A rapid assessment tool can be critical in evaluating a patient for shock when their personal history and a physical examination is inconclusive. The Tuesday morning session A Systematic Approach to Undifferentiated Shock: From POCUS to PACs! provided an overview of the available tools for determining the etiology of shock and their real-world usage.
“Waiting until you have frank manifestation of shock is a really difficult thing to salvage,” said Max Hockstein, MD, MS, Assistant Professor of Clinical Emergency Medicine at Georgetown University School of Medicine and MedStar Washington Hospital Center. Once irreversible organ damage sets in, ultrasound, pulmonary artery catheter (PAC), or other diagnostic modalities cannot undo the damage, he said.
Dr. Hockstein discussed the spectrum of invasive methods for phenotyping shock, including the arterial catheter, central venous catheter, transpulmonary thermodilution, and PAC.
There have been three generations of PAC devices, he explained. The first provided a thermodilution signal. The second provided relatively continuous cardiac output monitoring. The third generation integrates pulse wave analysis and inference regarding cardiac output.
Ultimately, he said, there must be a bidirectional relationship facilitated by the use of PAC and other invasive devices.
“You have to be able to do something for the patient, and they have to be able to provide you with actionable information,” Dr. Hockstein said. “Otherwise, that device inside the patient’s body is probably there for the wrong reason.”
If a patient has good cardiac output, for example, a device measuring cardiac output may not be needed. But each patient is different, and the assessment tool and the length of its use will vary from patient to patient.
“Your screen is a treasure trove of information,” Dr. Hockstein said. “Whether it is your arterial line that can give you a heart rate or a MAP [mean arterial pressure] or a dP/dt [derivative of pressure over time], whether it is a PAC where you can derive your pulmonary artery versatility index, whatever it is, squeeze all information that you can out of the screen, because waveforms and numbers are a treasure trove of information.”
Regardless of the diagnostic device that is used, care teams need to have a defined plan of action—beyond monitoring blood pressure and lactate—to determine whether a patient is experiencing shock, said Matthew Siuba, DO, MS, Assistant Professor of Medicine in the Department of Critical Care Medicine, Respiratory Institute, Cleveland Clinic.
“I don’t want to guess about the cause of shock,” Dr. Siuba said.
Siddharth Dugar, MBBS, FCCP, Assistant Professor of Medicine and Director for Point-of-Care Ultrasound, Cleveland Clinic, gave an overview of minimally invasive cardiac output monitors to diagnose shock, including the finger cuff plethysmograph, bioreactance/bioimpedance, and pulse contour analysis.
“If we know the filling pressures and the cardiac output, we can differentiate obstructive cardiogenic shock from distributive shock,” Dr. Dugar said. “Hence, most of the monitoring devices are targeting to find us what the cardiac output or cardiac index of the patient is.”
He said these noninvasive devices are most useful in assessing fluid responsiveness.
“Use them, resuscitate the patient, and if the patient is still not improving, maybe a more invasive device is needed,” Dr. Dugar said.
Casey Cable, MD, MSc, FCCP, Assistant Professor, Virginia Commonwealth University School of Medicine, highlighted the potential of noninvasive point-of-care ultrasound (POCUS) in the diagnosis of shock.
“Cortical ultrasound is amazing. It’s easily accessible. Typically, it’s at the bedside. It’s noninvasive and relatively inexpensive,” she said. “So, it’s a great tool that we can utilize to differentiate shock, to figure out what’s going on with patients.”
POCUS isn’t without downsides. Its value is dependent, in part, on the expertise of the person conducting the imaging. It also is most effective with patients who were previously healthy and have only one type of shock, Dr. Cable noted. Still, research has shown diagnostic accuracy for patients with undifferentiated shock improved from 60.6% to 85% with the use of structured POCUS, affecting initial management in 24% to 50% of patients, she said.