Pupillary reflex dilation and skin temperature to assess sensory level during combined general and caudal anesthesia in children.
BACKGROUND
Regional anesthesia causes sympathetic blockade, vasodilation and higher skin temperature in anesthetized dermatomes. Measurement of skin temperature changes might provide a useful estimate of the level of caudal anesthesia in children. Pupillary reflex dilation (PRD) allows estimation of the sensory level during combined general/epidural anesthesia in adults, but has not been assessed in children. This study was designed to evaluate skin temperature and PRD as methods of estimating sensory level in children receiving combined general/caudal epidural anesthesia.


METHODS
Twenty ASA I and II children aged 10 months-5 years were enrolled. Anesthesia was induced with sevoflurane and N2O in O2 and maintained with 1 MAC isoflurane and air in O2. Caudal epidural anesthesia was achieved by injection of 1 ml x kg(-1) 0.25% bupivacaine. Skin temperature was measured by rapid response infrared thermometry. PRD was measured using an ophthalmic ultrasound biomicroscope (UBM). The three criteria used to estimate sensory level were a drop in skin temperature of 0.5 degrees C between dermatomes, PRD of 50% and PRD of 0.2 mm.


RESULTS
A drop in skin temperature of 0.5 degrees C between dermatomes allowed estimation of the sensory level in only 20% of patients. PRD of 50%, and PRD of 0.2 mm allowed estimation of the sensory level in 45 and 100% of patients, respectively. PRD was significantly greater above the T10 dermatome compared with L2 (P < 0.01). The maximum pupillary dilation was significantly greater in children over 2 years of age [1.3 +/- 0.8 mm sd)] compared with children less than two years of age [0.6 +/- 0.3 mm sd)].


CONCLUSIONS
Skin temperature cannot be used to estimate sensory level during combined general/caudal epidural anesthesia. PRD of 0.2 mm is sensitive to the loss of analgesia but is not clinically useful. PRD may be useful above 2 years of age.
Emery
John
J
Department of Anaesthesia, University of Toronto and The Hospital for Sick Children, Toronto, Ontario, Canada. jgbemery@doctors.org.uk
Ho
David
D
MacKeen
Leslie
L
Héon
Elise
E
Bissonnette
Bruno
B
D000704:Analysis of Variance; D000763:Anesthesia, Caudal / Q000379:methods*; D000768:Anesthesia, General / Q000379:methods*; D019162:Anesthetics, Combined / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000779:Anesthetics, Local / Q000494:pharmacology; D002045:Bupivacaine / Q000494:pharmacology; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007530:Isoflurane / Q000494:pharmacology; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology; D009609:Nitrous Oxide / Q000494:pharmacology; D011446:Prospective Studies; D012025:Reflex, Pupillary / Q000187:drug effects*; D012680:Sensitivity and Specificity; D012684:Sensory Thresholds / Q000187:drug effects*; D000077149:Sevoflurane; D012881:Skin Temperature / Q000187:drug effects*
D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane; D009609:Nitrous Oxide; D002045:Bupivacaine