Thinking Outside the “Box”—The Ultrasound Contrast Controversy

Abstract

Deposition of local anaesthetic in the proximity of nerves, plexi, within fascial planes, in the paravertebral, epidural or subarachnoid space, is the ever expanding core activity of a regional anaesthetist. Advantages of using ultrasound in this clinical setting include detection of anatomic variants, reduction of volume of local anaesthetic needed with the implication of a lower potential for systemic toxicity, faster onset, real-time assessment of needle advancement avoiding key structures such as blood vessels or pleura, and observation of local anaesthetic spread patterns, all of which are key elements of block success and safety [1]. In addition, we have developed approaches aimed at reducing or quantifying side effects, such as sparing the phrenic nerve when performing an interscalene block [2,3] or assessing the degree of the resulting diaphragm paralysis [4]. From the preoperative to the postoperative period, there appear to be many more opportunities for ultra-sound users to improve patient assessment and management in the ultimate hope of improved perioperative outcomes. Recent guidelines on vascular access recommend the use of ultrasound guidance for all routes of access where the vessel cannot be directly seen or palpated [5]. Routine use of ultrasound had been previously documented for internal jugular central venous catheterisation (unless in emergency or other unusual situations), and early in other procedures (arterial and peripheral venous), if difficult. Clearly, ultrasound makes many steps safer including: evaluation of puncture site, eliminating seeker needles , needle guidance, verification of guidewire/catheters in a vessel, information on central catheter tip position and recognition of complications [5]. As an emerging application, ultrasound has been shown to aid airway evaluation and management with obvious potential benefits for both clinician and patient. Ultrasound can identify vocal cord dysfunction and pathology before induction of anaesthesia thus highlighting potential difficulties. It may be utilized to determine airway size and predict the appropriate diameter of single-and double-lumen endotracheal tubes as well as tracheostomy tubes [6]. It appears to reliably differentiate between tracheal, oesophageal, and bronchial in-tubation. Taken a step forward, ultrasonography of the neck can accurately locate the cricothyroid membrane for emergency airway access and identify tracheal rings for ultrasound-guided tracheostomy. Upper airway point-of-care ultrasound has thus the potential to become the first-line non-invasive adjunct assessment tool in airway management [6]. Much has been published in recent years on the utility of ultrasound for evaluation of gastric content. Inhalation of gastric content during induction, maintenance or emergence from anaesthesia has devastating consequences leading to significant morbidity and mortality. Therefore, evaluation of gastric contents is most helpful in order to inform an assessment of aspiration risk and thus guide anaesthetic management ...

Scavenging dissolved oxygen via acoustic droplet vaporization

“…Blood circulates through the adult human body approximately once per minute [51]. As the blood circulates through the pulmonary capillary bed, the dissolved oxygen in the blood would return to normal oxygen levels and the perfluoropentane microbubbles would be exhaled similar to the excretion of other perfluorocarbon-based ultrasound contrast agent gases [52,53].…”

Overview of the 2008 Food and Drug Administration Advisory Committee on Safety Considerations in the Development of Ultrasound Contrast Agents

“…The cardiovascular community reacted during the subsequent months with several editorials criticizing the box warning. [3][4][5][6] In one of these editorials, Main and colleagues 3 reviewed the 4 cases in which patients died after receiving perflutren lipid microsphere (Definity) and found support for pseudocomplications, adverse events that were not due to cause and effect from the contrast but were just coincidental to the timing that contrast was administered, ie, an epiphenomenon. Given the clinical scenarios of the 4 cases and the severity of underlying disease in these patients, death would not be unexpected in any of these patients.…”

Safety of ultrasound contrast agents: 'Primum non nocere'?

“…Although, UCA still account for a small proportion of diagnostic examinations 9 , it was estimated that in 2006, 1∞∞million diagnostic examinations with UCA were performed and that by the end of 2007, Definity ® (the European name is Luminity ® ) has been administered to approximately 2∞ ∞ million patients since approval in 2001 9,10 . In cardiac applications, the reporting of some adverse events after UCA has led to some restriction imposed by the European Medicines Agency (EMEA) and the U.S. Food and Drug Administration (FDA).…”