FURTHER MANAGEMENT

The volume of gas a patient inspires every minute is known as the minute volume (MV).  Where:

MV = tidal volume x respiratory rate

A small infant of 3.5kg may have a MV of only 700mls/min.  Therefore giving 1litre of oxygen via a nasal cannula could result in a high concentration of oxygen.  A 70kg adolescent however may have a resting MV of 6l/min and therefore giving 1l of nasal oxygenation will only result in a modest increase in inspired oxygen (approximately 4% increase). 

If a patient's peak inspiratory demand (minute volume) is greater than the flow delivered by the device (e.g. a simple face mask) then room air will be sucked in around the side of the mask and reduce the concentration of oxygen being delivered, this is known as "entrainment".

Equipment and Methods for Oxygen Delivery and Support of Ventilation: In resuscitation of an acutely unwell child oxygen should ideally be given immediately at a flow rate of 15 litres per minute.  Different methods of oxygen delivery are used depending on the age of the child and their clinical condition.

Oxygen Administration in Patients with Spontaneous Respiratory Effort

• Oxygen mask with a reservoir bag (non-rebreathe mask)
  This should be used as a first line device in acutely unwell children who are maintaining their own airway.  This device will ensure a high concentration of oxygen is delivered (up to 90%). Always remember to fill the reservoir bag with oxygen before applying the mask to the patient (by covering the valve between the reservoir bag and the mask whilst it inflates).  The mask works on the principle of 3 way valves.  When the child inhales the valves on both sides of the mask close and the valve to the reservoir bag opens to allow the child to inhale oxygen from the bag without inhaling any room air.   On exhalation the opposite occurs. 

• Simple face mask
  A simple face mask without reservoir bag can be used when a high oxygen concentration is not required.  These can also be used to give "flow by" oxygen to children who are only needing a low oxygen concentration but who will not tolerate anything on their face.

• Nasal Cannulae
  These are again used when only a low concentration of oxygen is required and can be used in all ages particularly in preschool age.  An oxygen concentration of up to 40-60% can be delivered using this method.  These are often ineffective in children with excessive nasal secretions. 

• Headbox Oxygen
  This tends to be used in babies as it allows humidified oxygen delivery and maintains a heated environment.  It is mainly used in babies with bronchiolitis as they often do not tolerate facial masks or nasal cannulae.  The humidification of the oxygen also facilitates loosening of the nasal secretions, aiding airflow. 

Oxygen delivery methods

Low-flow	Low flow nasal cannula 1-4 litres per minute (lpm), this should be humidified if >2lpm.
	Simple face-mask delivers 6-12lpm at concentration of 28-50% oxygen
	Non-rebreathe mask (reservoir) delivers 10-15lpm and can reach concentrations of 100% oxygen
High-flow	High flow mask. As the flow of gas delivered is very high (and therefore entrainment is unlikely) the concentration can be tightly controlled
	High flow nasal (Vapotherm) High flow of humidified gas through nasal cannula.

Oxygen Administration in Patients Who Do Not Have Spontaneous Breathing

If the patient is not breathing (apnoeic) then it will be necessary to ventilate them.  Either mouth to mask ventilation can be used (usually done in out of hospital situations) or a self-inflating bag-valve mask (BVM) device can be used. Prior to ventilation ensure that the airway is patent using the techniques described above. An obstructed airway will become obvious if attempted ventilation fails to push air/oxygen through the airway.  

Patients who are not quite apnoeic but are failing to breathe enough to maintain oxygenation and carbon dioxide levels will also require ventilation.

Patients who are peri-arrest may appear to be 'gasping' or have irregular breathing. Ventilation can still be done with a bag-valve mask (BVM) device in this situation until help arrives for a more definitive plan such as intubation.

•  Face Masks
  There are different shapes and sizes of face mask for artificial ventilation and the appropriate size should be selected dependent on the size of the child.
  
  Technique for mouth to mask ventilation:
  • The resuscitator should be positioned behind the head of the supine child
  • The child should be placed in the correct head position ("sniffing" in children, neutral in babies)
  • The correct size mask should be placed on the child's face with both thumbs on either side pressing down and the jaw should be pushed upwards into the mask.  (The correct size mask covers the mouth and nose with a good seal and does not cover the eyes).
  • Blow into the one way valve and look for chest movement
  • Continue this technique ventilating the child at 12-20 breaths per minute (dependent on the age of the child).  If being used in CPR a ratio of 2:15 ventilations to compressions should be used in children and a ratio of 1:3 ventilations to compressions should be used in neonates.
  • If there is a port for supplemental oxygen this should be attached.
  
  

• Self-inflating bags
  Self-inflating bag-valve mask devices consist of a mask attached to a bag which the resuscitator squeezes to deliver a breath.  

Video:  Using a Bag-valve mask (BVM) device.  The two person technique in a child is the same as an adult.  In an infant the major variation is the neutral head position to maintain the airway.

Figure: Bag-valve mask (BVM) device. This is a self-inflating bag that can be connected to a mask in order to apply positive pressure to ventilate a patient. In this figure you will see a BVM device being used on an infant with the infant's head in the neutral position and a single hand to support the mask.  The self-inflating bag can also be connected to an LMA (Laryngeal Mask Airway) or ETT (endotracheal tube) if either is in situ. This device can also be referred to as a bag-valve-mask or the proprietary name - an AMBU bag. 

A BVM is usually used with an oxygen source to enable children to be ventilated using a high concentration of inspired oxygen.  If connected to an oxygen source they can deliver up to 50% oxygen and if a reservoir bag is also connected this allows an oxygen concentration of around 90% to be delivered.  Self-inflating bags can also be used to ventilate patients with endotracheal tubes already in situ.

Two person technique for ventilating patients with a bag-mask device (see figure below)

1. The resuscitator should stand behind the supine child
2. The head should be placed in the correct head position for ventilation (as above)
3. The oxygen should be connected and the reservoir bag needs to be filled before applying the mask to face
4. The correct size mask should be applied to the face over the mouth and nose to give a good seal with the thumbs pressing down on either side of the mask at the same time as pulling the jaw upwards into the mask (preferably with two hands but a one handed technique can be used if only one rescuer)
5. Squeeze the bag and observe chest movement
6. Continue ventilations at 12-20 breaths per minute depending on the age of the child.  If being used in CPR a ratio of 2:15 ventilations to compressions should be used in children and a ratio of 1:3 ventilations to compressions should be used in neonates.

Figure: Ventilation of a child using two-person technique.

If the patient is not breathing (apnoeic) then it will be necessary to ventilate them with a BVM device. Prior to ventilation ensure that the airway is patent using the techniques described above. An obstructed airway will become obvious if attempted ventilation fails to push air/oxygen through the airway. A self-inflating bag (e.g. AMBU® bag) is connected to a mask, which is held tightly to the patient's face to form a seal, then the bag is squeezed to give a breath. This is best done as a two-person technique with one person holding the mask and the other squeezing the bag at a rate of 10-12 per minute. Observation for chest movement is required to ensure adequate ventilation. A self-inflating bag can also be attached to an endotracheal tube if already in situ.

Patients who are not quite apnoeic but are failing to breathe enough to maintain oxygenation and carbon dioxide levels will also require ventilation. Patients who are peri-arrest may appear to be 'gasping' or have irregular breathing. If there is insufficient respiratory function then ventilation should be instigated with a BVM device until help arrives for a more definitive plan such as intubation.

Nasogastric tube

Patients who vomit can aspirate fluid into their lungs.  Therefore it is important to site a naso-gastric tube and aspirate stomach contents to prevent aspiration and protect the lungs.  This becomes especially important when mechanically ventilating a child with a bag-valve mask (BVM) device, as the stomach will be filled with air.  A stomach full of air can cause splinting of the diaphragm making ventilation more difficult.  Therefore use a nasogastric tube to decompress the stomach, once the airway and ventilation have been established.