A graph neural network framework for causal inference in brain networks.

A central question in neuroscience is how self-organizing dynamic interactions in the brain emerge on their relatively static structural backbone. Due to the complexity of spatial and temporal dependencies between different brain areas, fully comprehending the interplay between structure and function is still challenging and an area of intense research. In this paper we present a graph neural network (GNN) framework, to describe functional interactions based on the structural anatomical layout. A GNN allows us to process graph-structured spatio-temporal signals, providing a possibility to combine structural information derived from diffusion tensor imaging (DTI) with temporal neural activity profiles, like that observed in functional magnetic resonance imaging (fMRI). Moreover, dynamic interactions between different brain regions discovered by this data-driven approach can provide a multi-modal measure of causal connectivity strength. We assess the proposed model's accuracy by evaluating its capabilities to replicate empirically observed neural activation profiles, and compare the performance to those of a vector auto regression (VAR), like that typically used in Granger causality. We show that GNNs are able to capture long-term dependencies in data and also computationally scale up to the analysis of large-scale networks. Finally we confirm that features learned by a GNN can generalize across MRI scanner types and acquisition protocols, by demonstrating that the performance on small datasets can be improved by pre-training the GNN on data from an earlier study. We conclude that the proposed multi-modal GNN framework can provide a novel perspective on the structure-function relationship in the brain. Accordingly this approach appears to be promising for the characterization of the information flow in brain networks.

Autologous blood salvage in the era of patient blood management.

Almost 150 years after the first autologous blood transfusion was reported, intraoperative blood salvage has become an important method of blood conservation. The primary goal of autologous transfusion is to reduce or avoid allogeneic red blood cell transfusion and the associated risks and costs. Autologous salvaged blood does not result in immunological challenge and its consequences, provides a higher quality red blood cell that has not been subjected to the adverse effects of blood storage, and can be more cost-effective than allogeneic blood when used for carefully selected surgical patients. Cardiac, orthopaedic and vascular surgery procedures with large anticipated blood loss can clearly benefit from the use of cell salvage. There are safety concerns in cases with gross bacterial contamination. There are theoretical safety concerns in obstetrical and cancer surgery; however, careful cell washing as well as leucoreduction filters makes for a safer autologous transfusion in these circumstances. Further studies are needed to determine whether oncologic outcomes are impacted by transfusing salvaged blood during cancer surgery. In this new era of patient blood management, where multimodal methods of reducing dependence on allogeneic blood are becoming commonplace, autologous blood salvage remains a valuable tool for perioperative blood conservation. Future studies will be needed to best determine how and when cell salvage should be utilized along with newer blood conservation measures.

Nomogram to predict perioperative blood transfusion for hepatopancreaticobiliary and colorectal surgery.

BACKGROUND: Predictive tools assessing risk of transfusion have not been evaluated extensively among patients undergoing complex gastrointestinal surgery. In this study preoperative variables associated with blood transfusion were incorporated into a nomogram to predict transfusion following hepatopancreaticobiliary (HPB) or colorectal surgery. METHODS: A nomogram to predict receipt of perioperative transfusion was developed using a cohort of patients who underwent HPB or colorectal surgery between January 2009 and December 2014. The discriminatory ability of the nomogram was tested using the area under the receiver operating characteristic (ROC) curve and internal validation performed via bootstrap resampling. RESULTS: Among 4961 patients undergoing either a HPB (56·3 per cent) or colorectal (43·7 per cent) resection, a total of 1549 received at least 1 unit of packed red blood cells, giving a perioperative transfusion rate of 31·2 per cent. On multivariable analysis, age 65 years and over (odds ratio (OR) 1·52), race (versus white: black, OR 1·58; Asian, OR 1·86), preoperative haemoglobin 8·0 g/dl or less (versus over 12·0 g/dl: OR 26·79), preoperative international normalized ratio more than 1·2 (OR 2·44), Charlson co-morbidity index score over 3 (OR 1·86) and procedure type (versus colonic surgery: major hepatectomy, OR 1·71; other pancreatectomy, OR 2·12; rectal surgery, OR 1·39; duodenopancreatectomy, OR 2·65) were associated with a significantly higher risk of transfusion and were included in the nomogram. A nomogram was constructed to predict transfusion using these seven variables. Discrimination and calibration of the nomogram revealed good predictive abilities (area under ROC curve 0·756). CONCLUSION: The nomogram predicted blood transfusion in major HPB and colorectal surgery.

Variation in triggers and use of perioperative blood transfusion in major gastrointestinal surgery.

BACKGROUND: The decision to perform intraoperative blood transfusion is subject to a variety of clinical and laboratory factors. This study examined variation in haemoglobin (Hb) triggers and overall utilization of intraoperative blood transfusion, as well the impact of transfusion on perioperative outcomes. METHODS: The study included all patients who underwent pancreatic, hepatic or colorectal resection between 2010 and 2013 at Johns Hopkins Hospital, Baltimore, Maryland. Data on Hb levels that triggered an intraoperative or postoperative transfusion and overall perioperative blood utilization were obtained and analysed. RESULTS: Intraoperative transfusion was employed in 437 (15·6 per cent) of the 2806 patients identified. Older patients (odds ratio (OR) 1·68), patients with multiple co-morbidities (Charlson co-morbidity score 4 or above; OR 1·66) and those with a lower preoperative Hb level (OR 4·95) were at increased risk of intraoperative blood transfusion (all P < 0·001). The Hb level employed to trigger transfusion varied by sex, race and service (all P < 0·001). A total of 105 patients (24·0 per cent of patients transfused) had an intraoperative transfusion with a liberal Hb trigger (10 g/dl or more); the majority of these patients (78; 74·3 per cent) did not require any additional postoperative transfusion. Patients who received an intraoperative transfusion were at greater risk of perioperative complications (OR 1·55; P = 0·002), although patients transfused with a restrictive Hb trigger (less than 10 g/dl) showed no increased risk of perioperative morbidity compared with those transfused with a liberal Hb trigger (OR 1·22; P = 0·514). CONCLUSION: Use of perioperative blood transfusion varies among surgeons and type of operation. Nearly one in four patients received a blood transfusion with a liberal intraoperative transfusion Hb trigger of 10 g/dl or more. Intraoperative blood transfusion was associated with higher risk of perioperative morbidity.

The wisdom of the body revisited: the adrenomedullary response to mild core hypothermia in humans.

OBJECTIVE: In the 1920s, Walter B. Cannon first described the adrenomedullary response to cold, using an ingenious in vivo bioassay based on a denervated heart preparation. Studies in humans about antecubital venous plasma concentrations of norepinephrine, the sympathetic neurotransmitter, and of epinephrine, the main adrenomedullary hormone, have suggested sympathetic nervous system activation without adrenomedullary activation. The present study used arterial levels of these catecholamines, to determine whether adrenomedullary stimulation occurs in response to decreased body temperature. METHODS: Eleven healthy volunteers underwent central intravenous infusion of warm (37 degreeC) physiological saline, followed by infusion of the same volume of cold (4 degreeC) saline. Brachial arterial and antecubital venous plasma concentrations of norepinephrine and epinephrine were measured by liquid chromatography with electrochemical detection. RESULTS: Antecubital venous concentrations of norepinephrine increased markedly during cold saline infusion, with smaller and statistically borderline increases in concentrations of epinephrine. In contrast, concurrently obtained arterial concentrations of both norepinephrine and epinephrine increased significantly. CONCLUSIONS: The results confirm Cannon's original inference that cold evokes adrenomedullary activation. Prior studies about antecubital venous levels of catecholamines did not take into account the local hemodynamic effects of cold, which would increase extraction of circulating catecholamines and underestimate the arterial epinephrine response.

Warmed humidified inspired oxygen accelerates postoperative rewarming.

STUDY OBJECTIVE: To investigate the efficacy of warmed, humidified inspired oxygen (O(2)) for the treatment of mildly hypothermic postoperative patients. DESIGN: Prospective, randomized, unblinded clinical trial. SETTING: Postanesthesia care unit in a tertiary care hospital. PATIENTS AND INTERVENTIONS: 30 ASA physical status I, II, and III patients following intraabdominal surgical procedures were randomly assigned to receive either routine O(2) therapy (control group, n = 15), or warmed (42 degrees C) humidified O(2) (treatment group, n = 15) for the initial 90 postoperative minutes. MEASUREMENTS: Core (tympanic) temperature, dry mouth score and shivering score. MAIN RESULTS: Tympanic temperature was similar in both groups on admission ( approximately 35.8 degrees C). Rewarming rate in the first postoperative hour was greater in the treatment group (0.7 +/- 0.1 degrees C. hr(-1)) compared to the control group (0.4 +/- 0.1 degrees C. hr(-1)) (p = 0.03). Patients receiving the warmed, humidified O(2) had a lower incidence of dry mouth compared to the control group (p = 0.03). The incidence of shivering was low and similar in both groups. CONCLUSIONS: Warming and humidifying inspired O(2) hastens recovery from hypothermia in postoperative patients.

Age-related thermoregulatory differences during core cooling in humans.

The current study assessed sympathetic neuronal and vasomotor responses, total body oxygen consumption, and sensory thermal perception to identify thermoregulatory differences in younger and older human subjects during core cooling. Cold fluid (40 ml/kg, 4 degrees C) was given intravenously over 30 min to decrease core temperature (Tc) in eight younger (age 18-23) and eight older (age 55-71) individuals. Compared with younger subjects, the older subjects had significantly lower Tc thresholds for vasoconstriction (35.5 +/- 0.3 vs. 36.2 +/- 0.2 degrees C, P = 0.03), heat production (35.2 +/- 0.4 vs. 35.9 +/- 0.1 degrees C, P = 0.04), and plasma norepinephrine (NE) responses (35.0 vs. 36.0 degrees C, P < 0.05). Despite a lower Tc nadir during cooling, the maximum intensities of the vasoconstriction (P = 0.03) and heat production (P = 0.006) responses were less in the older compared with the younger subjects, whereas subjective thermal comfort scores were similar. Plasma NE concentrations increased fourfold in the younger but only twofold in the older subjects at maximal Tc cooling. The vasomotor response for a given change in plasma NE concentration was decreased in the older group (P = 0.01). In summary, aging is associated with 1) a decreased Tc threshold and maximum response intensity for vasoconstriction, total body oxygen consumption, and NE release, 2) decreased vasomotor responsiveness to NE, and 3) decreased subjective sensory thermal perception.

Determinants of core temperature at the time of admission to intensive care following cardiac surgery.

OBJECTIVE: To determine the predictors of core temperature on arrival in the intensive care unit (ICU) after cardiac surgery. DESIGN: Prospective, randomized trial. SETTING: Tertiary care medical center, operating rooms (ORs), and ICU. PATIENTS: 72 patients presenting for coronary artery bypass surgery. INTERVENTIONS: Randomized assignment for ambient OR temperature (16-18 degrees C vs. 21-23 degrees C) and rewarming endpoint on cardiopulmonary bypass (CPB; nasopharyngeal and urinary bladder temperatures >/=36.5 degrees C and 34.0 degrees C, respectively, vs. nasopharyngeal and urinary bladder temperatures >/=37.5 degrees C and 36.0 degrees C, respectively) at the time of separation from bypass. MEASUREMENTS AND MAIN RESULTS: The best (and only significant) predictor of core temperature on arrival in the ICU was rewarming endpoint at the time of separation from CPB (p = 0.004). Patient weight, height, body habitus, and nitroprusside administration did not significantly predict core temperature. Ambient temperature affected only body temperature when the duration of time in the OR after separation from bypass was prolonged (>90 min). A weighted average body temperature was a better predictor of complete rewarming than was any single monitoring site. CONCLUSIONS: To reduce the incidence of hypothermia after cardiac surgery, the most important variable is rewarming endpoint achieved before separation from bypass. A warm ambient temperature (>21 degrees C) may be beneficial if the duration of time in the OR after bypass is prolonged (>90 min).

Lumbar sympathetic block for sympathetically maintained pain: changes in cutaneous temperatures and pain perception.

UNLABELLED: Lumbar sympathetic block (LSB) is used in the management of sympathetically maintained pain states. We characterized cutaneous temperature changes over the lower extremities after LSB. Additionally, we examined the effects of iohexol, a radio-opaque contrast medium, on temperature changes and pain relief. After institutional review board approval and written, informed consent, 28 LSBs were studied in 17 patients. Iohexol or normal saline was injected in a randomized, double-blinded fashion before bupivacaine. Lower extremity cutaneous temperatures were measured. Pain, allodynia, interference with daily function, and perceived pain relief were reported in a subset of 15 LSBs for 1 wk after the block. The distal lower extremity ipsilateral to the LSB had the greatest magnitude (8.7 degrees +/- 0.8 degrees C) and rate (1.1 degrees +/- 0.2 degrees C/min) of temperature change. The great toe temperature was within 3 degrees C of core temperature within 35 min after LSB. There were no differences in temperature change between the groups. The iohexol group had greater relief of pain until the morning of the first postblock day (P = 0.002) and longer perceived relief of pain (P = 0.01). The maximum temperature of the great toe correlated with allodynia relief (P = 0.0007). Thus clinicians should expect ipsilateral toe temperatures to increase to within approximately 3 degrees C of core temperature. Iohexol does not alter the efficacy of LSB and may improve relief of symptoms. The magnitude of temperature change may predict relief of allodynia. IMPLICATIONS: Cutaneous toe temperatures approaching core temperature provide a useful monitor of lumbar sympathetic block and may predict relief of sympathetically maintained pain. Iohexol will not compromise temperature changes or pain relief.

Predictors of hypothermia during spinal anesthesia.

BACKGROUND: Body temperature often is ignored during regional anesthesia, despite evidence that hypothermia occurs commonly. Because hypothermia is associated with adverse clinical outcomes, it is important to recognize predictors of hypothermia and to monitor and control body temperature in patients at risk. The current study was designed to determine the predictors of core hypothermia in patients receiving spinal anesthesia for radical retropubic prostatectomy. METHODS: Forty-four patients undergoing radical retropubic prostatectomy were studied. A lumbar intrathecal injection of 18-22 mg bupivacaine, 0.75%, with 20 microg fentanyl was given. No active warming measures were used other than intravenous fluid warming. The following clinical variables were assessed as potential predictors of core (tympanic) temperature at admission to the postanesthesia care unit: duration of surgery, average ambient operating room temperature, body habitus, age, and spinal blockade level. RESULTS: The mean core temperature at admission to the postanesthesia care unit was 35.1 +/- 0.6 degrees C (range, 33.6-36.3 degrees C). Duration of surgery, ambient operating room temperature, and body habitus were not predictors of hypothermia. A high level of spinal blockade and increasing age were predictors of hypothermia. For each incremental increase in block level, core temperature decreased by 0.15 degrees C, and for each increase in age, core temperature decreased by 0.3 degrees C. CONCLUSIONS: Although high-level spinal blockade has been associated with decreased thermoregulatory thresholds, no previous study has shown that a higher level of blockade is associated with a greater magnitude of core hypothermia in the clinical setting. As with general anesthesia, advanced age is associated with hypothermia during spinal anesthesia.

The accuracy and precision of body temperature monitoring methods during regional and general anesthesia.

UNLABELLED: We tested the hypotheses that accuracy and precision of available temperature monitoring methods are different between spinal anesthesia (SA) and general anesthesia (GA), and that patients receiving SA are at equal risk for hypothermia as those receiving GA. Patients scheduled for radical retropubic prostatectomy were enrolled. Either GA (n = 16) or SA (n = 16) was given according to patient and clinician preference. Temperatures were monitored with thermocouple probes at the tympanic membrane, axilla, rectum, and forehead skin surface. Tympanic temperatures were also measured with an infrared device, and forehead skin temperatures were monitored with two brands of liquid crystal thermometer strips. Accuracy and precision of these monitoring methods were determined by using tympanic membrane temperature, measured by thermocouple, as the reference core temperature (T(c)). At the end of surgery, T(c) was similar between SA (35.0 +/- 0.1 degrees C) and GA (35.2 +/- 0.1 degrees C) (P = 0.44). Accuracy and precision of each temperature monitoring method were similar between SA and GA. Rectal temperature monitoring offered the greatest combination of accuracy and precision. All other methods underestimated T(c). These findings suggest that patients receiving SA or GA are at equal and significant risk for hypothermia, and should have their temperatures carefully monitored, recognizing that most monitoring methods underestimate T(c). IMPLICATIONS: Body temperature should be monitored during spinal anesthesia because patients are at significant risk for hypothermia. Rectal temperature is a valid method of measuring core temperature, whereas other methods tend to underestimate true core temperature.

Age-related thermoregulatory differences in a warm operating room environment (approximately 26 degrees C).

UNLABELLED: Inadvertent hypothermia occurs frequently at typical ambient operating room (OR) temperatures, especially in elderly patients receiving general anesthesia. The aims of the current study were to 1) determine the incidence and magnitude of core hypothermia in an unusually warm OR environment, and 2) to assess age-related differences in perioperative thermoregulatory responses under these circumstances. Forty patients receiving general anesthesia for orthopedic surgical procedures (20 younger patients, 20-40 yr old) and (20 older patients, 60-75 yr old) were enrolled. Mean ambient temperature in the ORs was 25.8 degrees +/- 0.2 degrees C. Core temperature, vasoconstriction, and shivering were compared in the younger and older age groups. Mean core temperature on admission to the postanesthesia care unit was not significantly different in the younger (36.7 degrees +/- 0.1 degrees C) and older (36.4 degrees +/- 0.1 degrees C) age groups. Only 10% of patients (n = 4, 1 younger, 3 older) were admitted with a core temperature <36.0 degrees C. Only 2% of patients (n = 1, older group) had a core temperature <35.5 degrees C. This very mild degree of hypothermia was associated with postoperative vasoconstriction in 80% of the younger and 55% of the older patients (P = 0.18). Postoperative shivering occurred in 40% of the younger patients and in 10% of the older patients (P = 0.06). In summary, an ambient OR temperature near 26 degrees C (79 degrees F) is effective in preventing core hypothermia during general anesthesia regardless of patient age. Even very mild postoperative hypothermia may initiate thermoregulatory responses. IMPLICATIONS: By increasing ambient temperature in the operating room to 26 degrees C (79 degrees F), the incidence of core hypothermia can be dramatically reduced in both younger and older patients.

Heart rate variability as a predictor of autonomic dysfunction in patients awaiting liver transplantation.

Chronic liver disease, both alcoholic and nonalcoholic, has been shown to be associated with autonomic neuropathy, as well as other hemodynamic and circulatory disturbances. In a longitudinal study, the presence of autonomic neuropathy and the severity of liver disease were independent risk factors for mortality. The aim of this study was to determine whether the severity of liver disease correlated with measures of heart rate variability. We studied 21 patients being evaluated for liver transplantation to determine if severity of disease correlated with heart rate variability and compared them to seven healthy controls. Heart rate variability was determined for a series of 500 consecutive R-R intervals during quiet breathing. Standard deviation, pNN50, a marker of parasympathetic function, and approximate entropy (ApEn), a recently described measure of regularity, were calculated. Four standard tests of autonomic function were also performed. pNN50 was significantly reduced in all liver disease patients compared to controls (P < 0.05). Both standard deviation and ApEn were significantly reduced in Child's class C patients suggesting a generalized dysfunction in cardiovascular homeostasis. ApEn was significantly lower in the nonsurvivors during follow-up than the survivors (P < 0.05). In conclusion, increasing severity of liver failure is associated with a reduction in total heart rate variability and regularity. Measurement of heart rate variability offers a simple, noninvasive means of assessing the cardiovascular and autonomic effects of liver disease, particularly in those awaiting liver transplantation.

Forced-air warming decreases vasodilator requirement after coronary artery bypass surgery.

Postoperative hypothermia is common and associated with adverse hemodynamic consequences, including adrenergically mediated systemic vasoconstriction and hypertension. Hypothermia is also a known predictor of dysrhythmias and myocardial ischemia in high-risk patients. We describe a prospective, randomized trial designed to test the hypothesis that forced-air warming (FAW) provides improved hemodynamic variables after coronary artery bypass graft. After institutional review board approval and written informed consent, 149 patients undergoing coronary artery bypass graft were randomized to receive postoperative warming with either FAW (n = 81) or a circulating water mattress (n = 68). Core temperature was measured at the tympanic membrane. A weighted mean skin temperature was calculated. Heart rate, mean arterial blood pressure, central venous pressure, cardiac output, and systemic vascular resistance were monitored for 22 h postoperatively. Mean arterial blood pressure was maintained by protocol between 70 and 80 mm Hg by titration of nitroglycerin and sodium nitroprusside. The two groups had similar demographic characteristics. Tympanic and mean skin temperatures were similar between groups on intensive care unit admission. During postoperative rewarming, tympanic temperature was similar between groups, but mean skin temperature was significantly greater in the FAW group (P < 0.05). Heart rate, mean arterial pressure, central venous pressure, cardiac output, and systemic vascular resistance were similar for the two groups. The percent of patients requiring nitroprusside to achieve the hemodynamic goals was less (P < 0.05) in the FAW group. In conclusion, aggressive cutaneous warming with FAW results in a higher mean skin temperature and a decreased requirement for vasodilator therapy in hypothermic patients after cardiac surgery. This most likely reflects attenuation of the adrenergic response or opening of cutaneous vascular beds as a result of surface warming. IMPLICATIONS Forced-air warming after cardiac surgery decreases the requirement for vasodilator drugs and may be beneficial in maintaining hemodynamic variables within predefined limits.

Elevated thermostatic setpoint in postoperative patients.

BACKGROUND: The mechanism and clinical relevance of increased core temperature (Tc) after surgery are poorly understood. Because fever is used as a diagnostic sign of infection, it is important to recognize what constitutes the normal postoperative thermoregulatory response. In the current study the authors tested the hypothesis that a regulated increase in Tc setpoint occurs after surgery. METHODS: The authors prospectively studied 271 patients in the first 24 h after a variety of vascular, abdominal, and thoracic surgical procedures. Tc measured in the urinary bladder, skin-surface temperatures, thermoregulatory responses (vasoconstriction and shivering), and total leukocyte counts were assessed. In a subset of 34 patients, plasma concentrations of tumor necrosis factor, interleukin (IL)-6, and IL-8 were measured before and after surgery. RESULTS: In the early postoperative period, the maximum increase in Tc above the preoperative baseline averaged 1.4 +/- 0.8 degrees C (2.5 +/- 1.4 degrees F), with the Tc peak occurring 11.1 /- 5.8 h after surgery. Fifty percent of patients had a maximum Tc greater than or equal to 38.0 degrees C (100.4 degrees F) and 25% had a maximum Tc greater than or equal to 38.5 degrees C (101.3 degrees F). The progressive postoperative increase in Tc was clearly associated with cutaneous vasoconstriction and shivering, indicating a regulated elevation in Tc setpoint. The elevated Tc was associated with an increased IL-6 response but not with leukocytosis. Maximum postoperative Tc was positively correlated with duration and extent of the surgical procedure. CONCLUSIONS: A regulated elevation in Tc setpoint (fever) occurs normally after surgery. The association between Tc elevation, extent and duration of surgery, and the cytokine response suggests that early postoperative fever is a manifestation of perioperative stress.

Comparison of lower extremity cutaneous temperature changes in patients receiving lumbar sympathetic ganglion blocks versus epidural anesthesia.

STUDY OBJECTIVE: To investigate if paravertebral lumbar sympathetic ganglion block and lumbar epidural anesthesia result in comparable cutaneous temperature changes in the lower extremity. DESIGN: Nonrandomized comparison study. SETTING: Operating rooms and pain clinic procedure rooms in a tertiary care hospital. PATIENTS AND INTERVENTIONS: 18 patients undergoing lumbar sympathetic ganglion blocks for the diagnosis and/or treatment of chronic pain, and 13 patients undergoing lumbar epidural anesthesia for radical prostatectomy. MEASUREMENTS: Cutaneous temperatures were measured over the great toe, calf, and thigh in all patients. Mean maximum temperature (Tmax), rate of change of skin temperature (from 5% to 95% of maximum temperature change), and mean time to 1 degrees C increase, and 50% and 95% of maximum temperature change for each group were compared. Temperature changes for the epidural and lumbar sympathetic block patients were compared. MAIN RESULTS: Epidural and lumbar sympathetic block resulted in similar Tmax (34.1 +/- 0.2 and 33.8 +/- 0.9 degrees C, respectively, mean +/- SEM; p = 0.18) and rate of temperature change (0.64 +/- 0.09 and 0.49 +/- 0.07 degrees C/min; p = 0.2) in the great toe. The onset of cutaneous temperature change after lumbar sympathetic block was slower than after epidural anesthesia (1 degrees C increase: 17 and 11 min, respectively, 50% of Tmax: 25 and 17 min, respectively, and 95% of Tmax: 40 and 31 min, respectively; p < 0.05 for each). CONCLUSIONS: The similar rate and magnitude of cutaneous temperature change in the distal lower extremity suggests the degree of sympathetic blockade is similar with lumbar sympathetic blockade and epidural anesthesia. Either technique should provide adequate sympathectomy for treating sympathetically maintained pain once the diagnosis has been confirmed using selective sympathetic blockade.

Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans.

Subjective thermal comfort plays a critical role in body temperature regulation since this represents the primary stimulus for behavioral thermoregulation. Although both core (Tc) and skin-surface (Tsk) temperatures are known afferent inputs to the thermoregulatory system, the relative contributions of Tc and Tsk to thermal comfort are unknown. We independently altered Tc and Tsk in human subjects while measuring thermal comfort, vasomotor changes, metabolic heat production, and systemic catecholaminergic responses. Multiple linear regression was used to determine the relative Tc/Tsk contribution to thermal comfort and the autonomic thermoregulatory responses, by using the ratio of regression coefficients for Tc and Tsk. The Tc/Tsk contribution ratio was relatively lower for thermal comfort (1:1) than for vasomotor changes (3:1; P = 0.008), metabolic heat production (3.6:1; P = 0.001), norepinephrine (1.8:1; P = 0.03), and epinephrine (3:1; P = 0.006) responses. Thus Tc and Tsk contribute about equally toward thermal comfort, whereas Tc predominates in regulation of the autonomic and metabolic responses.

Perioperative plasma endothelin-1 and Big endothelin-1 concentrations in elderly patients undergoing major surgical procedures.

UNLABELLED: Plasma concentrations of the vasoconstrictor endothelin-1 (ET-1) increase during acute physiologic stress, but the role of ET-1 in the pathophysiology of stress remains largely undefined. Whether ET-1 mediates thermoregulatory changes in vasomotor tone is unknown. ET-1 and its more stable precursor, Big ET-1, were measured in plasma obtained at several perioperative time points from 95 consecutive elderly patients (mean age 70 +/- 1 yr) randomized to receive either normothermic or hypothermic perioperative care while undergoing major surgical procedures. In the postoperative period, there were no significant changes in plasma ET-1 concentrations, but Big ET-1 concentrations increased considerably (P < 0.0001). There were no significant differences in mean ET-1 or Big ET-1 levels in normothermic and hypothermic patients. Preoperative and postoperative ET-1 concentrations were significantly higher in patients with a history of hypertension (P < 0.002) and in those requiring treatment for postoperative hypertension (P < 0.003). Patients with cancer and those undergoing abdominal surgery had significantly higher Big ET-1 concentrations (P < 0.0001 and P < 0.003, respectively). These data support the hypothesis that Big ET-1 is a more sensitive measure of endothelin system activation after major surgery. Premorbid conditions and location and type of surgery influence perioperative ET-1/Big ET-1 concentrations. IMPLICATIONS: The endothelin response seems to be significantly associated with perioperative hemodynamic aberrations. The endothelin-1 (ET-1) precursor Big ET-1 is a more sensitive measure of the endothelin system activation in response to surgical stress than ET-1 alone. Thermoregulatory vasoconstriction in response to mild perioperative hypothermia occurs independently of the endothelin system.

Temperature monitoring practices during regional anesthesia.

UNLABELLED: Monitoring and maintaining body temperature during the perioperative period has a significant impact on the risk of myocardial ischemia, cardiac morbidity, wound infection, surgical bleeding, and patient discomfort. To test the hypothesis that body temperature is inadequately monitored during regional anesthesia (RA), we randomly surveyed 60 practicing anesthesiologists to determine practice patterns for temperature monitoring. Only 33% of the clinicians surveyed routinely monitor body temperature during RA. Although skin temperature monitoring has limitations, it was the most commonly used method among the survey respondents. When temperature is monitored during RA, most clinicians use either liquid crystal skin-surface monitoring or axillary temperature probes. Of those surveyed, < 15% use acceptable core temperature monitoring techniques (urinary bladder or tympanic membrane). In conclusion, it seems that body temperature is often not monitored in patients receiving RA. IMPLICATIONS: The results of this survey of practicing anesthesiologists indicate that body temperature is often not monitored in patients receiving regional anesthesia. It is therefore likely that significant hypothermia goes undetected and untreated in these patients.

Pain and quality of life following radical retropubic prostatectomy.

PURPOSE: We assess pain and quality of life following radical retropubic prostatectomy and determine whether intraoperative anesthetic management has any long-term effects on outcomes. MATERIALS AND METHODS: A total of 110 patients undergoing radical retropubic prostatectomy were randomly assigned to receive epidural and/or general anesthesia. Patients responded to a questionnaire mailed 3 and 6 months following surgery that assessed prostate symptoms, pain related to surgery, quality of life and mood. RESULTS: No long-term effects of anesthesia were observed. Of the 103 respondents (94%) at 3 months 49% had some pain related to surgery. Although pain was not related to anesthesic technique, patients who had it at 3 months used significantly more pain medication on postoperative day 3. Pain at 3 months was mild, averaging 1.5 on a scale of 0 to 10, and associated with poor perceptions of overall health (p <0.02), and reduced physical (p <0.01) and social (p <0.01) functioning. Pain at 3 months was associated with higher levels of preoperative anxiety (p <0.05). At 6 months 36 of 90 patients (35%) had some pain related to surgery and the impact was similar. CONCLUSIONS: Long-term effects of intraoperative anesthesic technique were not apparent. Mild pain following radical retropubic prostatectomy was common and associated with reduced quality of life, particularly social functioning. Affective distress, particularly anxiety, before surgery and use of pain medications following surgery may be predictors of chronic pain following radical retropubic prostatectomy.