The management of functional dystocia in the first stage of labor.

To summarize: Functional dystocia is easily diagnosed in laboring patients by lack of cervical dilatation for 2 hours in association with weak uterine contractions. If the membranes are intact, amniotomy should be performed. If cervical dilatation at a rate of at least 1 cm/h does not occur promptly, oxytocin should be begun. Efficient and safe use of oxytocin requires knowledge of its clinical pharmacologic characteristics: that the maximum level of a dose is not reached for approximately 40 minutes, that the blood level needed is a reflection of the sensitivity of the myometrium, and the blood level produced by a specific dose is a manifestation of the plasma clearance rate. While it has never been demonstrated that continuous electronic monitoring of the uterus and fetus with intermittent visits from professional personnel is better than palpation and auscultation performed by an educated attendant present continuously, the former practice is more common in the United States than the latter. If maximum use is to be made of the information provided by the uterine monitor, the data must be quantitated. When the patient's inadequate contractility fails to improve in response to the initial dose of 1 mU/m, the dose must be increased until some improvement is noted. Geometric incrementation should be limited to nulliparas in whom each dose of oxytocin is evaluated after a 40-minute infusion period.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous rupture of the membranes, functional dystocia, oxytocin treatment, and the route of delivery.

The details of clinical management were examined in 96 nulliparous patients with functional dystocia who had spontaneous rupture of the membranes before admission and were treated with oxytocin in the first stage of labor. It was our hypothesis that if the allegedly "high" rate of cesarean sections was the result of mediocre or flawed practices, these should be most evident in patients delivered abdominally. A group of 59 patients delivered vaginally were compared with 37 patients delivered by cesarean section. The means of many variables were not statistically different. The cesarean section group was characterized by smaller stature, a lesser cervical dilatation rate both before and after oxytocin administration, a larger maximum oxytocin dose, a longer period of oxytocin administration, more frequent cessation of oxytocin administration or dose reduction because of hypercontractility or an abnormal fetal heart rate or both, and a higher incidence of intra-amniotic infection. We conclude that the decision to perform cesarean section in nulliparous women with functional dystocia arises from disabilities of the patient and not from differences in the application of our management principles, services, or treatments.

Amniotomy and oxytocin treatment of functional dystocia and route of delivery.

The details of clinical management were examined in 101 nulliparous patients with functional dystocia who underwent amniotomy and were treated with oxytocin in the first stage of labor. It was our hypothesis that if the alleged "high" rate of cesarean sections was the result of mediocre or flawed practices, these should be most evident in patients delivered abdominally. A group of 68 patients delivered vaginally are compared with 33 patients delivered by cesarean section. The means of many variables were statistically similar. The cesarean group was characterized by less cervical dilatation at admission, greater birth weights, larger maximum doses of oxytocin, and longer durations of oxytocin therapy. We conclude from our analysis that the decision to perform cesarean section in nulliparous women with functional dystocia arises from disabilities of the patient and not from differences in the application of our management principles, services, or treatments.

Oxytocin and prolactin responses associated with nipple stimulation contraction stress tests.

Levels of oxytocin in plasma of pregnant women in the third trimester undergoing nipple stimulation-contraction stress tests were found, by parametric (paired t test) statistical analysis to be elevated. No differences in the plasma increases in oxytocin levels were found between those patients undergoing successful and those undergoing unsuccessful nipple stimulation-contraction stress tests. No significant differences in plasma levels of prolactin were associated with nipple stimulation in these patients.

Amniotomy and the use of oxytocin in labor in nulliparous women.

A group of 242 nulliparous women in spontaneous, term, first-stage, true labor, with cephalic presentations and intact membranes, underwent amniotomy in the first stage. Sixty-nine of 242 (29%) received oxytocin prior to complete dilatation. The group that received oxytocin was characterized by fewer women less than 20 years of age, more patients with an additional diagnosis such as preeclampsia, longer labors, and slower mean rates of dilatation before and after amniotomy. There was no correlation between the last dilatation rate before and the first after amniotomy. The only significant predictors of oxytocin use were cervical dilatation at amniotomy and the first rate of dilatation afterward. Of patients with dilatation at a rate of greater than or equal to 1 cm/hr from admission to amniotomy, 16% received oxytocin; if less than 1 cm/hr, 39%. Two different rate standards were used to differentiate "unsatisfactory" from "satisfactory" labor: (1) less than 1 or greater than or equal to 1 cm/hr and (2) no change or some change in dilatation. Neither of these standards, when applied to the first examination after amniotomy, predicts patients who will receive oxytocin with any reasonable degree of efficiency. Examination of cervical dilatation after amniotomy in patients who did not receive oxytocin demonstrated failure of the cervix to dilate in approximately 20% of each of three sequential examinations. Contrariwise, no dilatation for 2 hours was uncommon. Amniotomy appears to enhance the dilatation rate in patients with well-dilated cervices that are already dilating at a satisfactory rate and slows dilatation in some patients, particularly those with cervices that are less dilated. These results suggest that amniotomy should be performed for specific indications only.

Oxytocin augmentation of dysfunctional labor. V. An alternative oxytocin regimen.

A regimen is described in which the time from the start of a large dose of oxytocin to a myometrial response was used for selection of a maintenance dose. The method is based on our experience that continuous intravenous doses of oxytocin in the therapeutic range for the augmentation of labor require about 40 minutes of intravenous infusion to achieve a steady-state plasma concentration of oxytocin. The method effectively identified the proper maintenance dose on the first attempt in 43 of 59 patients (73%) and on the second in 58 of 59. The doses selected effected cervical dilatation in 55 of 59 cases (93%). Comparison of the timed dose method with an arithmetic progression regimen revealed the former method to select the minimum effective dose more rapidly, but that method had no advantage in shortening the time from the start of oxytocin to complete cervical dilatation. Examination of the plasma concentration of oxytocin by radioimmunoassay demonstrates that the maintenance dose selected by the duration of the interval from the start of infusion to a myometrial response sustains the plasma oxytocin concentration obtained by the initial dose. These data lend additional evidence that any particular dose of oxytocin in the therapeutic range requires approximately 40 minutes to achieve a steady-state plasma concentration.

Oxytocin augmentation of dysfunctional labor. IV. Oxytocin pharmacokinetics.

Plasma oxytocin levels ([OT[p) were measured every 20 minutes during infusions of oxytocin. The initial dose of 1 mU/min was incremented, if necessary, by 1 mU/min at 40-minute intervals until sufficient contractility was obtained to effect cervical dilatation. The results demonstrated: the [OT]p rises linearly with each dose for the first 40 minutes of the infusion; there is no difference between the 40- and 60-minute sample values, suggesting that the peak [OT]p of each dose is achieved in 40 minutes; the increment in [OT]p required to produce effective contractility varies widely from 0.58 to 5.09 microU/ml; the plasma clearance rate varied from 11.2 to 32.5 ml/kg/min. Approximately 40 minutes is required for any particular dose of oxytocin to reach a "steady-state" [OT]p and the maximal uterine contractile response. The design of regimens for the augmentation or induction of labor should be based on this knowledge.

Studies of oxytocin in plasma of women during hypocontractile labor.

Oxytocin (OT) was measured by RIA in plasma of women during hypocontractile labor before and during graded doses of iv infused synthetic OT. Based upon in vitro studies of recovery of OT from pregnancy plasma, blood was collected into heparinized tubes which were kept at 4 C. The addition of EDTA and phenanthrolene to an aliquot of each sample resulted in measured levels of OT in plasma that correlated closely with levels measured in the absence of these reagents (r2 = 0.86). Comparison of OT levels in plasma of normal individuals determined in the presence and absence of these reagents also yielded a high degree of linear correlation (r2 = 0.97). The mean level of OT in 11 women during hypocontractile labor before the infusion of OT was 1.01 +/- 0.31 (+/- SEM) microU/ml. There was a linear correlation between the dose of OT infused and the level of OT in plasma with infused doses of OT between 1 and 4 mU/min (r2 = 0.99). The time of onset of adequate uterine contractility was recorded by on-line computer analysis, and the level of OT in plasma obtained simultaneously was variable among the women. The mean OT MCR in these women was 17.4 +/- 9.2 (+/- SEM) ml/kg X min, similar to the MCR in normal men (17.6 +/- 2.1 ml/kg X min). Levels and pharmacokinetics of OT during hypocontractile labor were similar to those in nonpregnant individuals and women in late pregnancy. The variability in OT concentrations at the time of adequate uterine contractility suggests that individual myometrial sensitivity is an important determinant of the response to administered OT in humans.

Oxytocin augmentation of dysfunctional labor. III. Multiparous patients.

The effectiveness of a specific oxytocin regimen characterized by a small dose, a slow rate of oxytocin incrementation, and a specific computer-defined goal of contractile activity was evaluated. The group managed by this protocol was compared with a similar group of multiparous patients managed by the same physicians using their own choice of oxytocin therapies and electronic monitoring of intrauterine pressure. The patients managed by protocol and computer had shorter mean durations of time from onset of treatment to complete cervical dilatation and received smaller mean doses of oxytocin than the control group of patients. The most significant factor determining these results was the rate of incrementation of the oxytocin dose.

Oxytocin augmentation of dysfunctional labor. II. Uterine activity data.

The intrauterine pressure data obtained from oxytocin-treated patients in dysfunctional labor, managed by a specific oxytocin regimen and a computer-defined goal of uterine activity, are analyzed. Questions asked concern the efficacy of the computer diagnosis of hypocontractility, the quantity of uterine activity needed to effect cervical dilatation, and the effectiveness of the quantitative data as an aid in selecting the necessary dose. The false positive diagnostic rate was one of 45 and the false negative, one of 42. The results demonstrate that there were no statistically significant differences between the computer-defined goal of activity and that associated with cervical dilatation if the dose used was permitted the time to accomplish its maximum effect. Quantitation of uterine contractility provided the information necessary to select the dose of oxytocin associated with cervical dilatation in approximately 75% of the patients.

Oxytocin augmentation of dysfunctional labor. I. Clinical data.

The effectiveness of a specific oxytocin dosage regimen and a specific computer-defined initial goal of a contractile activity is compared to groups of similar nulliparous women managed by the same physicians who used their own choices of oxytocin therapy and electronic monitoring of the intrauterine pressure. The patients managed by a specific regimen and a computer-defined therapeutic goal had oxytocin stopped or the dosage reduced because of concerns with fetal distress or, less frequently, hypercontractility, had shorter intervals from the initiation of oxytocin to full dilation, required smaller doses to accomplish cervical change, and received smaller maximum doses of oxytocin. The most significant factor determining these results was the rate of incrementation of the oxytocin dose.

Cesarean delivery in nulliparous women for failed oxytocin-augmented labor: route of delivery in subsequent pregnancy.

Fifty-eight patients experienced cesarean section for termination of their first term pregnancy subsequent to a failed trial of oxytocin therapy. Cephalopelvic disproportion and "failure to progress" were the sole indications for the initial cesarean section. All 58 women returned to our hospital for a subsequent trial of labor during the years 1977-1979 inclusive, and 40 of the 58 were able to have a vaginal delivery. Parameters investigated included first and subsequent pregnancy birth weights; birth weight difference; duration and maximal dose of oxytocin; status of the cervix at admission, prior to oxytocin, and before cesarean section; and the clinical and/or radiologic estimation of pelvic dimensions. Subsequent birth weight less than 3,500 gm was the only statistically significant factor associated with a high rate of vaginal delivery.

Quantitating uterine contractility in clinical context.

Objective quantitative on-line analysis of the intrauterine pressure of patients in active labor can be made by using a small bedside computer. A retrospective study has been performed comparing the uterine contractility of patients in normal active labor with that of patients in arrest of labor. Examination of the data suggests that averaging each 3 successive contractions and combining the values for amplitude, period, and Montevideo units into a 3-contraction score provide an efficient and rapid means for differentiating the contractility of normal and hypocontractile labor. Further, the method appears to have the potential for selecting the appropriate minimal effective dose of oxytocin and avoiding hypercontractility.

Measure of contraction strength in labor: area and amplitude.

A retrospective, off-line study of the relationship of the area under the intrauterine pressure waveform (Area) to amplitude was performed on contractions from patients in normal labor and hypocontractile labor before and during oxytocin therapy. A linear correlation of Area and amplitude can be identified in the study of large numbers of contractions. Unfortunately, the wide scatter of the values of either measure for a narrow range of values of the other precludes the use of Area as a clinically useful aid in assessing hypocontractility or oxytocin response from small numbers of contractions.

A computer-based obstetric data retrieval system.

A computer-based obstetric patient data retrieval system is described which permits physicians with no prior computer knowledge or experience to access a patient data base. The advantages are minimal physician instruction, opportunity to examine maternal and neonatal outcome of defined diagnostic or therapeutic subsets of the data base, and rapid recall of individual patients' data, without need for continuous assistance from computer specialists. Disadvantages are the costs and our inability to interface our medical information with hospital business office data. Two brief examples of use of the system are provided.

Intrauterine pressure wave form characteristics of successful and failed first stage labor.

A retrospective study was designed to contrast the intrauterine pressure wave form characteristics of hypocontractile labor in patients with and without obstruction and before and after oxytocin therapy. No differences were observed between the patient groups (vaginal delivery vs. cesarean section), either before or after oxytocin. Problems in defining adequate contractility in patients with possible obstructed labors are discussed, and new parameters of potential value are identified.

Oxytocin-induced uterine hypercontractility pressure wave forms.

To identify similarities and differences between uterine contractions in patients with spontaneous labor, oxytocin-corrected hypocontractility, and oxytocin-induced hypercontractility, measurements were made of specific characteristics of the intrauterine wave form, including pressure, rate of change of pressure, and duration. Contractions from oxytocin-treated patients differed from contractions of those with spontaneous labor in their disproportionately high rates of rise of the pressure. The time to reach the maximum rate of the pressure--the start-up time--was reduced in oxytocin-induced hypercontractility. The data demonstrate that the contractions of spontaneous labor and oxytocin-augmented labor are not identical, and the physiologic implications are discussed.

Intrauterine pressure wave form characteristics in hypocontractile labor before and after oxytocin administration.

The data demonstrate that the contractions of hypocontractile active labor and normal spontaneous labor are different in several measures in addition to maximal amplitude. Furthermore, when the pathophysiology is corrected by the use of oxytocin, the contractions resemble those of normal spontaneous labor except in the maximal rate of tension development. Our data tend to support the subcellular model of uterine contractility, although the incompleteness of these models limits interpretation.