Immunological assessment of SARS-CoV-2 infection in pregnancy from diagnosis to delivery: A multicentre prospective study.

BACKGROUND: Background Population-based data on SARS-CoV-2 infection in pregnancy and assessment of passive immunity to the neonate, is lacking. We profiled the maternal and fetal response using a combination of viral RNA from naso-pharyngeal swabs and serological assessment of antibodies against SARS-CoV-2. METHODS: This multicentre prospective observational study was conducted between March 24th and August 31st 2020. Two independent cohorts were established, a symptomatic SARS-CoV-2 cohort and a cohort of asymptomatic pregnant women attending two of the largest maternity hospitals in Europe. Symptomatic women were invited to provide a serum sample to assess antibody responses. Asymptomatic pregnant women provided a nasopharyngeal swab and serum sample. RT-PCR for viral RNA was performed using the Cobas SARS-CoV-2 6800 platform (Roche). Umbilical cord bloods were obtained at delivery. Maternal and fetal serological response was measured using both the Elecsys® Anti-SARS-CoV-2 immunoassay (Roche), Abbott SARS-CoV-2 IgG Assay and the IgM Architect assay. Informed written consent was obtained from all participants. RESULTS: Ten of twenty three symptomatic women had SARS-CoV-2 RNA detected on nasopharyngeal swabs. Five (5/23, 21.7%) demonstrated serological evidence of anti-SARS-CoV-2 IgG antibodies and seven (30.4%, 7/23) were positive for IgM antibodies. In the asymptomatic cohort, the prevalence of SARS-CoV-2 infection in RNA was 0.16% (1/608). IgG SARS-CoV-2 antibodies were detected in 1·67% (10/598, 95% CI 0·8%-3·1%) and IgM in 3·51% (21/598, 95% CI 2·3-5·5%). Nine women had repeat testing post the baseline test. Four (4/9, 44%) remained IgM positive and one remained IgG positive. 3 IgG anti-SARS-CoV-2 antibodies were detectable in cord bloods from babies born to five seropositive women who delivered during the study. The mean gestation at serological test was 34 weeks. The mean time between maternal serologic positivity and detection in umbilical cord samples was 28 days. CONCLUSION: Using two independent serological assays, we present a comprehensive illustration of the antibody response to SARS-CoV-2 in pregnancy, and show a low prevalence of asymptomatic SARS-CoV2. Transplacental migration of anti-SARS-CoV-2 antibodies was identified in cord blood of women who demonstrated antenatal anti-SARS-CoV-2 antibodies, raising the possibility of passive immunity.

Optical Sensor for Real-Time pH Monitoring in Human Tissue.

This article reports on a fiber-based ratiometric optical pH sensor for use in real-time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol-gel-based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model. The pH sensor performance in the laboratory environment outperforms the state-of-the-art reported in the current literature. It exhibits the highest sensitivity in the physiological pH range, resolution of 0.0013 pH units, excellent sensor to sensor reproducibility, long-term stability, short response time of <2 min, and drift of 0.003 pH units per 22 h. The sensor also exhibits promising performance in in vitro whole blood samples. In addition, human evaluations conducted under this project demonstrate successful short-term deployment of this sensor in vivo.

Arterial blood gases and oxygen content in climbers on Mount Everest.

BACKGROUND: The level of environmental hypobaric hypoxia that affects climbers at the summit of Mount Everest (8848 m [29,029 ft]) is close to the limit of tolerance by humans. We performed direct field measurements of arterial blood gases in climbers breathing ambient air on Mount Everest. METHODS: We obtained samples of arterial blood from 10 climbers during their ascent to and descent from the summit of Mount Everest. The partial pressures of arterial oxygen (PaO(2)) and carbon dioxide (PaCO(2)), pH, and hemoglobin and lactate concentrations were measured. The arterial oxygen saturation (SaO(2)), bicarbonate concentration, base excess, and alveolar-arterial oxygen difference were calculated. RESULTS: PaO(2) fell with increasing altitude, whereas SaO(2) was relatively stable. The hemoglobin concentration increased such that the oxygen content of arterial blood was maintained at or above sea-level values until the climbers reached an elevation of 7100 m (23,294 ft). In four samples taken at 8400 m (27,559 ft)--at which altitude the barometric pressure was 272 mm Hg (36.3 kPa)--the mean PaO(2) in subjects breathing ambient air was 24.6 mm Hg (3.28 kPa), with a range of 19.1 to 29.5 mm Hg (2.55 to 3.93 kPa). The mean PaCO(2) was 13.3 mm Hg (1.77 kPa), with a range of 10.3 to 15.7 mm Hg (1.37 to 2.09 kPa). At 8400 m, the mean arterial oxygen content was 26% lower than it was at 7100 m (145.8 ml per liter as compared with 197.1 ml per liter). The mean calculated alveolar-arterial oxygen difference was 5.4 mm Hg (0.72 kPa). CONCLUSIONS: The elevated alveolar-arterial oxygen difference that is seen in subjects who are in conditions of extreme hypoxia may represent a degree of subclinical high-altitude pulmonary edema or a functional limitation in pulmonary diffusion.

Oxygen on Everest: the development of modern open-circuit systems for mountaineers.

The use of supplemental oxygen on Mt. Everest is now commonplace. From 1990 to 2006, more than 95% of those summiting the mountain did so using supplemental oxygen at some point during their ascent. The open circuit systems currently in use can be traced back to the device first used by George Finch on Mt. Everest in 1922. Wearing equipment weighing 33 lb (15 kg), Finch and his colleague Geoffrey Bruce set a world altitude record by reaching a height of 27,250 ft (8175 m). However, it would be with a lighter system weighing just 22 lb (10 kg) that Sir Edmund Hillary and Tenzing Norgay made the first ascent of the mountain in 1953. In the years since then considerable improvements in weight, comfort, and efficiency have been made; however, the original "open" principles first used by Finch almost a century ago still remain steadfastly in place.

Near infra-red spectroscopy and arterial oxygen extraction at altitude.

The ratio of oxygenated to total haemoglobin (Hb), or rSO2, obtained by near infrared spectroscopy (NIRS), includes both arterial and venous blood of the region examined. The relationship of arterial oxygen extraction, E, and saturation, SaO2, to rSO2 can be expressed, for normally functioning tissue, as E = 1.39 (1 - rSO2/SaO2). Cerebral E, at rest, is constant at lower altitudes but is reduced at 5000 m. This corresponds to constant values of E for SaO2 values above 90% (approximately). E declines linearly for lower SaO2 values, either including measurement at high altitude or at sea level with a reduced inspiratory oxygen concentration. In addition to measurements of brain NIRS resting oxygen extraction of liver, muscle and kidney have also been calculated from NIRS measurements made, on normal inspired air, at sea level and after acute ascent to 2400 m and 5050 m. At 5050 m E was reduced for all four regions but at 2400 m was the same as at sea level for brain, liver and muscle; for the kidney E was elevated at 2400 m. Cerebral oxygen extraction was calculated for rest and the full range of exercise. It was constant at sea level for the lower levels of exercise and, if the calculated extraction value assumptions still hold at lower SaO2 values, reduced for the higher work rates at intermediate altitudes. The present study confirms constancy of oxygen extraction and hence the ratio of oxygen delivery to oxygen consumption (1/E), within physiological limits, and appears to show where those limits lay and, to some extent, show how matters change beyond ordinary physiological limits.

Pulse oximetry.

PURPOSE OF REVIEW: Pulse oximetry is now a ubiquitous and essential tool of modern medicine, and while it is a relatively recent invention, the technology has rapidly matured since the first commercially available oximeters were introduced in the 1970s. This review seeks to provide an overview of the basic physical operation of the probe and discuss its limitations, sources of error and some current advances in the use of multi-wavelength probes. RECENT FINDINGS: New multi-wavelength oximeters and plethysmographic waveform analysis may expand the information that we can collect and use non-invasively. This includes distinguishing between haemoglobinopathies, monitoring volume status and volume loss, and potentially monitoring cardiac output non-invasively. SUMMARY: The pulse oximeter, like any basic tool, must be used properly. There is considerable misunderstanding and lack of education among junior clinicians as to the use and interpretation of pulse oximeters. The introduction of the pulse oximeter has demonstrated a cost saving, although the cost-benefit of new multi-wavelength probes remains unproven.