Medical Emergency Teams and Critical Care Outreach services are used to try to
improve the care of patients in the ward environment. The limited treatment options
include oxygen therapy, non-invasive ventilation, intravenous fluid therapy and in
some institutions, inotropic support. The efficacy of such interventions is unclear.
Four studies used both lung models and clinical observation to assess oxygen
therapy. The model demonstrated a deterioration in oxygen delivery for the variable
flow systems (Hudson mask, Hudson non-rebreather mask and nasal cannulae) as
minute ventilation increased. Performance was relatively preserved for a venturi
system and a high flow nasal cannula system (Vapotherm®).
Peak inspiratory flow rates (PIFR) were assessed in patients with respiratory distress
and matched controls. This demonstrated a higher median PIFR of 76.5 l.min-1 (IQR
51.25 l.min-1) in patients when compared with controls, median of 30.00 (IQR 6.00
l.min-1) (p<0.0001).
The model was used to assess continuous positive airway pressure (CPAP) and
showed no deterioration in oxygen delivery with respiratory rate, with or without a
CPAP valve. When applied clinically in patients with acute respiratory distress, a
significant increase in mean arterial oxygenation was observed on moving from a
venturi mask (FiO2 0.6) to CPAP even without the valve, with a mean increase of
PaO2 of 10.69 kPa (SD 5.14 kPa) p<0.0001 (n=53). The application of pressure with
the CPAP valve did not increase this value over the 2 hours studied.
The use of intravenous fluid resuscitation (IFR) in the ward was audited. Delay in
fluid administration, a wide range of volume delivered and a lack of monitoring were
demonstrated. This audit produced the hypothesis that better monitoring of fluid
therapy in the wards may reduce the volume delivered and incidence of
complications. The final study thus compared a simple-to-use cardiac output monitor
(Vigileo Flotrac®) to a dye-dilution system (LiDCO®). The two systems were found to
have good agreement both in terms of cardiac output (bias positive in favour of the
LiDCO 0.58 l.min-1). The upper 95% limit is +1.40 l.min-1 and the lower 95% limit, -
0.28 l.min-1). And stroke volume variation (Bias of 0 with 95% limits of +/- 3.3%).
In conclusion this thesis demonstrates the impact of abnormal ventilation on oxygen
delivered by some mask systems. It shows the efficacy of a tight fitting CPAP mask
and high flow generator, but incidentally demonstrates that, at least initially it is the
mask system rather than the pressure that has a pronounced effect on oxygenation.
Fluid management in the ward patient appears poorly controlled and often excessive
so may benefit from improved monitoring. To this end a cardiac output monitor that
may be suitable for ward use has been shown to be comparable with a more
established technique
