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🌱 來自: Huppert’s Notes
Respiratory Support🚧 施工中
Respiratory Support
TABLE 3.6 • Supplemental oxygen delivery devices
TABLE 3.7 • Noninvasive positive pressure ventilation (NIPPV)
Intubation and mechanical ventilation
• Purpose:
- Relieve respiratory distress
- Improve gas exchange for CO2 (hypercarbia) and O2 (hypoxemia)
- Decrease work of breathing
- Protect airway in cases of low GCS (<8), apnea, inability to clear secretions
• Indications: Typically try noninvasive forms of ventilation before progressing to invasive mechanical ventilation, except in the setting of altered mental status, cardiac arrest, or severe respiratory compromise with impending arrest. Following are other clinical situations where intubation and mechanical ventilation may be appropriate:
- Hypoxemic respiratory failure: PaO2 <55 mmHg
• Common causes: Pneumonia, hemorrhage, ARDS, pulmonary edema
- Hypercarbic respiratory failure: PaCO2 >45 mmHg with acidemia pH <7.35
• Common causes: COPD, asthma, hypoventilation
- Upper airway obstruction:
• Common causes: Tumor, angioedema, stenosis
- Severe acidemia with inability to compensate:
• Common causes: DKA, severe sepsis, other conditions with increased respiratory/ventilatory demands
- Neuromuscular weakness:
• Common causes: Amyotrophic lateral sclerosis (ALS), Guillan Barré Syndrome (GBS), toxins, myasthenia gravis
- To safely perform procedures or imaging (relative indication)
- Hemodynamic instability (relative indication)
• How to intubate:
- There are various methods for intubation: Endotracheal vs. nasal, awake vs. paralyzed and sedated, direct visualization vs. video-assisted
- Most common: Paralyzed and sedated orotracheal intubation by direct larnygoscopy (DL)
- Often institution-specific protocols for who intubates: ED, anesthesia, and/or critical care–trained clinicians
- Difficult intubations or those with airway obstructions often require backup support with ENT involvement or options for tracheostomy
• Ventilator modes and key parameters: See Table 3.8, Figure 3.5
TABLE 3.8 • Ventilator Modes
FIGURE 3.5: Volume control and pressure control modes in mechanical ventilation. Pressure, volume, and flow curves during inspiration (purple) and expiration (blue).
• Complications of intubation:
- Inability to intubate (often abnormal anatomy, severe obesity), inability to ventilate, hypotension (e.g., due to auto-PEEP physiology or sedation/induction medications → decreased vascular tone and SVR), aspiration (especially for patients who were not NPO prior), hypoxemia, arrhythmia
- Risk factors: Conditions that reduce patients’ ability to augment cardiac output such as aortic stenosis and pulmonary hypertension are risk factors for hemodynamic collapse during intubation, because induction medications reduce vascular tone
• Placing an arterial line permits closer hemodynamic monitoring and earlier intervention in patients at risk for hemodynamic collapse
• Complications of mechanical ventilation:
- Ventilator-associated pneumonia: Pneumonia diagnosed >48 hours after intubation; see hospital-acquired pneumonia and ventilator-associated pneumonia in Infectious Diseases Chapter 8
- Laryngeal edema, ulceration: Consider tracheostomy after 14 days of intubation
- Oxygen toxicity: Higher risk with higher FiO2, often >0.7 (at present this is a theoretical concern based on lab studies without robust human evidence)
- Oversedation and delirium: Particularly for patients with ARDS and those who require paralysis with deeper sedation goals
- Barotrauma complications: Pneumothorax, subcutaneous emphysema
- Ventilator-associated lung injury (VALI)
- Diaphragmatic weakness: Atrophy from mechanical ventilation and muscle disuse
TABLE 3.9 • Key Parameters Affecting Oxygenation and Ventilation
• Managing refractory hypoxemia:
- Mechanical: Increase FiO2, increase PEEP, increase inspiratory time
- Nonmechanical: Neuromuscular blockade (decrease ventilator dyssynchrony), prone positioning (improve V/Q mismatch), inhaled pulmonary vasodilator (e.g., nitrous oxide or prostacyclin), ECMO
• Criteria for extubation:
- Perform daily assessment of readiness for spontaneous breathing trial (SBT)
- Screening criteria for consideration of SBT:
• Most important: Ensure that the reason why the patient was intubated in the first place has been resolved or is significantly improved
- If not, then the patient requires ongoing mechanical ventilation
• Minimal ventilator settings
- FiO2 <0.5 (which can be provided by other means)
- PEEP <8 cm H2O
• Intact gag/cough. Ideal if the patient is also responding to commands but this is not always essential
• Minimal secretions and ability to handle any secretions after extubation
• Hemodynamically stable off vasopressors OR vasopressors titrating off and stable on low-dose pressors
• If prolonged intubation (>5–7 days):
- Consider checking “cuff leak” to assess for upper airway edema, which could lead to post-extubation stridor if present. This is more common in women, patients who are obese, and patients with prolonged courses or volume overload.
• Performing SBT:
- All options are roughly equivalent to determine who will be successful and reduce risk of reintubation
- SBT options:
• Favored approach: 30–120 minutes of pressure support at PS 7 and PEEP 5
- Note there is no evidence suggesting a benefit of checking ABG during an SBT
- Note that longer SBTs are not necessarily better and may tire the patient out
• Alternate approach: 30 minutes of T-piece with blow-by oxygen
- Note: Patient must overcome resistance of T piece and circuit with this method
- Rapid Shallow Breathing Index (RSBI)
• RSBI = RR / Tidal Volume (in liters)
- Slow, deeper breaths are more reassuring
- RSBI >105 predicts extubation failure
• Deciding to discontinue mechanical ventilation:
- Underlying reason for intubation is reversed or significantly improved
- Patient must pass SBT
• Hemodynamically stable throughout
• Stable RR and TV (= stable MV) throughout
• No desaturations
• Stable PaCO2 or EtCO2
- If increased, not ventilating sufficiently
• Patient is awake, following commands, ideally wants to be extubated
• Minimal secretions
• Good cough and gag to clear secretions and protect airway
- If patient tolerates SBT, consider extubation. If patient fails SBT, identify cause and correct it if possible.
• Rationale for extubation failure:
- Physiology: Imbalance between respiratory load (what the lungs are being asked to do) and the combination of ventilatory muscle power and central drive to breathe
• Increased respiratory load
- Poor compliance
- Increased dead space
- Metabolic acidosis requiring higher minute ventilation
• Muscle power diminished by deconditioning, often from prolonged intubation and mechanical ventilation
• Reduced or impaired central drive to breathe, often from sedation
• Causes of extubation failure:
- Post-extubation stridor
- Respiratory muscle weakness
- Aspiration
- Mucus plugging
- Pulmonary edema
• Removal of positive pressure leads to increased preload and afterload
• Consider diuresis especially in patients with HFrEF or impaired myocardial function
- Failure to reverse the reason for intubation
Extracorporeal membrane oxygenation (ECMO)
• Definition: Temporary external bypass of the lungs and/or heart to treat life-threatening organ failure
• Types:
- Venovenous (VV): Treats hypoxemic/hypercarbic respiratory failure only. No circulatory support.
• Blood is extracted from the venous system, externally oxygenated, CO2 is removed, and it is returned to the venous system
• Relies on patient’s own cardiovascular system to support their hemodynamics
- Venoarterial (VA): Treats hypoxemic/hypercarbic respiratory failure and provides circulatory support.
• Blood is extracted from the venous system, externally oxygenated, CO2 is removed, and it is returned to the arterial system
• Bypasses both the heart and the lungs
FIGURE 3.6: Venovenous (VV) and venoarterial (VA) extracorporeal membrane oxygenation. Top: Venovenous ECMO; Bottom: Venoarterial ECMO.
• Indications:
- Severe pulmonary and/or cardiac failure causing refractory hypoxemic/hypercarbic respiratory failure or cardiogenic shock; should exhaust all less invasive treatments first
- Etiology of organ failure is reversible (e.g., massive PE, ARDS) or with known definitive replacement planned (e.g., VADS, transplant)
• Contraindications:
- Absolute: Etiology cannot be reversed and no definitive treatment options, other comorbidities that will prohibit survival
- Relative: Thrombocytopenia, severe brain injury, severe comorbidities, life-limiting condition
• Complications:
- Bleeding: Systemic heparization required and patients are also more coagulopathic with ECMO
- Thrombosis: Cannula-associated thrombus, LV thrombus
- Cannulation-related: Line infections, pneumothorax, leg ischemia with femoral artery insertion