ICU book reading

Chap 27 Discontinuing mechanical ventilation

Outline Readiness criteria

Rapid-shallow breathing index Maximum inspiratory pressure

The spontaneous breathing trial Breathing through the ventilator Breathing through the T-piece Protocol An approach to Rapid breathing

Failure of spontaneous breathing Low cardiac output Overfeeding Respiratory muscle weakness

Tracheal decannulation Protect airway Laryngeal edema Postextubation period

Who can be considerate for weaning trial

Respiratory criteria: PaO2 60mmhg on FiO2 40-50% and PEEP 5-≧ ≦ ≦

8cmH2O. PaCO2 normal or baseline (except for permissive

hypercapnia Patient is able to initiate an inspiratory effort

Cardiovascular criteria No evidence of myocardial ischemia Heart rate 140 beats/minute.≦ Blood pressure normal without vasopressors or with

minimum vasopressor support (e.q., dopamine < 5ug/kg/min)

Who can be considerated for weaning trial

Adequate mental status Patient is arousable or Glosgow coma score 13.≧

Absence of correctible comorbid condition Patient is afebrile There are no significant electrolyte abnormalities

Measurements Used to Identify Patients Who Will Tolerate aSpontaneous Breathing Trial (SBT)

The predictive value

The Spontaneous Breathing Trial

Breathing Through the Ventilator

Breathing Through the T-Piece

Breathing Through the Ventilator

The advantage: Monitor the tidal volume and respiratory rate

during spontaneous breathing to detect the rapid and shallow breathing

Disadvantage: increased work of breathing the negative pressure that must be generated to

open an actuator valve in the ventilator and receive the inhaled oxygen mixture

the resistance created by the ventilator tubing between the patient and the ventilator

Pressure-Support Ventilation

add enough inspiratory pressure to reduce the work of breathing through the endotracheal tube and ventilator circuit without augmenting the spontaneous tidal volume

A positive pressure of 5–7 cm H2O is routinely used for this purpose.

inspiratory pressure support is not necessary during spontaneous breathing trials

Breathing through endotracheal tubes and ventilator circuits is not associated with an increased work of breathing, at least in comparison to the early time period following extubation

Breathing Through the T-Piece

Breathing Through the T-Piece

Advantage: it creates a “suction effect” that carries the exhaled gas out

of the apparatus and prevents rebreathing of exhaled gas. it prevents the patient from inhaling room air from the exhal

ation side of the apparatus.

The disadvantage inability to monitor the patient's spontaneous tidal volume a

nd respiratory rate less work of breathing when compared to spontaneous bre

athing while connected to the ventilator

Protocol

Allow 30 to 120 minutes for the initial trial Increase the FiO2 by 10% for the period of spontane

ous breathing Judgement:

Combination of patient appearance (comfortable versus labored breathing), breathing pattern (i.e., the presence or absence of rapid, shallow breathing) and gas exchange (e.g., ability to maintain SaO2 =90% and end-tidal PCO2 normal or constant throughout the trial).

Protocol

Our practice for patients who have been ventilator-dependent for one week or longer is to permit at least 8 hours (and sometimes up to 24 hours) of spontaneous breathing before deciding to remove the ventilator from the room.

An Approach to Rapid Breathing

Anxiety versus ventilatory failure Abdominal Paradox

Rapid breath

Tidal volume

Decreased No Decreased

Aterial PaCO2

Decreased No Decreased

Resume ventilator support

Sedation Resume ventilator support

Low Cardiac Output

positive-pressure ventilation to negative-pressure spontaneous breathing => increase in left-ventricular afterload=> decrease in cardiac output => promoting pulmonary congestion (which reduces lung compliance) => impairing diaphragm function (Diaphram depend heavily on Cardiac output)

Low Cardiac Output

O2 EXTRACTION: (SaO2 - SvO2) Arterial-End Tidal PCO2 Gradient: (PaCO2

– PetCO2)increase in the (PaCO2 – PetCO2) difference=> A decrease in cardiac output=> increase in dead-space ventilation from lung disease

Myocardial Ischemia

Continuous Positive Airway Pressure

CPAP can help by eliminating the increased afterload caused by negative intrathoracic pressures

CPAP has been used effectively in patients with acute cardiogenic pulmonary edema,

Overfeeding

An increase in the daily intake of calories is associated with an increase in metabolic CO2 production

Respiratory Muscle Weakness

the diaphragm becomes weak during mechanical ventilation

the diaphragm is not a voluntary muscle that will stop contracting during mechanical ventilation.

The diaphragm is controlled by the respiratory neurons in the lower brainstem, and these cells fire automatically throughout life.

Critical Illness Polyneuropathy and Myopathy

These conditions often accompany cases of severe systemic sepsis with multiorgan failure, and they can prolong the need for mechanical ventilation

The diagnosis is usually made by exclusion (although nerve conduction studies and electromyography can secure the diagnosis).

There is no treatment for these disorders, and recovery takes weeks to months.

Electrolyte Depletion

Depletion of magnesium and phosphorous can impair respiratory muscle strength

Tracheal Decannulation

Protecting the Airway the gag and cough reflexes, the volume of respiratory secretions.

Laryngeal Edema reported in as many as 40% of cases of prolonge

d translaryngeal intubation

Protecting the Airway

The ability to protect the airway = the gag and cough reflexes, the volume of respiratory secretions.

Cough strength can be assessed by placing a file card or piece of

paper 1-2 cm from the end of the tracheal tube and asking the patient to cough. If wetness appears on the card, the cough strength is considered adequate

The Cuff-Leak Test

The test is performed while the patient is receiving volume-cycled ventilation, and it involves measuring the volume of gas exhaled through the endotracheal tube before and after deflating the cuff

a decrease in exhaled volume after cuff deflation is used as evidence against the presence of a significant obstruction at the level of the larynx.

The Cuff-Leak Test

Different studies have used volumes of 110-140 mL, and a 25% change in volume as the threshold.

volume leak during positive-pressure lung inflation, related to lung compliance and airways resistance

the diameter of the endotracheal tube relative to the diameter of the trachea.

Fenestrated Tracheostomy Tubes

Laryngeal injury maybe related to prior endotracheal tube or ischemic injury.

Steroids for Anything That Swells?

Controversial it seems unlikely that one dose of steroids (or

one day of therapy) will reverse the cumulative effects of days of trauma to the larynx

The Postextubation Period

The Work of Breathing Endotracheal tube is smaller in diameter.

But work of breathing is lessendotracheal tubes should never be removed based on the assumption that it will be easier for the patient to breathe.

Posrtextubation Stridor Postextubation stridor is not always an indication for immed

iate reintubation aerosolized epinephrine (2.5 mL of 1% epinephrine) Breathing a helium-oxygen (heliox) gas mixture

A Final Word

recognizing when a patient is ready to try spontaneous breathing

A trial of spontaneous breathing If the patient does well, then consider extubat

ion,