Why 1/2 normal saline?

Nurses General Nursing

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I'm trying to figure out why 1/2 normal saline would be ordered in my patient? Patient is here for uti and aki. BUN is in the 50-60 range, creatinine 2.5-3. Initial sodium was 131 and is now 136. Saw a note from the doc about continuing diuresis and holding lasix until the creatinine drops. I don't even see lasix or any diuretic in the MAR, but let's just say it is I can't figure the reason for using 1/2 NS instead of NS.

Specializes in ER, Med/Surg.

Was Lasix a home med?

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I'm trying to figure out why 1/2 normal saline would be ordered in my patient? Patient is here for uti and aki. BUN is in the 50-60 range, creatinine 2.5-3. Initial sodium was 131 and is now 136. Saw a note from the doc about continuing diuresis and holding lasix until the creatinine drops. I don't even see lasix or any diuretic in the MAR, but let's just say it is I can't figure the reason for using 1/2 NS instead of NS.

0.45% NS is a maintenance fluid. Its purpose is to replace insensible fluid loss (water loss through the skin and respiratory tract).

The fact that the serum sodium is normalizing indicates that the patient is not volume overloaded, hence no need for Lasix. Lasix would be of no benefit, and potentially harmful.

Elevated creatinine in the setting of Lasix therapy indicates to me that perhaps this patient's AKI was prerenal in nature (i.e. severe dehydration due to Lasix therapy?), which would be a good reason to hold Lasix until the creatinine decreases.

"Continuing diuresis and holding Lasix until the creatinine drops" could indicate that the patient is making urine and is euvolemic, and so the plan would be supportive care while giving the kidneys a chance to heal.

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Specializes in Nursey stuff.

Lasix does tend to cause creatinine levels to creep up, so I am thinking he was on this at home and now on hold.

With .45 being hypotonic, Na will go into the cell (hypoactive = fat cells), risk for hyponatremia and (drum roll please…) hyponatremic encephalopathy, so I don't think he will be on that long either—or let's hope not especially with low Na to begin with.

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Specializes in Urology.
Yep. However across a semipermeable membrane, water will cross the membrane to reach sodium equilibrium, sodium will not cross the membrane from high side to low side. Remember, that's why it's said "water follows sodium" because water will go to the higher concentration of sodium until equilibrium is reached.

Now on to another thought: because the patient is diuresing, why didn't the Doc order 1/4 NS?

Serum Osmolarity should also give a good indication of why 1/2 NS. Consider question, what's being protected by continuing the diuresis without adding diuretics to the mix?

Correct, I just used the semi permeable as a descriptor for equilibrium not as the actual mechanism of transport. The treatment for hyponatremia is isotonic correction and hypertonic for severe (per aafp guidelines, also depends on the type of hyponatremia) but at the same time we also don't know much about the patient other than chf. My assumption of the 1/2 NSS is to not overly lose sodium on diuresis (also I'm assuming they are doing this or have plans to do this). Again the guidelines that are out are just guidelines and each patient given their history should warrant a different approach. For example, we don't know how much sodium this person eats in a day. Perhaps they love their salt (as most elderly people do due to decreased taste sensation). Given the CHF diagnosis we also don't want to put a lot of fluid in vascular space so perhaps this could be the major reason we aren't seeing a more aggressive approach. To get the full reason you would have to ask the doc!

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With .45 being hypotonic, Na will go into the cell (hypoactive = fat cells), risk for hyponatremia and (drum roll please…) hyponatremic encephalopathy, so I don't think he will be on that long either—or let's hope not especially with low Na to begin with.

No, water goes into the cell. Hyponatremic encephalopathy is due to the swelling of the brain cells with water. Serum sodium levels decrease due to dilution.

Psst! You guys are way overthinking this! It's maintenance fluid.

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No, water goes into the cell. Hyponatremic encephalopathy is due to the swelling of the brain cells with water. Serum sodium levels decrease due to dilution.

Psst! You guys are way overthinking this! It's maintenance fluid.

Yep, I think you are right. Now that it is not 3am and I've had some sleep my brain is working a little more clearly. It was pretty simple - dehydration. I did not talk to the doc, but the house supervisor and asked her. (I am not even going to feel bad for not knowing this answer 2 other nurses gave me the answers of "physician preference" and "because she can't take LR because she's diabetic".) Anyway, the nearest I figure is she was dehydrated, on fluid restrictions for CHF, and having kidney issues from an untreated UTI. The fluids were for the dehydration and the 1/2 NS to expand the intravascular space and draw fluids into the cells. If I had brushed up on my IV fluids I would have remembered that 1/2 NS is used to draw water into the cells since the intra cellular fluid would have more sodium that the extra cellular. If the fluids go into the cell and the sodium stays outside the cells then 1/2 NS would make sense. I could not find anywhere in her chart that she actually takes Lasix as a home medicine or at any time during hospitalization so not sure about that piece, but I feel a lot more comfortable having a better idea why this fluid would be chose. I do like to know why I am giving something and have already seen in my short career that doctors make mistakes so I like to have an idea on the line of thought with any treatments.

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The kidney injury is evidently due to the BUN and creatinine.

How so?

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