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Biomedical subjects

D I Sessler

Publications and source records attributed to D I Sessler.

At least 271 records · Page 15Linked to original sources
PubMed1989

Intraoperative temperature monitoring sites in infants and children and the effect of inspired gas warming on esophageal temperature.

This study tested the hypotheses that 1) temperatures of "central" sites are similar in infants and children undergoing noncardiac surgery and 2) airway heating and humidification increases distal esophageal temperature. Twenty children were randomly assigned to receive 1) active airway humidification using an airway heater and humidifier set at 37 degrees C (N = 8), 2) passive airway humidification using a heat and moisture exchanger (N = 6), or 3) no airway humidification and/or heating (control, N = 6). There were no statistically significant differences between tympanic membrane, esophageal, rectal, and axillary temperatures. The temperatures of the peripheral skin surface (forearm and fingertip) were significantly lower than tympanic membrane temperature and significantly different from each other. Although esophageal and tympanic membrane temperatures in the entire group were similar, esophageal temperatures in patients receiving active and passive airway humidification were about 0.35 degrees C above tympanic temperatures after induction of anesthesia. In contrast, esophageal temperatures in patients without airway humidification were 0.25 degrees C below tympanic temperatures after induction of anesthesia. Esophageal-tympanic membrane temperature differences in the patients given active and passive humidification differed significantly from the corresponding sum in the control group at all times, but not from each other.

Anesthesia, Inhalation↗
PubMed1988

The thermoregulatory threshold in humans during halothane anesthesia.

Although suppression of thermoregulatory mechanisms by anesthetics is generally assumed, the extent to which thermoregulation is active during general anesthesia is not known. The only thermoregulatory responses available to anesthetized, hypothermic patients are vasoconstriction and non-shivering thermogenesis. To test anesthetic effects on thermoregulation, the authors measured skin-surface temperature gradients (forearm temperature--finger-tip temperature) as an index of cutaneous vasoconstriction in unpremedicated patients anesthetized with 1% halothane and paralyzed with vecuronium during elective, donor nephrectomy. Patients were randomly assigned to undergo maximal warming (warm room, humidified respiratory gases, and warm intravenous fluids; n = 5) or standard temperature management (no special warming measures; n = 5). Skin-surface temperature gradients greater than or equal to 4 degrees C were prospectively defined as significant vasoconstriction. Normothermic patients [average minimum esophageal temperature = 36.4 +/- 0.3 degrees C (SD)] did not demonstrate significant vasoconstriction. However, each hypothermic patient displayed significant vasoconstriction at esophageal temperatures ranging from 34.0 to 34.8 degrees C (average temperature = 34.4 +/- 0.2 degrees C). These data indicate that active thermoregulation occurs during halothane anesthesia, but that it does not occur until core temperature is approximately equal to 2.5 degrees C lower than normal. In two additional hypothermic patients, increased skin-temperature gradients correlated with decreased perfusion as measured by a laser Doppler technique. Measuring skin-surface temperature gradients is a simple, non-invasive, and quantitative method of determining the thermoregulatory threshold during anesthesia.

Anesthesia, Inhalation↗
PubMed1988

Spontaneous post-anesthetic tremor does not resemble thermoregulatory shivering.

Spontaneous post-anesthetic tremor that resembles shivering is common during recovery from anesthesia. Risks to postoperative patients include an increase in metabolic rate of up to 400%, hypoxemia, wound dehiscence, dental damage, and disruption of delicate surgical repairs. The etiology of spontaneous post-anesthetic tremor is most commonly attributed to normal thermoregulatory shivering in response to intraoperative hypothermia. However, the mechanism of this tremor remains unknown, hampering prevention and treatment. The present study was designed to determine whether mechanisms other than thermoregulation contribute to the tremor. The electromyograms (EMGs) of eight muscles were observed in nine women during recovery from isoflurane anesthesia. Signals from each muscle were compared to those of pathologic clonus induced by plantar flexion in unanesthetized patients with spinal cord transections and to those of cold-induced shivering in normal, unanesthetized subjects. Two distinct EMG patterns were identified: 1) regular, bursting signals of 5-7 Hz similar to those produced by pathologic clonus in patients with spinal cord transections; and 2) tonic, irregular signals of 5-15 Hz which had poorly defined bursts that did not demonstrate the synchronous 4-8-cycle/min waxing and waning pattern typical of normal shivering. EMG activity occurred most often at expired isoflurane concentrations of 0.1-0.19%, and was not related to rectal temperature. During the later part of recovery when isoflurane concentrations were less than or equal to 0.1%, hypothermic patients frequently demonstrated no clinical or EMG evidence of muscular activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

The thermoregulatory threshold in humans during nitrous oxide-fentanyl anesthesia.

Narcotics and nitrous oxide (N2O) inhibit thermoregulatory responses in animals. The extent to which N2O/fentanyl anesthesia lowers the thermoregulatory threshold in humans was tested by measuring peripheral cutaneous vasoconstriction using skin-surface temperature gradients (forearm temperature-fingertip temperature) and the laser Doppler perfusion index. Fifteen unpremedicated patients were anesthetized with N2O (70%) and fentanyl (10 micrograms/kg iv bolus followed by 4 micrograms.kg-1.h-1 infusion) during elective, donor nephrectomy. Patients were randomly assigned to undergo additional warming (humidified respiratory gases, warmed intravenous fluids, and a heating blanket over the legs; n = 5) or standard temperature management (no special warming measures; n = 10). Significant vasoconstriction was prospectively defined as a skin-surface temperature gradient between forearm surface and finger-tip surface greater than or equal to 4 degrees C, and the thermoregulatory threshold was defined as the esophageal temperature at which such vasoconstriction occurred. Vasoconstriction did not occur in the patients who received additional warming and thus remained nearly normothermic [average minimum esophageal temperature = 35.8 +/- 0.4 degrees C (SD)] but did in six hypothermic patients at a mean esophageal temperature of 34.2 +/- 0.5 degrees C. Four hypothermic patients developed a passive thermal steady state without becoming sufficiently cold to trigger vasoconstriction. Thus, active thermoregulation occurs during N2O/fentanyl anesthesia but does not occur until core temperatures are approximately 2.5 degrees C lower than normal. The thermoregulatory threshold during N2O/fentanyl anesthesia is similar to that previously determined during halothane (34.4 +/- 0.2 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1988

Preparation of anesthesia machines for patients susceptible to malignant hyperthermia.

Malignant hyperthermia is a potentially lethal syndrome that can be triggered by inhaled anesthetics. Thus, it may be appropriate to utilize equipment that minimizes exposure of susceptible patients to inhaled anesthetics. The rate of release of anesthetic stored in anesthesia delivery systems is unknown. To determine residual anesthetic concentrations, the washout rates of halothane and isoflurane were compared, and the effects of a 1-l/min and a 10-l/min fresh gas flow were evaluated. Halothane concentrations were also measured in samples taken from the fresh gas outlet and the Y-piece of the circle system during four separate studies in which various components of the anesthesia system were replaced. In each study an Ohio Modulus anesthesia machine equipped with an Air-Shields ventilator was exposed to 2% halothane for 18 h. Anesthetic concentrations were determined by a gas chromatograph having a sensitivity of 0.1 ppm. Isoflurane washed out 3-4 times faster than halothane. Residual halothane concentration was approximately equal to tenfold greater when the fresh gas flow was 1 l/min rather than 10 l/min: 194 versus 19 ppm after 1 h of washout. Using a 10-l/min fresh gas flow, halothane concentrations in samples obtained from the Y-piece were similar with original or fresh soda lime but were more than tenfold lower after the fresh gas outlet hose and circle system were replaced (approximately equal to 50 ppm vs. approximately equal to 5 ppm after 5 min of washout).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1987

An in vivo study of halothane uptake and elimination in the rat brain with fluorine nuclear magnetic resonance spectroscopy.

A recent NMR study reported the elimination of halothane from the brain of rabbits to be ten times slower than expected, based on known anesthetic solubility and cerebral blood flow. The authors conducted a study in five rats using fluorine nuclear magnetic resonance (NMR) spectroscopy to see if major pharmacokinetic discrepancies are associated with the uptake, maintenance, and elimination of halothane from the brain. The rats underwent a 60-min period of halothane anesthesia. They employed a spatially selective NMR spectroscopy technique known as surface coil "depth-pulsing" to assure that the fluorine NMR signals originated in brain tissue, and not in the scalp, muscle, adipose tissue, and bone marrow that surround the brain. After the inspired anesthetic concentration was decreased to zero, the amplitude of the fluorine NMR signal decreased to 40% of its maximum value within 34 +/- 8.0 minutes (n = 5), rather than after 7 h as in the recent study, where the fluorine signal may have contained substantial contributions from metabolites or tissues outside the brain. Fluorine was barely detectable in all of the animals 90 min after stopping the administration of halothane. The authors' results are in agreement with model calculations and several other investigations.

Anesthesia↗
PubMed1987

An in vivo 19F nuclear magnetic resonance study of isoflurane elimination from the rabbit brain.

19F nuclear magnetic resonance spectroscopy was performed at 2.0 Tesla to evaluate the washout of isoflurane from the adult rabbit brain after 90 min of anesthesia. This investigation reconciles previous in vivo NMR studies of others, which observed a slow anesthetic washout, with invasive non-NMR studies that found a rapid washout, as predicted by perfusion-limited models of anesthetic uptake and elimination. Two NMR surface coil experiments were performed: in the first, a 1-cm surface coil was placed directly over the exposed dura to be certain that the washout was observed only from the brain; in the second, a 3-cm coil was placed noninvasively over the intact scalp to emulate previous NMR experiments. As in previous NMR experiments, a slow washout of isoflurane was observed with the large coil. The NMR signal that is observed with the large coil cannot be attributed solely to brain tissue. Fat surrounding the brain contributes significantly to the fluorine NMR spectra that are observed with the 3-cm coil, and its contributions lengthen the apparent washout time. A rapid washout of isoflurane from the rabbit brain was observed with the small coil, whose signal unambiguously arises only from brain tissue. The observed rapid washout is consistent with previous invasive biochemical measurements of anesthetic washout from the brain.

Anesthesia↗
PubMedDate not supplied

Intraoperative warming therapies: a comparison of three devices.

STUDY OBJECTIVE: To compare the effectiveness of three commonly used intraoperative warming devices. DESIGN: A randomized, prospective clinical trial. SETTING: The surgical suite of a university medical center. PATIENTS: Twenty adult patients undergoing kidney transplantation for end-stage renal disease. INTERVENTIONS: Patients were assigned to one of four warming therapy groups: circulating-water blanket (40 degrees C), heated humidifier (40 degrees C), forced-air warmer (43 degrees C, blanket covering legs), or control (no extra warming). Intravenous fluids were warmed (37 degrees C), and fresh gas flow was 5 L/min for all groups. No passive heat and moisture exchangers were used. MEASUREMENTS AND MAIN RESULTS: The central temperature (tympanic membrane thermocouple) decreased approximately 1 degree C during the first hour of anesthesia in all groups. After three hours of anesthesia, the decrease in the tympanic membrane temperature from baseline (preinduction) was least in the forced-air warmer group (-0.5 degrees C +/- 0.4 degrees C), intermediate in the circulating-water blanket group (-1.2 degrees C +/- 0.4 degrees C), and greatest in the heated humidifier and control groups (-2.0 degrees C +/- 0.5 degrees C and -2.0 degrees C +/- 0.7 degrees C, respectively). Total cutaneous heat loss measured with distributed thermal flux transducers was approximately 35W (watts = joules/sec) less in the forced-air warmer group than in the others. Heat gain across the back from the circulating-water blanket was approximately 7W versus a loss of approximately 3W in patients lying on a standard foam mattress. CONCLUSION: The forced-air warmer applied to only a limited skin surface area transferred more heat and was clinically more effective (at maintaining central body temperature) than were the other devices. The characteristic early decrease in central temperature observed in all groups regardless of warming therapy is consistent with the theory of anesthetic-induced heat redistribution within the body.

Adult↗
PubMedDate not supplied

Mild core hyperthermia does not alter electroencephalographic responses during epidural-enflurane anesthesia in humans.

STUDY OBJECTIVES: To determine the electroencephalographic (EEG) changes induced by mild hyperthermia during enflurane anesthesia and to test the reliability of two new infrared thermometers. DESIGN: Prospective laboratory evaluation. SETTING: The Thermoregulation Research Laboratory at the University of California, San Francisco. VOLUNTEERS: 6 healthy female volunteers aged 30 +/- 8 years. INTERVENTIONS: Epidural anesthesia (approximately T10 dermatome) was induced and maintained using 2-chloroprocaine anesthesia. General anesthesia was induced by inhalation of nitrous oxide and enflurane and maintained with enflurane at an end-tidal concentration of 1.7%. A minimum of 2 degrees C core hyperthermia was induced by active cutaneous warming, and the volunteers subsequently were passively cooled. MEASUREMENTS AND MAIN RESULTS: EEG data were recorded from gold cup electrodes positioned at FP1 and FP2, with the reference electrode at CZ and the ground lead on the mastoid. In addition to routine EEG parameters, we evaluated the bispectral index. Bispectral analysis quantifies the phase coupling between various frequencies in the power spectrum and may be a useful measure of anesthetic depth. Core temperature was measured at the left tympanic membrane and distal esophagus. Core temperature also was determined from the right ear using two new, infrared tympanic membrane thermometers. One of these directly measures tympanic temperature, and the other extrapolates core temperature from the external ear canal. Induction of 2 degrees C core hyperthermia did not produce statistically significant or clinically important changes in beta or delta power, the 95% spectral edge frequency, or the bispectral index. Temperatures recorded from the right ear by the direct thermometer were 0.27 degrees C +/- 0.33 degrees C less than those measured in the left ear, but the values correlated well (r2 = 0.95 +/- 0.04). Temperatures recorded from the right ear by the core temperature extrapolater were 0.42 degrees C +/- 0.33 degrees C lower than those measured in the left ear, and the correlation between values was slightly worse (r2 = 0.83 +/- 0.16). CONCLUSIONS: Since mild core hyperthermia does not alter routine EEG parameters or the bispectral index, typical perianesthetic thermal disturbances are unlikely to obscure EEG estimates of anesthetic depth. Both the direct thermometer and the core temperature extrapolater were found to be sufficiently accurate and precise for routine clinical use, but the direct thermometer would be preferable in the perioperative period.

Adult↗
PubMedDate not supplied

Lidocaine does not depress reflex dilation of the pupil.

BACKGROUND AND OBJECTIVES: Pupillary dilation in response to dermatomal electrical stimulation is one method of determining sensory block level during combined epidural and general anesthesia. Use of this technique may, however, be confounded by systemic absorption of epidurally administered local anesthetics. Accordingly, the effects of intravenous lidocaine on the magnitude and duration of reflex pupillary dilation were evaluated. METHODS: Six volunteers were each anesthetized twice with desflurane 3.5-6.0%. During one anesthetic, intravenous lidocaine was administered to a plasma concentration of 5.3 +/- 1.5 micrograms/mL. When the plasma concentrations were stable, a 5-second tetanic electrical stimulus was applied. Pupil size was then recorded for 8 minutes. RESULTS: Lidocaine, at plasma concentrations near 5 micrograms/mL, did not significantly alter the pupillary response to electrical stimulation. In contrast, stimulus-induced increase in heart rate was obliterated. Painful stimulation did not increase systolic blood pressure in either case. CONCLUSIONS: Typical plasma lidocaine concentrations observed during epidural anesthesia are unlikely to prevent the use of pupillary responses to evaluate sensory block level.

Adult↗
PubMedDate not supplied

Thermoregulatory effects of spinal and epidural anesthesia during cesarean delivery.

BACKGROUND AND OBJECTIVES: Hypothermia is likely to develop faster during spinal anesthesia than epidural anesthesia. A natural consequence of the rapid temperature decrease during spinal anesthesia is that the shivering threshold will be reached sooner and that more shivering will be required to prevent further hypothermia. We tested the hypotheses that the onset of hypothermia is more rapid and the onset and intensity of shivering earlier during spinal than epidural anesthesia. METHODS: Patients undergoing cesarean delivery were randomly assigned to spinal anesthesia or epidural anesthesia. Spinal anesthesia was induced by injecting 2 mL 0.5% dibucaine into the L4-L5 interspace. Epidural anesthesia was induced with 20 mL 2% mepivacaine injected into the L2-L3 interspace. Thermal comfort and shivering were scored by a blinded observer. RESULTS: Fifteen patients given each type of anesthesia had upper sensory levels > or =T4 dermatome. Sensation was entirely absent from the leg during spinal anesthesia, but lower block levels were near S5 during epidural anesthesia. Tympanic membrane temperatures initially decreased faster during spinal anesthesia, but subsequently decreased at a rate of 0.5 degrees C/h in both groups. The onset and incidence of shivering (detected qualitatively) did not differ significantly between the two groups, but shivering intensity was significantly reduced during spinal anesthesia. Furthermore, the shivering thresholds were 36.4+/-0.3 degrees C (mean+/-SD) during spinal anesthesia versus 37.1+/-0.4 degrees C in those given epidural anesthesia (P=.006). There were no clinically important differences in thermal comfort with the two kinds of neuraxial anesthesia. CONCLUSIONS: We failed to confirm our hypothesis, but for an unexpected reason: Thermoregulation was impaired more by spinal anesthesia than epidural anesthesia. It seems likely that in our patients spinal anesthesia inhibited thermoregulatory control more than epidural anesthesia because it better blocked sensory input from the legs.

Adult↗
PubMedDate not supplied

Centrally and locally mediated thermoregulatory responses alter subcutaneous oxygen tension.

Mild perianesthetic hypothermia decreases resistance to infections. Decreased resistance likely results in part from direct immune inhibition. However, decreased tissue oxygen partial pressure also decreases resistance to infection by impairing oxidative killing by neutrophils and collagen deposition. Thermoregulatory vasoconstriction decreases skin blood flow and may also decrease subcutaneous tissue oxygen tension. Accordingly, we determined the influence of centrally and locally mediated thermoregulatory vasomotion on subcutaneous oxygen tension. We also compared subcutaneous oxygen tension to other potential markers of tissue perfusion: laser Doppler flowmetry and transcutaneous oxygen tension. Arterial oxygen tension was maintained near 325 mm Hg in five volunteers. Control subcutaneous oxygen tension values were recorded after 1 hour of euthermia (no sweating or vasoconstriction). Volunteers were then cooled with a circulating-water mattress positioned under the trunk and legs. After 1.5 hours of cooling sufficient to produce shivering, the right upper arm was covered for 1 hour with a small circulating water blanket set to 40 degrees C while systemic cooling continued. The volunteers were then systematically warmed to produce sweating, and the right arm was locally cooled. There was no correlation among laser Doppler flowmetry, transcutaneous oxygen tension, and subcutaneous oxygen tension. Systemic cooling significantly decreased subcutaneous oxygen tension, but subcutaneous oxygen tension in the right arm returned to control values during local heating. Systemic warming significantly increased subcutaneous oxygen tension, and 1 hour of local cooling failed to fully reverse the increase. These data indicate that thermoregulatory vasoconstriction significantly decreases tissue oxygen availability. Decreased subcutaneous oxygen tension may be one mechanism by which mild perianesthetic hypothermia facilitates development of surgical wound infections.

Journal Article↗
PubMedDate not supplied

Effects of epidural anesthesia on thermal sensation.

BACKGROUND AND OBJECTIVES: Epidural anesthesia decreases the core temperatures triggering vasoconstriction and shivering, presumably by increasing apparent (as opposed to actual) lower-body temperature. We therefore tested the hypothesis that epidural anesthesia also increases the overall perception of warmth. METHODS: We studied 8 volunteers in a randomized, cross-over protocol separated by at least 48 hours. On one day, epidural anesthesia was induced to a T11 sensory level; the other day was a control without anesthesia. Core temperature and upper-body skin temperatures (33 degrees C) were kept constant throughout. Lower-body skin temperature was set in a random order to 31 degrees C, 32 degrees C, 33 degrees C, 34 degrees C, 35 degrees C, and 36 degrees C and maintained by circulating water and forced air. At each temperature, the volunteers rated their thermal sensation with a visual analog scale (0 = cold, 100 = hot). Core temperature was 36.8 +/- 0.1 degrees C on the control day and 36.7 +/- 0.1 degrees C on the epidural day. RESULTS: Scores for thermal sensation on the epidural day were near 47 mm at each lower-body skin temperature. On the control day, visual analog scores at a lower-body skin temperature of 31 degrees C were 16 +/- 10 mm and increased linearly to 61 +/- 6 mm at 36 degrees C. Control thermal sensation scores thus equaled those during epidural anesthesia when lower-body skin temperature was near 34 degrees C. CONCLUSIONS: Thermal sensation with and without epidural anesthesia was comparable at a lower-body temperature near 34 degrees C, which is a normal leg skin temperature. This suggests that autonomic and behavioral thermoregulatory consequences of epidural anesthesia differ-or that the current explanation for reduced vasoconstriction and shivering thresholds during epidural anesthesia is incorrect.

Adult↗