Hemodynamic measurements in preeclampsia: Preliminary observations

R. Groenendijk, M.D., J. B. M. J. Trimbos, M.D., Ph.D., and H. C. S. Wallenburg, M.D., Ph.D.

Rotterdam, The Netherlands

Ten patients with preeclampsia were monitored with a Swan-Ganz thermodilution catheter before the start of treatment. Reference data were obtained by right-heart catheterization in four normal pregnant women. In the preeclamptic group the effects of volume expansion and vasodilatation were studied. All patients showed a low cardiac index, low pulmonary capillary wedge pressure, and a high systemic vascular resistance. Following volume expansion the pulmonary capillary wedge pressure and cardiac index rose to normal pregnant values whereas blood pressure showed no significant change and systemic vascular resistance decreased, but normal pregnant values were not obtained. Vasodilatation with dihydralazine resulted in a further decrease in systemic vascular resistance, a fall in blood pressure accompanied by a further increase in cardiac index with a stable pulmonary capillary wedge pressure. It is concluded that pregnant women with preeclampsia are unable to cope with a circulating volume necessary to maintain a cardiac index and ventricular filling pressure which is considered to be physiologic in normal pregnancy. In preeclampsia the capacity for vasodilatation is inadequate. (AM J OBSTET GYNECOL 1984;150:232-6.)

Increased vascular resistance and decreased circulat­ing blood volume with impaired perfusion of various organs, including the uteroplacental unit, are recog­nized as important pathophysiologic features of the preeclamptic syndrome. 1

-2 Nevertheless, only few re­

ports can be found in the literature in which hemody­namic variables in this condition were determined with reliable invasive techniques. Results of studies in which a Swan-Ganz thermodilution catheter was used have been published, but in all of these studies measure­ments were carried out during labor or post partum after treatment had been instituted.3

-6 These data can­

not be considered to be representative of untreated preeclamptic patients. An additional problem is caused by the fact that little quantitative information is avail­able on systemic and pulmonary hemodynamics in nor­mal pregnant women. Data on cardiac output and pul­monary artery pressures obtained by cardiac catheter­ization in normal pregnant women in various stages of pregnancy have been reported by Rose eta!. in 1956.7

The objective of the present study was to obtain he­modynamic data in untreated preeclamptic pregnant women by means of a Swan-Ganz thermodilution cath­eter and to determine the effects of volume expansion and pharmacologic vasodilatation. In addition, refer-

From the Department of Internal Medicine, Sint Franciscus Gasthuis, and the Department of Obstetrics and Gynecology, Erasmus Uni­versity School of Medicine.

Received for publication November 9, 1983; revised March 7, 1984; accepted April 13, 1984.

Reprint requests: H. C. S. Wallenburg, M.D., Ph.D., Erasmus Uni­versity School of Medicine, EE 2283, P.O. Box 1738,3000 DR., Rotterdam, The Netherlands.

232

ence values were obtained in four pregnant women in the last trimester of their uncomplicated pregnancies.

Material and methods

Ten nulliparous patients with preeclampsia in the third trimester of pregnancy were studied. Preeclamp­sia was defined as the occurrence of a diastolic blood pressure of 2: 100 mm Hg measured in sitting position on two occasions at least 6 hours apart and proteinuria of 2:0.5 gm/L. The patients were not known to have preexisting hypertension, renal disease, or heart dis­ease. All patients had a live fetus, and they were not in labor during the study. All patients were on a mildly sodium-restricted diet before admission, but diuretics or antihypertensive drugs were not used. Some of the patients received oral diazepam before the measure­ments were started. A normal electrocardiogram was obtained from all patients. The following laboratory tests were done on admission: complete blood count, urinalysis, serum creatinine, uric acid, liver function tests (serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, and lactic dehydroge­nase) and pliitelet count. These tests were repeated after the hemodynamic measurements.

In addition, one nulliparous and three parous women with uncomplicated pregnancies were studied in the third trimester of pregnancy. None of these women were in labor during the study, and they received no drugs. They underwent the same laboratory tests as the preeclamptic patients. Informed consent was obtained from all preeclamptic and control patients.

A radiopaque, flow-directed Swan-Ganz thermodi­lution catheter was inserted under continuous pressure

Volume 150 Number 3

Hemodynamic measurements in preeclampsia 233

Table I. Individual patient data and laboratory findings of preeclamptic patients (Nos. 1-10) and normal control subjects (Nos. 11-14) on admission

Blood Liver Platelet Patient Age Gestational pressure H ernoglobin Hematocrit Uric acid Proteinuria function count

No. (yr) Parity age (wk) (mm Hg) (mmol/L) (%) (mrnol/L) (grn/L) tests* (X 109 /L)

1 23 0 30 1601110 6.0 0.30 0.45 8 A 76 2 23 0 28 160/105 8.8 0.39 0.32 7 A 130 3 23 0 35 170/120 8.0 0.37 0.45 1.6 N 135 4 22 0 35 160/110 7.1 0.34 0.36 0.5 N 310 5 21 0 34 1801120 9.6 0.45 0.53 0.9 A 30 6 25 Ot 37 160/110 8.4 0.42 0.63 0.5 A 165 7 28 0 31 180/130 9.0 0.41 0.42 6.9 N 61 8 25 0 27 1401100 7.8 0.35 0.52 1.6 A 175 9 34 0 29 1501115 8.1 0.40 0.32 1.2 N 100

10 35 0 34 140/100 7.8 0.40 0.60 0.5 A 45 11 26 1 34 140/70 6.6 0.31 0.33 N 275 12 25 1 32 130/80 8.0 0.37 0.26 N 200 13 22 1 32 120170 7.8 0.36 0.19 N 210 14 30 0 28 140/90 7.4 0.34 0.35 N 235

*A, Abnormal; N, normal. tTwin gestation.

Table II. Hemodynamic variables (mean and range) in preeclamptic patients and control subjects

Preeclamptic patients ( n = 10)

I After volume

_I J After l Control subjects Initial expansion p* vasodilatation pt (n = 4)

Diastolic blood pressure 106 (100-120) 102 (90-120) NS:j: 85 (75-100) <0.01 77 (70-90) (mmHg)

Mean arterial pressure 121 (113-136) 116 (103-136) <0.02 102 (97-116) <0.01 95 (93-106) (mmHg)

Heart rate (bpm) 100 (90-130) 81 (60-110) <0.01 82 (70-100) NS 84 (70-90) Pulmonary capillary wedge 3.3 (1-5) 8 (7-10) <0.01 8 (7-9) NS 9 (6-12)

pressure (mm Hg) Systemic vascular resistance 1943 (1480-2580) 12114 (1073-1600) <0.01 947 (7112-1028) <0.01 886 (805-1 021)

(dynes· sec· em-') Cardiac index (L/min/m') 2.75 (1.97-3.33) 3.77 (3.26-4.05) <0.01 4.40 (3.94-5.00) <0.01 4.53 (3.96-4.97)

Wilcoxon signed-rank test (two-tailed). *As compared with initial values. t As compared with values after volume expansion. :j:NS, Not significant.

monitoring through a Cordis introducer placed in a subclavian vein.

The position of the catheter tip was confirmed by one single chest radiograph. Right atrial pressure and pulmonary capillary wedge pressure were measured in supine position, cardiac output was determined in both supine and in left lateral positions. The zero reference point chosen was 5 em below the third intercostal space. Cardiac output was measured in triplicate by the ther­modilution method with a cardiac output analogue computer (Edwards Laboratories, Irvine, California). During the procedure heparin was administered intra­venously at a rate of 15,000 units per 24 hours.

In the preeclamptic women baseline values were ob­tained after a stabilization period of at least 1 hour. Since the values of the cardiac index appeared to be

below the normal mean of 3.9 L/min/m2 as reported by Rose et aU in all cases, plasma volume was expanded over the next 12 to 24 hours, under continuous moni­toring, with a 3.5% colloid plasma substitute (Haemac­cel) until a cardiac index of approximately 4 L!min/m2

was obtained with an upper limit of pulmonary capil­lary wedge pressure of 10 mm Hg. The amount of plasma expander needed varied between 1500 and 3500 ml. Following this regimen dihydralazine was administered by slow intravenous infusion in a dose of 2 to 5 mg/hr until a systemic vascular resistance of ap­proximately 1000 dynes · sec · cm-5 was reached in the presence of a diastolic blood pressure of< 100 mm Hg.

When stabilization of the circulatory system was ob­tained and the relationship between right arterial pres­sure and pulmonary capillary wedge pressure was es-

234 Groenendijk, Trimbos, and Wallenburg

130

co J: E .5

110

c.. <(

~ 90

120

100

'E 0..

..c 80

0::: J:

60

"'~ I

E 2400 '! u Cli

"' ,;, 2000 Cli c >-. "0

1600 0::: > V'J

1200

BOO

10

co 8 J:

E E 6

c.. ~ 4 u c..

2

0

::- 5.00 E --c E 4.00

--....1

3.00 u -----

2.00

A B c

Fig. 1. Individual hemodynamic values before (A) and after (B) volume expansion and after vasodilatation (C). Dotted lines represent the normal range for nonpregnant individuals. MAP, Mean arterial pressure; HR, heart rate; SVR, systemic vascular resistance; PCWP, pulmonary capillary wedge pres­sure; CI, cardiac index.

October I, 1984 Am J Obstet Gynecol

tablished, the Swan-Ganz catheter was replaced by a conventional central venous pressure catheter through the Cordis introducer. Values in the four control women were obtained following a 1-hour stabilization period, after which the catheter was removed.

Since the results could not be accepted to follow a gaussian distribution, data were compared by means of paired or unpaired nonparametric tests, and 0.05 was taken as the level of significance.

Results

Maternal population. The mean age of the pre­eclamptic patients was 26 years (range, 21 to 35) and

the mean gestational age in weeks was 32 (range, 27 to 35). Twin pregnancy was present in one patient. The mean diastolic blood pressure on admission was 112 mm Hg (range, 100 to 130). Individual patient data and laboratory findings of the preeclamptic patients and the normal pregnant women are presented in Table I. Urine production was below 500 ml/24 hr in seven of the 10 preeclamptic patients.

Hemodynamic measurements in preeclamptic pa· tients. The mean hemodynamic values obtained before and after volume expansion and after vasodilatation are summarized in Table II. Individual changes are presented graphically in Fig. 1. There was no sig­nificant difference between the paired values of cardiac output measured in supine and left lateral position (Wilcoxon signed-rank test). The initial measurements revealed a low pulmonary capillary wedge pressure, a low cardiac index, and a high systemic vascular resis­

tance. Maternal heart rate appeared to be elevated. Volume expansion induced a significant increase in

both pulmonary capillary wedge pressure and cardiac index as well as a significant decrease in systemic vascular resistance and maternal heart rate. Diastolic blood pressure showed a small but not significant de­crease, whereas the mean arterial pressure decrease was statistically significant, mainly due to a reduced sys­tolic blood pressure. Vasodilatation with dihydralazine failed to cause a significant change in pulmonary capil­

lary wedge pressure, but the cardiac index showed a

significant increase accompanied by a further decrease in systemic vascular resistance. Mean diastolic blood

pressure and mean arterial pressure fell significantly,

whereas maternal heart rate remained stable in most

cases. Hemodynamic measurements in control women.

Hemodynamic variables obtained in the four women with uncomplicated pregnancies are also summarized

in Table II. Also in this group no difference was

apparent between cardiac output values determined in supine and left lateral positions, but no statistical

Volume !50 Number 3

test was applied because of the small number of indi­viduals.

Outcome of pregnancy. Nine preeclamptic patients were delivered of live infants with a mean birth weight

of 1675 gm (range, 910 to 2235). Two patients were delivered vaginally, and a cesarean section was per­formed in seven women. Fetal death occurred in one patient (No. 8) at a gestational age of 29 weeks, 2 weeks after the hemodynamic measurements were per­formed. All control women had spontaneous vaginal term deliveries with live infants with birth weights be­tween 2800 and 3730 gm.

Comment

To our knowledge this is the first report on hemo­dynamic values obtained by means of a Swan-Ganz thermodilution catheter in untreated preeclamptic pa­tients. The results are compatible with the presence of arteriolar vasoconstriction and contracted volume in preeclamptic women. Although the number of normal

pregnant women investigated in our study is small, the hemodynamic values are in close agreement with those

reported by Rose et al./ which were obtained by right­heart catheterization between 28 and 35 weeks' gesta­tion. In our study there were no significant differences between values of cardiac output measured with the patient lying on her back and in left lateral position. This means that no serious impediment of venous re­turn by the pregnant uterus occurred in our patients, probably because they were not in late pregnancy.

Systemic vascular resistance in preeclamptic patients was elevated to approximately twofold the normal val­ues for pregnant women and even higher than values

reported in nonpregnant individuals.8 The cardiac index in all preeclamptic women was below the lowest values determined in the four normal pregnant women studied and even low in comparison with normal non­pregnant values.8 These results are in contrast with other observations published in the literature, in which cardiac index in preeclamptic patients has been found to be in the normal range for pregnancy.3

-6 The dis­

crepancy may be attributed to the fact that these mea­surements were performed during labor or post par­

tum following treatment. The reason that normal cardiac index values have

also been reported in untreated preeclamptic pa­tients9· 10 is not clear but may be due to differences in definition and in severity of the preeclampsia as well as

to the methods used. A low cardiac index in the presence of a low pulmo­

nary capillary wedge pressure accompanied by an ele­vated heart rate in the absence of heart disease is in agreement with the hypothesis of the existence of a low

Hemodynamic measurements in preeclampsia 235

output state caused by hypovolemia in preeclamptic pa­tients. This hypothesis is also supported by the occur­rence of a low urine production. We observed a small but nonsignificant fall in diastolic blood pressure

following volume expansion. In another study a

marked antihypertensive effect of plasma volume ex­pansion in patients with pregnancy-associated hy­pertension is reported." However, these data cannot be compared with ours because the study concerns a group composed of pregnant women with hypertension of unspecified severity, with and without proteinuria. We observed that volume expansion leads to an increase in cardiac index and to a partial reduction in systemic vascular resistance in the presence of an unchanged or somewhat reduced blood pressure. To further reduce systemic vascular resistance and blood pressure, admin­istration of a vasodilator appears to be necessary. This observation indicates that a pregnant woman with pre­eclampsia is not able to cope with a circulating volume necessary to maintain a cardiac index and a ventricular

filling pressure, which is considered physiologic in un­complicated pregnancy. This suggests that, at least in severe preeclampsia, the capacity for vasodilatation is

inadequate, which may be due in part to an elevated vasopressor sensitivity. The question as to whether the

observed hemodynamic changes are the cause or the effect of pregnancy-induced hypertension remains to be answered.

We acknowledge the support by the staff members of the Departments of Obstetrics and Gynecology in both hospitals.

REFERENCES

l. Chesley LC. Plasma and red cell volumes during preg­nancy. AMJ 0BSTET GYNECOL 1972;112:440.

2. Zuspan FP. Problems encountered in the treatment of pregnancy-induced hypertension. AMJ OBSTET GYNECOL 1978;131:591.

3. Rafferty TD, Berkowitz RL. Hemodynamics in patients with severe toxemia during labor and delivery. AM J 0BSTET GYNECOL 1980;138:263.

4. Benedetti TJ, Cotton DB, Read JC, Miller FC. Hemody­namic observation in severe preeclampsia with a flow­directed pulmonary artery catheter. AM J OBSTET GYNE­COL 1980;136:465.

5. Rolbin SH, Cole AFD, Hew EM. Hemodynamic monitor­ing in the management of severe pre-eclampsia and eclampsia. Can Anaesth Soc J 1981 ;28:363.

6. Phelan JP, Yurth DA. Peripartum hemodynamic obser­vations. AM J 0BSTET GYNECOL 1982; 144: 17.

7. Rose DJ, Bader MJ, Bader RA, Braunwald E. Catheter­ization studies of cardiac hemodynamics in normal preg­nant women with reference to left ventricular work. AM J 0BSTET GYNECOL 1956;72:233.

8. Barry WH, Grossman W. Cardiac catheterization. In: Braunwald E. Heart disease. Philadelphia: W.B. Saun­ders, 1980:278.

9. Werko L. Studies in the problems of circulation in preg-

Groenendijk, Trimbos, and Wallenburg

nancy. In: Hammond J, Browne FJ, Wolstenholm GEW, ed. Toxemias of pregnancy: human and veterinary. Phil­adelphia: Blakiston, 1950: 155.

10. Assali NS, Holm LW, Parker HR. Systemic and regional hemodynamic alterations in toxemia. Circulation 1964;30 (suppl 2): 11.

October I, 1984 Am J Obstet Gynecol

11. Gallery EDM, Delprado W, Gyory AZ. Antihypertensive effect of plasma volume expansion in pregnancy-associ­ated hypertension. Aust NZJ Med 1981;11:20.

Determinants of size at birth in a Canadian population

Gary D. Anderson, Ph.D., lisa N. Blidner, M.A., Sharon McClemont, M.A., and John C. Sinclair, M.D.

Hamilton, Ontario, Canada

Anthropometric, medical, and sociodemographic characteristics and smoking habit of a random sample of

postpartum women in a Canadian population were determined. These characteristics were analyzed in

relation to the birth size of their babies. With controls for gestational age and fetal sex, the following

maternal variables were positively correlated with birth weight: prepregnant weight, weight gain in

pregnancy, stature, bicristal and biacromial diameter, calf and upper arm circumference, and triceps and subscapular skinfold thickness. Smoking during pregnancy reduced birth weight by 13 gm per cigarette

smoked daily. Similar associations of maternal size and smoking habit were observed with respect to infant length, head circumference, and chest circumference. The predictors of birth weight are proposed for use

in adjusting upward or downward the population distribution of birth weight to reflect the individual

characteristics of the mother. (AM J OssTET GYNECOL 1984;150:236-44.)

Birth weight has been shown to depend on many

factors including maternal size, maternal nutrition, ma­ternal smoking habit, and parental sociodemographic characteristics. The relative importance of such influ­ences on birth weight may differ in different popula­tions; for example, the effects of maternal nutrition and socioeconomic status are readily apparent in de­veloping countries but may be less important in indus­trialized societies.

We have reported the size at birth (birth weight, crown-heel length, head circumference, chest circum­

ference) of a random sample of all births occurring in a Canadian city. 1 The objectives of the present report are (1) to quantify the effects on size at birth

of maternal anthropometric, medical, and sociodemo­

graphic characteristics and of smoking habit in this par­turient population; (2) to derive adjustment factors for

predicting size at birth from individual maternal

characteristics.

From the Departments of Clinical Epidemiology and Biostatistics and Pediatrics, McMaster University.

Supported by Medical Research Council of Canada Grant MT-5194. ReceivedforpublicationDecember 5, 1983; revisedApril18, 1984;

accepted April23, 1984. Reprint requests: Dr. ]. C. Sinclair, Department of Pediatrics,

McMaster University Medical Centre, 1200 Main St. West, Hamilton, Ontario, Canada L8N 3Z5.

236

Methods

Over an 18-month period, postpartum mothers and their babies were surveyed at all Hamilton, Ontario, hospitals with obstetric services. Identified by the sam­pling strategy for participation in the survey were 2409 women, of whom 2332 (96.8%) actually participated. Included in the survey were 357 cases who had been nonrandomly selected and who have been excluded, leaving 1975 cases who contribute to this report. Further details of the design and implementation of the study have previously been described. 1

Tables I and II list the variables that were studied.

Data on maternal characteristics were collected by a

structured review of the maternal hospital chart and a

structured maternal interview conducted during the first 5 postpartum days. A postpartum maternal an­

thropometric assessment was undertaken at the time of the interview. Birth weight was recorded within the first hour of life with the use of calibrated scales.

Crown-heel length, head circumference, and chest cir­cumference of the infant were measured between 24

and 96 hours after birth, at which time an assessment of gestational age by means of the Dubowitz scoring system2 was also performed. The methods used for an­

thropometric measurements of the mothers and their

infants have been described previously. 1