The NASG was adapted from the PASG by the National Aeronautics and Space Administration (NASA) in 1971, when the NASA/Ames Research Center developed a prototype pressure suit designed to protect hemophiliac children from bleeding into elbow and knee joints by straightening and compressing the joint until medical attention was available21. Both PASG and NASG provide circumferential counter pressure in the lower body, but the NASG is simpler in design, more quickly and easily applied, less expensive and avoids the risk of over-inflation and excessive pressure22.
The NASG is particularly suited to use in low-resource settings. Lighter and more flexible than the PASG, it is more comfortable for a woman to be inside the suit for longer periods of time, something necessary in the long transport times and delayed treatment conditions of low-resource settings. As with the PASG, within minutes of being placed in the NASG, a patient's vital signs are restored and, if confused or unconscious, their sensorium generally clears1. Women can remain in the NASG for as long as is required to restore their circulatory volume with crystalloids and to replace blood. In prior reports of cases where blood transfusions were not readily available, this has often required 18-24 h, and, in one case, a woman remained safely in the NASG for 57 h23. Compared to the PASG, with pressures of 100 mmHg or more, the NASG only applies 30-40 mmHg. Higher pressures appear to be responsible for skin and muscle ischemia and adverse effects on pH as well as the occasional anterior compartment syndrome.
A second benefit of the NASG for obstetric indications is that the design of the garment permits complete perineal access so that genital lacerations can be repaired, speculum or bimanual examinations can be performed, and manual removal of placenta or emptying of the uterus with manual vacuum aspiration or curet-tage can all be accomplished with the NASG in place. Thus, the source of most obstetric hemorrhages can be located and attended to while the garment maintains vital signs.
A third benefit of the NASG is that it significantly reduces further blood loss. When the NASG is applied, the external circumferential counter pressure is distributed evenly throughout the abdominal cavity and to the outside of the circulatory vessels - tamponading venous bleeding. In the event of an arterial injury, continued bleeding results from the tension in the wall of the artery keeping the defect open. However, the NASG compresses all the intraabdominal vessels including the internal iliac and uterine arteries. This compression reduces the radius of the arteries and reduces the transmural pressure (the difference between the pressure inside the artery and the pressure outside the artery) which, in turn, reduces the tension in the arterial wall, closing the defect and reducing blood loss. Although the mean pressure applied by the NASG is only in the range of 30-40 mmHg, this low pressure, which is below arterial pressures, can still stop arterial bleeding when applied externally to the abdomen and the lower extremities24. Because the applied pressures could interfere with uterine blood flow, the NASG is not recommended for obstetric bleeding when the fetus is still viable, such as might be the case with placenta previa or abruption. Post-delivery, however, or when the fetus is not viable or is dead, the NASG can be used for any obstetric hemorrhage.
Another potential benefit for the use of the NASG for obstetric hemorrhage in low-resource settings is that persons with no medical background can learn to apply the garment safely with minimal training. Such training, which includes hands-on practice in application and removal of the NASG, takes approximately 1 h. Once the garment has been properly applied, patients can safely be transported and/or await definitive treatment in a more stable physical condition. This final point is critical, as the majority of maternal deaths due to obstetric hemorrhage occur in areas where skilled birth and critical care attendance are limited or absent.
The improvement in maternal morbidity and mortality can presently only be discussed as potential benefits, because there have been no definitive trials of the NASG, and there is only very limited experience with its use for obstetric hemorrhage in low-resource settings. The case series and pilot studies discussed below indicate how the NASG functions to decrease blood loss, reverse shock, and stabilize women for many hours while awaiting blood transfusions. As such, use of the NASG might contribute to decreased maternal mortality and morbidity. Experience with transport from lower-level facilities to referral centers, while theoretically beneficial, is only anecdotal at this point.
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