An inhaler device using liquid injection of isoflurane for short term anesthesia in piglets

To test a novel inhaler for administering isoflurane (ISO) anesthesia to piglets during castration and other surgical procedures of short duration.

Prospective, randomized study. Animals Fifty-seven male piglets aged 6-10 days, body weight 1.1-3.5 kg.

An inhaler was developed which consisted of a mask, center body with open-close valve, vaporization chamber with wick and injection port, and a rebreathing bag. Liquid ISO required for induction of anesthesia and surgery was calculated, based on a desired alveolar ISO concentration of 1.82%. Dose was calculated using a square root of time model and metabolic size (B.W. 0.75). For practical use the calculated dose was expressed in relation to scale weight (kg). Isoflurane was delivered into the liquid injection port, followed by oxygen to fill the rebreathing bag and initiate vaporization. After the mask was fitted over the piglet's nose, the sliding open-close valve was opened to allow respiratory flow to move gases in and out of the inhaler and rebreathing bag. Fifty-seven male piglets received anesthesia prior to castration. Morbidity and mortality were assessed relative to unanesthetized litter mates. Induction, recovery and total anesthetic times were measured. End-tidal CO2 was measured immediately after mask removal by capnography. Costs of equipment and anesthetic agent were calculated.

Mean induction time was rapid, 47.5 +/-8.7 seconds, generally with minimal or no struggling. Surgery usually lasted less than 30 seconds and was always completed prior to the 120 seconds allotted for induction and surgery. Anesthesia was adequate and recovery time was 122 +/- 44 seconds. Total time from start to standing was 260 +/- 51 seconds. The end-tidal CO2 was 5.2 +/- 1.1 kPa (39.4 +/- 8.4 mmHg). No morbidity or mortality was associated with either group. Inhaler construction costs were below $100, and liquid ISO cost ranged between $0.02 and $0.03 per piglet.

Isoflurane delivered in a novel inhaler has the potential to provide economical, safe, rapid anesthetic induction and safe, smooth recovery in piglets.