The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

HIGH DOSE TRIS-HYDROXYMETHYL AMINOMETHANE (THAM) REDUCES ARTERIAL CARBON DIOXIDE TENSION (PACO2) DURING PERMISSIVE HYPERCAPNEIC VENTILATION (PHV) IN PATIENTS WITH ACUTE LUNG INJURY (ALI)

RH Kallet MS RRT, RM Jasmer MD,L. Lin MD, JM Luce MD, JD Marks MD; Department of Anesthesia University of California, San Francisco at San Francisco General Hospital, 1001 Potrero Ave. San Francisco, CA 94110

Background: PHV in ALI requires induced respiratory acidosis that may compromise cellular function in the presence of metabolic acidosis and shock. The renal excretion of protonated THAM lowers CO2 production in metabolic acidosis(1) and directly lowers PaCO2.(2) We report the use of THAM in 4 cases of PHV and one case of severe acidosis with eucapnea in ALI.

Methods: THAM was administered at a mean dose of 2.1 ± standard deviation (sd) of 1.63 mmol/kg/hour. Arterial blood gases were taken before, and within an hour after THAM started. Alveolar ventilation ([Vdot]A) was calculated from measurements of minute ventilation and physiologic deadspace. Deadspace was measured on Assist/Control ventilation using a Deltatrac metabolic monitor (3) Wilcoxon Sign-Rank tests were used for paired comparisons (Alpha = 0.05.).

Results: Mean PaCO2 was significantly lower at equivalent levels of [Vdot]A.

Pre-THAM Post-THAM
Case pHa PaCO2 mmHg [Vdot]A L/min pHa PaCO2 mmHg [Vdot]A L/min
1 7.18 110 7.6 7.26 95 7.9
2 7.07 39 11.5 7.34 30 11.5
3 7.14 66 10.4 7.26 51 10.4
4 7.09 52 16.0 7.12 44 13.9
5 7.11 60 18.8 7.31 44 13.7
Mean 7.12 65.4 12.9 7.26? 52.8? 11.5
± sd ± .04 ± 26.9 ± 4.5 ± .08 ± 24.8 ± 2.5
?P < 0.05.

Conclusions: High dose THAM directly lowers PaCO2. Buffering acidosis with THAM may facilitate the use of PHV during ALI.

1. Nahas G, Reveillaud A, Strauss J: Renal effects of tris (hydroxymethyl) aminomethane during CO2 load. Am J Physiol. 1963; 204(1): 113-118.

2. Nahas G: Use of an organic carbon dioxide buffer in vivo. Science 1959; 129: 782-783.

3. Lum L, Saville A, Venkataraman ST: Accuracy of physiologic deadspace measurement in intubated pediatric patients using a metabolic monitor: Comparison with the douglas bag method. Crit Care Med. 1998;26: 760-754.

OF-99-095

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