Epidural versus general anesthesia, ambient operating room temperature, and patient age as predictors of inadvertent hypothermia

Pre-induction low dose pethidine does not decrease incidence of postoperative shivering in laparoscopic gynecological surgeries

OBJECTIVES

The incidence of shivering in patients undergoing a laparoscopic procedure is stated to be about 40%. A majority of laparoscopic gynecological procedures are taken up on an outpatient basis. Postoperative shivering may delay hospital discharge and is a common cause of discomfort in patients recovering from anesthesia.

AIMS

To determine the effect of pre-induction, low-dose pethidine on postoperative shivering in patients undergoing laparoscopic gynecological surgeries.

SETTING AND DESIGN

Sixty females between 25 and 35 years of age, of American Society of Anesthesiologists (ASA) class 1 and 2, were randomly divided into three groups of 20 patients each. Group I and II patients received i.v. pethidine 0.3 mg/kg and 0.5 mg/kg, respectively, while Group III received i.v. 0.9% normal saline just before induction of general anesthesia. Temperature of the Operating Room and the Post Anesthesia Care Unit was standardized and all fluids given during the study period were warmed to 37°C.

MATERIALS AND METHODS

Temperature, measured with a tympanic membrane probe, was recorded preoperatively, after induction of anesthesia, on arrival at the Post Anesthesia Care Unit, and postoperatively at 15 minutes and 30 minutes. Shivering was graded (0 - 4 scale) at arrival of the patients to the PACU and every five minutes thereafter, up to 30 minutes.

STATISTICAL ANALYSIS

ANOVA, Chi-square test, Kruskal-Wallis ANOVA and Mann-Whitney U tests were used. A P-value of less than 0.05 was considered significant.

RESULTS

Core body temperatures were statistically insignificant between groups at pre-induction, post-induction, and in the PACU (P > 0.05). At the end of surgery, shivering was present in 18 patients (30%). In groups I, II, and III, six (30%), three (15%), and nine (45%) patients shivered, respectively. The differences in incidence and grading of shivering among groups was found to be statistically insignificant (P > 0.05). The core body temperature of shiverers and non-shiverers were compared. In the PACU at 0, 15, and 30 minutes, the temperature among shiverers was significantly lower than that in the non-shiverers. Rescue drug i.v. pethidine 20 mg was given to patients with shivering grade ≥2. None of the patients had shivering after 10 minutes.

CONCLUSIONS

Prophylactic pre-induction, low-dose pethidine does not have major role in preventing postoperative shivering.

Prevention of hypothermia by infusion of warm fluid during abdominal surgery

Perioperative hypothermia can lead to a number of complications for patients after surgery. The aim of this pilot study was to evaluate the efficacy of warm fluids in maintaining normal core temperature during the intraoperative period. We studied 30 American Society of Anesthesiologists (ASA) physical status I or II adult patients who required general anesthesia for abdominal surgery. In the control group (n = 15), fluids were infused at room temperature; in the test group (n = 15), fluids were infused at 37° C. In the control group, core temperature decreased to 35.5 ± 0.3° C during the first 3 hours, and then stabilized at the end of anesthesia. In the test group, core temperature decreased during the first 60 minutes, but increased to 36.9 ± 0.3° C at the end of anesthesia. In the control group, eight patients shivered at grade ≥2. In the test group, none of the patients reached grade ≥2 (P < .01). Infusion of warm fluid is effective in keeping patients nearly normothermic and preventing postanesthetic shivering. It may provide an easy and effective method for prevention of perioperative hypothermia.

Temperature control and the role of supplemental oxygen

Unrecognized and untreated intraoperative hypothermia remains a common avoidable scenario in the modern operating room. Failure to properly address this seemingly small aspect of the total operative care has been shown to have profound negative patient consequences including increased incidence of postoperative discomfort, surgical bleeding, requirement of allogenic blood transfusion, wound infections, and morbid cardiac events. All of these ultimately lead to longer hospitalizations and higher mortality. To avoid such problems, simple methods can be employed by the surgeon, anesthesiologist, and ancillary personnel to ensure euthermia. Similarly, another effortless method to potentially improve surgical outcomes is the liberal use of supplemental oxygen. Promising preliminary data suggests that high-concentration oxygen during and after surgery may decrease the rate of surgical site infections and gastrointestinal anastomotic failure. The precise role of supplemental oxygen in the perioperative period represents an exciting area of potential research that awaits further validation and analysis. In this article, the authors explore the data regarding both temperature regulation and supplemental oxygen use in an attempt to define further their emerging role in the perioperative care of patients undergoing colorectal surgery.

The effect of epidural and general anesthesia on newborn rectal temperature at elective cesarean section

Both epidural and general anesthesia can impair thermoregulatory mechanisms during surgery. However, there is lack of information about the effects of different methods of anesthesia on newborn temperature. The purpose of this study was to determine whether there are differences in newborn rectal temperature related to type of anesthesia. Sixty-three pregnant women were randomly assigned to receive general or epidural anesthesia. Maternal core temperature was measured three times with a rectal probe just before anesthesia, at the beginning of surgery and at delivery. In addition, umbilical vein blood was sampled for pH. The rectal temperatures of the babies were recorded immediately after delivery, and Apgar scores were determined 1, 5, and 10 min after birth. The duration of anesthesia and the volume of intravenous fluid given during the procedure (833 +/- 144 vs 420 +/- 215 mL) were significantly higher in the epidural group than in the general anesthesia group (P < 0.0001). Maternal rectal temperatures were not different in both groups at all measurements. In contrast, newborn rectal temperatures were lower in the epidural anesthesia group than in the general anesthesia group (37.4 +/- 0.3 vs 37.6 +/- 0.3 degrees C; P < 0.05) immediately after birth. Furthermore, the umbilical vein pH value (7.31 +/- 0.05 vs 7.33 +/- 0.01; P < 0.05) and Apgar scores at the 1st-min measurement (8.0 +/- 0.9 vs 8.5 +/- 0.7; P < 0.05) were lower in the epidural anesthesia group than in the general anesthesia group. Since epidural anesthesia requires more iv fluid infusion and a longer time for cesarean section, it involves a risk of a mild temperature reduction for the baby which, however, did not reach the limits of hypothermia.

Phenylephrine Attenuates Intra-Operative Hypothermia during Spinal Anaesthesia

Inadvertent hypothermia is common during spinal anaesthesia. This study was based on the hypothesis that phenylephrine might attenuate core hypothermia by inhibiting core-to-peripheral redistribution of body heat during spinal anaesthesia. In this prospective randomized study, 20 patients who underwent elective orthopaedic surgery under spinal anaesthesia were randomly assigned to receive either normal saline (control group) or continuously-infused phenylephrine 0.5 μg/kg per min (phenylephrine group). Core temperature, heart rate (HR) and mean arterial pressure (MAP) were monitored. Mean ± SE core temperature at the end of surgery was significantly higher in the phenylephrine-treated group compared with the control group (35.9 ± 0.1 °C versus 35.0 ± 0.1 °C, respectively), although there was no significant difference in baseline core temperature (both groups 36.3 ± 0.1 °C). Mean HR and MAP were not significantly different between the two groups. In conclusion, continuously-infused phenylephrine attenuated core hypothermia during spinal anaesthesia without any haemodynamic complications.

Intra-Operative Warming with a Forced-Air Warmer in Preventing Hypothermia after Tourniquet Deflation in Elderly Patients

This randomized, single-blind study aimed to explore the effects of intraoperative warming with a forced-air warmer in the prevention of hypothermia after tourniquet deflation in elderly patients undergoing unilateral total knee replacement arthroplasty under general anaesthesia. Patients were randomized to receive either intra-operative warming using a forced-air warmer with an upper body blanket (warming group; n = 12) or no intra-operative warming (non-warming group; n = 12). Oesophageal temperature was measured as core body temperature. At 30 min following tourniquet inflation, the core body temperature started to increase in the warming group whereas it continued to drop in the non-warming group. This difference was statistically significant. The final core body temperature after tourniquet deflation was significantly higher in the warming group (mean ± SD 36.1 ± 0.2 °C) than in the non-warming group (35.4 ± 0.3 °C). Intra-operative forced-air warming increased the core body temperature before tourniquet deflation and prevented subsequent hypothermia in elderly patients under general anaesthesia.

Thermoregulatory responses of sevoflurane, desflurane, and isoflurane during gynecologic laparoscopic surgery

BACKGROUND

Core temperature decreases rapidly after the induction of general anesthesia, because the heat is redistributed to peripheral tissues. Thermoregulatory responses of volatile anesthetics have been tested, but their effects have not been directly compared. Therefore, we evaluated the thermoregulatory responses to sevoflurane, desflurane, and isoflurane.

METHODS

Sixty healthy patients scheduled for laparoscopic myomectomy or radical hysterectomy were allocated into three groups; Group S (sevoflurane, n = 20), Group D (desflurane, n = 20), and Group I (isoflurane, n = 20). Anesthesia was maintained with 1 minimum alveolar concentration (MAC) of sevoflurane, desflurane, and isoflurane in a 50/50 mixture of N2O/O2. Patients were maintained in a normovolemic and normocapnic state. The core temperature and forearm minus fingertip skin-temperature gradient (an index of peripheral vasoconstriction) were monitored after the induction of general anesthesia.

RESULTS

Each of the seven patients given sevoflurane, desflurane, and isoflurane vasoconstricted at a core temperature of 35.3 +/- 0.5degrees C, 33.6 +/- 0.4degrees C, and 35.2 +/- 0.4degrees C, respectively. The vasoconstriction threshold was the lowest in patients anesthetized with desflurane. The core temperature gradient (Ti-Tf) was significantly higher in patients that were anesthetized with desflurane than in those that were anesthetized with sevoflurane or isoflurane. The core temperature of desflurane was significantly lower than that of sevoflurane or isoflurane 15 minutes after the induction of anesthesia until 180 minutes of anesthesia.

CONCLUSIONS

These results indicate that the core temperature is maintained at a higher level in patients that have been anesthetized with sevoflurane or isoflurane than in those that have been anesthetized with desflurane.

Hipotermia no período intra-operatório em pacientes submetidos a cirurgias eletivas

OBJETIVO: Analisar a temperatura corporal do paciente submetido a cirurgia eletiva no período intra-operatório. MÉTODOS: Para a coleta de dados elaborou-se um instrumento que foi submetido à validação aparente e de conteúdo e a amostra foi constituída de 70 pacientes. As variáveis mensuradas foram: temperatura e umidade da sala de cirurgia e temperatura corporal do paciente em diferentes momentos do período intra-operatório. RESULTADOS: Em relação à temperatura corporal dos pacientes observou-se que no final do procedimento anestésico-cirúrgico a média foi de 33,6º C. A temperatura média da sala na chegada dos pacientes foi de 24,6º C e na quarta hora de procedimento anestésico-cirúrgico foi de 22,4ºC. Houve correlação estatisticamente significante e positiva entre as variáveis mensuradas. CONCLUSÃO: Os resultados apontaram a necessidade de implementação de intervenções efetivas para a prevenção da hipotermia e, neste cenário, a atuação do enfermeiro é crucial para a melhoria da assistência prestada ao paciente cirúrgico.

The effects of irrigation fluid on core temperature in endoscopic urological surgery

AIMS AND METHOD

A prospective observational study of 100 patients undergoing various types of endoscopic urological surgery including transurethral resection of the prostate (TURP), transurethral resection of bladder tumour (TURBT), percutaneous nephrolithotomy (PCNL) and Cystoscopies, was reformed to determine the temperature difference between preoperative and postoperative core temperatures and to determine whether this change was related to the age, weight, type of anaesthetic, operation duration, type of operation, amount of irrigant fluid used and whether warming the fluid to 370C made a difference to the degree of temperature change. All the above variables were recorded for each patient as well as the preoperative and postoperative temperatures. Statistical analysis was carried out using SPSS.

RESULTS

The mean age was 64 years and the mean weight was 75kg in the study. Seventy-six patients had a general anaesthetic while 24 had a spinal anaesthetic. The study included 29 TURPs, 10 TURBTs, six PCNLs and 55 Cystoscopies. Age and type of anaesthetic did not correlate significantly with temperature change. As weight increased patients tend to preserve their core temperature more efficiently. The highest degree of temperature drop was in the PCNL group. There was a significant relationship between the duration of operation and temperature drop (p<0.05) as well as the amount of irrigation fluid used (p<0.05). Average temperature drop for patients who underwent irrigation with fluid at room temperature (n=43) was 1.37 degrees C and 0.95 degrees C for those whose fluids were warmed to body temperature (n=57). This difference was statistically significant (p=0.03).

CONCLUSIONS

There is a drop in temperature in patients undergoing most endoscopic operations on the GU tract and this appears to be multifactorial in origin, relating significantly to weight, amount of irrigation fluid used, type and duration of operation. Warming irrigant fluid to body temperature appears to significantly reduce the degree of temperature drop with consequent potential benefit.

Hypothermia control in elderly surgical patients in the intraoperative period: evaluation of two nursing interventions

OBJECTIVES: To evaluate the efficacy of two different nursing interventions regarding control of body heat loss, using blankets during the intraoperative period of elderly patients. METHODS: This was an experimental, comparative, applied, longitudinal prospective study with a quantitative approach. Eighty-one elderly patients undergoing elective surgery with a surgical time frame of at least one hour were selected by systematic probability sampling into two Experimental and one Control Group. Informed consent was obtained from participants. Data was collected by biophysiological measurement, using a tympanic thermometer. RESULTS: After the homogeneity of variables - gender, surgical duration, age, BMR, anesthesia, room humidity and temperature, drugs and liquid infusion- had been demonstrated, the interventions were confronted. Incidence of hypothermia (59.3%) and body heat loss (E1=-0.6ºC , E2=-0.6oC and C=-0.7ºC) were not significantly different between the groups (p=0.85 and p=0.7 respectively). CONCLUSIONS: Results show the need for associated extra body warming methods to maintain normothermia.

Anaesthesia and the elderly

As a result of age-related physiological changes and multi-comorbidity, which both result in reduced functional reserve of the organ systems, old patients are more vulnerable to surgical stress and perioperative impairment in organ functions. Therefore, the incidence of severe complications during the perioperative course is increased in the elderly. Regional anaesthesia or a combination of regional and general anaesthesia is considered to be beneficial in elderly patients, because neuraxial blockade may reduce sympathetic activation, and has been demonstrated to reduce postoperative mortality. Other protective strategies to maintain organ functions in elderly patients include medication with beta-blockers in patients with cardiovascular risks, the avoidance of hypothermia, the maintenance of systemic oxygen delivery, and patient-controlled pain therapy.

Preoperative warming combined with intraoperative skin-surface warming does not avoid hypothermia caused by spinal anesthesia in patients with midazolam premedication

CONTEXT AND OBJECTIVE

Inadvertent perioperative hypothermia is common during spinal anesthesia and after midazolam administration. The aim of this study was to evaluate the effects of intraoperative skin-surface warming with and without 45 minutes of preoperative warming in preventing intraoperative and postoperative hypothermia caused by spinal anesthesia in patients with midazolam premedication.

DESIGN AND SETTING

Prospective and randomized study at Hospital das Clínicas, Universidade Estadual Paulista, Botucatu.

METHODS

Thirty patients presenting American Society of Anesthesiologists (ASA) physical status I and II who were scheduled for elective lower abdominal surgery were utilized. The patients received midazolam premedication (7.5 mg by intramuscular injection) and standard spinal anesthesia. Ten patients (Gcontrol) received preoperative and intraoperative passive thermal insulation. Ten patients (Gpre+intra) underwent preoperative and intraoperative active warming. Ten patients (Gintra) were only warmed intraoperatively.

RESULTS

After 45 min of preoperative warming, the patients in Gpre+intra had significantly higher core temperatures than did the patients in the unwarmed groups (Gcontrol and Gintra) before the anesthesia (p < 0.05) but not at the beginning of surgery (p > 0.05). The patients who were warmed intraoperatively had significantly higher core temperatures than did the patients in Gcontrol at the end of surgery (p < 0.05). All the patients were hypothermic at admission to the recovery room (T CORE < 36 degrees C).

CONCLUSIONS

Forty-five minutes of preoperative warming combined with intraoperative skin-surface warming does not avoid but minimizes hypothermia caused by spinal anesthesia in patients with midazolam premedication.

A Systematic Review of Intraoperative Warming to Prevent Postoperative Complications

This systematic review examines whether preventing hypothermia during surgery prevents postoperative complications and thereby improves outcomes for patients. Twenty-six randomized controlled trials were identified, and data extraction and assessment of study quality were carried out by two researchers independently. The results of studies with similar patients, surgical procedures, and outcomes were pooled. Outcomes measured included postoperative pain levels, thermal comfort, and treatment costs. Postoperative complications identified were shivering, cardiac events, need for blood transfusion, wound infections, and pressure ulcers. The majority of studies favored treatment.

Effects of Mild Hypothermia on Blood Coagulation in Patients Undergoing Elective Plastic Surgery

BACKGROUND

The aim of this prospective, controlled study was to evaluate the effects on coagulation function of active patient warming during elective plastic surgery.

METHODS

Seventy-six patients undergoing elective plastic surgery (additive and reductive mastoplasty, rhinoplasty, and liposuction) were either covered with standard sterile drapes (control group, n = 38) or actively warmed during surgery with countercurrent fluid warming and forced-air skin warming (treatment group, n = 38). Complete evaluation of the coagulation activity was performed 1 hour before general anesthesia was induced and then at the end of surgery.

RESULTS

Although no differences in preoperative core temperature were observed (36.0 +/- 0.5 degrees C in the control group and 36.1 +/- 0.4 degrees C in the treatment group; p = 0.12), core temperature was lower at the end of surgery in the control group (34 +/- 1.0 degrees C) than in the treatment group (36 +/- 0.6 degrees C) (p = 0.0005). No differences in prothrombin time and fibrinogen plasma concentrations were observed between the two groups. At the end of surgery, control group patients showed significantly larger activated partial thromboplastin times (36.8 +/- 3.5 seconds) and bleeding times (8.1 +/- 1.6 minutes) as compared with patients maintained normothermic during surgery (34.0 +/- 2.9 seconds and 4.3 +/- 1.1 minutes; p = 0.0005 and p = 0.0005, respectively).

CONCLUSION

Actively maintaining intraoperative normothermia allows patients to maintain normal coagulation function during elective plastic surgery lasting longer than 2 hours, potentially reducing the occurrence of bleeding-related complications after plastic surgery.

Hypothermia in a surgical intensive care unit

BACKGROUND

Inadvertent hypothermia is not uncommon in the immediate postoperative period and it is associated with impairment and abnormalities in various organs and systems that can lead to adverse outcomes. The aim of this study was to estimate the prevalence, the predictive factors and outcome of core hypothermia on admission to a surgical ICU.

METHODS

All consecutive 185 adult patients who underwent scheduled or emergency noncardiac surgery admitted to a surgical ICU between April and July 2004 were admitted to the study. Tympanic membrane core temperature (Tc) was measured before surgery, on arrival at ICU and every two hours until 6 hours after admission. The following variables were also recorded: age, sex, body weight and height, ASA physical status, type of surgery, magnitude of surgical procedure, anesthesia technique, amount of intravenous fluids administered during anesthesia, use of temperature monitoring and warming techniques, duration of the anesthesia, ICU length of stay, hospital length of stay and SAPS II score. Patients were classified as either hypothermic (Tc < or = 35 degrees C) or normothermic (Tc> 35 degrees C). Univariate analysis and multiple regression binary logistic with an odds ratio (OR) and its 95% Confidence Interval (95%CI) were used to compare the two groups of patients and assess the relationship between each clinical predictor and hypothermia. Outcome measured as ICU length of stay and mortality was also assessed.

RESULTS

Prevalence of hypothermia on ICU admission was 57.8%. In univariate analysis temperature monitoring, use of warming techniques and higher previous body temperature were significant protective factors against core hypothermia. In this analysis independent predictors of hypothermia on admission to ICU were: magnitude of surgery, use of general anesthesia or combined epidural and general anesthesia, total intravenous crystalloids administrated and total packed erythrocytes administrated, anesthesia longer than 3 hours and SAPS II scores. In multiple logistic regression analysis significant predictors of hypothermia on admission to the ICU were magnitude of surgery (OR 3.9, 95% CI, 1.4-10.6, p = 0.008 for major surgery; OR 3.6, 95% CI, 1.5-9.0, p = 0.005 for medium surgery), intravenous administration of crystalloids (in litres) (OR 1.4, 95% CI, 1.1-1.7, p = 0.012) and SAPS score (OR 1.0, 95% CI 1.0-1.7, p = 0.014); higher previous temperature in ward was a significant protective factor (OR 0.3, 95% CI 0.1-0.7, p = 0.003). Hypothermia was neither a risk factor for hospital mortality nor a predictive factor for staying longer in ICU.

CONCLUSION

The prevalence of patient hypothermia on ICU arrival was high. Hypothermia at time of admission to the ICU was not an independent factor for mortality or for staying longer in ICU.

Methicillin-resistant Staphylococcus aureus infections in ICU patients

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections in patients admitted to the intensive care unit has dramatically increased in recent years, with an associated increase in morbidity and mortality and the costs of caring for patients with MRSA infections. Although indiscriminate and inappropriate use of antibiotics has contributed to this phenomenon, horizontal transmission of MRSA between patients and health care providers is the principal cause of this observed increase. This article discusses the pathogenesis, epidemiology, treatment, and prevention of MRSA infections in critically ill patients.

Factors influencing preoperative stress response in coronary artery bypass graft patients

Background

In many studies investigating measures to attenuate the hemodynamic and humoral stress response during induction of anaesthesia, primary attention was paid to the period of endotracheal intubation since it has been shown that even short-lasting sympathetic cardiovascular stimulation may have detrimental effects on patients with coronary artery disease. The aim of this analysis was, however, to identify the influencing factors on high catecholamine levels before induction of anaesthesia.

Methods

Various potential risk factors that could impact the humoral stress response before induction of anaesthesia were recorded in 84 males undergoing coronary aortic bypass surgery, and were entered into a stepwise linear regression analysis. The plasma level of norepinephrine measured immediately after radial artery canulation was chosen as a surrogate marker for the humoral stress response, and it was used as the dependent variable in the regression model. Accordingly, the mean arterial blood pressure, heart rate and the calculated pressure-rate product were taken as parameters of the hemodynamic situation.

Results

Stepwise regression analysis revealed that the oral administration of low-dose clonidine (mean dose 1.75 μg·kg^-1) on the morning of surgery was the only significant predictor (p = 0.004) of the high variation in preoperative norepinephrine plasma levels. This intervention decreased norepinephrine levels by more than 40% compared to no clonidine administration, from 1.26 to 0.75 nmol·l^-1. There was no evidence for dose-responsiveness of clonidine. All other potential predictors were removed from the model as insignificant (p > 0.05). The use of beta-blocker, ace-inhibitors, ejection fraction, and body mass index were significant determinants for the hemodynamic situation (heart rate, mean arterial pressure, pressure rate product) of the patient during the pre-induction period.

Conclusion

The oral administration of clonidine is the only significant predictor for the observed variation of norepinephrine levels during the preoperative period. Lack of significant dose responsiveness suggests that even a low dose of the drug can attenuate the preoperative stress response and thus is recommended in cardiovascular high risk patients.

General versus spinal anesthesia in patients undergoing radical retropubic prostatectomy: results of a prospective, randomized study

OBJECTIVES

To evaluate the impact of general anesthesia (GA) versus spinal anesthesia (SpA) on intraoperative and postoperative outcome in patients undergoing radical retropubic prostatectomy.

METHODS

Seventy-two consecutive patients with clinically localized prostate cancer were randomized into group 1 (GA: 34 patients) or group 2 (L2-L3 or L3-L4 SpA: 38 patients) and underwent radical retropubic prostatectomy. The intraoperative and postoperative anesthetic and surgical variables were evaluated.

RESULTS

The mean +/- SEM operative time was not significantly different between the two groups (P = 0.43). The overall blood loss was less in group 2 (P = 0.04). The mean +/- SEM postoperative time in the postoperative holding area was significantly shorter after SpA than after GA (P <0.0001). The perioperative pain outcome in the postoperative holding area was significantly better for group 2 than for group 1 (P = 0.0017), but postoperative pain on day 1 was not significantly different between the two groups. The postoperative sedation score was significantly less in group 2 than in group 1 (P <0.0001). On day 1, first flatus passed in a significantly larger number of patients in group 2 (P <0.0001), and the overall gait was greater for group 2 patients (P = 0.02).

CONCLUSIONS

These results suggest that SpA allows good muscle relaxation and a successful surgical outcome in patients undergoing radical retropubic prostatectomy with pelvic lymphadenectomy for clinically localized prostate cancer. Moreover, SpA results in less intraoperative blood loss, less postoperative pain, and a faster postoperative recovery than GA.

Monitoring and thermal management

Anaesthesia alters normal thermoregulatory control of the body, usually leading to perioperative hypothermia. Hypothermia is associated with a large number of serious complications. To assess perianaesthetic hypothermia, core temperature should be monitored vigorously. Pulmonary artery, tympanic membrane, distal oesophageal or nasopharyngeal temperatures reflect core temperature reliably. Core temperatures can be often estimated with reasonable accuracy using oral, axillary and bladder temperatures, except during extreme thermal perturbations. The body site for measurements should be chosen according to the surgical procedure. Unless hypothermia is specifically indicated, efforts should be made to maintain intraoperative core temperatures above 36 degrees C. Forced air is the most effective, commonly available, non-invasive warming method. Resistive heating electrical blankets and circulating water garment systems are an equally effective alternative. Intravenous fluid warming is also helpful when large volumes are required. In some patients, induction of mild therapeutic hypothermia may become an issue for the future. Recent studies indicate that patients suffering from neurological disease may profit from rapid core cooling.

Fever during anaesthesia

Fever occurs when pyrogenic stimulation activates thermal control centres. Fever is common during the perioperative period, but rare during anaesthesia. Although only a limited number of studies are available to explain how anaesthesia affects fever, general anaesthesia seems to inhibit fever by decreasing the thermoregulatory-response thresholds to cold. Opioids also inhibit fever; however, the effect is slightly less than that of general anaesthesia. In contrast, epidural anaesthesia does not affect fever. This suggests that hyperthermia, which is often associated with epidural infusions during labour or in the post-operative period, may be a true fever caused by inflammatory activation. Accordingly, this fever might be diminished in patients who receive opioids for pain treatment. Post-operative fever is a normal thermoregulatory response usually of non-infectious aetiology. Fever may be important in the host defence mechanisms and should not be routinely treated lest the associated risks exceed the benefits.

Hypothermia during head and neck surgery

OBJECTIVE

To determine the predictors and incidence of hypothermia in patients undergoing head and neck surgery.

STUDY DESIGN

Retrospective analysis.

METHODS

Patients were either not warmed (n = 43) or actively warmed with forced-air warming (n = 25). Clinical variables that were assessed as predictors of core body temperature included age, body mass, duration of procedure, estimated blood loss, amount of intravenous fluids administered, and the use of forced-air warming. The incidence of severe intraoperative hypothermia and potential hypothermia-related complications was also examined.

RESULTS

The study demonstrated that advanced age is a risk factor for hypothermia and decreased body mass is associated with lower final body temperatures in the groups of patients that was not warmed. After adjusting for differences in the ages and weights between the two groups, the mean core body temperature was found to be 0.4 degrees C lower in the patients who were not warmed. Severe intraoperative hypothermia occurred in 5 of 38 patients (11.6%) who were not warmed and 2 of 23 patients (8.0%) who were warmed. The complications associated with hypothermia included delayed time to extubation, the development of neck seromas, and flap dehiscence.

CONCLUSIONS

Patients undergoing head and neck surgery are at risk for the development of intraoperative hypothermia and require careful temperature monitoring. Elderly patients and patients with low body mass are more prone to develop low intraoperative core body temperatures. Active warming with forced-air warmers should be considered for patients at risk for intraoperative hypothermia and for patients who develop hypothermia intraoperatively, to avoid hypothermia-related complications.

Preoperative combined with intraoperative skin-surface warming avoids hypothermia caused by general anesthesia and surgery

STUDY OBJECTIVES

To evaluate the effects of intraoperative skin-surface warming with and without 1 hour of preoperative warming, in preventing intraoperative hypothermia, and postoperative hypothermia, and shivering, and in offering good conditions to early tracheal extubation.

DESIGN

Prospective, randomized, blind study.

SETTING

Teaching hospital.

PATIENTS

30 ASA physical status I and II female patients scheduled for elective abdominal surgery.

INTERVENTIONS

Patients received standard general anesthesia. In 10 patients, no special precautions were taken to avoid hypothermia. Ten patients were submitted to preoperative and intraoperative active warming. Ten patients were only warmed intraoperatively.

MEASUREMENTS AND MAIN RESULTS

Temperatures were recorded at 15-minute intervals. The patients who were warmed preoperatively and intraoperatively had core temperatures significantly more elevated than the other patients during the first two hours of anesthesia. All patients warmed intraoperatively were normothermic only at the end of the surgery. The majority of the patients warmed preoperatively and intraoperatively or intraoperatively only were extubated early, and none had shivering. In contrast, five unwarmed patients shivered.

CONCLUSIONS

One hour of preoperative warning combined with intraoperative skin-surface warming, not simply intraoperative warming alone, avoided hypothermia caused by general anesthesia during the first two hours of surgery. Both methods prevented postoperative hypothermia and shivering and offered good conditions for early tracheal extubation.

Predictor of core hypothermia and the surgical intensive care unit

Inadvertent postoperative core hypothermia is associated with multiple physiological effects, especially in patients admitted to the intensive care unit (ICU). Despite previous reports of the relationship between patient, surgical, and anesthetic factors and immediate postoperative core hypothermia, this information might need to be reconsidered in the light of progress in surgery, anesthetic, and warming techniques. We designed this prospective study of 194 postgeneral surgical patients to assess the incidence, predictive factors, and outcome of core hypothermia (tympanic membrane core temperature [Tc] <36.0 degrees C) at the time of admission to the general ICU in a large tertiary university medical center from December 2000 to March 2001. The following variables were studied: age, sex, body weight, body surface area, preoperative body temperature, ASA physical status, history of diabetic neuropathy, emergency surgery, surgical subspecialty performing surgery, type of surgery, type of anesthesia (general, regional, or combined epidural and general), temperature monitoring, use of a forced air warming technique, amount of fluid and blood replacement, duration of anesthesia, duration of surgery, and the ambient operating room temperature. Other outcomes, i.e., length of ICU stay and mortality, were also assessed. The incidence of core hypothermia was 57.1%, 41.3%, and 28.3% according to the definition of Tc <36.0 degrees C, <35.5 degrees C, and <35.0 degrees C, respectively. Multiple logistic regression showed the following risk factors for core hypothermia: high ASA physical status (odds ratio, 2.87; 95% confidence interval [CI], 0.82-10.03 for ASA II; odds ratio, 8.35; 95% CI, 1.67-41.88 for ASA >II), magnitude of surgical procedure (odds ratio, 6.60; 95% CI, 1.66-26.19 for medium surgery; odds ratio, 22.23; 95% CI, 5.41-91.36 for major surgery), use of combined epidural and general anesthesia (odds ratio, 3.39; 95% CI, 1.05-10.88), and duration of surgery >2 h (odds ratio, 4.50; 95% CI, 1.48-13.68). Not using temperature monitoring seems to be a risk factor as well (odds ratio, 3.00; 95% CI, 0.87-10.12). Significant protective factors against core hypothermia were heavier body weight (odds ratio, 0.94; 95% CI, 0.89-0.98), higher preoperative body temperature (odds ratio, 0.31; 95% CI, 0.15-0.65), and warmer ambient operating room temperature (odds ratio, 0.67; 95% CI, 0.51-0.88). In conclusion, the incidence of core hypothermia (Tc <36.0 degrees C) at the time of admission to the general ICU is still frequent. To reduce the incidence, more efforts and concern should be taken to prevent core hypothermia, especially in the patient with high ASA physical status, undergoing more intensive and lengthy surgery, and using combined epidural and general anesthesia.

IMPLICATIONS

In an effort to decrease the frequent incidence of core hypothermia at the time of admission to the general surgical intensive care unit, this prospective study showed that high ASA physical status, the use of a combined epidural and general anesthesia, surgery lasting longer than 2 h, and extensive surgery were the important risk factors, whereas heavier body weight, higher preoperative body temperature, and warmer ambient operating room temperature were important protective factors.

Amino acid infusion induces thermogenesis and reduces blood loss during hip arthroplasty under spinal anesthesia

The thermic effect of amino acids is augmented under general anesthesia and counteracts hypothermia. Mild hypothermia may increase surgical bleeding. We studied whether amino acids also induce thermogenesis under spinal anesthesia and whether this endogenous heat production reduces bleeding during hip arthroplasty. Rectal temperature, oxygen uptake, and perioperative bleeding were measured in 22 patients receiving an IV amino acid mixture (Vamin 18), 240 kJ/h) for 1 h before and then during spinal anesthesia and in 24 control patients receiving acetated Ringer's solution. Blood loss was calculated after surgery by weighing the swabs and the content of the suction tubes after subtraction of the saline used. After surgery, the closed drains were weighed after 24 h. In the amino acid group, the preanesthesia temperature increased by 0.4 degrees C +/- 0.2 degrees C (P < 0.01) and was unchanged in controls. At end of surgery, core temperature had decreased by 0.9 degrees C +/- 0.4 degrees C in controls and by 0.4 degrees C +/- 0.3 degrees C in the amino acid patients (P < 0.01). Oxygen uptake increased by 26 +/- 7 mL/min, or 16% +/- 5% (P < 0.05), from baseline in the amino acid patients, whereas it was unchanged in the controls. Blood loss during surgery was significantly larger in the control patients (702 +/- 344 mL) than in the amino acid patients (516 +/- 272 mL) (P < 0.05). After surgery, there were no significant differences in shed blood volume. In conclusion, amino acid infusion also induced a thermogenic response under spinal anesthesia. In addition, the prevention of temperature decrease during spinal anesthesia seemed to have a positive effect on intraoperative blood loss.

IMPLICATIONS

Infusion of a balanced mixture of amino acids during spinal anesthesia prevented core body temperature decrease. Bleeding was also less pronounced.

Preoperative risk factors of intraoperative hypothermia in major surgery under general anesthesia

Preoperative factors, such as age and body habitus, affect intraoperative hypothermia during general anesthesia. In a preliminary study, we developed a logistic model to retrospectively evaluate predictors of intraoperative hypothermia in patients who received major surgery. The following factors were selected to develop the model: Z = -15.014 + 0.097 x (Age) + 0.263 x (Height) - 0.323 x (Weight) - 0.055 x (Preoperative systolic blood pressure) - 0.121 x (Preoperative heart rate). By using this model, the probability of hypothermia can be estimated by applying the following formula: Probability = 1/(1 + e(-)(Z)). If an estimated probability of hypothermia was >0.5, the sensibility of prediction was 81.5% and the specificity was 83%. In the second study, the model was applied prospectively to other patients, and the validity of the logistic model was evaluated. The core temperature showed a significant decrease in patients with a probability >0.7, who were predicted to be hypothermic, and their thermoregulatory vasoconstriction threshold also showed a significant decrease, compared with the patients with a probability <==0.3, who were predicted to be normothermic. We concluded that intraoperative hypothermia could be predicted from preoperative characteristics such as age, height, weight, systolic blood pressure, and heart rate.

IMPLICATIONS

Increases in age and height and decreases in weight systolic blood pressure and heart rate are major preoperative risk factors of intraoperative hypothermia during major surgery.

[Severe hypothermia associated with cesarean section under spinal anesthesia]

Temperature monitoring and prevention of hypothermia are rarely used during spinal anaesthesia for caesarean section because hypothermia risk is considered very low. However, in same conditions, we observed two cases of severe hypothermia. We report these two cases and discuss the effects of spinal anaesthesia on thermoregulatory system. Hypothermia seems explained by the effects of perimedullar anaesthesia that decrease the shivering and the vasoconstriction thresholds. These effects are potentiated by morphinomimetic adjunction. At last, we recall prophylactics measures.

A novel thermoregulatory system maintains perioperative normothermia in children undergoing elective surgery

BACKGROUND

Body heat loss during anaesthesia may result in increased morbidity, particularly in high-risk populations such as children. To avoid hypothermia, a novel thermoregulatory system (Allon) was devised. We tested the safety and efficacy of this system in maintaining normothermia in children undergoing routine surgical procedures.

METHODS

The system consists of a computerized body, which receives continuous afferent data, i.e. core (rectal) temperature. These data are then compared with a preset temperature (37 degrees C) and a microprocessor heating/cooling unit warms/cools the temperature of circulating water in a garment that is specially designed to allow maximal coverage of body surface area, without impingement on the surgical field. Water temperature to the garment was limited to a maximum of 39.5 degrees C. Continuous perioperative monitoring of skin and rectal temperature, heart rate and blood pressure was performed. Postoperative shivering and adverse effects were also assessed.

RESULTS

The Allon system was used in 38 patients aged 3 months to 14 years undergoing surgery under general anaesthesia lasting more than 30 min. Fifty to 80% body surface area was covered by the garment. Mean operative and postoperative core temperatures were 36.9 +/- 0.5 degrees C and 36.7 +/- 0.5 degrees C, respectively. Intraoperative skin temperatures were maintained at 34.4 +/- 2.7 degrees C. The average core- to-periphery intraoperative gradient was 2.9 +/- 4.9 degrees C. Postoperative shivering was absent in 36 cases and mild in two cases. No device-related adverse effects were observed.

CONCLUSIONS

Perioperative thermoregulation using the Allon system is safe and effective in maintaining body temperature within a narrow range in children undergoing brief surgical procedures.

What are the most important risk factors for a patient's developing intraoperative hypothermia?

Anesthesiologists attempt to maintain perioperative normothermia for surgical patients. We surveyed clinical anesthesiologists and physician researchers and asked them to prioritize risk factors for a patient to develop intraoperative hypothermia. The questionnaire included 41 factors associated with changes in patient temperature identified during a computerized literature search. We asked respondents to estimate the relative importance of each risk factor on a 10-point scale. The survey was mailed to two groups: 1) 180 anesthesiologists (n = 84 respondents) randomly selected from the 1999 American Society of Anesthesiologists Members Directory and to 2) 24 physician researchers (n = 12 respondents) in thermoregulation. Researchers rated the following to be the most important risk factors for hypothermia (in sequence): neonates, a low ambient operating room temperature, burn injuries, general anesthesia with neuraxial anesthesia, geriatric patients, low temperature of the patient before induction, a thin body type, and large blood loss. The results for the clinician group were similar, because the median differences between the groups' results were two or fewer units for all items. The risk factors identified to be most important can now be further evaluated in clinical trials to develop a multivariate predictive tool for calculating a patient's a priori risk for developing hypothermia.

IMPLICATIONS

Surveys of clinicians and physician researchers identified what they consider to be the most important risk factors for perioperative hypothermia (e.g., neonates, a low ambient operating room temperature, burn patients, and general anesthesia with neuraxial anesthesia).

Infection control in the ICU

Nosocomial infections (NIs) now concern 5 to 15% of hospitalized patients and can lead to complications in 25 to 33% of those patients admitted to ICUs. The most common causes are pneumonia related to mechanical ventilation, intra-abdominal infections following trauma or surgery, and bacteremia derived from intravascular devices. This overview is targeted at ICU physicians to convince them that the principles of infection control in the ICU are based on simple concepts and that the application of preventive strategies should not be viewed as an administrative or constraining control of their activity but, rather, as basic measures that are easy to implement at the bedside. A detailed knowledge of the epidemiology, based on adequate surveillance methodologies, is necessary to understand the pathophysiology and the rationale of preventive strategies that have been demonstrated to be effective. The principles of general preventive measures such as the implementation of standard and isolation precautions, and the control of antibiotic use are reviewed. Specific practical measures, targeted at the practical prevention and control of ventilator-associated pneumonia, sinusitis, and bloodstream, urinary tract, and surgical site infections are detailed. Recent data strongly confirm that these strategies may only be effective over prolonged periods if they can be integrated into the behavior of all staff members who are involved in patient care. Accordingly, infection control measures are to be viewed as a priority and have to be integrated fully into the continuous process of improvement of the quality of care.

Preoperative blood pressure and intraoperative hypothermia during lower abdominal surgery

BACKGROUND

Preoperative factors including age and body habitus affect intraoperative hypothermia during general anesthesia. We hypothesized that preoperative blood pressure also plays a contributory role in the induction of intraoperative hypothermia.

METHODS

We evaluated the effect of preoperative systolic blood pressure (SBP) on core temperature during lower abdominal surgery under general anesthesia. In 36 female patients under 65 years of age, patients with a preoperative SBP of 140 mmHg or greater upon arrival in the operating theater were assigned to the high SBP group (n=18), while those with SBP below 140 mmHg were assigned to the normal SBP group (n=18). Anesthesia was maintained with isoflurane and nitrous oxide combined with epidural buprenorphine, and routine thermal care was provided intraoperatively.

RESULTS

There were no significant differences in age, height or weight between the two groups. Tympanic membrane temperature in the normal SBP group started to decrease significantly from 15 min after induction of anesthesia compared to that in the high SBP group, and continued to decrease further at two hours after induction. Vasoconstriction threshold, determined to be tympanic membrane temperature at the time when a forearm minus finger skin surface gradient exceeded 0 degrees C, was significantly higher in the high SBP group than in the normal SBP group.

CONCLUSION

These results suggest that preoperative SBP has some preventive effect on the decrease in intraoperative core temperature during lower abdominal surgery under general anesthesia.

Effects of warming therapy on pressure ulcers--a randomized trial

Postoperative pressure ulcers are a common and expensive problem. Intraoperative hypothermia also is a common problem and may have a connection with impaired tissue viability. Researchers in this study hypothesized that intraoperative control of hypothermia may reduce the incidence of postoperative pressure ulcers. A randomized clinical trial (n = 338) was used to test the effects of using forced air warming therapy versus standard care. Results indicated an absolute risk reduction in pressure ulcers of 4.8% (i.e., 10.4% to 5.6%) with a relative risk reduction of 46% in patients who received warming therapy. Although not reaching statistical significance, the clinical significance of almost halving the pressure ulcer rate is important. A correlation between body temperature and postoperative pressure ulcers was established.

Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: results from overview of randomised trials

OBJECTIVES

To obtain reliable estimates of the effects of neuraxial blockade with epidural or spinal anaesthesia on postoperative morbidity and mortality.

DESIGN

Systematic review of all trials with randomisation to intraoperative neuraxial blockade or not.

STUDIES

141 trials including 9559 patients for which data were available before 1 January 1997. Trials were eligible irrespective of their primary aims, concomitant use of general anaesthesia, publication status, or language. Trials were identified by extensive search methods, and substantial amounts of data were obtained or confirmed by correspondence with trialists.

MAIN OUTCOME MEASURES

All cause mortality, deep vein thrombosis, pulmonary embolism, myocardial infarction, transfusion requirements, pneumonia, other infections, respiratory depression, and renal failure.

RESULTS

Overall mortality was reduced by about a third in patients allocated to neuraxial blockade (103 deaths/4871 patients versus 144/4688 patients, odds ratio=0.70, 95% confidence interval 0.54 to 0.90, P=0. 006). Neuraxial blockade reduced the odds of deep vein thrombosis by 44%, pulmonary embolism by 55%, transfusion requirements by 50%, pneumonia by 39%, and respiratory depression by 59% (all P<0.001). There were also reductions in myocardial infarction and renal failure. Although there was limited power to assess subgroup effects, the proportional reductions in mortality did not clearly differ by surgical group, type of blockade (epidural or spinal), or in those trials in which neuraxial blockade was combined with general anaesthesia compared with trials in which neuraxial blockade was used alone.

CONCLUSIONS

Neuraxial blockade reduces postoperative mortality and other serious complications. The size of some of these benefits remains uncertain, and further research is required to determine whether these effects are due solely to benefits of neuraxial blockade or partly to avoidance of general anaesthesia. Nevertheless, these findings support more widespread use of neuraxial blockade.

Hypothermia After Vascular Surgery: Complications, Prevention, and Treatment

Virtually all anesthetics render patients poikilothermic and body temperature invariably decreases during surgery. Dur ing vascular occlusion and resulting ischemia to the brain, kidneys, and spinal cord, hypothermia is often beneficial by decreasing metabolic demands and protecting from injury. Residual hypothermia, however, in the postoperative period is rarely desirable and hypothermia-related complications are well-known. Even mild hypothermia can exacerbate the stress response by activation of the sympathetic nervous system, resulting in increased catecholamines, which can precipitate myocardial ischemia and cardiac morbidity. As little as 2°C of core hypothermia impairs coagulation and predisposes to postoperative bleeding, which is especially problematic in the presence of fresh vascular anastomoses. Hypothermia also slows emergence from general anesthesia by both pharmacokinetic and pharmacodynamic mecha nisms. In vascular surgery patients, body temperature should be carefully monitored and controlled with the same level of attention that is given to the other vital signs. By active cooling and warming at the appropriate perioperative timepoints, outcomes can be improved and morbidity re duced in patients undergoing vascular surgery. Copyright © 2000 by W.B. Saunders Company.

"Deep-forehead" temperature correlates well with blood temperature

PURPOSE

To evaluate the accuracy and precision of "deep-forehead" temperature with rectal, esophageal, and tympanic membrane temperatures, compared with blood temperature.

METHODS

We studied 41 ASA physical status 1 or 2 patients undergoing abdominal and thoracic surgery scheduled to require at least three hours. "Deep-forehead" temperature was measured using a Coretemp thermometer (Terumo, Tokyo, Japan). Blood temperature was measured with a thermistor of a pulmonary artery. Rectal, tympanic membrane, and distal esophageal temperatures were measured with thermocouples. All temperatures were recorded at 20 min intervals after the induction of anesthesia. We considered blood temperature as the reference value. Temperatures at the other four sites were compared with blood temperature using correlation, regression, and Bland and Altman analyses. We determined accuracy (mean difference between reference and test temperatures) and precision (standard deviation of the difference) of 0.5 degrees C to be clinically acceptable.

RESULTS

"Deep-forehead" temperature correlated well with blood temperature as well as other temperatures, the determination coefficients (r2) being 0.85 in each case. The bias for the "deep-forehead" temperature was 0.0 degrees C, which was the same as tympanic membrane temperature and was smaller than rectal and esophageal temperatures. The standard deviation of the differences for the "deep-forehead" temperature was 0.3 degrees C, which was the same as rectal temperature.

CONCLUSIONS

We have demonstrated that the "deep-forehead" temperature has excellent accuracy and clinically sufficient precision as well as other three core temperatures, compared with blood temperature.

Temperature monitoring and management during neuraxial anesthesia: an observational study

Temperature monitoring and thermal management are rare during spinal or epidural anesthesia because clinicians apparently restrict monitoring to patients with an expected risk of hypothermia. This implies that anesthesiologists can predict patient thermal status without monitoring core temperature. We therefore, tested the hypotheses that during neuraxial anesthesia: 1) amount of core hypothermia depends on the magnitude and duration of surgery; 2) temperature monitoring and thermal management are used selectively in patients at high risk of hypothermia; and 3) anesthesiologists can estimate patient thermal status. We evaluated thermal status on arrival in the recovery room along with intraoperative thermal management and monitoring in 120 patients. Anesthesiologists were asked if their patients were hypothermic (<36 degrees C). There was no correlation between the magnitude or duration of surgery and initial postoperative core temperature in unwarmed patients. Temperature monitoring and thermal management were not used selectively in high-risk patients. Initial postoperative tympanic membrane temperatures were <36 degrees C in 77% of patients and <35 degrees C in 22%. Body temperature was monitored intraoperatively in 27% of the patients and forced-air warming was used in 31%. Anesthesiologists failed to accurately estimate whether their patients were hypothermic. Our results suggest that temperature monitoring and management during neuraxial anesthesia is currently inadequate.

IMPLICATIONS

In this observational study, we evaluated core temperatures and intraoperative thermal management in patients undergoing spinal or epidural anesthesia. Hypothermia was common, however, rarely detected either by temperature monitoring or estimates by anesthesiologists. In addition, it was not treated with active warming. Consequently, temperature monitoring and management have to be done during neuraxial anesthesia.

Association between postoperative hypothermia and adverse outcome after coronary artery bypass surgery

BACKGROUND

We examined the effect on outcome of mild hypothermia (< 36 degrees C) upon intensive care unit (ICU) admission on patient outcome after coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB).

METHODS

We performed a retrospective database analysis of 5,701 isolated CABG patients requiring CPB, operated upon from January 1995 to June 1997. Patients were classified as either hypo- (< 36 degrees C) or normothermic (> or = 36 degrees C) upon ICU admission. ICU admission bladder core temperature (BCT) versus outcome was evaluated. Outcome measures included mortality, resource utilization (mechanical ventilation time, ICU and hospital length of stay, and postoperative packed red blood cell transfusion), and major morbidity (cardiac, renal, neurologic, or major infection).

RESULTS

Overall, patients admitted to the ICU with BCT < 36 degrees C had a significantly greater mortality (p = 0.02), prolonged mechanical ventilation (p = 0.007), packed red blood cell transfusion (p = 0.001), ICU (p = 0.01), and hospital (p = 0.005) length of stay.

CONCLUSIONS

BCT of less than 36 degrees C, upon ICU admission, has a significant association with adverse outcome after CABG with CPB. M An __ Tl QA_7_t-0

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.