Choking on a foreign body: a physiological study of the effectiveness of abdominal thrust manoeuvres to increase thoracic pressure

Background

Foreign body airway obstruction (FBAO) is a common cause of death, particularly in older people. The National Safety Council USA reports that FBAO is the fourth leading cause of unintentional injury death, with 4864 reported deaths in 2013.¹ The ‘Heimlich’ manoeuvre is a technique for expelling an obstructing food bolus where a first-aider places their arms round the subject from behind and delivers a sharp inward and upward thrust to the abdomen below the rib cage. Heimlich described 162 cases where life was saved following successful administration of abdominal thrusts.²

European Resuscitation Council³ guidance for treatment of FBAO in conscious adults is a combination of back blows and abdominal thrusts with no preference on order. The Australian and New Zealand Resuscitation Councils recommend back blows and chest thrusts for the management of FBAO in conscious adults, but advise against abdominal thrusts, citing concern about complications.⁴

External pressure on the abdomen should be transmitted through the diaphragm regardless of where it is applied, so there is no theoretical reason why force needs to be directed upwards. Motivated in part by three cases of near death from choking involving UK chest physicians (see online supplement), we describe experiments to address these two questions.

Methods

Detailed methods are available in the online supplement. Briefly, different expulsive manoeuvres (see box 1) were performed on and by four consenting adult physiology researchers median (range): age 56.5 (46, 74) years and body mass index (BMI) 25.9 (25, 26) kg/m². Oesophageal and gastric balloon catheters were placed to record pressures generated. Detailed statistical analysis is available in the online supplement.

Results

Maximum peak oesophageal (P_oes) and gastric (P_gas) pressures were similar for the different abdominal thrusts when performed by the experimenters or by the subjects on themselves (see figure 2 and online supplementary table E1). For the upthrust Heimlich manoeuvre, P_oes was 57±17 cm H₂O and for the circumferential abdominal thrust 53±11 cm H₂O (p=0.7). The chair thrust generated a significantly higher P_oes than both; 115±27 cm H₂O (p=0.008 compared with Heimlich).

In one participant, three further manoeuvres were performed. The P_oes generated by back slaps (7 cm H₂O) and chest compressions when supine (position taken as for CPR) (42 cm H₂O) were lower than both the Heimlich manoeuvre (64 cm H₂O) and cough (179 cm H₂O) in that subject. P_oes from supine abdominal compressions was 86 cm H₂O, comparable to abdominal thrusts when upright.

Discussion

Abdominal thrusts caused a sharp rise in abdominal and thoracic pressures, exceeding or equal to those produced by these and alternative manoeuvres in previous studies.^5–8

In 12 supine cadavers, mean airway pressure was 40.8 cm H₂O for chest and 26.4 cm H₂O for abdominal thrusts.⁵ In six anaesthetised and intubated healthy adult male volunteers airway pressures from abdominal thrusts, low-chest thrusts and mid-chest thrusts in the horizontal lateral and sitting positions were compared.⁶ Low-chest thrusts in the horizontal lateral position (34.0 cm H₂O) and mid-chest thrusts in the sitting position (46.2 cm H₂O) produced the highest pressures. In eight intubated and anaesthetised pigs, anterior chest thrusts and Heimlich manoeuvres, both performed in a seated position, produced airway pressures of 6.5  and 13.8 cm H₂O, respectively, with lateral chest thrusts in the side-lying position producing 18.0 cm H₂O.⁷ Day et al⁸ compared alveolar pressure change for back blows (17.7 cm H₂O) and the Heimlich manoeuvre (36.7 cm H₂O).

An upward thrust may be more likely to cause injury to the ribcage or other organs and the person performing it may be inhibited by this possibility. Given the similar pressures generated by circumferential abdominal thrusts, we recommend that the manoeuvre should be performed by inward thrust over the fleshy part of the abdomen, around the level of the navel. This is important information for first aid providers with mismatched height to victim; a smaller individual can perform the circumferential abdominal thrust and produce the same intrathoracic pressure as the Heimlich manoeuvre that requires upthrust.

Australian and New Zealand ALS guidance does not recommend abdominal thrusts.⁴ Studies on pigs, cadavers or anaesthetised subjects are unlikely to be representative of the situation and lung volumes in an upright, conscious choking individual. In our study, manoeuvres were all performed with the subjects at functional residual capacity, which may be more representative of the situation in an emergency. Given our data, we suggest that these guidelines should be amended. Concern about possible risk needs to be balanced against the almost certain risk of death if obstruction persists and the further reduction in risk if a circumferential approach is used.

Self-administered abdominal thrusts were as effective as operator-delivered thrusts and indeed they had been used successfully in two of our cases (online). Repeated manoeuvres can be performed quickly and effectively without relying on an external operator. People choking may be encouraged to try this before a rescuer makes an attempt. Self-administering the manoeuvre is also a clear signal to rescuers (compared with clutching one's throat, which might be misinterpreted as distress due to another cause such as a heart attack). A novel finding is that self-administered thrusts over the back of a chair generated greater pressures than operator-delivered thrusts or self-administered ones. Most food is consumed seated, so there is likely to be a chair available when choking occurs.

Conclusion

The key to diagnosing complete airway obstruction is a conscious subject, in the process of eating, who is unable to breathe at all, nor to speak. Autoadministered thrusts appear as physiologically effective as first-aider-administered ones to generate expulsive intrathoracic pressures, and chair thrusts appear to be the most physiologically effective. We advise that everyone with complete airway obstruction should, in the first instance, either autoadminister abdominal thrusts or perform a chair thrust. The various manoeuvres should be more widely taught in schools, first aid courses, to staff in restaurants and publicised as widely as possible. We would like to see suitable notices in eating places.