In this blog "the diary of a compulsive learner" is focussing on why our capnograph is so important at detecting decreased cardiac output; cardiac arrest, assessing compressions and return of spontaneous circulation.
What is End tidal Capnography (ETCO2)?
Its a quantitate measurement of our patients exhaled carbon dioxide, which is the bi-product of cellular metabolism.
In the body our patients cells use oxygen which creates carbon dioxide (CO2). The body requires adequate cardiac output (a working pump) to pump the CO2 back to the lungs so it can be exhaled and measured.
You can think of it as the exhaust of a car, the car is filled up with fuel(oxygen), the engine (heart) uses the fuel and pushes out the exhaust (CO2).
When we get our cars assessed for level of emissions, the garage will measure the exhaust to see if there is a problem with the engine. This is similar to what we are doing when we measure end tidal CO2 in our patients.
In veterinary practice the most common way we use our capnographs is to assess our patients ventilation status in spontaneously breathing animals, monitor for equipment errors and manage mechanical ventilator settings. Our normal ETCO2 being between 35-45mmHg for dogs and 28-35mmHg for cats.
Why should we be using our capnographs in cardiac arrest?
During cardiac arrest our capnographs can be used to help us assess the function of the heart. It can also help us determine the effectiveness of our cardiac compressions if the heart fails and if we achieve return of spontaneous circulation.
1. Loss of ETCO2 may be the first sign the CPR is required
Capnography is the most reliable monitoring device that we can use to detect loss of circulation. As soon as there is a reduction in cardiac output the ETCO2 will start to decrease; if the heart stops, the capnography waveform will disappear altogether and the ETCO2 reading will change to zero. This is even true for patients receiving positive pressure ventilation.
2. ETCO2 enables us to assess quality of chest compressions
Consistent, uninterrupted high quality chest compressions are essential for successful cardiac arrest resuscitation and should be delivered at a rate of 100-120/min with a 1:1 compression to relaxation ratio. The thorax should be compressed to 1/3rd of its width ensuring total recoil is achieved between compressions to allow refilling of the great vessels in the heart.
ETCO2 provides feedback on how effective compressions are at perfusing vital organs.
A higher ETCO2 reading during resuscitation correlates with improved cardiac output and patient outcomes. An ETCO2 reading above 15 mmHG indicates compressions are generating perfusion. The higher the ETCO2, the better the perfusion generated by CPR, and the better the chances of survival are.
Low ETCO2 (below 10 mmHG) may be due to poor compression technique, or from low perfusion and metabolism despite good compressions.
Want to know more about capnography?
Why not book an in-house CPD session that your whole team can enjoy?
3. Waveform capnography confirms airway placement and helps guide ventilation rates.
The presence of a capnography trace will help to confirm correct endotracheal intubation.
Excessive positive pressure ventilation frequently occurs during resuscitation and is extremely harmful. Each time positive pressure ventilation is on board the intrathoracic pressure increases resulting in a reduction of venous return to the heart which reduces CO² and a reduction in cerebral and coronary perfusion. Hyperventilation also causes vasoconstriction and decreased perfusion to the brain.
The RECOVER guidelines recommend a ventilatory rate of < 10–12bpm, these lower ventilation rates and are an essential part of the guidelines. Care should be taken not to over-ventilate the patient by squeezing slowly, over one second, and only enough tidal volume should be delivered to make the chest rise. Timing ventilation can be difficult under stress during resuscitation, and when applied, waveform capnography has been shown to reduce the incidence of patient hyperventilation.
4. Capnography helps determine when to terminate resuscitation or when to continue.
ETCO2 can help the veterinary team determine whether to continue with resuscitation.
In patients receiving high-quality chest compressions, who have a patent airway, a persistent ETCO2 reading below 10 mmHG after 20 minutes of resuscitation is an indication to terminate efforts.
A high ETCO2 shows that CPR is providing effective circulation to vital organs whilst appropriate treatment is initiated.
Data from the human side shows an ETCO2 reading above 15 mmHG, or one that increases from baseline, is an indication to continue resuscitation efforts.
5. An increase in your ETCO2 reading is a good sign of ROSC. A drop in ETCO2 is an indication of loss of cardiac resuscitation.
A sudden increase in ETCO2 is often the first sign of return of spontaneous circulation (ROSC), this is because impaired circulation during arrest causes CO2 to build up in the bloodstream and is pushed out of the lungs.
Patients with ROSC are at high risk for rearrest, especially in the first 10 minutes, a steady decline in ETCO2 indicates that CPR may soon be needed, or that a vasopressor is needed to support blood pressure.
If the ETCO2 is abruptly lost, it may be caused by rearrest or displacement of the airway. First check a pulse, and then confirm airway placement.
Waveform capnography provides information about both circulation and ventilation before, during, and after cardiac arrest. If we can use capnography early in resuscitation, we can apply the information it provides to clinical decisions.
We'd love you to join us for our webinar Getting to grips with capnography on 24th October 2018. Click here if you'd like to register
1. Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiac life support: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S729-S767.
2. Davis DP, Dunford JV, Ochs M, et al. The use of quantitative end-tidal capnometry to avoid inadvertent severe hyperventilation in patients with head injury after paramedic rapid sequence intubation. J Trauma 2004; 56(4):808-814, Apr 2004.
3. Davis J. Extended resuscitation improves outcomes. MedicCast (podcast) episode 438. Retrieved from: http://www.mediccast.com/blog/2015/06/01/extended-resuscitation-improves-outcomes/
4. White RD, Goodman BW, Svoboda MA. Neurologic recovery following prolonged out-of-hospital cardiac arrest with resuscitation guided by continuous capnography. Mayo Clinic Proceedings 2011; 86 (6): 544-548.
5.Peberdy MA, Callaway CW, Neumar RW, et al. Part 9: post-cardiac care: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation 2010; 122 (suppl 3): S768-S786.