Intravenous fluid administration is among the most common interventions nurses perform — and arguably one of the most misunderstood.
We are efficient and confident when we spike a bag and open the roller clamp. But how often do we stop to ask: Where is this fluid actually going? And just as important: What is it doing once it gets there?
For trauma and critical care nurses, IV fluids are not benign. They are powerful physiologic tools that can restore perfusion — or, when used without intention, quietly worsen outcomes.
Understanding how fluids move through the body, and how different solutions behave, is essential for safe resuscitation across trauma and shock states.
Refresher: Where do fluids go?
Roughly 55% to 60% of the human body is water. That water lives in two main compartments:
- The intracellular (inside the cells) compartment, where the predominant components are K, magnesium, phosphates and proteins.
- The extracellular (outside the cells) compartment, where the predominant components are sodium, calcium, chloride and bicarb.
The extracellular compartment includes the intravascular (inside the blood vessels) space. However, the intravascular space — which is where we want IV fluids to work — is only a small fraction (about 3 liters in an average adult) of the total extracellular space.
That brings us to a key point: Most crystalloids do not stay in the intravascular space for long.
After infusion, crystalloids rapidly redistribute into the interstitial space. This is why a liter of saline does not equal a liter of sustained circulating volume — and why repeated fluid boluses can quickly lead to tissue edema without meaningfully improving perfusion.
The takeaway for nurses: This matters because hypotension, tachycardia and rising lactate may reflect poor vascular tone or hemorrhage, but they can also reflect ongoing volume loss.
So we have to ask ourselves two things: Where is volume loss coming from? and What components are being lost? When you have to answer these two questions, your knowledge and understanding of the IVF you hang becomes very important.
LR vs NS: Not all fluids are equal
Normal saline (0.9% NaCl) has long been the default IV fluid in many emergency settings. For trauma patients, we are quick to grab NS because it “plays nicely” with banked blood that contains citrate preservatives.
However, we now understand that large volumes of saline can contribute to hyperchloremic metabolic acidosis, renal vasoconstriction and worse outcomes, particularly in trauma and septic shock. If this is surprising to you, consider the components of NS and how it moves freely from the vascular space (where we put it) into the interstitial space (back to the tissues).
In comparison, Lactated Ringer’s (LR) more closely resembles plasma electrolyte composition. It is considered a balanced crystalloid because its pH of 6.0-7.0 more closely matches normal human pH.
The advantages of LR in trauma resuscitation include:
- Less chloride load
- Reduced risk of metabolic acidosis
- Improved acid-base balance during resuscitation
Despite lingering myths, LR does not worsen lactic acidosis. In fact, the lactate in LR is metabolized by the liver and can actually support buffering.
The takeaway for nurses: LR is often preferred when crystalloids are needed, especially early in care or alongside blood products.
Trauma Is Different: Fluids matter more than you think
Trauma patients are uniquely vulnerable to the harms of over-resuscitation. Uncontrolled hemorrhage, endothelial injury, inflammation and capillary leak mean that excessive crystalloids worsen:
- Tissue edema
- Abdominal and thoracic compartment pressures
- Coagulopathy and dilution of clotting factors
- Hypothermia and acidosis
The takeaway for nurses: In trauma, fluids should never be a substitute for hemorrhage control or blood products. Balanced, goal-directed resuscitation, often emphasizing blood over crystalloids, improves outcomes and reduces secondary injury.
Fluids Across Shock States: One size does not fit all
It is also important to understand that different types of hypotension call for different approaches to IV fluids.
- Hemorrhagic shock: Prioritize blood products and use crystalloids sparingly and intentionally. LR is favored over saline for patients in shock due to blood loss. But be aware that we can use crystalloids (or even colloids) as a temporary measure while we wait for blood, but these fluids don’t carry oxygen, platelets or clotting factors — they dilute whatever is left.
- Septic shock: Administering fluid early is beneficial, but excessive volumes worsen edema and respiratory failure. Balanced fluids outperform saline in long-term outcomes.
- Hypovolemic shock (non-hemorrhagic): Crystalloids play a larger role, but be aware that redistribution still limits the intravascular benefit of IV fluid.
- Cardiogenic or obstructive shock: When the heart cannot pump enough blood to maintain blood pressure, fluids may actually worsen the problem. For these patients, assessment and restraint are critical.
The takeaway for nurses: Hypotension does not automatically mean “give more fluid.” Clinical context matters — identify the type of shock your patient is exhibiting and understand where the water loss is coming from and what components are being lost.
Fluid Resuscitation: Knowing when to stop
A critical and often overlooked skill in trauma nursing is recognizing when a patient is no longer fluid-responsive. Endpoints of effective resuscitation include:
- Hemodynamic stability
- Improved lactate or base deficit
- Adequate end-organ perfusion
- Decreasing need for blood products or vasopressors
The takeaway for nurses: Continuing fluids beyond these endpoints increases harm without benefit. At this stage, attention must shift to vasopressors, temperature control, calcium replacement and correction of coagulopathy.
Nurse’s Role: The fluid gatekeeper
Nurses are the gatekeepers of fluid administration. IV fluids are not “just fluids.” They are drugs with indications, side effects and consequences.
Be vigilant about monitoring labs such as calcium, fibrinogen, platelets, renal function and acid-base status, especially during massive transfusion. Hypocalcemia, hypothermia and acidosis are common and deadly if unrecognized.
The takeaway for nurses: Whether you are new to trauma nursing or decades into practice, fluid resuscitation deserves a second look. Understanding where fluids go, how they behave and when they help (or hurt) empowers nurses to make safer decisions and advocate effectively for their patients.