Prehospital Acute Appendicitis

Appendicitis refers to the acute inflammation of the appendix, a small, narrow, finger-like pouch attached to the caecum—the beginning of the large intestine. Although the exact function of the appendix remains uncertain, it’s thought to play a role in gut immunity. In pre-hospital settings, recognizing the signs and symptoms of appendicitis early is crucial to avoid complications such as perforation or sepsis which is associated with increased morbidity and mortality.

Pathophysiology Of Acute Appendicitis

The appendix is rich in gut-associated lymphoid tissue (GALT), which plays an important role in mucosal immunity, particularly during childhood. This lymphoid tissue can undergo hyperplasia in response to various immunological stimuli, such as viral or bacterial infections.

Although the exact aetiology of acute appendicitis remains unclear, luminal obstruction is widely accepted as the primary initiating event in approximately 50% of cases. Obstruction may be caused by GALT hyperplasia (particularly in younger patients), by faecoliths (hardened masses of stool), or by less common factors such as ingested foreign bodies, intestinal worms, or neoplasms. Once the lumen becomes obstructed, continued mucosal secretion leads to a rise in intraluminal pressure. This pressure compromises venous outflow, resulting in congestion and oedema of the appendiceal wall. Over time, arterial perfusion also becomes impaired, causing ischaemia and promoting bacterial overgrowth. The local microbiota, particularly anaerobic organisms like Bacteroides spp. and facultative anaerobes such as Escherichia coli, proliferate within the stagnant, obstructed lumen.

The ensuing infection and inflammation can progress to transmural necrosis and, ultimately perforation of the appendiceal wall if not promptly managed. In some cases, the body attempts to contain the infection by forming an appendiceal mass or “phlegmon,” in which adjacent structures such as loops of bowel and omentum adhere to the inflamed appendix, walling off the infection and limiting the spread of peritonitis.

Incidence/Epidemiology – Acute Appendicitis

Appendicitis is a common condition that can occur at any age, but it is most frequently seen in individuals between 10 and 20 years old and approximately one-fifth of patients with acute appendicitis will present with or progress to perforation. Although the condition itself is more common in males, females are more likely to undergo appendicectomy.

Appendicitis is the most common abdominal surgical emergency worldwide and the leading non-obstetric surgical emergency in pregnant women. In the UK alone, around 50,000 acute appendicectomies are performed annually. While the overall incidence of appendicitis has stabilised, a steady decline in appendicectomy rates has been observed. This trend is thought to be due to improved hygiene, advancements in diagnostic imaging, and evolving approaches to medical and surgical management.

Risk Factors/Causes Of Acute Appendicitis

Several factors may increase the risk of developing appendicitis:

Symptoms Of Acute Appendicitis

The time between symptom onset and definitive treatment is directly correlated with the risk of perforation. Delayed diagnosis may lead to longer hospital stays, extended antibiotic therapy, and more severe post-operative complications. Early recognition of acute appendicitis is therefore critical.

Pain is the hallmark symptom of acute appendicitis. However, not all patients will present with the classic features. Atypical presentations are more common in pregnant women, young children, and older adults.

Pain

Typically begins as vague periumbilical discomfort and migrates to the right lower quadrant over 24 to 48 hours. Migratory pain is the most significant symptom in acute appendicitis. The pain usually worsens with time and movement. If the appendix perforates, patients may experience a sudden temporary relief followed by generalised abdominal pain.

Fever – usually low grade fever accompanied by general malaise

Nausea and vomiting – typically occur after the onset of pain

Constipation – may be present

Loss of appetite – often one of the earliest symptoms

Increased urinary frequency – this may occur if the appendix lies in a pelvic position and causes irritation to the bladder

Confusion – more likely in older patients

Symptoms of sepsis – generalised malaise, breathlessness, feeling cold and clammy

ABCDE Observations Of Acute Appendicitis

Acute appendicitis is a surgical emergency and requires prompt recognition. Patient assessment should begin with the structured ABCDE approach, followed by a full general examination and an abdominal examination. A pelvic examination may also be necessary to rule out other causes of abdominal pain, such as incarcerated hernia or testicular torsion in males, and gynaecological conditions in females.

Definitive tests and investigations are typically carried out in a hospital setting, but pre-hospital assessment plays a critical role in early recognition and triage.

Altered Mental Status – Confusion may be observed in cases of sepsis, particularly in older patients.

Oxygen Saturation – Monitor with pulse oximetry; aim for SpO₂ >94%. In septic patients, peripheral readings may be unreliable due to poor circulation.

Respiratory Rate – Tachypnoea may be present, either from pain or as a compensatory response to sepsis.

Pulse Rate – Tachycardia is a common finding.

Capillary Refill Time – Particularly useful in assessing children under 12 years old. Prolonged refill may indicate shock.

Blood Pressure – Should be interpreted in context. May be normal or low; note that normal readings do not rule out sepsis.

Temperature – Low-grade fever is common early on; hypothermia may be observed in septic shock.

Urinary Output – May be reduced or absent in shock states.

Acute Appendicitis Abdominal Examination

A thorough abdominal examination is crucial in evaluating a patient with suspected acute appendicitis. Key findings often localise to the right lower quadrant (RLQ) of the abdomen, where the appendix is typically situated.

McBurney’s Point Tenderness: The most classic and reliable physical sign in appendicitis is tenderness at McBurney’s point — located one-third of the way from the anterior superior iliac spine to the umbilicus. This area corresponds to the base of the appendix, as illustrated in the image above.

Palpable Mass: In some cases, especially if the appendix has perforated and formed a contained infection, a firm mass may be palpable in the RLQ. This could indicate an appendiceal abscess or phlegmon (inflammatory mass without a discrete collection of pus).

Peritoneal irritation indicates more advanced disease, such as appendiceal rupture. The following signs are suggestive of peritoneal involvement:

Guarding: Involuntary tensing of the abdominal muscles in response to palpation, indicating underlying inflammation.

Rebound Tenderness: Pain that is more intense when pressure is suddenly released than when it is applied.

Percussion Tenderness: Pain elicited on gentle tapping of the abdomen, often used to assess generalised peritoneal irritation.

Abdominal Distension: May occur in late or complicated cases, such as perforation or ileus.

Decreased or Absent Bowel Sounds: Indicative of paralytic ileus or generalised peritonitis, especially if associated with perforation.

Pain in the right lower quadrant with palpation of the left side.

Pain elicited with passive extension of the right thigh while patient lies on their left side.

Pain with internal rotation of the flexed right hip.

If there are no signs of peritoneal irritation, the chances of acute appendicitis are reduced. In patients who present with right iliac fossa pain but show no signs of peritonism, have normal blood results, and a normal ultrasound scan, the likelihood of appendicitis is considered very low.

Varitations By Appendix Position

The appendix can lie in several anatomical positions, and each can lead to different symptoms and signs, sometimes making diagnosis tricky. This refers to non-pregnant patients.

Commonest position (~65%)

Symptoms

Right flank or loin pain instead of typical lower abdominal pain.

Signs

Deep tenderness may be absent because the caecum shields the inflamed appendix.

May have a positive psoas sign (pain on hip extension) due to irritation of the psoas muscle.

Symptoms

May resemble gastroenteritis.

Nausea, vomiting, and diarrhoea can dominate due to irritation of the small bowel (ileum).

May mislead clinicians into thinking it’s a GI infection rather than appendicitis.

Symptoms

Suprapubic pain

Urinary symptoms like frequency (irritation of bladder)

Tenesmus (feeling of needing to pass stool)

Rectal discomfort

Signs

Abdominal tenderness might be minimal or absent.

May find tenderness during vaginal or rectal examination, especially on the right side.

Atypical Presentation Of Acute Appendicitis

Children – May present with vague symptoms such as irritability, anorexia, or lethargy.

Older Adults – Often lack typical symptoms; may present with confusion, minimal fever, or shock.

Pregnancy – The gravid uterus may displace the appendix, leading to pain in the right upper quadrant or flank. Nausea and vomiting may be mistaken for pregnancy-related symptoms.

Additional Investigations For Acute Appendicitis

Additional investigations are often necessary to support the diagnosis of acute appendicitis or to rule out other differential diagnoses, particularly in patients with atypical presentations or equivocal clinical findings. These tests can aid decision-making and reduce the risk of diagnostic delay or misdiagnosis.

Full Blood Count (FBC) – An elevated white cell count is commonly observed in appendicitis, particularly with a predominance of neutrophils (neutrophil-predominant leukocytosis). This finding is present in approximately 80–90% of patients with acute appendicitis. An increased granulocyte count or a shift to the left (indicating an increase in immature white blood cells) may also be noted. While a raised WBC supports the diagnosis, it is non-specific and must be interpreted in the clinical context.

C – Reactive Protein (CRP) – Raised CRP levels, especially when combined with a high white cell count, enhance the diagnostic accuracy for appendicitis. However, CRP alone is not diagnostic and may remain normal in early or atypical cases. A rising CRP trend over time can also help distinguish appendicitis from self-limiting causes of abdominal pain.

Urine Dipstick Testing – This is an important bedside investigation to help exclude urinary tract infection (UTI) or renal colic, both of which can mimic appendicitis. However, interpretation must be cautious due to the anatomical proximity of the appendix to the ureter and bladder, local inflammation may cause sterile pyuria or microscopic haematuria. As many as 40% of patients with appendicitis may have leukocytes or trace blood in their urine, which can lead to diagnostic confusion if considered in isolation.

Pregnancy Testing (β-hCG) – In all females of reproductive age, a pregnancy test is essential to rule out ectopic pregnancy, which can present with similar lower abdominal pain. It can also help identify other pregnancy-related causes of abdominal symptoms, such as a ruptured ovarian cyst or round ligament pain. Pregnancy must always be excluded before considering imaging involving ionising radiation or planning surgical intervention.

Imaging For Acute Appendicitis

Imaging plays a pivotal role in confirming the diagnosis, particularly when the clinical picture is unclear. The choice of imaging depends on the patient’s age, sex, pregnancy status, and the availability of imaging modalities.

Computed Tomography (CT) with Intravenous Contrast – CT is currently the most accurate imaging tool for diagnosing appendicitis in adults, offering high sensitivity and specificity. It can visualise the inflamed appendix directly and detect complications such as perforation, abscess, or alternative diagnoses. Despite its diagnostic utility, CT is contraindicated during pregnancy due to ionising radiation exposure and is relatively contraindicated in young patients due to long-term radiation risks.

Ultrasound – Ultrasound is the first-line imaging modality in children, pregnant women, and those of reproductive age. It is non-invasive and free of radiation, making it a safer alternative when CT is not appropriate. However, its accuracy is highly operator-dependent, and visualisation of the appendix can be limited by patient body habitus or overlying bowel gas.

Magnetic Resonance Imaging (MRI) – MRI is primarily used in pregnant patients when ultrasound findings are inconclusive. It offers excellent soft tissue contrast without radiation exposure. In cases where the appendix is not visualised on MRI and no secondary signs of inflammation are present, the likelihood of appendicitis is considered low. While MRI is not routinely used in non-pregnant adults, it is increasingly accessible in certain settings.

Suspect Acute Appendicitis?

If acute appendicitis appears less likely based on clinical assessment and initial investigations, further diagnostic workup should be undertaken to rule out alternative causes of abdominal pain. During this period, clear patient communication is essential. Patients should be advised on red-flag symptoms such as worsening abdominal pain, pallor, confusion, shortness of breath, or blotchy skin and instructed to seek immediate care at the emergency department if these develop.

All patients with suspected acute appendicitis should be referred for urgent hospital admission for further evaluation, imaging, and surgical assessment. This is particularly important in vulnerable populations, including children, pregnant women, the elderly, and patients presenting with signs of complications such as sepsis or perforation. Early specialist involvement is crucial to reduce the risk of adverse outcomes. Supportive care should be carried out while enroute to hospital

Prehopsital Care Of Acute Appendicitis

Paracetamol is often a safe first-line analgesic that can be administered orally or intravenously, depending on patient condition and route availability.

Opioids (e.g. morphine sulphate) may be administered intravenously if pain is moderate to severe and not relieved by paracetamol alone.

Always follow local guidelines or PGDs for dosing and administration.

There is no evidence that appropriate analgesia obscures the diagnosis of appendicitis—it is encouraged to treat pain.

Establish intravenous access if any of the following are present:

Persistent vomiting – to allow fluid and medication administration.

Fever – may indicate systemic infection or developing sepsis.

Signs of haemodynamic compromise – such as tachycardia, hypotension, or delayed capillary refill.

Cannulation also provides a route for analgesia, antiemetics, and emergency intervention if deterioration occurs.

If the patient shows clinical signs of dehydration or sepsis, administer a fluid bolus:

Typically 0.9% Sodium Chloride (NaCl) 250–500 mL for adults (as per local protocols).

Reassess response after each bolus:

Improvement in heart rate, blood pressure, mental status, and urine output (if measured).

Avoid overloading unless hypotensive or clinically indicated, particularly in older patients or those with cardiac history.

Administer an antiemetic such as ondansetron or metoclopramide if the patient is nauseous or actively vomiting.

This helps improve comfort and reduces the risk of aspiration.

Ondansetron is generally preferred due to its lower side-effect profile (e.g., less risk of extrapyramidal symptoms).

Perform baseline observations (heart rate, blood pressure, respiratory rate, oxygen saturation, temperature, level of consciousness).

Repeat observations regularly, especially if:

• Symptoms are evolving
• Pain increases
• There are signs of clinical deterioration

Watch for signs of shock or peritonitis enroute.

Consider using a track-and-trigger tool (e.g. NEWS2) to monitor trends and escalate if necessary.

Surgical Management Of Acute Appendicitis

Surgical removal of the appendix (appendicectomy) remains the gold standard for definitive treatment of uncomplicated acute appendicitis. This can be performed via either an open or laparoscopic approach.

Is increasingly preferred due to its association with reduced post-operative pain, lower risk of surgical site infection, shorter hospital stays, faster recovery, and better cosmetic outcomes.

May be indicated in certain cases, such as when there is extensive intra-abdominal infection or in patients with previous abdominal surgeries.

Differential Diagnosis

Given the wide range of conditions that can mimic acute appendicitis, it is essential to maintain a broad differential, particularly in atypical presentations. A thorough clinical assessment, supported by targeted investigations, is key to excluding other potentially serious or more likely pathologies as mentioned below:

Key Points

Bibliography

Baird, D. L. H., Simillis, C., Kontovounisios, C., Rasheed, S., & Tekkis, P. P. (2017). Acute appendicitis. BMJ, 357, j1703. https://doi.org/10.1136/bmj.j1703

Joint Royal Colleges Ambulance Liaison Committee. (2022). UK ambulance services clinical practice guidelines. Class Professional Publishing.

National Institute for Health and Care Excellence. (2021, May). Appendicitis. https://cks.nice.org.uk/topics/appendicitis/

National Institute for Health and Care Excellence. (2024, March 19). Sepsis: Recognition, diagnosis and early management (NICE guideline NG51). https://www.nice.org.uk/guidance/ng51

NHS. (2019). Appendicitis. https://www.nhs.uk/conditions/Appendicitis