J Neurocrit Care.  2018 Dec;11(2):63-70. 10.18700/jnc.180069.

Monitoring and Interpretation of Mechanical Ventilator Waveform in the Neuro-Intensive Care Unit

Affiliations
  • 1Department of Critical Care Medicine, Ewha Womans University Mokdong Hospital, Seoul, Korea. jinegero@hotmail.com
  • 2Department of Neurology, Ewha Womans University Mokdong Hospital, Seoul, Korea.

Abstract

Management of mechanical ventilation is essential for patients with neuro-critical illnesses who may also have impairment of airways, lungs, respiratory muscles, and respiratory drive. However, balancing the approach to mechanical ventilation in the intensive care unit (ICU) with the need to prevent additional lung and brain injury, is challenging to intensivists. Lung protective ventilation strategies should be modified and applied to neuro-critically ill patients to maintain normocapnia and proper positive end expiratory pressure in the setting of neurological closed monitoring. Understanding the various parameters and graphic waveforms of the mechanical ventilator can provide information about the respiratory target, including appropriate tidal volume, airway pressure, and synchrony between patient and ventilator, especially in patients with neurological dysfunction due to irregularity of spontaneous respiration. Several types of asynchrony occur during mechanical ventilation, including trigger, flow, and termination asynchrony. This review aims to present the basic interpretation of mechanical ventilator waveforms and utilization of waveforms in various clinical situations in the neuro-ICU.

Keyword

Brain injuries; Intensive care units; Respiration, Artificial; Ventilator-induced lung injury

MeSH Terms

Brain Injuries
Humans
Intensive Care Units
Lung
Positive-Pressure Respiration
Respiration
Respiration, Artificial
Respiratory Muscles
Tidal Volume
Ventilation
Ventilator-Induced Lung Injury
Ventilators, Mechanical*

Figure

  • Figure 1. Indications and simplified strategies of mechanical ventilation in neuro-ICU. GBS, Guillain-Barre syndrome; IICP, increased intracranial pressure; ARDS, acute respiratory distress syndrome; MG, myasthenia gravis; CIP, critical illness polyneuropathy; CIM, critical illness myopathy; FiO2, fraction of inspired oxygen; PEEP, positive end expiratory pressure; SBT, spontaneous breathing trial; SAT, spontaneous awakening trial; ICU, intensive care unit.

  • Figure 2. Modes of mechanical ventilation. SIMV, synchronized intermittent mandatory ventilation.

  • Figure 3. Basic waveforms of volume control and pressure control mode. Pplat, plateau pressure; Ppeak, peak airway pressure.

  • Figure 4. Actual monitor display of mechanical ventilator in different manufacturers. (A) Servo-I (MAQUET, Rastatt, German). (B) G-5 (Hamilton Medical, Bonaduz, Switzerland).

  • Figure 5. Change of volume-pressure loop depending on lung compliance. Relationship between volume and pressure during inspiration and expiration. To maintain the same tidal volume, more airway pressure is needed when the lung compliance is below normal.

  • Figure 6. Ventilator waveforms of air leak and auto-PEEP. Difference between air leak and auto-PEEP on flow-pressure loop. It is important to make sure that the initiation of inspiration and termination of expiration cross at the same point on the flow-pressure loop. Air leak and auto-PEEP are seen in the volume graph and flow graph, respectively. PEEP, positive end expiratory pressure.

  • Figure 7. Mechanical ventilator waveforms of patient-ventilator asynchronies. (A) Trigger asynchrony: missed trigger and auto-triggering. (B) Flow asynchrony: overshooting and air hunger. (C) Termination asynchrony: premature termination and delayed termination.


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