Cardiovascular Effects
Steep head-down tilt + pneumoperitoneum → the demand spiral
Steep Trendelenburg → ↑ venous returnGravity autotransfuses the central circulation
↑ Preload → ↑ cardiac output; pneumoperitoneum & sympathetic stimulation → ↑ SVR
↑ Myocardial O₂ demandIn a patient with coronary disease, this can precipitate ischaemic events
Pneumoperitoneum also causes a sympathetic/neurohumoral surge (catecholamines, vasopressin, renin–angiotensin) at insufflation → transient hypertension & tachycardia. Very high intra-abdominal pressure or hypovolaemia can conversely reduce venous return — so the net effect depends on filling and insufflation pressure.
Respiratory Effects
📉 A stiff, small-volume lung
- The pneumoperitoneum + head-down abdominal contents push the diaphragm cephalad → ↓ FRC, ↓ compliance, ↑ airway pressures, basal atelectasis, V/Q mismatch.
- CO₂ absorption from the peritoneum → hypercarbia (a widened EtCO₂–PaCO₂ gradient) → needs ↑ minute ventilation.
- Cephalad shift of the carina can cause endobronchial migration of the ETT after positioning — always re-check.
Cerebral, Ocular & Renal Effects
Cerebral
- Head-down tilt + ↑ intrathoracic/intra-abdominal pressure + hypercarbia → ↑ ICP, cerebral venous congestion, ↑ cerebral blood volume
- Facial, conjunctival, laryngeal & airway oedema
Ocular
- ↑ Intra-ocular pressure (IOP) rises with duration of steep Trendelenburg → risk of post-operative visual loss (POVL) / ischaemic optic neuropathy
Renal
- Pneumoperitoneum → ↓ renal perfusion & ↓ urine output (renal-vein compression, ↑ ADH) — and a small risk of renal injury
Regurgitation
- Head-down position + raised intra-abdominal pressure → ↑ risk of regurgitation & aspiration — secure the airway with an ETT and decompress the stomach