Intravenous versus Oral Rehydration: Which is best for your athletes?

IV vs. Oral
The practice of using intravenous (IV) fluids to rehydrate athletes appears to be fairly common, whether it's in the NFL, collegiate football¹, at a marathon or after a triathlon. There are unquestioned medical benefits for providing an IV to a dehydrated athlete who is semi- or unconscious or who can not tolerate oral fluids. The prevailing notions among many sports health professionals are that an IV:

• Is more effective than oral rehydration in rehydrating a dehydrated athlete.
  
• Will provide a greater performance edge (over rehydrating orally) for an athlete between two bouts of exercise, such as the first and second halves of a football game or in between multiple daily workouts.

Many are surprised to learn that fluid taken orally has comparable physiological benefits compared to fluid given via IV. Of particular interest are studies that show oral rehydration may lead to lower body temperature² and improved athletic performance².

When you consider these advantages against the disadvantages associated with using an IV (i.e., treatment is invasive, requires trained medical staff, must be given off the field, increases risk of infection and bruising), an oral rehydration protocol is usually a more effective hydration approach.

Research Findings
To compare the response to IV and oral rehydration, researchers at the University of Connecticut conducted two studies summarized below.

Study 1: Halftime Scenario^2-4
In this experiment, researchers compared rehydration methods when rapid fluid replacement is needed, as is often the case during halftime in a football or soccer game.

Subjects were first dehydrated by -4% of their body mass by exercise in the heat before a fluid-replacement protocol was administered:

1. Fifty percent of fluid loss replaced over 20 minutes by ingestion.
2. Fifty percent of fluid loss replaced over 20 minutes by IV (normal saline).
3. No fluid replaced.

Immediately following the 20-minute rehydration period, the subjects cycled at 70 percent VO₂max until they exhausted. The ambient room temperature was set at 98.6ºF and the relative humidity was 50%.

The researchers found that during exercise:

• Plasma volume and osmality, skin blood flow, stroke volume, cardiac output and stress hormone response were similar for IV and oral rehydration.
• Skin and rectal temperatures were lower with oral replacement than in the IV trial.
• Thirst and ratings of perceived exertion were lower in the oral trial than in the IV trial.
• Performance for the group receiving oral fluids tended to be better than the group receiving the IV, but did not reach statistical significance.
• Subjects who were partially rehydrated (in both the oral and IV treatments) experienced greatly enhanced physiological responses and performance for nearly all variables as compared to subjects who were not rehydrated.

Study 2: Two-a-Days Scenario^5-7
In this study, researchers compared multiple rehydration techniques over a longer rehydration period, a scenario not unlike what happens with multiple daily workouts.

Subjects were first dehydrated to -4% body mass before rehydration:

1. Seventy-five percent of fluid loss replaced orally over 45 minutes.
2. Seventy-five percent of fluid loss replaced via IV (1/2 normal saline) over 45 minutes.
3. Seventy-five percent of fluid loss replaced via IV (normal saline) over 45 minutes.
4. No fluid replacement.

Seventy-five minutes passed before the subjects walked at 50 percent VO₂max for 90 minutes with the ambient room temperature set at 98.6ºF.

The results indicated that:

• Rectal temperature, skin temperature, sweat rate, performance and stress hormone responses were similar in the IV and oral groups.
• Interestingly, thirst and rating of perceived exertion were lower in the oral trial than in the IV trials.

Why Oral Rehydration is Better
These results demonstrate no discernable advantage for IV compared to oral rehydration. The data also suggest that oral fluid replacement may provide a performance advantage, reduce the subjective perception of thirst and make exercise feel easier (lower RPE). Additional research is needed to further characterize these differences.

Perhaps the greatest advantage of an effective oral rehydration protocol is that it encourages athletes to take an active role in rehydrating themselves, thus avoiding psychological dependence on intravenous fluids. Keeping the athlete responsible for his or her fluid replacement needs is the best approach to reduce the risks associated with dehydration.

Courtesy of the Gatorade Sports Science Institute (gssiweb.com)
For more information on this article, please contact Douglas J. Casa, PhD, ATC,, FACSM, at the University of Connecticut at douglas.casa@uconn.edu