Hospital-acquired and ventilator-associated pneumonia

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

HAP and VAP are syndromes rather than culture results. Intubated patients commonly have colonised airways, abnormal chest radiographs and systemic inflammation from other causes. A defensible diagnosis therefore combines timing, a new pulmonary deterioration, imaging and microbiology while actively considering mimics. Overdiagnosis exposes patients to nephrotoxicity, Clostridioides difficile and selection of resistant organisms; underdiagnosis risks sepsis and respiratory failure.

Early-onset disease without resistance risks may involve usual respiratory organisms, whereas prolonged admission, broad-spectrum exposure, critical illness and previous resistant Gram-negative or MRSA carriage change the empirical choice. National tables cannot replace the current local antibiogram. The safe sequence is culture where possible, prompt severity-adjusted therapy, daily reassessment and deliberate de-escalation.

Key points

Hospital-acquired pneumonia develops 48 hours or more after admission and was not incubating at entry; ventilator-associated pneumonia usually begins more than 48 hours after endotracheal intubation.
Require a compatible new clinical syndrome—fever or hypothermia, purulent secretions, inflammatory response, worsening gas exchange—and new or progressive radiographic infiltrate; no single sign proves VAP.
Distinguish pneumonia from atelectasis, pulmonary oedema, aspiration pneumonitis, pulmonary embolism, acute respiratory distress syndrome, alveolar haemorrhage and ventilator-associated tracheobronchitis.
Send a good-quality lower-respiratory sample before antibiotics when this causes no harmful delay; interpret growth against prior colonisation, airway device, Gram stain and the clinical trajectory.
Choose empirical antibiotics using illness severity, time in hospital, recent antibiotics, previous resistant isolates, local ICU ecology, renal function, allergy and the possibility of MRSA.
NICE recommends starting treatment as soon as possible after diagnosis and within 4 hours; sepsis pathways may require still faster administration.
Review IV therapy and microbiology at about 48 hours, narrow or stop when the diagnosis is unsupported, and review after 5 total days with stopping considered when clinically stable.
Prevention centres on minimising unnecessary ventilation and sedation, safe airway care, head-up positioning when appropriate, oral care, hand hygiene and antimicrobial stewardship.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Healthcare-associated bacterial exposure

Hospital flora colonise the oropharynx and airways, with pathogen and resistance patterns shaped by local ecology and recent antimicrobial exposure.

Artificial-airway bypass

An endotracheal or tracheostomy tube bypasses upper-airway defence, impairs cough and allows contaminated secretions to track into the lower lung.

Aspiration and immobility

Reduced consciousness, dysphagia, supine positioning and gastric reflux increase microaspiration, while immobility promotes dependent collapse and secretion retention.

Host vulnerability

Critical illness, frailty, chronic lung disease and immune suppression reduce mucociliary, cellular and systemic defences against lower-airway infection.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Airway colonisation
Hospital organisms establish themselves in the oropharynx, dental plaque, ventilator circuit condensate or biofilm on an artificial airway.
2
Microaspiration
Colonised secretions pass below the vocal cords and overwhelm clearance in dependent bronchi and alveoli, thereby altering ventilation, gas transfer or respiratory mechanics.
3
Alveolar infection
Microbial replication recruits neutrophils and protein-rich exudate, producing new inflammatory infiltrates and impaired ventilation, which links the underlying lesion to the observed respiratory dysfunction.
4
Systemic and gas-exchange effects
Consolidation causes shunt and hypoxaemia, while severe infection triggers sepsis, haemodynamic instability and multi-organ dysfunction, with effects that increase as the pathological process progresses.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Non-ventilated HAP

New cough, purulent sputum, dyspnoea, fever or hypothermia and focal signs arising at least 48 hours after admission, with new infiltrate and no better explanation.

Ventilator-associated pneumoniaRed flag

New or progressive infiltrate with worsening oxygenation, increased or purulent secretions and systemic inflammatory features after more than 48 hours of invasive ventilation; rising ventilator support is a severity marker.

Severe or resistant-pathogen riskRed flag

Shock, organ dysfunction, rapidly increasing FiO2, late onset, recent broad-spectrum antibiotics, known resistant colonisation, bronchiectasis or prolonged ICU exposure justify urgent broad initial cover and specialist review.

Colonisation or tracheobronchitis

A positive tracheal aspirate without a convincing new infiltrate or physiological deterioration may represent colonisation; ventilator-associated tracheobronchitis causes secretions and fever without clear pneumonia.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Chest radiographFirst step
Why
Identify a new infiltrate and complications while comparing with prior films.
Interpretation and limitations
Portable films are insensitive and nonspecific; rapid clearing after recruitment or diuresis supports atelectasis or oedema, while cavitation or effusion prompts CT or pleural assessment.
02
Lower-respiratory culture
Why
Identify plausible pathogens and enable de-escalation before antibiotics when practical.
Interpretation and limitations
Use sputum in non-intubated patients and tracheal aspirate or locally approved sampling in VAP. Heavy growth is not automatically causal in a colonised airway; relate it to quality, Gram stain and prior isolates.
03
Blood cultures and sepsis bloods
Why
Detect bacteraemia, organ dysfunction and an alternative infection source in severe illness.
Interpretation and limitations
Take cultures before antimicrobials if this does not delay treatment. FBC, renal/liver profile, CRP and lactate support severity and dosing but cannot establish pneumonia alone.
04
Blood gas and continuous oximetry
Why
Quantify hypoxaemia, hypercapnia and ventilatory failure.
Interpretation and limitations
Escalating oxygen, acidosis, fatigue or rising PaCO2 requires airway and critical-care review; prescribe oxygen to 94–98% for most adults or 88–92% when hypercapnic failure risk applies.
05
CT chest or thoracic ultrasound
Why
Resolve uncertain radiography and identify abscess, empyema, obstruction or embolic alternatives.
Interpretation and limitations
Use when deterioration is unexplained or response is poor; imaging must not delay initial stabilisation or antibiotics in severe sepsis.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Airway colonisation

A positive endotracheal or sputum culture without a compatible new clinical and radiographic syndrome may reflect colonisation rather than pneumonia.

Atelectasis

Dependent collapse after surgery or ventilation causes opacity and hypoxaemia but often lacks purulent inflammatory evidence and may improve with recruitment and mobilisation.

Pulmonary oedema

Fluid balance, cardiac findings and bilateral congestion support hydrostatic oedema, though fever and secretions may coexist in critical illness.

Pulmonary embolism

Acute unexplained oxygen or circulatory deterioration with thrombosis risk requires embolism assessment despite fever or non-specific infiltrates.

Acute respiratory distress syndrome

Diffuse permeability injury from sepsis or another insult can cause bilateral opacities without a new focal bacterial pneumonia.

Additional chapter-specific clues

Important mimic

Dependent atelectasis, fluid overload, aspiration, pulmonary embolism, ARDS and drug or transfusion reactions can produce fever, hypoxaemia and bilateral shadowing without bacterial pneumonia.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01First hourStabilise and establish the syndromeFirst stepSuspected HAP or VAP with new physiological deterioration.

1EscalationPerform ABCDE assessment, prescribe target-based oxygen, check the airway and ventilator circuit, obtain chest imaging and involve critical care early for shock or escalating support.
2Review admission timing, aspiration, recent procedures, fluid balance, antibiotics, prior cultures and resistance risks; search for non-pulmonary sepsis and common radiographic mimics.
3Collect lower-respiratory and blood cultures when indicated without harmful delay, then start a locally approved empirical regimen within the NICE timeframe.

02Empirical choiceMatch spectrum to riskA working diagnosis is established before culture results.

1For non-severe disease with low resistance risk, use the current NICE/local narrower oral or IV option after checking allergy, renal function and swallowing.
2For severe disease, VAP or resistance risk, select broad Gram-negative coverage from the local ICU policy and add MRSA cover only when epidemiology or previous isolates justify it.
3Document why each component is present, the intended review time and the samples that will permit narrowing; avoid duplicating anaerobic or atypical cover without a reason.

0348-hour reviewDe-escalate deliberatelyEscalationClinical response and preliminary microbiology are available.

1Reassess diagnosis, temperature, oxygen/ventilator requirement, haemodynamics, inflammatory markers and imaging; stop antibiotics if infection is no longer credible.
2Narrow to the least broad active agent, switch IV to oral when stable and able to absorb safely, and adjust for renal function and susceptibilities.
3Review after 5 total days and consider stopping if clinically stable; extend only for a documented complication, slow response or organism-specific reason.

04FailureInvestigate non-responseShock, respiratory deterioration or absent improvement after 48–72 hours.

1Check source control, dosing, delivery and resistance; repeat cultures selectively and seek microbiology and respiratory review.
2Use CT or pleural ultrasound to look for empyema, abscess, obstruction, embolism, oedema or ARDS rather than reflexively adding antibiotics.
3EscalationEscalate organ support and drain pleural infection when indicated; consider fungal, viral or mycobacterial disease in the relevant host.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Provides a narrower first-line option for non-severe HAP when local susceptibility and individual risk support it.

Co-amoxiclav for low-resistance-risk HAP

A typical NICE oral option is 500/125 mg three times daily for 5 days; use IV therapy if oral treatment is unsafe or severity requires it.

Check immediate penicillin allergy, hepatic history and renal function. This is not adequate empirical therapy for shock, known resistant Gram-negative infection or many ICU VAP settings.

Broad antipseudomonal empirical cover for severe HAP or VAP when local ecology supports its use.

Piperacillin with tazobactam

A common severe-infection regimen is 4.5 g IV every 8 hours, increased to every 6 hours in selected severe infection according to local policy and renal function.

Obtain cultures, renal-adjust promptly and de-escalate. Consider sodium load, allergy, cytopenia with prolonged use and local resistance; it does not reliably cover MRSA.

Adds MRSA activity only when carriage, prior infection, necrotising features or local epidemiology make MRSA credible.

Vancomycin or linezolid for suspected MRSA

Use current local weight, renal and concentration-guided vancomycin dosing, or linezolid 600 mg orally or IV twice daily when the approved pathway selects it.

Vancomycin requires renal and level monitoring. Linezolid can cause cytopenia, neuropathy and serotonergic interactions; seek microbiology advice and stop unnecessary MRSA cover early.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Respiratory failure

Increasing shunt and secretion burden can destabilise spontaneous breathing or prolong and intensify ventilatory support, and potentially prolonging treatment and functional recovery.

Septic shock

Invasive infection and dysregulated inflammation may cause vasodilatation, low perfusion and multi-organ failure, creating an additional need for recognition and targeted treatment.

Lung abscess or empyema

Necrotising pathogens or delayed source control can cavitate lung or extend infection into pleura, and increasing the burden of otherwise local respiratory disease.

Antimicrobial resistance

Broad or repeated empirical treatment selects resistant organisms and increases toxicity and secondary infection risk, adding morbidity beyond the initial pulmonary disorder.

Prolonged critical illness

Pneumonia extends ventilation, sedation, immobility and hospital stay, increasing weakness, delirium and further healthcare-associated infection, and increasing the burden of otherwise local respiratory disease.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Record NEWS2 or equivalent observations, oxygen or ventilator settings, secretion burden, urine output and mental state frequently until clearly stable.
Review culture results and antibiotic spectrum daily; document the 48-hour IV-to-oral and de-escalation decision even when treatment is unchanged.
Trend renal and liver function for dose adjustment and toxicity, especially with broad beta-lactams, vancomycin or concurrent nephrotoxins.
At day 5, apply clinical-stability criteria rather than extending automatically; persistent instability requires a revised diagnosis and source-control search.
Monitor ventilator prevention measures, cuff/airway care and sedation goals through the local ICU bundle without allowing a checklist to replace individual assessment.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Culture does not equal infection

Endotracheal tubes rapidly acquire biofilm. A resistant organism in a tracheal aspirate may be a coloniser unless the clinical, radiological and inflammatory picture supports pneumonia.

A normal film is not decisive

Portable radiography can miss early or dependent disease, but CT should be reserved for unresolved diagnostic or complication questions rather than used routinely.

Duration is an active decision

NICE now brings HAP review into a five-day framework when stable. Longer treatment needs a reason such as abscess, empyema, bacteraemia or slow response.

VAP prevention is multidisciplinary

Avoiding unnecessary intubation and sedation, safe mobilisation, airway care, oral hygiene and infection control matter more than prophylactic antibiotics.

Failure is often diagnostic

Worsening despite apparently active therapy should trigger a search for oedema, embolism, ARDS, obstruction or undrained pleural infection before indiscriminate spectrum escalation.

11Common pitfallsFrequent interpretation and management errors.

01
Treating a positive tracheal aspirate as VAP without a new pulmonary syndrome.
02
Choosing empirical antibiotics without checking prior isolates and the current local antibiogram.
03
Continuing every initial drug after cultures permit narrowing or the diagnosis becomes doubtful.
04
Calling persistent fever treatment failure without looking for line infection, C. difficile, thrombosis or drug fever.
05
Extending uncomplicated HAP automatically beyond five days despite clinical stability.