2015B03 What effect does placing a patient in the right lateral position have on
lung ventilation and perfusion?

Awake

·   R > L lung ventilation

·   R > L lung perfusion

·   Improved V/Q matching c.f. supine

Anaesthetised

·   L > R lung ventilation

·   R > L lung perfusion

·   Worse V/Q matching

·   Even worse with open chest, one lung ventilation

·   High risk hypoxaemia

V

·   Distribution:

o L lung traction -> ↑alveolar volume -> ↓ compliance -> ↓ventilation 10%

o R lung compression -> ↓ alveolar volume -> ↑ compliance -> ↑ventilation 10%

·   FRC: erect > lateral > supine

o R lung compression -> ↓volume

o ↓Diaphragm displacement

·   Time constants ( = resistance x compliance)

o L lung: ↑volume -> ↓compliance, ↓resistance -> ↓time constant

o R lung: ↓volume -> ↑compliance, ↑resistance -> ↑time constant

o Hence hypoventilation of R lung if high respiratory rate

Q

·   Shorter hydrostatic column. More even distribution than when supine.

·   L lung: mostly West zone 2 (↓perfusion 10%)

·   R lung: mostly West zone 3 (↑perfusion 10%)

V

·   L lung: hypotonia -> volume reduced to normal -> restored compliance -> ↑ventilation

·   R lung: hypotonia -> further loss of volume -> worse compliance -> ↓ventilation

Q

·   Inhibition of HPV -> ↓PVR

·   ↓Lung volume -> ↑PVR

·   ↓Venous return, ↓right heart output -> ↓pulmonary arterial pressure -> ↑West zone 1

V

-

Q

·   Obstruction to venous return -> ↓perfusion

·   ↑Alveolar pressure, ↓pulmonary arterial pressure -> ↑West zone 1

V

·   L lung: ↑volume and ↑ventilation possible

·   R lung: loss of negative L intrapleural pressure -> ↑mediastinal shift -> ↑ R lung compression -> ↓volume -> ↓compliance -> ↓ventilation

Q

·   L lung: loss of negative intrapleural pressure -> ↓perfusion

·   R lung: ↓volume -> ↑PVR -> ↓perfusion

V

·   L lung: no ventilation. Massive shunt.

·   R lung: ↑ventilation, risk barotrauma and volutrauma.

Q

·   L lung: collapse and ↓PAO₂ -> ↑PVR -> ↓perfusion (note HPV impaired under GA)