Solutions and Tonicity

Transcript

1. Solutions and Tonicity By: Jonathan Croom 1
2. Objectives • Review key terms and concepts related to the tonicity of solutions. • Discuss the relevance of tonicity as it relates to IV solutions. • Define hypotonic, isotonic, and hypertonic solutions. 2
3. Tonicity describes how an extracellular solution can change the volume of a cell by affecting osmosis. 3
4. In order to understand tonicity, you must also understand osmosis & osmolarity. 4
5. Osmosis is the diffusion of water through a semipermeable membrane 5
6. Osmolarity describes the total solute concentration of the solution. 6
7. What is a solute and a solvent? 7
8. A solute is the substance being dissolved by the solvent in order to create a solution. 8
9. In the case of saltwater • Salt is the solute which is being dissolved by water • Water is the solvent 9
10. For the purpose of illustrating the concept of osmolarity, imagine that we have two separate 8oz. cups of saltwater 10
11. Cup A has 2 tablespoons of salt in it and cup B has 1 tablespoon of salt in it. 11
12. Which cup has higher osmolarity? 12
13. Cup A There is a higher concentration of salt, the solute, in cup A since we said it had 2 Tbsp. versus the 1 Tbsp. in cup B 13
14. Now let’s say that we take the solutions from cups A&B and put them in a beaker separated by a membrane. 14
15. • Solution A is represented by the solution on the right side of the beaker. • Has a higher tonicity than solution B • Solution B is represented by the solution on the left side of the beaker. 15
16. In a situation in which solutions of two different osmolarities are separated by a membrane permeable to water, though not to the solute, water will move from the side of the membrane with lower osmolarity (and more water) to the side with higher osmolarity (and less water). 16
18. Now that we’ve covered osmosis and osmolarity, let’s talk tonicity. 18
19. Three terms—hypotonic, isotonic, and hypertonic—are used to relate the osmolarity of a cell to the osmolarity of the extracellular fluid that contains the cells. 19
20. Isotonic Crystalloids One of the most common pharmacological interventions in prehospital medicine 20
21. Volume Replacement • We commonly use Isotonic Crystalloids to increase fluid volume in the vascular space • Has (approx.) the same tonicity/osmolarity as blood. 21
22. Treating isotonic fluid deficiency with IV fluid resuscitation • Situations that may lead to an isotonic fluid deficiency include: • Dehydration from excessive sweating • Massive hemorrhage • Diarrhea 22
23. Isotonic fluid deficiency is just a fancy way of saying • There is a deficiency in total body water • This leads to a decrease in the intravascular fluid volume 23
24. When the intravascular fluid volume gets low... • Migration of fluid from the extravascular compartment to the intravascular compartment occurs. 24
25. Giving isotonic fluids via IV will increase the volume in the intravascular compartment. • Some of the fluid will move from the intravascular compartment to the extravascular compartment. • This will help increase total body water. 25
26. Hypertonic Solutions • In a hypertonic solution, the solution has a higher osmolarity that the blood. • Net movement of fluid into the vascular space. • Not commonly given in the prehospital setting. 26
27. Hypertonic Saline - Clinical Use Case Example • A patient with increased ICP • Hypertonic Saline has a higher osmolarity than the fluid in the brain. • Through osmosis, fluid is pulled into the vascular space which reduces ICP. 27
28. Hypotonic Solutions • In a hypotonic solution, the solution has lower osmolarity than the blood. • Net movement of fluid out of the vascular space. • Not commonly given in the prehospital setting. 28
29. Picture This... • We place a red blood cell in a hypotonic solution. • Fluid is pulled into the cell due to the higher tonicity/osmolarity of the ICF. • If too much fluid is pulled into the cell...BOOM! Hemolysis 29
31. Sources • https://cnx.org/contents/ GFy_h8cu@9.85:6X9o-0n6@12/Passive-Transport • https://study.com/academy/lesson/osmolarity- definition-formula- calculations.html#transcriptHeader 31