"The Tortoise and the Hare" fable has been used as a metaphor for the epidemiological differences between slower, low-intensity exercise versus faster, high-intensity physical activity.

"Current physical activity recommendations are predicated on the idea that both the hare and the tortoise can win the race for better health, but the provocative studies give an edge to the hare's higher-intensity approach,"

Regular physical activity is associated with significant health benefits, including decreased risk of cardiovascular disease, cancer, and all-cause mortality.

Traditional research has focused on exercise volume (150 minutes/week) over intensity.

Two recent studies looked at the benefits of shorter bouts of vigorous activity at higher intensities. 

A recent large population-based cohort study of middle-aged adults used objective measurement of activity (wrist accelerometer) over self-reporting to investigate the role of exercise intensity and CV health.

Higher intensity physical activity is associated with lower rates of incident CVD.

This makes theoretical sense as greater stimulation will result in greater physiologic CV adaptations resulting in overall improved CV fitness.

For example. the authors extrapolate that an ambling 14-minute stroll has roughly the same cardiovascular benefits as an up-tempo 7-minute walk at a brisk pace.

Increasing the total amount of activity is not the only means of achieving health goals which can be met with raising overall intensity.

Vigorous physical activity is a time-efficient means to achieve overall health benefits of exercise.

A recent study (Ahmadi et al., 2022) involved 71,893 older adults with a mean age of 62.5. Authors found that quick bursts of vigorous physical activity throughout the day can lower older adults' risk of premature death by 16% to 27%, depending on daily frequency and weekly totals (from 15-20 min/week up to 50-57 min/week).

For example, doing one two-minute burst of high-intensity exercise every day for a total of 14 minutes per week was associated with an approximately 18% lower risk of all-cause mortality. The authors also found that doing as little as one to nine minutes per week of vigorous activity in quick bursts versus doing no vigorous activity was associated with significantly lower all-cause mortality risk over five years.

Exercise may not need to be a planned hour-long session at the gym for our middle-aged and older population. Accruing small amount sporadically over the day/week is an attractive option to reap the CV benefits of exercise. Existing exercise guidelines will need to be modified with future research to pinpoint the optimal exercise intensity and duration for adults in different stages of life.

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Although extubation has historically been the purview of critical care, as ED lengths of stay continue to worsen, and as we see more and more rapidly reversible respiratory failure (e.g. opioid overdose), it is valuable for ED providers to be facile in extubating patients.  In addition, a longstanding debate in critical care has revolved around the proper device to extubate patients to, specifically: regular nasal cannula (NC) vs high flow nasal cannula (HFNC) vs noninvasive positive pressure ventilation (NIPPV).  Although data are mixed, the literature suggests extubation to HFNC or NIPPV may reduce risk of reintubation, esspecially in patients at a high risk of reintubation, but doesn't show a clear difference between HFNC and NIPPV.  

Hernandez et al recently conducted an RCT in two Spanish ICUs looking at HFNC vs NIPPV upon extubation for high risk patients.  NIPPV was associated with a lower reintubation rate (23%) as opposed to HFNC (39%).  Hospital LOS was also shorted in the NIPPV group, but no other differences were observed.  

It should be noted that this study, and pretty much the entirety of this literature base, is in ICU patients.  In fact, in this study, patients were excluded if they were intubated less than 24 hours.  Generally speaking, patients with shorter intubation tend to be lower risk for reintubation and other post-extubation negative outcomes, so I would use caution extrapolating this too much to the ED.  Unfortunately however, there is very limited literature to guide ED extubation practices.  

Bottom Line:

1) Know how to assess readiness for extubation and consider extubation in the ED if they meet  criteria

2) For patients at higher risk of reintubation (older, sicker, CHF, COPD, obesity, airway issues) who you are considering extubating, you may wish to extubate them to Noninvasive Positive Pressure Ventilation, even though there is little solid literature showing best practices in terms of post-extubation respiratory support in the ED.

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In follow-up to last week’s pearl regarding the inequitable distribution of trauma care, there were a few more thoughts:

1.     A huge shout out to those ED physicians working in critical access facilities without surgical back up, access to specialists, and who are regularly struggling to get their patients transferred to trauma centers to receive the care they need.

2.     All centers, big and small, are struggling with crowding, staffing, and patient flow. It is critical to the entire system that these issues get addressed. They need to be addressed at a system level by all stake holders. Smaller EDs, critical access EDs, or Level 2 and 3 centers holding patients that need to be transferred has a deleterious effect not only on that individual patient, but the patients that can’t be seen while the most critically ill are being attended to.

3.     Hospital administrators, medical directors, national organizations, department leaders, and each of us in the trenches owe it to our communities and patients to get involved in fixing the problems. These issues are best addressed by a meeting of stake holders than by an overwhelmed ED provider at 2 am desperately trying to do the right thing for their patient.

4.     The best systems have:

a.     ongoing education for EMS providers, hospital providers, nurses and the general public,

b.     pre-hospital protocols regarding trauma patients,

c.      a timely means to get patients to the correct facility,

d.     injury prevention programs,

e.     post-acute care rehabilitation services, and

f.      family support services in place.

5.     Those with well-functioning systems, please publish your results and the steps you have taken to become well-functioning. We need leadership. We do not need to reinvent the wheel. Please take an active role in lifting the less functional systems to your level.

6.     Those that are struggling, ask for help! Also publish your efforts, your struggles, and your needs.

For those interested in a deeper dive into where we have come from and the concept of trauma systems, please read the attached reference. This is a call to all that care for the critically ill to work to improve our stressed system, publish your work so we ca all learn and to advocate and lobby for your patients.

This pearl's author is open to comments, criticism, concerns and questions. 

Back to clinical pearls next week.

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Childhood vaccination has significantly decreased the incidence of bacterial meningitis and bacteremia in infants and young children, specifically vaccines against H. influenzae and S. pneumoniae, shifting broad workups for these disease and empiric antibiosis to younger age groups as rates declined. In recent years the percentage of unvaccinated and under-vaccinated children has been rising due to multiple factors; now over 1% of children in the US under 2 years of age are unvaccinated. The question becomes, should these children be treated more similarly to young infants as they lack to immunity to these organisms?

Literature on this topic is sparse, although, Finkel, Ospina-Jimenez, et al. reviewed the literature available and proposed an algorithm for well appearing children 3-24 months of age without a clear source and a temperature of >39C (102.2F). Recommendations included UA (to determine possible source) in the following patients: fever > 2 days, prior UTI, female or uncircumcised male <12 months, or male <6 months. They also recommended evaluation with viral panel. If no source was determined, they then recommended CBC and procalcitonin with a CXR for WBC > 20,000/mm³. For WBC >15,000/mm³, ANC >10,000/mm³, absolute band count >1,500/mm³, or procalcitonin >0.5ng/mL they recommended blood culture, ceftriaxone 50 mg/kg, and follow up within 24 hours.

Bottom line: Literature is scarce and practice patterns are likely to evolve as ramifications of decrease in vaccination rates become clearer. The above algorithm is proposed, however covers limited situations and may not be practical in all settings. Clinical judgement should be used in the evaluation and management of these patients. A more conservative approach compared to vaccinated infants is reasonable at this time.

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Transcutaneous Cardiac Pacing

• Transcutaneous cardiac pacing (TCP) is often attempted while preparing for transvenous cardiac pacing in critically ill patients with symptomatic bradycardia unresponsive to medical therapy.
• For TCP, pacer pads can be placed in either the anterolateral (AL) or anteroposterior (AP) positions.  
• Current resuscitation guidelines from the American Heart Association and the European Resuscitation Council do not identify a preferred pacer pad placement for TCP.
• In a recent study of patients who received TCP following cardioversion from atrial fibrillation or flutter, Moayedi and colleagues found that pacer pads placed in the AP position required less mA to capture and chest wall contractions were less severe when compared to the AL position.
• In fact, capture was approximately 80% more likely with pacer pads placed in the AP position compared to the AL position.
• Take Home Point: Consider placing the pacer pads in the AP position the next time you need to initiate TCP.

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Approximately 1.4 million transgender and gender nonbinary patients live in the United States. Unfortunately, prior research has shown negative experiences with the health system are common after disclosing their trans/NB status. As a result, almost a ¼ report avoiding or delaying needed health care.

This qualitative study interviewed a subset of trans/NB individuals about their experiences visiting emergency departments. Several key themes emerged:

• ED intake forms are commonly unequipped to reflect patients’ pronouns and chosen names. This leads to downstream misgendering and the use of deadnames.
• Patients often fielded inappropriate questions and comments unrelated to their medical care
• Many patients felt they had to educate clinicians regarding issues of trans health, rather than the other way around
•  These negative experiences decreased the likelihood patients would return for needed medical care

Overall, the study found that clinicians have many opportunities to improve the care of transgender and nonbinary patients, including updating forms, using inclusive language, avoiding medically unnecessary questions, and providing training for staff on trans/NB health.

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This study found that 22% of Americans do not have access to a trauma center within 60 minutes. Eight percent of the population relied on Level III centers.  Not unexpectantly, Black and Native Americans were overly represented in the group receiveing care at Level III centers. White and Native Americans were over represented in the group without access to trauma care within 60 minutes. Most disappointing of all, none of this has changed since 2010. Some states have a robust trauma network, while others need to evaluate their needs and potentially add Level III centers to cut down the time to trauma care.  What is your area's trauma coverage and what level?

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Dog ownership has become more common especially during the pandemic.

Almost 70% of US households own a pet and almost half own ≥1 dogs.

There are many health benefits associated with dog ownership including: reduced risk of asthma and allergic rhinitis in children exposed to pets during early ages, improvement in symptoms of PTSD, overall wellbeing & alleviation of social isolation in elderly individuals and increased physical activity.

The main positive impact of dog ownership seems to be in relation to cardiovascular risk including an association with lower blood pressure levels, improved lipid profile, and diminished sympathetic responses to stress.

Study:  A systematic review and meta-analysis (10 studies, over 3 million participants) to evaluate the association of dog ownership with all-cause mortality, with and without prior cardiovascular disease, and cardiovascular mortality. Mean follow up 10 years.

Results: Dog ownership was associated with a 24% risk reduction for all-cause mortality as compared to non-ownership (relative risk, 0.76; 95% CI, 0.67–0.86) with 6 studies demonstrating significant reduction in the risk of death.

In individuals with prior coronary events, dog ownership was associated with an even more pronounced risk reduction for all-cause mortality (relative risk, 0.35; 95% CI, 0.17–0.69). When authors restricted the analyses to studies evaluating cardiovascular mortality, dog ownership conferred a 31% risk reduction for cardiovascular death (relative risk, 0.69; 95% CI, 0.67–0.71).

The cause of this benefit is unclear. Though some activities such as the act of petting a dog has been observed to lower blood pressure levels, the mechanism for the longer survival is likely through enhanced physical activity provided by dog walking.

Conclusion:  Dog ownership is associated with reduced all-cause mortality likely driven by a reduction in cardiovascular mortality. Dog ownership as a lifestyle intervention may offer significant health benefits, particularly in populations at high-risk for cardiovascular death.

Finally, meet Winston, a French bulldog who, last night, won the National Dog Show!

https://static.onecms.io/wp-content/uploads/sites/47/2022/11/22/national-dog-show-winner-french-bulldog-winston-2022-2000.jpg

This small study looked at patients with penetrating neck injuries and tried to determine in those with "hard signs" of injury (hemorrhage, expanding hematoma, or ischemia)  if they required immediate operative managment.  The authors concluded:

"Although hard signs in PCVIs are associated with the need for operative intervention, initial CT imaging can facilitate endovascular options or nonoperative management in a significant subgroup. Hard signs should not be considered an absolute indication for immediate surgical exploration."

This is a small study and it is unclear why some patients went to CT vs directly to the operating room. This may not be a practice changing study, but it may validate provider gestalt of CT vs direct to operating room. We can add this to the growing body of evidence that CT scanning in penetrating trauma can be used to diffrentiate who needs emergent operative intervention vs. endovascular therapy vs close observation. This study certainly opens the door for further reaserch in the area of management of penetratign neck injuries. 

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This was a cross-sectional survey for the Diversity-Related Research Committee of the Women in Critical Care (WICC) Interest Group of the American Thoracic Society.

Settings: 62 sites in Canada and the US

Participants: Attending physicians who worked in ICUs

Questionaire:

·         Measure of Moral Distress for healthcare professionals (27 items),

·         Maslach burnout inventory (2 items),

·         Stanford Professional Fulfilment Index (14-items), Brief Cope scale (14-items)

Study Results:

1.       Demographics:

·         431 participants (approximately 43.3% response rate).

·         334 (65%) participants worked at University-affiliated hospitals

·         387 (89.0%) worked in Adult ICUs.

·         Pre-pandemic, clinical days/months was 10.1 (± 14) days, and increased to 13.1 (± 16) days during the pandemic.

2.       Measure of moral distress: Average score 95.6 ± 66.9 (maximum 417).

·         The highest score (mean 8.5 ± 4.8), for distress, came from the item: “Follow the family insistence to continue aggressive treatment even though it is not in the best interest of the patient.” ((Family wanted to do everything).

3.       Stanford Fulfillment Index:

·         387 (91.9%) intensivists found their work meaningful and 365 (86.5%) felt worthwhile at work, although most felt physically (297, 71.6%), emotionally (266 [63.8%]) exhausted.

4.       Coping strategies:

·         Participants resorted to a wide variety of scoping strategies ranging from Acceptance (90%), Self-distraction (85%) to Substance abuse (32%) and Denial (18%).

·         Most physicians (231 [55.9%]) reported that their coping remained the same before and during the pandemic.

Discussion:

·         Physicians are quite resilient. The authors found that physicians who worked more days experienced significantly more moral distress but with similar Stanford Professional Fulfillment score.

·         This finding was similar to an exploratory analysis from a meta-analysis that showed physicians, among other healthcare workers, were less likely to have severe symptoms of PTSD (2).

·         Women and physicians who were persons of color experienced significantly higher moral distress and burn-out.

Conclusion:

There was moderate moral distress and burn-out, although physicians who worked in ICUs still achieved moderate professional fulfillment.  Up to 20% of ICU physicians used a maladaptive coping strategy

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Opioids & NSAIDs for MSK pain in the ED:  Effectiveness and Harms

Study selection:  A recent systematic review in Annals of Internal Medicine attempted to evaluate the effectiveness and harms of opioids for musculoskeletal pain in the emergency department.

Included were RCTs of any opioid analgesic as compared with placebo or a nonopioid analgesic.

Conditions studied:  bone injuries, soft tissue injuries, spinal pain, and mixed presentations.

Out of 2464 articles, they included 42 trials (n=6128).

Effectiveness data:  Opioids were statistically but not clinically more effective in reducing pain in the short term (approximately 2 hours) versus placebo and Tylenol but were not clinically or statistically more effective than NSAIDs.

Take home: Opioids and NSAIDs may have about the same pain outcomes.

Harm data:  The results on harms were very mixed. Overall, there were fewer harms with NSAIDs than opioids. However, many studies showed less of a difference. The benefit with NSAIDs due to fewer harms may be less in patients with mixed musculoskeletal conditions.

Opioids may carry higher risk for harms than placebo, Tylenol, or NSAIDs. Authors also found that an increased opioid dose may increase harms from opioids.

Limitations: Limited data on long-term outcomes and longer-term pain management

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DOSE VF (DOuble SEquential External Defibrillation for Refractory VF) Trial 

Background - High quality data regarding the use of double sequential external defibrillation (DSED) and vector-change (VC) defibrillation in refractory vfib is limited

Study

-Three-group, cluster-randomized, controlled trial in six Canadian paramedic services

-Study population: 

-OHCA with refractory vfib (initial presenting rhythm of vfib or pulseless VT that was still present after three consecutive rhythm analyses and standard defibrillations separated by 2 minute intervals of CPR) of presumed cardiac etiology (405 patients)

-Some notable exclusion criteria: 

-suspected drug overdose, hypothermia, traumatic cardiac arrest

-Protocol:

-First 3 defib attempts in the standard (anterior-lateral) position

-If remained in vfib after three consecutive shocks randomized to one of:

1. Standard defib for all subsequent attempts (136 pts)

2. VC defib (all subsequent attempts in anterior-posterior position) (144 pts)

3. DSED (applied second set of pads in AP position) with near simultaneously (<1 sec) defib shocks (125 pts)

Results

-Primary outcome: survival to hospital discharge

-38 patients (30.4%) in the DSED group vs. 18 (13.3%) in the standard group (RR 2.21; 95% CI, 1.33 to 3.67) (Fragility index of 9)

-31 patients (21.7%)  in the VC group (RR [vs. standard], 1.71; 95% CI, 1.01 to 2.88) (Fragility index of 1)

-Notable secondary outcome: survival with a good neurologic outcome

-34 patients (27.4%) who received DSED vs. 15 patients (11.2%)  with standard defibrillation (RR, 2.21; 95% CI, 1.26 to 3.88)

Takeaways/Caveats:

-68% of arrests witnessed, 58% received bystander CPR, median response time of 7.4-7.8 min

-Did not reach planned sample size 2/2 COVID pandemic

-No reporting of post-arrest care (e.g. TTM, PCI)

-Overall rates of survival and good neuro outcome on the higher side even with standard of care

-More/larger studies needed, but can consider DSED for refractory vfib, particularly if you are in a setting without more advanced circulatory support/resources

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IPV can occur once or over years by a current or former romantic partner.  Types of IPV include: Physical and/or Sexual violence, Stalking, and Psychological/Financial aggression (the use of verbal and non-verbal communication to harm mentally or emotionally and to exert control over another partner). 

IPV is more prevalent that Aortic Dissection and Pulmonary Embolism combined.   Think about how risky it is to NOT recognize IPV.

1:4 women and 1:10 men have been victims of IPV during their lifetime.

1:5 homicide victims are killed by an intimate partner.

Over 50% of female homicide victims are killed by a current or former intimate partner.  Patients who have been strangled are 4 times more likely to be killed within a year.

Your Spidey Sense should go off when:

1. Stories Change
2. History doesn’t match up with injuries
3. Injuries in areas that are concealed, multiple injuries of varying ages, defensive wounds
4. Major delays in seeking care
5. Non-specific complaints - headache, gastric issues
6. Multiple ED visits at odd hours
7. Refusing the use of an interpreter by partner (why we always use an official interpreter)

Once patient is identified as a victim:

1. Place victim in a safe, inaccessible by visitors, and hidden area
2. Treat all medical issues
3. Contact Social Work/SAFE/SANE examiner (some institutions will have IPV specific resources)
4. Contact police if patient is willing to report
5. Safe disposition
6. If unable to ensure a safe disposition, be very careful about documentation provided in discharge paperwork and language used

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Sugammadex works by chelating non-depolarizing neuromuscular blocking agents (NMBA) such as rocuronium and vecuronium to reverse the effects of paralysis.  Dosing per package insert varies based on time from administration of the NMBA, and side effects, although rare, include severe bradycardia, hypotension, and asystole. While sugammadex is routinely used by our anesthesia colleagues, it is rarely utilized in the emergency department (ED) or intensive care unit (ICU) setting. 

A recent single-center study assessed 11 patients with either a traumatic brain injury (TBI) or intracranial hemorrhage (ICH) who received sugammadex for neurologic assessment in the ED or ICU.  The median dose was 240mg and the median time since last NMBA administration was 101 minutes.

In 6/11 patients, the neurosurgical plan changed and it affirmed a poor prognosis in 3/11 patients. In the ICU patients, sugammadex was associated with reduction in unnecessary tests.

All patients had a GCS of 3T prior to administration and 67% responded to sugammadex with a median increase to 8T (P=0.0156).  MAP reductions were common with a median of -8 mmHg.

Bottom Line:  Sugammadex can assist in determining a neurosurgical or clinical prognosis plan in patients with TBI and ICH.  Larger studies are needed in this patient population and caution should be used inpatients who are already hypotensive or bradycardic.  A reasonable dose, especially when given >1h from intubation would be 200mg.  The team should be available at administration to note changes in GCS.

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This retrospective study compared plain radiographs to CT scan for the detection of pelvic fractures in patients over 65 years of age. The authors concluded “Pelvic radiographs have low sensitivity in detecting traumatic pelvic fractures. These radiographically occult fractures may be clinically significant as a cause of long-term pain and may require orthopedic consultation and possible surgical management.”

If you have a high clinical suspicion due to pain or inability to ambulate, CT may be warranted if the X-Ray is negative. 

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Subcutaneous Fluid Administration for Rehydration

• An old school technique (described in the 1800’s) that fell out of favor but still has applicability - primarily in pediatrics although it has been explored for use in geriatrics and mass casualty events (due to ease and speed of use)
• Most appropriate for stable but mildly to moderately dehydrated patients who need rehydration, are not tolerating PO, and in whom an PIV is difficult to establish (this should not replace an IO in a critically ill child)
• Either a small gauge angiocath or butterfly can be used for access
• Most common area to access in younger children is between the shoulder blades, although the lateral abdomen, thighs, or outer upper arms can be used as well; the site must have adequate subcutaneous tissue (can test by pinching between the fingers)
• Subcutaneous catheter placement is generally quite easy, however care should be taken with securing the catheter as there will be expected swelling at the area which can cause dislodgement or discomfort
• Mild erythema may also occur at the site of administration
• Injection of hyaluronidase (150 U) at the site being used increases the volume that can be administered as well as speed of absorption (hospitals may carry this product for treatment of severe PIV infiltration events)
• It is not necessary to have hyaluronidase to utilize subcutaneous fluid administration, but improves efficiency and efficacy
• Fluids administered should be isotonic and can be administered at 20 mL/kg over an hour – this can be repeated as necessary

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Airway Pressure Release Ventilation (APRV) is an "advanced" mode of mechanical ventilation that has long been considered a "rescue" mode of ventilation and has recently garnered much more attention during the COVID pandemic.  Given the long boarding times of critical care patients in the ED with widespread improvement in sight, I wanted to send out some great resources that have come out recently delineating the difference in thought process between APRV as a "rescue" mode and as a "primary" mode.

Rory Spiegel of EMNerd and former UMMC CCM fellow has recently given a great talk on APRV and its use as a rescue mode of ventilation. See also Phil Rola's recent paper listed on that webpage.

https://emcrit.org/emcrit/aprv-for-lung-rescue/

APRV as a primary mode of ventilation has been used in the STC for years and is often referred to in the literature according to the basic ventilatory philsophy called Time Controlled Adaptive Ventilation. I realize this may be heresy to some and perhaps a curiousity to others. I recommend you take some time to peruse the following resources:

1. Dr. Habashi has done a great deal of work in the basic and translation literature on APRV and TCAV. His recent review dispels many myths and concerns surrounding APRV

Myths and Misconceptions of Airway Pressure Release Ventilation: Getting Past the Noise and on to the Signal - https://www.frontiersin.org/articles/10.3389/fphys.2022.928562/full

2. The TCAV Network has great resources for those who want to do a deeper dive into this topic. 

https://www.tcavnetwork.org/

(Can also find their recommended protocols at the Multi Trauma Critical Care education website: https://stcmtcc.com/handouts/)

Attachments

fphys-13-928562_(2).pdf (5,575 Kb)

Standard_Settings_for_APRV_using_the_TCAV_Method.pdf (1,525 Kb)

APRV_TCAV_Rescue_Strategy_Strategy_Guidelines_2020.pdf (1,614 Kb)

Traditional trauma teaching is to admit trauma patients with abdominal wall ecchymosis caused by seat belts (seat belt sign) for fear of missing a hollow viscus injury leading to peritonitis and sepsis.  

Over the past few years there have been studies pointing toward the safety of discharging blunt abdominal trauma patients with a negative CT even if they do have a seat belt sign.

In this most recent study, a negative CT was defined as 

1. No free fluid (free fluid was the leading indicator of occult hollow viscus injury)

2. No solid organ injury

3. No bowel wall irregular contours, thickening, hematoma or air

4. No abdominal wall soft tissue contusion

5. No mesenteric stranding or hematoma

6. No bowel dilatation

If the patient’s CT did not include any of these findings, there was a 0.01% chance of finding a delayed hollow viscus injury. The authors conclude it is safe to discharge patients meeting these criteria. 

If we include no rebound or guarding on physical exam along with a negative CT scan, it appears to be safe to discharge trauma patient’s with seat belt sign.

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Takeaways

Arterial line waveform interpretation and troubleshooting are essential skills for any physician caring for critically ill patients. Overdamping and underdamping of the arterial line waveform leads to inaccurate systolic and diastolic blood pressure readings which can lead to unidentified hypertension or hypotension. In addition to scrutiny of the arterial waveform pattern, the square-wave test is a tool to identify overdamped or underdamped arterial lines. 

Overdamped arterial waveforms will underestimate systolic blood pressure and overestimate diastolic blood pressure. Underdamping will have the opposite effect and overestimate systolic blood pressure and underestimate diastolic blood pressure. In both cases, the mean arterial pressure (MAP) often remains the same.  

The square-wave test is a rapid flush that is applied to the arterial line for approximately 1 second. This rapid high-pressure surge results in vibration and oscillation of the arterial catheter. These oscillations are then read by the pressure transducer and the number and amplitude of these oscillations can be measured. 0 or 1 oscillations is suggestive of overdamping. 3 or more oscillations is suggestive of an underdamped system. 

Major causes of an overdamped arterial line waveform include low infusion bag pressure, loose connectors, air bubbles in the tubing, blood clot in the circuit, or kinking of vascular catheter. An underdamped arterial line, however, is caused by overly stiff circuit tubing or a defective transducer.   

Scrutiny of the arterial waveform and utilization of the square-wave test can be helpful to both identify erroneous arterial line blood pressure readings as well as suggest likely corrective measures.  

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Attachments

Arterial_line_overdamped_and_underdamped_examples.jpg (112 Kb)