the bellows followed by passive expiration via the manually
opened valve. Spirometry and the pressure-volume loops
showed that consecutive inflations were cumulative and
provided tidal volumes that ranged from 2678 to 8300 ml
(7.6–23.7 ml/kg bwt) ( Fig 2 ). Four to 10 breaths/min (6.3 1.9
breaths/min) were administered generating a mean peak
inspiratory pressure of 24 6.6 cmH 2O (17–39 cmH 2O), a mean
minute volume of 68.5 13 l/min and a mean PaCO 2of 6.18 
3.06 kPa. Mild hypoxaemia developed in all ventilated horses
despite an inspired oxygen concentration of 26–46% (36 7%).
The arterial partial pressure of oxygen (PaO 2) ranged from
8.38–11.03 kPa (10.1  0.93 kPa). Recovery from anaesthesia
was uneventful in all cases.
Discussion
This study demonstrated that it is possible to generate a
sufficient tidal volume, minute volume and peak inspiratory
pressure to maintain PaCO 2within clinically acceptable
values for anaesthetised intubated horses using a modified foot
pump as an emergency ventilator. This is possible with quick
consecutive compressions of the bellows whereby the short
filling time constant of the pump and relatively long expiratory
time constants of the equine lung lead to accumulation of
insufflated volumes as illustrated in the pressure-volume loops of
Figure 2 . Although the target tidal volume was 10 ml/kg bwt, it
proved possible in a short-term trial during this study to generate
higher volumes (up to 23.7 ml/kg bwt) with a peak inspiratory
pressure of up to 39 cm H 2O by increasing the number of
successive compressions. This proves that although only horses
of about 350 kg bodyweight were used in this study, larger tidal
volumes can be realised (up to 8 l), sufficient to ventilate larger
horses in emergency situations (unpublished data).
Foot pump-type emergency devices to provide IPPV to
large animals in field conditions have not been recently
described, and older ones are not available anymore and were
probably too bulky to be practical (Rankin et al . 1952). This
modified foot pump is a cheap, lightweight device and easily
transported and connected to an endotracheal tube. The use
of the pump as an emergency ventilator (opening and closing
the valve by rolling the ball aside) is easy to understand and also
untrained assistants are able to take over mechanical
ventilation within short notice. The operator must be aware of
safety issues when using the device. First, there is no airway
pressure indication and thus no warning for excessively high
airway pressure. Airway pressure release will also depend on the
tension of the rubber fixation and can be increased when the
operator exerts manual pressure on the valve ball during
inspiration. Second, the operator needs to keep an eye on the
presence of spontaneous respiratory efforts. In this case it is
mandatory to assure an open valve position if negative airway
pressures with the risk of subsequent negative pressure
pulmonary oedema are to be avoided. This can occur when
the horse tries to breath from the limited volume of the foot
pump. During emergency ventilation ideally inspired air should
be enriched with oxygen and this modified foot pump can be
used with or without oxygen supplementation. Impaired
oxygenation due to V/Q mismatch and hypoventilation can be
partially treated by increasing fraction of inspired oxygen
(Marntell et al . 2005). In this study, IPPV provided with the foot
pump yielded clinically acceptable PaCO 2levels, although
higher levels ( >6.65 kPa) could certainly be tolerated; this
should allow a practitioner to provide sufficient IPPV in
emergency or resuscitation situations until spontaneous
respiration resumes. It is noteworthy that mechanical ventilation
with the foot pump corrected hypercapnia in all horses in the
present study but could not prevent hypoxaemia.
Alternatively to a foot pump a demand valve can be used
to provide IPPV and oxygen to intubated horses. Although
application of oxygen is a major advantage with the demand
valve there are also some drawbacks. A disadvantage is the
need for a transportable pressurised gas source and the need
for high oxygen flows (40–275 l/min) to operate the device
(Hartsfield 2007). The oxygen flow needed to enrich inspired air
in horses is much lower (up to 15 l/min) than the flow needed
to operate the demand valve and hence longer operational
times are possible for example a 2 l oxygen cylinder will last
< 10 min. Furthermore, transport of oxygen cylinders in a car
carries a health and safety risk and is regulated by law in
Europe.
Conclusion
The modified foot pump is a cheap and lightweight device
that enables the practitioner to provide IPPV to large animals
in emergency situations as suggested by the guidelines
Fig 2: Videoprint of the display of the Datex Capnomac Ultima monitor showing pressure-volume loops, airway pressure and flow during intermittent positive pressure ventilation with a modified foot pump.
© 2013 EVJ Ltd
583 EQUINE VETERINARY EDUCATION / AE / NOVEMBER 2013