Hemodynamic stability seen with each of 2 lidocaine doses via thoracic epidurals in both young and older adult patients

Objectives. Optimal initial dosing for thoracic epidural blockade has not been established in dose response studies, although the effects of a single dose have been reported1-2'3. In lumbar epidurals, age has been shown to be an important factor in blockade spread4'5. To determine dosing for optimal spread and hemodynamic stability in different age groups, we compared the effects of two doses of 2% lidocaine via mid-thoracic epidurals in young and older adult patients. In addition to continuous arterial blood pressure and pulse measurements, serum catecholamine levels and non-invasive cardiac output parameters were determined at baseline and during maximum neuraxial blockade for evaluation. Methods. After IRB approval at Naval Medical Center Portsmouth, all suitable ASA 1-3 patients ages 18-55 (Group 1) and 56-80 (Group 2) scheduled for thoracic or upper abdominal surgery were offered enrollment in the study. After placement of IV and arterial lines, a thoracic epidural catheter was inserted in a T6 to T10 interspace, and secured 3 cm into the epidural space. After supine positioning, monitors were placed and the pt was allowed to relax for 10 minutes. Using thoracic bioimpedance technology, baseline non-invasive cardiac output parameters (cardiac index (CI) and total peripheral resistance (TPR) ), arterial blood pressure and routine vital signs were obtained and serum catecholamine levels (epinephrine, norepinephrine and dopamine) were drawn. A 3ml test dose of 2% lidocaine was then given via the epidural, followed in three minutes by an additional randomized study dose of 2 ml (total 5 ml (A) or 6 ml (total 9 ml (B)) of 2% lidocaine. Vital signs and arterial blood pressures were recorded every 5 minutes for 30 minutes, serum catecholamines were drawn at 20 min and available cardiac output measurements were averaged between 15 and 25 minutes after the study dose. Results. f of pts MAP Pulse CI TPR Total Catechol (Baseline/20 min) (B/20m) (B/l 5-25 m mean) (B/l 5-25 m mean) (B/20m) Group 1 Young Adults A 5 ml total 10 92/87 77/80 4.1/4.0 1008/975 418/376 B 9 ml total 10 90/86 72/76 4.2/4.0 1031/1049 332/354 Group2 Older Adults A 5 ml total 14 96/92 73/72 3.2/3.0 1284/1300 598/579 B 9 ml total 14 94/84 69/67 3.2/3.4 1443/1194 570/477 SBP. MAP. DBP (mmHo.) ond Pulse Role lo, Group 1 (Figure Presented) Baseline differences between groups in CI, TPR, and Total Catecholamines were statistically significant (p=0.0047, 0.0067, 0.0017 respectively). Changes at peak neuraxial blockade (approx. 20 min) were not significant between groups or volumes. A tendency towards decreased TPR was noted in the high volume older group which was not significant (p=. 14). Two patients (both in the 9 ml group) required interventions for hypotension and bradycardia. Discussion. Despite significantly higher baseline values for TPR and catecholamines, and lower cardiac index, older patients had comparable hemodynamic stability to young patients for the two initial epidural doses tested. Endogenous catecholamines played no statistically significant role in this hemodynamic stability. Although the typical patient had minimal change in the hemodynamic parameters measured, vigilant monitoring, especially 15-25 minutes after dosing, allowed prompt treatment in our two episodes of decompensation. The authors recommend the smaller dose (5ml) in older patients based on the hemodynamic stability and excellent spread seen (14 seg blocked, reported in another abstract).