This document discusses intraoperative hypoxemia. It defines hypoxemia and classifies its causes. Causes are problems with oxygen delivery systems like ventilators, circuits or endotracheal tubes. Or problems with patients like reduced lung volumes, atelectasis or increased oxygen demand. Specific risk factors are discussed like obesity, pregnancy, elderly and one lung ventilation. Diagnosis involves monitoring like pulse oximetry. Management focuses on giving high oxygen, ventilation support and treating underlying causes. Prevention emphasizes machine checks and safety features.

1. INTRA OPERATIVE
HYPOXEMIA
Presenter: Dr.T.Kumar
Moderator : Dr.Sreevani

2. HYPOXIA
 Failure of oxygenation at the tissue level.
 Hypoxemia is defined as a condition where arterial oxygen
tension (Pao2) is below normal (normal Pao2 = 80–100
mmHg).
 Hypoxia and hypoxemia may or may not occur together
 Nevertheless, hypoxemia is by far the most
common cause of tissue hypoxia.

3. Classification:
 Hypoxemic hypoxia: Insufficient oxygen reaching the
blood
 Stagnant or circulatory hypoxia: Decreased blood
flow to the tissues
 Anaemic hypoxia: Decreased oxygen carrying
capacity of blood
 Histotoxic hypoxia: Impaired utilisation of oxygen by
the tissues

4. Causes of Hypoxemia :
Classified into two
I.Problems with oxygen delivery system
• at the level of central oxygen supplies
• at the level of pipeline distributing system
• at the level of oxygen cylinders attached to
anaesthesia machine
• at the level of anaesthesia machine
• at the level of anaesthesia ventilator
• at the level of anaesthesia circuit
• at the level of endotracheal tube

5. At level of central Oxygen
 Liquid tank may be filled with nitrogen or argon
 Gasleak
 Inadequate pressure at central supply
 Decreased oxygen level at the tank
 Depleted cylinders
 Failure of master alarm system

6. At the level of pipeline distributing system
 Leak
 Contamination of gases
 Cross connection
 Connecting wrong hose to Oxygen yoke
 Inadvertent switching of schrader adapter of piped lines
At the level of 0xygen cylinders attached to
anaesthesia machine
 Empty cylinders
 Substitution of non oxygen cylinder at the yoke
 Insufficiently opened cylinder

7. At the level of anaesthesia
machine
 Incorrect setting of flow meter
 Crack in the oxygen flow meter tubes
 Transposition of rotameter tubes
 Leak in machine
At the level of anaesthesia Ventilator
 Low tidal volume
 Low respiratory rate
 Inadequate minute volume
 Disconnection of tubing

8. At the level of the anaesthesia
circuit
 Disconnection
 Leak
At the level of Endotracheal tube
 Esophageal intubation
 Endobrochial intubation
 Accidental extubation
 Kinking of tube
 Tube obstructing opening of rt. Upper lobe
bronchus

9. II.Problems with patient
• Hypoventilation
• Reduced functional residual capacity
• Increased airway resistance
• Atelectasis
• Absorption atelectasis
• Diffusion defect
• Shunt
• Inhibition of hypoxic pulmonary vasoconstriction
• Poor oxygen delivery yo tissues
• Increased oxygen demand

10. A.Hypoventilation :
 A Spontaneously anaesthetised patient may
hypoventilate due to drug induced respiratory
depression.
 In patient who is paralysed and ventilated ,
hypoventilation may occur due to inadequate
IPPV

11. B.Reduced functional residual capacity:
 Induction of GA will cause reduction in FRC by 15-20%
invariably
 This will be more in patients with preexisting lung
disease, obese patients.
 The reduction FRC is continued in post operative
period.
 Decreased FRC causes increase in PAO2 –PaO2
gradient.
 The reduction in FRC may be restored normal by
application of PEEP.

12. C. Increased airway resistance
 Due to following factors
a.Reduction in FRC
b.Decrease in calibre of airways
c.Endotracheal intubation
d.Anaesthesia apparatus
e.Laryngospasm
f.Obstruction of ETT

13. D.Atelectasis
 It is a condition of alveolar collapse .
 It may be micro atelectasis,macro atelectasis or
lobar collapse.
 Leads to V/Q mismatch , R-L shunting and
arterial hypoxemia
 Atelectasis occur due to airways secretions,
compression packs, wedge and prolonged
procedures
 PEEP may be useful in such situation

14. E. Absorption atelectasis
 Alveloar collapse occur when the patient is getting
high FiO2.
 When PAO2 rises , the rate at which O2 moves from
the alveoli to capillary blood increases.
 When the absorption rate is more than the inspired
flow gases , lung unit collapses
 So, absorption atelectasis occurs when
a. Fio2 is high ;
b. V/Q is low ;
c. time of exposure of lung unit low V/Q ratio to high FiO2
is long
d. CvO2 is low

15. F. Diffusion defect:
 Even though adequate oxygen is supplied to the
alveoli, defect at alveloar level which prevents its
absorption in to blood
 This is due to
a.Thickened alveloar membrane
b.Thickening of air-blood interface
c.Inflammation
d.Edema
e.Fibrosis or loss of alveolar surface area
(Eg:sarcoidosis ,Emphysema)

16. G.Shunt:
I) inadequate ventilation :
a. Absorption atelectasis
b. Airway secretions
c. Pulmonary aspiration
d. Pulmonary edema
e. Inhibition of HPV- vasodilators(SNP, NTG)
II)Inadequate perfusion :
a. ASD/VSD
b. Patent foramen ovale
c. Pulmonary embolism

17. H. Inhibtion of hypoxic pulmonary
vasoconstriction (HPV)
 It is a protective phenomenon. When PaO2
decreases in a region pulmonary vasoconstriction
occurs at that particular region.
 HPV diverts blood flow from the hypoxic regions of
the lung to better ventilated normoxic regions , thus
decreases V/Q mismatch maintaning PaO2
 Inhibition of HPV lead to arterial hypoxemia
 Factors inhibit HPV
a.Inhaled anaesthetics
b. vasodilators(SNP, NTG)
c.Hypocapnia
d.Hypothermia
e. Thrombo embolism

18. I. Poor oxygen delivery to
tissues:
 Due to following
a.Systemic hypo perfusion
b. Embolus
c.Sepis
d.Local problems ( cold limb , reynaud phenomenon ,
sickle cell disease )
J. Increase oxygen demand :
a.Malignant hyperpyrexia
b.Shivering
c.Sepsis

19. Intra operative hypoxemia
during special situations
Laproscopic surgery
• It is very common, it may be due to
• i.Pre exisiting conditions : obesity , cardio pulmonary
dysfunction
• ii. Hypoventilation : position , pneumo peritoneum ,
ETT obstruction , inadequate ventilation
• iii. Intra pulmonary shunting : Decreased FRC ,
pneumothorax , emphysema , endobronchial
intubation
• iv. Reduced cardiac output : hemorrhage , impaired
venous return ,arrhytmia , myocardial depression ,
CO2 embolism

20. Pneumothorax:
• Causes decreases in FRC
• Pts with previous COPD ,blunt injury chest
• suspect this following central line insertion
• Treat immediately by decompressing pleural cavity
with an open cannula in 2nd intercostal space
midclavicular line
• ASPIRATON of gastric contents during induction can
be prevented by doing RSI APPLYING CRICOID
PRESSURE

21. In Children
Neonates & infants are prone for more rapid
desaturation
• Smaller diameter of airways
• Chestwall & airway are highly compliant
• Increased oxygen consumption
• Premature infants have deficient surfactant
• Difference in airway anatomy – difficult intubation, mask
ventilation
• Early fatigue & apnoea due to lack of type 1 muscle fibres

22. In pregnancy
• FRC reduced by 20% , oxygen reserve
decreased
• Oxygen consumption increased by 20%
• More prone for precipitous fall in PaO2 even
after brief period of apnoea
• Difficult intubation , difficult ventilation ,
aspiration worsen the situation
• Preoxygention is must , rapid sequence
induction is prefered using sellick’s maneuver

23. In elderly
More prone hemoglobin desaturation
• Compromised respiratory system ( loss of elastin ,
reduced compliance,increased residual volume ,
loss of vital capacity , impaired efficiency of gas
exchange, increased work of breathing )
• Compromised cardio vascular system
• Prolonged drug effect seen after sedatives ,
narcotics& muscle relaxants

24. In obese patients,
• Difficult mask ventilation, difficult
laryngoscopy,difficult intubation
• Decreased lung volumes & capacities
FRC,ERV,VC.
• ERV is the only oxygen reserve.
• Preoxygenation is less effective
• FRC is further reduced in supine position
• More sensitive to depressant effects of
hypnotics & opioids

25.  During one lung ventilation
Hypoxemia occurs in almost all cases during one lung
ventilation
This is due to V/Q mismatch , because the non-dependent
lung is not ventilated but continues to get perfused .
Measures to be taken to maintain oxygenation during OLV
1. Two lung ventilation as long as possible
2. High FiO2=1.0
3. Begin OLV with Vt=10ml/kg
4. Adjust RR so that PaCO2 =40mm of hg
5. Monitor oxygenation & ventilation continously
6. Non-dependent lung CPAP
7. Depedent lung PEEP
8. Intermittent two lung ventilation
9. Clamp pulmonary artery as soon as possible

26. Diffusion hypoxia (Fink’s effect )
• It occurs at the end of G.A when N20 :O2 is switched off
and patient allowed to breathe air .
• N2O 31 times more soluble than nitrogen.
• For every one molecule of nitrogen entering into blood from
alveoli , 31 molecules of N2O enters into alveoli from blood.
• The alveolar oxygen is diluted and hypoxemia results.
• This is more common during first 5-10 minutes of recovery .
• Administration of 100% O2 is essential to overcome this
situation

27. Diagnosis:
 During early days of anaesthesia , defective
oxygenation of the patient was identified by cyanosis
&dark blood in the surgical field .
 Cyanosis occurs when the deoxygenated hb is >5g
/100ml
 Appreciation of blusih dicolouration is a subjective
phenomenon.
 Cyanosis usually observed when Hb saturation is
85%.this corresponds to PaO2 of 45-50mm hg in
adults 35-40mm hg in infants
 Cyanosis may be observed when there is no
hypoxemia Eg : methemoglobinemia
 Cyanosis may not be apparent in the presence of
anaemia or peripheral vasoconstriction

28.  Several monitors are used now to detect
hypoxemia .
 Pulse oximeter is most commonly used one
 Other monitors –
a) oxygen analyser
b) ABG
c) Scvo2
d) Capnography
e) Airway pressure monitor

29. ASA monitoring standards
 Standard I –states that a qualified anaesthesia
provider will be present with the patient throughout
the anesthetic
 Standard II-the patients oxygenation ,ventilation
,circulation & temperature will be continously
monitored
 Assesment of oxygenation involves two parts:
1. Measurement of inspired gas with an oxygen
analyzer
2. Assessment of haemoglobin saturation with a pulse
oximeter and observation of skin colour
Oxygen analyser placement :
The sensor should be placed on the inspiratory side of
the system , it should be upright or tilted slightly to
prevent moisture from accumulating membrane.

30. Management
a.Expose the chest, & all airway
connections
b.Give 100%O2(FiO2=1.0)
c.Hand ventilation
d.Confirm FiO2
e. Confirm ETT position
(auscultation,endobronchial, obstruction)

31. f. Check the ventilator pattern is correct
g. Find out the leak
h.Decreased FRC – hyperventilate gently with PEEP
i.Absorption Atelectasis – decrease FiO2, remove
secretions
j.Increased airway resistance- deepen anaesthesia,
salbutamol nebulisation , volatile anaesthetics, inj.
Aminophylline infusion

32. l. Hypvolemia – IVF , Blood
m. Increased O2 demand : give
100%O2
n.Pneumothoarx : ICD
o. Methemoglobinemia -100%O2
, inj methylene blue1-2 mg /iv

33. Prevention
A.Anaesthesia machine check up should carried out properly
before every anaesthetic procedure.
B. Use machine with O2 pressure failure alarm
C. Hypoxic guard
D.O2 proportinating devices
E.O2 flow meter tubes placed down stream
F. Check valve to prevent flow of gases from the machine to
cylinder or pipeline