Non-invasive Ventilation - Types, Contraindications and Complications

Introduction:

Non-invasive ventilation refers to mechanical ventilation without the use of endotracheal intubation. It delivers oxygen via a face mask and can be used in acute and chronic respiratory failure as a replacement for invasive ventilation. However, patient selection is crucial for non-invasive ventilation because it cannot be used in emergency intubation patients.

What Is Non-invasive Ventilation?

Artificial or mechanical ventilation stimulates or assists breathing for persons who cannot breathe or have difficulty breathing. The exchange of gasses happens via external respiration, internal respiration, and pulmonary ventilation. Artificial ventilation is achieved by using mechanical devices.

Mechanical ventilation is divided into invasive and non-invasive ventilation. Invasive ventilation delivers oxygen directly into the patient's airway via endotracheal intubation (a tube inserted into the airway) or tracheostomy (a tube inserted into the airway via an opening created in front of the neck). Non-invasive ventilation is positive or negative pressure ventilation that delivers oxygen without requiring endotracheal intubation.

What Are the Types of Non-invasive Ventilation?

Non-invasive ventilation is divided into positive and negative pressure ventilation.

Positive Pressure Ventilation - Positive pressure ventilation delivers air or a mixture of oxygen and other gasses into the lungs. It forces air and delivers oxygen to the lungs' alveoli (air sacs). Positive pressure ventilators can be pressure-controlled, volume-controlled, or dual control. Non-invasive positive pressure ventilators are of three types which include:

• Continuous Positive Airway Pressure (CPAP) - The basic level of support delivers constant fixed and steady positive air pressure. It uses mild pressure to open the airway for patients with breathing problems during sleep. A CPAP machine consists of a mask that fits the mouth, a tube that connects the mask to the motor, and a motor that pumps air into the tube. It is usually used for obstructive sleep apnea and acute pulmonary edema patients. CPAP is indicated in complete or partial lung collapse, hypoxia, type I respiratory failure, congestive heart failure, cardiogenic pulmonary edema, obstructive sleep apnea, pneumonia, and rib fractures - to splint the fracture and prevent lung collapse.

• Automatic Positive Airway Pressure (APAP) - It is used in patients with sleep apnea. It automatically changes positive air pressure according to the breathing requirement of the patient.

• Bilevel Positive Airway Pressure (BiPAP) - Bilevel positive airway pressure delivers differing positive air pressure during inspiration and expiration. It is used in chronic obstructive lung disease (COPD) and obstructive or central sleep apnea. It is also used in COPD (chronic obstructive pulmonary disease) exacerbation. It has a timer to program the number of breaths per minute. BiPAP is indicated in type II respiratory failure, exacerbation of COPD, hypercapnia, neuromuscular disorders, and weaning from endotracheal intubation.

Negative Pressure Ventilation - A negative pressure ventilator provides negative air pressure to the entire body below the neck. It lowers the pressure around the thorax, creates subatmospheric pressure, and passively expands the lungs. The negative pressure then reduces and compresses the lungs for expiration. Various negative-pressure ventilators were used, but they are of little use now. However, it is still indicated for conditions like chronic respiratory failure.

The types of negative pressure ventilators are:

• Iron Lung - This was the first negative pressure ventilator used. It is also referred to as a tank ventilator. It has a large, sealed horizontal cylinder. The patient lies down on the cylinder with the head protruding from one end. An air pump lowers and raises the negative air pressure in continuous alterations. This causes the patient's chest to rise and fall to stimulate inspiration and expiration through the patient's nose and mouth, which is outside the cylinder.

• Cuirass Ventilator - A cuirass ventilator is also known as a chest shell, turtle shell, or tortoiseshell ventilator. A small shell is attached to the patient's chest with a strap, creating negative air pressure. It is easy to wear and suitable for home use.

• Exovent - It is a newly developed ventilator. It was developed during COVID (coronavirus disease). The patient lies on the internal mattress inside the event. The cover is placed over the entire body and arms. It is fitted with neck and hip seals to deliver negative air pressure.

• Jacket Ventilator - It is also called a poncho or raincoat ventilator. It consists of an inner metal or plastic framework covered with an anorak-like jacket that seals around the neck, arms, and thighs. Intermittent evacuation of air inside the ventilator provides negative pressure ventilation.

• Pulmotor - It consists of a positive and negative pressure ventilator. It uses pressure from a tank of compressed oxygen. The valve system forces air into the patient's airway using alternative positive and negative pressure. However, some medical professionals consider it dangerous because of the risk of barotrauma (damage to the body tissues due to continuous changes in the air pressure) and vomiting.

• Hayek Oscillator - It is a versatile ventilator with a lightweight, flexible, airtight chest enclosure with a soft seal around the chest and abdomen. It rests on a backplate or a loose cushion. This ventilator is attached to a piston pump that provides a baseline and high-frequency negative pressure.

What Are the Techniques of Non-invasive Ventilators?

Non-invasive positive pressure ventilation (NPPV) can be delivered using volume or pressure-cycled ventilators, bilevel positive airway pressure (PAP) devices, or continuous PAP (CPAP) devices. Volume-controlled ventilators deliver a set volume per breath, often causing discomfort due to increased pressure. Bilevel PAP adjusts inspiratory and expiratory pressures, while CPAP provides continuous pressure but requires spontaneous breathing. NPPV is typically initiated in a hospital or home setting for patients with respiratory failure.

What Are the Indications for Non-invasive Ventilators?

• Acute respiratory failure due to COPD.

• Acute respiratory failure not related to COPD.

• Asthma exacerbation and status asthmaticus.

• Cardiogenic pulmonary edema.

• Chronic respiratory failure due to thoracic deformities, neuromuscular disease, and idiopathic hypoventilation.

• Severe stable COPD.

What Are the Contraindications of Non-invasive Ventilators?

• Coma.

• Pneumothorax.

• Coughing up blood.

• Vomiting blood.

• Vomiting.

• Hypoxemia.

• Fixed airway obstruction.

• Facial fractures or burns.

• Cardiovascular instability.

• Cardiac arrest.

• Recent gastrointestinal surgery.

• Active tuberculosis.

• Lung abscess.

• Severe comorbidity.

What Are the Complications of Non-invasive Ventilation?

• Facial mask discomfort.

• Skin rashes.

• Nasal bridge ulcers.

• Retention of secretions.

• Gastric distention.

• Nasal congestion.

• Aerophagia.

• Sialorrhea.

• Ear and sinus pain.

• Pneumothorax.

• Pneumocephalus.

• Pneumomediastinum.

• Aspiration.

Conclusion:

Respiratory failure is a serious condition that requires mechanical ventilation. Non-invasive ventilation is vital in the management of acute and chronic respiratory failure. However, non-invasive ventilation is not suitable for all respiratory conditions. It can be used in acute respiratory failure as an alternative to invasive ventilation. It also helps in weaning from mechanical ventilation. It preserves speech, swallowing, and airway defense mechanisms. It is used to prevent re-intubation in patients with signs of incipient respiratory failure. Non-invasive ventilation is a widely recognized integral tool in managing respiratory failures.