Mechanical Ventilation Introduction and Management Flashcards

Introduction to Mechanical Ventilation Seminar

• Seminar Focus: The primary focus of the clinical seminar has been mechanical ventilation. The goal is for students to feel more confident and prepared for the workforce than they did at the start of the summer (April/May).

• Clinical Competency: A good clinician should be able to identify ventilator-related issues that even a preceptor might overlook.

• Examination Scope: The upcoming test will focus heavily on mechanical ventilation. However, it will be a cumulative "know a little about a lot" assessment, potentially including Pulmonary Function Test (PFT) questions.

Cardiopulmonary Effects of Mechanical Ventilation

• Impact on the Heart: Mechanical ventilation exerts positive pressure in the thoracic cavity, which puts pressure on the heart.

• Decreased Venous Return: This pressure makes the heart harder to fill, leading to decreased venous return (less blood returning to the right side of the heart). This is a major concern when managing ventilated patients.

• Lung Overdistention: Clinicians must monitor ventilator pressures carefully to avoid overdistention, which causes additional lung damage.

• Mean Arterial Pressure (MAP): It is critical to balance ventilator pressures (like PEEP) with the patient's arterial pressure to ensure the heart is not overly compressed.

Hemodynamic Management and Support

• Managing High PEEP and Dropping Blood Pressure: If high PEEP is necessary for failing lungs but causes blood pressure to drop, clinicians typically do not turn down the PEEP. Instead, they support the blood pressure using fluid or medication.

• Fluid Resuscitation / Fluid Challenge:

  • Fluid Resuscitation: Administering a large volume, such as $1\,liter$ of saline, very quickly to a patient with low volume.

  • Fluid Challenge: Administering smaller increments, typically $500\,mL$ of saline at a time, to see if blood pressure responds. If it rises, the patient was likely hypovolemic.

• Blood Pressure Support Medications (Vasopressors): These medications cause peripheral vasoconstriction to shunt more blood to the heart. Examples include:

  • Dopamine

  • Dobutamine

  • Levophed (Norepinephrine)

• Patient Positioning for Low Blood Pressure:

  • Flat Position: Laying the patient flat can help with low blood pressure.

  • Trendelenburg Position: If the blood pressure is extremely low (e.g., a systolic of $60$), the head of the bed is lowered below the feet.

  • Note on Bed Controls: Students should practice using bed controls in empty ICU rooms to become proficient in moving a patient to the flat or Trendelenburg position quickly during emergencies (precodes).

Initiating and Adjusting Ventilator Settings

• Initial Setup Strategy: When a physician allows a Respiratory Therapist (RT) to choose settings (common in collaborative hospital environments), the RT must use specific clinical tools.

• Ideal Body Weight (IBW): This is the essential metric for determining appropriate tidal volume ($V_T$).

• Tidal Volume Targets ($ml/kg$):

  • Normal/Healthy Range: $6-8\,mL/kg$.

  • Healthy Post-Op Patient: For a patient with healthy lungs (e.g., a $35$-year-old post-abdominal surgery), aim for the higher end of the range, specifically $8\,mL/kg$.

• Initial Mode Selection: Volume Control (VC) or Assist Control (AC) is preferred for a patient coming out of surgery who is still under the effects of anesthesia.

• Oxygenation ($F_iO_2$):

  • Patients are often transported from the OR on $100\%$ oxygen.

  • Once stabilized, the goal is to titrate down quickly. A common initial drop is from $100\%$ to $60\%$.

  • The standard hospital goal for weaning is often $40\%$. If a patient can be oxygenated at $40\%$, they can likely be managed with a regular mask (venti mask, aerosol mask, or large volume nebulizer) after extubation.

  • Extubating at $60\%$ or higher requires high-flow devices or non-rebreathers.

• Standard Starting Parameters (Healthy Adult Example):

  • Tidal Volume ($V_T$): Approximately $450\,mL$ (based on IBW).

  • Respiratory Rate ($f$): $12-16\,breaths/min$.

  • Oxygen Concentration ($F_iO_2$): $40\%$.

  • Positive End-Expiratory Pressure (PEEP): $5\,cmH_2O$ (widely considered the standard minimum).

Ventilator Liberation and Weaning Criteria

• Terminology: While clinicians often say "weaning," the board exams and clinical tests may use the term "liberation."

• Spontaneous Mode Transition: Once the patient is awake and following commands, move them to a spontaneous mode with Pressure Support (PS).

• Setting Pressure Support: PS helps augment tidal volume. In an adult, the goal is to achieve spontaneous exhaled tidal volumes of at least $250-300\,mL$.

• Rapid Shallow Breathing Index (RSBI):

  • Formula: $f/V_T$ (Frequency divided by Tidal Volume in liters).

  • Acceptable Threshold: Less than $100-105$.

• Negative Inspiratory Force (NIF):

  • Measures the strength of respiratory muscles.

  • Indicates the patient's ability to cough and clear secretions (the #1 reason for re-intubation).

  • Acceptable Threshold: More negative than $-20\,cmH_2O$ (e.g., $-30\,cmH_2O$ or $-40\,cmH_2O$).

• Forced Vital Capacity (FVC):

  • Technique: The patient is placed in spontaneous CPAP; PS is removed while PEEP is maintained. The patient is coached to take the biggest breath possible and blow it all out.

  • Acceptable Threshold: $10-15\,mL/kg$.

Advanced Weaning Techniques and Tube Compensation

• Work of Breathing (WOB): Pressure Support is used to overcome the resistance of the endotracheal tube (ETT).

• Minimal Settings: Often referred to as "Five and Five" ($5\,cmH_2O$ PEEP and $5\,cmH_2O$ PS).

• ZEEP Trial: "Zero PEEP." Some facilities use a setting of $0$ PEEP and $0$ PS to challenge the patient. Passing this suggests a high likelihood of successful extubation.

• Tube Compensation: A ventilator setting available on Drager and Puritan Bennett (PB) models.

  • Instead of a static PS of $5$, the RT inputs the ETT size (e.g., $8.0$).

  • The ventilator calculates the known resistance and adjusts pressure dynamically to make it feel as if the patient is breathing through their natural airway at the end of the tube.

Airway Management, Cuff Care, and Extubation

• Cuff Leak Test: Should be performed prior to extubation to check for airway swelling.

• Stridor: Defined as a high-pitched inspiratory sound. It results from swelling or spasm after the tube is removed. Tests may describe the sound rather than using the word "stridor."

• Cuff Pressure Monitoring:

  • Acceptable Range: $25-30\,cmH_2O$ (or $20-30\,cmH_2O$ in some settings).

  • High pressure compress tracheal capillaries; low pressure allows oral secretions to enter the lungs, causing Ventilator-Associated Pneumonia (VAP).

• Cuff Inflation Techniques:

  • Minimal Leak Technique (MLT): Withdrawing air until a small leak is heard at peak inspiration, then adding a small amount back.

  • Minimal Occlusive Volume (MOV): Inflating just until the leak stops.

• Tools: Manometers (e.g., the Posey cuffylator or plastic manometers at Wellington) used to measure pressure accurately. Plastic manometers are intended for single-patient use.

Clinical Lab Competencies and Regulatory Standards

• Blood Gas (ABG) Analysis:

  • Requires annual competency with a lab supervisor.

  • Pre-analytical Errors: Avoiding air bubbles in the syringe and ensuring proper calibration.

  • Infection Control: Gloves must be worn during draws and machine operation but should not be worn in hospital hallways while transporting samples.

• Joint Commission (JACHO): Known for conducting surveys between June and August. Focus areas include:

  • Prohibiting gel nails (observed at Palms West).

  • Monitoring if MDIs are administered by RTs rather than RNs.

  • Checking for expired items and hallway obstructions (stretchers).

Questions & Discussion

• Question: What is the first thing you think of regarding the effect of mechanical ventilation on the heart?

• Response (Mary): It decreases venous return because the pressure makes the heart harder to fill.

• Question: What was that blood pressure medication? Versed?

• Response: No, Versed is a sedative. Medications that support blood pressure (vasopressors) include Dopamine, Dobutamine, or Levophed (Norepinephrine). You will study these extensively next semester.

• Question: How do you perform an FVC on a ventilator?

• Response: Some vents have a dedicated button that removes support for one breath. Otherwise, put the patient in spontaneous mode, remove pressure support, and coach them through a deep breath and full exhalation.

• Question: Should students run blood gases?

• Response: Technically, no. In the eyes of regulatory bodies like the Joint Commission, every person running the machine must have a documented annual competency to ensure the results (which guide medical care) are accurate.