Pulmonary Alterations and Mechanical Ventilation Overview

Carina

A landmark that the ventilators should end about 2-3 cm above to ensure each lung gets equal volume of inflation.

Pleural Space

The area between the parietal pleura and visceral pleura that contains fluid allowing the lungs to slide during breathing.

Parietal Pleura

Membrane lining the chest wall.

Visceral Pleura

Membrane lining the lung parenchyma.

Pleural Pressure

-5 cm H20 pressure (vacuum pressure) between the pleura that helps keep the lungs from collapsing.

Alveoli

Structures where gas exchange occurs, with walls so thin that only one cell gets through at a time.

Type I Cells

Cells that make up 90% of the alveolar surface area.

Type II Cells

Cells that produce pulmonary surfactants, decreasing surface tension in alveoli.

Pulmonary Surfactants

Substances produced by Type II cells that decrease surface tension in alveoli, making it easier to inflate them.

Ventilation

Movement of air in and out of the lungs, all the way down to the alveolar level and back out.

Perfusion

Movement/flow of blood to the tissues.

Diffusion

Movement of gases across the pulmonary membrane, occurring from an area of high concentration to low concentration.

Alveolar Diffusion Factors

Factors affecting diffusion include surface area, thickness of alveolar capillary membrane, partial pressure of gases, and solubility of the gas.

Solubility of Gas

CO2 diffuses across the alveolar-capillary membrane 20 times faster than O2.

Ventilation/Perfusion (VQ)

The relationship between ventilation and perfusion in the lungs.

Normal Unit

A state where normal ventilation (V) and normal perfusion (Q) are occurring.

Shunt Unit

A state where perfusion is greater than ventilation, causing blood to pass alveolus without gas exchange.

Causes of Shunt Unit

Conditions such as pneumonia, atelectasis, tumor, or mucus plug that lead to perfusion greater than ventilation.

Deadspace Unit

Does not participate in gas exchange

Causes of Deadspace Unit

Pulmonary embolism, Pulmonary infarction

Covid pneumonia acute respiratory distress syndrome

Condition where one lung would be whited out with fluid

Proning

Practice that displaces fluid and increases perfusion to different areas of the lung

Oxygenation vs Ventilation

Oxygen is carried in the blood in two ways: 97% bound to hemoglobin (SaO2) and 3% dissolved in plasma (PaO2)

SaO2

Saturation of arterial blood, measured by ABGs or pulse oximetry

PaO2

Partial pressure of oxygen, only measured with ABGs

Pulse Oximetry (SpO2)

Indirect measurement of hemoglobin saturation, can give false readings

Signs and Symptoms of Hypoxemia

Tachypnea, Hyperventilation, Dyspnea, use of accessory muscles, cool skin, cyanosis, restlessness, confusion, tachycardia

PaCO2

Tells us the patient's ventilation status; adequacy of ventilation is measured by looking at the patient's PaCO2

Hyperventilation

Condition where the PaCO2 is too low, indicating the patient is moving too much air

Hypoventilation

Condition where the PaCO2 is too high, indicating the patient is not moving enough air

End-Tidal CO2 Monitor (Capnography)

Noninvasive monitor that measures the exhaled CO2 of each breath

Signs & Symptoms of Hypercapnia/Hypercarbia

Headache, drowsiness, confusion, seizures, flushed skin

Acid Base Balance

Maintain pH balance compatible with metabolic life, measured through arterial blood gases (ABG)

ABG Normal Values

pH: 7.35-7.45, PaO2: 80-100 mm Hg, SaO2: 93-99%, PaCO2: 35-45 mm Hg, HCO3: 22-26 mEq/L

pH

Normal range is 7.35 - 7.45; < 7.35 = ACIDOSIS; > 7.45 = ALKALOSIS

HCO3-

Bicarbonate, normal is 22-26 mEq/L, regulated by the kidneys

ABG Interpretation Steps

1. Evaluate the pH. 2. Evaluate the pCO2. 3. Evaluate the HCO3-. 4. Determine the primary disorder.

Correction

The process by which the same system that is affected changes to bring pH back to normal resp fixes resp issue.

Compensation

Process by which the other system changes to attempt to bring the pH back to normal- kidneys fix a resp issue.

Primary Disorder Determination

Label pH as A or B; Label CO2 as A or B; Label HCO3 as A or B; If CO2 matches the pH, label as respiratory; If the HCO3 matches the pH, label as metabolic.

Compensation Determination

If the component that does not match your pH is labeled opposite of the primary component, compensation is occurring.

Respiratory Alkalosis

Respiratory alkalosis is partially compensated because the kidneys are trying to return the pH to normal.

Partial Compensation

pH= 7.32 A; CO2 = 50 A; HCO3 = 30 B- high CO2 trying to compensate for the respiratory acidosis.

Full Compensation

pH = 7.36 Normal- slightly acidic; CO2 = 50 A; HCO3 = 33 B; Fully compensated, respiratory acidosis the kidneys are compensating for the high acid.

PaO2 Normal Range

Normal = 80-100; < 80 = hypoxemia; PaO2 < 60 = critical zone- will have major issues.

SaO2 Normal Range

Normal = 93-99%; < 90% = Critical zone.

Alkalemia

↑ pH; Too much HCO3 or Too little CO2.

Acidemia

↓ pH; Too much CO2 or Too little HCO3.

Uncompensated Respiratory Acidosis

pH 7.29 A; CO2 65 A; HCO3 24 N; PaO2 88; SaO2 86.

Partially Compensated Respiratory Acidosis

pH 7.32 A; CO2 60 A; HCO3 30 B; PaO2 78; SaO2 86.

Partially Compensated Metabolic Alkalosis

pH 7.49 B; CO2 48 A; HCO3 38 B; PaO2 88; SaO2 86.

Fully Compensated Metabolic Alkalosis

pH 7.43 N- B; CO2 54 A; HCO3 30 B; PaO2 82; SaO2 86.

Mixed Disorders

pH : 7.25 A; CO2 : 56 A; HCO3 : 15 A; PaO2 : 66 Hypoxemic; SaO2 : 91 low.

Acute Respiratory Failure

A problem of Inadequate gas exchange; Usually occurs secondary to another disorder (like resp failure caused by pneumonia, a tumor, PE, atelectasis).

Oxygen Delivery Methods

GOAL - deliver the least amount necessary.

Nasal Cannula

1-6 L/min - Low flow device delivers 21 - 44% FiO2.

High-Flow Nasal Cannula

1-60 L/min - High flow device delivers 21-100% FiO2.

Face Mask

(40-60% or 5-10 L/min).

Venturi Mask

(25-60% or 4-15 L/min) (AKA Venti mask).

Nonrebreather

(85-95% or 10-15 L/min).

Non-Invasive Ventilation (NIV)

Uses a mask that fits tightly over the mouth and nose, or just the nose (nasal pillows).

BiPAP

Positive pressure on both inspiration AND expiration; inspiratory and expiratory pressures are different.

IPAP

Inspiratory positive airway pressure - a bump on inspiration to get more tidal volume to breathe in and exhale deeply to breathe off CO2.

EPAP

Expiratory positive airway pressure - helps maintain alveoli pressure, keeps them open, and helps recruit more to assist with ventilation and oxygenation.

CPAP

Continuous Positive Airway Pressure; inspiratory pressure and expiratory pressure is the same.

V60

A bipap that uses FiO2 up to 100%.

Airway protection

Ensuring patients are alert enough to prevent silent aspiration and manage vomiting to avoid aspiration pneumonia.

Nutrition & Hydration

Breathing takes precedence over eating; patients are usually NPO or have an NG tube.

Oral care

To decrease bacteria and keep it out of the lungs.

Skin care

To prevent pressure ulcers from mask suction; Mepelex can be used on the nose.

Communication

Will be muffled; consider writing or other methods to communicate.

Endotracheal Tubes (ETT)

A tube placed in the trachea between vocal cords, preventing speech.

Intubation

The process of placing a tube in the trachea for ventilation.

ETCO2 monitor

A device that indicates correct placement of the tube by color change (purple to yellow).

Coughing

Indicates the need for suctioning or inappropriate tube placement.

Nursing Interventions for Intubation

Ensure equipment is ready, monitor vital signs, and administer medications as directed.

Mechanical Ventilation Goals

Improve ventilation, decrease work of breathing, correct inadequate breathing patterns, and improve oxygenation.

Ventilator settings

Settings that affect the amount of air moved in and out of the lungs.

Tidal Volume (VT)

The size of each breath; larger in = large out.

Rate (f)

The number of breaths per minute; easiest to change based on a patient's body weight.

Assist Control (AC)

A mode that assists or controls breaths; delivers a preset tidal volume at a preset rate.

Synchronized Intermittent Mandatory Ventilation (SIMV)

A mode that allows for both mandatory and spontaneous breaths.

Pressure Support Ventilation (PSV)

A mode that provides support during spontaneous breaths.

Assist Control

Negative deflection, triggering assisted breath.

Synchronized Intermittent Mandatory Ventilation (SIMV/IMV)

Ventilator delivers a preset volume at a preset rate that is a minimum. In between mandatory breaths, the patient can breathe spontaneously, with a pressure-supported breath.

Advantages of SIMV

Helps keep respiratory muscles active and coordinated and can be used as a weaning mode.

Pressure Support (PSV)

When on IMV or Spontaneous breathing trial, this 'boost' from the ventilator increases spontaneous breath volume and makes it easier for the patient to inspire.

Settings that Affect Oxygenation

Settings that affect oxygenation are those that increase the uptake of oxygen at the alveolar/capillary level.

FiO2 (Fraction of Inspired Oxygen)

The percentage of oxygen delivered via the ventilator, ranging from 30-100%.

Positive End Expiratory Pressure (PEEP)

Positive pressure applied at the end of expiration of ventilator breaths, increases oxygenation by preventing collapse of alveoli.

Complications of PEEP

Hemodynamic compromise due to decreased venous return, and volutrauma or barotrauma along the thin capillary membrane.

PEEP

The amount of pressure remaining in the lung at the END of the expiratory phase.

What is the percent of oxygen in room air?

Around 21%.

If a patient is at 100% FiO2, what can PEEP do?

PEEP can help recruit more alveoli and open collapsed alveoli for improved oxygenation.

Increase FiO2

Increase oxygen to correct elevated PaCO2.

Increase PEEP

Recruit more alveoli to correct elevated PaCO2.

Decrease TV

Lower volume of breath to correct elevated PaCO2.

Increase rate

Faster breathing to blow off more CO2.

Patient stops breathing

They will still receive the preset volume at the preset rate.

Weaning modality

Pressure support is used to see what the patient can do without maximum ventilator support before Extubation.