Monitoring central venous pressure,arterial pressure and pulmonary wedge pressure

Direct measurement of vascular pressure requires the insertion of a cannula into a vessel. The cannula is connected to saline filled tubing attached to a transducer apparatus for measurement and display of the vascular pressure waveform. The transducer apparatus is essentially the same for all intravascular pressure measurement. Direct measurement of arterial pressure is indicated where rapid fluctuations in pressure are anticipated, where accurate control of pressure is required, and for repeated sampling of blood gases. Central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) measurement indicate the preload of the right and left side of the heart respectively; and when considered in conjunction with other physiological measures can give a guide to the volume status of a patient. Trends in response to therapeutic intervention should be used rather than any individual value being used in isolation. Direct measurement of vascular pressure involves invasive procedures which carry a risk of complications relating to insertion of the cannulae and duration of use.     

Ambulatory blood pressure monitoring: mean blood pressure and blood pressure load

Ambulatory blood pressure monitoring (ABPM) is commonly used to diagnose pediatric hypertension. Using ABPM, hypertension is usually defined as a mean BP greater than the 95th percentile for height. A BP load >30% (% of BP readings greater than the 95th percentile) is also used for the diagnosis of hypertension. The objective of this study was to determine the agreement between mean BP greater than the 95th percentile and 30% BP load for the diagnosis of hypertension using ABPM. All ABPM records (n =1,009) of patients referred for hypertension to a pediatric center were retrieved. Scans were excluded if: age was >19 and height <115 cm or >185 cm. Mean BP and BP loads were calculated for 728 scans. Agreement between mean BP greater than the 95th percentile for height and various BP loads were calculated using the kappa coefficient. The kappa coefficient of agreement between mean BP greater than the 95th percentile and 30% BP load was 0.56 and 0.57 for daytime systolic and diastolic BP, respectively. The agreement between mean night-time BP greater than the 95th percentile and 30% BP load was 0.70 and 0.66 for systolic and diastolic BP, respectively. Agreement between mean BP greater than the 95th percentile and 30% BP load is only moderate to good. Maximum agreement between mean BP greater than the 95th percentile and BP load is achieved at 50% BP load.     

Artificial sphincter pressure versus detrusor leakage pressure

Increasing urethral occlusion pressures were created with an artificial sphincter in fresh bladder-urethra specimens of adult pigs. Detrusor leakage pressures remained about 25 per cent below the associated sphincter cuff pressures. The same relation was found when, during abrupt variations of cuff pressure, the detrusor leakage pressures were measured with antegrade urethral perfusion pressure measurement through a new sleeve catheter. Side-hole perfusion pressure measurements showed 100 per cent transmission of abrupt variations of cuff pressures to the inner urethral wall. No rotational differences could be detected. From the results it has been concluded that a probable pressure loss of about 25 per cent must be taken into account when converting artificial sphincter pressures into bladder pressures at which leakage will occur.     

Lumbar cerebrospinal fluid pressure waves versus intracranial pressure waves in idiopathic normal pressure hydrocephalus

The aim of this study was to explore how the lumbar cerebrospinal fluid pressure (CSFP) waves recorded during lumbar infusion compared with the intracranial pressure (ICP) waves recorded, either during lumbar infusion or during long-term, overnight monitoring. For this purpose, we assessed 27 simultaneous lumbar CSFP/ICP recordings made during lumbar infusion and 27 long-term, overnight ICP recordings in 27 consecutive idiopathic normal pressure hydrocephalus (iNPH) patients. Pressure waves during lumbar infusion were explored by computing pulse pressure amplitude and mean single wave pressure of every corresponding CSFP/ICP wave pair; among our 27 lumbar CSFP/ICP recordings a total of 35,532 CSFP/ICP wave pairs were available for analysis. We as well computed mean values of pulse pressure amplitude (i.e. mean CSFP wave amplitude or mean ICP wave amplitude) and mean values of mean single wave pressure (i.e. mean CSFP or mean ICP) during consecutive 6-s time windows, as well as average values for the individual recordings. During lumbar infusion, the cerebrospinal fluid pulse pressure amplitudes were about 2 mmHg smaller than the corresponding intracranial pulse pressure amplitudes. The mean CSFP wave amplitudes recorded during lumbar infusion correlated significantly with the mean ICP wave amplitudes recorded either during lumbar infusion or during long-term, overnight ICP monitoring. In 21 of 27 lumbar infusion tests (78%), the presence of elevated lumbar mean CSFP waves was related to presence of elevated mean ICP wave amplitudes during long-term, overnight ICP monitoring. Hence, the lumbar cerebrospinal fluid pulse pressure amplitudes recorded during lumbar infusion could be used to predict the intracranial pulse pressure amplitudes recorded during long-term, overnight ICP monitoring.     

Intra-abdominal pressure measurement: validation of intragastric pressure as a measure of intra-abdominal pressure

Background: The diagnosis of abdominal compartment syndrome depends uponthe demonstration of an elevated intra-abdominal pressure (IAP).Direct measures of IAP are impractical in the critical careunit; intravesical pressure (IVP) and intragastric pressure(IGP) should represent acceptable surrogate measures. IVP isthe preferred measure of IAP in critical care. We consideredthat IGP represents a practical alternative. The objective ofthis preliminary study was to observe the relationship betweenIGP and IAP. Methods: After Institutional Ethics Board approval, 29 patients havingelective laparoscopic surgery were recruited. IAP was measureddirectly via the abdominal trochar. This was compared with IGPmeasured via a commercial balloon catheter placed into the stomach. Results: Measured IGP was always more positive than IAP; both showedlinear correlation (r²>0.9). When IGP was calibrated againstIAP, an estimated difference between the IGP and IAP of ±2.5 mm Hg for 95% of the measurements was seen. Conclusions: The study demonstrates the strength of the relationship betweenIGP and IAP in normal individuals. Application of IGP measurementin the critical care patient is necessary to demonstrate itssuitability for continuous IAP assessment.     

Central venous pressure and pulmonary artery pressure monitoring

Central venous pressure and pulmonary artery pressure are used as measures of cardiovascular filling. While pressure–volume relationships are not constant, trends in central venous pressure give an indication of increasing or decreasing right ventricular filling, while pulmonary artery pressure gives an indirect indication of left ventricular filling pressure. Cardiac output can be estimated by use of thermodilution.     

Intracranial pressure

Background: The effects of pneumoperitoneum on intracranial pressure (ICP) have received relatively little attention. This study was undertaken to investigate the changes in ICP occurring as a result of increased intraabdominal pressure (IAP) and positioning in animals with normal and elevated ICP. Method: Five pigs (average weight 60 lb) were studied. A subarachnoid screw was placed for ICP monitoring. End tidal CO₂ was monitored. Ventilation was performed to keep PCO₂ between 30 and 50 mmHg. Measurements of arterial blood gases, mean arterial blood pressure, and ICP were recorded at four different levels of intraabdominal pressure (IAP 0, 8, 16, and 24 mmHg), both in the supine and Trendelenburg positions. A Foley catheter was introduced into the subarachnoid space to elevate the intracranial pressure, and the same measurements were performed. Results: There was a significant and linear increase in ICP with increased IAP and Trendelenburg position. The combination of increased IAP of 16 mmHg and Trendelenburg position increased ICP 150% over control levels. Conclusions: Patient positioning and level of IAP should be taken into consideration when performing laparoscopy on patients with head trauma, cerebral aneurysms, and other conditions associated with increased ICP. Received: 19 March 1996/Accepted: 24 May 1996     

Central venous pressure and pulmonary artery pressure monitoring

Stroke volume is a key determinate of cardiac output. It is affected by the preload, contractility and afterload of the myocardium. It is possible to gain insight into the right and left ventricular preload following the insertion of a central venous catheter and pulmonary artery catheter to measure central venous pressure and pulmonary capillary wedge pressure, respectively. Abnormal measurements can indicate a pathophysiological state and guide management.     

Carpal-tunnel pressure

Using the constant infusion technique, we have measured the pressures within the carpal tunnel in 30 hands in patients with carpal tunnel syndrome and in 4 hands in control subjects. The mean pressure in the normal, control subjects was 13 mmHg and in the carpal tunnel syndrome patients 26 mmHg. In the normal subjects the pressures did not change along the canal, whereas in the patients the values in the middle section were 50 percent higher than the mean. Our results correspond to reports of computed tomography and magnetic resonance recordings of nonuniform dimension of the carpal tunnel.     

Carpal-tunnel pressure

Using the constant infusion technique, we have measured the pressures within the carpal tunnel in 30 hands in patients with carpal tunnel syndrome and in 4 hands in control subjects. The mean pressure in the normal, control subjects was 13 mmHg and in the carpal tunnel syndrome patients 26 mmHg. In the normal subjects the pressures did not change along the canal, whereas in the patients the values in the middle section were 50 percent higher than the mean. Our results correspond to reports of computed tomography and magnetic resonance recordings of nonuniform dimension of the carpal tunnel.     

Cricoid pressure

Purpose

Although encoid pressure (CP) is a superficially simple and appropriate mechanical method to protect the patient from regurgitation and gastnc insufflation, in practice it is a complex manoeuvre which is difficult to perform optimally. The purpose of this review is to examine and evaluate studies on the application of (CP). It deals with anatomical and physiological considerations, techniques employed, safety and efficacy issues and the impact of CP on airway management with special mention of the laryngeal mask airway.

Source of material

Three medical databases (48 Hours, Medline, and Reference Manager Update) were searched for citations containing key words, subject headings and text entnes on CP to October 1996.

Principle Findings

There have been no studies proving that CP is beneficial, yet there is evidence that it is often ineffective and that it may increase the nsk of failed intubation and regurgitation. After evaluation of all available data, potential guidelines are suggested for optimal use of CP in routine and complex situations.

Conclusions

If CP is to remain standard practice dunng induction of anaesthesia, it must be shown to be safe and effective. Meanwhile, further understanding of its advantages and limitations, improved training in its use, and guidelines on optimal force and method of application should lead to better patient care.