case 87 - resp failure

Question 1

what are the two main types of acute respiratory failure?

Answer 1

• hypoxemic resp failure
• hypercapnic resp failure

Hypoxemic resp failure:

4 causes:

• hypoventilation (hypercapnia) - affects A-a gradient
• v/q mismatch
• intrapulmonary shunt
• diffusion impairment

Hypercapnic resp failure:

2 causes:

• ineffective elimination
  
  • decrease RR (opioids, brainstem lesion)
  • decrease TV (residual neuromusclar block, splinting, myasthenia gravis)
  • increased physiologic dead space (COPD, ARDS)
• increase Co2 production
  
  • MH
  • thyrotoxicosis (thyroid storm)

Question 2

you extubate a patient after surgery. In the PACU, he is tachypenic, saO2 is 88%. Would you re-intubate him, what is your clinical indications?

Answer 2

clinical indications for reintubation:

• fatigue
• accessory msucel use
• paradoxical breathing pattern
• inability to protect airway
• hypoxemic (paO2 < 60 or Sao2 < 90%), increasing use of Fio2 to maintain sats, hypercarbia (> 50 mm Hg) –> intubate and mech ventilate

Question 3

when should noninvasive ventilation be considered, what modes are out there?

Answer 3

• consider NIPPV if resp distress is expected to be short-lived:
  
  • mild to mod pulm edema
  • COPD exacerbation
  • splinting
• two forms CPAP & BiPAP
  
  • CPAP is continuous airway pressure
  • BiPaP = PS/CPAP - basically CPAP with inspiratory pressure support

Question 4

what are the four causes of hypoxemia, and distinguish each of them?

Answer 4

four causes: Hypoventilation, shunt, V/Q mismatch, diffusion impairment

1) hypoventilation

• alveolar gas equation:
  
  • PAo2 = Fio2 (Patm-Ph2o) - (PaCO2/RQ)
  • increase PaCo2 will decrease PAO2
  • eqn also explains supplemt O2 wil increase FiO2 and will maintain Sao2 in face of increase PacO2 = delayed dx of hypoventilation
• causes: dec RR, dec TV: opioid, residual nmb, etc

2) Shunt

• intrapulmonary or intracardiac = R to L shunt
• aka perfusion without ventilation
• mixing of oxygenated blood with deoxygenated blood = lower PaO2 –> result in decrease SVO2
• increasing FiO2 will not improve PaO2

3) V/Q mismatch

• ventilation without perfusion
• aka dead space ventilation
• EtCo2 - PacO2 / EtcO2 = 0.3 = normal
• FiO2 will improve SaO2
• hypercarbia if mismatch severe

4) Diffusion impairment

• alveolar/capillary barrier
• thickened walls = decrease diffusion between both compartments
• measure with carbon monoxide testing
• affected in interstial fibrosis, asbestosis, sarcoidosis

Question 5

if patient has ARDS, how would you manage ventilation?

Answer 5

1) VCV or PCV - no difference
2) oxygenation

• reduce FiO2 to maintain PaO2 > 60
• increase PEEP
  
  • increases FRC, allows greater portion of ventilation to occur in opened alveoli, improves gas exchange and therefore oxygenation

3) ventilation

• 4- 6 cc/kg
• increase RR as needed, maintain Pplat < 30
• maintain pH 7.3 - 7.4

4) ventilator induced lung injury

• increase PEEP to open collapsed alveoli
• low TV
• low airway pressure (< 30 cm h2O)

5) consider dry state (as opposed to liberal fluid use)

Question 6

Discuss the different modes of ventilation: CMV (PCV and Vcv), assist-control, SIMV, PS

Answer 6

1) Controlled mech ventilation

• either VCV or PCV
• both are Time Trigger
• VCV - set tidal volume, pressure variable
• PCV - set presure, tidal volume variable

2) Assist - Control

• preset number of mandatory breaths patients recieve and TV
• time and patient trigger
• additional effort of patient (sensed by negative pressure) will deliever a supported breath of the same set tidal volume
  
  • ex: set TV to 600, each supported breath of patient will be a TV of 600.

3) SIMV

• preset mandatory ventilator breaths patient takes and TV
• time and patient trigger
• spontaneous breath of patient is not supported.
• mandatory breaths and spontaneous breaths are synchronzied at a set rate

4) PS

• preset pressure
• patient trigger
• ventilator senses inspiratory flow generated by patient, and delivers preset pressure until insp flow decreases.
• no mandatory breaths by ventilator, patient driven

Question 7

what does trigger refer to during mech ventilation

Answer 7

two types of trigger: Time and Patient

1) TIme

• set RR determines when a breath will bedelivered.
• ex: set rate at 12 breaths per minute, a breath will be delivered every 5 sec

2) Patient

• ventilator detects inspiratory effort generated by patient
• negative pressure sensed = AC Mode
• set Inspiratory Fow sensed = PS mode

Question 8

what modes of ventilation would you use for somebody who has no resp effort, some resp effort, and significant resp effort?

Answer 8

1) No resp effort
* VCV or PCV
2) some effort
* SIMV or SIMV/PS
3) signifcant effort
* PS

Question 9

how is clinical manifestations of PE, how to dx and tx it

Answer 9

PE

clinical mainfestations

• acute decrease PaO2
• tachypnea, tachycardia, hypotensive
• sometimes SVT occurs
• an S1Q3T3 pattern
  
  • a prominent S wave in lead I
  • a Q wave and inverted T wave in lead III

Dx:

• CT angiogram = gold standard
• V/Q scanning

Tx:

• if high suspicion start tx
• iv heparinzation guided by PTT ( 60-90)
• high risk bleeders -> IVC filter placement

Question 10

what is your extubation criteria?

Answer 10

two factors: General and respiratory-specific

General criteria:

1) awake, alert, follows commands -> able to protect airway
2) HD stable, minimal pressor support
3) no high fever or gross manifestations of sepsis
4) do not require additional testing or further surgical interventions in immediate post-op period

Resp - specific criteria:

1) SaO2 > 90% on minimal FiO2 < 40%
2) PaCo2 is within baseline
3) spont breathing trial for at least 30 - 60 min placed on minimal vent support: PS 5-10cm H2O or T-piece
* successful trial: absence of tachycardia, HTN, hypotension, resp distress, agitation, Spo2 < 90%
4) RSBI < 100
* RR / TV (in liters)