Blood Gas Values During Intermittent Positive Pressure Ventilation and Spontaneous Ventilation in 160 Anesthetized Horses Positioned in Lateral or Dorsal Recumbency

Abstract

One hundred sixty horses were anesthetized with xylazine, guaifenesin, thiamylal, and halothane for elective soft tissue and orthopedic procedures. Horses were randomly assigned to one of four groups. Group 1 (n = 40): Horses positioned in lateral (LRG1; n = 20) or dorsal (DRG1; n = 20) recumbency breathed spontaneously throughout anesthesia. Group 2 (n = 40): Intermittent positive pressure ventilation (IPPV) was instituted throughout anesthesia in horses positioned in lateral (LRG2; n = 20) or dorsal (DRG2; n = 20) recumbency. Group 3 (n = 40): Horses positioned in lateral (LRG3; n = 20) or dorsal (DRG3; n = 20) recumbency breathed spontaneously for the first half of anesthesia and intermittent positive pressure ventilation was instituted for the second half of anesthesia. Group 4 (n = 40): Intermittent positive pressure ventilation was instituted for the first half of anesthesia in horses positioned in lateral (LRG4; n = 20) or dorsal (DRG4; n = 20) recumbency. Spontaneous ventilation (SV) occured for the second half of anesthesia. The mean time of anesthesia was not significantly different within or between groups. The mean time of SV and IPPV was not significantly different in groups 3 and 4. Variables analyzed included pH, PaCO2, PaO2, and P(A-a)O2 (calculated). Spontaneous ventilation resulted in significantly higher PaCO2 and P(A-a)O2 values and significantly lower PaO2 values in LRG1 and DRG1 horses compared with LRG2 and DRG2 horses. Intermittent positive pressure ventilation resulted in normocarbia and significantly lower P(A-a)O2 values in LRG2 and DRG2 horses. In LRG2 the PaO2 values significantly increased from 20 minutes after induction to the end of anesthesia. The PaO2 and P(A-a)O2 values were not significantly different from the beginning of anesthesia after IPPV in DRG2 or DRG3. The PaO2 values significantly decreased and the P(A-a)O2 values significantly increased after return to SV in horses in LRG4 and DRG4. The PaO2 values were lowest and the P(A-a)O2 values were highest in all horses positioned in dorsal recumbency compared with lateral recumbency and in SV horses compared with IPPV horses. The pH changes paralleled the changes in PaCO2. Blood gas values during right versus left lateral recumbency in all groups were also evaluated. The PaO2 values were significantly lower and the P(A-a)O2 values were significantly higher during SV in horses positioned in left lateral (LRLG1) compared with right lateral (LRRG1) recumbency.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical assessment of anesthesia with isoflurane and medetomidine in 300 equidae

“…All 7 horses were heavy horses weighing between 520 and 600 kg, 6 of them positioned in dorsal recumbency. Arterial hypoxemia is most likely to occur in horses positioned in dorsal recumbency, but can occur in laterally recumbent horses as well (Day et al 1995, Steffey et al 1977. In 4 horses hypoxemia resolved by changing the gas flow to pure oxygen.…”

Efeitos do modo ventilatório sobre variáveis hemogasométricas em equinos submetidos à mudança de decúbito durante a anestesia geral inalatória com halotano

“…É improvável que as reduções da PaO 2 , observadas após a mudança de decúbito nos equinos submetidos à V E deste estudo, estejam relacionadas à progressão do tempo de anestesia. Em estudos prévios, não se observaram diminuição da PaO 2 ou piora na relação V/Q com a progressão do tempo de anestesia (Hall et al, 1968;McDonell et al, 1979;Hornof et al, 1986;Steffey et al, 1987 (Steffey et al, 1977;Wagner et al, 1990;Day et al, 1995;Khanna et al, 1995). Parte da depressão cardiovascular observada durante a anestesia com ventilação artificial pode ser atribuída à prevenção da hipercapnia e da consequente liberação de catecolaminas (Khanna et al, 1995;Wagner et al, 1990).…”

“…Nessa condição, a relação entre a ventilação e a perfusão pulmonar (relação V/Q) é ideal, não havendo interferência dos fármacos e do decúbito sobre a função pulmonar (Robinson, 1991). Por outro lado, em equinos anestesiados posicionados em decúbito lateral ou dorsal, em função do desenvolvimento de hipoventilação e de shunts intrapulmonares (relação V/Q = 0), é comum a ocorrência de hipercapnia (PaCO 2 >45mmHg) e hipoxemia (PaO 2 <60mmHg) (Taylor, 1984;Nyman e Hedenstierna, 1989;Day et al, 1995).…”

Intravenous fluid therapy in the horse

“…The development of low arterial partial pressure of oxygen (PaO 2 ) during general anaesthesia despite the use of a high inspired oxygen fraction is common in horses (Day et al 1995). Predisposing factors are adoption of dorsal recumbency (Steffey et al 1977), a typical thoraco-abdominal contour (Moens et al 1995) and the presence of abdominal distension, gastric content or severe obstipation (Whitehair and Willits 1999).…”