The 6 Hs of Pulseless Electrical Activity (PEA)

6-Hs

When you find someone without a pulse but then hook up the monitor and there is a rhythm, your first thought it probably “CRAP!” But as you start CPR, you need to be thinking about what caused it because not much will help the person except correcting the underlying problem.

So like most of medicine, there is a handy mnemonic for remembering the main causes: The 6 Hs and 5Ts

The 6 Hs

  1. Hypoglycemia
  2. H+ (acidosis)
  3. Hyperkalemia/Hypokalemia (potassium disturbances only get counted once)
  4. Hypovolemia
  5. Hypoxia
  6. Hypothermia

The 5 Ts

  1. Trauma
  2. Tension pneumothorax
  3. Tamponade
  4. Toxins
  5. Thrombosis

(I’ll make a T doodle at a later date)

The other handy mnemonic for the Hs I learned from this video (so I take no credit for it)Diabetic crashing with a wide QRS

  • Diabetic = Hypoglycemia or H+ acidosis
  • Crashing = bad vitals
    • Low BP +/- tachycardia (hypovolemia)
    • Low O2 (hypoxia)
    • Low temperature (hypothermia)
  • Wide QRS = hyperkalemia

Vertebral Disc Prolapse (slipped disc)

A prolapsed (slipped) disc is when the squishy innards of the disc (nucleus pulposus) bulge out past the stiffer wall of the disc (annulus fibrosis). The problem is that sometimes when this happens, the bulge can impinge the spinal cord or the spinal nerve root. This could result in an anterior cord syndrome (remember this doodle) or it could just knock out the nerve root, resulting in a specific radiculopathy (check out this doodle for where to check for numbness and weakness).

The tricky thing to remember is that though, for example, the L3 root exits at L3, if the L3,4 disc herniates, it doesn’t hit the L3 root but the L4.

Slipped L3,4 disc = L4 nerve injury

The disc hits the nerve after it has branched off the spinal cord, but before it has exited the  vertebral canal.

Intracranial Hemorrhages

For the most part, bleeding in the brain (intracranial hemorrhage) is a pretty bad thing. Though like most things in medicine, there are varying degrees of badness, all with different mechanisms that help us sort of why we really wouldn’t want something to happen.

Intracranial hemorrhages are categorized into 5 subtypes, and are given obvious sounding names depending on where the bleed is in the brain and in relation to the layers of the meninges.

  1. Epidural (above the dura, right under the skull)
  2. Subdural (below the dura, above the arachnoid)
  3. Subarachnoid (below the arachnoid, above the brain)
  4. Intraventricular (in the ventricles)
  5. Intraparenchymal (in the meat* of brain)

* The brain is not meaty, “parenchyma” means the functional part of the organ

The poor pia mater did not get any hemorrhage named after it, but if you want you can think of intraparenchymal as “subpial” just so it doesn’t feel left out.

Telling them apart

The most confusing thing, and thing that likes to get asked the most on exams, is the difference between epidural and subdural hematomas.

Epidural Subdural Subarachnoid
Above the dura Below the dura Below the arachnoid
Respects suture lines Doesn’t respect suture lines No respect for anything
High force trauma Low force trauma Aneurysm rupture or high force trauma
Arterial blood (commonly the middle meningeal artery) Venous (from venous plexus) Arterial from the circle of Willis
Lentiform (lens-shaped) or biconcave on CT Cresent (banana-shaped) on CT Lining surface, going into fissures and sulci and sella (death-star)
Acute presentation May be insidious (worsening headache over days) Acute presentation (thunderclap headache)

The reason intraventricular and intraparenchymal aren’t included in the table as they each have a bunch of causes, but for both of them trauma is a potential cause as well as hypertension and stroke. It’s good to remember that premature infants are at a much higher risk of intraventricular hemorrhages.

Blood on CTs

  • New blood: bright white
  • 1-2 weeks: isodense
  • Old blood (2-3 weeks): dark grey

Innervation of the lower leg

The lower leg (and especially the foot) have a pretty fancy pattern of skin innervation by the terminal branches. For example, the skin of the foot is innervated by 7 separate nerves:

  1. Superficial peroneal nerve
  2. Deep peroneal nerve
  3. Sural nerve
  4. Saphenous nerve
  5. Calcaneal branch of the tibial nerve
  6. Medial branch of plantar nerve
  7. Lateral branch of plantar nerve

Also good to keep in mind that the anterior compartment is innervated by the deep peroneal nerve, the lateral compartment by the superficial peroneal nerve and the posterior compartment by the tibial nerve.

Layers of the Epidermis

The epidermis is divided into five layers. From outside to inside (dermis). The stem cells are located in the stratum basale and migrate outwards in their differentiation process

  1. Stratum corneum: The outmost layer, made of dead keratinocytes with a layer of protein around them (they have undergone keratinization)
  2. Stratum lucidum: Also dead keratinocytes (there is no real distinction here other than that the poor keratinocytes have died but have not finished the keratinization process)
  3. Stratum granulosum: the keratinocytes are still on the move, by this point they have kertahyalin granules
  4. Stratum spinosum: the keratinocytes migrating up, they have nice oval nuclei
  5. Stratum basale: Single layer of proliferating columnar keratinocytes, melanocytes (pigmented cells) and Merkel cells (mechanoreceptors) also live here

Of note, Langerhans cells, which are specialized antigen-presenting cells are present in all layers of the epidermis but are mostly in the stratum spinosum.

Glasgow Coma Scale (GCS)

BUY THIS AS A STUDY CARD

The Glasgow Coma Scale is a scoring system used to evaluate someone’s level of consciousness. It is scored out of 15 with 15 being totally awake and alert and 3 being totally not.

The important thing to remember is that the lowest score possible is 3.

Absolutely anything can score a 3, however if you are a living, breathing human being, hopefully you are scoring well up into the 10s.

Generally the GSC is applied in trauma situations and can be used as part of the decision making process of such thing things like should this patient be intubated?

  • ≥13 correlates with mild brain injury (or being ok)
  • 9-12 correlates with moderate injury
  • ≤8 represents severe brain injury – you should probably consider intubating them as they most likely cannot protect their airway
Thanks to Mike for the guest doodle!

The Menstrual Cycle

The menstrual cycle. What more of a classic drawing can you get? Though it has been done a million times over, here’s the Sketchy Medicine version of the classic hormonal interplay that allows for the endometrial lining to build up, shed, build up, shed, build up, shed…

The nice thing is the the pituitary hormones are aptly named so that FSH (follicle stimulating hormone) stimulates the follicle to grow and LH (luteinizing hormone) causes ovulation (the infamous LH surge) and subsequent corpus luteum development.

Meanwhile the developing follicle secretes estradiol which stimulates the proliferative phase of the cycle. Then the corpus luteum secretes estradiol and progesterone to kick things into high gear for the secretory phase.

You can now passively study this all the time (and keep your own notes) on a notebook or a mug. Nothing says “mmm, coffee” like the hormonal phases of the female reproductive system.

Signs of Meningitis

Meningitis is very literally inflammation of the meninges. Something swollen in a closed space is never good, so it’s important to not miss meningitis when it presents.

Classic triad of meningitis

  1. Fever
  2. Neck stiffness
    • Brudzinski
    • Kernig
  3. Mental status change – in babies this can be an increase in somnolence or irritability (unconsolably crying)

Important organisms:

  • Bacterial
    • Listeria*
    • E. coli*
    • GBS (Group B strep)*
    • Neisseria meningitidis
    • Strep pneumoniae
    • Staph aureus
    • Gram neg bacilli
    • Haemophilus influenza
  • Viral (“aseptic”)
    • HSV
    • Enterovirus
    • HIV
    • Mumps

* These are the common ones in the neonatal period

Bacterial:

  • Positive Gram stain
  • CSF white blood cell (WBC) count >1000/uL with a predominance of neutrophils
  • Low CSF glucose concentration <40 mg/dL (2.2 mmol/L)
  • Empiric treatment: high doses of a 3rd generation cephalosporin (cefotaxime, ceftriaxone) and vancomycin (this covers antibiotic-resistant S. pneumoniaeN. meningitidis, and Hib)

Kawasaki Disease

Kawasaki Disease is one of the pediatric rashes that you always need to have in the back of your mind. Most of the time the disease is self-limiting, but the consequences of not catching it are pretty bad (turns out coronary artery aneurysms often lead to things like infarction and DEATH).

Warm CREAM is an unrelated (and somewhat unpleasant) mnemonic to help remember the signs and symptoms of Kawasaki. The “warm” is a fever (one lasting more than 5d) and then you need 4/5 of the other criteria (non-purulent conjunctivitis, rash, palmar erythema/swelling, cervical adenopathy, dry and red mucous membranes, the infamous strawberry tongue). The kid doesn’t need all 4 as he or she is sitting in front of you, but the presentation and the history combined should include those criteria.

Treatment is with high doses ASA and IVIG, you do this to prevent the sequelae of coronary artery aneurysms and myocarditis, and it’s best to get an echo to check up on things.

Acyanotic vs Cyanotic Congenital Heart Defects

You separate congenital heart defects into acyanotic and cyanotic. Basically, is the baby (or kid) nice and pink, or is he or she dusky as they like to say. Sometimes the blueishness only happens when they’re working really hard, like feeding and crying (or thinking about the pathophysiological mechanisms of heart disease).

One of the important things to remember is that acyanotic heart defects can switch over if they’re left alone for too long because of pulmonary hypertension caused by the extra flow. This is called Eisenmenger Syndrome.

It’s also important to realize that many of the cyanotic lesions are duct dependent, meaning that as long as the ductus arteriosus is open, they are happy and pink. The problems start in that time 6-24h after delivery when the ductus closes. Thankfully you can keep it open by giving prostaglandin E1.

Need the ductus for systemic circulation:

  • Coarctation of the aorta
  • Critical aortic stenosis
  • Hypoplastic left heart syndrome

Need the ductus for pulmonary circulation:

  • Pulmonary atresia
  • Critical pulmonary stenosis
  • Tricuspid atresia
  • Tetralogy of fallot

Also, I realize that the 5 Ts of cyanotic heart lesions are a pentad of 6 (plus some), but mnemonics can only do so much, and the T thing is just so catchy.

For a more detailed illustration of PDAs, you can check out this doodle!

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