Khattab, A. K. M. H. (2022). Regional distribution of lung ventilation during high-frequency jet ventilation in anesthetized patients [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2022.101100
Electrical Field Tomography; High-Frequency Jet Ventilation; Aneasthesia
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Abstract:
Electrical Impedance Tomography (EIT) is a radiation-free non-invasive imaging technique that allows a bedside continuous monitoring of lung regional ventilation distribution. It is a novel imaging tool that is cheap, portable, easily accessible, and can be a part of the intensive care unit or the operation rooms. The High-Frequency Jet Ventilation (HFJV) is one of the common mechanical ventilation techniques used in patients under anesthesia during airways surgeries.The main objective of this thesis is to evaluate the regional ventilation distribution of the lung during the application of two different HFJV modes by the usage of the EIT tool in patients under anesthesia. First, Single High-Frequency Jet Ventilation mode (Single HFJV), where a single high-frequency portion of the gas is used for the ventilation process. The second mode is the Superimposed High-Frequency Jet Ventilation mode (SIHFJV), where two different ventilation frequencies are combined together and delivered simultaneously to the lung. Patients undergoing surgeries in the airways were ventilated through a mask with a Tidal Volume (TV) of 6 mL/kg for 2 minutes and Respiration Rate (RR) of 12/min, followed randomly by the 2 modes of the HFJV sequentially. The SIHFJV mode was provided supraglotticaly via a Jet Laryngoscope for 5 minutes with a low-frequency RR of 12/min combined with a high-frequency RR of 600/min. The Single HFJV mode was provided subglotticaly via a thin Catheter for 5 minutes with a high-frequency RR of 120/min. The jet ventilation Driving Pressure (DP) was a function of the body weight. Twenty-Seven patients undergoing different elective endotracheal surgeries requiring HFJV were enrolled for This clinical study. Four patients were excluded and the final analysis included 23 patients. The regional ventilation distribution of the lung Region of Interest (ROI) was recorded by the EIT during the whole process and analyzed offline. There was no significant difference in the ventilation distribution of the lung ROIs and the Silent Spaces (SS) between the HFJV modes. The Tidal Impedance Variation significantly decreased (P-value < 0.05) from an average of 1566AU during the SIHFJV to an average of 300AU during the Single HFJV, which reflects more TV during the SIHFJV mode compared to Single HFJV mode. Furthermore, during the SIHFJV, increasing the DP by .5 bar is considered to be effective. Increasing the DP increases the TV by over-inflation of the already ventilated lung regions without change in the lung ventilation distribution. During the Single HFJV, the Jet Catheter's position and tip direction inside the trachea change the ventilation distribution in the lung ROIs and in between the right and the left lung. In some cases, the tip direction could lead to more than 90% of the TV in only one lung or in a specific lung ROI. In the supine position, the dorsal regions (dependent regions) develop more SS than the ventral regions (non-dependent regions) which is significant during mask and SIHFJV modes. SIHFJV mode develops an average of 8% as dependent SS, while develops only average of 3% as Non-dependent SS. There was no significant difference in the developed SS between the dorsal and ventral regions during the Single HFJV mode. In this study, EIT was an effective imaging technique to detect the ventilation inhomogeneity in the lung. It reflected that there was no significant improvement in the ventilation distribution or in the developed SS between the HFJV modes. Increasing the DP of HFJV is applied clinically to increase the TV. This study proves that the TV increases due to increased ventilation of the already ventilated lung ROIs without distributing the ventilation to the less ventilated areas. The anesthesiologists should be careful while handling the DP during HFJV modes to avoid ventilator-induced lung injury.
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