INFERIOR VENA CAVAL PRESSURE IN LATE PREGNANCY

Impact of Altered Vena Cava Flow Rates on Right Atrium Flow Characteristics

The right atrium (RA) combines the superior (SVC) and inferior vena cava (IVC) flows. Treatments like extracorporeal membrane oxygenation (ECMO) and hemodialysis by catheter alter IVC/SVC flows. Here we assess how altered IVC/SVC flow contributions impact RA flow. Four healthy volunteers were imaged with CT, reconstructed and combined into a patient-averaged model. Large Eddy Simulations (LES) were performed for a range of IVC/SVC flow contributions (30-70% each, increments of 5%) and common flow metrics were recorded. Model sensitivity to reconstruction domain extent, constant/pulsatile inlets and hematocrit was also assessed. Consistent with literature, a single vortex occupied the central RA across all flowrates with a smaller counter-rotating vortex, not previously reported, in the auricle. Vena cava flow was highly helical. RA turbulent kinetic energy (TKE) (P=0.027) and time-averaged wall shear stress (WSS) (P<0.001) increased with SVC flow. WSS was lower in the auricle (2 Pa, P<0.001). WSS in the vena cava were equal at IVC/SVC =65/35%. The model was highly sensitive to the reconstruction domain with cropped geometries lacking helicity in the vena cavae, altering RA flow. RA flow was not significantly affected by constant inlets or hematocrit. The rotational flow conventionally described in the RA is confirmed however a new, smaller vortex was also recorded in the auricle. When IVC flow dominates, as is normal, TKE in the RA is reduced and WSS in the vena cavae equalize. Significant helicity exists in the vena cava, a result of distal geometry and this geometry appears crucial to accurately simulating RA flow.

Supine hypotensive syndrome of pregnancy: A review of current knowledge

Since the first description of supine hypotensive syndrome in the 1950s, its potentially detrimental effects on otherwise healthy women during late pregnancy have become a persistent challenge in obstetric practice. Establishing a 15° left lateral tilt during labour and caesarean section is a fundamental principle of obstetric care, universally adopted and upheld by current guidelines and recommendations. Reassessment of the original landmark studies in the light of current physiological and anatomical knowledge questions adherence to this standard in clinical practice. The modern practice of providing vasopressor support during caesarean delivery under neuraxial anaesthesia appears to negate any potential negative effects of a maternal full supine position. Recent MRI studies provide evidence as to the cause of supine hypotension and the physiological effects of different maternal positions at term. This review highlights current data on the acute supine hypotensive syndrome in contrast to traditional knowledge and established practice.

Review article: chronic liver disease and pregnancy

BACKGROUND

The prevalence of chronic liver disease in women of child bearing age is increasing, leading to a higher incidence of pregnancy in this cohort. Chronic medical conditions have a significant adverse effect on maternal morbidity and mortality. To date, reviews on this topic have been written either from a hepatology or obstetrics viewpoint, and no specific guidelines are available solely for the management of chronic liver disease in pregnancy.

AIMS

To produce a comprehensive review on the clinical management of women with chronic liver disease during pregnancy, addressing the risks of pregnancy to mother and child, how these risks can be ameliorated, and what additional considerations are required for management of chronic liver disease in pregnancy.

METHODS

Data were collected up to May 2020 from the biomedical database PubMed, national and international guidelines in gastroenterology and hepatology.

RESULTS

During pregnancy, women with cirrhosis are more likely to develop decompensated disease, worsening of portal hypertension, and to deliver premature infants.

CONCLUSIONS

The risks associated with pregnancy can be ameliorated by advanced planning, assessing risk using the model for end stage liver disease score and risk reduction through varices screening. A multidisciplinary approach is paramount in order to minimise complications and maximise the chance of a safe pregnancy and birth for mother and baby.

The effect of body position on maternal cardiovascular function during sleep and wakefulness in late pregnancy

INTRODUCTION

An association between the increased risk of late stillbirth and the maternal supine sleeping position has been recently established. The risk of stillbirth following supine sleep has been suspected to occur as a result of aortocaval compression by the gravid uterus. A number of studies conducted during wakefulness have reported compromised cardiovascular function during supine rest, as demonstrated by reductions in cardiac output, blood pressure and utero-placental blood flow. It remains unclear whether similar effects are also present during sleep, due to the presence of key sleep-specific changes in cardiovascular function.

OBJECTIVE

To investigate the changes in maternal cardiovascular function between the supine and left-lateral positions during wakefulness and non-rapid eye movement (NREM) sleep in late pregnancy.

METHODS

Twenty-nine women with a singleton pregnancy between 24.7 and 36.7 weeks' gestation participated in a single overnight sleep study. Physiological measures (blood pressure, heart rate, heart rate variability - HRV, and pulse arrival time - PAT) were measured and recorded throughout the night using standard polysomnography equipment and the Portapres Model-2 device. As the present study evaluated cardiovascular changes during natural rest and sleep in pregnancy, participants were not given explicit instructions on which position to adopt. Body position was continuously recorded using a position monitor and verified with video recording.

RESULTS

No changes in systolic, diastolic or mean arterial blood pressure were observed between the left-lateral and supine positions during wakefulness or sleep. However, heart rate was significantly higher in the supine position compared to the left during wakefulness (p= .03), with a similar trend present during sleep (p= .11). A significantly shorter PAT was measured in the supine position (compared to the left) during wakefulness (p= .01) and sleep (p= .01). No change in HRV measures was observed between the left and supine positions in either state.

CONCLUSION

Blood pressure did not appear to differ significantly between the left-lateral and supine positions during wakefulness and sleep. The lack of blood pressure differences may reflect elevated sympathetic activity during rest and sleep in the supine position (compared to the left), suggesting that some degree of compensation for aortocaval compression may still be possible during sleep.

Effects of Vasoactive Medications and Maternal Positioning During Cesarean Delivery on Maternal Hemodynamics and Neonatal Acid-Base Status

Maternal hemodynamics, positioning, and anesthesia technique for cesarean delivery influence neonatal acid-base balance; direct effects from drugs that cross the placenta also have an influence. Spinal anesthesia limits fetal exposure to depressant drugs and avoids maternal airway instrumentation, but is associated with hypotension. Hypotension may be prevented/treated with vasopressors and intravenous fluids. Current evidence supports phenylephrine as the first-line vasopressor. Fifteen degrees of lateral tilt during cesarean delivery has been advocated to relieve vena caval obstruction, but routine use may be unnecessary in healthy nonobese women having elective cesarean delivery if maternal blood pressure is maintained near baseline.

Toward Automation of the Supine Pressor Test for Preeclampsia

Preeclampsia leads to increased risk of morbidity and mortality for both mother and fetus. Most previous studies have largely neglected mechanical compression of the left renal vein by the gravid uterus as a potential mechanism. In this study, we first used a murine model to investigate the pathophysiology of left renal vein constriction. The results indicate that prolonged renal vein stenosis after 14 days can cause renal necrosis and an increase in blood pressure (BP) of roughly 30 mmHg. The second part of this study aimed to automate a diagnostic tool, known as the supine pressor test (SPT), to enable pregnant women to assess their preeclampsia development risk. A positive SPT has been previously defined as an increase of at least 20 mmHg in diastolic BP when switching between left lateral recumbent and supine positions. The results from this study established a baseline BP increase between the two body positions in nonpregnant women and demonstrated the feasibility of an autonomous SPT in pregnant women. Our results demonstrate that there is a baseline increase in BP of roughly 10-14 mmHg and that pregnant women can autonomously perform the SPT. Overall, this work in both rodents and humans suggests that (1) stenosis of the left renal vein in mice leads to elevation in BP and acute renal failure, (2) nonpregnant women experience a baseline increase in BP when they shift from left lateral recumbent to supine position, and (3) the SPT can be automated and used autonomously.

Left Lateral Table Tilt for Elective Cesarean Delivery under Spinal Anesthesia Has No Effect on Neonatal Acid–Base Status

Background

Current recommendations for women undergoing cesarean delivery include 15° left tilt for uterine displacement to prevent aortocaval compression, although this degree of tilt is practically never achieved. We hypothesized that under contemporary clinical practice, including a crystalloid coload and phenylephrine infusion targeted at maintaining baseline systolic blood pressure, there would be no effect of maternal position on neonatal acid base status in women undergoing elective cesarean delivery with spinal anesthesia.

Methods

Healthy women undergoing elective cesarean delivery were randomized (nonblinded) to supine horizontal (supine, n = 50) or 15° left tilt of the surgical table (tilt, n = 50) after spinal anesthesia (hyperbaric bupivacaine 12 mg, fentanyl 15 μg, preservative-free morphine 150 μg). Lactated Ringer’s 10 ml/kg and a phenylephrine infusion titrated to 100% baseline systolic blood pressure were initiated with intrathecal injection. The primary outcome was umbilical artery base excess.

Results

There were no differences in umbilical artery base excess or pH between groups. The mean umbilical artery base excess (± SD) was −0.5 mM (± 1.6) in the supine group (n = 50) versus −0.6 mM (± 1.5) in the tilt group (n = 47) (P = 0.64). During 15 min after spinal anesthesia, mean phenylephrine requirement was greater (P = 0.002), and mean cardiac output was lower (P = 0.014) in the supine group.

Conclusions

Maternal supine position during elective cesarean delivery with spinal anesthesia in healthy term women does not impair neonatal acid–base status compared to 15° left tilt, when maternal systolic blood pressure is maintained with a coload and phenylephrine infusion. These findings may not be generalized to emergency situations or nonreassuring fetal status.

Position in the second stage of labour for women without epidural anaesthesia

BACKGROUND

For centuries, there has been controversy around whether being upright (sitting, birthing stools, chairs, squatting, kneeling) or lying down (lateral (Sim's) position, semi-recumbent, lithotomy position, Trendelenburg's position) have advantages for women giving birth to their babies. This is an update of a review previously published in 2012, 2004 and 1999.

OBJECTIVES

To determine the possible benefits and risks of the use of different birth positions during the second stage of labour without epidural anaesthesia, on maternal, fetal, neonatal and caregiver outcomes.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register (30 November 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised, quasi-randomised or cluster-randomised controlled trials of any upright position assumed by pregnant women during the second stage of labour compared with supine or lithotomy positions. Secondary comparisons include comparison of different upright positions and the supine position. Trials in abstract form were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and assessed trial quality. At least two review authors extracted the data. Data were checked for accuracy. The quality of the evidence was assessed using the GRADE approach.

MAIN RESULTS

Results should be interpreted with caution because risk of bias of the included trials was variable. We included eleven new trials for this update; there are now 32 included studies, and one trial is ongoing. Thirty trials involving 9015 women contributed to the analysis. Comparisons include any upright position, birth or squat stool, birth cushion, and birth chair versus supine positions.In all women studied (primigravid and multigravid), when compared with supine positions, the upright position was associated with a reduction in duration of second stage in the upright group (MD -6.16 minutes, 95% CI -9.74 to -2.59 minutes; 19 trials; 5811 women; P = 0.0007; random-effects; I² = 91%; very low-quality evidence); however, this result should be interpreted with caution due to large differences in size and direction of effect in individual studies. Upright positions were also associated with no clear difference in the rates of caesarean section (RR 1.22, 95% CI 0.81 to 1.81; 16 trials; 5439 women; low-quality evidence), a reduction in assisted deliveries (RR 0.75, 95% CI 0.66 to 0.86; 21 trials; 6481 women; moderate-quality evidence), a reduction in episiotomies (average RR 0.75, 95% CI 0.61 to 0.92; 17 trials; 6148 women; random-effects; I² = 88%), a possible increase in second degree perineal tears (RR 1.20, 95% CI 1.00 to 1.44; 18 trials; 6715 women; I² = 43%; low-quality evidence), no clear difference in the number of third or fourth degree perineal tears (RR 0.72, 95% CI 0.32 to 1.65; 6 trials; 1840 women; very low-quality evidence), increased estimated blood loss greater than 500 mL (RR 1.48, 95% CI 1.10 to 1.98; 15 trials; 5615 women; I² = 33%; moderate-quality evidence), fewer abnormal fetal heart rate patterns (RR 0.46, 95% CI 0.22 to 0.93; 2 trials; 617 women), no clear difference in the number of babies admitted to neonatal intensive care (RR 0.79, 95% CI 0.51 to 1.21; 4 trials; 2565 infants; low-quality evidence). On sensitivity analysis excluding trials with high risk of bias, these findings were unchanged except that there was no longer a clear difference in duration of second stage of labour (MD -4.34, 95% CI -9.00 to 0.32; 21 trials; 2499 women; I² = 85%).The main reasons for downgrading of GRADE assessment was that several studies had design limitations (inadequate randomisation and allocation concealment) with high heterogeneity and wide CIs.

AUTHORS' CONCLUSIONS

The findings of this review suggest several possible benefits for upright posture in women without epidural anaesthesia, such as a very small reduction in the duration of second stage of labour (mainly from the primigravid group), reduction in episiotomy rates and assisted deliveries. However, there is an increased risk blood loss greater than 500 mL and there may be an increased risk of second degree tears, though we cannot be certain of this. In view of the variable risk of bias of the trials reviewed, further trials using well-designed protocols are needed to ascertain the true benefits and risks of various birth positions.

Can preeclampsia be considered a renal compartment syndrome? A hypothesis and analysis of the literature

The morbidity and mortality associated with preeclampsia is staggering. The physiology of the Page kidney, a condition in which increased intrarenal pressure causes hypertension, appears to provide a unifying framework to explain the complex pathophysiology. Page kidney hypertension is renin-mediated acutely and ischemia-mediated chronically. Renal venous outflow obstruction also causes a Page kidney phenomenon, providing a hypothesis for the increased vulnerability of a subset of women who have what we are hypothesizing is a "renal compartment syndrome" due to inadequate ipsilateral collateral renal venous circulation consistent with well-known variation in normal venous anatomy. Dynamic changes in renal venous anatomy and physiology in pregnancy appear to correlate with disease onset, severity, and recurrence. Since maternal recumbent position is well known to affect renal perfusion and since chronic outflow obstruction makes women vulnerable to the ischemic/inflammatory sequelae, heightened awareness of renal compartment syndrome physiology is critical. The anatomic and physiologic insights provide immediate strategies to predict and prevent preeclampsia with straightforward, low-cost interventions that make renewed global advocacy for pregnant women a realistic goal.

Changes in Sonographically Measured Inferior Vena Caval Diameter in Response to Fluid Loading in Term Pregnancy

OBJECTIVES

The purpose of this study was to determine whether the inferior vena caval (IVC) diameter is influenced by intravascular volume changes in pregnancy.

METHODS

A prospective observational study was done on 2 groups of normal term gravidas. In 24 patients, we measured the IVC diameter, blood pressure, and heart rate (HR) before and after a 1-L fluid infusion in preparation for regional anesthesia, after initiation of an epidural block, and within 24 hours postpartum. In a second group of 15 women, we measured the IVC diameter sequentially during a 1-L crystalloid infusion.

RESULTS

In the first group, the mean baseline IVC diameter ± SD at end-inspiration was 1.45 ± 0.32 cm, which was 19% smaller than at end-expiration (1.73 ± 0.31 cm; P= .003). This respiratory cycle variation remained significant at each measurement epoch. The mean caval diameter at end-inspiration increased by 23% after the fluid bolus (P = .012). Hydration was not, however, accompanied by any significant change in the HR, mean arterial pressure, or collapsibility index of the inferior vena cava. With epidural anesthesia, the mean arterial pressure decreased from 88 ± 9 to 80 ± 7 mm Hg (P= .018), but the HR and collapsibility index remained unchanged. Postpartum values were not significantly different from their baseline measurements, except for the mean arterial pressure, which was lower by about 6 mm Hg (P = .042). In the second group, the IVC diameter at end-inspiration increased by 31% after the 1-L infusion, and there was a positive correlation between the volume infused and the IVC diameter (r= 0.67; P< .0001).

CONCLUSIONS

Measurable variations in the IVC diameter occur in response to volume changes in normal term pregnancy and postpartum.

Theoretical Analysis of the Relative Impact of Obesity on Hemodynamic Stability During Acute Hemorrhagic Shock

Background:

Evidence suggests that morbid obesity may be an independent risk factor for adverse outcomes in patients with traumatic injuries.

Objectives:

In this study, a theoretic analysis using a derivation of the Guyton model of cardiovascular physiology examines the expected impact of obesity on hemodynamic changes in Mean Arterial Pressure (MAP) and Cardiac Output (CO) during Hemorrhagic Shock (HS).

Patients and Methods:

Computer simulation studies were used to predict the relative impact of increasing Body Mass Index (BMI) on global hemodynamic parameters during HS. The analytic procedure involved recreating physiologic conditions associated with changing BMI for a virtual subject in an In Silico environment. The model was validated for the known effect of a BMI of 30 on iliofemoral venous pressures. Then, the relative effect of changing BMI on the outcome of target cardiovascular parameters was examined during simulated acute loss of blood volume in class II hemorrhage. The percent changes in these parameters were compared between the virtual nonobese and obese subjects. Model parameter values are derived from known population distributions, producing simulation outputs that can be used in a deductive systems analysis assessment rather than traditional frequentist statistical methodologies.

Results:

In hemorrhage simulation, moderate increases in BMI were found to produce greater decreases in MAP and CO compared to the normal subject. During HS, the virtual obese subject had 42% and 44% greater falls in CO and MAP, respectively, compared to the nonobese subject. Systems analysis of the model revealed that an increase in resistance to venous return due to changes in intra-abdominal pressure resulting from obesity was the critical mechanism responsible for the differences.

Conclusions:

This study suggests that obese patients in HS may have a higher risk of hemodynamic instability compared to their nonobese counterparts primarily due to obesity-induced increases in intra-abdominal pressure resulting in reduced venous return.

Postural change from lateral to supine is an important mechanism enhancing cephalic spread after injection of intrathecal 0.5% plain bupivacaine for cesarean section

BACKGROUND

Spinal anesthesia is widely used for cesarean section, but the factors that affect the spread of the block in pregnant patients are still not fully explained. This study was designed to investigate the effect of postural changes on sensory block level.

METHODS

Thirty patients scheduled for elective cesarean section under combined spinal-epidural anesthesia were randomly allocated into three groups. After intrathecal injection of 0.5% plain bupivacaine 7.5mg, patients in group S were immediately placed in the supine position with left tilt, patients in group L5 were kept lateral for 5 min and then turned to the supine position with left tilt, and patients in group L10 were kept lateral for 10 min and then turned to the supine position with left tilt.

RESULTS

At 5 min, median cephalad level of sensory block was lower in groups L5 and L10 compared with group S (corrected P<0.001); at 10 min, median cephalad sensory block level was lower in group L10 compared with group S (corrected P<0.001) and group L5 (corrected P<0.001), and lower in group L5 compared with group S (corrected P=0.033); at 15 min, median cephalad level of sensory block was lower in group L10 compared with group S (corrected P=0.003) and group L5 (corrected P=0.015).

CONCLUSIONS

In our population, using 0.5% plain bupivacaine 7.5mg, postural change from the lateral position to the supine position is an important mechanism enhancing cephalic spread of spinal anesthesia during late pregnancy.

Risk of inferior vena cava compression syndrome during fetal MRI in the supine position - a retrospective analysis

OBJECTIVES

Inferior vena cava compression syndrome (VCCS) is a serious complication of supine fetal magnetic resonance imaging (MRI) examinations, particularly during late gestation. This morphologic study correlated the occurrence of VCCS with the grade of inferior vena cava (IVC) compression.

MATERIALS AND METHODS

There were 56 fetal MRI in the supine position [median gestational weeks (GW) 27+4] and 16 fetal MRI in the lateral position (median GW 30+6) retrospectively analyzed. The grade of maternal IVC compression was determined by the maximal anterior-posterior diameter (DAP) at the level of L4/L5. Fetal head position and right-sided uterus volume were analyzed. Clinical VCCS-related symptoms during fetal MRI were assessed.

RESULTS

A noncompressed IVC was present in 1.8% (n=1) and a DAP of 5 to <10 mm in 33.3% (n=19) and 1 to <5 mm in 64.9% (n=36). The DAP was independent of fetal head position (P=0.99) and showed no significant correlation with gestational age (r=0.33). IVC compression increased with right-sided uterus volume (r=-0.328; P=0.014). There was a significant difference in DAP in the lateral position compared with the supine position (P<0.001). Clinical assessment revealed no symptoms of VCCS in any woman.

CONCLUSIONS

The presented data support the concept of physiologic compensation for significantly reduced venous backflow in the supine position during the second and third trimesters of pregnancy.

Intra-abdominal pressure, intra-abdominal hypertension, and pregnancy: a review

The last several decades have seen many advances in the recognition and prevention of the abdominal compartment syndrome (ACS) and its precursor, intra-abdominal hypertension (IAH). There has also been a relative explosion of knowledge in the critical care, trauma, and surgical populations, and the inception of a society dedicated to its understanding, the World Society of the Abdominal Compartment Syndrome (WSACS). However, there has been almost no recognition or appreciation of the potential presence, influence, and management of intra-abdominal pressure (IAP), IAH, and ACS in pregnancy. This review highlights the importance and relevance of IAP in the critically ill parturient, the current lack of normative IAP values in pregnancy today, along with a review of the potential relationship between IAH and maternal diseases such as preeclampsia-eclampsia and its potential impact on fetal development. Finally, current IAP measurement guidelines are questioned, as they do not take into account the gravid uterus and its mechanical impact on intra-vesicular pressure.

Position in the second stage of labour for women without epidural anaesthesia

BACKGROUND

For centuries, there has been controversy around whether being upright (sitting, birthing stools, chairs, squatting, kneeling) or lying down have advantages for women delivering their babies.

OBJECTIVES

To assess the benefits and risks of the use of different positions during the second stage of labour (i.e. from full dilatation of the uterine cervix).

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group Trials Register (28 February 2012).

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials of any upright or lateral position assumed by pregnant women during the second stage of labour compared with supine or lithotomy positions. Secondary comparisons include comparison of different upright positions and the lateral position.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and assessed trial quality. At least two review authors extracted the data. Data were checked for accuracy.

MAIN RESULTS

Results should be interpreted with caution as the methodological quality of the 22 included trials (7280 women) was variable.In all women studied (primigravid and multigravid) there was a non-significant reduction in duration of second stage in the upright group (mean difference (MD) -3.71 minutes; 95% confidence interval (CI) -8.78 to 1.37 minutes; 10 trials, 3485 women; random-effects, I(2) = 94%), a significant reduction in assisted deliveries (risk ratio (RR) 0.78; 95% CI 0.68 to 0.90; 19 trials, 6024 women, I(2)= 27%), a reduction in episiotomies (average RR 0.79, 95% CI 0.70 to 0.90, 12 trials, 4541 women; random-effects, I(2) = 7%), an increase in second degree perineal tears (RR 1.35; 95% CI 1.20 to 1.51, 14 trials, 5367 women), increased estimated blood loss greater than 500 ml (RR 1.65; 95% CI 1.32 to 2.60; 13 trials, 5158 women, asymmetric funnel plot indicating publication bias), fewer abnormal fetal heart rate patterns (RR 0.46; 95% CI 0.22 to 0.93; two trials, 617 women). In primigravid women the use of any upright compared with supine positions was associated with: non-significant reduction in duration of second stage of labour (nine trials: mean 3.24 minutes, 95% CI 1.53 to 4.95 minutes) - this reduction was largely due to women allocated to the use of the birth cushion.

AUTHORS' CONCLUSIONS

The findings of this review suggest several possible benefits for upright posture in women without epidural, but with the possibility of increased risk of blood loss greater than 500 mL. Until such time as the benefits and risks of various delivery positions are estimated with greater certainty, when methodologically stringent data from trials are available, women should be allowed to make choices about the birth positions in which they might wish to assume for birth of their babies.

Measurement of intra-abdominal pressure in term pregnancy: a pilot study

BACKGROUND

This study was conducted to assess the feasibility of measuring intra-abdominal pressure in term parturients under spinal anesthesia.

METHODS

Intra-abdominal pressure was measured in 20 term parturients after spinal anesthesia for elective caesarean section. Pressure was measured in the supine and 10° left lateral tilt positions with a constant reference point throughout.

RESULTS

Intra-abdominal pressure measurement was feasible and safe to perform. Pressure was significantly lower in the left lateral tilt position than supine (10.9 mmHg ± 4.67 vs. 8.9 mmHg ± 4.87, P=0.0004). The range of intra-abdominal pressure in pregnancy was wide, from 2 to 20 mmHg, with >25% of patients resting with pressures above 12 mmHg in both positions.

CONCLUSIONS

Under spinal anesthesia, intra-abdominal pressure in >25% of healthy term parturients was > 12 mmHg, which has conventionally been defined as intra-abdominal hypertension. The intra-abdominal pressure in term pregnancy should be performed in the left lateral tilt position to avoid falsely elevated pressure measurements.

Pulmonary CT angiography protocol adapted to the hemodynamic effects of pregnancy

OBJECTIVE

The purpose of this study was to compare the image quality of a standard pulmonary CT angiography (CTA) protocol with a pulmonary CTA protocol optimized for use in pregnant patients with suspected pulmonary embolism (PE).

MATERIALS AND METHODS

Forty-five consecutive pregnant patients with suspected PE were retrospectively included in the study: 25 patients (group A) underwent standard-protocol pulmonary CTA and 20 patients (group B) were imaged using a protocol modified for pregnancy. The modified protocol used a shallow inspiration breath-hold and a high concentration, high rate of injection, and high volume of contrast material. Objective image quality and subjective image quality were evaluated by measuring pulmonary arterial enhancement, determining whether there was transient interruption of the contrast bolus by unopacified blood from the inferior vena cava (IVC), and assessing diagnostic adequacy.

RESULTS

Objective and subjective image quality were significantly better for group B-that is, for the group who underwent the CTA protocol optimized for pregnancy. Mean pulmonary arterial enhancement and the percentage of studies characterized as adequate for diagnosis were higher in group B than in group A: 321 ± 148 HU (SD) versus 178 ± 67 HU (p = 0.0001) and 90% versus 64% (p = 0.05), respectively. Transient interruption of contrast material by unopacified blood from the IVC was observed more frequently in group A (39%) than in group B (10%) (p = 0.05).

CONCLUSION

A pulmonary CTA protocol optimized for pregnancy significantly improved image quality by increasing pulmonary arterial opacification, improving diagnostic adequacy, and decreasing transient interruption of the contrast bolus by unopacified blood from the IVC.

Theoretical analysis of the effect of positioning on hemodynamic stability during pregnancy

OBJECTIVES

A left lateral tilt of 15° has been advocated during trauma resuscitation of near-term pregnant patients to avoid the potential for hemodynamic compromise caused by aortocaval compression in the supine position. This recommendation is supported by limited objective evidence, and an experimental determination of the optimal tilt required would be very difficult to accomplish logistically. A derivation of the Guyton/Coleman/Summers computer model of cardiovascular physiology was used to analyze the theoretically expected hemodynamic responses to varying degrees of lateral tilt for a normal pregnancy and during a simulated hemorrhagic shock.

METHODS

Computer simulation studies were used to predict the degree of left lateral tilt required to restore hemodynamic normalcy during the final 20 weeks of gestation. The analytic procedure involved recreating the clinical conditions for a virtual subject through a simulated reenactment of the clinical transfer of a pregnant patient from a lateral to a supine positioning. An analysis of model validity in the context of this particular clinical condition found the model predictions to be within 5% to 12% of experimental results.

RESULTS

During the simulated lateral to supine position transfer, the virtual patient with Class I hemorrhage had a 7% greater fall in cardiac output and a 17% greater fall in mean arterial pressure (MAP) than the corresponding nonhemorrhagic patient. The model suggests that 15° of tilt will result in hemodynamic normalization only up to 26 weeks of gestation. In addition, 13% greater tilt is required to achieve hemodynamic normalcy in the hemorrhaged term pregnant patient.

CONCLUSIONS

Current trauma guidelines suggest that the pregnant trauma patient be placed in a 15° left lateral tilt position to prevent aortocaval compression. A computer simulation study suggests that this tilt may be inadequate to offload the vena cava and normalize the circulation.

Pulmonary embolism in pregnancy: comparison of pulmonary CT angiography and lung scintigraphy

OBJECTIVE

The purpose of this study was to retrospectively compare the diagnostic adequacy of lung scintigraphy with that of pulmonary CT angiography (CTA) in the care of pregnant patients with suspected pulmonary embolism.

MATERIALS AND METHODS

Patient characteristics, radiology report content, additional imaging performed, final diagnosis, and diagnostic adequacy were recorded for pregnant patients consecutively referred for lung scintigraphy or pulmonary CTA according to physician preference. Measurements of pulmonary arterial enhancement were performed on all pulmonary CTA images of pregnant patients. Lung scintigraphy and pulmonary CTA studies deemed inadequate for diagnosis at the time of image acquisition were further assessed, and the cause of diagnostic inadequacy was determined. The relative contribution of the inferior vena cava to the right side of the heart was measured on nondiagnostic CTA images and compared with that on CTA images of age-matched nonpregnant women, who were the controls.

RESULTS

Twenty-eight pulmonary CTA examinations were performed on 25 pregnant patients, and 25 lung scintigraphic studies were performed on 25 pregnant patients. Lung scintigraphy was more frequently adequate for diagnosis than was pulmonary CTA (4% vs 35.7%) (p = 0.0058). Pulmonary CTA had a higher diagnostic inadequacy rate among pregnant than nonpregnant women (35.7% vs 2.1%) (p < 0.001). Transient interruption of contrast material by unopacified blood from the inferior vena cava was identified in eight of 10 nondiagnostic pulmonary CTA studies.

CONCLUSION

We found that lung scintigraphy was more reliable than pulmonary CTA in pregnant patients. Transient interruption of contrast material by unopacified blood from the inferior vena cava is a common finding at pulmonary CTA of pregnant patients.

Comparison of the maternal experience and duration of labour in two upright delivery positions-a randomised controlled trial

OBJECTIVE

To compare two upright delivery positions at the second stage of labour in healthy primiparous women with regard to duration of the second stage of labour and maternal experience.

DESIGN

A randomised controlled trial.

SETTING

A county hospital delivery ward.

SAMPLE

Primiparous subjects (n=271) were randomly allocated to a kneeling (n=138) or a sitting (n=133) position during the second stage of labour. A postpartum questionnaire was answered by 264/271 women (97%) participating in the trial.

METHODS

Primiparous subjects were randomised to a kneeling or sitting delivery position during second stage of labour. Analysis was performed on an intention-to-treat basis.

MAIN OUTCOME MEASURE

Duration of the second stage of labour.

RESULTS

A comparison of the duration of the second stage of labour (kneeling 48.5 minutes+/-27.6 SD, sitting 41 minutes+/-23.4 SD) revealed no significant difference between the groups. A sitting position during the second stage of labour was associated with a higher level of delivery pain (P<0.01), a more frequent perception of the second stage as being long (P=0.002), less comfort for giving birth (P=0.03) and more frequent feelings of vulnerability (P=0.05) and exposure (P=0.02). There were no significant differences in the frequency of sphincter ruptures although a sitting position was associated with a higher degree of postpartum perineal pain (P<0.001) (Table 3).

CONCLUSIONS

Kneeling and sitting upright during the second stage of labour do not significantly differ from one another in duration of the second stage of labour. In healthy primiparous women, a kneeling position was associated with a more favourable maternal experience and less pain compared with a sitting position.

Position for women during second stage of labour

BACKGROUND

For centuries, there has been controversy around whether being upright (sitting, birthing stools, chairs, squatting) or lying down have advantages for women delivering their babies.

OBJECTIVES

To assess the benefits and risks of the use of different positions during the second stage of labour (i.e. from full dilatation of the cervix).

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (16 April 2003).

SELECTION CRITERIA

Trials that used randomised or quasi-randomised allocation and appropriate follow up and compared various positions assumed by pregnant women during the second stage of labour.

DATA COLLECTION AND ANALYSIS

We independently assessed the trials for inclusion and extracted the data.

MAIN RESULTS

Results should be interpreted with caution as the methodological quality of the 19 included trials (5764 participants) was variable. Use of any upright or lateral position, compared with supine or lithotomy positions, was associated with: reduced duration of second stage of labour (10 trials: mean 4.29 minutes, 95% confidence interval (CI) 2.95 to 5.64 minutes) - this was largely due to a considerable reduction in women allocated to the use of the birth cushion; a small reduction in assisted deliveries (18 trials: relative risk (RR) 0.84, 95% CI 0.73 to 0.98); a reduction in episiotomies (12 trials: RR 0.84, 95% CI 0.79 to 0.91); an increase in second degree perineal tears (11 trials: RR 1.23, 95% CI 1.09 to 1.39); increased estimated blood loss greater than 500 ml (11 trials: RR 1.68, 95% CI 1.32 to 2.15); reduced reporting of severe pain during second stage of labour (1 trial: RR 0.73, 95% CI 0.60 to 0.90); fewer abnormal fetal heart rate patterns (1 trial: RR 0.31, 95% CI 0.08 to 0.98).

REVIEWER'S CONCLUSIONS

The tentative findings of this review suggest several possible benefits for upright posture, with the possibility of increased risk of blood loss greater than 500 ml. Women should be encouraged to give birth in the position they find most comfortable. Until such time as the benefits and risks of various delivery positions are estimated with greater certainty, when methodologically stringent trials' data are available, women should be allowed to make informed choices about the birth positions in which they might wish to assume for delivery of their babies.

Acute management of preterm labor

We are continually reminded that the preterm birth rate has failed to improve; in fact, it has increased over the last 20 years. Much of this increase is related to the tremendous strides made by neonatologists and the resulting increased willingness of obstetricians to deliver preterm babies from hostile intrauterine environments. However, there is still much to learn concerning the pathogenesis, accurate early detection, treatment, and prevention of spontaneous preterm labor. This article concentrates on the clinical diagnosis and acute management of this enigmatic clinical problem.

Women’s position during labour: influence on maternal and neonatal outcome

AIM

To assess the maternal, perineal and neonatal outcomes of an upright position compared with a supine position during vaginal delivery, in terms of defined outcome variables.

METHODS

This case-control study was carried out at the Department of Obstetrics and Gynaecology of the University Hospital Vienna between 1997 and 2002. A total of 307 women who delivered in an upright position were enrolled in the study. Upright position was defined as free squatting and was also described as an alternative birth position. 307 controls, delivering in a supine position, were selected from the delivery database as the next parity-matched normal spontaneous vaginal delivery. Our analysis was restricted to a sample of women with a gestational age > 37 weeks, a normal sized fetus and a pregnancy with cephalic presentation. Women with medical or obstetric risk factors were excluded.

RESULTS

A statistically significant decrease for the use of medical analgesia (p = 0.0001) and oxytocin (p = 0.001) was observed in women using the upright birth position. The length of the first and second stages of labour did not significantly differ between the two groups (p > 0.05). A significantly lower rate of episiotomy was detected in women who delivered in an upright position compared with women delivering supine (p = 0.0001). The frequency of perineal tears, and vaginal and labial trauma did not differ between the two groups (p > 0.05). When analysing maternal blood loss, no significant differences between the two groups were found (p > 0.05). No differences in APGAR score < 7 at 1 and 5 minutes or cord pH < 7.1 were observed (p > 0.05).

CONCLUSIONS

The data indicate that labouring and delivering in an upright position is associated with beneficial effects such as a lower rate of episiotomy, and a reduced use of medical analgesia and oxytocin. In our opinion, the best recommendation is to give low-risk maternity patients the option of bearing in the mode that is most comfortable for them.

Hemodynamic changes and baroreflex gain in the supine hypotensive syndrome

OBJECTIVE

The purpose of this study was to determine whether supine hypotensive syndrome is caused by a decreased baroreflex gain that results in inadequate compensatory responses to restore cardiac output.

STUDY DESIGN

Ten third-trimester gravid women with symptoms that were suggestive of supine hypotensive syndrome and 10 control subjects without symptoms were studied. Patients were studied initially for 30 minutes in the lateral recumbent position with continuous heart rate, blood pressure, external cardiotocography, and cardiac output determinations every 5 minutes. After 30 minutes, the patient was repositioned supine for up to an additional 30 minutes, and all measurements were repeated similarly. This lateral-supine sequence was repeated twice or until symptoms precluded further testing.

RESULTS

The two groups were demographically similar. With maternal position change to supine, cardiac output (-2.7 L/min vs -1.0 L/min, P =.04) and mean arterial blood pressure (-10.7 mm Hg vs -2.5 mm Hg, P =.03) were respectively lower, and heart rate (+26.9 vs +14.4 beats/min, P =.04) was higher in the subjects with supine hypotensive syndrome than in the control subjects. Baroreflex gain, however, did not differ between the subjects with supine hypotensive syndrome and control subjects (P =.26).

CONCLUSION

We were unable to demonstrate a decrease in baroreflex gain as a possible cause of supine hypotensive syndrome. Inadequate pelvic collateral circulation that leads to a greater decrease in cardiac output may be causative in the syndrome.

Maternal posture in labour

The position adopted naturally by women during birth has been described as early as 1882 by Engelmann. He observed that primitive woman, not influenced by Western conventions would try to avoid the dorsal position and was allowed to change position as and when she wished. Different upright positions could be achieved using posts, slung hammock, furniture, holding on to a rope, knotted piece of cloth, or the woman could kneel, crouch, or squat using bricks, stones, a pile of sand, or a birth stool. Today the majority of women in Western societies deliver in a dorsal, semi-recumbent or lithotomy position. It is claimed that the dorsal position enables the midwife/obstetrician to monitor the fetus better and thus to ensure a safe birth. This paper examines the historical background of the different positions used and its evolution throughout the decades. We have reviewed the available evidence about the effectiveness, benefits and possible disadvantages for the use of different positions during the first and second stage of labour.

The acute abdomen and the obstetrician

An acute abdomen in pregnancy can be caused by pregnancy itself, be predisposed to by pregnancy or be the result of a purely incidental cause. These various conditions are discussed. The obstetrician often has a difficult task in diagnosing and managing the acute abdomen in pregnancy. The clinical evaluation is generally confounded by the various anatomical and physiological changes occurring in pregnancy itself. Clinical examination is further hampered by the gravid uterus. The general reluctance to use conventional X-rays because of the pregnancy should be set aside when faced with the seriously ill mother. A reluctance to operate during pregnancy adds unnecessary delay, which increases morbidity for both mother and fetus. Such mistakes should be avoided as prompt diagnosis and appropriate therapy are crucial. A general approach to acute abdominal conditions in pregnancy is to manage these problems regardless of the pregnancy.

Woman's position during second stage of labour

BACKGROUND

For centuries, there has been controversy around whether being upright (sitting, birthing stools, chairs, squatting) or lying down have advantages for women delivering their babies.

OBJECTIVES

The objective of this review was to assess the benefits and risks of the use of different positions during the second stage of labour (i. e. from full dilatation of the cervix).

SEARCH STRATEGY

Relevant trials are identified from the register of trials maintained by the Cochrane Pregnancy and Childbirth Group, and from the Cochrane Controlled Trials Register.

SELECTION CRITERIA

Trials were included which compared various positions assumed by pregnant women during the second stage of labour. Randomised and quasi-randomised trials with appropriate follow-up were included.

DATA COLLECTION AND ANALYSIS

Trials were independently assessed for inclusion, and data extracted, by the two authors. Disagreements would have been resolved by consensus with an editor. Meta-analysis of data is performed using the RevMan software.

MAIN RESULTS

Results should be interpreted with caution as the methodological quality of the 18 trials was variable. Use of any upright or lateral position, compared with supine or lithotomy positions, was associated with: 1. Reduced duration of second stage of labour (12 trials - mean 5.4 minutes, 95% confidence interval (CI) 3.9 - 6.9 minutes). This was largely due to a considerable reduction in women allocated to use of the birth cushion. 2. A small reduction in assisted deliveries (17 trials - odds ratio (OR) 0.82, 95% CI 0.69 - 0.98). 3. A reduction in episiotomies (11 trials - OR 0.73, 95% CI 0.64 - 0.84). 4. A smaller increase in second degree perineal tears (10 trials - OR 1.30, 95% CI 1.09 - 1.54). 5. Increased estimated risk of blood loss > 500ml (10 trials - OR 1.76, 95% CI 1.34 - 3.32). 6. Reduced reporting of severe pain during second stage of labour (1 trial - OR 0.59, 95% CI 0.41 - 0.83). 7. Fewer abnormal fetal heart rate patterns (1 trial - OR 0.31, 95% CI 0.11 - 0.91).

REVIEWER'S CONCLUSIONS

The tentative findings of this review suggest several possible benefits for upright posture, with the possibility of increased risk of blood loss > 500ml. Women should be encouraged to give birth in the position they find most comfortable. Until such time the benefits and risks of various delivery positions are estimated with greater certainty when methodologically stringent trials data are available, then women should be allowed to make informed choices about the birth positions in which they might wish to assume for delivery of their babies.

The effect of pregnancy on the lower-limb venous system of women with varicose veins

OBJECTIVES

to assess the effect of pregnancy on the lower-limb venous system of women with varicose veins. Design a longitudinal prospective study of 11 pregnant women, with varicose vein disease.

METHODS

eleven pregnant women with varicose veins were recruited as part of a larger study. Veins were assessed in both lower limbs using colour-flow duplex scanning at a 75 degrees head-up tilt. The diameter and velocity and duration of reflux were measured in each vein at 12, 20, 26, 34, 38 weeks gestation and 6 weeks postpartum.

RESULTS

eleven women had reflux and varicose veins demonstrated at first scan. All veins dilated with increasing gestation. This was maximal in the superficial system, reaching significance (p</=0.05) in the right long saphenous, superficial femoral and posterior tibial veins, left long and short saphenous, popliteal, peroneal, anterior and posterior tibial veins. The velocity of reflux increased while the duration decreased with increasing gestation. This was most obvious in the long saphenous veins but did not reach statistical significance.

CONCLUSIONS

maximum changes were seen in the superficial venous system in the thigh. The effect was more pronounced on the left and the changes in reflux returned to pre-pregnancy levels in the puerperium.

Randomised trial comparing the upright and supine positions for the second stage of labour

OBJECTIVE

To assess the maternal and neonatal effects of upright compared with recumbent positions during delivery, in terms of defined outcome variables.

DESIGN

A randomised controlled trial.

SETTING

St Monica's Nursing Home, a midwife based maternity unit in Cape Town, South Africa.

PARTICIPANTS

Five hundred and seventeen women of low obstetrical risk assigned to deliver at the nursing home.

RESULTS

The trial showed that women who adopted the upright posture for delivery experienced less pain. perineal trauma and fewer episiotomies than those who delivered in the supine position.

CONCLUSION

The data suggest that in women of low obstetrical risk, choice of posture during delivery may be encouraged.

Influence of compression of the inferior vena cava in the late second trimester on uterine and umbilical artery blood flow

OBJECTIVE

To evaluate the inferior vena cava compression and its influence on the uterine and umbilical artery blood flow in the late second trimester when the mother is supine.

METHODS

The inferior vena cava diameter was measured by ultrasound B mode scan, and Doppler flow velocimetry of the uterine and umbilical artery was performed in 90 women at 24-27 weeks in the supine and complete left lateral position.

RESULTS

The inferior vena cava diameter in the supine position was significantly smaller than that in the lateral position. The degree of the vena cava compression was associated with an elevation in the uterine artery RI in the supine position. The umbilical artery RI did not couple with either the degree of the compression or the changes in the uterine artery RI.

CONCLUSION

The inferior vena cava is compressed in the majority of pregnant women in the second trimester, and the compression may affect the uterine artery blood flow but not the fetal circulation.

The effect of maternal posture on fetal cerebral oxygenation during labour

OBJECTIVE

To measure the effect of changes in maternal posture on fetal cerebral oxygenation during normal labour.

DESIGN

A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, measured by near infrared spectroscopy, in women with effective epidural analgesia when moved from the left lateral to the supine position during labour.

SETTING

A London teaching hospital obstetric unit.

SUBJECTS

Fourteen women during uncomplicated labour at term.

RESULTS

When compared with the left lateral position, the supine position was associated with a significant decrease in the mean concentration of fetal cerebral oxyhaemoglobin of 1.12 (SD 1.0, 95% CI 0.49 to 1.75) mumol. 100 g-1 (P < 0.01) without any significant change in the mean concentration of deoxyhaemoglobin and cerebral blood volume. These changes were associated with a significant decrease in the mean cerebral oxygen saturation of 8.3 (SD 8.8, 95% CI 1.5 to 15.1)% (P < 0.05, n = 9).

CONCLUSION

Changes in maternal posture during labour, in women with effective epidural analgesia, are associated with a significant decrease in fetal cerebral oxygenation.

The squatting position for the second stage of labor: effects on labor and on maternal and fetal well-being

A cohort study was designed to assess the effects of maternal squatting position for the second stage of labor on the evolution and progress of labor, and on maternal and fetal well-being. Outcomes from 200 squatting births, randomly selected from a sample of 1000, were compared with 100 semirecumbent births, randomly selected from a sample of 300. Data collection was by chart review. The two groups were similar with respect to most antepartal, intrapartal, and socioeconomic variables likely to affect labor outcomes. The mean length of the second stage of labor was 23 minutes shorter in squatting primiparas and 13 minutes shorter in squatting multiparas than in semirecumbent women. Squatting women required significantly less labor stimulation by oxytocin during second stage (P = 0.0016), and they showed a trend toward fewer mechanically assisted deliveries. Significantly fewer and less severe perineal lacerations occurred, and fewer episiotomies were performed in the squatting group (P = 0.0001). No statistically significant differences were found between groups for third-stage complications and infant complications.

Maternal and fetal effects of the supine and pelvic tilt positions in late pregnancy

Material and fetal cardiovascular effects of position change were assessed in 20 women in late pregnancy. On changing from the left lateral to the supine position, there was a 45% reduction in leg blood flow, measured by strain guage plethysmography. Arterial resistance, measured with Doppler ultrasound in the femoral, brachial and uterine arteries, remained unchanged, confirming the absence of compensatory vasoconstriction. There was no change in blood pressure (BP) in the leg, indicating no significant aortic compression, but a rise in maternal heart rate in the supine position suggested the presence of inferior vena cava (IVC) compression. Neither the left or the right pelvic-tilt position was associated with a significant change in leg blood flow or maternal heart rate compared to the supine position. A possible 'sluice' effect in the placental circulation was not confirmed, as fetal heart rate and umbilical Doppler resistance did not change in any position. In the absence of active vasoconstriction and significant aortic compression, IVC compression is the likely cause of the decrease in leg blood flow, and also of the previously demonstrated decrease in uterine blood flow. Leg BP and Doppler ultrasound measurements of uterine artery resistance may not be adequate measures of the effect of posture on uteroplacental perfusion.

Alternative positions in the second stage of labour: a randomized controlled trial

A controlled clinical trial involving 151 primigravidae and 18 midwives assessed the acceptability and outcome of second-stage labour in upright positions. Women who had no specific antenatal preparation and preferences regarding labour positions were managed either conventionally (semi-recumbent and lateral), or encouraged to adopt upright positions (squatting, kneeling, sitting or standing) according to individual preference. Of the women allocated to the upright position 74% completed the second stage upright, with kneeling being the most favoured position, but squatting was, despite all assistance, too difficult to maintain. Adoption of upright positions resulted in a higher rate of intact perineums. There was a clinically apparent reduction of forceps deliveries in the upright group which influenced midwives' attitudes. Moving the parturient from recumbent to upright positions was often perceived to be beneficial when there was slow progress. Estimated blood loss was similar in the two groups, as was the condition of the newborn (Apgar score and umbilical artery pH). Alternative positions in the second stage of labour, in particular kneeling, are achievable even without specific birth aids and antenatal preparation. They appear safe, acceptable to most parturients and their midwives, and are easily integrated into modern labour ward practice; they may have clinical advantages which need further investigation.

An experiment of squatting birth

Women throughout the ages have preferred to be delivered with their trunks vertical and most delivery positions illustrated in historical texts show birth in an upright posture with abducted thighs. A consumer attitude study in our hospital showed that patients have considerable interest in alternative birth positions. Squatting has been advocated to prevent caval compression, increase the diameter of the pelvic outlet and, perhaps with least justification, to enlist the force of gravity and thereby facilitate maternal expulsive effort. Despite the extensive literature advocating squatting birth, the suggested advantages of this method have not been examined in any formal, let alone unbiased study. We therefore conducted a randomised trial to examine the effect of squatting on the duration of second stage of labour, the duration of pushing, and several other variables.

The vertical birthing position of the Trobrianders, Papua New Guinea

During an ethnomedical field study the author succeeded in participating and photographing 4 traditional birthgivings among the Trobrianders/Papua New Guinea. Their various vertical postures are described with special reference to specific Trobriand practices and discussed by literature review. The results suggest that vertical birthing positions are advantageous to horizontal ones and should be reconsidered by modern Western obstetrics.

Hemodynamic effects of caval and uterine venous occlusion in pregnant sheep

In chronically instrumented pregnant ewes we studied the systemic, uterine, and fetal effects of increased uterine venous pressure with and without simultaneous changes in cardiac output, by occluding either the inferior vena cava or both uterine veins. Increased uterine venous pressure with no reduction in venous return of blood to the heart resulted in a reflex increase in arterial blood pressure. Infrarenal obstruction of the inferior vena cava resulted in a moderate reduction in venous return and cardiac output with no change in arterial blood pressure, while suprarenal obstruction of the inferior vena cava caused a major decrease in cardiac output as well as in arterial pressure. Uterine blood flow varied in proportion with perfusion pressure at all levels of obstruction. Uterine oxygen consumption and fetal oxygenation only decreased with suprarenal obstruction of the inferior vena cava, when uterine blood flow fell more than 50%.

Maternal haemodynamic changes during caesarean section: a comparison of epidural and general anaesthesia

Haemodynamic measurements were performed on 20 healthy women before and during elective caesarean section under epidural (10 women) or general anaesthesia (10 women). The influence of the two anaesthetic techniques on the haemodynamic changes associated with operative delivery was compared. The following haemodynamic variables were studied: cardiac output (CO), stroke volume (SV) determined non-invasively with impedance cardiography, heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP), pulse pressure, mean arterial pressure (MAP) and total peripheral vascular resistance (TPR). During epidural anaesthesia, SV was largely unchanged before delivery but increased (P less than 0.05) following delivery. However, CO increased (P less than 0.05) prior to delivery due to an increase (P less than 0.01) in HR. A further increase (P less than 0.05) in CO was recorded following delivery. SBP, DBP, MAP and TPR decreased (P less than 0.01) during epidural anaesthesia. In the patients undergoing general anaesthesia, SV decreased (P less than 0.05) prior to delivery. However, CO remained largely unchanged due to an increase (P less than 0.01) in HR. Following delivery, CO (P less than 0.05) and SV (P less than 0.01) increased whereas HR decreased (P less than 0.01). SBP, DBP and MAP increased (P less than 0.01) prior to delivery, returning to the same level as prior to induction of anaesthesia following delivery. TPR was largely unchanged prior to delivery but decreased (P less than 0.01) following delivery.