Optimal fluid management is crucial for patients who undergo major and prolonged surgery. Persistent hypovolemia is associated with complications, but fluid overload is also harmful. We evaluated the ...effects of a restrictive versus conventional strategy of crystalloid administration during goal-directed therapy in high-risk surgical patients.
We conducted a prospective, randomized, controlled study of high-risk patients undergoing major surgery. For fluid maintenance during surgery, the restrictive group received 4 ml/kg/hour and the conventional group received 12 ml/kg/hour of Ringer's lactate solution. A minimally invasive technique (the LiDCO monitoring system) was used to continuously monitor stroke volume and oxygen delivery index (DO₂I) in both groups. Dobutamine was administered as necessary, and fluid challenges were used to test fluid responsiveness to achieve the best possible DO₂I during surgery and for 8 hours postoperatively.
Eighty-eight patients were included. The patients' median age was 69 years. The conventional treatment group received a significantly greater amount of lactated Ringer's solution (mean ± standard deviation (SD): 4, 335 ± 1, 546 ml) than the restrictive group (mean ± SD: 2, 301 ± 1, 064 ml) (P < 0.001). Temporal patterns of DO₂I were similar between the two groups. The restrictive group had a 52% lower rate of major postoperative complications than the conventional group (20.0% vs 41.9%, relative risk = 0.48, 95% confidence interval = 0.24 to 0.94; P = 0.046).
A restrictive strategy of fluid maintenance during optimization of oxygen delivery reduces major complications in older patients with coexistent pathologies who undergo major surgery.
ISRCTN: ISRCTN94984995.
Seismic shaking has been regarded as an essential source of resurfacing on asteroids. The Small Carry‐on Impactor (SCI) operation on Hayabusa2 has been expected to be a unique opportunity for testing ...in situ seismic shaking whose energy is sufficiently large to excite observable surface modification. However, no obvious regolith hopping was identified even immediately outside of the crater formed by the SCI impact. To understand this discrepancy from the expectation, we simulate seismic wave propagation on Ryugu with a wide range of surface material properties and evaluate maximum acceleration on the surface. Numerical results reveal that low‐quality factor or low seismic efficiency is required to explain the lack of geomorphological change after the SCI experiment. Considering that scattering under anhydrous conditions cannot efficiently dissipate energy, such a low‐quality factor is not plausible. The weak yield strength in porous materials can efficiently decrease seismic wave energies, making the apparent seismic efficiency extremely low. Based on this hypothesis, we propose a formulation of surface mobility on asteroids that considers the physical properties of regolith. We consistently estimate the occurrence of seismic shaking with the existence of unstable boulders on Ryugu.
Plain Language Summary
The Japanese asteroid exploration mission, Hayabusa2, successfully performed an artificial impact cratering operation on April 5, 2019. Extensive surface modification was expected to be excited by the impact‐induced seismic waves; however, boulders stayed at almost the same location. We conduct seismic wave propagation simulations to resolve this apparent discrepancy and to understand the physical properties of Ryugu. We show that surface changes are strongly dependent on a shallow subsurface. Our results suggest that the conversion of impact energy to seismic waves is less efficient than previously thought. The weakness of powdery regolith may limit asteroid‐quakes at the surface. Based on this hypothesis, we propose a formulation how the surface moves on asteroids that considers the unclear properties of regolith. The lack of seismic shaking agrees with the mysterious discovery that boulders stay unstably on other boulders.
Key Points
Unexpectedly little movement of boulders due to the Small Carry‐on Impactor impact experiment on Ryugu is investigated by seismic wave propagation simulation
Low‐yield strength of asteroid regolith is likely to limit seismic wave amplitude
Meteoroid impacts on small asteroids possibly cause seismic shaking, but its contribution to resurfacing is localized
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