Critically ill patients often show signs of low blood flow and are administered IV fluids to increase stroke volume. The described method can help predict when fluid therapy will be ineffective by measuring the response of a stroke volume surrogate to a preload challenge. Knowing when fluids are ineffective can reduce the risk of harm associated with fluid overload like pulmonary edema or kidney injury.
This technique could also help direct diuresis, for example in patients with congestive heart failure chronic kidney disease, pulmonary hypertension or patients who fail to liberate from mechanical ventilation. To begin, position the patient in the semi recumbent or semi Fowler position in the hospital bed or gurney, adjust the bed such that the torso is at an angle of 30 to 45 degrees above the horizontal. Turn on the wearable Doppler ultrasound by pressing the round button in the center of the ultrasound device.
Blue lights around the periphery of the button will flash, signaling that the device is on and ready to pair with a smart device. Turn on the dedicated application on the smart device and press the start button. Observe the list displayed on the application showing the discoverable, wearable ultrasound devices within physical proximity of the smart device.
Match the number affixed to the face of the desired ultrasound device to the indicated device on the application list press connect to pair the ultrasound device to the application. Confirm the ultrasound device is paired by observing the flashing lights around the button in the center of the device. Press correct on the smart device application to complete the pairing.
Apply a small amount of ultrasound gel to the face of the transducer on the back of the ultrasound device. Next, turn on the volume on the smart device application by pressing the volume icon button in the top right corner of the application display. Tap the face of the transducer to ensure the device is live and paired to the smart device application.
With the patient's neck slightly extended note the laryngeal prominence and hold the ultrasound device so that the label is oriented right side up. Place the device on the lateral aspect of the laryngeal prominence, and look for an audio and video response on the device application. The top portion will display a waveform spectrum for the carotid artery and jugular vein.
Slowly slide the ultrasound device laterally slightly by a few millimeters while looking at the dichotic notch on the artery spectrum to ensure that a clear velocity nadir was observed reliably. If the dichotic notch velocity becomes difficult to see repeat this step, but slide the ultrasound device medially. While holding the device in place, observe the carotid doppler spectrum and its features on the top of the application display.
The application will automatically begin tracing the Doppler spectrum once a strong enough signal is obtained, indicated by a white line around the maximum of the waveform. Next, observe the velocity measurements using the scale on the top left hand side of the smart device display. Using the auto trace over the carotid artery maximum ensure that the trace is in a typical range.
Repeat these steps over the contralateral carotid artery to assess the presence of a clearer dichotic notch velocity. After observing the clear dichotic notch velocity on both carotid arteries, select the side of the neck to which the device will adhere. Adhere the device to the chosen carotid artery by visually noting where the best signal is obtained on the neck.
If needed, use a skin marking pen to identify the optimal placement position. Lift the device from the neck and remove the protective backing from the adhesive attached to the ultrasound device. Observe the transducer face on the ultrasound device, if needed, reapply the ultrasound gel to the transducer face.
Remove excess ultrasound gel from the neck that may have remained during signal discovery. As this interferes with the adhesion of the device. Return the device to the identified location on the neck smooth the wings of the adhesive across the neck.
Remove the protective backing from the tips of the adhesive after pulling tight and place the filming against the skin to secure the device to the neck fully. Monitor the carotid and jugular spectra throughout adhesion to ensure the signal is not lost. Clear the smart device application data by pressing restart.
Then press Begin Assessment to obtain the baseline measures for the passive leg raise or PLR with 30 to 60 seconds of resting baseline. The bottom portion of the device application quantifies the corrected flow time or CCFT for each cardiac cycle displayed as green bars. Look for a marker displayed on the bottom portion of the application display to signify the beginning of the assessment.
Then on the smart device screen press Mark Intervention to signify the beginning of the preload challenge. To perform a PLR without touching the patient. Reposition the hospital bed or gurney so that the torso is moved downward to the horizontal and the legs are lifted to 30 to 45 degrees above the horizontal.
Keep the patient in the PLR position for 90 to 120 seconds. Observe the jugular Doppler spectrum during the intervention and assess for changes in the absolute jugular venous velocity and its pattern as a surrogate for the jugular venous pressure. Observe the evolution of the green bars during the intervention and assess for changes in CCFT before and after the start of the preload challenge for each cardiac cycle.
Once the intervention is complete on the smart device screen press End Assessment of the preload challenge. Return the patient to the semi recumbent position. Observe the assessed changes in the CCFT displayed in a yellow box on the lower right side of the application.
If desired, press save to save the assessment and export the data files. In a patient with a normal upright cardiac function curve a small increase in the cardiac preload is accompanied by a relatively large rise in the stroke volume. Change in the venous doppler morphology indicates that the jugular vein has increased in diameter and is beginning to follow the right atrial pressure deflections.
In contrast, an abnormal response during a preload challenge is marked by a venous doppler waveform that evolves as above, but with an arterial response that reveals no significant change or even a decrease in the CCFT as compared to baseline. A preload challenge showing no significant change in the venous doppler waveform represents an inadequate change in the cardiac filling. A rising stroke volume in the arterial signal.
Coupled with a venous doppler morphology suggesting diminished venous pressure. It is important to obtain a strong doppler signal that can be easily traced and quantified and to maintain this strong signal throughout the assessment. This technique can be repeated multiple times over the course of a patient's resuscitation to confirm and help predict the effective preload.
This technique has paved the way for several pilot projects assessing both fluid resuscitation and removal in the acute care setting.
