Pre-oxygenation

1. Kerry Gomes

2.  Inadequate alveolar oxygenation
◦ Low environmental oxygen pressure
◦ Alveolar hypoventilation
 Diffusion abnormalities
 Dead space
◦ High ventilation, low perfusion (V/Q)
 Low V/Q mismatch
 Shunt
 Low venous blood saturation

3.  Physiological shunt is the major cause of poor
oxygenation in ill ED patients.
 Areas of alveoli that are blocked from
conducting oxygen, but still have intact blood
vessels surrounding them.
 Causes
◦ Pneumonia
◦ Atelectasis
◦ Pulmonary oedema
◦ Mucus plugging
◦ ARDS

4.  In normal patients, Hb reaching lungs has a
saturation of 65-70%
 Only small amount of exposure to O2 needed
to rapidly bring saturation to 100%
 In shocked state, venous blood with lower
states reach the lungs, and will require more
exposure to O2 to reach 100%
◦ In injured lungs this may not occur
 Always consider the circulatory system when
evaluating respiratory status.

5.  Preoxygenation allows a safety buffer during
periods of hypoventilation and apnoea.
 Extends the period of safe apnoea, defined as
the time until a patient reaches a saturation
level of 88% - 90%, to allow for the placement
of a definitive airway.
 Below this level, oxygen saturation can
decrease to critical levels <70% within
moments.
Weingart SD and Levitan RM: Ann Emerg Med 2011

7.  Patients breathing room air before RSI,
desaturation occurs in 45-60sec
 Heller et al. showed marked time to
desaturation if patients received
preoxygenation with 100% oxygen.
 Ideally preoxgenate for 3 minutes with high
FiO2 source.
◦ Can augment denitrogenation by asking patient to
take 8 large breathes
◦ Difficult in ED setting and paediatric patients

8.  1. Achieve 100% oxygenation saturation prior
to procedure
 2. Denitrogenate the residual capacity of the
lungs, maximizing oxygen storage
 3. Denitrogenate and maximally oxygenate
the bloodstream.
Weingart SD and Levitan RM: Ann Emerg Med 2011

9.  If patients do not achieve a saturation >93%-
95% pre intubation, they have a high
likelihood of desaturation during the apnoeic
and intubation periods.
 If patients do not achieve this with a high
flow source, it is likely they are exhibiting a
physiological shunt.
 In short term shunt can be partially overcome
by augmenting mean airway pressures.

10. Study Patients Intervention Comparator Outcome
Delay et al RCT 28
obese,
operative
pts
NIV Spon vent at
zero
pressure
NIV pts achieved faster
and more complete
denitrogenation
Gander et al RCT 30
morbidly
obese,
operative
pts
CPAP preO2 Spon vent at
zero
pressure
Time to reach a saturation
of 90% after apnoea was
extended by 1min
Herriger et al RCT 40
ASA I-II
operative
pts
CPAP preO2 Spon vent at
zero
pressure
Prolonged the non-
hypoxic apnoea by >
2min

11.  Critically ill pts requiring tracheal intubation in ICU.
 At end of preoxygenation period:
◦ Noninvasive positive pressure grp had 98% mean SpO2
◦ Std grp had 93% mean SpO2
 During intubation procedure, oxygen saturation fell to:
◦ 93% in Noninvasive positive pressure grp
◦ 81% in Std grp
 12 of Std grp and 2 NIV grp had saturations below 80%
 6 of 26 in NIV grp were unable to improve hypoxymic
saturation with high FiO2 until they received positive
pressure.
Baillard et al. Am J Resp Crit Care Med. 2006

12. Study Intervention Method Outcome
Lane et al RCT pts preO2 in
20 degree head
up
3min preO2
Sedation & mus. relax.
Time to desat 100 – 95%
386 vs 283
sec
Ramkumar
et al
RCT pts preO2 in
20 degree head
up
3min preO2
Sedation & mus. relax.
Time to desat 100 – 95%
452 vs 364
sec
Altermatt
et al
RCT in BMI >31,
sitting position
RSI
Intubated, left apneic and
disconnected
Time to desat 100 – 90%
214 vs 162
sec
Reverse Trendelenburg position also improves preoxygenation and may be
useful in patients who cant bend at shoulder or waist, i.e. possible spinal injury
patients.

13.  Lung O2
◦ 450ml in patient breathing room air
◦ 3000ml in patient breathing 100% O2 for sufficient time
to replace alveolar nitrogen.
 O2 reservoir in lungs and bloodstream
◦ 1 -1.5L in patient breathing room air
◦ 3.5 – 4L in patient optimally preoxygenated
 Oxygen consumption during safe apnoea is
250ml/min in healthy patient.
 Duration of safe apnoea
◦ 1 min in room air
◦ 8 min breathing high FiO2

14. Benumof JL et al. Anesthesiology. 1997

15.  Benumof curves
◦ Assume preO2 with device generating ~90% FiO2
and optimal time
◦ Assume complete denitrogenation
◦ Ignore pulse oximeter lag time
 Times depicted not applicable to critically ill
ED pts, or pts poor cardiac output.
 Farmery and Roe, desaturation to 85% may be
as short as 23 sec in critically ill vs 502 sec in
healthy adult.

16.  During apnoea
◦ 250ml/min O2 will move from alveoli to bloodstream
◦ 8-20ml/min CO2 moves into alveoli
◦ Net pressure in alveoli - slightly sub-atmospheric,
generating a mass flow of O2 form pharynx to alveoli.
 Apnoeic oxygenation
◦ Under optimal conditions PaO2 can be maintained for
>100mmHg for up to 100min without a breath.
◦ Lack of ventilation will eventually cause marked
hypercapnia and significant acidosis.
Nielsen et al. ASAIO j. 2008

17. Study Patients Intervention Outcome
Teller et al
1998
RCT 12 pts,
blind
crossover
Nasopharyngeal
cathethers 100%
FiO2 at 3L/min vs
room air
Sat ≤92 or
10min
No desat <98%
in 10min
Taha et al
2006
RCT 30 pts Nasal catheters
5L/min of 100% vs
room air
No desat in O2
arm
Control desat
<95%in average
3.65 min
Ramachandran
2010
RCT 30
obese pts
Nasal catheters
5L/min of 100% vs
room air
O2 grp had
longer duration
of SpO2 ≥ 95%
5.29 vs 3.49min

18.  Nasal cannula provide limited FiO2 to
spontaneously breathing patient.
 Decreased oxygen demand during apnoea
allow nasal cannula to fill pharynx with high
level FiO2 gas.
 Increasing rate to 15L/min, near FiO2 can be
obtained.
 Nasal cannula can be left on during intubation
 High-flow nasal cannula also available, can
humidify O2 and allow rates <40L/min.

19.  Ventilation provides 2 potential benefits
◦ Ventilation
 Minimal, exception in profound met. Acidosis and
raised ICP
◦ Increased oxygenation through alveolar distension
and reduction in shunting
 lengthening duration of safe apnoea
 But, pressures > 25mmHg H2O can overwhelm
oesophageal sphincter – risk regurg and aspiration
 Keep bagging pressures < 25mmHg H2O
 Slow breathes over 1-2 sec at low vol 6ml/kg
and at a low rate 6-8breaths/min

20.  Operative pts receiving succinylcholine desat.
faster than those receiving rocurononium.
◦ Adult pt: Succ 242s vs Roc 378s to desat (Taha SK et al. 2010)
◦ Obese pt: Succ 283 sec vs Roc 329s to desat (Tang et al.
2011)
 When doses >1.2mg/kg used, intubating
conditions identical.
 ? Fasciculation's induced by succinylcholine
may cause increased oxygen use.

21.  Breaking sequence of sedative and paralytic
agent to allow adequate preoxygenation.
 Administration of specific sedative agents,
which do not blunt spontaneous ventilations
or airway reflexes.
 Ketamine
◦ 0.3mg/kg titrated up to 1.5 mg/kg by slow iv push
 Advantage of DSI is that frequently patients
on NIV improve their respiratory parameters
and intubation can be avoided.

22. Risk category PreO2 period Onset of muscle
relaxation
Apnoeic period
during
intubation
Low risk
SpO2 96-100%
NRB mask with
max O2 flow
rate
NRB mask and
nasal O2 at
15L/min
Nasal O2 at
15L/min
High risk
SpO2 91-95%
NRB mask or
CPAP or BVM
with PEEP valve
NRB mask,
CPAP, or BVM
with PEEP and
nasal O2 at
15L/min
Nasal O2 at
15L/min
Hypoxemic
SpO2 <90%
CPAP or BVM
with PEEP
CPAP or BVM
with PEEP and
nasal O2 at
15L/min
Nasal O2 at
15L/min
Weingart SD and Levitan RM: Ann Emerg Med 2011

23.  Conventional preoxygenation techniques
provide safe intubation techniques for
majority of ED patients.
 Subset of patients, will desaturate.
 Optimising preoxygenation and preventing
deoxygenation is needed to safely intubate
this group.
 NIV as preoxygenation technique, apnoeic
oxygenation, head-up and breaking the
sequence of RSI may make the prei-
intubation period safer.