Mechanical Ventilation Exam Review

Flashcards covering key vocabulary terms and definitions related to mechanical ventilation, respiratory mechanics, pressure gradients, compliance, resistance, types of ventilation, ARF, and patient care from the lecture notes.

Spontaneous Ventilation

Movement of air into and out of the lungs.

Respiration

Exchange of O₂ and CO₂ between the body and environment.

External Respiration

Gas exchange between alveoli and pulmonary capillaries.

Internal Respiration

Gas exchange between systemic capillaries and body tissues.

Inspiration (Spontaneous)

Muscles contract, intrapleural and alveolar pressure drop, alveolar pressure < airway opening, gas flows in.

Expiration (Spontaneous)

Muscles relax, thoracic volume decreases, alveolar pressure rises, gas flows out.

Accessory Muscles of Inspiration

Scalene, sternocleidomastoid, pectoralis, trapezius.

Accessory Muscles of Active Expiration

Rectus abdominis, obliques, transverse abdominis, serratus, latissimus dorsi.

Pressure Gradient for Airflow

Air flows from high pressure to low pressure.

Intrapleural Pressure during Inspiration

Becomes more negative.

Alveolar Pressure during Expiration

Becomes positive.

Transairway Pressure (PTA)

Pressure between the airway opening and the alveolus; needed to overcome airway resistance. Formula: Paw − Palv.

Transthoracic Pressure (PTT or Pw)

Pressure between the alveolar space and the body surface; required to expand or contract lungs + chest wall. Formula: Palv − Pbs.

Transpulmonary Pressure (PTP or PL)

Pressure difference between the alveolus and the pleural space; needed to keep alveoli open (alveolar distending pressure). Formula: Palv − Ppl.

Transrespiratory Pressure (PTR)

Pressure difference between the airway opening and the body surface; required to inflate lungs and airways during PPV. Formula: Pawo − Pbs (combines PTA + PTT).

Compliance (C)

The ease with which the lungs and thorax expand. Formula: ΔV / ΔP.

Normal Spontaneous Compliance

50–170 mL/cmH₂O.

Normal Intubated Compliance (Males)

40–50 mL/cmH₂O (up to 100).

Normal Intubated Compliance (Females)

35–45 mL/cmH₂O (up to 100).

Static Compliance (Cs)

Compliance measured on a ventilator. Formula: VT / (Pplat – EEP).

Elastance (E)

The tendency of a structure to return to its original form after being stretched; opposite of compliance. Formula: E = 1 / C.

Resistance (Raw)

Opposition to gas flow through the airways. Formula: (PIP – Pplat) / Flow or PTA / Flow.

Normal Non-intubated Resistance

0.6–2.4 cmH₂O/L/s.

Normal Intubated Resistance

~6 cmH₂O/L/s or higher.

Compliance vs. Resistance (Mnemonic)

"Compliance is ease, Resistance is squeeze."

Negative Pressure Ventilation (NPV)

Mimics normal breathing by pulling the chest wall outward, making intrapleural pressure more negative to expand alveoli (e.g., Iron lung).

Positive Pressure Ventilation (PPV)

Ventilator pushes air into the lungs, raising airway opening pressure above alveolar pressure, causing gas flow in.

Ppeak (PIP)

Peak inspiratory pressure; the highest pressure reached during inspiration.

Pplat

Plateau pressure; measured after inspiration with an 'inspiratory hold' manoeuvre, representing alveolar pressure.

PEEP (Baseline Pressure)

Positive pressure maintained in the airways at the end of exhalation.

Auto-PEEP

Trapped air in the lungs that causes unintended positive end-expiratory pressure.

Electrically Powered Ventilators

Ventilators that depend on electricity (outlets, batteries) for operation.

Pneumatically Powered Ventilators

Ventilators that use pressurized gas (e.g., wall O₂/air) for operation, common in ICUs.

Open-loop System (Ventilator)

An "unintelligent" control system that cannot adjust settings if the output doesn't match patient needs ('set and forget').

Closed-loop System (Ventilator)

A "smart" control system that measures output and adjusts to achieve a set goal, using feedback ('feedback and fix').

Patient Circuit

The external circuit connecting the ventilator to the patient's airway, consisting of an inspiratory limb, expiratory limb, and Y-connector.

Adjuncts with a Patient Circuit

Heated humidifiers, HMEs (heat moisture exchangers), bacterial/viral filters, nebulizers.

Pawo (PM)

Airway opening pressure, usually 0 unless the ventilator applies pressure.

Pbs

Body surface pressure; atmospheric pressure, considered ~0 reference.

Palv

Alveolar pressure; changes with breathing (−1 cmH₂O inspiration, +1 expiration spontaneously).

Ppl

Pleural pressure; ~−5 cmH₂O at end-exhalation, −10 cmH₂O at inspiration spontaneously.

Effect of Decreased Compliance

Stiff lungs require increased pressure (↑ PIP, ↑ Pplat) to deliver the same volume.

Effect of Increased Resistance

Narrow airways result in higher PIP, but a normal Pplat (as alveolar pressure is unaffected).

Decision for Intubation (MIP & VC Mnemonic)

"−20 and 10–15" = danger zone for intubation in neuromuscular patients regarding MIP and Vital Capacity.

Critical pH in ARF

Critical PaCO₂ in ARF

55 mmHg and rising.

Critical VD/VT in ARF

0.6.

Critical PaO₂ in ARF

Critical P(A-a)O₂ in ARF

450 mmHg (on O2).

Critical PaO₂/PAO₂ in ARF

Critical PaO₂/FiO₂ (P/F Ratio) in ARF

Critical MIP in ARF (Neuromuscular Patients)

−20 to 0 cmH₂O.

Critical MEP in ARF

Critical Vital Capacity (VC) in ARF (Neuromuscular Patients)

Critical Tidal Volume (VT) in ARF

Critical Respiratory Frequency (f) in ARF

35 breaths/min.

Critical FEV₁ in ARF

Critical Peak Expiratory Flow (PEF) in ARF

75–100 L/min.

Big Four Reasons for Mechanical Ventilation

Apnea, acute ventilatory failure, impending ventilatory failure, refractory hypoxemic respiratory failure with increased work of breathing (WOB).

Big 5 Triggers for Invasive Mechanical Ventilation

Apnea/impending respiratory arrest, acute exacerbation of COPD/severe asthma (failing therapy), neuromuscular disease with ventilatory insufficiency, acute hypoxemic respiratory failure, need for airway protection/secretion management.

Trigger Variable

Begins inspiration; can be time (vent-initiated), pressure, or flow (patient-initiated).

Limit Variable

Limits the value of pressure, volume, or flow during inspiration but does not end inspiration.

Cycle Variable

Ends inspiration; can be volume-cycled (preset volume), pressure-cycled (preset pressure), or time-cycled (set inspiratory time).

Baseline Variable

Controlled during exhalation, usually pressure (PEEP or zero/atmospheric).

Mandatory (Machine) Breath

Ventilator initiates and controls inspiration; patient has no control over start or volume/pressure.

Spontaneous Breath

Patient initiates and controls flow/volume; ventilator may assist but patient drives it.

Volume Control (VC)

A control variable where tidal volume is set and guaranteed; flow and volume are fixed, while pressure varies with lung mechanics.

Pressure Control (PC)

A control variable where inspiratory pressure is set and guaranteed; pressure is fixed, while flow and volume vary depending on compliance and resistance.

Physiological Objectives of Mechanical Ventilation

Support/manipulate pulmonary gas exchange, increase lung volume, reduce work of breathing (WOB).

Clinical Objectives of Mechanical Ventilation

Reverse acute respiratory failure/distress, reverse hypoxemia, prevent/reverse atelectasis, reverse respiratory muscle fatigue, allow sedation/paralysis, reduce systemic/myocardial O₂ consumption, minimize complications, reduce mortality.

Acute Respiratory Failure (ARF)

Inability to maintain normal PaO₂, PaCO₂, and pH despite therapy.

Hypoxemic ARF (Type I)

Severe V/Q mismatch, shunt, or diffusion defect, with PaO₂ < 60 mmHg on FiO₂ ≥ 0.6. ('No O₂').

Hypercapnic ARF (Type II)

Ventilatory pump failure leading to inadequate CO₂ removal, with PaCO₂ > 50 mmHg and pH < 7.25. ('Too much CO₂').

Best Indicator of Ventilation

PaCO₂.

Best Indicator of Oxygenation

PaO₂.

PaO₂/FiO₂ Ratio (P/F Ratio)

Normal: 350–450; Critical: < 200 (indicating ARDS/hypoxemia).

Indications for NIV in ARF

RR > 25 breaths/min, moderate–severe acidosis (pH 7.25–7.30, PaCO₂ 45–60 mmHg), moderate–severe dyspnea with accessory muscle use or paradoxical breathing (at least 2 criteria).

Absolute Contraindications for NIV

Respiratory or cardiac arrest, cardiovascular instability, nonrespiratory organ failure, tracheoesophageal fistula, inability to protect airway/high aspiration risk, uncooperative patient, recent facial/head surgery or trauma.

Criteria to Switch from NIV to Invasive Ventilation

Respiratory arrest, RR > 35 breaths/min, severe dyspnea, life-threatening hypoxemia (PaO₂ < 40 mmHg or P/F < 200), severe acidosis (pH < 7.25 + PaCO₂ > 60 mmHg), worsening mental status, cardiovascular complications, NIV trial failure, other serious causes.

Importance of Oral Care in Ventilated Patients

Prevents VAP, maintains oral health, increases comfort.

Importance of Tracheostomy Care

Prevents infection, maintains patency, protects skin around the stoma.

Bedside Measurements for Neuromuscular Respiratory Muscle Strength

Maximum Inspiratory Pressure (MIP) and Vital Capacity (VC).

Control Variable (Ventilation)

The primary variable that the ventilator adjusts to produce inspiration (e.g., volume or pressure).

Volume Ventilation (VC) Outcome

Tidal Volume (Vt) is guaranteed, while Peak Inspiratory Pressure (PIP) changes.

Pressure Ventilation (PC) Outcome

Inspiratory Pressure is guaranteed, while Tidal Volume (Vt) changes.