Overview of Fluid Resuscitation
The main purpose of fluid resuscitation, or giving a person fluids, is to make sure their organs are working properly and getting enough blood (hemodynamics), as well as the right amounts of oxygen, electrolytes, and other important substances. This can be done by giving someone fluids to drink, but if they can’t eat or drink, doctors can also replace the lost fluids by giving them through an IV, or a tube that goes into a vein.
Anatomy and Physiology of Fluid Resuscitation
Your body water is split into two parts: inside your cells (intracellular) and outside your cells (extracellular). Most of your body water is inside your cells. The fluid outside your cells can be found in areas like between your cells (interstitial), inside your blood vessels (intravascular), and other places like around your eyes or in your spinal cord (trans-cellular).
Your body fluids have a lot of different types of minerals, called electrolytes. Two important electrolytes are sodium and potassium. Sodium is mostly found in the fluid outside your cells, while potassium is mostly found inside your cells. There are other minor minerals present too, like sodium and magnesium in the fluid inside your cells. These are balanced by other types of minerals called phosphate, sulfate, and bicarbonate. In the fluid outside your cells, you can find minor amounts of calcium and magnesium. These are balanced by chloride, bicarbonate, phosphate, and sulfate.
Why do People Need Fluid Resuscitation
Trauma is the main cause of death for individuals between the ages of 1 and 44 in the United States. Among these cases, serious blood loss, also known as hemorrhagic shock, is responsible for about 30% to 40% of deaths within the first 24 hours after the injury. If you lose more than 5% to 10% percent of your blood, your body automatically starts adjusting to restore normal blood volume. If you lose more than 20% of your blood, you’ll need to have fluids put into your body to ensure that oxygen continues to be delivered to your vital organs.
When your body experiences trauma and severe blood loss, it will try to restore the blood volume to ensure that your vital organs continue to receive enough blood. This involves a shift of fluid from the spaces around your cells into your blood vessels due to changes in the walls of your capillaries (tiny blood vessels) and decreased pressure in your blood. This shift can move about one liter of fluid into your blood vessels. Then, a system in your body that regulates blood pressure gets activated, causing your kidneys to hold on to more water and salt.
These actions aim to refill the blood veins and arteries. But, doctors have to be careful because giving too much fluid too quickly can lead to a lower body temperature, a change in the acid level of your blood and a problem with blood clotting. Doctors usually go for giving fluids when your systolic blood pressure (the top number in a blood pressure reading) goes below 80 to 85 mmHg or is rapidly dropping, or if your mental state worsens and there’s no evidence of head trauma.
The two main types of fluids used to refill your blood vessels are colloids and crystalloids. Colloids mainly increase the volume of your blood, while crystalloids quickly increase the blood volume but also move into the spaces around your body cells. In cases of severe blood loss, doctors often give crystalloids as large doses. However, recent research suggests that for patients with injuries that caused the bleeding, giving a lot of fluid may worsen the bleeding. Therefore, it’s better to give small amounts of fluid and keep the blood pressure a bit low until the bleeding is under control. This method has proven to be safer and reduces the amount of fluid needed.
It’s important to note that it’s only safe to maintain low blood pressure if there’s clear evidence that your organs are still getting enough blood, like producing enough urine and maintaining a healthy mental state. Crystalloids are typically used to keep blood circulation going until blood products can be given to a patient with severe blood loss. This is why it’s typically wise to consider limited small doses for patients without shock or nearing shock until blood products become available.
Sepsis is one of the main reasons for sickness and death in critically ill patients, with death rates ranging from 20% to 45%. Sepsis is often accompanied by unchecked inflammation, low blood supply to tissues, changes and dysfunction at the smallest vessel and cell levels, leading to multiple organ failure and poor health outcomes. Sepsis shock is a kind of septic shock where there is continuous low blood pressure caused by a serious body-wide inflammatory state(referred to as Systemic inflammatory response syndrome (SIRS)) from a suspected or confirmed infection.
The main trait of septic shock is a body-wide expansion of blood vessels that results in low blood volume, decreased oxygen supply and delivery to body tissues. The aim of giving more fluids is to restore normal blood flow and optimize blood supply to the tissues, hence increasing oxygen delivery to these tissues.
For resuscitation, doctors often give fluids, such as crystalloids, as soon as possible, typically within the first three hours at a dose of 30 ml/kg of ideal body weight. If shock persists, they can guide fluid resuscitation using central venous pressure (CVP), mean arterial pressure (MAP), and central venous oxygen saturation (ScvO2). They aim to achieve certain targets for these measurements within the first six hours of resuscitation, which have been shown to improve patient survival. Doctors also monitor lactate levels, as a boost in levels can indicate a decrease in tissue perfusion.
When a Person Should Avoid Fluid Resuscitation
If you have a certain type of brain bleed called a subarachnoid hemorrhage, or if you have had recent surgery that caused acute kidney injury (a sudden episode of kidney damage or failure), 0.9% saline (a common type of IV fluid) should be used carefully. This is because these conditions can influence the level of sodium in your blood, either making it too high or too low.
Another type of IV fluid, called hydroxyethyl starch (HES), should not be used in people who are in septic shock. Septic shock is a severe infection that can cause organ failure. This is due to negative effects this fluid can have on blood clotting and kidney function. There was a large study done in Scandinavia on very sick patients in the ICU, where they found that using 6% HES increased the chances of death after 90 days compared to another fluid, Ringer’s acetate.
Finally, if you have a traumatic brain injury, a type of fluid called intravenous albumin should not be used. This is a protein that helps transport hormones, drugs, and other substances through the blood.
Possible Complications of Fluid Resuscitation
Receiving large amounts of fluids through an IV can lead to a condition called hypervolemia, or having too much fluid in your blood. It can also throw off the balance of minerals, or electrolytes, in your body. This can be particularly problematic for those in septic shock, a severe infection that affects the whole body. Giving them too much IV fluid over a prolonged period can increase the total amount of water in their bodies. This can be especially dangerous for patients with kidney, heart, or liver problems.
This excess water often ends up in places it shouldn’t be, like in the lungs (causing a condition called pulmonary edema) and under the skin in the feet or lower back (resulting in pedal or sacral edema). These issues can cause problems during recovery, such as making it hard to remove the breathing tube (ventilator) or causing muscle weakness. Both of these issues can increase the time a patient stays in the hospital and the risk of hospital-acquired complications.
Also, using too much of a specific IV fluid, a 0.9% saline solution, can lead to a type of metabolic acidosis (a condition that occurs when the body produces too much acid) resulting from too much chloride. This condition is associated with kidney damage.
What Else Should I Know About Fluid Resuscitation?
Fluid resuscitation, in simple terms, means making sure your body has enough fluids to function well. It’s all about keeping a balance – enough fluid to keep your blood flowing properly, making sure your organs are supplied with enough blood, and also the right balance of electrolytes, elements in blood that are essential for the body’s functions.
There are several reasons why someone might need fluids given directly into their veins (this is what we call an intravenous or IV fluid). For example, if a person can’t eat or drink anything before surgery, or if they’re unable to drink because they’re vomiting a lot. The amount of fluid a person needs depends on their weight. For children, the amount of IV fluid they need will depend on how much they weigh. For adults, they’ll usually need about 35 ml of fluid for each kilogram of body weight per day.
Besides giving fluids, it’s also crucial to think about electrolytes which are important substances like sodium and potassium that help our bodies work properly. We usually need about 1-2 milligrams (mEq) of sodium and 0.5 to 1 mEq of potassium per day, depending on our body weight. These can be given as a part of the IV fluids.
