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Year : 2021  |  Volume : 19  |  Issue : 3  |  Page : 179-184

Aspiration during emergency intubation in the emergency department: A review

Department of Emergency Medicine, Chettinad Super Speciality Hospital, Chennai, Tamil Nadu, India

Date of Submission21-Apr-2021
Date of Decision02-May-2021
Date of Acceptance07-May-2021
Date of Web Publication05-Jul-2021

Correspondence Address:
Dr. Ramgopal Roshan
Department of Emergency Medicine, Chettinad Super Speciality Hospital, Chennai, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/cmi.cmi_40_21

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Endotracheal intubation is considered the gold standard airway management in the Emergency department (ED) for patients requiring definitive airway. It is one of the most commonly performed invasive procedures in the ED. Due to limited time for preparation, unstable condition of the patient, and urgency of the situation, it is always considered a high-risk procedure. The risk of aspiration is high in patients with low sensorium while the intubation process itself is associated with an increased risk of aspiration. It is therefore important to take preventive steps and recognize early signs of aspiration as treatment is difficult and could prolong and complicate hospital stay. Until a gold standard definition and a reliable diagnostic marker for aspiration pneumonia (AP) is available, it would always be a challenging task for clinicians to diagnose AP.

Keywords: Aspiration, aspiration pneumonia, emergency department, intubation, pepsin

How to cite this article:
Roshan R. Aspiration during emergency intubation in the emergency department: A review. Curr Med Issues 2021;19:179-84

How to cite this URL:
Roshan R. Aspiration during emergency intubation in the emergency department: A review. Curr Med Issues [serial online] 2021 [cited 2021 Dec 4];19:179-84. Available from: https://www.cmijournal.org/text.asp?2021/19/3/179/320654

  Introduction Top

The Emergency Department (ED) is considered as the face of the hospital and the first line of contact to health care for the critically ill.[1] Survival of a critically ill patient reflects the standards of the ED. Endotracheal intubation is considered the gold standard airway management in the ED for patients requiring definitive airway.[2] It is one of the most commonly performed invasive procedures in the ED. Due to limited time for preparation, unstable condition of the patient and urgency of the situation, it is always considered a high-risk procedure.[3] A 12%–26% intubation-related adverse events have been previously reported in the literature.[3],[4],[5]

Rapid sequence induction (RSI) includes the use of an induction agent followed by a paralytic agent to achieve optimal conditions for intubation. The drug regimen should produce sedation, neuromuscular paralysis, maintain hemodynamic stability, and must prevent vomiting.[6] Drugs with rapid onset, short duration of action, and minimal adverse effects are usually administered.

Aspiration is defined as the inhalation of either oropharyngeal or gastric contents into the lower airways, that is, into the lungs. This can cause several syndromes determined by the content of the aspirated material, the frequency of aspiration, and the host factors that predispose the patient to aspiration and modify the response.[7]

The diagnosis of aspiration pneumonia (AP) can be made when a patient with risk of aspiration, has evidence of infiltrates in the characteristic bronchopulmonary segments on a chest radiograph.[8] However, a negative chest radiograph is likely during the early stages of the disease. Both Community-Acquired Pneumonia (CAP) and AP have a similar course of illness, while the latter has a higher risk of developing cavitation and abscess formation, if unrecognized or untreated.[8] Negative pressure pulmonary edema (NPPE) might have a similar clinical picture similar to that of AP. NPPE can occur following breathing against a closed airway after general anesthesia, choking or near drowning, all being risk factors for aspiration.[9]

In general, the risk of developing aspiration and other complications is higher among patients intubated in the ED compared to those in intensive care units (ICU) and Operating Rooms.[10] In the Indian scenario, most of the primary and secondary healthcare centers function as referral centers. This adds up to the burden on the EDs in tertiary care centers. However, there are minimal data across the world to signify the association of ED intubations and the development of AP.

  Epidemiology Top

In the absence of specific and sensitive diagnostic criteria and markers, it has always been challenging to clinicians to diagnose AP and differentiate it from other aspiration syndromes such as aspiration pneumonitis and chemical pneumonitis. Also making it difficult for researchers to conduct a large-scale study on the epidemiology of aspiration syndromes.

AP accounts for 5%–15% of all CAP, while the same incidence could not be estimated for Hospital Acquired Pneumonia (HAP).[7] It is also estimated that AP accounts for about 300,000–600,000 deaths in patients with dysphagia secondary to neurological disorders in the United States.[11],[12] One of the most common complications following general anesthesia is AP, it occurs in every 2000–3000 cases. Miyashita et al., conducted a study on the geriatric population who underwent cardiovascular surgery reported a 9.8% incidence of AP.[13] Silent aspiration or unwitnessed aspiration events are high; hence the true prevalence is difficult to estimate.

It is uncertain how aspiration occurs following endotracheal intubation in the ED. The incidence of 1%–20% has been observed in previous studies. This variation in the estimated rate of incidence can be attributed to the lack of a clear definition of AP This variation in results may be attributed due to the lack of a clear definition of AP. The endpoints based on which aspiration was defined in these studies were suspicion of aspiration, witnessed aspiration during endotracheal intubation presence of infiltrates on chest radiograph, sputum cultures, and arterial blood gas analysis. None of these markers were found to have a high sensitivity or specificity for detecting aspiration.[7]

  Aspiration Pneumonia and Aspiration Pneumonitis Top

Pulmonary aspiration is defined as a constellation of clinical features resulting from the inhalation by the patient or the passive introduction of oropharyngeal or gastric contents into the larynx and lower respiratory tract. AP is best considered as a continuum of events following the entry of oral, pharyngeal, and gastric contents into the lower respiratory tract.

Differentiating AP from aspiration pneumonitis has always been challenging for clinicians. The inflammatory process following entry of sterile gastric contents into the lower airways contributes toward aspiration pneumonitis, whereas AP is an infective pathology that occurs following colonized oropharyngeal and gastric substances.

Aspiration of small amounts of oropharyngeal and regurgitated gastric secretions is considered normal in healthy individuals during sleep, yet micro-aspiration is considered to be one of the major pathogenetic mechanisms for developing AP and other pneumonia as well.[14] Aspiration of large quantities of colonized oropharyngeal and gastric contents is the hallmark of AP.

One study conducted on patients admitted in the ICU showed that Staphylococcus aureus, Staphylococcus pneumoniae, Haemophilus influenzae, and Enterobacteriaceae were the main isolates causing AP among CAP group and Pseudomonas aeruginosa without anaerobes in the HAP group.[15]

Another study which was conducted to estimate the incidence of anaerobic bacteria in Ventilator-Associated Pneumonia (VAP) and AP, had 63 patients and 12 patients owing to bacterial origin in the VAP group and AP group, respectively. Among the subjects in the AP group, enteric Gram-negative organisms where isolated in those who had prior gastrointestinal disorders. Whereas S. pneumoniae and H. influenzae were predominately found in patients with community-acquired aspiration events. Only one anaerobic organism was isolated among both the study groups questioning the need of anaerobic cover for both AP and VAP.[16]

Driver et al.[17] in their study defined various types of pneumonia. Patients with predisposing factors such as seizure, vomiting, vomitus seen on their clothing or in the oropharynx during the attempt to intubate presenting to the ED with unexplained hypoxemia and radiographic opacities on chest X-ray were considered to have aspirated before endotracheal intubation. CAP was diagnosed in patients in patients without a prior history of aspiration with radiologic opacities on chest X-ray. HAP was diagnosed in patients who had prior admission in a health care facility or nursing home in the last 3 months, without a history of aspiration and with radiographic opacities on chest X-ray. AP was diagnosed in patients with unexplained hypoxemia, infiltrates on chest X-ray, and pathogenic growth on cultures occurring 48 h after intubation and within 48 h of extubation. HAP, on the other hand, was diagnosed in patients with radiographic evidence of pneumonia, hypoxia, and positive sputum cultures occurring after 48 h following intubation.

Bohman et al. conducted a randomized control trial to access the effect of cricoid pressure in preventing microaspiration. The study population included patients who are having risk factors of microaspiration. Postintubation, their lower airway secretions were collected and assayed for pepsin. Among the 95 recruited patients, 46 were randomized into the cricoid pressure arm, while 49 patients were randomized into no cricoid pressure arm. It was found that there was no significant difference among both arms for micro-aspiration.[18] Though this study did not was done on the population at risk for micro-aspiration, theoretically application of gentle cricoid pressure reduces the risk of aspiration. Further studies are needed to question the ineffectiveness of cricoid pressure during RSI.

  Risk Factors Top

For the development of AP, usually, there is a compromise in the airway protective mechanisms, i.e., glottic closure, cough reflex, and clearing mechanisms or there is direct inoculation of gastric acids which have a direct toxic effect on the lower airways, leading to inflammatory response, or can cause obstruction.

Patients with prior history of cerebrovascular accident (CVA), esophageal diseases such as achalasia or esophageal web, and patients fed by nasogastric tube are at higher risk of aspiration.[19] In a case-control study oropharyngeal dysphagia increased the risk of pneumonia (odds ratio-11.9), with 92% of the study population having dysphagia.[20]

Patients admitted in the ED, are mostly in the supine position. When regurgitation or vomiting occurs, there is a flow of gastric contents from the esophagus into the pharynx and there is a high risk of the patient aspirating the gastric contents.[21]

Patients with depressed level of consciousness are more predisposed for developing aspiration pneumonitis. Aspiration pneumonitis can occur at any age but may be seen in young adults. Most of the patients with aspiration pneumonitis will have an event of witnessed aspiration and present with symptoms ranging from cough, tachypnea, bloody/frothy sputum, and respiratory distress with 2–5 h of aspiration.

Aspiration of gastric contents into the lower respiratory tract is one of the recognized complications of Gastroesophageal Reflux Disease.[22] The ability to accurately diagnose aspiration is of paramount importance in diagnosing AP, presently, there is no gold standard test to diagnose of AP.

  Pathophysiology Top

Forty-five percent of normal healthy adults and 70% of adults with impaired consciousness can aspirate during sleep.[23] Lung injury is a result of damage to the alveoli by the action of gastric materials and acids. Initial sputum or cultures from lavage fluids may not show any microorganisms but can lead to subsequent bacterial infection. AP, on the other hand, results due to the aspiration of colonized oropharyngeal material. Following which there is a notable pulmonary inflammatory response to aspirated materials. Gram-positive cocci, Gram-negative rods, and anaerobic bacteria are the most commonly isolated organisms on cultures. Dysphagia and gastric dysmotility are the recognized predisposing factors for the development of aspiration of pneumonia. It is commonly seen in elderly adults and the aspiration event is usually unwitnessed. These patients present with complaints of cough, breathing difficulty and clinical features of pneumonia, and radiographic evidence of infiltrates in the dependent bronchopulmonary segments.

The pulmonary injury after gastric aspiration is mediated by a variety of inflammatory cells, mediators, cellular adhesion factors and is aided by the enzyme cyclooxygenase, tumor necrosis factor, interleukin-6, interleukin-8, lipoxygenase, and other reactive oxygen species.[24] Following aspiration event, due to physical and chemical irritation of airways, there is reflex laryngospasm and bronchospasm. This leads to decreased surfactant activity which ensues rapid development of alveolar injury and fluid exudation. The outcome of this process is intrapulmonary shunting and hypoxemia. Increase in damage to lung tissues leads to decrease in lung compliance.

Miniscule food particles which enter the lower respiratory tract, initiate a foreign body reaction. This reaction is characterized by acute to subacute inflammation, which eventually leads to the formation of granuloma over a period of time. Kennedy et al., in a study on rats, showed that there is a biphasic pattern of pulmonary mucosal injury after aspiration of acid. The first phase occurs 1–2 h after aspiration due to its direct effect on the alveolar-capillary cells, while the second phase peaks around 4–6 h. This is due to the inflammatory infiltration of polymorphs into the alveolar space and into the interstitial area, leading to features of acute inflammation.[25]

  Rapid Sequence Induction in the Current COVID Pandemic Top

RSI includes the use of an induction agent, usually, a sedative followed by a neuromuscular blocker to achieve favorable conditions for intubation without causing hemodynamic instability and vomiting.[6] Drugs with rapid onset, short duration of action, minimal adverse effects are usually administered. The most commonly used drugs for induction are etomidate, ketamine, midazolam, fentanyl, thiopental, and propofol. Succinylcholine and rocuronium are the most frequently used NMBA. Aspiration of gastric contents is one of the feared complications during endotracheal intubation.[26] The rate of witnessed aspiration during endotracheal intubation is estimated to be 5%.[4] This can lead to a spectrum of pulmonary complications, so it is necessary to diagnose aspiration and prevent its progression into AP.

Sakles et al., in an observational study, to determine the success rate, methods and immediate complications following endotracheal intubation performed in the ED reported RSI to be preferred in 84% with an overall success rate of 98.9% with 7 patients requiring cricothyrotomy.[27] Simpson et al., reported a first-attempt success rate of 83% and 99.4% of the patients' airway secured by endotracheal intubation.[28]

A prospective multicentric study was done to compare the effectiveness of RSI and non-RSI airway management and to determine the rate of success and complications related to airway management. Only 32% of all intubations were RSI compared to 68% in non-RSI intubations. It was noted that RSI had a higher success rate on the first attempt when compared to non-RSI intubations (73% vs. 63%). The complication rates were the same in both groups.[29] Data from the SARS epidemic in 2002–2003 stated that health care workers had six times higher risk of getting infected with the coronavirus during intubation.

The Aerosol Box (AB) was initially designed by Dr. Lai Hsien Yung, has now become a widely used equipment during endotracheal intubation across the World. By design, it is a transparent box placed over the patient's head with two holes for the intubator to perform the procedure.[30] In the current pandemic situation, performing endotracheal intubation is considered a high-risk procedure owing to high aerosol production. The intubator and the accompanying healthcare worker are at increased risk of exposure to the aerosols generated while performing the procedure. Though universal precautions such as goggles and face shields are currently being used, some hospitals encourage the use of AB to limit the spread of aerosols. Studies have shown that the use of AB is associated with longer Time to Intubate (TTI).[31],[32],[33],[34] TTI was shorter when performed by physicians with experience and using a video laryngoscope. The first attempt success rate was relatively lower when AB was used.[32] The use of Personal Protective Equipment (PPE) is now advocated for all aerosol-generating procedures. Fogging of glasses/eyewear while wearing PPEs has been a common practical problem faced by the intubator in around 80% of the cases. The use of anti-fog measures and soap liquid has been recommended to overcome this issue. Though protection officered to the healthcare workers is indisputable, the added difficulty of the procedure would probably increase the risk of complications like delayed intubation and aspiration. More data regarding this is needed to shed light on the dilemma.

  Diagnosis of Aspiration Pneumonia Top

Aspiration can be suspected when there is evidence of new infiltrates in the characteristic bronchopulmonary segments, in a patient who has a high risk of aspiration.

  Chest X-ray Top

Radiographically, infiltrates are evident within several hours and resolves by the next 48–72 h. The commonly involved bronchopulmonary segments are posterior segments of upper lobes and apical segments of lower lobes, in patients who are in the recumbent position. Basal segments of the lower lobes are involved in patients in an upright position.[8]

  Computed Tomography Chest Top

Owing to the poor sensitivity of chest radiographs in the early stages of the diseases, a computed tomography (CT) is currently used to identify the disease in its early stages. In a study, out of 208 patients with pneumonia, 60% had aspiration. CT chest was used to identify 28% of these patients who had a negative chest radiograph.[13]

  Pepsin Assay Top

Pepsin is a digestive enzyme, secreted by the chief cells which are present in the antrum in the stomach. They act on the food particles and degrade them into peptides. It is secreted as pepsinogen (inactive form) which on stimulation by gastrin, acetylcholine, other gastric enzymes, and neurotransmitters is converted into pepsin. Pepsin activity is seen only in an acidic environment, between pH of 1.5–2 and attains its inactive form when the pH is >4.[35]

For gastric content to be aspirated into the lower respiratory tract, it must be preceded by gastroesophageal reflux. Approximately 50%–75% of intubated patients were reported to have developed aspiration.[36] For this reason, pepsin was considered as a potential diagnostic marker to identify aspiration.[37] Pepsin was found to be highly specific and sensitive in diagnosing aspiration.[38] The presence of pepsin in the respiratory tract ascertains aspiration and demonstration of pepsin from the ET Aspirate would confirm it.[38]

Krishnan et al. conducted a study to find out whether pepsin could be used as a reliable marker for micro-aspiration. Pepsin was demonstrated in 31 children with prior history of reflux disease or chronic respiratory symptoms and was absent in 26 children who did not have prior history of reflux disease or respiratory tract symptoms. Based on his study, he concluded that pepsin could be used as a reliable marker for reflux aspiration as it was found significant in children with reflux symptoms.[39]

Ufberg et al. conducted a study to compare the incidence of aspiration of gastric contents into the lower airway among patients intubated in the prehospital setting and in the ED. The tracheal aspirate was collected postintubation and was assayed for pepsin, using fibrogen digestion technique. Pepsin assay was positive in 50% of patients who were intubated in the prehospital setting compared to 22%, who were intubated in the ED, implying that patients getting intubated in the prehospital setting are at a higher risk of aspiration compared to the hospital setting.[26]

  Alpha Amylase Assay Top

Alpha-Amylase which is secreted by the salivary glands and the pancreas helps in the hydrolysis of complex carbohydrates. Typically, not found in the lung, the presence of α-Amylase in the lower respiratory tract indicates prior aspiration. Studies on Bronchoalveolar lavage (BAL) amylase levels state that estimation of BAL amylase results are rapidly available and more reliable compared to pepsin and pepsinogen with a longer testing window.[40]

Though levels of α-Amylase were elevated in ventilated patients, higher values were correlating to the risk factors rather than correlating to the development of AP and chemical pneumonitis, making it unsuitable for using it as a diagnostic marker.[40],[41]

  Serum Procalcitonin Levels Top

Procalcitonin (PCT) is a 116 amino acid peptide. Its sequence is similar to that of prohormone of calcitonin, without its hormonal activity. Following its application to distinguish between bacterial and non-bacterial sepsis, it has been widely used as a marker for bacterial infection.[42] It is also found that the levels of PCT in rise within 3 h, plateaus by 6 h and remains until 24 h, making it a sensitive agent for identifying severe infection.[43]

  Radionucleotide Salivagram Top

Yu et al., conducted a study in South Korea, to investigate the usefulness of radionucleotide salivagram to predict AP in patients with prior history of CVA. He concluded that mini-mental state examination can be used as a clinical predictor in supratentorial strokes and the combined results of Modified Barthel Index and salivagram could be used as clinical predictor in infratentorial strokes.[44]

  Management of Aspiration Pneumonia Top

For aspiration pneumonitis, failing to clear within 48 h, antibiotic therapy is indicated.[45] Steroids on the other hand are not routinely recommended in patients with aspiration.[46] The recommended antibiotics in AP are fluoroquinolones, third-generation cephalosporins and piperacillin, as they are effective against Gram-negative spectrum.[45],[47]

Prevention of AP and aspiration pneumonitis is important as early diagnosis and treatment are difficult. For patients' requiring intubation, the duration of the procedure must be as brief as possible. Airway suctioning must be carried out by sterile manner. Gastric distension must be avoided in tube-fed patients. It is recommended to maintain good oral hygiene and place the patient in semi-erect position to reduce the risk of passive regurgitation.

  Complications Top

Aspiration can lead to chemical pneumonitis, necrotizing pneumonia, lung abscess, or empyema. Development of these complications should be considered as continuum stages of aspiration.[48]

  Conclusion Top

The risk of aspiration is high in patients with low sensorium while the intubation process itself is associated with an increased risk of aspiration. Whether emergency intubation results in a reduction in the risk of aspiration of comatose patients remains to be determined. It is therefore important to take preventive steps and recognize early signs of aspiration as treatment could be delayed and could prolong and complicate the hospital stay. Therefore, until we have a gold standard definition and a reliable diagnostic marker for AP, it will always be a challenging task for clinicians to diagnose AP.

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