Read the pH: below 7.35 is acidosis, above 7.45 alkalosis.
Find the value that explains it: PaCO₂ moving opposite to the pH is respiratory, HCO₃⁻ moving with the pH is metabolic.
Look at the other value: normal means uncompensated, abnormal in the compensating direction means partial compensation, and a normal pH with both abnormal means full compensation.
In a metabolic acidosis, compare PaCO₂ with Winter’s formula, 1.5·HCO₃⁻ + 8 ± 2, and calculate the anion gap Na⁺ − (Cl⁻ + HCO₃⁻).
Check a high anion gap with the delta ratio and, when albumin is low, with the corrected gap.
Clinical pharmacokinetics
Rate constant and half-life
k = ln 2/t½ = 0.693/t½
First-order decay
C = C₀·e−kt = C₀·(1/2)t/t½
Two levels
k = ln(C₁/C₂)/Δt
Volume and clearance
Vd = dose/C₀, CL = k·Vd
Loading dose
LD = Vd·C/(S·F)
Maintenance rate
R = CL·Css/(S·F)
Average steady state
Css,avg = S·F·D/(CL·τ)
Steady state
1 − (1/2)ⁿ after n half-lives; ≈ 97% after 5
Infusion
C = (R/CL)(1 − e−kt)
Interval and dose from peak and trough
τ = ln(Cpeak/Ctrough)/k, D = Vd·(Cpeak − Ctrough)
Cockcroft–Gault
CrCl = (140 − age) × kg/(72 × SCr mg/dL), × 0.85 for women
Pick the relation: C = C₀·e−kt, LD = Vd·C/(S·F), maintenance rate = CL·Css/(S·F), τ = ln(Cpeak/Ctrough)/k.
For kidney function, estimate CrCl with Cockcroft–Gault first, then scale the dose or the interval.
Check the result: levels fall by half every half-life, and steady state takes about five half-lives.
2Practice problems
1.Lab values & electrolytesMedium
Which finding during a transfusion suggests transfusion-associated circulatory overload (TACO)?
ABack pain with dark red urine output
BA low temperature and slow heart rate
CCrackles, hypertension and a raised BNP
DHives and itching without other signs
2.Lab values & electrolytesHard
An RN cares for a patient on a 24-hour urine collection. Which task can be delegated to unlicensed assistive personnel (UAP), such as a nursing or healthcare assistant?
ASaving all urine in the collection container as instructed
BDeciding whether to restart the collection after a missed sample
CInterpreting the creatinine clearance result when it comes back
DTeaching the patient why the 24-hour collection is needed
3.Arterial blood gas interpretationMedium
A practice arterial blood gas shows pH 7.38, PaCO₂ 28 mmHg (3.7 kPa) and HCO₃⁻ 16 mmol/L. The primary disorder is metabolic acidosis. How far is it compensated? Click your answer.
pH 7.38PaCO₂ 28 mmHg (3.7 kPa)HCO₃⁻ 16 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
A practice gas shows a metabolic acidosis: pH 7.34, PaCO₂ 31 mmHg (4.1 kPa), HCO₃⁻ 16 mmol/L. Compare the measured PaCO₂ with Winter’s formula. Click your interpretation.
pH 7.34PaCO₂ 31 mmHg (4.1 kPa)HCO₃⁻ 16 mmol/L
1appropriate compensation
2added respiratory acidosis
3added respiratory alkalosis
5.Clinical pharmacokineticsMedium
Practice exercise (made-up values, not clinical guidance). A 52 kg patient receives a theophylline infusion. The clearance is 0.05 L/kg/h. What infusion rate R in mg/h gives a steady-state level of 15 mg/L?
52 kgCL = 0.05 L/kg/hCss = 15 mg/L
R = mg/h
6.Clinical pharmacokineticsHard
Practice exercise (made-up values, not clinical guidance). An 83 kg patient on regular gentamicin doses is at steady state. The target is a peak of 8 mg/L and a trough of 1 mg/L, and the volume of distribution is 0.3 L/kg. Assuming rapid IV doses, what dose D raises the level from the trough to the peak?
83 kgVd = 0.3 L/kgCpeak = 8 mg/LCtrough = 1 mg/L
D = mg
7.Clinical nursingMedium
When a patient returns to the ward from theatre, what should the nurse assess first?
AThe discharge date
BThe patient's dietary preferences for the next meal
CWhether visitors are waiting to see the patient
DAirway, breathing, circulation and level of consciousness
8.Clinical nursingHard
A patient has a full-thickness burn all the way round the forearm. Which complication must be watched for closely?
AExcessive bleeding from the burn surface needing an urgent blood transfusion
BLoss of circulation to the hand as swelling builds under tight burned skin
CDelayed hair growth on the arm
DHypoglycaemia caused by the body using glucose to heal the burn
3Solutions
1.Lab values & electrolytes
Answer: C · Crackles, hypertension and a raised BNP
Why this is the answer
TACO is fluid overload, often in older adults or those with heart or kidney disease. It causes dyspnea, crackles, hypertension, distended neck veins and a raised BNP. The transfusion is stopped, the patient is sat up and diuretics may be prescribed.
Answer
C · Crackles, hypertension and a raised BNP
2.Lab values & electrolytes
Answer: A · Saving all urine in the collection container as instructed
Why this is the answer
UAP can help with routine, standard tasks such as saving urine and keeping the container cool as instructed. Teaching, clinical decisions and interpreting results require nursing judgment and stay with the RN.Checked against:24-Hour Urine Collection and Analysis · StatPearls (NCBI Bookshelf) (2024)
Answer
A · Saving all urine in the collection container as instructed
3.Arterial blood gas interpretation
Answer: fully compensated
Reading a blood gas (ROME): first the pH: below 7.35 is acidaemia, above 7.45 alkalaemia. Then find the value that explains it. PaCO₂ (normal 35–45 mmHg, 4.7–6.0 kPa) is the respiratory part and moves Opposite to the pH in a respiratory disorder; HCO₃⁻ (normal 22–26 mmol/L) is the metabolic part and moves in the same direction as the pH (Respiratory Opposite, Metabolic Equal). The other value shows the compensation: normal means uncompensated; abnormal in the direction that pulls the pH back while the pH is still abnormal means partially compensated; a normal pH with both values abnormal means fully compensated. Ranges differ slightly between laboratories; these are practice values.
ROME, value by value
pH 7.38: within 7.35–7.45
PaCO₂ 28 mmHg: low (35–45)
HCO₃⁻ 16 mmol/L: low (22–26)
Compensation
Clinically, also check the expected compensation: Winter’s formula expects PaCO₂ 30–34 mmHg, so the measured 28 mmHg points to an additional respiratory alkalosis (a mixed disorder). The answer above is the ROME exam classification.
fully compensated
Answer
fully compensated
4.Arterial blood gas interpretation
Answer: appropriate compensation
Expected compensation: in metabolic acidosis Winter’s formula predicts PaCO₂ = 1.5·HCO₃⁻ + 8 ± 2 mmHg; a measured value above that range points to an additional respiratory acidosis, below it to an additional respiratory alkalosis. The anion gap AG = Na⁺ − (Cl⁻ + HCO₃⁻), normally about 8–12 mmol/L, separates high-gap from normal-gap metabolic acidosis; low albumin hides a high gap (add 2.5 per g/dL that albumin is below 4.0). The delta ratio (AG − 12)/(24 − HCO₃⁻) between about 0.8 and 2 fits a pure high-gap acidosis (some texts use 1 instead of 0.8), below that an added normal-gap acidosis, and above 2 an added metabolic alkalosis.
Expected PaCO₂
1.5·16 + 8 = 32 → 30–34 mmHg
Compare
measured: 31 mmHg → appropriate compensation
Answer
appropriate compensation
5.Clinical pharmacokinetics
Answer: R = 39 mg/h
Clearance and volume: at steady state the dosing rate equals the elimination rate, so the maintenance rate = CL × Css. A loading dose is LD = Vd × C/(S × F), with S the salt factor (fraction of active drug in the salt) and F the bioavailability (1 for IV). From two levels, k = ln(C₁/C₂)/Δt; for an IV bolus Vd = dose/C₀ and CL = k × Vd. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Clearance
CL = 0.05·52 = 2.6 L/h
Infusion rate
R = 2.6·15 = 39 mg/h
Answer
R = 39 mg/h
6.Clinical pharmacokinetics
Answer: D = 174.3 mg
Designing a regimen: with rapid IV doses the level falls from peak to trough during the interval, so τ = ln(Cpeak/Ctrough)/k and the dose that restores the peak is Vd × (Cpeak − Ctrough). The average steady-state level is Css,avg = S·F·dose/(CL·τ). An infusion rises as C = (R/CL)(1 − e−kt). For a drug cleared by the kidneys, the dose is scaled with the creatinine clearance. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
Volume of distribution
Vd = 0.3·83 = 24.9 L
Dose
D = 24.9·(8 − 1) = 174.3 mg
Answer
D = 174.3 mg
In practice the dose is rounded to a convenient amount.
7.Clinical nursing
Answer: D · Airway, breathing, circulation and level of consciousness
Why this is the answer
Early postoperative assessment checks the airway, breathing, oxygen saturation, circulation, consciousness, pain, wound and drains. This detects anaesthetic and surgical complications early.
Answer
D · Airway, breathing, circulation and level of consciousness
8.Clinical nursing
Answer: B · Loss of circulation to the hand as swelling builds under tight burned skin
Why this is the answer
Circumferential full-thickness burns form a tight eschar that acts like a tourniquet as oedema develops. Neurovascular checks are needed, and escharotomy may be required.
Answer
B · Loss of circulation to the hand as swelling builds under tight burned skin