The Impact of the pH on Cardiac Function in the Critically Ill Patient

The Impact of Systemic pH on Cardiac Function and Clinical Outcome in the Critically Ill Patient

Study Title: The Impact of the pH on cardiac function in the critically ill patient Sponsor: King's College Hospital NHS Foundation Trust Chief Investigator: Dr Sancho Rodríguez-Villar IRAS Number: 227870

Hypothesis:

Titration studies in animals with normal cardiac function show that a reduction in blood pH (and presumably that of the intracellular and interstitial compartments) from the normal level of 7.40 to 7.20 is associated with a rise in cardiac output. However, when blood pH is less than 7.20, cardiac output is reduced. Similar studies in humans with or without normal cardiac function have not been done, and yet blood pH at which aggressive treatment is recommended has been set at 7.20 based solely on animal experiments. The investigators hypothesize that a change in blood pH in humans will also affect cardiac function, but the level of blood pH at which this is observed might be similar or different in humans. In addition, the presence or absence of underlying cardiac disease and the type of acid-base abnormality present might modify the response of the heart to changes in blood pH.

Primary Objectives:

1. Assess whether there are significant changes in cardiac function associated with changes in blood pH.
2. Relate the changes in cardiac function to the presence or absence of underlying cardiac disease.

Study Design:

A prospective multicenter observational study in 6 ICU´s (between two Trusts). During a year study period, a minimum of 300 patients will be recruited.

Aim The aim of this study is to test the hypothesis that a change in the acidity of the blood (pH) will affect cardiac function in critically ill patients. It will also explore if the presence or absence of underlying cardiac disease and the type of pH abnormality may affect the response of the heart to changes in pH.

Justification for design Blood pH and cardiac function are monitored routinely in critically ill patients and so a prospective observational study design would be a feasible and useful method to address this question.

Inclusion/exclusion criteria explanation In intensive care practice, if a patient requires close cardiac function monitoring clinicians will use a special system for continuously monitoring the cardiac output and other heart functions to guide therapy. The system most commonly used is called PiCCO (pulse contour cardiac output).

Adult patients who are on PiCCO as part of their routine care in ICU for more than 24 hours will be eligible for inclusion in the study.

All patients who do not already have PiCCO in situ will be excluded from the study.

Identification of patients The direct care team will identify all eligible patients in the participating Units. The investigators have agreed to conduct the study in 6 different intensive care units across 2 Trusts and 4 sites - King's College Hospital Foundation Trust - including 3 ICU's at Denmark Hill site and 1 at Princess Royal University Hospital site; Lewisham and Greenwich NHS Trust - including ICU at University Hospital Lewisham and Queen Elizabeth Hospital, Woolwich.

Justification for sample size

In order to examine the relationship between a change in pH and cardiac contractility with power 80% and a 95% confidence interval, it has been calculated that it will be necessary to analyse 363 cases. Statistical analysis will be based on a retrospective audit of the numbers of a patient who fit the criteria, the investigators have assessed that across the 7 units the target sample size will be easily achieved in less than 1 year.

Data collection Data will be collected from ICU charts, medical notes and electronic patient records. This data is routinely collected as part of standard hospital care. The data will be collected by the direct care team and anonymised before it is transferred securely to a statistician for statistical analysis. The patient will not undergo any additional assessments or tests.

Consent All the data to be analysed is routinely collected as part of standard hospital care. There will be no additional tests or assessments in relation to this study. All data will be anonymised prior to analysis therefore, the investigators request approval to enrol patients without obtaining consent.

Data handling A case report form will be completed for each participant. Each participant will be given a unique study identification number. The patient's hospital number will be recorded on the case report form, and data will be collected by the direct care team. When data collection is completed at day 30, the direct care team will remove the top section of the case report form so that the hospital number is removed.

An enrolment log will be stored in the Site File securely on-site in a locked cupboard.

The data will be analysed according to the statistical plan. Results will be published in a peer-review journal.

Inclusion Criteria (the three criteria):

• Inclusion Criteria ALL patients on PiCCO monitoring system
• Over 18 years old.
• On PiCCO for more than 24 hours

Exclusion Criteria:

ALL patients WITHOUT PiCCO monitoring system AND:

• < 18 years old
• Vulnerable patients
• Atrial or ventricular arrhythmia: you need a stable pulse to measure the contour.
• Aortic, mitral or tricuspid valve insufficiency. In the case of valve insufficiency the valve does not close correctly. Therefore, the thermodilution curve is affected by indicator regurgitation, resulting in a prolonged indicator decay time.
• Intra-Aortic Balloon pump: once again, the pulse contour is all wrong; but you can still get thermodilution cardiac output measurements.
• Aortic aneurysm: the contour will be bizarre because the arterial compliance is going to be weird, with the aortic aneurysm acting as a damping system by absorbing all the pressure wave.
• Extracorporeal circuit: when you are on bypass, there is no real arterial waveform
• Pneumonectomy: PiCCO relies on there being a relatively normal pulmonary vasculature.
• Massive pulmonary embolism: as above; it is essentially a pneumonectomy by embolism.
• Intracardiac shunt: the PA catheter will also give an inaccurate thermodilution reading.
• Less than a minimal tidal volume 6-8mL/kg
• NON-positive pressure ventilated patients:
• Why does Stroke Volume Variation only apply to positive pressure ventilated patients? It still applies in spontaneously breathing patients; however it is a poorer predictor of fluid responsiveness.
• Why? The sensitivity is decreased: its only 63%. The spontaneous breathing efforts draw a smaller tidal volume, and from such minor changes in thoracic pressure there would insufficient change in ventricle loading; so there may still be changes to stroke volume, but they would be tiny and difficult to measure.
• If there is profound hypovolemia, the IVC can collapse on inspiration. Obviously this decreases preload and confuses your SVV. You cannot predict fluid responsiveness this way, because you never get an accurate impression of preload.
• In spontaneous respiration, inspiration increases the right ventricular preload, which means the right ventricular filling is likely still appeared adequate even if there is some hypovolemia. In spite of low overall volume, the right ventricular preload remains adequate, and thus at least one of the ventricles is likely to be operating in the preload-independent straight part of the Frank-Starling curve
• Severe obesity: In obese patients, Extravascular Lung Water Index (EVLWI) is underestimated because it is related to body weight.