Usability of ultrasound assessment of gastric content. Case reports.

The paper presents the use of ultrasound assessment of gastric content in anesthesiological practice. Factors influencing pulmonary aspiration of gastric content and the risk of a complication in the form of aspiration pneumonia are discussed. The examination was performed on two patients hospitalized in a state of emergency who required surgical intervention. The first patient, a 46-year-old male with a phlegmon of the foot, treated for type 2 diabetes, ischemic heart disease and renal insufficiency, required urgent incision of the phlegmon. The second patient, a 36-year-old male with a post-traumatic pericerebral hematoma, qualified for an urgent trepanation. Interviews with the patients and their medical documentation indicated that they had been fasting for the recommended six hours before the surgery. However, during a gastric ultrasound examination it was found that food was still present in the stomach, which caused a change in the anesthesiological procedure chosen. The authors present a method of performing gastric ultrasound examination, determining the nature of the food content present and estimating its volume.

Introduction

Aspiration of gastric content into the respiratory tract is a rare but very serious perioperative complication. Patients undergoing urgent surgical procedures are at the greatest risk for pulmonary aspiration. Aspiration occurs usually during laryngoscopy and endotracheal intubation (32.9%) or extubation (35.9%)(. Pneumonia caused by aspiration is associated with high mortality: it accounts for as many as 9% of all anesthesiarelated deaths(.

European and American societies of anesthesiologists recommend in guidelines published in 2011 that patients qualified for planned surgeries abstain from eating solid food for 6 hours and drinking for 2 hours before the procedure is scheduled to begin(. One has to bear in mind, however, that in emergency cases in individuals receiving anti-peristaltic drugs as well as in those suffering from certain diseases the time of stomach voiding may be significantly prolonged. It is not uncommon during anesthesiological duty to come across situations in which it is necessary to anesthetize unconscious patients, who cannot provide information on the time of the last meal. For this reason a simple method allowing to identify patients “with a full stomach” before the surgery is being searched for. It seems that ultrasound examination can play such a role since it allows for non-invasive assessment of both the degree of stomach fullness and the nature of the gastric content. In order to illustrate the problem above two cases recorded recently in the hospital where the authors of this article work are presented.

Case one

A 46-year-old male with a phlegmon of the foot was admitted to the hospital. The patient was treated for type 2 diabetes, ischemic heart disease and renal insufficiency. Physical examination revealed blood pressure of 110/60 mm Hg, increased pulse (110/min) and elevated body temperature (38°C). Laboratory tests revealed hyperglycemia and an elevated level of creatinine. The surgeon on duty qualified the patient for emergency foot incision surgery. The patient claimed that he had eaten the last meal over six hours and drank fluids three hours before arriving at the hospital. Before the induction of anesthesia an abdominal ultrasound examination was performed in which the presence of fluid content in the stomach was demonstrated. The patient, however, did not consent to regional anesthesia and the placement of a gastric tube. Since the surgery could not be postponed due to extensive infection of the lower leg tissues, quick induction of anesthesia was performed according to the RSII protocol (Rapid Sequence Induction Intubation) and after the patient was intubated a gastric tube was inserted into the stomach and 250 ml of fluid gastric content was sucked out.

Case two

A 36-year-old male with aphasia was qualified for an urgent neurosurgical procedure due to a post-traumatic pericerebral hematoma. The medical documentation indicated that the patient had been fasting for 12 hours. During this time he was receiving infusion fluids intravenously, including analgesics (non-steroid antiinflammatory drugs and morphine).

Immediately before the anesthesia an abdominal ultrasound examination was performed and it was found that the stomach was filled with fluid. A gastric tube was inserted and 300 ml of fluid content was sucked out. Several minutes later rapid anesthesia induction (RSII) was performed without problems.

Discussion

The cases described above illustrate the usability of ultrasound examination for the assessment of how much the stomach is filled with food immediately before general anesthesia. Abdominal ultrasound examination revealed that despite the many hours that had passed after the last meal both patients had a large volume of gastric content, which could have had potentially fatal consequences for them if it had entered the respiratory tract. The risk of aspiration is present when the volume of gastric content in the stomach lumen exceeds 1.5 ml/kg body weight( and aspiration pneumonia occurs once 25 ml of content of pH < 2.5 is aspired(.

In the first patient the longer stomach-voiding time was probably due to diseases (diabetes and uremia) which can lead to the neuropathy of the autonomic system, which is responsible for the control of the digestive tract.

As far as the other patient described is concerned, the prolonged presence of gastric content in the stomach could have been caused by the stress associated with the trauma as well as the influence of opioid analgesics.

In both cases the result of the ultrasound examination determined the choice of the RSII protocol. If it is found or even suspected that fluid content is still present in the stomach, it should be sucked out through a gastric tube before the anesthesia procedure is started. The first patient did not consent to this procedure.

Ultrasound examination makes it possible not only to determine the presence of gastric content in the stomach, but also to determine its nature and estimate its volume. Empty stomach is visible along the sagittal axis as a round or elliptic shape resembling “a bull's eye” (fig. 1)(. This characteristic image is due to the different wall layers being visible. Stomach filled with fluid content looks differently - an image of “a starry sky” can be seen (fig. 2)(, which is created by the presence of anechogenic fluid and hyperechogenic spots reflecting the presence of gas bubbles. Food present in the stomach generates a hyperechogenic image of “a frosted glass” with a thinned wall (fig. 3)(.

Fig. 1

Ultrasound image of an empty stomach. W – liver (Polish: wątroba), Ż – stomach (Polish: żołądek)

Fig. 2

Ultrasound image of a stomach filled with fluid. W – liver, Ż – stomach

Fig. 3

Ultrasound image of a stomach filled with solid food content. W – liver, Ż – stomach

Various methods of estimating stomach volume are described in the literature (. Some of them are derived from mathematical models and others from empirical formulas based on the volume of gastric content sucked out in various cases. However, all methods require determining the gastric orifice cross section area (CSA). This is done by calculating two perpendicular dimensions of the orifice along the cephaliccaudal (CC) and anterior-posterior axis (AP), assuming that its shape is elliptical. The following formula is used: CSA = (CC × AP × π)/4. A simpler method to determine CSA is to draw the boundaries of the orifice (with the help of the trace function available in the menu). The measurements should be taken in between gastric contractions in order to avoid false results leading to underestimation of the volume during contraction. There are differing opinions as to whether the whole thickness of the gastric wall should be taken into account in the measurements (interserosal measurement) or just the mucosa (intermucosal measurement). The formulas for the estimation of gastric volume published in the literature often take into account the age and body weight of the patient. An example of such a formula was developed by Perlas et al.(: gastric volume (ml) = 27.0 + 14.6 × CSA-1.28 × age.

In the literature examination in a semi-sitting position, sitting position and when lying on the right side is usually described(. The examination is performed using a convex probe (3.5-5 MHz) in the substernal view, with the probe placed in the sagittal plane (the tracker should be directed cephaladly).

Conclusions

Ultrasound examination allows for the assessment of the volume and nature of gastric content. The data thus obtained can influence the choice of anesthesiological procedure during the induction of anesthesia and reduce the risk of dangerous complications. According to the authors of the article the ability to perform and interpret a bedside ultrasound examination of the stomach can be very useful to every anesthesiologist.