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Unlabelled: The transient hyperemic response (THR) test has been used to assess cerebral autoregulation in anesthesia and intensive care. To date it has not been compared with the static autoregulation test for assessing graded changes in cerebral autoregulation. We compared the two tests during propofol, desflurane, and nitrous oxide anesthesia. Seven subjects were studied. For the THR test, changes in the middle artery blood flow velocity were assessed during and after a 10-s compression of the ipsilateral common carotid artery. Two indices of autoregulation--THR ratio (THRR) and strength of autoregulation (SA)--were calculated. For the test of static autoregulation, changes in the middle cerebral artery flow velocity after a phenylephrine-induces increase in mean arterial pressure were assessed, and the static rate of regulation (sROR) was calculated. The tests were performed before induction and after equilibrium at 0.5 minimum alveolar anesthetic concentration (MAC) and then at 1.5 MAC of desflurane. THRR, SA and sROR decreased significantly (P < 0.001) at 0.5 MAC and then at 1.5 MAC desflurane. CHanges in THRR and SA reflected the changes in sROR with a sensitivity of 100%., Implications: When compared with the established test of static autoregulation, the transient hyperemic response test provides a valid method for assessing graded impairment in cerebral autoregulation.

We measured the effect of 5 and 10 cm H(2)O continuous positive airways pressure (CPAP) on middle cerebral artery blood flow velocity (FV) in 15 awake, healthy volunteers by using transcranial Doppler ultrasonography. Mean, systolic, and diastolic FV plus pulsatility index were recorded. No significant change in any measured variable was observed with the application of 5 or 10 cm H(2)O CPAP. These results are in contrast to those of a previous study, which found a significant increase in mean FV and a decrease in pulsatility index during the application of 12 cm H(2)O CPAP.

Unlabelled: We describe video imaging as a technique for assessing neuromuscular blockade at the larynx. We sought to determine the stability and reproducibility of this technique and to compare the effect of succinylcholine at the adductor pollicis and the larynx. Ten patients were studied. Anesthesia was induced and maintained with propofol. The recurrent laryngeal nerve was stimulated superficially and movements of the vocal cords were recorded on videotape by using a fiberoptic bronchoscope passed via a laryngeal mask airway. Neuromuscular function was recorded at the adductor pollicis by using a mechanomyograph. Twenty images of the vocal cords were examined repeatedly by one investigator and by ten independent observers. The mean difference between the two sets of observations was 0.86 degrees with a correlation coefficient (r) of 0.997. For 3 min before the administration of relaxant the coefficient of variation in the cord movement during supramaximal stimulation ranged from 1%-4% (median 2.7%). After the administration of succinylcholine 1 mg. kg(-1) the times to loss of T1 at the larynx and hand were 63 +/- 15 s and 63 +/- 12 s respectively. Times to 25% recovery were 215 +/- 36 s at the larynx and 436 +/- 74 s at the hand and times to 75% recovery were 285 +/- 55 s and 525 +/- 85 s respectively. These results indicate that video imaging may be a useful research technique for estimating neuromuscular blockade at the larynx and that the time to onset of succinylcholine at the larynx is similar to that at the hand, whereas the duration of blockade is significantly shorter at the larynx., Implications: Assessment of neuromuscular blockade at the larynx is possible by using a video imaging technique. By using this technique, the time to onset of neuromuscular blockade at the larynx is similar to that at the hand after the administration of succinylcholine; this finding is different from previously published data obtained by using a cuff pressure measurement technique.

Implications: We report three cases of prolonged paralysis resulting from rapacuronium in the presence of sevoflurane.

Unlabelled: We studied the effects of sevoflurane, with and without nitrous oxide, on the indices of cerebral autoregulation (transient hyperemic response ratio and the strength of autoregulation) derived from the transient hyperemic response (THR) test. Twelve patients (ASA physical status I or II) aged 18-40 yr presenting for routine non-neurosurgical procedures were recruited. The middle cerebral artery blood flow velocity was continuously recorded using transcranial Doppler ultrasonography. Preinduction THR tests were performed before the patients were anesthetized with alfentanil, propofol, and vecuronium. End-tidal carbon dioxide concentration and mean arterial pressure (to within 10% with a phenylephrine infusion) were maintained at their preinduction values. THR tests were performed sequentially at the following end-tidal sevoflurane concentrations: 2.2% in oxygen, 3.4% in oxygen, 3.4% with 50% nitrous oxide in oxygen, and 2.2% with 50% nitrous oxide in oxygen. Neither 2.2% nor 3.4% sevoflurane significantly affected cerebral autoregulation. The addition of 50% nitrous oxide to the 2.2%, but not the 3.4%, concentration of sevoflurane increased middle cerebral artery blood flow velocity and decreased autoregulatory indices significantly., Implications: Transient hyperemic response is preserved during sevoflurane anesthesia but is significantly impaired when nitrous oxide is added to the lower concentration of sevoflurane (2.2%). These findings have implications for neurosurgical patients undergoing general anesthesia.

Unlabelled: The aim of this study was to determine the effects of breathing 100% oxygen or 50% nitrous oxide in oxygen on the indices of cerebral autoregulation derived from the transient hyperemic response (THR) test in human volunteers. Data were analyzed from nine healthy subjects. Middle cerebral artery (MCA) blood flow velocity (FV) was measured by transcranial Doppler ultrasound, and the THR test was performed using 10-s compression of the common carotid artery. Continuous measurement of P(ETCO2) and expired fractions of oxygen (F(ETO2)) and nitrous oxide (F(ETN2O)) was established, and mean arterial pressure (MAP) was recorded at 2-min intervals. All measurements were performed while the volunteers were breathing room air and were repeated 10 min after achieving F(ETO2) >0.95 and 10 min after achieving F(ETN2O) 0.48-0.52. Two indices derived from the THR test, the transient hyperemic response ratio (THRR) and strength of autoregulation (SA), were used to assess cerebral autoregulation. P(ETCO2) and mean arterial pressure did not change significantly throughout the study period. Breathing 100% oxygen did not change MCA FV, THRR, or SA. Inhalation of nitrous oxide resulted in a marked and significant increase in the MCA FV (from 48+/-9 to 72+/-8 cm/s; mean +/- SD) and a significant decrease in the THRR (from 1.5+/-0.2 to 1.2+/-0.1) and the SA (from 1.0+/-0.1 to 0.8+/-0.1) (P<0.05 for all). We conclude that breathing 50% nitrous oxide in oxygen results in both a significant increase in MCA FV and impairment of transient hyperemic response., Implications: Our study suggests that nitrous oxide impairs cerebral autoregulation and may have implications for its use in neurosurgical anesthesia and for interpretation of the results from studies of anesthetics in which nitrous oxide is used in the background.

Unlabelled: Neuromuscular block (NMB) at the larynx has been assessed by measuring the cuff pressure (CP) in an endotracheal tube (ETT) placed between the vocal cords. In this study, we evaluated the decrease in resting cuff pressure (RCP) after the administration of rocuronium and the effect of this decrease on the assessment of NMB, and we compared CP measurement with an alternative technique, video imaging (VI). In 20 patients, NMB was determined at the hand by mechanomyography and at the larynx initially by CP and subsequently by VI, recording images using a fiberoptic bronchoscope via a laryngeal mask. Train-of-four stimuli were applied at both sites. After baseline measurements, the ETT was replaced, and rocuronium was infused to achieve a steady-state 50% (n = 10) or 75% (n = 10) block at the hand. CP measurements were recorded before and after restoration of RCP to prerocuronium pressure, followed by further VI measurements. The mean RCP decreased from 21 +/- 4 to 12 +/- 5 mm Hg after rocuronium. At 50% block at the hand, the CP estimate of block at the larynx with reduced RCP was 62% +/- 18%, and that after restoring RCP was 29% +/- 13%; VI estimated 27% +/- 14% block. At 75% block at the hand, CP and VI estimated 52% +/- 11% and 46% +/- 9% block, respectively (RCP maintained). We conclude that RCP decreases after the administration of rocuronium, that restoring RCP significantly alters CP estimates of NMB, and that VI is in agreement with CP measurement if RCP is maintained at prerelaxant values., Implications: In this study, we show that a muscle relaxant-induced decrease in resting tension at the larynx may confound the assessment of neuromuscular block by cuff pressure measurement. The preliminary data suggest that video imaging may provide a suitable alternative to cuff pressure measurement to assess neuromuscular block at the larynx.

Unlabelled: The transient hyperemic response (THR) in the middle cerebral artery (MCA) after the release of brief compression of the ipsilateral common carotid artery has been used to study cerebral autoregulation. We conducted the present study to evaluate the reliability of THR to detect changes in cerebral autoregulation induced by graded variations in PETCO2. Seven healthy adult volunteers were recruited. Fifteen THR tests were performed on every volunteer: three at baseline PETCO2, three each at PETCO2 of 7.5 mm Hg and 15 mm Hg above the baseline, and then three each at PETCO2 of 7.5 mm Hg and 15 mm Hg below the baseline. Transient hyperemic response ratio (THRR) and strength of autoregulation (SA) were calculated using established formulae. Both THRR and SA were highly sensitive (96%) in detecting the changes in cerebral autoregulation induced by graded changes in PETCO2. The within-individual variability of SA was significantly smaller than that of THRR at all levels of PETCO2., Implications: This study demonstrates the reliability of the THR test, when used for repetitive measurements, in detecting changes in cerebral autoregulation induced by graded changes in PETCO2. This test may provide a simple and noninvasive method of evaluating changes in cerebral autoregulation within an individual.

Accelerometry is increasingly being used for neuromuscular monitoring. We sought to determine whether this system is sensitive to the period of stabilization of muscle twitch prior to the administration of neuromuscular relaxant. We recruited 20 patients. No premedication was given, and anesthesia was induced with propofol and alfentanil and maintained by a propofol infusion. An accelerometer was attached to each wrist. One of the ulnar nerves was stimulated for 20 min and the other for 3 min using a train-of-four pattern at 15-s intervals. Ten patients then received vecuronium 0.1 mg/kg and a subsequent 10 received atracurium 0.5 mg/kg. The time to onset of maximum block was recorded. The data collected was subjected to a paired t-test with P < 0.05 taken as significant. The mean onset times for patients who received vecuronium was 148.5s for the arms stabilized for 3 min and 151.5s for the arms stabilized for 20 min, and in those who received atracurium it was 138.0s and 130.5s, respectively. We conclude that there is no significant difference in the onset of neuromuscular block with either vecuronium or atracurium after stabilization periods of 3 or 20 min when assessed by accelerometry.

We questioned whether the side effects outweighed the advantages of priming doses of nondepolarizing neuromuscular relaxants in awake patients. We have assessed lung function and clinical evidence of muscle weakness in 10 elderly patients, eight women and two men, aged 67-78 yr, ASA grade I or II, before and 3 min after a priming dose (0.01 mg/kg) of vecuronium. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), maximum midexpiratory flow rate (MMEF), peak expiratory flow rate (PEFR), inspiratory capacity (IC), functional residual capacity (FRC), expiratory reserve volume (ERV), residual volume (RV), slow vital capacity (SVC), and total lung capacity (TLC) were measured by using a Morgan transfer test machine and oxygen saturation (SpO2) was measured by pulse oximetry. All the patients developed ptosis, six had diplopia and were unable to perform the Valsalva maneuver for 10s, and four were unable to swallow or lift their head for > 4s, demonstrating significant muscle weakness. Significant reductions occurred in FVC, FEV1, FRC, ERV, SVC, and TLC. SpO2 decreased in 8 of 10 patients, and in 4 the decrease exceeded 4%. We conclude that priming with vecuronium 0.01 mg/kg in elderly patients causes significant impairment of lung function and a significant decrease in oxygen saturation.

Two separate studies of the effects of nitroglycerin (NTG) on intraocular pressure (IOP) were conducted. In study I, 12 healthy adults received 3 ml NTG solution (2 mg/3 ml) intranasally during steady-state anesthesia. This resulted in a significant decrease in IOP along with decreases in arterial blood pressure and central venous pressure. In study II, 30 patients, classified randomly into two equal groups, received either normal saline (3 ml) or NTG solution (2 mg/3 ml) intranasally, in a double-blind manner, 2 minutes before anesthetic induction with thiopental followed by succinylcholine (1.5 mg/kg). In patients given saline, IOP increased significantly above the preinduction levels after succinylcholine. Tracheal intubation increased it further. In the NTG group, increases in IOP after succinylcholine and after tracheal intubation were significantly less than in the control (saline) group. It is concluded that intranasal administration of NTG decreases IOP in anesthetized patients and, when employed as pretreatment, allows the use of succinylcholine to facilitate tracheal intubation without an increase in IOP above preinduction levels.