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Biomedical subjects

D I Sessler

Publications and source records attributed to D I Sessler.

At least 127 records · Page 7Linked to original sources
PubMed1998

The implications of hypothermia for early tracheal extubation following cardiac surgery.

Thermoregulation is impaired during anesthesia for cardiac surgery. Redistribution of body heat and heat loss to the environment result in mild hypothermia before cardiopulmonary bypass. Maintenance of normothermia, rather than hypothermia, may facilitate early tracheal extubation. Hypothermia alters the distribution and decreases the metabolism of most drugs, including anesthetic drugs and muscle relaxants, thus prolonging recovery. Postoperative shivering increases metabolic rate and potentially leads to myocardial ischemia; prevention is therefore critical to the success of early tracheal extubation after cardiac surgery. Coagulopathies, increased incidence of surgical wound infection, and perioperative cardiac morbidity are other potential risk factors identified in noncardiac patients. Hypothermia, however, does have potential benefits to the patient, including protection from cerebral ischemia and hypoxemia. Mild core hypothermia (approximately 34 degrees C) may represent the optimal balance between risks and benefits for fast-track patients.

Anesthesia Recovery Period↗
PubMed1997

Perioperative thermoregulation and heat balance.

In summary, both regional and general anesthesia markedly impair the normal precise regulation of core body temperature. Consequently, inadvertent perioperative hypothermia is common. Hypothermia develops because the typical operating room environment is cold; however, it is anesthetic-induced impairment of thermoregulatory responses that contributes most. Internal redistribution of body heat is a surprisingly important factor, contributing more to core hypothermia than net heat loss in most patients. There is now convincing evidence that a typical amount of intraoperative hypothermia, say 2 degrees C, predisposes numerous complications and alters patient outcome. Fortunately, effective methods are available for preventing hypothermia.

Anesthesia, General↗
PubMed1997

Isoflurane produces marked and nonlinear decreases in the vasoconstriction and shivering thresholds.

In summary, we present a new model for evaluating thermoregulatory effects of drug administration, pregnancy, illness, etc. Specifically, we experimentally manipulated both skin and core temperatures, and subsequently compensated for the changes in skin temperature using the relationships between skin and core contributions to thermoregulatory control. We thus were able to report our results for warm- and cold-responses in terms of calculated core-temperature thresholds at a single designated skin temperature. Advantages of this model include its being nearly noninvasive and requiring relatively little core temperature manipulation. Using this technique, we have shown that the shape and magnitude of thermoregulatory impairment produced by various anesthetic drugs differs. Propofol linearly increases the sweating threshold and linearly decreases the vasoconstriction and shivering threshold. In contrast, volatile anesthetics produce a nonlinear reduction in the major cold-response thresholds, reducing the vasoconstriction and shivering thresholds disproportionately at higher anesthetic concentrations. Midazolam not only produces a different magnitude of thermoregulatory impairment, but also a novel pattern of threshold changes. Anesthetic-induced thermoregulatory impairment thus depends both on anesthetic type and dose.

Anesthetics, Inhalation↗
PubMed1997

The effect of opioids on thermoregulatory responses in humans and the special antishivering action of meperidine.

In summary, both mu-receptor and combined mu/kappa-receptor opioids impair thermoregulatory control. Alfentanil, a pure mu-receptor agonist slightly increased the thresholds for sweating and markedly decreased the thresholds for vasoconstriction and shivering. However, the vasoconstriction-to-shivering range remained normal during alfentanil administration as it does during general anesthesia. Meperidine, a combined mu- and kappa-receptor agonist, also slightly increased the threshold for sweating and reduced the thresholds for vasoconstriction. However, meperidine reduced the shivering threshold twice as much as the vasoconstriction threshold, thus significantly increasing the vasoconstriction-to-shivering range. Furthermore, shivering during meperidine administration, once triggered, was of low intensity suggesting that the drug also decreased the gain of shivering. The special antishivering action of meperidine appears to result, at least in part, from its kappa-receptor activity.

Alfentanil↗
PubMed1997

Thermoregulatory vasoconstriction does not impede core warming during cutaneous heating.

Recent studies evaluating perioperative cutaneous-to-core heat transfer indicate that: Thermoregulatory vasoconstriction prevents further core cooling in anesthetized subjects during mild cooling. Thermoregulatory vasoconstriction only slightly decreases core cooling rates in anesthetized subjects during vigorous cooling. Thermoregulatory vasoconstriction does not impair vigorous core rewarming during anesthesia. Vigorous postanesthetic cutaneous warming increases core temperature much faster than passive insulation. Under conditions of mild thermal stress, thermoregulatory vasoconstriction is thus able to protect core temperature by reducing cutaneous heat transfer and functionally isolating the peripheral and core thermal compartment. Consequently, anesthetic-induced alterations in vasomotor tone is one of the major factors influencing core temperature in patients who are not actively cooled or warmed. In contrast, thermoregulatory tone is insufficient to prevent core temperature perturbations in patients undergoing vigorous cutaneous cooling or warming.

Body Temperature Regulation↗
PubMed1997

Comparison of distal oesophageal temperature with "deep" and tracheal temperatures.

PURPOSE: To compare distal oesophageal (reference) temperature with "deep-sternal," "deep-forehead," and tracheal temperatures, establishing the accuracy and precision of each. METHODS: We studied 20 patients undergoing general anaesthesia for gynaecological surgery. Their lungs were mechanically ventilated with a circle system, at a fresh-gas flow rate of 6 L.min-1 Respiratory gases were not warmed or humidified. Tracheal temperatures were recorded from a Trachelon tube inserted approximately 21 cm. Deep-body temperatures were measured at the sternum and forehead using a Coretemp thermometer. The principle of the method is to null thermal flux through a cutaneous disk, thus obliterating thermal gradients between the sides of the disk, skin surface, and subcutaneous tissues. Distal oesophageal temperatures were measured from thermocouples incorporated into oesophageal stethoscopes. Tracheal and deep-tissue temperatures were compared with oesophageal temperature using regression and Bland and Altman analyses. RESULTS: Tracheal, sternal, and forehead temperatures correlated similarly with distal oesophageal temperature, correlation coefficients (r2) being 0.7 in each case. The offset (oesophageal temperature minus study site) was considerably larger for tracheal temperature (0.7 degree C) than for the other sites (0.2 degree C). However, the precision was only 0.3 degree C at each site. CONCLUSION: Our data suggest that tracheal temperatures may not be an adequate substitute for conventional core-temperature monitoring sites. In contrast, the accuracy and precision of deep-tissue temperature monitoring at the sternum and forehead was sufficient for clinical use.

Anesthesia, General↗
PubMed1997

Late intraoperative clonidine administration prevents postanesthetic shivering after total intravenous or volatile anesthesia.

Postoperative administration of clonidine is an effective treatment for shivering. However, the ability of this drug to stop postanesthetic shivering when administered intraoperatively remains controversial. Furthermore, the relative efficacy of clonidine during isoflurane and propofol anesthesia remains unknown. We therefore evaluated the incidence of postanesthetic shivering in patients given clonidine during nitrous oxide/isoflurane or propofol anesthesia. Because clonidine is an analgesic, we also evaluated postoperative pain and analgesic requirements. We studied 60 patients undergoing elective ear or nose surgery. General anesthesia was induced with 2.0 mg/kg propofol, 1.5 micrograms/kg fentanyl, and 0.1 mg/kg vecuronium. General anesthesia was maintained with isoflurane and 70% nitrous oxide in one group of patients; in the other, a continuous infusion of propofol (8 mg.kg-1.h-1) was administered (without nitrous oxide). Five minutes before tracheal extubation, patients in each group were randomly assigned to receive saline, placebo, or 3 micrograms/kg clonidine intravenously. Postanesthetic shivering was evaluated by a blind investigator. Postoperative pain was assessed using a visual analog scale. Postoperative shivering was observed in 53% of the patients given isoflurane without clonidine and in 13% of the patients given propofol without clonidine. No patient given clonidine shivered. Clonidine administration significantly reduced postoperative pain. The incidence of postanesthetic shivering was significantly less after propofol anesthesia than after isoflurane/nitrous oxide anesthesia. However, a late intraoperative bolus administration of 3 micrograms/kg clonidine prevents postoperative shivering in patients given either type of anesthesia.

Adult↗
PubMed1997

The threshold for thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is reduced in the elderly.

Elderly patients become more hypothermic during surgery, shiver less postoperatively, and take longer to rewarm than younger patients. Similarly, the vasoconstriction threshold (triggering core temperature) is reduced approximately 1 degree C in elderly patients during nitrous oxide/isoflurane anesthesia. Accordingly, we tested the hypothesis that the vasoconstriction threshold in the elderly is also reduced approximately 1 degree C during nitrous oxide and sevoflurane anesthesia. Eleven young patients aged 30-50 yr and 14 elderly patients aged 60-80 yr were anesthetized with nitrous oxide (50%) and sevoflurane (1%). Mean skin temperature was calculated from four sites. Fingertip blood flow was estimated using forearm minus fingertip skin-temperature gradients, with a gradient of 0 degree C identifying onset of vasoconstriction. The distal esophageal temperature triggering onset of vasoconstriction identified the threshold for this thermoregulatory defense. The data from five patients who did not vasoconstrict at minimum core temperatures of 33-34 degrees C were eliminated, leaving 10 patients in each group. The vasoconstriction threshold was significantly less in the elderly (35.0 +/- 0.8 degrees C) than in younger patients (35.8 +/- 0.3 degrees C), despite similar mean skin temperatures (mean +/- SD, P < 0.01, Student's t-test). Age dependence of thermoregulatory vasoconstriction during nitrous oxide/sevoflurane anesthesia is similar to that previously observed during nitrous oxide/isoflurane anesthesia.

Adult↗
PubMed1997

The arterial blood propofol concentration preventing movement in 50% of healthy women after skin incision.

To target appropriate drug concentrations and to facilitate comparisons between drugs, the potency of propofol must be firmly established. We therefore determined the arterial blood propofol concentration preventing movement in 50% of patients after skin incision and the ability of arterial blood pressure and heart rate to predict movement after incision. Fifteen healthy women scheduled for breast surgery were randomly assigned to computer-targeted propofol blood concentrations. No other drugs were administered. Fifteen minutes after starting the propofol infusion, a 5-cm skin incision was made. Patients were observed for gross purposeful movement for 1 min. Arterial blood was sampled for propofol to confirm steady-state blood concentrations. Arterial blood pressure and heart rate were measured noninvasively. Logistic regression was used to calculate the propofol blood concentrations and arterial blood pressures at which 50% and 95% of patients did not move after skin incision (CP50 and CP95, MABP50 and MABP95, respectively). The CP50 and CP95 values for propofol were 14.3 +/- 1.6 microg/mL (mean +/- SE) and 20.6 microg/mL, respectively. The MABP50 and MABP95 values were 63 +/- 4 mm Hg and 43 mm Hg, respectively. Heart rate did not differ significantly in patients who moved and who did not move. Propofol blood concentrations required to prevent movement in most patients resulted in significant arterial hypotension.

Adult↗
PubMed1997

Thermoregulatory vasodilation increases the venous partial pressure of oxygen.

UNLABELLED: Thermoregulatory arteriovenous shunt vasoconstriction may facilitate deep-vein thrombosis by producing relative venous stasis and hypoxia. Accordingly, we evaluated the effect of vasomotion on leg blood flow and venous oxygen tension. We studied five male volunteers, each of whom was warmed enough to trigger vasodilation and then cooled sufficiently to provoke thermoregulatory vasoconstriction. The process was then repeated during N2O/desflurane anesthesia. Venous oxygen tension and saturation (with a fraction of inspired oxygen of 1.0) were evaluated in blood samples taken from a catheter that was inserted into a saphenous vein at the ankle and advanced until the tip was proximal to the knee. Thermoregulatory vasodilation with or without general anesthesia significantly increased arteriovenous shunt flow by approximately 10-fold, and increased total leg flow approximately sixfold. However, vasodilated flows were similar with and without general anesthesia, as were vasoconstricted flows. Before induction of anesthesia, thermoregulatory vasodilation increased venous oxygen tension from 46 +/- 6 to 187 +/- 99 mm Hg and venous saturation from 79% +/- 6% to 99% +/- 2%. After induction of anesthesia, thermoregulatory vasodilation increased venous oxygen tension from 55 +/- 11 to 356 +/- 103 mm Hg and venous saturation from 84% +/- 8% to 100% +/- 0%. Our data thus indicate that thermoregulatory vasodilation markedly increases both leg flow and venous oxygenation; and that both factors may help prevent perioperative venous thrombosis. IMPLICATIONS: Thermoregulatory arteriovenous shunt vasoconstriction may facilitate deep-vein thrombosis by producing related venous stasis and hypoxia. In male volunteers, the authors found that when vasodilation induced by warming was produced, both blood flow and venous oxygenation increased, both of which may help prevent perioperative venous thrombosis.

Adult↗
PubMed1997

Postanesthetic vasoconstriction slows peripheral-to-core transfer of cutaneous heat, thereby isolating the core thermal compartment.

UNLABELLED: Forced-air warming during anesthesia increases core temperature comparably with and without thermoregulatory vasoconstriction. In contrast, postoperative forced-air warming may be no more effective than passive insulation. Nonthermoregulatory anesthesia-induced vasodilation may thus influence heat transfer. We compared postanesthetic core rewarming rates in volunteers given cotton blankets or forced air. Additionally, we compared increases in peripheral and core heat contents in the postanesthetic period with data previously acquired during anesthesia to determine how much vasomotion alters intercompartmental heat transfer. Six men were anesthetized and cooled passively until their core temperatures reached 34 degrees C. Anesthesia was then discontinued, and shivering was prevented by giving meperidine. On one day, the volunteers were covered with warmed blankets for 2 h; on the other, volunteers were warmed with forced air. Peripheral tissue heat contents were determined from intramuscular and skin thermocouples. Predicted changes in core temperature were calculated assuming that increases in body heat content were evenly distributed. Predicted changes were thus those that would be expected if vasomotor activity did not impair peripheral-to-core transfer of applied heat. These results were compared with those obtained previously in a similar study of anesthetized volunteers. Body heat content increased 159 +/- 35 kcal (mean +/- SD) more during forced-air than during blanket warming (P < 0.001). Both peripheral and core temperatures increased significantly faster during active warming: 3.3 +/- 0.7 degrees C and 1.1 +/- 0.4 degrees C, respectively. Nonetheless, predicted core temperature increase during forced-air warming exceeded the actual temperature increase by 0.8 +/- 0.3 degree C (P < 0.001). Vasoconstriction thus isolated core tissues from heat applied to the periphery, with the result that core heat content increased 32 +/- 12 kcal less than expected after 2 h of forced-air warming (P < 0.001). In contrast, predicted and actual core temperatures differed only slightly in the anesthetized volunteers previously studied. In contrast to four previous studies, our results indicate that forced-air warming increases core temperature faster than warm blankets. Postanesthetic vasoconstriction nonetheless impeded peripheral-to-core heat transfer, with the result that core temperatures in the two groups differed less than might be expected based on systemic heat balance estimates. IMPLICATIONS: Comparing intercompartmental heat flow in our previous and current studies suggests that anesthetic-induced vasodilation influences intercompartmental heat transfer and distribution of body heat more than thermoregulatory shunt vasomotion.

Adult↗
PubMed1997

Time-dependent changes in heart rate and pupil size during desflurane or sevoflurane anesthesia.

UNLABELLED: To better characterize alterations in autonomic function associated with prolonged anesthesia, we tested the hypothesis that the time-dependent effects of sevoflurane and desflurane differ. We studied seven male volunteers, each anesthetized for 8 h with 1.25 minimum alveolar anesthetic concentration desflurane on one study day and with 8 h sevoflurane on another. These volunteers did not undergo surgery and were minimally stimulated during the study. Measurements included blood pressure, heart rate, pupillary size and light reactivity, concentrations of serum catecholamines, and carbon dioxide production. Over time, heart rate and pupil size increased significantly. During 6 of the 14 anesthetics (45%), heart rate at some point exceeded 95 bpm; similarly, pupil size at some time exceeded 5 mm during 8 anesthetics (57%). In contrast, plasma catecholamine concentrations and carbon dioxide production remained unchanged, and blood pressure remained nearly constant. There are thus substantial time-dependent changes in autonomic functions during prolonged anesthesia, even in unstimulated, nonsurgical volunteers, but we could not detect a difference in these changes during desflurane compared with sevoflurane anesthesia. IMPLICATIONS: Pupil size and heart rate changes are used to guide the delivery of anesthesia. In volunteers, pupil size and heart rate increased with increasing duration of constant desflurane or sevoflurane anesthesia. Thus, anesthetic duration alters heart rate and pupil size independent of surgery and changes in anesthetic delivery.

Anesthesia, Inhalation↗
PubMed1997

Influence of thermoregulatory vasomotion and ambient temperature variation on the accuracy of core-temperature estimates by cutaneous liquid-crystal thermometers.

BACKGROUND: Recently, liquid crystal skin-surface thermometers have become popular for intraoperative temperature monitoring. Three situations during which cutaneous liquid-crystal thermometry may poorly estimate core temperature were monitored: (1) anesthetic induction with consequent core-to-peripheral redistribution of body heat, (2) thermoregulatory vasomotion associated with sweating (precapillary dilation) and shivering (minimal capillary flow), and (3) ambient temperature variation over the clinical range from 18-26 degrees C. METHODS: The core-to-forehead and core-to-neck temperature difference was measured using liquid-crystal thermometers having an approximately 2 degrees C offset. Differences exceeding 0.5 degree C (a 1 degree C) temperature range) were a priori deemed potentially clinically important. Seven volunteers participated in each protocol. First, core-to-peripheral redistribution of body heat was produced by inducing propofol/desflurane anesthesia; anesthesia was then maintained for 1 h with desflurane. Second, vasodilation was produced by warming unanesthetized volunteers sufficiently to produce sweating; intense vasoconstriction was similarly produced by cooling the volunteers sufficiently to produce shivering. Third, a canopy was positioned to enclose the head, neck, and upper chest of unanesthetized volunteers. Air within the canopy was randomly set to 18, 20, 22, 24, and 26 degrees C. RESULTS: Redistribution of body heat accompanying induction of anesthesia had little effect on the core-to-forehead skin temperature difference. However, the core-to-neck skin temperature gradient decreased approximately 0.6 degree C in the hour after induction of anesthesia. Vasomotion associated with shivering and mild sweating altered the core-to-skin temperature difference only a few tenths of a degree centigrade. The absolute value of the core-to-forehead temperature difference exceeded 0.5 degree C during approximately 35% of the measurements, but the difference rarely exceeded 1 degree C. The core-to-neck temperature difference typically exceeded 0.5 degree C and frequently exceeded 1 degree C. Each 1 degree C increase in ambient temperature decreased the core-to-fore-head and core-to-neck skin temperature differences by less than 0.2 degree C. CONCLUSIONS: Forehead skin temperatures were better than neck skin temperature at estimating core temperature. Core-to-neck temperature differences frequently exceeded 1 degree C (a 2 degrees C range), whereas two thirds of the core-to-forehead differences were within 0.5 degree C. The core-to-skin temperature differences were, however, only slightly altered by inducing anesthesia, vasomotor action, and typical intraoperative changes in ambient temperature.

Adult↗
PubMed1997

Lack of nonshivering thermogenesis in infants anesthetized with fentanyl and propofol.

BACKGROUND: Sweating, vasoconstriction, and shivering have been observed during general anesthesia. Among these, vasoconstriction is especially important because-once triggered-it minimizes further hypothermia. Surprisingly, the core-temperature plateau associated with vasoconstriction appears to preserve core temperature better in infants and children than adults. This observation suggests that vasoconstriction in anesthetized infants may be accompanied by hypermetabolism. Consistent with this theory, unanesthetized infants rely on nonshivering thermogenesis to double heat production when vasoconstriction alone is insufficient. Accordingly, the authors tested the hypothesis that intraoperative core hypothermia triggers nonshivering thermogenesis in infants. METHODS: With Ethics Committee approval and written parental consent, the authors studied six infants undergoing abdominal surgery. All were aged 1 day to 9 months and weighed 2.4-9 kg. Anesthesia was maintained with propofol and fentanyl. The infants were mechanically ventilated and allowed to cool passively until core (distal esophageal) temperatures reached 34-34.5 degrees C. Oxygen consumption-the authors' index of metabolic rate-was recorded throughout cooling. Because nonshivering thermogenesis triples circulating norepinephrine concentrations, arterial blood was analyzed for plasma catecholamines at approximately 0.5 degree C intervals. Thermoregulatory vasoconstriction was evaluated using forearm-fingertip, skin-surface gradients, with gradients exceeding 4 degrees C, indicating intense vasoconstriction. The patients were subsequently rapidly rewarmed to 37 degrees C. Regression analysis was used to correlate changes in oxygen consumption and plasma catecholamine concentrations with core temperature. RESULTS: All patients were vasoconstricted by the time core temperature reached 36 degrees C. Further reduction in core temperature to 34-34.5 degrees C did not increase oxygen consumption. Instead, oxygen consumption decreased linearly. Hypothermia also failed to increase plasma catecholamine concentrations. CONCLUSIONS: Even at core temperatures approximately 2 degrees C below the vasoconstriction threshold, there was no evidence of nonshivering thermogenesis. This finding is surprising because all other major thermoregulatory responses have been detected during anesthesia. Infants and children thus appear similar to adults in being unable to increase metabolic rate in response to mild intraoperative hypothermia.

Adipose Tissue, Brown↗