Mr. Critical ICU Nursing: Comprehensive Study Notes

1) Quick Critical Values & Must-Act Triggers

Airway & Breathing

• SpO₂ < 90% (or drop >4% from baseline) despite O₂ → escalate, check airway, consider ABG.

• pH < 7.20 with rising PaCO₂ or refractory hypoxemia → consider ventilatory support.

Circulation

• MAP < 65 mmHg (or below patient-specific goal) after fluids → start/adjust vasopressors.

• Lactate ≥ 4 mmol/L or rising trend → search for shock/sepsis, optimize perfusion.

• Urine output < 0.5 mL/kg/hr for >2 hours → assess volume, perfusion, obstruction.

Electrolytes (action thresholds; follow local protocols)

• K⁺ < 3.0 or > 6.0 mEq/L

• Mg²⁺ < 1.6 mg/dL

• Ionized Ca²⁺ < 0.9 mmol/L

• Na⁺ change > 10–12 mEq/L in 24 h → risk of osmotic injury

Bleeding/Coagulation

• Hgb < 7 g/dL (individualize for ACS, neuro, active bleed).

• INR > 2.0 or platelets < 50k with planned procedures → correct per protocol.

Neuro

• Sudden GCS drop ≥ 2, new focal deficit, or pupil asymmetry > 1 mm → emergent eval.

• ICP > 22 mmHg sustained, CPP < ordered goal (often 60–70 mmHg).

2) Core ICU Labs: What They Mean & What To Do

Arterial/Venous Blood Gases

• ABG: pH, PaCO₂, PaO₂, HCO₃⁻, SaO₂

  • Respiratory acidosis: ↑PaCO₂ → ↑ventilation (rate/VT), fix obstruction, sedation PRN.

  • Respiratory alkalosis: ↓PaCO₂ → reduce ventilation or treat pain/anxiety.

  • Metabolic acidosis: ↓HCO₃⁻ → check lactate, ketoacids, renal failure, toxins.

  • Metabolic alkalosis: ↑HCO₃⁻ → assess chloride, volume status, diuretics.

• VBG: good for pH/CO₂ trends (not oxygenation).

Key Formulas

• Anion Gap (AG) = Na – (Cl + HCO₃). Normal ~8–12.

• Winter’s Formula (expected PaCO₂ in metabolic acidosis) = 1.5 × HCO₃ + 8 ± 2.

• A–a Gradient = [FiO₂ × (Pb – PH₂O) – PaCO₂/R] – PaO₂.

Lactate

• Shock marker.

• Clearance (>10–20% at 2–4 h) = improving perfusion.

• Elevated from: tissue hypoxia, seizures, β-agonists, liver dysfunction, thiamine deficiency.

Electrolytes & Action Pearls

• K⁺: target 4–5 in arrhythmia risk. ~10 mEq KCl ↑ serum K⁺ by 0.1 (variable). Monitor on cardiac monitor.

• Mg²⁺: keep ≥ 2.0 mg/dL with arrhythmia risk; treat torsades aggressively.

• Ca²⁺: check ionized. Replace in massive transfusion or hyperK⁺ ECG changes.

• Phosphate: low Phos (<2.0) → diaphragm weakness. Replace carefully.

• Na⁺: correct chronic changes slowly.

  • Hyponatremia: check serum/urine osmolality & urine Na.

  • Hypernatremia: free-water deficit, correct gradually.

Renal & Urine Studies

• BUN/Cr: trends > absolute values.

• FENa/FEUrea: differentiate pre-renal vs intrinsic (FEUrea <35% → pre-renal).

Cardiac Markers

• Troponin: trend + ECG + symptoms; distinguish type 1 vs type 2 MI.

• BNP/NT-proBNP: assess volume/pressure overload; integrate with exam/echo.

Coagulation

• PT/INR, aPTT, anti-Xa, fibrinogen, D-dimer.

• Anti-Xa preferred for heparin titration where adopted.

Inflammatory/Infectious

• Procalcitonin/CRP = trends only.

• Draw cultures (blood before antibiotics).

• Don’t anchor on one biomarker.

Medication Levels

• Vancomycin (AUC/trough), aminoglycosides, digoxin, phenytoin, lithium.

• Time draws correctly; adjust for renal function.

Metabolic/Endocrine

• Glucose: target 140–180 mg/dL (avoid hypoglycemia).

• Triglycerides: monitor on propofol.

• TSH/Free T4: if myxedema concern.

• Cortisol: if adrenal insufficiency suspected.

3) Hemodynamic Monitoring & “The Notches”

Arterial Line (A-line)

• Radial site most common. Level at phlebostatic axis. Zero to air.

• Waveform: systolic upstroke → dicrotic notch (aortic closure) → diastolic runoff.

• Damping:

  • Underdamped: exaggerated systolic.

  • Overdamped: blunted waveform.

• Square-wave test: 1–2 oscillations optimal.

• PPV/SVV: preload markers in controlled ventilation (not reliable with arrhythmia, low TV, high PEEP, or spontaneous breaths).

Central Venous Pressure (CVP)

• Normal: 2–8 mmHg (use trends).

• Waveform:

  • a wave = atrial contraction

  • c wave = tricuspid bulge

  • v wave = venous filling

  • x/y descents = relaxation/filling

• Giant v waves: TR. Prominent a waves: pulm HTN or ↓RV compliance.

Pulmonary Artery Catheter (PAC)

• Normal pressures: RA 2–8, RV 15–30/2–8, PA 15–30/5–15, PAOP 6–12.

• RV waveform = tall systolic, near-zero diastolic.

• PA waveform = dicrotic notch.

• PAOP = atrial-type waveform when wedged.

• Derived metrics: CO/CI, SV, SVR, PVR.

• SvO₂ vs ScvO₂ = O₂ delivery/consumption balance.

Noninvasive/Advanced

• POCUS Echo: LV/RV function, IVC, effusions, tamponade.

• Pulse contour devices: PiCCO, FloTrac.

4) Cardiac Monitoring (ECG) Essentials

Rapid Review

1. Rate & rhythm

2. PR/QRS/QT

3. Axis

4. Ischemia (ST/T)

5. Blocks

6. Compare to prior

Key Pearls

• ST elevation/depression: correlate with baseline, symptoms, troponins.

• QTc: use Fridericia in tachy. Check meds/electrolytes.

• BBB: STEMI can hide in LBBB (Sgarbossa criteria).

• Pacers: verify capture on ECG + perfusion on A-line.

Arrhythmia Quick Guide

• Unstable tachy: synchronized cardioversion.

• Stable narrow tachy: vagal → adenosine → meds.

• A-fib RVR: rate control, anticoagulation, treat triggers.

• VT/VF arrest: defibrillate, CPR, epi, fix H’s & T’s.

• Torsades: IV Mg, overdrive pacing.

5) Mechanical Ventilation & Oxygenation

Initial Settings

• ARDS: VT 4–6 mL/kg IBW, RR 16–24, PEEP per FiO₂, keep plateau ≤30.

• Obstructive: longer expiratory time, lower RR.

Troubleshooting

• Double trigger = low VT/set RR.

• Shark fin flow = obstruction.

• Scooped flow = air trapping.

• Auto-PEEP = incomplete exhalation → allow more time, bronchodilate.

Oxygenation/Ventilation Targets

• SpO₂ 92–96%. Avoid hyperoxia.

• Correct acidosis only if clinically significant.

Liberation

• Daily SAT/SBT, minimal sedation, adequate cough, stable hemodynamics, cuff leak if prolonged intubation.

VAP Prevention Bundle

• HOB 30–45°, oral care with CHG, subglottic suction, sedation holiday, DVT/GI prophylaxis, early mobility.

6) Shock: Types, Profiles, First Moves

• Distributive (sepsis): warm, low SVR, high CO → early antibiotics, fluids, norepinephrine.

• Cardiogenic: cool, high filling pressures, low CO → gentle fluids, dobutamine ± vasopressors.

• Hypovolemic: flat veins, tachy, narrow PP → stop bleed, MTP, TXA, calcium.

• Obstructive: tension pneumo (needle decompression), tamponade (pericardiocentesis), PE (lysis/embolectomy).

Monitor: lactate, ScvO₂/SvO₂, UO, mentation, skin perfusion.

7) Medication Titration: Principles & Common Drips

Vasopressors

• Norepinephrine: first-line; titrate to MAP.

• Vasopressin: fixed dose, adjunct.

• Epinephrine: refractory shock; ↑lactate risk.

• Phenylephrine: use if tachy with hypotension.

• Dopamine: high arrhythmia risk → rarely used.

Inotropes

• Dobutamine: ↑CO, may ↓BP.

• Milrinone: PDE-3 inhibitor, long half-life, avoid in AKI.