Nagelhout Ch 23 Flashcards
(139 cards)
1
Q
What is the importance of positioning during surgery?
A
Positioning is critical to prevent patient injury, enable optimal surgical access, and manage anesthesia-related physiologic changes.
2
Q
What vulnerabilities do patients have after anesthesia is administered?
A
Patients lose voluntary motor control, making them vulnerable to pressure injuries, nerve compression, and hemodynamic compromise.
3
Q
What must providers understand regarding positioning?
A
Providers must understand position-induced physiologic shifts, particularly in vulnerable populations such as the elderly, those with cardiac disease, and hypovolemia.
4
Q
Which physiologic systems are affected by positioning?
A
The cardiovascular system, respiratory system, nervous system, and vulnerable pressure-prone areas (skin, eyes, genitalia, breasts).
5
Q
What are the general cardiovascular effects under anesthesia?
A
Vasodilation and myocardial depression lead to decreased preload, systemic vascular resistance (SVR), and mean arterial pressure (MAP), along with decreased baroreceptor response and impaired compensatory mechanisms.
6
Q
How do opioids and beta blockers affect the cardiovascular system?
A
They can blunt the sympathetic response and further depress cardiac output.
7
Q
How does MAP change with height difference?
A
MAP changes approximately 2 mm Hg per inch height difference between the heart and the body region.
8
Q
What is the baseline for cardiovascular comparison?
A
The supine position is the baseline for comparison, where central venous pressure (CVP), cardiac index (CI), and pulmonary capillary wedge pressure (PCWP) are typically stable.
9
Q
What happens to hemodynamics in sitting, lateral, and flexed lateral positions?
A
Blood pools in legs leading to decreased preload; hemodynamic changes depend on elevation, with 45° elevation causing minor CV effects and 90° elevation causing decreased preload, decreased cardiac output, and possible hypotension.
10
Q
What are the cardiovascular effects of the prone position?
A
In the prone position, CVP increases due to abdominal compression, while left ventricular (LV) compliance decreases, leading to decreased cardiac output.
11
Q
What is the autotransfusion effect in the lithotomy position?
A
Leg elevation leads to increased preload and cardiac output temporarily, but in patients with limited cardiac reserve, there is a risk of overload and increased myocardial work.
12
Q
What are the effects of the Trendelenburg position?
A
Head-down tilt increases central blood volume, CVP, pulmonary artery pressure (PAP), and PCWP, with conflicting evidence on CI and MAP. In normovolemic patients, stroke volume and MAP increase, but in hypovolemic or cardiac patients, CI decreases and myocardial oxygen demand increases.
13
Q
What are the risks associated with Lithotomy + Trendelenburg positions?
A
Compounded increase in central volume, ↑ risk of myocardial ischemia, ↑ PCWP, PAP, CVP, ↓ cardiac output, worsened performance on Frank-Starling curve in heart failure.
14
Q
What is the effect of elevated legs above the heart in patients with Peripheral Vascular Disease?
A
It leads to ↓ perfusion pressure to distal limbs, increasing the risk of ischemia and compartment syndrome.
15
Q
What are the concerns with Trendelenburg and Prone positions?
A
They increase venous pressures in the head, leading to facial, orbital, and pharyngeal edema, ↑ ICP due to jugular congestion, and ↓ cerebral perfusion pressure (CPP).
16
Q
What complications are associated with increased venous pressures in the head?
A
Post-op vision loss (POVL), airway edema, macroglossia.
17
Q
What is a preventative strategy for patients in prone position?
A
Keep head level or above heart.
18
Q
What strategies can minimize positional hemodynamic changes?
A
Use lower MAC (< 0.5), consider invasive monitoring, judicious fluid administration, gradual position changes, terminate volatile agents if unstable.
19
Q
What are the key takeaways regarding positioning?
A
Positioning affects cardiac output, preload, ICP, airway safety, and organ perfusion. Be cautious in elderly, cardiac compromised, hypovolemic patients, and those at risk of POVL or edema.
20
Q
What happens to lung mechanics during normal respiration?
A
Diaphragm and intercostal muscles expand the thoracic cavity, creating negative intrathoracic pressure to pull air into the lungs.
21
Q
How does general anesthesia affect respiratory mechanics?
A
It causes muscle relaxation, loss of diaphragmatic tone, positive pressure ventilation, and blunts compensatory reflexes, leading to decreased compliance and ventilation.
22
Q
What are the effects of the Supine position on lung volumes?
A
Diaphragm is pushed cephalad, leading to ↓ FRC and TLC, and increased risk of atelectasis.
23
Q
What are the benefits of the Prone position?
A
Improved oxygenation and V/Q matching, better expansion of dorsal lung segments, and uniform ventilation distribution.
24
Q
What are the risks associated with the Lateral Decubitus position?
A
In anesthetized patients, ventilation shifts to nondependent lung, leading to V/Q mismatch and increased risk for hypoxemia.
25
What happens in exaggerated lithotomy position?
It limits diaphragmatic excursion, reduces lung compliance, decreases tidal volumes, and increases airway pressures.
26
What are the advantages of the Sitting position?
Favorable for ventilation, improves diaphragmatic movement, and maintains near normal FRC and FVC.
27
What are the downsides of the Sitting position?
Elevated or flexed legs can cause abdominal compression, reducing FRC and posing hypotension risk in hypovolemic or cardiac patients.
28
Why is the Trendelenburg position considered detrimental for respiratory mechanics?
It severely restricts diaphragmatic movement, decreases FRC, increases closing volumes, and poses risks of airway edema and facial swelling.
29
What are the gravitational effects on ventilation-perfusion (V/Q) changes?
Gravity creates a perfusion gradient with more blood to dependent regions, while ventilation is generally better in nondependent regions.
30
How does anesthesia disrupt normal V/Q patterns?
Anesthesia disrupts normal V/Q patterns due to compliance changes, diaphragmatic inhibition, and paralysis or mechanical ventilation altering gas exchange.
31
What are the new imaging findings related to V/Q changes?
A concentric perfusion pattern may occur, where central lung areas receive more flow regardless of gravity, influenced by cardiac output, pulmonary artery pressures, pleural pressure, and vessel branching architecture.
32
What factors affect diaphragm movement?
Diaphragm movement can be affected by obesity, abdominal surgery, pneumoperitoneum, and positional compression, especially in Trendelenburg and prone positions.
33
How can positioning devices impact diaphragm excursion?
Positioning devices can impair diaphragm excursion if placed incorrectly, making proper support crucial to avoid hypoventilation or compartment pressures.
34
What is transection in the context of peripheral nerve injury?
Transection is the complete severance of the nerve fiber or fascicle, typically due to surgical scalpel or traumatic incision, resulting in loss of sensory and motor function distal to injury.
35
What are the consequences of nerve compression?
Compression occurs when a nerve is trapped between a rigid surface and external force, leading to mechanical deformation of the nerve sheath, ischemia, and impaired axonal transport.
36
What is the impact of stretch (traction) on nerves?
Excessive elongation of nerves causes axoplasmic flow disruption, microvascular injury, and potential axon rupture or demyelination, particularly at susceptible sites like the brachial plexus and sciatic nerve.
37
What is traction over fixed structures?
This subtype of stretch injury occurs when a nerve is tethered over a ligament or bone, increasing localized stress, such as femoral nerve traction when hips are flexed.
38
What role does ischemia play in nerve injury?
Ischemia is central to nerve injury pathophysiology, affecting intraneural blood flow and leading to cycles of ischemic injury.
39
What happens during the cycle of ischemic injury?
The cycle includes reduced capillary blood flow, decreased ATP production, failure of Na⁺/K⁺ ATPase, intracellular Na⁺ accumulation, cellular swelling, and further collapse of capillary perfusion.
40
How does low systemic MAP affect ischemia?
A drop in systemic MAP worsens ischemic perfusion by reducing the arterial-venous gradient.
41
What are the structural layers of peripheral nerves?
The structural layers from inside out are axon, neurolemma (Schwann cell), endoneurium, perineurium, inner epineurium, outer epineurium, and nerve trunk covering.
42
What is the significance of vascular supply in nerve injury susceptibility?
Epineurial vessels form collateral loops, while perineurial and endoneurial capillaries are more vulnerable to compression from edema, which can restrict capillary flow.
43
What are clinical risk factors for nerve injury?
Risk factors include inadequate padding, prolonged surgical time, extremes of positioning, hypotension during anesthesia, obesity or edema, and pre-existing neuropathy.
44
What strategies can prevent nerve injury?
Strategies include avoiding excessive joint angles, using soft padding over bony prominences, monitoring surgical time, maintaining MAP > 65 mmHg, and conducting pre- and post-op neuro exams.
45
What are the multifactorial etiologies of Peripheral Nerve Injuries (PPNI)?
PPNIs arise from a complex interplay of mechanical forces, patient factors, and procedural variables.
46
What are common contributing factors to PPNIs?
Improper use of positioning devices, prolonged surgery (>4–5 hrs), and certain anesthetic choices.
47
What are the physiologic risk enhancers for nerve ischemia?
Systemic hypotension, hypoxia, hypothermia, and electrolyte disturbances can worsen nerve ischemia.
48
What can improper positioning devices cause?
Overtight straps or improperly placed padding can cause skin breakdown or compress nerves.
## Footnote
Example: Lateral femoral cutaneous nerve compressed by tight tape across the groin → meralgia paresthetica.
49
What are the risks associated with arm positioning?
Shoulder braces in Trendelenburg or prone can compress the brachial plexus, and arm abduction > 90° can stretch the brachial plexus.
50
What is the most frequent nerve injury post-op?
Ulnar Neuropathy is the most frequent nerve injury post-op.
51
What are the mechanisms leading to Ulnar Neuropathy?
Elbow flexion >90°, direct pressure on the medial elbow, prolonged immobility, and improper pronation on armboards.
52
What are the risk factors for Ulnar Neuropathy?
Male gender, thin body habitus, prolonged bedrest, and subclinical neuropathy.
53
What is the most commonly injured upper extremity nerve group?
Brachial Plexus Injury is the most commonly injured upper extremity nerve group.
54
What are the risk factors for Brachial Plexus Injury?
Arm abduction >90°, head rotation away from the abducted arm, shoulder braces in Trendelenburg or prone, and improperly placed sternal retractors.
55
What is the consequence of misplacing the axillary roll?
Placing the roll too high in lateral decubitus can compress the brachial plexus or axillary vessels.
56
What are the mechanisms of spinal cord injury?
Most often related to neuraxial blockade in anticoagulated patients and hyperflexion of the neck.
57
What is the pathophysiology of spinal cord ischemia?
Cord moves anteriorly when neck is flexed, leading to compression against the vertebral body and reduced spinal cord perfusion.
58
What are the prevention strategies for spinal cord injury?
Maintain ≥2 fingerbreadths between sternum and mandible, avoid excessive Trendelenburg, and monitor MAP.
59
What is postoperative visual loss (POVL)?
A rare, non-ophthalmic complication of spine, cardiac, and head/neck surgeries, presenting as unilateral or bilateral vision loss.
60
What are the five major causes of POVL?
Ischemic Optic Neuropathy (ION), Central Retinal Artery Occlusion (CRAO), Central Retinal Vein Occlusion, cortical blindness, and glycine toxicity.
61
What are the types of Ischemic Optic Neuropathy (ION)?
AION (anterior) and PION (posterior) are the types of ION.
62
What risk factors are associated with Ischemic Optic Neuropathy?
Male sex, obesity, longer surgery duration (>6 hrs), blood loss & anemia, prone positioning, and intraoperative hypotension.
63
What typically causes Central Retinal Artery Occlusion (CRAO)?
Direct external eye pressure, often from headrests, typically causes CRAO.
64
What are the risk factors for Central Retinal Vein Occlusion?
Trendelenburg position, elevated intraabdominal pressure, and improper head positioning increase the risk.
65
What are key preventive measures for POVL?
Avoid deliberate hypotension, maintain safe hematocrit, and avoid direct pressure on eyes.
66
What is the preferred headrest for preventing POVL?
Foam headrests with cutouts are preferred to avoid direct pressure on the eyes.
67
What should be monitored during prone positioning?
Monitor face, eyes, and neck frequently to ensure no compression of the globe or orbit.
68
What are position-related injuries in surgery?
Injuries resulting from improper or prolonged surgical positioning, ranging from minor to catastrophic.
69
What are minor complications of position-related injuries?
Skin abrasions and muscle soreness, which may cause discomfort or delayed discharge.
70
What are major complications of position-related injuries?
Nerve injury, compartment syndrome, tissue necrosis, renal failure, leading to prolonged hospitalization, permanent disability, emotional trauma, and legal implications.
71
What is compartment syndrome?
A surgical emergency where increased pressure in a closed fascial compartment leads to decreased tissue perfusion.
72
What are the consequences of untreated compartment syndrome?
Nerve ischemia, muscle infarction, rhabdomyolysis, crush syndrome, limb loss, or death.
73
What initiates the pathophysiology of compartment syndrome?
Initial ischemia due to hypotension, leg elevation, or local compression.
74
What are the hemodynamic considerations in compartment syndrome?
Arterial pressure decreases by ~0.75 mmHg per cm above the right atrium, leading to potential drops in local perfusion pressure.
75
What are high-risk positions for compartment syndrome?
Lithotomy position (beyond 2–3 hours), Trendelenburg position, combined lithotomy and Trendelenburg, tightly wrapped limbs, and improper shoulder supports.
76
What are surgical/positional risk factors for compartment syndrome?
Long surgical duration, prolonged limb elevation, use of leg holders or tight straps, steep Trendelenburg, or abdominal packing.
77
What are physiologic/patient-related risk factors for compartment syndrome?
Obesity, advanced age, vascular insufficiency, diabetes, hypotension, anemia, hypothermia, and use of vasoconstrictors.
78
What are anesthetic-related risk factors for compartment syndrome?
General anesthesia masking pain, regional anesthesia obscuring feedback, and paralytics preventing muscular tension response.
79
What are early signs of compartment syndrome?
Deep, intense pain, exacerbated by passive stretching of the involved muscle group.
80
What are late signs of compartment syndrome indicating irreversible damage?
Pulselessness, paralysis, dark urine, and renal failure.
81
How is compartment syndrome diagnosed?
High clinical suspicion; compartment pressure measurement if uncertain.
82
What is the definitive treatment for compartment syndrome?
Emergent fasciotomy and supportive management including IV fluids.
83
What are prevention strategies for anesthesia providers?
Monitor surgical duration, periodically return legs to horizontal, maintain adequate MAP, avoid prolonged hypotension, and ensure appropriate padding.
84
What are the implications for CRNA/SRNA regarding compartment syndrome?
Perform preoperative risk assessment, ensure precise positioning, maintain vigilance, and facilitate rapid diagnosis.
85
What is venous air embolism (VAE)?
Occurs when air enters the venous system, often due to a negative pressure gradient.
86
What increases the incidence of VAE?
Surgeries performed in the sitting position and procedures where the surgical site is above the heart.
87
What are the physiologic effects of VAE?
Small amounts have no effect; moderate amounts can cause hypotension and arrhythmias; large volumes can lead to pulmonary hypertension and cardiac arrest.
88
What is paradoxical air embolism (PAE)?
Occurs when venous air crosses into arterial circulation via a right-to-left shunt.
89
What is the gold standard for diagnosing VAE?
Transesophageal echocardiography (TEE), which is the most sensitive method.
90
What is an alternative method for monitoring VAE?
Precordial Doppler, which is noninvasive and sensitive for detecting VAE.
91
What are the signs and clinical presentations of VAE?
Decreased ETCO₂, sudden hypotension, hypoxia, arrhythmias, and neurologic symptoms if arterial emboli reach the brain.
92
What is the management for air embolism?
Aspiration of air embolus, positioning to trap air, and supportive management with 100% oxygen.
93
What are prevention strategies for VAE?
Identify at-risk patients, use appropriate monitoring, maintain venous pressure, and minimize elevation of the surgical field.
94
What increases the risk for airway compromise in anesthetized patients?
Loss of muscle tone, positional changes, and invasive airway devices.
95
What are common causes of ET tube displacement during surgery?
Occurs most commonly during repositioning or after draping.
96
What can happen to an ET tube during positional changes?
It may become dislodged, kinked, or disconnected from the ventilator circuit.
97
What positions commonly lead to right mainstem bronchus intubation?
Neck flexion and steep Trendelenburg position.
98
What is the mechanism of right mainstem bronchus intubation?
Flexion causes the ET tube to advance downward, possibly entering the right main bronchus, leading to unilateral ventilation and possible hypoxia.
99
What positions increase the risk of facial and airway edema?
Prone, Trendelenburg (head-down), and sitting with neck hyperflexed.
100
What factors contribute to airway edema?
Gravitational forces and hydrostatic pressure impair venous return from the face, tongue, and oropharynx.
101
What devices can contribute to mechanical compression and edema?
Oral airways, endotracheal tubes, and esophageal stethoscopes.
102
What is macroglossia?
Tongue swelling due to venous congestion, lymphatic obstruction, or mechanical compression.
103
What are the signs of supraglottic edema?
Swelling of the arytenoids, epiglottis, and pharyngeal tissues.
104
What should be done intraoperatively to manage airway?
Secure the ET tube well before position changes and monitor breath sounds and capnography after repositioning.
105
What should be considered during postoperative extubation if macroglossia or airway edema is suspected?
Delay extubation until swelling resolves and consider direct laryngoscopy to inspect the airway.
106
What are some preventive tips for airway complications?
Avoid excessive neck flexion, use proper padding, minimize intraoral instrumentation time, and suction airway secretions.
107
What is the most commonly used surgical position?
Supine position (dorsal decubitus).
108
What are the positioning guidelines for the supine position?
Head in neutral position, arms tucked at sides or on padded armboards, knees slightly flexed, and heels elevated.
109
What complications can arise from the supine position?
Ulnar nerve injury, brachial plexus injury, back pain, alopecia, and pressure sores.
110
What is the indication for the Trendelenburg position?
Temporarily used to improve venous return during hypotension.
111
What are the physiologic effects of the Trendelenburg position?
Increased intracranial, intraocular, and central venous pressures, and risk of ETT migration into the right mainstem bronchus.
112
What complications can occur in the Trendelenburg position?
Brachial plexus injury, sliding on the OR table, airway edema, and increased risk of POVL.
113
What is the indication for the reverse Trendelenburg position?
Laparoscopic upper abdominal surgeries and head/neck surgeries.
114
What complications can arise from the reverse Trendelenburg position?
Risk of cerebral hypoperfusion and pressure ulcers from over-tightened table straps.
115
What is the indication for the lithotomy position?
Procedures involving the perineum, rectum, bladder, and gynecologic organs.
116
What complications can occur in the lithotomy position?
Peroneal nerve injury, saphenous nerve injury, and hip dislocation.
117
What is the indication for the lateral decubitus position?
Thoracic, renal, and orthopedic surgeries.
118
What complications can arise from the lateral decubitus position?
Brachial plexus injury, eye/ear pressure injuries, and rhabdomyolysis.
119
What is the indication for the sitting position?
Posterior fossa, cervical spine, and shoulder surgeries.
120
What complications are associated with the sitting position?
Venous air embolism, paradoxical air embolism, and cervical spine injury.
121
What is the indication for the prone position?
Spine surgery, posterior cranial procedures, and rectal surgeries.
122
What complications can occur in the prone position?
POVL, corneal abrasions, and airway complications.
123
What are key clinical considerations for CRNAs/SRNAs?
Secure airway after repositioning, document positioning, and assess for nerve compression.
124
What is the purpose of closed-claims studies?
Closed-claims studies provide retrospective analysis of malpractice claims that have been filed and resolved. They help identify trends in anesthesia-related injuries, common types of harm, contributing factors, and gaps in documentation and standards of care.
125
Who collects data for closed-claims studies?
Data are collected by professional liability insurers—not specifically for patient safety research.
126
What is the ASA Closed Claims Project (ASA-CCP)?
Established in 1985 to evaluate anesthesiologist-related malpractice claims, the ASA-CCP excludes dental injuries.
127
What is the AANA Foundation (AANA-F) Closed Claims Study?
Modeled after ASA-CCP, it focuses on claims involving Certified Registered Nurse Anesthetists (CRNAs) and offers insight into CRNA-specific practices and complications.
128
What are the top outcomes of closed claims according to the ASA-CCP study?
Top outcomes include death (26%), nerve injury (22%), and permanent brain damage (9%).
129
What types of nerve injuries are most common in closed claims?
Common nerve injuries include ulnar nerve (28%), brachial plexus (20%), lumbosacral nerve root (16%), spinal cord (13%), and all others (8%).
130
What trends were observed regarding ulnar and spinal cord injuries?
Ulnar nerve claims have decreased over time, while spinal cord injury claims have increased.
131
What percentage of ulnar nerve injuries occurred under general anesthesia?
85% of ulnar nerve injuries occurred under general anesthesia, not regional.
132
What was the appropriateness of care for nerve and spinal cord injury claims?
66% of nerve injury claims were judged as appropriate care, while only 46% of spinal cord injury claims had care deemed appropriate.
133
What were the findings from the AANA-F study regarding CRNA-related claims?
Total CRNA-related claims analyzed: 223. CRNA contributed to adverse event in 151 claims (68%); did not contribute in 72 claims (32%).
134
What are the primary injuries in CRNA-related claims?
Primary injuries include death (32%), nerve injury (12%), brain injury (12%), and eye injury (10%).
135
What is the quality of care judgment in CRNA-related cases?
Inappropriate in 52% of CRNA-related cases, appropriate in 30%, and unable to assess in 18%.
136
What are the limitations of closed-claims data?
Limitations include non-random sampling, data bias, not for risk calculation, variable documentation quality, and reviewer bias.
137
Why is documentation critical in closed-claims studies?
Complete, accurate, and timely charting helps in claims review and defense. Documentation should reflect positioning strategy, equipment used, and any intraoperative changes.
138
What are the legal and clinical implications of closed-claims studies?
Standards of care must be upheld to protect patients and providers. Preventive practices and intraoperative assessments must be consistent and well-documented.
139
How does severity influence litigation outcomes?
Larger payouts are associated with severe outcomes and judged substandard care. However, even with appropriate care, settlements are still frequently made, suggesting preventability is not the sole factor.
