Troubleshooting the Ventilator

pO2 Is Too Low (i.e., < 60)

• AC/SIMV: increase PEEP or FiO2

• APRV: increase PHigh, THigh, or FiO2

• HFOV: increase mean airway pressure or FiO2

pCO2 Is Too High (i.e., > ??)

• VCAC/SIMV: increase RR or TV

• PCAC/SIMV: increase RR or driving pressure

• APRV: increase the gradient between PHigh and PLow; decrease the THigh; increase TLow

• HFOV: decrease the frequency, increase amplitude, increase Ti%, allow a 5 cm cuff leak

pCO2 Too Low (i.e. < 35)

• VC-AC/SIMV: decrease RR or TV

• PC-AC/SIMV: decrease RR or driving pressure

• APRV: increase THigh, lower PHigh, decrease TLow

• HFOV: increase the frequency, decrease the amplitude, decrease Ti%

High Peak Pressures (PIPs or Paws)

• perform an inspiratory pause & obtain a Pplat

  • Pplat represents the portion of PIP actually applied to the small airways & alveoli during inspiration

  • difference between PIP & Pplat: pressure due to airway resistance

  • difference between Pplat & PEEP: pressure due to lung compliance

• ↑ PIP & ↓ Pplat: problem is ↑ airway resistance

  • kinked ET tube (unkink the tube)

  • mucus plugging (pass a suction catheter)

  • bronchospasm (inhaled bronchodilators)

  • too narrow of an ETT (change the tube)

• ↑ PIP & ↑ Pplat: problem is ↑ lung compliance

  • mainstem intubation (retract ETT)

  • atelectasis (chest percussion, or broncho to open airway)

  • pulmonary edema (diuresis or inotropes)

  • ARDS (decrease TV, increase PEEP, paralyze, prone)

  • PTX (chest tube)

Dynamic Hyperinflation (Auto-PEEP)

• PEEP is the alveolar pressure above atmospheric pressure that exists at the end of expiration, and there are 2 types

  • Extrinsic PEEP (or applied PEEP): PEEP provided by the mechanical ventilator to mitigate end-expiratory alveolar collapse

  • Intrinsic PEEP (or auto-PEEP): PEEP secondary to incomplete expiration, leading to progressive air trapping (i.e., dynamic hyperinflation); usually due to inadequate time for exhalation, & is exacerbated by high airway resistance (i.e., bronchospasm, COPD, mucus plugging)

• potential sequelae

  • hypotension esp. if hypovolemic (↑ intra-thoracic pressure → ↓ VR → ↓ CO)

  • VILI (i.e., volutrauma, barotrauma)

  • patient-ventilator asynchrony (due to ↑ WOB)

• therapy incl.

  • lower RR to 10-14

  • shorten Ti to keep I:E ratio 1:3 to 1:5

  • keep TV 6-8 mL/kg

  • if air hungry, increase inspiratory flow to 60-80 LPM

  • narcotic sedation can blunt tachypneic response

  • treat bronchospasm w/inhaled bronchodilators & systemic steroids

Sudden Drop in SpO2

• disconnect pt from ventilator & BVM

• re-confirm ETT / trach placement

• obtain an ABG & chest XR

• consider PE as the cause

• if unilateral absent breath sounds, pull ETT back a few cm

• if still absent, consider PTX or mucus plugging w/complete atelectasis

• consider tension PTX if absent breath sounds & pt is hypotensive

Fighting the Ventilator

• before sedating and/or paralyzing the pt, always check TSS

  • T: tube (confirm placement & not obstructed)

  • S: sounds (present & equal bilaterally)

  • S: sats (ensure pt is not hypoxemic)

• other things to consider incl.

  • dynamic hyperinflation

  • untreated pain esp. in trauma / surgery pts

  • ensure the RR and TV are adequate

  • switch to AC if the pt is getting fatigued

  • consider other causes of distress (cardiac ischemia, fever, abdominal distention, neurologic deterioration, etc.)

Change in EtCO2

• confirm the EtCO2 waveform is present; if not present, it means one of three things

  • tube is not in the trachea (emergency)

  • tube is occluded (emergency)

  • EtCO2 sensor is faulty (diagnosis of exclusion)

• if the waveform is present, obtain an ABG for the paCO2

• ↑ EtCO2 & ↑ paCO2: either ↑ CO2 production or alveolar hypoventilation due to

  • fever

  • malignant hyperthermia

  • thyrotoxicosis

  • suppressed respiratory drive w/o sufficient ventilation

• ↓ EtCO2 & ↑ paCO2 (or unchanged): the widening between the two suggests an increase in dead space ventilation from

  • PE

  • ↓ CO (cardiogenic, hypovolemic shock)

  • dynamic hyperinflation (auto-PEEP)

• ↓ EtCO2 & ↓ paCO2: there is an increase in alveolar ventilation

  • pain

  • agitation

  • fever

  • sepsis

Abbreviations

• airway pressure release ventilation (APRV)
• assist control (AC)
• end-tidal carbon dioxide (EtCO2)
• fraction of inspired oxygen (FiO2)
• high-frequency oscillatory ventilation (HFOV)
• high-frequency percussive ventilation (HFPV)
• inspiratory pressure (IP)
• inspiratory time (Ti)
• inspiratory to expiratory ratio (I:E ratio)
• lung-protective ventilation (LPV)
• maximum pressure (Pmax)
• minute ventilation (MV)
• neuromuscular blockade (NMB)
• partial pressure of carbon dioxide (pCO2)
• peak airway pressure (Paw)
• peak inspiratory pressure (PIP)
• peak pressure (Ppeak)
• plateau pressure (Pplat)
• positive end-expiratory pressure (PEEP)
• pressure control (PC)
• pressure high (Phigh)
• pressure low (Plow)
• pressure support ventilation (PSV)
• pressure-regulated volume control (PRVC)
• respiratory rate (RR)
• synchronous intermittent mandatory ventilation (SIMV)
• tidal volume (TV)
• time high (Thigh)
• time low (Tlow)
• ventilator-induced lung injury (VILI)
• volume control (VC)
• work of breathing (WOB)