This document discusses preoperative respiratory assessment, management of hypoxia during one-lung ventilation (OLV), and strategies to prevent hypoxia during OLV for thoracic surgery. It outlines tests to assess cardiopulmonary function and risk thresholds. It describes how to calculate predicted postoperative lung function and optimize gas exchange during OLV through lung recruitment maneuvers and ventilator settings. Factors that increase risk of hypoxia on OLV are identified. Pharmacologic interventions like inhaled nitric oxide, phenylephrine, and epoprostenol can help treat hypoxia if it occurs.

1. DR THANSEEL T H

2.  PRETHORACOTOMY RESPIRATORY ASSESSMENT
 MANAGEMENT OF HYPOXIA DURING OLV

3. Pre-thoracotomy respiratory
assessment
 Respiratory mechanical function:predicted
postoperative (pp0)FEV1(most valid test)
Threshold for increased risk <30-40%
 Lung parenchymal function :ppo DLCO(Diffusing
capacity of CO)(most valid)
Threshold for increased risk <30-40%
 Cardiopumonary reserve :maximal o2 consumption
Threshold for increased risk <15 ml/kg/min

4. 1.Respirtory mechanics:ppo FEV1
ppoFEV1 %=Preoperative FEV1*(1-%Functional tissue
removed/100)
Total subsegments=42
Eg:for left lower lobectomy
Post op FEV1 Decrease =10/42=24%
Preop FEV1(Or DLCO) 75% Or 60%
For left lower lobectomy
Ppo FEV1 (Or DLCO) 57% 46%

6. 3.Cardiopulmonary interaction
 O2 consumption (vo2)-sitting quietly=3.5
ml/kg/min(1 MET)
 Climbing one flight (3 m or 10 feet)of stairs=4METS
 Preop vo2 max <15 ml/kg/min; morbidity /mortality
 Vo2 max <10ml/kg/min; morbidity /mortality
 Calculation of vo2 max in 6 min walk test -450 m
;450/30=15
 Two markers 10 m apart ;<250 m;vo2 <10

8. MANAGEMENT OF OLV
GOALS: To maximize atelectasis in the non- ventilated lung
to improve surgical access AND to avoid atelectasis in the
ventilated lung to optimize gas exchange
 Gas mixture in the non ventilated lug immediately before
OLV has effect on speed of collapse of this lung
 N2- low blood gas solubility, so air-O2 mixture will delay
collapse
 De-nitrogenate the operative lung by ventilating with
oxygen, before lung collapse

9.  N2O is more effective in speeding lung collapse , but
not preferred as most pts have bullae
 Atelectasis will develop in the dependent lung during
TLV before OLV
 Recruitment: Hold the lung at an end inspiratory
pressure of 20 cmH2O for 15- 20 seconds, soon after
start of OLV to decrease atelectasis imp. To prevent
desaturation

10. HYPOXEMIA DURING OLV
 No universally accepted figure for the safest lower limit of
oxygen saturation during OLV
 Saturation >90%( PaO2 > 60 mmHg) is accepted usually
 Brief periods of saturation in the high 80s – acceptable in
pts without significant co- morbidity
 Lowest acceptable saturation is higher in pts with organs
at risk of hypoxia or with limited O2 transport
 COPD patients desaturate more quickly on OLV, during
isovolemic hemodilution than normal pts
 Incidence of hypoxemia on OLV has decreased from 20-
25% to less than 5%: improved lung isolation techniques,
better anaesthetic agents and better understanding of the
pathophysiology of OLV

11. HYPOXEMIA DURING OLV contd..
 Goal during OLV: maximize PVR in the non ventilated
lung and minimize PVR in the ventilated lung
 PVR is correlated with lung volume in a hyperbolic
fashion
 PVR – lowest at FRC and increases as lung volume rises
or falls above or below FRC
 Maintain the ventilated lung as close as possible to
FRC while facilitating collapse of the non ventilated
lung to increase its PVR

12. Ventilation strategies -OLV
 7-8 ml/kg TLV & 5-6 ml/kg during OLV
 RR to target PaCO2 of 40-50/60 mmhg
 PEEP ;Normal lung,5 cmH2O;Obstructive lung,2-5
cmH2O;Restrictive lung,5-10 cmH2O
 Optimum FiO2 to maintain SpO2 >90%
 I:E ratio :normal ,1:2;obstructive lung,1:3-4;restrictive
lung 1:1
 Airway pressure :peak pressure <35 cmH2O
 Ventilation mode VCV or PCV

14. Who will develop hypoxia during
OLV
 Right sided thoracic surgery with right lung collapse
 Normal preop FEV1
 Low PaO2 during TLV
 Morbidly obese
 Previous contralateral lung sx
 Supine position
 High alveolar-arterial co2 gradient
 Patients on chronic vasodilator therapy

16. Management of hypoxia during
OLV

18. Pharmacologic manipulations
 The combination of NO ( 20 ppm) to the non
ventilated lung and an IV infusion of
PHENYLEPHRINE which enhances HPV has
been shown to restore PaO2 values during OLV
 INHALED EPOPROSTENOL (FLOLAN)
 Eliminate known potent vasodilators such as
nitroglycerin & halothane and large doses of other
volatile anaesthetics.