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AirWave overview

The SonarMed® AirWave™ provides direct, precise, real-time monitoring of endotracheal tube (also called an ETT or artificial airway) position and obstructions. Clinicians may use this information to assist with placing the tube properly and to receive early warnings about tube movement and obstruction development so they may take corrective action to prevent patient harm.
The SonarMed® AirWave™ provides precise and continuous information on:
  • Placement, via size of the passageway around the endotracheal tube tip: Helps the clinician identify whether the endotracheal tube is in the correct place (the trachea) instead of the main-stem bronchus (endobronchial intubation) or esophagus (esophageal intubation).
  • Tube tip movement: Alerts clinicians to significant tube movement that may increase the risk of unplanned extubation or endobronchial intubation, allowing them to proactively reposition the tube.
  • Obstructions in the tube: Provides information about the size and location of obstructions that may be developing in the endotracheal tube to help the clinician proactively remove blockages before they harm the patient. Obstruction location information may help the clinician distinguish between lung secretions and patient biting or kinking of the tube.


intubation issues  

When a hospital patient is unable to breathe on his own, he is connected to a mechanical ventilator. The patient is first intubated, a procedure in which an endotracheal tube is inserted through the nose or mouth into the trachea (wind pipe). The tube is then connected to a ventilator, which forces air into the lungs. Each year, approximately 60 million intubations requiring endotracheal tubes are performed worldwide. 

Assuring proper placement of the endotracheal tube within the trachea and assuring that it hasn’t moved or become obstructed are significant clinical problems. Failure to correct a misplaced or clogged endotracheal tube can lead to serious complications to the patient, most notably conditions consistent with lack of oxygen such as brain damage or death.
Complications with endotracheal tubes include: 
  • Unplanned Extubation: The endotracheal tube unexpectedly comes out of the patient’s trachea. Unplanned extubation has an incidence rate of 10% in adult ICU patients.
  • Endobronchial Intubation: The endotracheal tube is placed too far down into the trachea, past the first branching, and enters a main stem bronchus (the airway pipe which leads to one of the two lungs) or, after proper positioning, patient movement or other factors cause the tube to advance into a bronchus. 
  • Endotracheal Tube Obstruction: Lung secretions or other substances block the tube, the tube kinks in the patient’s throat, or the patient bites excessively on the tube.
  • Esophageal Intubation: The endotracheal tube is accidentally inserted into the esophagus (food pipe) instead of the trachea.
Today, the primary clinical method of monitoring endotracheal tube status to prevent patient harm is to perform periodic visual spot checks in conjunction with inferential monitoring technologies. There is no single technology on the market that can provide direct, precise, real time information to assist clinicians in identifying correct tube placement and provide early warnings for tube movement or blockage.

how it works

How It Works 

The AirWave™’s sound waves monitor the airway, alerting clinicians in real time of situations that may lead to unplanned extubations, endotracheal tube obstructions, endobronchial intubation, or esophageal intubation.

TOP: The AirWave™ home screen showing airway management information.
BOTTOM: The Airwave™ waveform screen showing airway management data.

Using principles similar to sonar, the SonarMed® AirWave™ sends a sound signal into the endotracheal tube and records the returning echoes that arise from within the tube and patient airways. The timing and amplitude of these echoes are analyzed by the system to non-invasively measure:
  • Passageway Size Around Tube Tip: The system analyzes the echo that comes from the tube tip to estimate the size of the passageway relative to tube diameter. This information may help clinicians identify and correct esophageal intubation and endobronchial intubation.
  • Degree and Location of Obstructions Within the Tube: The system analyzes the timing and amplitude of echoes that come from within the tube to estimate the location and size of obstructions. This may help clinicians identify an obstruction that forms in the endotracheal tube so it can be removed (suctioned) before the patient is harmed. It may also help the clinician differentiate patient biting or tube kinking from lung secretion buildup by noting the reported location of the obstruction.
  • Tube Tip Movement: The system estimates relative movements of the tube by tracking the timing of an echo that comes from within the lungs. This information may help clinicians identify and correct situations that can lead to unplanned extubation or endobronchial intubation.

the AirWave™ system in depth

The AirWave™ system consists of an AirWave™ adapter connected to the proximal end of an ETT and to a monitor. Embedded inside the AirWave™ adapter are a miniature speaker and a microphone array. With these components, the system employs acoustic reflectometry by emitting sound waves from the speaker into an intubated ETT, detecting the returning acoustic reflections, or echoes, with the microphones, and then examining the echo timings and amplitudes to infer characteristics of the ETT and airway. The monitor’s proprietary algorithms analyze the echo signal and provide information about the size of the passageway around the ETT tip, location and size of ETT obstructions, and relative movement of the ETT tip within the trachea.

The microphone array allows the system to determine the direction from which echoes arrive. As a result, the system can selectively filter all echoes that arise from devices on the ventilator side of the adapter, such as closed circuit suction catheters, Y-connectors, ETCO2 sensors, and filters, for example. This selective filtering allows the system to obtain an echo waveform from the ETT and airways that is free of ventilator circuit echoes.
The AirWave™ adapter contains advanced design features for protecting the sensors from the high-humidity and airway-secretion-prone environment of an artificial airway circuit including a micro-heater to keep them dry and acoustic membranes to shed away secretions.

echoes inside tubes

How do echoes occur inside tubes? As a sound wave travels inside a tube, a fraction of its energy reflects each time it meets with a change in cross sectional area. If it encounters a decrease in cross sectional area (see figure a), a positive pressure wave is reflected. This shows up as a positive deflection in the echo signal. If the sound wave encounters an increase in cross sectional area (see figure b), a negative pressure wave is reflected. This shows up as a negative deflection in the echo signal. The delay time of each echo identifies the distance of the changing area that caused the echo. The amplitude of each echo identifies the approximate amount of area change.


echoes in the ett and airways 

How do echoes form inside the airways? The human airways are a network of bifurcating branches starting at the trachea and ending at the alveoli—the small sacs where the oxygen and carbon dioxide exchange takes place. An interesting property of the airways is that even though the cross sectional area of each individual segment decreases as the branching depth increases, the total cross sectional area (arrived at by adding up the cross sectional areas of all parallel segments) undergoes a rapid increase after several generations of airway branching. In other words, the airways behave acoustically like a horn with a bell at the end, and sound waves traveling down the airways will be reflected at the bell. The negative pressure wave from this bell-shaped region is used by the system as a reference to which changes in ETT tip position are tracked. The bell begins around the 6th branching generation (approximately 5 cm past the carina in adults).
We are often asked if there is an echo from the carina that can be tracked. Unfortunately, since the additive cross sectional area of the two main stem bronchi is approximately equal to the trachea’s cross sectional area, there are no echoes of significance that arise from the carina. However, the AirWave™ provides a feature to synchronize the system with the ETT tip-to-carina distance as measured from one chest x-ray and thereafter provide continuous carina distance tracking.
Relationship of AirWaveTM adapter and intubated ETT (top) to the corresponding echo signal recorded by the AirWaveTM system (bottom).
To illustrate the relationships between cross sectional area, amplitude, and time delay, the figure to the left shows an intubated ETT (top) with its corresponding echo signal, as recorded by the AirWave™ system (bottom). The pressure amplitude is represented on Y-axis and the time delay is represented on X-axis. For each deflection in the echo signal, an arrow denotes the corresponding region in the ETT and airways from which that echo arises.
Referring to the figure, the first echo is a positive deflection (positive pressure) indicating a cross sectional area decrease. This corresponds to the decrease in the nozzle’s diameter from 9 mm to 8 mm. The second echo is a positive deflection immediately followed by a negative deflection, indicating a cross sectional area decrease and then an increase. This echo could be from a small obstruction in the ETT, from a kink in the ETT, or from a patient biting on the ETT. If the echo amplitude were larger, this would correspond to a larger obstruction. The AirWave™ estimates the obstruction size from the echo amplitude and the obstruction location from the echo delay time.
The third echo is a negative deflection indicating a cross sectional area increase. This echo, referred to as the ETT tip echo, is analyzed by the AirWave™ to estimate the passageway size (or effective diameter) around the ETT. A negative deflection echo indicates that the ETT is located in a passageway that has a larger cross sectional area than the ETT. This would be the case for an ETT that is in the trachea. If this echo were to change to a positive deflection, it would indicate that the ETT is located in a passageway that has a smaller cross sectional area than the ETT. This may correspond to an ETT that is in the esophagus or bronchus or that it is clogged at the tip, for example, from mucus.
The last echo, referred to as the airway echo, arises from the bell shaped region in the lower airways. The AirWave™ tracks the time delay of this airway echo, estimating relative changes in the distance between the ETT tip and the airway echo region. For example, if the time delay between the ETT tip echo and the airway echo is decreasing (airway echo moving to the left), then this indicates that the ETT tip is getting closer to the airway echo region or that the ETT is migrating down the trachea. 

AirWave™ sounds are audible

While a majority of medical devices that use acoustics operate in the ultrasonic frequency range, the AirWave™ operates in an audible range below 8 kHz because of the frequencies at which tubes behave as waveguides. Since the sounds typically found in the ventilator circuit—such as respiratory sounds, secretion sounds, or cuff leak sounds—can potentially interfere with the echo signals used by the system, a series of advanced data collection algorithms are used to obtain a clean echo signal during ventilation.
When connected to a patient, the AirWave™ collects a majority of its measurements during the quiet period of ventilation between end expiration and inspiration. As a result, the AirWave™ monitor provides updates to the ETT status approximately every patient breath, depending on the level of noise present between breaths. For cases where excessive noise interferes with acoustical measurements such that the ETT status is not updating, the AirWave™ gives the clinician the option to listen directly to the adapter microphones via the monitor speaker. This assists the clinician in determining the interfering noise source so they can rectify it if possible. Examples of interfering noise sources may include: a leaky ETT cuff, secretions in the airway and/or ETT, a high respiratory rate, a nebulizer, or patient coughing. 


financial benefits

The expected financial benefits for hospitals using the AirWave™ are summarized in a white paper. Sources of savings may include reduced mechanical ventilation time, reduced ICU length of stay, reduced chest x-rays, reduced procedures such as suctioning and bronchoscopy, and reduced therapeutic expenses.



study opportunities


SonarMed® is pleased to announce “Partners in Progress” (PIP), a new program designed to foster independent clinical research in the respiratory field.
The PIP program provides opportunities for researchers to conduct independent studies for publication using the SonarMed® AirWave™. Researchers may study the impact of the system on clinical practices and/or outcomes, or they may use the AirWave™ to conduct studies that were previously not possible or practical, but are now enabled by the unique capabilities of the AirWave™.

By increasing the availability of the AirWave™ for research, and by deferring some of the costs associated with acquiring and using the AirWave™ for research, SonarMed® hopes to enable independent research on a wide variety of respiratory topics that might not otherwise move forward. The program is open to any clinician interested in conducting research in the respiratory space. 

Clinicians are encouraged to submit study ideas or abstracts to SonarMed® for consideration. If the proposal is accepted into the PIP program, SonarMed® will assist with study costs by providing study equipment on a loan, donation or discount basis. The investigator remains responsible for all other study costs.

For a list of study idea starters, contact us.


system components

the AirWave™ monitor

The AirWave™ monitor is a handheld, portable device with a color LCD display that provides information about the endotracheal tube position, obstruction, and movement. The monitor has sophisticated circuitry for sending, receiving and processing audio signals from the AirWave™ adapter. 

SonarMed®’s proprietary algorithms interpret the signals received from the patient’s airway and provide feedback to the clinician through intuitive text and graphics.
The AirWave™ monitor is equipped with a strap for carrying or hanging the unit and a kickstand for propping the unit on a cart or table. The unit can also be accessorized with a mounting clamp to provide even more options for placing it at the patient bedside.

the AirWave™ adapter

The AirWave™ adapter is a small, latex-free, single-patient use disposable device that inserts into the breathing circuit between the ventilator hose and the endotracheal tube, replacing the standard airway adapter. The AirWave™ adapter contains an array of acoustic sensors used for interrogating the artificial airway and communicates with the AirWave™ monitor through a cable. The AirWave™ adapter can be connected to endotracheal tube sizes 6.5 to 9.0 mm ID.

the AirWave™ monitor mounting bracket

The AirWave™ monitor mounting bracket is an accessory to the AirWave™ monitor designed to provide flexibility for positioning the monitor near the patient bedside. The bracket is designed to quickly attach to the back of the AirWave™ monitor. It allows the monitor to be mounted to a round pole (such as  an IV stand), or a rectangular rail (such as those found on many ventilators). The bracket also rotates easily between vertical and horizontal orientations, and allows the monitor to be positioned to an optimum viewing angle.

the Standard Adapter Removal Tool (StART)

The AirWave™ StART is a small plastic hand tool designed to assist in removing a tightly attached adapter (standard or AirWave™) from an endotracheal tube. This is especially useful when a patient is already intubated and an attempt to manually remove the adapter could inadvertently dislodge the ETT. The wedge-based design of the StART allows the adapter to be removed in one smooth, linear motion rather than requiring the caregiver to rock, pull, or twist the adapter.



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