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 = 80100 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
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
sellicks 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 (Finks 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
