Mechanical Ventilation Nursing Guide

🫁Indications for Mechanical Ventilation

Acute Hypoxaemic Failure

PaO₂/FiO₂ ratio <200 mmHg despite high-flow oxygen. Causes: pneumonia, ARDS, pulmonary oedema.

Acute Hypercapnic Failure

pH <7.25 with PaCO₂ >50 mmHg. Causes: COPD exacerbation, neuromuscular disease, overdose.

Respiratory Muscle Fatigue

Increased WOB, paradoxical breathing, accessory muscle use, RR >35, inability to speak in sentences.

Airway Protection

GCS ≤8, aspiration risk, upper airway obstruction, inability to manage secretions, agitated trauma patient.

🔄Phases of Ventilation

Inspiration

Ventilator generates positive pressure to inflate lungs
Flow delivered until set volume or pressure limit reached
Inspiratory time (Ti) typically 0.8–1.2 seconds
I:E ratio normally 1:2 (allows adequate expiration)
In ARDS: may use inverse I:E ratio (1:1 or 2:1)

Expiration

Passive — driven by lung/chest wall recoil
Expiratory time (Te) must be adequate to prevent air-trapping
PEEP valve maintains alveolar pressure at end-expiration
Time constant (τ) = Compliance × Resistance
3τ = ~95% exhalation complete; 5τ = complete

Auto-PEEP (Intrinsic PEEP)

Trapped air from incomplete exhalation. Measure with expiratory hold manoeuvre (10 sec pause on ventilator — note elevated baseline pressure). Risk factors: high RR, long Ti, short Te, bronchospasm, high VT.

📐Compliance & Resistance

Key Formulas

Static Compliance (Cstat)

Cstat = VT ÷ (Pplat − PEEP)

Normal: 60–100 mL/cmH₂O

Requires inspiratory hold for Pplat

Dynamic Compliance (Cdyn)

Cdyn = VT ÷ (PIP − PEEP)

Lower than Cstat (includes resistance)

Affected by airway resistance

Interpreting Compliance Changes

Parameter	Cstat ↓	Cdyn ↓ (Cstat unchanged)
Indicates	Reduced lung/chest wall compliance (parenchymal problem)	Increased airway resistance
Causes	ARDS, pulmonary oedema, atelectasis, pneumonia, obesity	Bronchospasm, secretions, kinked tube, biting on ETT
PIP vs Pplat	Both elevated	PIP elevated, Pplat normal

Time Constant (τ)

τ = Compliance (L/cmH₂O) × Resistance (cmH₂O·s/L)

3τ ≈ 95% tidal volume exhaled | 5τ ≈ complete exhalation

⚙️Volume-Controlled Ventilation (VCV / CMV)

Principle: Set tidal volume (VT) delivered at set respiratory rate. Pressure varies depending on lung compliance and airway resistance.

SET Parameters

Tidal volume (VT)
Respiratory rate (RR)
FiO₂
PEEP
Flow rate & waveform
I:E ratio

VARIABLE Output

PIP (varies)
Pplat (varies)
Mean airway pressure

Best Used When

Volume control required
Paralysed patient
Unstable lung mechanics
Initial stabilisation
Neuromuscular disease

⚙️Pressure-Controlled Ventilation (PCV)

Principle: Set inspiratory pressure (PInsp) delivered for set Ti. Tidal volume varies with lung compliance and resistance.

SET Parameters

Inspiratory pressure (PInsp)
Respiratory rate (RR)
Inspiratory time (Ti) or I:E
FiO₂
PEEP

VARIABLE Output

Tidal volume (varies)
Flow (decelerating)

Advantage / Caution

Decelerating flow → better gas distribution
Pressure-limited → safer for lungs
Monitor VT carefully
VT drops if compliance worsens

⚙️Pressure Support Ventilation (PSV)

Principle: Patient-triggered, pressure-supported breaths. Patient controls RR and Ti. Ventilator augments each breath with set pressure support level.

Characteristics

Requires patient respiratory drive
PS level set (e.g., 10 cmH₂O above PEEP)
Breath cycles off at flow threshold (~25% peak flow)
VT & RR determined by patient effort + PS level
Primary weaning mode

Weaning with PSV

Start at PS 12–14 cmH₂O
Reduce by 2 cmH₂O increments
Target: PS 5–8 cmH₂O before SBT
Monitor VT, RR, WOB during reduction

⚙️SIMV with Pressure Support

Principle: Set number of mandatory breaths (volume or pressure-controlled) synchronised to patient effort; additional patient breaths supported by PS.

Hybrid mode: mandatory + spontaneous breaths
Synchronisation window: ventilator detects patient trigger before delivering mandatory breath
PS level applied to spontaneous breaths above mandatory rate
Weaning: gradually reduce mandatory RR → patient assumes more WOB
Less preferred than PSV-based weaning (associated with prolonged weaning in some studies)

⚙️Advanced Modes

PRVC / APV (Pressure-Regulated Volume Control)

Volume-guaranteed mode using pressure-controlled breaths. Ventilator auto-adjusts PInsp breath-by-breath to achieve target VT. Combines benefits of PCV (decelerating flow) with guaranteed VT.

APRV / BiLevel (Airway Pressure Release Ventilation)

Designed for ARDS. Maintains high continuous pressure (P_high) for long T_high (4–6 sec), with brief release to P_low (short T_low ~0.4–0.6 sec). Allows spontaneous breathing throughout. Recruits alveoli; may reduce sedation needs.

CPAP (Continuous Positive Airway Pressure)

Provides constant positive pressure throughout respiratory cycle. No mandatory breaths — patient breathes spontaneously. Used as extubation bridge or for obstructive sleep apnoea via mask. Low CPAP (5 cmH₂O) often used for SBT assessment.

📊Mode Comparison Summary

Mode	Trigger	VT Control	Pressure Control	Patient Work	Best For
VCV	Time/Patient	Fixed	Variable	Low	Initial stabilisation, paralysis
PCV	Time/Patient	Variable	Fixed	Low	ARDS, improved distribution
PRVC/APV	Time/Patient	Guaranteed	Auto-adjusted	Low–Mod	Variable compliance, universal
PSV	Patient only	Variable	Fixed support	High (by design)	Weaning, cooperative patients
SIMV+PS	Both	Set mandatory	PS on spont	Moderate	Gradual weaning
APRV	Spontaneous	Variable	High P+release	Preserved	Refractory ARDS
CPAP	Patient only	Patient-driven	Constant CPAP	Full	SBT, extubation bridge

🎯Lung-Protective Ventilation Targets

Tidal Volume

6–8 mL/kg IBW
Start at 6 mL/kg in ARDS. Use IBW — NOT actual body weight.

Plateau Pressure

≤30 cmH₂O
Measure with 0.5–2 sec inspiratory hold in VCV. Reflects alveolar distension risk.

Driving Pressure

≤15 cmH₂O
Pplat − PEEP. Strongest independent predictor of VILI. Target <13 cmH₂O in ARDS.

PEEP

5–10 cmH₂O
Higher PEEP (10–18) for moderate-severe ARDS. Balance between recruitment and overdistension.

Rate (RR)

12–20 /min
Up to 35 in ARDS if needed for permissive hypercapnia strategy.

SpO₂ Target

88–95%
PaO₂ 55–80 mmHg acceptable. Avoid hyperoxia (SpO₂ >96% on high FiO₂).

FiO₂

Start at 1.0, titrate down to maintain SpO₂ target. Prolonged FiO₂ >0.6 carries oxygen toxicity risk.

⚖️IBW & Tidal Volume Calculator

Step 1: Calculate Ideal Body Weight (IBW)

Biological Sex

Height (cm)

Ideal Body Weight (IBW)—

VT at 6 mL/kg IBW (protective)—

VT at 7 mL/kg IBW (standard)—

VT at 8 mL/kg IBW (upper limit)—

Driving Pressure Calculator

Plateau Pressure (cmH₂O)

PEEP (cmH₂O)

Driving Pressure (ΔP)—

Assessment—

📈PEEP Optimisation Strategies

PEEP/FiO₂ Table (ARDSNet): Use standard lookup table pairing FiO₂ with PEEP to achieve SpO₂ 88–95%. Lower PEEP table: FiO₂ 0.3→PEEP 5; Higher PEEP table for severe ARDS.

Incremental PEEP Trial: Increase PEEP in 2 cmH₂O steps, assess oxygenation and compliance. Stop if Pplat >30, BP drops, or driving pressure increases.

Lung Recruitment Manoeuvre: Sustained inflation at 40 cmH₂O for 40 seconds (40/40 manoeuvre) or stepwise approach. ICU physician order required. Monitor for haemodynamic deterioration and pneumothorax.

Permissive Hypercapnia

Acceptable strategy in ARDS to allow lung-protective low VT. Target: pH ≥7.20. Compensatory renal bicarbonate retention occurs over 24–48 hours. Contraindicated in raised ICP, pulmonary hypertension, right heart failure.

🔢IBW Formula Reference

Male IBW

IBW = 50 + 0.91 × (height in cm − 152.4)

Female IBW

IBW = 45.5 + 0.91 × (height in cm − 152.4)

🚨HIGH PRESSURE Alarm — DOPE Mnemonic

High pressure alarm = PIP exceeds set upper limit.

Always assess the patient FIRST. If in doubt — disconnect from ventilator and bag-valve mask with 100% FiO₂ while investigating.

Displacement — ETT displaced (right mainstem intubation, partial extubation). Check: equal chest rise, capnography, auscultation, CXR.

Obstruction — Tube kinking, biting, secretions blocking airway, mucus plug. Check: pass suction catheter, bite block in place, suction.

Pneumothorax — Tension pneumothorax = emergency. Signs: absent breath sounds, hypotension, tracheal deviation, ↑ HR. Needle decompression if tension suspected.

Equipment — Water in circuit, kinked tubing, circuit disconnection, bronchospasm, high airway resistance from COPD/asthma, coughing/breath-stacking.

Common High Pressure Causes

Cause	Clue	Action
Tube kinking/biting	Cdyn ↓, Cstat normal	Reposition head, bite block, suction
Secretion plug	↑ PIP, suction yields plugs	Suction, saline lavage if needed
Bronchospasm	↑ PIP, wheeze, Cdyn ↓	Nebulised bronchodilator, MDI via circuit
Pneumothorax	↑ PIP + ↑ HR + ↓ BP	Bag-mask, urgent CXR, physician alert
Right mainstem intubation	Unilateral breath sounds	Deflate cuff, pull ETT back 2 cm, CXR
Patient agitation/coughing	Synchronous with cough	Assess sedation/analgesia need
Auto-PEEP	Baseline pressure elevated	Expiratory hold, reduce RR/VT

⬇️LOW PRESSURE / LOW VOLUME Alarm

Cause	Signs	Action
Circuit disconnection	No chest rise, audible hiss	Reconnect circuit immediately
Cuff leak	Gurgling sound, low exhaled VT	Check/inflate cuff to 20–30 cmH₂O, check pilot balloon
ETT displacement/extubation	No CO₂ waveform, air at mouth	Remove ETT, BVM ventilation, call physician for re-intubation
Bronchopleural fistula	Large air leak post chest drain	Physician assessment, adjust ventilator settings

📉Low SpO₂ on Ventilator — Nursing Response

Disconnect from ventilator → BVM with 100% FiO₂. This is the safest immediate action while you assess the cause.

Assess patient: Is chest rising? Equal breath sounds? Skin colour? Haemodynamic status? Mental status change?

Check ETT: Position, depth at teeth, cuff pressure, patency (pass suction catheter).

Check ventilator circuit: Water in tubing, connections, FiO₂ sensor, oxygen supply connected and flowing.

Call physician if cause not rapidly identified. Prepare for CXR, ABG. If pneumothorax suspected → urgent physician review for chest decompression.

🛡️Ventilator-Induced Lung Injury (VILI) Prevention

VILI Mechanisms (VILI Pentagon)

Barotrauma: Excess pressure → alveolar rupture (Pplat >30)
Volutrauma: Excess volume → overdistension (VT >10 mL/kg)
Atelectrauma: Repetitive open/collapse of alveoli (low PEEP)
Biotrauma: Inflammatory mediator release → systemic MODS
Stress riser: Interface between aerated/non-aerated lung (driving pressure)

Prevention Targets

VT 6–8 mL/kg IBW (6 in ARDS)
Pplat ≤30 cmH₂O
Driving pressure ≤15 cmH₂O
Adequate PEEP to prevent atelectrauma
FiO₂ titration — avoid prolonged hyperoxia
Prone positioning in severe ARDS (PaO₂/FiO₂ <150)

📋Daily Weaning Readiness Screen (SAT + SBT)

ABCDEF Bundle: Assess, Both SAT + SBT, Choice of analgosedation, Delirium monitoring, Early mobility, Family engagement — the evidence-based framework for ICU liberation.

SBT Eligibility Criteria (all must be met)

FiO₂ ≤ 0.40 and SpO₂ ≥ 90% PEEP ≤ 8 cmH₂O Haemodynamically stable (no or minimal vasopressor support) Patient demonstrating inspiratory effort / triggering ventilator Reversible cause of respiratory failure identified and treated No active bronchospasm, seizures, or agitation Spontaneous Awakening Trial (SAT) passed — patient awake and following commands Adequate cough and secretion clearance

🌬️Spontaneous Breathing Trial (SBT) Methods

T-Piece Trial

Disconnect from ventilator → patient breathes humidified oxygen through T-piece. Duration: 30–120 minutes. Tests patient's ability to breathe independently. Higher work of breathing than low PSV.

Low PSV SBT

Maintain on ventilator at PSV 5–8 cmH₂O + PEEP 5 cmH₂O for 30–120 minutes. Overcomes ETT resistance (~5 cmH₂O). Preferred in most ICU protocols — nurse can monitor alarms.

SBT Failure Criteria (stop immediately if any present)

Parameter	Failure Threshold	Action
Respiratory rate	>35 breaths/min	Return to full support, notify physician
SpO₂	<90%	Return to support, assess cause
Heart rate	>140 or <60 bpm	Return to support, 12-lead ECG
Blood pressure change	>20% from baseline	Return to support, haemodynamic assessment
Distress / agitation	Marked anxiety, diaphoresis	Return to support, reassess sedation
Paradoxical breathing	Abdominal/thoracic dyssynchrony	Return to support, muscle fatigue assessment

📏RSBI — Rapid Shallow Breathing Index

RSBI = Respiratory Rate (breaths/min) ÷ Tidal Volume (litres)

Measured during 1 minute of spontaneous breathing (T-piece or CPAP)

RSBI <105

Predictive of successful extubation. Sensitivity ~97%, specificity ~64%.

RSBI 105–130

Borderline. Consider clinical context, secretion burden, cough strength.

RSBI >130

Predicts SBT failure. Return to support, investigate remediable causes.

✅Extubation Criteria Checklist

SBT passed (30–120 min without failure criteria) RSBI <105 (supportive but not standalone criterion) Adequate cough strength (cuff leak cough test or peak expiratory flow) Patient follows commands (show me 2 fingers, open eyes) Minimal secretion burden — suction <2 hourly Cuff leak test passed (if prolonged intubation >72h to assess laryngeal oedema) Physician order obtained Reintubation equipment at bedside (BVM, suction, ETT, laryngoscope, ETCO₂) Discuss HFNC post-extubation to reduce re-intubation risk

Post-Extubation HFNC (High-Flow Nasal Cannula)

Strong evidence supports HFNC immediately post-extubation in high-risk patients (elderly, cardiac/pulmonary disease, obesity, failed SBT requiring ≥24h ventilation). Start at 40–50 L/min, FiO₂ to maintain SpO₂ ≥94%. Has been shown to reduce re-intubation rates vs conventional oxygen therapy.

🦠VAP Bundle — GCC ICU Standard

VAP (Ventilator-Associated Pneumonia)

Pneumonia occurring ≥48–72 hours after intubation. Incidence: 9–27% of ventilated patients. Attributable mortality: 13–50%. GCC ICUs target bundle compliance >95%.

Core VAP Bundle Elements

HOB elevation 30–45° — reduces microaspiration of gastric content. Document degree at each nursing check. Contraindications: spinal instability, haemodynamic instability.

Oral care with chlorhexidine 0.12% BD — reduces oropharyngeal bacterial colonisation. Use soft toothbrush + suction. Every 12 hours minimum.

Subglottic secretion drainage — suction pooled secretions above cuff before migration past ETT. Continuous (low-pressure −20 to −30 mmHg) or intermittent (every 1–2 hours). ETT must have subglottic port.

Daily sedation hold (SAT) — interrupts sedation infusion at set time, assess patient. Reduces ventilator days. Paired with SBT screening.

DVT prophylaxis — LMWH per protocol (or compression devices if anticoagulation contraindicated).

Peptic ulcer prophylaxis — PPI or H2-blocker per protocol for mechanically ventilated patients.

Additional Infection Prevention

Hand hygiene before and after any circuit/airway manipulation
Sterile technique for ETT suctioning (open circuit)
Closed suction catheter systems preferred — change every 5–7 days or if visibly soiled
Ventilator circuit change only when visibly soiled or malfunctioning
Drain water condensate away from patient — do NOT flush back
Passive humidification (HME) filter change every 48 hours
Avoid unnecessary ETT manipulation
Early mobilisation (head of bed, passive ROM, sit to chair)

GCC VAP Rates

Regional target: <2 per 1,000 ventilator-days. Bundle compliance monitoring should be performed as part of daily ICU quality audit. Report VAP events via hospital infection control pathway.

🔧ETT Cuff Pressure Monitoring

Target Range

Maintain cuff pressure at 20–30 cmH₂O (15–22 mmHg).

Too low (<20 cmH₂O): Microaspiration risk → VAP

Too high (>30 cmH₂O): Tracheal mucosal ischaemia → stenosis, tracheomalacia

Monitoring Method

Manual cuff manometer: check every 4–8 hours and after any ETT manipulation
Automated cuff pressure devices: continuous monitoring — preferred in prolonged ventilation
Document in nursing chart
After position changes, CXR, or bronchoscopy — recheck cuff
If cuff leak persists despite adequate pressure → suspect ETT damage

💧Humidification Systems

Type	Description	Advantages	Disadvantages	Change Frequency
HME (Heat & Moisture Exchanger)	Passive filter placed on Y-piece; uses patient's own heat/moisture	Cheap, simple, no water condensate, acts as bacterial filter	Adds dead space (~30–50 mL), may not humidify adequately in high-minute ventilation, not suitable if secretions copious or bloody	Every 48 hours (or sooner if soiled)
Heated Humidifier (HH)	Active water chamber heated to 37°C, maintains humidity 33–44 mgH₂O/L	Superior humidification, suitable for all patients including ARDS, thick secretions, hypothermia	Water condensate in circuit (infection risk), requires filling, circuit weight, cost	Circuit change when visibly soiled; water chamber check every 4h

Clinical Preference:

HME for most short-term ventilated patients. Heated humidifier preferred in ARDS, copious secretions, prolonged ventilation (>48h), hypothermia, high minute ventilation (>10 L/min), or if secretions becoming dry/tenacious.

🔬Tracheal Suctioning Guidance

Indication-Based Suctioning — NOT routine timed suctioning.

Suction when clinically indicated: visible secretions in ETT, audible secretions (coarse breath sounds), ↑ PIP, ↓ SpO₂, patient distress, before/after position change.

ABCDE Assessment Before Suctioning

A — Assess need (indication present?)
B — Breathe (pre-oxygenate: SpO₂ >95% target before; FiO₂1.0 for 30–60 sec if borderline)
C — Catheter size (≤½ internal ETT diameter; typically Fr10–12 for 7.5–8 mm ETT)

D — Depth (insert without suction until resistance; withdraw 1 cm, apply suction while withdrawing)
E — Evaluate (SpO₂, HR, BP, waveform, secretion character/colour)

Closed Suction System

Preferred — maintains PEEP, reduces infection risk, allows continuous ventilation. Indicated for ARDS, high PEEP, haemodynamically unstable, infectious precautions (MDR organisms).

Open Suction System

Sterile single-use catheter with gloves. Requires temporary ventilator disconnect. Acceptable for routine use but causes PEEP loss and derecruitment. Use fresh catheter each time.