Comparison of Traditional and Plethysmographic Methods for Measuring Pulsus Paradoxus

ARTICLE Comparison of Traditional and Plethysmographic Methods for Measuring Pulsus Paradoxus

Jeff A. Clark, MD, FAAP; Mary Lieh-Lai, MD, FAAP; Ron Thomas, PhD; Kalyani Raghavan, MD; Ashok P. Sarnaik, MD, FAAP, FCCM

Background: In the evaluation of patients with acute (PPpleth) on the pulse oximeter. Mean difference and asthma, pulsus paradoxus (PP) is an objective and non- 95% confidence intervals were calculated for each invasive indicator of the severity of airway obstruction. method. The 2 methods were also analyzed for correla- However, in children PP may be difficult or impossible tion and agreement using the Pearson product moment to measure. Indwelling arterial catheters facilitate the mea- correlation and a Bland and Altman plot. surement of PP, but they are invasive and generally reserved for critically ill patients. Results: Patients with status asthmaticus had higher PPausc and PPpleth readings compared with nonasthmatic pa- Objective: To determine the utility of the plethysmo- tients. Pulsus paradoxus measured by plethysmography graphic waveform (PPpleth) of the pulse oximeter in mea- in patients with and without asthma was similar to PPausc suring PP. readings (mean difference, 0.6 mm Hg; 95% confidence interval, −0.6 to 2.1 mm Hg). Individual PPpleth readings Methods: Patients from the pediatric intensive care showed significant correlation and agreement with PPausc unit, emergency department, and inpatient wards of a readings in patients both with and without asthma. tertiary care pediatric hospital were eligible for the study. A total of 36 patients (mean age [SD], 11.2 [4.7] Conclusion: Measurement of PP using the pulse oxim- years) were enrolled in the study. Pulsus paradoxus was eter–pulse plethysmographic waveform offers a simple measured using the traditional auscultatory (PPausc) and noninvasive method for evaluating patients with air- method with a sphygmomanometer. Pulsus paradoxus way obstruction. was then measured using a blood pressure cuff observ- ing for the disappearance and reappearance of the Arch Pediatr Adolesc Med. 2004;158:48-51

ESPITE ADVANCES IN THE etry, blood gas sampling, and bedside spi- treatment and preven- rometry. However, a decrease in oxygen tion of asthma, it re- saturation may occur with only very mild mains one of the most airway obstruction or, conversely, may not common reasons for hos- occur at all even with severe airway ob- pitalizationD in the pediatric age group.1 Pe- struction. In addition, hypoxemia may be riodic assessment of the severity of air- masked by administration of small way obstruction is an integral part of the amounts of supplemental oxygen, such as management of status asthmaticus. How- with aerosol treatments. Spirometry, such ever, there are limitations to the various as peak expiratory flow rate, can be use- subjective and objective factors that are ful as an indicator of airway obstruction routinely used for assessment. There is a and as a measure of decreased pulmo- wide variation in how patients perceive and nary function from baseline in asthmatic describe their symptoms.2 The symp- individuals who use them regularly. De- toms of an attack such as cough, diffi- spite this, the utility of the peak expira- culty breathing, and wheezing frequently tory flow rate is limited in a child with se- do not correlate with severity. In addi- vere respiratory distress. Measurement of tion, there is a significant interobserver the partial pressure of arterial carbon di- From Critical Care Medicine, Department of Pediatrics, variability among physicians in evaluat- oxide (PaCO2) is a useful tool in evaluat- Children’s Hospital of ing physical signs such as the extent of ing alveolar ventilation. In mild and mod- Michigan, Wayne State wheezing and magnitude of respiratory dis- erate asthma the PaCO2 is usually low. University School of Medicine, tress.3,4 Some helpful tools in evaluating “Normalization” or significant elevations Detroit. the severity of asthma are pulse oxim- in PaCO2 are encountered only when air-

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/25/2021 way obstruction is severe enough to result in overall al- ting with the arm at the side, an appropriately sized arm cuff veolar hypoventilation. In addition, measurement of PaCO2 was inflated until all Korotkoff sounds disappeared. The cuff requires blood sampling. was deflated approximately 2 mm Hg per second until a few Pulsus paradoxus (PP) reflects an exaggeration of intermittent Korotkoff I sounds were heard. This pressure was the normal decrease in systolic blood pressure (SBP) dur- assumed to be the SBP during exhalation (Pex). The cuff pressure was similarly decreased until all Korotkoff I sounds were ing inspiration and is a quantifiable indicator of airway heard. This pressure was assumed to be the SBP during inspi- obstruction. It has been shown to correlate well with other ration (Pin). The difference between Pin and Pex was the PPausc. CO objective indicators of airway obstruction such as Pa 2 If Pex and Pin were not well defined during the initial deflation, and peak expiratory flow rate5,6; however, it is noninva- the cuff was reinflated once and an attempt at measurement sive and does not require cooperation with pulmonary was repeated. If Korotkoff I sounds were again not well heard, function tests. Pulsus paradoxus may be a useful ad- the cuff was deflated completely, and this process was re- junct in assessing the severity of airway obstruction at a peated after a short wait, a maximum of 3 times in total. The given time, as well as documenting response to therapy, first PP that was clearly heard was recorded as PPausc.IfPPwas especially in situations in which more invasive tests are not clearly discernible by auscultation, the patient was ex- not readily available, such as an office setting. Timing of cluded from the study. Pulsus paradoxus was then determined in the same pa- PP measurement to inspiration and expiration can be dif- tient using the PPpleth from a standard patient transport moni- ficult in asthmatic children who are tachypneic, tachy- tor (Marquette Electronics, Milwaukee, Wis). The pulse ox- cardic, and likely to be uncooperative. Therefore, in- imeter probe (Nellcor, Pleasanton, Calif) was placed on the stead of attempting to correlate SBP with phases of patient’s second or third finger of the same arm used for PPausc respiration, measurement of PP using variations in SBP and an adequate signal quality was ascertained by comparison 7 has been proposed in children. Nevertheless, such a mea- of the displayed PPpleths to the palpable pulse. The appropriate- surement is cumbersome and subject to considerable in- sized cuff was placed on the arm and inflated until the PPpleth terrater and intrarater variability as well as observer bias. disappeared from the monitor. The cuff pressure was then de- Improvements in the method of determining PP may al- creased at approximately 2 mm Hg per second in a similar fash- low it to be a more useful tool in evaluating airway ob- ion to PPausc determination, until intermittent PPpleths appeared and this pressure was assumed to be the SBP during Pex. The struction. cuff pressure was lowered further until all PP were dis- Newer pulse oximeters are equipped with a visual pleths played. This pressure was the SBP during Pin. The difference display of the pulse plethysmographic waveform (PPpleth). between Pex and Pin was the PPpleth. We proposed that the PPpleth of the pulse oximeter would Pulsus paradoxus by auscultation and PPpleth means (SDs) be an acceptable substitute for Korotkoff sounds for the were calculated, as well as the mean difference between the 2 measurement of PP. Our hypothesis was PP measured methods with 95% confidence intervals. Pearson product mo- by the pulse oximetry PPpleth would be greater in asth- ment correlation was used to compare values obtained by the matic children compared with nonasthmatic children. different methods. In addition, because of concerns regarding Furthermore, PP measured using the pulse oximeter ple- the use of the product moment correlation for the comparison thysmograph would have good agreement with the value of different methods of measurement, we also compared the readings using a Bland and Altman plot, giving an estimation obtained by the traditional method of auscultation of of agreement. Korotkoff sounds.

RESULTS METHODS

Thirty-six patients from the pediatric intensive care unit, emer- During a 4-month period, 36 patients were enrolled. Their gency department, and inpatient wards of the Children’s Hos- ages ranged from 27 months to 20 years, with a mean pital of Michigan, Detroit, were enrolled over a 4-month pe- (SD) age of 11.2 (4.7) years. Twenty patients were male, riod. Both asthmatic and nonasthmatic patients were evaluated. and 16 were female. Eleven were admitted having a di- All asthmatic patients were at the time of evaluation diag- agnosis of status asthmaticus; the remaining 25 patients nosed as having status asthmaticus, which was defined as the had various diagnoses none of which was expected to gen- acute onset of symptomatic expiratory airflow obstruction with- erate a significant PP (Table 1). Five patients were ex- out significant improvement after administration of aerosol- ized ␤-agonist treatments. Verbal consent was obtained by the cluded after consent owing to the inability to measure primary investigator (J.A.C.) from the guardian or patient and PPausc because of the patient’s inability to remain still dur- documented in the patient’s medical record. This study was ap- ing PP measurement. In all patients whose PPausc was dis- proved by the Wayne State University Human Investigations cernible, PPpleth was able to be measured as well. Committee. The patients were chosen by their ability to coop- The PP was significantly higher in the asthmatic erate with study requirements (ie, remain still) from the emer- group compared with the nonasthmatic group when mea- gency department and inpatient populations (generally aged sured by either auscultation or plethysmography from 0 to 18 years). (Table 2). When PPpleth readings were compared with All demographic data and PP measurements were taken PPausc readings, no statistically significant difference was by a single investigator (J.A.C.). Age, sex, and underlying dis- found (Table 2). ease were recorded for all patients. Rhythm strip showed all patients to be in sinus rhythm with a stable rate. Blood pres- Pearson product moment correlation was used to sure was obtained manually using an aneroid sphygmomanom- determine the correlation between the values for PP de- eter (Welch-Allyn, Skaneateles Falls, NY). Pulsus paradoxus termined by the 2 methods (Figure 1). The PPausc and was determined using the traditional auscultatory (PPausc) the PPpleth method showed significant correlation among method with the sphygmomanometer. With the patient sit- both asthmatic patients (r2=0.76, PϽ.01) and nonasth-

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14 No. of ( ) Diagnosis Patients 12 () Status asthmaticus 11 10 Sickle cell anemia 4

Gastroenteritis 3 , mm Hg 8

Malignancy 3 pleth 6 Pneumonia 2 PP Intussusception 1 4 Ventriculoperitoneal shunt malfunction 1 Asthmatic Patients r 2 = 0.76 Seizure 1 2 Nonasthmatic Patients r 2 = 0.54 Congenital heart disease 1 Varicella 1 0421061281416 Bone marrow transplantation 1 PP , mm Hg Diabetic ketoacidosis 1 ausc Pharyngitis 1 Figure 1. Correlation between pulsus paradoxus measured by auscultation Bladder augmentation 1 (PPausc) and pulsus paradoxus measured by the plethysmographic waveform Chronic renal failure 1 method (PP ). Lung abscess 1 pleth Adjustment disorder 1 Decubitus ulcer 1 5 4 +1.96 SD 3.8 3 2

, mm Hg 1 Mean

Table 2. Pulsus Paradoxus Values for Asthmatic pleth 0 –0.1

and Nonasthmatic Patients –PP –1

ausc –2

No. of PP –3 –1.96 SD No. of Asthmatic Nonasthmatic –4 –3.9 Patients Patients –5 Variable (n = 11) (n = 25) 2641081416 12 Mean of PP and PP , mm Hg PPausc, mean (SD), mm Hg 10.9 (2.6) 5.6 (1.7) ausc pleth

PPpleth, mean (SD), mm Hg 10.2 (2.2) 6.0 (1.7)

Mean difference, PPausc−PPpleth 0.6 −0.4 Figure 2. Bland and Altman plot for all patients. PPausc indicates pulsus 95% CI −0.6 to 2.1 −1.2 to 0.4 paradoxus measured by auscultation; PPpleth, pulsus paradoxus measured by the plethysmographic waveform method.

Abbreviations: CI, confidence interval; PPausc, pulsus paradoxus measured by auscultation; PPpleth, pulsus paradoxus measured by plethysmographic racic pressure increases the pressure gradient against waveform method. which the left ventricle has to pump (left ventricular afterload), which decreases left ventricular stroke vol- 2 Ͻ matic patients (r =0.54, P .01). In addition, a Bland and ume. As left ventricular stroke volume falls during Pin, Altman plot (Figure 2) shows good agreement be- SBP decreases. During Pex, these physiologic changes are tween the 2 methods, with all differences being 1 SD or reversed, resulting in an increase in preload and a de- less from the mean. crease in afterload of the left ventricle, leading to an increase in stroke volume and an increase in the SBP. With COMMENT airway obstruction, such as that seen in asthma, these changes are magnified, resulting in a greater drop in SBP Pulsus paradoxus is a phasic variation in SBP with the during Pin, and an increase in PP. The magnitude of PP 6 lowest pressure occurring during Pin and the highest dur- has been shown by Galant et al to correlate with other ing Pex. The physiologic mechanisms for this are thought objective indicators of airway obstruction, such as an in- to be related to changes in left ventricular stroke vol- crease in PaCO2, and a decrease in forced expiratory volume and afterload during the respiratory cycle.8,9 Dur- ume in the first second and peak expiratory flow rate in ing Pin, the reduction in pleural pressure causes a de- asthmatic children. crease in intrathoracic pressure, and increases the pressure Because PP provides an objective measure of air- gradient from the systemic venous reservoir to the right way obstruction, the National Heart, Lung, and Blood In- ventricle. This increases venous return to the right ven- stitute has recommended its measurement as one esti- tricle. Since there is no increase in the gradient from the mate of the severity of an asthma exacerbation.3,5 The pulmonary veins to the left ventricle, a concurrent in- recommendations of the National Heart, Lung, and Blood crease in left ventricular filling does not occur. There- Institute for management of an acute asthma exacerba- fore, the interventricular septum at end-diastole is dis- tion are based on severity, so PP provides an objective placed to the left, and left ventricular end-diastolic volume measure to guide treatment. The National Heart, Lung, decreases, with a resultant drop in left ventricular stroke and Blood Institute recommendations for measuring PPausc volume. In addition, an increase in negative intratho- in children are to determine

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/25/2021 the difference in systolic blood pressure between the pressure What This Study Adds at which an observer first hears sporadic, faint pulse sounds and the pressure at which he or she hears all sounds. No attempt should be made to correlate pulsus paradoxus with the Pulsus paradoxus has been shown to be one of the few phase of respiration in small children.7(p508) noninvasive and objective indicators of airway obstruction. However, in children, PP can often be difficult or Despite this, relative tachypnea, tachycardia, small size, impossible to measure. Therefore, any technique that and inability of children to remain still make the mea- would facilitate its measurement would enhance our abil- surement of PP difficult or impossible. Indeed, it was nec- ity to objectively assess asthma severity in children. essary to exclude 5 patients from our study because of It is apparent from the existing literature that the an inability to determine PPausc.The use of indwelling ar- reappearance of the pulse oximeter PPpleth during arm cuff terial catheters has made the measurement of PP easier, deflation correlates with the return of pulsatile blood flow but their use is invasive and not without risk, and is gen- as measured from a radial artery catheter. It has not been erally reserved for critically ill patients. demonstrated that the reappearance of the pulse oxim- Newer pulse oximeters are equipped with a visual eter PPpleth can be used to measure PP. From our data, display of the (PP ). The generation of the PP is based we believe that PPpleth offers an easier yet accurate alter- pleth pleth native to PP . on the fact that the pulsatile absorbance between the light ausc source and the detector of the pulse oximeter probe is from arterial blood. A PPpleth is generated by separating the pulsatile component of the absorption from the nonpulsatile component. The nonpulsatile component rep- terial catheter placement. Unfortunately, this technology resents absorption from the tissue bed, including the ve- is not widely available. Until such time, we recommend nous, capillary, and nonpulsatile arterial blood. The the use of the PPpleth for the measurement of PP when PPausc amount of “pulse-added” absorption is calculated by the may be difficult to obtain. pulse oximeter and a PPpleth is generated that corre- sponds to pulsatile flow through the tissue.10 To our Accepted for publication July 3, 2003. knowledge, the use of measuring PP using the pulse ox- Presented at the 67th Annual Scientific Meeting of the imeter PPpleth has not been examined. American Academy of Pediatrics, Section on Critical Care Potential pitfalls in the method used here are that a Medicine; October 19, 1998; San Francisco, Calif. single observer (J.A.C.) obtained all data, and PP read- Corresponding author and reprints: Jeff A. Clark, MD, ings were not taken randomly. Both of these issues intro- FAAP, Critical Care Medicine, Department of Pediatrics, duce the possibility of observer bias. Because PP is pre- Children’s Hospital of Michigan, 3901 Beaubien Blvd, De- sent under normal conditions, our design was meant to troit, MI 48201-2196 (e-mail: [email protected]). demonstrate the utility of using the pulse oximeter to measure PP. However, most patients included in this study had REFERENCES mild asthma, and it is possible that agreement between the PPausc and PPpleth methods may yield results that do not agree 1. Centers for Disease Control (CDC) National Asthma control program. asthma con- when PP is further exaggerated. Additional study into this trol programs and activities related to children and adolescents: reducing costs and improving quality of life. Available at: http://www.cdc.gov/nceh/airpollution is warranted, possibly including comparison to PP mea- /asthma/children.htm. Accessed April 1, 2002. sured by intra-arterial pressure monitoring. 2. Li JTC, O’Connell E. Clinical evaluation of asthma. Ann Allergy Asthma Immu- nol. 1996;76:1-10. 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