Perinatal asphyxia is the medical condition resulting from deprivation of oxygen (hypoxia) to a newborn infant long enough to cause apparent harm. It results most commonly from a drop in maternal blood pressure or interference during delivery with blood flow to the infant's brain. This can occur as a result of inadequate circulation or perfusion, impaired respiratory effort, or inadequate ventilation. There has long been a scientific debate over whether newborn infants with asphyxia should be resuscitated with 100% oxygen or normal air. It has been demonstrated that high concentrations of oxygen lead to generation of oxygen free radicals, which have a role in reperfusion injury after asphyxia. Research by Ola Didrik Saugstad and others led to new international guidelines on newborn resuscitation in 2010, recommending the use of normal air instead of 100% oxygen.

Compressive asphyxia (also called chest compression) is mechanically limiting expansion of the lungs by compressing the torso, hence interfering with breathing. Compressive asphyxia occurs when the chest or abdomen is compressed posteriorly. In accidents, the term traumatic asphyxia or crush asphyxia usually refers to compressive asphyxia resulting from being crushed or pinned under a large weight or force. An example of traumatic asphyxia includes cases where an individual has been using a car-jack to repair a car from below, and is crushed under the weight of the vehicle. Pythons, anacondas, and other constrictor snakes kill through compressive asphyxia. In cases of co-sleeping ("overlay"), the weight of an adult or large child may compress an infant's chest, preventing proper expansion of the chest. Risk factors include large or obese adults, parental fatigue or impairment (sedation by drugs or alcohol) of the co-sleeping adult and a small shared sleeping space (for example, both adult and infant sharing a couch).

In fatal crowd disasters, compressive asphyxia from being crushed against the crowd causes the large part of the deaths, rather than blunt trauma from trampling. This is what occurred at the Ibrox disaster in 1971, where 66 Rangers fans died; the 1979 The Who concert disaster where 11 died; the Luzhniki disaster in 1982, when 66 FC Spartak Moscow fans died; and at the Hillsborough disaster in 1989, when 96 Liverpool fans were crushed to death in an overcrowded terrace. In confined spaces, people push and lean against each other; evidence from bent steel railings in several fatal crowd accidents have shown horizontal forces over 4500 N (equivalent to a weight of approximately 450 kg, or 1014 lbs). In cases where people have stacked up on each other forming a human pile, estimations have been made of around 380 kg (838 lbs) of compressive weight in the lowest layer.

"Positional" or "restraint" asphyxia is when a person is restrained and left alone prone, such as in a police vehicle, and is unable to reposition himself or herself in order to breathe. The death can be in the vehicle, or following loss of consciousness to be followed by death while in a coma, having presented with anoxic brain damage. The asphyxia can be caused by facial compression, neck compression, or chest compression. This occurs mostly during restraint and handcuffing situations by law enforcement, including psychiatric incidents. The weight of the restraint(s) doing the compression may contribute to what is attributed to positional asphyxia. Therefore, passive deaths following custody restraint that are presumed to be the result of positional asphyxia may actually be examples of asphyxia occurring during the restraint process.

Chest compression is also featured in various grappling combat sports, where it is sometimes called wringing. Such techniques are used either to tire the opponent or as complementary or distractive moves in combination with pinning holds, or sometimes even as submission holds. Examples of chest compression include the knee-on-stomach position; or techniques such as leg scissors (also referred to as body scissors and in budō referred to as "do-jime"; 胴絞, "trunk strangle" or "body triangle") where a participant wraps his or her legs around the opponent's midsection and squeezes them together.

Pressing is a form of torture or execution that works through asphyxia e.g. burking.

Administration of oxygen at 15 litres per minute by face mask or bag valve mask is often sufficient, but tracheal intubation with mechanical ventilation may be necessary. Suctioning of pulmonary oedema fluid should be balanced against the need for oxygenation. The target of ventilation is to achieve 92% to 96% arterial saturation and adequate chest rise. Positive end-expiratory pressure will generally improve oxygenation. Drug administration via peripheral veins is preferred over endotracheal administration. Hypotension remaining after oxygenation may be treated by rapid crystalloid infusion. Cardiac arrest in drowning usually presents as asystole or pulseless electrical activity. Ventricular fibrillation is more likely to be associated with complications of pre-existing coronary artery disease, severe hypothermia, or the use of epinephrine or norepinephrine.

Drowning victims who arrive at a hospital with spontaneous circulation and breathing usually recover with good outcomes. Early provision of basic and advanced life support improve probability of positive outcome.

Longer duration of submersion is associated with lower probability of survival and higher probability of permanent neurological damage.

Contaminants in the water can cause bronchospasm and impaired gas exchange, and can cause secondary infection with delayed severe respiratory compromise.

Low water temperature can cause ventricular fibrillation, but hypothermia during immersion can also slow the metabolism, allowing a longer hypoxia before severe damage occurs. Hypothermia which reduces brain temperature significantly can improve outcome. A reduction of brain temperature by 10 °C decreases ATP consumption by approximately 50%, which can double the time that the brain can survive.

The younger the victim, the better the chances of survival. In one case, a child submerged in cold () water for 66 minutes was resuscitated without apparent neurological damage. However, over the long term significant deficits were noted, including a range of cognitive difficulties, particularly general memory impairment, although recent magnetic resonance imaging (MRI) and magnetoencephalography (MEG) were within normal range.

Mild and moderate cerebral hypoxia generally has no impact beyond the episode of hypoxia; on the other hand, the outcome of severe cerebral hypoxia will depend on the success of damage control, amount of brain tissue deprived of oxygen, and the speed with which oxygen was restored.

If cerebral hypoxia was localized to a specific part of the brain, brain damage will be localized to that region. A general consequence may be epilepsy. The long-term effects will depend on the purpose of that portion of the brain. Damage to the Broca's area and the Wernicke's area of the brain (left side) typically causes problems with speech and language. Damage to the right side of the brain may interfere with the ability to express emotions or interpret what one sees. Damage on either side can cause paralysis of the opposite side of the body.

The effects of certain kinds of severe generalized hypoxias may take time to develop. For example, the long-term effects of serious carbon monoxide poisoning usually may take several weeks to appear. Recent research suggests this may be due to an autoimmune response caused by carbon monoxide-induced changes in the myelin sheath surrounding neurons.

If hypoxia results in coma, the length of unconsciousness is often indicative of long-term damage. In some cases coma can give the brain an opportunity to heal and regenerate, but, in general, the longer a coma, the greater the likelihood that the person will remain in a vegetative state until death. Even if the patient wakes up, brain damage is likely to be significant enough to prevent a return to normal functioning.

Long-term comas can have a significant impact on a patient's families. Families of coma victims often have idealized images of the outcome based on Hollywood movie depictions of coma. Adjusting to the realities of ventilators, feeding tubes, bedsores, and muscle wasting may be difficult. Treatment decision often involve complex ethical choices and can strain family dynamics.

To counter the effects of high-altitude diseases, the body must return arterial p toward normal. Acclimatization, the means by which the body adapts to higher altitudes, only partially restores p to standard levels. Hyperventilation, the body’s most common response to high-altitude conditions, increases alveolar p by raising the depth and rate of breathing. However, while p does improve with hyperventilation, it does not return to normal. Studies of miners and astronomers working at 3000 meters and above show improved alveolar p with full acclimatization, yet the p level remains equal to or even below the threshold for continuous oxygen therapy for patients with chronic obstructive pulmonary disease (COPD). In addition, there are complications involved with acclimatization. Polycythemia, in which the body increases the number of red blood cells in circulation, thickens the blood, raising the danger that the heart can’t pump it.

In high-altitude conditions, only oxygen enrichment can counteract the effects of hypoxia. By increasing the concentration of oxygen in the air, the effects of lower barometric pressure are countered and the level of arterial p is restored toward normal capacity. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 4000 m, raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an altitude equivalent of 3000 m, which is much more tolerable for the increasing number of low-landers who work in high altitude. In a study of astronomers working in Chile at 5050 m, oxygen concentrators increased the level of oxygen concentration by almost 30 percent (that is, from 21 percent to 27 percent). This resulted in increased worker productivity, less fatigue, and improved sleep.

Oxygen concentrators are uniquely suited for this purpose. They require little maintenance and electricity, provide a constant source of oxygen, and eliminate the expensive, and often dangerous, task of transporting oxygen cylinders to remote areas. Offices and housing already have climate-controlled rooms, in which temperature and humidity are kept at a constant level. Oxygen can be added to this system easily and relatively cheaply.

A prescription renewal for home oxygen following hospitalization requires an assessment of the patient for ongoing hypoxemia.

Treatment of infants suffering birth asphyxia by lowering the core body temperature is now known to be an effective therapy to reduce mortality and improve neurological outcome in survivors, and hypothermia therapy for neonatal encephalopathy begun within 6 hours of birth significantly increases the chance of normal survival in affected infants.

There has long been a debate over whether newborn infants with birth asphyxia should be resuscitated with 100% oxygen or normal air. It has been demonstrated that high concentrations of oxygen lead to generation of oxygen free radicals, which have a role in reperfusion injury after asphyxia. Research by Ola Didrik Saugstad and others led to new international guidelines on newborn resuscitation in 2010, recommending the use of normal air instead of 100% oxygen.

IH/BA is also a causitive factor in cardiac and circulatory birth defects the sixth most expensive condition, as well as premature birth and low birth weight the second most expensive and it is one of the contributing factors to infant respiratory distress syndrome (RDS) also known as hyaline membrane disease, the most expensive medical condition to treat and the number one cause of infant mortality.

For newborn infants starved of oxygen during birth there is now evidence that hypothermia therapy for neonatal encephalopathy applied within 6 hours of cerebral hypoxia effectively improves survival and neurological outcome. In adults, however, the evidence is less convincing and the first goal of treatment is to restore oxygen to the brain. The method of restoration depends on the cause of the hypoxia. For mild-to-moderate cases of hypoxia, removal of the cause of hypoxia may be sufficient. Inhaled oxygen may also be provided. In severe cases treatment may also involve life support and damage control measures.

A deep coma will interfere with body's breathing reflexes even after the initial cause of hypoxia has been dealt with; mechanical ventilation may be required. Additionally, severe cerebral hypoxia causes an elevated heart rate, and in extreme cases the heart may tire and stop pumping. CPR, defibrilation, epinephrine, and atropine may all be tried in an effort to get the heart to resume pumping. Severe cerebral hypoxia can also cause seizures, which put the patient at risk of self-injury, and various anti-convulsant drugs may need to be administered before treatment.

There has long been a debate over whether newborn infants with cerebral hypoxia should be resuscitated with 100% oxygen or normal air. It has been demonstrated that high concentrations of oxygen lead to generation of oxygen free radicals, which have a role in reperfusion injury after asphyxia. Research by Ola Didrik Saugstad and others led to new international guidelines on newborn resuscitation in 2010, recommending the use of normal air instead of 100% oxygen.

Brain damage can occur both during and after oxygen deprivation. During oxygen deprivation, cells die due to an increasing acidity in the brain tissue (acidosis). Additionally, during the period of oxygen deprivation, materials that can easily create free radicals build up. When oxygen enters the tissue these materials interact with oxygen to create high levels of oxidants. Oxidants interfere with the normal brain chemistry and cause further damage (this is known as "reperfusion injury").

Techniques for preventing damage to brain cells are an area of ongoing research. Hypothermia therapy for neonatal encephalopathy is the only evidence-supported therapy, but antioxidant drugs, control of blood glucose levels, and hemodilution (thinning of the blood) coupled with drug-induced hypertension are some treatment techniques currently under investigation. Hyperbaric oxygen therapy is being evaluated with the reduction in total and myocardial creatine phosphokinase levels showing a possible reduction in the overall systemic inflammatory process.

In severe cases it is extremely important to act quickly. Brain cells are very sensitive to reduced oxygen levels. Once deprived of oxygen they will begin to die off within five minutes.

When the pulmonary capillary pressure remains elevated chronically (for at least 2 weeks), the lungs become even more resistant to pulmonary edema because the lymph vessels expand greatly, increasing their capability of carrying fluid away from the interstitial spaces perhaps as much as 10-fold. Therefore, in patients with chronic mitral stenosis, pulmonary capillary pressures of 40 to 45 mm Hg have been measured without the development of lethal pulmonary edema.[Guytun and Hall physiology]

Hypoxia exists when there is a reduced amount of oxygen in the tissues of the body. Hypoxemia refers to a reduction in PO2 below the normal range, regardless of whether gas exchange is impaired in the lung, CaO2 is adequate, or tissue hypoxia exists. There are several potential physiologic mechanisms for hypoxemia, but in patients with COPD the predominant one is V/Q mismatching, with or without alveolar hypoventilation, as indicated by PaCO2. Hypoxemia caused by V/Q mismatching as seen in COPD is relatively easy to correct, so that only comparatively small amounts of supplemental oxygen (less than 3 L/min for the majority of patients) are required for LTOT. Although hypoxemia normally stimulates ventilation and produces dyspnea, these phenomena and the other symptoms and signs of hypoxia are sufficiently variable in patients with COPD as to be of limited value in patient assessment. Chronic alveolar hypoxia is the main factor leading to development of cor pulmonale—right ventricular hypertrophy with or without overt right ventricular failure—in patients with COPD. Pulmonary hypertension adversely affects survival in COPD, to an extent that parallels the degree to which resting mean pulmonary artery pressure is elevated. Although the severity of airflow obstruction as measured by FEV1 is the best correlate with overall prognosis in patients with COPD, chronic hypoxemia increases mortality and morbidity for any severity of disease. Large-scale studies of LTOT in patients with COPD have demonstrated a dose-response relationship between daily hours of oxygen use and survival. There is reason to believe that continuous, 24-hours-per-day oxygen use in appropriately selected patients would produce a survival benefit even greater than that shown in the NOTT and MRC studies.

Providers such as pediatricians and dentists can provide information to parents and caregivers about what food and toys are appropriate by age to prevent choking. The American Academy of Pediatricians recommends waiting until 6 months of age before introducing solid foods to infants. Caregivers can supervise children while eating or playing. Also, caregivers can avoid giving children younger than 5 foods that pose a high risk of choking such as hot dog pieces, cheese sticks, cheese chunks, hard candy, nuts, grapes, marshmallows, or popcorn. Parents, teachers, child care providers, and other caregivers for children get training in choking first aid and cardiopulmonary resuscitation (CPR).

In the US, manufacturers of children's toys and products must follow requirements to prevent choking and include appropriate warning labels. However, toys that are resold may not be marked with warning labels. Caregivers can try to prevent choking by considering the features of a toy (such as size, shape, consistency, small parts) before giving it to a child. Children's products that are found to pose a choking risk can be recalled.

Inert gas asphyxiation is a form of asphyxiation which results from breathing a physiologically inert gas in the absence of oxygen, or a low amount of oxygen, rather than atmospheric air (which is largely composed of nitrogen and oxygen). Examples of physiologically inert gases, which have caused accidental or deliberate death by this mechanism, are: argon, helium, nitrogen and methane. The term "physiologically inert" is used to indicate a gas which has no toxic or anesthetic properties and does not act upon the heart or hemoglobin. Instead, the gas acts as a simple diluent to reduce oxygen concentration in inspired gas and blood to dangerously low levels, thereby eventually depriving all cells in the body of oxygen.

According to the U.S. Chemical Safety and Hazard Investigation Board, in humans, "breathing an oxygen deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths. The exposed person has no warning and cannot sense that the oxygen level is too low." In the US, at least 80 people died due to accidental nitrogen asphyxiation between 1992 and 2002. Hazards with inert gases and the risks of asphyxiation are well established.

An occasional cause of accidental death in humans, inert gas asphyxia with gases including helium, nitrogen, methane, and argon, has been used as a suicide method. Inert gas asphyxia has been advocated by proponents of euthanasia, using a gas-retaining plastic hood device colloquially referred to as a suicide bag.

Nitrogen asphyxiation has been suggested by a number of lawmakers and other advocates as a more humane way to carry out capital punishment. In April 2015, the Oklahoma Governor Mary Fallin signed a bill authorizing nitrogen asphyxiation as an alternative execution method in cases where the state's preferred method of lethal injection was not available as an option.

For children less than 1 year, the American Heart Association recommends performing cycles of 5 back blows (or slaps) followed by 5 chest compressions. These cycles of 5 back blows then 5 chest compressions are repeated until the object comes out of the infant's airway or until the infant becomes unresponsive. If the infant becomes unresponsive, the American Heart Association recommends starting CPR. The reason that abdominal thrusts are not recommended in children less than 1 year is because they can cause liver damage.

Diving animals such as mink and burrowing animals, such as rodents and rats, are sensitive to low-oxygen atmospheres and (unlike humans) will avoid them, making purely hypoxic techniques possibly inhumane for them. For this reason, the use of inert gas (hypoxic) atmospheres (without CO) for euthanasia, is also species-specific.

A 2008 bulletin from the World Health Organization estimates that 900,000 total infants die each year from birth asphyxia, making it a leading cause of death for newborns.

In the United States, intrauterine hypoxia and birth asphyxia was listed as the tenth leading cause of neonatal death.

The mortality rate of meconium-stained infants is considerably higher than that of non-stained infants; meconium aspiration used to account for a significant proportion of neonatal deaths. Residual lung problems are rare but include symptomatic cough, wheezing, and persistent hyperinflation for up to five to ten years. The ultimate prognosis depends on the extent of CNS injury from asphyxia and the presence of associated problems such as pulmonary hypertension. Fifty percent of newborns affected by meconium aspiration would die fifteen years ago; however, today the percent has dropped to about twenty.

There is current controversy regarding the medicolegal definitions and impacts of birth asphyxia. Plaintiff's attorneys often take the position that birth asphyxia is often preventable, and is often due to substandard care and human error. They have utilized some studies in their favor that have demonstrated that, "...although other potential causes exist, asphyxia and hypoxic-ischemic encephalopathy affect a substantial number of babies, and they are preventable causes of cerebral palsy." The American Congress of Obstetricians and Gynecologists disputes that conditions such as cerebral palsy are usually attributable to preventable causes, instead associating them with circumstances arising prior to birth and delivery.

High risk infants may be identified by fetal tachycardia, bradycardia or absence of fetal accelerations upon CTG in utero, at birth the infant may look cachexic and show signs of yellowish meconium staining on skin, nail and the umbillical cord, these infants usually progress onto Infant Respiratory distress syndrome within 4 hours. Investigations which can confirm the diagnosis are fetal chest x-ray, which will show hyperinflation, diaphragmatic flattening, cardiomegaly, patchy atelectasis and consolidation, and ABG samples, which will show decreased oxygen levels.

Promoters of this suicide method recommend it to terminally ill patients. However, across the world, most people who use suicide bags are physically healthy. Instead of having incurable cancer or other life-threatening physical diseases, most of the users have psychiatric disorders or substance abuse problems that might possibly be addressed through medical and psychological treatment. The demographics of its users varies; in one survey, the method had been used mostly by middle-aged adults in failing health, who were attracted to the relative nonviolence of the method.

This suicide method is also typically used by younger or middle-aged adults, rather than by older adults. In the US, it is more commonly chosen by non-Hispanic white males than by women or people of other races.

Transient tachypnea of the newborn occurs in approximately 1 in 100 preterm infants and 3.6-5.7 per 1000 term infants. It is most common in infants born by Cesarian section without a trial of labor after 35 weeks' gestation. Male infants and infants with an umbilical cord prolapse or perinatal asphyxia are at higher risk. Parental risk factors include use of pain control or anesthesia during labor, asthma, and diabetes.

TTN is a diagnosis of exclusion as it is a benign condition that can have symptoms and signs similar to more serious conditions, such as respiratory distress syndrome. A chest X-ray may show a radiopaque line - fluid - in the horizontal fissure of the right lung, fluid infiltrate throughout alveoli or fluid in individual lung lobes. The lungs may also appear hyperinflated.

Well-designed clinical trials for stroke treatment in neonates are lacking Recent clinical trials show that therapeutic intervention by brain cooling beginning up to 6 hours after perinatal asphyxia reduces cerebral injury and may improve outcome in term infants, indicating cell death is both delayed and preventable

Pancaspase inhibition and Casp3-selective inhibition have been found to be neuroprotective in neonatal rodents with models of neonatal brain injury, which may lead to pharmacological intervention In a study done by Chauvier, "et al.", it is suggested that a Caspase inhibitor, TRP601, is a candidate for neuroprotective strategy in prenatal brain injury conditions. They found a lack of detectable side effects in newborn rodents and dogs. This may be a useful treatment in combination with hypothermia.

MRI has proven valuable for defining brain injury in the neonate, but animal models are still needed to identify causative mechanisms and to develop neuroprotective therapies. In order to model human fetal or neonatal brain injury, one needs a species in which a similar proportion of brain development occurs in utero, the volume of white to grey matter is similar to the human brain, an insult can be delivered at an equivalent stage of development, the physiological outcome of the insult can be monitored, and neurobehavioral parameters can be tested. Some animals that meet these criteria are sheep, non-human primates, rabbits, spiny mice, and guinea pigs.

Transplantation of neural stem cells and umbilical cord stem cells is currently being trialed in neonatal brain injury, but it is not yet known if this therapy is likely to be successful.

Suicides using bags or masks and gases are well documented in the literature.

Suicide bags have been used with gases other than inert gases, with varying outcomes. Examples of other gases are propane-butane and natural gas.

Suicides using a suicide bag and an inert gas produce no characteristic post-mortem macroscopic or microscopic findings. Forensic death investigations of cause and manner of death may be very difficult when people commit suicide in this manner, especially if the apparatus (such as the bag, tank, or tube) is removed by someone after the death. Petechiae, which are often considered a marker of asphyxia, are present in only a small minority of cases (3%). Frost reported that of the two cases he studied that featured death from inert gas asphyxiation using a suicide bag, one had "bilateral eyelid petechiae and large amounts of gastric content in the airways and that these findings challenge the assumption that death by this method is painless and without air hunger, as asserted in "Final Exit"." A review study by Ely and Hirsch (2000) concludes that conjunctival and facial petechiae are the product of purely mechanical vascular phenomena, unrelated to asphyxia or hypoxia, and do not occur unless ligatures were also found around the neck. The authors wrote,

There are also documented cases of suicide attempts using the suicide bag that failed. A case report study in 2015 discussed the risks associated with failed attempts using this method. The authors wrote, "If the process is interrupted by someone, there is no gas or the tube slips out of the bag, there is a high risk of severe hypoxia of the central nervous system."

Some evidence suggests that magnesium sulfate administered to mothers prior to early preterm birth reduces the risk of cerebral palsy in surviving neonates. Due to the risk of adverse effects treatments may have, it is unlikely that treatments to prevent neonatal strokes or other hypoxic events would be given routinely to pregnant women without evidence that their fetus was at extreme risk or has already suffered an injury or stroke. This approach might be more acceptable if the pharmacologic agents were endogenously occurring substances (those that occur naturally in an organism), such as creatine or melatonin, with no adverse side-effects.

Because of the period of high neuronal plasticity in the months after birth, it may be possible to improve the neuronal environment immediately after birth in neonates considered to be at risk of neonatal stroke. This may be done by enhancing the growth of axons and dendrites, synaptogenesis and myelination of axons with systemic injections of neurotrophins or growth factors which can cross the blood–brain barrier.

Cord blood gas analysis can be used to determine if there is perinatal hypoxia/asphyxia, which are potential causes of hypoxic-ischemic encephalopathy or cerebral palsy, and give insight into causes of intrapartum fetal distress. Cord blood gas analysis is indicated for high-risk pregnancies, in cases where C-sections occurred due to fetal compromise, if there were abnormal fetal heart rate patterns, Apgar scores of 3 or lower, intrapartum fever, or multifetal gestation.

Evidence of brain injury related to the hypoxic-ischemic events that cause neonatal encephalopathy can be seen with brain MRIs, CTs, magnetic resonance spectroscopy imaging or ultrasounds.

Neonatal encephalopathy may be assessed using Sarnat staging.