Surfactant replacement therapy

Surfactant Driven Post-Deposition Spreading of Aerosols on Complex Aqueous Subphases. 2: Low Deposition Flux Representative of Aerosol Delivery to Small Airways

BACKGROUND

Cystic fibrosis (CF) is associated with the accumulation of dehydrated mucus in the pulmonary airways. This alters ventilation and aerosol deposition patterns in ways that limit drug delivery to peripheral lung regions. We investigated the use of surfactant-based, self-dispersing aerosol carriers that produce surface tension gradients to drive two-dimensional transport of aerosolized medications via Marangoni flows after deposition on the airway surface liquid (ASL). We considered the post-deposition spreading of individual aerosol droplets and two-dimensional expansion of a field of aerosol droplets, when deposited at low fluxes that are representative of aerosol deposition in the small airways.

METHODS

We used physically entangled aqueous solutions of poly(acrylamide) or porcine gastric mucin as simple ASL mimics that adequately capture the full miscibility but slow penetration of entangled macromolecular chains of the ASL into the deposited drop. Surfactant formulations were prepared with aqueous solutions of nonionic tyloxapol or FS-3100 fluorosurfactant. Fluorescein dye served as a model "drug" tracer and to visualize the extent of post-deposition spreading.

RESULTS

The surfactants not only enhanced post-deposition spreading of individual aerosol droplets due to localized Marangoni stresses, as previously observed with macroscopic drops, but they also produced large-scale Marangoni stresses that caused the deposited aerosol fields to expand into initially unexposed regions of the subphase. We show that the latter is the main mechanism for spreading drug over large distances when aerosol is deposited at low fluxes representative of the small airways. The large scale convective expansion of the aerosol field drives the tracer (drug mimic) over areas that would cover an entire airway generation or more, in peripheral airways, where sub-monolayer droplet deposition is expected during aerosol inhalation.

CONCLUSIONS

The results suggest that aerosolized surfactant formulations may provide the means to maximize deposited drug uniformity in and access to small airways.

Prospective risk of late stillbirth in monochorionic twins: a regional cohort study

OBJECTIVE

Monochorionic (MC) pregnancies are routinely delivered electively at late preterm gestation with the aim of avoiding stillbirth at term. The aim of this study was to evaluate the prospective risk of late stillbirth in a large regional cohort of twin pregnancies of known chorionicity.

METHODS

This was a retrospective study of all twin pregnancy births of known chorionicity between 2000 and 2009 from a large regional cohort consisting of nine hospitals. Prospective risk was calculated per 1000 fetuses rather than pregnancies, as each twin pregnancy had two gestations at risk of stillbirth.

RESULTS

A total of 3005 twin pregnancies delivered after 26 weeks' gestation in the Southwest Thames Obstetric Research Collaborative. The total risk of stillbirth after 26 weeks in MC twins (19.1 per 1000 fetuses) was significantly higher than in dichorionic (DC) twins (6.5 per 1000 fetuses), with an odds ratio (OR) of 2.97 (95% CI, 1.71-5.18). The risk of stillbirth in MC twins did not change significantly between 26 weeks (1.8 per 1000 fetuses) and 36 weeks (3.4 per 1000 fetuses), with an OR of 1.85 (95% CI, 0.3-13.2). The equivalent figures for DC twins were 0.6 per 1000 fetuses and 2.1 per 1000 fetuses, respectively (OR, 3.4 (95% CI, 0.9-13.2)).

CONCLUSIONS

The risk of stillbirth in MC twins does not appear to increase significantly near term. This may be due to a policy of routine surveillance and elective delivery from 36 weeks. The data do not support a policy of elective delivery before 36 weeks' gestation in MC pregnancies.

Advances with surfactant

In this article, the physiology of surfactant is reviewed along with the research that lead to its current clinical uses. Acute lung injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) will also be reviewed because they represent pulmonary disease processes in which secondary deficiency and surfactant inactivation occur, for which surfactant may prove to be an effective treatment. Finally, research using surfactant as a treatment for other pulmonary diseases, such as bronchiolitis and asthma, will be briefly highlighted. These studies may one day lead to new treatment opportunities in the realm of emergency medicine.

High perinatal survival in monoamniotic twins managed by prophylactic sulindac, intensive ultrasound surveillance, and Cesarean delivery at 32 weeks' gestation

OBJECTIVES

Increased perinatal mortality in monoamniotic twin pregnancies is attributed to cord accidents in utero and at delivery. We evaluated the following parameters in monoamniotic pregnancies: (1) the incidence of cord entanglement; (2) the effect of sulindac on amniotic fluid volume and stability of fetal lie; and (3) the perinatal outcome with our current management paradigm.

METHODS

This is a retrospective review of monoamniotic pregnancies of >or=20 weeks' gestation managed with serial ultrasound surveillance, medical amnioreduction and elective Cesarean delivery at 32 weeks' gestation. Mean amniotic fluid index (AFI) and change in AFI in monoamniotic pregnancies managed with oral sulindac was compared with 40 gestation-matched monochorionic-diamniotic controls.

RESULTS

Among 44 monoamniotic pregnancies, 20 with two live structurally normal twins at 20 weeks' gestation satisfied the inclusion criteria. All fetuses survived to 28 days postnatally despite early prenatal cord entanglement in all but one case. Whereas AFI remained stable throughout gestation in the controls, the AFI fell in those patients on sulindac from a mean value of 21.0 cm (95% CI, 18.5-23.6 cm) at 20 weeks to a mean of 12.4 cm (95% CI, 10.1-14.6 cm) at 32 weeks (ANOVA P across gestation = 0.001) but mainly remained within normal limits. Fetal lie was stabilized in 11/20 cases in the monoamniotic group compared with 13/40 in the control group (P < 0.0001).

CONCLUSIONS

Cord entanglement appears unpreventable, as it typically occurs in early pregnancy. Sulindac therapy reduces AFI, leads to more stable fetal lie, and may prevent intrauterine death by diminishing the risk of constricting cords that are already entangled. Perinatal survival in monoamniotic pregnancies managed by a regime of sulindac from 20 weeks' gestation, close ultrasound surveillance and elective abdominal delivery at 32 weeks' gestation seems empirically higher than that in the literature.

Perinatal outcomes in monoamniotic gestations

OBJECTIVE

A comprehensive review of monoamniotic twin gestations reported between 1990 and 2002 was performed to estimate current perinatal mortality and morbidity rates, as well as the predictive value of an antenatal diagnosis of cord entanglement for poor obstetric outcomes.

METHOD

A Medline literature review using the search term 'monoamniotic' and limited to articles published in the English language between 1990 and 2002 was performed.

RESULTS

A total of 133 continuing, non-conjoined twin monoamniotic pregnancies with delivery information were identified. Perinatal loss per 2-week interval was relatively constant at 2-4% from 15 to 32 weeks. However, of the 131 fetuses reaching 33 weeks, the percentage loss significantly increased to 11.0% at 33-35 weeks and 21.9% at 36-38 weeks compared to that at 30-32 weeks. Overall perinatal mortality was 23.3%. Of all losses, 61.2% involved both twins and 38.8% involved only one fetus. Cord entanglements were documented antenatally in 22.6% of reports. There was a statistically significant decrease in the average number of neonatal intensive care unit days for non-anomalous neonates (10.6 +/- 7.7 vs. 32.6 +/- 32.0), average gestational age at the time of delivery (30.4 +/- 7.6 vs. 32.6 +/- 4.1), as well as a decrease in the prevalence of total (8.3% vs. 27.7%) and non-anomalous (7.0% vs. 21.6%) perinatal mortality in pregnancies with an antenatal diagnosis of cord entanglement compared to those without the antenatal diagnosis of cord entanglement. The presence of fetal anomalies was associated with a 42.9% perinatal mortality rate.

CONCLUSIONS

Contrary to previous reports, there is a significant increase in the incidence of perinatal loss beyond 32 weeks among monoamniotic twins, suggesting that delivery after corticosteroid therapy should be strongly considered at this gestational age.

Role of ureaplasma urealyticum in lung disease of prematurity

AIM

To examine the role of Ureaplasma urealyticum colonisation or infection in neonatal lung disease.

METHODS

Endotracheal aspirates from ventilated infants less than 28 weeks of gestation were cultured for U urealyticum and outcomes compared in infants with positive and negative cultures.

RESULTS

U urealyticum was isolated from aspirates of 39 of 143 (27%) infants. Respiratory distress syndrome (RDS) occurred significantly less often in colonised, than in non-colonised infants (p=0.002). Multivariate logistic regression analysis showed that in singleton infants, ureaplasma colonisation was the only independent (negative) predictor of RDS (OR 0.36; p=0. 02). Both gestational age (OR 0.46; p=0.006) and isolation of U urealyticum (OR 3.0; p=0.05) were independent predictors of chronic lung disease (CLD), as defined by requirement for supplemental oxygen at 36 weeks of gestational age. Multiple gestation was also a major independent predictor of RDS and CLD.

CONCLUSIONS

Colonisation or infection with ureaplasma apparently protects premature infants against the development of RDS (suggesting intrauterine infection). However, in singleton infants, it predisposes to development of CLD, independently of gestational age. Treatment of affected infants after birth is unlikely to significantly improve the outcome and methods are required to identify and treat the women with intrauterine ureaplasmal infection, before preterm delivery occurs.

Continuous neonatal blood gas monitoring using a multiparameter intra-arterial sensor

AIMS

To compare arterial blood gas (ABG) readings obtained with a multiparameter intra-arterial sensor with those from an ABG analyser.

METHODS

An MPIAS with the ability to measure continuously pH, PaCO2, and PaO2 was introduced via an umbilical arterial catheter in 27 neonates requiring intensive care. They underwent 3260 hours of MPIAS monitoring, during which 753 ABG readings were performed.

RESULTS

Overall bias (mean difference: MPIAS-ABG) and precision (standard deviation of differences) values were: -0.002 and 0.022, respectively, for pH; +0.26 and 0.52 for PaCO2 (kPa); and -0.19 and 0.99 for PaO2 (kPa). This gave 95% limits of agreement as: -0.047 to +0.042 for pH, -0.76 to +1.28 kPa for PaCO2, and -2.13 to +1.75 kDa for PaO2. For each variable, precision across readings from the same individual was better than overall precision for all data. No complications related to the use of the catheter were observed.

CONCLUSIONS

Continuous MPIAS ABG monitoring is an exciting development, with the potential to reduce blood transfusions and improve ABG homeostasis.

Compositional, structural, and functional alterations in pulmonary surfactant in surgical patients after the early onset of systemic inflammatory response syndrome or sepsis

OBJECTIVES

Sepsis is one of the most important predisposing factors for the development of the acute respiratory distress syndrome (ARDS). Alterations of pulmonary surfactant contribute in the pathogenesis of ARDS. However, little is known about surfactant in patients with less severe grades of lung injury related to sepsis or systemic inflammatory response syndrome (SIRS). Therefore, the purpose of this study was to characterize endogenous surfactant in surgical intensive care patients with sepsis or SIRS.

DESIGN

Prospective, observational study.

SETTING

University-affiliated, interdisciplinary intensive care unit.

PATIENTS

Eleven patients after major surgery with SIRS or sepsis included within 12 hrs of onset and 11 controls without infection or lung disease.

INTERVENTIONS

Operating room and standard intensive care unit management.

MEASUREMENTS AND MAIN RESULTS

Four serial bronchoalveolar lavage samples (BAL) were recovered over 7 days from the patients and single BAL samples were obtained from controls. BAL cells, total protein, surfactant-associated protein A (SP-A), surfactant alveolar transition forms, and surface activity were analyzed. Two of 11 patients met criteria for acute lung injury and six of the 11 patients met ARDS consensus conference criteria but acute lung injury or ARDS was not persistent. The mean Pao2/F(IO)2 for the patients over 7 days was 253.2+/-15.1 (SEM) and Murray's lung injury score was 1.12+/-0.12, indicating mild-to-moderate lung injury. BAL neutrophil counts were increased (p< .01), and the ratio of poorly functioning light aggregate surfactant to superiorly functioning heavy aggregate surfactant was increased compared with controls (0.32+/-0.06 vs. 0.09+/-0.01, p < .05). SP-A was decreased (1.9+/-0.4 vs. 3.5+/-0.6 microg/mL of BAL, p< .05) and there were increases in the ratios of phospholipid to SP-A (p < .05), protein to SP.A (p < .01), and protein to phospholipid (p < .05). The surface tension-lowering ability of purified heavy aggregate surfactant was significantly impaired (15.6+/-1.6 vs. 2.8+/-0.6 milliNewtons/m, p< .05).

CONCLUSIONS

These observations show that surgical patients with SIRS or sepsis who have mild-to-moderate lung injury develop surfactant dysfunction detectable within 7 days of onset. We propose, therefore, that therapeutic strategies to modulate these severe surfactant abnormalities should be considered, as these strategies may have the potential to reduce lung injury, which is associated with a high mortality in sepsis.

Rotational dynamics of spin-labelled surfactant-associated proteins SP-B and SP-C in dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol bilayers

Pulmonary surfactant proteins SP-B and SP-C have been isolated from porcine lungs and selectively labelled with 2,2,6, 6-tetramethylpiperidine-N-oxyl (TEMPO)-isothiocyanate at their N-terminal amine ends, to analyse the mobility of both proteins on the nanosecond time scale using electron spin resonance (ESR) spectroscopy. Reconstitution of the labelled forms of these proteins in bilayers of dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) results in much broader and anisotropic ESR spectra, indicating a large restriction in rotational mobility of the protein-attached probe when inserted in membranes. Distinctive differences were found between the ESR spectra of the two polypeptides, that were consistent with intrinsic differences in mode of interaction of SP-B and SP-C with phospholipid bilayers. The mobility of the protein spin probes was sensitive to temperature on the time scale of conventional spin-label ESR. Both proteins, TEMPO-SP-B and TEMPO-SP-C, showed considerable increases in mobility at temperatures above the pretransition of pure DPPC. Finally, the mobility of the spin probes attached to both SP-B and SP-C was more restricted in DPPG than in DPPC bilayers, demonstrating that electrostatic interactions of the positively charged residues at the protein surface influence the rotational dynamics of the proteins in anionic lipid bilayers. Although some residual segmental mobility of the thiourea-linked probes cannot be discounted, the results clearly reflect preferential differences in overall protein dynamics in gel and fluid phases of the two phospholipids that could be important for the biophysical properties of surfactant bilayers and monolayers.

Advances in neonatal care and surgery

Neonatology has seen many advances over the past decade. Exogenous surfactant therapy is now a mainstay treatment for respiratory distress syndrome. Partial liquid ventilation, high-frequency ventilation, and inhaled nitric oxide are all relatively new modalities, which have enabled neonatologists to treat with varying degrees of success ever younger and smaller patients. The purpose of this review is to examine studies regarding the long-term outcome of high-risk neonates, the various treatment modalities, and current neonatal surgical techniques, all of which will influence our care of the neonate.