Respiratory Monitoring

anatomic dead space

conducting airways where gas exchange naturally does not occur

alveolar dead space

alveoli that are ventilated but inadequately perfused so gas exchange does not occur

physiologic dead space

combination of anatomic and alveolar dead space

gas diffusion formula

(SA x diffusion coefficient x partial-pressure gradient) / membrane thickness

bronchial circulation

Normal anatomic shunt. Arteries branch off aorta to supply conducting airways, veins drain some venous blood into pulmonary veins.

pulmonary vascular resistance

resistance to blood flow through pulmonary circulation. usually due to change in diameter of pulmonary vasculature. Normal = less than or equal to 2 Wood units.

Factors that increase PVR

Hypoxemia, hypercapnia, acidemia, atelectasis, mechanical ventilation

Factors that decrease PVR

High O2, Low CO2, pulmonary vasodilation, nitric oxide, prostacyclin analogues

oxygen content formula (CaO2)

(1.36 ml O2/g Hgb x #g Hgb x SaO2) + (0.0031 x PaO2). How many seats are taken + how long is the line. Normal = 17-20 ml/100 ml blood

DO2

CO x CaO2 x 10 = ml O2/min

DO2i

CI x CaO2 × 10 = ml O2/min

oxygen consumption formula (VO2)

CO x 10 x Hgb x 1.36 x (SaO2 - SvO2). How much O2 was delivered and how much went missing.

factors that increase VO2

Fever, shivering, seizures, agitation, exercise, catecholamine response

factors that decrease VO2

anesthesia, muscular paralysis, hypothermia

hypoxia

low oxygen delivery to tissues

hypoxemia

low oxygen level in blood

paroxysmal nocturnal dyspnea

Sudden SOB awaking from sleep after lying down. Associated with L sided HF where blood volume backs up in lungs causing pulmonary edema

P/F ratio

PaO2/FiO2. Ideal is a high ratio - 476. <300 may mean ARDS, need for ECMO

A-a oxygen gradient

Alveolar pO2 - PaO2. Assesses efficiency of diffusion/gas exchange from alveoli to arterial blood. Elevated = V/Q mismatch, RL shunt

Cor Pulmonale

Enlargement of RV due to pulmonary disease (high PVR). Blood backs up in venous system causing generalized edema

forced vital capacity (FVC)

Max volume forcibly exhaled after max inhalation

Functional expiratory volume 1 (FEV1)

Volume exhaled during first second of forced expiratory maneuver (FVC)

FEV1/FVC ratio

Percentage of FVC exhaled in first second. V - 1st second/ V - total moved

peak expiratory flow (PEF)

maximum flow rate achieved during forced expiration after full inspiration

Tidal volume (TV)

Volume moved per breath

p50

PaO2 level when SaO2 (Hgb saturation) is at 50%. Generally 26-27 mmHg.

PaCO2

Reflects ventilation

PaO2 & SaO2

Reflect oxygenation

FiO2

Fraction of inspired O2 within the gas mixture. Room air = 21%, supplemental increases it above that level.

PaO2/FiO2 ratio

Describes arterial oxygenation across different FiO2 levels. Ideal = 476, <300 may indicate ARDS and need for ECMO. Lower ratio indicates more severe hypoxemia.

Hgb-oxygen dissociation curve

Shows the level of Hgb-oxygen binding in the blood under different conditions. Shift left = tighter O2-Hgb binding, shift right = easier O2 unloading.

Shifts Hgb-oxygen dissociation curve left

Increased pH, decreased CO2, decreased 2,3 DPG, decreased temp

Shifts Hgb-oxygen dissociation curve right

Decreased pH, increased CO2, increased 2,3 DPG, increased temp

2,3 DPG

Medication given to facilitate greater oxygen delivery to tissues by stabilizing deoxy-Hgb. This increases PaO2 and shifts the curve to the right

compliance

Ability of lungs to stretch and expand during inhale. Decreased in restrictive pulmonary disease.

Normal PVR

About 2 Wood units or 20-120 dynes x s x cm^-5

external respiration

Gas exchange between alveoli and pulmonary capillary blood

internal respiration

Gas exchange between systemic capillaries and tissue cells

gas exchange events for cellular respiration

ventilation, pulmonary diffusion, transport/perfusion, tissue diffusion

ventilation

Movement of air into and out of alveoli

Pulmonary diffusion

O2 moves from alveoli to pulmonary capillary blood. CO2 moves from blood to alveoli

transport/perfusion

Circulating blood transports O2 from lungs to systemic tissues and returns CO2 to the lungs

tissue diffusion

O2 moves from systemic capillary blood to body cells, CO2 moves from body cells to blood

Cellular respiration

Use of O2 for aerobic ATP production within body cells via electron transport chain and the Krebs cycle

conducting zone

Passage for air to and from gas exchange regions via ventilation. Includes upper airways, trachea, bronchi, bronchioles, terminal bronchioles

respiratory zone

Primary site of pulmonary gas exchange. Includes respiratory bronchioles, alveolar ducts, alveoli.

byproducts of aerobic metabolism

CO2 & H2O

byproducts of anaerobic metabolism

Lactate, pyruvate, CO2

Peripheral chemoreceptors

Located in carotid bodies and aortic arch, respond to decreased PaO2 and changes in PaCO2/pH.

Pons and medulla

Generate and modulate respiratory rhythm in response to peripheral chemoreceptors. Increased H+ (low pH) and PaCO2 increase RR.

phrenic nerve

Drives contraction of diaphragm, the primary muscle in ventilation. Can be damaged in LIMA harvest, esp in peds

hemoptysis

Coughing up sputum containing blood. Old = clots, new = pink/red streaks. Symptom of pulmonary embolism, edema, severe hypertension, tumors, chronic bronchitis, PA catheter trauma.

dyspnea causes

asthma, bronchoconstriction, ARDS, pulmonary edema, atelectasis, hypoxemia or hypercapnia, pneumothorax

pulmonary edema

Fluid accumulation in alveoli caused by increased pulmonary pressure, usually due to congestive heart failure. Decreases gas diffusion by increasing membrane thickness

percussion

Evaluating sounds from tapping the chest wall to assess the density or consistency of the lungs

pulmonary function test (PFT)

Multiple studies, mainly spirometry, that provide insight into underlying pathology by comparing measured values. Percentage of predicted normal grades severity of abnormality.

total lung capacity (TLC)

Max volume of air the lungs can hold after max inhale

Diffusing capacity of lung for carbon monoxide (DLCO)

Measures gas transfer across alveolar-capillary membrane. Normal in asthma, low in emphysema (reduced SA)

factors affecting ventilation

alveolar pO2, CO2 production, RR, tidal volume, dead space

factors affecting oxygenation

FiO2, V/Q, shunt, diffusion, Hgb

hypercapnia

PaCO2 > 45 mmHg

cyanosis

diffuse bluish discoloration of skin, nail beds, and mucous membranes. central or peripheral

central cyanosis

Occurs when LV-ejected blood is deoxygenated

peripheral cyanosis

Occurs when LV-ejected blood is O2-rich but desaturates in vascular beds due to stagnation

abnormal breath sounds

crackles, wheezes, rhonchi, stridor, pleural friction rub

regional breath sounds

tracheal, bronchial, bronchovesicular (near sternum & scapulae), vesicular (peripheral)

restrictive pulmonary disease

Reduced TLC & FVC with normal or high FEV1/FVC. Capacity and compliance are reduced rather than air movement itself. Eg. pulmonary fibrosis, pneumonia, pleural disease, neuromuscular disorders

obstructive pulmonary disease

Reduced FEV1 & FEV1/FVC. Airflow limitation with normal capacity & compliance. RV/TLC may increase from air trapping. Eg. asthma, COPD, ephysema, bronchiectasis

flow volume graph

Restrictive = decreased volume (squished), Obstructive = decreased expiratory flow (PEF, FEF & FEV1)

FEV1 & FVC % predicted

>70 = mild, 60-69 = moderate, 50-59 = moderate-severe, 35-49 = severe, <35 = very severe

TLC % predicted

>80 = mild, 60-79 = moderate, 50-59 = moderate-severe, 35-49 = severe, <35 = very severe