A recent study by Segond et al. reviewed in Literature Rounds here, showed worse outcomes with continuous insufflation of oxygen (CIO) via a Boussignac insufflation device, compared with intermittent positive-pressure ventilation with BVM during conventional CPR.
This is the review of an editorial on that study. I have presented it as a review of 'How does each breath we deliver duting CPR affects survival'
THE EDITORIAL
Lurie K. Editorial: Pressurizing the lungs during cardiopulmonary resuscitation: a matter of life and breath. Resuscitation 225(2026)111134
The breath we deliver during CPR is not just about oxygenation, it's also about ventilation ie., CO2 clearance and the affects on circulation. Small pressure changes in the lungs can have significant flow-on physiological effects, especially in terms of cerebral perfusion pressure..
The Agonal Gasp
Let's start with what our own physiology does, to try and keep us alive during cardiac arrest; The agonal gasp.
The agonal gasp is an involuntary reflex, where the patient makes sudden involuntary gasping, gurgling or snorting-like sounds. Gasping for air.
Gasping results in negative intrathoracic pressure, and is assoicated with improved survival and improved neurological outcomes in cardiac arrest.
It results in:
↑ venous return → ↑ right-heart filling → ↓ ICP → ↑ systemic and cerebral perfusion
What happens during CPR?
We know the difference between low flow and no flow. No flow is when we do nothing. Low flow is when we are performing chest compressions. It's low, because at best we are able to re-establish 30-50% of normal flow.
During a normal duty cycle of chest compression, when we allow the chest to recoil, it results in negative intrathoracic pressure which draws venous blood back into the thorax and back to the heart.
Chest compressions also affect intracranial pressure (ICP), which rises with chest compression and falls during decompression.
The cerebral perfusion pressure(CPP) is dependent on ICP by the relationship CPP = arterial pressure − ICP
We can see that if we have a low arterial pressure which occurs in the low flow state, any increase in ICP can affect the CPP.
Factors that may exacerbate this include:
- hyperventilation and/or excessive tidal volumes
- Increased intrathoracic pressure from overinsufflation of the lungs, decreases venous return to the heart and thus decreases cardiac output.
- incomplete chest recoil
- decreases the negative intrathoracic pressure genrated by chest recoil
- ↓ systemic venous return
- ↓ right-heart filling
- ↓ cardiac preload during recoil
- ↑ right-sided venous pressure
- ↑ cerebral venous congestion
- ↑ intracranial pressure (ICP)
- ↓ coronary and cerebral perfusion
- sustained positive intrathoracic pressure
- This relates to devices such as the Boussignac insufflation device, which increase intrathoracic pressure and thus decrease venous return to the heart.
- It also relates to the valveless paravertebral venous plexus connecting the abdomen and thorax with the spinal canal and cranial vault, transmitting increased thoracic pressure to the intracranial compartment.
- abdominal pressure and head-down positioning.
Why continuous lung pressurisation such as with a Boussignac insufflation device may be harmful
Continuous oxygen insufflation produces sustained positive intrathoracic pressure during both compression and decompression.
Normally, chest recoil creates a relative negative intrathoracic pressure that helps draw venous blood back into the thorax. Sustained positive pressure can blunt this effect, leading to:
- ↓ systemic venous return
- ↓ right-heart filling
- ↓ cardiac preload during recoil
- ↑ right-sided venous pressure
- ↑ cerebral venous congestion
- ↑ intracranial pressure (ICP)
- ↓ coronary and cerebral perfusion
Lokking at this closely, it is the opposite of the agonal gasp.
What we should aim for during CPR, to maximise its effectiveness.
We should aim to maximise venous return and minimise increases in intrathoracic and intracranial pressure:
- Allow complete chest recoil.
- Avoid excessive compression rates and force.
- Avoid hyperventilation.
- Avoid excessive tidal volumes.
- Consider active compression–decompression CPR where appropriate.
- Consider an impedance threshold device in appropriate systems.
- In selected settings, gradual head-and-thorax elevation while maintaining forward blood flow may improve cerebral perfusion.
These approaches potentially work synergistically to improve venous return and cerebral perfusion.
What does this mean for our CPR practice?
We need to pay as much attention to our ventilation practice as we do to our chest compressions. Ventilation during CPR is not just about oxygenation, its also about circulation.
- Don't hyperventilate.
- Don't overinflate the lungs.
- Allow complete chest recoil.
- Minimise unnecessary positive intrathoracic pressure.
Continuous oxygen delivery such as with Boussignac insufflation device, may not be physiologically benign because they can result in increased intrathoracic pressure, negating the results of chest recoil and decreasing venous return to the heart. It has not been shown to be effective.
Although the Segond study was a registry based study with obvious limitations, discussed in the review, it's findings are important: continuous low-flow oxygen insufflation during conventional CPR may actually be harmful.
Important other literature to read
- Aufderheide TP, Lurie KG. Death by hyperventilation: a common and life-threatening problem during cardiopulmonary resuscitation. Crit Care Med 2004;32(9 Suppl):S345–51. PMID: 15508657.
- Moore JC, et al. Evaluation of the Boussignac cardiac arrest device (B-card) during cardiopulmonary resuscitation in an animal model. Resuscitation 2017;119:81–8. PMID: 28800887.
- Greif R, et al. 2024 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations: summary from the Basic Life Support ; Advanced Life Support; Pediatric Life Support; Neonatal Life Support; Education, Implementation, and Teams; and First Aid Task Forces. Circulation 2024;150(24).
