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Biomedical subjects

D I Sessler

Publications and source records attributed to D I Sessler.

At least 253 records · Page 14Linked to original sources
PubMed1991

Isoflurane anesthesia and circadian temperature cycles in humans.

Cognitive performance in postsurgical patients may be impaired by disturbances of normal circadian rhythm analogous to those produced by rapid transmeridian travel ("jet lag"). We therefore tested the hypothesis that isoflurane anesthesia alone produces a phase-delay in the human circadian temperature rhythm. We monitored central body temperature rhythms (using an ingested sensor) in five young, healthy, male volunteers at 3-min intervals for a total of 5 days. On the 3rd day, 3 h of 1.0% isoflurane anesthesia was administered beginning at approximately 10:00 AM. Thiopental, opioids, and other medications were not administered; volunteers were kept normothermic during anesthesia. Visual inspection of the data confirmed that periodicity of the temperature cycles remained near 24 h and that the curve was sinusoidal. Data were fit using a two-step sine and cosine regression for each 24-h period. Before anesthesia, volunteers demonstrated a consistent 24-h cycle, with a mean temperature (mesor) of 36.8 +/- 0.2 degrees C, amplitude of 0.8 +/- 0.2 degrees C, and time of maximum temperature (acrophase) of 3:06 PM +/- 2.4 h. Isoflurane anesthesia did not produce significant changes in the central temperature mesor. Peak-to-trough range (amplitude) of the temperature cycle was significantly reduced on the day of anesthesia (0.5 +/- 0.2 degrees C) but returned to normal on the subsequent day. Compared with the 2 days preceding isoflurane administration, there was no statistically significant change in acrophase on the day following anesthesia. These data do not support our hypothesis and suggest that the internal timer controlling circadian temperature cycles is resistant to clinical concentrations of isoflurane.

Adult↗
PubMed1991

Sweating threshold during isoflurane anesthesia in humans.

Isoflurane anesthesia in humans markedly decreases the threshold temperature triggering peripheral thermoregulatory vasoconstriction (i.e., central temperature triggering vasoconstriction). However, it is not known whether the sweating threshold remains unchanged (e.g., near 37 degrees C), decreases along with the vasoconstriction threshold, or increases during anesthetic administration. Accordingly, the hypothesis that isoflurane anesthesia increases the thermoregulatory threshold for sweating was tested. Forehead sweating was evaluated in five healthy patients given isoflurane anesthesia. The sweating threshold was prospectively defined as the distal esophageal temperature at which significant sweating was first observed. Sweating was observed in each patient at a mean central temperature of 38.3 +/- 0.3 degrees C and an end-tidal isoflurane concentration of 1.1% +/- 0.2%. The interthreshold range (difference between vasoconstriction and sweating thresholds) without anesthesia is approximately 0.5 degrees C; isoflurane anesthesia increases this range to approximately 4 degrees C.

Adult↗
PubMed1990

Extradurals and shivering: effects of cold and warm extradural saline injections in volunteers.

We tested the hypothesis that cooling the extradural space may provoke shivering, by giving three 80-ml extradural injections of warm (39.8 +/- 1.2 degrees C) or cold (17 +/- 2.2 degrees C) saline to four healthy volunteers, whilst recording central temperature and electromyographic activity from four muscles. The first injection (always cold) did not induce shivering in any of the subjects. The second and third injections, randomly cold or warm, were given after induction of shivering with cold blankets, but had no detectable effects on the intensity of shivering. This suggests that shivering in extradural anaesthesia does not result solely from cooling of the extradural space.

Adult↗
PubMed1990

The effect of local surface and central cooling on adductor pollicis twitch tension during nitrous oxide/isoflurane and nitrous oxide/fentanyl anesthesia in humans.

This study aimed to determine whether: 1) the method of cooling the hand (i.e. central [total body] vs. local surface [hand only]) influences the relationship between the adductor pollicis temperature and twitch tension; and 2) decreased evoked twitch response during hypothermia is due to reduced muscle temperature and/or the anesthetic drug used. First, the effect of local surface cooling on adductor pollicis twitch tension during isoflurane anesthesia was determined in 15 patients, while central body temperature was not allowed to decrease. Adductor pollicis temperature and twitch tension decreased in a linear manner (P less than 0.05). However, the magnitude of the decreased response was only 43% of that observed during central cooling in the authors' previous study under otherwise similar experimental conditions. Second, the effect of central cooling on adductor pollicis twitch tension during nitrous oxide/fentanyl anesthesia was determined in five patients. The twitch tension did not decrease until the adductor pollicis temperature decreased below 35.2 degrees C. Below this temperature, twitch tension decreased 16%/degrees C reduction in muscle temperature. These results are similar to those obtained in the authors' previous study in patients anesthetized with nitrous oxide/isoflurane anesthesia. The authors conclude that both central and local surface cooling of the adductor pollicis muscle reduces twitch tension and that the decrease in adductor pollicis twitch tension is the same during nitrous oxide/isoflurane and nitrous oxide/fentanyl anesthesia.

Adult↗
PubMed1990

Shivering during epidural anesthesia.

The authors tested the hypothesis that during epidural anesthesia: 1) shivering-like tremor is primarily normal thermoregulatory shivering; 2) hypothermia does not produce a subjective sensation of cold; and 3) injectate temperature does not influence tremor intensity. An epidural catheter was inserted into ten healthy, nonpregnant volunteers randomly assigned to skin-surface warming below the T10 dermatome (warmed group) or no extra warming (unwarmed group). Each volunteer was given two 30-ml epidural injections of 1% lidocaine (16.0 +/- 4.7 degrees C and 40.6 +/- 0.7 degrees C at the catheter tip), in random order separated by at least 3 h. Skin-temperature gradients (forearm-fingertip) and tympanic membrane and average skin temperatures were recorded; significant vasoconstriction was prospectively defined as a gradient greater than or equal to 4 degrees C. Integrated electromyographic (EMG) intensity was recorded from four upper-body muscles. Overall thermal comfort was evaluated using a visual analog scale. Tympanic membrane temperatures decreased significantly in the unwarmed group (n = 6). Tremor occurred following ten of 12 injections in unwarmed volunteers, but only following one of eight injections in the warmed group. Integrated EMG intensity did not differ significantly following epidural injection of warm and cold lidocaine: tremor started when tympanic membrane temperature decreased about 0.5 degrees C and continued until central temperature returned to within 0.5 degrees C of control. Tremor always was preceded by hypothermia and vasoconstriction in the arms. Thermal comfort increased in both groups after epidural injection, with maximal comfort occurring at the lowest tympanic temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

The thermoregulatory threshold is inversely proportional to isoflurane concentration.

This study tested the hypothesis that the threshold for thermoregulatory vasoconstriction is lowered as isoflurane concentration increases, but the intensity of vasoconstriction, once triggered, is well preserved during isoflurane anesthesia. The thermoregulatory threshold was prospectively defined as the central temperature at which vasoconstriction occurred, and significant vasoconstriction was defined as a skin-surface temperature gradient (forearm-fingertip) greater than or equal to 4 degrees C. The threshold for thermoregulatory vasoconstriction and the intensity of vasoconstriction, measured as maximum skin-temperature gradient, was determined in six unpremedicated patients electively donating a kidney during isoflurane anesthesia, and in four healthy, awake volunteers. All anesthetized patients were deliberately cooled and became hypothermic. Vasoconstriction occurred in five of six at central temperatures between 35.3 and 32.4 degrees C, at end-tidal isoflurane concentrations between 0.74 and 1.65%. The patient who did not vasoconstrict received the highest isoflurane concentration (approximately 2.5%) and reached a central temperature of 31 degrees C. Unanesthetized volunteers also were exposed to cold and each vasoconstricted at a temperature near 37 degrees C. The threshold for thermoregulatory cutaneous vasoconstriction was inversely correlated with anesthetic dose, the thermoregulatory threshold decreasing approximately 3 degrees C/% isoflurane concentration. There were no statistically significant differences between maximum skin-surface temperature gradients in awake volunteers and patients given isoflurane, or between any of the groups when patients from previous studies given halothane or nitrous oxide/fentanyl anesthesia were included in the comparison. These data indicate that the intensity of vasoconstriction, once triggered, is similar during several different types of anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Thermoregulatory vasoconstriction decreases cutaneous heat loss.

To determine the extent to which thermoregulatory vasoconstriction decreases heat loss to the environment, we measured regional heat flux, average skin temperature, and tympanic membrane temperature before and after thermoregulatory vasoconstriction in five minimally clothed volunteers maintained in a 30.8 +/- 0.1 degrees C environment. Thermoregulatory vasoconstriction was induced by central venous infusion of cooled fluid. Peripheral cutaneous blood flow was evaluated with venous-occlusion volume plethysmography and skin-surface temperature gradients. Laser Doppler flowmetry was used to measure vasoconstriction in centrally located skin. This model mimics the common clinical situation in which patients in a warm environment are centrally cooled by administration of cold intravenous fluids or by lavage of internal cavities with cold fluids. Tympanic membrane temperature decreased 1.5 +/- 0.3 degrees C in the first 15 min after the cold fluid infusion was started and remained approximately 1 degrees C below control values during the rest of the study. Average skin-surface temperature decreased slowly to approximately 0.7 degrees C below control. Flow in capillaries of centrally distributed skin, determined with laser Doppler flowmetry, decreased only approximately 40%. Total heat flux, and flux from the arms and legs decreased approximately 25% (15.5 +/- 0.3 W). Heat loss from the trunk and head decreased only 17%, whereas, loss from the hands and feet (10.5% of the body surface area) decreased approximately 50%. All measured values decreased significantly following vasoconstriction (P less than 0.01). Therefore, thermoregulatory vasoconstriction in a thermoneutral environment appears to decrease cutaneous loss of metabolic heat approximately 25%.

Adult↗
PubMed1990

The thermoregulatory threshold in infants and children anesthetized with isoflurane and caudal bupivacaine.

Hypothermia in anesthetized adults provokes centrally mediated, peripheral thermoregulatory vasoconstriction at threshold temperatures approximately 2.5 degrees C below normal. The weight dependence of thermoregulatory vasoconstriction was evaluated in 33 unpremedicated pediatric patients receiving isoflurane/oxygen anesthesia (end-tidal concentrations approximately 0.9%) and caudal anesthesia with bupivacaine. The patients were prospectively assigned to four weight groups (5-10 kg, 10-20 kg, 20-30 kg, and 30-50 kg). Central temperature was measured at the tympanic membrane, and average skin surface temperature was determined from four cutaneous sites; mean body temperature was calculated from central and average skin temperatures. Finger blood flow was determined using laser Doppler flowmetry and forearm-fingertip skin temperature gradients. Significant peripheral vasoconstriction was prospectively defined as a laser Doppler flow index 50% of the value recorded 10 min after induction of anesthesia. Thermoregulatory thresholds were defined as the tympanic membrane or mean body temperatures at which significant vasoconstriction occurred. Vasoconstriction occurred in 32 of the patients at temperatures ranging from 34.4 to 35.3 degrees C. Central and mean body threshold temperatures did not differ among the groups, and were similar to those observed previously in adults. There was a good correlation between laser Doppler flowmetry and forearm-fingertip skin temperature gradients in individual patients.

Anesthesia, Caudal↗
PubMed1990

Skin-surface warming: heat flux and central temperature.

The authors determined the efficacy of four postoperative warming devices by measuring cutaneous and tympanic membrane temperatures, and heat loss/gain using 11 thermocouples and ten thermal flux transducers in five healthy, unanesthetized volunteers. Overall thermal comfort was evaluated at 5-10 min intervals using a 10-cm visual analog scale. The warming devices were: 1) a pair of 250-W infrared heating lamps mounted 71 cm above the abdomen; 2) the Thermal Ceiling MTC XI UL (500 W) set on "high" and mounted 56 cm above the volunteer; 3) a 54-by-145-cm circulating-water blanket set to 40 degrees C placed over the volunteer; and 4) the Bair Hugger forced air warmer with an adult-sized cover set on "low" (approximately 33 degrees C), "medium" (approximately 38 degrees C), and "high" (approximately 43 degrees C). Following a 10-min control period, each device was placed over the volunteer and activated for a 30-min period. All devices were started "cold" and warmed up during the study period. The Bair Hugger set on "medium" decreased heat loss more than each radiant warming device and as much as the circulating-water blanket. All methods reached maximum efficacy within 20 min. Set on "high," the Bair Hugger increased skin-surface temperature more than the circulating-water blanket. The Bair Hugger (all settings) and the water blanket raised skin temperature more than the radiant heaters. The circulating-water blanket was the most effective device for heating an optimally placed transducer on the chest (directly under and parallel to the radiant heat sources, and touching the water and Bair Hugger blankets).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Skin-surface temperature gradients correlate with fingertip blood flow in humans.

Skin-surface temperature gradients (forearm temperature - fingertip temperature) have been used as an index of thermoregulatory peripheral vasoconstriction. However, they have not been specifically compared with total finger blood flow, nor is it known how long it takes fingertip temperature to fully reflect an abrupt change in finger blood flow. Steady-state skin-temperature gradients were compared with total fingertip blood flow in 19 healthy volunteers. There was an excellent correlation between steady-state skin-surface temperature gradients and total fingertip blood flow measured with venous-occlusion volume plethysmography: gradient = 0.2-5.7.log(flow), r = 0.98. The half-time for fingertip cooling after complete arterial obstruction (in 8 volunteers) was 6.6 +/- 1.2 min. The authors conclude that skin-temperature gradients are an accurate measure of thermoregulatory peripheral vasoconstriction.

Adult↗
PubMed1990

Efficiency of airway heat and moisture exchangers in anesthetized humans.

The efficiencies of airway heat and moisture exchanging filters in reducing respiratory water losses and increasing airway temperatures during general anesthesia were studied in five tracheally intubated patients given isoflurane, nitrous oxide, and oxygen anesthesia during controlled ventilation. Filters (Humid-Vent Filter, Humid-Vent 1, Pall Conserve, Siemens 150, and ThermoVent 600) were placed between the Y-piece of the anesthesia circle system and the endotracheal tube for 40 min each. Airway temperature, esophageal temperature, and water loss (determined by weighing expired water collected in CaSO4) were measured every 10 min. All of the filters reached near-maximum efficiency in reducing water losses within 10 min. The Humid-Vent Filter and Siemens 150 filters were most efficient, the Pall Conserve and ThermoVent 600 less efficient. Airway temperature rapidly increased 2 degrees-8 degrees C during each trial. The more efficient the filter in conserving water, the greater the airway temperature. The respiratory heat conserved by these filters represents 5.5%-7.2% of the estimated total metabolic heat production during anesthesia in adults.

Anesthesia, Inhalation↗
PubMed1989

Lower esophageal contractility predicts movement during skin incision in patients anesthetized with halothane, but not with nitrous oxide and alfentanil.

The frequency of spontaneous lower esophageal contractions (SLEC) has been proposed as one measure of anesthetic depth. The authors tested the hypothesis that SLEC frequency can predict movement in response to skin incision during halothane or nitrous oxide/alfentanil anesthesia. The incidence of movement during skin incision was compared with the frequency of spontaneous lower esophageal contractions in 20 healthy patients anesthetized with halothane. Esophageal contractility was determined using the Lectron 302, which senses the pressure in a water-filled balloon positioned in the distal esophagus. Absence of SLEC in the 6 min preceding incision correlated with no movement, with one exception (n = 9). All but one patient having greater than or equal to 2 SLEC in the 6 min preceding skin incision moved (n = 8) (P less than 0.01). Sixteen additional patients anesthetized with nitrous oxide (70%) and alfentanil demonstrated no correlation between SLEC frequency and movement. These data suggest that the frequency of spontaneous lower esophageal contractions, and its ability to predict movement, depends on anesthetic type.

Adult↗
PubMed1989

Atracurium, vecuronium, and pancuronium do not alter the minimum alveolar concentration of halothane in humans.

The authors studied 64 unpremedicated, healthy surgical patients, aged 42 +/- 14 yr, to determine the effects of atracurium, vecuronium, and pancuronium on the minimum alveolar concentration (MAC) of halothane. Anesthesia was induced using halothane/nitrous oxide/oxygen via a mask without the administration of other drugs. Nitrous oxide was discontinued, the trachea was intubated without prior administration of neuromuscular blocking drugs, and anesthesia was maintained with halothane in oxygen. Participating patients were assigned to one of five groups: 1) no neuromuscular blocking drug (control group, n = 9); 2) atracurium 0.5 mg/kg (n = 10); 3) atracurium 1.0 mg/kg (n = 15); 4) vecuronium 0.1 mg/kg (n = 20); or, 5) pancuronium 0.1 mg/kg (n = 10). Tourniquets, inflated to 300 mmHg immediately before iv administration of neuromuscular blocking drug and 15-30 min prior to skin incision, were used to isolate extremities from circulating neuromuscular blocking drug in all patients. A positive response to stimulation was defined as movement of at least one extremity occurring distal to the tourniquet within 1 min following skin incision. The first patients in the control and atracurium groups were studied at an end-tidal halothane concentration of 0.95%. The first patient in the pancuronium group was studied at a halothane concentration of 0.75%, and the first patient in the vecuronium group at 0.70%. Subsequent patients were studied at end-tidal halothane concentrations 0.10% above or below that of the preceding patient, depending on the presence or absence of movement with skin incision. Control MAC for halothane was 0.74% +/- 0.09% (mean +/- SEM).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Passive and active inspired gas humidification in infants and children.

The hypothesis that both active and passive airway humidification prevents hypothermia in infants and children, but that neither decreases the duration of postoperative recovery was tested. Twenty-seven ASA physical status 1 or 2 patients were studied who weighed between 5 and 30 kg, underwent superficial operations, were anesthetized with halothane and 70% N2O, and whose lungs were ventilated via a Rees modification of an Ayre's t-piece. The children were randomly assigned to receive active airway humidification and warming using an MR450 Servo airway heater and humidifier set at 37 degrees C (n = 10), passive airway humidification using the Humid-Vent 1 heat and moisture exchanger placed between the Ayre's t-piece and the endotracheal tube (n = 8), or no airway humidification and heating (control, n = 9). Distal tracheal and tympanic membrane temperatures and airway humidity were recorded during the first 90 min of surgery. Rectal temperature was measured during the postanesthetic recovery period. Relative humidity of inspired respiratory gases was approximately 30% in the control group and approximately 90% in the group given active airway humidification. Initial inspired humidity in the passive humidification group (50%) increased to approximately 80%, a level not significantly different from that in the active group after 80 min of anesthesia. Central body temperature increased 0.25 degrees C during active active airway humidification and heating, whereas temperature decreased 0.25 degrees C during passive humidification and 0.75 degrees C without airway humidification. Distal tracheal temperature was significantly higher in the groups given passive and active humidification than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia Recovery Period↗
PubMed1989

The relationship between adductor pollicis twitch tension and core, skin, and muscle temperature during nitrous oxide-isoflurane anesthesia in humans.

Temperature and volatile anesthetic agents influence neuromuscular transmission. Because mild hypothermia is common during general anesthesia, the authors sought to determine the relationship between the core temperature, adductor pollicis muscle temperature, and the twitch response of the adductor pollicis muscle, during isoflurane anesthesia in 15 patients undergoing elective surgery in which muscle relaxants were not required. Five patients were allowed to cool spontaneously, five were cooled actively, and normothermia was maintained actively in the remaining five. In the normothermic patients (core greater than 36.5 degrees C, muscle greater than 35.7 degrees C), the twitch response of the muscle remained unchanged from control values. In the patients who were cooled passively or actively, a muscle temperature threshold was observed (35.2 degrees C), below which twitch response of the muscle diminished by 10-15%/degrees C decrease in muscle temperature. To ensure that the adductor pollicis muscle temperature remained above 35.2 degrees C, the core temperature had to be maintained above 36 degrees C. A significant linear relationship (P less than 0.05) was found between the adductor pollicis muscle temperature and twitch tension below the threshold for each individual patient in the cooled groups (correlation coefficient range, 0.80-0.99). Thus, there is a temperature-related decrease in adductor pollicis twitch response during isoflurane anesthesia, and the temperature of this muscle should be maintained above 35-35.5 degrees C during studies of neuromuscular transmission. This can be achieved by maintaining core temperature above 36 degrees C.

Anesthesia, Inhalation↗
PubMed1989

Passive or active inspired gas humidification increases thermal steady-state temperatures in anesthetized infants.

We tested the hypothesis that active and passive airway humidification minimize hypothermia in infants, but that maintaining normothermia does not decrease the duration of postoperative recovery. A circle system was used to ventilate the lungs of anesthetized, intubated infants who were randomly assigned to active airway humidification and warming with use of an MR450 Servo airway heater and humidifier set at 37 degrees C (n = 10), passive airway humidification with use of the Humid-Vent Mini heat and moisture exchanger placed between the Y-piece of the circle and the endotracheal tube (n = 10), or no airway humidification and heating (control, n = 10). Anesthesia was induced with thiopental and maintained with isoflurane and nitrous oxide in oxygen. The relative humidity of inspired respiratory gases was approximately 35% in the control group and approximately 90% in the group undergoing active airway humidification. Initial inspired humidity in the passive humidification group (45%) increased to approximately 80% after 1 h of anesthesia. Humidity differed significantly across groups at all times (P less than or equal to 0.05). Steady-state rectal temperatures (100-120 min after induction) were 36.2 +/- 0.7 degrees C in patients given active humidification and heating, 35.7 +/- 0.9 degrees C in the passively humidified group, and 35.2 +/- 0.4 degrees C in the control group (P less than or equal to 0.05 between each group). Recovery from general anesthesia was rapid in all patients and did not correlate with central temperature changes or type of humidification (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗