Gas exchange & oxygenation

The airways

Air in

• Right lung: 3 lobes. Left lung: 2 lobes (the left is smaller to make room for the heart).
• Each lung sits inside the pleura, a double layer: the visceral pleura covers the lung and the parietal pleura lines the chest wall. A thin film of pleural fluid between them lets the lung glide as it expands. Air, blood or fluid collecting in that space keeps the lung from expanding (see chest tubes).
• The diaphragm (the dome-shaped muscle under the lungs) and the intercostal muscles between the ribs do the work of breathing.

The nervous system and the airways

The airways are wrapped in smooth muscle, and both branches of the autonomic nervous system control it.

The heart and the two circulations

The heart has four chambers. The right side pumps blood that has given up its oxygen to the lungs (pulmonary circulation). The left side pumps freshly oxygenated blood to the rest of the body (systemic circulation). The left ventricle has the thickest wall because it alone pushes blood out to the whole body.

Blood through the heart and lungs

• The pulmonary artery is the one artery that carries low-oxygen blood (to the lungs). The pulmonary veins are the veins that carry oxygen-rich blood (back to the left atrium).
• The heart muscle itself needs a constant oxygen supply. Myocardial blood flow is the blood (through the coronary arteries) that feeds the heart muscle so it can keep pumping.
• Diastole: the ventricles relax and fill (the mitral and tricuspid valves are open). Systole: the ventricles contract and eject blood (the aortic and pulmonic valves open).
• S1 ("lub") is the mitral and tricuspid valves closing as systole starts. S2 ("dub") is the aortic and pulmonic valves closing as systole ends.

Diagnostic tests

Three words to keep apart

Gas exchange needs all three: air has to reach the alveoli, blood has to reach the capillaries next to them, and the gases have to cross. Once in the blood, oxygen rides on the hemoglobin inside red blood cells.

Breathing in and out

• Surfactant, a substance made in the lungs, lowers surface tension so the alveoli don't collapse at the end of each breath out.
• In a normal breathing pattern, exhalation takes longer than inhalation (about twice as long).

What controls breathing

• The respiratory center in the brainstem (medulla) sets the rate and depth.
• Chemoreceptors sense the blood's CO2 (carbon dioxide) and O2 (oxygen): central ones in the medulla, peripheral ones in the carotid arteries and the aortic arch.
• CO2 is the main trigger to breathe. When CO2 rises, breathing speeds up and deepens to blow it off. Fever and exercise raise the body's demand, so rate and depth go up.
• Normal adult respiratory rate at rest: 12 to 20 breaths per minute.

How well the lungs move air

Lung volumes

Cardiac output Key point

Cardiac output (CO) is the amount of blood the left ventricle pumps in 1 minute. A healthy adult at rest pumps about 3 to 6 L/min.

• If either number drops too far, CO drops. A very fast heart rate shortens filling time, so each beat ejects less (SV falls). A very slow rate gives fewer beats per minute. Either way, cardiac output can fall.

What sets stroke volume

The Frank-Starling mechanism: the more the ventricle is stretched by the blood filling it, the harder it contracts and the more it ejects (up to a point).

The conduction system Key point

The electrical path of each beat

• The SA (sinoatrial) node is the heart's natural pacemaker; it starts every normal beat.
• The AV (atrioventricular) node briefly holds the signal so the atria can finish emptying into the ventricles.
• The bundle of His carries the signal down to the bundle branches and Purkinje fibers, which make the ventricles contract.
• A beat that follows this path at a normal rate is normal sinus rhythm.

Risk factors

• History: the client's own and family history, all medications (prescription, OTC (over the counter), herbal, recreational), tobacco and alcohol use, home and work environment, recent travel. Ask teens about vaping too.
• For smoking, ask how much per day and for how many years. Quitting cuts the risk of heart disease substantially, and the benefit keeps growing each year without nicotine.
• Weigh the client in the morning after voiding. A sudden weight gain can mean fluid retention from heart failure.

The physical exam

• Jugular vein distention (JVD) reflects pressure and volume on the right side of the heart. Recline the client to 30° to 45°, face turned a little to the opposite side, and look for the top of the pulsation; a column of pulsation higher than about 1.5 in (4 cm) is abnormal and points to increased pressure on the right side.
• Pitting edema is graded 1+ (slight imprint) to 4+ (deep imprint that's slow to rebound).

Lung sounds

Normal: bronchial sounds over the trachea and large bronchi, vesicular sounds (soft and low) over the lung fields.

Heart sounds

Hyperventilation vs hypoventilation

Carbon dioxide and the drive to breathe

• CO2 is a waste product of metabolism, normally breathed out. A rising CO2 is the body's main signal to breathe.
• In some chronic lung disease, most notably COPD, the body gets used to a high CO2 and comes to rely on a low oxygen level as its signal to breathe. Giving too much oxygen can take that signal away, so breathing slows and CO2 climbs further.
• That's why the SpO2 goal for these clients is lower (see oxygen therapy).

Atelectasis

Atelectasis is the collapse of alveoli and small sections of lung, usually from shallow breathing. Collapsed alveoli leave less surface for gas exchange, and the pooled secretions can turn into pneumonia.

• Highest risk: clients after surgery (anesthesia, opioids and pain make breathing shallow) and clients on prolonged bed rest or immobility.
• Prevention: incentive spirometer, deep breathing and coughing, early ambulation, turning, and pain control so the client can breathe deeply.

Asthma, COPD and pneumonia

Respiratory medications

Clients often use both: one opens the airway, the other calms the swelling.

• Nebulizer: turns a liquid medication into a mist breathed in through a mask or mouthpiece; a good choice when a client can't coordinate an inhaler.
• MDI (metered-dose inhaler): a measured dose with each press of the canister; needs coordination between pressing and breathing in, so a spacer helps.
• DPI (dry-powder inhaler): breath-activated; needs a strong, fast breath in.

Rhythm (electrical) problems

• Treatment depends on the cause and on whether the client has symptoms: lifestyle changes (less caffeine and alcohol, more sleep, no smoking), medications, ablation, a pacemaker or a defibrillator.
• Other things that can disturb the rhythm: hypoxia, caffeine or alcohol, thyroid problems, and low potassium or magnesium.

Pump (mechanical) problems

Both can be heard as a murmur. The aortic valve is the one most often diseased.

Ischemia, angina and MI

One leads to the next

Hypotension and poor perfusion

• Low BP usually means hypoperfusion: not enough blood reaching the tissues.
• Causes: hypovolemia, dehydration, medications, heart failure, arrhythmias.
• Signs: chest pain, syncope, arrhythmias, a change in level of consciousness, decreased urine output, lactic acidosis.
• The heart, brain and kidneys are hit hardest, and the damage can become permanent if it isn't treated quickly.

Signs, early to late

Intercostal retractions (the muscles between the ribs pulling in on inhalation) can mean the airway is blocked; treat them as an emergency.

Causes

• Too few red blood cells to carry oxygen: anemia
• Poor diffusion: pneumonia, asthma, COPD
• Poor perfusion: hypotension, low cardiac output
• Poor ventilation: bronchoconstriction, medications that slow breathing (opioids)
• Not enough oxygen in the air or blocked by smoke: high altitude, smoke inhalation

What to do

The basics

• Room air is 21% oxygen. FiO2 (fraction of inspired oxygen) is the percentage the client actually breathes in.
• Oxygen is a medication. Starting it and changing the flow rate need a provider's prescription.
• Give the lowest amount that meets the goal, titrate to the prescribed saturation, and wean it gradually.

Pulse oximetry

• A clip or band on a finger, toe, earlobe, bridge of the nose or forehead shines infrared light through the tissue to estimate how much hemoglobin is carrying oxygen.
• Use it whenever breathing looks off: increased work of breathing, wheezing, coughing, cyanosis, a change in rate or rhythm, adventitious sounds, restlessness or confusion, dyspnea, orthopnea (shortness of breath lying down).
• Falsely low readings: cold skin or hypothermia, poor circulation, movement, nail polish, bright light, low hemoglobin, jaundice, edema.

A reading under 90%

1. Check that the probe is placed correctly (and look at the client).
2. Check that the oxygen is on, connected and at the prescribed flow.
3. Raise the head of the bed (semi-Fowler's or Fowler's) to help the chest expand.
4. Encourage deep breathing.
5. Stay with the client and keep them calm; report if it doesn't improve.

Delivery devices

Positive pressure and manual breaths

• In obstructive sleep apnea, the upper airway closes during sleep and breathing stops for more than 10 seconds at a time. Signs: loud snoring, restlessness, morning headache, extreme daytime sleepiness.

Oxygen toxicity

Too much oxygen for too long damages cells. The risk rises with high concentrations (above about 50%), long use (more than 24 to 48 hours) and severe lung disease.

Prevention: the lowest oxygen that keeps the SpO2 at goal, lower the FiO2 as the SpO2 improves, and report findings. Teach home oxygen clients to report nausea, a new cough or trouble breathing.

Fire safety

• No smoking, ever, around oxygen; post "No Smoking" and "Oxygen in Use" signs on the door (and inside and outside a home).
• Keep oxygen away from open flames and heat: candles, fireplaces, heaters, gas or electric stoves, curling irons, hair dryers.
• No flammable products nearby: alcohol, acetone, paint thinner, cleaning fluids, aerosol sprays (air freshener, hair spray). Let alcohol hand sanitizer dry completely before handling the equipment.
• No petroleum-based products (such as VASELINE) on the face or upper chest; use a water-soluble lubricant for dry nares.
• Cotton gowns and bedding; wool and synthetic fabrics can make static sparks.
• Electrical devices (razors, radios, hearing aids) must work properly, and machines (monitors, suction) must be grounded.
• Know where the nearest fire extinguisher is; homes need a smoke alarm, and the fire department and electric company should know oxygen is in use.

Cylinders and equipment

• Keep tanks upright and secured (in a holder or chained), full or empty, so they can't fall and rupture the valve. Don't store them in a closet.
• The pressure gauge on the regulator shows how much is left; a needle in the red zone means change the cylinder soon. The E cylinder is the usual size for transport and home.
• Before starting, check the flow meter and regulator work and the tank has enough oxygen; set the flow to the prescribed L/min before putting the device on the client.
• In the hospital, plug the flow meter into the green oxygen outlet, not the yellow air outlet. Read the flow at the middle of the ball.
• Keep tubing short enough not to trip over, and away from foot traffic.

Home oxygen systems

Home oxygen is usually needed when a client can't keep the SpO2 at 88% or more. Teach the client and family to set the flow, check the supply, keep the system in a well-ventilated, uncluttered spot away from heat, and know whom to call if the equipment fails.

Breathing exercises

Chest physiotherapy

Chest physiotherapy (CPT) uses percussion, vibration and postural drainage to shake thick mucus loose and shift it up to the large airways, close enough to cough out or suction. It helps clients with thick secretions they can't clear, such as in cystic fibrosis, pneumonia and COPD.

• Order: positioning comes first, percussion and vibration next, and coughing or suctioning last to clear what came loose.
• Timing: on an empty stomach, to avoid vomiting and aspiration (before meals and at bedtime). Early morning works well because secretions pool overnight. Stop a continuous tube feeding at least 30 minutes before.
• Give a prescribed bronchodilator or nebulizer treatment before; have tissues and an emesis basin ready; oxygen and suction may be needed.
• Don't use CPT with rib, chest, head or neck injury, increased intracranial pressure, recent abdominal surgery, pulmonary embolism, bleeding disorders, osteoporosis, or pregnancy.
• Document vital signs and the color, amount and character of the sputum.

Sputum specimens

• Used to find infection (culture and sensitivity), cancer cells (cytology, in a container with preservative) and TB (tuberculosis; acid-fast bacilli on 3 morning samples in a row).
• Best early in the morning, when secretions have pooled overnight. Rinse the mouth with water (no mouthwash), take several deep breaths, then cough deeply to bring sputum up from the lungs (not saliva).
• 1 to 2 teaspoons (5 to 10 mL) into a sterile container without touching the inside. Label, bag and send it promptly; record the time.
• Can't bring it up? Try CPT first; then suctioning. Older adults often have a weak cough and may need suctioning.

When to suction

• As needed, not on a schedule, when the client can't clear secretions: restlessness, rising heart and respiratory rates, falling SpO2, adventitious sounds, secretions you can see or hear, cyanosis, no effective cough.
• Try having the client cough first.
• Judge how well it worked from breath sounds, vital signs and SpO2 before and after. The amount and look of the secretions hint at infection or inflammation; how well the client tolerates it tells you about their overall condition.

Types

If both the trachea and the mouth need suctioning, do the mouth last: the mouth is clean, the trachea sterile.

Tracheal suctioning, step by step

1. Hand hygiene and PPE (personal protective equipment): gloves plus goggles or a face shield.
2. Position the client in semi-Fowler's or Fowler's if possible; encourage a deep breath and cough first.
3. Check baseline breath sounds, vital signs and SpO2 (keep the pulse oximeter on throughout).
4. Set the suction: 80 to 120 mm Hg for tracheal suctioning.
5. Hyperoxygenate with 100% oxygen (a bag-valve mask or the ventilator).
6. Insert the catheter without applying suction until you feel resistance or the client coughs (about the level of the carina).
7. Pull back 1 to 2 cm.
8. Apply suction intermittently while rotating and withdrawing the catheter, for no more than 10 to 15 seconds.
9. Reoxygenate and let the client rest; wait at least 1 minute before another pass, and limit it to 2 or 3 passes.
10. Rinse the catheter and tubing with sterile saline; throw away an open-system catheter after the session.

• Complications: hypoxia, airway injury and bleeding, infection, and dysrhythmias (stop if the heart rate drops or the client desaturates).
• Closed system: advance the catheter through the sleeve, apply suction while withdrawing (it isn't rotated), pull it back until the black mark shows, rinse with 5 to 10 mL of saline, and lock the suction control before leaving.

The four airways

Living with a tracheostomy

• A tracheostomy bypasses the upper airway, so air reaches the trachea without being warmed, filtered or humidified. Give humidified air and fluids to keep secretions thin and prevent mucus plugs.
• The lower airway makes more mucus to make up for it, so these clients need suctioning more often.

At the bedside

Tracheostomy care

Every 4 to 8 hours (or per policy) and as needed, using sterile technique; oral care every 2 hours.

1. Suction first if needed; give oxygen if the SpO2 drops during care.
2. Remove the inner cannula and clean it with sterile technique, or replace a disposable one.
3. Remove the soiled dressing; clean the stoma first, then the plate (flange).
4. Place a precut split tracheostomy dressing; never cut gauze to fit, since loose fibers can be breathed in.
5. Change the ties only if wet or soiled. Secure the new ties before removing the old ones. Check that 1 or 2 fingers fit under them; any knot is a square knot at the side of the neck.

When the tube comes out (decannulation)

Other complications: tube obstruction (a mucus plug), pneumothorax, subcutaneous emphysema, bleeding (a small amount is expected), infection (purulent drainage, redness, pain, swelling), and tracheal narrowing or tissue damage from too much cuff pressure.

Why a chest tube

A chest tube goes into the pleural space (or the mediastinum after heart surgery) to drain air, blood or fluid and restore the negative pressure the lung needs to re-expand. It can be placed in an emergency or after surgery.

• Pneumothorax: air
• Hemothorax: blood
• Pleural effusion: fluid (empyema: infected fluid, pus)

The three chambers

• No more tidaling can mean the lung is back up, yet the same thing happens when the tubing is kinked, blocked or has a dependent loop, or the suction isn't working. Check the tubing before deciding the lung is up.
• To find a leak, briefly clamp near the dressing (if prescribed): if the bubbling stops, the leak is at the insertion site or in the chest; if it keeps going, it's in the tubing or the unit.

Caring for the client

• Respiratory status: color, SpO2, rate, depth and effort, breath sounds, trachea at the midline, pain.
• Site: check the dressing; palpate around it for crepitus (subcutaneous emphysema), which feels like crackling under the skin. Report it.
• Tubing: follow it from the client to the unit: no kinks, no dependent loops (coil it flat on the bed), connections taped. Don't strip or milk it.
• Unit: upright and below the level of the chest, always, including during transport and walks.
• Drainage: note the color, amount and consistency (hourly at first); mark the level each shift. A sudden large amount (such as more than 100 mL in an hour after the first hours), or bright red drainage, is a red flag.
• Head of the bed at 30° or higher, turning every 2 hours, deep breathing and incentive spirometer, walks every 4 to 6 hours when allowed, pain medication, range of motion for the arm on that side.
• At the bedside: sterile water, two rubber-tipped clamps, and sterile or occlusive gauze dressing.

Complications and emergencies Key point