The Endotracheal Tube (ETT) and The Laryngeal Mask Airway (LMA) for General Anesthesia
General anesthesia induces unconsciousness, which usually requires airway support.
Airway Management during General Anesthesia
Providing oxygen during general anesthesia is the most essential requirement of anesthesia providers. General anesthesia means that unconsciousness is induced to block awareness and the senses. It is possible to breathe spontaneously and maintain your own airway during general anesthesia, but most people cannot do so adequately once unconscious with anesthesia.
The anesthesiolgist, therefore, must provide airway support and assistance. An endotracheal tube, placed into the windpipe, has been the most widely used device for this function. The laryngeal mask airway, described below, is a newer and less invasive method of securing the airway and delivering oxygen and gas anesthesia during a "general".
The decision of which to use is determined by many factors that have to be evaluated on a case-by-case basis.
*********************** THE ENDOTRACHEAL TUBE -- ET TUBE ***********************
Endotracheal Tube in Sterile Packaging.
What Do We Mean by Your "Airway"?
When we talk about your airway, we mean the passageway that air uses when you breathe on its way to your lungs.
- pharynx- palate, back of the tongue, uvula
- submental tissue
Endotracheal Intubation with an ET Tube
The standard method of securing the airway during general anesthesia has been intubation with an endotracheal tube. Once placed, the endotracheal tube (ET tube or ETT) reliably provides a pathway from an outside source of oxygen to the windpipe and lungs.
THE AIRWAY ASSESSMENT
The anesthesiologist begins to assess your airway in the preoperative evaluation. While he or she is talking to you, several points are noted about your mouth, head and neck. There are actually 11 points that are potential indicators of the ease or difficulty with which you can be intubated.
Placing the Endotracheal Tube
Breathing tubes are placed in unconscious patients (with special exceptions) to ensure and assist breathing. The end result of this essential function is delivery of oxygen to all the tissues of the body and elimination of carbon dioxide from the body. Once an ET tube is in place, a patient can breathe on their own, or have a ventilator (respirator) breathe for them.
During general anesthesia, a patient is rendered unconscious via IV medications in adults and anesthesia gases in small children after an adequate amount of oxygen has been given through a mask. Once "asleep", the breathing tube can be placed.
- The head is gently extended back
- The mouth is opened carefully
- A special lighted scope, called a laryngoscope is inserted along the tongue to the back of the throat.
- The lower jaw is lifted up and out to expose the vocal cords
- The ET tube is placed between the vocal cords into the trachea (windpipe).
- The ET tube's cuff is inflated
- Position of the ET tube is checked by at least 2 different methods
- The tube is secured with tape (usually) to the face
Complications and Side Effects of Intubation
- Failed Intubation resulting in brain damage or death
- Chipped or broken tooth (more common)
- Sore throat (most common due to sensitivity of lining of throat)
- Lacerations to lining of lips, mouth, pharynx or throat
- Hoarse voice - temporary or permanent damage to vocal cords
- Exacerbation of asthma in susceptible people
- Increased blood pressure due to nervous system effects
- Increased or decreased heart rate due to nervous system effects
- Risk of spinal cord injury in patients at risk (broken neck, rheumatoid arthritis with neck involvement, severe deformity with cord compromise, etc).
Benefits of Endotracheal Intubation
- Definitively secure airway
- Easier to use and adjust ventilator and breathing parameters
- Deeper levels of anesthesia possible
- Better protection from aspiration and aspiration pneumonia
Intubation Complications: Potential Issues
Complications of intubation with an endotracheal tube range from the very minor to life-threatening. Luckily, the more serious the complications, the more unlikely it is to occur.
The biggest and most serious risk during intubation is FAILURE TO INTUBATE. Anesthesiologists learn during their training to identify and prepare for the possibility that certain people will have what we call a "difficult airway". There are about 11 indicators that could point to a difficult airway. These range from characteristics of the mouth -- like limited opening or high palate -- to the obese neck with thick tissue that obstructs view of the internal structures.
The most serious consequence of inability to intubate is oxygen deprivation. Once the patient is asleep, there is a limited time frame to resume oxygen delivery. If unable to provide oxygen and ventilation, brain damage and possibly, death can result. This is a catastrophic event in anesthesia for everyone involved.
Other serious complications tend to also occur in specific patients for specific surgeries (e.g. increased internal pressure on the brain, dangerously high blood pressure, etc)
Most adverse effects are not life-threatening. Sore throat is the most common side-effect and can be expected to occur most of the time. Chipped or broken teeth are the most common complication (unexpected, but possible event). The laryngoscope has a metal tongue-depressor like blade that sometimes can contact the teeth. Pressure may be put on the upper front teeth if there is limited space inside the mouth or if the intubation is proving to be difficult. Often, teeth can be damaged if the patient bites down on the tube or bite block while waking up.
******************THE LARYNGEAL MASK AIRWAY -- THE LMA*******************
The Laryngeal Mask Airway
Close-up of the Underside of the LMA
Laryngeal Mask Airway: The LMA is an Alternative to the Breathing Tube
The laryngeal mask airway is an alternative to the ET tube that can sometimes be used. There are some factors that preclude use of the LMA (discussed below).
An LMA is a soft, inflatable plastic or rubber device that is essentially an oxygen mask that goes inside the mouth to deep in the throat. There is a hole in the device that sits over the opening to the windpipe. This opening is above the vocal cords and glottis (a natural flap over the windpipe), so we call it a supra-glottic device. It does NOT enter the windpipe like the endotracheal tube.
The opening on the mask leads to a wide tube that extends out of the mouth to be connected to the oxygen (and anesthesia gas) supply.
Because it does not go between the vocal cords, and because it is made of soft, flexible rubber, the LMA is less irritating to the airway than an endotracheal tube. Patients will still often report a sore throat after LMA use, but it tends to be less bothersome and of shorter duration than with a tube.
LMA Contraindications - When an LMA Can't Be Used
The LMA is a great alternative to the ET tube when it can be used. There are several reasons when the LMA cannot be used, however.
Certain patients and surgeries are not recommended or cannot be done with an LMA. These include:
- Emergency surgeries where the patient has not fasted
- Laparoscopic surgery
- Chest surgery
- Neuro and cardiac surgery where ventilation MUST be controlled
- Lengthy surgery
- Airway surgery
- History of GERD/severe reflux
- Obese patients
- Patients with abnormal anatomy of the head, airway or neck
- Patients with airway masses or obstructions
Potential Benefits of LMA
- Less invasive/irritating, with less severe postoperative sore throat
- No muscle relaxant/paralysis needed
- Patient can breathe on his own
- Less coughing and agitation on awakening from anesthesia
Breathing Tube (ETT) vs. LMA: How do We Choose
The LMA does have limitations to its use, as discussed. Because it is a supra-glottic (above the glottis) device, it does nothing to isolate the opening to the trachea (windpipe) from the opening to the esophagus (food pipe). This means that anything that could cause stomach contents to come up the esophagus put the patient at risk of getting those contents into the lungs.
Risk of aspiration is considered high or too high for certain patients and LMA use is not safe and an endotracheal tube must be utilized.
This category of contraindications includes people with moderate to severe reflux, those who have eaten within 6-8 hours, those who are obese, diabetics whose stomachs don't empty properly, pregnant women and others.
In addition, there are many surgical considerations that indicate an LMA can't be used for various reasons
- lengthy surgeries (the LMA tends to lose function after a few hours)
- surgeries in the prone position (if a patient is face-down and the LMA dislodges, it is difficult or impossible to replace it, causing a dangerous situation.
- certain types of surgeries (e.g. laparoscopic surgery requires high pressure in the abdomen which makes ventilation with an LMA difficult)
- surgery in which the breathing must be carefully controlled (brain, heart and chest/lung surgery)
- surgery in the nose and mouth (any bleeding can drip into the back of the throat and potentially irritate the vocal cords or lungs)
Placement of LMA. This video helps visualize where the LMA sits in the back of the throat.
Potential Complications of LMA Insertion and Use
The biggest problem with LMA use is that, sometimes, it just doesn't fit or seal properly to adequately deliver oxygen. In this case, it can be removed and replaced with an endotracheal tube.
Because the esophagus and trachea are not separated (the openings are not isolated like they are with the endotracheal tube that blocks the trachea), there is a risk of aspiration in susceptible individuals. This can lead to problems with oxygen levels, damage to the lungs and a dangerous pneumonia.
Sore throats still occur with LMA, as mentioned.
Nerve damage has been reported with LMA use. This is a current area of study and more information should be forthcoming. It does not seem to be a common enough problem to advise against using an LMA
Choosing an endotracheal tube or laryngeal mask airway
Choice for morbidly obese
Good for lengthy surgery
Choice for Surgery on Airway Structures (tonsils, nose, mouth)
Choice for laparoscopy
Choice for surgery in prone position
Requires Visualization of Vocal Cords