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Physiologic oscillations produced by an infusion pump
796
Clinical and laboratory observations
function in low birth weight infants: A cross-sectional assessment of free thyroxine and thyroid hormone binding globulin. Eur J Pediatr 139:244, 1982. 3. Mizuta H, Miyai K, Ichihara K, Amino N, Harada T, Nose O, Tanizawa O: Radioimmunoassay of "free thyroxine" in dried blood spots on filter paper: Preliminary observations on the effective differentiation of subjects with congenital hypothyroidism from those with subnormal thyroxin-binding globulin and normal subjects. Clin Chem 28:505, 1982. 4. Usher R: The respiratory distress syndrome of prematurity:
The Journal of Pediatrics November 1983
Clinical and therapeutic aspects. Pediatr Clin North Am 8:525, 1961. 5. Oddie TH, Fisher DA, Bernard B, Lain RW: Thyroid function at birth in infants of 30 to 45 weeks' gestation. J PEDIATR 90:803, 1977. 6. Kulin HE, Kaplan M, Utiger R: Thyroid function in the preterm infant: A longitudinal assessment9 J PEDIATR92:968, 1978. 7. Cuestas RA, Engel RR: Thyroid function in preterm infants with respiratory distress syndrome. J PEDIATR 94:643, 1979.
Physiologic oscillations produced by an infusion pump Karl F. Schulze, M.D., Michael Graft, M.D., Michael S. Schimmel, M.D., Andrew Schenkman, M.D., and Patricia Rohan, R.N. New York, iV. Y.
THE PROLIFERATION OF MEDICAL TECHNOLOGY in neonatal intensive care nurseries has advanced so rapidly t h a t physicians and nurses m a y occasionally use new health devices without fully u n d e r s t a n d i n g their operating principles. Failure to appreciate the inherent limitations of intensive care e q u i p m e n t m a y inadvertently jeopardize patients whose conditions are unstable. W e report potentially u n f a v o r a b l e physiologic effects produced by the peristaltic, action of a n intravenous infusion pump. CASE REPORT This infant boy weighing 1810 gm was born at approximately 32 weeks' gestation to a 24-year-old woman who had two live children from four previous pregnancies9 Delivery was by e m e r gency cesarian section, through intact membranes, because of abruptio placenta. Apgar scores were 6 at I minute and 7 at 5 minutes. Resuscitation included tracheal intubation and infusion of bicarbonate and albumin. After stabilization, the patient was transported to Babies Hospital9 On admission the patient's vital signs, with assisted ventilation, were normal, and a complete blood count at 4 hours of life was
normal. At 24 hours of life the patient's condition deteriorated rapidly, marked by increasing and refractory metabolic acidosis and hypoxemia. After obtaining of surface, blood, and cerebrospinal fluid specimens for culture, the infant was given ampieillin 100 mg/kg/day and gentamicin 5 mg/kg/day. A leukocyte count at 24 hours of age was 1100/#1, with no polymorphonuclear cells; the platelet count was 30,000/~zl. During the subsequent 12 hours, the infant's blood pressure fell from 60/25 to 44/14, and a dopamine infusion was begun, with improvement in blood pressure to 71/26. Adequate oxygenation was maintained during this critical period only after the ventilation rate was increased to 100/rain. The next day the blood cultures were reported positive for group B streptococcus, and the infant underwent double-volume exchange transfusion, during which his condition imProved considerably, allowing a reduction in Fio2 from 1.0 to 0.70. At the time when the patient was critically ill and receiving dopamine intravenously, 10 #g/kg/min at a rate Of 3 ml/hr by means of a peristaltic pump (IVAC 530), regular oscillations of transcutaneous PO2 were noted. The unusual regularity of the oscillations seemed to preclude a physiologic cuase, and it was speculated that it might be related to the irregular delivery of dopamine. RESULTS
From the Division of Perinatal Medicine, Human Infant Physiology Laboratory, Department of Pediatrics, College of Physicians and Surgeons, Columbia University and The Babies Hospital. Supported by Public Health Service SCOR Grant HL 14218. Reprint requests: Karl F. Schulze, M.D.. Department of Pediatrics, College of Physicians and Surgeons, Columbia University, 630 IV. 168th St., New York, N Y 10032.
Simultaneous and continuous m e a s u r e m e n t s of transcutaneous Po2, m e a n aortic blood pressure, and h e a r t r a t e were m a d e during the infusion of d o p a m i n e while the p u m p was changed from one with peristaltic action to a continuous-infusion p u m p (Figure, A). W i t h the peristaltic pump, synchronous oscillations were noted in each of these physiologic m e a s u r e m e n t s a t a cycle frequency of 2.7
Volume 103 Number 5
Clinical and laboratory observations
Change
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Figure. A, Continuous recordings of tcPo2, heart rate, and mean aortic blood pressure before, during, and after change from peristaltic to continuous infusion pumps. B, Inset from A. Temporal relationship of intravenousdrops (vertical lines) to oscillations in mean aortic blood pressure.
minutes. The oscillation in blood pressure had a mean amplitude of 6.5 mm Hg (18% change from baseline); the mean z.mplitude of the cycle in transcutaneous Po2 was 5 mm Hg (9.6% change from baseline); and the mean amplitude of the cycle of the heart rate was 11 bpm (8.8% change from baseline). These oscillations disappeared when the intravenous infusion of dopamine was delivered by a continuous-infusion pump, and reappeared with the reintroduction of the peristaltic pump. To examine the relationship between the physiologic oscillations and the infusion of dopamine, the time course of the drops delivered by the peristaltic pump was charted. The time course of drops, represented by vertical lines (Figure, B), was also 2.7 min/cycle, demonstrating the clear relation of the oscillation of blood pressure to the infusion rate. Alternative explanations for these observed oscillations in tcPo2 were also considered. The cyclical effect of the radiant heater on the heat-sensitive tcPo2 probe was studied. A radiant shield was placed over the electrode, with no change in the amplitude of the oscillations. Rhythmicity of spontaneous ventilation did not play a role, as the infant remained completely apneic during the period of these recorded oscillations.
DISCUSSION We have demonstrated that peristaltic infusion pumps delivering potent medications at slow rates can cause unexpected physiologic alterations. A recent report by Seki et al? describes oscillation of transcutaneous Po2 in patients with pulmonary atresia. The singular regularity of the oscillations and the synchronous changes in blood pressure raise the question of whether variations in infusion of vasoactive medications could have produced the observed changes in tcPo2. The type of infusion system and the composition of the infusate are not described. These observations illustrate the complex interplay between technology and physiology in today's neonatal intensive care unit. Initially, what appeared to be a rhythmic variation in arterial oxygenation, as measured by a tcPo2 monitor, ultimately proved to be a variation in tissue perfusion. The source of this variation was a peristaltic infusion pump, a standard instrument in intensive care. Variations in intravenous infusion rate can be of great clinical significance in the care of critically ill infants who are dependent on potent medications with short half-lives, such as dopamine. Such infants test the limits of many aspects of critical care medicine, including technologic support. The margin for error may be quite small. It is
798
Clinical and laboratory observations
imperative, therefore, that physicians, nurses, and biomedical engineers independently examine the limitations of medical instrumentation if patient care is not to be jeopardized. Reference sources are available to assist medical personnel in these evaluations. ~ REFERENCES 1. Seki S, Murakami N, Kuraya K, Sumiyoshi M, Ikenoue T, Ohnishi Y, Terahara E, Hokanishi H, Nishibatake S, Satoh
The Journal of Pediatrics November 1983 Y, Matsuoka Y, Hayakawa K, Taira A: Sinus0idal transcutaneous oxygen pressure pattern in infants with pulmonary atresia. J PEDIATR102:96, 1983. 2. Evaluation of infusion pumps. Health Dev 8:103, 1979.
Clinical and laboratory observations
function in low birth weight infants: A cross-sectional assessment of free thyroxine and thyroid hormone binding globulin. Eur J Pediatr 139:244, 1982. 3. Mizuta H, Miyai K, Ichihara K, Amino N, Harada T, Nose O, Tanizawa O: Radioimmunoassay of "free thyroxine" in dried blood spots on filter paper: Preliminary observations on the effective differentiation of subjects with congenital hypothyroidism from those with subnormal thyroxin-binding globulin and normal subjects. Clin Chem 28:505, 1982. 4. Usher R: The respiratory distress syndrome of prematurity:
The Journal of Pediatrics November 1983
Clinical and therapeutic aspects. Pediatr Clin North Am 8:525, 1961. 5. Oddie TH, Fisher DA, Bernard B, Lain RW: Thyroid function at birth in infants of 30 to 45 weeks' gestation. J PEDIATR 90:803, 1977. 6. Kulin HE, Kaplan M, Utiger R: Thyroid function in the preterm infant: A longitudinal assessment9 J PEDIATR92:968, 1978. 7. Cuestas RA, Engel RR: Thyroid function in preterm infants with respiratory distress syndrome. J PEDIATR 94:643, 1979.
Physiologic oscillations produced by an infusion pump Karl F. Schulze, M.D., Michael Graft, M.D., Michael S. Schimmel, M.D., Andrew Schenkman, M.D., and Patricia Rohan, R.N. New York, iV. Y.
THE PROLIFERATION OF MEDICAL TECHNOLOGY in neonatal intensive care nurseries has advanced so rapidly t h a t physicians and nurses m a y occasionally use new health devices without fully u n d e r s t a n d i n g their operating principles. Failure to appreciate the inherent limitations of intensive care e q u i p m e n t m a y inadvertently jeopardize patients whose conditions are unstable. W e report potentially u n f a v o r a b l e physiologic effects produced by the peristaltic, action of a n intravenous infusion pump. CASE REPORT This infant boy weighing 1810 gm was born at approximately 32 weeks' gestation to a 24-year-old woman who had two live children from four previous pregnancies9 Delivery was by e m e r gency cesarian section, through intact membranes, because of abruptio placenta. Apgar scores were 6 at I minute and 7 at 5 minutes. Resuscitation included tracheal intubation and infusion of bicarbonate and albumin. After stabilization, the patient was transported to Babies Hospital9 On admission the patient's vital signs, with assisted ventilation, were normal, and a complete blood count at 4 hours of life was
normal. At 24 hours of life the patient's condition deteriorated rapidly, marked by increasing and refractory metabolic acidosis and hypoxemia. After obtaining of surface, blood, and cerebrospinal fluid specimens for culture, the infant was given ampieillin 100 mg/kg/day and gentamicin 5 mg/kg/day. A leukocyte count at 24 hours of age was 1100/#1, with no polymorphonuclear cells; the platelet count was 30,000/~zl. During the subsequent 12 hours, the infant's blood pressure fell from 60/25 to 44/14, and a dopamine infusion was begun, with improvement in blood pressure to 71/26. Adequate oxygenation was maintained during this critical period only after the ventilation rate was increased to 100/rain. The next day the blood cultures were reported positive for group B streptococcus, and the infant underwent double-volume exchange transfusion, during which his condition imProved considerably, allowing a reduction in Fio2 from 1.0 to 0.70. At the time when the patient was critically ill and receiving dopamine intravenously, 10 #g/kg/min at a rate Of 3 ml/hr by means of a peristaltic pump (IVAC 530), regular oscillations of transcutaneous PO2 were noted. The unusual regularity of the oscillations seemed to preclude a physiologic cuase, and it was speculated that it might be related to the irregular delivery of dopamine. RESULTS
From the Division of Perinatal Medicine, Human Infant Physiology Laboratory, Department of Pediatrics, College of Physicians and Surgeons, Columbia University and The Babies Hospital. Supported by Public Health Service SCOR Grant HL 14218. Reprint requests: Karl F. Schulze, M.D.. Department of Pediatrics, College of Physicians and Surgeons, Columbia University, 630 IV. 168th St., New York, N Y 10032.
Simultaneous and continuous m e a s u r e m e n t s of transcutaneous Po2, m e a n aortic blood pressure, and h e a r t r a t e were m a d e during the infusion of d o p a m i n e while the p u m p was changed from one with peristaltic action to a continuous-infusion p u m p (Figure, A). W i t h the peristaltic pump, synchronous oscillations were noted in each of these physiologic m e a s u r e m e n t s a t a cycle frequency of 2.7
Volume 103 Number 5
Clinical and laboratory observations
Change
~ ~ SS ~E
50
~"
4S
-M
Pump
1
f
797
130 f
|
1:120
~ II0
~
r .... i
40
~= ~~t 30
|
1 i
llilltllllllllt tll t 11 t I I 1 IIIIIIIIIIIlUl III I II I I I I
i_____l
I
I
0
15
/ 30
I
I
4.~
60
Time (min.)
I 11111111111]I11Iti 11111 I III1111111111111III11111 I
|
___1
Figure. A, Continuous recordings of tcPo2, heart rate, and mean aortic blood pressure before, during, and after change from peristaltic to continuous infusion pumps. B, Inset from A. Temporal relationship of intravenousdrops (vertical lines) to oscillations in mean aortic blood pressure.
minutes. The oscillation in blood pressure had a mean amplitude of 6.5 mm Hg (18% change from baseline); the mean z.mplitude of the cycle in transcutaneous Po2 was 5 mm Hg (9.6% change from baseline); and the mean amplitude of the cycle of the heart rate was 11 bpm (8.8% change from baseline). These oscillations disappeared when the intravenous infusion of dopamine was delivered by a continuous-infusion pump, and reappeared with the reintroduction of the peristaltic pump. To examine the relationship between the physiologic oscillations and the infusion of dopamine, the time course of the drops delivered by the peristaltic pump was charted. The time course of drops, represented by vertical lines (Figure, B), was also 2.7 min/cycle, demonstrating the clear relation of the oscillation of blood pressure to the infusion rate. Alternative explanations for these observed oscillations in tcPo2 were also considered. The cyclical effect of the radiant heater on the heat-sensitive tcPo2 probe was studied. A radiant shield was placed over the electrode, with no change in the amplitude of the oscillations. Rhythmicity of spontaneous ventilation did not play a role, as the infant remained completely apneic during the period of these recorded oscillations.
DISCUSSION We have demonstrated that peristaltic infusion pumps delivering potent medications at slow rates can cause unexpected physiologic alterations. A recent report by Seki et al? describes oscillation of transcutaneous Po2 in patients with pulmonary atresia. The singular regularity of the oscillations and the synchronous changes in blood pressure raise the question of whether variations in infusion of vasoactive medications could have produced the observed changes in tcPo2. The type of infusion system and the composition of the infusate are not described. These observations illustrate the complex interplay between technology and physiology in today's neonatal intensive care unit. Initially, what appeared to be a rhythmic variation in arterial oxygenation, as measured by a tcPo2 monitor, ultimately proved to be a variation in tissue perfusion. The source of this variation was a peristaltic infusion pump, a standard instrument in intensive care. Variations in intravenous infusion rate can be of great clinical significance in the care of critically ill infants who are dependent on potent medications with short half-lives, such as dopamine. Such infants test the limits of many aspects of critical care medicine, including technologic support. The margin for error may be quite small. It is
798
Clinical and laboratory observations
imperative, therefore, that physicians, nurses, and biomedical engineers independently examine the limitations of medical instrumentation if patient care is not to be jeopardized. Reference sources are available to assist medical personnel in these evaluations. ~ REFERENCES 1. Seki S, Murakami N, Kuraya K, Sumiyoshi M, Ikenoue T, Ohnishi Y, Terahara E, Hokanishi H, Nishibatake S, Satoh
The Journal of Pediatrics November 1983 Y, Matsuoka Y, Hayakawa K, Taira A: Sinus0idal transcutaneous oxygen pressure pattern in infants with pulmonary atresia. J PEDIATR102:96, 1983. 2. Evaluation of infusion pumps. Health Dev 8:103, 1979.