF, or HF rehospitalization. However, the fluid restriction group showed a more favorable quality of life, including symptoms related to HF.
Fluid restriction commonly causes thirst in healthy subjects and ADHF patients, even in cases of hyponatremia, and significantly and negatively impacts quality of life. Xerostomia, altered taste, dry skin, and itching are also seen as side effects in fluid restriction.
Compensated Heart Failure
There have been only two randomized controlled trials conducted to evaluate the benefits of fluid restriction alone in patients with compensated HF. Several studies have investigated the impacts of combined dietary interventions involving fluid and sodium restriction or cardiac rehabilitation, emphasizing adherence to diet, physical activity, and fluid.
One notable trial, called FRESH-UP, enrolled 504 people with heart failure and compared a fluid restriction group (1500 mL daily) to a group with unrestricted fluid intake. The results showed a trend toward improved health status for those with unrestricted fluid intake, but the difference between study groups was not statistically significant for the study’s primary endpoint. The researchers concluded that in patients with stable heart failure, there is no need for fluid restriction. Patients assigned to fluid restriction consumed an average of 1,480 mL per day, and those assigned to unrestricted fluid intake consumed an average of 1,760 mL per day, an average difference of less than 10 ounces. Participants assigned to restrict their fluid intake reported more thirst. Importantly, there were no differences between groups in terms of death, heart failure hospitalizations, need for intravenous diuretics, or acute kidney injury at six months.
Practical Guidelines for a 1500 ml Fluid Restriction Diet
If a 1500 ml fluid restriction is recommended by a cardiologist, the following guidelines can help manage fluid intake effectively:
Understand Fluid Sources: Recognize that fluids come from various sources, including water, juice, carbonated drinks, teas, coffees, milk, jello, and even ice cubes. All these sources must be factored into the fluid restriction.
Use a Small Cup: Use a small cup that holds no more than 150ml for drinks.
Measure Daily Fluid Volume: Measure out the allowed volume of liquid using a marked jug to keep track of intake.
Spread Fluid Intake Throughout the Day: Distribute fluid intake evenly throughout the day rather than consuming large amounts at once.
Drink Between Meals: Take drinks between meals instead of with meals to help control the volume consumed.
Choose Thirst-Quenching Drinks: Opt for drinks that effectively quench thirst. Very sweet or salty drinks may not be as effective.
Sip Slowly: Sip drinks slowly, avoiding gulping. Using a straw with cold drinks can help slow down consumption.
Vary Drink Flavors: Have a variety of different flavored drinks to make the restriction more palatable.
Ice Cubes: Suck on small ice cubes if thirsty, counting each ice cube as approximately 15ml. Ice cubes can be flavored with squash if preferred.
Mouth Care: Rinse the mouth with mouthwash or ice-cold water to alleviate thirst, but avoid swallowing.
Cooking Water: The water used to cook pasta or rice does not need to be counted.
Limit Salt Intake: Avoid salt and salty foods, as they can increase thirst. Reduce the amount of salt used during cooking gradually. Instead of salt, use alternative flavorings such as spices, pepper, garlic, herbs, lemon juice, or vinegar. Avoid salt substitutes, as they can be high in potassium.
Limit Processed Foods: Limit the consumption of takeaway and processed foods, as they often contain high levels of salt. Cook homemade meals or choose lower-salt ready meals when possible.
Monitor Weight: Monitor body weight daily as a surrogate marker for fluid retention, but be aware of its limitations.
Additional Considerations
- Consult a Dietitian: Consult with a registered dietitian who can provide personalized guidance on managing fluid and sodium intake, especially if there are other dietary restrictions.
- Communicate with Healthcare Providers: Maintain open communication with healthcare providers about any difficulties in adhering to the fluid restriction or any symptoms of dehydration or fluid overload.
- Adjust for Environmental Factors: Adjust fluid intake based on climatic conditions, such as high heat and humidity, and in cases of fluid loss due to nausea, vomiting, or diarrhea.
- Avoid Over-Restriction: Avoid excessive fluid restriction, as it can lead to dehydration, increased thirst, and reduced quality of life.
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