Maximizing Scarce Fluid Resources Far Forward: Carotid Velocity Time Interval for Assessing Fluid Responsiveness during Prolonged Field Care

Introduction: With the prospect of near-peer adversaries, large-scale combat operations, and irregular warfare, superiority in air, sea, and land are no longer as relatively assured, and prolonged field care (PFC) stands to become a more frequent and critical dimension of the medical care that special forces combat casualties receive. Fluid resuscitation is among the most important interventions that casualties can receive, but fluids—including whole blood—are scarce resources during PFC. A reliable indicator of fluid responsiveness is therefore paramount. Velocity time integral (VTI) variability is a predictor of fluid responsiveness that can be obtained using point-of-care ultrasound imaging of the carotid artery. Ultrasound systems are already carried by special mission units medics. VTI variability of greater than 15% indicates that a patient is likely to be fluid responsive and therefore a good candidate for receipt of scarce fluid resources during PFC. We undertake to train 18D medics to obtain carotid VTI and assess their confidence in performing the procedure.

Methods: We propose to teach 18D medics of the 10th Special Forces Group (A), in Fort Carson, Colorado, to obtain carotid VTI variability. The one-day training will have two parts: a one-hour lecture, and a four-hour hands-on component. Trainees will be required to obtain ten VTI variability measurements on multiple standardized patients, using at least two different ultrasound systems (one of them handheld), prior to completion of the hands-on training. We will administer pre- and post-training surveys to assess their confidence in obtaining and applying VTI variability measurements during PFC.

Results: Pending study completion.

Discussion: Carotid VTI variability provides an objective data point to guide fluid resuscitation. During PFC, where fluids are especially scarce, carotid VTI variability has the potential to maximize resource allocation and improve patient care. Our hypothesis is that special mission units medics can rapidly acquire the skill to obtain and apply carotid VTI variability measurements. Further analysis is pending study completion.

Conclusion: Carotid VTI variability may prove to be paramount for resource allocation and patient-centered outcomes during PFC. While further research remains to be done in the field, training medics to perform this procedure is the first step.