Respiratory Assessment & Diagnostics - Cheat Sheet
Your last-minute exam companion for respiratory physical assessment, ABG interpretation, oxygen delivery systems, and chest-tube management. Master the high-yield concepts that appear repeatedly on the NLE.
Respiratory Physical Assessment (IPPA)
Common values
Value
12–20 breaths/min
Symbol
RR
Quantity
Normal respiratory rate (adult)
Value
~5 g/dL
Symbol
N/A
Quantity
Deoxygenated Hb threshold for visible cyanosis
Important facts
- Normal adult respiratory rate: 12–20 breaths/min.
- IPPA order is critical: Inspection → Palpation → Percussion → Auscultation (never percuss first).
- Always compare side to side for symmetry and baseline abnormalities.
- Pursed-lip breathing = expiratory braking; slows airflow, reduces air trapping in emphysema.
- Tripod position = severe dyspnoea; patient leans forward on arms to fix chest muscles.
- Nasal flaring + retractions = increased respiratory effort = urgent assessment needed.
Key definitions
Tactile fremitus
Example
Pneumonia patient with increased fremitus over left lower lobe = consolidation present.
Vibration felt on chest wall when patient phonates 'ninety-nine'; increases over consolidation, decreases over effusion/pneumothorax.
Accessory muscle use
Example
COPD exacerbation with visible intercostal and subcostal retractions = severe dyspnoea.
Use of scalene, sternocleidomastoid, and intercostal muscles during breathing; indicates increased work of breathing and respiratory distress.
Barrel chest
Example
Emphysema patient with characteristic barrel chest appearance and pursed-lip breathing.
Increased anteroposterior (A-P) diameter of thorax from chronic air trapping and loss of elastic recoil.
Cyanosis (central vs peripheral)
Example
Central cyanosis in acute pneumonia with PaO2 <60 mmHg; peripheral cyanosis in cold or shock.
Central: lips/tongue blue = true hypoxaemia (late sign, needs ~5 g/dL deoxygenated Hb); Peripheral: fingers/toes = poor perfusion.
Clubbing
Example
Bronchiectasis or lung cancer patient with digital clubbing.
Finger/toe enlargement from chronic hypoxaemia; indicates long-standing respiratory or cardiac disease.
Diagrams to know
- Normal vs abnormal breath sound waveforms
- Thoracic anatomy: lobes, segments, landmarks (2nd intercostal = sternal angle)
Breath Sounds & Adventitious Findings
Important facts
- Crackles = FLUID or ATELECTASIS; wheezes = AIRWAY NARROWING.
- Stridor = immediate airway emergency; prepare for intubation.
- Bilateral symmetric wheezes in asthma; unilateral/asymmetric findings suggest lobar disease.
- Absent breath sounds = severe obstruction, pleural effusion, pneumothorax, or massive consolidation.
- Egophony: ask patient to say 'E'; if sounds like 'A' = consolidation (increased transmission).
- Whispered pectoriloquy: patient whispers '1–2–3'; normally faint but loud over consolidation.
Key definitions
Vesicular breath sounds
Example
Expected finding on healthy patient's bilateral lung base assessment.
Soft, low-pitched, heard over most lung fields; normal.
Bronchovesicular breath sounds
Example
Heard at T1–T4 anteriorly and posteriorly between lobes.
Intermediate pitch/intensity, heard over main bronchi (paratracheal, between scapulae).
Bronchial/tracheal breath sounds
Example
Bronchial breath sounds in pneumonia over consolidated area = consolidation confirmed.
Loud, high-pitched, hollow, heard only over trachea; abnormal anywhere else (suggests consolidation).
Crackles (rales)
Example
Fine crackles in pulmonary oedema (heart failure); coarse in pneumonia (secretions).
Discontinuous, fine popping sounds from fluid in airways or atelectasis (alveoli opening); heard in early inspiration.
Wheezes
Example
Widespread expiratory wheezes in acute asthma attack.
Continuous, musical, high-pitched; from narrowed airways; typically expiratory but can be biphasic in severe obstruction.
Rhonchi
Example
Patient with pneumonia and thick secretions in bronchi.
Low-pitched, snoring, rattling; from secretions in large airways; usually clears with cough.
Stridor
Example
Post-extubation stridor from vocal cord swelling or laryngeal oedema.
High-pitched, crowing sound heard WITHOUT stethoscope; upper-airway obstruction; EMERGENCY.
Pleural friction rub
Example
Pleurisy or pulmonary infarction with pleural irritation.
Grating, scratchy sound from inflamed pleura (visceral and parietal); worse on deep breathing.
Diagrams to know
- Breath sound characteristics table (pitch, intensity, duration, location)
- Decision tree: abnormal sound → crackles (fluid/atelectasis) or wheeze (airway) or stridor (upper airway)
Arterial Blood Gas (ABG) Analysis
Formulas
ROME Method: Respiratory Opposite, Metabolic Equal
Meaning
CO2 moves OPPOSITE to pH (Respiratory); HCO3 moves SAME direction as pH (Metabolic).
Watch out
Students often confuse which way CO2 and HCO3 move. REMEMBER: Respiratory Opposite (high CO2 = low pH), Metabolic Equal (low HCO3 = low pH).
When to use
Every time you interpret ABGs; always interpret pH first, then use ROME.
Common values
Value
7.35–7.45
Symbol
pH
Quantity
pH
Value
35–45 mmHg
Symbol
PaCO2
Quantity
PaCO2
Value
22–26 mEq/L
Symbol
HCO3
Quantity
HCO3
Value
80–100 mmHg
Symbol
PaO2
Quantity
PaO2
Value
95–100%
Symbol
SaO2
Quantity
SaO2
Important facts
- Normal ABG values (MUST MEMORIZE): pH 7.35–7.45, PaCO2 35–45, HCO3 22–26, PaO2 80–100, SaO2 95–100%.
- Always START with pH to determine if acidosis or alkalosis.
- Use ROME: check if the PaCO2 and HCO3 are CONSISTENT with the pH abnormality.
- Look for COMPENSATION: if one system is abnormal, the other may shift to normalize pH.
- Uncompensated: one system abnormal, pH abnormal, no compensation yet.
- Fully compensated: one system abnormal, pH normalized, other system has shifted fully.
- Partially compensated: one system abnormal, pH still abnormal, other system has partially shifted.
- A-a gradient (Alveolar-arterial): calculates expected PaO2; widened gradient = pulmonary disease (not hypoventilation).
- Remember: SpO2 DOES NOT reflect ventilation; normal SpO2 can hide CO2 retention.
Key definitions
pH
Example
pH 7.30 = acidosis; pH 7.50 = alkalosis.
Measure of acidity/alkalinity; <7.35 = acidosis, >7.45 = alkalosis, 7.35–7.45 = normal.
PaCO2 (respiratory component)
Example
PaCO2 50 = hypoventilation/CO2 retention (COPD, respiratory depression); PaCO2 30 = hyperventilation.
Partial pressure of CO2 in arterial blood; 35–45 mmHg normal; reflects ventilation adequacy.
HCO3 (metabolic component)
Example
HCO3 16 = metabolic acidosis (DKA, diarrhoea, shock); HCO3 30 = metabolic alkalosis (vomiting, antacid overdose).
Bicarbonate; 22–26 mEq/L normal; reflects kidney acid–base regulation and metabolic status.
PaO2 (oxygenation)
Example
PaO2 60 = hypoxaemia; requires oxygen therapy and investigation.
Partial pressure of oxygen in arterial blood; 80–100 mmHg normal; indicates gas exchange.
SaO2 (oxygen saturation)
Example
SaO2 88% = mild hypoxaemia; SaO2 <80% = severe, life-threatening.
Percentage of Hb bound to oxygen; 95–100% normal; indirect measure of PaO2.
Respiratory acidosis
Example
COPD exacerbation: pH 7.30, PaCO2 60, HCO3 24 (uncompensated respiratory acidosis).
pH <7.35 + PaCO2 >45 (high CO2); lungs cannot eliminate CO2; uncompensated if HCO3 normal.
Respiratory alkalosis
Example
Anxiety, pain, early sepsis: pH 7.50, PaCO2 28, HCO3 24.
pH >7.45 + PaCO2 <35 (low CO2); hyperventilation blows off CO2.
Metabolic acidosis
Example
DKA or lactic acidosis: pH 7.25, PaCO2 32, HCO3 14 (respiratory compensation expected).
pH <7.35 + HCO3 <22 (low bicarbonate); kidney dysfunction, organic acid accumulation, or loss of base.
Metabolic alkalosis
Example
Post-vomiting or NG suction: pH 7.50, PaCO2 40, HCO3 32.
pH >7.45 + HCO3 >26 (high bicarbonate); loss of acid or gain of base.
Diagrams to know
- ABG interpretation flowchart (pH → acid/base → PaCO2/HCO3 direction → diagnosis)
- ROME method quick reference table
Reactions or equations
Alveolar Gas Equation: PAO2 = (PB − PH2O) × FiO2 − (PaCO2 / R)
Note
Used to calculate expected PaO2 on room air (FiO2 21%) to detect pulmonary disease.
Conditions
PB = barometric pressure (760 at sea level), PH2O = water vapour pressure (47 mmHg), R = respiratory quotient (0.8), FiO2 = fraction of inspired oxygen.
Pulse Oximetry
Common values
Value
95–100%
Symbol
SpO2
Quantity
Normal SpO2
Value
90–94%
Symbol
SpO2
Quantity
Mild hypoxaemia
Value
80–89%
Symbol
SpO2
Quantity
Moderate hypoxaemia
Value
<80%
Symbol
SpO2
Quantity
Severe hypoxaemia
Important facts
- Normal SpO2: 95–100% on room air.
- SpO2 is UNRELIABLE in: poor perfusion, hypothermia, motion, nail polish, carbon monoxide poisoning (falsely elevated), anaemia.
- CRITICAL: SpO2 does NOT measure ventilation; patient can have normal SpO2 while retaining CO2 → always confirm with ABG if concerned.
- Pulse oximetry relies on pulsatile flow; non-pulsatile states (atrial fibrillation, cardiac arrest) may give false readings.
- Carbon monoxide binds Hb with high affinity → SpO2 falsely HIGH; must check carboxyhaemoglobin level.
- In anaemia, SpO2 may appear normal despite inadequate oxygen content because fewer Hb molecules are available to desaturate.
- Rightward shift of Hb-O2 dissociation curve (fever, acidosis, 2,3-DPG ↑) = Hb releases O2 more easily → tissue oxygenation improved despite lower SpO2.
Key definitions
SpO2 (oxygen saturation via pulse oximetry)
Example
SpO2 94% on room air in healthy patient; SpO2 88% in hypoxaemic COPD.
Non-invasive estimate of percent Hb saturated with oxygen; normal 95–100%; unreliable in poor perfusion/hypothermia.
Diagrams to know
- Limitations of SpO2 in various clinical conditions
Pulmonary Function Tests (PFTs) & Spirometry
Formulas
FEV1/FVC Ratio = (Forced Expiratory Volume in 1 sec) / (Forced Vital Capacity) × 100%
Meaning
FEV1 = volume of air exhaled in first 1 second; FVC = total volume exhaled from maximal inspiration; ratio differentiates obstructive vs restrictive.
Watch out
REVERSED values between obstruction and restriction are a common exam trap. Remember: Obstruction = FEV1/FVC DOWN (<70%); Restriction = FVC down but ratio normal/HIGH.
When to use
PFT interpretation; <70% = obstructive disease (asthma, COPD), ≥70% = restrictive disease or normal.
Common values
Value
≥70% of predicted
Symbol
N/A
Quantity
Normal FEV1/FVC ratio
Value
<70%
Symbol
N/A
Quantity
Obstructive disease FEV1/FVC
Value
Normal/high (≥70%) with low FVC
Symbol
N/A
Quantity
Restrictive disease FEV1/FVC
Value
50–79% predicted
Symbol
N/A
Quantity
Mild COPD FEV1
Value
30–49% predicted
Symbol
N/A
Quantity
Moderate COPD FEV1
Value
<30% predicted
Symbol
N/A
Quantity
Severe COPD FEV1
Value
≥80% personal best
Symbol
PEFR
Quantity
PEFR green zone
Value
50–79% personal best
Symbol
PEFR
Quantity
PEFR yellow zone
Value
<50% personal best
Symbol
PEFR
Quantity
PEFR red zone
Important facts
- FEV1/FVC ratio is the KEY DISCRIMINATOR between obstructive and restrictive patterns.
- Obstructive: FEV1/FVC <70% (airflow limitation); restrictive: FEV1/FVC ≥70% (volume limitation).
- Asthma is reversible obstruction (improves with bronchodilators); COPD is irreversible (no full reversal).
- PEFR traffic-light zones: Green ≥80% personal best = good control; Yellow 50–79% = use reliever; Red <50% = emergency.
- Teach patient to establish personal best PEFR first (when asthma well-controlled), then monitor trends.
- Predicted values vary by age, sex, height, and race; compare patient's result to predicted for their demographics.
- Effort-dependent test; poor effort = falsely low values → may need repeat testing.
Key definitions
FEV1 (Forced Expiratory Volume in 1 second)
Example
FEV1 75% of predicted = mild obstruction; FEV1 <50% = severe COPD.
Volume of air forcibly exhaled in first 1 second; indicator of airway resistance and ventilatory power.
FVC (Forced Vital Capacity)
Example
FVC 60% of predicted = restrictive disease (pulmonary fibrosis, obesity).
Total volume of air that can be forcibly exhaled from maximal inspiration; reduced in restrictive disease.
Obstructive disease
Example
Asthma: low FEV1/FVC; REVERSES with bronchodilator. COPD: low FEV1/FVC; does NOT fully reverse.
Airflow obstruction on exhalation; FEV1/FVC <70%; examples: asthma, COPD, bronchiectasis.
Restrictive disease
Example
Pulmonary fibrosis: FVC 50% predicted, FEV1/FVC 82% (normal ratio despite low volumes).
Reduced lung volume capacity; FVC ↓ but FEV1/FVC normal/high; examples: pulmonary fibrosis, chest-wall deformity, obesity.
PEFR (Peak Expiratory Flow Rate)
Example
Patient's personal best PEFR 500 L/min; current reading 380 L/min = 76% = yellow zone (caution).
Maximum flow rate during forced expiration; used at home in asthma; reported as % of personal best.
Diagrams to know
- Obstructive vs restrictive PFT pattern comparison
- FEV1/FVC ratio interpretation flowchart
Chest X-Ray (CXR) Assessment
Common values
Value
21–23 cm (oral); confirm on CXR tip above carina
Symbol
N/A
Quantity
Normal ETT depth from teeth
Important facts
- Always REMOVE metal (jewellery, buttons, zippers) before CXR.
- Confirm patient NOT pregnant or shield appropriately (RA 9173 radiation safety).
- No special preparation; no fasting required.
- Look for ETT/central-line placement: ETT tip should be 2–3 cm above the carina; central line should NOT be in the heart.
- Consolidation = WHITE; hyperinflation = dark/lucent (air-filled); effusion = opaque at base with blunted angle.
- Mediastinal shift = indicates tension (emergency); trachea/heart shifted away from pneumothorax side.
- Bilateral infiltrates = possible pulmonary oedema (heart failure) vs bilateral pneumonia vs ARDS.
- Look for signs of respiratory distress: elevation of hemidiaphragms, mediastinal widening, air bronchograms.
Key definitions
Consolidation/infiltrate
Example
Right lower lobe pneumonia shows right lower lobe infiltrate.
White/opaque appearance on CXR from fluid/cells filling alveolar spaces; seen in pneumonia, pulmonary oedema, pulmonary infarction.
Hyperinflation
Example
COPD patient with CXR showing flattened diaphragms and hyperlucent lung fields.
Increased air in lungs; flattened diaphragms and increased anteroposterior (A-P) diameter on CXR; seen in COPD/emphysema.
Pleural effusion
Example
Heart failure with bilateral pleural effusions; left lower costophrenic angle blunted.
Fluid accumulation in pleural space; blunted costophrenic angles and fluid level on CXR.
Pneumothorax
Example
Tension pneumothorax: collapsed right lung, trachea shifted left, hypotension, distended neck veins (EMERGENCY).
Air in pleural space; collapsed lung with visible pleural line and mediastinal shift (if tension).
Atelectasis
Example
Post-operative atelectasis from shallow breathing and secretion retention.
Alveolar collapse; appears as white/opaque area; caused by obstruction, compression, or loss of surfactant.
Diagrams to know
- Normal CXR landmarks and anatomy
- Common pathological CXR findings (consolidation, effusion, pneumothorax, hyperinflation)
Oxygen Therapy — Delivery Devices & FiO2
Formulas
FiO2 (Fraction of Inspired Oxygen) by Device
Meaning
Percentage of inspired gas that is oxygen; varies by device and flow rate; critical for matching therapy to patient need.
Watch out
MOST COMMON ERROR: assuming nasal cannula can deliver high FiO2 (it cannot exceed ~44%), or forgetting that flow >6 L/min does NOT increase FiO2 on nasal cannula. COPD target = 88–92%, NOT 94–98%.
When to use
Every oxygen order; match FiO2 to patient's oxygenation target (88–92% for COPD, 94–98% for others).
Common values
Value
24–44% FiO2 at 1–6 L/min
Symbol
N/A
Quantity
Nasal cannula FiO2 range
Value
40–60% FiO2 at 5–10 L/min (min 5 L/min)
Symbol
N/A
Quantity
Simple face mask FiO2 range
Value
60–80% FiO2 at 6–11 L/min
Symbol
N/A
Quantity
Partial rebreather mask FiO2 range
Value
80–95% FiO2 at 10–15 L/min
Symbol
N/A
Quantity
Non-rebreather mask FiO2 range
Value
24%, 28%, 31%, 35%, or 40% (fixed, precise)
Symbol
N/A
Quantity
Venturi mask FiO2 options
Value
88–92% (controlled oxygen)
Symbol
SpO2
Quantity
COPD target SpO2
Value
94–98%
Symbol
SpO2
Quantity
Standard target SpO2 (non-COPD)
Important facts
- Oxygen is a DRUG and requires an order in most settings per RA 9173.
- Nasal cannula FiO2: roughly 4% increase per L/min above room air (21%). At 1 L/min ≈ 24%; at 6 L/min ≈ 44%.
- Simple mask MINIMUM 5 L/min to prevent CO2 accumulation in mask dead space.
- Partial/non-rebreather: keep reservoir bag 1/3 to 1/2 full on inspiration; if it completely collapses, increase flow or switch device.
- Non-rebreather is EMERGENCY oxygen; highest concentration available in low-flow systems.
- Venturi mask = precise FiO2; unaffected by respiratory pattern; ideal for controlled oxygen therapy.
- COPD SpO2 TARGET = 88–92% (NOT 94–98%); higher SpO2 can suppress hypoxic drive and cause CO2 retention.
- NEVER fully withhold oxygen from hypoxic patient; instead, titrate carefully and monitor ABGs in COPD.
- Provide HUMIDIFICATION at flows >4 L/min to prevent mucosal drying, nosebleeds, and skin breakdown.
- NO SMOKING / NO OPEN FLAME near oxygen (fire hazard); secure cylinders upright; post signage.
Key definitions
Nasal cannula
Example
Patient on nasal cannula 3 L/min = ~32% FiO2; comfortable, can eat and talk.
Low-flow system; delivers 24–44% FiO2 at 1–6 L/min; allows eating/talking; comfortable; flows >6 L/min dry mucosa without increasing FiO2.
Simple face mask
Example
Post-operative patient on simple mask 6 L/min = ~50% FiO2; prevents CO2 rebreathing.
Low-flow system; delivers 40–60% FiO2 at 5–10 L/min; MINIMUM 5 L/min needed to flush exhaled CO2 from mask.
Partial rebreather mask
Example
Moderate hypoxaemia: partial rebreather 8 L/min with bag maintained at appropriate fill level.
Low-flow with attached reservoir bag; delivers 60–80% FiO2 at 6–11 L/min; keep bag 1/3 to 1/2 full on inspiration.
Non-rebreather mask
Example
Acute hypoxaemia (PaO2 <60): non-rebreather 15 L/min with bag inflated; emergency oxygen delivery.
Low-flow, highest concentration; reservoir bag + one-way valves prevent rebreathing; delivers 80–95% FiO2 at 10–15 L/min; bag must STAY INFLATED.
Venturi mask
Example
COPD patient: Venturi mask 28% FiO2 to maintain SpO2 88–92% without suppressing hypoxic drive.
High-flow, fixed-performance system; delivers PRECISE FiO2 (24%, 28%, 31%, 35%, 40%) regardless of breathing pattern; DEVICE OF CHOICE IN COPD.
Hypoxic drive
Example
COPD patient given 100% O2 → loses hypoxic drive → hypoventilation → CO2 rises dramatically (CO2 narcosis).
In chronic CO2 retainers (COPD), hypoxaemia is PRIMARY respiratory stimulus (not CO2); excessive oxygen removes this drive → CO2 retention/respiratory depression.
Diagrams to know
- Oxygen delivery device FiO2 ranges and clinical use selection
- Flow rate titration decision tree (match patient need to device)
Chest Tubes & Water-Seal Drainage Systems
Common values
Value
100–300 mL (more after surgery, less after trauma)
Symbol
N/A
Quantity
Normal drainage first 24 hours
Value
>100 mL/hour or sudden increase
Symbol
N/A
Quantity
Drainage threshold for physician report
Value
Varies; 20–36 Fr; larger for fluid, smaller for air
Symbol
N/A
Quantity
Typical chest tube diameter
Value
At least 30–50 cm below
Symbol
N/A
Quantity
Height of chest tube below insertion site
Important facts
- TIDALING IS NORMAL; sudden absence may mean lung re-expanded (check patient first) OR tube kinked/clogged (assess immediately).
- Intermittent bubbling on expiration/cough = normal in pneumothorax; continuous bubbling = AIR LEAK (abnormal).
- Keep drainage system BELOW chest level AT ALL TIMES to prevent backflow of fluid into pleura.
- DO NOT routinely clamp, milk, or strip the tube unless specifically ordered by physician.
- Clamping a tube with air leak = TENSION PNEUMOTHORAX RISK → do not clamp without direct order.
- Monitor amount, colour, and rate of drainage; mark level with tape and time q1h initially.
- Assess patient's work of breathing, SpO2, breath sounds, and chest symmetry with each assessment.
- Chest tube DISLODGED: immediately cover site with sterile occlusive dressing taped on 3 SIDES (flutter-valve effect); tape all 4 sides = traps air = tension risk.
- Tube DISCONNECTED from system: submerge tube end in sterile water/saline bottle to re-establish seal; get new system.
- Encourage deep breathing, coughing, incentive spirometry to promote lung re-expansion.
- Report excessive drainage (>100 mL/h), sudden increase, change in colour (fresh blood = active bleed), or new/persistent air leak.
- Manage pain adequately before coughing/movement to maximize cooperation.
- Chest tube removal: usually after air leak stops, drainage minimal (<30 mL/day), and lung well-expanded on CXR; post-removal CXR ordered to rule out re-collapse.
Key definitions
Chest tube
Example
Pneumothorax or pleural effusion patient with chest tube to drain pleural contents.
Catheter inserted into pleural space to drain air, fluid, blood, or pus; re-expands lung and restores negative intrapleural pressure.
Three-chamber drainage system
Example
Classic Pleur-Evac or Atrium system used in most hospitals for closed chest drainage.
Standard water-seal system: collection chamber (drainage), water-seal chamber (one-way valve), suction-control chamber (regulates suction level).
Tidaling (fluctuation)
Example
Gentle tidaling in water-seal chamber = tube patent, normal intrapleural pressure cycling.
Rise and fall of fluid level in water-seal chamber with each breath; NORMAL and EXPECTED.
Intermittent bubbling in water-seal chamber
Example
Fresh pneumothorax with intermittent bubbling as air is gradually removed.
Air bubbles intermittently released from pleural space, especially on expiration/cough; NORMAL when air is being evacuated (pneumothorax) or initially post-op.
Continuous bubbling in water-seal chamber
Example
Continuous bubbling in water-seal = systematically check connections, then clamping order to locate leak source.
Constant stream of bubbles = AIR LEAK; either in patient's lung/insertion site or in tubing/system → MUST FIND AND FIX.
Air leak detection (clamping sequence)
Example
Continuous bubbling: clamp at chest tube insertion, then progressively down tubing; identify where leak is located.
Clamp progressively from patient toward drainage unit; if bubbling stops, leak is between clamp and patient; if continues, leak is in system.
Tension pneumothorax
Example
Clamped chest tube with ongoing air leak → pressure builds → sudden deterioration with hypotension, JVD, tracheal deviation.
One-way leak allows air INTO pleural space but not OUT; causes complete lung collapse, mediastinal shift, hypotension, distended neck veins, absent breath sounds, tracheal deviation → CARDIAC ARREST EMERGENCY.
Diagrams to know
- Three-chamber drainage system diagram with normal vs abnormal findings
- Chest tube troubleshooting flowchart (tidaling absent? Bubbling continuous? Drainage excessive?)
- Air leak detection clamping sequence
Arterial Puncture & ABG Collection
Important facts
- ALWAYS perform Allen test BEFORE radial artery puncture to confirm collateral circulation.
- Preferred puncture sites: radial (wrist), femoral (groin), brachial (elbow) in order of preference.
- AFTER puncture: apply firm pressure for AT LEAST 5 MINUTES (longer if patient on anticoagulants) to prevent haematoma/complications.
- Use heparinized syringe (1–2 mL heparin); flush to coat syringe and expel excess heparin (excess heparin falsely lowers PaCO2).
- Collect 2–3 mL of blood; no air bubbles (air changes PaO2); expel any air immediately.
- SEAL syringe cap immediately to prevent gas exchange with room air.
- Transport to lab IMMEDIATELY or place on ice (slows metabolism, prevents time-dependent changes in pH/PaCO2).
- Label with patient name, time collected, FiO2, temperature, and anticoagulant therapy.
- Note respiratory rate, oxygen therapy, and any sedation as these affect results.
Key definitions
Allen test
Example
Compress both radial and ulnar arteries, ask patient to make fist (blanches hand), release ulnar pressure; if hand flushes in <5 sec, test positive (safe for radial puncture).
Bedside test to confirm ulnar artery collateral flow before radial artery puncture; prevents hand ischaemia if radial artery injured.
Diagrams to know
- Allen test positive vs negative findings
- Correct arterial puncture technique
Complications of Respiratory Conditions & Oxygen Therapy
Common values
Value
>50% FiO2 for >24–48 hours = risk of toxicity
Symbol
N/A
Quantity
Critical oxygen exposure time
Important facts
- Oxygen toxicity risk increases with high FiO2 AND prolonged duration; >50% FiO2 for >48 hours is concerning.
- Prevent absorption atelectasis with PEEP, frequent position changes, incentive spirometry.
- CO2 narcosis is a medical emergency in COPD; reduce oxygen immediately to target SpO2 88–92% and consider non-invasive ventilation.
- Tension pneumothorax is a CARDIAC ARREST-LEVEL EMERGENCY; immediate needle decompression (2nd intercostal space midclavicular line) followed by chest tube insertion.
- Mucosal drying and nosebleeds from high-flow oxygen without humidification; add humidifier at flows >4 L/min.
- Skin breakdown behind ears and over nose from face mask; use protective padding, rotate masks, relieve pressure regularly.
- Aspiration risk increases with decreased consciousness, supine position, and endotracheal intubation; maintain aspiration precautions.
Key definitions
Oxygen toxicity
Example
Patient on 100% O2 for >48 hours may develop oxygen toxicity; switch to lower FiO2 or switch support modality (e.g., non-invasive ventilation).
Lung injury from prolonged exposure to high FiO2 (>50% for >24–48 hours); causes substernal discomfort, dry cough, decreased vital capacity, worsening gas exchange.
Absorption atelectasis
Example
High-flow oxygen without PEEP can predispose to atelectasis; use appropriate PEEP to recruit alveoli.
Alveolar collapse from absorbed gases when breathing high-concentration oxygen; occurs because N2 (normally holds alveoli open) is replaced by O2 (rapidly absorbed into blood).
CO2 narcosis
Example
COPD patient on 100% O2 → suppressed hypoxic drive → hypoventilation → CO2 rises → develops confusion and lethargy.
CNS depression from elevated CO2; manifests as drowsiness, headache, confusion, asterixis (flapping tremor); seen in severe CO2 retainers given excessive oxygen.
Tension pneumothorax
Example
Post-thoracotomy with clamped chest tube and ongoing air leak → sudden deterioration, hypotension, JVD → requires immediate needle decompression/tube release.
Air enters pleural space but cannot exit; builds pressure → collapses lung, shifts mediastinum, compresses heart → hypotension, distended neck veins, absent breath sounds, tracheal deviation → CARDIAC ARREST.
Diagrams to know
- Signs and symptoms of oxygen toxicity and CO2 narcosis
- Tension pneumothorax clinical presentation and emergency management
Must remember
- NORMAL ABG VALUES (memorize exactly): pH 7.35–7.45, PaCO2 35–45 mmHg, HCO3 22–26 mEq/L, PaO2 80–100 mmHg, SaO2 95–100%. Use ROME: Respiratory Opposite, Metabolic Equal.
- BREATH SOUNDS: Crackles = FLUID (pneumonia, pulmonary oedema); Wheezes = AIRWAY NARROWING (asthma, COPD); Stridor = UPPER-AIRWAY OBSTRUCTION (emergency).
- OXYGEN DEVICES: Nasal cannula 24–44% at 1–6 L/min (flow >6 L/min useless); Simple mask 40–60% at ≥5 L/min; Non-rebreather 80–95% (keep bag inflated); VENTURI = PRECISE FiO2 = COPD device.
- COPD SpO2 TARGET = 88–92% (NOT 94–98%). Excess oxygen suppresses hypoxic drive → CO2 retention/CO2 narcosis. Never fully withhold O2; titrate carefully and monitor ABGs.
- FEV1/FVC RATIO: <70% = OBSTRUCTIVE (asthma, COPD); ≥70% = RESTRICTIVE (pulmonary fibrosis). Asthma is reversible with bronchodilators; COPD is NOT fully reversible.
- CHEST TUBE: Tidaling is NORMAL and EXPECTED. Intermittent bubbling on expiration = normal. CONTINUOUS bubbling in water-seal = AIR LEAK (find and fix). Keep system BELOW chest level. Do NOT routinely clamp (risks tension pneumothorax).
- CHEST TUBE DISLODGED: Cover site with sterile occlusive dressing taped on 3 SIDES (flutter valve); tape all 4 sides = traps air = tension risk. Notify physician immediately.
- TUBE DISCONNECTED: Submerge tube end in sterile water/saline bottle to re-establish water seal; get new drainage system. Do NOT let air enter pleural space.
- ARTERIAL PUNCTURE: ALWAYS do Allen test BEFORE radial puncture. AFTER: hold firm pressure ≥5 minutes (longer if anticoagulated) to prevent haematoma. Use heparinized syringe, no air bubbles, seal immediately, transport on ice.
- TENSION PNEUMOTHORAX (EMERGENCY): Tracheal deviation, hypotension, distended neck veins, absent breath sounds, cyanosis. Caused by clamped chest tube with air leak. Requires immediate needle decompression (2nd ICS midclavicular) then chest tube insertion.
Last minute tips
- On any ABG question, START with pH (acidosis vs alkalosis), then check PaCO2 and HCO3 direction using ROME. Candidates often guess the disorder without this systematic approach—it costs 30 seconds but ensures accuracy.
- For oxygen delivery device questions, MEMORIZE FiO2 ranges by device. Nasal cannula CAN'T exceed 44% no matter what; if exam asks for 50% FiO2, the answer is NOT nasal cannula. Simple mask minimum 5 L/min or CO2 accumulates.
- Chest tube troubleshooting: 'Continuous bubbling in water-seal chamber' almost ALWAYS means AIR LEAK on exams. Know the clamping sequence: clamp near patient first; if bubbling stops, leak is patient-side; if continues, leak is system-side.
- COPD oxygen target is the SINGLE MOST MISSED point on the NLE. SpO2 88–92% is NOT a 'typo'—it's intentional because higher O2 kills the hypoxic drive. Candidates overtreat COPD and inadvertently cause CO2 narcosis.
- When reading a CXR finding, correlate with clinical signs. Pleurisy on exam (painful, pleural rub) but no effusion on CXR = early/resolving pleuritis. Effusion on CXR without signs = watch, may be heart failure. Don't diagnose from imaging alone.
Comparison tables
Breath Sounds Comparison (Normal vs Abnormal)
| Sound Type | Pitch & Quality | Duration | Location | Clinical Significance |
|---|---|---|---|---|
| Vesicular | Low-pitched, soft, rustling | Inspiration > expiration | Over most lung fields | Normal |
| Bronchovesicular | Medium pitch, hollow | Equal inspiration & expiration | Over main bronchi, between scapulae | Normal location; abnormal elsewhere |
| Bronchial/tracheal | High-pitched, loud, hollow | Expiration > inspiration | Over trachea only | Abnormal over lungs (suggests consolidation) |
| Crackles (rales) | Discontinuous, fine popping | Early inspiration (fine); late inspiration (coarse) | Usually bibasal, lower lobes | Fluid/atelectasis: pneumonia, pulmonary oedema, heart failure |
| Wheezes | Continuous, musical, high-pitched | Usually expiratory; can be biphasic | Diffuse or localized | Airway narrowing: asthma, COPD, bronchitis |
| Rhonchi | Low-pitched, snoring, rattling | Usually expiratory | Large airways (central) | Secretions in airways; may clear with cough |
| Stridor | High-pitched, crowing | Inspiratory (laryngeal); biphasic (subglottic) | Audible without stethoscope | Upper-airway obstruction: EMERGENCY |
| Pleural friction rub | Grating, scratchy, creaking | Throughout breathing cycle | Area of pleural irritation | Pleurisy, pulmonary infarction |
ABG Interpretation — Four Primary Disorders (ROME Method)
| Disorder | pH | PaCO2 | HCO3 | Cause/Example |
|---|---|---|---|---|
| Respiratory Acidosis | <7.35 (acidosis) | >45 (HIGH — respiratory component) | Normal (24) or elevated (compensation) | Hypoventilation: COPD exacerbation, respiratory depression, chest trauma |
| Respiratory Alkalosis | >7.45 (alkalosis) | <35 (LOW — respiratory component) | Normal (24) or low (compensation) | Hyperventilation: anxiety, pain, early sepsis, hypoxaemia |
| Metabolic Acidosis | <7.35 (acidosis) | Normal (40) or LOW (respiratory compensation) | <22 (LOW — metabolic component) | Acid gain or base loss: DKA, lactic acidosis, diarrhoea, renal failure |
| Metabolic Alkalosis | >7.45 (alkalosis) | Normal (40) or HIGH (respiratory compensation) | >26 (HIGH — metabolic component) | Base gain or acid loss: vomiting, NG suction, antacid overdose, diuretics |
Obstructive vs Restrictive Pulmonary Disease
| Feature | Obstructive | Restrictive |
|---|---|---|
| Pathophysiology | Airflow obstruction (resistance ↑) | Lung volume/capacity ↓ |
| FEV1/FVC ratio | <70% (low) | ≥70% (normal or high) |
| FVC | Normal or slightly low | Significantly LOW (reduced capacity) |
| TLC (Total Lung Capacity) | Normal or HIGH (air trapping) | LOW (reduced volume) |
| RV/TLC ratio | HIGH (air trapping, residual volume ↑) | Normal |
| Examples | Asthma, COPD, bronchiectasis, cystic fibrosis | Pulmonary fibrosis, sarcoidosis, chest-wall deformity, obesity, kyphoscoliosis |
| Bronchodilator response | Asthma: reversible (improves); COPD: NOT fully reversible | No bronchodilator response |
| Clinical presentation | Dyspnoea on exertion, wheezing, cough, barrel chest, pursed-lip breathing | Dyspnoea on exertion, dry cough, reduced exercise tolerance, restrictive pattern |
Oxygen Delivery Systems — FiO2 & Clinical Use
| Device | System Type | FiO2 Range | Flow Rate | Key Points | Best Use |
|---|---|---|---|---|---|
| Nasal cannula | Low-flow | 24–44% | 1–6 L/min | Flow >6 L/min does NOT ↑ FiO2; dry mucosa >4 L/min; allow eating/talking | Mild hypoxaemia, comfort, long-term O2 |
| Simple face mask | Low-flow | 40–60% | 5–10 L/min | MINIMUM 5 L/min to flush CO2 from mask dead space; prevents rebreathing | Moderate hypoxaemia |
| Partial rebreather mask | Low-flow | 60–80% | 6–11 L/min | Reservoir bag attached; keep bag 1/3–1/2 full on inspiration; high concentration | Higher FiO2 needs; moderate-to-severe hypoxaemia |
| Non-rebreather mask | Low-flow | 80–95% (highest low-flow) | 10–15 L/min | Reservoir + one-way valves; keep bag INFLATED; highest non-invasive O2 | EMERGENCY: severe hypoxaemia, acute decompensation |
| Venturi mask | High-flow (fixed) | 24%, 28%, 31%, 35%, or 40% (PRECISE) | Varies by setting (typically 4–8 L/min) | Precise FiO2 REGARDLESS of breathing pattern; unaffected by tidal volume | GOLD STANDARD in COPD; controlled, low-concentration O2 |
Chest Tube Water-Seal System — Normal vs Abnormal Findings
| Finding | Normal/Expected | Abnormal | Action |
|---|---|---|---|
| Tidaling (fluctuation) in water-seal chamber | Gentle rise and fall with breathing = NORMAL | Sudden absence = lung re-expanded OR tube kinked/clogged; continuous vigorous bubbling = air leak | Assess patient; ensure tubing patent; if concerned, check for air leak with clamping sequence |
| Bubbling in water-seal chamber | Intermittent bubbling during expiration/cough (air being evacuated) = NORMAL in pneumothorax | CONTINUOUS bubbling = AIR LEAK; abnormal | Systematically check connections, then clamp progressively from patient to identify leak source |
| Drainage amount | First 24 h: 100–300 mL (post-op) or less (post-trauma); decreases daily | >100 mL/h or sudden increase; bright red/frank blood (active bleed) | Notify physician; monitor carefully; may indicate infection, recurrent leak, or bleeding |
| Drainage colour | Serous/serosanguinous (yellow-red); gradually clears | Fresh bright red (active bleeding); cloudy/foul-smelling (infection) | Frank blood: may indicate intercostal vessel injury; foul odour: assess for empyema |
| Suction-control chamber bubbling | Gentle continuous bubbling (wet system) or dial set appropriately (dry system) | Vigorous bubbling (too much suction); no bubbling (suction OFF or disconnected) | Adjust suction level per order; ensure system connected; do not increase beyond prescribed level |
| Patient work of breathing / breath sounds | Improving effort; equal bilateral breath sounds; SpO2 ≥94%; symmetrical chest rise | Increased dyspnoea; absent breath sounds unilaterally; hypoxaemia; asymmetrical chest | Assess tube patency; check for re-collapse or tension pneumothorax; escalate care if deteriorating |
Diagrams
ABG Interpretation Systematic Approach (ROME Method)
Systematic flowchart for interpreting ABGs using the ROME method. Start with pH to identify acidosis or alkalosis, then determine whether the abnormality is respiratory (PaCO2) or metabolic (HCO3) in origin. Check for appropriate compensation from the other system.
Respiratory Physical Assessment (IPPA) Overview
Mind map showing the four components of respiratory assessment (Inspection, Palpation, Percussion, Auscultation) with key findings under each. Helps organize the systematic approach to respiratory physical examination.
Chest Tube Air Leak Detection & Troubleshooting
Practical troubleshooting flowchart for detecting and locating air leaks in chest tube systems. Guides nurses through systematic clamping and assessment to identify whether air leak is from patient, tubing, or drainage system.
Oxygen Device Selection by FiO2 Requirement
Decision tree for selecting appropriate oxygen delivery device based on target FiO2 and patient type. Emphasizes critical differences in flow rates, FiO2 ranges, and special considerations for COPD patients.
Post-Operative Chest Tube Management Timeline
Timeline showing typical progression of chest tube management post-operatively, from immediate monitoring through removal criteria and post-removal assessment. Helps students understand expected course and when interventions are needed.