Routine Point of Care Ultrasound (POCUS) Assessment of Gastric Antral Contents in Traumatic Emergency Surgical Patients for Prevention of Aspiration Pneumonitis: A Randomized Clinical Trial 


 Background: Polytrauma patients are at a higher risk of delayed gastric emptying. To assess gastric volume, a reliable diagnostic tool is needed to prevent the occurrence of aspiration pneumonia, which remains a serious complication associated with anesthesia. Gastric antral ultrasound can provide reliable information about the size of the gastric antrum in traumatized patients undergoing emergency surgery.Methods: A prospective observational study of 45 polytrauma patients undergoing emergency surgery under general anesthesia. Prior to induction of anesthesia in the emergency department, gastric ultrasound was performed to allow qualitative and quantitative assessment of gastric antrum in a supine position and right lateral decubitus (RLD) position. Followed by routine placement of nasogastric tube to aspirate and calculate the volume of the stomach contents.Results: Forty-five polytrauma patients who underwent gastric ultrasound examination showed that the risk assessment of aspiration and anesthesia technique changed in 14 patients (31.1%) after the ultrasound examination.A very good relationship existed between the expected stomach volume at the RLD position and the suction volume in the nasogastric tube. In all cases, no aspirations were documented.Conclusion: Ultrasound examination of the stomach in polytrauma patients allows assessing the size and type of stomach contents. The data obtained can influence the choice of anesthesia technique while inducing anesthesia and reduce the risk of aspiration pneumonia.Trial registration: This trial was registered at ClinicalTrials.gov. Registry number: NCT04083677.

Results: Forty-ve polytrauma patients who underwent gastric ultrasound examination showed that the risk assessment of aspiration and anesthesia technique changed in 14 patients (31.1%) after the ultrasound examination.
A very good relationship existed between the expected stomach volume at the RLD position and the suction volume in the nasogastric tube. In all cases, no aspirations were documented.
Conclusion: Ultrasound examination of the stomach in polytrauma patients allows assessing the size and type of stomach contents. The data obtained can in uence the choice of anesthesia technique while inducing anesthesia and reduce the risk of aspiration pneumonia.
Trial registration: This trial was registered at ClinicalTrials.gov. Registry number: NCT04083677.

Background:
Pulmonary aspiration of gastric contents is rare in elective surgical groups but is more common in trauma patients requiring emergency surgery because trauma affects gastric motility and emptying. [1] The presence of residual gastric contents at the time of induction of anesthesia is an important risk factor for aspiration pneumonia. The routine use of bedside ultrasound provides valuable information about the volume and type of gastric contents. Preoperative gastric contents determination helps the anesthesiologist assess the risk of pulmonary aspiration. [2,3] Ultrasonographic measurement of the antral cross sectional area (CSA) may determine the risk of occurrence of aspiration pneumonia during the perioperative period which can be determined by the size of the stomach (i.e., the presence of solid particles and/or gastric volume < 1.5 ml / kg). [4] The aim of our study is to allow routine use of point of care ultrasound (POCUS) of gastric contents in order to assess aspiration risk and guide the anesthetic management in trauma patients. We used Siemens low frequency curved probe (2)(3)(4)(5) and ACUSON x 300 ultrasound system from Siemens by an experienced radiologist as part of a focused assessment with sonography in trauma (FAST) studies. All patients were examined in the supine position, followed by the right lateral decubitus position (RLDP). Gastric antrum was determined at the level of sagittal scans in the epigastrium beneath the xiphoid and superior to the umbilicus. The liver (anteriorly), aorta, inferior vena cava and pancreas (posteriorly) were used as anatomical landmarks (Fig. 1).
The "empty" antrum appears collapsed and " at", as the anterior and posterior walls are too close to each other or round to ovoid shape and resemble the target of a "bull's eye" (Fig. 2).
The antrum appears to expand in a circle when it is lled with transparent liquid. Several gas bubbles appear as punctuate hyper-echoic regions within the hypoechoic uid and mimicking the formation of a "starry night" (Fig. 3).
The antrum with mixed echo contents appears to expand when lled with solid contents, giving the lm a "frosted glass" appearance ( Fig. 4).
If the stomach contains clear liquids, the volume measurement can help distinguish between small volume that correspond to baseline secretions and a larger volume than baseline.
The antral cross-sectional area (CSA) was calculated after measuring the two antral dimensions [Anteroposterior diameter (APD) and Craniocaudal diameter (CCD)] according to the following equation: π [APD X CCD] / 4. The volume of the transparent uid was calculated using the CSA measured in an RLD, and a previously published mathematical model: Volume (ml) = 27.0+ (14.6 x Right -Lat (CSA) -(1.28 x Age). This equation accurately predicts the size of the stomach up to 500 ml. [4] Additionally, the antrum is classi ed according to a three-point rating system (Perlas score 0-2) based on the absence or presence of clear liquid in the supine and RLD position. Grade 0 indicates that there are no contents in the antrum in the supine and RLD positions. The rst grade indicates a clear old liquid that can only be seen in the RLD. The second grade indicates a clear liquid, which is documented in both the supine and RLD positions. [3] With explanations of stomach ultrasound results and Perlas classi cation, we can plot this owchart of risk strati cation and decision making (Fig. 5).
Nasogastric tube was inserted preoperatively to con rm gastric ultrasound volume calculation.
Low risk class indicates that the risk of aspiration is low and it can be safe to perform surgery with slow induction of anesthesia with a laryngeal mask or by endotracheal tube.
A high-risk class indicates that the risk of aspiration is high, and these measures may be of help: 1, delay of the surgery depending on its urgency (which may not be acceptable), 2, acid aspiration prevention medications such as metoclopromide and drugs that neutralize stomach acid such as non-particle antacids, H2 inhibitor and proton pump inhibitor, 3, nasogastric tube for gastric drainage, 4, local anesthesia and neuraxial anesthesia and 5, general anesthesia with rapid sequence induction up to awake bro-optic intubation.
Primary endpoint: It included the incidence of change of aspiration risk after gastric ultrasonographic assessment in comparison to clinical assessment.

Secondary endpoints:
They included the incidence of perioperative aspiration and the correlation between predicted volume in RLD position and volume in nasogastric tube.

Sample size calculation:
Based on a study done by Sabry et al, [10] to show a difference in the incidence of change of aspiration risk after gastric ultrasonographic assessment in comparison to clinical assessment with a con dence interval at 95% and the acceptable margin of error at 5%. The p-value was considered signi cant if < 0.05 and needed minimally a sample size of 45 patients.

Statistical analysis:
Analysis of data was done by IBM computer using SPSS (a statistical program for social science, version 16). The quantitative variables were described as mean and standard deviation, while the qualitative variables expressed as number and percentage. Statistical analysis was performed using statistical tests which included the Chi-square test, a student test, and table analysis. P-value < 0.05 was considered signi cant.
Results: 45 polytrauma patients (25 males, 20 females) were planned for emergency surgery. Demographic data are summarized in table (1). An empty stomach was documented in 10 patients (22.2%). The remaining 35 patients (77.7%) showed a full stomach on gastric sonography, twenty-nine of them had solid content and six had clear uid of excess than 1.5 ml/kg. We found changed aspiration risk strati cation and anesthesia decision making in 14 patients (31.1%) following the gastric ultrasound assessment compared to the use of preoperative clinical examination and fasting hours assessment (Fig. 6). Two patients (cases 2 and 8) were found to have a lower aspiration risk than anticipated by history alone and more liberal anesthetic techniques were used as shown in the table (2) and gure (7).

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Twelve patients (cases 4,19,20,23,25,28,29,33,34,35,42 and 43) were found to have a higher aspiration risk than anticipated by history alone and more conservative anesthetic techniques were used as shown in table (2) and gure (7). As shown in table (3), the number of patients with a high risk of aspiration was increased after the gastric ultrasonographic examination (35 patients) than before it (25 patients) and the difference was statistically signi cant, also the number of patients with low risk of aspiration was decreased after the gastric ultrasonographic examination (10 patients) than before it (20 patients) and the difference was statistically signi cant. This re ects the importance of routine point of care ultrasound (POCUS) assessment of gastric antral contents in traumatic emergency surgical patients for prevention of aspiration pneumonitis.
Despite there is a highly signi cant statistical difference between the predicted volume in RLD position and volume in nasogastric tube, there was a good clinical correlation documented between them as shown in table (4).  All data were presented as mean ± SD *HS = highly signi cant.
No aspiration episodes were reported in all patients Discussion: Aspiration pneumonia remains a serious perioperative complication [5].
The presence of residual gastric contents at the time of induction of anesthesia is one of the major risk factors for pulmonary aspiration [6].
The motility of the digestive system can be affected by stress, pain, and anxiety, as well as the use of opioids, which makes prediction of the gastric contents di cult .Patients with a "full stomach" are at risk of aspiration during sedation or general anesthesia, as the tone of the lower esophageal sphincter and airway re exes are reduced. The problem of pulmonary aspiration is greater during emergency surgery. [7].
The severity of aspiration is directly proportional to the volume, type and the acidity of the contents of the stomach. Because of basal gastric acid secretion, stomach volume less than 1.5 ml/kg is common in fasting patients and is considered safe [4].
History taking about fasting hours may be unreliable in elderly people with poor awareness, in children, and in cases of delayed stomach emptying, as in emergency surgery in patients with multiple traumas [2].
In anesthesia, the use of gastric ultrasound provides more accurate information about gastric contents than the general assumption based on fasting hours [1].
Gastric ultrasound is a promising technology because it is readily available, non-invasive and relatively easy to use [8].
The Retrospective study by Van de Putte et al. (2018) indicated that gastric ultrasound may be a useful diagnostic tool in addition to the standard assessment of gastric contents if fasting guidelines were not followed in elective surgical patients. Also, this study revealed signi cant changes in aspiration risk strati cation and anesthetic management following a standard history-based clinical assessment compared to an assessment based on gastric sonography in elective surgical patients who had not followed fasting guidelines [9].
We concluded as Van de Putte et al. (2018) that gastric ultrasound allows planning anesthetic management to prevent the risk of aspiration [9], but we allowed routine ultrasound for trauma surgical patients when the risk of aspiration is higher. Bouvet et al. (2017) reported the prevalence of the full stomach in 56% of emergency surgery patients and suggested that preoperative ultrasound assessment of gastric contents may be particularly helpful in this case [4]. Sabry et al. (2019) demonstrated that gastric ultrasound is used as a reliable method to assess the residual gastric volume in fasting diabetics compared to the healthy control for elective surgery and reported that the residual gastric volume in diabetic patients fasting for 8 hours was higher than in patients without diabetes scheduled for elective surgery [10]. Cubillos et al. (2012) concluded that bedside ultrasound can determine the type of gastric contents (nil, clear uid, thick uid or solid content). This qualitative information can be useful on its own to assess aspiration risks, especially in cases where the fasting state is unknown or uncertain [2].
In our study, we used gastric antral ultrasonography before induction of anesthesia in polytrauma patients undergoing emergency surgery to allow qualitative and quantitative assessment of gastric antrum in supine and right lateral decubitus position for the prevention of aspiration pneumonitis.
Also, nasogastric tube was inserted preoperatively to aspirate the gastric contents to be compared with gastric ultrasound volume calculation with a very good correlation between them.
Our data suggest that routine gastric ultrasound in polytrauma patients allows to personalize aspiration risk assessment to guide anesthetic management.

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Conclusion: This study concluded that routine preoperative gastric ultrasound is a useful, safe and noninvasive tool for assessment of gastric contents in emergency surgical patients in order to plan the anesthetic management to prevent aspiration.   Bull's eye sign. L= Liver. P=Pancrease. Ao= Aorta.   Flow chart for analysis of ndings and medical decision-making based on gastric point-of-care ultrasound ndings.

Abbreviations
Page 18/19 Figure 6 Results of gastric ultrasound examination of gastric contents.

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