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11

Oxygen therapy

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Contents

Objectives

Oxygen therapy

11-1 What is oxygen?

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.

11-2 Why does the body need oxygen?

Energy for all the vital functions of the body is obtained by either aerobic or anaerobic metabolism:

  1. Aerobic metabolism releases energy from carbohydrates, proteins and fats by the process of oxygenation. Aerobic metabolism is used by most cells, as it produces large amounts of energy for prolonged periods of time, but requires the presence of oxygen.
  2. Anaerobic metabolism, in contrast, does not need oxygen but is far less efficient as it produces small amounts of energy and only functions for short periods of time.

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.

11-3 What is cyanosis?

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.

11-4 What is hypoxia?

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.

Measuring the amount of oxygen

11-5 How is the amount of oxygen in the atmosphere measured?

The amount of oxygen in the atmosphere is determined by measuring its concentration or partial pressure:

  1. The concentration of oxygen is given as a percentage (e.g. 40%) or as a fraction (e.g. 0.40).
  2. The partial pressure of oxygen is measured in kilopascals (kPa) or millimetres of mercury (mm Hg).

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.

11-6 How much oxygen is present in room air?

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.

Note
The atmosphere exerts a pressure as demonstrated by the collapse of a soap bubble. The total pressure in the atmosphere is approximately 100 kPa (760 mm Hg) at sea level; 21% of this total pressure is produced by oxygen. Therefore, the partial pressure of oxygen in the atmosphere is 21% of 100 kPa (760 mm Hg), which is 21 kPa (160 mm Hg).

The FiO₂ (fraction of inspired oxygen) of room air is 0.21.

11-7 How do you determine the amount of oxygen in the blood?

  1. This can be roughly assessed clinically as the infant appears peripherally and centrally cyanosed if there is not enough oxygen in the red cells. This clinical method is often inaccurate and should, whenever possible, be confirmed by measuring either the saturation of oxygen or the partial pressure in arterial blood.
  2. At the bedside the saturation of oxygen in arterial blood can be measured with a pulse oximeter (a saturation monitor), which simply clips onto the infant’s hand or foot and measures the oxygen saturation through the skin. A pulse oximeter can be used to accurately screen for hypoxaemia.
  3. In a laboratory the partial pressure of oxygen can be measured accurately in a sample of arterial blood using a machine called a blood gas analyser, which measures the pH and concentration of oxygen and carbon dioxide. The partial pressure of oxygen in venous or capillary blood is usually not used as it does not reflect accurately the amount of oxygen reaching the tissues. Taking an arterial blood sample if often painful and distressing to the infant.
Note
A pulse oximeter determines the saturation of oxygen in the arterial blood entering the capillaries by assessing the colour of the red cells. The red cell colour is determined through the skin and does not require a sample of blood. A sample of capillary blood can be used to measure the partial pressure provided that the puncture site (e.g. heel) is warmed and the blood allowed to run without squeezing. The result is very similar to arterial blood provided the sample is collected correctly.

11-8 How much oxygen is needed by the normal infant?

Healthy, normal infants (and adults) need 21% oxygen in the air they breathe (i.e. a FiO₂ of 0.21).

11-9 What is the normal partial pressure of oxygen in arterial blood?

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.

11-10 What is the normal saturation of oxygen in arterial blood?

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%.

Note
The SaO₂ is determined by the PaO₂ and the haemoglobin’s ability to take up oxygen. The SaO₂ increases in a linear manner as the PaO₂ rises until the SaO₂ reaches 92%. Thereafter there is a poor correlation between the two measurements. This explains why a SaO₂ above 92% is potentially dangerous as the PaO₂ may be very high. While the normal range of SaO₂ is slightly higher in term than preterm infants, for practical reasons a common normal range of 86–92% is used. The normal range of SaO₂ in older children and adults is above 95% (as they have adult haemoglobin).

The advantages and disadvantages of extra oxygen

11-11 When does an infant need extra oxygen?

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:

  1. The infant has central cyanosis (a blue tongue).
  2. The PaO₂ drops below 8 kPa.
  3. The SaO₂ falls below 86%.

11-12 Is too little oxygen dangerous?

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.

11-13 Which infants are usually given extra oxygen?

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.

11-14 Which infants do not need extra oxygen?

  1. Infants with normal Apgar scores at birth. Do not give oxygen to infants who do not need resuscitation.
  2. Many infants with low Apgar scores can be successfully resuscitated with room air. Not all infants needing resuscitation require extra oxygen.
  3. Some infants with peripheral but not central cyanosis. If there is peripheral cyanosis only, the cause is usually cold hands and feet with poor perfusion, rather than hypoxia.
  4. Many infants with recurrent apnoea. If oxygen is given during resuscitation, it should be stopped once spontaneous respiration has started. Infants with recurrent apnoea but no respiratory distress usually do not need oxygen.
  5. Small, preterm infants with a normal PaO₂ and SaO₂.

A normal SaO₂ indicates that extra oxygen is not needed.

Only give extra oxygen when there is a good clinical indication.

11-15 When indicated, how much oxygen should you give?

The FiO₂ should be increased until:

  1. Central cyanosis is corrected (the tongue is pink).
  2. The PaO₂ is 8–10 kPa or SaO₂ is 86–92%.

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.

11-16 Can you give an infant too much oxygen?

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.

Note
A SaO₂ above 96% is safe if the infant is in room air and not receiving oxygen. They will always have a normal PaO₂.

Too much oxygen is dangerous as it may damage the infant.

11-17 When is the concentration of inspired oxygen too high?

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.

11-18 What are the dangers of too much oxygen in the blood?

  1. If the PaO₂ is too high, the retina of the infant’s eyes can be damaged causing retinopathy of prematurity. However, if a very high FiO₂ is needed to maintain a normal PaO₂ and SaO₂, the retina is not likely to be damaged. Therefore, it is the raised PaO₂ and not the increased FiO₂ that causes retinopathy. The longer the period during which the PaO₂ is too high, the greater is the risk of retinopathy.
  2. A high FiO₂ for a long time, especially if the infant is intubated and on a ventilator, may damage the alveoli and small bronchi of the lung resulting in chronic lung disease (bronchopulmonary dysplasia).

A high PaO₂ in a preterm infant may cause retinopathy of prematurity.

11-19 What is 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.

11-20 How can you prevent retinopathy of prematurity?

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.

Note
Unfortunately the cause of retinopathy is not fully understood and some very immature infants may still get eye damage despite careful oxygen control. Infants of less than 32 weeks gestation should be screened for retinopathy at 6 weeks by direct fundoscopy.

Administering oxygen safely

11-21 What is a safe concentration of inspired oxygen?

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.

11-22 How can you safely administer the correct amount of oxygen?

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:

  1. It is very unusual for an infant to need a FiO₂ of 1.0 (100% oxygen). At all times the FiO₂ must be matched to the infant’s needs.
  2. The FiO₂ must be adjusted to give a PaO₂ of 8–10 kPa or a SaO₂ of 86–92%.
  3. If monitoring and laboratory facilities are not available, give just enough oxygen to correct central cyanosis. This clinical assessment is not accurate, however, so it is best to determine the PaO₂ or SaO₂ if at all possible.
  4. The easiest method of monitoring oxygen therapy is with a pulse oximeter to measure the SaO₂ repeatedly or continuously. If continuous monitoring is not available, the SaO₂ must be measured, at least every 6 hours. As the infant’s clinical condition improves or deteriorates, the required FiO₂ may need to be changed.
  5. Never give oxygen therapy unless it is indicated. Stop the oxygen therapy as soon as it is no longer needed.

Monitoring the percentage oxygen saturation with a pulse oximeter is very important.

11-23 What methods can you use to administer oxygen?

  1. Oxygen can be given by short nasal cannulas. The cannulas are about 1 cm long and lie just inside the nostrils. This is a simple and effective way of providing extra oxygen. It is useful but not essential to use an air/oxygen blender. Warmed humidification and routine suctioning of the nose are not needed. Low flow rates of 0.5 to 1 litres per minute are needed so little oxygen, a scarce resource, is used. However, with pure oxygen an FiO₂ of only 0.4 can be reached.
  2. Oxygen is can be given into a perspex head box if facilities are not available to use nasal cannulas. This is a simple and cheap method but is not as effective as nasal cannulas and uses a lot of oxygen. However, an FiO₂ of well above 0.4 can be provided. It is a useful method if medical air or a blender is not available. With an oxygen monitor the FiO₂ can be measured. A warm humidifier is not needed and there is no risk of nasal obstruction or gastric distension.
  3. Oxygen can be given via nasal prongs when continuous positive airways pressure is needed. This is particularly effective in infants with respiratory distress. However, medical air, a blender and warmed humidifier are required. It is also important to have adequate, experienced nursing.
  4. An endotracheal tube is used for most infants receiving oxygen via a ventilator. The oxygen must be warmed, humidified and blended with medical air.
  5. A bag and mask are often used during resuscitation. Some infants need oxygen during resuscitation.

There are advantages and disadvantages to each method of administering oxygen.

Nasal prongs are the best method of giving oxygen to newborn infants.

11-24 What methods should not be used to administer oxygen?

  1. Oxygen should not be given directly into a closed incubator as this method is wasteful, high concentrations of oxygen cannot be reached and the concentration of oxygen drops every time an incubator port is opened.
  2. Long nasal catheters are rarely used as they are often blocked with secretions.
  3. Giving 100% oxygen via a cardboard cup or face mask is extremely dangerous as it is almost impossible to control the FiO₂ accurately. This method should be used as the last resort only.
  4. Gastric oxygen via a nasogastric tube is valueless and dangerous.

11-25 Should you always humidify oxygen and medical air?

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.

Note
Warmed humidification is needed at high flow rates (more than 2 litres per minute) which dry out the nasal mucus and mucous membranes. While warmed humidification is not needed at low flow rates (less than 2 litres per minute).

11-26 How should you control the concentration of oxygen given?

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.

Note
A venturi is a simple apparatus that uses a jet of oxygen to suck in a fixed amount of room air. The resultant mixture of gases gives a known percentage of oxygen.

11-27 What flow rate of oxygen is best?

  1. When oxygen is given via nasal cannulas the flow rate should be set at 0.5 to 1 litre per minute. Do not use higher flow rates as this only dries out the nose.
  2. When oxygen is given into a headbox, either directly or via a blender or venturi, the flow should be at least 5 litres per minute to prevent carbon dioxide accumulation. It is also very difficult to accurately control the FiO₂ by altering the flow rate when low rates are used. Alternately a high flow rate, such as 10 litres, wastes oxygen and cools the infant. With few exceptions, a flow rate of 5 litres per minute is best.

11-28 Should the oxygen concentration in a head box be monitored?

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.

11-29 How long should an infant receive oxygen?

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.

11-30 Are fluctuations in the oxygen concentration important?

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.

11-31 How rapidly should you reduce the oxygen concentration?

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.

Note
Flip-flop is the name given to the clinical situation where a sudden, large drop in the FiO₂ causes a dangerous drop in the PaO₂ with collapse and sometimes death. Increasing the FiO₂ back to the original level fails to correct the cyanosis. This is because of the development of pulmonary hypertension with a right to left shunt in response to the low PaO₂.

Never remove an oxygen-dependent infant from oxygen, even for a short period of time.

11-32 What oxygen sources can be used?

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.

11-33 Is it safe to use an oxygen concentrator?

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.

11-34 What equipment do you need to give oxygen safely?

If oxygen is given without CPAP or ventilation:

  1. A source of pure (100%) oxygen. Either piped or cylinder oxygen is usually used in hospitals. The cylinder must have a reducing valve and a gauge that measures the amount of gas present.
  2. A source of medical air if possible. Either piped or from a cylinder.
  3. Plastic tubing
  4. An oxygen flow meter
  5. An oxygen-air blender if possible
  6. A venturi for head box oxygen if medical air or a blender is not available
  7. A ‘bubbler’ to humidify the oxygen
  8. Nasal cannulas or a perspex head box
  9. An oxygen monitor if possible when head box oxygen is used.
  10. A pulse oximeter (saturation monitor) if possible
  11. A blood gas analyser in level 2 or 3 hospitals

Providing continuous positive airways pressure (CPAP)

11-35 What is continuous positive airways pressure?

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).

11-36 How does CPAP work to improve respiratory function?

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.

11-37 Which infants benefit from CPAP?

Infants who suffer from mild or moderate:

  1. Hyaline membrane disease
  2. Wet lung syndrome
  3. Meconium aspiration
  4. Recurrent apnoea of prematurity

11-38 When should CPAP not be used?

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.

Note
CPAP is very useful after extubation from mechanical ventilation and may also be helpful in infants with pneumonia and large ductus arteriosus.

11-39 When should CPAP be started in infants with respiratory distress?

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.

11-40 How is CPAP given?

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.

Note
CPAP can be given without a Flow Driver if the special nosepiece is available. However, it is preferable to use a Flow Driver. The Pumani device is a cheap, easy and effective may to provide bubble CPAP.

11-41 How much CPAP is needed?

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.

11-42 When is CPAP successful?

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.

Note
With successful CPAP the pH should be above 7.25 and the PaC0₂ should be below 7.5 kPa.

11-43 Can infants on CPAP be fed?

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.

11-44 Can surfactant be used with CPAP?

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.

11-45 What are the problems with CPAP?

  1. It must be given in a newborn nursery by staff who have all the required equipment and are trained in the technique of giving CPAP correctly. It is dangerous if given by inexperienced staff. In this situation nasal cannula or headbox oxygen is safer.
  2. Nasal obstruction as the result of secretions or the prongs not being correctly positioned. Warmed humidified oxygen helps to prevent excessive nasal secretions. Routine nasal suctioning is not needed.
  3. The nasal prongs can be displaced (come out of the nostrils). Attaching the nose piece correctly to the cap is important.
  4. Damage to the nasal mucous membrane or cartilage (pressure necrosis). This is usually caused by using prongs that are too big and do not fit correctly.
  5. Pneumothorax
  6. Abdominal distension and vomiting. This can be prevented by an open orogastric tube.
  7. Water collecting in the tubing

Most of these complications can be avoided with correct care and careful monitoring.

11-46 When has CPAP failed?

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.

Note
Infants with a PaCO₂ above 7.5 kPa or pH below 7.25 are in respiratory failure and need ventilation.

11-47 When can CPAP be stopped?

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.

Case study 1

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.

1. How much oxygen is present in room air?

There is 21% oxygen in room air. Nitrogen forms most of the air we breathe.

2. What does SaO₂ mean?

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.

3. How is the SaO₂ measured?

With a pulse oximeter (a saturation monitor) which clips onto the infant’s hand or foot.

4. What is the normal range of SaO₂ in a newborn infant?

85% to 92%

5. What do you understand by FiO₂?

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.

6. How is the FiO₂ measured in a head box?

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.

7. What is the value of knowing all these measurements?

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.

Case study 2

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.

1. What equipment should be used to administer the oxygen?

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.

2. How should you control the fraction of oxygen given?

With an oxygen-air blender or a venture (in a head box).

3. Why should the oxygen or oxygen/air mixture be humidified?

Because unhumidified gas is very dry and will irritate the linings of the nose, throat and airways.

4. What volume of oxygen/air mixture should be given into the head box?

A flow rate of 5 litres per minute is best. This is measured on the flow meter.

5. What oxygen sources can be used if the hospital does not have piped oxygen?

Bottled oxygen or an oxygen concentrator.

Case study 3

A sick infant with respiratory distress is receiving oxygen via nasal cannulas. The FiO₂ is 0.75. Both the tongue and peripheries are pink.

1. What does an FiO₂ of 0.75 mean?

It means that the infant is receiving 75% oxygen.

2. Why should you be unhappy to decide the correct FiO₂ by simply examining the colour of the infant’s tongue?

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.

3. How should you determine whether this infant is receiving the correct concentration of oxygen?

The SaO₂ (saturation of oxygen in arterial blood) or the PaO₂ (partial pressure of oxygen in arterial blood) must be measured.

4. How is the PaO₂ measured?

A blood gas analyser is used to measure the PaO₂ on a sample of blood (usually arterial).

Case study 4

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).

1. What do you think about the SaO₂ reading?

It is too high as the normal range is 86–92%. This indicates that this infant is receiving too much oxygen.

2. What is the normal range for the PaO₂?

The PaO₂ should be between 8 and 10 kPa (60–75 mm Hg). Therefore, the reading in this infant is above the normal range.

3. How would you change the management of this infant?

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.

4. What is the danger of too much oxygen in this infant?

Retinopathy of prematurity. The high PaO₂ damages the immature retina and this may cause blindness.

5. What is the greatest danger of giving this infant too little oxygen?

Brain damage

6. What is the advantage of using CPAP?

It helps to prevent collapse of the alveoli and reduces the need for ventilation.