Pulmonary

▪Pulmonary Position

Pulmonary Positions

Position	Cardiac	Respiratory
Supine	Incr preload/CO	Decr FRC
Trendelenburg	Incr venous return Incr atrial pressures →CHF Decr CO/PVR/HR/BP	FRC decr 20%, VC/compliance decreased Pulmonary engorgement
Lithotomy	FRC decr 20%, VC/compliance decreased Pulmonary engorgement	FRC decr 20% Decr vital capacity
Prone	Decr preload/CO/BP IVC compression LE/gut pooling of blood	Decr TLC/compliance Incr work of breathing
Lateral	Arterial BP may decr due to decr vascular resistance	Decr lung volume of dependent lung, decr ventilation of dependent lung in anesthetized pt. Incr perfusion of dependent lung.
Sitting	Incr HR/SVR Decr CO/BP Air emboli (40%)	Incr lung volumes/FRC Decr work of breathing

▪Diagnosis of Gas Embolism

ETCO₂ decreases due to fall in cardiac output and increased dead space.
S/S: Gas lock of right heart produces HOTN, cyanosis, hypoxia, wheezing (S/S pulm edema) and hypocapnia with large embolism. ETCO₂ DROPS SUDDENLY AND NITROGEN INCREASES.
30-50% posterior fossa procedures entrain air (sitting position).
8% side-lying posterior fossa procedures entrain air.

Why Do Air Emboli Occur?

▪Treatment of Gas Embolism

▪Ventilation-Perfusion Ratios

Dependent areas of lungs are hypoxic and hypercarbic compared to nondependent areas.

PA = pressure alveolar

Pa = pressure arterial

Pv = pressure venous

Pisf = pulmonary interstitial space fluid

V/Q =ventilation-perfusion ratio

Zone 1

PA > Pa > Pv; V/Q > 1

Alveolar pressure continually occludes pulmonary arterial capillary flow.
Zone one areas are ventilated but not perfused.
Contribute to dead space ventilation.
Always > arterial; caliber of vessels around alveoli is dependent upon alveoli pressure.