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Volume 01

A study guide to critical care.

For the internal medicine resident who'd rather titrate pressors than panic on rounds. Designed to keep your critical care reasoning hemodynamically stable. Last revised 2026.

06 topics

Critical Care Medicine

Shock · Sepsis · Respiratory · ICU · Consciousness · Weakness

01

Shock

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Universal Features

Altered mentation · cap refill >2s · lactate >3 · hypotension · mottled skin · tachycardia · tachypnea · UO <0.5 mL/kg/h

Hemodynamic Profiles

The classic five-phenotype framework

TypeCOPCWPSVRClinical Picture
Cardiogenic ↓ ↑ ↑ ↑ CVP · S3 · pulmonary crackles · edema · CVD RF · MI most common cause
Hypovolemic ↓ ↓ ↑ Volume loss: hemorrhage · dehydration · vomiting · diarrhea
Obstructive ↓ ↕ ↑ Cardiac tamponade · PE · tension pneumothorax
Anaphylactic ↑ → ↓ Rash · urticaria · angioedema · wheezing · stridor
Septic ↑ → ↓ ↕ ↓ Infection
02

Sepsis

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Sepsis = infection + organ dysfunction.
SIRS Screen (≥2)

HR >90 · T >38 or <36 · RR >20 · PaCO₂ <32 · WBC >12 or <4

  • ICU required › admission ≤6h
  • Hypotension › rapid administration ≥30 mL/kg crystalloid within 3h › central line › norepinephrine 0.05–0.5 mcg/kg/min › vasopressin 2.4 units/hr · target MAP ≥65
    • Fluid responsiveness: 10–15% ↑ SV or CO after 500 mL IVF
    • Cardiac dysfunction › dobutamine 2.5–10 mcg/kg/min
    • Elderly › target MAP 60–65
  • BCs › broad-spectrum antibiotics within 1h · cover MRSA / MDR / fungal if RF
    • Source control · culture potential sites of infection · CXR · URM
    • Glucose target 7.8–10
    • PCT <0.5 › DC antibiotics
Septic Shock

Sepsis + persistent hypotension requiring vasopressors to maintain MAP ≥65 + lactate >2.

› ≥2 antibiotics from different classes. Norepinephrine ≥0.25 mcg/kg/min for >4 hrs › IV hydrocortisone 200–400 mg/day.

03

Acute Respiratory Failure

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  • Hypoxemic respiratory failure: V/Q mismatch › HFNC › NIV › MV
ARDS — Berlin Criteria

Onset <1 week · non-cardiogenic pulmonary edema · bilateral infiltrates on CXR/CT/US · SpO₂/FiO₂ <315 + SpO₂ ≤97%

ARDS Severity

SeverityPaO₂/FiO₂Support
Mild201–300NIV/CPAP PEEP ≥5 or HFNC >30 L/min
Moderate101–200PEEP ≥5
Severe≤100PEEP ≥5
  • Etiology: pneumonia, drowning, thoracic trauma, hemorrhagic shock, smoke/toxic inhalation, fat emboli, post lung transplant, severe sepsis, TRALI, shock, pancreatitis
  • MV: A/C-VC · Vt 4–8 mL/kg PBW · Pplat <30 cm H₂O
  • Target SpO₂ 88–92% or PaO₂ 55–80 mmHg · permissive hypercapnia · pH >7.25
  • Moderate/severe › high PEEP, prone positioning >12h/d
  • Severe › neuromuscular blockade, VV-ECMO (PaO₂/FiO₂ <80)
  • Dexamethasone 20 mg IV × 5d then 10 mg IV × 5d, started within 24–48h
Hypercapnic Respiratory Failure

Etiology: COPD, BA, MG, ALS, MS, chest wall skeletal disorders, obesity, opioids, sedatives › ABG › BiPAP.

Neuromuscular weakness: >20% FVC decrease while supine · MIP <−60 cm H₂O or <50% predicted · MEP <40 cm H₂O or <50% predicted.

Nocturnal hypoventilation › polysomnography. CO₂ narcosis › somnolence, myoclonic jerks. BA exacerbation with normal/high PaCO₂ › impending respiratory arrest.

Inhalation
Smoke Inhalation

Wheezing, cough, dyspnea, 12–36h after exposure. CO, cyanide › pneumonia (Staphylococcus, Pseudomonas).

Visibly damaged airway / stridor › immediate intubation.

Cyanide › ↑ serum lactate › hydroxocobalamin.

Trauma
Fat Embolism Syndrome

Long bone fracture › respiratory insufficiency · neurologic dysfunction · petechial rash.

04

Principles of Critical Care

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  • Indications: COPD exacerbation · cardiogenic pulmonary edema · neuromuscular disease · recently extubated high-risk patients · OHS
  • CI: respiratory arrest · inability to protect airway · excessive secretions/nausea/vomiting · agitation/lack of cooperation · facial surgery · facial trauma · airway obstruction · hemodynamic instability
  • No improvement ≤2h › consider intubation
↓ PaCO₂
↑ RR, ↑ Vt
↑ SpO₂
↑ FiO₂, ↑ PEEP, ↑ inspiratory time
PIP
Airway resistance + lung compliance · <35 cm H₂O
Pplat
Lung compliance · <30 cm H₂O
PEEP
Pressure at end of respiratory cycle
Driving pressure
Pplat − PEEP · <15
  • High RR + auto-PEEP › hypotension
  • Difficult ventilation: bronchospasm · secretions · obstructing mucus plug · agitation with dyssynchrony with MV
  • Daily SAT › stop all sedatives and analgesia and observe patient
  • Weaning criteria: reversal of reason for intubation · PaO₂ >60 · FiO₂ <40% · PEEP <8 · ability to perform work of breathing (normal CO₂, normal pH, adequate cardiac function, adequate diaphragm function)
  • Extubation criteria: adequate cough · minimal secretions · alert · following commands · no sedation · no increased risk of airway obstruction · SpO₂ >90% · FiO₂ ≤50% · PEEP <5 · pH >7.3
  • SBT: PSV 30 min
    • Failure: tachypnea · ↑ WOB · tachycardia · hypotension · desaturation
    • RSBI = RR / Vt >105 › predictor of extubation failure
  • MV › RASS −2 to +1 (light sedation) › propofol or dexmedetomidine
    • Dexmedetomidine › bradycardia, hypotension
  • Daily sedation interruption · nurse-driven titration
  • Analgesia › opioids › respiratory depression, delirium, dependence
    • Adjuncts: paracetamol, NSAIDs
    • Post-op › low-dose ketamine
    • Neuropathic › gabapentin, pregabalin, carbamazepine
  • Non-pharmacological analgesia: cold therapy · relaxation · music · massage
  • Sleep: reduce noise, light, and nighttime disruptions › melatonin
    • MV › assist-control overnight
  • Peripheral wide-bore IV catheter › highest flow rate
  • Undifferentiated shock › POCUS
  • Remove unneeded catheters and drains
  • RF: transfusions · aged ≥70y · dementia · prior coma · emergency surgery/trauma · high APACHE/ASA scores · h/o delirium · vision/hearing impairment · poor nutritional status · poor functional status · multiple medical comorbidities · kidney disease · alcohol use disorder · depression · polypharmacy
  • Triggers: poorly controlled pain · deliriogenic drugs (benzodiazepines, anticholinergics, opioids) · disruption of sleep-wake cycle · constipation · dehydration · urinary retention · severe illness · infection · hypoxia · surgical stress · urinary catheter · sensory deprivation
  • Screening: CAM-ICU
  • Early mobility · promote sleep · optimize hearing/vision · frequent reorientation · reduce deliriogenic drugs/transfusions · engage family members · allow sunlight · redirect with calm tones · manage pain. Avoid physical restraints.
  • Severe agitation/hallucinations/distress › haloperidol or sedation
  • MV › dexmedetomidine
  • Benzodiazepines: alcohol withdrawals, seizures
  • ↑ Risk of cognitive impairment and ICU length of stay
  • Enteral nutrition preferred · initiate at 24–48h
    • Gradually increase over 3–7 days
  • TPN › GI mucosal atrophy · translocation of gut bacteria into bloodstream › infection
    • Do not start <7d from acute illness
05

Disorders of Consciousness

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Neuroprognostication Post Cardiac Arrest
  • Absent pupillary reflex at 72h
  • Status myoclonus <7d
  • EEG bilaterally absent N20
  • CT brain ≤72h: reduced gray-white matter differentiation
  • MRI brain ≤72h: high DWI
Death Determination
DCC · Circulatory

Invasive arterial BP pulse pressure <5 mmHg for 5–10 min + continuous ECG.

Death Determination
DNC · Neurologic

Absence of consciousness (supraorbital notch + peripheral stimulation) + absence of brainstem function (pupillary, corneal, cough, gag, vestibulo-ocular reflexes) + absence of capacity to breathe (no respiratory effort, pH ≤7.28, pCO₂ >60, pCO₂ ↑ >20).

Prerequisites: mechanism causing devastating brain injury, neuroimaging, absence of confounders (core T ≥36, <48h after arrest, drugs, shock, metabolic disorders).

  • Neurological injuries › intubation if GCS <8 · head of bed >45° · normothermia · euglycemia · normocapnia · IVF NS
Increased ICP

Hypertonic 3% saline 250 mL bolus or mannitol 0.25–1 g/kg q6–8h · hyperventilation CO₂ 26–30 · ICP monitoring <20 mmHg · optimize sedation · CPP >60 · EVD for hydrocephalus · consider decompressive craniotomy.

  • Unexplained coma › thiamine, glucose if hypoglycemic, naloxone if opioid OD suspected
06

ICU-Acquired Weakness

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Risk Factors

Hyperglycemia · sepsis · multiple organ dysfunction · SIRS

Three Patterns of Weakness

Differential by distribution, sensation, and reflexes

PatternDistributionSensation / ReflexesAssociation
Critical illness
myopathy		 Flaccid quadriparesis · proximal > distal · normal CNs · weak facial muscles · failure to wean Sensation spared · normal or hyporeflexia Steroid use. CK may be ↑. Dx: NCS, EMG.
Critical illness
polyneuropathy		 Flaccid quadriparesis · failure to wean · normal CNs ↓ Distal pin prick/touch · hyporeflexia Severe sepsis
Glucocorticoid-induced
myopathy		 Gradual onset 1–3 months · proximal muscles · lower > upper Normal sensation · normal reflexes Cushing's syndrome: DM, mood alteration, skin fragility, osteoporosis. ↓ steroids › improvement in 3–4 weeks.
Prevention: early mobility · physical therapy · occupational therapy · avoidance of early parenteral nutrition · glucose control.
07

Hyperthermia & Hypothermia

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The Hyperthermia Syndromes

Differential by onset, rigidity, and reflexes

SyndromeOnsetTone / ReflexesTriggerAntidote
Serotonin syndrome <24h Hypertonia, hyperreflexia, clonus, bilateral babinskis Antidepressants, amphetamines, cocaine, MDMA, levodopa, tramadol, meperidine, St John's wort, valproate, triptans, ergotamine, fentanyl, buspirone Benzodiazepines › cyproheptadine
Neuroleptic malignant Days–weeks Lead-pipe/cogwheel rigidity, hyporeflexia, catatonia Antipsychotics, domperidone, metoclopramide, prochlorperazine, L-dopa withdrawal Benzodiazepines › dantrolene or bromocriptine
Malignant hyperthermia Intra-op Rigidity, hyporeflexia, rhabdomyolysis Inhaled volatile anesthetics (halothane, isoflurane), succinylcholine, decamethonium. RYR1 gene. ↑ EtCO₂, ↑ T >1°C. Dantrolene + rapid cooling
Heat stroke Exposure Variable · ± rhabdomyolysis · AKI Anticholinergics, sympathomimetics, diuretics, athlete, age >70y. Criteria: T >40°C + CNS abnormalities. Rapid cooling to <39°C
Hyperthermia Universal Steps

Stop offending agent · cool · supportive care. Genetic testing (RYR1) and muscle biopsy for MH.

Hypothermia Staging

StageTempFeaturesManagement
Mild 32–35°C Tachycardia · hypertension · tachypnea · shivering · alert · poor judgment Warming, supportive
Moderate 28–32°C Bradycardia · hypotension · ↓ RR · ↓ CO · ↓ AKI · somnolence · no shivering · supraventricular arrhythmia Active external warming · 42°C crystalloid fluids
Severe <28°C Coma · absent reflexes · apnea · ventricular arrhythmia · asystole ECMO or cardiopulmonary bypass · peritoneal/pleural lavage
  • ECG › Osborn waves
  • Cardiac arrest › prolonged CPR + active external warming
08

Anaphylaxis

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Clinical Picture

Pruritus · flushing · hives · conjunctival pruritus · angioedema · dyspnea · stridor · hypoxemia · wheeze · vomiting · diarrhea · cramping abdominal pain · hypotension · syncope · incontinence. Mediated by IgE and mast cells.

  • Triggers: foods, medications, insect stings, radiocontrast, perioperative agents, exercise, seminal fluid, idiopathic
Epinephrine IM 0.01 mg/kg (max 0.5 mg), repeat q5–15 min PRN. (1:1000 = 1 mg/mL)
  • IV: 0.05–0.1 mg over 5 min, then infuse 2–10 mcg/min titrated to BP (1:10,000 = 0.1 mg/mL)
  • Adjuncts: inhaled SABA, antihistamines, supplemental O₂, IV crystalloid fluids, vasopressors, corticosteroids
  • Observation ≥12h · prescribe self-administered epinephrine at discharge