Colleague's E-mail is Invalid. Your message has been successfully sent to your colleague. Save my selection. Address correspondence to Allison J. Address e-mail to al cumc. Since then, avoidance of the supine position has become a key component of clinical practice.

Author:Kazil Mezikasa
Language:English (Spanish)
Published (Last):22 August 2014
PDF File Size:14.30 Mb
ePub File Size:16.83 Mb
Price:Free* [*Free Regsitration Required]

Colleague's E-mail is Invalid. Your message has been successfully sent to your colleague. Save my selection. Address correspondence to Allison J. Address e-mail to al cumc. Since then, avoidance of the supine position has become a key component of clinical practice.

Indeed, performing pelvic tilt in mothers at term to avoid aortocaval compression is a universally adopted measure, particularly during cesarean delivery. The studies on which this practice is based are largely nonrandomized, utilized a mix of anesthetic techniques, and were conducted decades ago in the setting of avoidance of vasopressors.

Recent evidence is beginning to refine our understanding of the physiologic consequences of aortocaval compression in the context of contemporary clinical practice. This review presents a fresh look at the decades of evidence surrounding this topic and proposes a reevaluation and appraisal of current guidelines regarding entrenched practices. Avoidance of the supine position in late pregnancy, to prevent aortocaval compression ACC by the gravid uterus, is a fundamental principle in the management of pregnant women, particularly during labor or at cesarean delivery.

The negative consequences of ACC were first brought to light over 70 years ago, and much of clinical practice today is based on studies that are now decades old. Most of the clinical studies on which current obstetric anesthesia practice is based were not designed according to current modern standards, failed to account for confounding variables, failed to support maternal blood pressure BP , and failed to limit the risk of a type 1 error in the context of multiple comparisons.

In this review, we examined the body of literature that has accumulated since the s on the effect of the gravid uterus on maternal hemodynamic physiology, encompassing the earliest evidence of obstruction of the inferior vena cava IVC based on dye injection studies, to the more recent use of magnetic resonance imaging MRI.

The direct and indirect evidence for compression of the aorta is addressed, as well as the potential for detrimental effects on uteroplacental perfusion. The evidence for the practice of left uterine displacement during cesarean delivery is challenged, and we propose a critical reappraisal of common beliefs. The earliest report of the phenomenon of maternal postural shock, published in , is attributed to the German obstetrician, Hansen, 4 who incorrectly speculated that the etiology of maternal postural shock was mechanical pressure on the heart by the gravid uterus.

In , McRoberts 5 reported on 6 cases of circulatory collapse in the supine position in mid-to-late pregnant women, which could be relieved by transfer to the lateral position or by delivering the fetus. The term supine hypotensive syndrome was coined by Howard et al 7 in , during observations that 18 Several similar reports were published between and Supine hypotension tended to become less severe as the patient approached full term, which was thought to be explained by descent of the fetal head into the pelvis.

Significant exacerbation of postural hemodynamic changes with spinal anesthesia was recognized as early as , and several authors separately noted improvement with assuming the lateral position, by performing manual displacement of the uterus or in response to delivery.

The gravid uterus begins to compress the IVC in the supine position beginning at approximately the 20th week of pregnancy, with obstruction becoming virtually complete at term.

Higher venous pressure in the legs than arms was recorded before delivery, which was followed by a fall in leg venous pressure postpartum. In , Scott and Kerr 19 validated the premise that IVC compression by the gravid uterus occurs in the supine position and reported near-complete IVC occlusion using direct catheter transducer measurements of IVC pressure in women undergoing cesarean delivery.

In almost every case, before delivery, elevated pressure was measured along the length of the vessel 18—24 mm Hg and only normalized 4—8 mm Hg above the level of the diaphragm.

In , the same group reported on their evaluation using dye injection via bilateral femoral vein catheterization in supine women at term. In a subset of women rotated to the lateral position, more normal passage of dye upward in the IVC was noted, although some compression was still present.

Recent MRI of term pregnant women substantiates near-complete IVC compression by the gravid uterus at term in the supine position. This mechanism is blunted after administration of anesthesia, especially following the sympathectomy induced by neuraxial blockade, when women at term are at risk of severe hypotension if unmanaged with vasopressors and fluids.

In certain clinical scenarios, left uterine displacement is a crucial life-saving maneuver. During maternal cardiac arrest, relief of IVC obstruction is imperative to facilitate venous return and improve cardiac output. The most serious concern related to aortic compression in the supine position is impeded uteroplacental circulation, since the uterine arteries arise distal to the level of compression.

Decreased BP or blood flow in the lower extremity relative to the upper extremity in the supine position at late term has widely been interpreted to indicate aortic compression by the gravid uterus.

A plethora of modalities have been used to detect such changes summarized in Table 1. There is limited direct evidence that under normal circumstances significant compression of the thick-walled, high pressure aorta occurs.

The details of the spinal anesthetic, maternal hemodynamics, use of vasopressors, and maternal position were also not reported. The notion that in the supine position at term, compression of the abdominal aorta by the gravid uterus is commonplace, derives from landmark experiments in by Bieniarz et al. Among the subset of parturients, significantly increased aortic obstruction and complete iliac occlusion were observed during uterine contractions. In a second study that same year, Bieniarz et al 24 compared transduced femoral artery BP measurements concomitantly with external sphygmomanometric measurement of the brachial artery in the supine position.

During periods of severe maternal hypotension, there were much larger decreases in femoral BP relative to the brachial BP, which provides indirect evidence of aortic compression during severe hypotension. In cases where the BP subsequently improved, the disparity between femoral and brachial BP decreased. Investigators in the s continued to focus on the impact of maternal supine position on lower extremity BP relative to upper extremity BP, as evidence of aortic compression by the gravid uterus.

Brachial hypotension was only detected after week Factors associated with more severe decreases in lower extremity BP were lack of fetal head engagement and uterine contractions. By the s and s, the research focus shifted to studies of lower extremity blood flow relative to upper extremity blood flow, with variable findings.

Kinsella et al 31 used the Finapres digital arterial pressure instrument with probes placed simultaneously on a toe and finger, in 32 women at term, of whom 29 were in labor, to detect reversible decreases in toe pulse pressure and plethysmographic pulse amplitude. Episodes of decreased toe pulse pressure, which were believed to represent aortic compression, occurred in 12 of 32 women in left tilt, 5 of 21 in right tilt, and 2 of 4 while supine.

The investigators attempted to relieve the apparent aortic compression by incrementally increasing the degree of pelvic tilt until the pulse pressure returned to baseline. Despite the presumed aortic compression in some women, no fetal heart rate FHR abnormalities were observed, which was attributed to collateral placental supply from the ovarian arteries.

Kinsella et al 30 also evaluated leg blood flow during change of position from left lateral to supine using strain gauge plethysmography in women in late gestation. No positional changes in arterial resistance using Doppler assessment were found in the femoral, brachial, uterine, or umbilical arteries, suggesting no compensatory vasoconstriction. The authors concluded that leg BP and Doppler ultrasound measurements of uterine artery resistance may not be adequate measures of the positional effects on uteroplacental perfusion.

As early as , evidence began to emerge that during normotension the aorta appears more likely to be displaced than compressed in the supine position. For the same weight, the pulse pressure drop palpated in the popliteal artery was barely noticeable in cases of hypertension, average in normotension, and severe in hypotension. Recent MRI studies were unable to demonstrate compression of the aorta by the gravid uterus in the supine position in healthy pregnant women without anesthesia.

The bilateral common iliac arteries distal to the bifurcation could not be evaluated because of MRI low resolution, which raises the possibility of more distal obstruction. Taken together, MRI findings do not suggest significant aortic compression, by the gravid uterus, although the distal aorta is usually poorly visualized.

Both lack of fetal head engagement 12 , 27 , 34 , 39 and uterine contractions 29 , 31 , 34 have been implicated as factors exacerbating the severity of ACC.

Overall, the degree and significance of aortic compression by the gravid uterus during neuraxial anesthesia, in the setting of hypotension, and during uterine contractions, remains debatable. The 2 mechanisms, preferential perfusion and ovarian venous drainage, were suggested to be protective with respect to preserving uteroplacental perfusion and may partially compensate for any negative effects of ACC.

Radionuclide studies suggest that there is a decrease in intervillous flow associated with the maternal supine position in late pregnancy. Placental blood flow was determined after 20 minutes in each position.

The patients spent 15 minutes in each position. Myometrial blood flow was similar in both positions, suggesting that the autoregulation occurs only in the nonplacental component of uterine circulation of the gravid uterus. The recordings were made after spending 3 to 5 minutes in each position. In contrast, Witter and Besinger 44 in found no influence of the lateral decubitus and supine positions on uterine artery flow velocity waveforms using continuous wave Doppler techniques during nonstress testing in 10 nonlaboring women, suggesting no significant effect of maternal position on uterine artery hemodynamics; however, the small sample size may not have provided sufficient power to detect a difference.

The time spent in each position was not reported. Of note, the nonstress tests in 2 of 10 patients became nonreactive in the supine position. The authors noted that after being positioned supine, the MAP remained stable for 5. The findings support avoidance of the supine position in women who have documented symptoms of supine hypotensive syndrome. The supine position, even in the absence of maternal anesthesia, hypotension, or symptoms, has been implicated in possible negative consequences for the fetus.

Additionally, maternal nonleft lateral sleep position, particularly the supine sleep position, has been associated with late-pregnancy stillbirth in the compromised fetus. The duration of exposure to the supine position may be an important factor in assessing the adverse effects of maternal position. IVC obstruction by the gravid uterus has been implicated as a cause of placental abruption.

Mengert et al 48 attributed the phenomenon to venous congestion, based on their observation of premature separation of the placenta during cesarean delivery in 2 women, subsequent to intentional digital compression of the IVC before delivery.

Howard et al 7 had similarly observed the development of placental abruption in 1 of 5 late pregnant dogs during experimental ligation of the IVC; however, there is limited evidence to support IVC compression as a significant cause of placental abruption. Decreased venous return secondary to IVC compression by the gravid uterus in the supine position is typically associated with a decrease in maternal cardiac output CO , with or without a concomitant change in BP.

Because CO has been shown to be significantly correlated with UA pulsatility index difference between peak systolic and diastolic velocity divided by the mean velocity , yet no correlation has been found with BP or heart rate HR 49 ; there is concern that unrecognized decreases in CO may have a detrimental impact on uteroplacental perfusion.

A range of modalities, both invasive 17 , 39 , 50 , 51 and noninvasive, 20 , 52—56 have been utilized to quantify the global hemodynamic effects of the supine position in late pregnancy; not surprisingly, earlier studies from the s relied on more invasive dye-dilution techniques summarized in Table 2.

There has been little uniformity among studies describing maternal CO changes with position during late pregnancy. Specifically, studies have varied with respect to the modality used, laterality of positioning, and the degree of tilt.

Furthermore, many techniques utilized to measure CO have not been validated during pregnancy. Notably, they demonstrated no significant increase in CO from the supine position mean 6. The volunteers spent 2 minutes in each position before taking measurements over a 3-minute period.

With suprasternal Doppler performed on women with mean gestational age Measurements were made after a period of at least 5 minutes in each tilted position. Lower SVR and pulse pressure were seen with greater degrees of tilt, probably indicating a decrease in sympathetic tone when CO is increased.

Noninvasive sphygmomanometry was performed by placing a cuff on the left arm and left calf. Only one patient showed an arm SBP 25 mm Hg higher than the lower limb, which was believed to represent aortic compression. Measurements were made after spending 10 minutes in each position. Cardiac magnetic resonance imaging c-MRI is considered to have greater accuracy and reproducibility than other noninvasive techniques.

The dogma that left lateral tilt during cesarean delivery must be maintained until delivery, to prevent ACC and negative effects on uteroplacental perfusion, is based on a handful of studies from the s summarized in Table 3 , stipulating that women tilted during cesarean delivery had superior neonatal outcomes compared with women kept in the supine position.

The reports were published in the context of avoidance of vasopressors due to fears about uterine artery vasoconstriction. Most were not randomized trials, patients received varied anesthetic approaches, and many patients underwent surgery in the right tilted position because of surgeon preference.

The relevance of these studies is questionable considering the dramatic departure from contemporary study design and clinical practice that now incorporates superior control of maternal hemodynamics, using more ideal vasopressor agents such as phenylephrine. The women were monitored using photoelectric plethysmographic probes placed in the vaginal apex, a hallux, and a finger. Newborn depression occurred in 5 of the 7 cases. Only 1 of the 7 women had received general anesthesia, pointing to the increased risk of severe hypotension associated with neuraxial blockade.


Aortocaval compression syndrome

If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. This compression of the aorta and the inferior vena cava against the lumbar vertebral bodies results in decreased venous return from the lower extremities, thereby decreasing preload, stroke volume and cardiac output. Hypotension in the supine position usually does not occur due to a compensatory rise in peripheral vascular resistance. The syndrome has been demonstrated in pregnant females from the middle of the second trimester onward. Pregnant patients in the supine position have compression of the inferior vena cava and aorta by the gravid uterus, which leads to decreased venous return and thus hypoperfusion.


Register for a free account

Metrics details. Maternal cardiac arrest during cesarean section CS is an extremely rare but devastating complication. Preventing emergency events from developing into maternal cardiac arrest is one of the most challenging clinical scenarios. A year-old pregnant woman with subvalvular aortic stenosis who was scheduled for elective CS under epidural anesthesia, and experienced devastating supine hypotensive syndrome, but was successfully resuscitated after delivery.


Lee, K. Khaw, W. Ngan Kee, T. Leung, L.


NCBI Bookshelf. Diann M. Krywko ; Kevin C. Authors Diann M. Krywko 1 ; Kevin C. King 2. Aortocaval compression syndrome is also known as a supine hypotensive syndrome.

Related Articles