Hypoxaemia is a common complication in anaesthetised or immobilised elephants. It is presumably because of hypoventilation and ventilation-perfusion mismatch. To prevent hypoxaemia, orotracheal intubation and positive pressure ventilation are recommended. This case report describes a hypoxaemic period despite positive pressure ventilation in a 46-year-old female Asian elephant (
Hypoxaemia is a frequently reported complication in captive and free-ranging immobilised elephants (Honeyman, Pettifer & Dyson
A 46-year-old female
As a result of difficulties with intubation and a period of apnoea that developed after the medetomidine administration, 6
After 1 h into the anaesthetic, the SpO2 value decreased from 100% to 92%. A leak around the orotracheal tube was detected and another 30-mm ID tube with a slightly larger external diameter was placed. Although the PIP was increased to 20 cm H2O, the SpO2 value declined between 86% and 89%. An arterial blood gas analysis confirmed a diagnosis of hypoxaemia with a PaO2 of 49 mmHg and a PaCO2 of 55 mmHg (see
Cardiorespiratory variables over the duration of the anaesthetic for an elephant anaesthetised with etorphine-azaperone, medetomidine and an etorphine constant rate infusion.
Time | Event | HR | RR | SPO2 | ETCO2 | MAP | PaO2 | PaCO2 |
---|---|---|---|---|---|---|---|---|
9:07 | Etorphine/azaperone injection | - | - | - | - | - | - | - |
9:22 | Recumbency achieved | - | - | - | - | - | - | - |
9:23 | Cannulation of auricular vein, 4 mg medetomidine IV | 39 | 5 | 97 | - | - | - | - |
9:27 | First intubation attempt | 42 | 0 | 96 | - | - | - | - |
9:29 | Second intubation attempt with smaller ETT | 40 | 0 | 97 | - | - | - | - |
9:30 | Atipamezole 20 mg IV | 42 | 0 | 96 | - | - | - | - |
9:31 | Intubation | 37 | 0 | 99 | - | - | - | - |
9:32 | Commence IPPV | 37 | 6 | 100 | 34 | - | - | - |
9:37 | Commence etorphine CRI | 32 | 6 | 95 | 30 | - | - | - |
9:55 | Arterial line placement | 46 | 7 | 100 | 31 | 172 | 78 | 47.2 |
10:10 | Commence dental procedure | 47 | 7 | 97 | 28 | 170 | - | - |
10:16 | Desaturation | 40 | 7 | 92 | 30 | 138 | 76 | 56.8 |
10:25 | Extubate because of leaking ETT | 54 | - | 88 | - | 132 | - | - |
10:31 | Reintubate with larger ETT | 50 | 7 | 86 | 23 | 120 | - | - |
10:40 | Before start of PEEP | 33 | 7 | 89 | 25 | 91 | 49 | 54.9 |
10:50 | Removed arterial line | - | 7 | 94 | 19 | 70 | 59 | 23.6 |
10:55 | Removed remainder of monitoring | - | - | 97 | - | - | - | - |
11:00 | End anaesthesia, administered naltrexone and atipemazole | - | - | - | - | - | - | - |
11:02 | Standing | - | - | - | - | - | - | - |
EtCO2, end-tidal carbon dioxide; ETT, endotracheal tube; HR, heart rate; MAP, mean arterial pressure; PaCO2, partial pressure of arterial carbon dioxide; PaO2, partial pressure of arterial oxygen; RR, respiratory rate; SpO2, oxygen saturation; IPPV, intermittent positive pressure ventilation; PEEP, positive end-expiratory pressure; CRI, constant rate infusion.
To treat the hypoxemia, it was decided to add PEEP. At the end of the inspiration phase, the anaesthetist let the air pressure decrease until it reached 5 cm – 10 cm H2O. At that time, using his hand, the anaesthetist applied PEEP by blocking the ventilator’s exhaust tailpiece to prevent the air pressure from decreasing further until the next breath. The PIP, RR and the I:E ratio remained unchanged at 20 cm H2O, 7 breaths a minute and about 3.5:5, respectively. Within 7 min, the PaO2 increased to 59 mmHg (SpO2 of 92%), and shortly after, the SpO2 reached 97%; however, further blood gas analysis was not available.
While oxygenation improved with PEEP, BP declined from a mean arterial pressure of 132 mmHg immediately before PEEP to as low as 70 mmHg during PEEP. In preparation for recovery, the arterial catheter was removed and PEEP was discontinued because of the risk of unmonitored hypotension.
The potent opioid etorphine is often used to anesthetise elephants either alone or in combination with other drugs (Honeyman et al.
As a result of the use of potent respiratory depressants and the rapid development of V/Q mismatch, oxygen supplementation is recommended for all immobilised or anaesthetised elephants (Horne & Loomis
In this case, a combination of drug-induced hypoventilation and the development of V/Q mismatch are the likely causes of the observed hypoxaemia. Correction of hypoventilation by providing IPPV and increasing PIP was unsuccessful in correcting hypoxaemia. In anaesthetised horses, atelectasis forms rapidly, and the early implementation of IPPV is recommended to maintain and improve oxygenation (Moens et al.
This case utilised a commercially available assisted demand ventilator. The design of this specific ventilator is such that rapid and high flow oxygen delivery into the ventilator generates negative pressure at the tailpiece of the ventilator and draws in atmospheric air through entrainment. The increase of gas flow permits a quicker delivery of the required tidal volume. The resulting FiO2 was 33%, although a FiO2 of 42% is reported by the manufacturer (In Case of Anaesthesia,
Positive end-expiratory pressure, which is defined as the residual alveolar pressure above atmospheric pressure at the end of expiration, improved oxygenation (Ambrosio et al.
Positive end-expiratory pressure improves pulmonary gas exchange in multiple species under anaesthesia (Ambrosio et al.
On a modern mechanical ventilator, PEEP is a basic setting that applies pressure at the end of expiration. Otherwise, commercial PEEP valves or handmade water column can be adapted onto the expiratory limb of the circuit or the scavenge tubing of the anaesthesia machine (Allison et al.
The use of PEEP in elephants may be of particular use in recruiting collapsed alveoli and improving oxygenation because of their unique respiratory system. Elephants lack a pleural space, instead, they possess a distensible collagen fibre network that adheres to the pleura of the chest wall. In addition, the parenchyma itself is supported by an elastic septum that limits alveoli collapse (Browne et al.
As a result of the increased intrathoracic pressures generated by PEEP, cardiac output and consequently, BP often declines (Luecke & Pelosi
Although the application of PEEP may impair cardiac output, the period of hypotension in this animal may have been exacerbated by other factors. The withholding of water prior to anaesthesia may have produced a mild hypovolaemia resulting in hypotension. In addition, the use of azaperone and atipamezole may have caused vasodilation, thus further reducing BP. The aetiology of the hypotension was likely multifactorial and PEEP impaired the ability of the animal to compensate adequately for its impaired cardiovascular status.
In conclusion, PEEP could easily be generated on the Mega-Vertebrate demand ventilator and was effective at improving oxygenation in laterally recumbent
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.
J.L., M.L., S.F. and S.H.B. participated in the collection of data. J.L., T.B., M.L., S.F. and S.H.B. participated in the writing or editing of the manuscript.
Ethical approval was not required for this case report. This article followed all ethical standards for research without direct contact with human or animal subjects.
This research received no specific grant from any funding agency in the public, commercial or not for profit sectors.
The data that support the findings of this study are available from the corresponding author, S.H.B., upon reasonable request.
The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of any affiliated agency of the authors.