Original Article
A commercial foot pump for emergency ventilation of horses,
proof-of-principle during equine field anaesthesia
S. von Ritgen*, U. Auer, J. Schramel and Y. Moens
Anaesthesiology and Perioperative Intensive Care, University of Veterinary Medicine Vienna, Austria.
*Corresponding author email: stephanie.ritgen@gmail.com
Keywords: horse; field anaesthesia; mechanical ventilation; emergency
Summary
At present there is no alternative to the use of a demand valve
and pressurised oxygen for emergency ventilation in large
animal field anaesthesia, therefore we aimed at providing a
proof-of-principle of a small (2.5 l) commercial foot pump to
provide emergency intermittent positive pressure ventilation
(IPPV) in large animals. The study was performed during
elective field anaesthesia for castration of 5 Haflinger stallions.
Horses were premedicated with acepromazine i.m. after
catheterisation of the jugular vein, further sedation was
obtained with detomidine and butorphanol i.v. Anaesthesia
was induced with ketamine and midazolam i.v. and
maintained with a constant rate infusion of midazolam,
ketamine and xylazine. After endotracheal intubation the foot
pump, modified with a manually operated expiratory valve,
was connected to the endotracheal tube and oxygen (6 l/min)
was supplied. Anaesthesia was monitored using spirometry,
respiratory gas analysis, pulse oximetry and arterial blood
gas analysis. When arterial partial pressure of carbon dioxide
(PaCO 2) exceeded 6.65 kPa, IPPV was provided by 2–4
consecutive compressions of the pump aiming at a tidal
volume of 10 ml/kg bwt. The PaCO 2was maintained at
6.18 3.06 kPa (mean s.d.) with a respiratory rate of 4–10
breaths/min. The tidal volume was 2678–8300 ml with a peak
inspiratory pressure of 24  6.6 cmH 2O and a mean minute
volume of 68.5  13 l/min. Inspired oxygen concentration
ranged from 26–46% (36 7%) and arterial partial pressure of
oxygen from 8.38–11.03 kPa (10.1  0.93 kPa). The modified
foot pump enables the practitioner to provide IPPV to large
animals in emergency situations.
Introduction
Ventilatory support by means of application of intermittent
positive pressure ventilation (IPPV) is universally accepted
as a life-saving procedure in case of respiratory impairment
or arrest and is a standard feature of cardiopulmonary
resuscitation. This situation can occur in all species and
conditions but represents a particular challenge for large
animals and in field conditions. Guidelines for good
anaesthetic practice suggest that as a minimum requirement
every veterinarian should be able to perform IPPV manually by
using a self-inflating bag or – in horse s – a demand valve (AVA
Committee Meeting Barcelona 2008).
In the early periods of human anaesthesia and
resuscitation, emergency ventilation was provided with foot
pump-like devices (i.e. Fell-O’Dwyer apparatus) (Trubuhovich
2009). In the 1950s a large (20 l) bellows-foot pump was used to
perform artificial respiration in 12 horses (Rankin et al . 1952).
Such large foot pumps were also incorporated in anaesthetic
circle systems for horses (Schebitz 1955) or modified to
become a manually operated stand-alone device (Überreiter
1958). A comparable device to the small foot pump used in
this study has already been used in large animal emergencies
when IPPV was needed, but its performance was not
investigated in detail (H. Moerch, personal communication
2012).
The present study aims at providing a proof-of-principle of
a small (2.5 l) commercial foot pump to provide emergency
IPPV in large animals. The study was performed during field
anaesthesia for castration of stallions.
Materials and methods
Description of the modified foot pump
A commercial 2.5 l foot pump (Bravo 7 M) 1intended for the
inflation of recreational items was used. The original pump
consists of a bellows, an inlet valve and an exhaust valve
allowing the venting of gas into an exhaust pipe. Modifications
consisted of the addition of a custom made copper T-piece at
the distal end of the exhaust pipe. This T-piece served as
connector of the foot pump to endotracheal tubes of 25 or
30 mm inner diameter but was also designed to function as a
manually operated expiratory valve. A rubber ball is pressed
on the orifice (inner diameter of 30 mm) of the side port of the
T-piece via an elastic rubber strap through its centre ( Fig 1 ).
The valve can be opened manually by rolling the ball to the
side. When the bellows is compressed and the valve is in
closed position, the device delivers a volume of 2.5 l with each
step. When the valve is opened unobstructed expiration and
also – if present – spontaneous breathing is possible.
Furthermore the foot pump was provided with an inlet port for
the provision of supplemental oxygen.
Animals
The Ethical Committee of the University of Veterinary Medicine
Vienna approved the study. Five 2-year-old Haflinger stallions,
with a bodyweight of 350 15 kg were anaesthetised for field
castration in lateral recumbency. Food, but not water was
withheld for 12 h before anaesthesia.
Anaesthesia and monitoring
Each horse received 0.03 mg/kg bwt acepromazine
(Vanastress) 2 i.m. prior to catheterisation of the jugular
vein 3. Further sedation was obtained with 0.015 mg/kg bwt
detomidine (Medesedan) 4and 0.02 mg/kg bwt butorphanol
(Butomidor) 5i.v. Anaesthesia was induced with 2.2 mg/kg bwt
ketamine (Narketan 10%) 5and 0.1 mg/kg bwt midazolam
(Midazolam) 6i.v. Orotracheal intubation was performed and
anaesthesia maintained with an i.v. continuous rate infusion of
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EQUINE VETERINARY EDUCATION / AE / NOVEMBER 2013