All posts by The Trauma Pro

Equipment

The Lowly Blood Pressure Cuff: Is It Accurate?

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Yesterday, I described how the typical automated oscillometric blood pressure cuff works. We rely on this workhorse piece of equipment for nearly all pressure determinations outside of the intensive care unit. So the obvious question is, “is it accurate?”

Interestingly, there are not very many good papers that have ever looked at this! However, this simple question was addressed by a group at Harvard back in 2013. This study utilized an extensive ICU database from 7 ICUs at the Beth Israel Deaconess Medical Center. Seven years of data were analyzed, including minute by minute blood pressure readings in patients with both automated cuffs and indwelling arterial lines. Arterial line pressures were considered to be the “gold standard.”

Here are the factoids:

  • Over 27,000 pairs of simultaneously recorded cuff and arterial line measurements from 852 patients were analyzed
  • The cuff underestimated art line SBP for pressures at or above 95 torr
  • The cuff overestimated SBO for pressures below 95 torr (!)
  • Patients in profound shock (SBP < 60) had a cuff reading 10 torr higher
  • Mean arterial pressure was reasonably accurate in hypotensive patients

sbp-cuff-v-aline

Bottom line: The good, old-fashioned automated blood pressure cuff is fine for patients with normal pressures or better. In fact, it tends to understimate the SBP the higher it is, which is fine. However, it overestimates the SBP in hypotensive patients. This can be dangerous! 

You may look at that SBP of 90 and say to yourself, “that’s not too bad.” But really it might be 80. Would that change your mind? Don’t get suckered into thinking that this mainstay of medical care is perfect! And consider peeking at the mean arterial pressure from time to time. That may give you a more accurate picture of where the patient really is from a pressure standpoint.

Reference: Methods of blood pressure measurement in the ICU. Crit Care Med Journal, 41(1): 34-40, 2013.

 

Equipment

How Does It Work? The Lowly Blood Pressure Cuff

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The blood pressure cuff is one of those devices trauma professionals don’t give a second thought to. Old timers like me remember using the cuff with a sphygmomanometer and stethoscope to get manual blood pressures. I’ve had to do this twice in recent months on airplanes, and I had forgotten how much work this is.

But technology makes things easier for us. Now you just slap a cuff on the arm (or wrist), push a button, and voila! You’ve got the pressure.

But have you stopped to think about how this actually works? Why don’t we need the stethoscope any more? Here’s the scoop:

When you take a manual blood pressure, the cuff is inflated until a pulse can no longer be auscultated with the stethoscope. The pressure is slowly released using a little thumb wheel while listening for the pulse again. The pressure at which it is first audible is the systolic, and the pressure at which it softens and fades away is the diastolic.

The automatic blood pressure device consists of a cuff, tubing that connects it to the monitor, a pressure transducer in line with the tubing, a mini air pump, and a small computer. The transducer replaces the analog pressure gauge, and the pump and computer replace the human.

The transducer can “see” through the tubing and into the cuff. It is very sensitive to pressure and pressure changes. The computer directs the pump to inflate to about 20 torr above the point where pulsations in the air column cease. It then releases the pressure at about 4 torr per second, “feeling” for air column vibrations to start. When this occurs, the systolic pressure is recorded. Deflation continues until the vibrations stop, representing the diastolic pressure. Each manufacturer uses its own algorithm for this, adding or subtracting a few torr to obtain the most accurate reading for their particular device.

bpcuff

Piece of cake! But here’s the question: is it accurate? In my next post, I’ll write about how the automated cuff compares to an indwelling arterial line.

Abstracts

Best Of EAST 2024 #9: The Burden Of Transferred TBI Patients

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In theory, tiered trauma centers should allow patients with lesser injuries to be treated at lower levels and more severe trauma at higher-level centers. This parallels the resource availability at those centers. In reality, many patients with injuries that seem complex (solid organ, children, and TBI) are transferred due to a “lack of comfort” in taking care of them or the perception that they may deteriorate quickly.

The truth is that many, if not most, of these patients are discharged shortly after transfer to the higher-level center, with minimal intervention. This burdens the trauma system in several ways. First, trauma professionals at the lower-level centers slowly lose their skills and comfort in taking care of these patients. The prehospital system is already plagued with low resources and a shortage of personnel. Using one of the only ambulances in a rural area for transport to a distant center takes it out of the community, potentially putting the area population at risk for delayed care.

The University of Arizona at Tucson group performed another TQIP study to highlight this problem. They performed a four-year retrospective analysis of transfer data in patients with isolated TBI with intracranial hemorrhage. They observed the number of transferred patients who required CT scans, ICP monitoring or craniotomy/craniectomy, length of stay, and mortality.

Here are the factoids:

  • Of the nearly 120,000 patients with isolated TBI at Level I and II centers, 45% were transferred from other centers
  • Most patients had GCS 14-15 on arrival, but 10% had GCS 8
  • CT was performed in 58%, and another repeat CT in 4%
  • Four percent underwent ICP monitoring, and 12.5% had a crani
  • Mortality was 6.5%
  • Median length of stay was two days, with a range of 1-5
  • 18% were discharged within 24 hours, and 39% within 48 hours

The authors concluded that, while half of isolated TBI patients were treated at high-level trauma centers, one-third were discharged home within 48 hours with no intervention other than a CT scan. They recommend systemwide guidelines to improve resource utilization.

Bottom line: This straightforward analysis highlights one of the most significant issues facing trauma systems: unnecessary transfer. For decades, Level I and II centers were convenient and always available for transfer, even if the indications were questionable. Then COVID came along and changed everything.

Now, resources are tight everywhere. EMS is underpaid and under-reimbursed, and personnel are difficult to recruit. Hospital personnel of all types face low staffing levels, making it more stressful to provide the level of care we are accustomed to. Skilled nursing facilities, rehab centers, and other outpatient care settings face the same problems.

This has created a domino effect, where the lower-level centers want to transfer a patient but can’t find a bed at the higher-level centers. When they do, it takes forever to get them transported. Then, the higher-level centers can’t discharge them if they need any level of care other than home care.

There are many pieces to this puzzle, but this abstract clearly outlines one of them. Lower-level centers are transferring some patients who could actually be admitted to them. Several reasons may be given, but it typically boils down to the surgeons or the hospitalists not being “comfortable” with certain patients or worrying that they could deteriorate.

This paper does not tease out what kind of isolated TBI the patients had, and I recommend they do. There is a big difference in patients with a subarachnoid hemorrhage (SAH) vs. those with an epidural. The number of patients with SAH is far greater, and the vast majority can go home after a brief (or no) observation. The likelihood of deterioration in patients not on blood thinners is nearly zero. 

State trauma systems and higher-level trauma centers should work with their Level III and IV partners to adopt consistent practice guidelines and protocols to stratify these patients to identify those at low risk. The higher-level centers should provide education to help their referral partners develop a baseline comfort level with these patients. This is the only way we can begin to realign the levels of trauma centers with the levels of care needed by our patients.

Reference: Endless highways: the burden of transferred traumatic brain injury patients in the United States. EAST 2024, Podium paper #42.

Abstracts

Best Of EAST 2024 #8: Whole Blood And VTE

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The pendulum has swung from the use of whole blood in the early 20th century, to component therapy in the 1960s, and now a gradual move toward incorporating whole blood again. More and more papers are being published, and many trauma centers are looking for ways to integrate whole blood into their massive transfusion protocols.

Much of the literature has been dedicated to safety and effectiveness, but little has examined thrombotic complications from its use.  The trauma group at the University of Texas in Houston performed what looks to be a retrospective review of whole blood usage at two Level I trauma centers. Adult patients receiving at least one emergency-release whole blood unit were compared with those receiving only component therapy. They looked at the incidence of venous thromboembolic (VTE) complications such as pulmonary embolism (PE) or deep venous thrombosis (DVT).

Here are the factoids:

  • Nearly 3,500 patients were enrolled and were fairly evenly split between whole blood and component therapy only
  • Whole blood patients were slightly younger, were much more likely to have penetrating injury, and had significantly higher ISS (26 vs 19)
  • The whole blood patients were also significantly more likely to receive TXA, VTE chemoprophylaxis within 48 hours (86% vs. 79%) and lower 30-day survival (74% vs 84%)
  • Crude incidence of VTE was similar (7% whole blood vs. 9% component), but logistic regression “revealed that whole blood was protective of VTE,” while red cell transfusion and TXA increased VTE risk
  • Each unit of red cells increased VTE risk by 3%

The authors concluded that whole blood was associated with a 30% reduction in VTE, and TX was associated with a 2.5x increase in risk. They cautioned against the use of TXA in the setting of whole-blood resuscitation.

Bottom line: A lot is going on here. First, this is a retrospective study, which limits the number of variables that can be collected reliably. It also makes it much more difficult to perform regression analysis because there are many other possible variables to control for than just the ones collected. 

Next, as quoted in bullet point 4 above, this study can’t show that whole blood was protective, only that it was (maybe) associated with decreased VTE when the variables they collected were controlled. 

Most of the confidence intervals for the “significant” results were very close to the 1.0 line. This leaves the possibility that the result could easily be changed by adding other pertinent variables not included in the data. The only impressive one was the association of TXA exposure and VTE. I think this demands further work.

The authors need to answer several questions in their presentation to help explain the results:

  • Was there any relationship between the number of units of packed cells given and the likelihood of VTE?
  • Similarly, was there a relationship between the number of units of whole blood and possible “protection” from VTE?
  • Did you examine other physiologic or anatomic variables and their relationship with VTE? Specific ones that come to mind are shock, long bone or spine fractures, and TBI. These are some of the variables that need to be included in the regression model to improve it.

Overall, this is an interesting abstract that makes one think. But it either needs some good explanations during the presentation or additional data analysis to make it even more interesting.

Reference: Does whole blood resuscitation increase risk for venous thromboembolism in trauma patients? A comparison of component therapy vs whole blood in 3468 patients. EAST 2024, Podium paper 33.

Abstracts

Best Of EAST #7: King vs. I-Gel Supraglottic Airways

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Airway assessment and protection are of paramount importance during trauma care. Airway management is even more challenging in the prehospital environment, where lighting and patient positioning may be suboptimal, and injuries or policies may prohibit orotracheal intubation. A variety of devices have been developed to make airway control simpler and faster.

Both the King and i-gel airways were introduced around 2005. The former functions as an extraglottic airway, and the latter as a supraglottic one. Prehospital providers typically use these devices for airway control across the US. They are both designed for blind insertion without the need for other equipment, such as a laryngoscope.

The group at West Virginia University compared these two devices based on the incidence of hypoxia, cardiac arrest, successful insertion, and survival to hospital discharge. They performed a large database search and attempted to control for patient age, weight, pre-airway hypoxia, and the use of suction.

Here are the factoids:

  • A total of 1,557 patients were studied; one-third received a King airway, and two-thirds had i-gel insertion
  • Half of all patients experienced hypoxia, and a quarter experienced severe hypoxia (saturation < 80%) after insertion of any tube
  • But i-gel placement was not associated with hypoxia, severe hypoxia, cardiac arrest, or decreased survival to discharge, and had better success on first-pass placement

Bottom line: What? This is a first. I honestly can’t figure this abstract out. The two bullets in red above cancel each other out. If half of all patients had hypoxic episodes, and only one-third had King airways, that means that at least 16% of the i-gel patients experienced hypoxia. I can’t reconcile that with the last bullet, where i-gel was not associated with any adverse events.

Several other papers have compared the use of these two devices over the last two decades. Most suggest that the i-gel is simpler, with fewer misplacements and other complications, and tends to be preferred by prehospital personnel.

Unfortunately, I have to disregard this entire abstract due to the conflicting data listed. Perhaps the presenter will clarify or provide some corrections to the data. Otherwise, I have not learned anything from it, and it doesn’t appear to add anything new to the trauma literature.

Reference: A retrospective comparison of the King laryngeal tube and i-gel supraglottic airway devices for injured patients. EAST 2024 Podium paper #27.