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Effect of halogen light stimulation on nonstress testing
American Journal of Obstetrics and Gynecology (2004) 190, 1470e2
www.elsevier.com/locate/ajog
Effect of halogen light stimulation on nonstress testing Bruno J. Caridi, MD, HO IV,* Jay M. Bolnick, MD, Beverly G. Fletcher, RNC, William F. Rayburn, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, School of Medicine, University of New Mexico, Albuquerque, NM Received for publication September 3, 2003; revised December 31, 2003; accepted February 4, 2004
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– KEY WORDS Light stimulation Nonstress test Fetal heart rate
Objective: This study was undertaken to determine whether external stimulation using a halogen light source influences fetal heart rate (FHR) responsiveness and nonstress test results. Study design: A total of 107 patients at 32 to 42 weeks’ gestation undergoing a nonstress test were randomly assigned to have either transabdominal light stimulation or no light stimulation. The light (Vector Compact Sport Spot, Ft Lauderdale, Fla) was turned on for 10 seconds. If no qualifying FHR acceleration was observed, then the stimulus was repeated at 10-minute intervals for a maximum of 3 times. The investigators were blinded as to light stimulation for FHR interpretation. Results: Reactive results were present in 52 cases in each group. Light stimulation led to a significantly shorter time (P!.02) until the first FHR acceleration (difference: 2.1 minutes; 95% CI 0.4-3.8 minutes). The height and width of the first acceleration were indistinguishable between groups. The time until a reactive result was significantly shorter after light stimulation (difference: 4.2 minutes; 95% CI 2.0-6.4 minutes). Conclusion: The earlier onset of FHR accelerations after halogen light stimulation prompted a more rapid reactive nonstress test result. Ó 2004 Elsevier Inc. All rights reserved.
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
Fetal heart rate (FHR) monitoring during the third trimester is safe and reliable for assessing fetal well being. Less well defined is the ability of the nonstress test (NST) to predict fetal compromise. In an effort to reduce the incidence of falsely nonreactive or equivocal NSTs and to shorten the time to perform the test, presumably secondary to fetal sleep states, investigators Support provided by the Seligman Perinatal Research Fund. * Reprint requests: Bruno Caridi, MD, University of New Mexico, Department of Obstetrics and Gynecology, MSC 10 5580, Albuquerque, NM 87131-0001. E-mail: [email protected] 0002-9378/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ajog.2004.02.031
have used external exposure to mechanical stimulation, acoustic stimulation, and glucose administration with variable results.1 External light stimulation may affect behavioral states in the human fetus.2 We conducted a series of experiments about light penetration of tissue.3 Light from a halogen bulb penetrated tissues more than a photographic flash or a krypton bulb flashlight. No thermal injury or discomfort to the skin was observed for exposures less than 10 seconds. The objective of this randomized controlled trial was to evaluate the effect of halogen light stimulation on NST results.
1471
Caridi et al
Materials and methods Our Human Research Review Committee reviewed the protocol and safety issues and, after modification, approved this research proposal. The study population consisted of patients at 32 to 42 weeks’ gestation who underwent an NST. They were assigned either to transabdominal light stimulation (10 seconds) or to no light stimulation according to a computer-generated randomization schedule. The halogen light source (Vector Compact Sport Spot, Ft Lauderdale, Fla) was purchased at a local sports store. The 10-cm diameter light surface was placed gently to create a seal with the maternal abdominal midline just above the symphysis. In our prior study, we showed that indenting the abdominal wall did not affect tissue penetration by the halogen light.3 If an adequate FHR acceleration (R15 beats/min above baseline for R15 seconds) was absent after the 10-second light stimulation, then the stimulus was repeated at 10-minute intervals for a maximum of 3 times during the 20-minute NST. Two of the investigators were blinded as to the onset of any light stimulation for interpreting the FHR tracing. The times until the first adequate FHR acceleration and before a reactive pattern (R2 adequate accelerations) were our primary endpoints for comparison. Assuming that light stimulation led to a 50% shortening of time for a reactive result (usually 10 minutes), we calculated a sample size to be at least 47 cases in each group for an 80% power and a 5% significance level. Also, we looked at the height and width of the first FHR acceleration and at any explanation for a nonreactive test result. Statistical comparisons involved Student t test and c2 testing using In Stat Graph Pad version 3 software (San Diego, Calif). The 95% CIs were determined, and a P value less than .05 was considered to be statistically different.
Results All 107 patients agreed to enrollment, and there were no dropouts. There was no significant difference between the light stimulation group (n = 53) and no stimulation group (n = 54) for maternal age, maternal weight, gestational age, indication for testing, and proportion taking medications. Indications for testing included diabetes (n = 32), hypertension (n = 23), reduced fetal movement (n = 21), prolonged gestation (n = 17), and other medical complications (n = 14). Maternal medications included oral antihypertensives, antiepileptic drugs, oral hypoglycemics or insulin, and oral methadone maintenance.
Findings of the 104 reactive NST results are shown in Table I. The mean time before onset of the first adequate FHR acceleration was shorter in the light group than in the no light group (4.1 minutes vs 6.2 minutes). This difference of 2.1 minutes was statistically different (P!.02; 95% confidence level 0.4-3.8 minutes). The study failed to show significance in the height and width of the first FHR acceleration. The light stimulation group required 5.6 minutes before evidence of a reactive pattern compared with 9.8 minutes in the no light group. This difference of 4.2 minutes was statistically different (P!.01; 95% CI 2.0-6.4 minutes). Nonreactive NST results were present in 3 cases (light: 1, no light: 2). The 1 patient with a nonreactive NST despite light stimulation had a prolonged pregnancy (41 weeks 4 days) and was admitted promptly for an oxytocin induction. A prolonged fetal bradycardic episode despite complete cervical dilation led to an urgent cesarean delivery. The 3872 g, nonanomalous male had Apgar scores of 7 and 8 at 1 and 5 minutes, respectively. No umbilical cord encirclement, meconium, or gross placental abnormality was observed. The 2 cases with nonreactive NST results underwent labor induction because of oligohydramnios accompanied by either gestational hypertension or a prolonged gestation. The case with hypertension required cesarean delivery because of early onset meconium and repetitive variable FHR decelerations. Both infants did well without immediate complication.
Comments The mean duration of a reactive NST in our study population was more than 4 minutes shorter than without light stimulation. The few nonreactive results prohibited determining whether the light stimulus reduced the prevalence of nonreactive patterns. The shortened test time has a considerable impact on a busy antepartum service performing 20 or more tests daily. Time savings of 2 hours per day may be observed at our Fetal Testing Center. The more rapid onset of FHR accelerations in our investigation is most likely related to the type of light stimulus. A halogen bulb transmits more intense light than an electronic flash, krypton bulb, or incandescent bulb.3 Despite the deeper tissue penetration, light intensity from the halogen bulb is half that of the sun’s and the period of illumination (up to 10 seconds) was brief.3 Furthermore, the light becomes dispersed and must pass through amniotic fluid. We estimate the illumination to be equivalent to a 25-watt light bulb placed 1 foot away from a newborn infant. An alteration in the behavior state of the fetus is supported by the apparent occurrence of fetal movement after external stimulation with light.2 As early at 1975,
1472 Polishak et al4 reported fetal movement in response to light. This association was later confirmed by others. In addition, FHR changes were also noted after light stimulation with an electronic photographic flash and amnioscopy light.5,6 Further investigation as to the effect of external light stimulation on fetal behavioral states is ongoing. We observed that light stimulation prompts a slower startle response than from vibroacoustic stimulation, with a sustained propulsive body motion rather than a more rapid extension of the neck and body. In summary, external light stimulation with the use of a halogen bulb offers distinct advantages as an adjunct to the traditional nonstress test. The shortened period to achieve a reactive NST result reduces patient and provider anxieties and allows perinatal resources to be used more efficiently. Investigations as to whether use of this form of external stimulation leads to fewer nonreactive results are necessary. Although definite advantages with external light stimulation exist, its routine implementa-
Caridi et al tion also requires comparison with vibroacoustic stimulation, as an adjunct in screening for fetal well-being.
References 1. Miller D. External stimuli. Clin Obstet Gynecol 2002;45: 1054-62. 2. Kiuchi M, Naoki N, Ikeno S, Terakawa N. The relationship between the response to external light stimulation and behavioral states in the human fetus: how it differs from vibroacoustic stimulation. Early Hum Dev 2000;58:153-65. 3. Rayburn B, Theele D, Bolnick J, Rayburn W. Selection of a light source for fetal biophysical testing. J Reprod Med 2004 [in press]. 4. Polishak W, Laufer N, Sadovsky E. Fetal reaction to external light. Isr Med Assoc 1975;89:395-6. 5. Peleg D, Goldman J. Fetal heart rate acceleration in response to light stimulation as a clinical measure of fetal well being: a preliminary report. J Perinat Med 1980;8:38-41. 6. Boos R, Gnirs J, Auer L, Schmidt W. Controlled acoustic and photic stimulation of the fetus in the last pregnancy trimester [German]. Z Geburtshilfe Perinatol 1987;191:151-61.
www.elsevier.com/locate/ajog
Effect of halogen light stimulation on nonstress testing Bruno J. Caridi, MD, HO IV,* Jay M. Bolnick, MD, Beverly G. Fletcher, RNC, William F. Rayburn, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, School of Medicine, University of New Mexico, Albuquerque, NM Received for publication September 3, 2003; revised December 31, 2003; accepted February 4, 2004
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– KEY WORDS Light stimulation Nonstress test Fetal heart rate
Objective: This study was undertaken to determine whether external stimulation using a halogen light source influences fetal heart rate (FHR) responsiveness and nonstress test results. Study design: A total of 107 patients at 32 to 42 weeks’ gestation undergoing a nonstress test were randomly assigned to have either transabdominal light stimulation or no light stimulation. The light (Vector Compact Sport Spot, Ft Lauderdale, Fla) was turned on for 10 seconds. If no qualifying FHR acceleration was observed, then the stimulus was repeated at 10-minute intervals for a maximum of 3 times. The investigators were blinded as to light stimulation for FHR interpretation. Results: Reactive results were present in 52 cases in each group. Light stimulation led to a significantly shorter time (P!.02) until the first FHR acceleration (difference: 2.1 minutes; 95% CI 0.4-3.8 minutes). The height and width of the first acceleration were indistinguishable between groups. The time until a reactive result was significantly shorter after light stimulation (difference: 4.2 minutes; 95% CI 2.0-6.4 minutes). Conclusion: The earlier onset of FHR accelerations after halogen light stimulation prompted a more rapid reactive nonstress test result. Ó 2004 Elsevier Inc. All rights reserved.
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
Fetal heart rate (FHR) monitoring during the third trimester is safe and reliable for assessing fetal well being. Less well defined is the ability of the nonstress test (NST) to predict fetal compromise. In an effort to reduce the incidence of falsely nonreactive or equivocal NSTs and to shorten the time to perform the test, presumably secondary to fetal sleep states, investigators Support provided by the Seligman Perinatal Research Fund. * Reprint requests: Bruno Caridi, MD, University of New Mexico, Department of Obstetrics and Gynecology, MSC 10 5580, Albuquerque, NM 87131-0001. E-mail: [email protected] 0002-9378/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ajog.2004.02.031
have used external exposure to mechanical stimulation, acoustic stimulation, and glucose administration with variable results.1 External light stimulation may affect behavioral states in the human fetus.2 We conducted a series of experiments about light penetration of tissue.3 Light from a halogen bulb penetrated tissues more than a photographic flash or a krypton bulb flashlight. No thermal injury or discomfort to the skin was observed for exposures less than 10 seconds. The objective of this randomized controlled trial was to evaluate the effect of halogen light stimulation on NST results.
1471
Caridi et al
Materials and methods Our Human Research Review Committee reviewed the protocol and safety issues and, after modification, approved this research proposal. The study population consisted of patients at 32 to 42 weeks’ gestation who underwent an NST. They were assigned either to transabdominal light stimulation (10 seconds) or to no light stimulation according to a computer-generated randomization schedule. The halogen light source (Vector Compact Sport Spot, Ft Lauderdale, Fla) was purchased at a local sports store. The 10-cm diameter light surface was placed gently to create a seal with the maternal abdominal midline just above the symphysis. In our prior study, we showed that indenting the abdominal wall did not affect tissue penetration by the halogen light.3 If an adequate FHR acceleration (R15 beats/min above baseline for R15 seconds) was absent after the 10-second light stimulation, then the stimulus was repeated at 10-minute intervals for a maximum of 3 times during the 20-minute NST. Two of the investigators were blinded as to the onset of any light stimulation for interpreting the FHR tracing. The times until the first adequate FHR acceleration and before a reactive pattern (R2 adequate accelerations) were our primary endpoints for comparison. Assuming that light stimulation led to a 50% shortening of time for a reactive result (usually 10 minutes), we calculated a sample size to be at least 47 cases in each group for an 80% power and a 5% significance level. Also, we looked at the height and width of the first FHR acceleration and at any explanation for a nonreactive test result. Statistical comparisons involved Student t test and c2 testing using In Stat Graph Pad version 3 software (San Diego, Calif). The 95% CIs were determined, and a P value less than .05 was considered to be statistically different.
Results All 107 patients agreed to enrollment, and there were no dropouts. There was no significant difference between the light stimulation group (n = 53) and no stimulation group (n = 54) for maternal age, maternal weight, gestational age, indication for testing, and proportion taking medications. Indications for testing included diabetes (n = 32), hypertension (n = 23), reduced fetal movement (n = 21), prolonged gestation (n = 17), and other medical complications (n = 14). Maternal medications included oral antihypertensives, antiepileptic drugs, oral hypoglycemics or insulin, and oral methadone maintenance.
Findings of the 104 reactive NST results are shown in Table I. The mean time before onset of the first adequate FHR acceleration was shorter in the light group than in the no light group (4.1 minutes vs 6.2 minutes). This difference of 2.1 minutes was statistically different (P!.02; 95% confidence level 0.4-3.8 minutes). The study failed to show significance in the height and width of the first FHR acceleration. The light stimulation group required 5.6 minutes before evidence of a reactive pattern compared with 9.8 minutes in the no light group. This difference of 4.2 minutes was statistically different (P!.01; 95% CI 2.0-6.4 minutes). Nonreactive NST results were present in 3 cases (light: 1, no light: 2). The 1 patient with a nonreactive NST despite light stimulation had a prolonged pregnancy (41 weeks 4 days) and was admitted promptly for an oxytocin induction. A prolonged fetal bradycardic episode despite complete cervical dilation led to an urgent cesarean delivery. The 3872 g, nonanomalous male had Apgar scores of 7 and 8 at 1 and 5 minutes, respectively. No umbilical cord encirclement, meconium, or gross placental abnormality was observed. The 2 cases with nonreactive NST results underwent labor induction because of oligohydramnios accompanied by either gestational hypertension or a prolonged gestation. The case with hypertension required cesarean delivery because of early onset meconium and repetitive variable FHR decelerations. Both infants did well without immediate complication.
Comments The mean duration of a reactive NST in our study population was more than 4 minutes shorter than without light stimulation. The few nonreactive results prohibited determining whether the light stimulus reduced the prevalence of nonreactive patterns. The shortened test time has a considerable impact on a busy antepartum service performing 20 or more tests daily. Time savings of 2 hours per day may be observed at our Fetal Testing Center. The more rapid onset of FHR accelerations in our investigation is most likely related to the type of light stimulus. A halogen bulb transmits more intense light than an electronic flash, krypton bulb, or incandescent bulb.3 Despite the deeper tissue penetration, light intensity from the halogen bulb is half that of the sun’s and the period of illumination (up to 10 seconds) was brief.3 Furthermore, the light becomes dispersed and must pass through amniotic fluid. We estimate the illumination to be equivalent to a 25-watt light bulb placed 1 foot away from a newborn infant. An alteration in the behavior state of the fetus is supported by the apparent occurrence of fetal movement after external stimulation with light.2 As early at 1975,
1472 Polishak et al4 reported fetal movement in response to light. This association was later confirmed by others. In addition, FHR changes were also noted after light stimulation with an electronic photographic flash and amnioscopy light.5,6 Further investigation as to the effect of external light stimulation on fetal behavioral states is ongoing. We observed that light stimulation prompts a slower startle response than from vibroacoustic stimulation, with a sustained propulsive body motion rather than a more rapid extension of the neck and body. In summary, external light stimulation with the use of a halogen bulb offers distinct advantages as an adjunct to the traditional nonstress test. The shortened period to achieve a reactive NST result reduces patient and provider anxieties and allows perinatal resources to be used more efficiently. Investigations as to whether use of this form of external stimulation leads to fewer nonreactive results are necessary. Although definite advantages with external light stimulation exist, its routine implementa-
Caridi et al tion also requires comparison with vibroacoustic stimulation, as an adjunct in screening for fetal well-being.
References 1. Miller D. External stimuli. Clin Obstet Gynecol 2002;45: 1054-62. 2. Kiuchi M, Naoki N, Ikeno S, Terakawa N. The relationship between the response to external light stimulation and behavioral states in the human fetus: how it differs from vibroacoustic stimulation. Early Hum Dev 2000;58:153-65. 3. Rayburn B, Theele D, Bolnick J, Rayburn W. Selection of a light source for fetal biophysical testing. J Reprod Med 2004 [in press]. 4. Polishak W, Laufer N, Sadovsky E. Fetal reaction to external light. Isr Med Assoc 1975;89:395-6. 5. Peleg D, Goldman J. Fetal heart rate acceleration in response to light stimulation as a clinical measure of fetal well being: a preliminary report. J Perinat Med 1980;8:38-41. 6. Boos R, Gnirs J, Auer L, Schmidt W. Controlled acoustic and photic stimulation of the fetus in the last pregnancy trimester [German]. Z Geburtshilfe Perinatol 1987;191:151-61.