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Treating patients that are on mechanical ventilators is not only challenging and complicated, it requires the ability to apply different strategies for different types of patients. Considering you have an understanding of the basic key terms such as, ideal body weight, tidal volume, exhaled tidal volume, minute ventilation, respiratory rate, frequency of breathing, trigger, I:E ratio, Fraction of Inspired Oxygen/ FiO2 and PEEP.1
This is a great starting point for managing any patient on a mechanical ventilator, but there is much more to decide. The patients with Acute lung Injury (ALI) or Acute Respiratory Distress Syndrome (ARDS) can be problematic for even the most seasoned critical care providers.
Here are five quick tips, effective methods, and or strategies for treating patients with Acute Lung Injury or Acute Respiratory Distress Syndrome. The five quick tips are using synchronized intermittent mandatory ventilation/ SIMV, utilizing pressure mode of delivery, driving pressure, lung protective strategies in regard to tidal volume, and the PEEP/ FIO2 chart.
The first main topic I would like to cover is using synchronized intermittent mandatory ventilation/ SIMV. Synchronized Intermittent mandatory ventilation and Assist Control ventilation have a lot of similarities. When setting up the vent with either mode the provider will set the desired tidal volume and the desired respiratory rate. This guarantees the patient with a set minute ventilation pre calculated by the provider. The big difference between SIMV and AC is that SIMV allows the patient to take however large or small of a breath they want.1 The breath could be larger or smaller depending on factors such as sedation status, pain level, patient pathology and the patient’s sense of control.2 When treating patients with Acute Lung Injury or Acute Respiratory Distress Syndrome this is an essential tool for patient comfort.
The second topic I would like to cover is utilizing pressure vs volume mode of delivery. Pressure ventilation or better understood as volume targeted pressure regulated is a more gentle form of delivery. The amount of gas/ volume delivered is dependent on the lung compliance. If you have a young healthy lung compared to an ALI or ARDS lung when delivering the same pressure the volumes or VTE will be different. Pressure mode of delivery has a deceleration flow pattern which helps to keep the peak inspiratory and plateau pressures lower.3
Driving pressure is the difference between your tidal volume and static compliance. The driving pressure is the (Pplat-PEEP).2 The driving pressure must be equal to the opening pressure to open and ventilate the alveoli.
The goal for treating patients with Acute lung Injury or Acute Respiratory Distress Syndrome is to have a driving pressure of less than 15 cmH20. There are two ways to lower the driving pressure, lower Pplat and increase PEEP. This means that the provider will want to keep the Pplat as low as possible and increase the patient’s PEEP. In order to lower the Pplat the provider will need to lower the tidal volume, sometimes to 4 ml/ kg of ideal body weight. The other way is to increase the PEEP to keep the driving pressure lower than 15cmH2O.
The fourth topic for Acute Lung Injury and Acute Respiratory Distress Syndrome patients is to use lung protective strategies. This focuses on protecting the patient’s lung from further harm. The provider will calculate the patient’s ideal body weight and use either 4 ml/ kg of ideal body weight or 6 ml/ kg of ideal body weight for a tidal volume. When providers use lower tidal volumes, this lowers the plateau pressure (Pplat), thus lowering the driving pressure. This will place the patient’s respiratory rate at about 25 to maintain the proper minute ventilation. The lower tidal volumes protect the sick lungs from overinflation and over distention.
The last topic and arguably the most important in regard to treating Acute Lung Injury and Acute Respiratory Distress Syndrome is the PEEP/ Fio2 chart. PEEP or positive end-expiratory pressure maintains alveolar recruitment and optimizes the ability to provide effective oxygenation. When the mechanical ventilator delivers a breath, PEEP maintains the alveoli in an open state at the end of the expiration process. The higher the PEEP the longer the alveoli are held open.2 The physiologic PEEP is 3-5 cmH2O, so most providers will start most patients out at 5 cmh20 of PEEP.
FiO2 is the fraction of inspired oxygen. We all breathe 78% nitrogen and 21% percent oxygen as we breathe. One setting on a ventilator is the FiO2, meaning we can titrate the oxygen level between 21% and 100% depending on the patient’s presentation. When treating patients with Acute Lung injury or Acute Respiratory Distress Syndrome the provider should match the PEEP with the corresponding FiO2. The oxygenation goal is a PaO2 of 55-80 mmHg or Spo2 of 88-94% in ALI and ARDS patients.2
Patients with Acute Lung Injury or Acute Respiratory Distress Syndrome are complex and complicated patients to take care of while on a mechanical ventilator. The next time you are facing one of these challenging patients try to remember the five quick tips. The five quick tips are using synchronized intermittent mandatory ventilation/ SIMV vs assist control/ AC, utilizing pressure mode of delivery vs volume, keeping driving pressure below 15 cmH2O, using lung protective strategies, and utilizing a PEEP/ FiO2 reference table.
References
- UMBC. (2017). Critical Care Transport (M. McEvoy, J. S. Rabrich, & M. E. Murphy, Eds.). Jones & Bartlett Learning.
- Bauer, E. (2015). Ventilator Management: A Pre-Hospital Perspective. CreateSpace Independent Publishing Platform.
- Owens, W. (2021). The Ventilator Book (3rd ed.). First Draught Press.
John Gilpin is a paramedic for REMSA, Buchanan County Ambulance, in Saint Joseph, Missouri. He has been a paramedic for 10 years and has certifications in flight paramedicine and critical care paramedicine.
