Communication breakdown is a common cause for transfer-related incidents and is completely preventable. Communication should start as early as possible and should use closed and targeted terminology in order to avoid misunderstanding. Communication should always start by including senior members of the ICU team.

Once the decision has been made to transfer, this should be discussed with the patient (if feasible) and their relatives as early as possible. The receiving team should be contacted to discuss the patient’s history, reason for transfer, their current status and any anticipated problems that may arise before arrival. It is essential that any identified infections and micro-organisms are communicated to the receiving team as the patient may require isolation on arrival. There are myriad examples of multi-resistant organisms spreading due to transferred patients acting as the vector.

Details of the receiving hospital’s exact location and contact numbers should be established prior to departure and any specific access routes. Estimated times of departure and arrival should be discussed and further contact should be made if there is significant deviation from these. If any problems or deviations from the plan arise they should be communicated to the receiving team; the latter have an ethical obligation to retain a bed once transfer has been accepted. Once the patient is prepared, on the transfer trolley and in the process of leaving the referring hospital, it is customary for one of the referring ICU team to contact the receiving team to confirm departure.

The escorting staff should possess the appropriate skills and knowledge to manage the patient for the purposes of the transfer. As a minimum they should have theoretical knowledge of the common problems encountered during transfers and the management required should these problems arise. Ideally, all staff should have undergone training in critical care transfers. In the past, such training has been elusive, but it is increasingly available and can be accessed as free on-line training [13]. Usually, the escorting team will consist of a doctor with airway management skills and a nurse; however, patients may be transferred by any clinical staff provided they have the appropriate training and skills. The composition of the transfer team should be bespoke according to the patient’s needs. For the purposes of transferring a patient, the transfer vehicle becomes an extension of the escorting team’s usual place of work; as such, their usual employer’s insurance and indemnity apply.

A detailed system-based review of the patient should be performed during preparation for transfer; time spent stabilising and resuscitating the patient at this point can reduce problems during the transfer and has been shown to reduce length of ICU stay [14].

As part of the patient assessment, the airway must be assessed and secured if necessary. Adequate sedation, analgesia and muscle relaxation must be ensured for patients who are intubated.

As a guide, two large bore and well-secured intravenous cannulae should be in situ prior to transfer. The patient should be appropriately fluid resuscitated with an adequate cardiac output prior to departure; the forces of inertia experienced during acceleration and (more importantly) braking can result in clinically significant intravascular fluid shifts which are exaggerated in hypovolaemic patients. If inotropic agents are required to achieve haemodynamic stability, the patient should be stabilised using these agents prior to departure. Haemodynamic targets should be bespoke to the patient and may need to be significantly lowered for conditions such as ruptured aortic aneurysm (see subspeciality transfer section).

The level of monitoring used during transfer should mirror what is considered essential if the patient were to be managed in the intensive care unit; as a minimum for intubated patients, the following monitoring should be used: ECG, pulse-oximetry and non-invasive blood pressure with the addition of end-tidal CO₂ (EtCO₂), inspired oxygen concentration and airway pressure. It is preferable to monitor continuous invasive blood pressure as non-invasive blood pressure can be unreliable and results in greater drain on the monitor’s battery. In addition to the above, the patient’s temperature should be regularly checked (hypothermia is common during long transfers). Alarm limits and monitor volumes should be checked and amended as necessary.

For transfers that are not time critical, the patient should be established on the transfer monitor and equipment (including the transfer ventilator) for about half an hour before departing. Mains gases and electricity should be used to preserve battery life and portable gas supplies, and an arterial blood gas should be performed to ensure adequate ventilation. Any instability should be resolved before departure; this can result in delays but, if ignored, such deteriorations can result in challenging incidents while in transit.

The duration of transfer should be estimated and used to guide calculations for oxygen, battery and drug requirements. It is prudent to carry 50 % more than these calculated requirements to allow for delays. Where possible, electrical inverters should be used in the transfer vehicle; these convert the AC power supply generated from the vehicle’s engine into a DC supply that can be used to power equipment. Drug infusions should be rationalised according to patient requirements and administered via reliable syringe driver pumps; volumetric pumps should not be used during transfers due to the impact of movement artefact on the infusion rates.

A mechanical ventilator is a necessity for all intubated patients and modern transport ventilators are also capable of delivering non-invasive ventilation.

The main dynamic hazard posed to the patient during transfer is that of acceleration and deceleration. Newton’s third law states that ‘for every action there is an equal and opposite reaction’. Therefore when the patient is accelerated they will experience an equal and opposite force termed ‘inertia’. The most common effect experienced is acceleration towards the patient’s head with the resultant inertia causing blood to move towards their feet (N.B. in most countries, patients are loaded into ambulances head first with their head at the front of the ambulance). The reverse occurs when the patient is accelerated towards their feet (e.g. under heavy braking in an ambulance). In this situation the resultant inertia causes their blood and stomach contents to move towards their head and significant increases in intracranial pressure can occur [15]. A nasogastric or orogastric tube and urinary catheter should be inserted and left on free drainage prior to departure, the former to prevent aspiration of gastric contents as a result of inertial forces.

The exposure of critically ill patients to these forces can lead to significant physiological alterations and pathological consequences [16].

Prevention of instability is best achieved by travelling with an adequately fluid resuscitated patient, in the head-up tilt position, while minimising rapid acceleration and deceleration. It is important to highlight that the same forces will also act elsewhere in the ambulance; all objects (including the transfer personnel) will become ballistics unless secured. If the medical team need to attend to the patient during the transfer, they should inform the driver and wait for approval before removing their safety belt. Failure to wear a safety belt can result in staff not being insured in the event of subsequent injury.

Static hazards posed to the patient and staff include noise, vibration, temperature and atmospheric pressure. Noise hampers communication, can render audible alarms useless and makes the use of a stethoscope impossible. The damaging effects of vibration can be reduced by padding and protecting areas of the patient in contact with hard objects. Exposing the patient to open environments during transfer can result in rapid heat loss and hypothermia.

A static hazard specific to air transfers is the reduction in ambient pressure which leads to expansion of gas filled cavities and relative hypoxia. The hypoxia at altitude, even in a pressurised aircraft cabin must be considered when calculating the oxygen requirements for transfer.

The expansion of closed gas-filled cavities can result in injury and a pneumothorax may expand. Thus it is important to ensure drains are correctly placed and patent prior to take-off; there may be damage to the middle ear if the Eustachian tube is obstructed; and expansion of the gastrointestinal tract may be associated with nausea and vomiting, compromise of venous return or even perforation.