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Intra-abdominal pressure effects on porcine thoracic compliance in weightlessness: Implications for physiologic tolerance of laparoscopic surgery in space

Kirkpatrick, Andrew W. MD, MHSc, FACS; Keaney, Marilyn DVM, PhD, LLM; Hemmelgarn, Brenda MD, PhD; Zhang, Jianguo MSc; Ball, Chad G. BSc, MSc, MD, FRCSC; Groleau, Michelle DVM, Cert. LAM; Tyssen, Michelle Mrlat(R); Keyte, Jennifer BSc, DVM, CVA; Campbell, Mark R. MD, FACS; Kmet, Leanne MSc; McBeth, Paul MD; Broderick, Timothy J. MD, FACS

doi: 10.1097/CCM.0b013e3181954491
Laboratory Investigations

Objective: Laparoscopic surgery (LS) is envisioned as an option for spaceflight, but requires intra-abdominal hypertension (IAH) to create the surgical domain. Prolonged weightlessness induces physiologic deconditioning that questions the ability of ill or injured astronauts to tolerate IAH. On earth, IAH results in marked ventilatory embarrassment. As there has been no previous study of physiologic changes related to LS in weightlessness, we studied anesthetized pigs in parabolic flight.

Design: Parabolic flight research laboratory.

Subjects: Five anesthetized Yorkshire pigs.

Interventions: Subjects were transported from an animal care facility and secured aboard an aircraft capable of generating hypergravity and weightlessness. Mechanical ventilation was performed using pressure control and positive end-expiratory pressure at 15 and 2 cm H2O, respectively; rate 12 breaths/min. Three abdominal conditions were used during LS: insufflation to produce IAH, abdominal wall retraction (AWR), and no abdominal wall manipulation (baseline). During each parabola breath by breath-tidal volumes (Vt) were recorded by a transport ventilator (HT-50 Newport Medical).

Measurements and Main Results: Least square means (LS-means) of weight corrected Vt (milliliter per kilogram) by gravity (g) and abdominal condition were determined using a mixed effects model for repeated measures analysis. Increasing gravity (g) consistently reduced Vt (p = 0.0011) as did insufflation (p < 0.0001). In 1g, Vt (LS-mean 13.7, 95% confidence interval [CI]: 12.4–15.0) was relatively unaffected by AWR (LS-mean 12.8, 95% CI: 11.5–14.00), but markedly decreased by IAH (LS-mean 10.00, 95% CI: 8.9–11.1), an effect accentuated in hypergravity (LS-mean 8.1, 95% CI: 6.4–9.8). In weightlessness, Vt reduction during insufflation was near obviated (LS-mean 12.3, 95% CI: 10.6–14.1), and AWR regularly but inconsistently increased the Vt above 1g baseline (LS-mean 13.7, 95% CI: 11.7–15.8).

Conclusions: Weightlessness protects against thoracic compliance changes that are inherent in IAH during induced pneumoperitoneum in gravity. The technique-related physiologic cost of performing LS in space deconditioned astronauts should be incorporated into design concepts for space surgery systems.

From the Departments of Surgery (AWK, CGB, PM), Critical Care Medicine (AWK), Regional Trauma Services (AWK, LK), Medicine (BH, JZ), Calgary Heath Region and Foothills Medical Centre, Calgary, Alberta, Canada; Departments of Pathology (MK), Laboratory Medicine (MK), and Animal Care (MK, MG, MT, JK), University of Ottawa, Ottawa, Ontario, Canada; and Paris Regional Medical Center (MRC), Paris, TX; University of Cincinnati (TJB), Cincinnati, OH.

Supported, in part, by Grout (to MK) and Urebnimil Corporation (to AWK); and supported by the Canadian Space Agency through Contract 08/7004098 in addition to an unrestricted educational Grant from the Urodynamix Corporation (to AWK).

This manuscript was presented at the Society of Critical Care Medicine's 37th Critical Care Congress, Honolulu, Hawaii, February 3, 2008, where it was selected for a 2008 Annual Scientific Award.

The remaining authors have not disclosed any potential conflicts of interest.

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© 2009 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins