Genetic variations associated with red hair color and fear of dental pain, anxiety regarding dental care and avoidance of dental care.

BACKGROUND: Red hair color is caused by variants of the melanocortin-1 receptor (MC1R) gene. People with naturally red hair are resistant to subcutaneous local anesthetics and, therefore, may experience increased anxiety regarding dental care. The authors tested the hypothesis that having natural red hair color, a MC1R gene variant or both could predict a patient's experiencing dental care-related anxiety and dental care avoidance. METHODS: The authors enrolled 144 participants (67 natural red-haired and 77 dark-haired) aged 18 to 41 years in a cross-sectional observational study. Participants completed validated survey instruments designed to measure general and dental care-specific anxiety, fear of dental pain and previous dental care avoidance. The authors genotyped participants' blood samples to detect variants associated with natural red hair color. RESULTS: Eighty-five participants had MC1R gene variants (65 of the 67 red-haired participants and 20 of the 77 dark-haired participants) (P < .001). Participants with MC1R gene variants reported significantly more dental care-related anxiety and fear of dental pain than did participants with no MC1R gene variants. They were more than twice as likely to avoid dental care as were the participants with no MC1R gene variants, even after the authors controlled for general trait anxiety and sex. CONCLUSION: Dental care-related anxiety, fear of dental pain and avoidance of dental care may be influenced by genetic variations. CLINICAL IMPLICATIONS: Dentists should evaluate all patients, but especially those with naturally red hair, for dental care-related anxiety and use appropriate modalities to manage the patients' anxiety.

Aestiva ventilation mode selector switch failures.

We describe three cases of previously unreported failures of the Bag-Ventilator Switch in Aestiva/5 anesthesia machines (GE Healthcare/Datex-Ohmeda, Madison, WI). Each failure mode produced a large breathing-circuit leak. Examination of the switches revealed a cracked toggle actuator, residue build-up, and a cracked selector switch housing as causes for the failures. When a leak with no visible cause develops, consider advancing the mode selector switch fully to its mechanical limit or consider that the toggle actuator or its anchoring mechanism may have failed. These cases demonstrate that it is imperative to always be prepared to immediately use an alternate method for ventilation. Cases describing failure to ventilate due to sudden equipment malfunction underscore the need to always have functioning backup ventilation equipment available.

Women with red hair report a slightly increased rate of bruising but have normal coagulation tests.

There is an anecdotal impression that redheads experience more perioperative bleeding complications than do people with other hair colors. We, therefore, tested the hypothesis that perceived problems with hemostasis could be detected with commonly used coagulation tests. We studied healthy female Caucasian volunteers, 18 to 40 yr of age, comparable in terms of height, weight, and age, with natural bright red (n = 25) or black or dark brown (n = 26) hair. Volunteers were questioned about their bleeding history and the following tests were performed: complete blood count, prothrombin time/international normalized ratio, activated partial thromboplastin time, platelet function analysis, and platelet aggregation using standard turbidimetric methodology. Agonists for aggregation were adenosine diphosphate, arachidonic acid, collagen, epinephrine, and two concentrations of ristocetin. The red-haired volunteers reported significantly more bruising, but there were no significant differences between the red-haired and dark-haired groups in hemoglobin concentration, platelet numbers, prothrombin time/international normalized ratio, or activated partial thromboplastin time. Furthermore, no significant differences in platelet function, as measured by platelet function analysis or platelet aggregometry, were observed. We conclude that if redheads have hemostasis abnormalities, they are subtle.

Increased sensitivity to thermal pain and reduced subcutaneous lidocaine efficacy in redheads.

BACKGROUND: Anesthetic requirement in redheads is exaggerated, suggesting that redheads may be especially sensitive to pain. Therefore, the authors tested the hypotheses that women with natural red hair are more sensitive to pain and that redheads are resistant to topical and subcutaneous lidocaine. METHODS: The authors evaluated pain sensitivity in red-haired (n = 30) or dark-haired (n = 30) women by determining the electrical current perception threshold, pain perception, and maximum pain tolerance with a Neurometer CPT/C (Neurotron, Inc., Baltimore, MD). They evaluated the analogous warm and cold temperature thresholds with the TSA-II Neurosensory Analyzer (Medoc Ltd., Minneapolis, MN). Volunteers were tested with both devices at baseline and with the Neurometer after 1-h exposure to 4% liposomal lidocaine and after subcutaneous injection of 1% lidocaine. Data are presented as medians (interquartile ranges). RESULTS: Current perception, pain perception, and pain tolerance thresholds were similar in the red-haired and dark-haired women at 2,000, 250, and 5 Hz. In contrast, redheads were more sensitive to cold pain perception (22.6 [15.1-26.1] vs. 12.6 [0-20] degrees C; P = 0.004), cold pain tolerance (6.0 [0-9.7] vs. 0.0 [0.0-2.0] degrees C; P = 0.001), and heat pain (46.3 [45.7-47.5] vs. 47.7 [46.6-48.7] degrees C; P = 0.009). Subcutaneous lidocaine was significantly less effective in redheads (e.g., pain tolerance threshold at 2,000-Hz stimulation in redheads was 11.0 [8.5-16.5] vs. > 20.0 (14.5 to > 20) mA in others; P = 0.005). CONCLUSION: Red hair is the phenotype for mutations of the melanocortin-1 receptor. Results indicate that redheads are more sensitive to thermal pain and are resistant to the analgesic effects of subcutaneous lidocaine. Mutations of the melanocortin-1 receptor, or a consequence thereof, thus modulate pain sensitivity.

Anesthetic requirement is increased in redheads.

BACKGROUND: Age and body temperature alter inhalational anesthetic requirement; however, no human genotype is associated with inhalational anesthetic requirement. There is an anecdotal impression that anesthetic requirement is increased in redheads. Furthermore, red hair results from distinct mutations of the melanocortin-1 receptor. Therefore, the authors tested the hypothesis that the requirement for the volatile anesthetic desflurane is greater in natural redheaded than in dark-haired women. METHODS: The authors studied healthy women with bright red (n = 10) or dark (n = 10) hair. Blood was sampled for subsequent analyses of melanocortin-1 receptor alleles. Anesthesia was induced with sevoflurane and maintained with desflurane randomly set at an end-tidal concentration between 5.5 and 7.5%. After an equilibration period, a noxious electrical stimulation (100 Hz, 70 mA) was transmitted through bilateral intradermal needles. If the volunteer moved in response to stimulation, desflurane was increased by 0.5%; otherwise, it was decreased by 0.5%. This was continued until volunteers "crossed over" from movement to nonmovement (or vice versa) four times. Individual logistic regression curves were used to determine desflurane requirement (P50). Desflurane requirements in the two groups were compared using Mann-Whitney nonparametric two-sample test; P < 0.05 was considered statistically significant. RESULTS: The desflurane requirement in redheads (6.2 vol% [95% CI, 5.9-6.5]) was significantly greater than in dark-haired women (5.2 vol% [4.9-5.5]; P = 0.0004). Nine of 10 redheads were either homozygous or compound heterozygotes for mutations on the melanocortin-1 receptor gene. CONCLUSIONS: Red hair seems to be a distinct phenotype linked to anesthetic requirement in humans that can also be traced to a specific genotype.

Alternative management techniques for the difficult airway: optical stylets.

PURPOSE OF REVIEW: We present the newest devices being promoted for difficult-airway management. Our focus is on optical stylets which offer a forward view from the stylet end positioned within the tip of the endotracheal tube. RECENT FINDINGS: Reports suggest that these devices are mastered quickly and offer effective airway management aid. Available in adult and pediatric sizes they are economically priced at approximately US$ 3000. SUMMARY: Generally favorable experience with use of optical stylets continues to be reported. Our survey of clinicians' opinions reflects our own experience; these devices are unique and are attractive adjuncts to standard- and difficult-airway carts.

Dexmedetomidine and meperidine additively reduce the shivering threshold in humans.

BACKGROUND AND PURPOSE: Hypothermia might prove to be therapeutically beneficial in stroke victims; however, even mild hypothermia provokes vigorous shivering. Meperidine and dexmedetomidine each linearly reduce the shivering threshold (triggering core temperature) with minimal sedation. We tested the hypothesis that meperidine and dexmedetomidine synergistically reduce the shivering threshold without producing substantial sedation or respiratory depression. METHODS: We studied 10 healthy male volunteers (18 to 40 years) on 4 days: (1) control (no drug); (2) meperidine (target plasma level 0.3 microg/mL); (3) dexmedetomidine (target plasma level 0.4 ng/mL); and (4) meperidine plus dexmedetomidine (target plasma levels of 0.3 microg/mL and 0.4 ng/mL, respectively). Lactated Ringer's solution (approximately 4 degrees C) was infused through a central venous catheter to decrease tympanic membrane temperature by approximately 2.5 degrees C/h; mean skin temperature was maintained at 31 degrees C. An increase in oxygen consumption >25% of baseline identified the shivering threshold. Sedation was evaluated by using the Observer's Assessment of Sedation/Alertness scale. Two-way repeated-measures ANOVA was used to identify interactions between drugs. Data are presented as mean+/-SD; P<0.05 was statistically significant. RESULTS: The shivering thresholds on the study days were as follows: control, 36.7+/-0.3 degrees C; dexmedetomidine, 36.0+/-0.5 degrees C (P<0.001 from control); meperidine, 35.5+/-0.6 degrees C (P<0.001); and meperidine plus dexmedetomidine, 34.7+/-0.6 degrees C (P<0.001). Although meperidine and dexmedetomidine each reduced the shivering threshold, their interaction was not synergistic but additive (P=0.19). There was trivial sedation with either drug alone or in combination. Respiratory rate and end-tidal Pco2 were well preserved on all days. CONCLUSIONS: Dexmedetomidine and meperidine additively reduce the shivering threshold; in the small doses tested, the combination produced only mild sedation and no respiratory toxicity.