Respiratory arrest

Overview

•Respiratory arrest → hypoxia → cardiac arrest within minutes if untreated

•Paediatric arrest is almost exclusively respiratory in origin - oxygenation is the priority

•Agonal breathing - slow, irregular gasps; brainstem reflex present in ~40% of arrests; must NOT be interpreted as normal breathing - begin CPR

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Tension pneumothorax → one-way valve traps air → impairs venous return → reduced cardiac output → PEA. The conducting system remains intact, so organised electrical activity is present on ECG despite absent pulse.

Presentation

•Unresponsive - no response to voice or painful stimulus

•Absent or abnormal breathing - no chest rise, or agonal gasps only; look, listen, feel for no more than 10 seconds

•Absent pulse - carotid in adults, brachial in infants

Investigations

•Cardiac monitor/ECG - first and most critical; determines shockable (VF/pulseless VT) vs non-shockable (PEA/asystole)

•ABG - pH <7.35 + elevated PaCO2 = respiratory acidosis; PaO2 <8 kPa = type 2 respiratory failure

•Point-of-care echo - right ventricular dilatation = massive PE; tamponade; severe hypovolaemia

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Near-fatal asthma ABG: low pH + high PaCO2 + normal HCO3- = respiratory acidosis with NO metabolic compensation (compensation takes days). Normal or rising PaCO2 in severe asthma is ominous - patient is tiring, likely needs intubation.

Management - Adult vs Paediatric BLS

Adult vs paediatric BLS - key differences
FeatureAdultPaediatric
First intervention (after airway open, no breathing)30 compressions then 2 breaths5 rescue breaths first
Compression:ventilation ratio - 1 rescuer30:230:2
Compression:ventilation ratio - 2 trained rescuers30:215:2
Pulse check locationCarotidBrachial (infants)

Feature	Adult	Paediatric
First intervention (after airway open, no breathing)	30 compressions then 2 breaths	5 rescue breaths first
Compression:ventilation ratio - 1 rescuer	30:2	30:2
Compression:ventilation ratio - 2 trained rescuers	30:2	15:2
Pulse check location	Carotid	Brachial (infants)

🎯
In paediatric BLS, 5 rescue breaths come FIRST before any compressions - regardless of pulse status. Paediatric 2-rescuer ratio is 15:2, not 30:2.

Management - Shockable vs Non-Shockable Rhythms

Shockable vs non-shockable cardiac arrest
FeatureShockable (VF/pulseless VT)Non-shockable (PEA/asystole)
First actionDefibrillate immediatelyContinue CPR
AdrenalineAdrenaline 1 mg IV after 3rd shock, then every 3-5 minAdrenaline 1 mg IV as soon as IV access obtained, then every 3-5 min
AmiodaroneAmiodarone 300 mg IV after 3rd shock; 150 mg after 5th shockNot used

Feature	Shockable (VF/pulseless VT)	Non-shockable (PEA/asystole)
First action	Defibrillate immediately	Continue CPR
Adrenaline	Adrenaline 1 mg IV after 3rd shock, then every 3-5 min	Adrenaline 1 mg IV as soon as IV access obtained, then every 3-5 min
Amiodarone	Amiodarone 300 mg IV after 3rd shock; 150 mg after 5th shock	Not used

⚠️
Adrenaline 1 mg IV is for cardiac arrest. Adrenaline 500 mcg IM is for anaphylaxis. Do not confuse the doses.

Reversible Causes - 4Hs and 4Ts

4Hs and 4Ts
Hypoxia
Tension pneumothorax
Hypovolaemia
Tamponade (cardiac)
Hypo/hyperkalaemia (and metabolic)
Thrombosis - PE or coronary
Hypothermia
Toxins

•Massive PE causing PEA - post-surgical/orthopaedic patient + RV dilatation on echo → give alteplase (thrombolytic); continue CPR for at least 60-90 minutes after administration

•Tension pneumothorax causing PEA - tracheal deviation, asymmetrical chest expansion, absent breath sounds in mechanically ventilated patient → needle decompression

•Hyperkalaemia - sodium bicarbonate 50 ml of 8.4% IV shifts K+ intracellularly