Breathing

It is estimated that the relaxed diaphragm will be elevated by the gravid uterus by up to 4 cm in the third trimester. The decreased compliance of the chest wall and splinting of the lungs by the diaphragm makes lung expansion much more difficult to achieve and requires higher pressures to facilitate, again potentially increasing the risk of gastric distension, regurgitation and aspiration. The added weight of engorged breasts may also contribute to reducing chest wall movement. Consequently, the mother’s functional residual capacity will be reduced and the requirement of good bag–valve–mask (BVM) technique is paramount. The sizing of the face mask will remain unchanged.

Circulation

Due to the risk of aortocaval compression, a collapsed patient must be positioned in a left lateral tilt of between 15° and 30° or with the uterus manually displaced. However, when faced with a patient in cardiac arrest, the ability to deliver effective chest compressions is compromised when the patient is tilted and this will adversely affect the efficacy of any resuscitation attempt. Manual uterine displacement is now the recommended technique to overcome this. In addition to enabling effective chest compressions, manual uterine displacement enables easier access for airway management, bilateral vascular access and defibrillation.

Failure to reduce the risk of aortocaval compression will mean that oxygenated blood cannot be circulated to the mother or fetus. Occasionally, repositioning the uterus relative to the major blood vessels may reveal a profound syncope induced by aortocaval compression that has been misdiagnosed as a cardiac arrest.

Pre‐hospital management

Patient positioning

Manual uterine displacement can be performed from the left of the patient (Figure 7.1) where the practitioner ‘cups’ and ‘lifts’ the uterus upwards and to the left off the maternal vessels. If the patient is loaded into an ambulance head first, manual uterine displacement can also be achieved from the right of the patient (Figure 7.2), where the uterus is pushed upwards and to the left. Care must be taken not to inadvertently push down, which would increase the amount of inferior vena cava compression and cancel any potential benefit.

Lateral tilt can be achieved by using an improvised wedge under the patient or by placing the patient on an immobilisation device before tilting (see Chapter 6). It is also a technique that can be used when fewer team members are present, for instance when transferring a patient in the ambulance with only one clinician in the saloon.