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Approach to the Critical Patient
Immediate Priorities
Stabilization priorities
Airway patency and protection risk
GCS < 8
Copious secretions
Refractory hypoxemia
Severe hypercapnia with acidemia
Breathing status
SpO2 target strategy by risk group
Most patients 92% to 96%
COPD or chronic hypercapnia risk 88% to 92%
Carbon monoxide poisoning target 100% after high flow oxygen
Work of breathing severity
Accessory muscle use
Paradoxical breathing
Inability to speak full sentences
Circulation threats
Shock signs
SBP < 90 mmHg or MAP < 65 mmHg
Altered mental status
Mottling
Immediate monitoring
Continuous pulse oximetry
Poor waveform as unreliable reading trigger
Low perfusion state as unreliable reading trigger
Cardiac monitoring
Dysrhythmia trigger for airway escalation
Noninvasive blood pressure cycling
Q3 to Q5 minute frequency in unstable patient
End tidal CO2 if ventilatory support
Rising ETCO2 as hypoventilation marker
Escalation triggers
Resuscitation bay activation
SpO2 < 90% despite nonrebreather
RR > 35 breaths per minute with fatigue
pH < 7.25 with rising PaCO2
Immediate airway team activation
Apnea
Severe agitation or obtundation preventing mask therapy
Hemodynamic collapse
Oxygenation and Ventilation Strategy
Stepwise support selection
Standard oxygen
Nasal cannula 1 to 6 L/min
Simple mask 6 to 10 L/min
Nonrebreather 10 to 15 L/min
High flow nasal cannula
Hypoxemic respiratory failure with intact airway reflexes
Initial flow 40 to 60 L/min
FiO2 titration to SpO2 target
Noninvasive ventilation
COPD exacerbation with hypercapnic acidemia
Cardiogenic pulmonary edema
Obesity hypoventilation with acute on chronic hypercapnia
Endotracheal intubation and invasive ventilation
Failure of HFNC or NIV
Inability to protect airway
Severe ARDS with refractory hypoxemia
Key Concepts
Definitions and coding
Acute respiratory failure with hypoxemia
ICD-10 J96.01
SNOMED CT 409622000
Acute respiratory failure with hypercapnia
ICD-10 J96.02
SNOMED CT 409623005
Acute respiratory failure with hypoxia and hypercapnia
ICD-10 J96.00 with supporting gas data
Physiologic patterns
Hypoxemic failure
VQ mismatch
Shunt physiology
Diffusion limitation
Hypercapnic failure
Alveolar hypoventilation
Increased dead space ventilation
Impending fatigue pattern
Rising PaCO2 with falling RR
Diminishing tidal volumes
PITFALLS
Common errors
Over oxygenation in chronic CO2 retainers with loss of hypoxic drive risk
Target SpO2 88% to 92% when COPD or chronic hypercapnia risk
Delayed intubation after clear NIV failure
Worsening mental status
Persistent acidemia after 1 to 2 hours NIV
Unrecognized pneumothorax during positive pressure support
Sudden hypotension
Unilateral breath sound decrease
History
Presenting Pattern
Symptom timeline and trajectory
Onset time
Sudden onset minutes
Subacute hours
Progressive days
Triggering event
Aspiration
Allergen exposure
Viral prodrome
Exertion
Primary symptom cluster
Dyspnea
At rest
Exertional
Orthopnea
Cough
Productive
Hemoptysis
Chest symptoms
Pleuritic pain
Chest tightness
Functional impact
Speaking full sentences limitation
Unable to ambulate without stopping
Risk Factors and Exposures
Pulmonary history
Asthma
COPD
Interstitial lung disease
Obstructive sleep apnea
Cardiac history
Heart failure
Coronary disease
Valvular disease
Thromboembolic risk
Recent surgery or immobilization
Prior DVT or PE
Estrogen therapy
Malignancy
Infectious risk
Sick contacts
Immunosuppression
Recent antibiotics
Travel and exposure clusters
Toxic and environmental exposure
Smoke inhalation
Carbon monoxide exposure
Occupational dusts
Medications and Devices
Current therapies
Home oxygen use
Inhaler adherence
Diuretics
Sedating substances
Opioids
Benzodiazepines
Alcohol
Airway device history
Tracheostomy
Home NIV or CPAP
Physical Exam
General and Vitals
Severity markers
Respiratory rate
RR > 30 breaths per minute as severe marker
Declining RR with worsening mentation as fatigue marker
Oxygen saturation on room air and support level
SpO2 < 90% on high flow oxygen as severe marker
Mental status
Agitation from hypoxemia
Somnolence from hypercapnia
Work of breathing
Accessory muscle use
Nasal flaring
Intercostal retractions
Tripod positioning
Pulmonary Exam
Breath sounds
Diffuse wheeze
Asthma or COPD pattern
Focal crackles
Pneumonia pattern
Diffuse crackles
Pulmonary edema or ARDS pattern
Unilateral decreased breath sounds
Pneumothorax or large effusion pattern
Percussion and fremitus
Hyperresonance unilateral
Dullness at bases
Cardiovascular and Volume
Heart failure markers
JVP elevation
S3 gallop
Peripheral edema
Shock markers
Cool clammy skin
Delayed capillary refill
Focused Exam for Causes
Upper airway obstruction clues
Stridor
Voice change
Drooling
DVT signs
Unilateral leg swelling
Calf tenderness
PITFALLS
Misleading findings
Quiet chest in severe asthma
Minimal wheeze with severe airflow limitation
Normal lung exam in pulmonary embolism
Disproportionate dyspnea and tachycardia
Differential Diagnosis
Life Threats
Immediate threats
Pulmonary embolism
ICD-10 I26.99
SNOMED CT 59282003
Tension pneumothorax
ICD-10 J93.0
SNOMED CT 233783004
Acute cardiogenic pulmonary edema
ICD-10 I50.1
SNOMED CT 417996009
Status asthmaticus
ICD-10 J45.902
SNOMED CT 426656000
Severe COPD exacerbation
ICD-10 J44.1
SNOMED CT 195951007
Common Etiologies by Pattern
Hypoxemic predominant
Pneumonia
Community acquired pneumonia ICD-10 J18.9
ARDS
ICD-10 J80
Berlin criteria alignment
Aspiration pneumonitis or pneumonia
ICD-10 J69.0
Atelectasis
ICD-10 J98.11
Hypercapnic predominant
COPD exacerbation
Severe asthma
Obesity hypoventilation syndrome
Neuromuscular weakness
Myasthenic crisis
Guillain Barre syndrome
CNS depression
Opioid toxicity
Sedative hypnotic toxicity
Mimics and Mixed
Mixed cardiopulmonary
COPD plus heart failure
Pneumonia plus sepsis related vasodilation
Metabolic drivers
Severe metabolic acidosis with compensatory tachypnea
DKA
Sepsis lactic acidosis
Laboratory Tests
Core Tests
Baseline laboratory panel
Complete blood count for infection or anemia
Leukocytosis context for bacterial infection
Hemoglobin low as dyspnea contributor
Electrolytes and renal function for medication safety
Potassium for beta agonist and diuretic effects
Creatinine for contrast planning
Venous blood gas for ventilation and acid base screening
pH trend as severity marker
PCO2 trend as hypoventilation marker
Arterial blood gas when precise oxygenation needed
PaO2 for PFR calculation
A-a gradient consideration when on known FiO2
Cause Directed Tests
Infection evaluation
Lactate in suspected sepsis
Lactate mmol/l interpretation in perfusion context
Blood cultures in septic shock or severe pneumonia before antibiotics when feasible
Respiratory viral testing when results change isolation or antivirals
Procalcitonin as adjunct when uncertainty about bacterial infection
Cardiac evaluation
Troponin for ischemia or strain pattern
BNP or NT-proBNP for heart failure support
Thromboembolism evaluation
D-dimer in low to intermediate pretest probability PE pathway
Age adjusted threshold consideration in adults
Toxicology and Special
Carbon monoxide and smoke exposure
Carboxyhemoglobin level
Pulse oximetry falsely normal risk
Lactate for cyanide concern in smoke inhalation
Medication related hypoventilation
Acetaminophen level when overdose possible
Salicylate level when acid base pattern suggests
PITFALLS
Lab limitations
Normal lactate does not exclude sepsis early
Venous PCO2 may underestimate arterial PCO2 in shock
D-dimer elevation nonspecific in infection and pregnancy
Diagnostic Tests
Scoring Systems
Risk stratification and monitoring scores
ROX index for HFNC failure prediction
ROX definition SpO2 FiO2 divided by RR
Higher ROX associated with lower intubation risk
Serial ROX at 2 hours and 6 hours for trend
HACOR score for NIV failure risk
Components heart rate
Components acidosis
Components consciousness
Components oxygenation
Components respiratory rate
CURB-65 for pneumonia severity in adults
Confusion
Urea mmol/l threshold local lab reference mapping
Respiratory rate threshold
Blood pressure threshold
Age 65 or older
PESI or sPESI for PE risk in adults
Hemodynamic stability marker
Comorbidity burden marker
MRI
Indications
Spinal cord pathology with hypoventilation pattern
Cervical myelopathy suspicion
Brainstem stroke with central hypoventilation suspicion
Posterior circulation syndrome
Limitations
Unstable patient incompatibility
Time to imaging delay
Limited role in primary pulmonary causes
CT
Chest CT applications
CT pulmonary angiography for PE
Moderate to high pretest probability
Contrast nephropathy risk assessment
CT chest for unclear hypoxemia
Interstitial lung disease flare
Occult pneumonia
Complication evaluation
Abscess
Empyema
CT contraindications and cautions
Severe contrast allergy
Renal dysfunction with risk benefit assessment
Interpretation pearls
Right heart strain signs in PE
Diffuse ground glass and dependent consolidation in ARDS patterns
Ultrasound
Point of care ultrasound
Lung ultrasound profiles
Diffuse B lines for interstitial edema pattern
Focal B lines or consolidation for pneumonia pattern
Lung sliding absence for pneumothorax concern
Cardiac ultrasound
LV function gross assessment for cardiogenic edema
RV dilation for PE strain pattern
Pericardial effusion with tamponade physiology
IVC assessment as adjunct to volume status
Collapsibility limitations in ventilated patients
Procedure guidance
Thoracentesis guidance for large effusion
Vascular access guidance in shock
Disposition
Level of Care
ICU indications
Invasive mechanical ventilation
NIV with high failure risk
Persistent pH < 7.25
Rising PaCO2
Worsening mental status
Refractory hypoxemia
FiO2 > 0.6 to maintain SpO2 target
Hemodynamic instability
Vasopressor requirement
Stepdown indications
HFNC with improving ROX trend
NIV stable with improving gases
Ward with monitoring
Low flow oxygen with stable vitals
Clear etiology and response to therapy
Transfer and Consultation
Specialist involvement triggers
Critical care
Escalating oxygen requirements
Ventilator management complexity
Cardiology
Cardiogenic pulmonary edema
Suspected ACS with respiratory failure
Pulmonology
Severe asthma or COPD
Suspected ILD flare
Anesthesia or airway team
Anticipated difficult airway
Transfer triggers
ECMO capable center need
Severe ARDS with refractory hypoxemia despite optimal ventilation
Severe hypercapnia with unsafe airway pressures
Discharge Considerations
Discharge eligibility
Resolution of resting dyspnea
SpO2 stable on room air or baseline home oxygen level
Safe ambulation with stable saturation
Clear outpatient plan and follow up
Treatment
Oxygen and Noninvasive Support
Oxygen titration framework
Target saturation selection
Most patients 92% to 96%
COPD or chronic hypercapnia risk 88% to 92%
Device escalation path
Nasal cannula
Nonrebreather
HFNC
NIV
Intubation
High flow nasal cannula
Setup and targets
Flow 40 to 60 L/min
Increase flow first for dyspnea and work of breathing
Increase FiO2 for hypoxemia
FiO2 titration to SpO2 target
Reduce FiO2 to lowest effective once stable
Noninvasive ventilation
COPD hypercapnic exacerbation strategy
BiPAP initial settings
IPAP 10 to 15 cmH2O
Titrate by 2 to 3 cmH2O every 5 to 10 minutes for ventilation
EPAP 4 to 6 cmH2O
Titrate for oxygenation and intrinsic PEEP offset
Backup rate 10 to 16 breaths per minute when available
Response targets
Improved dyspnea within 30 to 60 minutes
Rising pH on repeat gas
Falling PaCO2 on repeat gas
Cardiogenic pulmonary edema strategy
CPAP 8 to 12 cmH2O
If CPAP not tolerated then BiPAP with similar EPAP
Adjunct diuresis and vasodilator pathway alignment
Contraindications
Vomiting or aspiration risk
Inability to protect airway
Facial trauma or recent upper airway surgery
Hemodynamic instability
Airway and Intubation
Indications for intubation
Refractory hypoxemia on HFNC or NIV
Severe hypercapnic acidemia
pH < 7.20 with clinical fatigue
Airway protection failure
Inability to handle secretions
Deteriorating mental status
Preoxygenation
NIV preoxygenation when feasible
3 to 5 minutes with 100% FiO2
Apneic oxygenation nasal cannula
10 to 15 L/min during laryngoscopy
RSI medications adult
Induction agents
Etomidate IV 0.3 mg/kg
Hemodynamic neutrality preference
Ketamine IV 1 to 2 mg/kg
Bronchodilation benefit in asthma
Caution severe hypertension or ischemia context
Propofol IV 1 to 2 mg/kg
Hypotension risk
Paralytics
Succinylcholine IV 1 to 1.5 mg/kg
Contraindications
Hyperkalemia
Neuromuscular disease
Major burns after 24 to 48 hours
Rocuronium IV 1.2 mg/kg
Longer paralysis duration planning
Post intubation sedation and analgesia
Analgesia first approach
Fentanyl IV 25 to 100 mcg bolus
Repeat every 5 minutes to comfort and ventilator synchrony
Hydromorphone IV 0.5 to 1 mg bolus
Repeat every 10 to 15 minutes as needed
Sedation infusions
Propofol IV infusion 10 to 50 mcg/kg/min
Titrate every 5 minutes to target RASS
Hypotension monitoring
Dexmedetomidine IV infusion 0.2 to 1.5 mcg/kg/hr
Bradycardia monitoring
Midazolam IV infusion 1 to 10 mg/hr
Delirium risk consideration
Mechanical Ventilation
Lung protective ventilation for ARDS risk
Tidal volume targets
6 ml/kg predicted body weight
Accept 4 to 8 ml/kg range based on plateau pressure
Pressure limits
Plateau pressure < 30 cmH2O
Driving pressure minimization strategy
PEEP strategy
Moderate to high PEEP in moderate to severe ARDS
Hemodynamic monitoring during PEEP escalation
Oxygenation targets
SpO2 88% to 95% in ARDS strategy
PaO2 55 to 80 mmHg in ARDS strategy
Obstructive lung disease ventilation
Dynamic hyperinflation avoidance
Lower RR strategy
Prolonged expiratory time
Permissive hypercapnia acceptance if pH acceptable
PEEP setting
Low external PEEP start 0 to 5 cmH2O
Cautious titration for auto PEEP offset
Etiology Specific Therapies
Asthma severe exacerbation
Bronchodilators
Salbutamol nebulized 5 mg
Repeat every 20 minutes for 1 hour
Continuous nebulization option 10 to 15 mg/hr
Ipratropium nebulized 0.5 mg
Repeat every 20 minutes for 1 hour
Steroids
Methylprednisolone IV 125 mg
Alternative prednisone PO 50 mg when able
Magnesium sulfate
Magnesium sulfate IV 2 g over 20 minutes
Hypotension monitoring
Epinephrine for anaphylaxis or severe bronchospasm with poor air movement
Epinephrine IM 0.3 to 0.5 mg of 1 mg/ml
Repeat every 5 to 15 minutes as needed
COPD exacerbation with hypercapnia
Bronchodilators
Salbutamol nebulized 2.5 to 5 mg
Repeat every 20 minutes initially
Ipratropium nebulized 0.5 mg
Repeat every 4 to 6 hours
Steroids
Prednisone PO 40 mg daily
Typical duration 5 days
Methylprednisolone IV 40 to 60 mg if unable PO
Antibiotics when indicated
Increased sputum purulence
Increased sputum volume
Increased dyspnea
Ventilatory support requirement
Cardiogenic pulmonary edema
Diuresis
Furosemide IV 40 mg
Higher initial dose if chronic loop diuretic use
Vasodilator when hypertensive and not preload dependent
Nitroglycerin IV infusion 10 to 200 mcg/min
Titrate every 3 to 5 minutes to symptom and BP response
Pneumonia and sepsis related respiratory failure
Antibiotics within 1 hour for septic shock
Local empiric pathway alignment
Fluids and vasopressors as sepsis bundle
Norepinephrine infusion 0.05 to 1 mcg/kg/min
Titrate to MAP >= 65 mmHg
Pulmonary embolism with respiratory failure
Anticoagulation when no contraindication
Unfractionated heparin infusion for high risk or planned procedures
Thrombolysis consideration for massive PE with shock
Alteplase systemic dosing per institutional protocol
Opioid induced hypoventilation
Naloxone titration
Naloxone IV 0.04 mg
Repeat every 2 minutes to adequate ventilation
Avoid full withdrawal in chronic opioid use
Evidence and Recommendations
Noninvasive ventilation in COPD hypercapnic exacerbation
Reduced intubation and mortality in acidemic COPD exacerbation
Strong recommendation in major society guidelines for appropriate candidates
Lung protective ventilation in ARDS
Lower tidal volume strategy associated with improved outcomes
Class I recommendation based on critical care consensus for suspected ARDS
Prone positioning in moderate to severe ARDS
PaO2 FiO2 <= 150 mmHg on FiO2 >= 0.6 with PEEP >= 5 cmH2O as common threshold
Class IIa recommendation based on ICU trials and guidelines
Special Populations
Pregnancy
Pregnancy considerations
Physiologic changes
Lower functional residual capacity
Higher oxygen consumption
Oxygenation targets
SpO2 >= 95% typical fetal oxygenation goal
Imaging
PE algorithm with pregnancy adapted pathways
Radiation risk counseling with CT or VQ decisions
Medications
Avoid teratogenic agents when alternatives exist
Magnesium sulfate compatible when indicated
Geriatric
Older adult considerations
Atypical infection presentation
Afebrile sepsis risk
Lower physiologic reserve
Earlier fatigue and decompensation
Medication sensitivity
Higher hypotension risk with sedatives
Delirium risk with benzodiazepines
Pediatrics
Pediatric considerations
Age specific respiratory rate thresholds
Tachypnea cutoffs by age band
Weight based dosing
Ketamine IV 1 to 2 mg/kg for RSI
Rocuronium IV 1.2 mg/kg for RSI
Common etiologies
Bronchiolitis
Croup and upper airway obstruction
Asthma exacerbation
Early escalation triggers
Grunting
Head bobbing
Cyanosis
Background
Epidemiology
Burden and settings
Common ED and ICU syndrome rather than single diagnosis
Frequent causes pneumonia
Frequent causes heart failure
Frequent causes COPD and asthma exacerbations
High mortality subgroup
ARDS and septic shock overlap
Massive PE with shock
Pathophysiology
Hypoxemia mechanisms
VQ mismatch
Pneumonia and COPD as common drivers
Shunt
Alveolar flooding in ARDS
Atelectasis
Diffusion limitation
Interstitial lung disease
Hypercapnia mechanisms
Alveolar hypoventilation
COPD with airflow limitation
CNS depression
Increased dead space
Pulmonary embolism
Work of breathing failure
Respiratory muscle fatigue
Sustained tachypnea
Hyperinflation in obstructive disease
Therapeutic Considerations
Oxygen as a drug
Targeted saturation to avoid hypoxemia and hyperoxia harm
COPD hypercapnia risk group with controlled oxygen strategy
Positive pressure benefits
Reduced work of breathing
Improved alveolar recruitment
Reduced preload and afterload in cardiogenic edema
Risks of positive pressure
Barotrauma and pneumothorax
Hypotension from reduced venous return
Ventilation targets
Permissive hypercapnia in obstructive disease when needed to avoid high pressures
Lung protective ventilation to reduce ventilator induced lung injury
Patient Discharge Instructions
Copy discharge instructions
Discharge plan for resolved or mild respiratory failure causes
Medications as prescribed
Inhaler technique review
Steroid course completion if given
Antibiotic course completion if prescribed
Home monitoring
Worsening shortness of breath
New chest pain
Fever or rigors
New confusion or severe sleepiness
Return to ED immediately
Trouble breathing at rest
Lips or face turning blue or gray
Fainting or severe weakness
SpO2 below instructed threshold if home oximeter
Follow up
Primary care within 24 to 72 hours
Pulmonology or cardiology when indicated
Smoking cessation support if applicable
References
Clinical Guidelines and Evidence
Society guidelines
ATS ERS clinical practice guidelines on noninvasive ventilation for acute respiratory failure
NIV recommended in acute hypercapnic COPD exacerbation with acidemia
NIV recommended in cardiogenic pulmonary edema
Surviving Sepsis Campaign guidelines
Early antibiotics in septic shock
Vasopressor target MAP >= 65 mmHg
ARDS management guidelines and landmark trials
Low tidal volume ventilation strategy
Prone positioning in moderate to severe ARDS
Decision tools and validation
ROX index studies for HFNC monitoring
HACOR score studies for NIV failure prediction
Wells criteria and PERC for PE pathways in appropriate populations
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.