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Effect of acute moderate changes in PaCO2 on global hemodynamics and gastric perfusion

Mas, Arantxa MD; Saura, Pilar MD; Joseph, Domènech MD; Blanch, Lluis MD, PhD; Baigorri, Francisco MD, PhD; Artigas, Antonio MD, PhD; Fernández, Rafael MD, PhD

Clinical Investigations
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Objective: To describe global hemodynamics and splanchnic perfusion changes in response to acute modifications in PaCO2 in hemodynamically stable patients.

Design: Prospective, randomized crossover study.

Setting: Medical-surgical intensive care unit at a community hospital (400,000 inhabitants).

Patients: Ten critically III patients who were sedated, paralyzed, and mechanically ventilated.

Interventions: Hypercapnia and hypocapnia were obtained by increasing and reducing instrumental deadspace in random order. After each intervention, patients returned to the basal condition. Each period lasted 80 min: 20 min to achieve stable PaCO2 and 60 min for tonometer equilibration. In each period, global hemodynamic variables and tonometric data were collected. The periods were compared using analysis of variance.

Measurements and Main Results: Acute hypercapnia (PaCO2 from 40 ± 3 to 52 ± 3 torr,p< .05) increased cardiac index (3.43 ± 0.37 vs. 3.97 ± 0.43 mL/min/m2,p< .05), heart rate (95 ± 6 vs. 105 ± 3 beats/min,p< .05), and mean pulmonary artery pressure (21 ± 1 vs. 24 ± 1 mm Hg,p< .05) and reduced systemic vascular resistance (992 ± 98 vs. 813 ± 93 dyne-sec/cm5,p< .05) and oxygen extraction ratio (27 ± 3% vs. 22 ± 2%,p< .05). Standardized intramucosal PCO2 increased from 49 ± 2 to 61 ± 3 torr (p< .05) with an associated decrease in calculated intramucosal pH ([pHi] 7.35 ± 0.03 vs. 7.25 ± 0.02,p< .05), but the gastro-arterial PCO2 gradient (ΔPCO2) did not change. Acute hypocapnia (PaCO2 from 41 ± 3 to 34 ± 3 torr,p< .05; pH 7.41 ± 0.01 to 7.47 ± 0.02,p< .05) induced slight increments in systemic vascular resistance (995 ± 117 vs. 1088 ± 160 dyne·sec/cm5,p< .05) and oxygen extraction ratio (28 ± 2% vs. 30 ± 2%,p< .05). Standardized intramucosal PCO2 decreased (50 ± 4 vs. 44 ± 3 torr,p< .05), pHi increased (7.33 ± 0.03 vs. 7.36 ± 0.02;p< .05), but ΔPCO2 did not change.

Conclusions: In this small group of stable patients, moderate acute variations in PaCO2 had a significant effect on global hemodynamics, but splanchnic perfusion, assessed by ΔPCO2, did not change. In these conditions, the use of pHi to evaluate gastric perfusion appears unreliable.

From the Intensive Care Services, Corporació Sanitaria Parc Taulí (Drs. Joseph, Blanch, Baigorri, Artigas, and Fernández), Sabadell; and the Centre Hospitalari i Cardiològic de Manresa (Drs. Mas and Saura), Manresa, Spain.

Supported, in part, by grant FIS 96/1384 from Ministerio de Sanidad y Consumo.

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