Abstract & Commentary

Should We Look at the Stomach with Ultrasound Prior to Intubation?

By Andrew M. Luks, MD, Pulmonary and Critical Care Medicine, University of Washington, Seattle, is Associate Editor for Critical Care Alert.

Dr. Luks reports no financial relationship to this field of study.

Synopsis: This single-center observational study demonstrated the feasibility of using ultrasound prior to urgent endotracheal intubation to prevent aspiration of gastric contents.

Source: Koenig SJ, et al. Utility of ultrasonography for detection of gastric fluid during urgent endotracheal intubation. Intensive Care Med 2011; 37:627-631.

Bedside ultrasound is increasingly being performed in the intensive care unit (ICU) for a variety of purposes including guiding volume resuscitation, central line placement, and marking pleural fluid collections for drainage. Koenig and colleagues sought to determine whether yet another use of the technique is feasible — ultrasound of gastric contents prior to endotracheal intubation in an effort to decrease the risk of massive gastric aspiration.

To investigate this issue, the authors conducted an observational study of patients undergoing urgent endotracheal intubation (UEI) in the medical ICU at a single center. UEI was defined as a patient requiring intubation who was not in full cardiac arrest or with such severe respiratory failure that any delay for the purposes of performing ultrasound or other tasks could lead to death. Included patients underwent UEI for hypoxemic respiratory failure (defined as respiratory rate > 34 and/or SpO2 < 90% on F1O2 1.0), hypercarbia (PaCO2 > 45 with altered mental status or inability to protect the airway), airway protection, septic shock, and for different procedures. Prior to sedation and intubation, a critical care attending physician scanned the left-upper quadrant (LUQ) in an effort to identify gastric fluid. In patients in whom gastric fluid was identified (several figures in the paper illustrate the typical appearance), a gastric tube was placed, tube position was confirmed with ultrasound, and the gastric contents were aspirated. The decision to place a gastric tube was made based on qualitative rather than quantitative assessment of the amount of fluid in the stomach. The patient was then sedated and endotracheal intubation was performed. All patients were monitored for aspiration of gastric contents, defined as visible regurgitation of stomach fluid into the oropharynx during intubation with subsequent penetration through the vocal cords.

LUQ ultrasonography was performed on a total of 80 patients, 19 of whom (24%) had gastric fluid identified on their scan. Gastric tubes were inserted in 13 of the 19 patients, but not placed in 5 of the remaining patients because the amount of fluid was deemed inconsequential, and not placed in another patient due to worsening clinical instability. An average of 553 ± 290 mL of gastric fluid was removed from the 13 patients (range 200-1100 mL). The patients who required gastric tube insertion had been nil per os (NPO) for several hours prior to intubation. Repeat ultrasonography following intubation showed no residual gastric fluid. The ultrasound protocol required 2 minutes to perform, although the authors do not specify whether this included time for gastric tube placement and aspiration of gastric contents. No aspiration events were witnessed in any patients in the study including the 13 who underwent gastric tube placement. The one patient in whom gastric tube placement was deferred due to clinical instability had a witnessed aspiration event.

COMMENTARY

Massive gastric aspiration at the time of intubation is not a common event but occurs frequently enough and is associated with sufficient morbidity that efforts to reduce the risk of this complication are clearly warranted. In fact, it is the primary reason why UEI is generally performed using rapid sequence intubation (RSI) in which sedative medications and paralytic agents are administered and intubation is performed without any attempt to manually ventilate the patient between these two steps. Unfortunately, the major precepts of RSI must be violated in some circumstances, such as when the oxygen saturation falls rapidly while waiting for the onset of paralysis or initial attempts at intubation are unsuccessful and the patient requires ventilation while preparations are made for subsequent attempts. Manual ventilation in these situations can lead to gastric insufflation, increasing the risk of emesis and aspiration. One might surmise that the risk of gastric aspiration would be low in patients who have been NPO prior to intubation, but the data in this paper suggest this may not be the case, as close to 25% of patients still had visible gastric contents despite being NPO for many hours.

Koenig and colleagues demonstrate that gastric ultrasound prior to intubation is both feasible and efficient from a time standpoint and may serve as a reasonable method for decreasing the risk of gastric aspiration. It is important to note, however, that their study does not prove that gastric ultrasound decreases the incidence of aspiration. Not only was the study performed at a single center but, more importantly, gastric tubes were placed in all patients in whom gastric contents were identified and no attempts were made to randomize these patients to gastric tube vs no gastric tube and then study the incidence of aspiration. While aspiration was not observed in any patient who underwent gastric tube placement, there is no way of knowing whether this was due to the gastric tube itself or conscientious application of RSI principles.

Despite these issues, gastric ultrasound seems to be a reasonable strategy when the patient's condition provides adequate time. In the hands of a trained operator, it is fast, does not appear to interrupt the overall flow of UEI, and should not add significant cost to the process, as it is performed with ultrasound units already in the ICU. We do not know from this study exactly how much gastric fluid warrants gastric tube placement but in general, the more fluid, the greater the likelihood of aspiration and the more providers should consider placing a gastric tube. The technique should not be attempted in patients in cardiac arrest or in severe acute respiratory failure; however, in those situations providers will need to remain vigilant about strict application of RSI techniques.