Final Kopp 6/22 Comprehensive Study Guide

Ventilatory Calculation Foundations

• Minute Ventilation ($V_E$):

  • Formula: $V_E = RR \times V_T$

  • Units: Typically expressed in liters per minute ($L/min$).

  • Conversion: To calculate from liters to milliliters, multiply by 1,000 (e.g., $15.3\,L/min = 15,300\,mL/min$).

• Calculating Tidal Volume ($V_T$) from Minute Ventilation:

  • Example: If $V_E = 15.3\,L/min$ and Respiratory Rate ($RR$) = 20.

  • Step 1: Convert $V_E$ to milliliters: $15.3 \times 1,000 = 15,300\,mL/min$.

  • Step 2: Divide by the rate: $\frac{15,300}{20} = 765\,mL$ (Note: Transcript mentions a simplified 750 estimate during calculation).

• Calculating Respiratory Rate ($RR$) from Minute Ventilation:

  • If $V_E = 15\,L/min$ ($15,000\,mL/min$) and $V_T = 750\,mL$, then $\frac{15,000}{750} = 20\,b/min$.

• Static Compliance ($C_{stat}$):

  • It is essential to know how to calculate static compliance for assessment.

Ventilator Timing and Cycle Parameters

• Key Timing Components:

  • Total Cycle Time (TCT).

  • Inspiratory Time ($T_I$).

  • Expiratory Time ($T_E$).

  • I:E Ratio.

• Measurement Thresholds:

  • Normal adult inspiratory time is approximately $1.0\,second$.

  • The acceptable range for adult $T_I$ is generally between $0.7\,seconds$ and $1.2\,seconds$.

  • A $T_I$ below $0.6\,seconds$ is usually insufficient to fill the lungs in an adult.

• Clinical Application:

  • Timing parameters on the ventilator are set based on the set rate.

  • In spontaneously breathing patients, these parameters fluctuate constantly and would "jump all over the place" if charted manually.

Modes of Mechanical Ventilation

• Three Main Modes:

  • Controller / CMV (Continuous Mandatory Ventilation): Full support.

  • SIMV (Synchronized Intermittent Mandatory Ventilation): Partial support with spontaneous breathing opportunities.

  • Spontaneous / CPAP: No mandatory breaths; the patient initiates everything.

• Hybrid Modes:

  • Examples include PRVC (Pressure Regulated Volume Control) and VC+.

  • These are pressure-based breaths that target a specific tidal volume.

  • The patient can get as much flow as they want and can change flow during the breath.

Volume Control vs. Pressure Control Delivery

• Volume Control (VC):

  • Advantage: Guarantees a set minute ventilation ($V_E$). You know exactly how many milliliters and liters the patient is receiving.

  • Disadvantage: Fixed flow. It is the most common mode for patient-ventilator dyssynchrony because patients cannot control the flow rate.

• Pressure Control (PC):

  • Advantage: Better synchrony due to decelerating flow; the patient can control the flow speed.

  • Disadvantage: Changes in lung compliance or resistance will change the tidal volume, meaning minute ventilation is not guaranteed.

• Clinical Preference: Most patients remain in Volume Control because clinicians are accustomed to managing $P_aCO_2$ by adjusting specific volumes.

Emergency Management and Clinical Procedures

• Emergency Response (The "Crashing" Patient):

  • If the ventilator and monitors are all alarming in a chaotic situation (e.g., patient crashing in the ICU):

    1. Protect the airway immediately.

    2. Disconnect the patient from the ventilator and begin manual ventilation (bagging the patient).

    3. Silence the alarms.

    4. Calm the environment down to figure out the cause (e.g., disconnect, leak, or ventilator failure).

• Airway Protection: Bagging allows the clinician to determine if the issue is patient-related or ventilator-related; sometimes ventilators do fail and must be replaced.

CPAP and Non-Invasive Ventilation

• CPAP (Continuous Positive Airway Pressure):

  • Primary use: Lung recruitment and oxygenation.

  • It does NOT help the patient ventilate ($CO_2$ removal).

  • Appropriate patient: A 22-year-old post-op patient with mild atelectasis who is otherwise ventilating well.

  • Drawbacks: It can be hard to exhale against; patients often feel uncomfortable.

• BiPAP/Two-Level:

  • Used in the hospital setting to provide ventilatory assistance alongside oxygenation.

  • Often used in EMS for pulmonary edema, though they may use CPAP devices initially.

Respiratory Failure Classifications

• Type 1: Hypoxemic Respiratory Failure:

  • Characterized by a large A-a gradient.

  • Example: A patient on $60\%$ oxygen ($F_IO_2 = 0.60$) should have a calculated $P_AO_2$ around $280\,mmHg$. If their blood oxygen ($P_aO_2$) is only $80\,mmHg$, they are in hypoxemic failure.

• Type 2: Hypercapnic Respiratory Failure:

  • Characterized by a P_aCO_2 > 45\,mmHg.

• Type 3: Chronic Respiratory Failure:

  • Typical of COPD patients.

Specialized Ventilation Strategies

• APRV (Airway Pressure Release Ventilation):

  • Uses a very prolonged inspiratory time ($T_{high}$) and very short expiratory times ($T_{low}$).

• High Frequency Oscillation (HFO):

  • Uses rapid pulses measured in Hertz ($Hz$).

  • $1\,Hz = 60\,cycles/minute$.

  • Example: A setting of $5\,Hz$ equals $300\,breaths/minute$.

• HFJV (High Frequency Jet Ventilation):

  • Uses high-frequency pulses for ventilation.

Triggering and Cycling Mechanisms

• Triggering (Starts the breath):

  • Pressure Trigger: Patient must generate negative pressure (e.g., $-1$ or $-2\,cmH_2O$) from the baseline to start the breath.

  • Flow Trigger: Patient must deflect a set amount of the bias flow (e.g., $2\,L/min$).

  • Time Trigger: If the patient doesn't breathe, the ventilator starts the breath based on the set rate (e.g., every $6\,seconds$ for a rate of 10).

• Cycling (Ends the breath):

  • Volume Cycling: Breath ends when the set tidal volume is reached (common in VC).

  • Time Cycling: Breath ends when the set inspiratory time is reached (common in PC).

  • Flow Cycling: Breath ends when the inspiratory flow drops to a certain percentage of the peak flow (e.g., $20\%$ or $25\%$). This is used in spontaneous/pressure support breaths.

Sensitivity, Leaks, and Auto-PEEP

• Pressure Triggering with PEEP:

  • If PEEP is set at $5\,cmH_2O$ and sensitivity is $-2\,cmH_2O$, the ventilator triggers when it senses a drop to $3\,cmH_2O$.

• Auto-PEEP Impact:

  • Auto-PEEP makes triggering harder. If a patient has Auto-PEEP, they must pull against that internal pressure PLUS the ventilator sensitivity to trigger a breath.

  • This increases the Work of Breathing ($WOB$).

• Auto-Triggering:

  • Often caused by leaks. In flow triggering, if there is a leak, the ventilator thinks the escaping flow is the patient taking a breath and triggers continuously.

  • Correction: In flow triggering, increase the trigger value (e.g., from $2\,L/min$ to $5\,L/min$) to compensate for the leak.

Clinical Adjustments and Patient Data

• Fever: Spiking a fever increases $CO_2$ production, which typically requires an increase in the ventilator rate to maintain normal $P_aCO_2$.

• PFTs (Pulmonary Function Tests):

  • Obstructive diseases are characterized by an $FEV_1/FVC$ ratio lower than normal.

  • The theoretical threshold is $80\%$, but it is clinically significant when it falls below $70\% - 75\%$.

• Mean Airway Pressure ($P_{mean}$):

  • Average pressure in the chest over the entire cycle.

  • Increasing inspiratory time ($T_I$) will increase $P_{mean}$.

  • The most effective way to increase $P_{mean}$ is to increase PEEP.

• Optimal PEEP Titration:

  • You must find the "sweet spot" where compliance is maximized and oxygenation is improved without dropping the Cardiac Output ($CO$) or Blood Pressure ($BP$).

Case Studies and Scenarios

• Tidal Volume Selection:

  • Standard selection: $6$ to $8\,mL/kg$ of Ideal Body Weight ($IBW$).

  • Lung Protection strategy: $4$ to $6\,mL/kg$ of $IBW$.

• COPD and Asthma:

  • Primary concern is avoiding Auto-PEEP (intrinsic PEEP).

• Laryngectomy Patients:

  • Tobacco use is the most common history for patients with total laryngectomy, though rare cancers can also be a cause.

  • These patients may use vibratory devices to speak.

• Alcohol Related Issues:

  • Chronic alcohol use is associated with high fall risks and frequent aspiration pneumonia due to passing out and vomiting.

Questions & Discussion

• Question: What if the patient spikes a fever?

• Response: $CO_2$ production goes up. You likely have to increase the rate on the ventilator because $P_aCO_2$ will rise.

• Question: What if I am in flow triggering and have a leak I can’t fix?

• Response: The ventilator will auto-trigger. To fix it, you go up on the flow trigger setting (making it less sensitive) until it covers the leak amount.

• Question: What is the best way to increase Mean Airway Pressure?

• Response: PEEP.

• Question: How many Hertz is 300 breaths per minute?

• Response: 5 Hertz ($5 \times 60 = 300$).

• Question: What is the normal rate for a healthy person on a vent?

• Response: 12 to 18 (or 20) breaths per minute.