Shock & Sepsis Progression
discuss some signs and symptoms which can differentiate meningococcal meningitis (CNS) from meningococcemia (bloodstream)
Nuchal rigitity, positive kernigs sign, positive brudzinskis sign, photophobia, pain localized to head and neck, elevated intracrania pressure, cerebral edema, seizures.
Explain the use of Starling Equation and which components Push fluid out of the capillary versus what pulls fluid IN
Jv = Kf * [(Pc - Pi) - σ * (πc - πi)]
JV= fluid flux, the volume filtration rate per unit area of endothelial surface
Kf = filtration coefficient
Pc= capillary hydrostatic pressure = pushes fluid out
Pi= interstitial hydrostatic pressure
σ= reflection coefficient
πp (or πc)= plasma oncotic pressure = keeps fluid in.
πi = interstitial oncotic pressure.
Give the classic lab trend (4 values) that defines progressing DIC.
↓ platelets, ↑ D-dimer, ↓ fibrinogen, ↑ PT/INR (and ↑ aPTT).
discuss the three key virulence structures of Neisseria meningitidis and the one-sentence job of each. (LO 10)
Type IV pili (attach/colonize nasopharyngeal epithelium), polysaccharide capsule (blocks phagocytosis and MAC insertion in the bloodstream), lipooligosaccharide/LOS (endotoxin that triggers the systemic inflammatory cascade)
Explain why cortisol is required for norepinephrine to actually raise blood pressure
Cortisol has a permissive effect on catecholamines — it's not vasoconstrictive itself, but norepinephrine can't do its job without it. Mechanistically: cortisol upregulates α1-adrenergic receptor expression/sensitivity, inhibits nitric oxide synthase and prostacyclin production (both of which otherwise drive vasodilation), and restores normal calcium-channel function in vascular smooth muscle needed for contraction.
A patient is warm, flushed, and has a wide pulse pressure despite hypotension. Explain the hemodynamic reason this looks so different from hypovolemic or cardiogenic shock.
Distributive/septic shock has profound SVR loss (vasoplegia) as the primary lesion, with compensatory ↑ CO — unlike the other three types where SVR rises reflexively. This produces warm extremities and wide pulse pressure instead of the cold, clammy, narrow-pulse-pressure picture.
Explain why Lactated Ringer's does not directly cause lactic acidosis, even though it contains lactate.
LR contains sodium lactate, not lactic acid — it's a buffer precursor metabolized (mostly hepatic/renal) into bicarbonate, so it doesn't add an acid load.
A patient has thrombocytopenia, schistocytes, and organ ischemia. What is the single most useful lab test to distinguish TTP from HUS, and what result points to each?
ADAMTS13 activity. <10% → TTP;
normal or mildly reduced with prominent renal failure → HUS.
Interpret a lumbar puncture showing low glucose, high protein, and neutrophil-predominant high WBC. Explain the physiologic reason behind each of those three findings, and state what additional result would make the diagnosis definitive for meningococcal meningitis specifically.
Low glucose — bacteria consume glucose as an energy source.
High protein — meningeal inflammation damages the blood-brain barrier, letting blood proteins leak into CSF.
High WBC, neutrophil-predominant — acute bacterial inflammatory response.
Together these are consistent with bacterial meningitis but not specific to meningococcus; the finding that makes it definitive for N. meningitidis is a Gram stain showing gram-negative diplococci with culture and/or PCR positive for N. meningitidis.
Two contacts of an index case are both fully vaccinated against meningococcus. Explain why they may still need chemoprophylaxis
Vaccination is not immediate (takes days–weeks to generate antibodies) and does not eliminate existing nasopharyngeal carriage; vaccines also don't cover every serogroup, so a vaccinated contact may already be colonized with, or exposed to, a covered or non-covered strain. Chemoprophylaxis eradicates carriage now — a different job than vaccination
DAILY DOUBLE
Draw it: build a chart comparing preload, cardiac output, SVR, and primary cause for each of the four shock types (hypovolemic, cardiogenic, obstructive, distributive)
Compare how sepsis changes each variable in the Starling equation (Kf, σ, πc, πi) and explain the net effect on capillary fluid movement
Sepsis ↑Kf (leakier capillary), ↓σ (protein escapes more easily), which lowers effective πc (capillary oncotic pressure) and raises πi (interstitial oncotic pressure) protein now pulling fluid into interstitium). Net effect: massive capillary leak — fluid/protein exit the vasculature into tissues, causing edema and relative intravascular depletion.
Explain the role of Protein C as a "brake" on coagulation, and what happens to that brake during severe meningococcal sepsis.
Thrombin normally binds thrombomodulin → activates Protein C, which (with Protein S) inhibits Factors Va/VIIIa to limit clotting. In sepsis, endothelial injury ↓ thrombomodulin, so Protein C activation falls, the brake is lost, and unopposed thrombin/fibrin formation drives purpura fulminans.
Compare time-dependent vs. concentration-dependent antibiotic killing using penicillin G/ceftriaxone vs. ciprofloxacin as examples, and explain how this should change dosing strategy.
Penicillin G/ceftriaxone are time-dependent (efficacy tracks time above MIC, favoring frequent or continuous/extended infusion); ciprofloxacin is concentration-dependent (efficacy tracks peak/AUC relative to MIC, favoring higher, less frequent dosing
Compare the receptor targets and net hemodynamic effect (SVR vs. CO) of vasopressin, epinephrine, and dobutamine.
Vasopressin — V1a receptors, ↑↑SVR, ~neutral CO.
Epinephrine — α1/β1/β2, ↑SVR and ↑↑CO (combined pressor + inotrope).
Dobutamine — predominantly β1, ↑↑CO with neutral/↓SVR (inotrope, not a primary pressor).
Explain why cardiac output is typically elevated early in distributive/septic shock but oxygen delivery can still fail to meet tissue demand
High CO can offset low SVR to preserve DO₂ numerically, but tissue/mitochondrial oxygen utilization is impaired (cytopathic hypoxia) and microvascular shunting/uneven flow means oxygen delivered isn't necessarily oxygen used.
A patient has received 3.5 L of crystalloid, and a repeat passive leg raise no longer increases stroke volume. What does this tell you physiologically, and what should happen next in management?
It means the patient is no longer fluid responsive — additional fluid won't meaningfully raise stroke volume/CO. Management should shift toward vasopressors and away from further large boluses.
Explain how DIC can cause a patient to be clotting and bleeding at the same time — connect this to consumption of specific components.
Widespread clotting consumes platelets, fibrinogen, and coagulation factors, and fibrin itself is broken down (raising D-dimer) — eventually there isn't enough left to maintain normal hemostasis, so bleeding occurs alongside ongoing microthrombosis.
Explain augmented renal clearance (ARC): what causes it, which drug classes it affects most, and why it can make "standard dosing" subtherapeutic
ARC = measured urinary CrCl >130 mL/min, occurring in critically ill patients (post-trauma, burns, sepsis) with normal serum creatinine and preserved/hyperdynamic cardiac output. It increases glomerular filtration and clearance of renally eliminated drugs (beta-lactams, vancomycin, aminoglycosides), shortening time above MIC and risking subtherapeutic standard dosing.
Compare ciprofloxacin, ceftriaxone, and rifampin for chemoprophylaxis in terms of mechanism and one major limitation/contraindication for each.
Ciprofloxacin — inhibits DNA gyrase/topoisomerase IV (bactericidal); limitation: rising local resistance, generally avoided in pregnancy. Ceftriaxone — binds PBPs, inhibits cell wall cross-linking;
limitation: true β-lactam allergy (though "penicillin allergy" label often overstated) — otherwise preferred in pregnancy.
Rifampin — inhibits bacterial RNA polymerase;
limitation: potent CYP450 inducer (Remember from NAP) with major drug interactions (OCPs, warfarin, anticonvulsants), contraindicated in pregnancy.
Trace the full positive-feedback loop from endothelial injury → hypoperfusion → cellular dysoxia → DAMPs → worsening shock. Why is this described as "self-perpetuating"?
Endothelial/glycocalyx injury → capillary leak + microthrombi → hypoperfusion → anaerobic metabolism/mitochondrial failure → organ injury → injured cells release DAMPs → DAMPs further amplify systemic inflammation and vasoplegia → worsens perfusion. It's self-perpetuating because organ injury becomes its own inflammatory trigger, independent of ongoing bacterial burden
Explain the concept of being "intravascularly dry while the lungs/tissues are wet" in septic shock, and justify why more fluid boluses at that point are more harmful than helpful.
Ongoing endothelial injury + repeated fluid raises Pc in an already leaky capillary, pushing more fluid into interstitium/alveoli (pulmonary edema/ARDS) without improving preload/CO once fluid responsiveness is lost — so you can be volume-overloaded in the tissues while still relatively empty intravascularly. This is why guidelines favor withholding boluses and starting norepinephrine once passive leg raise is negative.
Trace how complement activation (C3a/C5a) leads to endothelial injury, tissue factor expression, and ultimately purpura fulminans. Include where the kinin-kallikrein cascade fits into this picture and what bradykinin does hemodynamically.
C3a/C5a → neutrophil activation/inflammation → endothelial injury → tissue factor expression → coagulation cascade activation (→ DIC) and ↓ Protein C activity (→ purpura fulminans). In parallel, Factor XIIa activates the kinin-kallikrein/contact system → kallikrein cleaves HMWK → bradykinin, causing vasodilation, ↓SVR, and capillary leak — worsening hypotension/vasoplegia on top of the coagulopathy
A hypoalbuminemic septic patient is on ceftriaxone (85–95% protein bound). Explain how capillary leak/low albumin changes free drug concentration, and connect this to both efficacy and toxicity risk — then explain how the picture flips if the same patient develops AKI.
Low albumin means less drug is protein-bound, so more free (active) ceftriaxone is available — increasing antibacterial effect but also toxicity risk. If the same patient later develops AKI, clearance of the (now more free) drug falls, so exposure/accumulation risk climbs further — the two effects compound rather than cancel
Explain why hydrocortisone is given empirically in vasopressor-refractory shock without waiting for a cortisol level, and describe the non-genomic (rapid) mechanism by which it restores vascular responsiveness within hours.
Waiting for a cortisol level before treating vasopressor-refractory shock can be fatal, so hydrocortisone is given empirically once refractory shock is identified. Its rapid non-genomic effects (within minutes–hours) work through membrane-bound receptors altering calcium/sodium transport, decreasing ATP-sensitive K⁺ channel activity, inhibiting nitric oxide synthase, and enhancing α1-receptor responsiveness to catecholamines — restoring vascular tone before the slower genomic anti-inflammatory effects even kick in