Hernia/Abdo Wall Flashcards
What is a spigelian hernia
A hernia through the Spigelian fascia, which is composed of the aponeurotic layer between the rectus muscle medially and the semilunar line laterally
Almost all occur at or below the arcuate line (absence of posterior rectus fascia may contribute to inherent weakness in this area)
Often intraparietal, with the hernia sac dissecting posterior to the external oblique aponeurosis
What are the ideal properties of an implant?
- Non-allergenic
- Non-carcinogenic
- Mimics the tissue it replaces/reinforces
- Sterilisable
- Cheap
Discuss the physical properties of mesh
Material
- Synthetic
- Polypropylene, polyester, PTFE
- Biologic (derived from human, bovine and porcine tissue that has been decellularised to leave a collagen matrix which acts as a regenerative framework that supports remodelling & new collagen deposition)
- Bovine, porcine collagen
- Human collagen
- Porcine intestine
- Biosynthetic
- BioA (PGA:TMC), Vicryl (polyglactin 910)
- Paritally absorbable - composite
Fibre construction
- multifilament - increases surface area for ingrowth
- thus improves tissue incorporation
- monofilament - more resistant to microorganisms
Weight
- depends on polymer and amount used (pore size)
- light-weight = more flexible, less discomfort, less shrinkage, less risk of infection bc reduced bulk of FB implant (but note not just weight of mesh that imparts elasticity and flexibility - also the weaves of the strands in the mesh)
- heavy = increased tensile strength but less flexibility, increased shrinkage, increased infection risk
- lightweight <40g/m2, medium 40-80, heavy >80
Anisotropy
- varying flexibility and elasticity in multiple directions
Porosity (size of large holes in mesh)
- effective porosity = amount of empty space within the volume of the mesh made up of holes >1mm
- main determinant of tissue reaction
- fibrosis will occur around each strand of mesh; increased macroporosity produces a scar net rather than a scar plate, so less mesh/scar shrinkage and increased flexibility
- increased macropore size also decreases bulk of FB implant & use in contaminated fields becoming acceptable bc reduced bacterial adherence & increased clearance
- minimum macropore size: 1mm2 - but many have pores 3-5mm2
- micropores: ≥10um bc if smaller, bacterial can harbour in the pores out of reach of larger inflammatory cells
Advanced coating
- Tissue separating meshes; where the intraabdominal side of the mesh is coated w a product to minimise adhesion formation
- reduces adhesions but not completely
- includes: seprafilm (Sepramesh), and omega-3 (C-Qur) and Polyethylene Glycol (Parietex)
- Reduces adhesions but not completely.
What mesh do you use?
- Open hernias - Parietene light = macroporous monofilament polypropylene mesh
- Lap inguinal hernia - Progrip = monofilament polyester with absorbable polylactic acid grips (lap has coloured strip on one end)
- Lap umbilical - Symbotex composite mesh = monofilament polyester with absorbable collagen film
- Open umbilical hernia - Parietex composite ventral patch = monofilament polyester with absorbable collagen film and absorbable pollygllycoic-lactic acid expander
- Vicryl mesh (polyglactin 910) - absorbs in 2-3mo
Describe the coated meshes and their indications.
A number of tissue separating meshes are available , where the intraabdominal side of the mesh is coated with a product to minimise adhesion formation.
These products include seprafilm (Sepramesh) and omega-3 (C-Qur) and Polyethylene Glycol (Parietex).
In large, sponsored trials, Sepramesh has the lowest adhesion index.
Describe the biological meshes and their indications.
Biological mesh has gained popularity because of perceived advantages in para-visceral repairs and resistance to infection.
There is no good evidence that they are any better (or even as good as) polypropylene mesh in clean or contaminated environments.
They cost between 10-100 times as much.
What is abdominal compartment syndrome?
How is it managed?
- Normal IAP is approx 5-7mmHg in critically ill adults
- IAH = sustained or repeated pathological elevation in IAP >12mmHg
- ACS = sustained IAP >20mmHg (with or w/o an APP <60mmHg) that is associated with new organ dysfunction/failure
- APP = MAP - IAP
- insufficient evidence to define ACS as an APP <60mmHg but doesn’t necessarily rule out that a pt w hypotension and an intermediate IAH (15-19mmHg) and new organ dysfunction or failure, may, in some cases, benefit from abdominal decompression
- Causes may be
- primary - intra-abdominal peritonitis, mesenteric ischaemia, obstructed bowel or intra-abdominal bleeding
- secondary - to causes outside the abdomen, such as sepsis elsewhere causing pseudo-obstruction
- Consequences of raised intra-abdo pressure:
- resp failure and need for higher ventilator pressures in mechanically ventilated pts
- decreased venous return due to compression of IVC
- decreased renal perfusion causing acute renal failure
- reduced splanchnic perfusion causing intestinal ischaemia
- Measure IAP with a Foley catheter in bladder primed with 50mL fluid - but take in context of other parameters eg resp pressures and O2 sats, renal function and urine output, lactate levels and abdo distension
- Prevention
- avoid excessive crystalloids during resuscitation, permissive hypotension, avoid unnecessary fluid overload
- leave abdomen open after eg AAA repair if abdomen tense and difficult to close
- neuromuscular blockade if on a ventilator
- frusemide, renal replacement therapy
- effective pain relief - epidural if possible
- early enteral nutrition will stimulate bowel movements but need to check for accumulation & drain stomach if that happens
- treatment
- pain/anxiety relief
- neuromuscular blockade
- correction of electrolyte imbalance or other causes of paralytic ileus
- enteral decompression with nasogastric or rectal tubes when stomach/colon dilated +/- neostigmine/colonoscopic decompression if large bowel distended
- drainage of haemoperitoneum & control of intra-abdo bleeding
- drainage of ascites
- decompressive laparostomy
Why do hernias occur where they occur?
Herniation occurs where areas of fascia are not covered by striated muscle, and so are susceptible to effacement driven by pressure over time.
What is the latest pathophysiological theory regarding hernia formation?
The current notion is that the majority of hernias are a disease of collagen metabolism.
One of the key factors in this is the Type I to Type III collagen ratio.
The lower this ratio (usually ~5), the more likely the individual is to develop a hernia.
What is the distribution of abdominal wall hernias?
75% inguinal
- Indirect (2/3)
- Direct (1/3)
15% umbilical
- Congenital
- Paraumbilical
- Umbilical
8.5% femoral
3-5% epigastric
What are the different types of collagen?
Type I
- Bone, Skin, Tendon, Organs (most abundant)
Type II
- Cartilage
Type III
- Reticular collagen, blood vessels (often with Type I)
Type IV
- Basement membrane
Ratio of I:III <5 predisposes to hernia formation.
How is intra-abdominal compartment pressure calculated?
Gross
- Hold up urinary catheter at level of bladder in supine position and measure urinary column height.
Formal
- Prime manometry line
- Empty bladder; instill with 25ml of normal saline
- Ensure manometer is level with bladder in supine position
- Turn 3-way tap to be open to bladder and manometer
- Read pressure from manometer or pressure transducer.
Describe the classification of inguinal hernias.
The Nyhus Classification (1991)
Based on the integrity of the posterior wall and deep ring.
Type I
- Indirect hernia without dilatation of deep ring
Type II
- Indirect hernia with dilatation of deep ring
Type III
- Type IIIa
- Direct hernia (posterior wall defect)
- Type IIIb
- Indirect hernia with posterior wall defect
- Type IIIc
- Femoral Hernia
Type IV
- Recurrent hernia
How are parastomal hernias classified?
Historically, the Devlin classification:
Type I - Interstitial hernia
Type II - Subcutaneous hernia
Type III - Intrastomal hernia
Type IV - Peristomal hernia
More recently, the European Hernia Society Classification:
Type I - PH ≤5 cm without cIH.
Type II- PH ≤5 cm with cIH.
Type III - PH >5 cm without cIH.
Type IV - PH >5 cm with cIH.
- P: primary PH.*
- R: recurrence after previous PH treatment.*
Eponymous name for Meckel’s found in a femoral or inguinl hernia sac?
Littre’s hernia.
Described in 1700 by Alexis Littre; french surgeon and anatomist.
