Radiological Risks & Refeeding syndrome

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Radiological Risks Refeeding syndrome

• Kathy Lee
• March 17, 2006

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Is the imaging worth the risks?
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Outline

• XR
• CT
• Pediatric patients

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Introduction

• Xrays discovered by Roentgen in 1895
• Widespread use (including shoe fitting)
• Until reports of side effects
• Radiation dose expressed as millisievert (mSv)
• Background radiation 3mSv/yr
• Coast-to-coast round trip flight in a commercial
  airplane 0.03 mSv

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Commonly ordered XR
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• Radiation doses have been decreasing
• better equipment
• better training in its use
• Shielding further helps to lower exposure
• Distance cheap and effective
• I / D2 I / d2
• 3m for portable XR
• trauma room is 3m

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Pregnant patients

• Dr Martels presentation
• Consider US/MRI
• Shield uterus when possible
• Scan if necessary

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CT

• Dose burden concern to radiologists and to
  regulatory authorities
• high dose procedure
• Small individual risk of carcinogenesis from CT
• Atomic bomb survivors
• 600 increase in all Ct exams mid-80s to mid-90s
• UK National Radiological Protection Board (NRPB)
• increased lifetime risk of death from a
  malignancy induced by CT abdomen on the order
  of 1 in 2000
• Image quality improves with increasing dose
• Plain film will be overexposed if radiation dose
  increased

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Plain film and CT doses
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• Spiral CTs higher dose than regular CT
• Data set of higher and lower slice needed to
  recontruct highest/lowest slice
• Larger volume of body is scanned than that
  selected
• Image acquisition speed increased
• Larger body volumes in little time
• Responsibility of ordering MD, radiologist,
  manufacturer to lower radiation exposure to
  patients
• Necessary study
• Target suitable organs
• Modify parameters for patient size
• Avoid multiphase scans
• Preset low dose protocols for children

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Pediatric patients

• In USA, 2000, 11 of CT performed in children
  (2.7 million)
• 1 fatal cancer per 1000 pediatric CT exams
• Evidence that CT techniques not often suitably
  modified
• Smaller body volume
• Smaller organs
• Increase sensitivity to radiation 10x
• Girls more than boys
• Longer lifetime for radiation effects to manifest
• Increased radiosensitivity of certain tissues
• Thyroid gland, breast, gonads

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Is the anxiety justified?

• Small amount of radiation may actually be
  beneficial
• Established in animal/plant models, but not in
  man
• Epidemiological studies lower level of cancer
  after low-level exposure
• Below threshold of some 200 - 500mSv (66.7
  166.7 yrs of background radiation), evidence of
  beneficial effects
• Hormetic effect
• Decreased chormosomal aberration
• Immune response increased
• Some truth of therapeutic CT

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ALARA conference 2001

• As Low As Reasonably Achieavable radiation dose
  strategies to reduce CT radiation dose in
  children
• Judicious use of CT
• Consider alternate modalities such as US or MRI
• Adjust CT technique
• Minimize use of multiple scans
• Limit coverage to answer clinical questions
• avoid routine scanning of pelvis as part of
  abdomen to reduce exposure to gonads

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• Consider breast shielding
• Adjust individual settings based on indication
• detection of large vs small abnormality
• follow-up examination
• Adjust individual settings based on body region
  scanned
• lower tube current for chest and skeletal CT
• less radiation needed than abdo/head
• Adjust individual settings based on the size
• Use new scanner technology that makes automatic
  regional adjustments in radiation dose during
  scanning

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References

• http//www.radiologyinfo.org. Accessed March 12,
  2006
• Archer BR. 2005. Recent history of the shielding
  of medical X-ray imaging facilities. Health Phys.
  88(6)579-596
• Dawson P. 2004. Patient dose in multislice CT
  why is it increasing and does it matter? Brit J
  Rad 77S10-13.
• Frush DP, Donnelly LF, Rosen NS. 2003. Computed
  tomography and radiation risks What pediatric
  health care providers should know. Ped
  112951-957.
• Slovis TL. 2002. CT and computed radiography The
  pictures are great, but is the radiation dose
  greater than required? AJR 17939-41.

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Refeeding Syndrome
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Outline

• Pathogenesis
• Clinical manifestation
• Prevention and management

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Introduction

• Potentially lethal condition
• Severe lyte and fluid shifts
• Associated with metabolic abN in malnourished
  patients undergoing refeeding orally, enterally
  or parenterally

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• Patients at risk incl
• gt10 weight loss over mos - hunger strikers
• not fed for 7-10d - chronic EtOH
• prolonged IVF repletion - anorexia nervosa
• malnourished elderly Pt - post-op Pt
• oncology Pt undergoing chemoTx
• More common in those fed enterally, elderly

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Pathogenesis

• During starvation
• Overall catabolism of adipose tissue and muscle,
  loss of lean body mass
• Insulin decr, glucagon incr
• Glc synthesis via lipidand protein breakdown
  products
• Adipose tissue release FA, glycerol
• Muscle release aa
• KB and FFA replace glc as major energy source

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• During refeeding
• Shift from fat to CHO metabolism
• Incr protein synthesis
• glc load incr insulin release
• Incr cellular uptake of glc, PO4, K, Mg, water

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Clinical manifestation

• Disturbance of body-fluid distribution
• CHO / high protein decr water/Na excretion
• Protein incr Na excretion
• Resulting hyper/hypo-natremia, dehydration/fluid
  overload
• AbN glc and lipid metabolism
• Hyperglycemia can lead to ketoacidosis/metabolic
  acidosis ? hyperosmolar nonketotic coma
• Glc converted to fat ? hypertriglyceridemia,
  fatty liver, abN LFT, higher respiratory quotient
  ? incr CO2 production / incr PaCO2
• Level of hyperTG further decr in critically ill
  Pt

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• Thiamine deficiency
• Cofactor for enzymatic activity
• CHO refeeding incr cellular thiamine utlization
• Wernickes encephalopathy (ocular disturbance,
  confusion, ataxia, coma)
• Korsakovs syndrome (short-term memory loss,
  confabulation)

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• Hypophosphatemia
• Predominant feature, major intracell anion
• 80 in bony skeleton, 20 in soft tissues
• Rich source in protein-rich food, cereals, nuts
• Absorb 70, Excrete renal (90)
• Kidney recycle, homeostasis
• Buffer, part of PL, nucleic acid, enzymatic
  phosphorylation, ATP, chemotaxis
• Clinical manifestations
• Neurologic (fits, weakness, parethesia, acute
  encephalopathy)
• Muscular (weakness, myalgia, rhabdomyolysis,
  decreased cardiac contractility, cardiomyopathy)
• Hematologic (dysfunction of platelets and
  leukocytes, thrombocytopenia, hemolysis)
• Respiratory (impaired respiratory muscle function
  sometimes resulting in respiratory failure or
  ventilator dependency)
• Bone (osteomalacia)
• Renal (acute tubular necrosis)

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• Hypokalemia
• Intracell, maintaines cell-membrane action
  potential
• Homeostasis regulated by kidney
• Clinical manifestations
• Neurologic (paralysis, paresthesia)
• Musculoskeletal (rhabdomyolysis, respiratory
  depression, weakness)
• Cardiac (arrhythmias, hypotension, digoxin
  toxicity, cardiac arrest)
• GI (constipation, paralytic ileus)
• Renal (Decreased urinary concentrating ability)
• Metabolic (metabolic alkalosis, glc intolerance)

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• Hypomagesemia
• Intracell, found in bone and muscle
• Largely absorbed in upper sm intestine
• Absorb 30, Excrete kidneys
• Clinical manifestations
• lyte (hypo -K, hypo- Ca)
• Neurologic (tetany, paresthesiae, seizures,
  ataxia, tremor, weakness)
• Cardiac (arrhythmias, e.g., torsade de pointes,
  hypertension)
• Gastrointestinal (anorexia, abdominal pain)

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Prevention and Management

• Monitor lytes (Na, K, PO4, Mg
• Correct electrolyte disorders before refeeding
• Restore circulatory volume
• Correct vitamins (thiamine) / trace elements
• Cal repletion slowly at 20kcal/kg, 1.5g/kg protein

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• Repletion of PO4 not necessary unless lt0.30mmol/L
  or Sx
• PO PO4 ? diarrhea
• IV Na or K PO4 15-30mmol
• Stop refeeding
• Monitor urine output
• Repletion of Mg not necessary unless lt0.5mmol/l
  or Sx
• PO Mg ? GI upset, poorly absorbed
• IV MgSO4 4g
• Can treat refractory hypo-K

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References

• Crook MA, Hally V, Panteli JV. 2001. The
  importance of the refeeding syndrome. Nutrition
  17632-637.
• Marinella MA. 2005. Refeeding syndrom eand
  hypophosphatemia. J Intensive Care Med 20155-159.