General anesthesia is a state of deep sleep or unconsciousness, during which the patient has no awareness or sensation. While it is possible for a person to maintain spontaneous respirations (breathe on their own) in this state, many cannot do so reliably and require support by their anesthesiologist. This support can sometimes be as little as a chin lift or jaw thrust to help open the airway, but typically involves placement of either an endotracheal tube (ET tube) or a supraglottic airway (SGA), a device that sits above the vocal cords. Both of these devices allow for adequate delivery of oxygen and anesthetic gases. Choice of device is determined by many surgical and patient factors.
Endotracheal tube (ET tube or ETT)
An endotracheal tube (ETT) is plastic tube that is inserted into the trachea (windpipe) and allows for a direct route of delivery of oxygen and removal of carbon dioxide from the lungs. Placement of the ETT is referred to as intubation. Before a patient is intubated, the vital sign monitors are attached. The ETT is then placed after the patient is rendered unconscious following the administration of either intravenous (iv) medications, inhalation of anesthetic gases or both. When a patient is intubated a laryngoscope (blade with a light at the end of it) is used to displace the tongue and allow visualization of the vocal cords and airway. In most cases, the ETT has an inflatable cuff on it which is inflated to seal off the airway and allow for inflation of the lungs.
Complications of endotracheal tube placement
The possible complications of intubation and ETT placement range from a mild sore throat to the life-threatening inability to intubate. Luckily, the most common adverse events are not severe.
Complications of ETT placement:
- Sore throat
- Cuts to the lips, tongue, gums, throat
- Damage to the teeth
- Hoarseness from temporary or permanent damage to the vocal cords
- Increased blood pressure or heart rate
- Asthma exacerbation
- Brain damage and/or death secondary to inability to intubate
A mild sore throat is the most common complaint following general anesthesia and may last a few days. Small cuts to the lips, tongue or mouth can occur secondary to pressure from the metal laryngoscope blade. Chipped or broken teeth are uncommon, and there is an increased chance for this complication in patients with loose teeth, crown on the incisors or poor dentition. This can occur from pressure placed on the teeth by the laryngoscope blade or from a patient biting down on the endotracheal tube or bite block while waking up.
The most serious risk during intubation is the inability to intubate and inability to ventilate (unable to place a breathing tube or move air in and out of the lungs). During training, anesthesiologists learn to identify traits in a patient that could indicate their airway may be difficult to manage. These predictors of a “difficult airway” aid the anesthesiologist in developing an airway strategy that may include having additional supplies and manpower available or even performing an “awake” intubation, where a sedated patient has the ETT passed with special instrumentation while spontaneously breathing.
Other serious complications tend to occur in specific patients and situations. Examples include a dangerously elevated blood pressure or heart rate in a patient with a poorly functioning heart or increased intracranial pressure (pressure on the brain) in a patient with a large tumor or aneurysm.
Supraglottic Airway (SGA) (E.g. Laryngeal Mask Airway)
The supraglottic airway, or SGA is plastic tube with a large cuff that is placed into the back of the throat and is positioned above the opening to the trachea (windpipe). This is an alternative to an endotracheal tube and can be used in certain situations. It has become more popular as in can be placed quickly, has a lower incidence of sore throat and allows a patient to easily breathe on their own. There are a multitude of SGAs in the market. As with an endotracheal tube, SGAs are placed after a patient is completely asleep and unconscious. Placement of an SGA varies between providers and manufacturers. Most are designed to be placed without the use of a laryngoscope blade.
Anesthetic gases and oxygen are then administered to keep the patient anesthetized. Once the surgery is complete, the anesthetic gases are turned off and the SGA is removed once it has been ensured the patient is breathing adequately on their own.
Because the SGA sits above the opening to the trachea (windpipe), gases may also be delivered to the stomach via the esophagus (food pipe), particularly if the patient is being ventilated (the anesthesiologist is providing breaths for the patient) via the SGA. This also means that anything that is regurgitated could potential go into the lungs. Stomach contents entering the lungs is referred to as aspiration, and the risk of its occurrence is higher in certain patients. These patients include people with moderate to severe reflux, those who have eaten within the previous 6-8 hours, pregnant women, and diabetic patients whose stomachs do not empty properly. For these patients, a SGA is unsafe and intubation with endotracheal tube placement is warranted.
Other situations in which the utilization of an SGA is contraindicated are:
- Prone positioning (surgery performed with the patient lying on their stomach) – makes it very difficult or impossible to adjust or replace the SGA if it gets dislodged.
- Laparoscopic surgery – the high pressure created in the abdomen makes it difficult to ventilate with the SGA
- Surgery requiring careful control of breathing – includes brain, cardiac and thoracic/chest procedures
- Surgery in the nose or mouth – blood can drip from the surgical site onto the vocal cords or into the lungs and cause irritation; theSGA itself may interfere with the surgical site
- Obesity- SGAs can be used in obese patients but increased soft tissue in the airway and neck can make properly placing the SGA more difficult. The added weight of the abdomen can also make ventilation difficult, similar to the pressure created with laparoscopic surgery. The incidence of converting to endotracheal tube placement is higher in this population.
Complications of SGA Placement
The most common problem with SGA placement is that the device does not fit or seal well enough to deliver adequate amounts of anesthetic gases and oxygen. In this situation, the SGA is removed and an endotracheal tube is placed.
As mentioned above, the risk of aspiration is present.. An aspiration event can lead to difficulty delivering oxygen to the lungs, damage to lungs from the acidic stomach contents, or pneumonia.
A sore throat and small cuts to the mouth are still possible with SGA placement, but tend to be less bothersome and resolve faster than with intubation.
Nerve damage in the throat and neck is also a possibility. This can occur from over-inflation of the cuff putting pressure on surrounding nerves. This adverse event is currently being researched more, but its occurrence is very low and has not discouraged the routine use of SGAs.