The ‘agitation bubble ‘contrast’’ technique: A technique for using intra-peritoneal free air as contrast for the diagnosis of organ perforation

Abstract

We report a case using a novel ultrasound technique to diagnose suspected bowel perforation in the presence of peritoneal fluid. Our technique removed the need for radiological confirmation and expedited surgical intervention. This highlights the potential for using this bedside ultrasonographic technique to detect free peritoneal gas in the presence of peritoneal fluid secondary to viscus perforation.

Introduction

Pneumoperitoneum is often considered a radiological diagnosis that can be challenging to obtain in unstable patients within critical care. Ultrasonography has an important role to play in detecting free peritoneal gas and is considered a reliable diagnostic method. Point-of-care ultrasound is used increasingly in acute and critical care specialties, with the ultrasound device often being called ‘the modern clinician’s stethoscope’.¹ This imaging modality lends itself well to situations where patients are too unwell to transfer. Such non-invasive detection of free peritoneal gas at the bedside could potentially expedite surgical treatment. In our case, the use of bedside ultrasonography removed the need for computed tomography (CT), thereby enabling rapid surgical intervention and avoiding the delay and inherent risk associated with intra-hospital transfer. Even though CT remains an important investigation in the patient with a suspected viscus perforation, we consider the potential use of our novel technique as valuable ‘rule in’ bedside test that potentially removes the need for radiological diagnosis.

Case presentation

We present a 64-year-old male patient who was initially admitted to our ICU with a severe left-sided community acquired pneumonia that required mechanical ventilation and vasopressor support. Medical history included post-encephalitic orbitofrontal syndrome that resulted in emotional lability, paranoid delusions, speech defects and episodes of severe agitation. Other medical history included autoimmune encephalitis, hepatitis C, chronic obstructive pulmonary disease and adrenal insufficiency secondary to previous bilateral adrenal haemorrhage.

After 24 hours, the patient was successfully extubated, and he was placed on high-flow nasal oxygen, but still required low-dose vasopressor support. His condition continued to improve and he was stepped down to the respiratory ward from our high dependency unit for further management 72 hours later.

Initially, despite making good progress following discharge to the ward, within 24 hours he developed sudden breathing difficulties with copious amounts of secretions and hypoxaemia that necessitated readmission to our ICU. High-dose vasopressor support was required, and antibiotic therapy was started for a hospital-acquired pneumonia with piperacillin and tazobactam. Approximately 48 hours after readmission, the patient was placed on mechanical ventilation and continued to need vasopressor support. His chest X-ray showed left lower lobe collapse, but this re-expanded after we were able to clear the obstructing mucoid secretions with bronchoscopy. The patient was successfully extubated for a second time approximately five days after this second admission and weaned off his vasopressor support.

Clinical course and management

Almost eight days following the second admission, the patient rapidly deteriorated, requiring high-dose noradrenaline, adrenaline and vasopressin infusions with parenteral steroids. In addition, the patient’s abdomen became tender and distended. Following surgical consultation, a CT abdomen and pelvis was requested. Bedside ultrasonography was performed during preparation for transfer to CT to guide haemodynamic support and assess cardiac function. Trans-thoracic echocardiography confirmed the presence of hypovolaemia, but due to tachycardia, poor parasternal and apical windows, detailed assessment was not possible. Lung ultrasonography excluded pneumothorax and focused abdominal ultrasound confirmed the presence of peritoneal fluid. Peritoneal free gas was suggested through the identification of a reverberation artefact in the right paramedian view (Figure 1(a) and (b)).

Figure 1.

(a) Ultrasound images acquired from scanning the thorax and abdomen at the level of diaphragm in the right paramedian view. A reverberation artefact in the right paramedian view. Note presence of a reverberation artifact i.e. an A-line inferior to the diaphragm See part b for labelling; (b) labelling; (c) White arrows point to hyperechoic signals in the free abdominal fluid anterior to the liver generated by ballotting the abdomen (see supplemental material for demonstration).

As there was high clinical suspicion of a perforated viscus, we used a novel technique of gently balloting the patient’s abdomen whilst conducting abdominal ultrasonography to visualise the peritoneal free fluid. This technique created ‘bubbles’ within the peritoneal fluid and confirmed that the fluid and gas were both within the peritoneal cavity (Figure 1(c)). Following further discussion with our surgical colleagues, he was taken immediately to theatres, bypassing the requested CT examination. He was found to have a perforated duodenal ulcer with approximately 3 l of turbid fluid within the abdominal cavity. The ulcer was surgically repaired and the abdominal cavity washed out. The patient was transferred to our ICU uneventfully and continued to require cardiovascular support and mechanical ventilation.

Despite these interventions, the patient developed multiple organ failure and died six days after the operation.

Discussion

Reverberation artefacts, like those observed in our case, are generated by large differences in acoustic impedance, which in turn determine the reflectivity of sound waves at tissue interfaces.² It is important to distinguish between gas-filled bowel and free peritoneal gas, since both can give the appearance of high signal with an acoustic shadow or reverberation artefact beneath the gas/tissue interface. Whilst scanning the abdomen anteriorly with the patient supine, we balloted the abdomen which created bubbles from the mix of fluid and gas – confirming that the gas was in the same compartment as the fluid: in the peritoneal cavity. These bubbles can be considered similar to agitated saline used for bubble contrast.

Grechenig et al. demonstrated that the optimal position for sonographic detection of free intra-peritoneal air is in the supine patient elevated approximately 10–20° with the probe sited in the right paramedian epigastrium in the longitudinal direction.³ In one study of 72 patients, Karahan et al. introduced the ‘scissors manoeuvre’ to detect intraperitoneal free air superficial to the liver. The authors applied slight pressure to the right paramedian epigastric area with the patient in the supine position and visualised this intraperitoneal free air as ‘acoustic reverberations’. By alternating pressure along the length of a linear-array transducer, they effectively expelled the intraperitoneal free air from the anterior liver resulting in a much less prominent reverberation artefact, with the reverse occurring when the applied pressure on the probe was decreased. Remarkably, of the 16 patients that were surgically proven gastrointestinal tract perforation, both ultrasonography and radiography demonstrated pneumoperitoneum in 15 patients. This suggested that the sensitivity and specificity for both imaging modalities were 94% and 100%, respectively.⁴ A similar sensitivity of 92% was reported in another study involving 188 patients with suspected hollow viscus perforation.⁵ The sensitivity of our technique for detecting free peritoneal gas is not yet fully established. However, given the high sensitivities already described using other methods, we feel that our technique may also be used as an effective ‘rule-in’ bedside diagnostic test. Finally, the shifting gas artefact sign, which involves identifying reverberation artefacts that move with changes in the patient’s position, is also considered a useful ultrasonographic approach to diagnosing pneumoperitoneum in both non-traumatic abdominal pain and blunt abdominal trauma.⁶

Our ‘agitation bubble contrast’ (ABC) technique does possess certain limitations. Whereas CT possesses a high sensitivity for detecting free peritoneal gas, it also has a much higher accuracy for predicting the site of perforation (reported range between 82% and 90%) and remains the gold standard.⁷ In addition, our technique requires ballottement of the abdomen which could be prohibitively painful in the presence of peritonitis in the awake patient, thereby potentially necessitating the use of strong analgesia. Another potential limitation of this technique is that debris can be confused with bubbles; however, debris would more likely to collect at the most dependent part of the peritoneal fluid where as in our example the ballotment and scanning was performed at the anterior abdominal wall. To prevent this error, other areas of the peritoneal fluid should be examined for comparison. Finally, the generation of bubbles requires the presence of peritoneal fluid which, in the very early stages of viscus perforation, may not be of sufficient volume to be visualised using ultrasonography.

However, despite these limitations, compared to radiological investigations, our technique does not use harmful ionising radiation and avoids the need for nephrotoxic contrast. It is also very quick to perform and can elicit vital information within seconds at the bedside. This has a clear advantage over the logistical and clinical challenges of transferring an unstable critical care patient to a remote site. Additionally, compared to the previously described methods for detecting free peritoneal gas, our method does not rely on repositioning the patient.

We feel that these benefits alone will eventually lead to the introduction of the ABC technique into the clinician’s arsenal when using ultrasonography in the patient with suspected viscus perforation and peritoneal free fluid. We hope that use of the ABC becomes widespread as part of first-line bedside ultrasonography in the emergency setting to diagnose free peritoneal gas in the presence of peritoneal fluid. We recognise that further study is warranted to determine the reliability and validity of our technique before it is used in conjunction with bedside ultrasound protocols, such as the focused abdominal assessment in trauma or core ultrasound skills in intensive care protocols.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethics Approval

Ethical approval not required from a committee.

Guarantor

JW.

Contributors

JW wrote the first draft of the article and initiated the literature search. TS has significantly edited the article. The technique described in the article was the creation of MA.