3-24-26 kopp pt 2

The discussion revolves around the mechanisms of breath delivery in ventilators, particularly focusing on triggering mechanisms to facilitate patient breathing.

Important factors include volume and pressure.
- Volume refers to the amount of air delivered per breath (e.g., 500 cc).
- Pressure involves the force needed to deliver this air.

Triggering: How the ventilator knows when to deliver a breath, which can occur through three main methods:
1. Time-triggered: Based on a set respiratory rate.
2. Pressure-triggered: Based on the patient’s effort to inhale.
3. Flow-triggered: Detects patient’s sudden demand for a breath based on flow changes.

Definition: The ventilator cycles on at specified intervals depending on the respiratory rate set.
Example: For a rate of 10 breaths per minute:
- $ext{Time per breath} = rac{60}{ ext{Rate}} = rac{60}{10} = 6 ext{ seconds}$
If the rate was increased to 15:
- $ext{Time per breath} = rac{60}{15} = 4 ext{ seconds}$
Increasing the rate affects the I:E (Inspiratory to Expiratory) ratio.

Normal I:E Ratio: Typically 1:2 or 1:3.
When respiratory rates increase, this may decrease time available for expiration.
If set to 10 breaths/minute, with an I:E ratio of 1:2,
- Inspiratory time (I time) could be set at 1 second, leading to:
- $ext{Total cycle time} = 6 ext{ seconds}$
- Expiratory time (E time) would be 5 seconds to maintain balance: $I:E = 1:5$

Pressure Triggering:
- Constant monitoring of pressure. Standard sensitivity is negative two centimeters of water pressure (cmH2O).
- The patient must generate enough negative pressure, pulling down from baseline to trigger breath delivery.
- Example: If PEEP is 5 cmH2O, baseline pressure is adjusted based on patient effort.
Flow Triggering:
- More commonly used. The ventilator senses changes in the flow of gas within the circuit.
- When patient initiates a breath, the flow decreases from a set bias flow (e.g., 5 liters/min).
- This allowed flexible response to patient demand, minimizing the risk of auto-triggering.

Example Settings:
- Time-triggering: Set to 10 yields cycle every 6 seconds.
- Pressure-triggering: Adjust sensitivity to avoid auto-triggering.
- Flow-triggering: Commonly set at 3 liters/min.

Higher cycling rates lead to compromise of expulsion time, potentially resulting in air trapping especially in obstructive lung diseases.

Peak Inspiratory Pressure (PIP):
- The maximum pressure during expiration. Normal should not exceed 40 cmH2O.
- Affected by circuit resistance and secretions.
Plateau Pressure:
- Measured using an inspiratory hold maneuver.
Dynamic Compliance (C_dyn) and Static Compliance (C_st) relate to lung properties and should be monitored regularly.

Measurement of what volume is exhaled can indicate functional performance of ventilator settings.
Differences between delivered versus exhaled tidal volumes give insight into ventilator performance.
- E.g., Setting 500 cc but exhaling 485 cc may be acceptable due to minor leaks.

Essential for determining the rate of delivery and ensuring adequate I:E ratio.
Adjustments to flow directly affect the inspiratory times.
- The formula for total cycle time is based on the rate set.

Importance of maintaining ventilator circuits and associated components (e.g., HMEs) to prevent infection and ensure performance.
Daily checks for cleanliness, connections, and functionality should occur with regular monitoring of compliance.

Understanding ventilation requires knowledge of dynamic and static changes in compliance and pressure.
Continuous learning through clinical practice and additional resources (like YouTube channels related to respiratory therapy) is encouraged as well as familiarity with various machines and their functions.