Patient positioning Flashcards
Outline the CVS effects of supine positioning
Redistribution of pooled venous blood from LLs -> inc VR -> inc EDV -> inc preload -> inc SV and CO
May lead to inc myocardial O2 demand
Outline the pulmonary effects of supine
Upward movt of intra-abdominal contents on diaphragm -> dec total lung volume and FRC
Inc V/Q mismatch
Dec pulmonary compliance
Inc risk of aspiration from regurgitation
Which areas are particularly prone to pressure injury in supine positioning
Occiput, Elbows (esp Ulnar N), knees, sacrum, heels, greater trochanter of femur
Why is the ulnar N at particular risk in supine
Excessive head rotation can inc brachial plexus traction
Combined with excess abduction of the arm and forearm pronation = inc pressure on the Ulnar N in the ulna groove
Why is post-operative backpain a possible issue for patient’s in supine
Loss of natural lumbar lordosis in supine
What is Trendelenburg positioning and why is it used
Head down
Improves exposure of abdominal organs and pelvic surgery
Outline the pulmonary effects of trendelenburg
As for supine but more extreme
Dec FRC -> atelectasis -> V/W mismatch and risk of arterial hypoxaemia
Inc WOB for spont breathing pts
Higher airway pressures required to maintain adequate ventilation
Prolonged trendelenburg inc upper airway oedema -> inc risk of post-op airway obstruction
Endobronchial ETT migration, bronchospasm
Outline the CVS effects of Trendelenburg
As per supine
Inc VR -> inc blood volume ~1L -> inc SV & CO -> inc MAP
Baroreceptor reflex mediated systemic vasodilation and dec TPR to maintain MAP -> dec TPR, dec bloodflow -> dec perfusion pressure to organs
Outline the CNS effects of Trendelenburg
Gravity induced inc in CBF
Inc ICP due to gravity dependent dec in venous drainage
triggers vasoconstriction due to autoregulation -> inc CPP
Inc IOP for same reason
Is gastric aspiration more or less likely in Trendelenburg
Stomach positioned above ETT, inc risk of passive gastric aspiration on repositioning to supine
When is reverse Trendelenburg used
For head and neck, upper GIT and shoulder surgery
Outline the CVS effects of reverse Trendelenburg
Gravity induced inc in hydrostatic pressure which venous circulation must overcome -> inc venous pooling, dec venous return -> dec preload -> dec SV and CO -> dec MAP
Risk of air embolism
Increased head and neck venous drainage
Outline the respiratory effects of reverse Trendelenburg
Downward displacement of abdo contents and diaphragm -> inc FRC and VC
Dec risk of passive regurgitation
The dec MAP -> dec perfusion to non-dependent lung regions -> inc physiological dead space
Outline the CNS effects of reverse Trendelenburg
Dec MAP -> dec CPP which is counteracted by the gravity improved drainage of cranial veins dec ICP -> cerebral blood flow is maintained
When is Lithotomy positioning used
Lower GIT, urological and gynaecological surgery
What is lithotomy position
Hips flexed 80-100deg + hip abduction 30-45degs + knee flexion until lower legs are parallel to the torso
Outline the CVS effects of Lithotomy
Leg elevation inc VR and SVR
Compensatory baroreceptor reflex dec TPR -> dec sympathetic outflow and HR to maintain MAP
Hypotension may occur with lowering of legs
Outline the respiratory effects of lithotomy
Same as for supine
Which nerves are at risk in lithotomy and why
Sciatic or obturator N stretch with femoral N compression if hips flexed >90degs
Common peroneal N at head of fibula and saphenous N at medial tibial condyle at risk of compression against supports
Why is there an inc risk of VTE
The calf compression in the stirrups can lead to an inc risk of VTE or compartment syndrome
When is lateral decubitus positioning used
Hip, thoracic and renal surgery
Outline the respiratory effects of lateral positioning
With IPPV the dependent lung is relatively under-ventilated and overperfused, with the non-dependent lung have the opposite scenario -> inc V/Q mismatch
Dec movt of dependent ribs and diaphragm -> dec FRC and VC
Outline the possible pressure areas with lateral positioning
Ensure adequate lateral support for head and neck
Support shoulder and pelvis to prevent rolling
Avoid pressure on abdomen
Dependent arm - risk of nerve compression and ischaemia
High risk of corneal abrasions and pressure on dependent eye
Common peroneal N and saphenous N at risk of compression if inadequate padding between legs
When is prone positioning used
Access to posterior fossa of skull, posterior spine, buttocks, per-anal region, posterior compartments of the lower limbs
Outline the CVS effects of prone
Abdominal compression of IVC or iliac vessels -> dec VR -> dec SV & CO
Flow is diverted through low pressure systems -> venous plexus engorgement (perivertebral, lumbar and intercostals) -> inc risk of intraoperative bleeding in spinal surg
Can be offset with placement of wedges/pillows under chest and pelvis
Outline the pulmonary changes in prone
External pressure on abdo is transmitted to diaphragms -> dec FRC, dec compliance, inc peak airway pressure
BUT dorsal lung regions have inc FRC and improved V/Q = overall improved PaO2
Outline the CNS effects of prone
If head positioned at level of the heart - nothing
If below level of the heart -> as per head down
Which areas are at particular risk of pressure injury in prone
Forehead, nose, eyes, chest, breasts, genitals, pelvis (ASIS), knees and feet
Which nerves are at particular risk in prone
Nerves exiting superior orbital fissure
Brachial plexus
Ulna N
Lateral cutaneous N of the anterior thigh
How should the arms be positioned when in prone and why
Shoulder in anterior flexion + abduction + ER will minimise traction on axillary neurovascular bundle
