Emergency Medical Minute

Contributor: Aaron Lessen MD

Educational Pearls:

What is Carbamazepine (Tegretol)?

• Carbamazepine is an anti-epileptic drug with mood-stabilizing properties that is used to treat bipolar disorder, epilepsy, and neuropathic pain.
• It functions primarily by blocking sodium channels which can prevent repetitive action potential firing.

What are the symptoms of an overdose?

• Common initial signs include diminished conscious state, nystagmus, ataxia, hyperreflexia, CNS depression, dystonia, and tachycardia
• Severe toxicity can cause seizures, respiratory depression, decreased myocardial contractility, pulmonary edema, hypotension, and dysrhythmias.

How is an overdose treated?

• An overdose is treated with large doses of activated charcoal and correction of electrolyte disturbances.
• Be ready to intubate given the potential for respiratory depression.
• Carbamazepine is moderately dialyzable and dialysis is recommended in severe overdoses.

Additional educational pearl: Individuals in correctional facilities can occasionally self-administer medications which means that medication overdose should still be on the differential for any of these individuals.

References

1. Epilepsies in children, Young People and adults: NICE guideline [NG217]. National Institute for Health and Care Excellence. (2022, April 27). https://www.nice.org.uk/guidance/ng217
2. Ghannoum M, Yates C, Galvao TF, Sowinski KM, Vo TH, Coogan A, Gosselin S, Lavergne V, Nolin TD, Hoffman RS; EXTRIP workgroup. Extracorporeal treatment for carbamazepine poisoning: systematic review and recommendations from the EXTRIP workgroup. Clin Toxicol (Phila). 2014 Dec;52(10):993-1004. doi: 10.3109/15563650.2014.973572. Epub 2014 Oct 30. PMID: 25355482; PMCID: PMC4782683.
3. Seymour JF. Carbamazepine overdose. Features of 33 cases. Drug Saf. 1993 Jan;8(1):81-8. doi: 10.2165/00002018-199308010-00010. PMID: 8471190.
4. Spiller HA. Management of carbamazepine overdose. Pediatr Emerg Care. 2001 Dec;17(6):452-6. doi: 10.1097/00006565-200112000-00015. PMID: 11753195.
5. Tran NT, Pralong D, Secrétan AD, Renaud A, Mary G, Nicholas A, Mouton E, Rubio C, Dubost C, Meach F, Bréchet-Bachmann AC, Wolff H. Access to treatment in prison: an inventory of medication preparation and distribution approaches. F1000Res. 2020 May 13;9:357. doi: 10.12688/f1000research.23640.3. PMID: 33123347; PMCID: PMC7570324.

Summarized by Jeffrey Olson, MS2 | Edited by Meg Joyce & Jorge Chalit, OMSII

Contributor: Aaron Lessen, MD

Educational Pearls:

• Extracorporeal Membrane Oxygenation (ECMO) has been attempted as an adjunct to CPR during cardiac arrest but few studies on outcomes exist
• One prior small study stopped early when it showed ECMO with CPR (ECPR) was significantly superior to CPR
• Recent large, multicenter randomized control study in Netherlands evaluated neurologic outcomes in CPR versus ECPR
• At 30 days and 6 months no significant difference between the groups was found
• More studies are required determine if certain patients may benefit from ECPR

References

Belohlavek J, Smalcova J, Rob D, et al. Effect of Intra-arrest Transport, Extracorporeal Cardiopulmonary Resuscitation, and Immediate Invasive Assessment and Treatment on Functional Neurologic Outcome in Refractory Out-of-Hospital Cardiac Arrest: A Randomized Clinical Trial. JAMA. 2022;327(8):737-747. doi:10.1001/jama.2022.1025

Suverein MM, Delnoij TSR, Lorusso R, et al. Early Extracorporeal CPR for Refractory Out-of-Hospital Cardiac Arrest. N Engl J Med. 2023;388(4):299-309. doi:10.1056/NEJMoa2204511

Summarized by Kirsten Hughes, MS4 | Edited by John Spartz, MD, & Erik Verzemnieks, MD

The Emergency Medical Minute is excited to announce that we are now offering AMA PRA Category 1 creditsTM via online course modules. To access these and for more information, visit our website at https://emergencymedicalminute.org/cme-courses/ and create an account.

Contributor: Nick Tsipis MD

Educational Pearls:

• The scaphoid bone is the most proximal carpal bone just distal to the radius
• Fractures of the scaphoid bone are sometimes missed by plain X-rays
• A 2020 review found a 21.8% incidence of missed scaphoid fractures later diagnosed by advanced imaging modalities
• Only MRI has a sensitivity above 90% for diagnosing scaphoid fractures
• Sensitivity of plain-film radiography is low unless it is a displaced fracture
• Physical examination techniques fail to definitively rule out scaphoid fractures
• A 2023 systematic review assessed the sensitivity and specificity of several common physical exam maneuvers:
• Tenderness of the anatomical snuffbox has a sensitivity of 92.1% and specificity of 48.4%; i.e. absence reduces the likelihood of an occult scaphoid fracture but does not rule it out
• Another common physical exam maneuver is pain with ulnar deviation, which carries a sensitivity of 55.2% and specificity of 76.4%.
• Elicitation of pain with supination against resistance demonstrated a sensitivity of 100% and specificity of 97.9% in the study, so the authors recommend externally validating this method
• Patients should be counseled on the importance of follow-up given that a fracture may not show up on imaging unless an MRI or repeat XR is done

References

1. Bäcker HC, Wu CH, Strauch RJ. Systematic Review of Diagnosis of Clinically Suspected Scaphoid Fractures. J Wrist Surg. 2020;09(01):081-089. doi:10.1055/s-0039-1693147

2. Coventry L, Oldrini I, Dean B, Novak A, Duckworth A, Metcalfe D. Which clinical features best predict occult scaphoid fractures? A systematic review of diagnostic test accuracy studies. Emerg Med J. 2023;40(8):576 LP - 582. doi:10.1136/emermed-2023-213119

Summarized by Jorge Chalit, OMSII | Edited by Meg Joyce & Jorge Chalit, OMSII

Contributor: Aaron Lessen MD

Educational Pearls:

What is measured in an ABG/VBG?

• Blood values for oxygen tension (pO2), carbon dioxide tension (pCO2), acidity (pH), oxyhemoglobin saturation, and bicarbonate (HCO3) in either arterial or venous blood
• Other tests can measure methemoglobin, carboxyhemoglobin, hemoglobin levels, base excess, and lactate

What are they used for?

• Identification of ventilation/acid-base disturbances. For example: if a patient is in septic shock, oxyhemoglobin saturation can be used to guide resuscitation efforts (early goal- directed therapy)

What's the difference between an ABG and VBG?

• One of the main differences is how the blood samples are collected. Venous blood gas is normally collected from existing venous access such as a central venous catheter. Arterial blood gases must be drawn from an artery, such as the radial artery.
• Arterial blood draws can be difficult, painful, and contraindicated in many situations.
• ABGs have traditionally provided more accurate measurements for assessing oxygenation, ventilation, and acid-base status.
• However, several studies have found that VBGs can still be used to accurately assess pH, pCO2, HCO3, lactate, sodium, potassium, chloride, ionized calcium, blood urea nitrogen, base excess, and arterial/alveolar oxygen ratio. This is supported by a recent study in 2023 in the International Journal of Emergency Medicine which specifically studied patients with hypotension and use of VBGs for resuscitation guidance.

Are there other non-invasive methods that can be used to fill in the gaps to avoid ordering an ABG?

• Oxygenation can be measured by pulse oximetry
• Arterial carbon dioxide tension can be estimated by end-tidal carbon dioxide (PetCO2)
• Mixed venous blood gases are another alternative for patients who already have a pulmonary artery catheter

References

1. Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, Peterson E, Tomlanovich M; Early Goal-Directed Therapy Collaborative Group. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med. 2001 Nov 8;345(19):1368-77. doi: 10.1056/NEJMoa010307. PMID: 11794169.
2. Prasad H, Vempalli N, Agrawal N, Ajun UN, Salam A, Subhra Datta S, Singhal A, Ranjan N, Shabeeba Sherin PP, Sundareshan G. Correlation and agreement between arterial and venous blood gas analysis in patients with hypotension-an emergency department-based cross-sectional study. Int J Emerg Med. 2023 Mar 10;16(1):18. doi: 10.1186/s12245-023-00486-0. PMID: 36899297; PMCID: PMC9999648.

Summarized by Jeffrey Olson, MS2 | Edited by Jorge Chalit, OMSII

Contributor: Travis Barlock MD

Education Pearls:

• The Cushing Reflex is a physiologic response to elevated intracranial pressure (ICP)
• Cushing’s Triad: widened pulse pressure (systolic hypertension), bradycardia, and irregular respirations
• Increased ICP results from systolic hypertension, which causes a parasympathetic reflex to drop heart rate, leading to Cushing’s Triad.
• The Cushing Reflex is a sign of herniation
• Treatment includes:
• Hypertonic saline is comparable to mannitol and preferable in patients with hypovolemia or hyponatremia
• Give 250-500mL of 3%NaCl
• 20% Mannitol - given at a dose of 0.5-1 g/kg
• Each additional dose of 0.1 g/kg reduces ICP by 1 mm Hg
• 23.4% hypertonic saline is more often given in the neuro ICU
• 8.4% Sodium bicarbonate lowers ICP for 6 hours without causing metabolic acidosis
• Non-pharmacological interventions:
• Raise the head of the bed to 30-45 degrees
• Remove the c-collar to improve blood flow to the head
• Hyperventilation induces hypocapnia, which will vasoconsrict the cerebral arterioles
• You hyperventilate on the way to the OR. Otherwise, maintain normocapnia.

References

1. Alnemari AM, Krafcik BM, Mansour TR, Gaudin D. A Comparison of Pharmacologic Therapeutic Agents Used for the Reduction of Intracranial Pressure After Traumatic Brain Injury. World Neurosurg. 2017;106:509-528. doi:10.1016/j.wneu.2017.07.009
2. Bourdeaux C, Brown J. Sodium bicarbonate lowers intracranial pressure after traumatic brain injury. Neurocrit Care. 2010;13(1):24-28. doi:10.1007/s12028-010-9368-8
3. Dinallo S, Waseem M. Cushing Reflex. [Updated 2023 Mar 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK549801/
4. Godoy DA, Seifi A, Garza D, Lubillo-Montenegro S, Murillo-Cabezas F. Hyperventilation therapy for control of posttraumatic intracranial hypertension. Front Neurol. 2017;8(JUL):1-13. doi:10.3389/fneur.2017.00250

Summarized by Jorge Chalit, OMSII | Edited by Meg Joyce & Jorge Chalit, OMSII