The effects of inhalation salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance during general anaesthesia in the horse

Abstract

ABSTRACT:This research aimed to determine the effect of aerosolized salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance in healthy horses during general anaesthesia. Six healthy Thoroughbreds (body weight range 471-587 kg) underwent two general anaesthesias in dorsal recumbency with and without aerosolized salbutamol administration in randomized order with a one month washout period. The anaesthesia was induced by 1.1 mg/kg of xylazine, 0.02 mg/kg of diazepam and 2.2 mg/kg of ketamine, maintained with isoflurane in oxygen and air and horses were mechanically ventilated. Measurement of arterial and pulmonary arterial blood pressures, cardiac output and arterial and mixed venous blood gas analysis was carried out. Spirometry was performed using a Horse-lite. After achieving a steady state, baseline (T 0 ) values of cardiac output, systemic and pulmonary arterial blood pressures, heart rate, dynamic compliance, airway resistance and arterial and mixed venous blood gas values and pH were recorded in both groups. In the S-group (salbutamol), 2 µg/kg of aerosolized salbutamol were administered synchronously with inspirium into the tracheal tube. In both groups data were recorded at 15, 30, 45 and 60 min (T 15 , T 30 , T 45 , T 60 ) after the baseline. PaO 2 /FiO 2 ratio, oxygen consumption (VO 2 ), oxygen delivery (DO 2 ), pulmonary shunt values were calculated. Data were tested for normality and compared within each group: T 0 value with T 15 , T 30 , T 45 , T 60 values using Wilcoxon's test with Bonferoni correction (significance level 0.0125). For each time point, comparisons were made between the S-and C-groups (control) using Wilcoxon's test. In the S-group, there was a significant increase in values (mean ± SD) of cardiac output (l/min), T 0 (38 ± 7), a peak at T 15 (64 ± 25.5), significantly higher values persisted throughout the period of anaesthesia; heart rate (beats/min), T 0 (32 ± 2), T 15 (40 ± 6), T 30 (38 ± 5); DO 2 (l/min), T 0 (5.8 ± 0.8), a peak at T 15 (9.6 ± 3.2), significantly higher values persisted until the end of anaesthesia and VO 2 (l/min), T 0 (1.1 ± 0.5), T 30 (1.6 ± 0.7) and T 45 (1.8 ± 0.5). In the C-group, there was a significant decrease in values of PaO 2 /FiO 2 ratio from T 0 (176 ± 67) to a minimum at T 60 (114 ± 36) and in DO 2 from T 0 (6 ± 2.3) to a minimum at T 60 (4.3 ± 1.2). A comparison of the S-and C-groups did not reveal any difference in the baseline data. Subsequently, significantly higher values of cardiac output, heart rate, DO 2 , and the PaO 2 /FiO 2 ratio were found in the S-group compared to the C-group. Pulmonary arterial blood pressure was significantly lower in the S-group. Aerosolized salbutamol administration in healthy horses during general anaesthesia caused hemodynamic changes which resulted in an elevation of oxygen delivery. It can have a positive effect on arterial oxygenation, but the effect varies between individuals.

Cardiovascular changes after administration of aerosolized salbutamol in horses: five cases

“…This technique has been described by Robertson and Bailey [ 1 ] in clinical horses lying in dorsal recumbency and utilized by Patschova et al . [ 11 ] in experimental horses.…”

“…However, no tachycardia was observed in horses following salbutamol administration in clinical settings [ 1 ]. In experimental healthy horses in dorsal recumbency, a positive chronotropic effect without clinical relevance was temporarily recorded [ 11 ]. This case series reports the occurrence of clinically relevant cardiovascular effects i.e.…”

Oxygenation, oxygen delivery and anaesthesia in the horse

“…The horses were mechanically ventilated, and mean P was maintained above 70 mmHg. In a subsequent laboratory study, aerosolised albuterol (salbutamol, 2 μg/kg bwt) significantly increased cardiac output and DO 2 without changing CPS . The authors concluded that improvements in oxygen delivery resulted primarily from improved haemodynamics, indicating significant systemic absorption of the drug .…”

“…If hypoxaemia exists and the horse is normotensive (mean P>60 mmHg), minute ventilation should be normalised with controlled ventilation to produce a PaCO 2 of 5.3–6.7 kPa (40–50 mmHg). An additional intervention with little risk of significant side effects is the delivery of albuterol via the airway . A dose of 2 μg/kg bwt can be delivered via the endotracheal tube by interrupting the respiratory cycle, disconnecting the endotracheal tube from the anaesthetic machine, delivering the drug, reconnecting and delivering a V T .…”

Pulmonary Hemodynamics

“…This is a much lower driving pressure for the blood flow than the systemic circulation, where the arterial-venous pressure gradient is approximately 90 mmHg in humans. Table 1 summarizes the pulmonary hemodynamic parameters for other species from different studies (Barer and Nusser, 1957a;Drougas et al, 1996;Holm et al, 1998;Morris et al, 2000;Grant and Canty, 1989;Baxter et al, 1952;Duke and Stedeford, 1960;Chen et al, 2005;Yuan et al, 2011;Liu et al, 2005;Emery et al, 2001;Fesler et al, 2006;Chick et al, 1988;Franceschi et al, 2013;Chaliki et al, 2002;Romand et al, 1994;Takeda et al, 1987;Johnson et al, 1992;Ravikumar et al, 2011;Reddy et al, 1995;Polglase et al, 2006;Newman et al, 1993;Nachar et al, 2001;Krebs et al, 2007;Hinder et al, 1998;Pennington et al, 1992;Patschova et al, 2010;Stickland et al, 2007;Li et al, 2013;Goetz et al, 1999;Tournoux et al, 2011;Ortiz et al, 2002;Ullrich et al, 1999). Although the blood flow through the pulmonary circulation is essentially the same as the blood flow through the systemic circulation, the pulmonary vascular resistance is 10-to 15-fold lower than the systemic vascular resistance.…”