Positive Pressure Ventilation and Equipment Quiz

Positive Pressure Ventilation

• Hypoventilation has many causes.
• Apnea can occur during general anesthesia.
• Muscle relaxants can cause apnea.

Pulmonary Toilet

• Used for patients who cannot clear secretions.

Pharmacology

• Can provide a route of administration for certain drugs.

Equipment Required for Intubation

• Bag and mask apparatus (e.g. Laerdal/Ambu)
  • Used to deliver oxygen and manually ventilate.
  • Mask sizes and shapes should be appropriate for the patient's face type and age.
• Pharyngeal airway (nasal and oral types available)
  • Opens airway before intubation.
  • Oropharyngeal airway prevents patient biting on tube.
• Laryngoscope
  • Used to visualize vocal cords.
  • MacIntosh = curved blade (best for adults).
  • Magill/Miller = straight blade (best for children).
• Trachelight
  • An option for difficult airways.
• Fiberoptic scope
  • Used for difficult, complicated intubations.
• Endotracheal tube (ETT)
  • Many different ETT types exist for different indications.
  • ETTs have an inflatable cuff at the tracheal end to provide a seal, allowing positive pressure ventilation and preventing aspiration.
  • Pediatric ETTs do not have a cuff because there is a natural seal at the level of the cricoid cartilage.
  • The size of an ETT is marked by the internal diameter.
    • Adult female: 7.0 to 8.0 mm
    • Adult male: 8.0 to 9.0 mm
    • Child (age in years/4) + 4 or size of child's little finger = approximate ETT size
  • For nasotracheal intubation, the ETT should be 1-2 mm smaller and 5-10 cm longer.
  • An ETT smaller than the predicted size should be available in case the estimate is inaccurate.
• Malleable stylet
  • Available for inserting into the ETT to change the angle of the tip and facilitate the tip entering the larynx.
  • Removed after the ETT passes through the cords.
• Lubricant and local anesthetic
  • Optional.
• Magill forceps
  • Used to manipulate the ETT tip during nasotracheal intubation.
• Suction
  • With pharyngeal rigid suction tip (Yankauer) and tracheal suction catheter.
• Syringe
  • To inflate cuff (10 ml).

Complications of Mechanical Ventilation

• Decreased C02 due to hyperventilation.
• Disconnection from ventilator or failure of ventilator can result in severe hypoxia and hypercarbia.
• Decreased blood pressure (BP) due to reduced venous return from increased intrathoracic pressure.
• Severe alkalemia can develop if chronic hypercarbia is corrected too rapidly.
• Water retention can occur as antidiuretic hormone (ADH) secretion can be elevated in patients on ventilators.
• Pneumonia/bronchitis (nosocomial).
• Pneumothorax.
• Gastrointestinal (GI) bleeds due to stress ulcers.
• Difficulty weaning.

Supplemental Oxygen: Low Flow Systems

• Acceptable if tidal volume is 300-700 mL, RR < 25, and ventilation pattern is steady.
• Nasal canula
  • Low flow system, inspired O2 depends on flow rate and tidal volume.
  • Larger tidal volume, increased RR = lower FIO2.
  • For every increase from 1 L/min O2, inspired O2 concentration increases about 4%.
  • E.g. with normal tidal volume, at 1-6 L/min FIO2 = 24-44%.
• Facial mask
  • Low flow system, well tolerated, will have some rebreathing at normal tidal volumes.
  • Minimize rebreathing by increasing flow rate.

Anaphylactic

• Rare, potentially lethal.
• Occurs in IgA deficient patients with anti-IgA antibodies.
• Immune complexes activate mast cells, basophils, eosinophils, and the complement system.
• Symptoms: Apprehension, urticarial eruptions, dyspnea, hypotension, laryngeal and airway edema, wheezing, chest pain, shock, sudden death.
• Management: Circulatory support with fluids, catecholamines, bronchodilators, respiratory assistance as indicated. Evaluate for IgA deficiency and anti-IgA antibodies. Future transfusions must be free of IgA: washed/deglycerolized RBCs free of IgA, blood from IgA deficient donor.

Transfusion-Related Acute Lung Injury (TRALI)

• A form of noncardiogenic pulmonary edema.
• Occurs 2-4 hours post-transfusion.
• Immunologic cause, not due to fluid overload or cardiac failure - is a reaction to transfusion.
• Symptoms: Respiratory distress - mild dyspnea to severe hypoxia.
• ** Chest X-ray:** consistent with acute pulmonary edema, but pulmonary artery and wedge pressures are not elevated.
• Management: Usually resolves within 48 hours with O2, mechanical ventilation, and supportive treatment.

Immunosuppression

• Some studies show associations between perioperative transfusion and postoperative infection, earlier cancer recurrence, and poorer outcome.

Immune-Hemolytic

• Most serious and life-threatening transfusion reaction.
• Caused by donor incompatibility with the recipient's blood.

Ruptured Abdominal Aortic Aneurysm (AAA)

• and Head Trauma with Increased Intracranial Pressure (ICP)
  • Increased risk of needing airway management (9.4-51%).
• For emergency operations, add the letter E after classification.
• From the history, physical exam, and labs/investigations the anesthetist can determine whether or not the patient is in OPTIMAL condition for the proposed surgical procedure.
• The goal is to optimize non-surgical disease states prior to surgery.
• In emergency cases it is not always possible to optimize coexistent or chronic disease states; the goal is then to accomplish what is possible in the time available.

Postoperative Management

• Usually begins in the O.R. with discontinuation of anesthetic drugs and extubation (exception - if going to ICU).
• Patient can be transported to the post-anesthesia care unit (PACU) once ABC's are stable.
• Patient can be released from the unit when the PACU discharge criteria for ventilation, circulation, consciousness, motor function, and color have been met.
• Potential Complications:
  • CNS: Agitation, delirium, somnolence.
  • Respiratory: Aspiration, upper airway obstruction, hypoxemia, alveolar hypoventilation, upper airway trauma (intubation/extubation).
  • CVS: Hypothermia (rewarm patient), shivering (due to hypothermia or postanesthetic effect), hypotension, hypertension, dysrhythmias.
  • GI: Nausea and vomiting.

Volatile Inhalational Agents

• Halothane, Enflurane, Isoflurane, Sevoflurane
  • Liquid, colorless, non-flammable, non-explosive.
  • Vaporizer delivers controlled concentration of anesthetic agents to the respiratory system of the patient via the anesthetic machine.
• Nitrous Oxide (N2O)
  • Gas, colorless, mild sweet odor at room temperature (stored as liquid under pressure).
  • MAC: 104% (weak anesthetic).
  • Metabolism: 0%.
  • Effects: Second gas effect.
• MAC for all Volatile Agents & N2O:
  • Halothane: 0.75%
  • Enflurane: 1.68%
  • Isoflurane: 1.15%
  • Sevoflurane: 1.15%
  • Nitrous Oxide (N2O): 104% (weak anesthetic)
• Metabolism for all Volatile Agents & N2O:
  • Halothane: 20%
  • Enflurane: 2%
  • Isoflurane: 0.2%
  • Sevoflurane: 0.2%
  • Nitrous Oxide (N2O): 0%
• Effects for all Volatile Agents & N2O:
  • CNS:
    • Volatile agents: Increase cerebral blood flow, decrease cerebral oxygen consumption.
    • N2O: Second gas effect.
  • Resp:
    • Volatile agents: Respiratory depression (decreased tidal volume (TV), increased rate), decreased response to respiratory CO2 reflexes, bronchodilation.
  • CVS:
    • Volatile agents: Myocardial depression, vasodilatation.
  • MSK:
    • Volatile agents: Muscle relaxation, potentiation of other muscle relaxants, uterine relaxation.
• Uses for all Volatile Agents & N2O:
  • Volatile agents: Maintenance of anesthetic state.
  • Nitrous Oxide (N2O): Analgesia, allows for the use of lower doses of more potent anesthetics.
• MACs are additive:
  • E.g. 0.5 MAC of agent A plus 0.5 MAC of agent B will provide a gas mixture with a MAC of 1.0.
• Gas concentrations are often expressed as multiples of MAC:
  • E.g. if an agent has a MAC of 1.5% then 0.5 MAC = 0.75% and 2 MAC = 3.0%.