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Oxygen is one of the many gases that make up the earth’s atmosphere. It is produced by green plants (photosynthesis) and used by all animals. Oxygen is essential for many living organisms.
Energy for all the vital functions of the body is obtained by either aerobic or anaerobic metabolism:
Therefore the body needs oxygen to produce the large amount of energy required for most body functions such as moving, breathing, eating and digestion.
In the body, oxygen is carried by haemoglobin in red blood cells from the lungs to all the other organs. When loaded with oxygen the haemoglobin and red blood cells are red in colour and as a result the infant appears pink. However, if the red blood cells carry too little oxygen they become blue in colour and the infant appears cyanosed.
Oxygen is needed by the body to release large amounts of energy stored in carbohydrates, proteins and fats.
This is the blue colour of the body due to too little oxygen. The cyanosed infant may have central cyanosis, when the tongue is blue, or peripheral cyanosis, when the hands and feet are blue.
Hypoxia is the lack of enough oxygen in the tissues. It causes cyanosis. Hypoxaemia is too little oxygen in the blood. Hypoxaemia results in hypoxia.
The amount of oxygen in the atmosphere is determined by measuring its concentration or partial pressure:
The concentration of oxygen in room air is usually called the fraction of inspired oxygen, and abbreviated to FiO₂. For example, the FiO₂ is 0.40 if the percentage oxygen is 40%. It is preferable to speak about the fraction rather than the percentage of oxygen in inspired air (breathed in air) as the latter is often confused with the percentage of oxygen saturation in the blood.
The atmosphere of earth consists of a mixture of many gases such as nitrogen, oxygen and carbon dioxide. Oxygen forms 21% of the gas in the atmosphere. Therefore the fraction of oxygen in room air is 0.21. This is true, both at sea level and at high altitudes, and is adequate to meet the needs of aerobic metabolism in adults and newborn infants.
The FiO₂ (fraction of inspired oxygen) of room air is 0.21.
Healthy, normal infants (and adults) need 21% oxygen in the air they breathe (i.e. a FiO₂ of 0.21).
Normally a FiO₂ of 0.21 in the inspired air (i.e. room air) produces a partial pressure of oxygen in the arterial blood of 8–10 kPa (60–75 mm Hg). The partial pressure of oxygen in arterial blood is referred to as the PaO₂. Therefore a PaO₂ of 8–10 kPa is normal and adequate to fully load the haemoglobin in the circulating red blood cells with oxygen. In South Africa kPa is the unit usually used to express partial pressure.
The normal PaO₂ (partial pressure of oxygen in arterial blood) is 8–10 kPa.
The normal saturation of oxygen in arterial blood is 86–92% in newborn infants breathing room air. At this oxygen saturation the haemoglobin in arterial blood is fully loaded with oxygen. The degree of saturation of arterial blood with oxygen is referred to as the SaO₂. Therefore, at a FiO₂ of 0.21 the SaO₂ in a newborn infant is normally 86–92%.
The normal SaO₂ (saturation of oxygen in arterial blood) is 86–92%.
If the PaO₂ in both term and preterm infants falls below 8 kPa and the SaO₂ falls below 86%. At these levels (hypoxaemia) the red cells will not be adequately loaded with oxygen. The infant may now appear cyanosed and the cells of the body will not receive enough oxygen for aerobic metabolism (hypoxia). Therefore, extra oxygen is needed in the inspired air (i.e. a FiO₂ of more than 0.21) if:
Yes. If the cells of the body do not receive enough oxygen they can be damaged or die. Without adequate oxygen, cells are forced to change from aerobic to anaerobic metabolism. This markedly reduces the amount of energy the cells can produce. Toxic substances, such as lactic acid, are also produced as a by-product of anaerobic metabolism. This causes a metabolic acidosis. The cells of many organs, but particularly the brain, are affected by these metabolic changes.
Too little oxygen in the blood can cause brain damage.
Infants with respiratory distress due to clinical conditions such as hyaline membrane disease, pneumonia and meconium aspiration. Extra oxygen may also be needed by some infants who require resuscitation at birth.
A pulse oximeter is very helpful when deciding whether an infant needs extra oxygen.
A pulse oximeter is very helpful in deciding whether extra oxygen is needed.
A normal SaO₂ indicates that extra oxygen is not needed.
Only give extra oxygen when there is a good clinical indication.
The FiO₂ should be increased until:
The required FiO₂ to keep different infants pink may vary from 0.22 to 1 (i.e. 21 to 100%). For example, an infant with severe lung disease may need a FiO₂ of 0.9 while another with mild lung disease may need only 0.25 to achieve a normal PaO₂ and SaO₂.
Yes. If the FiO₂ is increased too much, the PaO₂ and SaO₂ will rise above the normal range. If the PaO₂ is above 10 kPa or SaO₂ above 92%, the excessive amount of oxygen in the blood may damage the infant.
If a particular infant needs an FiO₂ of 0.35 to give a normal PaO₂ and SaO₂, increasing the FiO₂ to 0.50 will be of no additional help to the infant and may be dangerous. Therefore, do not give oxygen unless it is needed. Also do not give more oxygen than is required. In an emergency, oxygen should be given for as short a time as possible. Giving oxygen can be dangerous when it is not required.
Too much oxygen is dangerous as it may damage the infant.
Any FiO₂ that increases the PaO₂ or SaO₂ above the normal range is too high. It is impossible to tell by clinical examination alone that the FiO₂ is too high. The risk of oxygen damage is determined by the PaO₂ or SaO₂ and not by the FiO₂. A high FiO₂ is not dangerous if the PaO₂ or SaO₂ are normal (e.g. with severe respiratory distress). A high FiO₂ is most dangerous if there are no lung or heart problems, e.g. oxygen given to healthy preterm infants during transport.
A high PaO₂ in a preterm infant may cause retinopathy of prematurity.
The immature blood vessels in the retina of preterm infants constrict (go into spasm) when exposed to a high PaO₂. This causes retinal ischaemia and haemorrhage with healing by fibrosis. This important eye problem is called retinopathy of prematurity. Mild degrees of retinopathy recover and vision is not affected. However, severe retinopathy with a lot of fibrosis causes a condition known as retrolental fibroplasia which can permanently impair vision and even result in blindness.
The lower the gestational age the greater is the risk of retinopathy of prematurity. The risk of retinopathy is greatest in infants under 32 weeks gestation. At term the risk of oxygen toxicity to the retina is much less. Retinopathy is diagnosed by examining the eye with an ophthalmoscope.
Most cases of retinopathy can be prevented by adjusting the FiO₂ so that the PaO₂ and SaO₂ are within the normal range. If these investigations are not available, give just enough oxygen to correct central cyanosis, i.e.just enough to keep the tongue pink.
No FiO₂ above 0.21 can be regarded as safe unless the PaO₂ or SaO₂ are measured and found to be in the normal range. Even a slightly raised FiO₂ in an infant with normal lungs will give a high PaO₂ and SaO₂. An increased FiO₂ is most dangerous in a preterm infant with recurrent apnoea but no respiratory distress, as the PaO₂ can become very high while they are breathing well.
As there are dangers in giving too much or too little oxygen, the following principles must be followed to ensure that oxygen administration is safe:
Monitoring the percentage oxygen saturation with a pulse oximeter is very important.
There are advantages and disadvantages to each method of administering oxygen.
Nasal prongs are the best method of giving oxygen to newborn infants.
Oxygen or medical air direct from a cylinder or wall piping is very dry and cold. It irritates the airways and can drop the infant’s temperature, especially at high flow rates. Therefore, oxygen and medical air should be bubbled through water at room temperature (a ‘bubbler’) if possible when giving cannula or head box oxygen.
Oxygen and medical air should always be humidified and warmed if it is being given at high flow rates via nasal prongs or an endotracheal tube. Warmed humidification is not necessary if oxygen and medical air is given into a head box or by nasal cannulas as a low flow is inspired through the nasal passages, where it can be warmed and humidified. Dangers of humidifiers include overheating, drowning and infection.
The best way to control the FiO₂ is with an air-oxygen blender. A blender accurately mixes pure oxygen with medical air to give the required FiO₂. A supply of both oxygen and medical air is needed for a blender.
If a supply of medical air or a blender is not available, a venturi can be used with a head box. Some venturis mix pure oxygen with room air to give any required FiO₂ while others only give a fixed FiO₂ (e.g. 40%). The flow rate must not be used to control the concentration of oxygen given as it is far too inaccurate.
Without medical air and a blender the FiO₂ cannot be controlled if nasal cannulas, nasal prongs or an endotracheal tube is used.
A blender or venturi should be used to control the concentration of oxygen given.
Yes. The concentration of inspired oxygen should, whenever possible, be measured with an oxygen monitor. This is the most accurate way of knowing what concentration of oxygen the infant is breathing from a head box. If an oxygen monitor is not available, the concentration of oxygen set on the air-oxygen blender or venturi is a good guide provided that the flow rate is 5 litres per minute or more.
Only as long as it is required to prevent central cyanosis and maintain a normal PaO₂ and SaO₂. Tachypnoea alone is not an indication for supplementary oxygen. Whenever possible the FiO₂ should be reduced. Stop as soon as possible. The time that oxygen is required varies widely from one infant to another.
Yes. Even small fluctuations in the FiO₂ may cause a change in the PaO₂ and SaO₂. With the correct equipment a stable FiO₂ can be maintained.
The FiO₂ must never be reduced suddenly in a single big step. Instead it should be reduced in small steps at a time (e.g. an FiO₂ decrease of 0.05 every 15 minutes). A sudden, large drop in FiO₂ may cause severe hypoxia and collapse. Never stop the oxygen, even for a short time (e.g. to take a blood sample), in an infant who still needs oxygen. A pulse oximeter is very helpful when the FiO₂ is being reduced.
Never remove an oxygen-dependent infant from oxygen, even for a short period of time.
Piped oxygen and medical air is the best source and should be available in all newborn intensive care and special care units.
Gas cylinders should be available in primary care units. A small oxygen cylinder can be used in emergencies in home deliveries.
An oxygen concentrator.
Some source of oxygen should be available for emergencies in all deliveries and in all nurseries.
In areas where piped or bottled (cylinder) oxygen is not available, an oxygen concentrator can be used to concentrate oxygen from room air. Modern concentrators are very efficient and can supply high concentrations of oxygen.
If oxygen is given without CPAP or ventilation:
Continuous positive airways pressure (CPAP) is a method of providing respiratory support by allowing the infant to breathe out against pressure. The wider clinical use of CPAP has made a major difference to the management of infants with respiratory distress, especially those with hyaline membrane disease. Usually oxygen is given with CPAP but sometimes CPAP is used with room air only (e.g. in infants with apnoea).
Normally the alveoli of the lungs remain open and do not collapse with expiration. However, in some respiratory complications in newborn infants the alveoli tend to collapse and these infants are not strong enough to expand them again during every inspiration. As a result the infant is not able to breathe normally and becomes cyanosed (hypoxic) and may die. CPAP prevents alveoli collapse and also helps to stimulate breathing, especially in infants with apnoea.
CPAP is not a form of mechanical ventilation. Therefore the infant must be able to breathe spontaneously while receiving CPAP.
CPAP helps to keep the alveoli expanded.
Infants who suffer from mild or moderate:
CPAP must not be used in infants with severe respiratory distress or severe recurrent apnoea. These infants need mechanical ventilation, especially if they have severe recession and grunting or need an FiO₂ of over 0.6 to keep their SaO₂ in the normal range.
CPAP is also not helpful in infants who do not breathe well at birth or have cyanotic heart disease.
CPAP is indicated in most infants needing extra oxygen, especially preterm infants with hyaline membrane disease. It is better to start CPAP early to prevent deterioration in their respiratory distress than wait until they need high percentages of oxygen. The early use of CPAP prevents many infants needing mechanical ventilation.
The early use of CPAP often prevents the need for mechanical ventilation.
CPAP is usually given via nasal prongs with a special CPAP apparatus. This is a machine which is designed to control and deliver CPAP. It includes a blender, flow meter, warm humidifier and pressure gauge. The device is linked by tubes (pipes) to a nose piece which has nasal prongs that are placed into the infant’s nostrils. There are 3 sizes of nasal prongs so that the nose piece can fit all newborn infants. A Flow Driver is a commercial device to deliver CPAP. CPAP can also be given with a ventilator set on CPAP mode. Do not try to give CPAP with nasal cannulas as this is very unreliable and ineffective.
CPAP must be given in a newborn nursery (usually in a level 2 hospital) where the correct equipment is available and the staff have been trained to give CPAP safely. Standard CPAP, high flow CPAP and bubble CPAP can be used.
Usually 4 to 5 cm water pressure is given. This usually requires a flow rate of 6 to 8 litres per minute. The FiO₂ should be increased until the SaO₂ is 86 to 92%. Some infants with recurrent apnoea may need CPAP with air and no added oxygen.
Most infants on CPAP will soon settle down without severe recession or apnoea. The FiO₂ should fall to below 0.4 with a normal SaO₂.
An orogastric tube should be inserted and left open to drain. This prevents CPAP distending the stomach with air. As a result infants on CPAP usually are not given milk feeds but require an intravenous infusion. The infant’s mouth acts as a natural safety valve if the CPAP pressure is too high. Therefore the mouth must not be taped closed.
CPAP and surfactant are often used together in infants with hyaline membrane disease. This prevents alveolar collapse and avoids the need for mechanical ventilation in many of these infants. Usually the infant is intubated to give the surfactant and then extubated and placed on CPAP. Infants with severe HMD need surfactant and mechanical ventilation.
Surfactant and CPAP are often used together to treat infants with mild hyaline membrane disease.
Most of these complications can be avoided with correct care and careful monitoring.
When CPAP does not correct severe respiratory distress, apnoea or hypoxia. Infants with severe recession, recurrent apnoea or a FiO₂ above 0.6 need mechanical ventilation.
Once the infant is clinically improving the FiO₂ can be slowly reduced. When the FiO₂ reaches 0.25 the CPAP can be slowly reduced in steps of 1 cm water at a time. Stop the CPAP and remove the nose piece when the pressure is less than 2 cm water and the FiO₂ is 0.21. It is important to monitor the SaO₂ carefully while weaning an infant off CPAP.
A preterm infant is nursed in a closed incubator in room air. The doctor asks that the infant’s SaO₂ be measured. When this is found to be low, she starts extra oxygen via nasal cannulas. The nurse is then asked to record the FiO₂.
There is 21% oxygen in room air. Nitrogen forms most of the air we breathe.
The SaO₂ is the saturation of oxygen in arterial blood, i.e. what percentage of the haemoglobin in the red cells are saturated (filled) with oxygen.
With a pulse oximeter (a saturation monitor) which clips onto the infant’s hand or foot.
85% to 92%
The FiO₂ is the fraction of oxygen in room air (how much of air the infant is breathing is made up of oxygen). The FiO₂ of room air is 0.21 (i.e. 21%). As more and more oxygen is added to the air the infant receives, the FiO₂ will increase. The FiO₂ will give you an accurate measurement of how much oxygen the infant is breathing in.
With an oxygen monitor. This is better than just reading the percentage oxygen on the air-oxygen blender or venturi and far better than using the reading on the flow meter to guess the percentage of oxygen in the inspired air.
Knowing how much oxygen is being breathed in and how much oxygen in present in the arterial blood is important information as it indicates whether there are problems in the infants lungs and heart. It also helps to assess how severe the problems are. The more oxygen that is needed to provide a normal saturation, the more severe is the problem.
A 3 day old, term infant has pneumonia in a level 1 hospital and is nursed in an incubator. The infant is cyanosed in room air and needs oxygen therapy.
Oxygen could be given via nasal cannulas or into a perspex head box. Giving oxygen directly into the incubator is unsatisfactory as it uses a lot of oxygen. In addition, high concentrations of oxygen cannot be reached with this method and the amount of oxygen in the incubator drops if a porthole is opened.
With an oxygen-air blender or a venture (in a head box).
Because unhumidified gas is very dry and will irritate the linings of the nose, throat and airways.
A flow rate of 5 litres per minute is best. This is measured on the flow meter.
Bottled oxygen or an oxygen concentrator.
A sick infant with respiratory distress is receiving oxygen via nasal cannulas. The FiO₂ is 0.75. Both the tongue and peripheries are pink.
It means that the infant is receiving 75% oxygen.
Central cyanosis indicates that the infant does not have enough oxygen in its red cells and, therefore, needs a higher FiO₂. However, the tongue will be pink whether the infant is receiving the correct amount of oxygen or too much oxygen. The FiO₂ of 0.75 may, therefore, be much too high for this infant.
The SaO₂ (saturation of oxygen in arterial blood) or the PaO₂ (partial pressure of oxygen in arterial blood) must be measured.
A blood gas analyser is used to measure the PaO₂ on a sample of blood (usually arterial).
An infant, born after 28 weeks gestation, has hyaline membrane disease and is receiving oxygen by nasal prongs which give CPAP of 7 mm. The FiO₂ is 0.55, the SaO₂ is 98% and the PaO₂ is 20 kPa (150 mm Hg).
It is too high as the normal range is 86–92%. This indicates that this infant is receiving too much oxygen.
The PaO₂ should be between 8 and 10 kPa (60–75 mm Hg). Therefore, the reading in this infant is above the normal range.
The FiO₂ must be reduced by adjusting the oxygen/air mixture on the blender. The FiO₂ should be reduced by 0.05 (5%) every 15 minutes while watching the SaO₂. The FiO₂ is correct when the SaO₂ falls within the normal range.
Retinopathy of prematurity. The high PaO₂ damages the immature retina and this may cause blindness.
It helps to prevent collapse of the alveoli and reduces the need for ventilation.