Anesthesia Case

Case (clinical stem)

65-year-old male for emergency laparotomy for suspected perforated viscus.

• Weight (TBW): 120.0 kg

• Height: 175 cm (5 ft 9 in)

• BP: 85/45 mmHg (MAP ≈ 58 mmHg) on norepinephrine infusion at 0.05 mcg/kg/min

• HR: 118 bpm

• SpO₂: 95% on 4 L O₂ by nasal cannula

• K⁺: 6.0 mEq/L (hyperkalemia)

• Lactate: 4.5 mmol/L

• Airway exam: Mallampati II, limited neck extension

• Labs: Hgb 9.0, Cr 2.0 (AKI), platelets 170k

• Problem list: Septic shock (MAP low on NE), hyperkalemia, acute kidney injury, need for urgent definitive airway and surgery.

Goal: perform rapid sequence induction (RSI) and safe induction/ventilation while minimizing hemodynamic collapse and avoiding drugs that worsen hyperkalemia.

Step 1 — Basic physiologic calculations

1) Convert height → inches and compute Ideal Body Weight (Devine formula)

Height 175 cm → (175/2.54 = 68.8976) in ≈ 68.9 in → that’s 5 ft 8.9 in (

]

Round sensibly → IBW = 70.5 kg. 

Step 2 — Choose induction agent (hemodynamic strategy & dosing)

Clinical reasoning: patient is septic and hypotensive (MAP ≈ 58 on low-dose NE) and has elevated lactate. For induction in hypotension, many clinicians favor ketamine (sympathomimetic) or reduced dose etomidate; etomidate has less immediate hemodynamic depression but is associated with adrenal enzyme suppression in sepsis (controversial). Ketamine preserves/increases blood pressure in many patients but high doses can still cause hypotension in catecholamine-depleted shock — so dose selection should be careful and often based on IBW or reduced dose in shock. 

Choice here (reasonable approach): Ketamine for induction, reduced RSI dose because of shock and possible catecholamine depletion. Use IBW for sedative dosing in obese/sepsis patients (so we don't overdose lipophilic drug on TBW). Literature/clinical resources often suggest 1–2 mg/kg for induction but recommend lower doses (e.g., 0.5–1 mg/kg) in profoundly shocked patients. 

Planned ketamine dose (chosen): 0.75 mg/kg × IBW (conservative shock dosing to balance induction vs hypotension risk).

Calculation (digit-by-digit):

• IBW = 70.4645 kg → use 70.5 kg.

• Dose = 0.75 mg/kg × 70.5 kg

  • (0.75 \times 70.5 = 52.875) mg.

Round → 53 mg IV ketamine given slowly (over 30–60 seconds) immediately before paralytic. (If patient is extremely obtunded, some clinicians use up to 1.0 mg/kg IBW; titrate to effect and be ready for vasopressor bolus). 

Step 3 — Paralytic choice (contraindications & dosing)

Key constraint: K⁺ = 6.0 mEq/L → succinylcholine is unsafe because it reliably increases serum K⁺ (≈ 0.5–1.0 mEq/L in normals; can cause life-threatening hyperkalemia when K is already high or in denervation states). Therefore use a non-depolarizing agent, rocuronium. (Succinylcholine contraindication for hyperkalemia and denervation states is well documented).

Rocuronium for RSI: to approximate fast onset like succinylcholine, use the higher intubating dose of 1.0–1.2 mg/kg (intubation conditions approach succinylcholine at 1.0–1.2 mg/kg). StatPearls/clinical sources cite 0.6–1.2 mg/kg for intubating conditions. We will dose on TBW to ensure adequate onset in obesity/large body habitus (many clinicians use TBW for rocuronium intubating dose to ensure rapid onset). 

Planned rocuronium dose (choose 1.2 mg/kg TBW):

Calculation:

• TBW = 120.0 kg.

• Dose = 1.2 mg/kg × 120.0 kg = (1.2 \times 120 = 144.0) mg.

→ Rocuronium 144 mg IV bolus for RSI.

(If you prefer to limit drug amounts in renal failure, 1.0 mg/kg could be chosen; note that rocuronium is renally cleared partly and will have prolonged duration with AKI — plan for sugammadex if needed).

Step 4 — Neuromuscular reversal contingency (sugammadex dosing)

If we need immediate reversal soon after giving rocuronium 1.2 mg/kg (e.g., can’t ventilate / can’t oxygenate, or rapid return of spontaneous ventilation is required), sugammadex 16 mg/kg is the recommended dose for immediate reversal within ~3 minutes after 1.2 mg/kg rocuronium. For more typical reversal later when T2 or PTC is present, lower doses (2–4 mg/kg) apply. 

Calculation for sugammadex 16 mg/kg (TBW):

• TBW = 120.0 kg.

• Dose = 16 mg/kg × 120.0 kg = (16 \times 120 = 1920) mg → ~1.92 g sugammadex (round to 2.0 g and give as bolus per formulary/vial sizes). 

Alternative planned routine reversal (if later, at T2 or PTC 1–2):

• T2 present → sugammadex 2 mg/kg = (2 \times 120 = 240) mg.

• PTC 1–2 / no TOF twitches → sugammadex 4 mg/kg = (4 \times 120 = 480) mg.
  (These are per the product label / prescribing info.)

Note: Sugammadex is renally excreted — caution/avoid in severe renal impairment and expect prolonged sugammadex/complex presence if AKI; but in emergencies the FDA-approved dosing is used with awareness of renal issues. 

Step 5 — Peri-intubation hemodynamic support plan

Preoxygenation & monitoring: 3–5 minutes or 4 vital-capacity breaths if not possible; have difficult airway cart, video laryngoscope, Bougie ready.

Vasopressor strategy (to treat likely post-intubation hypotension):

• Continue norepinephrine infusion; consider increase by 0.02–0.05 mcg/kg/min at induction if tolerated. (Current: 0.05 mcg/kg/min × 120 kg = 6.0 mcg/min NE infusion rate).

  • Calculation: (0.05\ \text{mcg/kg/min}\times 120\ \text{kg} = 6.0\ \text{mcg/min}.)

• Prepare push-dose vasopressor: phenylephrine 100 mcg IV bolus (mix/readily available) or push-dose epinephrine 10–20 mcg IV if poor cardiac output. Typical push doses: phenylephrine 50–200 mcg or epi 5–20 mcg. Use phenylephrine if tachycardic patients to raise BP via α-agonism; if cardiac output is poor, use small epi boluses. Have these drawn up and syringe labeled. 

Rationale: Intubation + induction often produces post-intubation hypotension; be proactive. If severe hypotension occurs (SBP < 70 or MAP < 50), consider immediate 1–2 mL of push-dose epinephrine (10–20 mcg) or phenylephrine 100–200 mcg, and bolus crystalloid (250–500 mL) while increasing NE infusion. 

Step 6 — Ventilator initial settings after successful intubation

Use lung-protective strategy based on IBW (PBW):

• Tidal volume (Vt): 6 mL/kg × IBW.

  • IBW = 70.5 kg → Vt = (6 \times 70.5 = 423.0) mL → set Vt ≈ 420 mL. (eCampus Ontario)

• Mode: VC-assist or PRVC; initial RR 14–18 (titrate to ETCO₂ ~35–45), adjust RR to maintain minute ventilation and pH.

• PEEP: start 5–8 cmH₂O (higher if hypoxemic or ARDS physiology).

• FiO₂: start 100% immediately post-intubation then rapidly titrate down to keep SpO₂ 92–96% (avoid hyperoxia).

• Plateau pressure target: keep ≤30 cmH₂O; if Pplat >30, reduce Vt stepwise to 5 mL/kg IBW if needed. 

Step 7 — Other immediate peri-op actions

1. Treat hyperkalemia pre-/post-intubation (because K=6.0): if time, give IV calcium (calcium gluconate 1 g IV) to stabilize myocardium, then insulin + dextrose (e.g., insulin 10 units IV + D50 25–50 g), nebulized albuterol, and consider furosemide if urine output and renal function allow or urgent dialysis if life-threatening levels persist. If immediate surgery cannot be delayed, at minimum give IV calcium prior to paralytic and be ready for cardiac monitoring/defibrillation. (This is a medical algorithm; coordinate with the team.) Important: succinylcholine is contraindicated — we chose rocuronium.

2. Antibiotics & source control: push broad-spectrum antibiotics per sepsis protocol (time-sensitive).

3. Fluids / vasopressors: if not volume overloaded, a small bolus (250–500 mL crystalloid) may be given; continue NE and escalate as needed per MAP targets. For septic shock guidelines suggest early fluids (30 mL/kg is guideline for initial resuscitation in septic shock, but individualize in peri-operative setting with AKI and possible third spacing).

4. Laboratory & monitoring: ABG immediately post-intubation, serial K⁺, urine output, arterial line placement for beat-to-beat BP if surgery and hypotension expected.

Quick summary (concise orders with computed doses)

• IBW (Devine): 70.5 kg.

• Induction agent: Ketamine 53 mg IV (0.75 mg/kg × 70.5 kg), given slowly.

• Paralytic (RSI): Rocuronium 144 mg IV (1.2 mg/kg × 120 kg TBW).

• If immediate reversal required within ~3 min after rocuronium → sugammadex 16 mg/kg = 1,920 mg (~1.92 g) (round to available vial dosing). Otherwise, T2→2 mg/kg (240 mg) or PTC 1–2→4 mg/kg (480 mg).

• Peri-intubation vasopressors: continue NE at 0.05 mcg/kg/min (6.0 mcg/min). Prepare push-dose phenylephrine 100 mcg IV (50–200 mcg PRN) or push epi 10–20 mcg if needed.

• Ventilator: Vt ≈ 420 mL (6 mL/kg × IBW 70.5 kg); RR 14–18; PEEP 5–8 cmH₂O; FiO₂ 100% then titrate down.

Key references for the most important claims

1. Devine IBW formula (used for weight-based dosing).

2. Ketamine for induction / lower doses in shock; etomidate considerations (ketamine favored in many hypotensive patients; etomidate has adrenal suppression concerns in sepsis).

3. Succinylcholine causes K+ rise and is unsafe with hyperkalemia — avoid succinylcholine when K is high.

4. Rocuronium intubating dose 0.6–1.2 mg/kg; higher dose approximates succinylcholine onset. 

5. Sugammadex dosing (2, 4, 16 mg/kg) — product labeling / prescribing info for routine and immediate reversal. 

Practical caveats & pearls

• Dose rounding & pharmacy: round doses to vial sizes and check local formulary (sugammadex vial sizes, ketamine prep, rocuronium vials).

• Renal dysfunction (Cr 2.0): rocuronium and sugammadex clearance affected; sugammadex accumulates in renal failure — but it remains the recommended reversal agent when needed in emergencies; discuss risk/benefit.

• If severe catecholamine depletion exists (very high shock index), even ketamine may not raise BP — be ready with push-dose vasopressor and immediate escalation of NE infusion.

• If airway is predicted difficult, consider awake intubation if time permits; otherwise, ensure video laryngoscope and bougie are ready and have ENT/back-up available.