Ventilator setting

Question 1

Discuss ventilator setting for ARDS

Answer 1

As per ARDS Network low tidal volume study trial LTVV management
Mode - SIMV – volume control
Tidal volumes 4-8mls
P-plat <30mmhg
RR is set to achieve minute ventilation requirements
PEEP is titrate with fio2 to achieve oxygenation – (see next question)

Start at intial tidal volume of 6ml/kg pbw

• For females: PBW (kg) = 45.5 + 0.91 * (height [cm] - 152.4)
• For males: PBW (kg) = 50 + 0.91 * (height [cm] - 152.4)

If p-plat is >30 reduce TV by 1ml/kg pbw to a min of 4ml/kg – will often require an adjustment in RR to maintain minute ventilation

permissive hypercapnia – PH >7.2 pco2 <100

Question 2

List PEEP titration values as per ARDS net

Answer 2

Ventilator setting usual start with fio2 of 1 and PEEP of 5 – this is rapidly reduced to maintain Pao2 and then is titrated to fio2 requirement as below

Fio2 0.3 Peep 5 
Fio2 0.4 Peep 5-8 
Fio2 0.5 PEEP 8-10
Fio2 .6 Peep 10
Fio2 .7 Peep 10-14
Fio2 .8 Peep 14
Fio2 0.9 Peep 14-18 
Fio2 1 Peep 18-24

Question 3

Discuss ventilator setting for severe pneumonia

Answer 3

Volume controlled
The initial ventilator settings after intubating a patient for refractory hypoxia is typically a tidal volume of
6 to 8 mL/kg ideal body weight, a respiratory rate of 12-16 breaths per minute, an FiO2 of 100%, and a positive end-expiratory pressure (PEEP) between 5 and 10 cm H2O.
Titrate the FiO2 setting down to below 80% once the patient stabilizes while maintaining an arterial saturation above 90%.
Patients who are hypoxic despite high PEEP and FiO2 may benefit from being placed in the prone position.

Question 4

Discuss ventilator setting for sever asthma/COPD

Answer 4

goals: avoid DHI and hypoventilation

• TV 6mL/kg
• RR 6-10
• short inspiratory time (flow rate 80-100L/min) -> high peak airway pressure but low plateau pressure -> –decreased barotrauma
• Platue pressure should be kept below < 25cmH2O to avoid breath stacking
• I:E of 1:>4
• permissive hypercapnia will result -> sedation and often paralysis initially
• PEEP – traditionally no PEEP was used out of fear of exacerbating Auto PEEP -> but it is now known that PEEP should be set at 60-80% of Auto-PEEP to augment distal airway emptying through splinting airways open

Adjustment of Ventilation
adjust ventilation to degree of DHI (not PaCO2 or pH)
if Pplat > 25cmH2O or cardiovascular suppression -> reduce rate
if Pplat < 25cmH2O -> ventilation can be liberalised with increase in RR and reduction in sedation
hypercapnia is well tolerated but can consider bicarbonate if pH < 7.2

Question 5

DIscuss physiological changes associated with obesity

Answer 5

Respiratory physiology

• Occur due to physical impingement on lung volumes and chest wall movement, increased metabolic requirement of excess tissue leading to increase WOB and increased o2 consumption and co2 production.
• The above causes
• –Decreased time to desaturation during apnoea
• –increased o2 reqruiements
• –hypoventilation with supine spont ventilation

CVS changes

• increased circulating blood volume
• decreased systemic vascular iresistance
• increased CO by 20-30ml per kg of excess body fat
• LVH

Question 6

Discuss vent setting in obesity

Answer 6

TV -6-8ml/kg of IBW
RR - adjust to maintain normocapnia (permissive hypercapnia is okay in patients without pulmonary hypertesnion)
-Fio2 to maitnain sats of >92 titrate with Peep likley starting at 10
-recruitment maneuvers if needed

Maintain revers trendelenburg