Vaso-occlusive sickle crisis

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

Deoxygenation, acidosis, dehydration, inflammation and cellular adhesion promote haemoglobin S polymerisation and rigid erythrocytes. Obstruction and reperfusion activate endothelium, platelets, leucocytes and nociceptive pathways, producing pain that can be severe without visible swelling or an abnormal radiograph. Episodes may follow infection, cold, exertion, stress or reduced intake, but many have no identifiable trigger. Making the patient prove a trigger before analgesia is biologically unsound and delays care.

The acute assessment does two jobs simultaneously: relieve pain and decide whether this is uncomplicated. Ask how location and quality compare with previous episodes, what has already been taken, and whether fever, cough, chest pain, dyspnoea, neurological change, urinary symptoms, priapism, pregnancy or trauma is present. Examine cardiorespiratory status, hydration, abdomen, joints, bones and neurology. Routine imaging of every painful area is low value; investigate a changed phenotype, focal infection, fracture, abdominal emergency or acute chest concern.

Analgesia is iterative. Use the individual plan, a rapid strong-opioid route for severe pain, regular paracetamol and an NSAID when safe, plus antiemetic, laxative and thrombosis assessment. Intramuscular injections are avoided. Fluids correct a measured deficit; they are not an analgesic infusion. Persistent pain calls for dose review, patient-controlled delivery, acute-pain or haematology input and renewed diagnostic assessment. It should not provoke punitive withholding or automatic dose escalation without sedation monitoring.

Key points

A vaso-occlusive episode is acute pain from microvascular obstruction and inflammation, usually in bone or marrow but potentially involving any organ.
Pain is whatever the patient says it is; previous opioid exposure and individual care plans should inform rather than discredit the assessment.
Use the person's analgesia plan when available, assess pain, observations and recent medicines, and deliver initial analgesia within 30 minutes of arrival.
For severe pain, NICE supports a strong opioid by a suitable route, with paracetamol and an NSAID unless contraindicated; pethidine should not be used.
Reassess pain, sedation and vital signs every 30 minutes until satisfactory control, then at least every four hours with adverse-effect review.
Give oxygen only for hypoxaemia or another physiological indication, and provide fluids to correct deficit without routine overhydration that can worsen pulmonary complications.
A chest examination and oxygen saturation are repeated because acute chest syndrome can develop after admission, opioid exposure or evolving infection.
Fever needs cultures and prompt antimicrobial assessment; focal bone pain with persistent inflammation may be osteomyelitis rather than uncomplicated vaso-occlusion.
Patient-controlled analgesia should be considered when repeated opioid boluses are needed, with settings informed by prior exposure and local acute-pain expertise.
Discharge requires stable observations, manageable oral analgesia, ability to drink and mobilise as appropriate, red-flag education and a follow-up route.

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

Polymerisation triggers

Hypoxia, dehydration, acidosis, infection and temperature stress can increase deoxygenated haemoglobin S polymerisation, although a substantial proportion of painful episodes has no identifiable precipitant.

Adhesive inflammation

Activated erythrocytes, leucocytes, platelets and endothelium adhere within post-capillary vessels, amplifying obstruction and inflammation beyond the mechanical effect of sickled cells alone.

Individual disease burden

Genotype, fetal haemoglobin, prior organ injury, pain sensitisation and access to disease modification influence frequency, anatomical pattern and analgesic requirement.

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

1
Microvascular obstruction
Rigid and adhesive blood cells slow or stop regional flow, reducing tissue oxygen and generating ischaemic nociception, particularly within highly vascular marrow.
2
Reperfusion inflammation
Restored flow releases oxidants and inflammatory mediators that recruit further cells, so pain and tissue injury can continue after the initial obstruction changes.
3
Pain-system amplification
Repeated acute episodes, inflammation and nerve injury can generate peripheral and central sensitisation, causing mixed acute-on-chronic pain that still requires respectful assessment.

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

Typical episode

Severe deep limb, back, rib or joint-region pain resembles prior crises without focal neurological, pulmonary or septic findings.

Pain is patient reported

Normal imaging, quiet behaviour or opioid tolerance does not disprove severe microvascular pain and must not delay treatment.

Pulmonary transitionRed flag

New cough, chest pain, falling saturation, tachypnoea or fever during treatment raises acute chest syndrome and needs immediate reassessment.

Focal infection

Persistent local heat, swelling, fever or restricted joint movement is atypical for uncomplicated crisis and requires targeted cultures and imaging.

Atypical pain

A new anatomical site, peritonism, trauma or progressive neurological symptom should be investigated on its own merits.

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
ABCDE observations and pain assessmentFirst step
Why
Identify physiological compromise and establish an analgesia baseline.
Interpretation and limitations
Repeat saturation, respiratory rate and sedation after opioids; a rising early-warning score is not explained by pain alone.
02
Full blood count and reticulocytes
Why
Compare anaemia and marrow response with personal baseline.
Interpretation and limitations
A large haemoglobin fall, reticulocytopenia, neutrophilia or thrombocytopenia suggests an additional complication and changes transfusion or infection review.
03
Renal, liver and haemolysis profile
Why
Assess dehydration, organ injury and altered medicine clearance.
Interpretation and limitations
Creatinine change constrains NSAIDs and opioids; a cholestatic pattern or disproportionate haemolysis prompts a separate cause search.
04
Chest radiograph
Why
Identify a new infiltrate when respiratory features are present.
Interpretation and limitations
Early films can be normal; repeat imaging and escalation are required if hypoxia or chest symptoms evolve.
05
Cultures and infection tests
Why
Find bacterial or viral triggers when fever or sepsis is possible.
Interpretation and limitations
Obtain blood cultures promptly where feasible but do not delay empirical antimicrobials in systemic illness or functional asplenia.
06
Targeted bone, joint or abdominal imaging
Why
Investigate a focal atypical pain generator.
Interpretation and limitations
Ultrasound or MRI is selected by suspected gallstone, effusion, osteomyelitis or avascular necrosis rather than ordered routinely for all crises.

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

Acute chest syndrome

Chest pain, cough, fever, hypoxia or a new infiltrate indicates a pulmonary sickle emergency rather than an isolated bone-pain episode.

Osteomyelitis or septic arthritis

Persistent focal tenderness, swelling, restricted joint movement, fever and sustained inflammatory markers raise infection; vaso-occlusion and infection can coexist.

Surgical abdomen

Localised peritonism, progressive vomiting, cholestasis or atypical abdominal pain requires evaluation for gallstones, appendicitis, pancreatitis, sequestration and other surgical disease.

Venous thromboembolism

Unilateral swelling, pleuritic symptoms or unexplained hypoxia warrants standard VTE assessment because sickle disease increases thrombosis risk and pain can mask it.

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

01First 30 minutesAssess and relieve pain togetherFirst stepA person with sickle-cell disease presents with an acute painful episode.

1Record pain, respiratory and cardiovascular observations, compare with the individual care plan and screen for chest, neurological, septic, abdominal and priapism red flags.
2Give initial analgesia within 30 minutes: a strong opioid by an appropriate route for severe pain, with paracetamol and an NSAID when not contraindicated.
3Correct measured fluid deficit, give oxygen for hypoxaemia and prescribe antiemetic, laxative and safety monitoring matched to the chosen opioid.

02ReassessmentTitrate benefit without losing ventilationPain remains severe after the initial dose or repeated opioids are required.

1Reassess pain, sedation, respiratory rate, saturation and observations every 30 minutes until satisfactory control and document response to each dose.
2Use patient-controlled analgesia when repeated boluses are needed, involving acute-pain and haematology teams for opioid tolerance, kidney impairment or persistent severe pain.
3Repeat examination for acute chest syndrome, infection, sequestration, thrombosis or a surgical cause before labelling ongoing pain a behavioural problem.

03RecoveryMove safely to home treatmentPain and physiology improve and no evolving complication is identified.

1Convert to a workable oral regimen with bowel and nausea prevention and observe that pain remains manageable during activity and between doses.
2Confirm hydration, mobility, support, medicine supply and written red flags, including fever, chest symptoms, neurological change and uncontrolled pain.
3Share the episode and any care-plan learning with the haemoglobinopathy team, reviewing disease modification after frequent or severe presentations.

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

Provides strong opioid analgesia while multimodal therapy and complication assessment proceed.

Morphine sulfate

For severe pain use the individual plan or local acute-sickle protocol for rapid intravenous or subcutaneous titration, then consider patient-controlled analgesia with opioid-tolerance adjustment.

Monitor sedation, respiratory rate, oxygenation, blood pressure, nausea, urinary retention and ileus; reduce or lengthen dosing in renal impairment and avoid uncoordinated duplicate routes.

Adds non-opioid analgesia and can reduce total strong-opioid requirement during an acute painful episode.

Paracetamol

Give 1 g orally or intravenously up to four times daily in most adults, reducing the maximum for low body weight, liver disease, malnutrition or chronic alcohol risk.

Count all combination products and recent home doses; intravenous administration offers no advantage when oral absorption is reliable.

Targets inflammatory nociception as part of multimodal pain treatment.

Ibuprofen

When renal, gastrointestinal and bleeding risks permit, use a short oral anti-inflammatory course at the lowest effective BNF dose within the local sickle analgesia plan.

Avoid or stop with acute kidney injury, dehydration, peptic bleeding, significant thrombocytopenia, NSAID-sensitive asthma or later pregnancy; reassess renal function during ongoing use.

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

Acute chest evolution

Hypoventilation from thoracic pain, atelectasis, infection, fat embolism and opioid sedation can produce a new pulmonary infiltrate and rapidly worsening hypoxia.

Opioid toxicity

Repeated doses without coordinated review can cause sedation, hypoventilation, nausea, urinary retention and ileus, especially with kidney impairment or other sedatives.

Acute kidney injury

Dehydration, sepsis, haem pigment, NSAID exposure and medullary ischaemia can reduce renal function, altering fluid and analgesic safety.

Hospital-associated harm

Immobility, thrombosis, sleep disruption, stigma and delayed analgesia prolong recovery and can erode trust in future emergency care.

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

Reassess pain score, patient-defined relief, sedation, respiration, saturation and blood pressure every 30 minutes until control is stable.
Repeat chest examination and oxygenation throughout admission because acute chest syndrome can emerge after initial assessment.
Track fluid input, urine output, creatinine and pulmonary signs, correcting dehydration without creating fluid overload.
Review opioid totals across emergency, ward and patient-controlled routes to prevent duplication and plan a safe oral transition.
Monitor bowel function, nausea, itching, urinary retention, mobilisation and venous-thromboembolism risk during hospital treatment.
Escalate fever, focal bone or joint findings, falling haemoglobin or reticulocytes and any new neurological or abdominal sign.

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

Visible injury is unnecessary

Marrow and microvascular ischaemia can cause extreme pain without swelling or a diagnostic plain radiograph.

Oxygen is physiological treatment

Routine oxygen in a normally saturated patient does not relieve vaso-occlusion and can conceal the significance of later deterioration.

Fluids need an indication

Correcting deficit helps, whereas indiscriminate high-volume infusion can worsen pulmonary oedema and acute chest syndrome.

Persistent pain prompts two reviews

Optimise analgesia and reopen the diagnostic assessment; neither task should be used to avoid the other.

11Common pitfallsFrequent interpretation and management errors.

01
Delaying analgesia while proving the diagnosis.
02
Using pethidine for recurrent sickle pain.
03
Giving oxygen automatically despite normal saturation.
04
Overhydrating without assessing deficit or lungs.
05
Repeating opioids without respiratory and sedation review.
06
Attributing every focal or atypical pain to vaso-occlusion.