In‐circuit high‐frequency jet ventilation to reduce organ motion in a child undergoing sarcoma ablation

Summary

Patients with primary or metastatic solid tumours can be treated with minimally invasive image‐guided procedures as an alternative to surgical resection. Reducing organ motion during these procedures is crucial so that tumours can be accurately targeted and treatment delivered within a small margin, limiting potential damage to adjacent structures. As ventilation is the main cause of motion, there has been a shift from conventional ventilation towards the use of in‐circuit high‐frequency jet ventilation techniques for these procedures. We present the case of a 7‐year‐old who required computed tomography‐guided microwave ablation of a right lung metastatic nodule under general anaesthesia. The patient's lungs were ventilated with in‐circuit high‐frequency jet ventilation in order to provide optimum conditions for ablation. The treatment was successfully completed and she was discharged home the following day. High‐frequency jet ventilation is regularly used in our institution for adult computed tomography‐guided treatments and to our knowledge, this application has not been described yet in a child this young. Our experience suggests that this technique can be safely used in paediatric patients, though further investigation of the optimum parameters for in‐circuit high‐frequency jet ventilation in this population is warranted.

Introduction

The development of minimally invasive image‐guided techniques to treat intrathoracic and intra‐abdominal tumours has resulted in the need to anaesthetise patients while minimising target organ motion. High‐frequency jet ventilation results in less thoracic and abdominal movement than conventional ventilation and has been used with this intended benefit in patients being anaesthetised for a variety of procedures, including atrial fibrillation ablation, extracorporeal shock‐wave lithotripsy and computed tomography (CT)‐guided ablation of liver, renal and lung tumours [1, 2, 3, 4, 5]. Although published evidence is limited, published case series have suggested that high‐frequency jet ventilation can reduce CT‐guided ablation procedure times and exposure to ionising radiation, as well as reduce the technical difficulty of CT‐guided percutaneous applicator placement [4, 5]. Developing these techniques further in the future will increase access and allow a greater number of patients to benefit from the reduced complication risk and more rapid recovery compared with open surgical procedures.

In the paediatric population, the use of high‐frequency jet ventilation to ventilate children's lungs during cardiac magnetic resonance imaging (MRI) has recently been described [6]. However, we are not aware of in‐circuit high‐frequency jet ventilation being used previously in a very young patients to enable minimally invasive CT‐guided cancer treatment.

Report

We present the case of a 23‐kg, 7‐year‐old girl with a rare alveolar soft part sarcoma of the nasopharynx who required CT guided‐microwave ablation of a metastatic right lung nodule under general anaesthesia. She had undergone primary tumour resection and subsequent proton beam radiotherapy several years earlier, followed by surgical excision of bilateral lung metastases 1 year later. Throughout this period, she was treated with sunitinib, an oral, targeted multityrosine kinase inhibitor [7]. At the time of her lung resection, the cardiothoracic surgeon was unable to locate a small soft tissue nodule within the right lower lobe. Subsequent CT scanning confirmed small volume growth of this nodule but no new disease, so she was referred for consideration of ablative treatment.

General anaesthesia was induced and maintained using a total intravenous technique with propofol and remifentanil. Following administration of 25 mg rocuronium bromide, the patient's trachea was intubated with a 5.5‐mm cuffed oral tracheal tube. Depth of anaesthesia was monitored throughout (Entropy; GE Healthcare, Helsinki, Finland). The procedure was carried out with the patient in the supine position.

Ventilation was initially provided via volume control ventilation (tidal volume 180 ml; peak inspiratory pressure 15–17 cmH₂O; positive end‐expiratory pressure 4 cmH₂O; respiratory rate 16 breaths.min^‐1). After 22 min, in‐circuit high‐frequency jet ventilation was commenced with a Monsoon jet ventilator (Acutronic Medical Systems, Hirzel, Switzerland) for 45 min, so the nodule could be identified and the ablation performed. This was achieved by using a jet swivel adaptor (Acutronic Medical Systems; Fig. 1) which sits between the anaesthetic breathing circuit and the tracheal tube. The swivel adaptor has a connector to attach to the jet ventilator tubing and its piston sits within the tracheal tube. A driving pressure of 30 kPa (0.3 bar) was applied, determined by assessing her chest wall movement, while maintaining adequate minute ventilation and normocarbia. The F_IO₂ was set at 100% and frequency at 120 cycles per minute. Her minute ventilation on the jet ventilator was 4.8 l.

Figure 1.

A jet swivel adaptor (Acutronic Medical Systems, Hirzel, Switzerland) connects the tracheal tube, conventional ventilator circuit and jet ventilator, and is used to deliver in‐circuit high‐frequency jet ventilation.

A few minutes after starting high‐frequency jet ventilation the end‐tidal carbon dioxide partial pressure (ETCO₂) was 4.5 kPa. This was measured via the anaesthetic machine capnography device (GE Healthcare gas module E‐CAi0‐00, Helsinki, Finland) by briefly suspending the jet ventilation and delivering intermittent positive‐pressure ventilation. As she was normocapnic, the jet ventilation settings were not adjusted further. The peak inspiratory pressure during jet ventilation was 3 cmH₂O.

During the procedure her cardiovascular and respiratory parameters remained stable. She received 35 µg fentanyl; a further 10 mg rocuronium bromide; 15 mg.kg^‐1 paracetamol; 1 mg.kg^‐1 diclofenac; 100 μg.kg^‐1 ondansetron; 100 μg.kg^‐1 dexamethasone; and 250 ml of compound sodium lactate.

The ablative treatment was completed successfully with no complications and at the end of the procedure, jet ventilation was discontinued and conventional positive‐pressure ventilation recommenced. Her ETCO₂ at this point was 4.1 kPa. Neuromuscular blockade was reversed with 50 mg sugammadex. Tracheal extubation and recovery were uneventful.

The patient was admitted to the ward for overnight observation and was discharged the following morning. Computed tomography scans at 1, 4 and 9 months confirmed successful ablation of the tumour, with no new disease or complications.

Discussion

Patients with solid primary or metastatic tumours can be treated with minimally invasive image‐guided ablative procedures as an alternative to surgical resection or radiotherapy. Under direct CT guidance, one or more needles are inserted into the tumour and induce tissue necrosis using heat (microwave ablation), cold (cryoablation) or an electric field (irreversible electroporation). Direct vision allows important structures such as bowel to be avoided using measures such as hydro‐ or pneumodissection. A target tumour is then destroyed with only a small margin of healthy tissue, resulting in low complication risk and rapid recovery.

Trials comparing ablation with standard treatments are few. A recent trial showed the use of ablative treatment added to standard chemotherapy in patients with unresectable colorectal liver metastases could significantly prolong overall survival [8]. Multiple comparative case series have also shown the effectiveness of cryoablation to treat small renal tumours, with similar rates of local recurrence but significantly lower complication risk compared with laparoscopic partial nephrectomy [9, 10].

Organ motion during these procedures is a major problem that may impact outcomes. Reducing organ motion secondary to conventional mechanical ventilation by using high‐frequency jet ventilation can reduce procedure time, decrease exposure to ionising radiation and assist with the technical difficulty of CT‐guided percutaneous applicator placement [4, 5]. The alternative is to perform these procedures in paralysed patients, intermittently pausing ventilation (‘breath‐holds’) during needle positioning. These periods of apnoea are limited to a maximum of only 1–2 min and there can be variation in position of the target structure between a series of breath‐holds. The shift to using high‐frequency jet ventilation requires careful anaesthetic consideration and potentially brings new risks to the procedure, which anaesthetists and the multidisciplinary team must manage appropriately.

High‐frequency jet ventilation delivers tidal volumes smaller than the dead space at high frequencies of 1–10 Hz. Important potential complications of this technique are barotrauma, hypoventilation and hyperventilation.

Barotrauma can occur if there is inadequate egress of air during expiration causing a rise in intrathoracic pressure. Modern jet ventilators have a second airway measurement line which monitors the airway pressure continuously and alarms at high pressures. Intrathoracic pressure during in‐circuit high‐frequency jet ventilation is also measured on the conventional ventilator via the anaesthetic circuit. Overall, mean and peak pressures are lower than in conventional ventilation, as demonstrated in this case.

Hypoventilation or hyperventilation can occur due to the difficulty in accurately monitoring ETCO₂, even when using the in‐circuit technique where oscillations are visible on the ETCO₂ trace. In a previous case series published by our centre, 50 patients received high‐frequency jet ventilation during renal tumour cryoablation and remained normocapnic throughout the procedure [4]. As in this case, these patients received intermittent ETCO₂ checks through delivering intermittent positive pressure breaths and, if necessary, adjusting the jet ventilator driving pressure. Other methods of monitoring carbon dioxide include transcutaneous carbon dioxide monitoring, intermittent arterial blood gas sampling or continuous blood gas analysis, though these are not routinely performed at our centre.

In order for high‐frequency jet ventilation to be delivered safely in this setting, appropriate resources and training must be in place. Patients undergoing these procedures are likely to have comorbidities and may be at high risk of anaesthetic complications. Pathways should exist for their pre‐assessment and pre‐procedure optimisation. Anaesthetists and anaesthetic practitioners must be competent in handling the jet ventilator and managing complications of high‐frequency jet ventilation. As this equipment is not frequently used in other settings, regular use for CT‐guided intervention requires a group of professionals to be trained and to develop expertise. Depth of anaesthesia monitors should be available for all patients receiving high‐frequency jet ventilation as they require total intravenous anaesthesia and neuromuscular blockade. Radiologists and radiographers should understand the specific anaesthetic challenges these procedures create and be trained to provide support if complications arise.

We have found few reports in the literature on the use of in‐circuit high‐frequency jet ventilation in children and minimal data on appropriate ventilator settings for in‐circuit high‐frequency jet ventilation in this population. A recent case series described the use of in‐circuit high‐frequency jet ventilation for cardiac MRI in four patients aged 4–15 years old [6]. The scans took 35 min or less to perform.

Differences noted between their cases and this current patient include that jet ventilation was delivered through a 40‐cm 7‐Fr catheter placed in the tracheal tube, rather than a jet swivel adaptor; higher driving pressures were set, starting at 70 kPa (0.7 bar), and reduced to 50 kPa (0.5 bar) in two cases to decrease thoracic movement; and patients developed hypercapnia (mean ETCO₂ of 8.6 kPa at the end of jet ventilation), unlike our patient who remained normocapnic.

High‐frequency jet ventilation offers a valuable adjunct during CT‐guided cancer treatment to reduce target organ motion. As these procedures are offered more widely, new groups of patients may benefit. In this case, we describe the successful use of high‐frequency jet ventilation in a 7‐year‐old child undergoing CT‐guided lung tumour ablation. Research may be required to establish the optimum in‐circuit high‐frequency jet ventilation settings in children.