Beth Glosten

Thermoregulatory vasoconstriction decreases cutaneous heat loss

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

Postcesarean analgesia with both epidural morphine and intravenous patient-controlled analgesia: neurobehavioral outcomes among nursing neonates.

PhD*‘I[ Departments of *Anesthesia and Critical Care, P[Statistics, and SObstetrics and Gynecology, University of Chicago, Chicago, Illinois; Department of Anesthesia, tuniversity of Washington, Seattle, Washington, and §Saint Francis Hospital, Blue Island, Illinois; and IlDepartment of Psychology, University of Beloit, Beloit, Wisconsin Among nursing parturients after cesarean delivery, in- travenous patient-controlled analgesia (PCA) with me- peridine is associated with significantly more neonatal neurobehavioral depression than PCA with morphine. A single dose of epidural morphine (4 mg) decreases postcesarean opioid analgesic requirements and may reduce or prevent neonatal neurobehavioral depres- sion associated with PCA meperidine. Prospectively, 102 term parturients underwent cesarean delivery with epidural anesthesia, 2% lidocaine and epinephrine 1:200,000. After umbilical cord clamping, each patient received epidural morphine 4 mg and was randomly allocated to receive either PCA meperidine or PCA morphine. Initial neonatal characteristics, included ges- tational age, Apgar scores, weight, and umbilical cord gas partial pressures. Brazelton Neonatal Behavioral Assessment Scale (NBAS) examinations were per- formed on each of the first 4 days of life. Nursing infants (n = 47) were grouped according to maternal PCA opi- oid in breast milk (meperidine [n = 241 or morphine [n = 231); bottle-fed infants (n = 56) served as the con- trol group. The three infant groups were equivalent with respect to initial characteristics and NBAS scores on the first 2 days of life. On the third day of life, infants in the morphine group were significantly more alert and oriented to animate human cues compared with infants in the meperidine or control group. On the fourth day of life, infants in the morphine group re- mained significantly more alert and oriented to animate human auditory cues than infants in the meperidine group. Average PCA opioid consumption through 48 h postpartum was equivalent (0.54 mg/ kg morphine and 4.7 mg/kg meperidine); however, even with these small doses, meperidine was associated with signifi- cantly poorer neonatal alertness orientation than morphine. Morphine is the PCA opioid of choice for postcesarean analgesia among nursing parturients. Im- plications: Among nursing parturients after cesarean delivery, intravenous patient-controlled analgesia with meperidine is associated with more neonatal neurobe- havioral depression than patient-controlled analgesia with morphine. In this study, we found that nursing infants exposed to morphine were more alert and ori- ented to animate human cues than those exposed meperidine. (Anesth Analg 1997;85:600-6)

THERMAL BALANCE AND TREMOR PATTERNS DURING EPIDURAL ANESTHESIA

Five healthy, nonpregnant volunteers were studied before and after induction of lumbar epidural anesthesia to determine the cause of central hypothermia during epidural anesthesia. Cutaneous heat loss was measured from 10 area-weighted sites using thermal flux transducers. Oxygen consumption was measured and converted to heat production in watts (W). After a 2-h control period at approximately 20 degrees C, epidural anesthesia was induced by injection of 30-50 ml 3% chloroprocaine. Additional boluses were given to extend the sensory blockade to at least the T5 dermatome. Tremor during epidural anesthesia was compared with normal shivering induced by rapid central venous infusion of approximately 4 l iced saline in six unanesthetized volunteers. Average skin temperature and cutaneous heat loss decreased during the control period, while tympanic membrane temperature remained stable. During the 1st h of epidural blockade, tympanic membrane temperature decreased 1.1 +/- 0.3 degrees C, and average skin temperature increased 0.9 +/- 0.5 degrees C. Cutaneous heat loss increased 16 +/- 6% (15 +/- 5 W), but metabolic heat production increased even more (and was associated with a shivering-like tremor). Tremor during epidural anesthesia and shivering induced by iced saline infusion had similar synchronous waxing-and-waning patterns. No abnormal EMG patterns were detected during epidural anesthesia. We conclude that central hypothermia during the 1st h of epidural anesthesia does not result from heat loss to the environment in excess of metabolic heat production, but results primarily from redistribution of body heat from central to peripheral tissues. Analysis of the tremor patterns suggests that oscillations recorded during epidural anesthesia in nonpregnant individuals is normal thermoregulatory shivering. Shivering occurred sooner and was more intense during iced saline infusion than during epidural anesthesia, despite comparable central hypothermia. The low intensity of shivering during epidural anesthesia, and in some individuals the delay in onset, may result from blockade of afferent cutaneous cold signals.

Subjective and Psychomotor Effects of Sub anesthetic Doses of Propofol in Healthy Volunteers

Propofol is increasingly being used in medical and surgical procedures in which conscious sedation of the patient is desired. The mood-altering and psychomotor effects of subanesthetic concentrations of propofol have not been well characterized. Therefore, we examined the effects of intravenous infusions of different subanesthetic doses of propofol on mood and psychomotor/cognitive performance in healthy volunteers (n = 10). A prospective, randomized, placebo-controlled, double-blind, crossover design was used in which subjects first were administered an intravenous loading dose of propofol or placebo (Intralipid) and then were infused over a 20-min period with a given dose of propofol or placebo. Each subject received placebo (Intralipid loading dose and infusion), low-dose propofol (0.08 mg/kg loading dose and 0.5 mg.kg-1.h-1 infusion), moderate-dose propofol (0.16 mg/kg loading dose and 1.0 mg.kg-1.h-1 infusion), and high-dose propofol (0.32 mg/kg loading dose and 2.0 mg.kg-1.h-1 infusion) in four sessions spaced approximately 1 week apart. Propofol induced changes in mood in a dose-related fashion. Some of these mood-altering effects lingered for as long as 30 min after termination of the infusion, but, in general mood had returned to baseline levels 1 h after termination of the infusion. Intralipid induced no changes in mood during the infusion period. Psychomotor functioning was impaired during, and anterograde amnesia was present after, the high-dose propofol infusion. These results suggest that propofol as a sedative has a spectrum of effects that are well-suited for ambulatory surgery (e.g., sedation, amnesia, and rapid and complete recovery).

Opioid antagonist adjuncts to epidural morphine for postcesarean analgesia: maternal outcomes.

This prospective, randomized, controlled investigation compared the effects of three prophylactic mu-opioid antagonists, epidural butorphanol (BU) 3 mg, epidural nalbuphine (NB) 10 mg, and oral naltrexone (NX) 6 mg, on postcesarean epidural morphine analgesia. After randomization, 102 term parturients underwent cesarean delivery with epidural anesthesia, 2% lidocaine and epinephrine 1:200,000. When the umbilical cord was clamped, each patient received one epidural solution (containing morphine 4 mg plus either saline or treatment drug), and one oral capsule (containing either placebo or treatment drug) in a double-blind manner. Maternal outcomes included pain and satisfaction [assessed with 100-mm visual analog scales (VAS)], and the incidence and severity of respiratory depression, somnolence, pruritus, nausea, and emesis. Through the first 12 h postpartum, the BU group achieved significantly greater analgesia than the morphine sulfate (control) (MS), NB, and NX groups, a significantly lower incidence of severe pruritus than the MS group, and significantly greater satisfaction than MS and NX groups. Epidural morphine and BU promoted better analgesia and satisfaction than any previously documented postcesarean regimen.

THE EPINEPHRINE TEST DOSE IN OBSTETRICS : NOTE THE LIMITATIONS

D espite an apparent decline in the frequency of fatal systemic toxic reactions to local anesthetics since 1980 (l), this complication represents the most serious anesthetic risk to the parturient during epidural anesthesia. Many safety steps were advocated after the concern over bupivacaine toxicity in 1979, including the epinephrine test dose introduced by Moore and Batra (2). They found that epinephrine 15 kg IV created a tachycardia sufficient to serve as a reliable indicator of unintentional vascular placement of an epidural needle or catheter. Guinard et al. (3) later refined this test by showing that a heart rate change of 20 bpm was a sensitive and specific threshold to indicate intravascular injection. Although this test is limited in the presence of p-adrenergic blockade, advanced age, and general anesthesia, it has remained a useful tool for the surgical anesthesiologist. Attempts to transfer this tool to the obstetrical suite have been less successful. Pain from ongoing uterine contractions results in maternal heart rate variations during labor, which confuse interpretation of a heart rate change after the injection of an epinephrine test dose. In addition, the pregnant patient has a different sensitivity to catecholamines, and the threshold for a positive heart rate response to epinephrine differs in obstetric patients. When Leighton et al. (4) applied surgical criteria (an increase in heart rate of 25 bpm within 2 min of injection) to laboring women who received epinephrine 15 PLg IV, only 5 of 10 responded with such a tachycardia. Of the 10 study patients, 9 had a positive response when an alternative (retrospectively derived) definition of a positive response (an increase in heart rate of >lO bpm over the maximal heart rate observed during the 2 min before injection) was applied. Color-ma-Roman0 et al. (5) later confirmed that the threshold of 10 bpm is appropriate in the laboring patient, but only if attention is paid to the rate of increase in the heart rate, which must be distinguished from the tachycardia associated with