Airway Management During Induction
1Airway Management During Induction
Aspiration of Gastric Contents
In any anesthesia induction, a primary concern is the presentation of pulmonary aspiration (Any liquid or solid matter that enters the trachea bronchioles and the lungs of gastric contents which result in life threatening bronchospasm and pneumonia). Unconsciousness results in loss of the normal airway reflexes the patient with stomach contents may regurgitate gastric material via the esophagus which may be aspirated into the lungs causing a severe pneumonitis (inflammation of the lungs) usually called "aspiration pneumonitis". This is especially severe, and often fatal, if the gastric contents are markedly acidic (pH <2.5), as little as 30mls will cause a severe reaction. When solid foodstuffs are aspirated complete obstruction of the airway may occur.
Regurgitation and Vomiting: regurgitation is a return of partially digested food from the stomach to the mouth. It is passive enhanced by muscle paralysis involving smooth muscles only. Vomiting is the force full expulsion of the stomach content to the mouth; is an active process and involves contraction of the abdominal muscles. Both regurgitation and vomiting may lead to aspiration of gastric contents with catastrophic results. Aspiration of gastric contents in to the lung is universally accepted as the most frequent single cause of death due to anesthesia.
Clinically aspiration may manifest as acute respiratory obstruction, acute chemical irritation, or total cardiovascular collapse.
Normally the specialized junction between the esophagus and the stomach, the oesphagogastric junction (which may also be called the cardiac sphincter) acts as a sphincter to prevent material returning to the esophagus after entering the stomach. When the conscious level is depressed this junction works less efficiently and if the pressure within the stomach (the intragastric pressure) is greater than the closing pressure of the sphincter then regurgitation will occur.
Before elective surgery, the patient routinely fasts from mid night until the induction of anesthesia. The purpose for NPO (nothing by mouth- no food or liquids) order is to minimize the amount of undigested food and gastric secretions present in the stomach. However these periods of fasting may not always guarantee an empty stomach. Patients who have been traumatized, or are suffering from intra-abdominal pathology, or who have had opioid drugs or are in labor do not empty their stomachs efficiently and should always be treated as if they have a full stomach The emergency surgical patient is unlikely to have fasted for six to eight hours and thus there is a real likelihood that there will be gastric contents to aspirate. Thus, patients presenting for emergency surgery are generally considered to have full stomachs.
The risk of regurgitation is greater if the intragastric pressure is increased by the presence of food or liquid within the stomach, the lithotomy position (legs up with patient on their back), obesity or an intra-abdominal swelling such as pregnancy after 24 weeks or ovarian masses.
Classification of Pulmonary Aspiration
- Aspiration pneumonitis Known as Mendelson's syndrome is the condition involves lung tissue damage as a result of aspiration of non-infective but very acidic gastric fluid. Clinically, this may be asymptomatic, or present as tachypnea, bronchospasm, wheeze, cyanosis and respiratory insufficiency.
- Aspiration pneumonia occurs either as a result of inhaling infected material or secondary bacterial infection following chemical pneumonitis. It is associated with typical symptoms of pneumonia such as tachycardia, tachypnea, cough and fever.
- Particulate-associated aspiration: If particulate matter is aspirated, acute obstruction of small airways will lead to distal atelectasis. If large airways are obstructed, immediate arterial hypoxemia may be rapidly fatal.