Diagnosing cardiac arrest

Healthcare personnel (doctors and nurses) have difficulty diagnosing cardiac arrest in infants and children if they rely on pulse palpation alone. Their accuracy is approximately 80% with a sensitivity of 0.85 and specificity of 0.65,⁵ which means that in 15% of circumstances they would not give CPR when needed and would give it in 35% when not needed. While application of CPR is not harmful when there is a circulation, the withholding of CPR when there is none dooms the patient to die. The time taken to diagnose cardiac arrest is longer than hitherto realised⁶ – as a group, healthcare personnel take an average of 15 seconds to exclude cardiac arrest by finding a pulse but 30 seconds to diagnose real cardiac arrest by the absence of a pulse. However, the accuracy and expediency of diagnosis are related to experience and training. Only experienced personnel who palpate pulses on a daily basis are able to detect a real pulse within 10 seconds but they, like inexperienced personnel, are unable to quickly diagnose cardiac arrest by the lack of a pulse and need on average about 25 seconds to confirm it. Clinical guidelines advise to spend no more than 10 seconds on pulse palpation and to combine whatever information is gained with observable signs of circulation such as responsiveness, movement and presence or absence of normal respiration. In short, if the patient is unresponsive and not breathing normally there is no point wasting time on pulse palpation (it is inaccurate and time consuming). Instead give CPR immediately.

Epidemiology

The causes of cardiopulmonary arrest in infants and children are many and include any cause of hypoxaemia or hypotension, or both. Common causes are trauma (motor vehicle accidents, near drowning, falls, burns, gunshots), drug overdose and poisoning, respiratory illness (asthma, upper airway obstruction, parenchymal diseases), post-operative (especially cardiac), septicaemia and sudden infant death syndrome.

Oxygen, ventilation and advanced airway support

Oxygen

Oxygen should be administered whenever hypoxaemia occurs but evidence from animal and newborn infant studies suggests that as soon as oxygenation is achieved the inspired oxygen (FiO₂) should be regulated to yield arterial oxygen partial pressure in the normal range in order to limit oxygen-mediated cell damage. The only exception to administration of oxygen is when it may cause pulmonary vasodilatation and thereby shunt blood to the lungs away from the systemic circulation, as may occur in an infant with a single ventricle which pumps blood to both circulations. Chronic hypoventilation is not an indication to withhold oxygen therapy during CPR for infants and children.

Numerous devices may be used to supply supplemental oxygen. The choice is dictated by the required inspired oxygen concentration (FiO₂), cost, avoidance of CO₂ rebreathing, imposed airway resistance and tolerance by the patient.

Oxygen catheters

These are easy to use, cheap, do not cause rebreathing and are well tolerated (permitting eating and drinking) but are limited to supply of up to 40% inspired O₂ because of restriction to gas flow (maximum 4 L min^–1) and limitation of gas reservoir (the nasopharynx). Sizes 6, 8 and 10 FG should be available and placed in the same nostril as the nasogastric tube, to limit airway resistance. Size 6 FG is suitable for infants, 8 FG for small children and 10 FG for older children. Excessive flow may desiccate mucosal membranes and cause gastric distension, which can embarrass respiration.

Oxygen is delivered by nasal cannulae (bi-pronged, ‘nasal prongs’), which sit at the entrance to the nose or a few centimetres inside, need no humidification and do not cause gastric distension. They may become obstructed by mucus and may obstruct the nose. Flow rates for infants should be regulated by a low-flow meter, graduated 0–2.5 L min^–1. Rates of 0.24–4 L min^–1 provide 40–70% O₂ to infants 1–10 kg body weight (BW). Improved oxygenation may be caused in part by positive end expiratory pressure (PEEP).

An oxygen catheter placed in the nasopharynx a distance equivalent to that from ala nasi to tragus provides a small amount of PEEP, and indeed may be used for that purpose. Oxygen concentrations of 30%, 40% and 50% approximately are provided by flows of 45, 80 and 150 mL kg^–1 min^–1 respectively. This technique to provide ‘PEEP’ may be useful to temporarily abort central apnoea in the young infant with RSV, whilst other treatment such as caffeine infusion is established.

Oxygen prongs

Non-humidified oxygen is subject to the same flow restriction as nasal catheters (up to 4 L min^–1). The use of ‘high flow’ (≥8 L min^–1) humidified oxygen as a means to provide CPAP and thereby prevent apnoea, although an attractive technique, has not yet proven to be advantageous in infants outside the premature age group.

Oxygen masks

Semi-rigid face masks of the Hudson type can supply approximately 35–70% O₂ at flow rates of 4–15 L min^–1. However, they may not be well tolerated by the infant or small child, and the distress they cause may consume energy in the tiring child. They may cause rebreathing or fail to deliver the desired FiO₂, especially when peak inspiratory flow rate (PIFR) is high, thus entraining excessive room air. Masks that incorporate a reservoir bag or a Venturi may deliver up to 80% O₂ but, likewise, may cause rebreathing if the flow rate does not match PIFR during respiratory distress.

Head boxes and incubators

A clear Perspex head box is the best way of administering a high concentration of oxygen to the unintubated infant. It allows a non-distressing delivery of oxygen and allows clear observation of the child. Precise oxygen therapy is possible but may be expensive and rebreathing, heat loss and desiccation are potential problems. To avoid rebreathing, a large flow rate (10–12 L min⁻¹) of fresh gas with predetermined oxygen content should be introduced. The practice of introducing a low-flow rate of 100% oxygen into a head box (to gain a lesser concentration) may cause hypercarbia. If 100% oxygen is the only compressed gas available, lesser concentrations of oxygen may be attained without rebreathing by using a flow of 100% oxygen and a Venturi device. The relatively large capacity of an incubator precludes the attainment of a high concentration of oxygen, but limited oxygen therapy, up to a maximum of 60%, can be achieved at the cost of very high flow rates. The concentration of oxygen in the head box can be monitored with an analyser and help monitor the progress of the lung disease and oxygen requirements.

Ventilation

Bag–mask ventilation

As soon as practicable, mechanical ventilation with added oxygen should be commenced with either a bag–mask (bag–valve–mask) or via endotracheal intubation. Although intubation is preferred (see below), valuable time should not be wasted in numerous unsuccessful attempts. Initial effective bag–mask ventilation is a necessary prerequisite for successful paediatric CPR but it is a relatively difficult technique to learn and to perform well in emergency circumstances. Practice on mannequins or in an anaesthetic setting is invaluable in learning to perform this well for the infrequent paediatric resuscitation.

Bags of appropriate sizes should be available for infants, small children and large children. A bag of approximately 500 mL volume should be available for newborn infants and infants.

Insertion of an oropharyngeal (Guedel) airway may be necessary to facilitate bag–mask ventilation. Two types of resuscitation devices are available: flow-inflating and self-inflating bags. They can be attached to a mask, laryngeal mask airway (LMA), endotracheal tube or tracheostomy.

Flow-inflating bags

These are designed to give either positive pressure ventilation or to allow a patient to breathe spontaneously. They are exemplified by Jackson-Rees modified Ayre’s T-piece. Gas flow must exceed 220 mL kg^–1 min^–1 for children and 3 L min^–1 for infants, to prevent rebreathing during manual ventilation. It is possible to control precisely the concentration of inspired oxygen, which is an advantage, especially for the premature neonate at risk of oxygen-induced retrolental fibroplasia. However, considerable experience is necessary to provide adequate ventilation without barotrauma in the intubated infant. A pressure gauge and a relief valve should be incorporated in the circuit to help prevent barotrauma.

Self-inflating bags

These bags are designed only to give positive pressure ventilation. Rebreathing is prevented by one-way duck-bill valves, spring disk/ball valves or diaphragm/leaf valves. The Laerdal bag series (infant, child, adult) typifies these devices. A pressure-relief valve (infant and child size) opens at 35 cm H₂O (3.5 kPa). A pressure monitor can be incorporated in the circuit. Supplemental oxygen is added to the resuscitation bag, with or without attachment of a reservoir bag, whose movement may serve as a visual monitor of tidal volume during spontaneous ventilation when intubated. However, the valve may offer resistance for spontaneous ventilation and this is important to consider in the spontaneously breathing child just prior to the effect of relaxants of rapid sequence induction prior to intubation.

These bags should not be used to provide supplemental oxygen to a spontaneously breathing patient with a mask placed near or loosely over the face. With Laerdal and Partner bags, negligible amounts of oxygen (0.1–0.3 L min^–1) issue from the patient valve when 5–15 L min^–1 of oxygen is introduced into bags unconnected to patients.⁷ The patient valve is unlikely to open unless the mask is sealed well on the face. Although not recommended, if they are used in this way, it is vital to ensure that the patient valve opens or the reservoir bags deflates in unison with the chest movement.

The delivered oxygen concentration is dependent on the flow rate of oxygen, use of the reservoir bag, and the state of the pressure relief valve (whether open or closed). In the Laerdal series, with use of the reservoir bag and oxygen flow greater than the minute ventilation, 100% oxygen is delivered. Without the reservoir bag the delivered gas is only 50% oxygen, despite oxygen flow rate at twice minute ventilation. At an oxygen flow rate of 10 L min^–1 to the infant resuscitator bag, the delivered gas is 85–100% oxygen without the use of the reservoir bag.

Rates and ratios of external cardiac compression and ventilation in ALS

The techniques of external cardiac compression and expired air resuscitation (mouth-to-mouth) or rescue breathing are described in Section 2.2. The recommended ratio of external cardiac compression to ventilation in basic life support by a single rescuer is 30:2^1–4 which if able to be repeated 5 times in 2 minutes, with pauses for ventilations, would yield approximately 75 compressions and 5 breaths per minute.

In advanced life support the recommended ratio of compressions to ventilation by 2 rescuers is 15:2^1–4 which, if repeated 5 times in 1 minute, with pauses for ventilation by bag–mask, would yield approximately 75 compressions and 10 ventilations per minute. When the patient is intubated, it is undesirable and not necessary to pause cardiac compressions to give ventilations because they can be delivered effectively during cardiac compressions and cardiac compressions can be given continuously without interruption. Every time cardiac compression is interrupted, cardiac stroke volume obviously falls to zero and then several successive compressions are required to re-establish the stroke volume achieved before interruption. Necessary interruptions to cardiac compressions should be minimized by co-ordinated planning, to for example, analyse the cardiac rhythm or to give DC shock. Effort must be directed towards minimizing ?hands-off time? during requirement for cardiac compression.

Advanced airway support

Tracheal intubation

The trachea should be intubated as soon as practicable but it can be deferred if successful bag–mask ventilation can be given and should not be undertaken by inexperienced personnel out-of-hospital ⁸ because of complications and poorer outcomes compared with use of bag–mask ventilation. Nonetheless, intubation has numerous advantages, which include establishment and maintenance of the airway, facilitation of mechanical ventilation, titration of oxygen therapy, minimisation of the risk of pulmonary aspiration, enablement of tracheal suction, provision of a route for the administration of selected drugs and preferred for transport and long-term ventilation. Regurgitation of gastric contents is common during cardiac arrest.

Hypoxaemia should be avoided during attempts at intubation – which should be limited to 30 seconds. If difficulty is experienced, oxygenation should be re-established with bag–mask ventilation before a reattempt at intubation. Initial intubation should be via the oral route, not via the nasal route. The oral route is invariably quicker, is less likely to cause trauma and haemorrhage and the endotracheal tube is more easily exchanged if the first choice is inappropriate. On the other hand, a tube placed nasally can be better affixed to the face and so is less likely to enter a bronchus or be inadvertently dislodged during transport or other procedures. A nasal tube is preferred subsequently for long-term management. A nasogastric tube should be inserted after intubation to relieve possible gaseous distension of the stomach sustained during bag–mask ventilation.

Correct placement of the endotracheal tube in the trachea must be confirmed immediately. In the hurried conditions of emergency intubation at cardiopulmonary arrest, it is not difficult to mistakenly intubate the oesophagus or to intubate a bronchus. There is no substitute for visualising the passage of the tip of the endotracheal tube through the vocal cords, confirmation of bilateral pulmonary air entry by auscultation in the axillae, continuous observation of rise and fall of the chest on ventilation and maintenance of a pink complexion. In addition, it is recommended that correct placement of the endotracheal tube be confirmed by capnography or CO₂ detection, with the realisation that CO₂ excretion can only occur with effective pulmonary blood flow. This implies that CO₂ detection cannot be expected unless spontaneous cardiac output returns or external cardiac compression is effective. Absent CO₂ detection mandates re-intubation or at least inspection that the tube is indeed passing through the vocal cords. High CO₂ indicates poor ventilation. Oxygenation should be confirmed with use of a pulse oximeter or measurement of arterial gas tension.

Endotracheal tube size (Table 2.3.1)

Uncuffed sizes are 2.5 mm for a premature newborn <1 kg, 3.0 mm for infants 1–3.5 kg, 3.5 mm for infants >3.5 kg and up to age of six months, size 4 mm for infants seven months to one year (Table 2.3.1). The approximate size may be chosen for children over one year by the formula: size (mm) = age (years)/4 + 4. Tubes one size larger and smaller should be readily available. The correct size should allow a small leak on application of moderate pressure but also enable adequate pulmonary inflation. If the lungs are non-compliant, however, it may be necessary to insert a tube without a leak or insert a cuffed tube. Appropriate- sized cuffed tubes may be estimated by the formula: size (mm) = age (years)/4 + 3.5.