Pocket Medicine

PULMONARYQ

MECHANICAL VENTILATION

Indications

•  Improve gas exchange

↑ oxygenation

↑ alveolar ventilation and/or reverse acute respiratory acidosis

•  Relieve respiratory distress

↓ work of breathing (can account for up to 50% of total oxygen consumption)

↓ respiratory muscle fatigue

•  Apnea, airway protection, pulmonary toilet

Choosing settings (NEJM 2001;344:1986)

1. Choose method (including potentially noninvasive ventilation, see later)

2. Pick ventilator mode, and (if appropriate) volume targeted or pressure targeted

3. Set or ✓ remaining variables (eg, FiO2, PEEP, I:E time, flow, airway pressures)

Tailoring the ventilator settings

•  To improve oxygenation: options include ↑ FiO2, ↑ PEEP

First, ↑ FiO2. If >0.6 and oxygenation remains suboptimal, then try ↑ PEEP:

If ↑ PaO2/FiO2 and Pplat stable, suggests recruitable lung (ie, atelectasis). Continue to ↑ PEEP until either can ↓ FiO2 to <0.6 or Pplat ≥30 cm H2O. If PEEP 20 & FiO2 1.0 and oxygenation remains suboptimal, consider rescue/expt strategies (see “ARDS”).

If ↑ PEEP yields no Δ or ↓ PaO2/FiO2 or ↑ PaCO2, suggests additional lung not recruitable and instead overdistending lung → ↑ shunt & dead space; ∴ ↓ PEEP

•  To improve ventilation: ↑ VT or inspiratory pressure, ↑ RR (may need to ↓ I time). Nb, tolerate ↑ PaCO2 (permissive hypercapnia) in ALI/ARDS (qv) as long as pH >7.15.

Acute ventilatory deterioration (usually ↑ PIP)

•  Response to ↑ PIP: disconnect Pt from vent., bag, auscultate, suction, ✓ CXR & ABG

Figure 2-7 Approach to acute ventilatory deterioration

Weaning from the ventilator (NEJM 2012;367:2233)

•  Perform daily assessment of readiness for spontaneous breathing trial (SBT)

•  Clinical screening criteria: VS stable, minimal secretions, adequate cough, cause of respiratory failure or previously failed SBT reversed

•  Vent parameters: PaO2/FiO2 >200, PEEP ≤5, f/VT <105, VE <12 L/min, VC >10 mL/kg rapid shallow breathing index (f/VT) >105 predicts failure; NPV 0.95 (NEJM 1991;324:1445)

•  Daily awakening trial (d/c all sedation; Lancet 2008;371:126): open eyes & w/o: agitation, RR >35, SaO2 <88%, resp distress or arrhythmias (if fail, restart sedation at 1/2 prior dose).

•  SBT = CPAP or T piece × 30–120 min

failure if: deteriorating ABGs, ↑ RR, ↑ or ↓ HR, ↑ or ↓ BP, diaphoresis, anxiety

•  Tolerate SBT → extubation. Fail SBT → ? cause → work to correct → retry SBT qd

Complications

•  Oxygen toxicity (theoretical); proportional to duration + degree of ↑ oxygen (FiO2 >0.6)

•  Ventilator-associated pneumonia (~1%/day, mortality rate ~30%)

typical pathogens: MRSA, PseudomonasAcinetobacter and Enterobacter species

preventive strategies (AJRCCM 2005;171:388): wash hands, HOB elevated, non-nasal intub., enteral nutrition rather than TPN, routine suction of subglottic secretions, avoid unnecessary abx & transfusions, routine oral antiseptic, stress-ulcer prophylaxis w/ ? sucralfate (↓ VAP, ↑ GIB) vs. H2RA/PPI, ? silver-coated tubes (  JAMA 2008;300:805)

•  Laryngeal

edema: for Pts vent >36 h; ? predicted by  cuff leak test. Methylprednisolone 20 mg IV q4h starting 12 h pre-extub. → ↓↓ edema and 50% ↓ in reintubation (Lancet 2007;369:1003)

ulceration: consider tracheostomy for patients in whom expect >14 d of mech vent → ↓ duration mech vent, ↓ # ICU days (BMJ 2005;330:1243); no benefit to performing at ~1 wk vs. waiting until ~2 wk (  JAMA 2010;303:1483)

•  Malnutrition (for all critically ill Pts): enteral nutrition initiated early is safe but not necessary (  JAMA 2012;307:795), but bolus may ↑ risk of VAP & C diff. (  JPEN 2002;26:174); no clear benefit to ✓ing gastric residuals (  JAMA 2013;309:249); parenteral nutrition should be delayed until after day 8 to ↓ risk of infections, cholestasis, RRT, ventilator days (NEJM 2011;365:506)

•  Oversedation/delirium: BDZs and polypharmacy are risk factors

propofol: HoTN in ~25%; propofol infusion syndrome (PRIS) ? esp. w/ high (>5 mg/kg/h) & prolonged (>48 h) infusions & concom vasopressors → ↑ AG, cardiac dysfxn, rhabdomyolysis, ↑ triglycerides, & renal failure (Crit Care 2009;13:R169)

dexmedetomidine: ↑ vent-free days, but brady & HoTN c/w BDZ (  JAMA 2012;307:1151)