The impact of volume loss during blood donation on continuous blood pressure measurements in spontaneously breathing subjects.

During a surgical procedure the cardiovascular system will be extended to the
use of anaesthetics, volume therapy, coagulants, blood pressure variations and
blood loss. In patients with existing co morbidities this cardiovascular
overload may lead to the development of postoperative complications such as
pulmonary edema, a temporarily hypertension or cardiac arrhythmias. The
department of Anesthesiology of the VUmc recently started to focus on
postoperative hemodynamic monitoring in surgical patients who have no arterial
entrance and are not ventilated. In order to do so, a continuous blood pressure
measurement device (Nexfin) should be validated in order to define its value in
this postoperative monitoring of patient hemodynamics. We recently showed that
postoperative non-invasive continuous blood pressure measurements during
autonomic function testing may be representative for predicting hemodynamic
changes using evaluation of the pulse pressure variation (PPV) in spontaneously
breathing patients.

In this study we aim to validate changes in the pulse pressure after controlled
volume loss during blood donation in spontaneously breathing subjects. This
validation will contribute to the development of a standardized manner in which
the Nexfin device can contribute to the early detection of postoperative
complications and to an early threatment of these complications. An adequatly
postoperative monitoring will therefore lead to an improvement of the
postoperative outcome of patients at risk for the development of mild
complications due to anesthesia and surgery.

This is an open, prospective, observational trial.
The study will be performed in the VU University Medical Center and the blood
donation department of Sanquin.
Inclusion of healthy volunteers giving a 500 ml full blood donation.
The study will end when the acquired sample size is reached.
Informed consent will be asked at the Sanquin blood blank before blood donation.
Volunteers are included in the study after signing their informed consent.
In order to perform continuous blood pressure measurements, an arterial blood
pressure finger cuff will be placed around the right middle index finger.
The end of the study is marked by the second blood pressure measurement after
blood donation.

Nexfin device:
Continuous blood pressure measurements will be performed by placing a finger
cuff around the middle index of the dominant hand. The hand will be placed in a
comfortable position on the abdomen when the patient or volunteer is in a
supine position. Volunteers are asked not to talk or move during testing. This
technique is associated with minimal discomfort and no risks for the volunteer.

Supine steady state:
The volunteer will be awake and breath normally while performing the supine
steady state for a period of 3 minutes. This is not regarded to induce any
discomfort.

Controlled breathing
Volunteers and patients will perform a cycle of metronome-controlled breathing
to mimic ventilation conditions. This is regarded to induce minimal
discomfort.

Valsalva maneuver:
The VM can be performed by forcibly exhaling against a closed glottis (a closed
airway), for instance to detect an inguinal hernia or to clear the ears during
diving. In the present study, volunteers and patients will perform a VM by
blowing into a manometer-controlled device that allows standardization of the
pressure which induces the Valsalva effects. This measurement is associated
with minimal discomfort. When necessary, lowering the pressure till 20 mmHg
will be tolerated in order to reach a comfortable level.