Authors S Laxman, L Yamanouchi and C Ong present the case of a patient presenting for lung cancer surgery, with a clinical condition affecting the efficacy of ultrasound, which influenced the conduct of regional anaesthesia.
Summary
Ultrasonography (US) is an important non-invasive adjunct for paravertebral block placement during thoracic surgery. This technique allows the visualisation of anatomy and the spread of the injected local anaesthetic in real-time, which may improve success and reduce needle-related complications such as peripheral nerve injury, local anaesthetic system toxicity (LAST) and pneumothorax. Poor image quality can occur with this technique and is related to the loss of energy of US waves as it travels through different types of media with varying acoustic impedances. We present a case of a patient presenting for lung cancer surgery, with a clinical condition affecting the efficacy of ultrasound, which influenced the conduct of regional anaesthesia.
Introduction
Direct ultrasonographic visualisation significantly improves the outcome of most techniques in regional anaesthesia [1]. It improves the accuracy of nerve blocks to increase efficacy and to avoid complications, including peripheral nerve injury, local anaesthetic system toxicity (LAST), hemi diaphragmatic paresis and pneumothorax [2].
Paravertebral block is the administration of local anaesthetic into the wedge-shaped space on the antero-lateral thoracic spine close to where spinal nerves emerge from intervertebral foramina resulting in ipsilateral somatic and sympathetic nerve blockade in multiple contiguous thoracic dermatomes above and below site of injection. In thoracic surgery, it provides effective postoperative analgesia comparable to epidural analgesia, reduced opioid consumption, and preserved respiratory function, with minimal side effects. It associated with the reduction of chronic post-thoracotomy neuralgia. Compared to general anaesthesia, thoracic paravertebral blocks have shown to reduce pain, nausea and vomiting in the post-operative period [3].
Under ultrasonography (US) for paravertebral block, the transverse process, pleura and superior costotransverse ligament can be identified, and the spread of the injected local anaesthetic can be observed in real-time. This facility may translate into improved technical outcomes, higher success rates, and reduced needle-related complications [1].
Ultrasound radiation is subject to several interactions as it travels through tissues: reflection, scatter and absorption. It loses energy when traversing different types of media with different acoustic impedances, the latter being a measure of resistance. The greater the difference in acoustic impedance between two materials, the stronger the reflection arising from their interface.
We present a case of a patient presenting for lung cancer surgery, illustrating a condition, not immediately anticipated, which rendered ultrasound imaging for regional anaesthesia to be impossible, and the importance in considering alternative options of conducting regional anaesthesia, when these difficulties arise.
Report
A 71-year-old woman who had been under lung cancer surveillance, presented with a tumour in the right upper lobe of the lung. The patient had had a previous robotic left lower lobectomy for T1 lung adenocarcinoma complicated by a prolonged postoperative stay in intensive care for respiratory complications.
To confirm diagnosis, patient underwent an interventional radiology (IR)-guided lung biopsy before the operation. This was complicated by a large right pneumothorax, treated with two chest drains. The patient subsequently developed progressive surgical emphysema in her back, face, right side of chest and upper limbs and neck despite chest drainage suction. There was a persistent air leak of the lung, but the surgical emphysema showed clinical improvement. The biopsy result was inconclusive. Surgery therefore was indicated for a definitive diagnosis, and two weeks later, the patient presented for a right thoracotomy, frozen section and lobectomy of the right upper lobe.
The patient was a small and frail lady, BMI 21.6, and she was a current smoker with chronic obstructive pulmonary disease (COPD), poor lung function and mobility. She presented with chest drains in situ. A chest x-ray taken a few days preoperatively demonstrated a re-inflated right lung and surgical emphysema (Fig 1A). On inspection, there was no clinical signs of surgical emphysema: previous crepitus and distension of skin and tissues were markedly absent.
Fig 1A: Preoperative Chest radiograph suggestive of subcutaneous emphysema
General anaesthesia, with full standard monitoring, was induced uneventfully. Arterial cannulation for arterial blood pressure monitoring proved difficult in both right and left radial arteries by landmark technique. It was also noted that the radial and brachial arteries in the right upper limb were poorly visualised by ultrasound, and eventually, the left brachial artery was cannulated using landmark technique. The patient was then positioned for surgery in the left lateral position in preparation for the paravertebral block and surgery.
The conventional practice at our thoracic unit is to administer a pre-operative ultrasound-guided paravertebral block for thoracic patients, followed by a postoperative surgically sited paravertebral local anaesthetic infusion, for perioperative pain management. Under aseptic technique, the chest was scanned with a linear 13-6MHz ultrasound transducer (Sonosite Ltd, Bedford, UK) to locate the paravertebral space. As the patient was slim, the quality of the image was anticipated to be good; however, the images revealed poor delineation of sono-anatomical landmarks below the skin and subcutaneous tissue with considerable difficulty in identifying the ribs (Fig 1B). Several measures were used to augment the scan – application of surplus sono-acoustic gel, change of probe cover, use of different ultrasound machines and transducers – with no improvement to the quality of the images and the conclusion was that surgical emphysema, despite being negligible on clinical evaluation was significant enough to distort ultrasound imaging.
Fig 1B: Ultrasound image of the right posterior chest. Poor delineation of sono-anatomy, preventing ultrasound-guided paravertebral block
A regional blockade was considered essential, and the operator performed a landmark technique paravertebral block. The patient had effective pain relief in the perioperative and postoperative period. The patient was able to mobilise well with intense rehabilitation, and though she developed a hospital acquired pneumonia, this was successfully treated, and she did not require ICU admission. The patient was discharged from hospital three weeks after her surgery.
Discussion
Our case demonstrated that ultrasound guided regional anaesthesia is limited by subcutaneous emphysema that is not visible on inspection, even in a slim patient. It became apparent that she had residual emphysema affecting her chest wall and both upper limbs. Ultrasound transmission was inhibited such that only the skin could be imaged, and the radial artery, a superficial structure could not be visualised.
Subcutaneous emphysema usually presents as a soft tissue swelling of upper chest, neck and face. It is identified on physical examination by the presence of crepitus and swelling and confirmed on chest x-ray as radiolucent streaks throughout subcutaneous tissue and muscle, often with minimal symptoms requiring no treatment. Involvement of deeper tissues of thoracic outlet and chest wall can be life threatening needing urgent intervention. Subcutaneous emphysema may take a substantial period to resolve depending upon the amount of air trapped and the rate of absorption. Our case demonstrated that resolving surgical emphysema though not detectable by inspection or palpation, can be significant enough to interfere with the transmission of ultrasound waves necessary for imaging. Such a small layer of air can have a dramatic impact on the success of ultrasound scanning. Additionally, this layer was widespread throughout the body, such that emphysema in the arms prevented even visualisation of superficial structures such as the radial arteries.
Impedance between air and skin is so great that all ultrasound will be reflected, and an air free path is critical to permit penetration of ultrasound beam which is usually achieved by an acoustic coupling agent or gel. Some studies have reported barriers to US scanning posed by subcutaneous emphysema; however, there is scarce information of the ultrasound images in a literature for a patient with subcutaneous emphysema [4]. Image quality in obese patients may be improved by setting the ultrasound machine to penetrate a greater depth and by utilising transducers with a lower frequency [5]. The use of harmonic imaging may also be considered, as this allows US waves to travel in a non-linear fashion, reducing the level of attenuation cause by increased adipose tissue [6, 7]. Novel ultrasound imaging techniques have also been attempted in order to improve image quality, including spatial compound imaging, which utilises multiple overlapping images frames from multiple US wave angles in order to generate a single image to reduce the effect of attenuation [6]. Several processing filters, such as speckle reduction may also improve image quality [8, 9]. Oedema has also shown to reduce US image quality for numerous reasons. Firstly, oedema may amplify ultrasound wave absorption, and reduce the level of contrast between nerves and surrounding tissues, making the nerves challenging to locate on ultrasound imaging [5]. Furthermore, oedema may displace or compress nerves, causing the nerves to deviate from its usual anatomical location or shape [10]. A common challenge also observed particularly in the elderly population is muscle atrophy as a result of muscle degeneration or chronic myositis [11]. Muscle atrophy may reduce image quality as US waves often fail to adequately penetrate atrophied muscles, as they reflect US waves and appear as hyperechoic structures [11].
In order to overcome these various anatomical factors that reduce image quality, numerous technological advancements have been introduced. Novel ultrasound machines can allow the characterisation of tissue elasticity and elastography, allowing the operator to differentiate between neural and extra-neural tissue, which currently may be challenging if the patient is obese or oedematous [5]. Three-dimensional ultrasound imaging can also allow the operator to observe multiple planes of view in order to gain further information about the spatial relationship between the anatomical structures [6]. Finally, the use of metamaterials in ultrasound machines can allow US waves to penetrate through certain tissues with a high acoustic index more easily, such as bone, adipose tissue and atrophied muscle [12].
When ultrasound imaging is identified as difficult or impossible to conduct regional anaesthesia, the adjustments required to improve the image, and a ‘plan B’ must be considered ahead. A ‘Plan B’ may involve choosing not to perform the regional block, as a ‘blind’ landmark technique may be associated with a greater risk of complications (vascular puncture, hypotension, epidural or intrathecal spread, pleural puncture and pneumothorax), as well as decreased success of blockade. The decision to proceed to a landmark technique will depend on operator proficiency. This can only be ensured by adequate training and retention of skills in landmark techniques which can be challenging in this era of Ultrasound guided regional anaesthesia and weighing benefits of this approach against the risks on a case to case basis. The patient in this case was frail, with poor lung function; a landmark paravertebral block was administered for effective analgesia to aid mobilisation, to reduce postoperative respiratory complication. Paravertebral block is known to provide comparable pain relief to thoracic epidural, with a better side effect profile in thoracic surgery patients [3].
Authors:
S Laxman,1 L. Yamanouchi2 and C. Ong3
- Consultant Anaesthetist, East Kent Hospitals University NHS Foundation Trust, Kent , UK.
- Foundation Year 1 Doctor, Guy’s and St. Thomas’ Hospitals NHS Foundation Trust, London, UK.
- Consultant Anaesthetist, Guy’s and St. Thomas’ Hospitals NHS Foundation Trust, London, UK.
Acknowledgements: No external funding and no competing interests declared. Published with written consent of patient.
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