Quantitative assessment of atelectasis formation under high frequency jet ventilation during liver tumour ablation-A computer tomography study

Abstract

Background: High frequency jet ventilation (HFJV) can be used to minimise sub-diaphragmal organ displacements. Treated patients are in a supine position, under general anaesthesia and fully muscle relaxed. These are factors that are known to contribute to the formation of atelectasis. The HFJV-catheter is inserted freely inside the endotracheal tube and the system is therefore open to atmospheric pressure.

Aim: The aim of this study was to assess the formation of atelectasis over time during HFJV in patients undergoing liver tumour ablation under general anaesthesia.

Method: In this observational study twenty-five patients were studied. Repeated computed tomography (CT) scans were taken at the start of HFJV and every 15 minutes thereafter up until 45 minutes. From the CT images, four lung compartments were defined: hyperinflated, normoinflated, poorly inflated and atelectatic areas. The extension of each lung compartment was expressed as a percentage of the total lung area.

Result: Atelectasis at 30 minutes, 7.9% (SD 3.5, p = 0.002) and at 45 minutes 8,1% (SD 5.2, p = 0.024), was significantly higher compared to baseline 5.6% (SD 2.5). The amount of normoinflated lung volumes were unchanged over the period studied. Only a few minor perioperative respiratory adverse events were noted.

Conclusion: Atelectasis during HFJV in stereotactic liver tumour ablation increased over the first 45 minutes but tended to stabilise with no impact on normoinflated lung volume. Using HFJV during stereotactic liver ablation is safe regarding formation of atelectasis.

Fig 1. Mean atelectasis in percentage (HU -100-+100) and standard deviation bars.

T = 0 being the first CT after initiation of HFJV (high frequency jet ventilation) and thereafter CT-scans every 15 minutes. A significant raise in the amount of atelectasis could be seen at timepoints T = 30 and T = 45 when compared to baseline.

Fig 2. The four lung compartments, described as the mean percentage of the lung, during the time period studied.

T = 0 being the first CT-scan after initiation of HFJV (high frequency jet ventilation) and thereafter CT-scans every 15 minutes. The normoinflated lung is unchanged during the whole time period studied (P = 0.8).

Fig 3. Mean atelectasis in percentage (HU -100-+100) at the four timepoints for the seven patients that started high frequency jet ventilation between 0–5 minutes before the first CT-image.

T = 0 being the first CT-scan after initiation of HFJV (high frequency jet ventilation) and thereafter CT-scans every 15 minutes. Significant difference in the amount of atelectasis between groups was seen only at T30 when compared to baseline (p = 0.04).

Fig 4. Mean atelectasis in percentage (HU -100-+100) at the four timepoints for the 15 patients with a body mass index<30.

T = 0 being the first CT-scan after initiation of HFJV (high frequency jet ventilation) and thereafter CT-scans every 15 minutes. For this subgroup no statistical difference could be seen between the timepoints even though an initial visual trend is noted.

Fig 5

Time spent in the post anaesthesia care unit (minutes, left y-axis) and the amount of atelectasis at time 30 minutes (percentage, right y-axis) after start of HFJV (high frequency jet ventilation). Blue bars represent minutes in the PACU and orange dots represents amount of atelectasis.