Nobuko Ohashi

Effects of ropivacaine concentration on the spread of sensory block produced by continuous thoracic paravertebral block: a prospective, randomised, controlled, double-blind study

Factors affecting the distribution of continuous thoracic paravertebral block have never been examined. We designed this prospective, double‐blind study to check whether continuous thoracic paravertebral block with a higher ropivacaine concentration would provide a wider segmental sensory block spread. Sixty consecutive patients undergoing pulmonary lobectomy or segmentectomy were randomly allocated to receive continuous paravertebral infusion of either 0.2% or 0.5% ropivacaine (6 ml.h−1). The primary outcome was the number of anaesthetised dermatomes as determined by loss of cold sensation 24 h after surgery. Twenty‐seven patients per group were included in the final analysis. The median (IQR [range]) number of anaesthetised dermatomes 24 h after surgery was 4 (3–6 [1–9]) with ropivacaine 0.2% and 4 (3–6 [2–11]) with ropivacaine 0.5% (p = 0.66). Contrary to our expectation, the segmental spread of sensory block produced by continuous thoracic paravertebral block does not depend on ropivacaine concentration.

Hydrogen peroxide modulates synaptic transmission in ventral horn neurons of the rat spinal cord

Excessive production of reactive oxygen species (ROS) is implicated in many central nervous system disorders; however, the physiological role of ROS in spinal ventral horn (VH) neurons remains poorly understood. We investigated how pathological levels of H2O2, an abundant ROS, regulate synaptic transmission in VH neurons of rats using a whole‐cell patch clamp approach. H2O2 increased the release of glutamate and GABA from presynaptic terminals. The increase in glutamate release involved N‐type voltage‐gated calcium channels (VGCCs), ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP3Rs); the increase in GABA release, which inhibited glutamatergic transmission, involved IP3R. Inhibiting N‐type VGCCs and RyRs attenuates excitotoxicity resulting from increased glutamatergic activity while preserving the neuroprotective effects of GABA, and may represent a novel strategy for treating H2O2‐induced motor neuron disorders resulting from trauma or ischaemia–reperfusion injury.

Hydrogen peroxide modulates neuronal excitability and membrane properties in ventral horn neurons of the rat spinal cord

Hydrogen peroxide (H2O2), a reactive oxygen species, is an important signaling molecule for synaptic and neuronal activity in the central nervous system; it is produced excessively in brain ischemia and spinal cord injury. Although H2O2-mediated modulations of synaptic transmission have been reported in ventral horn (VH) neurons of the rat spinal cord, the effects of H2O2 on neuronal excitability and membrane properties remain poorly understood. Accordingly, the present study investigated such effects using a whole-cell patch-clamp technique. The bath-application of H2O2 decreased neuronal excitability accompanied by decreased input resistance, firing frequency, and action potential amplitude and by increased rheobase. These H2O2-mediated changes were induced by activation of extrasynaptic, but not synaptic, GABAA receptors. Indeed, GABAergic tonic currents were enhanced by H2O2. On the other hand, the amplitude of medium and slow afterhyperpolarization (mAHP and sAHP), which plays important roles in controlling neuronal excitability and is mediated by small-conductance calcium-activated potassium (SK) channels, was significantly decreased by H2O2. When extrasynaptic GABAA receptors were completely blocked, these decreases of mAHP and sAHP persisted, and H2O2 increased excitability, suggesting that H2O2 per se might have the potential to increase neuronal excitability via decreased SK channel conductance. These findings indicate that activating extrasynaptic GABAA receptors or SK channels may attenuate acute neuronal damage caused by H2O2-induced hyperexcitability and therefore represent a novel therapeutic target for the prevention and treatment of H2O2-induced motor neuron disorders.

Tranexamic acid evokes pain by modulating neuronal excitability in the spinal dorsal horn.

Tranexamic acid (TXA) is an antifibrinolytic agent widely used to reduce blood loss during surgery. However, a serious adverse effect of TXA is seizure due to inhibition of γ-aminobutyric acid (GABA) and glycine receptors in cortical neurons. These receptors are also present in the spinal cord, and antagonism of these receptors in spinal dorsal horn neurons produces pain-related phenomena, such as allodynia and hyperalgesia, in experimental animals. Moreover, some patients who are injected intrathecally with TXA develop severe back pain. However, the effect of TXA on spinal dorsal horn neurons remain poorly understood. Here, we investigated the effects of TXA by using behavioral measures in rats and found that TXA produces behaviors indicative of spontaneous pain and mechanical allodynia. We then performed whole-cell patch-clamp experiments that showed that TXA inhibits GABAA and glycine receptors in spinal dorsal horn neurons. Finally, we also showed that TXA facilitates activation of the extracellular signal-regulated kinase in the spinal cord. These results indicated that TXA produces pain by inhibiting GABAA and glycine receptors in the spinal dorsal horn.

Administration of tranexamic acid to patients undergoing surgery for adolescent idiopathic scoliosis evokes pain and increases the infusion rate of remifentanil during the surgery

Background We recently reported that tranexamic acid (TXA) evokes pain in rats by inhibiting γ-aminobutyric acid and glycine receptors on neurons in the spinal dorsal horn. Although TXA is commonly used to reduce perioperative blood loss during various surgeries, its potential to induce intraoperative nociception, thereby increasing the need for more analgesics during surgery, has not been investigated. Therefore, this study aimed to investigate whether TXA evokes pain and increases the need for a higher infusion rate of remifentanil in patients undergoing surgery for adolescent idiopathic scoliosis (AIS). Methods Data were collected from patients with AIS who underwent posterior spinal fusion surgery from January 2008 to December 2015. All surgical procedures were performed under total intravenous anesthesia with propofol and remifentanil, by the same team of orthopedic surgeons and anesthesiologists at a single institution. Patients in the TXA group were administered TXA (loading and maintenance doses, 1000 mg and 100 mg/h) whereas those in the control group were not. Our primary outcome was the infusion rate of the intraoperative opioid analgesic remifentanil. Results The final analysis was based on data collected from 33 and 30 patients in the control and TXA groups, respectively. No differences were observed in the demographic data or the hemodynamic parameters between the two groups of patients. In the TXA group, the durations of surgery and anesthesia were shorter, intravascular fluid volume and total blood loss were lower, and the doses of fentanyl and ketamine administered were higher than they were in the control group (P < 0.05 for all). The mean infusion rate of intraoperative remifentanil was significantly higher in the TXA group than in the control group (control group: 0.23 ± 0.04 μg/kg/min; TXA group: 0.28 ± 0.12 μg/kg/min; P = 0.014). Conclusions Patients who received TXA during the AIS surgery required a higher infusion rate of remifentanil, indicating that TXA evoked pain during the surgery.

Acetaminophen Metabolite N-Acylphenolamine Induces Analgesia via Transient Receptor Potential Vanilloid 1 Receptors Expressed on the Primary Afferent Terminals of C-fibers in the Spinal Dorsal Horn

BACKGROUND The widely used analgesic acetaminophen is metabolized to N-acylphenolamine, which induces analgesia by acting directly on transient receptor potential vanilloid 1 or cannabinoid 1 receptors in the brain. Although these receptors are also abundant in the spinal cord, no previous studies have reported analgesic effects of acetaminophen or N-acylphenolamine mediated by the spinal cord dorsal horn. We hypothesized that clinical doses of acetaminophen induce analgesia via these spinal mechanisms. METHODS We assessed our hypothesis in a rat model using behavioral measures. We also used in vivo and in vitro whole cell patch-clamp recordings of dorsal horn neurons to assess excitatory synaptic transmission. RESULTS Intravenous acetaminophen decreased peripheral pinch-induced excitatory responses in the dorsal horn (53.1 ± 20.7% of control; n = 10; P < 0.01), while direct application of acetaminophen to the dorsal horn did not reduce these responses. Direct application of N-acylphenolamine decreased the amplitudes of monosynaptic excitatory postsynaptic currents evoked by C-fiber stimulation (control, 462.5 ± 197.5 pA; N-acylphenolamine, 272.5 ± 134.5 pA; n = 10; P = 0.022) but not those evoked by stimulation of Aδ-fibers. These phenomena were mediated by transient receptor potential vanilloid 1 receptors, but not cannabinoid 1 receptors. The analgesic effects of acetaminophen and N-acylphenolamine were stronger in rats experiencing an inflammatory pain model compared to naïve rats. CONCLUSIONS Our results suggest that the acetaminophen metabolite N-acylphenolamine induces analgesia directly via transient receptor potential vanilloid 1 receptors expressed on central terminals of C-fibers in the spinal dorsal horn and leads to conduction block, shunt currents, and desensitization of these fibers.

Pediatric Patients with High Pulmonary Arterial Pressure in Congenital Heart Disease Have Increased Tracheal Diameters Measured by Computed Tomography

OBJECTIVES Determination of the appropriate tracheal tube size using formulas based on age or height often is inaccurate in pediatric patients with congenital heart disease (CHD), particularly in those with high pulmonary arterial pressure (PAP). Here, the authors compared tracheal diameters between pediatric patients with CHD with high PAP and low PAP. DESIGN Retrospective clinical study. SETTING Hospital. PARTICIPANTS Pediatric patients, from birth to 6 months of age, requiring general anesthesia and tracheal intubation who underwent computed tomography were included. Patients with mean pulmonary artery pressure >25 mmHg were allocated to the high PAP group, and the remaining patients were allocated to the low PAP group. The primary outcome was the tracheal diameter at the cricoid cartilage level, and the secondary goal was to observe whether the size of the tracheal tube was appropriate compared with that obtained using predictable formulas based on age or height. MEASUREMENTS AND MAIN RESULTS The mean tracheal diameter was significantly larger in the high PAP group than in the low PAP group (p < 0.01). Pediatric patients with high PAP required a larger tracheal tube size than predicted by formulas based on age or height (p = 0.04 for age and height). CONCLUSIONS Pediatric patients with high PAP had larger tracheal diameters than those with low PAP and required larger tracheal tubes compared with the size predicted using formulas based on age or height.

Anesthetic management in a patient with giant growing teratoma syndrome: a case report

IntroductionGrowing teratoma syndrome is a rare occurrence with an ovarian tumor. Anesthesia has been reported to be difficult in cases of growing teratoma syndrome of the cystic type due to the pressure exerted by the tumor. However, there have been no similar reports with the solid mass type. Here, we report our experience of anesthesia in a case of growing teratoma syndrome of the solid type.Case presentationThe patient was a 30-year-old Japanese woman who had been diagnosed with an ovarian immature teratoma at age 12 and had undergone surgery and chemotherapy. However, she dropped out of treatment. She presented to our hospital with a 40cm giant solid mass and severe respiratory failure, and was scheduled for an operation. We determined that we could not obtain a sufficient tidal volume without spontaneous respiration. Therefore, we chose to perform awake intubation and not to use a muscle relaxant before the operation. At the start of the operation, when muscle relaxant was first administered, we could not obtain a sufficient tidal volume. An abdominal midline incision was performed immediately and her tidal volume recovered. Her resected tumor weighed 10.5kg. After removal of her tumor, her tidal volume was maintained at a level consistent with that under spontaneous respiration to avoid occurrence of re-expansion pulmonary edema.ConclusionsWe performed successful anesthetic management of a case of growing teratoma syndrome with a giant abdominal tumor. Respiratory management was achieved by avoiding use of a muscle relaxant before the operation to maintain spontaneous respiration and by maintaining a relatively low tidal volume, similar to that during spontaneous respiration preoperatively, after removal of the tumor to prevent re-expansion pulmonary edema.