1 Mechanical Ventilation, part 1

Question 1

The primary function of mechanical ventilation

Answer 1

To provide respiratory support while treating the underlying process that caused respiratory failure

Question 2

how to approximate alveolar pressure

Answer 2

measure the plateau pressure with an end inspiratory pause in a passively breathing or paralyzed patient

Question 3

target plateau pressure

Answer 3

less than 30 cm H2O

Question 4

initial settings in pressure control

Answer 4

start with a pressure control of 10 cm H2O above PEEP and adjust pressure up and down to target tidal volume of 6-8 mL/kg ideal body weight

Question 5

remarks for patients who are not intubated for severe hypoxemia or obstructive lung disease

Answer 5

consider transitioning to pressure support after a volume-targeted mode because the former may be more comfortable for the patient

Question 6

Remarks on setting the respiratory rate

Answer 6

1. Most adult patients with normal respiratory physiology have adequate ventilation at a respiratory rate of 10 to 20 breaths/min
2. However, anticipate demands, e.g., in severe metabolic acidosis (eg DKA), set a higher respiratory rate to maintain adequate minute ventilation
3. For patients with obstructive lung disease, set RR at 10-14 for longer expiratory time (counterintuitive, yes)

Question 7

remarks on obese patients

Answer 7

obese patients and those with tense abdomen require higher PEEP
start at 8-10 cm H2O

Question 8

remarks on hyperoxia

Answer 8

hyperoxia increases patient mortality in a dose-dependet relationship. Many recommend titrating the FiO2 to target an O2 saturation of no greater than 96% as soon as the patient recovers from the apneic induction period

Question 9

targets in sedation

Answer 9

target a Richmond Agitation-Sedation Scale (RASS) score of
-2 (awakens and makes eye contact to voice)
to 0 (awake, alert, and calm

Question 10

Remarks on PEEP

Answer 10

improvements in oxygen saturations through increased PEEP are not immediate, so use incremental changes in pEEP of 2 cm H2O every 10-20 minutes rather than rapidly increasing or decreasing because there is potential for unanticipated hemodynamic, intrathoracic, or intrapulmonary changes

Question 11

remarks on sedation in mechanical ventilation

Answer 11

although often not an ED issue, ending sedation or using sedation holidays allow for more prompt return to spontaneous ventilation

Question 12

Remarks on obstructive lung diseases and mechanical ventilation

Answer 12

1. The primary pathology is NOT improved by intubation.
2. The problems encountered are increased airway resistance, pulmonary hyperinflation, and increased dead space causing hypercapnia

Question 13

What is dynamic hyperinflation?

Answer 13

1. Arterial hypercapnia in obstrucive lung disesaes (asthma/copd) tempts the treating physician to increase the RR to exhale more CO2. However, this is counterproductive because it shortens exhalation time, leading to an additional breath prior to the lungs completely emptying.
2. This latter event is called DYNAMIC HYPERINFLATION
3. Incomplete emptying can be detected by monitoring the expiratory flow limb in a passively breathing patient

Question 14

What is auto-PEEP

Answer 14

A.k.a intrinsic PEEP
The difference between the total PEEP (from end-expiratory hold) and the set PEEP.

Question 15

Ventilator management for obstructive lung diseases

Answer 15

1. Slow respiratory rate
2. Tolerate hypercapnia
3. Check for gas trapping

Question 16

RR in obstructive lung diseases (OLD)

Answer 16

1. SLOW RESPIRATORY RATE
- start with a rate of 10-14 bpm
- a slow resiratory rate is the best way to increase emptying time compared with a decrease in inspiratory time

Question 17

Hypercapnia in OLD

Answer 17

2. TOLERATE HYPERCAPNIA
- tolerate a pH of ≥7.20
- if a respiratory acidosis is causing systemic effects, increase the TV >8 mL/kg while keeping a low RR to maximize alveolar ventilation

Question 18

How to check for gas trapping in OLD

Answer 18

1. Ensure the expiratory flow limb of the flow curve reaches zero before the next breath (in a passively breathing patient)
2. Calculate auto-PEEP by performing an end-expiratory hold (Total PEEP - set PEEP; should be less than 5)
3. If Auto-PEEP >5, decrease RR until expiratory flow limb approaches zero before inspiration or RR =10.
4. If hypotension occurs, disconnect the patient from the ventilator for 15-20 seconds and decrease the RR after reconnection

Question 19

Other maneuver for obstructive lung disease to prevent lung trapping

Answer 19

increase IFR (inspiratory flow rate)
*typically, it’s 60 LPM
*recommendation in COPD is 80-100 LPM

Question 20

ARDS definition

Answer 20

Berling definition:
Onset within 1 week of a known clnical insult or new or worsening repiratory symptoms
Bilateral opacities on chest imaging not fully explained by lobar/lung collapse or nodule
Respiratory failure not fully explained by cardiac failure or volume overload
PF ratio ≤300 mmHg with PEEP ≥5.0 cm H20

Question 21

Conditions that place patients at risk for ARDS

Answer 21

Pneumonia
Sepsis
Trauma
Pancreatitis
Any shock state

Question 22

Mainstays of treatment for suspected ARDS

Answer 22

1. Low TV ventilation
2. Adequate PEEP
3. Treatment of the underlying condition

Question 23

in patients with bilateral lug disease and at risk for ARDS, and the plateau pressure is above 30 cm H2O, what to do with tidal volume?

Answer 23

the tidal volume should be incrementally decreased by 1 mL/kg to as low as 4 mL/kg

these protective lower tidal volumes may lead to hypercapnea and acidemia although a pH of >7.20 is usually well tolerated

Question 24

Oxygenation in ARDS

Answer 24

1. Avoid hyperoxia; do NOT routinely seek a saturation of 98-100% in most patients.
2. in ARDS, many seek an O2 sat of 88% to 95% or PaO2 55 to 80 mm Hg

Question 25

other options in those with refractory hypoxemia and criteria for severe ARDS

Answer 25

neuromuscular blockade
prone positioning
pulmonary vasodilators
transfer to an ECMO-capable center

Question 26

remarks on ventilator care bundle

Answer 26

implement it in every patient ASAP. it includes:
-routine measurement of patient height to determine appropriate tidal volume for ventilation
-elevating the head of bed to at least 30 degrees
-decompressing the GI tract
-oral care with chlorhexidine solution every 2 hours (or 2-3x a day)

Question 27

other remarks in mechanical ventilation

Answer 27

decrease FIO2 quickly to avoid hyperoxia
start venous thromboembolism prophylaxis approach
adequate sedation
*but think early about Sedation holidays and Spontaneous breathing trials in patients expected to be housed in the ED for ≥24 hours