Giving normal saline for SIADH

First question: will giving normal saline even help? Normal saline has an osmolality of 308 mEq (Na+Cl). In hypovolemic and some cases of euvolemic hyponatremia, it can help raise Na appropriately. If the urine osmolality is too high, giving normal saline will actually worsen hyponatremia because it will be like giving a more dilute fluid. 

Example: You have a man with suspected SIADH (he’s a smoker and has a new diagnosis of lung cancer). His Na is 120. His serum osm is 265 and his urine osm is 320. Your total free water loss is -37.5 mL, which is to say, if you give him 1 L NS, you will make zero difference. 

Let’s say the same man has a urine osm of 100. Your total free water loss is +2.08 L. If you give him 1 L NS, you will dramatically increase his Na. 

Let’s say the same man has a urine osm of 600. Now your total free water loss is -486 mL, which means if you give him 1 L NS, you will actually cause him to gain free water and worsen his Na. 

*It’s technically serum “osmolality” 
**D5 1/2NS osmolarity is often listed around 405, but it’s really less than that because dextrose moves more freely across cell membranes, and what I care about is the Na component

This chart is also very helpful for understanding how fluids are selected in common scenarios. 

Second question: How much normal saline should I give? The equation below is extrapolated from a calculation for how much hypertonic saline to give (see this post)

How much hypertonic saline should I give?

You have a patient with hyponatremia and you’ve determined that salt tabs and normal saline just won’t do, they need some 3% hypertonic saline. Great! You go to write the order…how many cc’s should they get? At what rate? Is there a better way of calculating it rather than just saying, give 50 cc x1 and hope for the best? 

As it turns out, giving 50 cc boluses and checking Na every 2 hours is an accepted form of empiric treatment. But if that makes you uneasy, there is a more mathematical solution. (Reference

You are solving for “predicted Na.” 513 refers to the amount of Na in 1 L 3% NS. Total body water is kg x0.5 for women, kg x0.6 for men

Example: a 60 kg woman with an Na of 108. Your goal is to increase her Na by 4 mmol over the next 4 hours. 


So far, your answer should be: the predicted change in Na will be 13.06 for every 1 L 3% NS. Therefore, to increase Na from 108 to 112 over four hours: 

=0.294 L or 294 mL. However, because you want to run this over 4 hours, 294/4=73.5 mL/hour. And that’s your hypertonic saline infusion rate!

Remember your Na correction goals:

  • 2-4 mEq in the first 2-4 hours (if you go over that, consider giving some free water back)
  • <8-10 mEq over 24 hours
  • You can stop being aggressive about correction around the time Na >125 mmol/L

Who needs to be on stress dose steroids and how do you taper them?

This post is about perioperative stress dose steroids, for adult patients, only. 

Who is at risk for perioperative adrenal insufficiency? The goal of stress dose steroids is to prevent hypotension and adrenal crisis/shock. The Society of Hospital Medicine (in one of their great learning modules), states: 

  • Low risk: <5 mg prednisone daily or ❤ weeks of prednisone over the past year
  • Moderate risk: >5 mg prednisone for >3 weeks in the past year
  • High risk: >20 mg prednisone daily for >3 weeks in the past year
  • Obviously, someone with primary adrenal insufficiency is the highest risk. 

What kind of steroid should be used? IV hydrocortisone is the most physiologic (+mineralocorticoid effect) and should be used until the patient can be transitioned back to prednisone/oral steroids. This letter makes an argument for dexamethasone that is interesting–I myself have never seen dexamethasone used for this indication, though. 

Does the kind of surgery affect whether someone should get stress dose steroids? Yes. 

  • Low stress: local anesthesia, ophthalmologic procedures, some small joint or hernia surgeries <1 hour
  • Moderate stress: general anesthesia, open procedures (hysterectomy, hemicolectomy)
  • High stress: lengthy, complex surgeries (CABG, pancreatectomy)
  • Patients at moderate-high risk undergoing moderate-high stress surgeries should be given stress dose steroids in the perioperative period. (Take this with a grain of salt–the objective evidence is very limited and there are good arguments for being even more conservative and only giving steroids to patients at high risk.)
    • Should you test for HPA axis suppression prior to surgery? If the patient is at moderate risk and undergoing moderate or high stress surgery, and you have the time to wait on results, then sure, you can. What test should you use? You can probably get away with an AM cortisol, although the cort stim test is more accurate

How the heck do I taper stress dose steroids? Stress dose steroid tapers, like ALL steroid tapers, are made up. We as a medical community prescribe tapers based on what “sounds reasonable.” What is usually reasonable is something along the lines of: 

  • Moderate stress surgery: 50 mg IV hydrocortisone x1 –> 25 mg Q8H x24-48 hours –> 10 mg prednisone x3-4 days –> usual dose
  • High stress surgery: 100 mg IV hydrocortisone x1 –> 50 mg Q8H x24-48 hours  –> 20 mg prednisone x3-4 days –> 10 mg prednisone x3-4 days –> usual dose 

Some people would advocate going straight from IV hydrocortisone back to the home dose, which is fine if the patient looks clinically well. Patients at higher risk of complications from steroids (hyperglycemia, fluid retention, agitation) should be tapered more quickly and patients at higher risk of adrenal insufficiency should be tapered more slowly.

Can you use methadone to prevent opiate withdrawal?

The situation: a young woman with opiate use disorder comes into the hospital with a broken arm after a car accident. She tells you she has been been buying methadone off the street and taking 60 mg a day. How do you manage this patient’s pain regimen and what can you do to prevent opiate withdrawal?

Methadone is typically used for maintenance therapy for opiate use disorder (OUD) or chronic pain. If it is for OUD, they must receive their doses from a methadone clinic. You should always try to call the clinic to verify the correct dose. In this patient’s case, she was buying methadone on her own. Therefore, the first step is to do a urine tox test–if the patient has been using methadone in the past week, it should be positive. If she is negative, it is not a good idea to start methadone unless she’s having withdrawal symptoms.

A patient’s home methadone dose does not provide acute pain control. Patients undergoing surgery can continue their methadone perioperatively. A patient who comes in on methadone (or suboxone, for that matter) needs the same kind of pain management as everyone else. For the patient above with the broken arm, you should still start Tylenol, NSAIDs if possible, and opiates like oxycodone or dilaudid for severe breakthrough pain.

Methadone is effective for preventing withdrawal symptoms in the inpatient setting. This Cochrane review shows that compared to placebo, tapered doses of methadone helped prevent withdrawal symptoms. There is no universal methadone tapered dose protocol. This American Pain Society sheet states methadone can be safely and rapidly tapered in 7-14 days. This pamphlet created by Pain Topics (and written by a Univ. Iowa pharmacist) has helpful information on short and long tapers. In general, you want to get the patient to reduce their dose by at most 25% every few days, end on a dose of 10 mg daily, and then stop completely.

For management of symptoms like sweats, muscle cramps, and nausea, check out this sister post.

What is a Passy Muir or speaking valve?

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A speaking valve, commonly called a Passy Muir valve, is a cap that can be put over the trach cannula to allow patients to vocalize more.

Patients often have to practice wearing the Passy Muir valve, and may be more fatigued or have more coughing at first.

The Passy Muir website has a practical and interesting troubleshooting page. Of course, take the company website with a grain of salt, but I did find it helpful overall for understanding the applications and patient perspective better.

Are there contraindications to using a speaking valve? 

Yes. Patients with an an inflated cuff, fome cuff trach, history of laryngeal masses, stenosis, total laryngectomy, or thick copious secretions should hold off on a speaking valve.

What is the difference between cuffed and uncuffed trachs?

  Cuffed trach Uncuffed trach Fenestrated trach (comes with a cuff)
Indication Patients on a closed ventilator (cuff prevents airleak) Patients who are more stable, getting closer to decannulation Patients on a ventilator who aren’t ready for a speaking valve. Has a cuff but is more “in-between”
Compatible with speaking valve?  

Yes—must deflate the cuff first

 

Yes, speaking valve may not be necessary

 

No—if cuff is deflated can speak using vocal cords or a trach plug

Advantages Provides the most secure airway Is easier for the patient to tolerate Allows air to pass more “normally” through nose and mouth
Things to look out for Pressure necrosis

Tracheal stenosis

Cuffless or deflated cuffs are more prone to silent aspiration Many fit poorly, leading to granuloma formation and infection
Random things to know Cuff pressures are ideally checked twice a day: 20-30 mmHg generally good The decannulation plug is used when patients get decannulated, so hold on it it Patients can still wear a nasal cannula if the trach is plugged

The table above was made using this Hopkins page as a reference.

This guide from OHSU is seriously fantastic. (Except at the beginning I think they switched the labels for pilot line and cuff.)  I am shamelessly borrowing their pictures.   Screen Shot 2018-10-25 at 8.18.23 PM.png

What are the parts of a trach?

 

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What are the most common different brands of trachs?

  • Shiley (plastic/PVC piping)
  • Portex (plastic)
  • Bivona (silicone)
  • Jackson (metal)

See here for pictures and specifics of the above brands.

What do the different trach sizes mean?

The table below is taken from a very comprehensive paper on trachs in Respiratory Care. As you can see, even trachs that are the same size according to the company actually have different dimensions. So I would recommend discussing with your friendly respiratory therapist if you think a trach needs downsizing and what the right size to go to might be.Screen Shot 2018-10-25 at 9.14.20 PM.png