The cardiovascular effects of inspired oxygen fraction in anaesthetized patients.
OBJECTIVE
Increased inspired oxygen fractions (FiO2) have significant haemodynamic effects in awake volunteers. We sought to establish whether these effects are also present in anaesthetized patients.


METHODS
We prospectively studied 30 ASA I-II patients, 15 in each of a propofol and sevoflurane group. Their haemodynamic responses, awake and anaesthetized, when the FiO2 was changed between 0.3 and 1.0 were measured with a non-invasive transthoracic bio-impedance monitor.


RESULTS
While preoxygenating awake patients in both groups the FiO2 was increased from 0.21 to 1.0. This reduced the mean cardiac index (3.38 +/- 0.5 to 3.03 +/- 0.5 L min(-1) m(-2); P < 0.001); reduced the heart rate (HR) (68.1 +/- 10.4 to 62.8 +/- 9.4 beats per minute (bpm); P < 0.001); and reduced the stroke index (50.4 +/- 9.6 to 48.5 +/- 8.6; P = 0.02). It increased the systemic vascular resistance index (2060 +/- 319 to 2220 +/- 382 dyn s(-1) cm(-5) m(-2); P = 0.002); but did not change mean arterial pressure. In the anaesthetized patients, when decreasing the FiO2 from 1.0 to 0.3, mean cardiac index (L min(-1) m(-2) increased (3.06 +/- 0.57 to 3.25 +/- 0.56, P = 0.008 for sevoflurane; 2.76 +/- 0.46 to 2.89 +/- 0.42, P = 0.002 for propofol). The mean HR (bpm) increased (65.1 +/- 7.8 to 69.1 +/- 7.5, P < 0.001 for sevoflurane; 67.5 +/- 11.8 to 72.7 +/- 11.6, P = 0.001 for propofol). The mean systemic vascular resistance (dyn s(-1) cm(-5) m(-2)) decreased (1883 +/- 329 to 1735 +/- 388, P = 0.008 for sevoflurane; 2015 +/- 369 to 1771 +/- 259, P = 0.003 for propofol). Mean arterial pressure (mmHg) decreased (74.8 +/- 8.7 to 71.4 +/- 8.7, P < 0.001 for sevoflurane; 72.1 +/- 8 to 66.5 +/- 6.8, P = 0.002 for propofol).


CONCLUSIONS
O2 has haemodynamic effects in awake and anaesthetized patients. These effects were of overall similar magnitude for patients anaesthetized with propofol and sevoflurane.
Anderson
K J
KJ
Glasgow Royal Infirmary, University of Glasgow, Department of Anaesthesia, Glasgow, UK. keithanderson@doctors.net.uk
Harten
J M
JM
Booth
M G
MG
Kinsella
J
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D001784:Blood Gas Analysis; D017097:Electric Impedance; D005260:Female; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D008297:Male; D008738:Methyl Ethers; D008875:Middle Aged; D010100:Oxygen / Q000494:pharmacology*; D015742:Propofol; D012129:Respiratory Function Tests; D000077149:Sevoflurane; D013815:Thermodilution
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D000077149:Sevoflurane; D010100:Oxygen; D015742:Propofol