Point-of-care ultrasonography (POCUS) is the ultrasonography performed and interpreted by physicians at the bedside. POCUS allows real time findings that may be correlated with patient’s clinical condition, providing dynamic images. These images, depending on the user, could be repeatable in case patient’s condition changes. Ultrasound scanning is rapidly emerging as an easily accessible, portable and relatively inexpensive tool, that can be proven as an extremely useful diagnostic and monitoring modality in clinical practice.^{1 2}

Anesthesiologists in their daily practice face several emergencies and decision making challenges so, a rapid, dynamic, accurate, inexpensive and easily accessible modality could provide a valuable diagnostic tool. We usually need to get a quick answer to questions rising during physical examination instead of waiting for the results of imaging and laboratory studies performed and interpreted in later time, in other departments, by practitioners not directly involved with patient’s management. Therefore, it is important to make sure that anesthesiologists are aware of the expanding applications of this technology and train appropriately in its use.³

‘Classical’ ultrasound applications in the perioperative setting Many anesthesiologists are already acquainted with ultrasound scanning techniques and image interpretation. Historically, the primary application for perioperative ultrasound in anesthesia was transesophageal echocardiography. This was mainly used by cardiovascular anesthesiologists, many of them acquiring skills comparable to the skills of cardiologists and radiologists. Thankfully, ultrasound applications within the access of the non cardiovascular anesthesiologists are simpler than transesophageal echocardiography. Simplified protocols are used for ultrasound use in the surgery room, in the wards and in the acute care setting, aiming on finding answers to simple questions that the clinician seeks during patient treatment. For example, one of the protocols used for critically-ill patients, the FATE protocol (Focused Assessment in Transthoracic Echocardiography), requires only four views that are much easier to learn than the classical transesophageal echocardiography.^{4 5}

In terms of therapeutic interventions, ultrasound guided insertion of central venous catheters was also one of the first ultrasound uses in anesthesia. This has now become common practice and is recommended by the majority of international guidelines, i.e. the NICE guidelines in the UK or the IOM guidelines in the United States, requiring the use of ultrasound for any type of vascular approach.^{4 6}

Ultrasonography (US) in the hands of anesthesiologists raised to higher skill levels as a means to guide peripheral nerve blockades (PNB). This was first explored by anesthesiologists at the University of Vienna in the mid-1990s. Since then, a growing body of evidence supports the use of ultrasound guidance for regional anesthesia. For example, with ultrasound guidance compared to peripheral nerve stimulation, there was shown to be a significant decrease in the risk of vascular puncture, local anesthetic systemic toxicity (LAST), an increase in nerve block duration and a faster onset time.^{7 8} From this point on, US has been additionally widely used in interventional pain medicine. It has been studied as a comparable method, even suggested to be as effective as fluoroscopy for transforaminal nerve root and facet joint injections.³

US application in the acute care setting is based primarily on pattern recognition. the idea of the protocols is to perform short scans, focusing on abnormal ultrasound patterns, providing information on severe life-threatening conditions and not quantitative tests. These protocols have short learning curves.

Further ultrasound applications in the perioperative setting

It is more than obvious that anesthesiologists may become and actually should become proficient users of US, in areas beyond vascular access and regional anesthesia. as anesthesiologists are increasingly involved in patient management beyond the operating room, they are soon expected to use US to diagnose cardiopulmonary disorders and optimize hemodynamic condition perioperatively by means of transthoracic examination of the heart, monitoring for the collapsibility of the inferior vena cava and direct measurement of left ventricular end-diastolic area .⁹

Pulmonary point-of-care ultrasound has proven to be a valuable tool for the detection of pneumothorax, pleural effusion, consolidation and alveolar interstitial syndrome in the critical care setting, searching for signs like: Lung sliding (sliding of visceral and parietal pleura over one another with respiration), that may rule out pneumothorax, a lines (repeated parallel lines below pleura), suggesting that there is no parenchymal disease and B lines (vertical lines) indicating fluid in the lungs or an interstitial syndrome (ARDS, pneumonia).^{10 11}

The diaphragm can be examined as part of the respiratory muscle function assessment, in patients with neuromuscular disorders. Most commonly we evaluate: Diaphragm Thickness, Change in Thickness, Diaphragm Excursion, Side-to-side Variation (greater excursion on the left side) and Diaphragmatic Velocity. These measurements are used for identification of diaphragm paralysis and its etiology (intrinsic or extrinsic pathology), prognosis after diaphragm paralysis (with serial measurements of muscle thickness), assessment of Weaning Failure (decreased diaphragm excursion seems to predict weaning failure) and guidance for needle Electromyography.^{12 13}

Abdominal and gastric ultrasound The Focused Assessment with Sonography for Trauma (FAST) exam is the most commonly performed POCUS examination in the United States, aiming in identifying any extravasated fluid in the abdomen. as for gastric ultrasound, it has been suggested that it could play a vital role in quantifying gastric content, providing valuable information in emergency but also in elective cases. These modalities have a potential value in a variety of perioperative populations and setting and there are multiple tools to educate anesthesiologists in their use.¹⁴

Airway US can be used in the point of care evaluation and management of the airway. POCUS for airway evaluation has recently been demonstrated to identify difficult laryngoscopy, appropriate location of the endotracheal tube, and facilitate cricothyrotomy procedures by proper location of the cricothyroid membrane in patients with difficult anatomy like the morbidly obese.

Other areas in which point-of-care ultrasound can provide valuable assistance to the perioperative physician include the facilitation of placement of orogastric tubes, the evaluation of a patient with low urine output and the estimation of intracranial pressure (ICP).¹

In conclusion, POCUS is progressively becoming more readily available and indications are continuously increasing. as demand for our participation in perioperative care continuously grows, we, anesthesiologists, are required to be trained and adopt in our daily practice the perioperative point-of-care ultrasound.

References

1. Deshpande R, Ramsingh D. Perioperative point of care ultrasound in ambulatory anesthesia: thinking beyond nerve blocks. Curr Opin Anaesthesiol 2017;30:663–669.

2. Roche D, Iohom G. Point-of-care Ultrasound in Anaesthesia and Intensive Care Medicine. Rom J Anaesth Intensive Care 2018;25:95–96.

3. Terkawi AS, Karakitsos D, Elbarbary M, Blaivas M, Durieux ME. Ultrasound for the anesthesiologists: present and future. Scientific World Journal2013; 2013:683685.

4. Royse CF, Canty DJ, Faris J, Haji DL, Veltman M, Royse A. Core review: physician-performed ultrasound: the time has come for routine use in acute care medicine. Anesth Analg 2012;115:1007–28.

5. American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologist Task Force on Transesophageal Echocardiography. Practice guidelines for perioperative transesophageal echocardiography. An updated report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography. Anesthesiology 2010;112:1084–96.

6. Moore CL, Copel JA. Point-of-care ultrasonography. N Engl J Med 2011 Feb 24;364:749–57.

7. Kapral S, Krafft P, Eibenberger K, et al: Ultrasound-guided supraclavicular approach for regional anesthesia of the brachial plexus. Anesth Analg 1994;78:507–513.

8. Abrahams MS, Aziz MF, et al. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials. Br J Anaesth 2009;102:408–17.

9. Ramsingh D, Fox JC, Wilson WC. Perioperative Point-of-Care Ultrasonography: An Emerging Technology to Be Embraced by Anesthesiologists. Anesth Analg 2015;120:990–2.

10. Miller A. Practical approach to lung ultrasound. BJA Education 1 February 2016;16(2):39–45.

11. Lichtenstein D. Novel approaches to ultrasonography of the lung and pleural space: where are we now? Breathe (Sheff) 2017;13:100–111.

12. Fayssoil A, et al. Diaphragm: pathophysiology and ultrasound imaging in neuromuscular disorders. J Neuromuscul Dis 2018;5:1–10.

13. Sarwal A, et al. Neuromuscular ultrasound for evaluation of the diaphragm. Muscle & Nerve 2013;47:319–329.

14. Deshpande R, Ramsingh D. Perioperative point of care ultrasound in ambulatory anesthesia: thinking beyond nerve blocks. Curr Opin Anaesthesiol 2017;30:663–669.