Estudiante

Hemodynamic monitoring in the mechanically ventilated patient
Sheldon Magder
McGill University Health Centre, Montreal, Quebec,
Canada
Correspondence to Sheldon Magder, Royal Victoria
Hospital, 687 Pine Av W, Canada H3A 1A1
E-mail: sheldon.magder@muhc.mcgill.ca
Current Opinion in Critical Care 2011,
17:36–42

Purpose of review
Interactions between the heart and lungs are magnified inpatients undergoing
mechanical ventilation and the consequences of these interactions always need to be
considered when managing ventilated patients. In patients with normal lungs and normal
cardiovascular function monitoring needs are minimal, but when oxygenation and
cardiac function are compromised careful assessment of the consequences of changes
in ventilator settings needs to beconsidered to ensure that adequate oxygen delivery is
maintained.
Recent findings
Primary determinants of heart–lung interactions are first reviewed and then approaches
to the use of simple hemodynamic measurements such as respiratory variations in
central venous and pulmonary artery occlusion, or arterial pressure are described for
assessing oxygen delivery, volume responsiveness as well as indicatorsof ventilatory
mechanics.
Summary
Use of simple measurements available during routine monitoring can be very helpful to
the informed clinician for optimizing hemodynamic performance as well as patient
ventilator interactions.
Keywords
arterial pressure, central venous pressure, heart–lung interaction, pleural pressure,
preload
Curr Opin Crit Care 17:36–42
ß 2011 Wolters Kluwer Health |Lippincott Williams & Wilkins
1070-5295

Introduction
Maintenance of life requires the delivery of oxygen (O2)
to tissues and removal of the waste products of metabolism. The cardiovascular and respiratory systems are
intimately linked in these processes and must be functioning adequately to maintain steady state physiological
conditions. Apart from being functionally linked, the
heartresides in the thorax and the right and left ventricles
are in series with the lungs so that ventilatory processes
have direct effects on cardiovascular performance and
cardiac function has direct effects on ventilatory function
[1]. The importance of these interactions becomes
greater when the respiratory system fails and ventilation
is supported by mechanical ventilation for the mechanism oflung inflation changes from an increase in transpulmonary pressure due to a fall in pleural pressure, to an
increase in transpulmonary pressure due to an increase in
alveolar pressure. The author will first outline briefly
some key physiological points in heart–lung interaction.
Next the author will discuss what needs to be known
about blood flow and ventilation to ensure adequate
delivery of O2and removal of waste and what tools are
available to perform this task. Finally, the author will
1070-5295 ß 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

discuss how the information from dynamic variations
in hemodynamic signals can be used to evaluate cardiovascular function and give insights into pulmonary
mechanics.

Basic physiology of heart–lung interaction
Cardiacoutput is determined by the interaction of pump
function and return function [2,3,4] (Fig. 1). Pump
function is given by the Frank-Starling relationship
which determines the cardiac output for a given preload
at a given heart rate, afterload and contractility [2]. The
preload for the heart as a whole is the right atrial pressure
(Pra) which normally is the same as the central venouspressure (CVP). Return function describes the force that
determines the return of blood to the heart from the large
peripheral reservoir, which under resting condition contains approximately 70% of the blood volume. The
behavior of this reservoir region has been compared to
that of a bathtub [2,5]. Emptying of the reservoir is
determined by the blood volume that stretches the walls
of small...