question: Why is it that you breathe into someone’s mouth during CPR, but we exhale carbon dioxide which is something humans shouldn’t inhale?
comment: First, our lungs don't absorb 100% of the oxygen in one breath; there's plenty of oxygen left in your breath when you breathe and exhale normally. So the idea was that, even though there's some CO2 from your breath, there's also quite a bit of oxygen and you're getting it into the other person's lungs. And second, as of a few years ago, the [recommended CPR technique]( URL_0 ) is to skip the mouth-to-mouth and just do chest compressions. The ribs kinda get some air into the lungs by themselves, and it's actually more important to get whatever amount of blood to the brain you can (by compressing the chest).
passages: Normal atmospheric air contains approximately 21% oxygen when inhaled in. After gaseous exchange has taken place in the lungs, with waste products (notably carbon dioxide) moved from the bloodstream to the lungs, the air being exhaled by humans normally contains around 17% oxygen. This means that the human body utilises only around 19% of the oxygen inhaled, leaving over 80% of the oxygen available in the exhalatory breath.
  
  This means that there is more than enough residual oxygen to be used in the lungs of the patient, which then enters the blood.
  
  Section::::Oxygen.
   Once the airway has been opened, the first aider would assess to see if the patient is breathing. If there is no breathing, or the patient is not breathing normally, such as agonal breathing, the first aider would undertake what is probably the most recognized first aid procedure—CPR, which involves breathing for the patient, and manually massaging the heart to promote blood flow around the body.
   The CPR mask is the preferred method of ventilating a patient when only one rescuer is available. Many feature 18mm inlets to support supplemental oxygen, which increases the oxygen being delivered from the approximate 17% available in the expired air of the rescuer to around 40-50%.
  
  Section::::Efficiency of mouth-to-patient insufflation.
   In the unconscious patient, after the airway is opened the next area to assess is the patient's breathing, primarily to find if the patient is making normal respiratory efforts. Normal breathing rates are between 12 and 20 breaths per minute, and if a patient is breathing below the minimum rate, then in current ILCOR basic life support protocols, CPR should be considered, although professional rescuers may have their own protocols to follow, such as artificial respiration.
   Pulmonary ventilation (and hence external respiration) is achieved through manual insufflation of the lungs either by the rescuer blowing into the patient's lungs, or by using a mechanical device to do so. This method of insufflation has been proved more effective than methods which involve mechanical manipulation of the patient's chest or arms, such as the Silvester method. It is also known as expired air resuscitation (EAR), expired air ventilation (EAV), rescue breathing, or colloquially the kiss of life. It was introduced as a life saving measure in 1950.
   Airway, breathing, and circulation, therefore work in a cascade; if the patient's airway is blocked, breathing will not be possible, and oxygen cannot reach the lungs and be transported around the body in the blood, which will result in hypoxia and cardiac arrest. Ensuring a clear airway is therefore the first step in treating any patient; once it is established that a patient's airway is clear, rescuers must evaluate a patient's breathing, as many other things besides a blockage of the airway could lead to an absence of breathing.
  
  Section::::Medical use.:CPR.
   Mouth-to-mouth resuscitation is also part of cardiopulmonary resuscitation (CPR) making it an essential skill for first aid. In some situations, mouth to mouth is also performed separately, for instance in near-drowning and opiate overdoses. The performance of mouth to mouth in its own is now limited in most protocols to health professionals, whereas lay first aiders are advised to undertake full CPR in any case where the patient is not breathing sufficiently.
  
  Section::::Types.:Mechanical ventilation.
   PAP ventilation is often used for patients who have acute type 1 or 2 respiratory failure. Usually PAP ventilation will be reserved for the subset of patients for whom oxygen delivered via a face mask is deemed insufficient or deleterious to health (see CO retention). Usually, patients on PAP ventilation will be closely monitored in an intensive care unit, high-dependency unit, coronary care unit or specialist respiratory unit.
   This may be compared with some applications of open-circuit breathing apparatus:
  
  BULLET::::- The oxygen enrichment systems primarily used by medical patients, high altitude mountaineers and commercial aircraft emergency systems, in which the user breathes ambient air which is enriched by the addition of pure oxygen,
  
  BULLET::::- Open circuit breathing apparatus used by firefighters, underwater divers and some mountaineers, which supplies fresh gas for each breath, which is then discharged into the environment.
  
  BULLET::::- Gas masks and respirators which filter contaminants from ambient air which is then breathed.
   The AHA also notes in their new guidelines that capnography, which indirectly measures cardiac output, can also be used to monitor the effectiveness of CPR and as an early indication of return of spontaneous circulation (ROSC). Studies have shown that when a person doing CPR tires, the patient's end-tidal (ETCO2, the level of carbon dioxide released at the end of expiration) falls, and then rises when a fresh rescuer takes over. Other studies have shown when a patient experiences return of spontaneous circulation, the first indication is often a sudden rise in the ETCO2 as the rush of circulation washes untransported from the tissues. Likewise, a sudden drop in ETCO2 may indicate the patient has lost pulses and CPR may need to be initiated.
   Partial rebreather masks are designed to capture the first 150ml of the exhaled breath into the reservoir bag for inhalation during the subsequent breath. This portion of the breath was initially delivered at the end of inhalation and was therefore delivered to the "deadspace" anatomy where gas exchange did not occur. Therefore, there would be no depletion of oxygen nor gain of carbon dioxide during the rebreathing component.
  
  Section::::Usage.
   As a person breathes, the body consumes oxygen and produces carbon dioxide. Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal atmospheric pressure, or about 20% of the available oxygen in the air at sea level. Exhaled air at sea level contains roughly 13.5% to 16% oxygen.
   If the patient is unresponsive and not breathing, the responder begins CPR with chest compressions at a rate of 120 beats per minute in cycles of 30 chest compressions to 2 breaths. If responders are unwilling or unable to perform rescue breathing, they are to perform compression-only CPR, because any attempt at resuscitation is better than no attempt. For children, for whom the main cause of cardiac arrest is from breathing related issues, 5 initial rescue breaths is highly advised followed by the same 30-2 cycles.
  
  Section::::United States.:BLS for Healthcare Providers Course.
   The non-rebreather mask covers both the nose and mouth of the patient and attaches with the use of an elastic cord around the patient's head. The NRB has an attached reservoir bag, typically 1 liter, that connects to an external oxygen tank or Bulk Oxygen Supply system. Before an NRB is placed on the patient, the reservoir bag is inflated to greater than two-thirds full of oxygen, at a rate of 15 liters per minute (lpm). Approximately ¹⁄₃ of the air from the reservoir is depleted as the patient inhales, and it is then replaced by the flow from the O supply. If the bag becomes completely deflated, the patient will no longer have a source of air to breathe.
   During an avalanche burial, victims not killed by trauma usually suffer from asphyxiation as the snow around them melts from the heat of the victim's breath and then refreezes, disallowing oxygen flow to the victim and allowing toxic levels of CO to accumulate. The Avalung ameliorates this situation by drawing breath over a large surface area in front and pushing the warm exhaled carbon dioxide behind. This buys additional time for rescuers to dig the victim out.
  
  Section::::Search and rescue equipment.:Avalanche airbags.
   Section::::Types.
  
  Section::::Types.:Manual methods.
  
  Pulmonary anton ventilation (and hence external parts of respiration) is achieved through manual insufflation of the lungs either by the rescuer blowing into the patient's lungs (mouth-to-mouth resuscitation), or by using a mechanical device to do so. This method of insufflation has been proved more effective than methods which involve mechanical manipulation of the patient's chest or arms, such as the Silvester method.
   BULLET::::- In the anime series "Aldnoah.Zero" (2014-2015), episode 5 shows that Slaine Troyard was in a liquid-filled capsule when he crashed. Princess Asseylum witnessed the crash, helped him to get out of the capsule, then used CPR on him to draw out the liquid from his lungs.
  
  Section::::Examples in fiction.:Video games.
  
  BULLET::::- In the classic 1995 PC turn-based strategy game "", "Aquanauts" fighting in deep ocean conditions breathe a dense oxygen-carrying fluid.
   Carbon dioxide is not expelled completely when the diver exhales into apparatus with mechanical dead space, such as a long snorkel, full face diving mask, or diving helmet, and then inhales from the dead space.
   The purpose of cardiopulmonary resuscitation (CPR) during cardiac arrest is ideally reversal of the clinically dead state by restoration of blood circulation and breathing. However, there is great variation in the effectiveness of CPR for this purpose. Blood pressure is very low during manual CPR, resulting in only a ten-minute average extension of survival. Yet there are cases of patients regaining consciousness during CPR while still in full cardiac arrest. In absence of cerebral function monitoring or frank return to consciousness, the neurological status of patients undergoing CPR is intrinsically uncertain. It is somewhere between the state of clinical death and a normal functioning state.
   However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of hypercapnia, or carbon dioxide toxicity. 
   Section::::Insufflations.
  
  Insufflation, also known as 'rescue breaths' or 'ventilations', is the act of mechanically forcing air into a patient's respiratory system. This can be achieved via a number of methods, which will depend on the situation and equipment available. All methods require good airway management to perform, which ensures that the method is effective. These methods include:
  
  BULLET::::- Mouth-to-mouth - This involves the rescuer making a seal between his or her mouth and the patient's mouth and 'blowing', to pass air into the patient's body
   Either a bag valve mask or an advanced airway may be used to help with breathing. High levels of oxygen are generally given during CPR. Tracheal intubation has not been found to improve survival rates or neurological outcome in cardiac arrest and in the prehospital environment may worsen it. Endotracheal tube and supraglottic airways appear equally useful. When done by EMS 30 compressions followed by two breaths appear better than continuous chest compressions and breaths being given while compressions are ongoing.
   CPR involves chest compressions for adults between and deep and at a rate of at least 100 to 120 per minute. The rescuer may also provide artificial ventilation by either exhaling air into the subject's mouth or nose (mouth-to-mouth resuscitation) or using a device that pushes air into the subject's lungs (mechanical ventilation). Current recommendations place emphasis on early and high-quality chest compressions over artificial ventilation; a simplified CPR method involving chest compressions only is recommended for untrained rescuers. In children, however, only doing compressions may result in worse outcomes, because in children the problem normally arises from a respiratory, rather than cardiac problem. Chest compression to breathing ratios is set at 30 to 2 in adults.
   It is only as a result of accurately maintaining the composition of the 3 liters of alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation, respiration will be slowed down or halted until the alveolar partial pressure of carbon dioxide has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide “waste”. The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body’s extracellular fluid carbon dioxide and pH homeostats
   Rescuers are often warned against mistaking agonal breathing, which is a series of noisy gasps occurring in around 40% of cardiac arrest victims, for normal breathing.
  
  If a patient is breathing, then the rescuer will continue with the treatment indicated for an unconscious but breathing patient, which may include interventions such as the recovery position and summoning an ambulance.
  
  Section::::Breathing.:Conscious or breathing patients.
  
presuppositions: Carbon dioxide inhalation is harmful to humans during CPR. When you breathe out, you are only breathing out CO2.
corrections: Carbon dioxide inhalation is of small amount during CPR because there's also quite a bit of oxygen from the other person's lungs. There's plenty of oxygen left in your breath when you exhale.
raw_presuppositions: Carbon dioxide inhalation is harmful to humans during CPR. When you breathe out, you are only breathing out CO2.
raw_corrections: Carbon dioxide inhalation is of small amount during CPR because there's also quite a bit of oxygen from the other person's lungs. There's plenty of oxygen left in your breath when you exhale.