01Core principlesThe concepts and mechanisms needed to understand the subject.
Intensive care combines close observation with support for failing organs and treatment of the disease causing that failure. Mechanical ventilation, vasoactive infusions and renal replacement alter physiology but also introduce risks. The clinician must ask what problem an intervention is solving, what response would demonstrate benefit and what adverse effect would require modification. Escalation is most useful before a patient deteriorates beyond the ability to transfer safely.
Organ systems interact. Positive-pressure ventilation may improve gas exchange while reducing venous return, and large fluid volumes may improve circulation while worsening lung oedema. Kidney failure changes medicine handling and fluid tolerance. Decisions therefore need an integrated assessment rather than separate targets pursued independently. The patient’s prior function, wishes, likelihood of recovery and burdens of treatment also shape an appropriate plan.
Key points
- Organ support buys time for diagnosis and treatment of the cause; a normal displayed number can depend on substantial ongoing support.
- Assess oxygenation and ventilation separately, using blood gases and the actual respiratory support settings.
- In ARDS, use lung-protective tidal volumes based on predicted body weight and monitor plateau pressure.
- A higher blood pressure after a vasopressor does not necessarily mean adequate tissue perfusion or corrected circulating volume.
- Renal replacement is driven by clinical complications and response to treatment, not a creatinine threshold alone.
- Review daily whether each support remains necessary and start rehabilitation, communication and recovery planning during the ICU admission.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Distinguish hypoxaemia from inadequate carbon dioxide clearance and airway-protection failure. A satisfactory saturation on high inspired oxygen or marked support is evidence of treatment dependence, not proof that the lung problem has resolved.
Look at capillary refill, skin temperature, mentation, lactate trend and urine output alongside pressure. Persistent hypoperfusion can reflect volume loss, vasodilatation, pump failure or obstruction, each requiring a different strategy.
Rising potassium, acidaemia, fluid overload and uraemic complications may require urgent renal support. Oliguria alone needs investigation of perfusion, obstruction and medicines before an automatic treatment decision.
Sedation, delirium, immobility and the underlying illness can all reduce participation and function. Define why sedation is needed and assess pain, cognition, strength and communication as physiology permits.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Blood gases with recorded ventilator settings - Why
- Interpret gas exchange in relation to the support producing it.
- Interpretation and limitations
- Record inspired oxygen, mode, tidal volume and relevant pressures with the sample. A PaO2 value is difficult to interpret without FiO2, while rising PaCO2 may reflect inadequate minute ventilation or increased physiological dead space.
- 02
Ventilator measurements and mechanics - Why
- Limit injury while delivering sufficient support.
- Interpretation and limitations
- Check tidal volume against predicted body weight and measure plateau pressure appropriately. Peak pressure includes airway resistance as well as elastic pressure, so an isolated peak rise requires examination for obstruction and circuit problems.
- 03
Perfusion assessment and focused echocardiography - Why
- Identify the dominant circulatory mechanism and response to treatment.
- Interpretation and limitations
- Integrate clinical findings, lactate trend and focused cardiac assessment by a trained operator. Static pressure numbers alone cannot establish whether more fluid, a vasopressor or inotropic support is appropriate.
- 04
Renal, electrolyte and fluid-balance review - Why
- Identify urgent renal-replacement indications and avoid preventable complications.
- Interpretation and limitations
- Review potassium, acid-base state, urine output, cumulative balance and the cause of AKI. NICE recommends immediate renal-replacement referral for serious complications that are not responding to medical treatment.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked caseLung-protective ventilation after severe pneumoniaAn intubated adult has ARDS. Predicted body weight from height and sex is 70 kg, although actual weight is 105 kg. The team selects an initial tidal volume of 6 mL/kg predicted weight.+
- 1Calculate 6 × 70 = 420 mL, using predicted rather than actual weight. Confirm the measured delivered tidal volume and synchrony after setting the ventilator.
- 2Measure plateau pressure with an appropriate inspiratory hold when the measurement is valid. It is 34 cmH2O, above the usual protective target of below 30 cmH2O, so the setting requires reassessment.
- 3The critical-care team reduces tidal volume to 5 mL/kg predicted weight, or 350 mL, while reviewing respiratory rate, PEEP, acid-base status and potential causes of reduced compliance.
- 4Repeat assessment shows plateau pressure 28 cmH2O and acceptable gas exchange for the agreed patient-specific targets. Verify blood pressure and perfusion as well, because ventilator changes can affect circulation.
- 5Continue treating pneumonia and review positioning and other ARDS measures if hypoxaemia remains severe. The lower pressure demonstrates one benefit, but ongoing oxygen need and the overall trajectory determine the next decision.
02Circulatory branchPersistent shock after initial volume assessmentAn adult has ongoing hypotension and poor perfusion despite appropriate initial resuscitation, with no evidence that automatic further fluid would be beneficial.+
- 1Reassess the likely mechanism using examination, treatment response and focused cardiac information. Continue investigating bleeding, infection, obstruction or myocardial dysfunction instead of treating the pressure in isolation.
- 2Initiate an appropriately prescribed vasoactive infusion under critical-care supervision when indicated, with verified concentration, route, pump settings and a patient-specific pressure and perfusion target.
- 3Reassess tissue perfusion and adverse effects after each adjustment. A rising pressure with colder extremities, worsening lactate or reduced urine output demands review of flow, volume and the selected strategy.
03Renal branchComplications persist despite medical treatmentA patient with AKI has recurrent severe hyperkalaemia and pulmonary oedema despite appropriate emergency medical treatment.+
- 1Continue immediate monitoring and treatment of dangerous potassium-related or respiratory abnormalities while contacting nephrology and intensive care for urgent renal replacement.
- 2Base the decision on refractory complications and the patient’s overall condition rather than waiting for a particular creatinine or urea value. Agree the modality and haemodynamic requirements with the specialist team.
- 3After support begins, review electrolyte correction, acid-base state, fluid removal and circulatory tolerance. Adjust medicine doses for the actual renal-replacement method and reassess continuing need daily.
05Relevant medicines and safetySpecific regimens and precautions where medicines are relevant.
Noradrenaline infusion: concentration and titration example
For the cited 1 mg/mL concentrate, dilute 2 mL with 48 mL of 5% glucose to a total 50 mL: 40 micrograms/mL noradrenaline base. Its SmPC initial rate is 10–20 mL/hour, equivalent to 0.4–0.8 mg/hour, then titrate to the prescribed physiological target.This product specifies central venous administration by controlled infusion. Never give the concentrate undiluted. Check base versus salt units, correct volume deficit where present, monitor rhythm and perfusion, and reduce gradually when support is no longer needed.
06Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- At each review, record the amount of organ support as well as the resulting observations; falling support requirements can demonstrate improvement even before all laboratory values normalise.
- Reassess ventilator synchrony, pressure limits, oxygen exposure and readiness for reduced support, alongside the sedation level and ability to protect the airway.
- Review fluid balance, skin perfusion, renal function and vasoactive dose together; avoid achieving one numerical target at the expense of another organ system.
- Include nutrition, mobility, pressure-area care, thrombosis prevention, delirium assessment and communication needs in the multidisciplinary daily plan.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
An infusion calculation must preserve units
At 40 micrograms/mL, 10.5 mL/hour delivers 420 micrograms/hour. For a 70 kg adult this is 0.1 micrograms/kg/min: dividing by both weight and sixty verifies the prescription.
Renal replacement changes prescribing
Drug removal depends on the technique, settings and residual kidney function. A dose selected for anuric AKI without dialysis may become inappropriate when continuous renal replacement begins.
Rehabilitation begins during critical illness
GPICS V3 calls for early assessment and a personalised multidisciplinary rehabilitation plan. Recovery involves cognition, swallowing, psychological health and practical independence as well as muscle strength.
Treatment goals should be revisited
A time-limited trial of support may clarify reversibility when prognosis is uncertain. Agree what improvement would justify continuation and discuss changes with the patient or those close to them as appropriate.
08Common pitfallsFrequent interpretation and management errors.
- 01
Do not calculate an ARDS tidal volume from actual body weight in obesity, or accept a high plateau pressure without reassessing the protective strategy.
- 02
Do not equate a vasopressor-corrected blood pressure with adequate blood volume or satisfactory organ perfusion.
- 03
Do not postpone renal-replacement referral for refractory life-threatening complications while waiting for an arbitrary biochemical threshold.
- 04
Do not treat survival to ICU discharge as the only outcome; explain ongoing needs and hand over a coherent rehabilitation and follow-up plan.