The effect of fundal pressure manoeuvre on intrauterine pressure in the second stage of labour

Authors

  • Catalin S. Buhimschi,

    Corresponding author
    1. Department of Obstetrics, Gynaecology and Reproductive Sciences, The University of Maryland School of Medicine, Baltimore, MD, USA
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  • Irina A. Buhimschi,

    1. Department of Obstetrics, Gynaecology and Reproductive Sciences, The University of Maryland School of Medicine, Baltimore, MD, USA
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  • Andrew M. Malinow,

    1. Department of Obstetrics, Gynaecology and Reproductive Sciences, The University of Maryland School of Medicine, Baltimore, MD, USA
    2. Department of Anaesthesiology, The University of Maryland School of Medicine, Baltimore, MD, USA
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  • Jerome N. Kopelman,

    1. Department of Obstetrics, Gynaecology and Reproductive Sciences, The University of Maryland School of Medicine, Baltimore, MD, USA
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  • Carl P. Weiner

    1. Department of Obstetrics, Gynaecology and Reproductive Sciences, The University of Maryland School of Medicine, Baltimore, MD, USA
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*Dr C. Buhimschi, Department of Obstetrics, Gynecology and Reproductive Sciences, Wayne State University, Detroit, MI 48201, USA.

Abstract

Objective To investigate the relationship between intrauterine pressure and the application of a standardised fundal pressure manoeuvre, and to determine the maternal, fetal and labour characteristics that modulate the relationship.

Design Prospective measurement of intrauterine pressure during the second stage of labour.

Setting North American university hospital.

Population Forty full-term women in spontaneous labour were studied during the second stage. Each woman acted as her own control. All women laboured with requested epidural analgesia.

Methods A fundal pressure manoeuvre was performed so as to standardise the level of force and the surface area of application. Intrauterine pressure was measured using a sensor–tip catheter. Five interventions were analysed: 1. valsalva during a uterine contraction; 2. fundal pressure and valsalva during a contraction; 3. fundal pressure during a contraction without valsalva; 4. fundal pressure in the absence of uterine contractions; and 5. valsalva in the absence of uterine contractions.

Results Women in the second stage of labour transiently increased their expulsive force (as reflected by intrauterine pressure) by 86% of their baseline contraction using valsalva and fundal pressure simultaneously. The efficiency by which both contraction-enhancing manoeuvres increased intrauterine pressure was directly related to gestational age and inversely related to myometrial thickness.

Conclusion Fundal pressure applied under controlled conditions significantly increases intrauterine pressure in some, but not all women. Simultaneous measurement of intrauterine pressure, to maintain feedback during application will create a ‘controlled environment’ for the obstetrician and reassurance that this manoeuvre can be applied in a controlled fashion. Future delineation of the group of women that could benefit from fundal pressure, as well as the group that is refractory is essential to avoid unnecessary or delayed operative interventions.

Introduction

Mammalian parturition is characterised by intense, synchronous, and co-ordinated uterine contractions that develop after relative inactivity for most of pregnancy. During normal labour, the uterus produces maximal force during the second stage, leading to the successful expulsion of the fetus1. Previous studies emphasise that uterine contractions during normal labour are characterised by a co-ordinated sequence of mechanical events generating maximal force at the uterine fundus (fundal dominance)2. The force then gradually diminishes moving caudally toward the cervix. Several studies have described the second stage in terms of onset, duration, and techniques for pushing, with the aim of identifying when obstetric intervention becomes necessary3–5.

Fundal pressure is described as external force applied at the uppermost portion of the uterus in a caudal direction typically with the intent of shortening the duration of the second stage of labour. A nationwide review in 1990 found that 84% of surveyed US institutions practised fundal pressure but only 48% documented the practice in the medical record6. In 1996 Cosner7 suggested that fundal pressure application was associated with a longer second stage and a higher incidence of third and fourth-degree perineal lacerations; thus its use should be a cause of concern among nurses and physicians. Recently, Simpson and Knox8 noted that obstetric practice continues to lack medicolegal or professional regulations pertaining to the use of fundal pressure, and that despite the dogma, “never fundal pressure”, a high percentage of medical institutions use it. Simpson also questioned whether maternal exhaustion or nonreassuring fetal heart rhythm in the context of fetal head crowning might be considered indications for fundal pressure application.

There is no study of the mechanism(s) by which the application of an external force might speed delivery. Clinicians recommend ‘gentle’ or ‘steady’ pressure, but quantifying these terms with any degree of accuracy is impossible8. We hypothesised that one of the mechanisms by which fundal pressure might aid (or complicate delivery) is by increasing intrauterine pressure. The purpose of this investigation was to determine the relationship between fundal pressure and intrauterine pressure. We also sought to determine what (if any) maternal, fetal or labour characteristics modulate this interaction.

Methods

Intrauterine pressure was measured in 40 healthy women during the second stage of labour from November 1999 to August 2000. The University of Maryland Medical System Institutional Review Board approved the study, and all enrolees provided written informed consent. Approximately 70% of women solicited agreed to participate. In the admitting lounge, eligible candidates were told about the trial but enrolled only after they were comfortable with their pain. In our unit, epidural analgesia is the most frequent method of pain management; approximately 90% of women labour with an epidural.

The inclusion criteria required active labour at term with a singleton fetus in vertex presentation. The onset of second stage was defined as full dilatation of the cervix identified by digital examination. One investigator (C.S.B.) examined all patients. Exclusion criteria included: preterm labour (gestational age below 37 weeks), nonvertex presentation (breech or transverse), suspected fetal macrosomia, grand multiparity (para five and over), abnormalities of placentation (low lying placenta, abruptio placenta), uterine structural abnormalities, history of previous shoulder dystocia, previous uterine scar, fetal heart rate abnormalities at the time of enrolment (bradycardia, tachycardia or prolonged variable decelerations).

Before beginning intrauterine pressure monitoring, all women laboured at least one hour with requested epidural (or combined spinal–epidural) analgesia. Analgesia was induced by the incremental injection of 10–12 mL of 0.25% bupivacaine given via a catheter placed in the L2/3 or L3/4 epidural space. Some women received combined spinal/epidural analgesia induced with a combination of intrathecal bupivacaine (2.5 mg) and fentanyl (25 μg). Analgesia was maintained by either a continuous infusion of bupivacaine 0.0625%, fentanyl 0.0001%, epinephrine 1.67 μg/mL or 0.125% bupivacaine. Breakthrough discomfort was treated by the injection of 5–10 mL of bupivacaine (0.25%–0.5%) or lidocaine (‘alkalinised’ 1%–2% with epinephrine 2.5–5 μg/mL). All patients were alert and responsive during the course of the study. The assessment of motor blockade associated with epidural analgesia is traditionally done using a modified Bromage score. A score of 0–3 evaluates lower extremity motor block: 0 = no block, 1 = block at the hips but not at the knees or ankles and 3 = block at the hips, knees and ankles. A review of the Bromage scores assigned to participating women during the second stage of labour revealed a uniform distribution with a median value of zero for both right and left legs. A review of the rostral sensory dermatome achieved by the epidural analgesia revealed a median T6–7 sensory dermatome level as required for labour analgesia.

The median dose of oxytocin required for augmentation of uterine contractility was 6 mU/minute. This was the dose required to achieve adequate contractility (>200 Montevideo Units or cervical dilatation over 1 cm/h) during the active phase of labour. Once adequate contractility was achieved, the oxytocin dose was held constant for both first and second stage of labour.

An abdominal ultrasound survey (Ultramark 4, Advanced Technology Laboratories, Bothell, Washington, USA) was performed. The amniotic fluid index (four quadrant technique)9 and the thickness of the myometrium (anterior wall of the lower segment in the absence of contraction)10 were measured. Myometrium was defined as the homogeneous echo layer between the serosal surface and the decidua. At least two technically acceptable thickness measurements were obtained. Fetal weight was estimated by the combination of biparietal diameter, abdominal circumference and femur length11. The mean percent difference between the predicted and actual weight was 9.6% corresponding to a mean overestimation of 294 g or underestimation of 314 g. These values are consistent with most reports in the literature11.

Intrauterine pressure measurements and study protocol

Intrauterine pressure was measured using a sensor-tip catheter (Graphic Control, Buffalo, New York, USA) inserted into the uterine cavity under sterile conditions. The intrauterine pressure catheter was connected to a data acquisition system (CB Sciences, Dover, New Hampshire, USA) and the readings analysed using Chart V 4.0 AD-Instruments software (2000-Castle Hill, Australia). The recordings were begun once a digital examination confirmed full cervical dilatation with descent of the fetal head to at least a +2 station (on a −3/+3 scale).

Valsalva (closed glottis technique) was accomplished by encouraging the patient to bear down with maximal effort. All subjects were counselled and trained by the same investigator (C.S.B). Three valsalva manoeuvres were performed during the course of a spontaneous uterine contraction, each with an approximate duration of 10 seconds. This is the pushing technique routinely used in our Labour and Delivery unit.

Fundal pressure was applied at a 30–40° angle to the spine in the direction of the pelvis through a semi-inflated disposable pressure cuff (Vital Signs Inc, Totowa, New Jersey, USA) interposed between the investigator's hand and the abdominal wall. This technique standardises the force and surface area of application (220 cm2). The cuff was connected to a common blood pressure manometer (W.A. Baum Co. Inc, Copiague, New York, USA). The force applied was gradually increased until the pressure in the semi-inflated blood pressure cuff was constantly maintained between 80 and 90 mmHg with moderate effort. This pressure level was based on a pilot study where six independent researchers blinded to cuff manometer values were asked to apply fundal pressure with the force they naturally use in their practice.

Uterine activity was measured for at least 15 to 20 minutes before initiating any intervention. This period of spontaneous contractions constituted the contractile baseline (CTX). Each woman acted as her own control. Five interventions were studied: 1. valsalva superimposed over a uterine contraction (CTXV); 2. fundal pressure and valsalva during a spontaneous uterine contraction (CTXVFP); 3. fundal pressure over a contraction applied for three times (each time for 10 seconds) without valsalva (CTXFP); 4. fundal pressure (fundal pressure no CTX); or 5. valsalva alone (V no CTX). To assess the influence of these manoeuvres on intrauterine pressure in the absence of uterine activity, valsalva or fundal pressure were applied three times each with a duration of approximately 10 seconds. The pressure recordings were continued until delivery (CTXVrlf) to determine whether enrolment in the study influenced the strength of patient's pushing ability. In five of these 40 women, five independent clinicians performed manual fundal pressure during expulsion (without the interposing the semi-inflated cuff: CTXVFPrlf) to determine the reliability of our method in mimicking a real-life situation.

For each spontaneous or enhanced contraction, the following raw parameters were calculated: integral (area under the curve displaced from baseline and expressed as mmHg second), the maximum and minimum (tone) amplitude (in mmHg). Uterine activity (in Montevideo Units) was estimated as the product between the amplitude and number of contractions within 10 minutes12. For each patient, the integral, maximum amplitude, tone, duration and Montevideo Units were averaged (from at least two to three spontaneous or enhanced contractions) within each protocol.

Statistical analysis

After confirming normality using the Kolmogorov–Smirnov test, the raw parameters (integral, amplitudes, duration, and Montevideo units) (mean (SD)) were compared among protocols using one-way analysis of variance followed by multiple comparisons using Tukey–Kramer tests. A P < 0.05 was considered to indicate statistical significance. Multivariate analysis with linear regression model was used to identify associations between maternal, fetal and labour characteristics (independent variables listed in Table 1) and the percent increase in intrauterine pressure (dependent variable).

Table 1.  Maternal, fetal and labour characteristics. BMI = body mass index; GA = gestational age; AFI = amniotic fluid index.
Variables
Age (years): mean (SD) [range]23.0 (4.87)[15–36]
Parity16 P0 (39%)
Weight (kg) (SD) [range]80.7 (16.1)[57.6–125]
Height (m) (SD) [range]1.64 (0.16)[1.25–2.01]
BMI: mean (SD) [range]25.0 (6.16)[13.1–39.9]
GA (wks): mean (SD) [range]39.4 (1.0)[37.5–41.1]
Myometrial thickness (mm): mean (SD) [range]8.2 (3.1)[5–19]
AFI (mm): mean (SD) [range]61.0 (36.2)[10–145]
Fetal weight (g): mean (SD) [range]3304.7 (350.9)[2670–4380]
Head circumference (cm): mean (SD) [range]34.1 (1.4)[30.4–36.5]
Apgar at 5 min: median [range]8[5–9]
Apgar at 10 min: median [range]9[7–9]
Duration of second stage: min–median [range]63.2[7–169]
Oxytocin augmentation: yes [%][68] 
Operative delivery: yes [%][7.3] 
Perineal tears or episiotomy: yes [%][25.0] 

Results

The maternal, fetal and labour characteristics of the 40 women are presented in Table 1. Thirty-six of the 40 women (90%) delivered vaginally without intervention. Four women were delivered by outlet or low vacuum/forceps either for maternal exhaustion (n= 2) or severe variable decelerations (n= 2).

Table 2 illustrates the raw parameters for the intrauterine pressure measurements. Valsalva during contraction increased the expulsive force by 55% of the spontaneous contraction (CTX) (intrauterine pressure integral CTXV: 2316 mmHg·second [CI 2087–2546] vs CTX: 1490 [CI 1352–1625], P < 0.0001) (Fig. 1a and b). The addition of fundal pressure to valsalva further increased the contraction integral area another 460 mmHg·seconds to 2777 mmHg seconds [CI 2475–3080]. This represents an 86% increase over baseline (CTXVFP vs CTX, P < 0.0001 CTXVFP vs CTXV, P= 0.02). Fundal pressure during contraction but without valsalva increased the active contraction area 28% over baseline (CTXFP: 1902 mmHg·seconds [CI 1656–2147] (CTXFP vs CTX, P= 0.004).

Table 2.  Raw parameters for intrauterine pressure measurements.
IP parametersIntegral (mmHg·sec) mean (SD)Amplitude (mmHg) mean (SD)Montevideo units mean (SD)
CTX1490 (443)66 (14)218 (76)
CTXV2316 (731)98 (25)364 (144)
CTXVFP2777 (938)111 (31)423 (170)
CTXFP1902 (730)86 (30)310 (146)
V897 (487)64 (26)
FP509 (271)50 (16)
CTXVrlf2327 (1100)106 (38)410 (217)
CTXVFPrlf2496 (687)114 (15)507 (164)
Figure 1.

(A) Mean (SD) of intrauterine pressure (IP) integral during valsalva (V) and fundal pressure (FP) (mmHg·sec) practiced during or between contractions (CTX). (rlf: real life conditions). (B) Percent change from baseline contractility subsequent to the practice of enhancing maneuvers: valsalva (V) and/or fundal pressure (FP) during and in between uterine contractions (n= 40).

To determine the impact of these manoeuvres on uterine tone, fundal pressure and valsalva were performed between contractions. Both raised the intrauterine pressure, but significantly less than the baseline uterine contractions (V vs CTX, P < 0.001), (fundal pressure vs CTX, P < 0.001) (Table 2). Recordings performed under real-life conditions had similar characteristics to those performed under the study's standardised conditions (CTXVrlfversus CTXV, P= 0.965; CTXVFPrlfversus CTXVFP, P= 0.565). Analysis of the maximum expulsive force achieved (CTXVFP) revealed that 53% of the overall performance was generated by the uterine contraction. Valsalva added 30% more force. Overall, fundal pressure contributed only an additional 17%.

The efficiency by which fundal pressure was translated into an increased intrauterine pressure varied among patients. A scattergram of the individual percentage change in intrauterine pressure (Fig. 2) revealed three groups of patients. In one group, fundal pressure significantly contributes to the overall expulsive performance. In a second group, fundal pressure adds nothing to the expulsive force produced by a contraction and valsalva. In the third group of women, neither fundal pressure nor valsalva significantly elevated the intrauterine pressure above baseline. Multivariate analysis with linear regression revealed that the efficiency of valsalva and fundal pressure to increase intrauterine pressure when applied simultaneously was higher with thinner myometrium and greater gestational age (bivariate r = 0.60, P= 0.2, power of 0.96). In univariate analysis, the thickness of the myometrium (Fig. 3a) was a better predictor than gestational age (Fig. 3b) in predicting the extent of the change in intrauterine pressure subsequent to concomitant application of valsalva and fundal pressure (myometrial thickness: r = 0.5, P= 0.003; gestational age: r = 0.4, P= 0.012). The efficiency with which valsalva and fundal pressure increased intrauterine pressure was not influenced by parity.

Figure 2.

Scattergram of the percent change in intrauterine pressure (IP) integral induced by valsalva (CTXV) and fundal pressure (CTXVFP) in the 40 patients studied. The insert shows representative intrauterine pressure recordings in a patient were fundal pressure significantly added to the overall expulsive force.

Figure 3.

Scattergram of the percent change in intrauterine pressure (IP) integral induced by Valsalva and fundal pressure (CTXVFP) as a function of myometrial thickness (A) and gestational age (b). [MT: myometrial thickness, GA: gestational age, continuous line: regression line; dotted lines: prediction interval (confidence interval of the population)].

Discussion

This is the first investigation of the relationship between fundal pressure and intrauterine pressure during second stage of labour. The protocol was designed to elucidate the potential interplay between valsalva and fundal pressure. Our objective was to provide clinicians a clearer image of the evolution in intrauterine pressure when attempting to expedite delivery nonoperatively. A core design strength of the investigation was the standardisation of fundal pressure to closely mimic ‘real-life’.

We observed that contraction-enhancing manoeuvres during the second stage can increase intrauterine pressure by 86%. More than half of the maximal force originates from uterine contraction, 30% from valsalva and 17% from fundal pressure. Differences among labouring women suggest that certain maternal, fetal and labour features modulate the efficiency by which fundal pressure enhances the intrauterine pressure. As a result of this observation, we identify for the first time a subgroup of women who may benefit from fundal pressure when applied in a controlled fashion. Whether this is of clinical utility in the context of maternal exhaustion or nonreassuring fetal heart rhythm requires further investigation.

The efficacy by which contraction-enhancing manoeuvres translate into an increased intrauterine pressure was inversely dependent on myometrial thickness and gestational age. A ‘thinner’ myometrium and a ‘higher’ gestational age are good predictors of efficient transmission. However, the efficiency depended upon whether they are practiced separately or concomitantly with a uterine contraction. The greatest effect was achieved by joint performance. This suggests that the abdominal and/or myometrial wall tensions impact upon the efficiency of fundal pressure transmission.

A decrease in the number of experienced teaching physicians coupled to increased medical–legal concern has reduced the number of practitioners skilled in operative vaginal delivery13–15. Several reports link birth trauma (intracranial haemorrhage) with the use of vacuum, forceps and even caesarean section, perhaps explaining why up to 84% of American institutions continue to use fundal pressure despite a veritable absence of objective study7,16.

An earlier randomised controlled trial by Cox et al.17 assessed whether an inflatable obstetric belt that applied a type of fundal pressure synchronous with uterine contractions could influence obstetric outcome. The device failed when used during the second stage of labour to reduce the rate of operative delivery. Although our findings may seem at odds, there are several possible explanations. First, Cox et al.17 did not measure intrauterine pressure as intermediate outcome. Since our investigation suggests that fundal pressure increases intrauterine pressure only in a subgroup of women, it is possible that any positive effects in the Cox study was lost in the overall study population. Second, the obstetric belt was automatically inflated at a pressure of 200 mmHg for 30 seconds during a contraction, but did not control for the directionality of the force vector. In the present study, the fundal pressure was applied at 30–40° in the direction of the pelvic outlet with the goal of increasing intrauterine and not intra-abdominal pressure. Third, we sought to evaluate the relationship between fundal pressure application and intrauterine pressure. Due to a relative small number of women included, there was insufficient power to ascertain either potential harm or benefit of the manoeuvre in final obstetric outcome.

Despite the increase in intrauterine pressure from fundal pressure, we should not assume that delivery results solely from uterine contractions. Progress is also dependent upon the resistance to the descent of the presenting fetal part provided by the cervix and perineal muscles. Thus, not all patients will achieve sufficient uterine forces to overcome the resistance and deliver their fetus in a timely fashion. This diminished capability can necessitate obstetric intervention.

Fundal pressure is practiced worldwide to expedite delivery during the second stage of labour. The most frequent indications are a nonreassuring fetal heart rate and maternal exhaustion8. Interestingly, the Maryland State Board of Nursing recently issued a declaratory ruling concerning the role of nurses in fundal pressure application18, allowing them to apply fundal pressure only for the placement of a fetal scalp electrode, fetal scalp blood sampling and amniotomy in the absence of any objective study demonstrating benefit. Perhaps due to the frequency of complications reported in the literature, the same Board specifically excluded a nonreassuring fetal heart rhythm and/or maternal exhaustion as indication for nurse applied fundal pressure. Previous studies of fundal pressure during the second stage of labour associate this manoeuvre with complications such as shoulder dystocia, uterine rupture, uterine inversion or fetal distress19–21. Yet the ‘successes’ of fundal pressure application are not published since a good outcome is perceived as ‘normal’. The frequency of complications is often explained by an assumption of an extreme increase in intrauterine pressure. However, it is also possible the complication rate reflects an already abnormal labour and is unrelated to the application of fundal pressure itself. The present study delineates for the first time in a controlled fashion the forces generated. We believe that application of fundal pressure to an appropriate candidate may actually reduce the risks associated with either a prolonged second stage or the resulting operative interventions. The present study provides a framework for future investigation to identify these women during labour.

In conclusion, we demonstrate that fundal pressure applied under controlled conditions significantly increases intrauterine pressure in some, but not all women. These women can be identified prospectively in the labour suite. Further studies are necessary to define if and to what degree of intrauterine pressure after fundal pressure application outcome will be improved. In this context, the simultaneous measurement of intrauterine pressure, coupled with feedback during the application of fundal pressure, will create a ‘controlled environment’ for the obstetrician, preventing the application of excessive force. Only this way can the clinician be assured that this manoeuvre is applied in a controlled, safe and efficient fashion. Delineation of the group of women that benefit from fundal pressure, as well as the group that is refractory to contraction-enhancing could avoid unnecessary or delayed operative interventions.

Acknowledgements

The authors would like to thank the residents, anaesthesiologists, nurse–midwives and nurses who assisted in the enrolment and completion of the experimental protocol. The authors would also like to acknowledge the support provided by Dr L. Alger, Dr P. Lee, Dr M. Pupkin, and Dr W. Kramer.

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