Psychiatry Research. 21,359-360 Elsevier

Letter

Gravity Feed Administration of Sodium Lactate

To the Editors:

Sodium lactate infusions are commonly used to provoke panic attacks in panic disorder patients. These infusions are usually given in high volumes (6-10 ml/ kg over 20 min), and are administered by gravity feed (Pitts and McClure, 1967; Liebowitzetal., 1984; Pohlet al., 1985). With this method, it is sometimes impossible to infuse the target volume of lactate within a 20-min period (Liebowitz et al., 1984). We have experienced similar diffi- culties, and wanted to know if this difficulty could be attributed solely to high target volumes of lactate. We therefore compared the volume of lactate infused in patients and controls to other infusions with the same target volume for each subject.

The infusion data from 69 patients meeting Research Diagnostic Criteria (Spitzer et al., 1978) for panic disorder and 3 1 controls were analyzed. Subjects were between 18 and 58 years of age and had taken no psychotropic medication from at least 2 weeks before the first infusion and none untilafter the infusion series was completed. Patients were actively symptomatic, with an average of at least one panic attack weekly. The nonpsychiatriccon- trol subjects had no personal or family his- tory of panic disorder. There was no statistically significant difference (t = 1.58, df q 96) between the age of patients (mean f SD: 32.6 * 8.2 years) and controls (29.8 f 6.8 years). The mean (+ SD) weight ofeachgroup was similar: 74.6 + 15.9 kg for patients and 74.7 f 16.8 kg for controls.

359

The infusion solutions consisted of I M sodium lactate in 5% dextrose in water (D5W), 20 pg of isoproterenol in D5W or D5W alone. Infusions were administered double-blind, in random order, and at inter- vals of at least 1 week. Each infusion was administered through a 21-gauge butterfly needle placed in an antecubital veinand pre- ceded by a lo-min slow drip of S%dextrose in sterile water (DSW). The flow rates were adjusted by gravity feed by a registered nurse to deliver a target volume of 6 ml/ kg over 20 min. Infusions were stopped as soon as the patient met criteria for a panic attack.

Because the infusions were stopped at dif- ferent times, analyses were done using the number of ml infused per min rather than the total volume infused. A 2 x 3 analysis of variance (ANOVA) compared the volume of infusate administered per min for the two groupsofsubjects(patientsandcontrols)and the three types ofinfusions. Post hocanalyses WeredoneusingNeuman-Keuls tests. Weight is not a confounding variable in this study because patient and control gorups had almost identical weights, and the compari- sons among the three infusions are repeated measures in the same subjects.

The results are summarized in Table 1. There was no significant difference in the overall volume infused per min between patients and controls (F = 0.23, df = l/98, NS). There was a significant difference in the volume infused per min among the three

Table 1. Volume of infusate administered (mUmin)

Group Placebo Lactate lsoproterenol

Patients 19.0 i 3.5 16.6 ? 3.9 19.3 i 3.7

Controls 18.5 i 3.9 17.5 + 2.5 19.6 k 3.3

0165-1781/87/$03.50 @ 1987 Elsevier Scientific Publishers Ireland Ltd.

360

infusionconditions(F=21.2,df=2/ 196,p< 0.01). Post hoc Neuman-Keuls tests revealed a, significant difference between lactate and placebo (Q = 6.8, p < 0.01) and lactate and isoproterenol conditions (Q = 8.8,~ < 0.01). There was no significant interaction between patienthood and infusion condition (F= 1.3, df = 2/ 196, NS).

In this study, each subject received infu- sions of lactate, placebo, and isoproterenol in random order. The target volume of infusate was 6 ml/ kg for each infusion, based on the subject’s weight at the beginning of the infu- sion series. Although the nurse adjusting the gravity feed for the experimental infusions was, like other personnel, kept blind to the infusion conditon, subjects received less sodium lactate per min than placebo and isoproterenol. This finding was not affected by whether the subject was a patient or a control. Sodium lactate is very viscous, and this physical property may impede the flow of the solution.

We recommend that lactate infusions be performed with infusion pumps. We now use the IVACvariablepressurevolumetricpump model 560 (San Diego, CA). Because the maximal rate of infusion with this model is 333 ml in 20 min, for volumes over 333 ml (subjects over 55 kg), two pumps are con- nected in parallel. With this technique, even heavy subjects can beinfused witha sufficient amount of lactate if the lactate is given in a 1 M solution. Infusion pumps also assure that the infusion is administered at a constant rate. These pumps control infusion rateinde- pendent of venous or arterial pressure, solu- tion container height, and solution viscosity.

References

Liebowitz, M.R., Fyer, A.J., Gorman, J.M., Dillon, D., Appleby, I.L., Levy, G., Ander- son, S., Levitt, M., Palij, M., Davies, SO., and Klein, D.F. Lactate provocation of panic attacks: I. Clinical and behavioral findings. Archives of General Psychiatry, 41, 764 (1984).

Pitts, F.N., Jr., and McClure, J.N., Jr. Lactate metabolism in anxiety neurosis. New EnglanW fournal of Medicine, 277, 1328 (1967).

Pohl, R., Rainey, J., Ortiz, A., Balon, R., Singh, H., and Berchou, R. Isoproterenol- induced anxiety states. Psychopharma- cology Bulletin;21,424 (1985).

Spitzer, R.L., Endicott, J., and Robins, E. Research Diagnostic Criteria (RDC) for a Selected Group of Functional Disorders. 3rd ed. New York State Psychiatric Institute, New York (1978).

Robert Pohl, M.D. Vikram K. Yeragani, M.D. Richard Balon, M.D. Richard Berchou, Pharm. D. John M. Rainey, M.D., Ph.D. Department of Psychiatry Wayne State University, and Lafayette Clinic 951 E. Lafayette Detroit, Ml 48207, USA

Jimmy R. Fulgham, M.D. Mayo Clinic Rochester, MN 55905 USA

June 8.1987