Yoshihiro Ikuta

Skin vasomotor reflex predicts circulatory responses to laryngoscopy and intubation

Background An evaluation of autonomic reactivity may help to predict circulatory responses to intubation. The relation between the magnitude of the skin vasomotor reflex (SVmR) immediately before laryngoscopy and the circulatory responses to intubation was examined. Methods Forty‐four adult patients (classified as American Society of Anesthesiologists physical status I or II) were studied. General anesthesia was induced with fentanyl and thiamylal and maintained with nitrous oxide and sevoflurane. The SVmR was evoked by an electrostimulus to the ulnar nerve, and decreases in skin blood flow were detected using a laser‐Doppler flowmeter. In study 1, two groups of patients were studied. In the monitored group (n = 14), laryngoscopy was performed when the SVmR amplitude had decreased to less than 0.1. In the control group (n = 15), intubation was performed regardless of changes in the SVmR amplitude. In study 2, after induction, the end‐tidal concentration of sevoflurane was maintained at I MAC (n = 9) or 1.3 MAC (n = 6) for 5 min. The SVmR was tested by changing the electric intensity. Results In study 1, the blood pressure and heart rate of the control group increased significantly (P < 0.01) after laryngoscopy. The blood pressure of the monitored group did not increase. The SVmR amplitude and the systolic blood pressure changes showed a significant linear correlation (P < 0.001). In study 2, the relation between the electric intensity and the SVmR amplitude showed a weak but significant correlation (P < 0.01) in the 1 MAC group. Conclusion The evaluation of the SVmR provides useful information for determining the optimal anesthetic depth for laryngoscopy and intubation in individual patients.

Skin vasomotor reflex as an objective indicator to assess the level of regional anesthesia

We examined whether the absence of a skin vasomotor reflex (SVmR), which represents a sympathetic vasoconstrictive response to various stimuli, is an objective indicator of a somatosensory blockade.Skin blood flow was measured by using a laser Doppler flowmeter on the index finger tip. The somatosensory blockade level was determined in 15 patients under subarachnoid anesthesia. A cold stimulus, an ice cube applied to the skin, was repeated sequentially at each dermatome from L3 cephalad. The uppermost dermatome with negative response (the SVmR cold level) was determined, and the SVmR pain level was determined similarly using an electrical impulse (20-mA, 50-Hz, 0.25-ms square wave). The SVmR cold level and the SVmR pain level showed significant correlation with the conventionally assessed cold level (r = 0.83) and the pinprick level (r = 0.96). We conclude that the SVmR is useful to objectively estimate the level of somatosensory block induced by regional anesthesia. Implications: We evaluated the absence of decrease in skin blood flow after various stimuli as an indicator of somatosensory blockade. In patients under subarachnoid anesthesia, the uppermost level with negative response showed significant correlation with the conventionally assessed blockade level. This method is useful for objective assessment of regional anesthesia level. (Anesth Analg 1998;86:336-40)

Magnitude of skin vasomotor reflex represents the intensity of nociception under general anesthesia

Because nociceptive stimuli induce the skin vasomotor reflex (SVmR), the assessment of the SVmR would be a useful indicator to represent nociception. We examined 39 adult patients for the relationship between the magnitude of the SVmR and the intensity of nociceptive stimulus that induced the SVmR. Under oxygen-nitrous oxide (50%) and sevoflurane anesthesia, the SVmR was induced by an electrical impulse to the ulnar nerve and detected by a laser Doppler flowmeter. Study 1: under the end-tidal concentrations of sevoflurane at 1.2% (n = 10), 1.7% (n = 9) or 2.2% (n = 10), the SVmR was tested by a 2-s, 50-Hz tetanic electrical impulse with a current intensity changing (40, 50 or 60 mA) in a randomized order. Study 2: under the end-tidal concentration of sevoflurane at 1.7% (n = 10), the SVmR testing was performed with a 50-mA, 50-Hz tetanic electrical impulse with the current duration changing (2, 3 or 4 s) in a randomized order. The studies demonstrated significant correlations of (1) the current intensity which induces the skin vasomotor reflex (SVmR) vs. the magnitude of the SVmR under the three different anesthesia depths, (2) the anesthesia depth vs. the magnitude of the SVmR (inverse proportion) under the same current intensity and (3) the duration of electrostimulation vs. the magnitude of the SVmR. Thus, the SVmR could be helpful for the objective assessment of nociception and anti-nociceptive effects in individual cases.

The Current Perception Thresholds Vary Between Horizontal and 70° Tilt-Up Positions

UNLABELLED We investigated the influence of posture on current perception threshold (CPT). The subjects consisted of 20 healthy male volunteers (23-31 yr old). At both the horizontal and the 70 degrees tilt-up position (TUP), the CPTs (5, 250, and 2000 Hz) of the middle finger were determined by using the Neurometer CPT/C (Neuropteran, Baltimore, MD). Autonomic nervous activities were evaluated by heart rate variability (HRV) analysis and spontaneous baroreflex sensitivity analysis at the two postures previously mentioned. The three CPTs at the 70 degrees TUP were significantly lower than those at the horizontal posture (5 Hz, P < 0.05; 250 Hz, P < 0.001; 2000 Hz, P < 0.05). The changes in HRV and spontaneous baroreflex sensitivity at the 70 degrees TUP indicated decreasing parasympathetic tone. The CPTs of 5 and 250 Hz were significantly correlated with mean systolic blood pressure at the 70 degrees TUP. The CPT of 2000 Hz was significantly correlated with the 0.15-0.4 Hz component in HRV at both postures. The regression analysis of the difference of 5 Hz CPT with that of the mean systolic blood pressure showed a significant correlation (P < 0.001). To evaluate the clinical course of peripheral nerve disorders, the comparison of CPTs measured during the same posture is important. This suggests that CPTs must be measured at the horizontal posture. IMPLICATIONS Current perception thresholds at the 70 degrees tilt-up posture were significantly lower than those at the horizontal posture. When the compensatory mechanism for preserving blood pressure was emphasized, the current perception thresholds would have a relational connection to mean systolic blood pressure, similar to the concept of hypertension-induced hypoalgesia.

Quantitative assessment of the autonomic nervous system activities during atropine-induced bradycardia by heart rate spectral analysis

Using power spectral analysis of heart rate fluctuation, autonomic nervous system activities in bradycardia appearing in the initial phase of atropine administration were evaluated quantitatively in 16 healthy females. Atropine sulfate (10 micrograms/kg), diluted in 100 ml of 0.9% NaCl solution, was intravenously infused at a rate of 0.5 micrograms/kg per min. Electrocardiograms were sampled for 4 min for later analysis before and 0, 5, 10, 15 and 20 min after initiation of atropine infusion. Powers of low (LFC, 0.05-0.15 Hz) and high-frequency (HFC, 0.15-0.4 Hz) components in the power spectrum of R-R interval variations, and the LFC/HFC ratio were determined at each sampling point. HFC power at 0-4 min increased from 1.11 +/- 0.18 ms2 (mean) of baseline value to 1.37 +/- 0.19 ms2 (P < 0.05). The next 5-9-min value of 1.48 +/- 0.14 ms2 was the maximum, and the amount of atropine infused by 9 min was 4.5 micrograms/kg. The HFC powers following this point decreased. The 20-24-min value after 10 micrograms/kg atropine decreased to 0.21 +/- 0.03 ms2 (P < 0.01), which was lower than the previous 15-19-min value of 0.36 +/- 0.04 ms2 (P < 0.01). The LFC/HFC ratios showed no significant change for the initial 9 min of the atropine infusion. However, these ratios at 15-19 min and 20-24 min were increased from 0.50 +/- 0.04 (mean) of baseline value to 0.75 +/- 0.09 and 0.81 +/- 0.09, respectively (P < 0.01). A transient vagotonic state after atropine administration, followed by the well-known vagolytic state, was quantitatively detected by non-invasive spectral analysis of heart-rate fluctuation.

Mental strain in medical students during simulator training measured by forehead sweating.

Forehead sweating developed in 78% of medical students when they attempted tracheal intubation on a simulator, and increased during subsequent attempts if the first attempt was not successful. Thus, forehead sweating may be a useful index of mental strain.

Spinal function monitoring by evoked spinal cord potentials in aortic aneurysm surgery

Evoked spinal cord potentials (ESCPs) were monitored in 12 patients who underwent repair of thoracoabdominal aortic aneurysm with a high risk of spinal ischemia. A pair of bipolar catheter electrodes were introduced into the epidural space, one at the level of the C5-T2 vertebrae and the other at the level of T11-L2. Conductive mixed ESCP in seven patients, conductive sensory ESCP in one patient, and segmental descending ESCP in three patients were observed by applying a rectangular electric current to one of each pair of epidural electrodes and recording through the other. Segmental ESCP in response to posterior tibial nerve stimulation was observed in one patient. Following aortic cross-clamping, the I wave of conductive mixed ESCPs gradually decreased in amplitude with latency prolongation in five of the seven patients and disappeared in one of these five; transient augmentation of amplitude was observed before eventual decline in four of these five patients. The N wave of segmental descending ESCP subsequently flattened in two of the three patients and the N1 wave of segmental ESCP in the one patient. Three of the four patients in whom the ESCPs disappeared during aorta clamping recovered the ESCPs after declamping and showed no neurological disorders postoperatively. Intraoperative ESCP monitoring appears to be useful to detect spinal cord ischemia in the early stage and to alert surgeons and anesthesiologists so that timely resuscitative steps can be taken.

Even low doses of dexmedetomidine produced obstructive apnea during spinal anesthesia

To the Editor, Dexmedetomidine (DEX) is a sedative that produces less respiratory depression than midazolam or opioids. We examined whether DEX at \ 0.7 ng mL (an appropriate plasma concentration for sedation in the intensive care unit) provided a plasma concentration that would sedate surgical patients sufficiently under spinal anesthesia. The protocol of this study was approved by the Ethics Committee of Kumamoto University Hospital, Kumamoto, Japan and is registered in the UMIN Clinical Trial Registry (UMIN 000013558). The study included 23 patients who were scheduled for surgery with spinal anesthesia using 0.5% isobaric bupivacaine (puncture site at L3/4 or L4/5; upper effective level at Th5). In a pilot study, in which DEX was administered at a dose recommended in the package insert (1 lg kg for ten minutes and then 0.2 lg kg hr), we found that the mean (SD) plasma DEX concentration (DEXC) was 0.78 (0.21) ng mL at the end of surgery. In the present study, DEX was administered intravenously at a dose of 0.5 lg kg for ten minutes and then 0.2 lg kg hr after sensory blockade was achieved up to the appropriate level. Oxygen at 2 L min was administered using a nasal cannula. The respiratory pattern was evaluated during the entire surgical period by measuring chest and abdominal excursions, airflow at the nose and mouth, snoring sounds at the neck using SAS-3200 (Nihon Kohden, Tokyo, Japan), and measuring the CO2 concentration at the nose and mouth using Capnostream 20 (Nihon Kohden). Apnea was defined as airflow cessation for more than 15 sec. Obstructive apnea was defined as airflow cessation while chest and/or abdominal excursions were observed. The sedative effect was estimated using the Observer’s Assessment of Alertness/Sedation (OAA/S) score. Patient satisfaction level was evaluated using a five-point scale (5: very satisfied, 1: very unsatisfied) at the time of discharge. Dexmedetomidine concentration and PaCO2 were measured at the end of surgery. Dexmedetomidine concentrations were measured by its manufacturer (Maruishi Pharmaceutical, Osaka, Japan), with the precise measurement method not yet published. The mean (standard deviation [SD]) patient characteristics for the 21 men and two women were as follows: age 71 (10) yr; height 162 (7) cm; weight 60 (11) kg; body mass index 23.0 (3.6) kg m. The mean (SD) duration of DEX infusions was 49 (31) min. The mean (SD) cumulative dose of DEX was 42.6 (9.5) lg, with the DEXC at the end of surgery at 0.47 (0.09) ng mL. The minimum OAA/S score was 3.3 (range 1-5). The satisfaction level on the five-point scale was 4.2 (range 2-5). Overall, 17/23 (73.9%) patients had apnea, with each event being of an obstructive type. At the end of the surgery, the PaCO2 level was 43 (5) mmHg. There was no correlation between the DEXC and PaCO2 (see Figure, r = 0.39, P = 0.07). There was no difference between the DEXC of apnea(?) patients [(0.47 (0.10) ng mL] and that of apnea(-) patients [0.47 (0.09) ng mL] (see Figure, P = 0.9 by Student’s t test). Although the SpO2 Trial registration: www.umin.ac.jp/ctr/. Registered 30 March 2014.

Increased airway resistance in the prone position associated with heat and moisture exchangers with integral bacterial/viral filters

the HMEF was increased. The HMEF was replaced and the airway resistance and end-tidal CO2 immediately decreased to the previous levels. The weight of the HMEF was approximately 10 g, 1 g heavier than the new one (dry weight, 9 g). Neither sputum nor any foreign substance was observed in the HMEF. We examined whether as little as 1 ml in volume of water would signifi cantly increase the resistance of an HMEF (DAR Hygrobaby-M; Mallinckrodt Medical; capacity, 8 ml) and a heat and moisture exchanger (HME) without bacterial/viral fi lters (Humid vent; Gibeck, Upplands Väsby, Sweden, capacity, 7 ml). The HMEF or the HME was attached between an anesthesia circuit and a test lung (volume, 500 ml; fl ow resistance, 5 cmH2O · l·min−1). The anesthesia circuit pressure (ACP) was measured with a Datex AS/3 anesthesia monitor (Helsinki, Finland). The ventilator setting was: tidal volume, 300 ml; frequency, 15 cycles · min−1; inspiratory-expiratory (I : E) ratio, 1 : 1.5. After the ACP was measured with or without these devices, 0.5 ml distilled water was dripped into each device. After infi ltration was complete, change in the ACP was evaluated. An additional 0.5 ml distilled water was then infi ltrated and the ACP was measured. The results are shown in Fig. 1. The ACP increased in the HMEF but did not increase in the HME. In the operating manual, the resistance of the dry HMEF to gas fl ow was reported to be 1.9 cmH2O at 10 l·min−1, supporting our observation. These observations indicate that the bacterial/viral fi lter that absorbed water induced high airway resistance. The constituents of the HMEF electrostatic fi lter, made of a non-woven fabric consisting of polypropylene fi bers, and those of the HME, made of a Increased airway resistance in the prone position associated with heat and moisture exchangers with integral bacterial/viral fi lters

Evaluation of Continuous Monitoring of Jugular Venous Oxygen Saturation, Regional Cerebral Oxygen Saturation, and Electroencephalography Power Spectrum for Intraoperative Cerebral Ischemia

Brain damage caused by ischemia during reconstructive surgery of the main cerebral arteries is a most serious complication. Because neurological signs and symptoms of ischemic lesions are masked under anesthesia, an alternative measure is required for monitoring cerebral function.