Modalities of mechanical ventilation
Although technical developments have increased the options for many ventilated patients, therapy still remains challenging and complex. Mechanical ventilation includes invasive and non-invasive techniques.
Invasive mechanical ventilation (IV)
Invasive mechanical ventilation or conventional mechanical ventilation refers to the delivery of mechanical ventilation to the lungs using techniques that require an artificial airway. It is probably the most frequently life-saving procedure used in the management of critically ill patients with severe respiratory failure, and it is highly effective and reliable in supporting alveolar ventilation. However, it carries well-known risks of complications.
The interfaces used for invasive ventilation include the standard Endotracheal tube, the Laryngeal Mask Airway (LMA) and the Tracheostomy cannula/tube. As a general rule, intubated patients are hospitalised, submitted to a sedative process, and unconscious.
Complications of mechanical IV
As mentioned above, invasive ventilation carries risks of complications that fall into three main categories: complications directly related to the process of intubation and mechanical ventilation (e.g. aspiration of gastric contents), those caused by the loss of airway defence mechanisms (e.g. chronic bacterial colonisation, inflammation, and impairment of airway ciliary function), and those that occur after removal of the endotracheal tube (e.g. sore throat, cough, sputum production, haemoptysis).
Non-invasive mechanical ventilation (NIV)
Non-invasive ventilation refers to the provision of ventilatory support through the patient’s upper airway using a mask, mouthpiece or similar device. Hence, by definition, this technique is distinguished from those which bypass the upper airway with an artificial airway such as endotracheal tube, laryngeal mask airway or tracheostomy tube, and are therefore considered invasive. NIV refers mainly to Non-Invasive Positive Pressure Ventilation (NPPV), although there are other less commonly used techniques such as external negative pressure (iron lungs).
Non-invasive techniques are suitable in all patients using part time ventilation without major bulbar or upper airway problems. It is commonly used during the night time.
By averting airway intubation, NIV leaves the upper airway intact, therefore preventing problems such as injury to the vocal cords or trachea. It also preserves airway defence mechanisms, allows the patient to eat, drink, verbalise and effectively clear secretions. Several studies indicate that NIV reduces potential infections commonly associated with invasive mechanical ventilation, e.g. Nosocomial infection or hospital acquired infection and Ventilator Associated Pneumonia (VAP).
NIV also enhances patient comfort, convenience and mobility at no greater cost or even less cost, than endotracheal intubation. Furthermore, NIV may be administered outside the intensive care setting (which decreases hospital costs), as long as adequate nursing and respiratory therapy support can be provided. This allows healthcare providers to utilise acute-care beds more rationally, and it greatly simplifies care for patients with chronic respiratory failure at home.
NIV also decreases sedation requirements. Finally, several studies have demonstrated that NIV produces a significant reduction in endotracheal intubation need, in length of hospital stay, and in the in-hospital mortality.
Adverse effects and complications of NIV
In general, NPPV is considered safe and well tolerated when applied optimally in appropriately selected patients. The most frequently encountered adverse effects and complications are minor and are related to the mask and ventilator airflow or pressure where air leaks play an important role, causing ineffectiveness of NIV.
The most common ailments noted relating to the mask are: discomfort, nasal pain, nasal bridge erythema or ulceration and claustrophobia. These issues can be resolved by minimising strap tension, using forehead spacers, or switching to alternative interfaces such as nasal pillows.
Common adverse effects connected with air flow or pressure include conjunctival irritation (caused by air leakage under the mask into the eyes), and sinus or ear pain (related to excessive pressure). Refitting the mask or lowering inspiratory pressure may provide relief.
Another possible complication is nasal or oral dryness (caused by high airflow) which is usually indicative of air leaking through the mouth. Measures to minimise leakage may be useful, but nasal saline or emollients and heated humidifiers are often necessary to relieve these complaints. Nasal congestion and discharge are also frequent complaints, and may be treated with topical decongestants or steroids, and oral antihistamine/decongestant combinations.
Gastric inflation may occur and is responsive to simethicone and is usually well tolerated. Air leaking through the mouth (with nasal masks), through the nose (with mouthpieces), or around the mask (with all interfaces) is virtually universal with NPPV. Measures to reduce leakage include instructing the patient to keep their mouth closed, application of chin straps or bite blocks, or switching to oronasal masks or mouthpieces.
Although use of NIV is becoming more accepted in the medical community, failure of NPPV has been reported in 7 to 42% of patients. Stringent patient selection criteria can ensure a higher success rate. This is frequently observed in patients with COPD in the acute setting, and in neuromuscular patients in the chronic setting.