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Positioning for thoracic surgery (Respiratory physiology in the lateral…
Positioning for thoracic surgery
Position
Most often lateral decubitus
A supine, semisupine, or semiprone lateral position may also be used
Position change
Must be in charge of the operating team to direct positioning
Take responsibility for the head, neck and airway (head, neck and tube should be turned 'en bloc' with the thoracolumbar spine)
Secure all lines and monitors
Checks after position change
Airway and breathing - check endobronchial tube/blocker position and the adequacy of ventilation with auscultation and fibreoptic bronchoscopy
Circulation - Haemodynamics, lines
Potential neurovascular injuries (dependent eye, ear pinna, C spine in line, dependent arm (brachial plex, circulation), suprascapular nerves, sciatic nerve, peroneal nerve)
Monitors
Neurovascular structures at risk
Brachial plexus
Anatomically predisposed to injury
Two point fixation of brachial plexus (prox to cervical vertebrae, distal to axillary fascia)
Mobility of neighbouring musculoskeletal structures
Factors contributing to injury in lateral position
Dependent arm (compression injuries - majority) - arm directly under thorax, pressure on clavicle, cervical rib, caudal migration of thorax padding into the axilla
Non dependent arm injuries (stretch) - lateral flexion of C Spine, abduction of arm > 90 deg, semiprone or semisupine repositioning after arm fixed to suport
Prevention
'Axillary roll' caudal to the dependent axilla to keep the weight of the upper body off the brachial plexus - should not be placed in the axilla: will exacerbate pressure on brachial plexus
Pulse Ox in dependent arm to detect vascular compression
Majority resolve spontaneously over months
Suprascapular nerve
Mechanisms of traction injury
Anterior flexion of the arm at the shoulder (circumduction) across the chest
Lateral flexion of the neck towards the opposite side
Causes deep, poorly localised pain in the posterior and lateral shoulder - may be responsible for some cases of post sx pain
Legs
Dependent leg slightly flexed with padding under the knee to protect the peroneal nerve lateral to the prox head of the fibula
Non dependent leg: neutral extended position with padding between it and the dependent leg to prevent vascular compression
Excessively tight strapping at the hip level can compress the sciatic nerve of the non dependent leg
Respiratory physiology in the lateral position
Awake
Dependent lung
On a steep part of the compliance curve - increased ventilation
Ventilation is also enhanced by cephelad diaphragmatic movement
Increased perfusion secondary to gravity
Non dependent lung
On flat part of the compliance curve - reduced ventilation
V/Q matching is preserved
Anaesthetised and paralysed
Consequences
Loss of muscle activity in diaphragm and chest wall (reduced FRC in both lungs)
Weight of mediastinum - compression of dependent lung
This moves both lungs down the compliance curve
Dependent lung
On flat part of compliance curve - reduced ventilation
Increased perfusion due to gravity (unchanged)
Non dependent lung
On steep part of the compliance curve - increased ventilation (but poor perfusion)
Increased V/Q mismatching
Open chest
Consequences
Loss of negative pleural pressure of the non dependent lung - increased mediastinal shift - increased compression dependent lung - reduced ventilation
Much increased V/Q mismatch
One lung anaesthesia
Dependent lung
V/Q mismatch
Non dependent lung
Shunt: perfusion continues but ventilation does not - perfusion reduces vis HPV and surgical occlusion of pulm vessels
Left vs Right side