Anesthesia-related aspiration during surgery is a serious and potentially life-threatening complication that can lead to significant health issues. For patients undergoing thoracic surgery, the risk of such aspiration events is notably elevated due to several predisposing factors often associated with these procedures. Both thoracic surgeons and anesthesia teams must be acutely aware of these risk factors, understand conditions that increase susceptibility, implement strategies to minimize risk, and be prepared with immediate management options should aspiration occur. A crucial element in mitigating these risks, particularly in high-risk cases, is the presence of an experienced anesthesiologist, as many aspiration incidents can be traced back to provider-related factors.
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Defining Pulmonary Aspiration: What Happens and Why It Matters
What is Aspiration? Definition and Consequences
Pulmonary aspiration, in the context of anesthesia, is defined as the entry of liquid or solid materials into the trachea and lungs. This occurs when a patient, under anesthesia and lacking sufficient laryngeal reflexes, passively regurgitates or actively vomits gastric contents. The consequences of pulmonary aspiration can vary widely in severity, ranging from mild hypoxia to severe respiratory failure, acute respiratory distress syndrome (ARDS), and in the most critical cases, cardiopulmonary collapse and death. The types of lung injuries resulting from aspiration depend largely on the nature and volume of the aspirated material.
These injuries can manifest as several distinct pulmonary syndromes:
- Acid-associated pneumonitis: This is the most common lung injury following aspiration, caused by the inhalation of sterile, acidic gastric contents (or bile). First described by Mendelson in 1946, the severity of this pneumonitis is determined by the acidity (pH), volume of the aspirate, and presence of particulate matter. Even a small amount of highly acidic aspirate can lead to severe pneumonitis, while larger volumes with a higher pH may be better tolerated. As little as 50 ml of regurgitated gastric content is considered a ‘severe’ aspiration event.
- Particle-associated aspiration: When solid particles are aspirated, they can cause mechanical airway obstruction.
- Bacterial infection: Aspiration of non-sterile gastric contents or material containing particulate matter can lead to infectious complications, including lung abscess, exogenous lipoid pneumonia, chronic interstitial fibrosis, and Mycobacterium fortuitum pneumonia. Common pathogens involved include Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter species, anaerobes, Klebsiella species, and Escherichia coli.
Understanding what is aspiration and its potential consequences is paramount for medical professionals involved in surgical procedures, especially thoracic surgeries where the risk is heightened.
Risk Factors: Who is at Risk of Aspiration?
Several factors, related to both the patient and the surgical procedure, can increase the risk of anesthesia-related aspiration.
Medication-Related Risk Factors
Anesthesia itself inherently poses an aspiration risk. Anesthetic medications impact the lower esophageal sphincter tone, reduce consciousness levels, and diminish protective reflexes, all of which contribute to the potential for aspiration.
Medications commonly used in anesthesia known to decrease lower esophageal sphincter tone include:
- Propofol
- Volatile anesthetic agents
- β-agonists
- Opioids
- Atropine
- Thiopental
- Tricyclics
- Glycopyrrolate
These drugs are designed to induce a loss of consciousness, which inevitably leads to a reduction and eventual loss of protective airway reflexes. The risk is further amplified when topical anesthesia is applied to the larynx, as this directly compromises the cough reflex.
Predisposing Conditions: Underlying Health Issues
While anesthesia creates a baseline risk, most patients do not experience aspiration events. Predisposing conditions significantly increase the likelihood of aspiration when combined with anesthesia-induced loss of consciousness and reflexes. These conditions include:
- Gastrointestinal obstruction
- Emergency surgery
- Previous esophageal surgery
- Swallowing or respiration coordination issues
- Esophageal cancer
- Hiatal hernia
- Obesity
In individuals with these conditions, passive regurgitation during anesthesia induction is more common than active vomiting, often due to upper gastrointestinal stasis or obstruction.
Provider Expertise: The Human Factor
Studies indicate that provider-related factors, such as inadequate decision-making, lack of experience, and insufficient knowledge, are significant contributors to intraoperative aspiration events. Expertise is also crucial in the proper execution of preventive measures, such as applying cricoid pressure during rapid sequence induction. Variations in technique and experience among anesthesia providers can significantly impact patient safety, especially in high-risk cases.
Research has highlighted that improper anesthesia techniques and lack of experience are implicated in a substantial number of aspiration cases. For example, in a review of anesthesia-related aspirations, a significant portion were linked to failures in applying cricoid pressure or provider inexperience. Similarly, other studies have noted that a lack of anti-aspiration prophylaxis, errors in judgment, faulty techniques, inadequate patient preparation, and communication problems contribute to aspiration events.
Understanding what is aspiration, its risk factors, and the critical role of experienced providers is essential for enhancing patient safety during surgical procedures.
Alt text: Diagram illustrating the mechanism of aspiration during anesthesia, showing gastric contents moving into the trachea and lungs due to reduced protective reflexes.
Prevention: Minimizing the Risk of Aspiration
The most effective strategy for managing acute intraoperative aspiration is prevention. This requires a comprehensive approach involving preoperative risk assessment, appropriate fasting protocols, and careful anesthetic techniques.
Preoperative Risk Assessment: Identifying High-Risk Patients
A thorough preoperative assessment is critical for identifying patients at increased risk of aspiration. Both the anesthesiology and surgical teams must be knowledgeable about the patient’s medical history and predisposing conditions. According to the American Society of Anesthesiologists, the preoperative interview should include an evaluation for risk factors that increase the likelihood of regurgitation, such as:
- Gastroesophageal reflux disease (GERD)
- Esophageal dysmotility
- Difficulty swallowing (dysphagia)
- Diabetes mellitus
- Gas bloat or other signs of delayed gastric emptying
- Obstructing cancers causing esophageal stasis
Preoperative Fasting: Guidelines and Considerations
Adhering to preoperative fasting guidelines is crucial. Current recommendations from the American Society of Anesthesiologists Committee on Standards and Practice Parameters include:
- Light meal or non-human milk: Permitted up to 6 hours before elective procedures.
- Clear liquids: Allowed up to 2 hours before elective procedures (e.g., water, clear tea, carbonated beverages, pulp-free fruit juice, black coffee).
These guidelines are based on evidence suggesting that clear liquid intake within 2-4 hours of anesthesia induction results in lower gastric residual volumes compared to longer fasting periods, though the clinical significance of these volume differences is minimal. While shorter fasting times for clear liquids are generally considered safe, it is vital for thoracic surgeons to recognize a critical caveat: these recommendations have limited data supporting their application in patient populations at higher risk of regurgitation and aspiration. Conditions like large paraesophageal hernias, achalasia, and obstructing esophageal cancers may necessitate longer periods of clear or full liquid diet, potentially several days, due to impaired gastric emptying and the likelihood of retained solid food.
Preemptive Nasogastric Tube Placement: Weighing the Benefits and Risks
Preemptive placement of a nasogastric tube to empty the stomach before anesthesia induction has been considered as a way to reduce aspiration risk. However, robust evidence supporting this practice is lacking. Prospective, randomized studies evaluating its effectiveness are scarce, and retrospective data is limited. A large retrospective review of over 85,000 anesthetics found no evidence to support routine preoperative gastric emptying, even in emergency cases, except for patients with suspected ileus or obstruction. Therefore, the decision to use a nasogastric tube should be made collaboratively by the surgeon and anesthesiologist, based on the individual patient’s condition and the surgical context. Careful consideration is needed, as nasogastric tube placement can sometimes induce vomiting and aspiration in certain patients. Moreover, in patients undergoing esophageal surgery, particularly those with incarcerated paraesophageal hernias or obstructing esophageal cancer, nasogastric tube insertion carries a risk of injury. In such complex cases, surgeon consultation, or ideally, their presence during anesthesia induction, is advisable. If a nasogastric tube is already in place, gastric suctioning should be performed.
H2 Blockers, Proton Pump Inhibitors (PPIs), and Prokinetics: Limited Role in Routine Prevention
Histamine (H2) antagonists (e.g., cimetidine, famotidine) and proton pump inhibitors (PPIs) (e.g., omeprazole, pantoprazole) can effectively increase gastric pH and reduce gastric volume. Prokinetics (e.g., metoclopramide, erythromycin) promote gastric emptying, theoretically reducing aspiration risk. However, substantial high-quality evidence supporting the routine use of these medications to prevent aspiration is limited. A meta-analysis evaluating H2-receptor antagonists and PPIs for aspiration risk reduction showed a trend toward H2-receptor antagonists being more effective when given as a single oral dose preoperatively. It’s crucial to note that the endpoints in these studies (gastric pH and volume) are surrogate markers for actual pulmonary aspiration events, and the clinical efficacy of premedication in reducing aspiration is not definitively proven. Furthermore, increasing gastric pH does not eliminate the risk of aspiration pneumonitis, as materials like milk and bile can also cause significant lung damage. Current guidelines from the American Society of Anesthesiologists do not recommend the routine use of gastrointestinal stimulants, gastric acid secretion blockers, antacids, antiemetics, or anticholinergic agents to reduce pulmonary aspiration risk.
Rapid Sequence Induction (RSI): Securing the Airway Quickly
Studies have shown that most aspiration events occur during anesthesia induction, with fewer incidents during maintenance or emergence phases. Rapid sequence induction (RSI) is an anesthesia induction technique designed to quickly secure the airway in emergency or high-risk cases, minimizing aspiration of regurgitated gastric contents.
The RSI technique typically involves:
- Preoxygenation: Ensuring adequate oxygen reserves.
- Rapid administration of induction and paralytic agents: Using non-titrated doses for speed.
- Cricoid pressure: Historically used, but not universally recommended now.
- Avoidance of bag-mask ventilation: To prevent gastric inflation.
- Transoral endotracheal tube insertion: Using direct or video laryngoscopy for rapid intubation.
While RSI is theoretically sound, its actual impact on aspiration prevention is not definitively established, partly because aspiration is a relatively rare event, making large-scale studies challenging. The definition of RSI also varies, complicating study comparisons. A systematic review of numerous studies concluded that current literature is insufficient to definitively prove RSI reduces aspiration risk during anesthesia induction. The review also examined cricoid pressure and found no strong evidence to support its routine use. Studies have shown that cricoid pressure may displace the esophagus and potentially obstruct the airway in some patients. Current consensus suggests cricoid pressure is generally benign and may be used during RSI, but should be adjusted or released if it hinders airway management.
Patient Positioning During Induction: Optimizing Head and Neck Position
Optimal patient positioning during anesthesia induction is refined to minimize aspiration risk. Research suggests that combining a head-down tilt with specific head-neck positioning can help direct regurgitated contents away from the airway. Studies using manikins and volunteers explored different head-down tilt angles and head-neck positions (neutral, extension, sniffing, Sellick maneuver). Results indicated that a head-down tilt leveling the mouth with the larynx was necessary to prevent aspiration completely. For most healthy volunteers, a head-down tilt of less than 15° combined with the Sellick position achieved this alignment. Researchers concluded that a 15° to 20° head-down tilt with the Sellick position is optimal for minimizing aspiration. However, they cautioned that intubation with the Sellick position can be challenging and is contraindicated in cervical spine instability.
Lateral positioning has also been considered for high-risk patients, particularly in monitored anesthesia care for esophageal procedures, as it facilitates drainage of regurgitated contents away from the airway. However, most anesthesiologists have limited experience with intubating patients in the lateral position, making it less practical for general anesthesia. Studies examining airway management in lateral positioning have found that laryngoscopic views can deteriorate in a significant percentage of patients. Therefore, while lateral positioning may theoretically optimize airway-mouth orientation to minimize aspiration, it is generally not a preferred position for anesthesia induction in most thoracic surgery patients.
Alt text: Patient positioning for airway management during anesthesia induction, showing head-down tilt and Sellick maneuver for optimal airway protection against aspiration.
Management: Responding to Acute Intraoperative Aspiration
Effective intraoperative management of pulmonary aspiration requires prompt recognition and immediate action. The first critical step is recognizing gastric contents in the oropharynx or airways. Other signs of aspiration include persistent hypoxia, increased airway pressures, bronchospasm, and abnormal breath sounds after intubation. Visual confirmation of gastric contents in the oropharynx or airway during intubation allows for immediate suctioning before positive pressure ventilation is applied. In cases of confirmed or suspected aspiration, the patient should immediately be placed in a head-down and lateral (if possible) position. Orotracheal and endotracheal suctioning is indicated, either before or after intubation, depending on ongoing regurgitation and airway visibility. Securing the airway rapidly is paramount to prevent further contamination and facilitate airway clearance.
Flexible bronchoscopy is a valuable tool for airway clearance following aspiration. Having a flexible bronchoscope readily available for high-risk patients is advisable. If particulate matter is aspirated, rigid bronchoscopy may be necessary. Some clinicians advocate for steep Trendelenburg positioning after administering paralytics and before laryngoscopy, with Yankauer suction immediately available. Theoretically, this position allows regurgitated contents to flow away from the airway, minimizing tracheal spillage in paralyzed patients unable to inhale.
The decision to proceed with surgery depends on several factors, including the urgency of the procedure, the patient’s oxygen saturation, pulmonary compliance, and response to interventions like bronchodilators and positive end-expiratory pressure (PEEP). Routine use of antibiotics and steroids is not recommended and should be individualized based on the patient’s condition. Mechanical ventilation management should follow standard parameters, with careful monitoring for ARDS development, which is correlated with the volume of aspirated material and the likelihood of postoperative pulmonary complications.
In severe aspiration cases, cardiopulmonary arrest can occur. Immediate cardiopulmonary resuscitation (CPR) should be initiated, an orotracheal airway established, and airway clearance maneuvers performed. Early consideration of extracorporeal membrane oxygenation (ECMO), if available, may serve as a crucial bridge to stabilize the patient and assess lung recovery potential. While data on ECMO success in adults experiencing cardiac arrest due to massive aspiration is limited and recovery in such cases is unlikely, ECMO may offer benefit for patients developing ARDS secondary to aspiration, based on studies of ECMO in ARDS management. The decision to implement ECMO depends on its availability, the reversibility of the underlying condition, and the severity of comorbidities.
Summary: Key Takeaways on What is Aspiration and Its Management
Acute intraoperative aspiration is a severe complication with significant morbidity and mortality potential. Patients undergoing thoracic surgery face an increased risk of anesthesia-related aspiration due to predisposing conditions. Understanding what is aspiration, recognizing risk factors, implementing preventive strategies, and being prepared for immediate management are essential for both thoracic surgeons and anesthesia teams. Given that many aspiration events are linked to provider factors, ensuring experienced anesthesiologists are present for high-risk cases is of utmost importance.
Key Points
- Thoracic surgery patients have a threefold increased risk of intraoperative aspiration compared to other surgical specialties.
- Aspiration pneumonitis is the most common consequence of significant intraoperative aspiration, followed by aspiration pneumonia.
- The severity of lung injury from aspiration is determined by the acidity, volume, and presence of particulate matter in the aspirate.
- Predisposing conditions for aspiration include gastrointestinal obstruction, emergency surgery, prior esophageal surgery, esophageal cancer, hiatal hernia, impaired swallowing or respiration coordination, and obesity.
- Preoperative risk assessment, appropriate fasting, rapid sequence induction, considering anti-secretory medications, and rapid recognition and response to gastric regurgitation are critical for aspiration prevention and management.
Acknowledgments
Imani Herring, an undergraduate at Brown University, significantly contributed to the original article.
Footnotes
Disclosure for Financial Support: Dr. Nason’s work was supported by the National Cancer Institute of the National Institutes of Health (award number 5K07CA151613). The content reflects the authors’ views and not necessarily the NIH.
Publisher’s Disclaimer: This article is an early, unedited manuscript accepted for publication. It will undergo further editing, typesetting, and review before final publication. Errors may occur during production, and standard journal disclaimers apply.
