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
A patient has a calcium of 11.8 mg/dL (2.95 mmol/L) from bone metastases. Which nursing measure is appropriate?
AOffer extra milk and cheese at each meal
BGive calcium carbonate antacids for nausea
CEncourage fluids and mobility as tolerated
DEncourage bed rest and limit oral fluids
2.Lab values & electrolytesHard
A patient recovering from acute tubular necrosis now passes 4–5 L of urine a day. Which electrolyte changes should the nurse watch for?
AHigh calcium and high phosphate from bone loss
BHigh potassium and high sodium from retention
CNo changes, because the kidneys are now normal
DLow potassium and low sodium from urine losses
3.Arterial blood gas interpretationMedium
A practice gas shows PaCO₂ 66 mmHg (8.8 kPa). Use the rule that in chronic respiratory acidosis HCO₃⁻ rises by 3.5 mmol/L for every 10 mmHg that PaCO₂ is above 40, starting from HCO₃⁻ 24 mmol/L, to find the expected HCO₃⁻.
A practice gas shows a metabolic acidosis: pH 7.15, PaCO₂ 33 mmHg (4.4 kPa), HCO₃⁻ 11 mmol/L. Compare the measured PaCO₂ with Winter’s formula. Click your interpretation.
pH 7.15PaCO₂ 33 mmHg (4.4 kPa)HCO₃⁻ 11 mmol/L
1appropriate compensation
2added respiratory acidosis
3added respiratory alkalosis
5.Clinical pharmacokineticsMedium
Practice exercise (made-up values, not clinical guidance). Vancomycin is given as a continuous infusion to a patient whose vancomycin clearance is 4 L/h. What infusion rate R in mg/h gives a steady-state level of 20 mg/L?
CL = 4 L/hCss = 20 mg/L
R = mg/h
6.Clinical pharmacokineticsHard
Practice exercise (made-up values, not clinical guidance). A 79 kg patient has a theophylline level of 4 mg/L; the target is 10 mg/L. The drug is given intravenously as aminophylline (S = 0.8), and the volume of distribution is 0.5 L/kg. What extra loading dose LD raises the level to the target?
79 kgVd = 0.5 L/kgC = 4 → 10 mg/LS = 0.8
LD = mg
7.Clinical nursingMedium
Which type of painkiller should a patient with liver cirrhosis usually avoid?
ANon-steroidal anti-inflammatory drugs such as ibuprofen
BParacetamol (acetaminophen), given in a carefully reduced and monitored dose
CLocal anaesthetic creams
DHot packs applied to a painful joint
8.Clinical nursingHard
A patient suddenly develops a painful red eye with blurred vision, haloes around lights and vomiting. What should be suspected?
ASimple conjunctivitis from a viral infection
BA stye
CAcute angle-closure glaucoma
DDry eye syndrome
3Solutions
1.Lab values & electrolytes
Answer: C · Encourage fluids and mobility as tolerated
Why this is the answer
Hydration helps the kidneys excrete calcium and prevents stones, and weight-bearing mobility slows calcium loss from bone. Calcium-containing foods and antacids are not encouraged. The nurse also monitors for confusion, constipation and arrhythmias.Checked against:Hypercalcemia · MedlinePlus (NIH) (2026)
Answer
C · Encourage fluids and mobility as tolerated
2.Lab values & electrolytes
Answer: D · Low potassium and low sodium from urine losses
Why this is the answer
In the diuretic phase of AKI, the recovering tubules lose large amounts of water and electrolytes, so dehydration, hypokalemia and hyponatremia can occur. Daily weights, intake and output, and frequent electrolytes guide replacement.Checked against:Acute tubular necrosis · MedlinePlus (NIH) (2025)
Answer
D · Low potassium and low sodium from urine losses
3.Arterial blood gas interpretation
Answer: HCO₃⁻ = 33.1 mmol/L
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.
Change in PaCO₂
|66 − 40| = 26 mmHg → 2.6 × 10 mmHg
Expected HCO₃⁻
HCO₃⁻ = 24 + 3.5·2.6 = 33.1 mmol/L
Answer
HCO₃⁻ = 33.1 mmol/L
4.Arterial blood gas interpretation
Answer: added respiratory acidosis
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
1.5·11 + 8 = 24.5 → 22.5–26.5 mmHg
Compare
measured: 33 mmHg → added respiratory acidosis
Answer
added respiratory acidosis
5.Clinical pharmacokinetics
Answer: R = 80 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.
Infusion rate
R = 4·20 = 80 mg/h
Answer
R = 80 mg/h
6.Clinical pharmacokinetics
Answer: LD = 296.3 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 = 0.5·79 = 39.5 L
Rise needed
10 − 4 = 6 mg/L
Loading dose
LD = 39.5·6/(0.8·1) = 296.3 mg
Answer
LD = 296.3 mg
In practice the dose is rounded to a convenient amount.
7.Clinical nursing
Answer: A · Non-steroidal anti-inflammatory drugs such as ibuprofen
Why this is the answer
NSAIDs increase the risk of GI bleeding and can trigger kidney failure and fluid retention in cirrhosis. Paracetamol is usually preferred at a lower, carefully chosen dose.
Answer
A · Non-steroidal anti-inflammatory drugs such as ibuprofen
8.Clinical nursing
Answer: C · Acute angle-closure glaucoma
Why this is the answer
Acute angle-closure glaucoma causes a rapid rise in eye pressure, with pain, visual disturbance, haloes and vomiting. It is an emergency that can cause permanent sight loss without urgent treatment.