Clinical characteristics of women captured by extending the definition of severe postpartum haemorrhage with 'refractoriness to treatment': a cohort study

Background: The absence of a uniform and clinically relevant definition of severe postpartum haemorrhage hampers comparative studies and optimization of clinical management. The concept of persistent postpartum haemorrhage, based on refractoriness to initial first-line treatment, was proposed as an alternative to common definitions that are either based on estimations of blood loss or transfused units of packed red blood cells (RBC). We compared characteristics and outcomes of women with severe postpartum haemorrhage captured by these three types of definitions. Methods: In this large retrospective cohort study in 61 hospitals in the Netherlands we included 1391 consecutive women with postpartum haemorrhage who received either ≥4 units of RBC or a multicomponent transfusion. Clinical characteristics and outcomes of women with severe postpartum haemorrhage defined as persistent postpartum haemorrhage were compared to definitions based on estimated blood loss or transfused units of RBC within 24 h following birth. Adverse maternal outcome was a composite of maternal mortality, hysterectomy, arterial embolisation and intensive care unit admission. Results: One thousand two hundred sixty out of 1391 women (90.6%) with postpartum haemorrhage fulfilled the definition of persistent postpartum haemorrhage. The majority, 820/1260 (65.1%), fulfilled this definition within 1 h following birth, compared to 819/1391 (58.7%) applying the definition of ≥1 L blood loss and 37/845 (4.4%) applying the definition of ≥4 units of RBC. The definition persistent postpartum haemorrhage captured 430/471 adverse maternal outcomes (91.3%), compared to 471/471 (100%) for ≥1 L blood loss and 383/471 (81.3%) for ≥4 units of RBC. Persistent postpartum haemorrhage did not capture all adverse outcomes because of missing data on timing of initial, first-line treatment. Conclusion: The definition persistent postpartum haemo

The PHARUS Project; Real Time Digital Processing of Airborne Polarimetric Radar Signals

The Dutch PHARUS project aims for the developrlenÈ of a polarimetric C-band aircraft SAR, to be finalized in 1994. The PHARUS systen consists of three subsystens: the radar, the subsystem for the onboard data processing and recording and the ground-based subsystem for SAR processing. PHARUS is a very flexible system with numerous operating modes, intended for renote sensing research. Modes vary from a straighc forward single mode (e.g. HH polarisation)to a full polarimetric mode with alternating chirp patterns. This paper describes selected items of the onboard data processlng and recording subsystem, as it is under construction now. Data processing starts with high speed digitization of the offsec modulated radar slgnals. The digitized offsec modulated signals are demodulated and re-sampled (in range) to complex base band signals. A low pass filtering and decimation in flight direction is performed. Finally, pulse cornpression is performed based on FFT and IFFT

PHARUS: Airborne SAR Development in the Netherlands

The PHARUS project (PHARUS stands for Phased Array Universal SAR) aims for a polarimetric C-band aircraft SAR that will be finalized in 1994. The system will make use of a phased array antenna with solid state amplifiers. The project consists of two phases, a definition phase and a realization phase. The definition phase was intended to increase the knowledge on airborne SAR systems and to develop the critical technology that is used in the final system. As part of this phase a C-band SAR testbed called PHARS was developed, which made its first tesflight in november 1990. The testbed is based on the concept of a wide beamwidth antenna, rigidly fixed to the aircraft. Pulse compression and a high PRF ensure suficient sensitivity in this system, which is equipped with a 160 Watt peak pulse solid state transmitter. The processing is done off-line. In the current realization phase the polarinetric PHARUS sysæm is being developed. Its design is similar but more advanced when compared to the PHARS testbed. The system will make use of a phased array dual polarised patch antenna and will be equipped with solid state amplifiers and MMIC vector modulators. The number of microwave modules is increased (48 for PHARUS versus S in PHARS). The paper focuses on the design of these SAR sysæms and on the results obtained sofar with the PHARS testbed. A performance evaluation of this system using corner reflectors was part of the testrogram. PHARS was also operated during the ERS-1 CAL/VAL campaign in Norway in November 1991

The design of a phased array polarimetric C-band SAR

Since many years ground-based scatterometers (X and Q band) and a digital SLAR system (X-band), are used in studying the microwave scattering of vegetation, forests, sea and other targets in the Netherlands. Recently an airborne scatterometer system operating at six frequencies simuItaneously between 1 and 18 GHz has been added to the remote sensing research radars. Absolute calibration and high accuracy are the reasons for succes for these systems

First Results and Status of the PHARUS Phased Array Airborne SAR

PHARUS is an airborne fully polarimetric C band SAR. It uses a compact phased array antenna with electronic beam steering. Its design provides for a flexible and robust system concept, suited for operational use on small aircraft. PHARUS was developed in The Netherlands to cater for both the military and civil markets. Its development was initiated in 1987 and has now resulted in completion of the system, which made its maiden flight in September 1995. In the paper, the particulars of PHARUS will be discussed, with special attention to the antenna, followed by the SAR processing, use of the system, its history and status, and foreseen future developments

C-band solid state dual polarization T/R modules for airborne SAR systems

The use of distributed power in a, on a phased array antenna based, SAR system offers new possibilities for the system operation. As a preparation for future spaceborne SAR systems using solid state transmitters with electronically steerable phased array antenna, the PHARUS system has been constructed. The system is installed on a Cessna Citation II aircraft. The system will have a number of user selectable modes for polarizations (one to fully polarimetric), resolution (4 meter / 4 looks to 16 meter / 20looks), altitude (5 km to 12 km), swath width (4.4 km, high resolution, polarimetric until 20 km, low resolution, one polarization) and incidence angle range. The different features within a mode are more or less coupled due to signal to noise limitations and maximum data rate. The radar is set up in such a way that extensions in a later stage are possible. For example a larger bandwidth or the enlargement of the antenna including the number of T/R modules. This paper describes the dual polarization T/R module design, including the module charactenzation for calibration purposes

Design and Calibration of the PHARUS Polarimetric Airborne SAR

The PHARUS system uses a phased array antenna with solid state amplifiers. The project consisted of two phases, a definition phase and a realization phase. The definition phase consisted of the actual realization of a SAR research system called PHARS, which made its first successful testflight in November 1990. The research system is based on the concept of a wide beamwidth antenna, rigidly fixed to the aircraft. Pulse compression and a high PRF ensure sufficient sensitivity in this system, which is equipped with a 160 Watt peak pulse power solid state transmitter. The processing is done off-line. In the realization phase the Polarimetric PHARUS system has been developed. The design is based on the experience gained with the PHARS system. The system uses a phased array with dual polarized patch radiators and is equipped with solid state amplifiers. This paper will give an overview of the PHARUS design and operational use. Apart from the use as an advanced Polarimetrie airbome SAR, there is the perspective of using PHARUS as a demonstrator for ESA's future ASAR system

The Design and Development of a Polarimetric Phased Array Airborne SAR Sensor

A polarimetric C-band airborne SAR has been developed in the Netherlands. The system makes use of a phased array antenna with solid state amplifiers. The project consists of two phases, a definition phase and a realization phase. The definition phase consisted of the actual realization of a SAR research system, which made its first successful testflight in November 1990. The research system is based on the concept of a wide beamwidth antenna, rigidly fixed to the aircraft. In the current realization phase the polarimetric system is under its first airborne tests. Its design is based on the experience gained with the research system. The system makes use of a phased array with dual polarized patch radiators and will be equipped with solid state amplifiers. The technology used and the expected system performance are representative for future spaceborne systems. This paper will give an overview of the SAR research system and the results obtained with this system. The polarimetric system design and use will be discussed. Apart from the use as an advanced polarimetric airborne SAR, there is the perspective of using this system as a demonstrator for ESA's future ASAR system