Will Point-of-Care Ultrasound Be the New Standard of Care in the Management of Women Diagnosed With Preeclampsia?

In high-income countries, cardiovascular disease and hypertensive disorders of pregnancy have become the leading causes of severe maternal morbidity and mortality. With the advent of smaller and more affordable ultrasound machines, the availability of ultrasound devices has increased, making point-of-care ultrasound (POCUS) a user-friendly and readily accessible tool to support perioperative decision-making over all phases of clinical care. By detecting changes in cardiopulmonary function early over the clinical course, some consider POCUS as a fifth pillar of the physical examination, notably in the case of heart disease and acute cardiopulmonary failure. With cardiac disease considered the leading cause of maternal mortality in many regions of the world, several recent initiatives have identified POCUS as a routine tool to evaluate cardiopulmonary complications in obstetric patients.1,2 Emerging evidence suggests that POCUS may also play a key role in managing preeclampsia with severe features. Preeclampsia is a multisystem disorder primarily caused by endothelial dysfunction. The pathophysiology of pulmonary edema associated with this disease has long been attributed to an increase in capillary permeability, but emerging evidence suggests that changes in cardiac function likely contribute. In this issue of Anesthesia & Analgesia, a new study highlights the value of POCUS in evaluating severe pulmonary edema in preeclampsia. Yagani et al3 performed transthoracic cardiopulmonary ultrasound in a cohort of 70 women diagnosed with severe preeclampsia (SPE) and observed a strong association between diastolic dysfunction diagnosed on echocardiography and increased extravascular lung water (EVLW) identified on pulmonary ultrasound. Pulmonary ultrasound was performed at 3 time points; baseline images captured at admission were compared with follow-up POCUS examinations collected within 30 minutes and 24 hours after delivery. The authors defined increased EVLW as the presence of B-lines on pulmonary ultrasound in at least 1 of 4 anterior intercostal spaces, a finding observed in 64% of study participants on admission. Almost half of the examinations revealed signs of diastolic dysfunction, almost always in the presence of B-lines on pulmonary ultrasound. The authors also noted B-lines on pulmonary ultrasound in all women presenting with acute breathlessness or facial swelling. In addition, the number of B-lines on pulmonary ultrasound significantly correlated with arterial blood pressures and increased E/e’ ratio (the ratio of echocardiographic early diastolic transmitral flow velocity to early diastolic mitral annular tissue velocity), which suggests that B-lines could be considered an indirect measure of elevated left ventricular filling pressure and diastolic dysfunction. SPE-RELATED PULMONARY EDEMA IS MAINLY DRIVEN BY HIGH FILLING PRESSURES These findings are consistent with previous research. In nonobstetric patients, B-line number is associated with EVLW and an A-line pattern (absence of B-lines) indicates a low pulmonary artery occlusion pressures (PAOPs) of <13 mm Hg with a positive predictive value of 97%.4,5 Similar findings have been extended to the obstetric population. In a pilot study combining pulmonary ultrasound and transthoracic echocardiography in 20 women diagnosed with SPE, Zieleskiewicz et al6 first described in 2014 the prevalence of pulmonary interstitial syndrome and demonstrated a significant association between abnormalities on pulmonary ultrasound and increased left ventricular end-diastolic pressures (LVEDPs) on cardiac ultrasound. Subsequently, Ambrozic et al7 presented similar findings in a cohort of 33 preeclamptic patients; only 14% of women exhibited an increase in stroke volume with passive leg raising, with the remaining 86% showing no increase in stroke volume with passive leg raising, suggesting a high risk of fluid overload and need for fluid restriction. These signs resolved rapidly after delivery; by 4 days postpartum, cardiac filling pressures and pulmonary ultrasound patterns approached those seen in healthy pregnant controls. In a cohort of 95 women diagnosed with SPE and late-onset disease (>34 weeks gestation), Ortner et al8 further demonstrated a significant association between interstitial pulmonary syndrome on lung ultrasound, echocardiographic markers of diastolic dysfunction, and serum brain natriuretic peptide (BNP) as a laboratory marker for cardiac dysfunction. With no association between pulmonary interstitial syndrome on lung ultrasound and serum albumin as a surrogate parameter for oncotic pressures, Ortner et al further highlighted the cardiac origin of pulmonary edema in SPE. These findings are particularly relevant since late-onset SPE is normally associated with less cardiac impairment than early-onset SPE.9 Together, these articles suggest that capillary leak and decreased oncotic pressures may only play a minor role in the pathophysiology of pulmonary edema in SPE. Adding to this body of literature, the present work of Yagani et al suggests that lung ultrasound may provide novel patient-specific information about the importance and efficacy of antihypertensive treatment. In the present study, fluid balance was strictly monitored and controlled. The sequence of physical and echocardiographic findings in this setting with careful fluid management suggests that the pulmonary edema may have been related to a sudden rise in blood pressure that led to fluid extravasation in the pulmonary vasculature. In other words, the work by Yagani et al may indicate that due to altered diastolic function, patients with SPE may not be able to adapt to a sudden increase in afterload. Risk factors associated with a rise in PAOPs may be left ventricular hypertrophy associated with preeclampsia, or only subtle underlying systolic dysfunction that becomes symptomatic in the presence of a significant rise in systemic afterload. Therefore, future studies should further elucidate the effects of afterload reduction with blood pressure control, potentially resulting in changes in LVEDPs and EVLW. Although Yagani et al provide highly valuable data on POCUS applications in SPE, this interesting work has several limitations. The authors used a simplified echo comet score where the presence of 1 single B-line on pulmonary ultrasound was sufficient to define interstitial pulmonary syndrome (“B-profile”) and presence of increased EVLW. Original data comparing findings on pulmonary ultrasound with observations on computer tomography have shown that 3 or more B-lines on 2 or more lung ultrasound windows bilaterally are needed to correlate with the diagnosis of interstitial pulmonary edema and increased EVLW.4,5 One single B-line is a frequent observation in healthy pregnant and nonpregnant subjects and may explain the low specificity of B-lines observed by Yagani et al in predicting diastolic dysfunction.10 In addition, the high number of excluded patients and the short postdelivery study window may not have captured the full spectrum of disease. Finally, absolute conclusions about the pathophysiology of pulmonary edema in preeclampsia are not possible with an observational design, and future trials with small fluid bolus challenges or other hemodynamic interventions may provide more definitive results. IS POCUS THE MISSING TOOL FOR HEMODYNAMIC MANAGEMENT OF SEVERE PREECLAMPTIC PATIENTS? Regardless, pulmonary ultrasound has been shown to be a highly sensitive tool identifying increases in EVLW before a decrease in Pao2 or Sao2 can be observed clinically.6,11 As such, pulmonary ultrasound is an important diagnostic tool when managing preeclamptic patients in whom pulmonary complications remain an important cause of severe maternal morbidity. Although the presence of occasional B-lines on lung ultrasound does not necessarily predict a high degree of diastolic dysfunction, the absence of any B-lines has a high negative predictive value in excluding diastolic dysfunction.6,8 Furthermore, using echocardiography to predict fluid responsiveness in women with SPE and oliguria suggests that fewer than half of these patients are fluid-responsive.7,12 Combining these results suggests that POCUS may add important information on cardiopulmonary function in SPE that remains undetected with physical examination alone. The presence of a B-line on pulmonary ultrasound should prompt the managing physician to perform a focused cardiac ultrasound to assess left ventricular function. The current study adds information that even in a context of fluid restriction, a silent pulmonary edema may occur.3 Unfortunately, so far, there is little evidence validating the benefit of POCUS specifically when managing preeclamptic women, and its use is, therefore, rarely recommended in this setting.2 In the nonobstetric setting, there is good evidence that POCUS improves outcomes when applied for preoperative risk assessment or when managing patients with acute respiratory or circulatory failure.13 Furthermore, recent studies in critical care have demonstrated an association between fluid responsiveness evaluation and mortality.14 When managing the preeclamptic patient, POCUS may be used to assess cardiac output and systemic vascular resistance; astute clinicians could use this information to choose most effectively between a vasodilating and a β-blocking antihypertensive agent. In addition, assessing EVLW using pulmonary ultrasound and fluid responsiveness by measuring changes in stroke volume after passive leg raising with transthoracic echocardiography could influence decisions about fluid management, hemodynamic goals, and delivery timing.12,15 However, any clinical protocols guided by POCUS information need to be compared with general blood pressure control and restrictive fluid management protocols in prospective randomized controlled trials focusing on patient-centered outcomes. From a research perspective, planning for prospective clinical trials studying POCUS-guided interventions in SPE to prevent clinically overt pulmonary edema will likely require a multicenter design to achieve sufficient statistical power to demonstrate an impact on important maternal and perinatal outcomes. Such trials should be designed to test whether POCUS-guided cardiovascular optimization allows for prolonged expectant management. Every week that pregnancy can be safely extended results in substantial improvement in neonatal outcomes and reduction in health care expenditure. Finally, if individualized POCUS-guided management does lead to improved care and improved patient-centered outcomes, then access to this technology will become essential. Fortunately, an ultrasound device with an abdominal probe is almost always available on maternity units. Not only anesthesiologists but also obstetricians should be familiar with basic POCUS concepts.1 Pulmonary ultrasound has been shown to be easy to learn, and therefore, all physicians involved in maternal care should be at least trained in identifying B-lines. Thus, in the obstetrical context, during SPE, an easy and brief lung ultrasound examination may be the primary POCUS examination, giving information about EVLW, left ventricular filling pressure, and risk to develop pulmonary edema.3–8,15 Once evidence demonstrates this information can be used to guide clinical practice in a way that improves maternal and perinatal outcomes, this screening tool will be established as a new standard of care for women diagnosed with preeclampsia. DISCLOSURES Name: Clemens M. Ortner, MD. Contribution: This author helped draft and critically revise the manuscript. Conflicts of Interest: None. Name: Miha Lucovnik, MD. Contribution: This author helped draft and revise the manuscript. Conflicts of Interest: None. Name: Laurent Zieleskiewicz, MD, PhD. Contribution: This author conceived the editorial and critically revised the manuscript. Conflicts of Interest: L. Zieleskiewicz received fees from GE Healthcare for teaching ultrasound to GE Healthcare customers. This manuscript was handled by: Jill M. Mhyre, MD.