The effect of ventilation on the accuracy of pulmonary artery and wedge pressure measurements

Therapeutic Challenges and Emerging Treatment Targets for Pulmonary Hypertension in Left Heart Disease

Pulmonary hypertension (PH) attributable to left heart disease (LHD) is believed to be the most common form of PH and is strongly associated with increased mortality and morbidity in this patient population. Specific therapies for PH‐LHD have not yet been identified and the use of pulmonary artery hypertension‐targeted therapies in PH‐LHD are not recommended. Endothelin receptor antagonists, phosphodiesterase‐5 inhibitors, guanylate cyclase stimulators, and prostacyclins have all been studied in PH‐LHD with conflicting results. Understanding the mechanisms underlying PH‐LHD could potentially provide novel therapeutic targets. Fibrosis, oxidative stress, and metabolic syndrome have been proposed as pathophysiological components of PH‐LHD. Genetic associations have also been identified, offering additional mechanisms with biological plausibility. This review summarizes the evidence and challenges for treatment of PH‐LHD and focuses on underlying mechanisms on the horizon that could develop into potential therapeutic targets for this disease.

Reliance on end-expiratory wedge pressure leads to misclassification of pulmonary hypertension

Current guidelines recommend measurement of pulmonary artery wedge pressure (PAWP) at end-expiration. However, this recommendation is not universally followed and may not be physiologically appropriate. We investigated the performance of end-expiratory PAWP in the evaluation of precapillary pulmonary hypertension patients. 329 spontaneously breathing patients undergoing right heart catheterisation were retrospectively classified as having a precapillary, post-capillary or mixed phenotype based on standardised clinical criteria. Tracings were reviewed to compare end-expiratory PAWP with PAWP averaged throughout the respiratory cycle; these values were correlated with the clinical classifications. Predictors of large respirophasic variation in PAWP were determined. Elevated end-expiratory PAWP (>15 mmHg) occurred in 29% of subjects with precapillary phenotype. There were no differences in demographics or clinical history between those with elevated and normal end-expiratory PAWP. Those with elevated end-expiratory PAWP had greater right atrial pressure and respirophasic PAWP variation. Among all subjects, the magnitude of respirophasic variation in PAWP was positively correlated with body mass index and respirophasic variation in left ventricular end-diastolic pressure. A significant proportion of precapillary pulmonary hypertension patients have end-expiratory PAWP >15 mmHg. Spontaneous positive end-expiratory intrathoracic pressure may contribute; in those cases, PAWP averaged throughout respiration may be a more accurate measurement.

Maximal heart rate does not limit cardiovascular capacity in healthy humans: insight from right atrial pacing during maximal exercise

In humans, maximal aerobic power (VO2 max ) is associated with a plateau in cardiac output (Q), but the mechanisms regulating the interplay between maximal heart rate (HRmax) and stroke volume (SV) are unclear. To evaluate the effect of tachycardia and elevations in HRmax on cardiovascular function and capacity during maximal exercise in healthy humans, 12 young male cyclists performed incremental cycling and one-legged knee-extensor exercise (KEE) to exhaustion with and without right atrial pacing to increase HR. During control cycling, Q and leg blood flow increased up to 85% of maximal workload (WLmax) and remained unchanged until exhaustion. SV initially increased, plateaued and then decreased before exhaustion (P < 0.05) despite an increase in right atrial pressure (RAP) and a tendency (P = 0.056) for a reduction in left ventricular transmural filling pressure (LVFP). Atrial pacing increased HRmax from 184 ± 2 to 206 ± 3 beats min(-1) (P < 0.05), but Q remained similar to the control condition at all intensities because of a lower SV and LVFP (P < 0.05). No differences in arterial pressure, peripheral haemodynamics, catecholamines or VO2 were observed, but pacing increased the rate pressure product and RAP (P < 0.05). Atrial pacing had a similar effect on haemodynamics during KEE, except that pacing decreased RAP. In conclusion, the human heart can be paced to a higher HR than observed during maximal exercise, suggesting that HRmax and myocardial work capacity do not limit VO2 max in healthy individuals. A limited left ventricular filling and possibly altered contractility reduce SV during atrial pacing, whereas a plateau in LVFP appears to restrict Q close to VO2 max .

Usefulness of pulmonary capillary wedge pressure as a correlate of left ventricular filling pressures in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by a pulmonary capillary wedge pressure (PCWP) of ≤15 mm Hg, given a normal left ventricular filling pressure (LVFP). However, recent studies have shown that, in PAH patients, diagnosis based on PCWP can erroneously classify a significant number of patients compared with diagnosis based on left ventricular end-diastolic pressure (LVEDP). Therefore, we sought to compare the diagnostic accuracy of end-expiratory PCWP and LVEDP measurements in patients suspected of having pulmonary hypertension (PH).

METHODS

We reviewed the hemodynamic data from 122 patients suspected of having PH who underwent simultaneous right- and left-side heart catheterizations at a PH referral center from 2006 to 2011.

RESULTS

PH was diagnosed in 105 patients, 79% of whom (n = 83) showed a pre-capillary pattern according to the LVEDP measurement. Ninety percent of patients with PCWP ≤15 mm Hg were correctly classified as having pre-capillary PH. However, 39% of patients with a PCWP >15 mm Hg had LVEDP ≤15 mm Hg and would have been erroneously diagnosed with pulmonary venous hypertension based on their PCWP measurements alone. The sensitivity and specificity was 0.89 and 0.64, respectively. A Bland-Altman analysis of the PCWP and LVEDP measurements revealed a mean bias of 0.3 mm Hg with 95% limits of agreement of -7.2 to 7.8 mm Hg.

CONCLUSIONS

A PCWP ≤15 mm Hg was found to be a reliable indicator of normal LVFP in pre-capillary PH patients. When measured properly and analyzed in the clinical context, PCWP is a valuable tool for accurate diagnosis of PAH.

Current practice for determining pulmonary capillary wedge pressure predisposes to serious errors in the classification of patients with pulmonary hypertension

BACKGROUND

Accurate measurement of left ventricular filling pressure is important to distinguish between category 1 pulmonary arterial hypertension (PAH) and category 2 pulmonary hypertension (PH) from left heart diseases (PH-HFpEF). We hypothesized that the common practice of relying on the digitized mean pulmonary capillary wedge pressure (PCWP-digital) results in erroneous recordings, whereas end-expiratory PCWP measurements (PCWP-end Exp) provide a reliable surrogate measurement for end-expiratory left ventricular end-diastolic pressure (LVEDP-end Exp-end Exp).

METHODS

We prospectively performed left and right cardiac catheterization on 61 patients referred for evaluation of PH and compared the LVEDP-end Exp to end-expiration to the (a) PCWP-end Exp and (b) PCWP-digital.

RESULTS

The PCWP-end Exp was a more reliable reflection of LVEDP-end Exp (mean 13.2 mm Hg vs 12.4 mm Hg; P, nonsignificant) than PCWP-digital (mean 8.0 mm Hg vs 12.4 mm Hg, P < .05). Bland-Altman analysis of PCWP-digital and LVEDP-end Exp revealed a mean bias of -4.4 mm Hg with 95% limits of agreement of -11.3 to 2.5 mm Hg. Bland-Altman analysis of PCWP-end Exp and LVEDP-end Exp revealed a mean bias of 0.9 mm Hg with 95% limits of agreement of -5.2 to 6.9 mm Hg. If PCWP-digital were used to define LVEDP-end Exp, 14 (27%) of 52 patients would have been misclassified as having PAH rather than PH-HFpEF. Patients with obesity and hypoxia were particularly more likely to be misclassified as PAH instead of PH-HFpEF if PCWP-digital was used to define LVEDP-end Exp (odds ratio 8.1, 95% CI 1.644-40.04, P = .01).

CONCLUSIONS

The common practice of using PCWP-digital instead of PCWP-end Exp results in a significant underestimation of LVEDP-end Exp. In our study, this translated to nearly 30% of patients being misclassified as having PAH rather than PH from HFpEF.

Evaluation of the monitor cursor-line method for measuring pulmonary artery and central venous pressures

OBJECTIVE

To determine if the monitor cursor-line feature on bedside monitors is accurate for measuring central venous and pulmonary artery pressures in cardiac surgery patients.

METHODS

Central venous and pulmonary artery pressures were measured via 3 methods (end-expiratory graphic recording, monitor cursor-line display, and monitor digital display) in a convenience sample of postoperative cardiac surgery patients. Pressures were measured twice during both mechanical ventilation and spontaneous breathing. Analysis of variance was used to determine differences between measurement methods and the percentage of monitor pressures that differed by 4 mm Hg or more from the measurement obtained from the graphic recording. Significance level was set at P less than .05.

RESULTS

Twenty-five patients were studied during mechanical ventilation (50 measurements) and 21 patients during spontaneous breathing (42 measurements). Measurements obtained via the 3 methods did not differ significantly for either type of pressure (P > .05). Graphically recorded pressures and measurements obtained via the monitor cursor-line or digital display methods differed by 4 mm Hg or more in 4% and 6% of measurements, respectively, during mechanical ventilation and 4% and 11%, respectively, during spontaneous breathing.

CONCLUSION

The monitor cursor-line method for measuring central venous and pulmonary artery pressures may be a reasonable alternative to the end-expiratory graphic recording method in hemodynamically stable, postoperative cardiac surgery patients. Use of the digital display on the bedside monitor may result in larger discrepancies from the graphically recorded pressures than when the cursor-line method is used, particularly in spontaneously breathing patients.

Comparison of pulmonary artery and central venous pressure waveform measurements via digital and graphic measurement methods

BACKGROUND

Techniques to measure pulmonary artery (PA) pressure waveforms include digital measurement, graphic measurement, and freeze-cursor measurement. Previous studies reported the inaccuracy of digital and freeze-cursor measurements. However, many of the previous studies were small and did not thoroughly examine the circumstances of when digital measurements might be inaccurate.

OBJECTIVES

To compare digital measurements and graphic measurements of PA and central venous pressure (CVP) waveforms in patients with a variety of respiratory patterns, and to compare digital measurements and graphic measurements of CVPs in patients with abnormal or right ventricular waveforms.

METHODS

A total of 928 patients were enrolled in this study. Waveforms from the PA and CVP were collected from each patient. The monitor pressure value (digital measurement) printed on the recorded waveform was compared with the pressure value obtained by a graphic strip recording and measured by one of the primary investigators (graphic measurement).

RESULTS

Digital measurements were found to be inaccurate in measuring waveforms in all respiratory categories and in measuring right ventricular waveforms. PA diastolic values and CVP values were the most inaccurately measured waveforms. Digital errors of more than 4 mm Hg were common.

CONCLUSION

There were instances in which the monitor's digital measurement was substantially different from the graphically measured value. This difference has the potential to mislead interpretation of clinical situations. The monitor's ability to occasionally give digital measurement values similar to the graphic measurements may lead to a false sense of security in clinicians. Because the accuracy of the monitor is inconsistent, the bedside clinician should interpret waveforms through use of a graphic recording rather than rely on the digital measurement on the monitor.

Monitoring during paediatric cardiac anaesthesia

Monitoring of paediatric anaesthesia has become increasingly more complex in recent years and this is particularly true of cardiac anaesthesia. The purpose of this review is to give a comprehensive update of published material related to both routine and specialized cardiac monitoring. Routine monitoring can be particularly affected by the alterations of cardiac rhythm, blood flow, cardiac output and oxygenation which result from the congenital heart abnormalities themselves, the type of surgery undertaken and the effects of cardiopulmonary bypass. The use of specialized monitoring is becoming more widespread, particularly in the areas of cerebral function, mixed venous oxygenation, cardiac output measurement and coagulation. In the last five years, with the development of smaller probes, a great deal has been published on transoesophageal echocardiography. The use of the current monitors of cerebral function still remains controversial despite the need for a monitor of adequate brain perfusion, reflecting the need for a great deal of further research in this area. This review will concentrate on particular areas which have seen the most profound changes and on monitoring that may form the standards of tomorrow. Finally, amongst all the technology, it should not be forgotten that the most important clinical monitor is the bedside clinical monitoring of the physicians themselves.

Interobserver variability in the interpretation of pulmonary artery catheter pressure tracings

STUDY OBJECTIVE

We evaluated the ability of three independent reviewers (R1, R2, R3) using waveform analysis to accurately identify confirmed valid PCWP tracings, and their ability to consistently report the PCWP numerical value.

DESIGN

Sixty PA and PCWP tracings were prospectively obtained and blindly reviewed by three independent critical care physicians.

SETTING

The medical ICU of Wilford Hall USAF Medical Center.

PATIENTS OR PARTICIPANTS

Twenty mechanically ventilated patients with PA catheters inserted for hemodynamic assessment.

INTERVENTIONS

Sixty PA and PCWP tracings were reviewed blindly and independently for acceptability using waveform criteria by three critical care physicians. While recording all 60 tracings, blood was aspirated from the distal port of the PA catheter with the balloon "wedged" and blood gas analysis was done. Each reviewer analyzed the PCWP tracings for validity using waveform criteria, and reported a numerical PCWP reading for those tracings judged valid by waveform criteria. Reviewer sensitivity, specificity and accuracy in performing waveform analysis were assessed by comparing their predictions with those tracings that were confirmed their predictions with those tracings that were confirmed valid by the aspiration of pulmonary capillary blood. Inter-reviewer agreement upon which validity of PCWP tracings was based and reviewer agreement on the numerical PCWP reading were also assessed. All tracings were blindly reviewed by each physician, first without and then with an AP tracing to define end-expiration.

MEASUREMENT AND RESULTS

Thirty-eight of 60 PCWP tracings were confirmed valid by the aspiration of pulmonary capillary blood. In the remaining 22 tracings, mixed venous blood was aspirated with the balloon wedged, and tracing validity was unconfirmed. Reviewer accuracy in identifying was 50 percent for R1, 65 percent for R2 and 57 percent for R3. No reviewer's accuracy was significantly different from a random guess which would yield an accuracy of 50 percent. Agreement by all three reviewers in identifying valid PCWP tracings using waveform analysis varied from 37 percent in the absence of an AP tracing to 66 percent when an AP tracing was available to identify end-expiration (p less than 0.003). Agreement by all three reviewers on the PCWP numerical reading (within 4 mm Hg) was 79 percent without an AP tracing and 96 percent with an AP tracing (p = NS). The numerical reading reported by the ICU nurses and house staff correlated closely with the reviewers' readings. Agreement with the reported PCWP reading was improved only for R2 by the addition of an AP tracing.

CONCLUSION

We conclude that the validation of PCWP tracings by waveform analysis is subject to interobserver variability, and reviewer accuracy in identifying confirmed valid tracings was no better than a random guess. Agreement on the numerical PCWP reading was high among the reviewers as was agreement by each individual reviewer with the reported PCWP. Finally, the presence of an AP tracing, to define end-expiration, adds little to the interpretation of the PCWP numerical reading by experienced physicians.

Common artifacts of pulmonary artery and pulmonary artery wedge pressures: recognition and interpretation

Bedside measurement of pulmonary artery pressure and pulmonary artery wedge pressure has an important role in the management of critically ill patients. Unfortunately, waveform abnormalities and artifacts commonly distort numeric values and lead to incorrect therapeutic decisions. The clinical impact of these artifacts is magnified by the digital pressure displays used in most intensive care units. We present here an atlas and an analysis of the artifacts that commonly occur. Use of analog rather than digital pulmonary artery wedge pressure data, when combined with an understanding of the physiological characteristics of patients, can prevent critical errors in patient management.

Science and shock: a clinical perspective

In spite of all the scientific and technical advances in recent years, shock that is not rapidly correctable with fluid can have a morbidity rate exceeding 80%. Consequently awareness of such precipitating factors as sepsis and early diagnosis and treatment are essential. Treatment should be rapid and should follow a previously outlined protocol. Such protocols should include correction of the precipitating problem and aggressive resuscitation to assure adequate ventilation and oxygenation of the blood and optimal oxygen delivery to the tissues. Fluid and blood should be given as needed until filling pressures begin to rise rapidly with further fluid infusion. With hemorrhagic shock in previously healthy individuals, a hemoglobin level of 10.0 g/dL is usually adequate. In older, septic, or cardiogenic shock patients, a hemoglobin level of 12.5 to 14.0 may be preferable. If an optimal preload does not increase cardiac output to normal or higher levels, inotropic agents should be used. If shock still persists, one must be sure that the arterial pH is not excessively high or low. Glucocorticoids may then be given in low dose (200 mg hydrocortisone) in case some degree of adrenal insufficiency is present. They can also be given in high doses (equivalent to 150 mg/kg hydrocortisone) early in septic shock primarily to prevent excess complement activation and to preserve membrane integrity. Vasopressors may occasionally be required if there is excessive vasodilation, especially if there is persistent hypotension in the presence of high-grade coronary or cerebral artery stenosis. Vasodilators may be used to try to correct myocardial ischemia (nitroglycerin), excessive preload (nitroglycerin), or excessive afterload (nitroprusside or hydralazine). Combinations of vasodilators and inotropic agents may be required in some patients with high systemic vascular resistance and persistently low cardiac outputs. Mechanical assist with IABP can be of great value in persistent cardiogenic shock. Diuretics may occasionally help prevent renal failure in patients who are persistently oliguric after blood flow and pressure are restored. Heparin is occasionally of value if DIC develops with no concomitant fibrinolysis. Antibiotics are important in septic shock and may also be important if persistent shock has reduced gastrointestinal mucosal integrity so that bacteria and bacterial products can enter the portal system.(ABSTRACT TRUNCATED AT 400 WORDS)

Interpretation of beat-to-beat blood pressure values in the presence of ventilatory changes

When blood pressure is measured invasively in the operating room or intensive care unit, it is reasonable to expect useful systolic, diastolic, and mean pressure values to be displayed at all times. If blood pressure is stable from beat to beat, display of values from any beat will suffice. However, the pressure often fluctuates from beat to beat. Display of values from every beat would yield a confusing jumble of numbers. This article describes an algorithm for selecting values that appear physiological useful from blood pressure waveforms that vary with ventilation. Two classes of variation are discussed. The algorithm is optimized from the type of variation seen in pulmonary artery pressure waveforms.