What is PEEP? How to do a PEEP study?

PEEP is an abbreviation for Positive End Expiratory Pressure. It's a small amount of pressure above what is in room air that remains at the end of expiration.

The benefits of PEEP are.

1. Increased Residual Capacity. This essentially means that it increases the amount of air that stays in the lungs. This works to...
2. Recruit collapsed (atelectic) alveoli. This makes it so they participate in gas exchange. It also works to...
3. Keep alveoli from collapsing. It keeps alveoli open so the effects of fluid or atelectasis do not cause shunting. This also helps to reduce V/Q mismatching. This also makes it so you have an...
4. Increased PaO2 for a given FiO2. It's a good way of improving oxygenation. 
5. Decreases Cardiac preload and afterload. It reduces the amount of blood returning to the heart, and thereby reduces the amount of blood leaving the heart. In this way, it can help patients who are in heart failure (pulmonary edema) by reducing the amount of work their heart has to do to pump blood through your body. This also means that too much PEEP can be observed by drops in cardiac output, which can be measured by bloodpressure and oxygen saturation (SpO2). 
6. Reduction in tissue injury and inflammation. It prevents the alveoli from constantly opening and closing and thereby inuring them and causing inflammation, which may be associated with the development of ARDS. Studies have shown that it is protective against "ventilator induced lung injury." This is often called volutrauma. Volutrauma was more prevalent back in the days when it was thought that people on ventilators should be on higher tidal volumes, hence the old formula of setting tidal volumes based on 10-15cc/kg ideal body weight. This has now been lowered to 6-8cc/kg ideal body weight in order to prevent volutrauma. 

There are disadvantages of this.

1. Over-distention of alveoli. It causes too much air to stay in the lungs resulting in decreased cardiac output, as would be shown by blood pressure and SpPO2. There are certain instances where you would benefit from higher PEEP, although too much PEEP can lead to over-distention and volutrauma, which may mimic respiratory disease states. So, in such instances, you would want the highest PEEP that doesn't cause over-distention. (Described below is how to accomplish this with a PEEP study). Over-distention results in increased dead space, increased work of breathing, and medical disorders such as ARDS. 
2. Diminished Cardiac Function. As noted, PEEP that is set too high can decrease venous return and cardiac output. This can be measured by complex formulas, although the simplest way is by taking a blood pressure and monitoring pulse oximetry. 
3. Diminished Renal Function. May decrease renal blood flow resulting in diminished urinary output. So, this is another reason to keep PEEP as low as clinically possible, especially when you have a patient in heart or kidney failure. 
4. Increased Intracraneal Pressure. When venous return decreases, intracraneal pressure may increase. This is usually not clinically significant. However, if you have a patient who already has an elevated intracraneal pressure (ICP), such as due to a head trauma, this is something you'll need to watch out for. This is another reason to raise the head of the bed, as this may offset any increase in ICP (the other reason for raising the head is to prevent GERD, which can increase the risk for ventilator associated pneumonia). 

Now that you know about PEEP, along with its benefits and disadvantages, we can now get into how to perform a PEEP study. The purpose here is to determine the perfect PEEP for an individual patient at any given moment in time. Keep in mind here that the ideal PEEP may increase or decrease over time, especially as a patient's medical condition worsens or improves.

Here is the basics of any PEEP study.

1. Increase PEEP by 2-3 cwp every 20 minutes and continue to monitor the patient. You should write down the patients blood pressure and SpO2. If desired, you can also jot down the patients P/F Ratio and static compliance.
2. If static compliance, P/F Ratio &/or SpO2 increase, you know it's working. 
3. Stop when the patient's blood pressure and SpO2 start to drop. Also stop when the P/F Ration is equal or greater than 200. Also stop when the static compliance decreases. 
4. The required PEEP should be set at the PEEP setting used just prior to where the hazards of PEEP were observed. 
5. Do not increase PEEP if systolic BP is less than 90
6. Also, keep mean airway pressure (MAP) less than 15. This is one of the newer markers of too much PEEP. When it starts to drop, this is an early indicator that cardiac output is about to decrease. 
7. Ideally, static complliance should be between 60-100.

I also have a shortcut. Maybe I shouldn't teach you this, but here goes: essentially, based on the wisdom we learned above, all you really need to do is monitor pulse oximetry and blood pressure. If either starts to drop, then you know it's time to lower your PEEP by 2 cwp, which would be your ideal PEEP. This makes it simple. 

The optimal goal of any PEEP study is to find the optimal PEEP to maintain a desired SpO2 and PO2.

If any of my fellow respiratory therapists has anything further to add (any tips), please feel free to share.

(Post originally published on 8/9/08. It has been edited and updated by RT Cave Staff). 

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References:

1. Vincent, Jean Louis, editor, "Intensive Care Medicine: Annual Update 2002," 2002, Springer, pages 302-303
2. Criner, Gerard J., Rodger E. Barnette, Gilbert E. D’Alonzo, editors, “Critical Care Study Guide: Text and Review,” 2nd edition, 2010, Springer
3. Kacmarek, Robert M., James K. Stoller, Albert J. Heuer, “Egan’s Fundamentals of Respiratory Care,” 10th edition, 2013, Elsevier Mosby
4. Saura, Pilar, Lluis Blanch, "Conference Proceedings: How to set Positive End Expiratory Pressure," Respiratory Care, http://www.rcjournal.com/contents/03.02/03.02.0279.cfm, accessed 4/11/17
5. Respiratory Update: "Benefits, Contraindications, Adverse Effects for PEEP/CPAP," http://www.respiratoryupdate.com/members/Contraindications_for_PEEPCPAP.cfm, accessed 4/17/17
6. Valenza, et al., "Positive end-expiratory pressure delays the progression of lung injury during ventilator strategies involving high airway pressure and lung overdistention," Critical Care Medicine, 2003, July, 31 (7), pages 1993-08, https://www.ncbi.nlm.nih.gov/pubmed/12847394, accessed 4/11/17
7. Respiratory Therapy Cave: Respiratory Failure Lexicon
8. Respiratory Therapy Cave: ABG Lexicon

On vacation & forgot your meds: what can you do? How long do drugs last in the med cabinet?

Every day at MyAsthmaCentral.com we get lots of asthma related questions. Below are some questions I thought my readers at the RT Cave would enjoy.

Question: I forgot my nebulizer at home i dont have any of my asthma meds what can i do im felling very tight. I normally carry a resuce inhaler with Albuteral and use it in my nebulizer as well but i left everything at home

My humble answer:
First of all, know that you are not the first nor the last asthmatic to do something like this. I've done it, and so do many other asthmatic vacationers I see in the ER.

I have a couple options for you.

1. Most pharmacies allow prescriptions to be transferred. If you go to a Walgreens back home, for example, you can go to the Walgreens wherever you are vacationing and just have them transfer over your scripts. You won't be able to get a new nebulizer this way, but at least they should be able to get you a rescue inhaler. Other pharmacies that will do this are Rite Aid, Walmart, Kmart, etc.

2. In fact, I'm pretty sure any pharmacist would understand your predicament and help you out. I've gone to random pharmacies before and have never had a problem having my prescriptions transferred.

3. Don't be afraid to go to the nearest emergency room. The people that work there will understand your predicament, give you a quick breathing treatment in the ER, and send you home with a rescue inhaler. If you need it, they can also contact the local home health care company and have them supply you with a machine to use until you go home. The doctor there can also write prescriptions for any other medicines you might have forgotten. Since you should never wait too long to treat your asthma symptoms, this might be the best option for you.

4. You might be able to go to whatever home health care company in the area you are vacationing and see if they can hook you up with a nebulizer and vials of meds to last you until you get back home. I'm not positive exactly if they would be able to help you, but you could try.

Good luck!

Question: What is the shelf life of Theodur

My humble answer: Here is a neat article I found concerning the shelf life of medicines.

Basically, most new drugs like Theodur (theophylline) are good for 2-3 years from the date of manufacture. However, once the "original container is opened for use or dispensing, the expiration date on the container no longer applies." When the product is repackaged for you -- the consumer, it is "usually" dated by the pharmacist to expire within one year.

The expiration date of a medicine is the predicted date at which the drug will lose10% of its potency, according to this ABC News post.

The expiration date also assumes you are storing the medicine at the recommended temperature and humidity. According to our own site, theophylline should be "stored between 59-86 degrees F (15-30 degrees C) and away from light and moisture." This means that it should not be stored in the bathroom where it will be exposed to high humidities during and after showers.

While most drugs like Theodur are not hazardous if used after their expiration dates, the efficacy of the medicine after that date can no longer be guaranteed. Thus, if you are using an expired medicine you may not be getting the expected results.

Question: Is breathing-in more difficult for Asthma patient or breathing-out ?

My humble answer: Believe it or not, asthma is a disease of air trapping. What happens is air comes in, the airways constrict and swell, and air gets trapped in the lungs. While it may feel as though you can't get air in, the reality is you can't get air out. In fact, this air trapping is one of the reasons that during an asthma attack it often feels like you can only take in half a breath, or a quarter of a breath.

Those in the medical field may think of this air trapping as intrinsic PEEP. PEEP is air that is left in your lungs after you exhale. Normally PEEP is 2-3 CWP. During an asthma attack, this PEEP increases, thus causing hyperinflation of the lungs (which can be seen on an x-ray). If this intrinsic PEEP gets severe enough, it can lead to a severe asthma attack, and (possible although rare) even death.

This air trapping is also one of the reasons that diaphragmatic breathing is a technique often taught to asthma and COPD patients. The idea is if you give your lungs more time to exhale some more air might escape your clamped down air passages. Of course you probably know your rescue inhaler also works to relax your air passages to, thus letting out this trapped air.

Question: Intal versus Advair for asthma: have problems with asthma (wheezing sometimes) and respiratory allergies. Age 62M. I heard that Advair is a "ramp up" medication for sicker people and has more side effects and causes weight gain. Is Intal less problematic and am I better off with it if it helps or will I create more long term problems by not using Advair right away? Thanks

My humble answer:
You are wise to ask this question. Intal was a popular controller med for asthma in the past, (in fact I was on it in the 1980s) but it is less commonly used today due to much better medicines. It is a anti-inflammatory medicine, but I rarely ever see it used anymore, especially with adults.

The most common asthma controller medicines used today for asthma are inhaled corticosteroids such as Flovent (a ramp up from Intal). Flovent is much more effective for treating inflammation than Intal (at least most asthma experts conclude this).

If you continue to have trouble with your asthma despite inhaled corticosteroid use alone, your doctor might prescribe Advair (or Symbicort). Advair (a ramp up from Flovent) is a combination drug with both Flovent and a long acting bronchodilator called Serevent in it. Advair has been very effective in controlling asthma for many asthmatics, including myself.

There used to be a fear that inhaled corticosteroids had the same side effects as oral corticosteroids (prednisone), but many studies have been done to prove this is not true. If you take your Flovent or Advair properly, and you rinse really well after each use, side effects from these meds should be rare.

In my opinion, if Intal is working for you great. Your doctor may have been wise to have you try it before resorting to inhaled corticosteroids.

If, as you describe, Intal is not working, you might want to talk with your doctor about other options, such as the Advair you mention. Either way, it's always a good idea to keep in touch with you physician as I'm sure you are doing.

Good luck getting your asthma under control.

If you have any further questions you can contact me by clicking the "contact me" icon above.