A limited or completely lost respiratory function can be adopted or assisted with an artificial respirator. Modern respirators offer at least two basic modes of operation, which are the mandatory and spontaneous ventilation mode. When in mandatory ventilation mode, the respirator controls and performs the breathing work completely or, in case of minimal residual respiratory function, in complemented mode. While working in complemented mode, important parameters (inspiration pressure, tidal volume and ventilation frequency) are monitored and, if necessary, adjusted by the respirator at any time.

The spontaneous ventilation mode allows the patient to either completely breathe on his own or to be supported by the respirator [30]. The two most important parameters in artificial ventilation are volume and pressure. With adaption of these two parameters, literally every available ventilation mode can be implemented [31]. Just as the discussion over the optimal ventilation mode continues, so does the debate over the optimal control variable. Volume-controlled ventilation (VCV) offers the safety of a preset tidal volume and minute ventilation but requires the clinician to appropriately set the inspiratory flow, flow waveform and inspiratory time. During VCV, airway pressure increases in response to reduced compliance or increased resistance and may increase the risk of ventilator-induced lung injuries. Pressure-controlled ventilation (PCV), by design, limits the maximum airway pressure delivered to the lung but may result in variable tidal and minute volume. According to current recommendations, the target tidal volume should range between 6 and 8 ml/kg body weight in patients with a normal body-mass index (BMI) [32].

Most studies comparing the effects of VCV and PCV were not well controlled or designed and offer little to our understanding of when and how to use each control variable in invasive ventilation [31]. Nevertheless, in SCI patients PCV seems to be more advantageous for prevention of atelectasis and for potential compensation of volume loss (e.g. phonation while ventilated with an unblocked cannula).

When choosing the ventilation mode for an individual patient, the clinicians have to keep in mind that a spinal cord-injured patient suffers from an impairment of the respiratory pump without a primary pulmonary disease. Patients with SCI and associated severe pulmonary diseases have to be treated additionally according to pneumological respiratory guidelines [31] including carefully selected medications and adapted ventilation modes.

The aims of artificially assisted ventilation in persons with SCI are:

There are a few reports published about tidal volumes between 900 and 1000 ml (sometimes even higher) applied in patients with tetraplegia requiring invasive ventilation [33]. In case of a normal BMI, 10–15 ml/kg ideal body weight is recommended during the acute phase [34]. In the presence of atelectasis, a slow increase of 20 ml/kg ideal body weight with a maximal pressure of 30 cmH₂O is described in order to minimise the risk of a barotrauma [32, 35]. It was shown in a 10-year observational study that the risk for developing an atelectasis increases with lower tidal volumes [33]. As a consequence, it is recommended to apply higher tidal volumes for successful treatment of atelectasis while reducing the breathing frequency to avoid chronical hyperventilation [33].

On the basis of clinical experience with long-term ventilated tetraplegic patients with inserted unblocked tracheal cannula, six main advantages of using higher tidal volumes were stated [36]:

General observations of long-term ventilation with high tidal volumes show that the respiratory alkalosis associated with the hypocapnia can be completely renally compensated without pathological pH values. Theoretically possible negative effects of hypocapnia, e.g. reduced cerebral blood flow caused by vasoconstriction and thereby increased susceptibility for seizures, were not observed in the long-term course [37].

In principle, high tidal volumes with hyperventilation also offer the risk of potassium loss and increased osteoporosis by chronic hypocapnia [38]. The former has to be verified regularly and, if necessary, applied. Concerning osteoporosis it should be noted that tetraplegia by itself is leading to an increased osteoporosis in the long-term course, to which many factors beside the hypocapnia contribute.

In conclusion, according to the literature, the following recommendations can be given with regard to invasive long-term ventilation of lung-healthy persons with tetraplegia:

Invasively ventilated patients with SCI should be provided with the possibility to speak during the very acute phase of injury during the stay in the intensive care (ICU) and intermediate care (IMCU) units. Apart from the advantage of better communication and the associated higher quality of life, the opportunity to speak creates a higher level of laryngeal awareness. This may help to improve oral ingestion and to prevent episodes of aspiration [39].

The inability to speak poses a considerable restriction on participating in everyday life for patients which are in need of permanent or partial ventilation [40]. If only minor or moderate swallowing disorders are present, loud and clear phonation during invasive ventilation is feasible and can be learned [41–43]. Phonation always depends on airflow through the glottis enabling the vocal cords to vibrate and produce tones. Unrestricted patients normally phonate during expiration [44]. In contrast, phonation in ventilated patients mainly occurs during inspiration, because the required airflow from the ventilator is generated during the inspiration, while expiration mainly proceeds passively [45].

Acute and long-term ventilated patients have a high risk of developing pneumonia [46], decubital ulcers [47] and deep vein thromboses [48]. Therefore, mobilisation of those patients is recommended as early as possible, even in IC and IMC units [49–51]. To achieve this early mobilisation, appropriate equipment and personal resources must be present in the form of:

In the context of acute care of tetraplegic patients, a tracheotomy is often required to enable sufficient respiration and secretion management. Tracheostomy also may be needed in case of prolonged ventilator dependency if typical problems associated with the use of oropharyngeal or nasopharyngeal tubes appear. A tracheotomy can be done either by dilatation percutaneously (PT) or surgically as an open tracheostomy (OT). Further advantages of a tracheostomy are the early reduction or suspension of analgosedation resulting in an alert and compliant patient who is able to participate in a SCI-specific therapy programme, consisting of mobilisation into the wheelchair, phonation, food intake during ventilation and weaning.

In general, a tracheotomy is recommended in tetraplegic patients with:

Studies also demonstrated that an early tracheotomy (<10 days after the onset of paralysis) shortens both the duration of stay in an intensive care unit and the overall ventilation period (assuming that weaning was successful) [54]. With regard to complication rates of both techniques (PT and OT), there is inconsistent evidence [55, 56]. In the case of a permanently invasively ventilated patient, the current German Respiratory Society guideline “non-invasive and invasive ventilation” recommends stable medical care for outpatient ventilation and therefore the placement of an epithelial open tracheotomy [57]. Regardless of the used technique, PT can only be accepted for a short and successful weaning process in the ICU/IMCU or exceptionally in home mechanical ventilation due to the tendency to shrink and the risk of malposition of the cannula [57].

The innervation and strength of the diaphragm muscle determines the vital capacity of the lungs [63, 64]. The higher the vital capacity, the better the weaning prognosis [65]. Therefore the weaning process should not be initiated when the vital capacity of a lung-healthy patient is below 1000 ml [66]. The aim during the weaning process is to systematically train the diaphragm muscle while avoiding excessive fatigue of the muscle. Disregard may lead to an extension of the weaning period or failure of the weaning process [67].

The diaphragm muscle is prone to a fast conversion from slow-fatiguing type I to fast-fatiguing type IIb fibres after paralysis. The training during the weaning reverts this paralysis-induced fibre transformation and leads to more slow-fatiguing muscle fibres [68–71].

From the clinical experience, weaning should not be started or must be interrupted when at least one of the following confounding factors is present:

Weaning should be started in a lying or reclined position (bed or wheelchair) during daytime (e.g. 8 a.m.–8 p.m.) in the ICU under the control of certain vital parameters. This includes breathing frequency, breathing (tidal) volume and values of carbon dioxide (capnography). During night-time recovery of all respiratory muscles should be ensured by correct settings of mandatory ventilation modes of the external respirator [66].

During the daytime, every hour should consist of a spontaneous breathing (training) part and a ventilator (recovery) part. In clearly defined steps of 5–10 min, the training sessions (up to 12) are slowly increased day by day until the patient is breathing spontaneously 12 h without any ventilator support. If the patient is stable during daytime, the night-time weaning can be initiated with increasing periods of spontaneous breathing, e.g. 1 hour per night.

The mentioned vital parameters including spirometry should be monitored and the weaning process interrupted, if confounding factors evolve. The application of a standardised protocol is recommended [15, 72, 73].

The supervision and adaption of the weaning process requires a highly trained staff to achieve a successful outcome. This knowledge is normally only present in specialised SCI centres. Therefore, the rapid transfer of patients in need of artificial ventilation from the ICU to SCI centres is recommended by SCI societies worldwide to ensure an adequate weaning procedure.