Aspiration Syndrome

Mechanisms of gastric content entry into the airways

The entry of gastric contents into the respiratory tract can occur via two main pathways, each with its own pathophysiological features.

The first mechanism is aspiration associated with vomiting. In this case, there is an active expulsion of gastric contents, which then penetrate into the trachea and bronchial tree.

The second mechanism is regurgitation. Unlike vomiting, this is an entirely passive process of gastric contents flowing into the airways. The development of regurgitation requires a combination of two key factors: a full stomach and relaxation of the muscular sphincters. The highest risk of such passive reflux occurs under specific conditions of anesthetic management. In particular, the danger increases with the use of deep mask anesthesia, as well as immediately before endotracheal intubation, when muscle relaxants that completely abolish muscular tone have already been administered to the patient.

Pathogenesis and clinical presentation

The key damaging factor in aspiration is the pronounced acidic reaction of gastric juice. The pathogenetic chain of events unfolds rapidly:

1. Acidic gastric contents come into contact with sensitive zones of the vocal cords and the tracheal mucosa.
2. In response to chemical irritation, a powerful reflex laryngospasm (closure of the vocal cords) or bronchospasm occurs.
3. Airway patency is abruptly impaired, making adequate ventilation impossible.
4. Acute hypoxia—oxygen starvation of tissues—develops.

The clinical manifestation of acid aspiration is known as Mendelson's syndrome. This symptom complex is characterized by a classic triad of signs: progressive cyanosis (bluish skin discoloration), pronounced bronchospasm, and tachycardia.

In the long term, the main and most dangerous consequence of aspiration syndrome is severe aspiration pneumonia caused by chemical burns of the lung tissue from acid. This complication is associated with an extremely high mortality rate.

Preventive measures and emergency care

Since aspiration pneumonitis poses a colossal threat to the patient's life, preventive measures must be strictly implemented at all stages of the perioperative period.

Prophylaxis before anesthesia induction:

• Mandatory gastric emptying using a nasogastric tube.
• If the patient is diagnosed with peritonitis or intestinal obstruction, the tube is not removed, remaining in place for the entire duration of the surgical intervention. Meanwhile, the patient is placed in a moderate Trendelenburg position (with the head lowered).
• Performing the Sellick maneuver. Immediately before anesthesia induction and intubation, mechanical pressure is applied to the cricoid cartilage in a posterior direction. This physically compresses the esophagus and prevents passive reflux of contents.

Prophylaxis during the emergence stage:

• The patient is positioned strictly horizontally or in the Trendelenburg position.
• The patient's head must be turned to the side.
• Continuous visual and hardware monitoring (observation) is required.

Emergency care in case of reflux: If the complication has nevertheless occurred, the tactics depend on the mechanism. If vomiting has started, the contents must be immediately removed from the oral cavity using swabs or a surgical suction catheter. In the case of passive regurgitation, immediate aspiration of the aspirated contents from deep within the trachea and bronchi is required using suction through an inserted catheter.

Surgical context and choice of anesthesia

The risk of aspiration syndrome directly affects the choice of anesthetic technique, especially in obstetrical, gynecological, and abdominal practice.

At the stage of surgery planning (e.g., during anterior abdominal wall incision and hysterotomy), a careful selection of anesthetic management is carried out. Regional anesthesia (spinal or epidural) is considered the preferred method because the patient remains conscious and airway protective reflexes are preserved.

General anesthesia (endotracheal anesthesia) is used strictly according to indications and requires complete preparedness for the prevention of Mendelson's syndrome. Local infiltration anesthesia is used extremely rarely in modern practice and only for specific indications.

In addition to preventing aspiration pneumonitis, the complex of intraoperative prevention includes mandatory prophylaxis of venous thromboembolism (VTE), infectious processes (via antibiotic prophylaxis), intraoperative hypotension, and bleeding. Access to organs can be achieved through various approaches: from laparotomy (Pfannenstiel, Joel-Cohen, Misgav-Ladach, or lower midline) to specific uterine incisions (lower segment transverse or classical longitudinal).

Class and exam questions

What else to study on this topic

• Types of regional anesthesia: spinal and epidural
• Comparative characteristics of laparotomy approaches (Pfannenstiel, Joel-Cohen, Misgav-Ladach)
• Classical longitudinal incision versus lower uterine segment transverse incision
• Prevention of VTE and intraoperative hypotension

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.