Understanding Ventilator Graphics

Intubation is used when a patient cannot breathe on their own and may be used in the emergency room (ER) or during surgery.

Intubation is a procedure performed when patients are unable to breathe themselves. It may be performed as a life-saving procedure in the emergency room (ER) or during the surgery when patients are under general anesthesia. 

The doctor inserts a tube through the nose or mouth into the throat and trachea (windpipe). The tube facilitates air entry into and out of the lungs. The tube is connected to a machine called a ventilator that pumps air containing an increased amount of oxygen. 

The machine then helps in exhaling air containing carbon dioxide (CO2). The ventilator maintains normal oxygen and CO2 levels in the body. This is called mechanical ventilation. During mechanical ventilation, the cardiac function, blood pressure, and oxygen saturation/levels in the body are monitored continuously.

Most ventilators can be set to apply the delivered tidal volume (the total volume of air that is inspired [breathed in] and expired in one cycle of breathing/respiration) in a control or support mode.

• Control mode: In the control mode, the ventilator delivers a preset tidal volume once it is triggered irrespective of the patient’s effort. 
• Support mode: In the support mode, the ventilator assists during inspiration with the help of an assist pressure. The ventilator detects inspiratory effort (breathing effort) by the patient and supplies an assist pressure during inspiration. The assist pressure is terminated when it detects expiration. The support mode requires the patient to have an adequate respiratory drive. 

The main purpose of mechanical ventilation is to protect the airway and manage respiratory failure. Patients presenting with respiratory failure in the emergency room (ER) is usually a clinical diagnosis.

The decision to intubate and mechanically ventilate or use noninvasive ventilation support is typically made based on clinical assessment by the physician without delay for laboratory results.

It is also indicated for treating critical, life-threatening conditions, such as salicylate intoxication, major head injury with elevated intracranial pressure, or antidepressant toxicity.

Ventilator graphics are an important part of treating patients who are on mechanical ventilation. Ventilator graphics help in understanding the pathophysiology in mechanically ventilated patients. 

Patient-ventilator asynchrony is a common problem occurring in about 25% of patients on mechanical ventilation within the first 24 hours. The ventilator displays waveforms that help the physician to identify and manage any patient-ventilator asynchrony. 

Graphical displays are common in the intensive care setting (ICU). These waveforms are studied and interpreted by the physician who monitors the patient, identifies abnormalities and treats them appropriately. The following are examples:

• Ventilator waveforms
• Arterial waveforms
• Venous waveforms (central venous pressure [CVP])
• Intracranial pressure waveforms
• Intra-aortic balloon pressure waveforms

A mechanical breath is divided into four phases that help identify and correct asynchronies:

• Trigger phase
• Inspiratory phase
• Cycle phase
• Expiratory phase
• Trigger phase

Mechanical breaths are typically initiated by the patient (patient trigger) or as a function of time (time trigger). 

Inspiratory phase

The presence of inappropriate flow and patterns during the inspiratory phase can be identified in the ventilator graphics. Flow may be inadequate or excessive, which can lead to patient-ventilator asynchrony (incoordination).

Cycle phase

Cycling between breathing in and out is brought about by a drop in the flow rate and breath cycles. Other secondary cycling characteristics also are present as a safety precaution if the breath in time is unduly prolonged.

Expiratory phase

Shortened expiratory time may lead to auto-positive end-expiratory pressure (PEEP), which is caused by a progressively increasing accumulation of air (air trapping).

The common complications of mechanical ventilation include the following.

• Pulmonary (lung) complications
• Barotrauma (damage to the lungs due to pressure differences) may result in the following:
• Pneumomediastinum (air in the space between the two lungs)
• Pneumoperitoneum (presence of air in the abdomen)
• Pneumothorax (air in the space between the lungs and chest wall)
• Infection of the lungs
• Atelectasis (collapse of the lungs)

Cardiovascular (heart and blood vessels) complications

The heart and major blood vessels are present within the chest cavity. They are subjected to increased pressure in the chest due to mechanical ventilation. This reduces cardiac function leading to ischemia (decreased oxygenation in the body).