Nine cards, one per topic. Each one gives what the thing is, its parts or names, and what a student is asked to check in the skills lab or on a written exam. For study only: this is not a procedure manual, and your facility’s policy and your instructor come first.
Card 1
Positioning names: supine, prone, Sims, Fowler’s, Trendelenburg, lithotomy
What it is
The names describe where the body faces, how far the head of the bed is raised, or whether the whole bed is tilted. Fowler’s variations bend at the hips; Trendelenburg and reverse Trendelenburg tilt the entire flat bed. Pillows, wedges and rolled towels keep the body aligned in each one.
The positions
- Supine
- Flat on the back, a pillow under the head. The feet tend to fall into plantar flexion, so textbooks mention a support to prevent foot drop during long bed rest.
- Prone
- On the stomach, head turned to one side; pillows under the lower legs align the feet.
- Lateral (side-lying)
- On one side with the top leg flexed over the bottom leg. Relieves pressure on the coccyx.
- Sims (semi-prone)
- Halfway between lateral and prone, legs flexed, a pillow under the top leg, arms beside the body (not underneath). Used for some procedures, such as an enema.
- Fowler’s
- Supine with the head of the bed raised 45 to 90 degrees. High Fowler’s is 90 degrees. Promotes lung expansion and improves oxygenation.
- Semi-Fowler’s
- Head of the bed at 30 to 45 degrees. Same purposes as Fowler’s but better tolerated for long periods (less pressure on the coccyx).
- Orthopneic (tripod)
- Sitting and leaning forward onto an overbed table or the elbows on the knees. A position people short of breath take on their own because it eases chest expansion.
- Trendelenburg
- On the back with the whole bed tilted so the head is lower than the feet. Textbooks list it for promoting venous return to the head and heart in certain emergencies, and for pelvic and abdominal surgery.
- Reverse Trendelenburg
- On the back with the whole bed tilted the other way: head up, feet down, no bend at the hips. Listed for neurosurgical and upper abdominal procedures.
- Lithotomy
- On the back with both legs raised and supported in stirrups. The position for gynecologic and urologic procedures.
- Knee-chest and jackknife (Kraske)
- Knee-chest: kneeling with the chest and face on the table (or side-lying with the hips and knees flexed). Jackknife: prone on a split table that lifts the hips and lowers the head and legs.
What the student checks
- Supine versus prone: supine is on the back (think “spine down”), prone is on the front.
- The angle: Semi-Fowler’s 30–45°, Fowler’s 45–90°, High Fowler’s 90°. The bed bends at the hips.
- Tilt versus bend: Trendelenburg and reverse Trendelenburg tilt the entire flat bed; Fowler’s raises only the head section.
- Sims is semi-prone with the legs flexed, a pillow under the top leg, and the arms beside the body, not under it.
- Lithotomy means legs up in stirrups; lateral means side-lying with the top leg flexed.
- Repositioning schedule in the textbooks: commonly at least every two hours for someone who cannot turn alone. The facility’s policy sets the actual schedule.
Remember: SUPine = on your back looking UP. PRone = on your front. SIMS = Semi-prone, legs flexed.
Card 2
Chest tube drainage system: the three chambers
What it is
A chest tube is a sterile catheter placed in the pleural space (the thin gap between the visceral pleura on the lung and the parietal pleura on the chest wall, which normally holds about 10 to 20 mL of fluid). It is connected to a closed, airtight drainage system that lets air and fluid out, keeps them from going back in, and restores the negative pressure that lets the lung re-expand. Tubes placed to remove air sit higher on the chest (air rises); tubes placed to drain fluid sit lower (fluid settles).
The three chambers (right to left on a traditional unit)
- Collection chamber
- Usually the far right compartment. The tube from the chest drains into it. It is calibrated so the drainage can be measured, and the outside has a writing surface for the date, time and amount.
- Water seal chamber
- The middle compartment and the one-way valve of the system: air leaves the pleural space on exhalation and cannot re-enter on inhalation. It is filled with sterile water to the 2 cm mark. The water level rises and falls with breathing (“tidaling”), which shows the tube is patent; the pattern is reversed on a mechanical ventilator. Continuous bubbling here may mean an air leak. Some units have an air-leak meter, numbered 1 (low) to 5 (high).
- Suction control chamber
- Usually the far left compartment, used only when suction is ordered. Wet suction: the water level sets the amount, typically −20 cm H₂O for adults, and gentle continuous bubbling is expected while suction is connected. Dry suction: a regulator dial is set to the ordered level (typically −20 cm H₂O) and an indicator (a float or bellows) shows that suction is active; it is less affected by evaporation, spills or a change of position.
At a glance
Conditions a chest tube drains, by what is in the pleural space
Pneumothorax
What is in the pleural space: Air (a lung collapses because air leaked in); spontaneous, traumatic or tension types
Hemothorax
What is in the pleural space: Blood
Pleural effusion
What is in the pleural space: Fluid
Hydrothorax
What is in the pleural space: Serous fluid
Chylothorax
What is in the pleural space: Lymph
Empyema
What is in the pleural space: Pus (infection of the pleural space)
Conditions a chest tube drains, by what is in the pleural space| Term | What is in the pleural space |
|---|
| Pneumothorax | Air (a lung collapses because air leaked in); spontaneous, traumatic or tension types |
|---|
| Hemothorax | Blood |
|---|
| Pleural effusion | Fluid |
|---|
| Hydrothorax | Serous fluid |
|---|
| Chylothorax | Lymph |
|---|
| Empyema | Pus (infection of the pleural space) |
|---|
What the student checks
- The unit stands upright, below the level of the chest, with any floor stands pulled out so it cannot tip.
- Tubing is not kinked, connections are taped, and the tube is secured to the chest wall: a closed system.
- Water seal at the 2 cm mark; tidaling present; no continuous bubbling in the water seal chamber.
- Wet suction: water at the ordered level (typically −20 cm) with gentle bubbling. Dry suction: dial at the ordered level with the indicator showing.
- Drainage amount, color and character recorded, and the level marked on the chamber with the date and time. The textbook’s reporting threshold: drainage averaging more than 200 mL/hour for 4 hours.
- Bedside supplies the textbook lists: two rubber-tipped clamps, sterile gauze and petroleum gauze with tape, and a small container of sterile water or saline (a temporary water seal if the tubing disconnects).
- Two things textbooks teach, with facility policy first: the tubing is not “stripped” or milked, and the tube is not clamped routinely (both risk a tension pneumothorax). For transport, the suction tubing is disconnected from its source instead; gravity and the water seal keep working.
Remember: Collection collects, water seal seals (tidaling good, continuous bubbling = leak), suction control bubbles gently.
Card 3
Oxygen delivery devices and their typical flow ranges
What it is
Each device delivers a range of oxygen concentration (FiO₂, the fraction of inspired oxygen; room air is 21%) at a range of flow in liters per minute. Low-flow devices such as the nasal cannula mix oxygen with room air, so the exact FiO₂ depends on how the person breathes; a Venturi mask uses adapters to deliver a set percentage. The ranges below are the textbook figures used on written exams. The ordered flow and the facility’s policy decide the real settings.
The devices
- Nasal cannula
- Two short prongs in the nares. 1 to 6 L/min, about 24% to 44% FiO₂ (roughly 4% more per liter). Humidification is often added above 4 L/min or for long use, per policy. The person can eat and talk; the prongs dislodge easily and the tubing can press on the nose and ears.
- High-flow nasal cannula
- Heated, humidified oxygen at up to 60 L/min and up to 100% FiO₂. Set up by respiratory therapy; used for people who need close monitoring.
- Simple mask
- Covers the nose and mouth, with open exhalation ports and a metal strip shaped over the nose. 6 to 10 L/min. Both textbooks’ summary tables give 28% to 50% FiO₂ (Open RN’s text says 35% to 50%). Never set below 6 L/min, because exhaled carbon dioxide would be rebreathed.
- Partial rebreather mask
- A mask with a reservoir bag but no one-way valves, so some exhaled air mixes in. 10 to 15 L/min, about 35% to 50% FiO₂.
- Non-rebreather mask
- A mask with a reservoir bag and one-way valves, so exhaled air does not mix back into the bag. 10 to 15 L/min, about 60% to 80% FiO₂. The bag is inflated before the mask goes on and should never fully deflate.
- Venturi mask
- Interchangeable adapters set the flow to deliver an exact FiO₂ from 24% to 60%. Used when a precise amount matters, such as chronic obstructive pulmonary disease. Usually set up by respiratory therapy.
- Bag valve mask
- A hand-squeezed bag for someone who is not breathing or not breathing enough; it ventilates as well as oxygenates. At 15 L/min it delivers about 100% FiO₂. Squeezed once every 5 to 6 seconds for an adult, every 3 seconds for an infant or child; two rescuers are recommended, one holding the seal.
At a glance
Flow and FiO₂ at a glance (textbook figures)
Nasal cannula
Flow: 1–6 L/min
FiO₂: 24–44%
High-flow nasal cannula
Flow: up to 60 L/min
FiO₂: up to 100%
Simple mask
Flow: 6–10 L/min
FiO₂: 28–50%
Partial rebreather mask
Flow: 10–15 L/min
FiO₂: 35–50%
Non-rebreather mask
Flow: 10–15 L/min
FiO₂: 60–80%
Venturi mask
Flow: set by adapter
FiO₂: 24–60%
Bag valve mask
Flow: 15 L/min
FiO₂: 100%
Flow and FiO₂ at a glance (textbook figures)| Device | Flow | FiO₂ |
|---|
| Nasal cannula | 1–6 L/min | 24–44% |
|---|
| High-flow nasal cannula | up to 60 L/min | up to 100% |
|---|
| Simple mask | 6–10 L/min | 28–50% |
|---|
| Partial rebreather mask | 10–15 L/min | 35–50% |
|---|
| Non-rebreather mask | 10–15 L/min | 60–80% |
|---|
| Venturi mask | set by adapter | 24–60% |
|---|
| Bag valve mask | 15 L/min | 100% |
|---|
What the student checks
- Wall outlets: green is oxygen, yellow is medical air. The flow meter is attached to the green outlet.
- Reading the flow meter: the ordered line crosses the middle of the steel ball.
- Pulse oximeter: the textbook normal SpO₂ for an adult without lung disease is above 95%.
- Cannula prongs curve into the nares; a simple mask’s exhalation ports stay open; a non-rebreather’s bag is inflated first and never collapses fully.
- Skin under the tubing (nose, cheeks, ears) is checked for pressure; padding may be added per policy. Water-based lubricant only: petroleum-based products are a fire hazard near oxygen.
- Oxygen safety: no sparks or open flames; a home concentrator takes 21% room air to about 96% oxygen at 1 to 6 L/min.
Remember: Cannula 1–6, simple mask 6–10 (never under 6), non-rebreather 10–15 with the bag always up.
Card 4
Nasogastric (NG) tube basics
What it is
A nasogastric tube runs through the nose, down the esophagus and into the stomach. It has one lumen or two, and it is used for feeding, giving medication, or draining the stomach (decompression). Feeding tubes are small and flexible; suction tubes are larger and more rigid. NG tubes are for short-term use (under about four weeks); longer-term feeding uses a tube placed through the abdominal wall.
The tubes and their parts
- Small-bore feeding tube
- Single lumen, soft and flexible, for feeding and medication. Secured at the nose or cheek with tape or a fixation device; the skin there is checked daily.
- Large-bore double-lumen sump tube
- For gastric decompression. One lumen empties the stomach (by gravity or suction); the second, smaller vent lumen lets air flow in continuously so the suction does not pull the stomach lining into the tube. Its end has an anti-reflux valve so stomach contents do not come up the vent.
- Tubes through the abdominal wall
- PEG (percutaneous endoscopic gastrostomy) into the stomach and PEJ (percutaneous endoscopic jejunostomy) into the jejunum, placed with an endoscope for long-term feeding. Some facilities also use nasoduodenal tubes.
- Enteral-only connectors
- Feeding tubing is color-coded (often purple) and uses enteral-only connectors so it cannot be attached to an IV line. The Joint Commission issued an alert on tubing misconnections in 2006.
What the student checks
- Placement is verified by X-ray right after insertion, before anything goes through the tube. Then the tube is marked at the nostril and the external length is documented and passed on in handoff.
- Before every use and every four hours (the critical-care nursing association’s recommendation), the visible tube length is compared with the documented length. A changed mark calls for bedside checks (pH of aspirate) and, if in doubt, another X-ray.
- Two old methods are no longer used to confirm placement: pushing air in while listening (the “whoosh” sound) and looking at the aspirate.
- Flushing with water: at least once a shift, before and after intermittent feedings, and before and after medications. Water is also the first choice for a clog; acidic drinks make clogs worse.
- Gastric residual volume is measured with a 60-mL syringe when policy calls for it; the textbook notes feeding is not stopped for volumes under 500 mL without other signs of intolerance.
- Listening for bowel sounds in all four quadrants with suction paused; the abdomen should be soft and not distended.
Remember: X-ray first, then mark it, then measure it every four hours and before every use.
Card 5
Urinary catheter types and parts
What it is
A urinary catheter is a tube passed through the urethra to the neck of the bladder to drain urine. The types differ in whether they stay in (indwelling) or come out right away (intermittent), where they enter (urethra or abdominal wall), and whether they go inside the body at all (external devices). Catheter size is on the French scale: the larger the number, the larger the diameter.
The types
- Indwelling (“Foley”) catheter
- Stays in place. A balloon just behind the tip is inflated inside the bladder to hold it. The outer end has a drainage port that connects to the bag and a balloon port, marked with the volume needed to fill the balloon; the size is printed there too. A 14 French catheter is a typical indwelling size.
- Straight (intermittent) catheter
- No balloon: inserted, the bladder drains, and it comes right out. Used for urinary retention (once, or several times a day), for a sterile specimen, and by some people at home. The CDC prefers intermittent over indwelling catheters whenever feasible because the infection risk is lower.
- Coudé tip
- A curved tip that follows the natural curve of the urethra; often chosen for men with an enlarged prostate. A thin line on the catheter shows which way the curve points.
- Irrigation catheter
- A larger catheter (about 20 French versus the usual 14) used after prostate surgery to flush the bladder and clear clots.
- Suprapubic catheter
- Surgically placed through the abdominal wall into the bladder when the urethra is blocked; short-term or permanent. The insertion site is cleaned per policy.
- External devices
- A condom catheter fits over the penis and drains to a bag, noninvasive. A female external catheter uses a wicking material placed over the urinary meatus and connected to low suction. Both are alternatives to an indwelling catheter and are used to reduce catheter-associated urinary tract infection (CAUTI).
- Collection bags
- A large bag holds up to two liters and is emptied when half to two-thirds full so its weight does not pull on the urethra. A leg bag is smaller, worn under clothing, and emptied more often.
What the student checks
- The bag hangs below the level of the bladder, never on the floor, and the tubing is free of kinks with some slack: urine flows down and never back.
- The system stays closed, and slack is kept in the tubing so nothing pulls on the urethra.
- Reading the catheter: the French size and the balloon volume printed at the balloon port.
- The textbook’s CAUTI rule: an indwelling catheter is reviewed every day against the CDC indications, and the review is documented; intermittent catheterization is preferred whenever feasible because its infection risk is lower.
- Which type for which purpose: retention once → straight; long drainage → indwelling; clots after prostate surgery → irrigation; blocked urethra → suprapubic; incontinence without a tube inside → external device.
Remember: Bigger French number, bigger catheter. Bag below the bladder, off the floor, emptied at half to two-thirds.
Card 6
IV site and gauge basics
What it is
A peripheral IV is a short catheter (about ¾ to 1 inch) placed in a vein of the hand or arm and covered with a transparent dressing so the site can be seen. Catheters are sized by gauge, and the numbering runs backwards: a smaller number is a larger catheter. Longer devices (midline, PICC, central lines) are chosen for longer therapy or for solutions that irritate small veins.
Gauge, sites and devices
- Gauge
- Peripheral IVs run from 14 gauge (largest) to 24 gauge (smallest). 18, 20 and 22 gauge are the usual choices. 16 and 18 gauge give rapid infusions and blood; 16 gauge is common in surgery and intensive care. 22 gauge suits someone stable who needs slow, short therapy. 24 gauge is used most for pediatric and older adults and small veins.
- Common sites
- The back of the hand (dorsal venous network), the bend of the elbow (median cubital, the usual choice when access is needed fast), the upper forearm (accessory cephalic) and the inner forearm (median antebrachial). Start distal and move up the arm, so veins above a failed site stay usable. The non-dominant arm when possible.
- Sites to avoid
- Painful areas, wounds, infection and planned procedure sites. For days of continuous fluid, the antecubital, wrist and hand are poor choices because they bend. A “limb alert” marks an arm restricted after a mastectomy or lumpectomy, with an arteriovenous fistula, lymphedema, a clot, a fracture or scarring.
- Midline catheter
- 3 to 10 inches long, placed in a vein of the upper arm (basilic, cephalic or brachial) with the tip near the armpit, not in a central vein. Often 16 to 18 gauge, and can stay 14 days or longer.
- PICC and central lines
- A PICC goes in an upper-arm vein and ends in the superior vena cava; it can stay weeks to months. Other central lines enter the internal jugular, subclavian or femoral vein, with the tip in a vena cava or the right atrium. Total parenteral nutrition goes only through a central line. Central lines are flushed with a 10 mL syringe; smaller syringes create too much pressure.
At a glance
The four site complications named in the textbook
Phlebitis
What it is: Inflammation of the vein lining (mechanical, chemical or infectious)
Textbook signs: Redness, warmth, pain, swelling that can track up the vein, a palpable cord
Infiltration
What it is: A non-irritating solution leaks into the tissue around the vein
Textbook signs: Swelling, pain, cool and tight skin, slowed flow, leaking at the site, pump alarms
Extravasation
What it is: An irritating (vesicant) solution leaks into the tissue
Textbook signs: The signs of infiltration plus burning, stinging, blistering or tissue damage
Local infection
What it is: Infection at the insertion site
Textbook signs: Purulent drainage, typically two to three days after the start
The four site complications named in the textbook| Complication | What it is | Textbook signs |
|---|
| Phlebitis | Inflammation of the vein lining (mechanical, chemical or infectious) | Redness, warmth, pain, swelling that can track up the vein, a palpable cord |
|---|
| Infiltration | A non-irritating solution leaks into the tissue around the vein | Swelling, pain, cool and tight skin, slowed flow, leaking at the site, pump alarms |
|---|
| Extravasation | An irritating (vesicant) solution leaks into the tissue | The signs of infiltration plus burning, stinging, blistering or tissue damage |
|---|
| Local infection | Infection at the insertion site | Purulent drainage, typically two to three days after the start |
|---|
What the student checks
- The site label: date and time of insertion, gauge and initials; the transparent dressing is dry and intact and the site can be seen through it.
- Tubing labels: primary continuous sets are changed every 96 hours or up to 7 days per policy; a secondary set that has been detached is changed every 24 hours.
- Therapy longer than six days: the textbook says to assess for an intermediate or long-term device.
- Textbooks teach that patency is checked before an IV push, because infiltration is one of the most common complications.
- Rapid infusions and blood need a larger gauge in a larger upper-arm vein (hand veins are usually too small); the textbook says known vesicants go through a central line.
- A midline is not a central line: it ends near the axilla, so it carries a lower infection risk than a central line but cannot take total parenteral nutrition or vein-damaging solutions.
Remember: Smaller gauge number, bigger catheter: 16–18 for speed and blood, 20–22 everyday, 24 for small veins.
Card 7
Chain of infection and isolation precaution categories
What it is
An infection spreads only when all six links of the chain are present, so breaking any one link stops it. Standard precautions apply to every person in every setting; transmission-based precautions are added when a known or suspected organism needs a specific barrier. The textbooks call hand hygiene the single most important practice.
The six links
- 1. Infectious agent
- The pathogen: a bacterium, virus, fungus, protozoan, worm or prion.
- 2. Reservoir
- Where it lives and multiplies: most often a person (with or without symptoms; a carrier has no symptoms), also animals, insects, food, water and surfaces.
- 3. Portal of exit
- How it leaves the reservoir: body fluids, coughing and sneezing, stool. Usually the same body system where it lives.
- 4. Mode of transmission
- Direct contact (person to person, during care), indirect contact (through objects and hands), droplets larger than 5 µm that travel a short distance, airborne nuclei of 5 µm or smaller that stay suspended, vehicles such as food and water, and vectors such as mosquitoes, ticks and fleas.
- 5. Portal of entry
- How it gets in: often the same route it left by. In health care, wounds, surgical sites, IV sites and indwelling catheters are added portals.
- 6. Susceptible host
- Someone whose immunity cannot resist it: age, chronic illness and a weakened immune system raise the risk; antibodies from a previous infection or a vaccine lower it.
At a glance
Transmission-based precaution categories (added to standard precautions)
Contact
Used for: Organisms spread by touch or by draining wounds and stool: for example C. difficile, MRSA, VRE, RSV
PPE and room: Gloves and gown on entering; dedicated equipment stays in the room. Soap and water, not alcohol rub, for C. difficile and norovirus
Enhanced barrier
Used for: High-contact care of residents colonized with a multidrug-resistant organism, or at risk of one
PPE and room: Gloves and gown during those care activities
Droplet
Used for: Large respiratory droplets from coughing, sneezing or talking: for example influenza, coronavirus, pertussis
PPE and room: Mask plus goggles or a face shield
Airborne
Used for: Small particles that stay in the air: measles, tuberculosis, disseminated herpes zoster
PPE and room: Fit-tested N95 respirator or PAPR; an airborne infection isolation room, single occupancy, door closed; susceptible staff kept out
Transmission-based precaution categories (added to standard precautions)| Category | Used for | PPE and room |
|---|
| Contact | Organisms spread by touch or by draining wounds and stool: for example C. difficile, MRSA, VRE, RSV | Gloves and gown on entering; dedicated equipment stays in the room. Soap and water, not alcohol rub, for C. difficile and norovirus |
|---|
| Enhanced barrier | High-contact care of residents colonized with a multidrug-resistant organism, or at risk of one | Gloves and gown during those care activities |
|---|
| Droplet | Large respiratory droplets from coughing, sneezing or talking: for example influenza, coronavirus, pertussis | Mask plus goggles or a face shield |
|---|
| Airborne | Small particles that stay in the air: measles, tuberculosis, disseminated herpes zoster | Fit-tested N95 respirator or PAPR; an airborne infection isolation room, single occupancy, door closed; susceptible staff kept out |
|---|
What the student checks
- PPE for transmission-based precautions is kept in an isolation cart by the room, and a card on the door says which precautions apply.
- Donning order: gown (all ties tied) → mask or respirator → goggles or face shield → gloves last, pulled over the gown cuffs.
- A user-seal check every time a respirator goes on; a surgical mask is not a respirator.
- The gown comes off inside the room before leaving, outer side folded inward.
- Standard precautions cover everyone: hand hygiene, PPE when exposure is possible, sharps safety, cleaning of surfaces and shared equipment, and respiratory hygiene with more than 3 feet of separation in waiting areas.
- Tuberculosis has more than one route, so more than one category can apply at once.
Remember: Contact = gloves and gown. Droplet = mask and eyes. Airborne = N95 and a special room.
Card 8
ABG interpretation chart: the reference values
What it is
An arterial blood gas is drawn from an artery (most often the radial) and reports pH, PaCO₂, HCO₃, PaO₂ and SaO₂. PaCO₂ is the respiratory (acid) side, which the lungs adjust quickly; HCO₃ is the metabolic (base) side, which the kidneys adjust more slowly. Interpretation is three steps: is the pH acidic or alkaline, which value explains it, and is the other system compensating.
The three steps
- Step 1: pH
- Below 7.35 is acidosis; above 7.45 is alkalosis.
- Step 2: PaCO₂ (respiratory)
- Above 45 is acidotic, below 35 is alkalotic. If the PaCO₂ matches the pH problem, the cause is respiratory: low pH with high PaCO₂ is respiratory acidosis; high pH with low PaCO₂ is respiratory alkalosis.
- Step 3: HCO₃ (metabolic)
- Below 22 is acidotic, above 26 is alkalotic. Low pH with low HCO₃ is metabolic acidosis; high pH with high HCO₃ is metabolic alkalosis.
- Step 4: compensation
- Fully compensated: the pH is back in range while the causing value and the other value are both out of range. Partially compensated: the pH is still abnormal and both values are out of range. Uncompensated: the pH is abnormal and only the causing value is out of range.
- ROME
- Respiratory Opposite, Metabolic Equal: in a respiratory problem the PaCO₂ moves opposite to the pH; in a metabolic problem the HCO₃ moves the same way as the pH.
At a glance
Normal adult reference ranges (Open RN)
pH
Normal range: 7.35–7.45
Side: Acid–base balance
PaCO₂
Normal range: 35–45 mmHg
Side: Respiratory (acid); lungs
HCO₃
Normal range: 22–26 mEq/L
Side: Metabolic (base); kidneys
PaO₂
Normal range: 80–100 mmHg
Side: Oxygenation
SaO₂
Normal range: 95–100%
Side: Oxygenation
Normal adult reference ranges (Open RN)| Value | Normal range | Side |
|---|
| pH | 7.35–7.45 | Acid–base balance |
|---|
| PaCO₂ | 35–45 mmHg | Respiratory (acid); lungs |
|---|
| HCO₃ | 22–26 mEq/L | Metabolic (base); kidneys |
|---|
| PaO₂ | 80–100 mmHg | Oxygenation |
|---|
| SaO₂ | 95–100% | Oxygenation |
|---|
What the student checks
- The four combinations: respiratory acidosis (pH ↓, PaCO₂ ↑), respiratory alkalosis (pH ↑, PaCO₂ ↓), metabolic acidosis (pH ↓, HCO₃ ↓), metabolic alkalosis (pH ↑, HCO₃ ↑).
- Which system is fast: the lungs change PaCO₂ quickly by breathing faster or slower; the kidneys retain or excrete HCO₃ and take longer.
- Textbook examples of causes (for recognition only): hypoventilation raises PaCO₂; hyperventilation lowers it; prolonged vomiting or NG suction loses acid; severe diarrhea loses bicarbonate.
- PaO₂ measures oxygenation more accurately than SaO₂ (hemoglobin saturation), which is why an ABG reports both.
Remember: pH 7.35–7.45 · PaCO₂ 35–45 · HCO₃ 22–26. ROME: Respiratory Opposite, Metabolic Equal.
Card 9
Gram positive vs gram negative: the Gram stain
What it is
The Gram stain, developed by Hans Christian Gram in 1884, is a differential stain that sorts bacteria by their cell wall. Gram-positive cells have a thick layer of peptidoglycan that holds on to the purple primary stain; gram-negative cells have a thin layer that loses it and takes up the pink counterstain. It is still one of the first steps in identifying a bacterium.
The four steps
- 1. Crystal violet (primary stain)
- Applied to a heat-fixed smear; every cell turns purple.
- 2. Gram’s iodine (mordant)
- Sets the dye by forming a crystal violet–iodine complex that is trapped in thick peptidoglycan.
- 3. Decolorizer
- Ethanol or an acetone–ethanol mix. Thick-walled cells keep the purple; thin-walled cells wash clear.
- 4. Safranin (counterstain)
- Colors the decolorized cells pink; it barely shows on cells still holding crystal violet.
At a glance
Gram positive versus gram negative
Peptidoglycan layer
Gram-positive: Thick
Gram-negative: Thin
After decolorizer
Gram-positive: Keeps crystal violet
Gram-negative: Loses it
Final color
Gram-positive: Purple
Gram-negative: Pink to red
Classic example
Gram-positive: Staphylococcus aureus
Gram-negative: Escherichia coli
Gram positive versus gram negative| Feature | Gram-positive | Gram-negative |
|---|
| Peptidoglycan layer | Thick | Thin |
|---|
| After decolorizer | Keeps crystal violet | Loses it |
|---|
| Final color | Purple | Pink to red |
|---|
| Classic example | Staphylococcus aureus | Escherichia coli |
|---|
What the student checks
- The reagent order: violet, iodine, decolorizer, safranin.
- Two ways a result goes wrong: an old culture with damaged walls looks gram-negative even when the species is gram-positive, and decolorizer left on too long strips gram-positive cells so they stain pink.
- Related stains: acid-fast (carbolfuchsin; Ziehl-Neelsen uses heat, Kinyoun does not; waxy, acid-fast cells stay red against a blue counterstain), endospore (malachite green with heat, safranin counterstain: green spores in pink cells) and capsule (a negative stain such as India ink leaves a clear halo).
- Clinical relevance the textbook notes: gram-negative bacteria tend to resist certain antibiotics more than gram-positive ones, so the stain result guides what is tried next.
Remember: Positive = purple = thick wall. Negative = pink = thin wall.