What is Mendelson Syndrome?
In 1946, Curtis Lester Mendelson found a condition in pregnant patients under anesthesia where they inadvertently inhaled stomach acid into their lungs. This condition is now known as Mendelson’s syndrome and it leads to chemical pneumonia, a type of lung inflammation. Rewind back to the 1940s, during childbirth procedures, 66 pregnant women under anesthesia swallowed and breathed in gastric contents. This resulted in breathing problems and bluish skin (cyanosis) within two hours. X-rays showed infiltration in the lower lobes of the lungs indicating pneumonia. Though everyone in the series recovered, later studies indicated that this might cause a dangerous condition known as Acute Respiratory Distress Syndrome (ARDS). Aspiration pneumonia can be prevented by reducing oral intake during labor. This found the basis for the modern rule of ‘NPO’ (nil per os- Latin for nothing by mouth) for laboring women.
Skimming back through Mendelson’s study, he studied more than 44000 pregnancies from 1932 to 1945. The syndrome was first identified as inhaling stomach contents which led to chemical pneumonia, characterized by fever, bluish coloration (cyanosis), low oxygen level (hypoxia), water in the lungs (pulmonary edema), and the potential for death. It was found that amongst the subjects, 66 had inhaled gastric contents unintentionally, and sadly, two had passed away. The situations where two women died were due to the intake of solid food just before delivery, which got inhaled which led to suffocation. The rest inhaled liquid material and often had a complete recovery.
Mendelson simulated the same situation in rabbits to understand the situation further. He found that during labor, the stomach tends to withhold solids and liquids for a longer period, and there are higher chances of inhaling contents once the throat reflexes are numbed. Back then, general anesthesia used to be a standard for childbirth whether Cesarean or vaginal, in varying distributions. The process used to be administered without securing the airway, but despite the severity of the initial response, most cases were of nonfatal liquid aspirations. They rested back to normal within seven days clinically and showed recovery within 36 hours without the use of antibiotics.
However, based on Mendelson’s study, there were several changes in handling pregnancies for childbirth. Pregnant women are now treated as though they have a “full stomach” regardless of their last meal, and anesthesia without intubation is strictly avoided. Instead of the opaque rubber masks that conceal regurgitation, clear plastic masks are used, solid food ingestion during labor is discouraged. Moreover, if anesthesia is administered by an expert, it can significantly reduce the risk of aspiration.
Although a lot has changed since Mendelson’s time, these findings are still very relevant. Over the last three decades, the rate of aspiration in pregnant women has drastically reduced, thanks to advances in medical procedures during childbirth. Besides using local anesthesia as a standard procedure, there’s also greater awareness about the high risk of inhaling gastric contents. This has led to enhanced safety during labor and delivery. Introduction of new and advanced airway management devices, and the regular use of techniques to keep track of oxygen levels and difficulty in breathing have made the process much safer for pregnant women.
What Causes Mendelson Syndrome?
Pregnancy brings specific changes in a woman’s body that can increase the risk of food or drink going down the wrong way, also known as aspiration. These changes include an increase in breathing rate, oxygen use, and carbon dioxide production, especially early in pregnancy. Later in pregnancy, the growing baby pushes the diaphragm upward, reducing lung capacity.
Other changes in pregnancy include increased heart rate, blood flow, and amount of circulating blood. The growing belly also increases pressure on the stomach, making acid reflux more likely. A hormone produced during pregnancy, progesterone, relaxes the lower esophagus muscle, slowing down the emptying of the stomach and increasing the chance of acid reflux and aspiration during anesthesia.
If stomach content with a high acidity (pH lower than 2.5) and volume (at least 0.3 mL per kg of body weight) is aspirated, it can cause a type of lung inflammation called chemical pneumonitis. However, such aspiration is rare today due to advances in medical expertise and the implementation of fasting time before a medical procedure. It’s estimated that aspiration occurs only in 1 out of 3216 procedures. Even in cases of aspiration, most people do not develop noticeable symptoms. In those who do, lung problems are usually due to an inflammatory response involving certain molecules from the immune system.
During labor, a woman can usually drink clear liquids. This guideline is based on research by military surgeon William Beaumont, who found that liquids pass through the stomach soon after drinking, whereas solid food begins to pass into the small intestine about an hour after eating and takes a few more hours to completely empty.
As for factors that can increase aspiration risk, they include emergency surgical procedures, not deep enough anesthesia, issues with the digestive system, obesity, use of opioid medication, reduced consciousness, certain body positioning during childbirth, difficult airway, acid reflux, and hiatal hernia (a condition in which part of the stomach bulges up into the chest through an opening in the diaphragm).
The severity of any breathing problems resulting from aspiration depends on the amount and acidity of the material that was aspirated, the person’s age, and other health conditions. Aspirating large particles can cause severe breathing difficulty and even death, while smaller particles can cause one-sided wheezing, shortness of breath, cough, and collapse of small airway.
Risk Factors and Frequency for Mendelson Syndrome
The rate of pulmonary aspiration, which is when something enters the lungs or airways from the digestive tract, has fallen significantly in the last 30 years. Studies have shown that the incidence of aspiration during childbirth, specifically during cesarean deliveries under general anesthesia, decreased from 4.2% to 0.46% between 1990 and 2003 and further down to 0.4% in 2008. In 2014, another large study involving more than 30000 deliveries, reported zero aspiration events. However, for non-childbirth related emergency surgeries, the rates of aspiration can be between 1 in 373 and 1 in 895 cases.
In another research conducted from 1998 to 2011 involving cases of maternal cardiac arrest, aspiration was involved in 7.1% of cases. However, patients who experienced aspiration had a high survival rate of close to 83%. It was also found that inexperienced anesthesiologists were a leading cause of maternal mortality due to aspiration. Aspiration is also a common cause of community-acquired pneumonia, accounting for 5 to 15% of the 4.5 million cases. It occurs in 3 out of every 10000 patients under anesthesia, especially during emergency surgeries and in patients with a higher risk health status as indicated by the American Society of Anesthesiologists.
A review of past data indicated that the mortality rate after experiencing aspiration pneumonia is 21% overall and it increases to approximately 30% if the pneumonia was acquired in a healthcare setting.
Signs and Symptoms of Mendelson Syndrome
Mendelson syndrome is a condition that usually occurs after aspiration and can present similarly to fluid build-up in the lungs, also known as pulmonary edema. People with this condition often experience difficulty breathing, coughing, fever, and sometimes, pink, frothy sputum. These signs may appear slowly or progress quite rapidly, leading to severe conditions such as lung tissue death (pulmonary necrosis), lung abscess, or pus-filled lungs (empyema). If examined, these people would typically show signs of rapid breathing (tachypnea), fast heart rate (tachycardia), and a crackling sound in the chest, usually on the lower right part, which is where inhaled substances are most likely to settle.
- Difficulty in breathing
- Cough
- Fever
- Pink, frothy sputum
- Rapid breathing
- Fast heart rate
- A crackling sound in the chest, typically on the lower right part
Testing for Mendelson Syndrome
Mendelson syndrome, a lung condition, is usually diagnosed based on your health history, whether there has been a witnessed instance of aspiration (inhaling substances into the lungs), risk factors you may have for the conditions, and certain signs on chest X-ray images. However, these X-ray images may not show anything unusual at first.
An X-ray can show abnormal spots of density, particularly in the sections of the lung which are dependent i.e., the portions of the lungs that are most affected by gravity when you are lying down. These spots are primarily seen on the right side of the lung, as this side is more likely to experience aspiration due to the larger size and more vertical shape of its main airway (right mainstem bronchus).
Pulse oximetry, a non-invasive test that measures the oxygen level in your blood, may also show a low oxygen level (oxygen desaturation) and a rapid heart rate (tachycardia).
A computed tomography (CT) scan, which is a specialized type of X-ray that gives a detailed image of the internal structures of the chest, can also show areas of consolidation. Consolidation refers to an area of the lungs filled with fluid instead of air, usually due to an infection or inflammation such as Mendelson syndrome.
Treatment Options for Mendelson Syndrome
The best way to deal with illnesses is to prevent them from occurring. However, if a condition does occur, such as aspiration (inhaling food, drink, or foreign objects into the lungs), it needs to be handled quickly to prevent dangerous outcomes. If a patient is suspected of aspiration, the patient should be positioned in a way (referred to as the Trendelenburg position) that allows for quick suctioning of the oropharynx, or the back of the throat area.
If the patient starts to show signs of low oxygen levels and weakened airway reflexes, they may need to be intubated (a tube placed down the throat to help with breathing). Once the breathing tube is properly placed, another smaller tube may be inserted to help suction and prevent the aspirated material from moving further into the lungs with added breathing pressure from a ventilator machine. If the patient has inhaled solid or chunky materials into their lungs, a bronchoscopy (a procedure where a small camera is inserted into the lungs) and lung lavage (washing out of the lungs) might be needed.
Depending on the patient’s health status, it may be appropriate to put them on mechanical ventilation (a machine that helps them breathe) and admit them to the intensive care unit for close monitoring. While it may seem logical to give these patients antibiotics right away, it’s better to wait until they show signs of needing them.
There are specific guidelines from the American Society of Anesthesiology (ASA) to prevent patients from inhaling foreign substances, especially during surgeries when the patient is unconscious. For instance, patients in labor may have a small amount of clear fluids up to two hours before anesthesia. The presence of solid food or particles represents a higher risk of aspiration. Patients should avoid solid foods and those with added risk factors, like diabetes, extreme obesity, and difficulty in breathing, should be extra cautious. For elective surgeries, patients need to fast for 6 or 8 hours depending on the fat content of their last meal. Some sedative and antipsychotic medications can increase the risk of aspiration, so they should ideally be avoided.
For patients about to give birth, medications such as antacids and specific drugs can be used to reduce the risk of aspiration pneumonia. This includes clear, non-solid antacids such as sodium citrate given every 3 hours, which can maintain the acid level in the stomach. Histamine receptor-2 antagonists, a type of drugs such as ranitidine, can help by decreasing stomach acid volume and increasing the pH level. Certain medications like metoclopramide can decrease the volume of stomach content, increase the tone of the lower esophageal sphincter (the muscle that closes off the esophagus to prevent stomach contents from coming back up), and reduce nausea and vomiting during childbirth. These medications can minimize the risk of chemical pneumonia by neutralizing stomach acid.
What else can Mendelson Syndrome be?
When diagnosing Mendelson syndrome, which can seem like several other conditions, doctors need to ensure that they aren’t mistaking it for another ailment. Here are some of the issues that can appear similar:
- Foreign body aspiration
- Near drowning
- Barium aspiration
- Acute exogenous lipoid pneumonia
- Chronic exogenous lipoid pneumonia
- Necrotizing pneumonia
- Aspiration pneumonia due to periodontal disease
- Pulmonary abscess after a laryngectomy
- Aspiration bronchiolitis
- Obliterative bronchiolitis
- Bronchitis
- Tuberculosis
- COPD/emphysema
- Adult epiglottitis
- Mycoplasma pneumonia
- Viral pneumonia
It’s critical for doctors to distinguish Mendelson syndrome from these conditions to ensure correct treatment.
What to expect with Mendelson Syndrome
The outcome for Mendelson syndrome, which is a condition where stomach acid ends up in the lungs, usually depends on any other diseases the patient may have, the severity of the condition, any complications, and the overall health of the patient.
Back in 1946, when Mendelson’s research took place, 66 pregnant patients ended up with stomach acid in their lungs during anesthesia, and almost everyone fully recovered. However, more recent studies showed a higher mortality rate of 30 to 62% in elderly patients with other health issues. This is because a condition called chemical pneumonitis can develop, which can lead to Acute Respiratory Distress Syndrome (ARDS), a severe lung condition.
Without quick treatment, pneumonia could develop and cause more risks such as a lung abscess or bronchopleural fistula, which is an abnormal connection between the lung and the chest cavity.
In severe cases, where pneumonia leads to a pocket of infected fluid in the lung called an empyema, the mortality rate is about 20%. When pneumonia doesn’t have complications the mortality rate is about 5%.
Additionally, a study on mice with aspiration pneumonitis, a type of lung injury caused by inhaling vomit, showed that they have higher chances of having more lung infections later on.
Possible Complications When Diagnosed with Mendelson Syndrome
Mendelson syndrome can lead to grave health problems. These consist of:
- Bacterial infection in the lungs
- Lung abscess, which is a pus-filled cavity in the lung
- Blockage in the airway
- Bronchopleural fistula, an abnormal connection between the bronchus in your lungs and the space between the lungs
- Respiratory failure, a severe condition where the lungs cannot function properly
- Acute respiratory distress syndrome, a severe lung condition causing low oxygen levels in the blood
- Pleural effusion, excess fluid around the lungs
- Empyema, which is pus in the pleural space
- Shock, a life-threatening condition that requires immediate medical attention
- Sepsis, when the body responds to infection encompassing the entire body, which can lead to multi-organ failure
Preventing Mendelson Syndrome
Patients who are going into labor can usually have a small amount of clear liquids, like water or broth, up to two hours before they are given anesthesia. It doesn’t matter too much how much they drink, but it’s important that these liquids don’t have any chunks or particles, because these can enter the lungs if vomited up and cause complications. If patients are going into labor, they should abstain from solid foods, especially those who are at higher risk for complications, like people with diabetes, severe obesity, or those who have difficulty breathing or swallowing. Also, patients should not eat for 6 or 8 hours before they have planned surgery. This is because fats in the foods can take longer to digest, and may potentially still be in the stomach during surgery. Lastly, patients should avoid taking too many sedative or some kinds of mental health medicines during this time, as they can increase the risk of vomiting into the lungs.
