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

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.

Possible association between successful intubation via the right nostril and anatomical variations of the nasopharynx during nasotracheal intubation: a multiplanar imaging study.

PURPOSE: Most reported cases of nasopharyngeal laceration following impingement during nasotracheal intubation involved tube insertion via the right nostril. We postulated that recesses on the posterior wall of the nasopharynx might be associated with tube impingement. Using multiplanar imaging and clinical statistics, we evaluated whether anatomical variations in the recesses are related to successful intubation via the right nostril. METHODS: Using multiplanar computed tomography (CT) images of 97 patients, we investigated the locations of recesses relative to the mid-sagittal plane, nasal floor plane and posterior end of the nasal septum, and their shapes. Incidents of impingement of the tube during nasotracheal intubation and the shapes of the fossa of Rosenmüller on CT images were retrospectively evaluated in 170 patients. RESULTS: Eustachian tube orifices were located approximately 10 mm laterally from the sagittal plane, and approximately 10 mm above the nasal floor plane. The fossa of Rosenmüller was vertically elongated and located 7 mm laterally from the mid-sagittal plane. Pharyngeal bursae were found in 15 % of the subjects. Patients with failed insertion via the right nostril due to impingement frequently had a wide opening of the fossa of Rosenmüller. CONCLUSIONS: Successful intubation via the right nostril is related to the anatomy of structures on the posterior nasopharyngeal wall, particularly recesses located close to the path of nasotracheal tube insertion. Nasopharyngeal anatomical variations should be considered when one notices any resistance to advancement of the tube into the nasopharynx during nasotracheal intubation.

Roles of endotracheal tubes and slip joints in respiratory pressure loss: a laboratory study.

PURPOSE: The endotracheal tube (ETT) constitutes a significant component of total airway resistance. However, a discrepancy between measured and theoretical values has been reported in airway resistance through ETTs. The causes of the discrepancy were estimated by physical and rheological simulations. METHODS: The pressure losses through total lengths of ETTs and slip joints under a volumetric flow rate of 30 L/min were measured, and the pressure losses through the tubular parts of ETTs with internal diameters (IDs) of 6.0-, 6.5-, 7.0-, 7.5-, and 8.0 mm were measured. The Reynolds number of each setting was calculated, and the pressure losses through the total length of the ETT, the tubular part, and the slip joint of each size of tube were estimated. RESULTS: The Reynolds numbers were >5000 in all sizes of ETTs. Measured pressure losses were larger in small sized ETTs than in large sized ETTs-520.9 Pascals (Pa) in 6.0-mm ID and 136.4 Pa in 8.0-mm ID tubes. The measured pressure losses through the tubular part were comparable to the predicted values. The measured pressure losses through the slip joints were larger than the predicted values, and they accounted for approximately 25-40% of total pressure losses of the ETTs. CONCLUSION: Especially in small sized tubes, the pressure loss through the slip joint accounts for a large percentage of the total pressure loss through the ETT. The pressure loss through the slip joint may play a role in the discrepancy between measured and theoretical pressure losses through ETTs.

[Allergic reaction during anesthesia: two case reports].

We experienced two cases of serious and potentially life-threatening allergic reactions. The first patient was a 28-year-old male patient scheduled for surgery for cerebral arteriovenous malformations and another patient was a 66-year-old male patient scheduled for hepatic resection. After uneventful anesthetic induction, anesthesia was maintained with sevoflurane, air and oxygen. Both patients developed allergic reactions characterized by cardiovascular failure during anesthesia. Resuscitative treatment included rapid fluid infusion, administration of adrenaline and steroid. Both patients were successfully resuscitated without any lasting sequelae. The causative agent in one of these cases was probably a prophylactically used antibiotic, while that of the other case was a reaction to latex. Both patients showed elevated histamine and tryptase concentrations in blood samples. Recently, the incidence of allergic reactions to antibiotics and latex during anesthesia is increasing. Anesthesiologists should, therefore, be aware of the possibility of allergic reactions to all drugs and substances, especially to latex, during the perioperative period.

[Case of myocardial infarction during emergency clipping surgery of a cerebral aneurysm].

An 80-year-old woman with subarachnoid hemorrhage underwent emergency neck clipping of a cerebral aneurysm. She had previously undergone surgery for an abdominal aortic aneurysm 10 years before. Anesthesia was induced with propofol and maintained with a combination of fentanyl and sevoflurane (0.5-1.5%) in air and oxygen. Ventricular fibrillation occurred immediately before clipping of the aneurysm, in the absence of preexisting myocardial ischemia, and recurred 4 times thereafter during the surgery. The ventricular fibrillation was successfully treated with cardioversion. We administered catecholamines, nitrates, calcium antagonists, nicorandil and heparin, following which the patient's hemodynamics gradually improved. After the operation, the patient was transferred to the cardiovascular center of a neighboring university where she successfully underwent emergency percutaneous transluminal coronary angioplasty. The patient was discharged from hospital 10 days later without any complications. Patients undergoing vascular surgical procedures or having a preoperative history of prior vascular surgery are at high risk for perioperative myocardial infarction. It is necessary to perform cardiac examination, including coronary angiography, preoperatively in such patients, even in those who are otherwise asymptomatic.

Anesthetic management for the minimally invasive Nuss procedure in 21 patients with pectus excavatum.

The aim of this study was to assess the anesthetic management and postoperative analgesic effect of continuous epidural infusion for the minimally invasive Nuss procedure. A total of 21 operated cases were analyzed retrospectively. Thoracoscopy was used in all cases. General anesthesia with endotracheal intubation was induced and maintained with oxygen, air, sevoflurane, and fentanyl in all cases. Thoracic epidural anesthesia was performed after induction at the level between Th4 and 12. When the bar was placed via insertion under the sternum, six patients exhibited sinus tachycardia and one showed premature atrial contraction for 2-4 beats before recovering spontaneously within 1 min. Operations were uneventful. The mean operating time was 115 min and anesthetic time was 193 min. In X-ray findings, residual pneumothorax and pleural effusion were found in seven (33.3%) and eight (38.0%) patients, respectively. In all cases, these symptoms were resolved spontaneously within 5 days. Epidural fentanyl (0.3 microg.kg(-1).h(-1)) in 0.125% bupivacaine (0.15 ml.kg(-1).h(-1)) or 0.2% ropivacaine (0.15 ml.kg(-1).h(-1)) were used for 3 days to relieve postoperative pain. Postoperatively, 12 (57.1%) patients required no additional analgesics, and 4 (19.0%) patients required a single dose of dicrofenac sodium or pentazocine. Although the Nuss procedure is minimally invasive, we should pay attention to the possibility of many intra- and postoperative complications. Continuous epidural infusion of fentanyl with local anesthetics provides effective postoperative pain relief and prevents complications such as bar displacement after the Nuss procedure.

Strain differences to effects of aging on concentrations of amino acids in cerebrospinal fluid between Sprague Dawley rat and Wistar Kyoto rat.

Age-related alterations and differences of weights and those of amino acid concentrations in the cerebrospinal fluid (CSF) were evaluated between Sprague Dawley (SD) rats and Wistar Kyoto (WKY) rats from eight to twenty weeks of age. The weights of SD rats were heavier than WKY rats at all ages. The age-related alterations of the CSF concentration of many amino acids within each strain were significant but showed no significant trend with age. Between the strains, the concentration differences of excitatory and inhibitory amino acids were not frequent although the concentrations of arginine, alanine and threonine were significantly higher in SD rats than in WKY rats. These results suggest that the different CSF concentrations of amino acids may relate to characteristics of rat strains.

Yohimbine and flumazenil: effect on nitrous oxide-induced suppression of dorsal horn neurons in cats.

PURPOSE: The purpose of this study was to determine the mechanisms of nitrous oxide (N2O) antinociception at the spinal level with yohimbine (an α2-adrenergic antagonist) and flumazenil (a specific benzodiazepine antagonist) using chemonociceptive stimuli in spinal dorsal horn neurons in the cat. METHODS: A lumbar laminectomy extending from L4 to L6 was performed to allow insertion of a extracellular recording device via a microelectrode. Additional laminectomy was performed at the T12 level to transect the spinal cord. As a noxious stimulus, bradykinin (BK) was injected via the cannula inserted into the femoral artery. Animals were divided into four treatment groups for subsequent experiments: N2O+flumazenil, N2O+yohimbine, flumazenil (alone), and yohimbine (alone). RESULTS: N2O suppressed BK-induced nociceptive responses in transected feline spinal cords. The BK-induced neuronal firing rates were significantly suppressed: to 69.2%, 61.8%, and 52.2% of the baseline firing rate at 10, 20, and 30 min, respectively, after N2O administration. The 47.8% suppression on BK-induced neuronal responses at 30 min after N2O administration was reversed 5 min after administration of yohimbine (25.2% suppression). Similarly, N2O suppression (42.5%) on chemically induced neuronal responses was reversed by flumazenil (24.9% suppression) at identical postadministration intervals. CONCLUSION: These data imply that N2O suppresses the nociceptive responses in part probably through its agonistic binding activity to the α2-adrenergic, γ-aminobutyric acid (GABA)-benzodiazepine, or both receptor systems in dorsal born neurons of the feline spinal cord.

Suppressive action of enflurane on dorsal horn neurons in rabbits.

The neurophysiologic mechanism of the suppressive action of enflurane on spinal nociceptive transmission was examined in rabbits with intact and with transected spinal cords. Enflurane suppressed nociceptive responses in both intact and transected spinal cord groups. The suppressive effects of enflurane were significantly greater in the intact group than in the transected group. The suppressive effects of enflurane were not reversed by the addition of 0.2 mg·kg-1 of naloxone. These results suggest that enflurane suppresses nociceptive responses by activating descending inhibitory systems and directly suppressing activity at the spinal level. This suppressive action of enflurane does not interact with the opioid receptor.