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30-09-2010 | Anaesthesiology | Article

Inducing hypocapnia during general anesthesia called into question


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MedWire News: US researchers have warned against the common practice of inducing hypocapnia during general anesthesia, saying it may affect patient outcomes.

They found an association between increasing intra-operative end-tidal carbon dioxide levels (EtCO2) and a shorter hospital length of stay for two common surgical procedures on an anesthesia information management system.

The team says: "Our data show that hypocapnia occurred in 25% of patients, but that hypocapnia during general anesthesia may be detrimental, and that maintaining normocapnia or allowing hypercapnia may be beneficial."

Hypocapnia has been advocated during general anesthesia to suppress respiratory effort and reduce anesthetic requirements, explain David Wax and colleagues at Mount Sinai School of Medicine in New York.

However, hypocapnia and associated alkalosis can have detrimental physiological effects, including decreased cerebral blood flow and cognitive function, increased airway resistance and pulmonary cellular dysfunction, vasoconstriction and increased myocardial oxygen demand, hypercoagulability, and dysrhythmias.

Noting that hypercapnia may have beneficial effects including increased cardiac index, oxygen delivery and tissue oxygen tension, and attenuation of lung injury, they studied the relationship between EtCO2 and clinical outcomes.

The study included 3421 case records of elective colon resections and hysterectomies undertaken between 2002 and 2008, with patients divided into four groups depending on surgical procedure and use of laparoscopic technique.

The median EtCO2 was 31 mmHg, and the median hospital length of stay was 7 and 5 days for open and laparoscopic colon resections, and 3 and 2 days for open and laparoscopic hysterectomies, respectively.

Regression analysis revealed a significant independent association between higher EtCO2 and reduced length of stay for colon resection and open hysterectomy. Specifically, each 5 mmHg increase in mean intra-operative EtCO2 reduced the risk for another day LOS by 7% for open colon resection and 11% for both laparoscopic colon resection and open hysterectomy

Reporting in the European Journal of Anaesthesiology, Wax et al conclude: "The common practice of inducing (or allowing) hypocapnia may be deleterious. Maintaining normocapnia or permitting hypercapnia may improve clinical outcomes."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Anita Wilkinson