Despite absence of an accepted gold standard measure of volume status, central venous pressure (CVP) remains a commonly used metric in guiding circulatory management. Routine sitting of central venous catheters in all admitted patients is, however, impractical, and even when indicated associated with significant risk. As such, interest in minimally invasive methods for obtaining comparable data has grown. Recent studies demonstrating correlation between central and peripheral venous pressure (PVP) have prompted interest in substitution of PVP in clinical volume state assessment [1–5]. Cuff-occluded rate of rise of PVP (CORRP) has been additionally forwarded as a sensitive yet minimally invasive indicator of hypovolaemia . Normal values of PVP and CORRP, however, have not been reported in fit individuals.
The goal of the present study was to establish normal values of these minimally invasive measures of volume state. Specifically, we determined to document PVP in the dorsum of the hand and antecubital fossa (ACF), and CORRP derived from pressure assessment in the dorsum of the hand, in spontaneously ventilating healthy adults.
The present investigation was approved by the Northern Y Ethics Committee of the New Zealand Health and Disability Committees. Well adult volunteers of mixed sex and without pre-existing cardiovascular illness were studied. Participant characteristics and baseline haemodynamic metrics are presented in Table 1. All participants underwent peripheral venous catheterization of a dorsal vein of the hand, and contralateral vein in the ACF utilizing standard 20G cannula over needle (Insyte; Becton Dickinson Infusion Therapy Systems Inc., Utah, USA) intravascular catheter. Intravascular positioning was confirmed by aspiration. A 10-min period of supine positioning was afforded following sitting vascular catheters.
Dorsum hand and ACF cannula were connected through 3 mm internal diameter saline-filled intravenous tubing and three-way tap to Edwards Lifesciences pressure transducer (Irvine, California, USA), and thereby to Phillips MP30 (Phillips Medical Systems, Boeblingen, Germany) monitor. Pressure transducers were room-air zero calibrated at the estimated phlebostatic axis. The arm was then positioned with transducer, ACF, and hand catheter's level according to inverted U tube, to eliminate zero-error difference. Peripheral venous pressure recordings were made 30 s following mechanical flushing, at end-expiration. Hand and ACF values were alternately obtained following adjustment of the three-way tap. Pressures recorded represented a time-weighted average of venous pressure waves as per manufacturers' software. Three paired sets of hand/ACF recordings were obtained at 5-min intervals.
CORRP is defined as the average rate (in mmHg min−1) of rise of pressure measured in a peripheral vein after proximal cuff occlusion of that vein. In the actual measurement of CORRP, only the first 90% of the curve after occlusion of the cuff is used [6,7]. In the present study, peripheral venous pressure recordings were obtained from the hand cannula through the monitoring system described, following rapid inflation of a standard blood pressure arm cuff to a constant 40 mmHg. Pressure values were recorded via standardized data collection template at 5 s intervals from cuff inflation (time 0) to 90 s. CORRP values were then retrospectively computed through linear regression (SPSS for Windows version 10.0, SPSS, Chicago, Illinois, USA) of the plot PVP versus time (wherein PVP data from cuff occlusion to less than or equal to 90% peak PVP only were included). A schematic illustration of CORRP acquisition is presented in Fig. 1. CORRP values for individual participant represented the average of three recordings obtained at 5-min intervals.
Sample size estimation was based on pooled standard deviation data from a postcardiac surgical population in previous work , and sought a 95% confidence interval (CI) of less than or equal to 2.5 mmHg in PVP, indicating 32 participants. Statistical analysis of all variables was performed with SPSS for Windows (version 10.0, SPSS). Two-tailed Students' t-testing was utilized to compare continuous variables. A P less than 0.05 was retained as statistically significant.
Participant demographic data and baseline hemodynamic parameters are presented in Table 1. Peripheral venous pressure recorded in the dorsum of the hand was 8.3 ± 2.1 mmHg (95% CI 7.8–8.7 mmHg). Peripheral venous pressure recorded in the ACF was 7.6 ± 2.2 mmHg (95% CI 7.3–8.2 mmHg). Mean difference in hand versus ACF pressure recordings was 0.6 mmHg (P = 0.046). No statistically significant difference was observed between male and female participants, or left versus right positioning of vascular catheters. Mean CORRP values were 32.3 ± 6.7 mmHg min−1 (95% CI 28.0–36.6 mmHg min−1). Similarly, no significant difference was observed between male and female participants, nor left/right catheter positioning.
Peripheral venous pressure has been demonstrated to correlate with CVP in both the operating theatre and critical care setting in a variety of pathophysiologic conditions [1–5]. Utilization of PVP poses the obvious dual advantages of lesser morbidity associated with cannula insertion and greater potential scope of application, as virtually all admitted patients undergo peripheral venous cannulation. CORRP represents an additional, readily obtainable and minimally invasive pressure metric. CORRP has been demonstrated to correlate with hypovolaemia during graded haemorrhage in anaesthetized dogs [6,7] and with both right atrial pressure (RAP) and pulmonary capillary wedge pressure (PCWP) in human patients undergoing laparotomy .
The observation that PVP is greater in the hand than in the ACF, that is the more distally it is measured, is in keeping with previous findings . Consistency is furthermore demonstrated with a described framework for considering the clinical limitation of PVP in substitution for CVP. Increased resistance to flow between the peripheral and central veins, either greater distance or decreased dimension of the peripheral veins, leads to greater difference in their pressure between CVP and PVP .
CORRP is not an intuitively appreciable marker of the volume state, meriting exploration of the physiology responsible. The rate of rise of intraluminal venous pressure is dependent on two variables: rate of inflow of blood and venous capacitance. Three stages are described for peripheral veins in relation to their state of filling: collapsed, partially distended and fully distended . In the first of these states, a threshold pressure, equating to tissue pressure , must be reached for the vein to begin to dilate. This stage represents an initial low capacitance phase and seems likely to be passed through rapidly. The vessel then reaches a state of partial distension wherein increases in pressure effect venous dilatation with minimal increase in wall tension: a state of high capacitance. Once fully distended, wall stretch reaches a maximum, representing a low capacitance state.
The tendency for flow into the veins is productively viewed using the re-emerging terminology of the mean systemic filling pressure . The distending volume of the circulation is that volume which creates a pressure in the arrested circulation. From the dynamic circulation, this pressure has three contributors – the component of distending volume in the arterial side of the circulation, the component in the venous side and the energy present as flow which will become nondirectional (i.e. pressure) on stopping the circulation . In low volume states, the distending volume posited on the arterial side and cardiac output will diminish. Conversely, the resistance to flow across arterioles into the venous bed will increase. Therefore, in low volume states, on venous occlusion, the rate of inflow into the peripheral veins will tend to decrease; and the peripheral veins, after initial expansion from a collapsed state, are in a high capacitance state. Rate of rise within the venous conduit will correspondingly be low. It is suggested that this is the cause of a low CORRP exhibited in low volume states.
A number of limitations are inherent in the present study. Investigators were unblinded to study interventions, thereby potentially introducing observer or information bias. Pressure metrics were, however, transcribed directly to a standardized data collection template in a systemic fashion. Computation of CORRP was additionally performed by an investigator blinded to the contents of the study. The absence of a central venous catheter (and thereby CVP estimation) furthermore fails to allow correlation of PVP with CVP in the population studied.
In conclusion, we have documented normal values for the minimally invasive venous pressure metrics of PVP and CORRP in well adults. Knowledge of these may be gainfully employed when PVP and CORRP are utilized as adjuncts to clinical assessment of circulatory volume status when more invasive parameters are unavailable.
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