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

List:

· Summary

· Graphs

· Awake and spont vent

· Under GA

· IPPV

· Open chest

· One lung ventilation

Summary:

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 · Attenuated during one lung ventilation

Graphs:

Awake, spontaneously ventilating:

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%)

Under general anaesthesia:

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

With intermittent positive pressure ventilation:

V	-
Q	· Obstruction to venous return -> ↓perfusion · ↑Alveolar pressure, ↓pulmonary arterial pressure -> ↑West zone 1

Open chest:

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

One lung ventilation:

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)

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