Hypoxia: not indicated by vital signs.

Clinical bottom line (level 4)

  1. Significant hypoxia produces minimal changes in vital signs in healthy people.
Thrush et al: Journal of Clinical Anesthesia 1997; 9: 355-357
Expires June 2003

The study

Setting: university hospital, USA

16 patients (aged ?, ?% male) adult volunteers- not sedated or anaesthetised, who received low oxygen concentrations (down to 11%)

Independent unblinded reference standard, applied in all patients from a consecutive inappropriate spectrum.
Reference standard:
  • arterial blood gas PaO2
Diagnostic test: heart rate, blood pressure, respiratory rate, PaCO2

The evidence

  • Difference (95% CI) between PaO2 13 kPa and PaO2 5.5 kPa in vital signs:
    • heart rate (bpm): control 73 (9): experimental 71 (6): mean difference 2 (-4 to 8)
    • systolic blood pressure (mmHg): control 124 (11): experimental 117 (7): mean difference 7 (0.3 to 13)
    • diastolic blood pressure (mmHg): control 77 (9): experimental 74 (5): mean difference 6 (0.5 to 12)
    • respiratory rate (breaths/min): control 14 (2): experimental 16 (3): mean difference -2 (-5 to 1)
    • PaCO 2 (kPa): control 5.2 (0.67): experimental 4.9 (0.39): mean difference 0.3 (0.1 to 0.7)

Comments

  1. The study used healthy volunteers- it is unclear whether this also applies to sedated or anaesthetised patients.

Citation

  1. Thrush DN, Downs JB, Hodges M, et al: Does significant arterial hypoxemia alter vital signs?. Journal of Clinical Anesthesia 1997; 9: 355-357
Contributor: Chris Ball and Clare Wotton, January 1999
Reviewer: Malcolm Daniel

Clinical Question.
Patient adult volunteers
Intervention or Exposure heart rate, blood pressure, respiratory rate, pCO2
Outcome diagnosis of hypoxia