Positioning for Anesthesia/Surgery Flashcards
CV effects of General Anesthesia
CO and BP decrease d/t myocardial depression and vasodilation
Preload and SV____ during GA
Decrease
GA effect on Venous Return
Decrease d/t decreased muscle tone from NMBs
Opioids _______HR which does what?
Decrease HR, CO and BP
GA blunts compensatory mechanisms(HR/BP) which does what?
Make CO and BP more susceptible to gravitational forces
Positions that have minimal hemodynamic changes?
Supine and Lateral
CO and BP decrease with what positions?
sitting, prone, and flexed lateral positions (lower extremities are dependent)
CV effects of Prone positioning
-Increase CVP
-LV volume decrease d/t decrease venous return and increase intrathoracic pressure
-Increase venous pressure in head (swelling in face, pharyngeal, orbital structures)
-possible increase ICP
-Postoperative visual loss (POVL) from increase ocular pressures
Lateral decubitus w/ kidney rest elevated (CV)
-↓ BP d/t legs being dependent
-↓ venous return d/t extreme flexion
-Kidney rest may compress the vena cava
-Kidney rest should be placed under the dependent iliac crest
-Caution with large tidal volumes and high PEEP (high intrathoracic pressures w/ a subsequent reduction in venous return, right atrial filing, and C.O)
Lithotomy (CV) head?
-↑ venous pressure in the head → swelling in face, pharyngeal, and orbital structures
-Possibly ↑ ICP
CO if patient raised to 90 degrees?
C.O ↓ 20%
Interventions that Promote CV Stability
-Move pt slowly
-lighter plane of anesthesia (MAC < 0.5) gradually increase depth
-IV hydration
What positions can Hypotension go unrecognized?
Lithotomy and Trendelenburg
Pt may get hypotensive when returned to horizontal position (decreased SV, CO, BP)
Pts with CAD in lithotomy and head-down tilt (CV)
↑ CVP, PAPA, and PCWP and ↓ C.O
Trendelenburg CV effects
may ↑ myocardial work via ↑ central blood volume, ↑ C.O and ↑ SV, pts with poor cardiac function have ↓ C.O if the ↑ in central blood volume moves them to a worse position on the frank starling curve
Pts with PVD have ↑ risk for ischemia in lower extremities when________
placed in lithotomy and Trendelenburg position
When extremities are above the level of the heart pt is at ↑ risk for compartment syndrome
Compared to the awake spontaneously breathing pt, a spontaneously breathing anesthetized pt has:
↓ tidal volume
↓ FRC
↑ closing volume
Sitting: LUNG Dependent/Non-Dependent
Dependent: Base
Non-Dependent: Apex
Supine: LUNG
(dependent/non-dependent)
Dependent: Posterior
Non-Dependent: Anterior
Dependent lung region (V/Q)
V/Q DECREASE
Non-Dependent lung region (V/Q) during GA
V/Q INCREASE
Prone Position
(Respiratory effects)
-Improved oxygenation
-More lung volume is present posteriorly and better ventilated in prone position
-Ventilation is more uniform and V/Q matching is better d/t alleviation of pressure from anterior structures on the lungs
-Increased hydrostatic pressure → edema formation
Lateral Decubitus (Respiratory)
Awake= ventilation favors dependent lung during spontaneous respiration
Anesthesia, positive pressure ventilation, paralysis: upper lung becomes easier to ventilate
Supine (Respiratory)
FRC and TLC?
FRC and total lung capacity are ↓ compared to sitting d/t cephalad shift of the diaphragm caused by the pressure of the abdominal viscera
Favorable for ventilation? (Respiratory)
-Sitting
-Neck flexion can impair venous drainage from head → edema formation
Trendelenburg (Respiratory)
ETT movement?
-↓ FRC
-Movement of the mediastinum toward the head may result in the tip of the endotracheal tube migrating into the right mainstem bronchus
-Increased hydrostatic pressure → edema formation
Causes of Nerve Injury
-Transection (surgical/trauma)
-Compression
(Nerve forced against a boney prominence or hard surface)
-Stretching
Nerves don’t tolerate being pulled. Excess stretch can damage the structure of the nerve and damage the blood flow to the nerve
Patient predisposition for Nerve Injury
-Advanced Age
-Extremes of habitus
-Comorbidities (Diabetes, Smoking, Hypertension)
-Interop (Hypotension, Hypoxia, Hypothermia
Hypovolemia)
Factors contributing to Nerve Injury
-Positioning devices
-Length of procedure
( >4hours)
-Anesthetic techniques
What is susceptible to stretch and compression injuries?
Brachial Plexus
(Keep arms Abducted less than 90°)
Brachial Plexus picture
Randy Travis Drinks Cold Beer = Roots, Trunks, Divisions, Cords, Branches
Sensory Distribution of Brachial Plexus (Anterior)
Sensory Distribution of Brachial Plexus (Posterior)
Positions that increase Preload….
Trendelenburg, Lithotomy
Positions that decrease Preload….
Reverse Trendelenburg, sitting, flexed lateral
Trendelenberg and Lithotomy increase….
-Venous hydrostatic pressure (edema of face, eye, airway)
-increase ICP (hinders venous drainage)
PEEP and positive-pressure ventilation (lungs)
Increase intrathoracic pressure and decrease venous return
Which 4 body positions are associated with higher hemodynamic instability?
-Reverse T-burg
-Sitting
-Flexed lateral
-Prone
5 anesthesia techniques that attenuate the body’s compensation for CV stability
-GA
-Neuraxial anesthesia
-positive-pressure ventilation
-PEEP
-Muscle relaxants
Blood movement during T-burg and Lithotomy (F-S curve)
-blood shifts towards central circulation
-increase venous return
-shifts position on Frank-Starling curve to RIGHT
The T-burg position reduces_______ and increases________.
-Reduces pulmonary compliance
-increases the risk of endobronchial intubation
Picture to remember
Picture to remember
What locations are the brachial plexus anatomically fixed to?
cervical vertebrae and axillary fascia
Highest risk position for brachial plexus STRETCH injury?
arms ABducted > 90 degrees and head rotated to other side
What is common cause of compression injury for brachial plexus?
compression between clavicle and first rib (shoulder brace) or by external force (improperly placed axillary roll).
Most commonly injured peripheral nerve?
ULNAR
Many ulnar neuropathy cases don’t present until > 24hrs after surgery
Risk factors for ulnar injury:
-poor positioning/padding
-male gender (>50 years old)
-preexisting ulnar neuropathy
-extremes of body habits(thin/obese)
-prolonged hospital stay/bedrest
Ulnar nerve injury presentation?
-impaired sensation of fourth and fifth digits
-inability to ABduct pinky finger
Chronic= CLAW HAND
Which deficits are more common, less serious, and tend to resolve on their own? (ULNAR)
Sensory
-Motor deficits are more serious and can take up to 4-6 weeks to recover
Prone positioning recommendation (Brachial plexus)
-Don’t have saggy shoulders
-Keep shoulders and elbows at 90 degrees or less (NOT over the head)
Picture to remember (arm position)
Median nerve injury is _______.
How can it occur?
RARE
-IV placed in AC
-Elbow hyperextension
-carpal tunnel syndrome
How does median nerve injury present?
-reduced sensation over the palmar surface of thumb, index finger, middle finger and lateral aspect of ring finger.
-may be unable to oppose thumb
-Chronic= Ape Hand deformity
Causes of Radial nerve injury
-External compression by an IV pole
-Excessive cycling of the NIBP cuff
-Upper extremity tourniquet
-Sheets that are too tight (if the arms are tucked
Long thoracic nerve injury presents with….
winged scapula
Location of Suprascapular Nerve
anchored between cervical spine and suprascapular notch
innervates the supraspinatus and infraspinatus muscles
Cause of Suprascapular nerve injury
Ventral circumduction of the dependent shoulder in the lateral decubitus position can stretch the suprascapular nerve ( pt in lateral decubitus rolls onto their dependent arm)
presents as DULL shoulder pain
Obturator injury presentation
-Inability to ADDuct the leg
-Reduced sensation over the medial aspect of the thigh
prevention: minimize hip flexion
Femoral Nerve injury etiology, presentation and prevention
Etiology
Excessive traction during lower abdominal surgery
Presentation
Impaired knee extension and hip flexion
Reduced sensation over the anterior thigh and anteromedial aspect of the leg
Prevention
Surgical team should avoid excessive traction during the procedure
Saphenousl Nerve injury etiology, presentation and prevention
Etiology
MEDIAL aspect of the leg leans against the supporting cradle in the lithotomy position (the saphenous n. resides near the tibia)
Presentation
Reduced sensation over the anteromedial aspect of the leg
Prevention
Place padding between leg and stirrup
Most common lower extremity injury?
Common Peroneal Nerve
Common Peroneal Nerve Etiology
Very susceptible when pt is in stirrups
Nerve can be compressed when the LATERAL aspect of the leg leans against the stirrup bar or “candy canes”
Common Peroneal Nerve presentation
Foot drop
Inability to evert the foot
Inability to extend the toes dorsally
Common Peroneal Nerve prevention
-Placing padding between the leg and stirrup
-Pad under the fibular head
-Knees should be flexed with minimal rotation
Sciatic Nerve etiology, presentation and prevention
Etiology
Lithotomy- extreme hip flexion or external rotation of the legs
Sitting- Straight legs
Presentation
Foot drop
Prevention
Ample padding under the buttocks
Avoid excessive external rotation of the hips
Flex table at the knees
Which nerves can be damaged if patients legs are crossed?
Top leg–> sural injury
Bottom leg–> superficial peroneal injury
Position most common in lower extremity compartment syndrome?
Lithotomy
Legs are above the heart
Leg ischemia →edema→ more ischemia→ more edema
Risk factors for lower extremity Compartment Syndrome?
Risk factors:
Surgical time >2-3 hrs
↑ BMI
↓ Tissue oxygenation (hypotension)
Treatment: fasciotomy
Position most common in Air Embolism?
Sitting
Craniotomy done in sitting position is greatest risk for AIR EMBOLISM
Signs and Symptoms of Venous Air Embolism
Air seen on TEE (most sensitive)
-“Mill wheel” murmur on precordial doppler
-Decreased EtCO2
-Increased pulmonary artery pressure
-Hypotension
-Dysrhythmias
-Pulmonary Edema
-Hypoxia
-Cyanosis
Treatment for Venous Air Embolism
-100% O2
-flood surgical field with normal saline
-stop insufflation
-place patient on LEFT side (Durant maneuver)
-Aspirate air from CVC
-Hemodynamic support (pressors, inotropes, fluid)
Paraplegia risk factors
Extreme hyperextension of the lumbar spine in supine position can cause paraplegia
Risk factors:
Maximal retroflexion of the OR table
Raising the kidney rest to its highest position
Placing large rolls under the patient’s lumbar spine
Midcervical Tetraplegia is associated with?
hyperflexion of the neck (chin to chest)
Ischemia occurs as a result of stretching and compressing of the midcervical spinal cord (usually C5)
Most common in sitting position
Make sure you can place 2 fingers between the patients chin and chest
Can also occur postoperatively in patients who had a tracheal resection
Post-op Vision Loss cause
Anterior/Posterior ischemic optic neuropathy
Most common causes of ION are decreased perfusion & increased intraocular pressure
Post-op vision loss intraoperative factors:
-Prolonged surgical Procedure
-Prone Position
-Large Blood Loss/Low HCT
-Hypotension (SBP <100mmHg)
(MAP-IOP = OPP)
Increase hydrostatic pressure –> edema formation (Airway)
Prone and T-burg
Neck flexion impairs venous drainage from head–>Edema (Airway)
Sitting
Equipment (oral airway, esophageal temp probe) does what?
impairs lymphatic drainage —->edema formation
Long Thoracic Nerve Innervates?
SALT (Serratus Anterior Long Thoracic) Causes scapular winging with injury
In a patient with a mediastinal mass, 3 ways that worsen tracheobronchial compression (airway collapse)
- Supine position
- GA
- Loss of spontaneous ventilation (need for positive-pressure ventilation)
