Vohmte 93 Number 4
Editorial correspondence
but were obviously limited by the amount of tissue we had at our disposal. Microvilli were sampled in the same way and counted in a random fashion. No estimation of the gradient of microvillar density along the villus was made since it was felt that the sampling would correct for this. Microvilli were measured in each patient to account for variability in size. I appreciate Dr. Whitington pointing out the typographic error in the formula. The fact that there ',,.'asgood correlation between carbohydrate absorption and the morphologic abnormality at various levels of clinical disease as well as in normal infants could only lead me to conclude that a relationship exists. IVilliam J. Klish, 3LD. Assistant Professor Section of Nutrition and Gastroenterolog)" Department of Pediatrics Baylor College of Medicine 1200 ~lottrsttnd A re. tlouston, TX 77030
administration: "eyeballing," umbilical arterial catheter, radial and temporal catheters or punctures, heel or digital capillary samples, continuous indwelling electrodes, and transcutaneous electrodes. The important question for the neonatologist is "Which alternative is best?" The data of Karna and Poland do little to answer this question. ITqlliam 1:. Powers, 3LD., M.P.tI. Department of Pediatrics Peoria School of Medicine Peoria, IL 61605 REFERENCES I.
2. 3.
4.
Digital capillaly sampling 5.
To the Editor: Karna and Poland' present data which attempt to establish the reliability and safety of digital capillary sampling in neonates. To establish reliability these authors point to a 0.92 correlation between the Po: of digital capillary blood and the Po~ of blood drawn a few moments later from temporal or radial arteries. (By punciure or through indwelling lines?) However, the arterial Po~ averages 20% higher than the capillary Po_.. More importantly, the authors are comparing two unsteadystate values. Continuous Po~ monitoring shows that when pain is being inflicted (tracheal suctioning, radial artery puncture) infants are in an unsteady state. ~-~ Unsteady-state data are probably of limited utility for long-term monitoring. The authors acknowledge their infants' occasional unsteady state during sampling for they concede that "samples were discarded before analysis if the patient's clinical condition dramatically changed during the sampling procedures." If one takes the liberty of discarding data sets nmst likely to show poor correlation, the impressive 0.92 correlation is easier to attain. The authors cite the work of Corbet, and Burnard ~ ,a:mse results were consistent with their own, but fail to mention that of Due and Cumarasamy, a who found that digital arterial Po_~ consistently underestimated Po~ measured on blood drawn simultaneously through an umbilical catheter, even though the catheter was probably sampling postductal blood. No correlation was found. Is the digital sampling technique safe? Four of 68 (6%) of arterial Po~ samples were above 100 mm Hg, when the corresponding capillary samples were below 100 mm llg. One arterial sample was above 100 mm Ilg while the corresponding capillary sample was within the usual safe range of the authors. Certainly there ale many alternatives in monitoring oxygen
729
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7.
8.
Karna P, and Poland RL: Monitoring critically ill newborn infants with digital capillary blood samples: An alternative, J PEDIATR 92:270, 1978. Dodd KL: Evaluation of a continuous monitoring oxygen catheter, Arch Dis Child 51:727, 1976. Goddard P, Keith I, Marcovitch H, Robertson NRC, Rolfe ~', and Scopes JW: Use of a continuously recording intravascular oxygen electrode in the newborn, Arch Dis Child 49:853, 1974. Harris TR, and Nugent M: Continuous arterial oxygen tension monitoring in the newborn infant, J PEDIATR 82:929, 1972. Huch A, and Huch R: Transcutaneous noninvasive monitoring of Po:, Hosp Pract 11:43, 1976. ltuch R, Huch A, and Lubbers DW: Transcutaneous measurement of blood Po: (tcPo:)-Method and application in perinatal medicine, J Perinat Med 1:183, 1973. Corbet AJS, and Burnard ED: Oxygen tension measuremerits on digital blood in the newborn, Pediatrics 46:780, 1970. Duc GV, and Cumarasamy N: Digital arteriolar oxygen tension as a guide to oxygen therapy of the newborn, Biol Neonate 24:134, 19.74.
R ply To the Editor: D r . Powers is correct in pointing out that our arterial Po, values averaged 20% higher than the corresponding capillary values. We were struck by the consistency of the relationship and the ability to predict one value from the other with some degree of accuracy. The arterial samples were obtained by puncture and not by indwelling catheters. Dr. Powers is appropriately concerned about the unsteady state created in infants by the process of digital capillary sampling. We acknowledge that there have been articles that show a fall in Po_, in response to manipulation of the infant. We are not sure how often this reaction "occurs, but those graphs that have been published seem to .indicate that the fall is not precipitous nor severe in most cases. Dr. Powers takes issue with our discarding some samples before analysis. Since the .question we had in mind was whether the two procedures would yield similar data under similar circumstances, it made sense to us to discard those samples in w'hich it was clinically obvious that the circumstances were not similar. We discarded no sample retrospectively after the analysis
Editorial correspondence
but were obviously limited by the amount of tissue we had at our disposal. Microvilli were sampled in the same way and counted in a random fashion. No estimation of the gradient of microvillar density along the villus was made since it was felt that the sampling would correct for this. Microvilli were measured in each patient to account for variability in size. I appreciate Dr. Whitington pointing out the typographic error in the formula. The fact that there ',,.'asgood correlation between carbohydrate absorption and the morphologic abnormality at various levels of clinical disease as well as in normal infants could only lead me to conclude that a relationship exists. IVilliam J. Klish, 3LD. Assistant Professor Section of Nutrition and Gastroenterolog)" Department of Pediatrics Baylor College of Medicine 1200 ~lottrsttnd A re. tlouston, TX 77030
administration: "eyeballing," umbilical arterial catheter, radial and temporal catheters or punctures, heel or digital capillary samples, continuous indwelling electrodes, and transcutaneous electrodes. The important question for the neonatologist is "Which alternative is best?" The data of Karna and Poland do little to answer this question. ITqlliam 1:. Powers, 3LD., M.P.tI. Department of Pediatrics Peoria School of Medicine Peoria, IL 61605 REFERENCES I.
2. 3.
4.
Digital capillaly sampling 5.
To the Editor: Karna and Poland' present data which attempt to establish the reliability and safety of digital capillary sampling in neonates. To establish reliability these authors point to a 0.92 correlation between the Po: of digital capillary blood and the Po~ of blood drawn a few moments later from temporal or radial arteries. (By punciure or through indwelling lines?) However, the arterial Po~ averages 20% higher than the capillary Po_.. More importantly, the authors are comparing two unsteadystate values. Continuous Po~ monitoring shows that when pain is being inflicted (tracheal suctioning, radial artery puncture) infants are in an unsteady state. ~-~ Unsteady-state data are probably of limited utility for long-term monitoring. The authors acknowledge their infants' occasional unsteady state during sampling for they concede that "samples were discarded before analysis if the patient's clinical condition dramatically changed during the sampling procedures." If one takes the liberty of discarding data sets nmst likely to show poor correlation, the impressive 0.92 correlation is easier to attain. The authors cite the work of Corbet, and Burnard ~ ,a:mse results were consistent with their own, but fail to mention that of Due and Cumarasamy, a who found that digital arterial Po_~ consistently underestimated Po~ measured on blood drawn simultaneously through an umbilical catheter, even though the catheter was probably sampling postductal blood. No correlation was found. Is the digital sampling technique safe? Four of 68 (6%) of arterial Po~ samples were above 100 mm Hg, when the corresponding capillary samples were below 100 mm llg. One arterial sample was above 100 mm Ilg while the corresponding capillary sample was within the usual safe range of the authors. Certainly there ale many alternatives in monitoring oxygen
729
6.
7.
8.
Karna P, and Poland RL: Monitoring critically ill newborn infants with digital capillary blood samples: An alternative, J PEDIATR 92:270, 1978. Dodd KL: Evaluation of a continuous monitoring oxygen catheter, Arch Dis Child 51:727, 1976. Goddard P, Keith I, Marcovitch H, Robertson NRC, Rolfe ~', and Scopes JW: Use of a continuously recording intravascular oxygen electrode in the newborn, Arch Dis Child 49:853, 1974. Harris TR, and Nugent M: Continuous arterial oxygen tension monitoring in the newborn infant, J PEDIATR 82:929, 1972. Huch A, and Huch R: Transcutaneous noninvasive monitoring of Po:, Hosp Pract 11:43, 1976. ltuch R, Huch A, and Lubbers DW: Transcutaneous measurement of blood Po: (tcPo:)-Method and application in perinatal medicine, J Perinat Med 1:183, 1973. Corbet AJS, and Burnard ED: Oxygen tension measuremerits on digital blood in the newborn, Pediatrics 46:780, 1970. Duc GV, and Cumarasamy N: Digital arteriolar oxygen tension as a guide to oxygen therapy of the newborn, Biol Neonate 24:134, 19.74.
R ply To the Editor: D r . Powers is correct in pointing out that our arterial Po, values averaged 20% higher than the corresponding capillary values. We were struck by the consistency of the relationship and the ability to predict one value from the other with some degree of accuracy. The arterial samples were obtained by puncture and not by indwelling catheters. Dr. Powers is appropriately concerned about the unsteady state created in infants by the process of digital capillary sampling. We acknowledge that there have been articles that show a fall in Po_, in response to manipulation of the infant. We are not sure how often this reaction "occurs, but those graphs that have been published seem to .indicate that the fall is not precipitous nor severe in most cases. Dr. Powers takes issue with our discarding some samples before analysis. Since the .question we had in mind was whether the two procedures would yield similar data under similar circumstances, it made sense to us to discard those samples in w'hich it was clinically obvious that the circumstances were not similar. We discarded no sample retrospectively after the analysis
