Oxygenation, Ventilation, and Ventilator Management in the First 24 Hours

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Oxygenation, Ventilation, and Ventilator
Management in the First 24 Hours

• Robert L. Huck, M.D.

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• Financial disclosures Up to my ___ in
  alligators, Im just trying to help drain the
  swamp (i.e., none)
• A nuts and bolts talk (more nuts than
  bolts?, Ill leave you to decide)
• You getting my biases, and those of your local
  pulmonary support group (but no we are not a 12
  step program)
• Hopefully, knowing our thinking will smooth
  transitions

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Common In Hospital Etiologies for Respiratory
Failure

• Excess narcotics or sedatives
• In hospital aspirations
• Cardiopulmonary arrest

• COPD
• CHF
• Pneumonia
• Drug overdose
• Asthma
• Pancreatitis
• Stroke
• Sepsis

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Measures of Oxygenation

• Arterial oxygen saturation (SaO2)
• Arterial oxygen tension (paO2)
• Alveolar to arterial oxygen difference (A-a
  gradient) PAO2(FIO2xPatm-PH2O)-(PaCO2/R)
• PAO2/FIO2
• A/a oxygen ratio
• Oxygenation index (MAPxFIO2/PaO2x100)

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Mechanisms of Hypoxemia

• Hypoventilation
• Ventilation/perfusion mismatch
• Right to left shunt
• Diffusion limitation
• Decrease inspired oxygen tension

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Monitoring of Oxygenation

• Clinical subjective dyspnea, cyanosis, mental
  status changes (usually restless- ness,
  agitation, or confusion, particularly in the
  elderly)
• Pulse oxymetry
• Arterial blood gases

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Pulse Oxymetry

• Arterial oxygen saturation is physiologically the
  more important number
• O2 Content(1.34 ml/gm x Hgb gm/dl x SaO2)
  (0.0031x PaO2)
• Accuracy
• Best in normal or near normal range
• /- 2 in Caucasians, /- 4 in blacks

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Pulse Oxymetry

• Potential sources of error
• Abnormal hemoglobins carboxyhemoglobin,
  methemoglobin
• Hypoperfusion
• Hypothermia
• Anemia
• Venous congestion
• Pigmentation
• Nail polish
• Vital dyes (e.g. methylene blue)

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Monitoring Oxygenation

• Arterial blood gases
• Effected by temperature
• Provides information on ventilation and acid base
  balance as well as oxygenation
• Relationship of PaO2 and SaO2 the oxyhemoglobin
  dissociation curve

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Monitoring of Ventilation

• Arterial blood gases
• End tidal CO2 monitors (a complicated subject but
  useful for trending)
• CO2 detectors
• Useful for confirming ET placement
• Requires perfusion

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Indications for Mechanical Ventilation

• Refractory hypoxemia
• pO2 lt55 on supplemental oxygen (usually 100 NRB
  mask)
• Alveolar to arterial oxygen gradient gt450 on FIO2
  1.0
• paO2/pAO2 lt0.15
• Inadequate ventilation and respiratory acidosis
  (pHlt7.23 and decreased level of consciousness)
• Non sustainable work of breathing
• Respiratory rate gt 35-40 breaths per minute
• Marked use of accessory muscle
• Metabolic acidosis, i.e. lactic acidosis
  (especially if due to respiratory muscle work
  (e.g. asthma with normal pCO2 and decreased pH)
• RRlt10, NIFM lt -30 cm H2O, Vital Capacity lt 1L or
  lt 10 ml/kg

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Refractory Hypoxemia?

• Remember 100 by NRB mask does not equal 100
  FIO2
• The true FIO2 depends on both flaps being in
  place, seal, and the patients inspiratory flow
  rate and entrainment of room air. You can try
  increasing the O2 flow rate (oxymask or mask
  plus nasal prongs) or O2 reservoir

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Indications for Mechanical Ventilation

• Refractory hypoxemia
• pO2 lt55 on supplemental oxygen (usually 100 NRB
  mask)
• Alveolar to arterial oxygen gradient gt450 on FIO2
  1.0
• paO2/pAO2 lt0.15
• Inadequate ventilation and respiratory acidosis
  (pHlt7.23 and decreased level of consciousness)
• Non sustainable work of breathing
• Respiratory rate gt 35-40 breaths per minute
• Marked use of accessory muscle
• Metabolic acidosis, i.e. lactic acidosis
  (especially if due to respiratory muscle work
  (e.g. asthma with normal pCO2 and decreased pH)
• RRlt10, NIFM lt -30 cm H2O, Vital Capacity lt 1L or
  lt 10 ml/kg

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Indications for Mechanical Ventilation

• Any of the indications above and you are
  thinking I cant fix this any time soon.,
  think intubation and invasive mechanical
  ventilation
• If you are thinking I can fix this if I can
  just buy enough time., then think- non invasive
  ventilation! ( assuming no contraindications to
  NIPPV)

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Indications for NIPPV

• NIPPV is primarily a temporizing measure for
  ventilatory support.
• Buying time for other therapies (i.e. diuretics,
  bronchodilators, etc.) to work
• NIPPV generally augments, but does not replace,
  spontaneous ventilatory efforts

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Indications for Non-Invasive Ventilation

• Alert, cooperative patients not requiring
  emergent intubation with a need for relatively
  short term ventilatory support
• Problems known to respond to NIPPV
• COPD exacerbations with moderate
  hypercapnea(pCO2gt45, lt100 mmHg), and acidosis (pH
  lt7.3, gt7.00-7.10)
• Acute cardiogenic pulmonary edema
• Hypoxemic respiratory failure (other than ARDS)
• Post-extubation respiratory failure

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Contraindications to NIPPV

• Cardiac or respiratory arrest
• Inability to cooperate, protect airway, or clear
  secretions
• Significantly impaired consciousness(except
  possibly COPD)
• Non respiratory organ failures
• Facial trauma, surgery or deformity
• High aspiration risk (e.g., the pregnant
  asthmatic)
• Prolonged ventilatory support anticipated
• Recent esophageal anastomosis

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NIPPV Interfaces

• In acute care settings, generally start with a
  full face mask
• Most patients with acute respiratory failure are
  mouth breathers. Nasal ventilation results in a
  large oral air leak
• Normally the nasal airway contributes 50 of
  total airway resistance
• Full face masks make monitoring and management of
  aspiration more difficult
• Patients on chronic CPAP or BiPAP may do better
  with their usual kind of mask.

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NIPPV Modes

• Mostly at this institution NIPPV equates to
  bilevel positive airway pressure with a
  guaranteed back up respiratory rate.
• Can be used with assist control mode of a
  standard ICU ventilator (for greater assurance of
  minute ventilation)
• Can be used with pressure support ventilation
  with ICU ventilator (for better patient synchrony
  and comfort)

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NIPPV Monitoring

• Monitor Level of consciousness, vital signs, and
  ABGs.
• Improvement should be apparent in the first
  30-120 miuntes
• If no improvement, proceed to endotracheal
  intubation

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Advantages of NIPPV

• Lower mortality in acute respiratory failure
  (primarily COPD and CHF)-probable selection bias
  for less severe patients
• Reduced nosocomial infection
• Decrease length of stay
• Better patient comfort

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Endotracheal Intubation

• The patient is going down the tube, so you decide
  the tube is going down the patient.
• How to intubate is another talk
• Fast forward - the patient is intubated, now
  what?
• A couple of caveats from the intubation process
• Do not use succinylcholine, a depolarizing
  neuromuscular blocker, for hyperkalemic patients
  or patients with seizures
• Etomidate causes acute adrenal suppression

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Goals of Mechanical Ventilation Clinical

• Relieve respiratory distress
• Improve hypoxemia
• Alleviate respiratory acidosis
• Reverse ventilatory muscle fatigue
• Reduce systemic or myocardial oxygen consumption
• Permit sedation or neuromuscular blockade
• Prevent or improve atalectasis
• Stabilize the chest wall

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Goals on Mechanical Ventilation Physiologic goals

• Support gas exchange arterial oxygenation and
  alveolar ventilation
• Reduce metabolic cost of breathing by unloading
  respiratory muscles.
• Avoid ventilator associated lung injuries

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Ventilator Set Up

• Things you need to specify
• Ventilator mode (more on this coming)
• FIO2 start with 100, unless you are sure the
  patients lungs are normal, e.g. drug overdose,
  then 40 is OK
• Respiratory rate
• End expiratory pressure.
• Use the ventilator bundle order sheet. It will
  prompt you.

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Ventilator Set Up Modes

• Poll Volume control versus Pressure control?
• Available modes
• Volume control A/C, SIMV, CMV
• Pressure control PCV
• Flow limited PSV (pressure support ventilation)
• Time limited Home ventilators

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Ventilator Set Up Modes

• Each mode has things you need to specify
• In general, use the mode you trained with, and
  are comfortable using
• Our Bias If you are starting volume controlled
  ventilation for acute respiratory failure, start
  with Assist Control Ventilation.
• Advantage Minimizes WOB. The patient only has
  to trigger the ventilator.
• Disadvantage Every breath is a positive pressure
  breath, which impairs venous return.

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Ventilator Set Up Modes

• SIMV synchronized intermittent mandatory
  ventilation
• Allows spontaneous breaths between mandatory
  machine breaths. Mandated breaths are
  synchronized to be delivered when the patient
  is trying to inspire.
• Originally this was a weaning mode
• Advantage The patient can set minute ventilation
  in excess of set parameters, less muscle atrophy
• Disadvantage Patient does all the work of
  spontaneous breaths plus ventilator imposed work
• The acute concern is respiratory muscle fatigue

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Ventilator Set Up Modes

• SIMV synchronized intermittent mandatory
  ventilation
• A/C vs. SIMV If goal in the first 24 hrs is to
  reduce work of breathing and respiratory muscle
  work and fatigue, A/C is superior
• Effect on work of breathing is really only
  different with SIMV if the patient breaths above
  the set ventilator rate.

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Ventilator Set Up Modes

• Volume controlled ventilation
• FIO2
• Mode A/C, SIMV
• Tidal volume (usually 10ml/kg ideal weight,
  realize normal spontaneous tidal volume is
  5-6ml/kg)
• Respiratory rate
• Positive end expiratory pressure.

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Ventilator Set Up Modes

• Pressure control ventilation vs. Volume
  controlled ventilation
• Volume controlled ventilation delivers a set
  minute ventilation, unless pressure limits are
  exceeded, then some portion of the set minute
  volume is dumped (which takes time, so actual
  airway pressure may exceed desired airway
  pressures trying to deliver the preset volumes)
• How much volume actually gets delivered depends
  on the patients airway resistance and lung
  compliance, theoretically minute ventilation is
  guaranteed.

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Ventilator Set Up Modes

• Volume controlled ventilation vs. Pressure
  controlled ventilation
• Pressure controlled ventilation increases airway
  pressure to the preset inspiratory pressure.
• The actual tidal volume delivered depends on the
  patients airway resistance and lung compliance.
  Actual minute volume delivered can vary as these
  change.
• Advantage Limits peak airway pressures and
  possible barotrauma
• Disadvantage Minute ventilation may be
  inadequate for metabolic demands

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Ventilator Set Up Modes

• Pressure support ventilation
• Also originally a weaning mode
• Requires a patient with intact respiratory drive
  and spontaneous breathing, i.e. will not
  ventilate an apneic patient.
• Augments spontaneous tidal volume, depending on
  the patients airway resistance and lung
  compliance
• Advantage Less asynchrony with the ventilator
  and improved patient comfort

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Ventilator Set Up Modes

• Time limited ventilation
• Delivers preset flow for preset time. Tidal
  volume depends on airway resistance and lung
  compliance.
• Often used in home ventilators rugged , cheap,
  simple, dependable, but hospital RTs (and
  pulmonary docs) are often not familiar with them
• If home ventilated patient has respiratory
  problems on their ventilator, take them off
  theirs and put them on ours
• You probably will not see these patients

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Ventilator Set Up Modes

• Pressure control ventilation
• FIO2
• Inspiratory pressure (IPAP) (as in BiPAP)
• Expiratory pressure (EPAP) (EPAP PEEP)
• Delta P, the change in pressure. This must equal
  IPAP-EPAP
• Slope (how fast IPAP is achieved), usually,
  .1-.3, determines IE ratio
• Respiratory rate

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Ventilator Set Up Modes

• Pressure control ventilation
• Once ventilation is started, you need to assess
  if the tidal volume and minute ventilation that
  results are reasonable for the patients
  situation and metabolic demands
• Check ABGs to be sure

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Ventilator Set Up Modes

• Issues you do not have to specify, but RT has to
  set or cope with that you need to be aware of
• Triggering sensitivity and relation to end
  expiratory pressure
• IE ratio
• Inspiratory flow rates and patterns (square wave
  vs. accelerating or decelerating flow)
• These effect airway pressures and patient
  synchrony with the ventilator
• You need to listen, if RT says there is a problem
  with your ventilator settings (e.g., If the
  patient does not have adequate time to exhale
  between breaths you are headed for trouble)

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Tips on Starting Mechanical Ventilation

• Remember, the respiratory therapists and ICU
  nurses are your friends! They really do, do all
  this, all the time. Listen, to them! If you
  disagree, explain your reasoning, they will
  (believe it or not) listen to you! If you cant
  articulate it, think again!
• Check the chest xray! (The crisis is not over
  just because the tube is in!)
• Positive pressure ventilation initially reduces
  venous return, cardiac output, and blood
  pressure! Be prepared! (especially, if the
  patient was possibly intravascularly volume
  depleted prior to intubation). It is not
  necessarily sepsis, just because the blood
  pressure goes down after intubation. Start with
  IV fluids.

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Respiratory Distress on Mechanical Ventilation

• The tools you need a stethoscope, a chest xay,
  and your brain
• Disconnect patient from ventilator and assist
  ventilation with bagging.
• If the patient is easy to ventilate with bagging
  and this solves the distress ventilator problem
• If the patient hard to ventilate with bagging and
  still in distress patient problem

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Respiratory Distress on Mechanical Ventilation
Ventilator Problems

• Inadequate ventilator settings
• Inadequate inspiratory flow rate or pressure-
  previously the most common cause. Rarer now with
  modern ventilators with high flow rates and
  ability to meet patients inspiratory flow
  demands. Dyspneic patient have high inspiratory
  flow demands, even if their own spontaneous tidal
  volumes and minute ventilation are inadequate.
• Can be suspected from ventilator graphic
  displays, take your cues from the respiratory
  therapists.

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Respiratory Distress on Mechanical Ventilation
Ventilator Problems

• Inadequate FIO2- should be obvious from oxygen
  saturation or ABGs
• Inadequate tidal volumes - The patient may want
  higher than set tidal volumes. This is
  particularly true for neuromuscular patients and
  probably involves intrapulmonary stretch
  receptors. Given the possibilities of
  volutrauma, increasing tidal volume is not
  necessarily good for them, but short term (i.e. a
  few hours) it is ok to increase the tidal volume
  until they are satisfied (and call us in the
  morning, unless airway pressures are excessive)

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Respiratory Distress on Mechanical Ventilation
Ventilator Problems

• Incorrect positive end expiratory pressure,
  especially due to intrinsic PEEP
• Incorrect trigger sensitivity (the patient has to
  work too hard to trigger the next breath)
• Example Intrinsic PEEP 10 cm with trigger
  sensitivity 2cm (from atmospheric0), patient
  effort to trigger next breath -12cm
• Remedy Measure intrinsic PEEP, set ventilator
  PEEP at 80 of intrinsic PEEP, and set trigger
  sensitivity at -2 cm below set PEEP ( in this
  case 6 cm relative to atmospheric. Patient
  effort to trigger next breath -4cm

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Respiratory distress on Mechanical Ventilation
Ventilator factors

• Ventilator circuit leak
• Ventilator malfunction
• If the patient is OK off the ventilator, being
  assisted with bagging, these are the RTs
  problems. Have them fix them or get a new
  ventilator.
• Your problem Solved!

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Respiratory Distress on Mechanical Ventilation
Patient Problems

• Airway problems (increased peak airway pressure
  plateau pressure, meaning airway resistance has
  increased, parenchymal compliance is not changed)
  (i.e., the airways have a problem, the lung is no
  stiffer)
• Pulmonary parenchymal problems-(peak airway
  pressure- plateau pressure unchanged or
  decreased, meaning air way resistance is
  unchanged, parenchymal compliance has decreased)
  (i.e., more pressure required to create the same
  change in volume with no increase in airway
  resistance the lung is stiffer)
• Extrapulmonary problems, i.e. the problem is
  around the lungs but not in them.

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Respiratory Distress on Mechanical Ventilation
Endotracheal Tube Problems

• Airway Problems
• Endotracheal tube (Its the tube, stupid!)
• Patient is biting the tube (bite block,
  paralysis)
• The tube is occluded with secretions, foreign
  body, or blood (try forcing it out the distal end
  with a suction catheter or a stylette or tube
  changer, or calling for bronchoscopy. Extubate
  and reintubate, if the problem is acute, but you
  risk losing a secure airway)
• Cuff leak, deflation, or rupture (in this case
  airway resistance usually drops suddenly, but the
  air leak is usually obvious)
• Increased resistance from heat, moisture
  exchanger, or in line CO2 monitor ( removing the
  patient from the ventilator and bagging should
  indicate it is a ventilator circuit problem)

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Respiratory Distress on Mechanical Ventilation
Patient Problems

• Airway Problems If it is not the tube, the
  patient is the one with the problem.
• Bronchospasm (remember the stethoscope?)
• The lower airway is occluded with secretions,
  blood, or a foreign body (OK, go ahead and call
  us for bronchoscopy damn it!)

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Respiratory Distress on Mechanical Ventilation
Patient Problems

• Pulmonary parenchymal problems
• ET tube has migrated into the right mainstem.
  (Oh, wait, there is that stethoscope again, and
  when that fails there is always a chest xray)
  (Oops, it the tube again, stupid!)
• OK, the tube is really OK, its the patient that
  really has the problem

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Respiratory Distress on Mechanical Ventilation
Patient Problems

• True pulmonary parenchymal problems
• Pneumonia
• Atalectasis
• Pulmonary edema (cardiogenic or non-cardiogenic)
• Aspiration
• Pulmonary Embolism

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Respiratory Distress on Mechanical Ventilation
Patient Problems

• Extrapulmonary Problems
• Pneumothorax (suspect with acute changes in
  oxygen saturation, and airway and plateau
  pressures) (back to the stethoscope and chest
  xray again)
• Pleural effusion
• Abdominal distension ascites, gastic distension,
  ileus, pancreatitis, obesity, etc.
• Delirium, pain, anxiety, fever, acute CNS event,
  acidosis (increased respiratory drive)

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Respiratory distress on the Ventilator Paralysis

• Paralysis is not the same, or part of, sedation!
• If you need paralysis to control agitation times
  one, until other measures, (e.g. propofol) can
  work, OK.
• If you think paralysis is required to maintain
  ongoing ventilatory support, you need to be
  calling us. Paralysis to maintain ventilation is
  a last resort!
• Paralysis (as opposed to sedation) is usually
  only required in ARDS (and maybe severe asthma),
  where chest wall relaxation is required to reduce
  inspiratory pressures. (my opinion)

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Respiratory Distress on the Ventilator Paralysis

• Be sure you know the patients ABG, ventilator
  settings, and minute ventilation first!
• Do not paralyze for agitation on an IMV of 2 bpm
• Do not paralyze for tachypnea with a pH of 7.00,
  a pCO2 of 10, and a minute ventilation of 25
  L/min in order to start or continue ventilator
  settings delivering a minute ventilation of 10
  L/min

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you might need a pulmonologist

• I do not think I can ventilate this patient
  unless I keep them paralyzed
• The patient is asthmatic (or has COPD) with high
  airway pressures and inability to ventilate (may
  need permissive hypercapnea)
• You always use volume controlled ventilation, its
  not working, and and RT is suggesting possible
  PCV.

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you might need a pulmonologist

• The patient is on the ventilator and you can not
  achieve adequate oxygenation
• There is a problem with the endotracheal tube
• You think the patient is developing ARDS and
  airway pressures are high and oxygenation is low
• The patient is hemodynamically unstable, and is
  not responding to IV fluids

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you might need a pulmonologist

• I could go on (and on, and on, and on ), but you
  get the idea
• We need (and love) our sleep, but if in doubt
  call us.
• Thank you!

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