Pulmonary gas exchange in anaesthetised horses mechanically ventilated with oxygen or a helium/oxygen mixture |
| |
| Authors: | F Staffieri S H Bauquier P J Moate B Driessen |
| |
| Institution: | 1. Dipartimento delle Emergenze e dei Trapianti d'Organo, Sezione di Chirurgia Veterinaria, Università degli Studi di Bari, 70010 Valenzano, Bari, Italy;2. Section of Critical Care & Anesthesia, Department of Clinical Studies‐New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, USA;3. Section of Biostatistics, Department of Clinical Studies‐New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, USA;4. University of California‐Los Angeles, David Geffen School of Medicine, Department of Anesthesiology, Los Angeles, California 90095, USA |
| |
| Abstract: | Reason for performing study: It is unknown whether administration of gas‐mixtures high in inspired fraction of oxygen (FiO2) under general anaesthesia may increase formation of pulmonary atelectasis and impair gas exchange. Objective: To evaluate the effects of different FiO2 on pulmonary gas exchange in isoflurane‐anaesthetised horses breathing a helium/oxygen (He/O2) mixture. Methods: Thirty healthy mature horses were sedated with i.v. acepromazine (0.02 mg/kg bwt), detomidine (0.002 mg/kg bwt) and xylazine (0.2‐0.4 mg/kg bwt). General anaesthesia was induced with i.v. 5% guaifenesin to effect, diazepam (0.1 mg/kg bwt) and ketamine (2 mg/kg bwt), and maintained with isoflurane. Fifteen horses (Group HX) were ventilated mechanically with gas mixtures of successively increasing FiO2 (0.25‐0.30, 0.50‐0.55, >0.90), obtained by blending O2with Heliox (70% He/30% O2). The other 15 horses (Group O) were ventilated immediately with 100% O2(FiO2>0.90). After 20 min of ventilation at the different FiO2levels in Group HX and after 60 min in Group O, PaO2 and PaCO2 were measured and the alveolar to arterial PO2gradient (P(A‐a)O2) was calculated. Data analysis included robust categorical regression with clustering on horse (P<0.05). Results: Inhalation of a He/O2 mixture with FiO2 as low as 0.25‐0.30 ensured adequate arterial oxygenation and was associated with a smaller P(A‐a)O2 gradient than inhalation of pure O2 (P<0.05). In Group HX, PaO2 increased with each rise in FiO2 and so did P(A‐a)O2 (P<0.05). The PaO2 was significantly lower and the P(A‐a)O2 higher in Group O compared to Group HX at a FiO2 >0.90 (P<0.05). Conclusions and potential relevance: Administration of a He/O2gas mixture low in FiO2 can better preserve lung function than ventilation with pure oxygen. A step‐wise increase of FiO2 using a He/O2 gas mixture might offer advantages with respect to pulmonary gas exchange over an immediate exposure to 100% O2. |
| |
| Keywords: | horse helium/oxygen gas mixture inspired fraction of oxygen pulmonary gas exchange mechanical ventilation |
|
|
