The American Heart Association just announced the new 2005 Guidelines for performing CPR. They now call for compression to ventilation ratio of 30:2, at a rate of 100 compressions per minute. Another new change is to deliver only a single initial shock. They further advise that no interruptions in chest compression should occur when ventilations are delivered. As a practical consequence, nobody will get ventilated very well. This frightening reality has so profoundly shocked and dismayed me, that I must take strong issue with these new changes.
Under these new guidelines the cardiac arrest patient will only have an opportunity to receive a breath every 18 seconds. Breathing only every 18 seconds (3.33 times per minute) is the same thing as dead, but wait – it gets worse. The new guidelines also call for shortening the inspiratory time to 1 second. In order to deliver enough volume to observe chest rise in an adult (particularly a large adult), one will need to deliver the ventilation using a higher flow rate then before when the inspiratory time advised was longer (1.5-2.0 seconds). To get the same amount of air in over a shorter time, you must blow or squeeze it in faster. It is these higher flow rates that are the cause of high airway pressures. It is the high airway pressures, above the opening pressure of the esophagus that causes air to go in the stomach.
Actually, the very first CPR standard I learned was a one second inspiratory time. Back in the days of the Cadillac, we used high flow demands valves and BVM’s to achieve chest rise in this short time. But many patients aspirated so the guidelines increased the inspiratory time and changed (slowed down) the flow rates, like the change on demand valves to 40 LPM from 100+ LPM. So I guess we have finally come full circle, back to the future of 1975. This is progress? But wait – it gets even worse still.
Most of the very best controlled ventilation devices such as pneumatic ventilators, resuscitators, and other ventilatory adjuncts, have a pressure relief safety valve. When a breath is introduced and compression occurs during the inspiratory phase of ventilation, expiratory pressures are usually well above 40 cm H2O (and can be more than twice that pressure). If the ventilation device has a pressure relief valve, the chest compressions will trigger the relief valve ending the ventilation cycle. Since these compressions are now delivered once every .6 seconds, the maximum potential tidal volume can be predicted. If ventilation is delivered at a controlled 40 LPM flow rate, the maximum tidal volume delivered will be less than 400 cc (40,000 cc flow divided by 60 seconds in a minute, times .6 seconds = 399.9 cc). Two 400 cc breaths 3.3 times a minute is virtually no support at all. This dismal minute volume (400 cc breath x 2 breaths per cycle, times 3.3 times per minute = 2,640 cc minute volume or 2.6 LPM) assumes the unlikely, that the first breath is perfectly synchronized, and the second of two sequential breaths will be the same tidal volume as the first. Even then, this is about the same resting minute volume as a small dog.
I can understand how much easier it will be to teach lay rescuers the new CPR. With compression/ventilation guidelines now the same for all age patients, it should be easier to teach. But the professionals in pre-hospital care will have to recertify using this same curriculum and for me, that’s a big problem. I’m asking all my EMS colleagues out there – Has anyone ever have had a clinical save when the scenario was something like the following?
Patient in arrest upon arrival with no or poor CPR for an estimated 3-5 minutes of reported down time. First series of shocks, no conversion. After a couple minutes of good CPR including proper oxygenation, combined with effective airway control (intubation) and a first round of cardiac drugs – on the next shock patient converts to viable rhythm.
I have seen this happen twice, both surviving to discharge. We got there and prepped the heart with oxygen and epinephrine, “got them pinked up good”, and then got a positive outcome. I invite every Paramedic and EMT who has ever experienced this sort of code to drop a note on this blog. If I’m right and I’m not the only Paramedic in the world that has had this experience – well then, these new AHA CPR Guidelines may insure that none of us ever have another one.
Once ALS has arrived and performed endotracheal intubation, the new guidelines do call for more breaths. They then want 8-10 ventilations per minute at low tidal volumes, over a short 1 second or less inspiratory time, with no pause in compressions. They call for a one second inspiratory time but when you do not pause your compressions for 1 second, you really only have a little more than half that much time (.6 seconds) to get your breath in.
These changes will also virtually assure that the only device left that you can use to ventilate is the Bag-Valve Mask. Again, right back to 1975. The Bag Valve Mask which has a long history of poor performance with high complication rates, and the Pocket Mask*, are the only ventilatory devices (in America) without a pressure relief safety valve. In other countries they do use adult BVM’s with a 40 cm pressure relief safety valve, and of course these won’t work well either under this new standard. Only a very simple non-pressure relieved device, will deliver any significant tidal volumes under these guidelines. You will need to force some air in during compressions to get enough in. All of the more modern ventilation devices have safety relief valves, which will limit the potential delivered volume to that described above.
Even the studies cited in the new guidelines cause me to question their conclusions. Please take the time to read them for yourself. One cited rationale for lowering tidal volume concluded, "When ventilating an unintubated patient in cardiac or respiratory arrest, smaller tidal volumes of 500 ml instead of 800–1200 ml may be beneficial to decrease peak airway pressure, and to minimise stomach inflation. The purpose was to determine the effects of small (500 ml) versus large (1000 ml) tidal volumes given with pediatric versus adult self-inflatable bags ". There was no control (or documentation of) inspiratory flow rates. To conclude that you will lower the potential for aspiration by using a pediatric bag is not rocket science – it is a predictable outcome. If you do not ventilate the patient, airway pressures will remain low.
To extrapolate this finding from only one type of device, and apply the conclusions to all other types of ventilatory devices does not make sense. The problem is with the Bag Valve Mask device and not the tidal volume; the BVM puts a lot of air in the stomach because the flow rates are uncontrolled and typically very high. Another cited study concluded "Studies of anesthetized patients with no advanced airway in place showed that ventilation with 455 ml of room air was associated with an acceptable but significantly reduced oxygen saturation when compared with 719 ml".
- So my question is how is a lower O2 saturation better?
Another cited reference concluded that, "A study of cardiac arrest patients compared tidal volumes of 500 versus 1000 ml delivered to patients with advanced airways during mechanical ventilation with 100% oxygen at a rate of 12/min. Smaller tidal volumes were associated with higher arterial PCO2 and worse acidosis but no differences in PaO2."
So my next question is how is higher PCO2 and worsening acidosis better?
As a real expert on ventilation put it to me in a recent e-mail,
"What concerns me even more than the O2 issues is the CO2 issue. Experience has proven it is not that difficult to oxygenate patients, even with low Vt’s (tidal volumes). It is substantially more difficult to blow off the poisoning gas CO2, with all it’s negative cardiovascular effects. CO2 builds up with effective compressions and inadequate ventilation. I am curious how much thought has been given to that." KW
I worry that this general de-emphasis on ventilation will result in poor ventilatory performance on not just CPR patients, but more importantly on simple respiratory arrests with a very high potential for survival. Teaching that less tidal volume, short inspiratory times, and high flow rates are better, can only have one outcome. We might as well just put a pillow over their face.
So I guess we should just throw out the last 20 years of clinical advancements in emergency ventilation technology. Let’s try to forget about how important the drug oxygen is to a starved myocardium and dying brain. All we will have to left to ventilate with now are medical antiques. Get used to it, or get ready for the fight of your life. Me, I’m Ready to Roll. Today’s blog entry is just a warm up.
* You could use a pocket mask, but under these new Guidelines I doubt you will do it more than once. I hold the US Patent on the first disposable one-way non-rebreathing CPR valve. I learned a few hard lessons along the way to its final development. The one everybody needs to know about now is that disposable one-way non-rebreathing valves will fail when forced expiration occurs during the inspiratory or ventilation phase, driven by the high pressures generated during chest compression. Usually, most rescuers pause just long enough for the valve to move to the expiratory position. But with a high rate of compression and/or no pause you will learn that while the valve is open to the patient – exhaled gas from the patient can be pushed into your mouth. These inexpensive valves simply cannot handle the sudden flow direction change at high pressures. Fun, eh?