N. Ty Smith

Performance of the ARX-derived auditory evoked potential index as an indicator of anesthetic depth: a comparison with bispectral index and hemodynamic measures during propofol administration.

Background Autoregressive modeling with exogenous input of middle-latency auditory evoked potential (A-Line autoregressive index [AAI]) has been proposed for monitoring anesthetic depth. The aim of the current study was to compare the accuracy of this new index with the Bispectral Index (BIS), predicted effect-site concentration of propofol, and hemodynamic measures. Methods Twenty female patients scheduled for ambulatory gynecologic surgery received effect compartment controlled infusion of propofol. Target effect-site concentration was started at 1.5 &mgr;g/ml and increased every 4 min by 0.5 &mgr;g/ml. At every step, sedation level was compared with monitoring values using different clinical scoring systems and reaction to noxious stimulus. Results Bispectral Index, AAI, and predicted propofol effect-site concentration were accurate indicators for the level of sedation and loss of consciousness. Hemodynamic variables were poor indicators of the hypnotic-anesthetic status of the patient. BIS correlated best with propofol effect-site concentration, followed by AAI. Hemodynamic measurements did not correlate well. No indicators predicted reaction to noxious stimulus. Poststimulus, BIS and AAI showed an increase as a result of arousal. This reaction occurred more rapidly with the AAI than with BIS. Conclusion Bispectral Index, AAI, and predicted propofol effect-site concentration revealed information on the level of sedation and loss of consciousness but did not predict response to noxious stimulus.

Inorganic fluoride nephrotoxicity: prolonged enflurane and halothane anesthesia in volunteers.

The effects of prolonged enflurane and halothane administration on urine-concentrating ability were determined in volunteers by examining their responses to vasopressin before anesthesia and on days 1 and 5 after anesthesia. A significant decrease in maximum urinary osmolality of 264 +/- 34 mOsm/kg (26 per cent of the preanesthetic value) was present on day 1 after enflurane anesthesia, whereas subjects anesthetized with halothane had a significant increase in maximum urinary osmolality of 120 +/- 44 mOsm/kg. Serum inorganic fluoride level peaked at 33.6 muM and remained above 20 muM for approximately 18 hours. Thus, the threshold level for inorganic fluoride nephrotoxicity is lower than previously suspected.

Noninvasive continuous blood pressure measurement from the finger: optimal measurement conditions and factors affecting reliability.

We recorded finger arterial blood pressure (FINAP) in 50 male patients during various types of surgical operations. Three different types of cuffs were used on four fingers of each patient. Measurements were made by the arterial volume-clamp method of Penaz. The FINAP measurements were compared with pressure data obtained ipsilaterally from a radial artery catheter-transducer system (intraarterial pressure [IAP]) to find optimal recording conditions and to document factors affecting FINAP readings. The thumb, with a specially designed cuff, gave the most accurate results. The mean FINAP- IAP difference for the thumb was −4.8 mm Hg for systolic pressure, 1.49 mm Hg for diastolic pressure, and 0.29 mm Hg for mean pressure. The differences were statistically significant for systolic and diastolic pressure but not for mean pressure. The regression slope for thumb systolic FINAP/IAP was 0.979, that for thumb diastolic FINAP/IAP was 0.963, and that for mean thumb FINAP/IAP was 0.996, whereas the intercepts were 7.499 for systolic pressure, 0.802 for diastolic pressure, and 0.083 for mean pressure. The correlation coefficients were 0.945 (systolic), 0.884 (diastolic), and 0.949 (mean). The correlation coefficients with the other fingers ranged from 0.502 to 0.922 for systolic pressure, 0.757 to 0.932 for diastolic pressure, and 0.767 to 0.892 for mean pressure. The slopes for the various finger-cuff combinations ranged from 0.537 to 0.996, and the intercepts ranged from 0.083 to 32.387 from mean pressure. In 3 patients (6%) the FINAP measurement was not possible because of insufficient peripheral circulation. In 9 other patients (18%) the FINAP measurements were not accurate during some periods of time.In 5 of those 9 patients the difficulties were related to arterial cannulation and began immediately after cannulation. In 1 of those 5 patients the FINAP subsequently decreased dramatically after the onset of phenylephrine infusion because of peripheral vasoconstriction and diminished blood flow. In the 4 other patients the FINAP readings were accurate at the beginning of anesthesia but later decreased out of proportion to changes in IAP. These periods were associated with one-lung ventilation. The FINAP accurately reflects systemic arterial pressure. Measurements from the thumb fitted with a specially designed cuff approximate IAP best. Factors affecting peripheral circulation must be taken into consideration when this device is used in the monitoring of FINAP.

A comparison of morphine, fentanyl, and sufentanil anesthesia for cardiac surgery: Induction, emergence, and extubation

We compared anesthetic doses of three popular opiates, morphine (n = 10), fentanyl (n = 9), and sufentanil (n = 9) in patients undergoing cardiac surgery. Opiate administration after induction was based upon EEG and cardiovascular signs of the depth of anesthesia. Total doses were morphine, 4.4 ± 0.71 mg/kg, fentanyl, 95.4 ± 9.9 μg/kg, and sufentanil, 18.9 ± 2.2 μg/kg. Comparisons among opiates included times for induction of anesthesia, return of consciousness, return of spontaneous ventilation, return of adequate cardiovascular status, and extubation. The following times (mean and SEM) were significantly (P < 0.05) shorter for sufentanil than for fentanyl or morphine: induction (15 ± 2.3 min, 5.9 ± 0.7 min, and 3.0 ± 0.2 min for morphine, fentanyl, and sufentanil, respectively); return of consciousness (morphine 109.7 ± 34.4 min, fentanyl 62.3 ± 17.9 min, sufentanil 77 ± 8.7 min); return of acceptable and stable cardiovascular status (morphine 587.3 ± 239.3 min, fentanyl 537.9 ± 144.8 min, sufentanil 173.7 ± 56.8 min); and extubation (morphine 1122.3 ± 61.8 min, fentanyl 1005.7 ± 77.7 min, sufentanil 533.3 ± 67.8 min). We conclude that sufentanil administered in the dosage range of 19 μg/kg allows more rapid induction, earlier emergence from anesthesia, and faster extubation of patients than either morphine or fentanyl.

Evaluation of two prototype devices producing noninvasive, pulsatile, calibrated blood pressure measurement from a finger

We evaluated two prototype instruments that measure pulsatile blood pressure continuously and noninvasively and compared the mean arterial pressure obtained from these devices with that obtained mvasivcly m 17 male surgical patients. Each prototype consisted of an infrared photoplethysmograph mounted inside a finger cuff. The cuff was connected to a pressure control valve, which rapidly changed the cuff pressure so as to maintain a null pressure difference across the finger arterial wall. The resultant cuff pressure rapidly tracked the pulsatile intraarterial pressure. The prototypes reproduced absolute pressure, as well as pressure changes, accurately and linearly over a wide range of mean arterial pressures (from 2 to 164 mm Hg), with an average offset error of 0.8 mm Hg (SD ± 3.8; range, -4.6 to 7.9), a mean scatter error of 5.3 mm Hg (range, 3.6 to 8.6), a mean regression slope of 0.97 (range, 0.79 to 1.22) and a mean correlation coefficient of the regression of 0.96 (range, 0.89 to 0.98).Both prototypes worked satisfactorily on all 17 patients, but not all the time on all patients. In 7 patients, probable arterial spasm prevented measurement of finger blood pressure 12.1% of the time, or 5.4% of the time for all patients. Ninety-six percent of the lost samples occurred with prototype 2, suggesting an instrument-related cause, rather than one related to the principle itself.The prototypes were simple to use and were almost free from artifact. Continuous monitoring for up to 7 hours on a single finger caused no harm to the finger.

Effects of Halothane on Left Ventricular Function and Distribution of Regional Blood Flow in Dogs and Primates

Left ventricular and regional vascular effects of halothane were assessed in dogs and primates in which coronary, mesenteric, renal, and iliac blood flows, arterial blood pressure, left ventricular diameter and pressure, dD/dt (i.e., the velocity of myocardial fiber shortening), and dP/dt were continuously measured in the control resting state, while the conscious animals were breathing O2, and during halothane-O2 anesthesia maintained at 1% or at 2% for 90 minutes (separate experimental days). Halothane caused a concentration-dependent depression of myocardial contractility: (dP/dt)/P fell 68 ± 5% during 2% halothane anesthesia and left ventricular end-diastolic diameter rose. Halothane also caused a redistribution of regional blood flows. At a concentration of 1% halothane, the most intense vasodilatation occurred in the renal bed (renal resistance fell 46 ± 5%), but mesenteric resistance rose (42 ± 15%). With 1% halothane regional vascular resistances tended to rise with time, but with 2% halothane regional blood flows rose with time. A direct vasodilating action of halothane was observed following direct intra-arterial injection of the drug. Probably this action was responsible for the renal and iliac vasodilatations and for the opposition to the metabolically induced vasoconstriction in the coronary bed. Thus, the administration of the most commonly employed potent inhalation anesthetic, halothane, substantially alters myocardial contractility and regional blood flows and resistances. These effects are, in many instances, a function of the concentration of the anesthetic and the duration of its administration.

A measure of association for assessing prediction accuracy that is a generalization of non-parametric ROC area.

There is a need for a measure of prediction accuracy that generalizes non-parametric receiver operating characteristic (ROC) area to polytomous ordinal patient state. We describe such a measure, prediction probability PK derived from Kims measure of association. We show that the value of PK equals the value of non-parametric ROC area for dichotomous patient state and is a meaningful generalization of non-parametric ROC area for polytomous state.

Seizures during opioid anesthetic induction: are they opioid-induced rigidity?

The tape recorded EEGs of 127 patients anesthetized with large doses of opioids were retrospectively analyzed for evidence of opioid-induced seizures, and in particular, correlated with movements that occurred during induction and could be clinically interpreted as seizures. Bilateral EEG leads in patients receiving fentanyl (20), sufentanil (20), or alfentanil (87) were recorded. Forty-six of these patients from all opioid groups manifested intense rigidity, as assessed both clinically and by EMGs recorded from eight muscles in 69 of the patients receiving alfentanil. This intense rigidity often resembled seizures, in that the phenomenon entailed severe stiffness of both limbs and trunk, with an explosive onset of myoclonic limb movements, and associated vertical nystagmus. Electroencephalographic observations were extensive, entailing 69 h of paper recordings played back from the tapes, at paper speeds of 30 or 60 mm/s, with detailed annotations from the voice track. These paper recordings were examined in detail independently by three of the investigators, who were unaware of the clinical phenomena that had occurred. The only observed EEG activity that could have been interpreted as epileptiform consisted of small sharp waves related to muscle activity or other artifact. The EEG never indicated seizure activity during these drug-induced movements and rigidity. Reports of opioid-induced seizures are reviewed and a set of criteria is offered to help achieve future consistency and credibility in evaluating this phenomenon. The available evidence does not support the existence of opioid-induced seizures in the clinical setting.

An electroencephalographic comparison of alfentanil with other narcotics and with thiopental.

Using aperiodic analysis, we compared the EEC produced by alfentanil with the EEGs produced by two other opiates—fentanyl and sufentanil—on the one hand and with the EEG produced by a barbiturate—thiopental—on the other hand. Alfentanil and thiopental were injected over 1 minute: fentanyl and sufentanil were injected over 10 to 15 minutes. From the aperiodic analysis we derived up to seven single-number variables computed over 30- or 60-second epochs. All the opiates induced EEGs that were qualitatively similar to each other, although the maximum or minimum values tended to be greater and the time course more rapid with alfentanil than with the other two opiates. This finding may have been related to the fact that we injected relatively more alfentanil and administered it more rapidly. The EEGs produced by alfentanil and thiopental differed markedly, both qualitatively and quantitatively. The total power at 1 Hz and cumulative power at 3 Hz went to higher peak values with alfentanil, the latter tending to decrease with thiopental. The total number ot waves per epoch went to lower peak values with alfentanil; there was little change with thiopental. The frequency below which 90% ot the power resides went to considerably lower peak values with alfentanil than with thiopental. Finally, total power at 10 to 12 Hz (alpha waves; and average power at 17 to 19 Hz (beta waves) went to very high peak values with thiopental, but decreased with alfentanil. In spite ot differences in the opiate studies in the timing ot injection and the relative amount ot drug injected, the variables that proved useful in their response to fentanyl and sutentanil also proved useful with altentanil. In contrast, almost all variables showed a difference in response between alfentanil and thiopental.

Wakeful response to command indicates memory potential during emergence from general anesthesia

Objective. An important aspect of assessing anesthetic depth is determining whether a patient will remember events during surgery. We looked for a clinical sign that would indicate a patients potential for memory formation during emergence from anesthesia. A clinical sign indicating memory potential could be a useful endpoint for measuring the performance of anesthetic depth monitors and for titrating administration of anesthetic agents.Methods. We evaluated patients responses to commands to open the eyes, squeeze the hand four times, and count 20 numbers. These responses were correlated with results on recall, cued recall, and multiple-choice memory tests.Main Results. Patients did not have evidence of memory formation until they sustained wakefulness sufficiently long to complete at least four hand squeezes or count four numbers. Of 28 patients, 13 (46%) with this sustained wakeful response had memory. Of 22 patients, 0 (0%) had evidence of memory formation when they demonstrated a brief wakeful response, defined as being responsive to command but unable to complete more than one hand squeeze or count, or an intermediate response, defined as two or three hand squeezes or counts.Conclusions. We conclude that a brief wakeful response to command indicates that a patient is unlikely to form memories, while a sustained wakeful response indicates that a patient may form memories. Thus, a patients wakeful response to command could be a useful indicator of potential for memory.