One Lung Ventilation

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One Lung VentilationMalignant Hyperthermia

• Scott Stevens D.O.
• Gannon University
• College of Health Sciences
• Graduate Program Department of Nursing

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One lung ventilation

• Common for thoracic surgery, VATS (video assisted
  thoracic surgery), trauma to chest, any approach
  passing through the chest (mediastinum,
  esophagus), or need to isolate a single lung
  (bleeding, infection, bronchopleural fistula)
• Most often accompanied by a pneumothorax
• Can use a double lumen ETT, bronchial blocker
  inside a normal ETT, Univent ETT, intentional
  endobronchial intubation, or a normal ETT with
  positive pressure added to one side of thorax or
  a retractor to collapse the lung

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Positioning for thoracic surgery

• Most often in lateral decubitus position
• Dependent lung lower lung
• Nondependent lung upper lung
• Iatrogenic pneumothorax of the upper lung,
  provides access to surgical field
• Often a rigid bean bag is used to hold position
• Axillary roll placed on upper chest wall, NOT in
  the axilla
• Arms on padded arm holders or pillows between
  arms
• Restrict IVFs to basic maintenance due to risk
  of gravity dependent transudation of fluid to
  lower lung and edema of collapsed lung

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V/Q mismatch while lateral

• In the awake lateral position the dependent
  lung is better perfused (gravity) ventilated
• With induction of anesthesia, with a decrease in
  FRC, the upper lung ventilates more, V/Q mismatch
• Positive pressure ventilation favors the upper
  lung because it is more compliant
• Muscle paralysis favors ventilation of the upper
  lung due to abdominal contents pushing up more on
  the dependent hemidiaphragm
• Rigid bean bag hinders movement of dependent
  hemidiaphragm and favors ventilation of upper
  lung
• Open PTX of upper lung increases compliance
  favoring ventilation of upper lung

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Open pneumothorax

• The normal negative pleural pressure is lost
  causing the lung to recoil and collapse
• This collapse is overcome by the use of positive
  pressure ventilation
• Intentional collapse of the nondependent lung
  facilitates the thoracic procedure
• Upper lung is not ventilated but is still
  perfusing (although less than dependent lung),
  this causes a large right to left intrapulmonary
  shunt (20-30)
• Increased PA-a(Alveolar to arterial) O2 gradient
  can lead to hypoxemia

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Hypoxic pulmonary vasocontriction (HPV)

• Blood flow to the nonventilated nondependent
  upper lung is decreased by HPV, this improves the
  right to left shunt
• Surgical compression of the upper lung can also
  decrease blood flow which improves the shunt
• Several factors can inhibit HPV thus worsening
  the right to left shunt

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Factors that inhibit hypoxic pulmonary
vasoconstriction

• Very high or very low pulmonary artery pressures
• Hypocapnia
• High or very low mixed venous PO2
• Vasodilators nitroglycerin (NTG), nitroprusside
  (SNP), b-adrenegic agonists (dobutamine), calcium
  channel blockers
• Pulmonary infections
• Inhalation agents

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Factors that decrease blood flow to dependent lung

• Worsens R to L shunt by sending more blood to the
  nondependent or collapsed lung
• High mean airway pressures in ventilated lung
  from PEEP, hyperventilation, or increased PIP
• Low FIO2 causes HPV in ventilated lung
• Vasoconstrictors which may have a greater effect
  on normoxic vessels compared to hypoxic ones
• Intrinsic PEEP which develops from inadequate
  expiratory times

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CO2 and one lung ventilation

• CO2 elimination is usually not affected by one
  lung ventilation provided 1) minute ventilation
  is unchanged and 2) Preexisting CO2 retention was
  not present pre-op (COPD)
• Tidal volumes are kept roughly the same as two
  lung ventilation, around 10cc/Kg, may adjust due
  to changes in PIP, RR altered to maintain
  normocapnia
• FIO2 usually kept high as a safety margin against
  hypoxia

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Apneic oxygenation

• Ventilation can be stopped for short periods as
  long as O2 is supplied more than consumption
  (250-300cc/min.)
• During apnea PCO2 increases 5mmHg for the first
  minute and then 3mmHg for each additional minute
  of apnea
• Example if PCO2 was 40, then after 10 minutes of
  apnea, the PCO2 will be 72
• Progressive respiratory acidosis limits this
  technique to 10-20 minutes

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Hypoxia during one lung ventilation

• FIO2 of 0.8 to 1.0
• Check tidal volumes want 10cc/Kg, suction ETT
• Fiberoptic scope to ensure proper ETT placement
• Adjust RR to keep PaCO2 at 40mmHg
• Add 5cm H2O CPAP to nondependent lung warn
  surgeon
• Add 5cm H2O PEEP to dependent lung txs
  atelectasis but may increase vascular resistance
• Increase both CPAP and PEEP slowly
• Ask surgeon to clamp or ligate nondependent PA
• Return to two lung ventilation always an option

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Operability for pneumonectomy

• Clinical decision if pt can survive resection of
  one lung
• PFTs used to make decision
• Failed criteria necessitate split lung PFTs
• Most common criterion for operability is a
  predicted post-op FEV1 of gt800ccs
• Also pre-op FEV1 gt2L

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Double lumen tubes

• Come in left and right types, and sizes 35, 37,
  39, 41 French 39 Fr for most women and 41 Fr
  for most men
• Has a longer bronchial lumen with a blue cuff
• Has a shorter tracheal lumen with a larger clear
  cuff
• Curve at tip to allow endobronchial placement
• Allow for ventilating and suctioning of each lung
  independently
• Complications traumatic laryngitis, hypoxemia
  due to malpositioned tube, bronchial trauma from
  over inflation of cuff, inadvertent suturing of
  tube

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Double lumen tubes

• Left double lumen tube most commonly used by
  far, is easier to place due to anatomic
  differences in the bronchi
• Bronchial lumen placed down left mainstem
  bronchus and a symmetric cuff inflated with
  1-2ccs of air while the tracheal lumen (with
  cuff up) is above the carina and ventilates the
  right lung
• More room to place due length of left mainstem
• Can be used for all thoracic cases except surgery
  on left mainstem bronchus

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Double lumen tubes

• Right double lumen tube rarely used due to
  difficult placement
• Indicated for left mainstem bronchus surgery
• Bronchial lumen placed to the right and must
  align up with opening to the right upper lobe
  bronchus and an asymmetrical cuff with slotted
  opening laterally is inflated

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Placement of double lumen tube (L)

• First assemble connectors that come in box
• Lubricate tube due to its size
• Mac blade gives better visualization
• Small syringe (3cc) on bronchial cuff and larger
  syringe (10cc) on tracheal cuff
• DL, gently place curved tip with blue cuff
  anteriorly through the cords being careful not to
  cut cuffs on the teeth, once past cords pull out
  large stylet and rotate tube 90 degrees
  counterclockwise as you slowly advance, never
  forcing, until resistance is felt, average depth
  is 29 cm at teeth, you may feel clicking as the
  tip rubs against the tracheal cartilaginous
  rings, first inflate tracheal cuff and look for
  EtCO2, then bronchial cuff gently, listen for
  breath sounds as each side is occluded then
  reconfirm with fiberoptic scope, recheck after
  positioning patient

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Malignant Hyperthermia

• MH is a rare inherited myopathy triggered by
  inhaled agents (not N2O) and/or succinylcholine,
  leading to an acute hypermetabolic state with a
  variable presentation. The ryanodine receptor
  (Ca release channel) fails in the sarcoplasmic
  reticulum leading to decreased Ca reuptake from
  within the cell (myocyte) causing a 500-fold
  increase in intracellular Ca, leading to
  sustained muscle contraction, glycolysis, and
  heat production. Abnormal excitation-contraction
  coupling results in prolonged and irreversible
  muscle contracture.

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MH triggers

• An anesthetic related disease
• Succinylcholine (Anectine)
• Inhalational agents halothane, isoflurane,
  sevoflurane, desflurane, enflurane
• Other possible triggers stress, muscle trauma,
  exercise, heat stroke

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Clinical syndrome and intraoperative diagnosis

• First sign most sensitive unexplained
  tachycardia
• Most specific sign increasing EtCO2
  hypercapnia, 2-3X
• Also decrease in SaO2 SpO2, rigidity despite
  muscle relaxant onboard, dysrhythmias, tachypnea,
  cyanosis, sweating, unstable BP, mottling of
  skin, trismus (masseter spasm) after
  succinylcholine, darkening of blood in surgical
  field, decreased mixed venous saturation,
  cola-colored urine, heating and exhaustion of CO2
  absorber, hyperthermia (up to 2 degrees C per
  hour)
• Labs initial metabolic acidosis then a combined
  metabolic respiratory acidosis, hyperkalemia,
  hypercalcemia, hyperphosphatemia, creatinine
  kinase (CK) gt 1000 IU, myoglobinuria, hypoxemia

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Incidence of MH

• Children 1 in 12000 general anesthetics
• Adults 1 in 40000 general anesthetics with
  succinylcholine and 1 in 220000 without
  succinylcholine
• Genetic link familial autosomal dominant
  transmission with variable penetrance, on
  chromosome 19
• All closely-related members of a family in which
  MH has occurred must also be considered MH
  susceptible and managed accordingly, unless
  proven otherwise

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Mortality of MH

• 10 overall
• Up to 70 without dantrolene therapy
• Early dantrolene therapy reduces to lt5

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Treatment of MH

• Stop all triggering agents, CALL FOR HELP,
  expedite or abort procedure
• Hyperventilate with 100 O2 at high flows
• Dantrolene 2.5 mg/Kg IV as soon as possible then
  Q5min. until symptoms controlled or up to 10
  mg/Kg total, dantrolene must be mixed in sterile
  water, this is the mainstay of therapy
• Bicarbonate 1-2 meq/Kg IV then check ABG
• Cooling measures iced IV NS (not LR) 15cc/Kg
  every 10 min. X 3 if necessary, cold body cavity
  lavage, cooling blanket, ice bags

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Treatment of MH

• Treat hyperkalemia with bicarbonate or dextrose
  25-50g regular insulin 10-20 units IV
• Treat persistent ventricular arrhythmias with
  procainamide 200 mg IV
• Change to a clean circuit and new soda lime
• Promote urine output, want to maintain gt2cc/Kg/hr
  with IVFs, Lasix 0.5-1 mg/Kg IV, Mannitol 1 g/Kg
  IV
• A-line, foley, possible central line, ICU bed

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Treatment of MH

• Labs (6, 12, 24 hrs after episode) ABG, K, Ca,
  BUN/Cr, lactate, urine myoglobin, urine output,
  CPK, PT, INR, PTT, platelets, EtCO2, mixed venous
  saturation, core body temp.
• ICU for 24-48 hrs
• Continue dantrolene 1 mg/Kg IV Q6hrs for 72 hrs
  to prevent a recurrence
• Calcium channel blockers should not be given
  while on dantrolene due to life-threatening
  hyperkalemia and myocardial depression that may
  occur

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Dantrolene

• Dantrolene is a muscle relaxant that works
  directly on the ryanodine receptor to prevent the
  release of calcium
• A hydantoin derivative, directly interferes with
  muscle contraction by inhibiting Ca release from
  the sarcoplasmic reticulum
• Intracellular dissociation of excitation-contracti
  on coupling
• Packaged as 20 mg of lyophilized powder which is
  dissolved in 60 ccs of sterile water, it is time
  consuming to mix

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Dantrolene

• Safe drug, some generalized muscle weakness which
  may lead to respiratory insufficiency or
  aspiration pneumonia, GI upset, thrombophlebitis
• Dantrolene may cause significant muscle weakness
  in patients with pre-existing muscle disease and
  should be used with extreme caution in those
  patients.
• Dantrolene does not significantly potentiate the
  effects of non- depolarizing relaxants or prevent
  the ability to reverse non-depolarizong muscle
  relaxants with anticholinesterase agents.

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Late complications of MH

• Renal failure
• Coagulopathies
• Pulmonary edema
• Cerebral edema
• Hepatic failure
• Left heart failure
• DIC
• Skeletal muscle swelling
• Rhabdomyolysis
• Death

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Safe drugs in MH

• Benzodiazepines
• Barbiturates
• Etomidate
• Narcotics
• Local anesthetics
• Propofol
• Nondepolarizing muscle relaxants
• N2O
• Ketamine
• Use ketamine pancuronium with caution because
  the tachycardia may mask early MH

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Pts hx that may indicate MH

• Strabismus, myalgias on exercise, cramping
• Tendency to fever, history of heat stroke
• Myoglobinuria
• Muscular disease, muscular dystrophy
• Intolerance to caffeine
• Elevated CPK
• History of a family member with an adverse event
  associated with anesthesia, especially death.
• Gold standard preop test muscle biopsy with
  halothane-caffeine contracture test 78
  specific, and 97 sensitive caffeine causes
  muscle to contract and halothane in the MH pt
  causes more forceful contraction, only done at 6
  institutions

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Diseases associated with MH

• Several musculoskeletal diseases have a high
  incidence of MH
• Central-core disease, Multi mini core disease
• Duchennes muscular dystrophy
• King-Denborough syndrome
• Osteogenesis imperfecta
• Myotonia
• Fukuyamas muscular dystrophy
• Beckers muscular dystrophy

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King Denborough Syndrome

• A proportion of people with malignant
  hyperthermia may have particular characteristics.
  A 1972 report on a family with MH also described
  myopathy, short stature, cryptorchidism
  (undescended testicles), pectus carinatum (a
  chest wall deformity), lumbar lordosis and
  thoracic kyphosis (deformity of the spine), and
  unusual facial characteristics. Later reports
  have termed this combinations the King-Denborough
  syndrome, after the authors of the report.

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Points on MH

• Prior uneventful general anesthetic does not rule
  out the possibility of MH
• Trismus alone after succinylcholine is much more
  common (1) than the incidence of MH
• MH is an anesthetic emergency call for help
• Our anesthesia triggered the MH, we may be the
  only one to recognize it early and know how to
  treat it early and aggressively
• More common in children than adults
• Boys lt 9 yrs old who experience sudden cardiac
  arrest after succinylcholine in the absence of
  hypoxia should be treated for acute hyperkalemia
  first CaCl2 IV, Bicarbonate IV, they most
  likely have a subclinical muscular dystrophy

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Points on MH

• The symptoms usually develop within one hour
  after exposure to trigger substances, but may
  even occur several hours later in rare instances.
  
• MH does not occur with every exposure to
  triggering agents, and susceptible patients may
  undergo multiple uneventful episodes of
  anesthesia before developing an episode of MH
• Pretreatment with dantrolene has been advocated
  in the past to prevent MH, but this is probably
  unreliable, and the long half-life of the drug
  may leave patients weak for extended periods.

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Points on MH

• Treatment must be instituted rapidly on clinical
  suspicion of the onset of malignant hyperthermia.
  
• It is vital that all hospitals, ambulatory
  centers offices where general anesthesia is
  administered have a full supply of dantrolene
  immediately available (36 vials)
• Postoperative fever (pyrexia) alone is unlikely
  to signify MH.
• The only sure way to prevent MH is avoid the use
  of triggering agents in patients known or
  suspected of being susceptible to MH

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