Critical Care

Respiratory Failure

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Respiratory failure is commonly classified as one or both of the following:

  • Hypoxic (type 1): Characterized by failure of gas exchange resulting in PaO2 <50 mm Hg breathing a gas mixture of at least 50% oxygen (Figure 9-1)
  • Hypercapneic (type II): Characterized as failure of ventilatory pump or chronic structural changes (BPD, cystic fibrosis) (Figure 9-2)

eFigure 9-1

Workup of hypoxemia.Alveolar to arterial gradient (A–a) gradient = PaO2 estimated – PaO2 measured. PaO2 estimated = FiO2 × (PB– 47) – PaCO2/R (atmospheric pressure or PB at sea level is 760 mm Hg; respiratory quotient R is a unitless number representing basal metabolic rate; 0.7 is typically used in our ICU.) A normal A–a gradient is ∼10 mm Hg. (Adapted from Marino PL: The ICU Book, 2nd ed. Baltimore: Williams & Wilkins; 1990:349.)

eFigure 9-2

Mechanisms of hypercapnia.

Clinical Predictors of Impending Respiratory Failure

  • Early: Use of accessory muscles of respiration, markedly diminished or absent breath sounds, diaphoresis, inability to speak, AMS, irritability, cyanosis, hypercapnia
  • Late: Lethargy, apnea, gasping or agonal respiration, bradycardia, hypotension

Management of Respiratory Failure

Oxygen Delivery Modes and Noninvasive Ventilation Modalities

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Modality

Indication

Dose and Administration

Advantages

Risks and Adverse Effects

O2 via nasal cannula (provides roughly 25%–40% oxygen)*

(Use humidification system)

For non–life-threatening conditions, hypoxemia (asthma, pneumonia, bronchiolitis)

100% oxygen, typically no more than 4 L/min flow

Well tolerated, easy to use, readily available, no associated toxicity

Skin irritation from cannula, drying of nasal passages, nose bleeds

O2 via simple face mask (provides roughly 35%–50% oxygen)*

For non–life-threatening conditions, hypoxemia (asthma, pneumonia, bronchiolitis)

100% oxygenat no less than 5 L/min, typically 5–15 L/min

Well tolerated, easy to use, readily available, no associated toxicity, provides more oxygen than nasal cannula

If flow is <5 L/min, “rebreathing” CO2 may occur

O2 via Venturi™ mask (provides 24%–50% oxygen incrementally)

Weaning oxygen from high flow rates

The flow of 100% oxygen through the Venturi mask draws in a controlled, adjustable amount of room air (21% oxygen)

Well tolerated, easy to use, no associated toxicity, fixed and accurate concentration of oxygen

Not readily available

O2 via partial rebreathing face mask (provides roughly 50%–100% oxygen)*

For non–life-threatening conditions, severe hypoxemia (asthma, pneumonia, bronchiolitis)

100% oxygen, 5–15 L/min

Maintain reservoir at least half full on inspiration

High-flow system readily available, provides more oxygen than simple face mask

Nitrogen washout may lead to atelectasis

O2 via nonrebreather facemask (provides ∼80%–100% oxygen)*

Severe hypoxemia, hemodynamically stable pneumothorax (nitrogen washout)

100% oxygen 10–15 L/min

Maintain reservoir at least 2/3 full on inspiration and allow partial collapse on exhalation

Well tolerated, easy to use, readily available

Nitrogen washout may lead to atelectasis

Heliox**, 60%–80% He with 20%–40% O2

Upper airway obstruction (croup, bronchiolitis)

May be beneficial in treatment of lower airway disease (asthma)

Can be administered via nasal cannula and face mask

Do not use with oxygen tent or hood

Lower density gas decreases turbulent flow → increased O2 and medication delivery to distal airways

Beneficial effects of Helium not seen with <60%; therefore, not helpful if patient requires >40% O2

CPAP

Acute: Respiratory distress or failure, poor lung compliance, obstructive airway disease , muscle fatigue, CHF, asthma, acute chest syndrome

Chronic: OSA

Typically administer pressures of 5–10 cm H2O

May give supplemental oxygen as needed

Overcomes airway resistance to maintain FRC, ↓ muscle fatigue, ↑ lung recruitment, ↓ atelectasis, ↓ V/Q mismatch

Reduced risk of infection and local trauma to airway compared with ETT

Constant pressure throughout respiratory cycle; no ↑ with inspiration.

Masks may cause skin breakdown with chronic use

BiPAP

(same as above for CPAP)

Administer via nose mask

IPAP (8-20 cm H2O), EPAP (5-10) cm H2O, supplemental oxygen as needed

Less use of sedatives

May prevent intubation

Nasal prongs and masks may cause skin breakdown with chronic use

Not well tolerated by some patients

Distended stomach caused by swallowed air

Noninvasive positive pressure ventilation

Respiratory distress

Use a ventilator, set parameters (rate, Vt or PIP, PEEP)

Supplemental O2 as needed

As with BiPAP

May prevent intubation

As with BiPAP

*The final oxygen concentration delivered by this device depends on the amount of room air that mixes with the supplemental oxygen during respiration.

**70/30 Heliox is used at our institution.

The FiO2 can be reduced by blending with room air while still maintaining the same flow rate.

‡Cognitive behavioral therapy at the beginning of therapy dramatically increases compliance up to 148%. Sleep 2007;30(5):635.

Stepwise Approach to Managing Respiratory Failure

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Step 1: Preparation and intubation

Step 2: Pick ventilator mode (choose a familiar mode)

Step 3: Choose control mode (volume vs. pressure)

Step 4: Choose remaining variables

Step 5: Manage patient while intubated

Step 6: Wean and extubate as soon as possible

Step 1: Preparation and Intubation (STATS)

  1. Suction

  2. Tubes (anticipated ETT size + 1 size above and below)

  3. Airway adjuncts (oral airways)

  4. Tape

  5. Scopes: Laryngoscope, stethoscope

See accompanying PICU Pocket card for recommended mediations and equipment sizes.

Step 2: Pick Ventilator Mode (How the Patient and Machine Interact): Important Goals

  • Provide adequate ventilation and oxygenation.
  • Reduce the work of breathing.
  • Ensure patient comfort and synchrony with the ventilator.

Overview of Common Mechanical Ventilation Modalities

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Mode

Set Rate

Guaranteed Minimum MV

Support for Patient-Initiated Breaths “Over the Vent”

Notes

Controlled mechanical ventilation (CMV)

Y

Y

N

Vent delivers regular, identical breaths; no spontaneous breaths allowed

Rarely used, with the exception of neonatal transport ventilators

Assist-control ventilation (AC)

Y

Y

Y

Typically volume control; full preset TV is delivered at a preset rate; the patient may initiate additional supported cycles (also full preset VT); the patient may change MV as needed but cannot resume the work of breathing

Intermittent mandatory ventilation (IMV)

Y

Y

N

Similar to CMV but allows patient-triggered breaths in between mandatory breaths

Patient may change minute ventilation as needed and as vent rate is weaned, the patient can “take over” the work of breathing

Synchronized intermittent mandatory ventilation (SIMV)

Y

Y

N

Similar to IMV, but internal circuitry manipulates mandatory vent delivered breaths around patient-triggered breaths

Support mode (PS, VS)

N

N

Y

Set pressure or volume is delivered for patient-initiated cycles to support patient-initiated breaths (often combined with other modalities or as a weaning modality, i.e. SIMV + PS)

Pressure regulated volume control (PRVC, VC+)

Y

Y

Y

On some ventilators, these are AC modes, but in others, they are SIMV modes; ask the RT

Delivers preset rate and VT, but flow characteristics are regulated to deliver target volumes at the lowest possible pressure

High-frequency oscillatory ventilation (HFOV)

N/A

N/A

N/A

Escalation of care for patients who require high and have failed conventional ventilators

Consider when PEEP is 10 cm H2O or PIP is >35; better separates control of oxygenation and ventilation

Step 3: Choose Control Mode (Pressure vs. Volume)

  • Pressure control: Delivers a pressure-limited breath during a preset inspiratory time at the preset respiratory rate. The VT is determined by the preset pressure limit and the compliance and resistance of the patient’s respiratory system.
    • Goal PIP: <35 to 40 cm H2O to reduce ventilator-induced lung injury (barotrauma).
    • Does not guarantee VT.
    • Pressure control may be preferentially used for ELBW or VLBW patients because of limitations in ventilator ability to consistently deliver or control extremely low VT.
  • Volume control: Delivers a preset VT during a preset inspiratory time at the preset respiratory rate and constant inspiratory flow.
    • Guarantees VT at the expense of variations in PIP.
    • Monitor PIP closely; goal is <35 to 40 cm H2O to reduce ventilator-induced lung injury(barotrauma)

Step 4: Choose Remaining Variables (Starting Point)

Initial SIMV Ventilator Settings for Various Ages

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SIMV PC (Neonates)

SIMV PC (Children)

SIMV VC (Children)

SIMV VC (Adolescents)

Rate (bpm)

20–30

14–20

14–20

8–14

Ti (sec)

0.2–0.5

0.5–0.8

0.5–0.8

0.75–1

VT (cc/kg)*

N/A

N/A

6-8

6–8

PEEP (cm H2O)

2–5

2–5

2–5

2–5

PIP (cm H2O)

20–25

20–25

N/A

N/A

PS (cm H2O)

5–10 (in addition to PEEP)

FiO2

Start at 1.0 and wean as aggressively as possible to avoid O2 toxicity (goal <0.6)

*Monitor chest rise and titrate to the lowest VT with adequate chest rise (lung protective strategy: 6–8 cc/kg).

Shaded boxes indicate variables that are not set in this mode; values obtained will be based on other set variables.

Large or obese adolescents may require less VT for adequate chest rise.

Step 5: Manage Patient While Intubated

Ventilator Adjustments Affecting Oxygenation and Ventilation

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Goal

Action

Physiology

Caveats

Improving oxygenation

Increase Paw by ↑ PEEP, PIP, or Ti (PEEP has greater effect); increase FiO2

PEEP maintains FRC and ↓ V/Q mismatch; has >effect than PIP:

= K(PIP-PEEP) × [Ti/(Ti + Te)] + PEEP

Overdistension with PEEP will lead to worsening oxygenation

Consider HFOV if PEEP >10

Improving ventilation

Increase MV by ↑ RR or ↑ VT (in VC modalities) or PIP (in PC modalities)

CO2 directly related to minute ventilation. Rule of thumb: Current PaCO2 × Current respiratory rate = Desired PaCO2 × Desired respiratory rate

Allow for permissive hypercapnia (pCO2 ∼60 if pH >7.2) to reduce the potential for barotrauma

With obstructive airway diseases, reducing the respiratory rate may improve ventilation by allowing for a longer Te

Sedation and Analgesia

  • Consider for all intubated patients; neonates may need less than older patients to prevent patient–ventilator asynchrony and accidental extubation.

Maintenance Fluids

  • For all intubated patients not on diuretics, use 75% of maintenance IVF (these patients do not have respiratory insensible loss because of the enclosed humidified ventilator circuit) and follow volume status closely.
  • Nutrition: Start enteral feeds as soon as possible; if contraindicated, start TPN or PPN (ideally, the patient should start receiving adequate calories and nutrition 2–3 days after intubation).

Blood Gases and Clinical Parameters

  • Follow at least qAM blood gases (preferably ABG; may use CBG, or VBG via central line).
  • Follow oxygenation using pulse oximetry.
  • Follow ventilation using end-tidal CO2 if feasible (may be too bulky for neonates) and correlate or recalibrate daily with pCO2 from AM blood gases.
  • Follow lung compliance (want higher) and oxygenation index (want lower) daily trends

CDYN = VT/(PIP – PEEP)

CSTAT = VT/(PPLAT – PEEP

Oxygenation index = (FiO2 × Mean airway pressure)/PaO2 × 100

Diuresis and Metabolic Alkalosis

  • Diuretics should be considered in all intubated patients given impaired lymphatic or venous return 2/2 immobility: 0.5 to 2.0 mg/kg furosemide IV Q6 to 12 h. Keep balanced intake and output (other diuretics may be used).
  • Expect metabolic alkalosis. Anticipate depletion of Cl and retention of bicarbonate.
  • Start replacing Cl when <90 mEq/L.
    1. First choice: Use KCl (2–4 mEq/L) unless contraindicated (eg, renal insufficiency, hyperkalemia).

    2. Second choice: Use NaCl (2–4 mEq/kg); may cause more water retention 2/2 increased Na.

    3. If a and b have been exhausted and Cl <80 mEq/L, then use ammonia chloride. Dosing of mEq NH3Cl via the bicarbonate-excess method (refractory hypochloremic metabolic alkalosis):

      mEq NH3Cl = 0.5 (L/kg) × wt (kg) × [Serum HCO3 – 24]

      → Give ½ to ⅔ of the calculated dose; then re-evaluate

      (0.5 L/kg is the estimated bicarbonate volume of distribution, and 24 is the average normal serum bicarbonate concentration in mEq/L; use with caution in patients with hepatic insufficiency.)

    4. After Cl >90 (or spot urine Cl suggests saline-resistant alkalosis) while pH is >7.50, use acetazolamide (5 mg/kg IV Q8h for 3 doses only; check daily lytes).

Monitor for Complications of Mechanical Ventilation

  • Infection: The trachea will be colonized within ∼6 hours of intubation; monitor changes in color or quantity of secretions.
  • Decreased cardiac output: Increased intrathoracic pressure impedes RV filling and decreases cardiac output, especially if the patient is hypovolemic.
  • Ventilator-induced lung injury (VILI): Barotrauma: Repeated alveolar stretch (via pressure or volume) will activate the host inflammatory response. Therefore, keep VT or PIP as low as possible. Oxygen toxicity: Supplemental O2 may fuel inflammation; wean O2 aggressively.
  • Pneumothorax: Results from acute changes in airway pressures. If the pneumothorax is under tension, it is a life-threatening emergency. Signs and symptoms include agitation, decreased breath sounds on the affected side, asymmetrical chest rise, tracheal or mediastinal shift away from the affected hemi-thorax, increased CVP, decreased BP, increased HR, increased PIP, increased Paw. Always assume a pneumothorax has developed with any acute or rapid deterioration in clinical status and treat swiftly with needle decompression.
  • Subglottic stenosis: Results from too large of ETT, traumatic intubation, or patient agitation. Heliox may improve gas flow. Steroids may help avoid re-intubation if stridor is present upon extubation (dexamethasone 0.5 mg/kg IV Q6H (max dose 15 mg) × 4–8 doses).
  • Mechanical failure or accidental extubation: Hand ventilate patient, remove the ETT.

Step 6: Wean and Extubate as Soon as Possible

Weaning

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  • As the patient’s need for ventilatory support resolves, wean in the following order: FiO2 → PIP (if PC ventilation) → PEEP → Rate (ensure pressure or volume support is provided).
  • Criteria for extubation readiness (Crit Care Med 2000;28(8):2991 and JAMA 2002;288(20):2561):
    • PEEP ≤5
    • FiO2 <40%
    • Spontaneous effective VT >5 cc/kg
    • Glasgow Coma Scale >8 (ie, not comatose, sedation has been weaned)
    • Tracheal secretions are tolerable (ie, not thick and not requiring >Q1h suctioning)
    • Appears comfortable on PEEP 5 or pressure support of 5 with no trial failure (see below)

Criteria for CPAP Trial Failure

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Definition of trial: 2 h on respiratory support of CPAP ≤5 cm H2O or T-piece (CPAP = 0)

Clinical Criteria

  • Diaphoresis
  • Nasal flaring
  • Increasing respiratory effort
  • Tachypnea
  • Tachycardia (increase in HR >20–40 bpm)
  • Cardiac arrhythmias
  • Hypotension
  • Apnea

Laboratory Criteria

  • Increase of PETCO2 >10 mm Hg
  • Decrease of arterial pH to <7.32
  • Absolute decline in arterial pH >0.07
  • PaO2 <60 mm Hg with FIO2 >0.40 (PaO2/FiO2 ratio <!–150)
  • SpO2 declines >5%

(Ped Crit Care Med 2009;10(1):1)

Status Asthmaticus in the Intensive Care Unit

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  • Definition: An acute exacerbation of asthma that does not respond to treatment with bronchodilators and corticosteroids.
  • Symptoms: Chest tightness or pain, dyspnea, dry cough, or wheezing. Patients may have nausea, vomiting, difficulty speaking or speaking in single words, or altered mental status as part of the presentation, which indicates greater severity of illness.

Risk Factors for ICU Admission and for Sudden Death with Status Asthmaticus

  • Previous ICU admissions
  • Previous need for mechanical ventilation with an asthma exacerbation
  • Syncope during an asthma exacerbation
  • Seizures during an asthma exacerbation
  • History of cardiac arrest with asthma exacerbation
  • Poor adherence to controller therapy
  • Poor perception of severity of asthma
  • Comorbid psychiatric disorder
  • Rapid deterioration with current episode
  • Use of more than 1 canister of home β-agonist medication per month

Clinical Respiratory Score as a Guide for Evaluating Severity of Exacerbation and Following Response to Therapy

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Clinical Respiratory Score (CRS)

Assess

Score 0

Score 1

Score 2

Patient Score

Respiratory Rate

< 2 mos < 50

2-12 mos < 40

1-5 yrs < 30

> 5 yrs < 20

< 2 mos 50-60

2-12 mos 40-50

> 1-5 yrs 30-40

> 5 yrs 20-30

< 2 mos > 60

2-12 mos > 50

> 1-5 yrs > 40

> 5 yrs > 30

Auscultation

Good air movement, scattered expiratory wheezing, loose rales/crackles.

Decreased air movement, inspiratory and expiratory wheezes or rales/crackles

Diminished or absent breath sounds, severe wheezing or rales/crackles, or markedly prolonged expiration.

Use of Accessory Muscles

Mild to no use of accessory muscles. Mild to no retractions or nasal flaring on inspiration.

Moderate intercostal retractions, mild to moderate use of accessory muscles, nasal flaring.

Severe intercostal and substernal retractions, nasal flaring.

Mental Status

Normal to mildly irritable

Irritable, agitated, restless.

Lethargic

Room Air SpO2

> 95%

90 – 95 %

< 90%

Color

Normal

Pale to normal

Cyanotic, dusty

Total Score (Sum of the component scores)

Therapies for the Management of Status Asthmaticus

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First-Line Treatment

Medication

Type and Mechanism

Route

Dose

Albuterol

SABA (airway smooth muscle relaxation)

Inhaled (nebulized or MDI)

Nebulization: 0.15–0.5 mg/kg/h or 10–20 mg/h of continuous therapy; can give sequential nebulization × 3 (≤5 mg each)

Max, 20 mg/h

MDI: 4–8 puffs per dose Q20 min × 3; then Q1h

Levalbuterol

SABA (levorotary enantiomer, airway smooth muscle relaxation)

Inhaled (nebulized or MDI)

MDI: 4–8 puffs Q20 min × 3 then Q1h

Methylprednisolone

Steroid* (antiinflammatory)

IV

2 mg/kg IV once; then 1 mg/kg IV Q6h

Max, 60 mg/dose

Prednisone

Steroid* (antiinflammatory)

PO

2 mg/kg PO once; then 1–2 mg/kg/day divided Q12h

Max, 60 mg/dose

Second-Line Treatment

Ipratropium bromide

Anticholinergic (airway smooth muscle relaxation)

Inhaled (nebulized or MDI)

<12 yr: Nebulization 250 mcg Q20 min × 3 then Q2–4h prn; MDI 4–8 puffs per dose

>12 yr: Nebulization 500 mcg Q30 min × 3 then Q2–4h prn; MDI 4–8 puffs per dose

Can “spike” the albuterol nebulization solution with ipratropium bromide dose and give as one treatment

Magnesium sulfate

Electrolyte (smooth muscle relaxation)

IV

40 mg/kg IV over 20 min; max 2g

Although hypotension is exceedingly rare, watch for hypotension and be ready to give a 10–20 cc/kg NS bolus if it develops

Terbutaline†

β-agonist (smooth muscle relaxation)

Sub-Q, IV

IV: 10 mcg/kg IV once; then IV infusion starting at 0.5 mcg/kg/min, titrate as HR tolerates to goal 3–6 mcg/kg/min

Max, 10 mcg/kg/min

Aminophylline

Bronchodilator

IV

6 mg/kg load over 20–30 min; then continuous infusion

Ketamine

Dissociative anesthetic, bronchodilator

IV

0.5–2.0 mg/kg IV; may be used as a continuous infusion

May have bizarre dreams, hallucinations; watch for oversedation and need for immediate intubation

Often reserved as a last medication trial or sedative before intubation

Heliox

Gas

Inhaled

Available as 70/30 or 80/20 concentrations

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Jan 9, 2019 | Posted by in PEDIATRICS | Comments Off on Critical Care

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