Where I work the RTs do all the ABG draws, which I think is great. On the other hand, Drs have all control over when an ABG is to be drawn, and this results in a lot of needless pokes. I would absolutely love to work at a hospital that had patient driven protocols. That would be like an RT Heaven.

However, we do have a newly enacted ventilator protocol and are in the process of getting a Rapid Response Team. Things are changing for us RTs.

Clearly a solid set of patient ventilation/oxygenation parameters must follow any ABG if the data is to have any clinical relevance. We all know how dynamic pulmonary physiology is and an ABG is a static measure indicative of just those moments prior to/during its draw.

This also points to the need to better use the dynamic tools of etCO2 O2sat and transcutaneous O2/CO2 assessments. Trans-q in adults is way under utilized. Consider that the O2 sat is a poor indicator of O2 status changes once O2 sats reach the 90th%ile. etCO2 is less effective as pulmonary pathology increases (as are isopleth graphs BTW). Trans-q on adult skin does reflect dynamic changes in PaO2 and PaCO2. The PtcO2 vlues are lessened but relative and the PtcCO2 values have a time lag but are accurate. Consider doing a best PEEP search using PtcO2 to observe oxygenation tension changes as they occur. When they peak best PEEP is achieved whether best compliance is found or not because best PEEP should be best V/Q. Ptc O2 and PtcCO2 during weaning...essential, time saving, $$ saving.

Most RTs dislike trans-q on adults because they claim it's too perfusion limited. They cannot have confidence in the values because they may reflect poor perfusion and not arterial fluctuations. Capillary perfusion is the same in the skin as it is in the trachea and we do understand it and it can be easily confirmed. Capillary closing pressures are about 15-25 torr everywhere. You can challenge the perfussion under an in-situ TC sensor by pressing down on it ( BTW a properly membraned sensor will tolerate this and not lose calibration)and watching the recovery rate of the prior established values. If they recoup quickly and fully the perfussion is adequate and the sensor is tracking arterial values. If the O2 drops off and returns poorly or not at all then the skin perfusion is inadequate and perhaps also reflective of impending shock states. Lastly place TC sensors on adults on the upper thorax for fastest response to arterial changes. That skin is the 1st to get supplied in the body as part of cranial supply (also seen in caval block syndrome).

Dave,
I must disagree. Shouldn't the patient/vent assessment be done before your arterial draw, when the patient is in a steady state. Also, the use of TCM, if I'm not mistaken, is a daily charge at most hospitals and would use more DRG $$. Most RT's don't think about the cost, or don't care. In my opinion ETCo2 and TCM have their place, but only on a select few patients. We as RT's need to do more with less, if that makes sense. This is one of the reasons lots of hospitals have gone to therapist driven protocols. RT is one a the few departments that can save the hospital $$. My hospital uses 5+- RT's on day shift and we have protocols. Without protocols we would need more RT's or would be neb jockeys doing sixty tx a day.

GJ

GJ... No, we agree on the ABG draw data. When I wrote "follow" I meant "to accompany" as in "follow along with" and not to be done later. My bad. It was confusing.

Regarding Trans-q I would aver that it allows for faster, more accurate therapies and assessments. There's no need for multiple ABG draws or waiting to determine if a patient succeeds or fails therapy trials. This should provide better allocation of manpower resources while attaining a high quality of care. Trans-q is technology better accepted in neonatal care where, in fact, the data is better, the patients more labile and blood volume dependent. That said there is a way to prep adult (mature) skin that provides near instantaneous 100% arterial correlation using sensors at body temp. You introduce an atraumatic suction blister separating the epidermis from the dermis. The blister dome gets removed and the sensor (calibrated at body temp) is placed directly on the dermal capillary bed. The readings are immediate and do correlate 100% with arterial values with almost no lag time. Because the sensor temp is low it can use the same site for days. These blisters take about 30 minutes to make, can be made anywhere on the body and in any size or shape. The domes may be left intact until needed. Once finished the site is covered with duoderm and heals in about 7 days. It sounds more gruesome than it is. The sensor causes no pain on the exposed skin and once covered with duoderm the healing site is also pain free. Yet, on intact skin, a knowledgeable RT can work very effectively with tc sensors.

GJ.. We are in agreement on the ABG issue. When I wrote "to follow" I meant "to accompany" as in follow along with. I did not mean that the data should be collected afterwards. My bad, that was ambiguous.

Regarding trans-q I do appreciate your concern for expenditure. With therapist driven protocols incorporating TCM therapies should be able to advance faster, safer and with way fewer ABG draws. Faster and clearer (and hopefully better) patient outcomes should allow for better allocation of manpower resources. You should get more and better therapy per FTE with less time wasted (especially on ABGs). Ideally it would be nice if TCM did not require Q4 relocation. There is a skin prep technique for mature skin that allows the sensors to be used at body temp that offers excellent response and near perfect arterial gas correlation. You can separate the epidermis from the dermis by creating an atraumatic suction blister. This is done by placing vacumm of less than one atmosphere on the skin the size of the sensor membrane and it makes a perfect sized water blister with no pain. You remove the blister dome and place the sensor calibrated to 37C directly on the dermal capillary bed. The response is immediate and arterial correlation is nearly exact. Because the sensor is at low temps this same site can be used for days. The blister take about 1/2 hour to make and the dome can be left intact until needed. The sensor can stay on as long as it's calibration can be trusted. It sound worse than it is. There's no pain with the sensor and the site is covered with duoderm after use. It heals in around 7 days.

Dave,
This blister needing tcm site sounds interesting, i'm not familar with it. Does anyone else have an opinion on it. Thanks Dave for the info.

GJ

In the early 80's I worked as a research associate developing the TCM combined O2/CO2 sensor subsequently released by Sensormedics (an as yet subsidiary of Beckman Inst.) Part of the grant goals for that project was to try and quantify the diffusive resistance of intact mature epidermis for oxygen. The idea was hoping to define a constant that could be used to correct PtcO2 data. We tried a number of invitro approaches without success. Then we found this blister technique in the dermatology arena. It allowed direct A to B comparison and met that research goal demonstrating that defining a constant was not possible.

The technique is referred to as "dermal windows". I presented a paper on this at the 82 (I think) AARC convention in New Orleans and its abstract is published the the RT journal for that meeting. It's entitled, "Transcutaneous gas monitoing through dermal windows in adults". It's under my name (Dave Tolle) in the RC journal archives. Beckman (later Sensormedics) was clearly aware of the method but felt it was too invasive for a product touted as non-invasive. That work ended and it was the end of the road for that lab, it's professor, etc... (He retired from academia). No follow up was done (that I know of) for using this method though I presented the paper several times. Insofar as I was concerned I knew enough about TCM to work it well without using this approach.

I've always felt that this technique had a lot of clinical potential in a number of ways. One thing we did not look at doing was measuring Ph along with the gases. It should work just as well. It's also possible that other indices could as well be dynamically measured in this way. Electrolytes, blood sugar, whatever substrate whose transducer can be miniaturized.

The technique is so simple. We made a small chamber with two ports and an opening the diameter of the sensor membrane. The chamber was heated using the same heat coil and thermister circuitry as the tc sensor (so the same heat controller would empower and manage it). You clean the skin and set this chamber on it with the same double adhesive used for the tc sensor. Through one port you draw a vacuum with a syringe and close it. The other port was attached to a manometer. Heat the chamber to 43.5C and in 30 minutes you have a perfectly shaped blister. The process tickles, if anything. You remove the blister dome and sop up the excess fluid. The sensor goes on without interface medium using the remaining fluid already there. The sensor reads instantly not needing to heat up skin to get gas out. The site is sensitive if left open. But covered with the sensor or duoderm and it's quite pain free. It's pretty neat stuff and I thought it well suited for elective surgeries where the blister could be made and held until needed providing pre, intra and post-op monitoring. It would also be grand in XRCIZ testing and eslewhere I'm sure.

Amen, brother.

ABG sampling like many other procedures we do can be over or under utilized. Some departments I know still do routine suctioning as well as routine neb tx. Some therapists are lazy and always find an excuse not to do ABGs. Others who are less confident in there clinical skills do way to many. I'm sure Jeff is right on the mark when he says number of ABGs dropped by 75% when taken out of the hands of RTs. I guess will have to wait and see if someone does a study to see if number of ABGs has any correlation to patient outcomes.
Patient driven protocols are great but in the end it's the RTs clinical skills that determine if it's required or not. An ABG is just a quick snapshot of the patient's condition at any given time of the day. You can teach anyone to do an ABG but determining when its required requires a bit more thought process. I just wonder what where going to do when Continuous arterial Blood Gas Monitoring becomes routine at the bedside. Will we all sit there with our fingers on the vent making adjustments to every increase or decrease in ABG parameters.
So to answer GJ question, yes I've worked in many departments where we basically called all the shots when it came to ventilation and ABGs. Some excelled in this environment and others did just enough to get through the shift. Not sure any protocol will ever find a solution but a good clinical supervisor in your unit always seems to work.