a, Mode of Ventilation

i. Avoiding injurious ventilator settings is far more important than the mode of ventilation.

ii. There is no outcome-based evidence favoring one mode of ventilation over another.

iii. Patients in the landmark ARDSNet ARMA trial were all ventilated in volume assist-control ventilation and many clinicians choose to use this mode primarily.

1. However, pressure control has some theoretical advantages.

a. A decelerating flow waveform is more comfortable for the patient and may improve gas mixing. This is only available in PC mode on the 731 ventilator. VC mode on the 731 ventilator only allows square wave flow, unlike most ICU ventilators.

b. Inverting I:E ratio is an option for increasing the mean airway pressure (and thus improving oxygenation). This is easier to manage in PC than VC.

c. Setting a Peak Inspiratory Pressure (PIP) ensures that the Plateau Pressure (Pplat) will remain below PIP.

2. A theoretical drawback to Pressure Control is that close attention must be paid to tidal volumes delivered as they can change over time due to changes in the patient’s physiology.

b. Ventilator Settings

i. Initial approach and assessment

1. For patients on a ventilator, start by trying to match prior vent settings

2. Place patients with respiratory dysfunction on the transport vent early to verify stability

3. The presence of any of the below potentially harmful vent settings or patient characteristics should prompt consultation with the ECMO transport team. Consider consultation even if ECMO transport is not possible as they can offer additional management suggestions.

a. Pplat > 32

b. PIP > 40

c. FiO2 > 60% on appropriate PEEP

d. PEEP > 14

e. pH < 7.25 despite attempts to increase MV

f. P/F Ratio < 150 despite on appropriate PEEP and FiO2

4. Patients will likely require increased PEEP or FiO2, and possibly MV at altitude. Ensure that there is room to safely titrate up all vent settings by approximately 20% at altitude.

5. See below for guidance for newly intubated patients or patients not tolerating current vent settings.

ii. Tidal Volume (VT)

1. Tidal volume should be based on predicted body weight (PBW) according to: PBW = 50+2.3 (height in inches – 60) for males. Refer to Appendix B. (May use “wingspan” instead of height).

a. Goal VT is 4-8 cc/kg based on predicted body weight.

b. Patients with lung injury or concern for potential lung injury should have a target VT 6 ml/kg PBW

c. Other patients may find a VT of 8cc/kg more comfortable than lower volumes. This target may be appropriate as long as PIP ≤ 40 cmH2O and Pplat ≤ 30 cmH2O.

d. If a patient is not tolerating the target VT consider additional sedation and paralytic.

e. While VT can be manipulated to control pCO2, the best way to manage pCO2 is to alter the respiratory rate. If adjusting tidal volume, do not increase VT above 8 cc/kg to control pCO2

iii. Respiratory Rate

1. Respiratory rate should be 12-32

2. Adjust the respiratory rate to achieve a pH between 7.35 and 7.45. If this goal cannot be reached, permissive hypercapnia is appropriate for ARDS patients without TBI. Tolerance of pH as low as 7.25 may be appropriate for transport and allow for avoidance of injurious vent settings. See section on “Permissive Hypercapnia” below. If in doubt, consult the ECMO team.

3. The pH is more important that the actual pCO2 ***Not applicable to TBI patients***

4. Patients with baseline CO2 retention will have a normal pH at elevated pCO2, this is normal.

iv. Volume Control (VC)

1. Start at 6-8 ml/kg PBW for patients with minimal lung disease

2. Start at 6 ml/kg PBW for patients with respiratory dysfunction

3. Adjust Respiratory Rate (RR) for a Minute Ventilation (MV) that achieves the goal pH and PaCO2.

4. Check Pplat, if >30, VT can be titrated down to 4ml/kg to reach a safe Pplat. A VT of 4 ml/kg PBW is usually uncomfortable for the patient and may require increased sedation.

5. If PIP is elevated, consider increasing inspiratory time. Other measures to increase airway diameter including suctioning or bronchodilators may be considered in the appropriate clinical circumstances.

v. Pressure Control (VC)

1. Switching to PC mode allows the respiratory provider to target a safe upper limit for Peak Inspiratory Pressure (PIP) and Plateau Pressure (Pplat).

a. PIP is greater than or equal to Pplat in PC mode. If flow equals zero at the end of inspiration, PIP = Pplat, otherwise Pplat < PIP.

2. Plateau pressures equal to or less than 30 cmH2O are thought to be safe

3. Driving Pressure (ΔP) = Pplat – PEEP

a. Driving Pressures less than 15 mmHg correlate with better outcomes

b. Driving Pressure can be titrated up or down to change VT; this is the most direct way to change VT.

c. The Zoll 731 ventilator is not PEEP compensated. Increasing PEEP without changing the PIP will decrease Driving Pressure and VT.

4. Setting the PIP

a. Start by setting the vent PIP to 10 cmH2O above PEEP (Driving pressure of 10 cmH2O)

b. Quickly titrate the PIP up or down for a target VT of 4-8 ml/kg.

c. 8 ml/kg PBW VT may be appropriate for patients without respiratory dysfunction

d. Otherwise, for patients with any concern for lung injury, titrate PIP to achieve VT of 6ml/kg PBW

e. Changes of 2-4 cmH2O can be made every few breaths.

5. VT can change quickly in critically ill patients leading to changes in MV/pH/PaCO2.

a. Providers must be attentive for changes in VT and MV.

b. Decreases in Pulmonary Compliance will decrease VT

c. Increases in Pulmonary Resistance may decrease VT

6. Inspiratory Time can be increased or decreased to change VT

a. Increases in inspiratory time will increase VT

b. Decreases in inspiratory time will decrease VT

c. Changes in Respiratory Rate may change inspiratory time which may change VT

vi. Permissive Hypercapnia – Patients with hypercarbic respiratory failure (ex. ARDS or COPD) may require permissive hypercapnia to remain in safe pressure ranges on the ventilator.

1. Respiratory acidosis is well tolerated, to an extent. Titrating up ventilator pressures can be more harmful than tolerating moderate hypercarbia.

2. Prioritize lung protective ventilation with Pplat < 30 cmH2O.

3. Manipulate respiratory rate to maintain a minimum pH of 7.25.

4. Investigate non-respiratory causes of acidosis and treat appropriately

5. Bicarbonate administration may help in the treatment of non-anion gap acidosis. It may also be utilized as a temporizing measure for severe acidosis (pH < 7.15) with concern for high risk of cardiovascular collapse. However, note that bicarbonate will be rapidly converted to CO2 requiring increased minute ventilation for clearance, and thus may ultimately worsen respiratory acidosis for patients unable to ventilate.

vii. Oxygenation

1. Oxygen saturation goals should, in general, be between 93-99%.

a. While literature supports allowing for oxygen saturation as low as 90%, in the transport environment targeting a saturation of 93% or above allows for an increased degree of safety due to the number of patient handoffs and equipment challenges that can be encountered.

b. Oxygen saturation of 100% indicates a PaO2 of 100 mmHg or more and could indicate harmful hyperoxia. Targeting normoxia of 93-99% reduces the possibility of harm from hyperoxia and preserves a finite resource in flight.

2. FiO2

a. Start at 60% for patients with minimal lung disease

b. Start at 100% for patients with respiratory dysfunction

c. Titrate FiO2 in coordination with PEEP (see below)

d. FiO2 changes can be made rapidly and are best titrated to pulse oximetry, not PaO2 on ABG.

e. Consider increasing FiO2 by 20% immediately prior to take off in patients with marginal oxygenation

3. PEEP

a. Start PEEP of 5 mm Hg for patients with minimal lung disease

b. Start at a PEEP of 10-15 mm Hg for patients with hypoxic respiratory failure

c. Attempt to match PEEP and FiO2 per ARDSNet ARMA table in Appendix B

d. Increases in PEEP take 30-60 min to have an effect.

e. Decreases in PEEP take effect immediately. If PEEP is decreased too rapidly, it may take 30-60 min to re-recruit areas of atelectasis

f. Recruitment Maneuvers may speed response to changes increases in PEEP (see below)

g. Consider low PEEP and High FiO2 for patients with pneumothorax, air leaks from the chest tube, or recent lung surgery.

h. Recheck PIP and Pplat after titrating PEEP and ensure appropriate VT and MV

i. High PEEP can decrease cardiac output and may cause hypotension in hypovolemic patients. Additional volume loading may be necessary to maintain hemodynamics.

c. Alarms

i. Alarms should be set to alert the team to malfunctions or changes in physiology without causing frequent false alarms. The following guidance is a starting point, but each team will determine appropriate alarm settings for each mission.

ii. Suggested initial settings

1. High pressure alarm should be set 50% above the baseline PIP (1.5 X current PIP).

2. Low pressure alarm should be set 50% below the baseline PIP (0.5 X current PIP).

3. High respiratory rate alarm (731 only) should be set 10 above the patient's respiratory rate.

4. Low respiratory rate alarm (731 only) should be set 10 below the set rate.