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 starts high-dose prednisone. Which laboratory change should the nurse expect?
AA fall in serum sodium
BA fall in the white cell count
CA rise in blood glucose
DA rise in serum potassium
2.Lab values & electrolytesHard
A patient on clozapine for 2 years has been stable. Which statement shows a need for further teaching?
A"I'll keep all my scheduled blood test visits"
B"I'll tell other doctors that I take clozapine"
C"I'll report a sore throat or fever at once"
D"I can stop my blood tests since I feel well"
3.Arterial blood gas interpretationMedium
Practice values: Na⁺ 131 mmol/L, glucose 10.3 mmol/L and urea 20.4 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 131 mmol/Lglucose 10.3 mmol/Lurea 20.4 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
A practice gas shows a metabolic acidosis: pH 7.31, PaCO₂ 31 mmHg (4.1 kPa), HCO₃⁻ 15 mmol/L. Compare the measured PaCO₂ with Winter’s formula. Click your interpretation.
pH 7.31PaCO₂ 31 mmHg (4.1 kPa)HCO₃⁻ 15 mmol/L
1appropriate compensation
2added respiratory acidosis
3added respiratory alkalosis
5.Clinical pharmacokineticsMedium
Practice exercise (made-up values, not clinical guidance). A 70 kg patient is to receive an aminophylline infusion (salt factor S = 0.8: 80% of aminophylline is theophylline). The theophylline clearance is 0.04 L/kg/h. What aminophylline infusion rate R in mg/h gives a steady-state theophylline level of 10 mg/L?
70 kgCL = 0.04 L/kg/hCss = 10 mg/LS = 0.8
R = mg/h
6.Clinical pharmacokineticsHard
Practice exercise (made-up values, not clinical guidance). A vancomycin infusion runs at 75 mg/h with no loading dose. The patient's clearance is 3 L/h and the half-life is 6 h. What is the level C after 9 h?
R = 75 mg/hCL = 3 L/ht½ = 6 ht = 9 h
C = mg/L
7.Clinical nursingMedium
A patient on the ward has shingles with open blisters. Which people are most at risk from contact?
ANo one, because shingles cannot spread
BPeople who have already had chickenpox in childhood and are now healthy
COnly people over 80 who have already had shingles themselves
DPregnant women and immunocompromised people who have not had chickenpox
8.Clinical nursingHard
A patient with acute pancreatitis is in severe epigastric pain radiating to the back. Which nursing care is most important?
AA large fatty meal to stimulate the pancreas
BRestricting all fluids
CStrict bed rest without observations
DAdequate pain relief, IV fluids and close fluid balance monitoring
3Solutions
1.Lab values & electrolytes
Answer: C · A rise in blood glucose
Why this is the answer
Glucocorticoids raise blood glucose by increasing glucose production and reducing insulin sensitivity. They also tend to lower potassium, retain sodium and raise the white cell count by releasing neutrophils into the blood.Checked against:Blood Glucose Test · MedlinePlus (NIH) (2024)
Answer
C · A rise in blood glucose
2.Lab values & electrolytes
Answer: D · "I can stop my blood tests since I feel well"
Why this is the answer
Clozapine requires ongoing ANC monitoring according to the schedule, because severe neutropenia can occur without warning. The patient must keep blood test appointments and report signs of infection at once.
Answer
D · "I can stop my blood tests since I feel well"
3.Arterial blood gas interpretation
Answer: Osm = 293 mOsm/kg
Derived values: calculated serum osmolality is 2·Na⁺ + glucose + urea with all values in mmol/L (2·Na⁺ + glucose/18 + BUN/2.8 with glucose and BUN in mg/dL); normal is about 275–295 mOsm/kg. The P/F ratio is PaO₂ divided by FiO₂ as a fraction. The alveolar oxygen pressure is PAO₂ = FiO₂·(760 − 47) − PaCO₂/0.8 mmHg at sea level, and the A–a gradient is PAO₂ − PaO₂.
Calculated osmolality
Osm = 2·131 + 10.3 + 20.4 = 292.7 ≈ 293 mOsm/kg
Answer
Osm = 293 mOsm/kg
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
1.5·15 + 8 = 30.5 → 28.5–32.5 mmHg
Compare
measured: 31 mmHg → appropriate compensation
Answer
appropriate compensation
5.Clinical pharmacokinetics
Answer: R = 35 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 = 0.04·70 = 2.8 L/h
Infusion rate
R = CL·Css/S = 2.8·10/0.8 = 35 mg/h
Answer
R = 35 mg/h
6.Clinical pharmacokinetics
Answer: C = 16.16 mg/L
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.
Steady-state level
Css = 75/3 = 25 mg/L
Rate constant
k = 0.693/6 = 0.1155 h⁻¹
Level after the given time
C = 25·(1 − e−0.1155·9) = 16.16 mg/L
Answer
C = 16.16 mg/L
7.Clinical nursing
Answer: D · Pregnant women and immunocompromised people who have not had chickenpox
Why this is the answer
Someone who has never had chickenpox can catch chickenpox from contact with shingles blisters. Non-immune pregnant and immunocompromised people are at particular risk, so lesions are covered and precautions followed.
Answer
D · Pregnant women and immunocompromised people who have not had chickenpox
8.Clinical nursing
Answer: D · Adequate pain relief, IV fluids and close fluid balance monitoring
Why this is the answer
Acute pancreatitis can cause large fluid losses and organ failure. Care focuses on fluid resuscitation, analgesia, monitoring urine output, glucose and early nutrition when possible.
Answer
D · Adequate pain relief, IV fluids and close fluid balance monitoring