To the Editor
As surgical specialties advance, subspecialties within the field are uniting to combine modalities that ultimately benefit patient care. This is evident with hepatic surgeons assimilating laparoscopy for major hepatic resections. The advent of this new technique mandates that anesthesia professionals stay in touch with the changing physiologic environment that the operative field creates and demands. In open hepatic resections, the goals of minimizing hemorrhagic risk and venous air embolism are mitigated by maintaining a central venous pressure (CVP) from 0-5mmHg with the transducer leveled to the site of resection (Giordano C, Gravenstein N, Rice M—unpublished data). This effectively keeps sinusoidal venous pressure low enough to prevent excessive blood loss yet sufficient to minimize the risk of air entrainment. This physiologic milieu becomes unbalanced with the implementation of pneumoperitoneum pressure (PP) to facilitate laparoscopic surgery.
The conundrum begins by appreciating the pressure differential between the CVP and PP impacting the hemorrhagic tamponade effect1,2 and CO2 embolic risk.3-5 Complicating the physiology of these two risks are the compliance, compressibility, and collapsibility of the vessels being dissected. Puncturing a hole in the inferior vena cava as opposed to transecting hepatic sinusoids may result in differences in their volume and rate of CO2 ingress during PP. The surgical field creates more uncertainty when varying venous structures are periodically stented open by PP distension and mechanical retraction.
The anesthetic balancing act continues with a new variable resulting from the insufflation pressure: abdominal compartment syndrome. Anesthesia professionals must recognize the PP decreases preload and impacts cardiac output, and diminishes renal, hepatic, and splanchnic perfusion pressures. An additional concern is the reverse—the Trendelenburg positioning required to optimally expose the liver. Patient positioning results in significant venous pooling that decreases the intrathoracic CVP and preload, while augmenting the PP-CVP differential. This may abrogate blood loss, but it magnifies the pressure gradient from the operative field to the central venous circulation promoting CO2 embolization. Currently, no adopted stance on optimal CVP has been voiced, acknowledging the new variables within laparoscopic hepatectomy: PP (intraabdominal pressure [IAP]) and patient positioning.
If the significance of CO2 embolism is minimal, absent insertion of the insufflation needle into a vessel, then the opposing concerns are the maximum allowable insufflation pressure to view the field and balance hemostatic effects versus the appropriate organ perfusion pressures. Trials of insufflation limits have demonstrated that IAPs greater than 16 mmHg are ultimately detrimental to organ perfusion,6-8 and therefore should be maintained no higher then 12-14 mmHg. If this is our founding block, despite the notion that some procedures may be done with less PP to adequately view the surgical field, we must now decide on the optimal target CVP strategy and perhaps also intraoperative monitoring for the increasingly common laparoscopic hepatic resection operation. We pose two questions. First, should the target CVP during laparoscopic hepatic resections be different than for open cases and secondly, should transesophageal echocardiography or precordial Doppler monitoring be recommended during these operations?
Chris Giordano, MD Nik Gravenstein, MD Mark Rice, MD Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL
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