Fluid management is a critical aspect of patient care, especially in the inpatient medical setting. What makes fluid management both challenging and interesting is that each patient demands careful consideration of their individual fluid needs. Unfortunately, it is impossible to apply a single, perfect formula universally to all patients. However, one general principle for all patient scenarios is to replace whatever fluid is being lost as accurately as possible. These fluid losses can differ depending on patients’ medical conditions and differ by both volume and composition. For example, a patient admitted to the hospital with severe burns will have much greater fluid losses than a relatively healthy patient who is allowed nothing by mouth and awaiting a procedure. A patient admitted for dehydration from severe diarrhea might require different fluid compositions than a patient admitted in hypovolemic shock from a brisk upper gastrointestinal (GI) bleed.
An important distinction in managing fluids is differentiating between maintenance fluids and fluid replacement. Maintenance fluids should address the basic physiologic needs of the patient including both sensible and insensible fluid losses. Sensible fluid losses refer to typical routes of excretion such as urination and defecation. Insensible losses refer to other routes of fluid loss such as in sweat and from the respiratory tract. Fluid replacement goes beyond the normal physiologic losses and includes such conditions as vomiting, diarrhea, or severe cutaneous burns. One must consider these 2 categories of fluid loss separately when devising a fluid management strategy for an individual patient.
Fluid management is an essential part for any patient admitted to the hospital. If possible, it is preferable that patients take fluids enterally since this is the natural route of fluid intake. However, many patients who are sick enough needing admission to the hospital might have a reason they cannot tolerate oral intake. Alternative routes of administration such as intravenous access can deliver fluids directly to the vascular system.
There are many ways to assess a patient’s volume status to determine their fluid needs. Often, one can determine the patient’s fluid status clinically based on a variety of physical exam findings and objective data from their vital signs. Laboratory markers are helpful as adjunctive data. The following is a list of findings which can be useful in determining whether a patient is fluid depleted or volume overloaded.
Physical exam findings
Intravenous (IV) fluid solutions
Enteral fluid solutions
The pediatric population demands careful consideration of a child’s size in determining their rate of fluid maintenance. A 3-month-old infant has much different fluid needs than those of a more fully grown 8-year-old child. In many cases, a simple calculation called the 4-2-1 rule can determine the hourly rate of fluid maintenance required for a child based on his or her weight. The following example shows an application of this formula.
For example, a 22kg child would have the following maintenance fluid requirements.
Another commonly used formula predicts fluid needs over a 24-hour period. The following example shows an application of this formula.
For example, a 70-kg man would have the following maintenance fluid requirements.
One must exercise caution in applying these weight-based formulae to patients who are elderly or obese. Unfortunately, no standardized guidelines exist at this point to guide adult maintenance intravenous therapy. It is beyond the scope of this article to delve into the nuances of deciding between various tonicities and volumes of fluid administration. These choices demand clinical judgment based on the initial fluid status of the patient and predictions of ongoing fluid needs. The electrolyte derangements discussed below in the complications section show potential issues arising from certain fluid choices.
The strategy of managing a patient’s fluid differs depending on each patient’s clinical condition. If there can drink adequate fluid volumes by mouth, this should be the first choice. Some patient can tolerate other enteral options such as feeding tubes. IV plus oral orders are effective for those unable to meet their total daily fluid requirements enterally. Nursing staff can titrate the ratios accordingly depending on the patient’s ability to drink. Vital signs, physical exam, and adjunctive laboratory findings mentioned previously will show if each patient's fluid management strategy is appropriate. For example, a post-surgical patient with a new ileostomy might have additional fluid output from the stoma which clinicians must factor into the overall fluid management strategy.
Monitor serum sodium regularly. This is more of a risk when using hypotonic solutions. Many patients admitted to the hospital have risks of baseline elevated antidiuretic hormone (ADH) release leading to volume retention and worsening hyponatremia. Isotonic fluids are preferred for maintenance fluids in patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Risks of hyponatremia include cerebral edema with potentially dangerous neurologic sequelae such as seizures. If significant hyponatremia develops, it is important not to correct the serum sodium too quickly to avoid the devastating neurologic complication of central pontine myelinolysis.
Patients with renal failure who receive a potassium-containing solution might not handle clearing the potassium load and develop life-threatening hyperkalemia causing cardiac arrhythmias.
Monitor for peripheral edema, pulmonary edema, or hepatomegaly. It is important to consider underlying cardiac dysfunction or renal failure and adjust volumes of administration accordingly. These patients might require a lower maintenance fluid rate than expected for their body weight.
Normal saline is a slightly acidic solution relative to normal body pH. This can precipitate metabolic acidosis. Lactated ringers solution is a closer approximation to normal body pH; however, the use of lactated ringers vs. normal saline for fluid maintenance administration often depends on availability at each hospital institution and is an evolving paradigm undergoing discussion nationally.
Understating the importance of proper fluid management is difficult. Careful consideration of each patient’s current clinical status and relevant past medical history when determining a fluid management strategy is crucial to avoid iatrogenic problems such as dehydration, volume overload, electrolyte derangements, or pH imbalances. Close communication between all members of the healthcare team can mitigate these issues.
Interprofessional discussion within the healthcare team can optimize proper fluid management for patients admitted to the hospital. Bedside nurses often spend more time than any other healthcare member at the bedside with their patients and can provide useful assessments of patients’ volume status through documentation of vital signs and frequent visual assessments. Nurses can also be very helpful in assessing patients’ ability to tolerate enteral fluids and encouraging patients to drink by mouth if there is no NPO order which would prevent them from doing so. Nutritionists and dietitians are very helpful in determining caloric needs for patients to ensure that they meet their metabolic demand which is especially important during acute illnesses so that the body can heal properly. This is especially important in the pediatric population for infants who drink breast or formula. Total parenteral nutrition (TPN) is sometimes necessary as a temporizing measure for patients unable to take enteral fluid intake, but it comes with a variety of challenges such as the need for central venous access and risk of central line-associated bloodstream infections (CLABSI).