has been known to increase in patients with raised intra-abdominal pressure and the Trendelenburg position (10) Accordingly, the usefulness of PPV and SVV, which are affected by changes in intrathoracic pressure
, in predicting fluid responsiveness during laparoscopic surgery under these conditions may be questioned.
As the patient had chronic cough, a day later, the increased intrathoracic pressure
caused his lung to herniate during a coughing spell.
Variable Acronym aortic pressure (mm Hg) AoP mean arterial pressure (mm Hg) MAoP cardiac output (mL/min) CO "contractible" volume of veins (mL) CVV sympathetic (inotropic) homeostatic Sy contractility modulation ejection fraction of the left ventricle EF end-diastolic volume of left ventricle (mL) EDVLV end-diastolic volume of section S2 of EDVS2 left ventricle end-diastolic pressure in left ventricle EDPLV (mm Hg) end-systolic volume of left ventricle (mL) ESVLV stroke volume of the left ventricle (mL) SVLV left atrial pressure (mm Hg) LAtP left ventricular pressure (mm Hg) LVP left ventricular volume (mL) LVV intrathoracic pressure
(mm Hg) ITP
Hepatic vein flow patterns are under the effects of cardiac function and intrabdominal and intrathoracic pressure
can be transmitted from the lungs to the pulmonary vessels and change the intraluminal pressure (Marino, 2007).
In patients with OSA, the abrupt and repetitive inspiratory effort against a closed upper airway during the apnoeic episodes generate changes in negative intrathoracic pressure
that increase transmural gradients across the atria, ventricles and aorta (35,36) and may disrupt ventricular function (35).
We must also be aware that the Trendelenburg position increases intrathoracic pressure
, impairing venous return and accentuating the change in functional residual capacity.
Inspiratory resistance induced by breathing through an impedance threshold device (ITD) reduces intrathoracic pressure
and increases stroke volume (SV) in supine normovolemic humans.
Significant haemodynamic changes were found in an animal model resulting from the lengthy increase in intrathoracic pressure
and the decrease in cardiac deficit and compensatory vasoconstriction that is evident from the increase in systemic vascular resistance and mean arterial pressure (Anning et al 2003).
Another important pathophysiology in OSA relates to the increased negative intrathoracic pressure
generated by attempting to inhale against a collapsed airway.
Mechanically ventilated patients have a higher mean CVP, which is more indicative of mean intrathoracic pressure
than of cardiac filling or intravascular fluid status.
High intrathoracic pressure
increases central venous pressure and pulmonary artery wedge pressure without increasing the right or left ventricular end-diastolic volume.
According to this theory, increased intrathoracic pressure
or the change in intrathoracic pressure
during chest compressions forces blood from the thoracic vessels into the systemic circulation, with the heart acting as a conduit and not as a pump.
The increased intrathoracic pressure
is transiently transmitted to the superior vena cava and cerebral venules and capillaries, perhaps leading to a brief increase in oxygen availability.