Many disease processes may lead to the need for ventilatory support (Box 29.2). Mechanical ventilation is the artificial support of, or assistance with, breathing when adequate gaseous exchange and tissue perfusion can no longer be maintained (see Ch. 3). Ventilatory support can be administered ‘invasively’ through an endotracheal tube or tracheostomy or non-invasively through a mask or hood. Both methods can maintain vital function; the type of support required depends on the patient’s underlying condition. Patients with type I or type II respiratory failure or acute pulmonary oedema are likely to have a good response to non-invasive ventilation, which may avoid intubation (Tully 2002).

Ventilation modes

Practitioners must have specialist training in the equipment and processes involved in the care of patients requiring ventilation in order to deliver optimal care and recognise complications. The ventilation modes and care outlined below give a brief overview. The patient’s underlying medical condition, age and weight, will determine the prescribed mode of ventilation.

Invasive modes

• IPPV (intermittent positive pressure ventilation). This delivers a preset tidal volume at a preset rate. It ignores the patient’s own respiratory drive. Its use is restricted to heavily sedated or paralysed patients or those with central nervous system disturbance.

• SIMV (synchronised intermittent mandatory ventilation). The positive pressure breaths are synchronised with the patient’s own breathing and the patient is able to breathe spontaneously.

• BiPAP (biphasic positive airway pressure). Used in invasive ventilation, this mode uses pressure control to deliver the tidal volume. It also allows spontaneous breathing and is often used in acute lung injury (ALI).

• ASB/PS (assisted spontaneous breathing/pressure support). This senses when a patient takes a breath and gives them additional preset support. It can be used with SIMV or alone.

• PEEP (positive end-expiratory pressure). PEEP increases functional residual capacity, i.e. the amount of air left in the lungs at the end of expiration. The pressure prevents small alveoli collapsing and allows a longer period of gas exchange. It is used as an adjunct to IPPV, SIMV and ASB/PS. High levels of PEEP can reduce venous return and reduce cardiac output.

The potential complications of mechanical ventilation are outlined in Box 29.3.

Non-invasive modes

• CPAP (continuous positive airway pressure). This is equivalent to PEEP but is delivered via mask or hood (see Figure 29.1) Airway pressure is maintained above atmospheric pressure throughout the ventilatory cycle by pressurisation in the ventilatory circuit. This makes breathing easier for the patient and facilitates gas exchange.

• NIV (non-invasive ventilation) supports the patient’s breathing to a preset pressure level:

– IPAP (inspired positive preset pressure). This is the pressure level the patient receives on inspiration. The patient initiates a breath, and this breath is then supported by the ventilator to the preset IPAP pressure.

– EPAP (expired positive airway pressure). As the patient breathes out, the expired positive airway pressure prevents alveolar collapse.

Figure 29.1 A CPAP hood.

This mode is frequently employed in type II respiratory failure or as a maximum treatment option if the patient is not suitable for invasive ventilation (British Thoracic Society 2002).

Non-invasive ventilation has become a popular choice for clinicians in recent years. It has the potential advantage over invasive methods of reducing the risk of infection and reducing length of stay (Tully 2002).

Close observations of the patient’s face should be undertaken for pressure damage. Patients who are actively vomiting and those with gastrointestinal bleeds or facial trauma may not be suitable candidates for NIV. Clear explanations are required to ensure the patient understands the treatment. The patient is often anxious prior to treatment commencing due to feeling breathless, and the masks and hoods used can cause feelings of claustrophobia. The gradual implementation of treatment may be necessary to enable the patient to get used to the therapy.

Nursing management and health promotion: respiratory care

Monitoring respiratory function and maintaining safe ventilation

Monitoring and maintaining safe ventilation is crucial and, once the patient is intubated (see Ch. 28) and receiving ventilation support, constant and thorough observations are required as there are many associated complications (see Box 29.3).

• Use of subglottic secretion drainage in patients ventilated for more than 48 hours may prevent aspiration and lower airway colonisation (Lorente et al 2007). Potentially contaminated secretions collect in the patient’s oropharynx above the cuff of the tracheal tube. Endotracheal and tracheostomy tubes are now available with an additional port so the subglottic secretions can now be cleared from the patient’s oropharynx.

Each bundle element has its own set of exclusion criteria. Further information can be found on the Scottish Intensive Care Society website (www.sicsag.org.nhs.uk). An aide-memoire of the bundle is included on the website.

See website Figure 29.2

Humidification

The oxygen used to ventilate the patient must be warmed, humidified and filtered artificially as the endotracheal tube bypasses the natural processes of the nasal passages. Exposing the lungs and airways to cold gas has a number of potentially harmful effects: it can increase mucus viscosity, depress ciliary activity and obstruct the airways due to the build-up of the tenacious secretions. Disposable heat moisture exchange filters (HMEF) are now widely used, primarily because they are cheap and disposable. Temperature-controlled water humidifiers may be used if patients have tenacious secretions.

Ventilator and endotracheal (ET) tubes

The ventilator tubes must not be allowed to become kinked as this would reduce the desired respiratory effect. Patient comfort must be balanced with the safe and secure position of the ET tube in the patient’s mouth. This is achieved by tying a crepe bandage around the patient’s mouth to prevent movement of the ET tube. In the case of a patient with a head injury non-allergic adhesive tape should be used instead of a bandage to decrease the risk of raised intracranial pressure. Care should be given to pressure prevention and the position of the ET tube can be changed daily to facilitate this. Ventilator tubes must not be allowed to drag as this in turn pulls on the ET tube, thereby applying pressure to the lips. Ventilators usually have an ‘arm’ which will support the weight of the tubes. To prevent water from condensation in the tubing entering the ET tube and the lungs it is important that the tubes slope downwards from the patient towards the water traps. When turning the patient, care must always be taken to ensure that ET and ventilator tubes are guarded and supported.

Endotracheal cuff pressures

These need to be checked regularly using an endotracheal cuff manometer. While cuff pressures of 30 mmHg are recommended, pressures of 17–23 mmHg have been shown to be adequate. Complications arising from prolonged excessive ET cuff pressures include tracheal oedema, loss of mucosal cilia, ulceration, ruptured tracheo-oesophageal fistula, stenosis, necrosis, sore throat and hoarseness (Wood 1998). Prevention of these complications is the reason why a tracheostomy is recommended after 12–14 days of oral intubation.

Ventilator observations

Continual observation of the patient should include:

• the patient’s colour to check if well perfused or cyanosed

• oxygen saturation (SaO₂; see Ch. 3)

• level of consciousness, i.e. if sedated or whether drowsy due to CO₂ retention

• chest movements, i.e. are both lungs being ventilated?

• vital signs – changes in a patient’s vital signs can indicate problems with ventilation; blood pressure, heart rate and rhythm, temperature, and respiratory rate and pattern should all be closely monitored.

Observations of the ventilator should include:

• fraction of inspired oxygen (FiO₂)

• the prescribed ventilatory setting

• the expired minute volume

• the patient’s tidal volume

• airway pressures and respirations (spontaneous and ventilator breaths).

All observations should be recorded hourly allowing for continual respiratory assessment and the early detection and treatment of any problems.

Arterial blood gases (ABGs)

Judicious analysis of ABGs (see Ch. 3) will most accurately reveal a patient’s respiratory progress or deterioration and the adequacy of ventilatory support. Care must be taken not to oversample, to prevent iatrogenic anemia (Andrews & Waterman 2008).

Inhaled nitric oxide (NO) administration

The administration of inhaled nitric oxide can improve oxygenation of patients with acute respiratory distress syndrome (ARDS). Whilst there is good evidence of improvement of oxygenation in the short term (Hsu et al 2008) the treatment shows no mortality benefit. Nitric oxide is a highly toxic environmental pollutant and so closed suction systems should always be used.

Positioning

The position of the patient will depend on where the pulmonary abnormality is, and the patient should be positioned to maximise the matching of ventilation and perfusion. In a case of a left lower lobe collapse, it may be helpful to nurse the patient on the right side, thereby optimising the treatment to the affected area. Regularly turning patients will not only assist in the prevention of pressure ulcers but also facilitate pulmonary postural drainage. Nursing the patient in a semi-recumbent position with a 30 degree head tilt reduces the risk of aspiration and ventilator associated pneumonia.

When a patient’s oxygenation remains poor, despite high oxygen delivery and high PEEP levels (classically found in ALI), it may be decided to position the patient face down in the prone position. This manoeuvre increases lung compliance by recruiting underventilated areas of the posterior lung bases and improves oxygenation (Mancebo et al 2006).

Endotracheal suction

Together with hand ventilation (see below), ET suctioning is a procedure used to facilitate the clearance of secretions when a patient’s normal cough mechanism is either inadequate or disrupted. This may occur where there is underlying respiratory or neurological disease or where the cough reflex is suppressed by sedation, muscle relaxants or anaesthetic agents during IPPV. Its purpose is the removal of pulmonary secretions, to avoid the problems associated with their retention, such as increased airway pressures, pneumothorax, cardiovascular instability, lobar consolidation, ventilation–perfusion mismatch, pneumonia, hypoxaemia and atelectasis. However, endotracheal suction can produce complications and carries with it hidden risks (see Box 29.4). Maintaining a patent airway involves endotracheal suctioning and, while it is essential to keep the airway clear of secretions, it is also important not to oversuction and thereby cause unnecessary trauma, irritation and hypoxia (Wood 1998). In order to minimise these risks certain principles should be adhered to; these are discussed in Chapter 28.

Hand ventilation (manual hyperinflation)

Manual hyperinflation is a manual form of positive pressure ventilation using a rebreathing bag. It is used primarily to stimulate a cough in patients with either a poor or absent cough reflex, or when there is atelectasis or excessive bronchial secretions. This intervention must be carefully assessed on an individual patient basis as it is not without severe adverse effects (see Box 29.5) and may have a negative effect on patients with raised intracranial pressure. Hand ventilation may be necessary when there is a ventilator fault, or during cardiopulmonary resuscitation.

Weaning

Weaning is the term used to describe the gradual transition from mechanical to spontaneous ventilation (self-ventilation). During the weaning phase, patients may alternate between these modes until they are able to cope continually on a reduced mode, ultimately achieving spontaneous breathing. It should be individually tailored and begun as soon as it is established that the patient is physically capable of maintaining respiration. The nurse has a key role to play in this. Patients who are likely to require ventilation over a longer period of time will be considered for a tracheostomy (see Chapter 14), which is more comfortable and the patient will require less sedation. It is good practice to allow the patient to rest overnight by giving them increased ventilatory support, which will also allow the patient’s PaCO₂ to return to normal. Each patient should be assessed for readiness to wean each day, an example of an assessment tool can be found on the web.

See website Figure 29.3

Extubation

When spontaneous respiration is successfully maintained, the next step is the removal of the ET tube, a procedure known as extubation. Prior to this procedure, ABGs, oxygen saturation, tidal volumes, respiratory rate and pattern, vital signs, any evidence of tiring, and the presence of a gag reflex together with a strong cough reflex must all be reviewed. Extubation should not be considered unless the patient can cough, swallow and protect the airway, and is sufficiently alert to co-operate. If possible, a planned extubation early in the day is ideal, with more staff on duty. Emergency equipment should be available in case rapid re-intubation is necessary.

Cardiovascular care

In critical care settings, monitoring systems are essential in order to evaluate any potentially fatal physiological derangements and to allow timely treatment to correct any abnormalities. The cardiovascular system can be monitored by the measurement of volume, flow, pressure and resistance in different areas. Chapter 2 covers haemodynamic aspects of care and should be referred to in relation to this section. Patients admitted to critical care units undergo monitoring to glean information about tissue perfusion, blood volume, tissue oxygenation and vascular tone. It is the nurse’s responsibility to carefully monitor these parameters and identify changes.

Nursing management and health promotion: cardiovascular care

Monitoring heart rate and rhythm

The amount of information that can be gleaned from a three-lead ECG and, more importantly, a 12-lead ECG, must never be underestimated and a sound understanding of the heart’s electrical activity facilitates this (see Ch. 2). Cardiac arrhythmias are commonplace in patients in critical care. Hypoxia, shock, electrolyte abnormalities, sepsis, vagal stimulation from ET suctioning, irritation from central venous or pulmonary artery catheters, and medication are responsible for the majority of cardiac arrhythmias; however, some will be the result of myocardial ischaemia in patients with underlying heart disease. Accordingly, where possible, the nurse needs to be aware of any cardiac impairment the patient may have. Monitoring should be continuous, to enable early detection and prompt treatment of underlying problems. For information about the conduction pathways of the heart, arrhythmias and their management, see Chapter 2.