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Poster 70
High Frequency Jet Ventilation (HFJV) for CT Guided Cryoablation of Small Renal Tumors

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High Frequency Jet Ventilation (HFJV) for CT Guided Cryoablation of Small Renal Tumours
Thea Buchan BSc Hons PgD, Kathryn Jenkins BSc MBBS FRCA, Pervez Sultan MBChB, FRCA, MD(Res), Wenyu Quak MBBS, Miles Walkden MRCS FRCR, Steve Bandula PhD

Background: Renal cryoablation (RC) is widely accepted as a safe and effective treatment for small renal tumours (1,2). Target organ motion contributes to technical difficulty during percutaneous image guided intervention (3, 4, 5), with the majority of motion attributable to ventilation. HFJV allows delivery of small tidal volumes at high frequency (6), and it’s use during general anaesthesia can reduce organ motion providing in a near stationary target (3, 6). Reported benefits during CT guided ablation of lung and liver tumours include reduction in technical difficulty of needle placement, reduced total procedure times and reduced patient exposure to ionising radiation (6, 7, 8, 9).
We aimed to evaluate the use of high frequency jet ventilation (HFJV) in place of standard intermittent positive pressure ventilation (IPPV) for computed tomography (CT) guided cryoablation of small renal tumours under general anaesthesia. The effect on procedure times, complication rate and radiation dose was evaluated.

Methods: This retrospective review was undertaken at a single tertiary interventional oncology referral centre. The study was reviewed by the University College London (UCL) and University College London Hospital (UCLH) joint research office and considered to be a service evaluation exempt from regulatory approval.
One hundred consecutive patients undergoing CT guided cryoablation of a small renal tumour under general anaesthesia between December 2015 and January 2017 were evaluated - 50 with standard IPPV and 50 after introduction of HFJV as standard practice at our centre. The decision to treat with CYA was made at the local renal cancer network multidisciplinary team meeting. All patients gave fully informed consent, and in all cases treatment was performed with curative intent.
All patients were initially ventilated with conventional intermittent positive pressure ventilation, via a standard anaesthetic breathing system. For those patients in the HFJV group, a jet swivel adaptor (Acutronic Medical Systems) was introduced into the circuit between the patient’s airway device and the breathing circuit. HFJV was commenced at 120 breaths per minute, and with an initial driving pressure (DP) of 1.5 bar for an LMA and 1.0 bar for an ETT. DP was adjusted to maintain the end tidal carbon dioxide within the range 4.5 – 5.5 KPa, as measured by intermittent checks with the conventional ventilation system.
CT guided cryoablation was performed as per the standard protocol at our institution.
For each procedure, patient date, ionising radiation dose, total procedure time, anaesthetic setup time, number of cryoprobes, hydro and pneumodissection needles used; number of biopsy mode CT volume acquisitions and total time required to place the probes and needles were recorded.

Results: During the review period, 100 renal tumours were treated by CT guided cryoablation in 100 separate consecutive treatment sessions in 95 patients. 50 of these treatments were undertaken using IPPV and 50 using HFJV. None of the patients intended for HFJV required a switch in ventilation technique to IPPV.
Technical treatment success was achieved in all patients at time of procedure, at 1 month follow up three patients from the IPPV group were put on surveillance for residual disease with planned retreatment. None of the patients treated under HFJV required any additional treatment.
Patient demographics and tumour characteristics are summarised in tables 1 and 2, with comparable characteristics and ASA classification between groups. Table 3 displays details of treatment sessions including patient position, anaesthetic induction time, number of cryoprobes placed and the use of hydro and pneumodissection. Comparison between groups showed no significant statistical difference for these factors.
Needle placement time (p=<0.0001) and total procedure time (p=<0.0001) were significantly shorter for procedures undertaken with HFJV in comparison to IPPV (fig 1). The number of CT acquisitions required for needle placement (p=<0.0001) and total procedure patient radiation dose (p=0.0027) were also significantly lower in procedures which took place under HFJV. Anaesthetic induction time did not differ significantly (p=0.2788) between the 2 groups.
There were no complications or delays to discharge attributable to anaesthesia. There were no deaths within 30-days. All complications were rated using the Clavian-Dindo (CD) scoring system. There were 4 complications within the HFJV group (CD – 1,2,2,4a), and 9 in the IPPV group (CD – 1,1,1,1,1,2,2,3a,3a).

Conclusions: By reducing target tumour motion during CT guided renal cryoablation, HFJV can simplify needle insertion during CT guided cryoablation for small renal tumours. We report safe introduction of HFJV with no conversion to IPPV. The change lead to a 26% reduction in mean total procedure time, 34% reduction in needle insertion time, and a 27% reduction in radiation dose. HFJV then provides a useful adjunct to complex image-guided interventions, but further work is required to demonstration its effect on oncological outcomes.

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