Okay, to reintroduce Dr. Jihad Malad, clinical professor of medicine at the Cleveland Clinic Abu Dhabi and chair of the Critical Care Institute Abu Dhabi. Thank you for the introduction. So I have no conflict of interest related to this talk. So I'm going to start with some reminders of basic physiology. So we all know that total body water constitutes 60% of body weight, 66% are in the intracellular space, 33% is the extracellular space, of which 25% in the intravascular compartment and 75% in the interstitial compartment. So where do IV fluids go? So well, it depends on the osmolarity and the tonicity. Osmolarity is how much solute in the solution and tonicity is how well does the solute keep water in the extracellular space. So you can think of tonicity as effective osmolarity. Effective osmols stay in the extracellular space, such as chloride and sodium. This will increase the tonicity and keep water in the extracellular space. However, ineffective osmols will cross freely into the intracellular space. This won't affect tonicity and this don't shift water movement. So fluid tonicity or effective osmolarity is how it determines how much water stays in the extracellular space. So hypotonic solution shift water from intracellular space to the extracellular space and shrink the cell. However, hypotonic solutions will shift water from the extracellular space to the intracellular space and can blow up the cells. And these are the equations that we use to calculate osmolarity and tonicity. And you can see that they depend mainly on sodium and potassium. So what is a strong ion difference? You know that the Stuart approach to acid-based disorders, three independent factors can regulate the pH. Arterial PCO2, the total weak acid, which is mainly albuminate and phosphate, and the strong ion difference, which is a difference of the fully dissociated cation minus the fully dissociated anions. So the seed of the infused solution relative to the seed of plasma determine or predict the effects on acid base of the plasma. So if you have a solution with low seed, this will lead to acidifying effect. If you have a solution with high seed, this will lead to alkylifying effects. So types of fluids, as you know, we have crystalloid solution and we have colloid solutions. I'm not going to go into the details, but you know that crystalloids have shorter halftime, but also less expensive than colloid solutions. We're going to focus on crystalloid solutions. And here you can see that the crystalloid compositions of many crystalloid solutions compared to the plasma composition, for example, 0.9 saline solution is isotonic compared to the plasma and was in vivo seed of 0. The ringer lactate is hypotonic compared to the plasma with seed of 28. And of note, the in vivo seed of plasma is about 42 milliequivalent per liter. So we're going to talk a little bit about historical perspective. In 1832, during the cholera pandemic, Thomas Latta developed the first saline and water solution intended to be used IV to treat dehydration. Its composition was bicarbonate, sodium and chloride. And after he adjusted the solution several times, however, none of the IV solution described between 1832 and 1895 bear any resemblance to 0.9% saline solution. Hamburger was the first main authority for suggesting that a concentration of 0.92% saline was normal for mammalian blood. And in 1896, he created a solution he termed physiological serum to study the hemolysis of red blood cells in vitro. However, he never intended to use this solution clinically. And during the freezing point of amphibian and mammalian blood, Hamburger concluded that warm blood and 0.9 saline solution had the same freezing point. He considered this solution to be normal or physiological since it didn't cause hemolysis compared to hypotonic solutions. So the scientific evidence supporting the use of 0.9% saline solution in clinical practice seems to be based only on this in vitro study. It remains a mystery how it came into general use as intravenous fluid in vivo. As you can see, 0.9% saline solution is not physiological. Its pH is 5.4 compared to plasma. And the seed is 0 compared to 42 milliequivalent per liter in the plasma. And it causes, we all know, hyperchloric metabolic acidosis, hyperkalemia, and acute renal failure. So what's the ideal balanced glyceroid? The ideal balanced glyceroid is normotonic with a seed of 24 milliequivalent per liter. This can be achieved by removing 24 milliequivalent of liter of chloride from 0.9% saline solution and substituting it by bicarbonate or organic anions, such lactate or acetate, which disappear rapidly on infusion. Ringer lactate is another balanced solution. It was developed in 1882 by Sidney Ringer. He discovered Ringer lactate through frog heart experiment. He added calcium and potassium to the saline solution. And in 1889, Alexis Hartzman developed a similar solution to Ringer lactate by adding the component of lactate. And you can see that the pH of lactate is much higher than the pH of 0.9% saline solution with a seed around 28 milliequivalent per liter. And plasmalite is another balanced solution. You can see that the pH is closer to the plasma pH with a high seed of 50 milliequivalent per liter. So what about the balanced glyceroid versus 0.9% saline solution in clinical patients? This is a recent meta-analysis published in New England Journal of Medicine in 2022. Overall, you can see that there's no difference in term of 90-day mortality between the both solutions. However, when you look at the low risk of bias trials, you can see some trend in improving mortality in favor of balanced solution. And this is a secondary analysis of the basic trial, which was published recently in Intensive Care Medicine in 2023. And you can see that in septic patients, when they receive more than four liters of fluid resuscitation, a balanced solution decreased mortality compared to 0.9% saline solution. However, this effect was not observed in non-septic patients or in elective surgery patients even after receiving more than four liters of fluid resuscitation. So some fluids for PET to avoid. We should avoid using a normal 0.9% saline solution except in cases of acute metabolic alkalosis or acute brain injury. Avoid using hypotonic solutions such as ringly lactate albumin 4% in acute brain injury patients. Avoid using hydroxy stretch in septic patients because it induces AKI and increased mortality in this population. Avoid using ringly lactates in frank hepatic failure patients because the liver would be unable to metabolize the lactate. And avoid using ringly lactate in metformin-associated metabolic lactic acidosis because of the high production of lactate in such a situation. And avoid using ringly lactate when we administer septic because it's incompatible. And avoid using plasmalite in a situation of metabolic alkalosis because of its high seed more than 50, around 50 milliequivalent per liters. I'm going to talk a little bit about some misconceptions. We all heard about ringly lactate isn't safe in hyperkalemia patients. This is not true. Ringly lactate, it's fine in hyperkalemia patients. In fact, it's actually 0.9% saline solutions that might induce hyperkalemia. And the second misconception is about compatibility of ringly lactate with blood transfusion. This also seems to be a myth. Several studies have found that ringly lactate is compatible with blood transfusion. And the third misconception is about severe hyperkalemia and ringly lactate. This is also not true because ringly lactate contains only 1.5 millimole of calcium. And this would not worsen hyperkalemia. However, this is not the optimal solution to be used in this case. So in conclusion, I think we should move to a pH-guided resuscitation approach. We should look at the assessed metabolic and acid-based abnormalities. And then if you have a patient with non-onion gap metabolic acidosis, we should be using isotonic bicarbonate. In certain situations with acute metabolic acidosis, 0.9% saline solution would be indicated. And in situations with no pH disorders, treatable with glycerol, we should use ringly lactate or plasmolyte or any balanced solution. And thank you for your attention.

IV fluid dynamics

osmolarity

balanced crystalloids

pH-guided resuscitation

fluid compatibility