Updated: 2/23/2021

Mechanical Ventilation

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Snapshot
  • A 55-year-old alcoholic man presents to the emergency department acutely altered.  Upon initial workup it is noted that the patient has a Glasgow coma scale of 7 and is hypoxic and hypercapneic.  He is subsequently intubated and mechanically ventilated.  Secondary exam reveals a patient covered in vomit and urine who smells like alcohol. (Acute respiratory distress syndrome).
Introduction
  • Clinical definition
    • a ventilator that mechanically oxygenates/ventilates the patients with settings determined by the physician
  • Therapeutic indications for intubation and mechanical ventilation include
    • failure to oxygenate
    • failure to ventilate
    • inability to protect airway
      • GCS < 8 (less than 8, intubate)
    • suspected clinical course requiring intubation and ventilation
  • Main modes
    • assist-control (volume-cycled or pressure-targeted)
      • volume cycled
        • settings: tidal volume (TV), flow rate, flow waveform, fraction of inspired oxygent (FiO2), positive end-expiratory pressure (PEEP), and frequency
        • airway pressures and auto-PEEP are dependent on respiratory system
      • pressure-targeted
        • settings: pressure target, inspiratory time, inspiratory rise rate, FiO2, PEEP, and frequency
        • tidal volume and auto-PEEP are dependent upon respiratory system
    • pressure-support ventilation
      • usually with set continuous positive airway pressure (CPAP)
      • spontaneous mode where support can be adjusted 
      • cannot set frequency or tidal volume
        • these are dependent upon patient effort, strength, and compliance of respiratory system
      • tolerated well because flow, depth, and length are all patient controlled
    • synchronized intermittent mechanical ventilation (SIMV)
      • combination of spontaneous breathing and set number of ventilator breaths that are fully supported but coincide with spontaneous efforts
Complications
  • Cardiovascular impairment
    • positive intrathoracic pressure can decrease venous return, decreasing cardiac output  
  • Barotrauma (trauma from high pressures)
    • findings
      • subcutaneous emphysema
      • pneumomediastinum
      • pneumothorax
      • pneumoperitoneum
      • interstitial emphysema
    • etiologies
      • high mean alveolar pressure
      • high peak airway pressures
      • necrotizing lung pathology
      • high minute ventilation
      • longer duration of mechanical ventilation
  • Ventilator-induced lung injury (atelectrauma or trauma caused by atelectasis)
    • PEEP to prevent widespread alveolar unit closure and atelectasis
  • Acid-base status derangements
    • generally, changing the respiratory rate is preferred for responding to derangements (because TV is based on height)
      • increase respiratory rate
        • metabolic acidosis
        • respiratory acidosis
      • decrease respiratory rate (assuming adequate oxygenation)
        • respiratory alkalosis 
  • Infections
    • ventilator-associated pneumonia
      • broader antibiotic coverage for Staphylococcus aureusPseudomonas aeruginosa, and other gram-negative bacilli  
        • P. aeruginosa: cefepime, piperacillin-tazobactam, and imipenem/meropenem
        • Expanded gram-negative coverage: aminoglycosides
        • MRSA: vancomycin, linezolid
          • daptomycin cannot be used because it is inactivated by surfactant in the respiratory tract
 

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(M2.PL.17.86) A 66-year-old man presents to the emergency department with dyspnea. Two days ago, he hosted his grandchild's birthday party, and since has noticed general malaise, fever, and dry cough. He does not know if he feels more dyspneic while supine or standing but has noticed difficulty breathing even while watching television. He has a past medical history of congestive heart failure and hypertension, for which he takes aspirin, metoprolol, furosemide, lisinopril, and spironolactone as prescribed. His blood pressure is 90/50 mmHg, pulse is 120/min, and respirations are 30/min. His radial pulse is barely palpable, and his wrists and ankles are cold and clammy. Physical exam reveals a S3 and S4 with a soft holosystolic murmur at the apex, decreased breath sounds up to the middle lung fields, jugular venous distention to the auricles, and 3+ pitting edema to the mid thighs. EKG shows ST depressions consistent with demand ischemia. Bedside echocardiogram shows global akinesis with an ejection fraction (EF) of 20%; previous reports show EF at 40%. A portable chest radiograph shows bilateral pulmonary edema. Metoprolol is held, dobutamine and furosemide drips are started, and BiPAP is started at 20/5 cm H2O. After 15 minutes, the nurse reports that urine output is minimal and blood pressure is now 75/40 mmHg and pulse is 130/min. What is the best next step in management? Tested Concept

QID: 106159
1

Resume home metoprolol

7%

(10/136)

2

Decrease furosemide rate

21%

(28/136)

3

Decrease dobutamine rate

18%

(25/136)

4

Decrease positive inspiratory pressure

23%

(31/136)

5

Decrease positive end-expiratory pressure

22%

(30/136)

M 7 C

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