Immunohistochemical analysis of acid-sensing ion channel 2 expression in rat dorsal root ganglion and effects of axotomy

Several studies have suggested that acid-sensing ion channel 2 (ASIC2) plays a role in mechanoperception and acid sensing in the peripheral nervous system. We examined the expression and distribution of ASIC2 in the rat dorsal root ganglion, the co-localization of ASIC2 with tropomyosin-related kinase (trk) receptors, and the effects of axotomy on ASIC2 expression. ASIC2 immunoreactivity was observed in both neurons and satellite cells. ASIC2-positive neurons accounted for 16.5 +/- 2.4% of the total neurons in normal dorsal root ganglion. Most ASIC2-positive neurons were medium-to-large neurons and were labeled with neurofilament 200 kD (NF200). Within these neurons, ASIC2 was not evenly distributed throughout the cytoplasm, but rather was accumulated prominently in the cytoplasm adjacent to the axon hillock and axonal process. We next examined the co-localization of ASIC2 with trk receptors. trkA was expressed in few ASIC2-positive neurons, and trkB and trkC were observed in 85.2% and 53.4% of ASIC2-positive neurons, respectively, while only 6.9% of ASIC2-positive neurons were co-localized with trkC alone. Peripheral axotomy markedly reduced ASIC2 expression in the axotomized dorsal root ganglion neurons. On the other hand, intense ASIC2 staining was observed in satellite cells. These results show that ASIC2 is expressed in the distinct neurochemical population of sensory neurons as well as satellite cells, and that peripheral axotomy induced marked reductions in ASIC2 in neurons.

Pneumocephalus following an epidural blood patch

Pneumocephalus is a rare complication of epidural block. We report a case of pneumocephalus complicating an epidural blood patch performed 3 days after unintentional dural puncture. Pneumocephalus may occur during an epidural blood patch procedure, even if the epidural needle tip is within the epidural space.

Involvement of capsaicin-sensitive fibers in spinal NMDA-induced glutamate release

The activation of spinal NMDA receptors can evoke glutamate release through the production of nitric oxide (NO) within the spinal cord, resulting in pain-relating behavior. In this study, we investigated the involvement of capsaicin-sensitive primary afferents in this phenomenon using in vivo intrathecal microdialysis. Intrathecal NMDA perfusion evoked increases in the concentrations of NO metabolises and glutamate and in pain-related behavior in both neonatal capsaicin and vehicle-treated rats. Although the degrees of increase in NO metabolises in capsaicin- and vehicle-treated rats were not significantly different, capsaicin-treated rats showed significantly smaller increases in glutamate concentration and pain-related behavior than did vehicle-treated rats. Our results showed that glutamate release from capsaicin-sensitive primary afferent terminals is involved in spinal NMDA-induced pain.

Peripheral nitric oxide in carrageenan-induced inflammation

Recent studies have suggested that nitric oxide (NO) peripherally produced by different nitric oxide synthase (NOS) isoforms contributes to edema formation and development of hyperalgesia. The present study was designed to examine the effects of NOS isoforms on NO release in carrageenan-induced inflammation at various time points. A microdialysis probe was implanted subcutaneously into the glabrous skin of hindpaws of Sprague-Dawley rats under pentobarbital anesthesia. After sample collection to obtain the basal level of the total amount of nitrite and nitrate (NO2-/NO3-), modified Ringer solution, a non-selective NOS inhibitor, NG monomethyl-L-arginine acetate (L-NMMA), or an iNOS inhibitor, aminoguanidine hemisulfate (AG) was perfused through the microdialysis probe. 2 mg of carrageenan was injected into the plantar surface of the probe-implanted hindpaw. Carrageenan was also injected in rats that had undergone sciatic nerve sectioning. Carrageenan significantly increased the dialysate concentrations of NO2-/NO3- for more than 8 h. L-NMMA suppressed the carrageenan-induced increase in NO2-/NO3- concentration. Although AG did not suppress the increase in NO2-/NO3- for the first 2 h after carrageenan injection, significant suppression of the increase in NO2-/NO3- was observed from 2.5 h after carrageenan injection. In the rats in which the sciatic nerves had been denervated, the increases in concentrations of NO2-/NO3- were completely suppressed up to 3 h and partially suppressed 4.5-8 h after carrageenan injection. The results of the current study show that carrageenan induces peripheral release of NO, the production of which is mediated by nNOS in the early phase and by both nNOS and iNOS in the late phase of carrageenan-induced inflammation.

[The techniques to identify the epidural space do not influence the success rate in combined spinal-epidural anesthesia: a comparison between loss-of-resistance and hanging-drop]

The hanging-drop (HD) technique has been attributed to a negative epidural pressure induced by making a tent of the dura by the Tuohy needle. We, therefore, hypothesized that the HD technique would result in more successful intrathecal placement of the spinal needle in combined spinal-epidural anesthesia (CSEA) compared with the loss-of-resistance (LR). Seventy patients received CSEA using the needle-through-needle method with a spinal needle extending 9 mm beyond the Tuohy needle. Success rate in obtaining cerebrospinal fluid (CSF) at the first attempt was considerably low; 60% in HD and 57% in LR, which was not significantly different. Failure to obtain CSF after 3 attempts was not significantly different between the two techniques; 26% and 31% in HD and LR, respectively. In conclusion, there was no advantage of the HD technique for obtaining CSF in CESA compared with the LR. It seems that spinal needle length beyond the Tuohy needle should be more than 9 mm.

Changes in respiratory pattern and arterial blood gases during sedation with propofol or midazolam in spinal anesthesia

STUDY OBJECTIVE

To investigate changes in respiratory pattern and arterial blood gases during sedation with propofol or midazolam in spinal anesthesia.

DESIGN

Randomized, placebo-controlled study.

SETTING

Operating room of a university-affiliated hospital.

PATIENTS

40 ASA physical status I and II patients who required spinal anesthesia.

INTERVENTIONS

Spinal anesthesia with tetracaine and subsequent sedation with propofol (n = 15), midazolam (n = 15), or placebo (n = 10) was performed.

MEASUREMENTS

Respiratory pattern [rib cage contribution to the tidal volume (%RC) and phase shift between rib cage and abdominal movements (PSrc-ab)] with a respiratory inductive plethysmograph (Respigraph) and arterial blood gas analysis (pH, pO2, and pCO2) were recorded.

MAIN RESULTS

Spinal anesthesia per se increased %RC by 35% without changing PSrc-ab values (1.00). Sedation with propofol and midazolam decreased %RC by 60% and by 40%, respectively. PSrc-ab increased in both groups following sedation, and the increase in this parameter was higher in the propofol group (1.12) than in the midazolam group (1.04). In the placebo group, %RC decreased by 20% without any change in PSrc-ab. The decrease in pO2 was more significant in the propofol group (65.1 mmHg) than in the midazolam (74.2 mmHg) and placebo (83.1 mmHg) groups.

CONCLUSION

Significant decreases in %RC and pO2 during propofol sedation seem to depend on paradoxical respiration due, in part, to upper airway obstruction; therefore, attention should be directed to the respiratory pattern during sedation, especially with propofol.

[Evaluation of risks for postoperative pulmonary complications using a preoperative consultation system]

We retrospectively investigated the perioperative management and postoperative pulmonary complications of patients who had preoperative respiratory problems and consultations with anesthesiologists. These patients numbered eight hundred, 23.7% of all patients who had preoperative consultations, and 40.9% and 62.0% of the 800 had preoperative and postoperative respiratory management, respectively. Forty eight patients (6.0%) received postoperative artificial respiration. One hundred and twenty four patients (15.5%) had some respiratory complications post-operatively, and 5 patients (0.7%) died mainly because of the complications. In an evaluation of these patients with the modified predicted risk factors of Okutsu including the obesity factor and smoking history, there was no respiratory complication in patients under 14 points. Patients with high points of more than 20 included almost all of the patients (114 patients, 91.9%) who had postoperative respiratory complications. We conclude that our preoperative consultation system works well and that the modified predicted-risk factors for postoperative pulmonary complications is useful for the standardization and objectivity of preoperative patient evaluation.