- Email: [email protected]
Monitoring pudendal nerve function during labor
Instruments & Methods Monitoring pudendal nerve function during labor Matthew H. Clark, MD, Mattie Scott, MD, Val Vogt, MD, and J. Thomas Benson, MD Background: To determine methodology and feasibility of pudendal nerve monitoring during labor and delivery. Methods: With Institutional Review Board approval, 13 low-risk, singleton pregnant women were recruited. The latency and amplitude of the perineal branch of the pudendal nerve compound muscle action potential were recorded during the second stage of labor and after delivery. With the first two patients, a wire electrode was used to stimulate the pudendal nerve continuously at the ischial spine. For the remaining 11 patients, a St. Mark’s electrode was used to stimulate transvaginally. A urethral ring electrode on a 14 French foley catheter monitored the response from the urethral sphincter. All patients received prophylactic antibiotics. Experience: Twelve patients delivered vaginally, and one by cesarean. In two patients, continuous wire stimulation showed a gradual decrease in amplitude. Changes were minimal over 15-minute intervals. Wire electrode placement was technically difficult and dislodged easily. With the remaining 11 patients, all had data available for interpretation, and of the 85 potential perineal branch of the pudendal nerve compound muscle action potentials, 53 were obtained. No patients developed cystitis. Conclusion: Intrapartum assessment of pudendal nerve function is feasible. Continuous wire stimulation is technically more difficult and does not provide additional information beyond that available from intermittent stimulation. (Obstet Gynecol 2001;97:637–9. © 2001 by The American College of Obstetricians and Gynecologists.)
incontinence.1 Serial measurements of pudendal nerve function have shown that pregnancy, before delivery, does not cause nerve injury.2 Terminal branches of the pudendal nerve innervating the urethra (perineal nerve) are probably at greater risk than the pudendal nerve branches terminating behind the vagina (inferior hemordodal nerve).3 The objective of this study was to develop a methodology to monitor function of the perineal branch of the pudendal nerve during labor and delivery.
Materials and Methods Thirteen low-risk pregnant women were recruited during the third trimester from a residency-based obstetrics clinic. With institutional research board approval and written informed consent, nerve conduction studies were recorded during labor and delivery. These studies consisted of compound muscle action potential recorded from the urethral sphincter through the perineal nerve, a terminal branch of the pudendal nerve. One of two methods was used to stimulate the pudendal nerve. With two subjects, a disposable electromyographic (Nicolet, Madison, WI) single-hook wire 0.5 mm in diameter was placed transvaginally over the ischeal spine. Continuous-pulse stimulation was done. The second method used on the remaining 11 subjects was intermittent transvaginal stimulation with a St. Mark’s electrode (Medtronic, Shoreview, MN) at the ischial spine. This electrode attaches to the gloved hand of the examiner and was placed transvaginally for stimulation (Figure 1). With both methods, the stimulus was recorded by a recording ring electrode introduced into the urethra on a 14 French foley catheter and placed midurethra. Supramaximal stimulation was obtained and then averaged for ten stimuli. A Cadwell 5200A
The pudendal nerve and its branches innervate the urinary and rectal sphincters. Vaginal delivery is known to injure the pudendal nerve and has been implicated as a causal factor in urinary and fecal From the Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Indiana University/Methodist Hospital, Indianapolis, Indiana; and the Section of Urogynecology, University of Tennessee/Memphis, Memphis, Tennessee.
VOL. 97, NO. 4, APRIL 2001
Figure 1. Transvaginal stimulation of the pudendal nerve with a St. Mark’s electrode during the second stage of labor.
0029-7844/01/$20.00 PII S0029-7844(00)01207-2
637
Figure 2. An example of the compound muscle action potential obtained during the second stage of labor with intermittent stimulation.
electromyography (Cadwell Laboratories, Kennewick, WA) machine was used for recording the perineal branch of the pudendal nerve compound muscle action potential. Labor management was done by the admitting physician and standard obstetric practice was followed. During the second stage of labor, recordings were obtained continuously or every 15 minutes until either delivery occurred or the stimulus was disrupted by the fetal vertex dislodging the wire electrode or preventing stimulus by blocking access to the ischial spine by the vaginal hand. After delivery, the recording continued for up to 45 minutes. Subjects were allowed epidural anesthesia if desired. The subjects were given oral ampicillin for urinary tract infection prophylaxis and they were compensated for their participation.
Experience Thirteen subjects delivered, 12 vaginally and one by cesarean. All but one subject had an epidural anesthetic. No episiotomies were required. No subjects withdrew during testing because of discomfort or inconvience. In the two subjects stimulated continuously, there was a gradual decrease in amplitude over time. This change in amplitude was not appreciable in less than 15-minute intervals. The wire electrode proved technically difficult to work with and dislodged in both subjects with descent of the fetal head past the ischeal spines. No data were available after delivery with this technique. This technique was abandoned because of difficulties. For the other 11 subjects, intermittent stimulation with a St. Mark’s electrode was used. With this technique, nerve testing was accomplished, and recognizable perineal branch of the pudendal nerve compound muscle action potentials were obtained in all subjects during pushing and after delivery (Figure 2).
638 Clark et al
Pudendal Nerve Function During Labor
Before delivery, there were 55 potential 15-minute intervals to obtain a perineal branch of the pudendal nerve compound muscle action potential, of which 35 were obtained, for a 64% data acquisition rate. After delivery, there were 30 potential 15-minute intervals for perineal branch of the pudendal nerve compound muscle action potential, and 18 perineal branch of the pudendal nerve compound muscle action potentials were obtained, for a 60% data acquisition rate. Optimal testing was defined as obtaining a perineal branch of the pudendal nerve compound muscle action potential at least every 30 minutes for an individual patient. By this definition, four of 11 subjects had optimal testing before delivery and seven of ten were optimal after delivery. The remainder of the subjects had adequate testing eg, at least one perineal branch of the pudendal nerve compound muscle action potential available before and after delivery. There were no urinary tract infections or other complications resulting from the testing.
Comment The second stage of labor can be compared with compartment syndrome. In compartment syndrome, local tissue pressure increases sufficiently to cause microcirculatory ischemia to myoneural tissue. Testing during labor has shown that 240 cm H2O pressure is recorded from the vaginal sidewall during the peak of contractions.4 In vaginal delivery but not compartment syndrome, there is traction on the nerve that occurs with descent of the fetal head into the pelvis. We can apply knowledge from compartment syndrome experimental models to intrapartum pudendal nerve testing. During compartment syndrome experimental model testing, no change in amplitude or latency of the compound muscle action potential was seen before 30 minutes of
Obstetrics & Gynecology
increased pressure on the nerve.5 With the compartment syndrome findings and our results from continuous monitoring, we believe testing does not need to be continuous. Intermittent monitoring should be sufficient to assess whether nerve injury occurs during pushing or if delivery itself causes the insult. With testing every 15 minutes, one has a window into the events of the previous 15 minutes. Based on that assumption, any gap less than 30 minutes in monitoring is considered optimal. Because of the unpredictable nature of the birthing process, not all subjects will have optimal testing. Descent of the fetal head can block access to the ischeal spine and move the ring electrode out of position in the urethra. Even if a subject does not have optimal testing, the perineal branch of the pudendal nerve compound muscle action potential obtained can be useful. Amplitude and latency are the two values obtained from a perineal branch of the pudendal nerve compound muscle action potential. The reproducibility of these measurements has been shown previously.6,7 Amplitude is a measure of motor unit activity and latency measures the speed of nerve transmission. Any decrease in amplitude seen in labor would be attributed to the loss of axonal function and is likely caused by ischemia. Additionally any prolongation of latency would be slowing or loss of transmission of the larger myelinated fibers. None of our subjects had complete loss of nerve transmission during labor. Continuous monitoring is technically difficult and adds no unique information not obtained by intermittent stimulation. With intermittent stimulation maternal pelvic floor neurophysiology can be monitored during labor and delivery. Application of this technique to a homogenous population during labor should provide
VOL. 97, NO. 4, APRIL 2001
new insight into the effects of delivery on the maternal pelvic floor.
References 1. Sultan AH, Kamm MA, Hudson CN. Pudendal nerve damage during labour: Prospective study before and after childbirth. Br J Obstet Gynaecol 1994;101:22– 8. 2. Tetzschner T, Sorensen M, Jonsson L, Lose G, Christiansen J. Delivery and pudendal nerve function. Acta Obstet Gynecol Scand 1997;76:324 –31. 3. Podnar S, Lukanovic A, Vodusek DB. Anal sphincter electromyography after vaginal delivery: Neuropathic insufficiency or normal wear and tear. Neurol Urol 2000;19:249 –57. 4. Rempen A, Kraus M. Measurement of head compression during labor: Preliminary results. J Perinat Med 1991;19:115–20. 5. Gelberman RH, Szabo RM, Willamson RV, Hargens AR, Yaru NC, Minteer-Convery MA. Tissue pressure threshold for peripheral nerve viability. Clin Orthop 1983;176:285–91. 6. Benson JT, McClellan E. The effect of vaginal dissection on the pudendal nerve. Obstet Gynecol 1993;82:367–98. 7. Benson JT. Clinical neuropsychological techniques in urinary and fecal incontinence. In: Ostergard DR, Bent AE, eds. Urogynecology and urodynamics. 4th ed. Baltimore: Williams & Wilkins, 1996:223– 50.
Address reprint requests to:
Matthew H. Clark, MD Hoag Memorial Hospital Presbyterian Center for Urinary Continence 26671 Aliso Creek Road, # 205 Aliso Viejo, CA 92656 E-mail: [email protected]
Received July 3, 2000. Received in revised form October 30, 2000. Accepted November 9, 2000. Copyright © 2001 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
Clark et al
Pudendal Nerve Function During Labor
639
incontinence.1 Serial measurements of pudendal nerve function have shown that pregnancy, before delivery, does not cause nerve injury.2 Terminal branches of the pudendal nerve innervating the urethra (perineal nerve) are probably at greater risk than the pudendal nerve branches terminating behind the vagina (inferior hemordodal nerve).3 The objective of this study was to develop a methodology to monitor function of the perineal branch of the pudendal nerve during labor and delivery.
Materials and Methods Thirteen low-risk pregnant women were recruited during the third trimester from a residency-based obstetrics clinic. With institutional research board approval and written informed consent, nerve conduction studies were recorded during labor and delivery. These studies consisted of compound muscle action potential recorded from the urethral sphincter through the perineal nerve, a terminal branch of the pudendal nerve. One of two methods was used to stimulate the pudendal nerve. With two subjects, a disposable electromyographic (Nicolet, Madison, WI) single-hook wire 0.5 mm in diameter was placed transvaginally over the ischeal spine. Continuous-pulse stimulation was done. The second method used on the remaining 11 subjects was intermittent transvaginal stimulation with a St. Mark’s electrode (Medtronic, Shoreview, MN) at the ischial spine. This electrode attaches to the gloved hand of the examiner and was placed transvaginally for stimulation (Figure 1). With both methods, the stimulus was recorded by a recording ring electrode introduced into the urethra on a 14 French foley catheter and placed midurethra. Supramaximal stimulation was obtained and then averaged for ten stimuli. A Cadwell 5200A
The pudendal nerve and its branches innervate the urinary and rectal sphincters. Vaginal delivery is known to injure the pudendal nerve and has been implicated as a causal factor in urinary and fecal From the Division of Urogynecology and Reconstructive Pelvic Surgery, Department of Obstetrics and Gynecology, Indiana University/Methodist Hospital, Indianapolis, Indiana; and the Section of Urogynecology, University of Tennessee/Memphis, Memphis, Tennessee.
VOL. 97, NO. 4, APRIL 2001
Figure 1. Transvaginal stimulation of the pudendal nerve with a St. Mark’s electrode during the second stage of labor.
0029-7844/01/$20.00 PII S0029-7844(00)01207-2
637
Figure 2. An example of the compound muscle action potential obtained during the second stage of labor with intermittent stimulation.
electromyography (Cadwell Laboratories, Kennewick, WA) machine was used for recording the perineal branch of the pudendal nerve compound muscle action potential. Labor management was done by the admitting physician and standard obstetric practice was followed. During the second stage of labor, recordings were obtained continuously or every 15 minutes until either delivery occurred or the stimulus was disrupted by the fetal vertex dislodging the wire electrode or preventing stimulus by blocking access to the ischial spine by the vaginal hand. After delivery, the recording continued for up to 45 minutes. Subjects were allowed epidural anesthesia if desired. The subjects were given oral ampicillin for urinary tract infection prophylaxis and they were compensated for their participation.
Experience Thirteen subjects delivered, 12 vaginally and one by cesarean. All but one subject had an epidural anesthetic. No episiotomies were required. No subjects withdrew during testing because of discomfort or inconvience. In the two subjects stimulated continuously, there was a gradual decrease in amplitude over time. This change in amplitude was not appreciable in less than 15-minute intervals. The wire electrode proved technically difficult to work with and dislodged in both subjects with descent of the fetal head past the ischeal spines. No data were available after delivery with this technique. This technique was abandoned because of difficulties. For the other 11 subjects, intermittent stimulation with a St. Mark’s electrode was used. With this technique, nerve testing was accomplished, and recognizable perineal branch of the pudendal nerve compound muscle action potentials were obtained in all subjects during pushing and after delivery (Figure 2).
638 Clark et al
Pudendal Nerve Function During Labor
Before delivery, there were 55 potential 15-minute intervals to obtain a perineal branch of the pudendal nerve compound muscle action potential, of which 35 were obtained, for a 64% data acquisition rate. After delivery, there were 30 potential 15-minute intervals for perineal branch of the pudendal nerve compound muscle action potential, and 18 perineal branch of the pudendal nerve compound muscle action potentials were obtained, for a 60% data acquisition rate. Optimal testing was defined as obtaining a perineal branch of the pudendal nerve compound muscle action potential at least every 30 minutes for an individual patient. By this definition, four of 11 subjects had optimal testing before delivery and seven of ten were optimal after delivery. The remainder of the subjects had adequate testing eg, at least one perineal branch of the pudendal nerve compound muscle action potential available before and after delivery. There were no urinary tract infections or other complications resulting from the testing.
Comment The second stage of labor can be compared with compartment syndrome. In compartment syndrome, local tissue pressure increases sufficiently to cause microcirculatory ischemia to myoneural tissue. Testing during labor has shown that 240 cm H2O pressure is recorded from the vaginal sidewall during the peak of contractions.4 In vaginal delivery but not compartment syndrome, there is traction on the nerve that occurs with descent of the fetal head into the pelvis. We can apply knowledge from compartment syndrome experimental models to intrapartum pudendal nerve testing. During compartment syndrome experimental model testing, no change in amplitude or latency of the compound muscle action potential was seen before 30 minutes of
Obstetrics & Gynecology
increased pressure on the nerve.5 With the compartment syndrome findings and our results from continuous monitoring, we believe testing does not need to be continuous. Intermittent monitoring should be sufficient to assess whether nerve injury occurs during pushing or if delivery itself causes the insult. With testing every 15 minutes, one has a window into the events of the previous 15 minutes. Based on that assumption, any gap less than 30 minutes in monitoring is considered optimal. Because of the unpredictable nature of the birthing process, not all subjects will have optimal testing. Descent of the fetal head can block access to the ischeal spine and move the ring electrode out of position in the urethra. Even if a subject does not have optimal testing, the perineal branch of the pudendal nerve compound muscle action potential obtained can be useful. Amplitude and latency are the two values obtained from a perineal branch of the pudendal nerve compound muscle action potential. The reproducibility of these measurements has been shown previously.6,7 Amplitude is a measure of motor unit activity and latency measures the speed of nerve transmission. Any decrease in amplitude seen in labor would be attributed to the loss of axonal function and is likely caused by ischemia. Additionally any prolongation of latency would be slowing or loss of transmission of the larger myelinated fibers. None of our subjects had complete loss of nerve transmission during labor. Continuous monitoring is technically difficult and adds no unique information not obtained by intermittent stimulation. With intermittent stimulation maternal pelvic floor neurophysiology can be monitored during labor and delivery. Application of this technique to a homogenous population during labor should provide
VOL. 97, NO. 4, APRIL 2001
new insight into the effects of delivery on the maternal pelvic floor.
References 1. Sultan AH, Kamm MA, Hudson CN. Pudendal nerve damage during labour: Prospective study before and after childbirth. Br J Obstet Gynaecol 1994;101:22– 8. 2. Tetzschner T, Sorensen M, Jonsson L, Lose G, Christiansen J. Delivery and pudendal nerve function. Acta Obstet Gynecol Scand 1997;76:324 –31. 3. Podnar S, Lukanovic A, Vodusek DB. Anal sphincter electromyography after vaginal delivery: Neuropathic insufficiency or normal wear and tear. Neurol Urol 2000;19:249 –57. 4. Rempen A, Kraus M. Measurement of head compression during labor: Preliminary results. J Perinat Med 1991;19:115–20. 5. Gelberman RH, Szabo RM, Willamson RV, Hargens AR, Yaru NC, Minteer-Convery MA. Tissue pressure threshold for peripheral nerve viability. Clin Orthop 1983;176:285–91. 6. Benson JT, McClellan E. The effect of vaginal dissection on the pudendal nerve. Obstet Gynecol 1993;82:367–98. 7. Benson JT. Clinical neuropsychological techniques in urinary and fecal incontinence. In: Ostergard DR, Bent AE, eds. Urogynecology and urodynamics. 4th ed. Baltimore: Williams & Wilkins, 1996:223– 50.
Address reprint requests to:
Matthew H. Clark, MD Hoag Memorial Hospital Presbyterian Center for Urinary Continence 26671 Aliso Creek Road, # 205 Aliso Viejo, CA 92656 E-mail: [email protected]
Received July 3, 2000. Received in revised form October 30, 2000. Accepted November 9, 2000. Copyright © 2001 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.
Clark et al
Pudendal Nerve Function During Labor
639