Pneumoperitoneum Physiology — FRCA Final MCQ

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ModerateGeneral AnaesthesiaPneumoperitoneum PhysiologyFRCA Final

A 52-year-old man is undergoing laparoscopic Nissen fundoplication under general anaesthesia with volume-controlled ventilation. A carbon dioxide pneumoperitoneum is established at 15 mmHg and he is placed in 20° reverse Trendelenburg. Compared with measurements immediately before insufflation, which physiological change is most likely?

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Correct answer: B — Decreased cardiac output

The correct answer is B. At an intra-abdominal pressure of 15 mmHg, compression of the inferior vena cava and abdominal venous capacitance vessels increases resistance to venous return. Reverse Trendelenburg further reduces preload through gravitational pooling. Stroke volume and therefore cardiac output fall, although arterial pressure may be maintained or increased by sympathetic activation and increased systemic vascular resistance. Pneumoperitoneum displaces the diaphragm cephalad, reducing functional residual capacity and respiratory-system compliance; with volume-controlled ventilation, peak airway pressure therefore rises rather than falls. Venous return may transiently increase at low insufflation pressures because blood is displaced from abdominal capacitance vessels, but this is not the expected response at 15 mmHg in the head-up position. Renal blood flow and urine output also decrease as intra-abdominal pressure rises.

Reference: Dexter SP, Vucevic M, Gibson J, McMahon MJ. Hemodynamic consequences of high- and low-pressure capnoperitoneum during laparoscopic cholecystectomy. Surgical Endoscopy. 1999;13:376–381. https://pubmed.ncbi.nlm.nih.gov/10094751/