Role of tube size and intranasal compression of the nasotracheal tube in respiratory pressure loss during nasotracheal intubation: a laboratory study

Abstract Background Small nasotracheal tubes (NTTs) and intranasal compression of the NTT in the nasal cavity may contribute to increasing airway resistance. Since the effects of size, shape, and partial compression of the NTT on airway resistance have not been investigated, values of airway resistance with partial compression of preformed NTTs of various sizes were determined. Methods To determine the factors affecting the respiratory pressure loss during the nasotracheal intubation, physical and fluid dynamics simulations were used. The internal minor axes of NTTs in the nasal cavity of intubated patients were measured using dial calipers. In physical and fluid dynamics simulations, pressure losses through the tubular parts, compressed parts, and slip joints of NTTs with internal diameters (IDs) of 6.0, 6.5, 7.0, 7.5, and 8.0 mm were estimated under partial compression. Results The median internal minor axes of the 7.0- and 7.5-mm ID NTTs in the nasal cavity were 5.2 (4.3–5.6) mm and 6.0 (4.2–7.0) mm, respectively. With a volumetric air flow rate of 30 L/min, pressure losses through uncompressed NTTs with IDs of 6.0-, 6.5-, 7.0-, 7.5- and 8.0-mm were 651.6 ± 5.7 (6.64 ± 0.06), 453.4 ± 3.9 (4.62 ± 0.04), 336.5 ± 2.2 (3.43 ± 0.02), 225.2 ± 0.2 (2.30 ± 0.00), and 179.0 ± 1.1 Pa (1.82 ± 0.01 cmH2O), respectively; the pressure losses through the slip joints were 220.3 (2.25), 131.1 (1.33), 86.8 (0.88), 57.1 (0.58), and 36.1 Pa (0.37 cmH2O), respectively; and the pressure losses through the curvature of the NTT were 71.6 (0.73), 69.0 (0.70), 64.8 (0.66), 32.5 (0.33), and 41.6 Pa (0.42 cmH2O), respectively. A maximum compression force of 34.1 N increased the pressure losses by 82.0 (0.84), 38.0 (0.39), 23.5 (0.24), 16.6 (0.17), and 9.3 Pa (0.09 cmH2O), respectively. Conclusion Pressure losses through NTTs are in inverse proportion to the tubes’ IDs; greater pressure losses due to slip joints, acute bending, and partial compression of the NTT were obvious in small NTTs. Pressure losses through NTTs, especially in small NTTs, could increase the work of breathing to a greater extent than that through standard tubes; intranasal compression further increases the pressure loss

〈Originals〉The effect of sevoflurane or propofol with or without an anti-emetic dose of droperidol on the QTc interval and the transmural dispersion of repolarization

[Abstract]　Purpose : Sevoflurane and droperidol but not propofol induce QTc interval prolongation, but there are several conflicting reports. We investigated the effects of sevoflurane and propofol with or without an anti-emetic dose of droperidol on the QTc interval and the transmural dispersion of repolarization for 2 hours, and the QT interval was adjusted for the patient\u27s heart rate using 3 formulae. Methods : One hundred two American Society of Anesthesiologists (ASA) physical status I-II patients, aged 20-70, were randomly allocated to one of four groups : Group 1 (n＝25) receiving sevoflurane anesthesia without droperidol (1.25 mg), Group 2 (n＝26) receiving sevoflurane anesthesia with droperidol, Group 3 (n＝ 25) receiving propofol anesthesia without droperidol, or Group 4 (n＝26) receiving propofol anesthesia with droperidol. RR intervals, QT intervals, and Tp-e intervals, which indicates the dispersion of ventricular repolarization (TDR), were mea-sured. The QT interval was adjusted for the patient\u27s heart rate using the formulae of Bazett, Fridericia, and Matsunaga. Results : Sevoflurane significantly prolonged the QTc, but droperidol did not enhance sevoflurane- induced QTc prolongation in all the formulae. Conversely, propofol did not affect the QTc in all formulae. Tp-e intervals were not affected in any of the groups. Conclusion : Although it significantly prolongs the QTc interval, sevoflurane, even with droperidol, does not seem to cause lethal arrhythmias associated with QT prolongation, because it does not induce Tp-e prolongation. Propofol is safer than sevoflurane in terms of arrhythmias associated with QT interval prolongation. Bazett\u27s formula is reliable for detecting anesthetic- induced QT prolongation